Three-phase compensated AC voltage regulated power supply principle circuit
The three-phase compensated AC stabilized power supply consists of three parts: the main circuit, the control circuit, and the detection circuit. The main circuit is composed of three parts: a parallel part, a series part, and a filtering energy storage capacitor Cd in the DC part. The parallel part is composed of a low-pass filter and a three-phase PWM switch rectifier. The switch rectifier is actually a three-phase voltage type inverter, which mainly provides rectified DC power for the single-phase compensation inverter in the series part and maintains a constant voltage on the DC capacitor Cd. The DC capacitor Cd plays a filtering and energy storage role. The purpose of using a three-phase switch rectifier is twofold: firstly, to maintain the input power factor cos φ=1 of the mains power, and to make the waveform of the input current close to sine, in order to reduce pollution to the mains power; The second is to enable bidirectional flow of electrical energy, so that the reactive energy in the inverter load can be fed back to the mains power supply, improving the efficiency of the compensator. In addition, if a storage battery is connected to the DC capacitor Cd in parallel, the three-phase PWM switch rectifier can switch to the inverter state and be used as an online UPS for a short period of time when the mains power fails and is cut off. If additional control circuits are added, the three-phase voltage type inverter can also be used as a reactive power compensator or active filter to filter out harmonics in the load current. The series connection part consists of three single-phase full bridge inverters and their output transformers (i.e. compensation transformers), which are used to compensate for high and low changes in the mains voltage, three-phase asymmetry, harmonics, flicker, etc; The reason why three single-phase inverters and output transformers are used in the series connection is twofold. Firstly, the load carried by the three-phase four wire system is mostly asymmetric, so the three-phase voltage is also asymmetric, and it must be compensated by independent single-phase inverters that are not connected to each other. Secondly, it can also improve the reliability of the three-phase four wire power supply, so that in case one phase fails, the other two phases can continue to supply power. Three single-phase inverters can also work in both directions. When the mains voltage us is equal to the nominal reference voltage, the three single-phase inverters switch from compensation state to switch rectification state to supply power to the DC capacitor Cd or battery, ensuring the normal operation of the three-phase voltage type inverters in parallel circuit. In this way, the three-phase AC stabilized power supply becomes a customized power regulator for users
