Parallel PV Inverter Bus Voltage Control for Circulating Current Suppression
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Solution Overview
Problem
Circulating currents between inverters connected in series and parallel in photovoltaic systems lead to increased power consumption, efficiency loss, and potential inverter shutdown due to overcurrent protection, as well as leakage current mis-protection.
Innovation Solution
A photovoltaic system with a controller that adjusts direct current bus voltages based on the direct current component of a common-mode output current to equalize voltages across inverters, suppressing circulating currents and preventing overcurrent and leakage issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple inverters are connected in series and parallel to increase power capacity, then the power output is improved, but circulating current is generated between inverters causing power loss and efficiency degradation
Solution Approach 1:
The controller detects the common-mode current from each inverter and uses this feedback signal to adjust the DC bus voltage dynamically. By continuously monitoring the circulating current and adjusting voltages in response, the system eliminates the root cause of power loss while maintaining high power capacity operation
Solution Approach 2:
The system dynamically adjusts the DC bus voltage parameter of each inverter based on detected common-mode current levels. By changing the voltage parameter in real-time according to operating conditions, the controller suppresses circulating current and minimizes power loss during high-power operation
2Power
If multiple inverters are connected in parallel to increase power capacity, then the power output is improved, but circulating current causes inverter shutdown due to overcurrent protection triggering
Solution Approach 1:
The controller proactively suppresses circulating current by adjusting DC bus voltages before the current reaches dangerous levels that would trigger overcurrent protection. This preliminary action prevents shutdown events and maintains continuous reliable operation of inverters connected in parallel for high power capacity
3Power
If multiple inverters are connected in parallel to increase power capacity, then the power output is improved, but circulating current causes leakage current mis-protection action
Solution Approach 1:
By continuously monitoring common-mode current and using this feedback to adjust DC bus voltages, the system eliminates circulating current that causes false leakage protection trips. This maintains the reliability of both the power output and the protection system for inverters operating in parallel
4Ease of operation
If DC bus voltages of inverters are different, then circulating current is generated, but equalizing voltages requires active control to suppress circulating current
Solution Approach 1:
Each inverter's controller independently detects its own common-mode current and autonomously adjusts its DC bus voltage to suppress circulating current. This self-service approach simplifies the overall control architecture by eliminating the need for complex centralized voltage equalization control while achieving the desired suppression effect
Data Source
AI summary
A photovoltaic system and a circulating current suppression method. The system includes a controller and at least two inverters. A direct current input terminal of each inverter is connected to a corresponding photovoltaic array. Alternating current output terminals of the at least two inverters are connected in parallel. The controller is configured to: obtain a direct current component of a common-mode output current of at least one of the at least two inverters and adjust a direct current bus voltage of the corresponding inverter based on a magnitude of the direct current component of the common-mode output current, to suppress a circulating current between the at least two inverters. A circulating current between a plurality of inverters connected in parallel can be suppressed, thereby reducing loss caused by a circulating current, and improving power supply efficiency.