Research and design of solid-state high-voltage pulse power supply based on IGBT

Due to the intermittent power supply characteristics of pulse power supply, it has been widely used in many fields. For example, high-energy physics, particle accelerators, metal material processing, food sterilization, environmental dust removal and sterilization, etc., all require such a pulse energy - reliable, high-energy, adjustable pulse width and frequency, bipolar, flat-top voltage waveform. No matter what purpose this high-power pulse power supply is used for, the high-voltage pulse power supply is the core part of its design. Traditional high-power pulse power supplies generally use industrial frequency transformers to step up the voltage, and then use magnetic compression switches or rotating spark gaps to obtain high-voltage pulses. Therefore, most of them are bulky, and the obtained pulse frequency range is limited. Its repetition frequency is difficult to adjust, the pulse waveform is easy to change, the reliability is low, the control is difficult, and the cost is high. In this paper, a solid-state appliance - IGBT is used to obtain a high-voltage pulse waveform. IGBT is used as an electronic switch to obtain high-voltage pulses, and an LCC series-parallel resonant converter is formed by IGBT as a charging power supply for the high-voltage pulse power supply. At the same time, IGBT is used to form a full-bridge pulse forming circuit to output a bipolar high-voltage pulse waveform. The paper gives the system structure and the functional description of each part of the system, and simulates and analyzes the LCC charging process and pulse forming circuit through the simulation power electronics simulation software PSIM.

1 High-voltage pulse power supply system structure
1.1 Topology of high-voltage pulse power supply The
commonly used main circuit topologies of high-voltage pulse power supplies can be summarized into two categories: capacitor charging and discharging type and two-stage type of high-voltage DC switching power supply plus pulse generation. The capacitor charging and discharging type achieves the purpose of energy compression and outputting high-voltage and high-power pulses by charging for a long time and discharging instantly, that is, by controlling the time ratio of charging and discharging. The advantage is that the output pulse power and voltage level are higher, and the pulse rising edge is steeper; however, the accuracy of the output pulse is difficult to control, and the repetition frequency is low, so the application range is relatively limited, mainly used in nuclear electromagnetic physics research, flue gas dust removal, sewage treatment, liquid sterilization and other occasions. The two-stage structure is a structure of a high-voltage DC switching power supply stage plus a pulse forming stage. This two-stage topology is adopted in this paper, and the power system structure block diagram is shown in Figure 1. The two-stage type has the characteristics of stable pulse, good controllability, high precision, and a large range of repetition frequency variation. Therefore, it has a wide range of applications and good versatility.

1.2 Power supply main circuit structure and working principle
The power supply main circuit schematic diagram is shown in Figure 2. The circuit consists of power frequency AC input, rectification and filtering, LCC series-parallel resonant converter, capacitor charging and energy storage, inductor buffer isolation, IGBT full-bridge inverter, pulse boost transformer and other units. Circuit working process: 220 V AC is rectified and filtered to obtain low-voltage DC output, which is charged to the energy storage capacitor C after high-frequency boost through LCC series-parallel resonant inverter, and bipolar pulse output is achieved through IGBT full-bridge inverter topology.

The LCC series-parallel resonant converter in Figure 2 is the core part of this high-voltage pulse power charging circuit. It consists of four power switch tubes IGBT and resonant inductor Ls, series resonant capacitor Cs, and parallel resonant capacitor Cp. The working principle is: using the effect of resonant elements such as inductors and capacitors to make the current or voltage waveform of the power switch tube into a sine wave, quasi-sine wave or partial sine wave, so that the power switch tube can be turned on or off under zero voltage or zero current conditions, reducing the loss when the switch tube is turned on and off, while increasing the switching frequency, reducing switching noise, and reducing EMI interference and switching stress.
When analyzing the LCC series-parallel resonant charging circuit, it is assumed that: 1) all switching devices and diodes are ideal devices; 2) the distributed capacitance of the transformer is 0; 3) n2C>>Cs; 4) the switching device works in a full soft switching state.
According to the relationship between the switching frequency fs and the basic resonant frequency fr, the LCC resonant converter has three working modes: 1) fs<0.5fr current discontinuous mode (DCM), the switch tube works in zero current/zero voltage shutdown and zero current turn-on state, and the anti-parallel diode is naturally turned on and turned off; 2) fr>fs>0.5fr current continuous mode (CCM), the switch tube is zero current/zero voltage shutdown and hard turn-on, the anti-parallel diode is naturally turned on, but the diode has reverse recovery current when turned off, and the circuit switching loss is large; 3) fs>fr is still the current continuous mode (CCM), the difference from 2) is that the switch tube is zero current/zero voltage turn-on and hard turn-off, and the circuit switching loss is also large. The resonant frequency is:

where Lr is the resonant inductor and is the resonant capacitor. Depending on the working conditions, it is jointly determined by the series capacitor Cs and the parallel capacitor Cp.
In this design, reasonable inverter design parameters are selected to make the LCC series-parallel resonant converter work in DCM mode, combined with soft switching technology to minimize the switching loss. 1.3 High-voltage pulse forming circuit
The formation of high-voltage pulses is to use the full-bridge topology structure composed of IGBT to switch the high voltage generated by the previous stage to achieve bipolar pulse output, as shown in Figure 2.
Switches Q5, Q7 and switches Q6, Q8 are turned on alternately in the positive and negative half cycles, respectively, to obtain bipolar pulse output. By changing the switching frequency of the two sets of switches, the frequency of the output bipolar pulse can be changed, and the duty cycle of the output pulse can be adjusted by controlling the on-time of the switch tube, so as to obtain a bipolar high-voltage pulse wave with adjustable pulse width and frequency.
1.4 Control of high-voltage pulse power supply The
control of the entire system is realized by the TMS320F2812 DSP chip and IGBT driver. It mainly realizes the soft switching of the LCC series-parallel resonant charging circuit through the constant on-time-constant frequency control method, reduces switching losses, and adjusts the output voltage; and uses the variable frequency and variable width control method to realize the output pulse control of the subsequent pulse forming circuit and the synchronous triggering of IGBT. The TMS320F2812 development board integrates 16 12-bit A/D converters, two event manager modules, and a high-performance CPLD device XC95144XL. It can realize full digital control of the power system including overvoltage and overcurrent protection, and improve the accuracy and stability of the output voltage. And the control algorithm is implemented by software programming, making system upgrades and modifications more flexible and convenient. 1) Overvoltage protection The voltage signal Ui is obtained by detecting the primary voltage of the pulse boost transformer through a high-frequency step-down transformer. Ui is used as the input voltage of the overvoltage protection circuit, and the output signal of the overvoltage protection circuit is connected to the pin of DSPF2812, which forces the system to restart and achieve the purpose of overvoltage protection, so as to protect the safety of the load.

2) Overcurrent protection
When the load current exceeds the set value or a short circuit occurs, the power supply itself needs to be protected. The overcurrent protection of the system plays an important role in the safety of the system. The overcurrent protection circuit is similar to the overvoltage protection circuit, as shown in Figure 4. The converted voltage signal is input to the F2812, the protection program is started, the fault latch is set, and the system is reset and restarted.

2 Circuit simulation analysis
Let k = Cp/Cs, Figure 5(a) shows the resonant current and voltage waveforms when k = 0.25. Select the DC bus voltage Vin = 300 V, switching frequency fs = 25 kHz, pulse width tw = 10μs, Lr = 50 μH, Cs = 0.2μF, resonant frequency kHz, that is, satisfy fs < 1/2fr, LCC series-parallel resonant converter works in DCM mode, and the high-frequency boost transformer ratio is 1:4. In the high-voltage pulse forming circuit, the pulse boost transformer ratio is 1:12, and the bipolar pulse simulation waveform is shown in Figure 5(b).

3 Conclusions
This paper designs a high-voltage pulse power supply based on IGBT, analyzes the various components and functions of the power supply, and generates a trigger signal to control the IGBT by DSP to achieve overvoltage and overcurrent protection, realize digital control of the power supply, and can accurately control the output pulse voltage, output pulse width, frequency and output pulse number, etc., and uses the LCC series-parallel resonant charging circuit as the structure for charging the intermediate energy storage capacitor, which is conducive to the rapid charging and miniaturization of the device.