Chung-Ming Young

Cascade Cockcroft–Walton Voltage Multiplier Applied to Transformerless High Step-Up DC–DC Converter

This paper proposes a high step-up dc-dc converter based on the Cockcroft-Walton (CW) voltage multiplier without a step-up transformer. Providing continuous input current with low ripple, high voltage ratio, and low voltage stress on the switches, diodes, and capacitors, the proposed converter is quite suitable for applying to low-input-level dc generation systems. Moreover, based on the n-stage CW voltage multiplier, the proposed converter can provide a suitable dc source for an n + 1-level multilevel inverter. In this paper, the proposed control strategy employs two independent frequencies, one of which operates at high frequency to minimize the size of the inductor while the other one operates at relatively low frequency according to the desired output voltage ripple. A 200-W laboratory prototype is built for test, and both simulation and experimental results demonstrate the validity of the proposed converter.

Phase-Locked Bidirectional Converter With Pulse Charge Function for 42-V/14-V Dual-Voltage PowerNet

In this paper, a phase-locked bidirectional converter (BC) (PLBC) with pulse charge function is proposed to improve the battery charge efficiency. The circuit topology of the proposed PLBC is the same as that of the current-pump phase-locked loop (CP-PLL). Using CP-PLL inherent characteristics, a pulse current with bidirectional flow can be automatically implemented. A design example for a 42-V/14-V dual-voltage PowerNet is built to assess the PLBCs performance. Compared with the conventional BC, the battery charge efficiency ηb is improved by about 2.8%. Moreover, the battery increased temperature is reduced by about 5.7 °C simultaneously.

A Cockcroft–Walton Voltage Multiplier Fed by a Three-Phase-to-Single-Phase Matrix Converter With PFC

This paper proposes a single-stage three-phase-to-single-phase current-fed high step-up ac-dc matrix converter. The proposed converter inserts a boost-type matrix converter, which is formed by three boost inductors and six bidirectional switches, between a three-phase ac source and a Cockcroft-Walton voltage multiplier (CWVM). By using this topology associated with power factor correction technique, the proposed converter not only achieves almost unity power factor and sinusoidal input currents with low distortion but also obtains high voltage gain at the output end. Moreover, the matrix converter generates an adjustable-frequency and adjustable-amplitude current, which injects into the CWVM to regulate the dc output voltage and smooth its ripple. With this flexible injection current, the performance of the proposed converter is superior to the conventional CWVM, which is usually energized by a single-phase ac source. The operation principle, control strategy, and design considerations of the proposed converter are detailed in this paper. Finally, simulation and experimental results demonstrate the claims and validity of the proposed converter.

A novel single-phase ac to high voltage dc converter based on Cockcroft-Walton cascade rectifier

This paper proposes a novel single-phase ac to high voltage dc converter based on Cockcroft-Walton cascade rectifier with only adding one bi-directional switch and one boost inductor. This paper also derives a new method of circuit representation for Cockcroft-Walton cascade rectifier, which simplifies the equivalent circuit and is convenient for simulation. Compared with conventional Cockcroft-Walton rectifier, the proposed converter provides half-wave symmetric and low-distorted line current, adjustable power factor at the ac source, and regulated dc output voltage. Unit power factor is achieved by the average-current method and the dc output voltage is regulated by a PI compensator. Moreover, this paper employs a digital signal processor to implement a digital controller for operating the proposed converter and a prototype with 500w rating is implemented for test. Both simulation and experimental results demonstrate the validity of the proposed converter.

A Novel Active Interphase Transformer Scheme to Achieve Three-Phase Line Current Balance for 24-Pulse Converter

A new active interphase transformer (IPT) scheme to achieve three-phase line current balance for a 24-pulse converter is proposed in this paper. The proposed active IPT scheme consists of three IPT and a current-controlled inverter with required rating only 1.16% of system power rating. A current injection method for an active IPT is also proposed in this paper. The balance of three-phase current and high power quality can be achieved by injecting compensation current into the secondary winding of the active IPT. Moreover, the proposed scheme can operate in flexible load configurations, by which separated loads can be connected to the separated outputs of the converter independently. The operation criteria for flexible load arrangements are analyzed to obtain better performance. System simulation is conducted and a 6-kW laboratory prototype is built both for evaluation and test. Both simulation and experimental results demonstrate the validity of the proposed scheme.

A DC-Side Current Injection Method for Improving AC Line Condition Applied in the 18-Pulse Converter System

In this paper, a new compensation strategy for receiving clean power of a conventional 18-pulse ac/dc converter formed by three 6-diode bridges is proposed. According to the proposed strategy, a three-phase current-controlled inverter injects the compensation currents into the three positive terminals of the three six-diode bridges. The goal of injecting currents at dc side is to improve the quality of the ac line currents. Compared to the conventional active filter deployed at the ac side, the three-phase inverter used in this paper is with lower kVA rating, and the 18-pulse converter draws nearly sinusoidal currents from the ac main by the proposed compensation strategy. The theoretical compensation command is derived in this paper, and then an approximate approach is recommended to simplify the calculation. A digital-signal processor is employed as a digital controller to calculate the compensation command, and a 3-kW prototype including the 18-pulse converter and the current-controlled inverter is built for evaluation and measurement. Moreover, the performance affected by unbalanced ac source is investigated. The experimental results demonstrate that the proposed method not only improves the line current quality but also mitigates the effects caused by unbalanced source voltages.

Transformerless high step-up DC-DC converter with Cockcroft-Walton voltage multiplier

This paper proposes a high step-up dc-dc converter based on Cockcroft-Walton (CW) voltage multiplier without step-up transformer. Providing high step-up rate, the proposed converter is quite suitable for applying to low-input level dc generation systems. The proposed converter improves the impractical operation of the conventional boost dc-dc converter at high duty ratio due to non-ideal characteristics of the circuit components, such as the equivalent series resistance of the inductor. For easy design, a commercial average-current-control continuous conduction mode (CCM) integrated circuit (ICE1PCS01) and a complex programmable logic device (CPLD) LC4256V are used to implement the control strategy of the proposed converter. A modified switching function, which is built in CPLD, controls the switches to generate an alternating source to the CW voltage multiplier. Under CCM operation, the output voltage ripple of the proposed converter can be limited by the flexibly adjustable frequency. A 200W laboratory prototype is built for test and the experimental results demonstrate the validity of the proposed converter.

A novel control for active interphase transformer using in a 24-pulse converter

This paper proposes a new active interphase transformer for 24-pulse diode rectifier. The proposed scheme injects a compensation current into the secondary winding of either of the two first-stage interphase transformers. For only one of the first-stage interphase transformers being active, the inverter conducted the injecting current is with a lower kVA rating [1.26% pu (Po)] compared to conventional active interphase transformers. Moreover, the proposal scheme draws near sinusoidal input currents and the simulated and the experimental total harmonic distortion of overall line currents are only 1.88% and 2.27% respectively. When the inverter malfunctions, the input line current still can keep in the conventional 24-pulse situation. A digital-signal-processor (DSP) based digital controller is employed to calculate the desired compensation current and deals with the trigger signals needed for the inverter. Moreover, a 6kW prototype is built for test. Both simulation and experimental results demonstrate the validity of the proposed scheme.

A single-stage three-phase to single-phase current-fed high step-up AC-DC matrix converter with PFC

TMs paper proposes a novel single-stage three-phase to single-phase current-fed high step-up ac-dc matrix converter for high voltage dc applications. The proposed converter inserts a boost matrix converter, which is formed by three boost inductors and six bidirectional switches, between a three-phase ac source and a Cockcroft-Walton voltage multiplier (CW-VM) circuit. By using this topology associated with power factor correction technique, the proposed converter not only achieves almost unity power factor and sinusoidal input phase currents with low distortion but also obtains high voltage gain at the output end. Moreover, the matrix converter generates an adjustable-frequency and adjustable-amplitude current which injects into the CW-VM to regulate the dc output voltage and smooth its ripple. With this flexible injection current, the performance of the proposed converter is superior to the conventional CW-VM, which is usually energized by a single-phase ac source. Sourced by three-phase ac source, the proposed converter is quite suitable for high-power and high voltage applications. Both operation principle and control strategy of the proposed converter are detailed in this paper. Finally, simulation results demonstrate the performance of the proposed converter and the experimental work will be conducted in the near future.

A new multilevel inverter based on single DC input source and zig-zag connected transformers

This paper proposes an isolated multilevel inverter composed of four standard two-level voltage source inverters (modules), a single dc source and a specially connected three-phase transformer, zig-zag-connected transformer. The proposed configuration can reduce the number of transformers and current and voltage stresses compared with traditional three-phase multilevel inverters with same lower rating. Moreover, only 24h±1 characteristic harmonic components appear in output voltage with each inverter operating in square-wave mode. Therefore, the switching frequency is reduced dramatically. For further improving output waveform, selective harmonic elimination (SHE) strategy with five notch angles is applied to the proposed inverters to eliminate the lowest four 24h ± 1 characteristic harmonics. The solutions of notch angles for a wide range of the modulation index are solved and built in a DSP-based controller for implementing the proposed inverter system. Compared to the traditional SHE strategy that eliminates non-triplen odd harmonics, the proposed inverter provides lower switching frequency and more voltage levels. A 6kW laboratory prototype is implemented to verify the validity of the proposed configuration.