Design and implementation of the hottest high powe

Design and implementation of high-power variable-frequency adjustable power supply

1 introduction

sinusoidal pulse width modulation and variable-frequency speed regulation technology are widely used in the field of industrial control. Many power testing instruments require high power and high performance to meet the testing requirements of power equipment. At present, the core power devices of high-power switching power supplies in the market mostly use MOSFET semiconductor field effect transistors and bipolar power transistors, which can not meet the requirements of small size, high frequency and high efficiency. MOSFET has the characteristics of fast switching speed and voltage type control, but its on state resistance is large, which is difficult to meet the requirements of high voltage and high current; Although bipolar power transistor can meet the requirements of high withstand voltage and high current, it has no fast switching speed. It is a current controlled device and requires large power drive. The range of single set of insulated gate bipolar power crystal I device reaches 10000 tons/year. GBT integrates MOSFET field effect transistor and bipolar power transistor, and has the advantages of voltage type control, large input impedance, small driving power, fast switching speed, high working frequency, large capacity and so on. Using high-performance insulated gate bipolar power crystal IGBT as switching inverter and adopting frequency conversion and amplitude modulation technology, the inverter power supply has the advantages of high efficiency, reliable performance and small volume

2 working principle

the power supply adopts high-frequency inverter technology, digital signal generator, sinusoidal pulse width modulation, frequency conversion and amplitude modulation, timing control, power on and series resonant output. The power supply has the advantages of high efficiency, large output power and small volume. Its overall principle block diagram is shown in Figure 1

the sine wave generated by the digital signal generator is modulated by a 25kHz triangular modulation wave to obtain a sine pulse width modulation wave, which drives the inverter IGBT through the driving circuit. By changing the frequency of the sine wave, the amplitude can reach the frequency modulation and amplitude modulation output. The inverter output is a series resonant output, which filters out the high-frequency carrier signal, so as to obtain the sine signal of the required frequency. The time sequence control circuit is used to control the power supply of the power source to power on slowly when it is powered on, so as to ensure that the current is stable when the power supply is powered on, and at the same time, avoid the impact caused by the non zero crossing switch; In the control circuit, the fault locking function can be seen from the lower part of the force measuring cylinder. Once the power supply fails, the locking function will prohibit the opening of IGBT. When the fault occurs, the IGBT is opened by the locking point. At this time, the large capacity filter capacitor will store very high electric energy. Therefore, the power supply part has the function of fault protection, automatic power cut-off and automatic discharge. The whole machine is designed with perfect protection functions such as double overcurrent, overvoltage and overheating

3 control and drive circuit

control circuit refers to the main control circuit, including the generation of sinusoidal pulse width modulation wave, duty cycle adjustment and fault locking circuit. The sinusoidal modulation wave of the control circuit can adjust its frequency according to the actual application. The drive circuit adopts the IGBT special drive module EXB840 produced by Mitsubishi, which can drive IGBT up to 150A/600V and 75A/1200V. The internal drive circuit of the module delays the signal by 1 s, so it is suitable for switching operation up to 40KHz. When using this module, it should be noted that the IGBT grid emitter circuit wiring must be less than 1m, and the grid 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 series resonant inverter circuit, and the principle of the main circuit is shown in Figure 3. In the high-power IGBT resonant inverter circuit, the structure design of the main circuit is very important. Due to the parasitic inductance of the lead wire in the circuit, the surge peak voltage LDI/dt caused by the IGBT switch action on the inductance cannot be ignored. Because the power supply adopts the half bridge inverter circuit, it will produce a larger di/dt than the full bridge circuit compared with the full bridge circuit. It is very important for the normal operation of IGBT to correctly design the overvoltage protection, i.e. buffer circuit. If the buffer circuit is not designed properly, the loss of the buffer circuit will increase, which will lead to serious circuit heating, easy to damage components, and is not conducive to long-term work

the process is: when vt2 is turned on, with the rise of current, under the action of stray inductance LM, UAB drops to VCC LDI/dt. At this time, the buffer capacitor C1 charged to VCC in the previous working cycle is discharged through the anti parallel diodes VD1, vt2 and buffer 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 stray inductance current IL flowing through the line 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 effect of the line stray inductance LM, uce rises rapidly and is greater than the bus voltage Vcc. At this time, the buffer diode VD1 is biased forward, and the stored energy (lmi2/2) in LM is transferred to the buffer circuit, which absorbs the stored energy and will not cause the significant rise of uce

5 calculation and selection of buffer elements

where: F switching frequency; Rise time of RTR switching current; IO maximum switching current; UCEP transient voltage peak

in the component selection of the buffer circuit, the capacitor should be made of materials such as Peek (polyether ether ketone) or Pai (polyamide imide) resin, which can operate at high temperature, high speed and high voltage at the same time. The capacitor with high withstand voltage should be selected. The diode should preferably be a high-performance fast recovery diode, and the resistance should be non inductive resistance

6 conclusion

the power supply has been successfully applied to high-power power power testing instruments. Compared with traditional methods, it not only has high measurement accuracy, but also improves work efficiency, increases work safety, and reduces labor intensity

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