Saijun Mao

High voltage pulse speed study for high voltage DC-DC power supply based on voltage multipliers

The high voltage (HV) pulse speed is investigated for voltage multiplier based HV power supply. The key factors which influence the HV pulse rise and decay response time for HV power supply such as switching frequency, load resistance, and voltage multiplier capacitance are studied. When the stage number of voltage multiplier is determined, the switching frequency is the key influence factor for the HV pulse rise time. High switching frequency will lead to short HV pulse rise time. From the voltage multiplier HV pulse rise time simulation results, assuming sufficient power supply power rating, the load resistance and filter capacitor have little influence for the HV pulse rise time. The high voltage pulse decay time is proportional to load resistance and multiplier capacitance. Though switching frequency has indirect relation to decay time, multiplier capacitance can be decreased with higher switching frequency. So higher switching frequency can effectively decrease the both high voltage pulse rise and decay time. The experimental results of a 2kV output HV power supply switching at 300 kHz with 2-stage half-wave series voltage multiplier prototype verify the analysis and simulation results. The practical design guidelines for achieving desired HV pulse rise & decay time is provided finally.

High frequency high voltage power conversion with silicon carbide power semiconductor devices

This A novel high frequency high voltage (HV) generator with silicon carbide (SiC) power semiconductor devices is proposed in this paper to achieve high energy efficiency, fast HV pulse speed and compact size advantages. The electrical and HV insulation design and analysis high frequency HV transformer and voltage multiplier circuit based on 1.2kV SiC Schottky diode are discussed in details. 1.2kV SiC MOSFETs are introduced in the power inverter with switching frequency from 300 kHz to 500 kHz. The switching characteristics and detailed design consideration on the gate driver circuit are given. The packaging design considerations for HV generator are discussed. PCB based packaging technology is utilized to achieve compact size for HV generator. Finally, the 500W output power, 7kV output voltage HV generator prototype with 300 kHz to 500 kHz switching frequency is built in lab to validate the advantages on power density, energy efficiency and HV pulse speeds. The high frequency SiC HV generator prototype experimental results validate the power density, higher power efficiency and faster HV pulse speed advantages.

Investigation of CCM boost PFC converter efficiency improvement with 600V wide band-gap power semiconductor devices

Wide band-gap materials such as Gallium Nitride (GaN) and Silicon Carbide (SiC) offer improved performance for power electronic devices compared to traditional Silicon (Si) power semiconductor devices. This paper investigates a 600V GaN & Silicon CoolMOS transistor application in 400W single phase continuous conduction mode (CCM) Boost PFC converter circuits with GaN, SiC and ultrafast silicon diodes and compares power semiconductor device efficiency benefits. The 600V GaN & Silicon CoolMOS transistor power efficiency improvement study and loss analysis for CCM Boost PFC converter circuits are introduced in detail. Based on the experimental study, the 600V GaN transistor enables higher energy efficiency compared with 600V Si CoolMOS for CCM Boost PFC converter at 680 kHz switching frequency: around 1% higher at low line and about 0.5% higher at high line due to low switching loss. 600V SiC diode typically outperforms ultrafast Si diode & GaN diode for CCM Boost PFC converter due to low device charge, and forward voltage. 600V GaN diode suffers lowest efficiency at light load due to large device capacitive charge. The ultrafast Silicon diode has the highest efficiency at light load due to low device charge, but suffers from low efficiency at heavy load due to largest forward voltage and reverse recovery loss. According to the investigations, the combination of a 600V GaN transistor for the boost switch and a SiC rectifier for the freewheeling diode achieves the best efficiency for CCM Boost PFC converter with the lowest power loss.

Comparative study of half-bridge LCC and LLC resonant DC-DC converters for ultra-wide output power range applications

The Half-Bridge (HB) LCC resonant DC-DC converter and HB LLC resonant DC-DC converter circuit are comparatively studied for high efficiency ultra-wide output power range application in this paper. The output voltage ranges from minimum output voltage to twice that value. And the output current ranges from 10% load to 100% load. So the output power spans over a wide range, from minimum to 20 times that. The detailed resonant tank characteristics analysis for HB LCC and LLC resonant converter is provided. Through the 150W hard prototype experiments validation, it is shown that HB LLC resonant DC-DC converter can achieve better performance with flat efficiency, narrow switching frequency range compared with HB LCC resonant DC-DC converter for wide output current application at both 75V & 150V output voltage from 10% output current to 100 % output current conditions. HB LLC resonant DC-DC converter is more preferred power conversion circuit topology to achieve high performance with flat efficiency, narrow switching frequency range in ultra-wide output power range applications.

1200V SiC MOSFETS for high voltage power conversion

Recently, development and progress in information and telecommunications industry and service have gradually made significant increase in power consumption of Information and communication technology (ICT) equipment. To provide an energy-saving, floor space saving system solution for the data center or telecommunications, there exhibits a new trend moving towards high voltage power conversion. This paper presents a high voltage DC distribution power conversion using SiC MOSFET aiming at improving conversion efficiency. The characterization of SiC MOSFET is tested with double pulse and phase leg tests. A 5kW 380V DC rectifier is built and experimentally tested to compare the efficiency against the same prototype with Si device to demonstrate efficiency benefits.

Three-phase active front-end rectifier efficiency improvement with silicon carbide power semiconductor devices

This paper investigates SiC power semiconductor devices in a three-phase active front-end Boost PWM rectifier for power conversion efficiency improvement. Different from Si IGBT based Boost PFC rectifier, the SiC MOSFET based Boost PFC rectifier can achieve the synchronous rectification by MOSFET channel reverse conduction for efficiency improvement. The operation principle difference of three-phase active frontend Boost PWM rectifier with SiC MOSFET and Si IGBT is introduced. The switching characterizations of 1.2kV SiC MOSFET are provided. 5kW 380VAC input, 800VDC output three-phase active front-end Boost PWM rectifier prototype is built in lab to evaluate the efficiency advantage with SiC device. All SiC power semiconductor devices based circuit achieves about 1.2% more efficient compared with all Si devices, and around 0.5% more efficient than Si IGBT & SiC diode hybrid device pair for the three-phase Boost PWM rectifier due to low switching loss of 1.2kV SiC MOSFET and reduced conduction loss from the synchronous rectification operation for 1.2kV SiC MOSFET.

Review of high frequency high voltage generation architectures

The state-of-the-art architectures of high frequency high voltage (HFHV) generators are surveyed and classified according to their applications to achieve compact size, high energy efficiency and high power density. HFHV generation architectures and derivation methodology are concluded systematically based on the level of distributedness of the main sub-components. The characteristics for each HFHV generation architecture are described in details. Comparative qualitative evaluation of HV generation architectures are performed considering different output voltage and output power ratings in various industrial applications. The HV generation architecture with distributed HV transformer and distributed multiplier overall outperforms compared with other HV generation architectures. The recommendations for the HV generation architecture selections would be provided to identify the promising architectures for different output voltage and power applications with optimal performance finally.

Power packaging design considerations for high frequency high voltage generator

Power packaging technology plays an important role to achieve high performance for high voltage (HV) generator. The HV generator packaging techniques are systematically classified according to different component level packaging and system assembly technology. Both component level packaging and system assembly technology are included in the review and their advantages and disadvantages are discussed. Planar air-core multi-layer printed circuit board (PCB) winding transformer is introduced for HV generator with planar structure. A 450kHz switching frequency HV generator prototype with 310W output power and 1kV output voltage is built in lab. The high frequency HV generator prototype can achieve 1.09kW/L power density at rated 1kV output voltage and 310W full power. The litz wire air-core HV transformer prototype is built to compare the efficiency, thermal performance and size with planar air-core HV transformer. The planar PCB air-core transformer enables high voltage generation circuit system compact planar packaging. The litz wire air-core HV transformer behaves higher efficiency and thermal performance with low high frequency AC winding loss.

Diode reverse recovery analysis of Cockcroft-Walton voltage multiplier for high voltage generation

Cockcroft-Walton voltage multiplier circuit is widely used for high voltage generation circuit. The diode reverse recovery effect of Cockcroft-Walton voltage multiplier circuit is investigated by analysis and circuit simulation. According to the analysis and circuit simulation study, it can be concluded that the multiplier diode reverse recovery problem is mainly caused by the diodes in the first stage voltage multiplier. The most effective and economic way to alleviate the diode reverse recovery problem is employing diodes with good reverse recovery performance such as silicon carbide Schottky diodes only in the first stage for good system performance. The experimental results of 3 stages Cockcroft-Walton voltage multiplier circuit hardware prototype operating at 300kHz switching frequency validate the concept based on analysis and simulation study. The silicon carbide diode without reverse recovery needs to be used only in the first stage of voltage multiplier circuit to effectively mitigate the reverse recovery problems in high frequency operations with good circuit performance.

Equivalent circuit model for modular high voltage power generation architectures

This paper introduces the unified equivalent circuit model for modular high voltage(HV) power generation architectures. The HV generation architectures are introduced considering the modularity of key HV components such as transformers or rectifier circuits firstly. An equivalent resister and capacitor circuit network is adopted to model the HV transformer and multi-stage voltage multiplier circuit for HV generation architectures to simplifies the analysis, design and optimization for HV generation architectures. The expressions of equivalent resister and capacitor network in modular HV generation architectures are deduced. Based on the proposed equivalent circuit model, a 400kHz switching frequency 500W 20kV output HV generator prototype based on modular HV architecture is built to validate the equivalent circuit model. The experimental results of HV generator prototype are given finally.