When an inverter reports voltage issues or abnormal voltage measurements from the motor, it’s important to first determine whether the reported issue is genuine. If the inverter reports an overvoltage trip, the simplest way to verify this is by measuring the voltage on the DC bus. If the DC bus voltage reaches the overvoltage threshold, the inverter's report is accurate. However, if the voltage doesn't reach this level, the inverter may be giving a false alarm. This usually happens due to problems in the inverter's sampling detection circuitry.
To measure the DC bus voltage, use a 47-type multimeter set to the 1000V DC range and measure the voltage across the DC bus. Most inverters are designed with an overvoltage alarm set between 700-780V. If the measured voltage falls within this range, the inverter indeed has an overvoltage issue. Conversely, if the voltage is below 540-700V, it's likely a false alarm from the inverter's voltage detection circuit. For instance, an inverter might falsely indicate a DC bus voltage exceeding 540V without reaching the actual overvoltage alarm threshold.
In many cases, the inverter only generates feedback energy when the voltage exceeds 540V, indicating potential issues. To better understand the source of overvoltage, you can connect a voltmeter to continuously monitor the DC bus voltage and observe when the voltage spikes. Pay attention to any correlation between these voltage changes and the operating conditions of the load to identify the root cause.
Another common issue involves the motor working abnormally. If the motor sounds weak or produces unusual noises, start by checking the inverter’s output voltage. Since the output voltage is directly related to the output frequency, the voltage isn’t constant but should maintain balance among the three phases. Therefore, measuring the output voltage essentially checks whether the three-phase voltage remains balanced or if there are any disconnections. An imbalance in the inverter’s output voltage often results from a faulty or damaged switch bridge arm, leading to out-of-phase or uneven voltage outputs.
If the three-phase output voltage is balanced and consistent, the problem likely lies within the motor itself. Ensuring proper maintenance and monitoring of both the inverter and motor can help prevent such issues, ensuring smooth operation and preventing unnecessary alarms or malfunctions.
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