Once the power line is connected to the output terminals (U, V, W) of the inverter, one of the converter circuits may be activated due to a signal, resulting in a short circuit. This can cause serious damage to the inverter components. Therefore, during the design phase of the inverter’s main circuit, it is crucial to ensure that there is absolutely no possibility of power entering from the output side.
The inverter operates by first converting AC power into DC through a rectifier bridge, and then converting the DC back into three-phase AC using an inverter circuit. If the power line is mistakenly connected to the output terminals (U, V, W), a transistor may turn on due to a signal, creating a direct short. This can quickly lead to the destruction of the inverter’s switching devices, such as IGBTs or MOSFETs.
To avoid damaging the inverter, new users should carefully follow the installation instructions, manually wire the system, and avoid powering it up without proper verification. It's essential to understand the risks involved in incorrect wiring, as a single mistake can result in costly and dangerous failures.
Below are the potential consequences of reversing the input and output connections of a voltage-source high-voltage inverter.
Consequences:
When a high-voltage input line is incorrectly connected to the inverter’s isolation switch, and the user switch is closed, the power supply from the high-voltage bus will directly connect to the inverter’s output. The capacitors inside each unit will be at zero charge, and their maximum allowable voltage drop is less than ±18V/DC. They cannot withstand high voltages. In the case of a misconnection, the peak voltage across each phase could reach as high as ±8164V—far exceeding the rated limits of IGBTs, thyristors, and capacitors. This causes each phase cell to act like a conductor, forming a current path with no limiting resistance. The only limitation comes from the external relay system, which may not be sufficient. Excessive current can cause diodes in IGBT modules to explode, leading to cascading failures and damage to other parallel components. The heat generated can also melt cables and joints, while the short-circuit current may trip the user’s circuit breaker, halting the damage but leaving all units already destroyed.
Additionally, if the inverter is connected to high voltage with reversed input and output, the phase-shifting transformer on the inverter’s input side may become connected to the motor, preventing normal power delivery. The control system will have no power, and if the user hasn’t entered the operational state, the main control system won’t detect the fault. As a result, the computer may not record the time or details of the incident.
Preventive Measures:
1) After installation and commissioning, clearly label and distinguish the input and output cables for easy identification.
2) When replacing cables, ensure that the incoming and outgoing lines are properly identified, marked, and tested before installation.
3) Any cable replacement or testing work should be carried out by at least two people, with mutual checks. If necessary, an electrical engineer should verify and approve the work.
4) Always double-check the wiring labels on the inverter. Typically, L1, L2, and L3 indicate the input, while U, V, and W represent the output. Following these guidelines can significantly reduce the risk of connection errors and protect both equipment and personnel.
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