Research on the hottest three-phase high-frequency

Research on three-phase high-frequency chopper AC voltage stabilizing device

Research on three-phase high-frequency chopper AC voltage stabilizing device

industrial equipment and large computer stations and other occasions, a large number of high-power AC voltage stabilizing power supplies are used. In all kinds of AC voltage stabilizing equipment, voltage compensation principle is often used to stabilize the output voltage, such as high-power contact compensation AC voltage stabilizing power supply, contactless induction compensation AC voltage stabilizing power supply and switch compensation AC voltage stabilizing power supply. In these devices, the compensation circuit mostly works at the fundamental frequency (50Hz), so the equipment has large volume and weight and low conversion efficiency, which limits their application in high-power occasions

literature [1][2] and others have proposed some high-frequency compensation circuits, but due to the use of many components, complex circuit structure and high cost, it is difficult to be popularized and applied in practice

literature [3] proposed a three-phase high-frequency pwmac chain regulator. Because the circuit uses less switching devices, simple control, and the inductive elements of the compensation circuit are high-frequency elements, the number is small, so it is a conversion circuit with great development and application value. This paper mainly introduces the working principle, main parameter design, simulation waveform and experimental results of the circuit

2 circuit structure and working principle

this three-phase high-frequency chopper AC voltage regulating main circuit is shown in Figure 1. For the convenience of analysis, the transformer is not considered temporarily

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

in order to prevent S1, S2, S3 and S4 from conducting at the same time, a dead zone is set during their complementary conduction conversion. During the dead time, the capacitor CP provides a bypass for the load current, and the resistor RP discharges the capacitor CP after the dead time. The transformer is used to provide proper voltage to the load and isolate the load from the main circuit

when this circuit works normally, there are the following working modes:

2.1 energy supply mode

working in this mode, switches S1, S2, S3 are on, S4 is off, and the input voltage is added to the load. As shown in Figure 2, assume that the current direction is as shown in the figure

2 2 bypass mode

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

Figure 1 three-phase high-frequency chopping AC voltage regulation main circuit figure 2. Working principle of the tension machine

Figure 2 energy supply mode

Figure 3 bypass mode

Figure 4 freewheeling mode

figure 5 dead time equivalent circuit

(a) equivalent circuit (b) equivalent model

2.3 freewheeling mode

working in this mode, switches S1, S2, S3 are off, S4 is on, L1, L2, L3 release energy to keep the load current continuous through S4. As shown in Figure 4

3 main parameter design

the power supply channel mainly works in the two-way buck state, so the voltage at point a (or B, c) in Figure 1 can be decomposed by Fourier series to obtain ua=dv1 + vancos[(n s I) t] (start the oil pump to release air 1)

where: I is the angular frequency of the input voltage

s as the switching angular frequency

va n is the output harmonic amplitude

d is the duty cycle

its harmonic distribution is (n s I). As long as the switching frequency is high enough, the filter inductance L can be very small. Therefore, the design of power circuit is mainly to bypass capacitance and resistance or contact our customer service! Design of

as mentioned above, the function of bypass capacitor is mainly to continuously load current waveform during dead time. Its equivalent circuit is shown in Figure 5 (a) (taking the power supply of phase a circuit as an example)

due to the short acting time of capacitance (2 s ~ 3 s), the power supply voltage and load current can be regarded as constant values, and its equivalent model is shown in Figure 5 (b)

3.1 the design of bypass capacitor C and discharge resistance R takes the effective value of phase current and phase voltage of the circuit as the standard unit value respectively, and sets m=, k=, where ti is the input power cycle and TBP is the dead time. Peak value of capacitive current, then (2) since there is little difference between the peak value of bypass current and the minimum value, for simple calculation, use instead, Then the average value of current is: (3)

the capacitor voltage is:

vcbp=vpm[1 + cos (it +] (4)

where: is the initial phase angle

its average value is: (P, U) (5)

then its peak value and effective value are:

Figure 6 simulated load voltage waveform (three phases)

Figure 7 output voltage waveform (one phase)

(6) (7) due to (P.U) (8) (P.U) (9) and (P.U), Therefore, the bypass resistance is: (P.U) (10) because it is replaced by in the above derivation, RBP can be appropriately amplified in the actual value

3.2 simulation and experiment

design an AC regulated power supply with the following parameters:

rl=30, tbp=2 s, fs=20khz, ts=50 s, fi=50hz, m==10000, k===400, =5.77a. Then there is RBP ﹤ 37.5 (P.U), that is, RBP ﹤ 1.3k (the value of actual simulation and experiment is 1.5k); Cbp=, when taken as 11V, CBP is 1 f; The model of switch S1 ~ S4 (with parasitic reverse diode) is 1mbh60d 100, and the model of diode D4 ~ D9 is mur8100t

the simulated load voltage waveform is shown in Figure 6 (d=0.8)

when the effective value of the input line voltage is 100V, the load voltage waveform (a phase) of the experimental circuit is shown in Figure 7 (d=0.75)

4 conclusion

the simulation and experimental results show that under the action of small filter inductance and bypass capacitance, the output voltage can indeed be adjusted, and adding appropriate waveform feedback control can further optimize the output waveform