The THDi value of the mains input current can also be reduced by interleaving two three-phase Boost single switch SPWMPFC rectifiers, as shown in Figure 1-1.
The idea of this interleaving is to make these two three-phase single switch PFC circuits work as close to the critical state of DCM and CCM as possible, and then the drive signals of the two switches stagger 180 ° in phase.
In this way, a single three-phase single switch PFC circuit works in the DCM state, but the sum of the currents of the two modules may be continuous, thus significantly reducing the harmonic of the mains input current. The current waveform is shown in Figure 1-2.
The advantage of interleaving is that it not only reduces the THDi value of the mains input current, but also doubles the equivalent switching frequency of the system (because the driving signals of the two switches are staggered 180 ° in phase), which can increase the cut-off frequency of the EMI filter.
These two aspects can reduce the volume and quality of EMI filter.
Even if no current control mode is adopted, these two three-phase single switch Boost SPWMPFC circuits have good current sharing effect.
In order to reduce the current stress of the switch tube, the three-phase half controlled bridge rectifier circuit shown in Figure 1-3 can be used. The diode in the circuit should use a fast recovery diode. The three switch tubes use the same drive signal, and the inductance current works in the DCM state.
The advantage of this circuit is that the average current stress of each switch is very small, and the loss of semiconductor devices is relatively small
(Because when the switch tube is turned off, the current only flows through two semiconductor devices.), Its disadvantage is that the cost is high, the circuit still works in the DCM state, and the THDi is large.
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