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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Photovoltaic Power System: Modelling, Design and Control is an essential reference with a practical approach to photovoltaic (PV) power system analysis and control. It systematically guides readers through PV system design, modelling, simulation, maximum power point tracking and control techniques making this invaluable resource to students and professionals progressing from different levels in PV power engineering. The development of this book follows the author's 15-year experience as an electrical engineer in the PV engineering sector and as an educator in academia. It provides the background knowledge of PV power system but will also inform research direction. Key features: * Details modern converter topologies and a step-by-step modelling approach to simulate and control a complete PV power system. * Introduces industrial standards, regulations, and electric codes for safety practice and research direction. * Covers new classification of PV power systems in terms of the level of maximum power point tracking. * Contains practical examples in designing grid-tied and standalone PV power systems. * Matlab codes and Simulink models featured on a Wiley hosted book companion website.
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Veröffentlichungsjahr: 2017
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Table of Contents
Cover
Title Page
Copyright
Dedication
Preface
Technical Support
Acknowledgments
About the companion website
Chapter 1: Introduction
1.1 Cell, Module, Panel, String, Subarray, and Array
1.2 Blocking Diode
1.3 Photovoltaic Cell Materials and Efficiency
1.4 Test Conditions
1.5 PV Module Test
1.6 PV Output Characteristics
1.7 PV Array Simulator
1.8 Power Interfaces
1.9 Standalone Systems
1.10 AC Grid-connected Systems
1.11 DC Grid and Microgrid Connections
1.12 Building-integrated Photovoltaics
1.13 Other Solar Power Systems
1.14 Sun Trackers
Problems
References
Chapter 2: Classification of Photovoltaic Power Systems
2.1 Background
2.2 CMPPT Systems
2.3 DMPPT Systems at PV String Level
2.4 DMPPT Systems at PV Module Level
2.5 DMPPT Systems at PV Submodule Level
2.6 DMPPT Systems at PV Cell Level
2.7 Summary
Problems
References
Chapter 3: Safety Standards, Guidance and Regulation
3.1 Certification of PV Modules
3.2 Interconnection Standards
3.3 System Integration to Low-voltage Networks
3.4 System Integration to Medium-voltage Network
3.5 Summary
Problems
References
Chapter 4: PV Output Characteristics and Mathematical Models
4.1 Ideal Single-diode Model
4.2 Model Accuracy and Performance Indices
4.3 Simplified Single-diode Models
4.4 Model Selection from the Simplified Single-diode Models
4.5 Complete Single-diode Model
4.6 Model Aggregation and Terminal Output Configuration
4.7 Polynomial Curve Fitting
4.8 Summary
Problems
References
Chapter 5: Power Conditioning
5.1 PV-side Converters
5.2 Battery-side Converter for DC/DC Stage
5.3 DC Link
5.4 Grid-side Converter for DC/AC Stage
5.5 Grid Link
5.6 Loss Analysis
5.7 Conversion Efficiency
5.8 Wide Band-gap Devices for Future Power Conversion
5.9 Summary
Problems
References
Chapter 6: Dynamic Modeling
6.1 State-space Averaging
6.2 Linearization
6.3 Dynamics of PV Link
6.4 Dynamics of DC Bus Voltage Interfaced with Dual Active Bridge
6.5 Dynamics of DC Link for AC Grid Connection
6.6 Summary
Problems
References
Chapter 7: Voltage Regulation
7.1 Structure of Voltage Regulation in Grid-connected PV Systems
7.2 Affine Parameterization
7.3 PID-type Controllers
7.4 Desired Performance in Closed Loop
7.5 Relative Stability
7.6 Robustness
7.7 Feedforward Control
7.8 Voltage Regulation in PV Links
7.9 Bus Voltage Regulation for DC Microgrids
7.10 DC-link Voltage Regulation for AC Grid Interconnections
7.11 Sensor, Transducer, and Signal Conditioning
7.12 Anti-windup
7.13 Digital Control
7.14 Summary
Problems
References
Chapter 8: Maximum Power Point Tracking
8.1 Background
8.2 Heuristic Search
8.3 Extreme-value Searching
8.4 Sampling Frequency and Perturbation Size
8.5 Case Study
8.6 Start-stop Mechanism for HC-based MPPT
8.7 Adaptive Step Size Based on the Steepest Descent
8.8 Centered Differentiation
8.9 Real-time System Identification
8.10 Extremum Seeking
8.11 Multiple Power Peaks and Global MPPT
8.12 Performance Evaluation of MPPT
8.13 Summary
Problems
References
Chapter 9: Battery Storage and Standalone System Design
9.1 Batteries
9.2 Integrating Battery-charge Control with MPPT
9.3 Design of Standalone PV Systems
9.4 Equivalent Circuit for Simulation and Case Study
9.5 Simulation Model to Integrate Battery-charging with MPPT
9.6 Simulation Study of Standalone Systems
9.7 Summary
Problems
References
Chapter 10: System Design and Integration of Grid-connected Systems
10.1 System Integration of Single-phase Grid-connected System
10.2 Design Example of Three-phase Grid-connected System
10.3 System Simulation and Concept Proof
10.4 Simulation Efficiency for Conventional Grid-connected PV Systems
10.5 Grid-connected System Simulation Based on Module Integrated Parallel Inverters
10.6 Summary
Problems
References
Index
End User License Agreement
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Guide
Cover
Table of Contents
Preface
Begin Reading
List of Illustrations
Chapter 1: Introduction
Figure 1.1 Typical crystalline PV cell construction.
Figure 1.2 Lamination of PV module.
Figure 1.3 72-cell PV module: left, appearance; right, configuration.
Figure 1.4 PV power capacity built from cell to array.
Figure 1.5 Bipolar PV array formed from two monopolar subarrays.
Figure 1.6 PV circuit with bypass diodes and blocking diodes.
Figure 1.7 PV module 3-h output, as measured on 16 June 2006.
Figure 1.8 Laboratory for PV module testing.
Figure 1.9 PV output characteristics: left, normalized I–V curve; right, normalized P–V curve.
Figure 1.10 Normalized I–V curve to represent the PV generator outputs and the difference in fill factor. CIS, copper indium diselenide.
Figure 1.11 Agilent 4350B PV array simulator.
Figure 1.12 Typical standalone system configuration, with PV generator and energy storage. BOS, balance of system.
Figure 1.13 Typical waveforms output by voltage source inverter.
Figure 1.14 Solar Impulse 2.
Figure 1.15 Grid-connected PV power systems with PV generators and inverters: (a) simple system; (b) grid-connected system with battery storage; (c) PV power plant.
Figure 1.16 DC microgrid with PV power generation.
Figure 1.17 Example of building integrated photovoltaics in Langley, Canada.
Figure 1.18 SolTrak installation technology.
Figure 1.19 System diagram of Shams 1.
Figure 1.20 Shams 1 during construction in 2011.
Chapter 2: Classification of Photovoltaic Power Systems
Figure 2.1 Classification of grid-connected PV power systems with centralized maximum power point tracking.
Figure 2.2 Classification of grid-connected PV power systems with distributed maximum power point tracking.
Figure 2.3 Topology of centralized maximum power point tracker with galvanic isolation and three-stage power conversion.
Figure 2.4 Topology of centralized maximum power point tracker with galvanic isolation and two-stage power conversion.
Figure 2.5 Topology of centralized maximum power point tracker with galvanic isolation and single-stage power conversion.
Figure 2.6 Centralized maximum power point tracker without galvanic isolation: (a) with two-stage conversion; (b) with single-stage conversion.
Figure 2.7 Two PV modules installed on the same frame for a partial shading study.
Figure 2.8 Plots of data acquired by I–V tracer without PV partial shading.
Figure 2.9 Plots of data acquired by I–V tracer without partial shading of PV.
Figure 2.10 Plots of data acquired by I–V tracer with one cell shaded.
Figure 2.11 Plots of data acquired by I–V tracer with one cell shaded when two modules are connected in series.
Figure 2.12 Data acquisition and monitoring for centralized MPPT photovoltaic power systems.
Figure 2.13 Three-level monitoring of photovoltaic power systems using wireless communication technologies.
Figure 2.14 Trend towards distributed maximum power point tracking systems.
Figure 2.15 Distributed maximum power point trackers at PV string level sharing AC link.
Figure 2.16 Distributed maximum power point trackers at PV string level sharing DC link.
Figure 2.17 Configurations of module-integrated parallel inverters for grid interconnections.
Figure 2.18 Two types of module-integrated parallel inverter: (a) DC link for steady voltage (b) current-unfolding approach.
Figure 2.19 System configurations of module-integrated parallel converters for: (a) DC grid connection; (b) AC grid connection.
Figure 2.20 Configurations of module-integrated series converters to form a DC link.
Figure 2.21 Configurations of module-integrated differential power processors to form a DC link.
Figure 2.22 Series configurations of module-integrated series inverters for AC grid interconnection.
Figure 2.23 Series configurations of submodule-integrated series converters to form a DC link.
Figure 2.24 Series configurations of submodule-integrated differential power processors to form a DC link.
Figure 2.25 Series configurations of submodule-integrated isolated-port differential power processors to form a DC link.
Figure 2.26 Integrated power management architecture for DMPPT at PV cell level.
Chapter 3: Safety Standards, Guidance and Regulation
Figure 3.1 Interconnection terms defined by IEEE 1547.
Figure 3.2 A grid-connected PV system as defined by Article 690 of the National Electric Code.
Figure 3.3 Normal operation without DC ground fault.
Figure 3.4 DC ground fault and protection: (a) DC ground fault detected; (b) protection action responding to DC ground fault.
Figure 3.5 Grid interconnection to LV network through power distribution panel.
Figure 3.6 Active power throttling for medium voltage integration.
Figure 3.7 Fault ride-through for medium-voltage integration.
Chapter 4: PV Output Characteristics and Mathematical Models
Figure 4.1 Equivalent circuit of single-diode model.
Figure 4.2 Equivalent circuit of double-diode model.
Figure 4.3 Equivalent circuits of the ideal single-diode model.
Figure 4.4 Flowchart of the NR method for parameter identification of an ideal single-diode model.
Figure 4.5 I–V and P–V curves for the IM156B3 PV cell.
Figure 4.6 Voltage correction factors for modeling and simulation.
Figure 4.7 Flowchart for simulating PV cell output.
Figure 4.8 Modeled I–V curve of the PV cell IM156B3 with constant temperature () and variable irradiance.
Figure 4.9 Modeled I–V curve of the PV cell IM156B3 with constant irradiance (1000 ) and variable temperature.
Figure 4.10 Zoom-in plots of I–V and P–V for the IM156B3 PV cell.
Figure 4.11 Equivalent circuit of simplified single-diode model with shunt resistor.
Figure 4.12 Equivalent circuit of simplified single-diode model with series resistor.
Figure 4.13 Flowchart for identifying PV model parameters using Newton–Raphson iteration.
Figure 4.14 I–V and P–V curves of the IM156B3 PV cell modeled using ISDM and SSDM1.
Figure 4.15 Zoom-in plots of I–V and P–V of model outputs for the IM156B3 PV cell.
Figure 4.16 I–V and P–V curves of the IM156B3 PV cell modeled using ISDM and SSDM2.
Figure 4.17 Zoom-in plots of I–V and P–V of model output for the IM156B3 PV cell.
Figure 4.18 I–V curve for IM156B3 modeled with constant temperature () and variable irradiance.
Figure 4.19 Modeled I–V curve of the PV cell IM156B3 with constant irradiance (1000 ) and variable temperature.
Figure 4.20 Flowchart for model selection from ISDM, SSDM1, and SSDM2.
Figure 4.21 I–V curve of the JAC-M6SR-3 cell modeled with constant temperature () and variable irradiance.
Figure 4.22 I–V curve of JAC-M6SR-3 cell modeled with constant irradiance (1000 ) and variable temperature.
Figure 4.23 Block diagram for PV array aggregation and the terminal connection interface, representing the PV output as a current source.
Figure 4.24 Block diagram of the PV array aggregation and the terminal connection interface, representing the PV output as a voltage source.
Figure 4.25 Simulink model of PV array for simulation.
Figure 4.26 Integrated Simulink model for simulation.
Figure 4.27 Sixth-order polynomial output in comparison with measured data of MSX-83.
Figure 4.28 I–V characteristics of the fourth-order polynomial output and measured data of ST-10 module.
Figure 4.29 P–V characteristics of fourth-order polynomial output and measured data of ST-10 module.
Chapter 5: Power Conditioning
Figure 5.1 Block diagram of a grid-connected PV system with two-stage power conversion. PVSC, PV-side converter; GSC, grid-side converter.
Figure 5.2 Block diagram of grid-connected PV system with single-stage power conversion. GSC, grid-side converter.
Figure 5.3 Recommended procedure to design, simulate, and evaluate PV-side power interface.
Figure 5.4 I–V and P–V curves of PV module output.
Figure 5.5 Buck converter used for PV power interface.
Figure 5.6 Simulink model of buck converter used for PV power interface: (a) model composition; (b) integrated block.
Figure 5.7 Simulink system using the buck converter for PV-side converter.
Figure 5.8 Simulated waveforms of the PV power charger in the steady state.
Figure 5.9 Simulated waveforms of the PV power charger in the steady state.
Figure 5.10 Circuit of full-bridge DC/DC converter for PV-side converter: (a) full-bridge rectifier; (b) two-diode based rectifier.
Figure 5.11 Typical steady-state waveforms in full-bridge transformer isolated DC/DC converter.
Figure 5.12 Simulink model of full-bridge DC/DC converter for PV power interface.
Figure 5.13 Simulated waveforms of the full-bridge DC/DC converter at steady state.
Figure 5.14 Simulated waveforms of the full-bridge DC/DC converter at steady state: zoomed-in view to illustrate the ripple magnitude.
Figure 5.15 Typical steady-state waveforms in full-bridge transformer isolated DC/DC converter.
Figure 5.16 Boost converter for PV power interface.
Figure 5.17 Typical steady-state waveforms in boost DC/DC converter.
Figure 5.18 Simulink model of boost converter for PV power interface: (a) model composition; (b) integrated block.
Figure 5.19 Simulated waveforms of the PV power charger at steady state.
Figure 5.20 Simulated waveforms of the PV power charger at steady state. Zoomed-in view to illustrate ripple.
Figure 5.21 Tapped-inductor converter used for PV power interface.
Figure 5.22 Conversion ratio of tapped-inductor topology.
Figure 5.23 Simulink model of tapped-inductor boost converter for PV power interface: (a) model composition; (b) integrated block.
Figure 5.24 Simulated waveforms of PV power system based on a tapped-inductor converter.
Figure 5.25 Zoom-in illustration of the waveform at steady state.
Figure 5.26 Buck–boost converter used as PV power interface.
Figure 5.27 Simulink model of buck–boost converter for PV power interface: (a) model composition; (b) integrated block.
Figure 5.28 Simulated waveforms of a PV power system based on buck–boost topology.
Figure 5.29 Zoom-in illustration of the waveform at steady state.
Figure 5.30 Evolution of flyback topology from the buck–boost topology: (a) buck-boost; (b) Isolated buck-boost; (c) integrated magnetic inductor into transformer; (d) flyback converter.
Figure 5.31 Simulink model of flyback converter for PV power interface: (a) model composition; (b) integrated block.
Figure 5.32 Simulated waveforms of a PV power system based on the flyback topology.
Figure 5.33 Zoom-in illustration of the waveform at steady state.
Figure 5.34 Bidirectional DC/DC for battery power interface based on dual active bridge topology.
Figure 5.35 Typical waveforms of dual active bridge topology.
Figure 5.36 Simulink model of dual active bridge topology.
Figure 5.37 Simulated waveforms of the DAB topology at full power.
Figure 5.38 Simulated waveforms of the DAB topology when the phase shift is 45.
Figure 5.39 Simulated waveforms in charging mode.
Figure 5.40 Simulated waveforms in charging mode.
Figure 5.41 Simulated waveforms of the DAB topology when the magnitudes of and are equal.
Figure 5.42 Simulated waveforms of the DAB topology when losing ZVS.
Figure 5.43 Simulated waveforms of the DAB topology to maintain both ZVS and zero circulating of active power.
Figure 5.44 DC link in grid-connected PV power systems: (a) two-stage conversion; (b) single-stage conversion.
Figure 5.45 Simulink model of DC link with the current input.
Figure 5.46 Simulink model of DC link with the power input.
Figure 5.47 Balanced power flow at the DC link in steady state for single-phase AC grid connection.
Figure 5.48 Balanced power flow in steady state at the DC link for three-phase AC grid connection.
Figure 5.49 H bridge used for grid-side converter in two-stage conversion topology: (a) two-stage conversion; (b) single-stage conversion.
Figure 5.50 Simulink model of H bridge for grid-side converter.
Figure 5.51 Demonstration of grid current regulation using a hysteresis band of 5 A.
Figure 5.52 Simulink model of hysteresis controller for single-phase grid current modulation.
Figure 5.53 Demonstration of grid current regulation using a hysteresis band of 0.74 A.
Figure 5.54 Current unfolding circuit using H bridge for the DC to single-phase AC conversion.
Figure 5.55 Simulated waveform to demonstrate the current unfolding for the DC to single-phase AC conversion.
Figure 5.56 Current source inverter used as grid-side converter: (a) two-stage conversion; (b) single-stage conversion.
Figure 5.57 Simulink model for three-phase DC-to-AC conversion.
Figure 5.58 Simulink model for the hysteresis controller in regulating three-phase current source inverter.
Figure 5.59 Simulink model for the computation of .
Figure 5.60 Simulink model for L filter for single-phase applications.
Figure 5.61 Simulated waveform of grid voltage and current.
Figure 5.62 Simulink model for L filter for three-phase applications.
Figure 5.63 Demonstration of three-phase current regulation for grid interconnections.
Figure 5.64 LCL filter circuits: (a) undamped LCL filter; (b) LCL filter with damping resistor.
Figure 5.65 Simulink model for LCL filter without damping resistor.
Figure 5.66 Simulink model for damped LCL filter.
Figure 5.67 LC filter for AC loads.
Figure 5.68 Common current waveforms in switching-mode power converters: (a) trapezoidal waveform with rising top; (b) trapezoidal waveform with dropping top.
Figure 5.69 Common current waveforms in switching-mode power converters: (a) triangular waveform with DC offside; (b) triangular waveform without DC offside.
Figure 5.70 Common current waveform in switching-mode power converters.
Figure 5.71 IGBT and MOSFET models with consideration of parasitic capacitance.
Figure 5.72 Switching loss illustration for MOSFET turn-on state and turn-off state.
Figure 5.73 Submodule-integrated DC/DC converters constructed from GaN FETs.
Chapter 6: Dynamic Modeling
Figure 6.1 Electrical characteristics of the PV module showing dynamic conductance and resistance.
Figure 6.2 Three-zone definition based on I–V curve.
Figure 6.3 Location of poles and zero of the system model .
Figure 6.4 Dynamics comparison of simulation model and small-signal model when buck topology is used for the PVSC.
Figure 6.5 Dynamics comparison of simulation model and small-signal model.
Figure 6.6 Dynamics comparison of simulation model and small-signal model when boost topology is used for PVSC.
Figure 6.7 Dynamics comparison of simulation model and small-signal model when tapped-inductor topology is used for PVSC.
Figure 6.8 Dynamics comparison of simulation model and small-signal model when buck–boost topology is used for PVSC.
Figure 6.9 Dynamics comparison of simulation model and small-signal model when flyback topology is used for PVSC.
Figure 6.10 Bidirectional DC/DC circuit with dual active bridge topology for output voltage regulation.
Figure 6.11 Dynamics comparison of the simulation model and the small-signal model.
Figure 6.12 Simulink model for evaluating the small-signal model.
Figure 6.13 Dynamics comparison of the simulation model and the small-signal model.
Figure 6.14 Dynamics comparison of the simulation model and the small-signal model.
Chapter 7: Voltage Regulation
Figure 7.1 Control diagrams of two-stage conversion system for grid interconnection. FF, feedforward; FB, feedback.
Figure 7.2 Control diagrams of single-stage conversion system for grid interconnection.
Figure 7.3 Illustration of Q-parameterization.
Figure 7.4 Actions of P, I, and D terms in the time domain.
Figure 7.5 Bode diagram of typical PD controller.
Figure 7.6 Demonstration of gain margin and phase margin by Bode diagram.
Figure 7.7 Demonstration of gain margin and phase margin using Nyquist plot.
Figure 7.8 Demonstration of gain margin and phase margin by Nyquist plot.
Figure 7.9 Demonstration of sensitivity peak by Bode diagram.
Figure 7.10 Hybrid control system using both feedback and feedforward controllers.
Figure 7.11 Demonstration of gain margin, phase margin, and sensitivity peak by Nyquist plot.
Figure 7.12 Waveform of PV voltage regulation using boost converter.
Figure 7.13 Demonstration of gain margin, phase margin, and sensitivity peak by Nyquist plot.
Figure 7.14 Waveform of PV voltage regulation using tapped inductor converter.
Figure 7.15 Waveform of PV voltage regulation using buck converter.
Figure 7.16 Waveform of PV voltage regulation using buck–boost converter.
Figure 7.17 Waveform of PV voltage regulation using buck–boost converter.
Figure 7.18 Waveform of DC-link voltage regulation using DAB converter.
Figure 7.19 Diagram of DC-link voltage regulation with DC/AC grid-connected conversion.
Figure 7.20 Performance of DC voltage regulation for single-phase grid interconnection using only feedforward controller.
Figure 7.21 Performance of DC-link voltage regulation for single-phase grid interconnection using hybrid controller with both feedforward and feedback.
Figure 7.22 Diagram of DC-link voltage regulation implemented with both feedforward and feedback controllers.
Figure 7.23 Performance of DC voltage regulation for single-phase grid interconnection using hybrid with both feedforward and feedback controllers.
Figure 7.24 Diagram of DC-link voltage regulation implemented with both feedforward and feedback controllers.
Figure 7.25 Performance of DC voltage regulation for three-phase grid interconnection using hybrid with both feedforward and feedback control.
Figure 7.26 Cascade connection of sensor and signal conditioner.
Figure 7.27 Example of voltage measurement circuits: (a) DC voltage measurement and signal conditioning; (b) AC voltage measurement and signal conditioning.
Figure 7.28 Waveform in AC voltage measurement.
Figure 7.29 Feedback system with limiter.
Figure 7.30 Voltage regulation illustrating the windup effect.
Figure 7.31 Voltage regulation illustrating anti-windup using a slew-rate limiter.
Figure 7.32 Voltage regulation illustrating windup effect caused by sudden irradiance variations.
Figure 7.33 Detection and conditional integration for anti-windup action.
Figure 7.34 Voltage regulation illustrating the anti-windup effect of conditional integration.
Figure 7.35 Illustration of feedback form of biproper controller for anti-windup.
Figure 7.36 Illustration of feedback form of biproper controller for anti-windup with a negative static gain.
Figure 7.37 Voltage regulation illustrating the anti-windup effect of the feedback form of the controller.
Figure 7.38 Hybrid system with digital controller.
Figure 7.39 Sampled measurement of AC voltage signal.
Figure 7.40 Flowchart in a typical digital control loop.
Figure 7.41 Dynamic system representation and transformation in discrete and continuous time.
Figure 7.42 Bode diagrams to compare the analog control with redesigned digital counterparts.
Figure 7.43 Bode diagrams to compare analog control with the redesigned digital counterpart.
Figure 7.44 Typical sensing circuit including the A/D converter and the analog multiplexer for multiple channels.
Figure 7.45 Waveform of voltage regulation by digital controller.
Chapter 8: Maximum Power Point Tracking
Figure 8.1 Conductance match for maximum power point tracking: top, based on I–V curve; bottom, based on P–V curve.
Figure 8.2 Evolution of maximum power point tracking: (a) direct resistor match; (b) variable load match; (c) controllable power interface.
Figure 8.3 Hill climbing algorithm for maximum power point tracking.
Figure 8.4 Hill climbing based on the P–V curve.
Figure 8.5 Hill climbing based on the P–D curve.
Figure 8.6 Simulink model of the hill-climbing-based maximum power point tracking.
Figure 8.7 Flowchart for extreme value searching.
Figure 8.8 Waveforms of PV power (), voltage (), and current () measured on 9 July 2006.
Figure 8.9 Waveforms of PV power (), voltage (), and current () measured on 24 June 2006.
Figure 8.10 Simulink model of the buck converter used for PV-side power interface with MPPT.
Figure 8.11 Simulation result of the buck converter used for PV-side power interface with MPPT.
Figure 8.12 Simulation result of the buck converter used for PV-side power interface with MPPT.
Figure 8.13 Three-point oscillation caused by HC-based MPPT.
Figure 8.14 Flowchart of the start-stop mechanism for hill-climbing operation.
Figure 8.15 Simulink model for integration of start-stop mechanism with HC-based MPPT.
Figure 8.16 Simulink model of the start-stop mechanism.
Figure 8.17 Simulation result of the buck converter used for PV-side power interface with the start-stop mechanism for MPPT.
Figure 8.18 PV output: top, P–V curve; bottom, curve.
Figure 8.19 Maximum power point tracking based on steepest descent algorithm.
Figure 8.20 Centered differentiation based on the P–V curve.
Figure 8.21 Maximum power point tracking using centered differentiation.
Figure 8.22 System identification based on recursive least squares method.
Figure 8.23 Model-based determination of the MPP using the Newton–Raphson method.
Figure 8.24 Block diagram for extremum-seeking control.
Figure 8.25 Simulink model for the extremum seeking scheme.
Figure 8.26 Performance of maximum power point tracking using extremum seeking with the configuration of Case 1.
Figure 8.27 Performance of maximum power point tracking using extremum seeking with the configuration of Case 2.
Figure 8.28 Performance of maximum power point tracking using extremum seeking with the configuration of Case 3.
Figure 8.29 Test bench system for evaluating MPPT in DC microgrids and two-stage conversion systems.
Figure 8.30 Test bench system for evaluating MPPT in single-stage DC/AC conversion systems.
Chapter 9: Battery Storage and Standalone System Design
Figure 9.1 General classification of standalone PV systems.
Figure 9.2 Standalone systems without bulk energy storage: (a) direct-coupled; (b) with power conditioning; (c) hybrid solution.
Figure 9.3 Standalone PV system with bulk energy storage.
Figure 9.4 Hybrid system including PV and bulk energy storage.
Figure 9.5 Formation of battery power systems from cell to bank.
Figure 9.6 Cycle charge with constant current and constant voltage: top, charging voltage; bottom, charging current.
Figure 9.7 Charging voltage with temperature compensation.
Figure 9.8 Typical battery cell equalization techniques.
Figure 9.9 Balancing circuits based on heat dissipation: (a) zener diode; (b) fixed shunt resistor; (c) switched shunt resistor.
Figure 9.10 Balancing circuits using switched capacitors.
Figure 9.11 Semiconductor circuit for the single-pole-double-throw switch.
Figure 9.12 Balancing circuit based on switched capacitors.
Figure 9.13 Balancing circuits based on switched inductor.
Figure 9.14 Balancing circuits based on flyback topology.
Figure 9.15 Balancing circuits based on switched capacitor with resonance.
Figure 9.16 Transient response of battery voltage to step change of discharge current.
Figure 9.17 Simplified Thévenin model for battery modeling.
Figure 9.18 Simulink model for the simplified Thévenin battery model.
Figure 9.19 Battery voltage versus discharged capacity for model output and product data.
Figure 9.20 Open-circuit voltage () versus SOC: model output and BK-10V10T product data.
Figure 9.21 Simulink model for the voltage source to output based on the level of SOC corresponding to the battery current.
Figure 9.22 Simulation of four-hour charge and discharge of BK-10V10T battery module.
Figure 9.23 Modified Thévenin model for batteries.
Figure 9.24 Simulink model for the modified Thévenin battery model.
Figure 9.25 Simulation result of the dynamic response of the battery voltage for the impulsed current variation.
Figure 9.26 Comprehensive Thévenin model for battery modeling.
Figure 9.27 Simulink model for the voltage source to output based on the SOC and self-discharge rate.
Figure 9.28 Integration of maximum power point tracking for battery charge control.
Figure 9.29 System diagram of direct coupled PV system for ventilation.
Figure 9.30 A design procedure for PV-battery systems.
Figure 9.31 Single line diagram of standalone PV system with battery storage.
Figure 9.32 Equivalent circuit of standalone PV system with battery storage.
Figure 9.33 Simulink model for integrating MPPT and battery-charging cycles.
Figure 9.34 Output characteristics of the PV array.
Figure 9.35 Configuration of the standalone PV system with battery storage for short-term simulation.
Figure 9.36 Simulink model of the averaged synthesis of the buck converter.
Figure 9.37 Configuration of standalone PV system with battery storage for medium-term simulations.
Figure 9.38 Simulated waveforms showing maximum power point tracking for battery charging.
Figure 9.39 Simulated waveforms showing the transition from maximum power point tracking to battery voltage regulation.
Figure 9.40 Simulated waveforms showing the transition from the battery voltage regulation to maximum power point tracking.
Figure 9.41 Configuration of standalone PV system with battery storage for long-term simulation.
Figure 9.42 Simulated waveforms showing the two-hour operation.
Figure 9.43 Simulated waveform of the PV-link voltage, illustrating the details of MPPT.
Figure 9.44 Simulated waveforms for the two-hour operation.
Figure 9.45 Simulated waveform of the PV-link voltage illustrating the MPPT detail.
Figure 9.46 Simulation of eight-hour operation of standalone system.
Chapter 10: System Design and Integration of Grid-connected Systems
Figure 10.1 A design procedure for grid-connected PV systems.
Figure 10.2 Line diagram of inverter output circuit.
Figure 10.3 Single line diagram of the grid-connected system example for single-phase-low-voltage grid interconnection.
Figure 10.4 Line diagram of grid-connected system with MIPIs.
Figure 10.5 Grid-connected system example for medium-voltage grid integration. (OCP = overcurrent protection.)
Figure 10.6 Block diagram for simulating the power train of single-stage conversion systems.
Figure 10.7 Block diagram for simulating the power train of two-stage conversion systems.
Figure 10.8 Output characteristics of the HiS-M250RG PV module.
Figure 10.9 Output characteristics of the PV string that is formed by 12 HiS-M250RG modules.
Figure 10.10 Simulink model for the DC/DC stage.
Figure 10.11 Demonstration of gain margin, phase margin, and sensitivity peak by Nyquist plot.
Figure 10.12 PV string output in response to the temperature difference.
Figure 10.13 Simulink model of the DC/AC stage.
Figure 10.14 Simulink model of 6-kW grid-connected PV system.
Figure 10.15 PV system simulation result in response to the variation of irradiance and temperature difference: (a) power; (b) PV-link voltage; (c) grid current; (d) DC-link voltage.
Figure 10.16 Simulink blocks of the averaged model for boost DC/DC converters.
Figure 10.17 Simulink blocks of the averaged model for single-phase AC section.
Figure 10.18 Simulink blocks of the averaged model for three-phase AC section.
Figure 10.19 Simplified Simulink model of the 6-kW grid-connected PV system.
Figure 10.20 Simulation result using average model in response to variations of irradiance and temperature difference: (a) power; (b) PV-link voltage; (c) grid current; (d) DC-link voltage.
Figure 10.21 Comparison of the zoomed-in simulation results with the averaged model (AVG) and the switching model (SW): (a) PV output power; (b) PV-link voltage; (c) grid current; (d) DC-link voltage.
Figure 10.22 Simulation of eight-hour operation of grid-connected PV system: (a) PV power; (b) PV-link voltage; (c) grid current; (d) AC power; (e) DC-link voltage.
Figure 10.23 Efficiency curves of ABB-PVI-6000 PV inverter.
Figure 10.24 Simulink blocks of the averaged model for flyback converters.
Figure 10.25 Simulation comparison between the switching model and the averaged model: (a) PV-link voltage; (b) PV output current; (c) PV output power.
Figure 10.26 Single MIPI simulation unit for single-phase AC grid-connected PV system.
Figure 10.27 Simplified Simulink model of the 6-kW grid-connected PV system.
Figure 10.28 Simulation of grid-connected system with 24 module-integrated parallel inverters dealing with mismatch condition: (a) irradiance drops from 900 to 700 at 255 ms; (b) irradiance drops from 800 to 600 at 255 ms; (c) irradiance drops from 700 to 500 at 255 ms; (d) irradiance increases from 600 to 800 at 255 ms.
List of Tables
Chapter 1: Introduction
Table 1.1 Price schedule of feed-in tariffs in Ontario, Canada
Table 1.2 Common PV materials
Table 1.3 SRE for measurement of NOCT
Table 1.4 Four important values representing PV output characteristics
Table 1.5 Converters used for DC/DC power interfaces
Table 1.6 Converters for DC/AC power interfaces
Table 1.7 Record of Solar Impulse journey
Chapter 2: Classification of Photovoltaic Power Systems
Table 2.1 Specification of photovoltaic module BP350
Chapter 3: Safety Standards, Guidance and Regulation
Table 3.1 Standards related to PV products
Table 3.2 Inverter-related standards
Table 3.3 IEEE 1547 series of standards
Table 3.4 Clearing time in response to abnormal voltages
Table 3.5 Clearing time in response to abnormal frequency
Table 3.6 Limits of maximum harmonic current distortion in odd order
Table 3.7 Key components in solar PV systems
Table 3.8 Voltage correction factors for Si crystalline-based PV circuits
Table 3.9 Cable types
Table 3.10 Voltage levels for PV power integration
Chapter 4: PV Output Characteristics and Mathematical Models
Table 4.1 PV model coefficients
Table 4.3 PV model variables
Table 4.4 Sample solar cell data
Table 4.2 PV model parameters and constants
Table 4.5 Sample data
Table 4.6 Modeling comparison
Table 4.7 Modeling comparison for MSX-83 cell
Table 4.8 Polynomial parameters for the I–V curve of MSX-83
Table 4.9 Polynomial parameters for the P–V curve of MSX-83
Table 4.10 Polynomial coefficients for I–V output characteristics of ST-10
Table 4.11 Coefficients for P–V characteristics of ST-10
Chapter 5: Power Conditioning
Table 5.1 Specification of dual active bridge
Table 5.2 Switching operation of dual active bridge
Table 5.3 Switching operation of dual active bridge
Table 5.4 Specification of three-phase DC/AC conversion
Table 5.5 Specification of the DC to single-phase AC conversion
Table 5.6 Common converter topologies for PV-side converters
Table 5.7 Common converter topologies for AC grid-side power interfaces
Chapter 6: Dynamic Modeling
Table 6.1 Parameter impact on system dynamics
Chapter 7: Voltage Regulation
Table 7.1 Variation of PID-based controllers
Table 7.2 Percentage of overshoot for damping factors in second-order systems
Table 7.3 Feedback versus feedforward
Table 7.4 Category of signals
Chapter 8: Maximum Power Point Tracking
Table 8.1 Loss analysis of switching-ripple voltage at the PV output terminals
Table 8.2 Dynamic analysis of the buck converter used for the PV-side power interface
Table 8.3 Parameters and synthesis of ES scheme
Table 8.4 ES parameters in different case studies
Chapter 9: Battery Storage and Standalone System Design
Table 9.1 Common lead-acid battery types
Table 9.2 Common nickel-based batteries
Table 9.3 Typical applications of lithium-ion batteries
Table 9.4 Typical settings for charging lead-acid batteries
Table 9.5 Typical settings for charging lithium-ion batteries
Table 9.6 Polynomial curve fitting parameters for battery pack BK-10V10T
Table 9.7 Polynomial parameters for modeling battery module BK-10V10T
Table 9.8 Comparison of battery models
Table 9.9 Specification of Orion 12HBXC01A cooling fan
Table 9.10 Specification of Invensun i170-48P PV module
Table 9.11 Specification of DC load
Table 9.12 Weather information for PV power generation
Table 9.13 Key specification of the charge controller–FLEXmax 60
Table 9.14 Specification of PV module Q.PLUS BFR-G4.1
Table 9.15 Battery pack configuration and specification
Table 9.19 Specification of DC circuit breaker 1
Table 9.20 Specification of DC circuit breaker 2
Table 9.21 Specification of buck converter circuit
Table 9.22 Specification of the MPPT algorithm
Table 9.23 Specification of the simulation computer
Chapter 10: System Design and Integration of Grid-connected Systems
Table 10.1 Specification of a grid-connected system
Table 10.2 Specification of PV module HiS-M250RG l
Table 10.3 Specification of SMA-SB-240 inverter
Table 10.4 System specification of grid-connected system
Table 10.5 Design specification of PV source circuits
Table 10.6 Design specification of PV combiner boxes
Table 10.7 Design specification of DC disconnects
Table 10.8 Specification of DC/DC boost converter
Table 10.9 Design specification of DC/AC stage
Table 10.10 Specification of the flyback converter
Photovoltaic Power System
Modeling, Design, and Control
Weidong Xiao
University of SydneyAustralia
This edition first published 2017
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Library of Congress Cataloging-in-Publication Data
Names: Xiao, Weidong, 1969- author.
Title: Photovoltaic power system : modeling, design, and control / Weidong Xiao.
Description: Hoboken, NJ : John Wiley & Sons, 2017. | Includes bibliographical references and index.
Identifiers: LCCN 2016056659 (print) | LCCN 2017001056 (ebook) | ISBN 9781119280347 (cloth) | ISBN 9781119280361 (pdf) | ISBN 9781119280323 (epub)
Subjects: LCSH: Photovoltaic power systems.
Classification: LCC TK1087 .X56 2017 (print) | LCC TK1087 (ebook) | DDC 621.31/244-dc23
LC record available at https://lccn.loc.gov/2016056659
Cover Design: Wiley
Cover Images: (Background) © Alessandro2802/Gettyimages; (Circles: Top right corner to bottom left corner) © chapin31/Gettyimages; © PaulPaladin/Gettyimages; Courtesy of author; © Dwight Smith/Shutterstock
This book is dedicated to my son, William, and daughter, Emily, with deep love.
Preface
Photovoltaic (PV) power engineering has attracted significant attention in recent years. This book sets out to fulfil an important need in academia and industry for a comprehensive resource covering modeling, design, simulation, and control of PV power systems. Initially developed to support teaching senior-undergraduate and graduate courses, the work also covers practical design issues, that make it useful for industry practitioners seeking to master the subject through self-study and training. The book provides a smooth transition from fundamental knowledge to advanced subjects of interest to academics and to those working on system improvements in industry. A fundamental knowledge of power electronics and linear control theory is required to benefit fully from this book.
This comprehensive treatment covers fundamental and advanced subjects in technologies, power electronics, and control engineering for PV power systems. Throughout, the description of PV power systems follows a clear framework for each section.
The book is divided into ten chapters. The interrelationship of the chapters is illustrated in Figure 1. The step-by-step introduction of the individual system components and controls for PV power systems is covered in Chapters 4–8.With the support of the system classification and the safety guidelines, which are discussed in Chapters 2 and 3, respectively, the overall system integrations for standalone systems and grid-tied systems are set out in Chapters 9 and 10.
Figure 1 Organization and interconnection of Chapters 2 to 10.
Chapter 1 provides a brief introduction to solar power systems. This includes the clarification of vocabulary which proves integral to the remainder of the book.
Chapters 2 and 3 provide comprehensive classifications of PV power system configurations, in particular grid-tied systems, approached according to the level at which the MPPT is applied, MPPT techniques, power-conditioning topologies, and technologies for battery balancing. The reader is assisted, using clear definitions, to develop an understanding of the latest systems and directions of research and development, which later informs research directions for PV power systems. Reader understanding of relevant safety standards, guidance, and regulations is developed to prevent researchers deviating from standard practice in industry. A system of reference is provided for safe practice in engineering and design. Though the codes and guidelines cited are implemented in the USA and Europe, they are universally applicable and allow all readers to practice PV power engineering in a safe manner. These chapters also cover the certification of PV modules, the safety standards of power interfaces, the system requirements for grid interconnection, and the important means of protection. The main conversion units are the PV-side converters, battery-side converters, and grid-side converters. The interconnection of the conversion units are the PV link, DC link, and grid link. The PV generation section is divided into the PV source circuits and PV output circuits. Two types of modeling are demonstrated for the reader. Firstly, simulation models that represent a practical system and prove the design concept are discussed in Chapters 4 and 5. Secondly, mathematical models are developed to illustrate the system dynamics used for controller synthesis. Model development and verification are covered in Chapter 6.
Chapter 4 discusses PV output characteristics and mathematical models for simulation and analysis. It builds upon an understanding of PV product datasheets and provides a straightforward approach to building a mathematical model for simulation purposes. When model accuracy becomes the priority, an advanced approach is also provided. The tradeoff between model simplicity and accuracy is extensively considered, discussed, and demonstrated by practical examples.
Chapter 5 provides the information necessary to specify, design, simulate, and evaluate power-conditioning circuits and accessories for PV power applications. The main conversion units are PV-side converters, battery-side converters, and grid-side converters. The important interconnections are the PV link, DC link, and grid link. The description provided comprehensively covers application to all PV power systems. The chapter covers system design, steady-state analysis, and simulation verification. Current modulation for AC grid interconnection is introduced and simulated for design verification. This book places emphasis on computer-aided analysis, design, and evaluation. For universality, all included simulation models are built using the fundamental blocks of Simulink. The analysis reveals the fundamental system dynamics for the purpose of both time-domain simulation and control synthesis. Although provided with software such as Simscape Power Systems, written for power electronics and power systems, this is not used due to the aim to demonstrate the simulation principle and focus on fundamental implementations instead. The control system design, analysis and evaluations are based on the functions of Matlab and Matlab version R2010b. Simulink is used to demonstrate all simulation cases; the same or higher versions of this software can be used to duplicate simulation results or develop results further. Most chapters present practical examples in order to demonstrate designs and verify them, which are presented in case studies. Photographs, diagrams, flowcharts, graphs, equations, and tables are included to provide clear explanations of technical subject matter. Readers can then duplicate results through computer-aided design and analysis, leading to the development and evaluation of new systems.
Chapter 6 focuses on dynamic modeling of PV power systems. The mathematical modeling starts with the state-space averaging, followed by linearization. Dynamic models are developed for the voltage signals at the PV and DC links and the variety of converter topologies is also considered. The dynamics of the developed mathematical models are verified through simulation and comparison. One section is given over to modeling the dynamics of dual active bridges when used as the battery power interface.
Chapter 7 concerns the application of linear control theory. The chapter discusses evaluations of relative stability and system robustness. Voltage regulation for the PV and DC links is introduced and analyzed in depth. Examples and simulations are used to demonstrate the effectiveness of proposed approaches and methodology. Based on the system model, advanced control techniques, such as Affine parameterization, anti-windup, and feedforward implementation, are introduced. The implementation of sensing and digital control is briefly discussed at the end of the chapter.
Chapter 8 focuses on MPPT, which is important and unique to PV power systems. A comprehensive overview is provided, and MPPT algorithms are classified and discussed. The chapter introduces a simple algorithm and develops to consider advanced techniques to improve tracking performance. The simulation and implementation of MPPT techniques are also discussed in this chapter.
Chapter 9 discusses the integration of standalone PV power systems. The chapter enables readers to understand the latest progress and choose suitable battery types for standalone applications through the introduction and comparison of battery characteristics. This proceeds onto a discussion of battery characteristics and models and how they relate to system design and analysis. A new classification is proposed to avoid confusion seen in the earlier literature and provide a clear framework for understanding the methodologies used for battery balancing. A method to integrate the MPPT function with the battery cycle charge is proposed. Examples are given to demonstrate the effectiveness of modeling, design, control, and simulation. Simulation models for the controller and power interface are developed at different levels: short term, medium term, long term, and very long term. A simulation of eight-hour system operation is created, demonstrating the state of MPPT, battery voltage regulation, and variation of state of charge corresponding to solar irradiance and cell temperature.
The final chapter, Chapter 10, addresses the integration of grid-tied PV power systems, including two small-scale single-phase interconnections and one utility-level three-phase system. Examples are given demonstrating the effectiveness of the design, integration, control, and simulation with additional consideration for safety protection. The simulation study is divided into two parts: a short-term simulation that aims to capture the fast transient response of switching dynamics and grid disturbances, and a long-term simulation that illustrates the system operation in response to environmental conditions.
Technical Support
One advantage of this book is that all modeling and simulation for the case studies is based on the basic functions of Simulink and Matlab. The modeling and simulation approach is based on system dynamics, which helps readers to understand the fundamental principle behind various simulation tools. The construction of output models, power interfaces and control, and standalone and grid-tied systems are illustrated in detail. Version R2010b or higher of Matlab and Simulink can be used to duplicate the results or to develop new studies. Other software tools are unnecessary.
University of Sydney
Australia
Weidong Xiao
Acknowledgments
I would like to acknowledge the contributions of my former students in the Masdar Institute of Science and Technology (MIST). Dr Yousef Mahmoud initialized the study of PV modeling and simulation while he was a graduate student at MIST. Mr. Po-Hsu Huang continued this development and presented an effective method to solve the nonlinear equations involved and balance model complexity and accuracy. Mr. Edwin Fonkwe raised the idea of distributed PV generation at PV module level. Mr. Omair Khan continued studying fine granularity MPPT and state-of-the-art technologies of gallium nitride power devices for power conditioning. He also proposed the start–stop mechanism, which has been proven to be effective for the hill-climbing-based MPPT.
I received tremendous support from Dr. William G. Dunford, Dr. Antoine Capel, and Dr. Luis Martinez Salamero, during a period of graduate study at the University of British Columbia. In 2010, as a visiting scholar, I spent eight months at the Massachusetts Institute of Technology working with Prof. David Perreault and Prof. James Kirtley. I received great support in the research area of power interfaces for PV power systems. Over the past four years, my former colleague at MIST, Dr Mohamed Elmousi helped me to understand the grid concept when a PV power plant, significant in size, is connected to the network. Working with Dr Yang Du at MIST, I gained significant knowledge regarding the analysis of DC link voltage ripples in single-phase AC systems. I have also been working with my former classmates, Dr Fei Richard Yu and Dr Peng Zhang through collaborative research and joint publications.
Special thanks go to Alpha Technologies Ltd and MSR Innovations Corp, which are based in the beautiful British Columbia, Canada. Both companies provided generous support for my Masters and Doctoral degrees. Working with them, I gained invaluable industrial experience that has helped me to learn and understand the fundamentals of power electronics, and to research and develop practical PV power systems. A former colleague, Mr Tim Roddick, supported me by providing photos and initializing the discussion about building integrated PV.
I would like to thank Ms Ella Mitchell and Ms Nithya Sechin, the editors at John Wiley & Sons, for their professional support for this project through all its phases. Last but not least, I heartily thank all of my family members; I was so focused on writing, that I have spent little time with them over the past 13 months. Without their patience and understanding, this book would have been impossible.
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Chapter 1Introduction
The photovoltaic (PV) effect is the generation of DC electricity from light. Alexandre Edmond Becquerel, a French experimental physicist, discovered the effect in 1839. More recently, scientists have discovered that certain materials, such as silicon, can produce a strong PV effect. In the 1950s, Bell Labs of the USA produced PV cells for space activities. This can be considered as the beginning of the PV power industry. The high cost of PV materials mostly prevented applications elsewhere.
Over the past 20 years, the PV power industry has experienced significant growth. PV power generation has become more and more common. The capacity of PV systems ranges from milliwatts for portable devices such as calculators, to gigawatts for power plants connected to the electricity grid. A grid-connected PV power system can be economically installed, and can be rated as low as just a few hundred watts. The advantages of PV power systems that have led to their rapid growth are:
green, renewable
reliability and long lifetime
advanced manufacturing process
static, so noise-free operations
improving efficiency
decreasing prices
flexibility of construction
highly modular nature
availability of government support and incentives.
Using the latest technologies, the manufacturing of crystalline-based PV cells consumes significant amounts of energy, which prevents further cost reductions. The levelized cost of electricity generated using solar PVs is still high in comparison with conventional generation resources, such as coal, natural gas, and wind, according to a technical report published by the US Department of Energy's National Renewable Energy Laboratory (Stark et al. 2015). The report was based on a study of the USA, Germany, and China. Several large-scale PV power systems were announced in 2016 and projected significantly lower costs, but these must be treated as special cases. The project feasibility and system reliability need to be carefully evaluated until the projects are successfully delivered. It is clear that the price of PV products mostly reflects their quality and reliability. High-quality, certified PV products are usually more expensive than non-certified ones. It is unrealistic to judge a PV power system only on the installation cost since reliable and long-lifetime operations are always expected.
The feed-in tariff (FIT) is the major driver of the boom in PV power all over the world. The regulatory incentives are different from country to country, but all are designed to accelerate investment in PV-related technologies. One FIT example can be found on the website of the Ontario Power Authority, Canada. Parts of the FIT price schedule are shown in Table 1.1, which covers projects under 500 kW in capacity. It shows that the government contributes significant funds for PV system installations since the listed price is higher than the charge for residential consumption. It should be noted that the listed price is based on the 2016 schedule. Like FITs in most other countries, it is always subject to change. Another disadvantage of PV power systems lies in their low power density, which limits their use mainly to static applications rather than vehicles. Motor vehicles are usually considered as one of the major contributors to air pollution.
Table 1.1 Price schedule of feed-in tariffs in Ontario, Canada
Type
System capacity (kW)
Price ($/kWh)
*
Rooftop
10
0.294
10–100
0.242
100–500
0.225
Non-rooftop
10
0.214
10–500
0.209
* Canadian dollars.
1.1 Cell, Module, Panel, String, Subarray, and Array
A PV cell, also commonly called a solar cell, is the fundamental component of a PV power system. A crystalline-based solar cell features a p-n junction, as shown in Figure 1.1. The manufacturing process includes melting, doping, metallization and texturing. The positive and negative sides of the junction form the DC voltage and supply electricity when a load is connected. However, the voltage of a single p-n junction cell is less than 1 V, which is low for most practical applications. Moreover, it is mechanically fragile, and must be laminated and protected for practical use.
Figure 1.1 Typical crystalline PV cell construction.
To end users, the basic unit is the PV module or solar panel, which can produce higher voltages and more power than a single cell. A PV module consists of cells that are interconnected and laminated together. The old PV panel was usually designed to match the nominal voltage of batteries, since standalone systems were the beginning of the PV industry. For example, traditional 36-cell PV modules used to be popular for direct charging of batteries with a nominal voltage of 12 V. Nowadays, with the increasing numbers of grid-connected systems and the advances in power-conditioning devices, the number of cells in each PV module is no longer limited to matching the nominal voltages of batteries or loads. The manufacturers are more concerned with cost-effective solutions and supply all different sizes of solar panels: usually incorporating 48, 54, 60, or 72 cells. Solar cables and connectors are usually integrated with the module for straightforward interconnection and installation.
To form a PV panel, crystalline-based PV cells are sandwiched by the superstrate and substrate for protection, as illustrated in Figure 1.2. Tempered glass is commonly used as the superstrate, supporting the module lamination and protecting the fragile cells. Glass also has the same ratio of thermal expansion as a crystalline PV cell, since both are made of silicon. Furthermore, tempered glass is strong and has good transparency, with about 94% light transmission. The glass surface is also textured to reduce light reflections. Metal conductors connect the PV cells from the surface to the bottom for series interconnection. The cells are also protected by an encapsulant, which is a material that surrounds the PV cells between the superstrate and substrate.
Figure 1.2 Lamination of PV module.
Figure 1.3
