H.L. Hey

A true ZCZVT commutation cell for PWM converters

This paper introduces a true zero-current and zero-voltage transition (ZCZVT) commutation cell for DC-DC pulsewidth modulation (PWM) converters operating with an input voltage less than half the output voltage. It provides zero-current switching (ZCS) and zero-voltage switching (ZVS) simultaneously, at both turn on and turn off of the main switch and ZVS for the main diode. The proposed soft-switching technique is suitable for both minority and majority carrier semiconductor devices and can be implemented in several DC-DC PWM converters. The ZCZVT commutation cell is placed out of the power path, and, therefore, there are no voltage stresses on power semiconductor devices. The commutation cell consists of a few auxiliary devices, rated at low power, and it is only activated during the main switch commutations. The ZCZVT commutation cell, applied to a boost converter, has been analyzed theoretically and verified experimentally. A 1 kW boost converter operating at 40 kHz with an efficiency of 97.9% demonstrates the feasibility of the proposed commutation cell.

Comparison of digital control techniques with repetitive integral action for low cost PWM inverters

This paper presents a comparison among digital control techniques with repetitive integral action applied to voltage-source PWM inverters. As a result of the repetitive integral action, these digital control schemes can reduce steady-state errors and distortions caused by unknown periodic disturbances, which usually result from the input source and output load. Moreover, these digital control schemes measure only the output voltage, decreasing the amount of sensors and the overall system cost. The control laws, stability analysis, common and distinguishing features of these control algorithms are discussed. Experimental results from a PWM inverter (110 V/sub RMS/, 1 kVA) controlled by a low cost microcontroller are presented to demonstrate the control techniques performance under different load conditions, output filters and command strategies.

A ZCT auxiliary commutation circuit for interleaved boost converters operating in critical conduction mode

This paper investigates a power-factor-corrector (PFC) circuit based on interleaved boost converters in critical conduction mode (C-DCM) with a zero current transition (ZCT) circuit. By using the interleaved converters technique, the input current ripple is minimized, and due to the operation in C-DCM, the main switches turn-on occurs naturally under zero current and the reverse recovery losses of the diodes are minimized. The use of auxiliary commutation circuits provides ZCT at main switches turn-off, minimizing the related turn-off losses. The command circuit of the converters has been implemented by using a single erasable programmable logic device (EPLD) EPM7128SLC84-15. Operating principles, theoretical analysis, design guidelines and a design example are described and verified experimentally by a 1.2 kW prototype. Finally, the measured losses in the PFC interleaved boost converters with and without the proposed ZCT commutation cell, as well as a previously published ZCT cell are presented and discussed.

Analysis and Design of a New High-Efficiency Bidirectional Integrated ZVT PWM Converter for DC-Bus and Battery-Bank Interface

This paper proposes a high-efficiency bidirectional integrated zero-voltage transition (iZVT) pulsewidth-modulation (PWM) converter for dc-bus and battery-bank interface. The proposed converter can operate as battery charger when the utility is within its acceptable voltage range and can supply energy to critical loads when the utility fails. The converter practically eliminates both low- and high-frequency current ripple on the batteries, thus maximizing battery life without penalizing the volume of the converter. Moreover, soft switching of all switches is achieved using the proposed integrated auxiliary commutation circuit (iACC). Just one iACC is used to provide soft-switching conditions for the three converters that compose the system: the preregulator (boost), the battery charger (bidirectional converter operating as a buck), and the backup converter (bidirectional converter operating as a boost). This auxiliary circuit has few components and low reactive energy, increasing the systems overall efficiency. Experimental results based on a 580-W prototype are presented to validate the analysis and the proposed design procedure and to demonstrate the performance of the proposed approach

Space vector modulation for voltage-source inverters: a unified approach

This paper presents a unified approach of the space vector modulation for voltage-source inverters. To demonstrate the proposed unified approach, five fundamental inverters topologies are analyzed: single-phase full-bridge, three-phase three-wire, three-phase four-wire, three-phase four-leg and three-phase three-level inverters. Switching vectors, separation and boundary planes in the inverter output space as well as decomposition matrices and possible switching sequences are derived for each one of these inverters. Experimental results are shown to validate the proposed unified approach.

A modified discrete control law for UPS applications

This paper presents a model reference controller with a repetitive control action for uninterruptible power supply (UPS) applications. The model reference controller modifies the structure of the plant so that the closed-loop transfer function is equal to a chosen reference model transfer function, whereas the repetitive control action minimizes periodic distortions caused by unknown periodic disturbances. Design procedure and stability analysis of the control scheme are discussed. Simulation and experimental results for a single-phase PWM inverter (110 V/sub RMS/, 1 kVA) controlled by a low cost microcontroller are presented to verify the performance of the proposed control approach under different load conditions.

Analysis and comparison of hybrid multilevel voltage source inverters

This paper analyzes different hybrid multilevel inverters for high-power applications. With these hybrid topologies, it is possible to minimize the number of series-connected inverters for a given number of levels and, consequently, to reduce the THD of output voltage. Moreover, this paper develops a comparison among different hybrid multilevel inverters, especially between binary and trinary hybrid multilevel inverters. Several points are discussed, taking into account number of levels, spectral performance and power processing of hybrid multilevel inverters. Finally, a design procedure to obtain the number of H-bridge cells and DC voltage source of each cell for a given number of levels is proposed, so that few H-bridge cells synthesize a voltage waveform with a large number of levels, in order to minimize the circulating energy among cells.

Analysis and design of a repetitive predictive-PID controller for PWM inverters

This paper presents a predictive PID controller including a feedforward control and a repetitive controller for UPS applications. This digital control scheme can minimize periodic distortions resulted from nonlinear cyclic loads. Design procedure and stability analysis of the control scheme are discussed. Simulation and experimental results for a single-phase PWM inverter (110 V/sub RMS/, 1 kVA) controlled by a low cost microcontroller are presented to demonstrate the performance of the proposed control approach under periodic load disturbances.

Isolated interleaved-phase-shift-PWM DC-DC ZVS converters

This paper describes the operation principles of an isolated ZVS DC-DC converter, which is composed by two half-bridge converters. Soft-switching is achieved for a wide load range. This ZVS DC-DC converter operates at constant frequency and it is phase-shift modulated. The main advantage of the phase-shift interleaving is the equalization of the input capacitor voltage, where each capacitor shares one-quarter of the total input voltage. The converter can be an alternative for ZVS phase-shift full-bridge DC-DC converter for high voltage applications, as result of the series arrangement in one of the two half-bridge converters. Analysis, operating principle and design procedures are presented in the paper. Experimental results from a 1.5 kW prototype converter operating at 100 kHz with isolated 60 V/25 A output are presented to validate the theoretical analysis.

Coupled-Filter-Inductor Soft-Switching Techniques: Principles and Topologies

Pulsewidth-modulation inverters and rectifiers are required in widespread applications such as energy-storage power plants, telecommunication systems, and electric-vehicle propulsion systems. Some of the stringent requirements of these applications can be achieved by high switching frequency. On the other hand, the use of high switching frequency may degrade the overall system efficiency, which can be alleviated by the utilization of soft-switching techniques. In this paper, a generic soft-switching diagram that can generate topologies for turn-on snubber, zero- voltage transition, zero-current-zero-voltage transition inverters with coupled filter inductor is proposed. This approach facilitates the understanding of these techniques by both newcomers and senior engineers, making the advantages and disadvantages of each soft-switching technique much clearer.