PV String Voltage Balancing Control for Parallel DC Converters
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Solution Overview
Problem
In photovoltaic systems, a series-parallel mismatch between photovoltaic modules due to shading or other factors leads to inefficient operation of inverters, resulting in low energy yield due to voltage differences between different strings connected in parallel.
Innovation Solution
A power conversion apparatus with a control module that adjusts the output voltages of photovoltaic strings by controlling switching transistors in direct current conversion modules to ensure that the voltage difference between the output voltage of one string and the bus voltage is minimized, while maintaining maximum power point tracking for both strings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If different photovoltaic strings with different quantities of smart modules are connected in parallel to increase system energy yield, then the system can handle series-parallel mismatch and improve adaptability, but the voltage difference between strings causes low operating efficiency of the inverter
Solution Approach 1:
The patent implements dynamic voltage adjustment by controlling switching transistors in direct current conversion modules. The control module dynamically adjusts the output voltages of different photovoltaic strings based on real-time voltage comparisons, ensuring that voltage differences remain within acceptable thresholds while maintaining adaptability to different string configurations.
Solution Approach 2:
The patent changes the voltage parameter of photovoltaic strings by controlling the switching transistors in the direct current conversion modules. By adjusting the duty cycle of the switching transistors, the output voltage of each string is dynamically modified to minimize voltage differences between parallel-connected strings, thereby improving inverter operating efficiency.
2Power
If converters are connected to each photovoltaic module to implement MPPT at module level, then maximum power extraction is improved, but the voltage difference between strings with different module quantities causes energy loss
Solution Approach 1:
The patent implements a feedback control mechanism where the control module continuously monitors the output voltages of different photovoltaic strings and adjusts the switching transistor states accordingly. This closed-loop feedback ensures that voltage differences are minimized while maintaining maximum power point tracking capability for each string, thereby reducing energy loss.
Solution Approach 2:
The system dynamically adjusts the operating voltage of each photovoltaic string by controlling the switching transistors in real-time. This dynamic voltage regulation allows each string to maintain its MPPT capability while adapting to voltage differences caused by different quantities of smart modules, thus minimizing energy loss.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach improves the operating efficiency of the power conversion apparatus and increases the overall energy yield of the photovoltaic system by reducing voltage differences and optimizing power output from all strings.
Implementation Method 1
control a switching transistor in the first direct current conversion module to be turned on or off to decrease the output voltage of the first photovoltaic string and a switching transistor in the second direct current conversion module to be turned on or off to increase the output voltage of the second photovoltaic string
Data Source
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AI summary
This application provides a power conversion apparatus and a control method. The apparatus includes a first direct current conversion module, a second direct current conversion module, and a control module. An input end of the first direct current conversion module is configured to connect to a first photovoltaic string. An input end of the second direct current conversion module is configured to connect to a second photovoltaic string. An output end of the first direct current conversion module and an output end of the second direct current conversion module are connected in parallel to a direct current bus. The control module is configured to: control, when an output voltage of the first photovoltaic string is greater than an output voltage of the second photovoltaic string and a comparison value between the two output voltages is greater than a first threshold, a switching transistor in the first direct current conversion module to be turned on or off to decrease the output voltage of the first photovoltaic string and a switching transistor in the second direct current conversion module to be turned on or off to increase the output voltage of the second photovoltaic string, so that a comparison value between the output voltage of the second photovoltaic string and a bus voltage of the direct current bus is less than a second threshold. This application can improve operating efficiency of the power conversion apparatus and increase a system energy yield.