How to distinguish high frequency machine from power frequen

In the power frequency UPS circuit, the three-phase AC input of the main circuit passes through the commutation inductance, receives the rectifier composed of three SCR bridge arms, and then transforms into the DC voltage. The output DC voltage value is adjusted by controlling the on angle of the rectifier bridge SCR. Since SCR is a semi controlled device, the control system can only control the opening point. Once SCR is turned on, even if the gate drive is cancelled, it cannot be turned off. Only when the current is zero can it be turned off naturally. Therefore, its opening and closing are based on a power frequency cycle, and there is no high-frequency opening and closing operation. Since SCR rectifier is a step-down rectifier, the output AC voltage of DC bus voltage through inverter is lower than the input AC voltage. In order to obtain a constant 220 V voltage of output phase voltage, a step-up isolation transformer must be added to the inverter output.

 

 

 

In contrast, high frequency UPS rectifier belongs to boost rectifier, whose output DC bus voltage is higher than the peak value of input line voltage. Generally, the typical value is about 800V. If the battery is directly connected to the bus, the number of standard batteries required is 67, which brings great limitations to the practical application. Therefore, in general, a battery voltage converter will be separately configured for high-frequency ups. When the power supply is normal, the battery converter will reduce the 800V bus voltage to the battery voltage; when the power supply fails or exceeds the limit, the battery converter will increase the battery voltage to the 800V bus voltage. Because the bus voltage of HF generator is about 800V, the output phase voltage of inverter can reach 220V directly. After the inverter, there is no need for step-up transformer. Therefore, whether there is isolation transformer or not is the main difference between power frequency machine and high frequency machine in structure.

 

 

 

Power frequency machine and high frequency machine are distinguished according to the working frequency of UPS design circuit. The power frequency machine is designed based on the traditional analog circuit principle, which is composed of SCR rectifier, IGBT inverter, bypass and power frequency step-up isolation transformer. Because the working frequency of rectifier and transformer is 50Hz, as the name implies, it is called power frequency ups. High frequency machine is usually composed of IGBT high frequency rectifier, battery converter, inverter and bypass. IGBT can be turned on and off by controlling the drive added to the gate. The switching frequency of IGBT rectifier is usually from several thousand Hz to dozens of kilohertz, even up to hundreds of kilohertz, which is far higher than the power frequency machine, so it is called high frequency ups.