Inverter Common-Mode Voltage Matching Before AC Switch Turn-On
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Solution Overview
Problem
Existing inverter systems experience disconnection from the power grid and operational malfunctions due to common mode impulse currents generated when an alternating current switch is switched on, which can trigger external leakage current protectors and cause transient interference.
Innovation Solution
A method involving a compensation power supply to adjust the common mode voltage between the inverter and ground to a target value before switching on the alternating current switch, ensuring zero voltage difference, thereby suppressing the common mode impulse current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the common mode voltage difference between two ends of the alternating current switch is not eliminated before switching on, then the common mode impulse current passes through the RCD and may trigger it to open, but adding complex voltage matching circuits increases device complexity
Solution Approach 1:
The patent makes the DC/DC converter multi-functional by using it for both common mode voltage adjustment and existing power conversion functions. The DC/DC converter is controlled to adjust the common mode voltage of the capacitors while maintaining its primary function, thereby eliminating the need for separate common mode voltage adjustment circuits and reducing overall device complexity
Solution Approach 2:
The inverter system performs self-adjustment of its common mode voltage using its existing DC/DC converter and control system. The control device automatically detects the common mode voltage difference and adjusts the capacitor voltages accordingly, making the system self-sufficient without requiring external complex voltage matching equipment
Data Source
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Figure 2b~2c
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AI summary
A method for suppressing a common mode impulse current for an inverter generated when an alternating current switch is switched on and a device for applying the method are provided. Before the alternating current switch is switched on for the inverter, a target value of a common mode voltage between the inverter and ground is calculated based on at least one of a voltage between an alternating current port and ground, a voltage between the inverter and ground and a voltage across the alternating current switch sampled in real time (S101). Then, a compensation power supply arranged between a main circuit of the inverter and ground is controlled to change the common mode voltage to the target value, so that a common mode voltage difference between two ends of the alternating current switch is zero (S102). Subsequently, the inverter is controlled to switch on the alternating current switch (S103).