“The working principle of series resonant power supply with frequency modulation and amplitude modulation output by using sinusoidal pulse width modulation (SPWM) technology is introduced. The power supply adopts a half-bridge inverter circuit composed of IGBT modules, which has the functions of IGBT drive, overvoltage, overcurrent, overheating protection and fault locking.
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This paper introduces the working principle of series resonant power supply which realizes frequency modulation and amplitude modulation output by sine pulse width modulation (SPWM) technology. The power supply adopts a half-bridge inverter circuit composed of IGBT modules, which has the functions of IGBT drive, overvoltage, overcurrent, overheating protection and fault locking.
1 Introduction
The application of sinusoidal pulse width modulation and variable frequency speed regulation technology in the field is becoming more and more extensive. Many power test instruments require high power and high performance to meet the test requirements of power equipment. At present, most of the high-power switching power supplies on the market use MOSFET semiconductor field effect transistors and bipolar power transistors, which cannot meet the requirements of small size, high frequency and high efficiency. The MOSFET field effect transistor has the characteristics of fast switching speed and voltage control, but its on-state resistance is large, which makes it difficult to meet the requirements of high voltage and high current; although bipolar power transistors can meet the requirements of high voltage and high current, there is no fast The switching speed is a current-controlled device and requires a large power drive. Insulated gate bipolar power crystal IGBT integrates MOSFET field effect transistor and bipolar power transistor, and has the advantages of voltage control, large input impedance, low driving power, fast switching speed, high operating frequency, and large capacity. The high-performance insulated gate bipolar power crystal IGBT is used as the switching inverter element, and the inverter power supply developed by the frequency conversion and amplitude modulation technology has the advantages of high efficiency, reliable performance and small size.
2 How it works
The power supply adopts high-frequency inverter technology, digital signal generator, sinusoidal pulse width modulation and variable frequency amplitude modulation, timing control power-on and series resonance output. The power supply has the advantages of high efficiency, large output power and small size. Its overall principle block diagram is shown in Figure 1.
The sine wave generated by the digital signal generator is modulated by the 25kHz triangular modulation wave to obtain a sine pulse width modulation wave, which drives the inverter element IGBT. By changing the frequency of the sine wave, the amplitude can reach the FM and AM output. The inverter output is a series resonance output, and the high-frequency carrier signal is filtered out to obtain a sine signal of the required frequency. The sequence control circuit is used to control the power supply of the power source to be powered on slowly when powered on, to ensure that the current is stable when the power is powered on, and to avoid the impact caused by the non-zero-crossing switch; the control circuit is also designed with a fault locking function. In case of power failure, the locking function will prohibit turning on the IGBT. When the failure occurs, the IGBT is turned on by the locking point, and the large-capacity filter capacitor will store a high amount of electric energy. Therefore, the power supply part has fault protection to automatically cut off the working power supply and automatic discharge function, and the whole machine is designed with perfect protection functions such as double overcurrent, overvoltage and overheating.
3 Control and drive circuit
The control circuit refers to the main control circuit, including the generation of the sinusoidal pulse width modulation wave, the duty cycle adjustment and the fault locking circuit. The sinusoidal modulation wave of the control circuit can be adjusted according to the actual application. The drive circuit adopts the IGBT special drive module EXB840 produced by Mitsubishi Corporation. The drive module can drive IGBTs up to 150A/600V and 75A/1200V. The internal drive circuit of the module makes the signal delay ≤1μs, so it is suitable for switching operations up to 40kHz. When using this module, it should be noted that the IGBT gate-emitter loop wiring must be less than 1M, and the gate-emitter drive wiring should be stranded. The drive circuit of EXB840 is shown in Figure 2.
4 Inverter and buffer circuit
The power supply adopts a half-bridge structure series resonant inverter circuit, and the main circuit principle is shown in Figure 3. In the high-power IGBT resonant inverter circuit, the structural design of the main circuit is very important. Due to the parasitic inductance of the leads in the circuit, the surge peak voltage Ldi/dt caused by the inductance during the IGBT switching action cannot be ignored. What is adopted is a half-bridge inverter circuit, which will generate a larger di/dt than a full-bridge circuit relative to a full-bridge circuit. The correct design of the overvoltage protection, that is, the snubber circuit, is very important for the normal operation of the IGBT. If the buffer is improper, the loss of the buffer circuit will increase, which will lead to serious heating of the circuit, which is easy to damage the components, which is not conducive to long-term work.
The process is: when VT2 is turned on, as the current rises, under the action of the line stray inductance Lm, Uab drops to Vcc-Ldi/dt. At this time, the previous working cycle is charged to the buffer capacitor C1 of Vcc, Discharge through the anti-parallel diodes VD1, VT2 and snubber resistor R2 of VT1. In the buffer circuit, the instantaneous conduction current ID1 flowing through the anti-parallel diode VD1 is the sum of the current IL flowing through the line stray inductance and the current IC flowing through the buffer capacitor C1. That is, ID1=IL+IC, so IL and di/dt are much smaller than unbuffered circuits. When VT1 is turned off, due to the action of the line stray inductance Lm, Uce rises rapidly and is greater than the bus voltage Vcc. At this time, the snubber diode VD1 is forward biased, and the stored energy in Lm (LmI2/2) is transferred to the snubber circuit. , the buffer circuit absorbs the stored energy and will not cause a significant increase in Uce.
5 Calculation and selection of buffer components
In the formula: f-switching frequency; Rtr-switching current rise time; IO-large switching current; Ucep-transient voltage peak value.
In the selection of components of the buffer circuit, the capacitor should be selected with a higher withstand voltage, the diode should be a high-performance fast recovery diode, and the resistor should be a non-inductive resistor.
6 Conclusion
The power supply has been successfully applied to high-power electric test instruments. Compared with the traditional method, it not only has a high degree of measurement, but also improves work efficiency, increases work safety, and reduces labor intensity.
The Links: LQ15X01 SKIIP39AC065V1