Introduction To The Working Principle Of Ac Voltage Stabilizer

Dynamic Voltage Regulator (DVR) (voltage stabilizer) is currently the most suitable for imported equipment and high-precision equipment, scientific research institutes, national defense, industrial equipment and large computer stations. Nowadays, high-power AC voltage stabilizer is widely used. In various AC voltage stabilizer equipment, the voltage compensation principle is often used to stabilize the output voltage, such as: high-power contact compensation type AC voltage stabilizer, contactless induction compensation type and switch compensation type AC voltage stabilizer. In these devices, the compensation circuit mostly works at the base frequency (50Hz), so the equipment is large in size and weight, and the conversion efficiency is low, which limits their application in high-power occasions.

Some high-frequency compensation circuits have been proposed, but due to the large number of components used, the complex circuit structure and high cost, it is difficult to be promoted and used in practice.

A three-phase high-frequency PWMAC chain regulator is proposed. Because the circuit uses fewer switching devices, the control is simple, and the inductive components of the compensation circuit are high-frequency components, the number is small, it is a conversion circuit with great development and application value. This article mainly introduces the working principle of the circuit, the main parameter design and simulation waveform and experimental results.

2 Circuit structure and working principle

Three-phase high-frequency AC voltage regulation main circuit

Switches S1, S2, S3 are used for AC, and switch S4 is used to continue the load when switches S1, S2, S3 are turned off. S1, S2, S3 and S4 are complementary. C1, C2, C3 are bypass capacitors for each phase, represented by CP, and R1, R2, R3 are bypass resistors for each phase, represented by RP. L1, L2, L3 are filter inductors, and R4, R5, R6 are loads.

In order to prevent S1, S2, S3 and S4 from being turned on at the same time, a dead zone is set when they are complementary. During the dead zone, capacitor CP provides bypass for the load current, and resistor RP discharges capacitor CP after the dead zone. The transformer is used to provide a suitable voltage to the load and isolate the load from the main circuit.

When this circuit is working normally, there are several working modes:

2.1 Power supply mode

In this mode, switches S1, S2, S3 are turned on, S4 is turned off, and the input voltage is applied to the load.

2.2 Bypass mode

In this mode, switches S1, S2, S3, and S4 are all turned off. The load current is kept continuous through the bypass capacitor CP and the diodes in the three-phase rectifier bridge and the parallel diodes of the switch tube. As shown in Figure 3. During this period, a part of the energy will be stored in the bypass capacitor CP, and this energy will be discharged through the resistor RP after the dead zone ends.

2.3 Freewheeling mode

In this mode, switches S1, S2, and S3 are turned off, S4 is turned on, and L1, L2, and L3 release energy to keep the load current continuous through S4.

3 Main parameter design

The power supply path mainly works in the bidirectional Buck state

Where: ωi is the input voltage angular frequency; ωs is the switching angular frequency; Va′n is the output harmonic amplitude; D is the duty cycle.

The harmonics are distributed in (nωs±ωi). As long as the switching frequency is high enough, the filter inductance L can be very small. Therefore, the design of the power circuit is mainly the design of bypass capacitors and resistors.

As mentioned above, the role of the bypass capacitor is mainly to continuously generate the load current waveform during the "dead zone".

Since the capacitor action time is very short (2μs~3μs), the power supply voltage and load current can be regarded as constant values