1) Voltage source inverter DC circuit uses capacitor filtering. In the wave peak (higher voltage), the capacitor will store the electric energy field, and in the wave trough (lower voltage), the capacitor will release the electric field energy to replenish, thus keeping the DC voltage smooth. DC circuit is a voltage source, so it is called voltage source type. Its characteristics are.

(1) The DC side is connected in parallel with a large capacitor, which is equivalent to a voltage source. The DC voltage is basically pulsation-free, and the DC circuit shows low impedance.

(2) Due to the clamping effect of the DC voltage source, the output voltage waveform on the AC side is a rectangular waveform, and is independent of the impedance angle. The output current waveform and phase of the AC side are different depending on the load impedance.

(3) When the AC side is an impedance load, it needs to provide reactive power, and the DC side capacitor plays the role of buffering reactive energy. Because the feedback reactive energy when the current to invert the phase, so the switching devices need to be connected in reverse parallel diodes at both ends.

2) Current-source inverter DC circuit uses reactor filtering. In the wave peak (higher current), the reactor is used to store the magnetic field energy.

The reactor stores the magnetic field energy at the peak (higher current), and at the trough (lower current), the reactor will release the magnetic field energy to replenish it, so that the DC current can be kept smooth. The DC circuit is a current source, so it is called current source type. Its characteristics are.

(1) The DC side is connected in series with a large inductor, which is equivalent to a current source. The DC current is basically pulse-free, and the DC circuit shows high impedance.

(2) Since the switching device only changes the flow path of the DC current, the output current waveform on the AC side is a rectangular waveform and is independent of the impedance angle. The output voltage waveform and phase of the AC side are different depending on the load impedance.

(3) When the AC side is an impedance load, reactive power needs to be provided, and the DC side inductor plays the role of buffering reactive energy. Because the DC current is not inverted when the reactive energy is fed back, it is not necessary to inverse parallel diodes to the switching devices as in the case of voltage source inverter circuits.