PV Inverter Grounding Control for PID and Surge Current
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Solution Overview
Problem
Existing power supply systems for photovoltaic cell panels suffer from potential induced degradation (PID), leading to power output reduction due to bias voltage issues, with limited voltage compensation range and surge currents causing inverter shutdowns.
Innovation Solution
A power supply system and method that includes a voltage controller capable of continuously adjusting voltage to earth from 0, using a DC converter to expand the compensation range and prevent surge currents, by adjusting bus voltage and input/output voltage of the inverter and DC converter based on sampled voltages and currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bus is grounded to resolve PID degradation, then the bias voltage to earth of the cell panel string is adjusted, but a surge current is generated due to parasitic capacitance, causing inverter shutdown
Solution Approach 1:
The patent applies preliminary action by gradually adjusting the bus voltage from a low initial value (e.g., 100V) to the target voltage (e.g., 400V) over a period of time before fully grounding the bus. This gradual voltage ramp-up prevents sudden discharge through the parasitic capacitance, thereby avoiding surge current generation while still achieving the PID degradation resolution through controlled bias voltage adjustment.
2Reliability
If the bus voltage is adjusted to compensate for PID, then the bias voltage to earth is modified, but the compensation range is narrow because the minimum voltage is half of the uncontrolled rectified voltage
Solution Approach 1:
The patent applies dynamics by implementing a dynamic voltage adjustment mechanism where the bus voltage can be continuously varied from a low initial value (e.g., 100V) up to the full rectified voltage (e.g., 800V), rather than being constrained to a fixed range starting from half the rectified voltage. This dynamic adjustment capability expands the compensation range and allows flexible adaptation to different PID degradation conditions.
Solution Approach 2:
The patent applies parameter changes by modifying the operating voltage parameter of the bus from a fixed minimum (half rectified voltage) to a variable range starting from a lower value (e.g., 100V) up to the full rectified voltage. This parameter change enables broader voltage compensation capability and allows the system to adapt to various PID degradation scenarios with different voltage requirements.
3Reliability
If an inverter shuts down due to excessive leaked current from surge, then safety is protected, but the power generation capacity of the entire power station is affected
Solution Approach 1:
The patent applies preliminary action by implementing a gradual voltage ramp-up procedure before grounding the bus, where the voltage is increased from a low initial value (e.g., 100V) to the target value (e.g., 400V) over time. This preliminary gradual adjustment prevents surge current generation that would trigger inverter shutdown, thereby maintaining continuous power generation while still achieving the necessary bias voltage adjustment for PID degradation resolution.
Data Source
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AI summary
This application provides a power supply system and a power supply method. The power supply system includes: at least one cell panel string, at least one inverter, a transformer, and a voltage controller. An input end of the at least one inverter is connected to an output end of the at least one cell string, an output end of the at least one inverter is connected to an input end of the transformer, and an output end of the transformer is configured to output a power supply voltage. The output end of the at least one inverter is connected to an output end of the inverter unit. The voltage controller further includes: a first sampling unit, a control unit connected to the first sampling unit, and the inverter unit connected to the first sampling unit. The voltage controller further includes a second sampling unit and a DC converter connected to the second sampling unit. In the power supply system, a voltage to earth of the voltage controller is compensated starting from 0, to resolve a problem that the inverter is shut down or cannot normally work due to a surge current generated at a moment in which the voltage controller is grounded.