软开关APFC倍频感应加热电源的研究
时间:2010-09-18
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作者：admin
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With the development of power switching devices, power electronic devices of increasing miniaturization and high frequency electrical properties of a substantial increase, but the resulting grid high harmonic Quedui cause serious pollution. In power electronic devices, rectifier (AC / DC converter) account for a large proportion of the major sources of pollution. As the solid state induction heating power supply for the power grid is nonlinear characteristics of the output current from the power grid is not the standard sine curve. High-frequency harmonic current generated electricity facilities overheating or other damage.
Boost power factor correction circuit applied to the already relatively mature, low-power for a few hundred watts of power factor correction, the conventional circuit can be realized. But for high-power, such as induction heating power supply, there are many practical problems. To address the switching devices as diode reverse recovery current generated when they pass the impact of damage to reduce the switching device switching losses at high frequencies, this paper, a passive lossless snubber circuit to replace the traditional LC filter circuit. In the analysis of the working principle of soft switching circuit and the inverter module time-sharing - phase power control strategy, the application of Matlab software simulation and the experiment results verify the validity of theoretical analysis.
An overall power system topology
Shown in Figure 1, the main circuit topology mainly by the rectifier, soft-switching Boost power factor correction, inverter, load matching the composition of several links.
Single-phase rectifier output DC voltage buffer access Passive Soft Switching Boost circuit, the circuit to take Boost to replace the traditional LC filter circuit. Boost circuit where there are two main effects: First, to improve power factor rectifier input side; Second, for the inverter side to provide a stable DC voltage. Boost correction circuit output voltage added to the inverter bridge inverter is IGBT modules by the eight single-phase full-bridge inverter, each IGBT has an anti-parallel diode with parallel, as anti-voltage inverter When added to the stream. * Rate of the device by the inverter control circuit controls the periodic pulse signal driving the switch; isolation transformer T is the role of electrical isolation and load impedance matching. General T for the step-down transformer, the transformer turns ratio due to change can reduce the resonant tank road in the inductor, capacitor voltage, the load impedance matching can be different. Output pulse voltage through the step-down isolation transformer added to the compensation after the induction coil and capacitor and the load form a resonant loop.
1.1 The principle of soft switching APFC circuit
Figure 2 shows the passive soft-switching Boost circuit, series inductor and lossless SNUBBER circuit. Boost circuit compared with the normal increase of inductor L1 limits the reverse recovery for VD0 arising from the impact of current VT0 open, C2 → VD7 as VD0 the SNUBBER circuit, VD5 → VD6 → VD7 the series structure and the L1 → C1 → C2 resonant energy transfer between and is also conducive to the opening rush current suppression VT0.
Main circuit in a cycle of work can be divided into six stages:
(1) mode 1 [t0, t1]: at the time t0, C0 discharge through the resistor R, VT0 open in ZCS mode, C1 discharge current flows through C1 → C2 → L1 loop, because the role of L1, VT0 opening current gradually increased steadily.
(2) mode 2 [t1, t2]: inductor L1 on the current increased, C1 after discharge, the current through the loop L0 → L1 → VD5 → VD6 → C2 flows.
(3) mode 3 [t2, t3]: C2 is slowly charged up all the energy transferred from L1. Finally the current flowing through VT0 equal size and L0, C2 charging end.
(4) Mode 4 [t3, t4]: t4 time VT0 off in ZVS Shimonoseki, when through the C2-VD6-C1's voltage and rectifier output voltage Vin is equal to, C2 discharges through VD7, L1 of the current economic L0 → L1 → VD5 → C1 to C1 charge.
(5) mode 5 [t4, t5]: When the C1 voltage and Vin equal to cease charging. L1 current through VD5 → VD6 → VD7 flow load.
(6) mode 6 [t5, t6]: L1 current decay to the 0 bus inductor current L1 through VD7 charge to C2, when C2 voltage is 0, the flow through the L0 load current flows through VD0 R0 C0 and then back to mode 1 .
1.2 Frequency inverter circuit after the class
Frequency high frequency inverter power supply circuit shown in Figure 1, the right part. In the figure, the VT11 ~ VT41 constitute the first group of inverter bridge, constituted by the VT12 ~ VT42 second inverter, two inverter turns on-a resonant cycle, each IGBT devices with rated load current work. Thus, if the permission of IGBT switching frequency f0, the power output frequency 2f0.
Time-sharing - phase control method is by adjusting the diagonal leg turn to adjust the power of the phase difference. VT11 and VT41 have a shift between the phase angle, full power, when the angle is 0, time - phase power regulator is the phase angle φ by adjusting the size to achieve power change.
2 System Control
Control system is mainly used Altera's MAX Ⅱ series CPLD chip and TI's TMS320LF2407A EPMl270T144C5 type DSP. Part of the digital phase locked loop control, PWM control module, time-pulse control module, DSP phase power regulation areas and formed part of DSP-PFC. CPLD PLL module to track the load resonance frequency, while the number receiving DSP output phase angles, which by the PWM, time-sharing computing module 8 phase trigger output pulse. DSP computation load output power, compared with the power settings, separated by points PI algorithm output phase angle; DSP also on the CCM mode soft-switching average current controlled Boost circuit. Moreover, you should realize settings, protection and display.
