Shaoxiang Ma

Analysis of the Soft-Start Circuit of the High Voltage Power Supply Based on PSM Technology

The power supply based on pulse step modulation technology has been widely used as the high-voltage power supply (HVPS) for additional heating systems. The topology contains numbers of converters and multisecondary transformers. For the magnetizing inrush of the transformer and charging current of the converters connecting with the secondary windings of transformer, the power up of the power supply system is quite complex. There are resistor branches series with the transformer and each converter is used to limit the inrush current. A lot of resister branches and parallel contactors in the converter modules are required, and as a result the dissipation and electromagnetic interference inside the module are serious. In this paper, the soft-start circuit is simplified to only one resistor branch. The precharge circuits of the converters, which are connected to the secondary, are diverted from the inside of the modules to the primary winding of transformer. Since the multisecondary transformer powers up at the same time as converters, the capacitors in all converters will limit the ramp up rate of the transformer voltage, and the magnetic inrush current can be ignored. To analyze the characters of the precharge branches, all converters can be equaled as parallel during the soft-start process. The equivalent circuit, a series RLC circuit, is proposed in this paper. A 1.2-kV power supply, contains 12 converters, with soft start has been built up in laboratory. Simulation and experiment results are shown to verify the theoretical analysis. A new soft-start circuit of 100-kV HVPS system was designed.

High-voltage power supply for ECRH system on J-TEXT Tokamak

A 100kV/60A high-voltage power supply (HVPS) has been established to energize the electron cyclotron resonance heating (ECRH) system for J-TEXT tokamak. With the pulse step modulation (PSM) technology, the HVPS has many advantages, especially the low stored energy and short protective time in case of short-circuit fault. This paper gives a description and key design features for the isolated transformers, switch power supplies (SPS) modules, measurement equipments and controller. In this HVPS, 4 dry-type transformers with 36 secondary-windings drive the 144 series SPS modules and isolate the high voltage between the rectifiers and the 6.3kV AC bus. A controller based on the PXI technology, which conforms to the ITER CODAC standard, has been developed to operate the series switches in each SPS module. The error signals from all the modules are monitored by the controller and the fast protection responses any over current fault in less than 5 μs. Moreover, to acquire better dynamic response and stability, a control strategy improved from the conventional PWM phase-shift modulation method has been proposed. The experimental results are also presented and show that the power supply system performing good.

Modeling and Analysis of Inverter-Type High Voltage Power Supply for NBI Accelerator Grid

The acceleration grid power supply (AGPS) is an important part of the neutral beam injector (NBI) system. With the increase in NBI power, the requirement for output voltage of the AGPS is becoming higher and higher, even reaching to 1000 kV. As the inverter-type high voltage power supply uses inverters located at the lower voltage side to regulate and cut off the output voltage, it is very suitable for high-voltage applications. The proposed scheme for the AGPS of the International Thermonuclear Experimental Reactor (ITER) NBI system comprises five stages, where each stage has an inverter-type power supply with an output voltage of 200 kV. This paper investigates the inverter-type power supply based on neutral point clamped three-phase three-level (TPTL) inverter and three-phase step-up transformer, which is equivalent to an insulated TPTL dc-dc converter connected with a dual dc link. In order to design a preferable controller for the inverter-type power supply, the topology and principles of the TPTL dc-dc converter with duty cycle modulation have been analyzed. It indicates that only when the converter operates at a large duty cycle, the output voltage ripple can be limited to ±5%. Hence, the small signal model of the converter at a duty cycle larger than 2/3 is established. Following the mathematical model, a single-loop PID controller has been designed and a 400 V/6 A prototype has been built. Simulation and experimental results verify the correctness of the theoretical analysis. The system achieves a lower output voltage ripple and fast dynamic response.

Modeling and analysis of the inverter type high voltage power supply with duty cycle modulation

The acceleration grid power supply (AGPS) is an important part of neutral beam injector (NBI) system. With the increasing of the NBI power, the requirement for output voltage of the AGPS is becoming higher and higher, even reaching to 1000 kV. As the Inverter type high voltage power supply uses the inverters located at lower voltage side to regulate and cut off the output voltage, its very suitable for high voltage applications. The advised scheme for the AGPS of ITER NBI system is composed of five stages, each stage is an inverter type power supply with an output voltage of 200 kV. This paper investigates the inverter type power supply based on neutral point clamped (NPC) three phase three level (TPTL) inverter and three phase step-up transformer, which is equivalent to an insulated TPTL dc-dc converter connected with a dual dc link. In order to design a preferable controller for the inverter type power supply, the topology and principles of the TPTL dc-dc converter with duty cycle modulation has been analyzed. Our results indicate that only when the converter operates at a large duty cycle, the output voltage ripple can be limited to ± 5%. So the small signal model of the converter at a duty cycle larger than 2/3 is established. Following the mathematical model, a single loop PID controller has been designed. Simulation results verify the correctness of the theoretical analysis. The system achieves lower output voltage ripple and fast dynamic response.

Research of the soft start circuit for the high voltage power supply based on PSM technology

The power supply based on pulse step modulation (PSM) technology has been widely used as the high voltage power supply for additional heating systems, such as RF H&CD and NBI in tokamaks. The topology contains numbers of converters and multi-secondary transformers. For the magnetic inrush of the transformer and the charge current of the converters connecting with the secondary windings of transformer, the power up of the power supply system is quite complex. PSM power supply starts up by two steps: the soft start of transformer and the pre-charge of the converters. Resistor branches series with the transformer and each converter are used to limit the inrush current. A lot of resister branches and parallel contactors in the converter modules are required, as a result the dissipation and electromagnetic interference (EMI) are serious. In this paper, the soft start circuit is simplified to only one step for decreasing the dissipation and EMI. The pre-charge circuits of the converters which are connected to the secondary at first are diverted to the primary winding of transformer can also limit the magnetic inrush current. Since the multi-secondary transformer powers up as the same time as converters, the capacitors in all converters will limit the ramp up rate of the transformer voltage, and the magnetic inrush current can be ignored. To analyze the characters of the precharge branches, all converters can be equaled as parallel during the soft start process. The equivalent circuit, a series RLC circuit, is proposed in this paper. A 1.2kV power supply, contains 12 converters, with soft-start has been built up in laboratory. Simulation and experiment results are shown to verify the theoretical analysis. A new soft start circuit of 100kV high voltage power supply system was designed.