PV Converter Output Curve Control for Shaded String Power Retention
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Solution Overview
Problem
In photovoltaic power generation systems, when a plurality of photovoltaic modules in a string are seriously blocked, the input voltage of the inverter exceeds the voltage limiting point, causing the inverter's input current to drop to zero, resulting in a significant reduction of power output and affecting energy yield.
Innovation Solution
A converter control method that simulates the output power-voltage curve of photovoltaic modules by incorporating a simulated voltage limiting section and a constant power section, allowing the converter to mimic the behavior of a photovoltaic module, thus enabling the inverter's existing MPPT control policy to adapt and maintain stability and energy yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed voltage limiting method is used to control converter output voltage, then voltage stability is improved and inverter overvoltage protection is enabled, but when photovoltaic modules are blocked the input voltage exceeds the limiting point causing power to drop to zero
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed voltage limiting method to a dynamic output PV curve simulation method. The converter dynamically adjusts its output characteristics based on simulated PV curves that adapt to different operating conditions, including blocked module scenarios. This allows the system to maintain voltage stability while preventing power drop to zero by dynamically adjusting the voltage-current relationship according to the simulated PV curve rather than using a static voltage limit.
Solution Approach 2:
The patent changes the control parameter from fixed voltage limiting to simulated output PV curve characteristics. By simulating the PV curve of the photovoltaic module at the converter output, the system adjusts both voltage and current parameters dynamically. When modules are blocked, the simulated PV curve automatically adapts to the reduced power capability, allowing the inverter to operate at a reduced but non-zero power level while maintaining voltage within acceptable limits.
2Adaptability or versatility
If the inverter operates in fixed input voltage control mode to match converter voltage limiting, then voltage compatibility is improved, but MPPT functionality is lost and energy yield decreases
Solution Approach 1:
The patent applies copying by creating a simulated output PV curve that replicates the characteristics of the photovoltaic module's natural PV curve. Instead of forcing the inverter to operate in fixed voltage mode, the converter copies the module's PV characteristics at its output. This allows the inverter to continue using its MPPT control policy which relies on detecting PV curve characteristics, while the converter ensures voltage compatibility through the simulated curve. The copying approach maintains both voltage compatibility and MPPT functionality simultaneously.
3Productivity
If converters are added to enable module-level MPPT and voltage-limited output, then energy yield improvement is achieved, but system complexity increases
Solution Approach 1:
The patent applies universality by designing the converter to perform multiple functions: it provides voltage-limited output protection, enables module-level MPPT through simulated PV curve output, and maintains compatibility with standard inverter MPPT control policies. The single converter device handles all these functions through the simulated output PV curve approach, avoiding the need for separate control systems for each function. This multi-functionality reduces overall system complexity while achieving the energy yield improvements from module-level control.
Data Source
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AI summary
This application relates to a converter in a photovoltaic power generation system and a converter control method. An input end of the converter is connected to at least one photovoltaic module, and an output end is connected to an inverter. The control method includes: determining an output PV curve of a converter based on an output power-voltage (PV) curve of the photovoltaic module; and controlling a voltage output of the converter based on the output PV curve. The output PV curve includes at least a simulated voltage limiting section and a constant power section that are connected. The simulated voltage limiting section means that an output voltage that is of a transformer and that corresponds to any point in the section is proportional to an output voltage of the photovoltaic module and there is a same proportional coefficient. The constant power section means that any two points in the section correspond to different output voltages and a difference between output powers corresponding to any two points in the section is less than a first preset threshold. In this application, an existing MPPT control policy of the inverter can be adapted when a voltage-limited output is implemented, to avoid a case in which a power of a photovoltaic string drops to zero.