Stable and efficient power regulator inverter power supply circuit design

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Overview:
This paper introduces a power-regulated inverter power supply, which is applied to the long-delay thermal trip test of low-voltage electrical appliances. It is suitable for the verification and test of long-delay characteristics of low-voltage electrical appliances such as circuit breakers and thermal relays. It has stable and reliable operation. The utility model has the advantages of high input power factor, high output precision, small waveform distortion and high efficiency.

At present, most of the long-term thermal trip test schemes adopted in China use a transformer to directly apply a voltage to the circuit breaker to obtain a test current. During the test, due to the fluctuation of the grid voltage, the change of the lead resistance in the current-carrying circuit, and the change in the resistance of the load itself, the test current changes accordingly, and it is difficult to meet the requirements of the national standard. This paper introduces a power regulated inverter power supply, which has the advantages of stable and reliable operation, high input power factor, high output precision, small waveform distortion and high efficiency. Inverter power supplies with a nominal power of 300W are not a problem for home electric fans, televisions, and daily lighting. The 300W inverter uses 12V/60AH batteries to supply power to the above household appliances. After a full charge, it can be used for nearly 5 hours. However, even if the battery voltage is sufficient, it is still difficult to start the 180-liter refrigerator, and the output voltage drops to less than 180V at the start of the startup. The nominal power of the refrigerator compressor is about 100W. The actual starting current can reach more than 2A. If the starting voltage is not very obvious, the output power must be increased to 600VA. If the output power is increased, The PWM voltage regulator system can significantly reduce the step-down amplitude of the startup. Regardless of the electric fan or the refrigerator, when applying the inverter power supply, the LC filter in Figure 1 should be added at the output of the inverter to improve the waveform and avoid the pulse rising edge rushing through the motor winding.

figure 1

In an inverter using a bipolar switching transistor, the base driving current is substantially 1/β of the switching current. Therefore, the high current switching circuit must adopt multi-stage amplification, which not only complicates the circuit, but also degrades reliability and When the output power is increased, the switching tube driving current needs to be larger than 1/β of the collector current, so that the ordinary driving IC cannot be directly driven. Although multi-stage amplification can achieve the purpose, the waveform distortion is significantly increased, resulting in an increase in the on/off loss of the switching tube. At present, the driving schemes for high-power inverter power supplies and UPS are mostly used, and MOSFET tubes are mostly used as switching devices.
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