This paper investigates the diode reverse recovery process and reduction of a half-wave (HW) series Cockcroft-Walton (CW) voltage multiplier based on the steady-state analysis for high-frequency high-voltage (HV) generator applications. The diode reverse recovery process for a multistage voltage multiplier is analyzed after the introduction of steady-state operation. The diode reverse recovery problem is the bottleneck to further increase the circuit operation switching frequency for achieving high power density and short HV pulse rise and decay times. The diode reverse recovery problem is mainly caused by the diodes in the first-stage voltage multiplier. It is suggested that the most effective and economic way to alleviate the diode reverse recovery problem is by employing diodes without reverse recovery such as silicon carbide Schottky diodes in the first stage only. The silicon carbide Schottky diode without reverse recovery needs to be used only in the first stage of the voltage multiplier to effectively mitigate the reverse recovery problems at high frequency. The 300 kHz switching frequency three-stage voltage multiplier circuit hardware prototype experimental results finally validate the analysis. A technology demonstrator of a 300 kHz 8 kW 160 kV HV generator based on the proposed hybrid silicon carbide and silicon diode solution for the HW series CW voltage multiplier is provided finally.

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This thesis explores a modular HV pulse converter technology with short rise and decay times. A systematic methodology to derive and classify HV architectures based on a modularization level of power building blocks of the HV pulse converter is developed to summarize existing architectures and explore new possible architectures.The optimal architecture has been identified and recommendations for architecture selections are provided. The effect of modularization and increasing switching frequency for the HV transformer are addressed. The key influence factors for HV pulse rise and decay times are studied. A method is proposed to mitigate the diode reverse recovery effect for the multi-stage voltage multiplier. A generic equivalent steady-state circuit model and comprehensive design methodology are developed to simplify the analysis and design of the series parallel(LCC) resonant based modular HV pulse converters. Finally, the experimental results of a HV pulse converter prototype based on the architecture with multiple transformers and voltage multipliers validate the equivalent steady state circuit model and the comprehensive design methodology. @en

In this paper, a unified equivalent circuit model which can simplify the design and analysis of a family of high-voltage (HV) generation architectures based on the series-parallel (LCC) resonant converter is proposed. First, four HV generation architectures are reviewed in terms of the modularization level of HV transformers and rectifiers. Next, the steady-state, unified equivalent resistor and capacitor (RC) model that can be easily embedded into the resonant tank to replace the complex HV transformers and rectifiers is derived. The generic model can be applied to the HV generators with different architectures, different voltage multiplier topologies, stage, and polarities number. Further analysis of the power factor of the resonant tank, the voltage gain of HV generators, and electrical stresses of power components is achieved with the derived equivalent circuit model. The analysis reveals the inherent circuit properties among HV generators with different configurations. Subsequently, a comprehensive design methodology considering the power factor, conduction angle, and quality factor is presented, which leads to low electrical stresses on the components and high efficiency. Furthermore, the parameter selection constraint based on the power factor, conduction angle, and quality factor is derived, which can ensure the effective design outputs. Finally, the proposed unified equivalent model and comprehensive design methodology are validated by the experimental results of a 250 V input, 20 kV output 500 W HV generator hardware prototype with distributed transformers and voltage multipliers.

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A novel high frequency high voltage (HV) generator circuit with air-core transformer is proposed in this paper to achieve high power density packaging structure and compact size advantages. Planar multi-layer printed circuit board(PCB) winding and litz wire wound winding structure are investigated for air-core HV transformer. The electrical design of air-core HV transformer with HV multiplier circuit based on 1.2kV SiC Schottky diode are introduced. A with 450 kHz switching frequency HV generator prototype with 310W output power and 1kV output voltage is built in lab. 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 based on HV generator can achieve 80.5% efficiency and 1.09kW/L power density. The litz wire wounded transformer based HV generator provide 89.0% efficiency and around 0.53kW/L power density. The design with planar PCB air-core transformer enable high voltage generation circuit system compact planar packaging. The design with litz wire air-core HV transformer behaves higher efficiency and thermal performance with low high frequency AC winding loss.

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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.

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This paper introduces the high voltage generation architectures derivation methodology and comparative evaluation of high voltage power generation architectures based on the key performance items such as efficiency, power density, high voltage pulse speed, high voltage pulse ripple, HV insulation and scalability for different output voltage and output power ratings. Based on comparative evaluation of high voltage generation architectures with single inverter configuration, high voltage generation architecture with single inverter, multiple high voltage transformers and multiple stage voltage multiplication circuits overall outperforms other high voltage generation architectures based on architecture performance comparative analysis and evaluation at 100kV/10kW output rating as case study.

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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.

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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.

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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.

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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.@en

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. 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.@en

This paper investigates the planar transformer for high frequency high voltage (HV) generator applications. The electrical and insulation design of 2kW 400 kHz 5kV HFHV planar transformers for 2kW 35kVDC HV generator are discussed in details. A hardware prototype of 2kW 400 kHz 35kVDC HV generator with planar transformer structure is built in lab to validate the concept finally. The power density of 2kW 35kVDC HV generator with proposed high frequency HV planar transformer is higher than 2kW/L with attractive performance. The HV planar transformer is promising for high frequency HV generator applications.@en

This paper proposes a half bridge CLL resonant DC-DC converter for wide output power range applications. This topology can achieve zero-voltage switching at entire load and zero-current switching for output rectifiers. The characteristics of the CLL resonant DC-DC converter are analyzed firstly. Then the design considerations for CLL resonant DC-DC converters based on wide output power range are introduced. An 150W CLL resonant converter prototype is built to verify the circuit performance with good performances on flat efficiency, narrow switching frequency range for wide output power range application at both 75V & 150V output voltage from 10% output current to 100 % output current.@en

This paper investigates the high frequency high voltage (HFHV) planar transformer for high power density high voltage generator applications. The design procedure of HFHV transformer is introduced firstly. The electrical and insulation design of 2kW 400 kHz 5kV HFHV planar transformers for 2kW 35kVDC HV generator are discussed in details. The HFHV planar transformer hardware prototype experimental results verify the electrical and insulation design. The dielectric loss dominates HFHV planar transformer power loss at 400 kHz switching frequency based on transformer power loss analysis. The power density of 2kW 35kVDC HV generator with proposed HFHV planar transformer is higher than 2kW/L with attractive performance. The proposed design methodology on planar transformer can be applied to other HFHV generator applications.@en

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.@en