Z-source Ac-ac Converter Research Articles

A Class of Bidirectional Single-Phase Z-Source AC–AC Converter With Continuous Input Current and Reduced Component Count

In this paper, a class of single-phase Z-source ac-ac converters is proposed. Share ground and continuous input current are the common features of the proposed converters. The proposed converters have unique features that differentiate them from their counterparts. These features include the buck operation in both in-phase and out-of-phase mode, being bidirectional, the minimum component counts, the ability to boost without duty cycle limitation, and reducing total power ratting of switches is known as switching device power (SDP) parameter. Reducing SDP leads to a reduction in the voltage and current rating of the semiconductors and consequently to a reduction in converter' cost. A safe commutation strategy is applied to eliminate voltage and current spikes on the switches without snubber circuits. The experimental results verify the performance of the laboratory prototype of the proposed converters.

입력 전류의 스위칭 맥동이 개선된 LCCT Z-소스 AC-AC 컨버터

In the conventional trans-quasi Z-source AC-AC converter(TqZAC) method, the voltage gain can be improved by replacing the inductor of the Z-impedance network with a high-frequency transformer, but there is a problem in that a switching ripple occurs in the input current and the capacitor voltage. In this study, the Inductor-Capacitor-Capacitor-Trans Z-source AC-AC converter (LCCT-ZAC) method was presented to solve this problem. The proposed method replaces the conventional harmonic transformer with a three-winding high-frequency transformer and capacitor to alleviate the switching ripple problem of the previous method, while controlling the output voltage with in-phase boost and out-of-phase buck-boost for the input voltage. To prove the validity of this study, PSIM simulation and DSP-based experiments were performed. As a result, the output voltage was controlled by the in-phase boost mode at duty ratio D=0.15 and the out-of-phase buck mode at D=0.5. Also, the efficiency with respect to the change of duty ratio D under the load condition of 50Ω and the efficiency with respect to the load change under the condition of D=0.05 were almost the same between the two methods.

A Class of Single-Phase Z-Source AC–AC Converters With Magnetic Coupling and Safe-Commutation Strategy

This article proposes a family of single-phase transformer based Z-source ac-ac converters (ZSACs). The proposed converters inherit all the benefits associated with the classical single-phase ZSAC, which are providing the buck-boost operation, maintaining or reversing the phase angle, and improving reliability. The proposed converters also have the improved input profile, continuous input current, and shared ground between input and output. Moreover, they use the turns ratio of transformers to produce the required voltage gain, which can be tuned by either increasing or decreasing the turns ratio of transformer depending on the configuration of Z-source structure. A safe-commutation strategy is also presented to achieve the soft commutation, which eliminates the voltage and current spikes without any additional snubber circuits. The features of proposed converters are comprehensively discussed with the detailed theoretical analysis. Thereafter, its performances are evaluated by both simulation and experimental tests.

Modeling and reliability analysis of three phase z-source AC-AC converter

Abstract This paper presents the small signal modeling using the state space averaging technique and reliability analysis of a three-phase z-source ac-ac converter. By controlling the shoot-through duty ratio, it can operate in buck-boost mode and maintain desired output voltage during voltage sag and surge condition. It has faster dynamic response and higher efficiency as compared to the traditional voltage regulator. Small signal analysis derives different control transfer functions and this leads to design a suitable controller for a closed loop system during supply voltage variation. The closed loop system of the converter with a PID controller eliminates the transients in output voltage and provides steady state regulated output. The proposed model designed in the RT-LAB and executed in a field programming gate array (FPGA)-based real-time digital simulator at a fixedtime step of 10 μs and a constant switching frequency of 10 kHz. The simulator was developed using very high speed integrated circuit hardware description language (VHDL), making it versatile and moveable. Hardware-in-the-loop (HIL) simulation results are presented to justify the MATLAB simulation results during supply voltage variation of the three phase z-source ac-ac converter. The reliability analysis has been applied to the converter to find out the failure rate of its different components.

전력전자 변압기로 동작하는 저전압 직류배전 기능을 갖는 Quasi Z-소스 AC-AC 컨버터

This paper proposes a quasi Z-source AC-AC converter with the low DC voltage distribution capability operating as a power electronic transformer. The proposed system has configuration that the input terminals of two quasi Z-source AC-AC converters are connected in parallel, also their output terminal are connected in series. Simple control method of duty ratio was proposed for the in phase buck-boost AC voltage mode and the DC output voltage control. DSP based experiment and PSIM simulation were performed. As a result, the PSIM simulation results were same with the measured results. By controlling the duty ratio under the condition of 100 [Ω] load, quasi Z-source AC-AC converter could buck and boost the AC output voltage in phase with the AC input voltage, and the same time, the constant DC voltage could be output without affecting the AC output characteristics. And, the DC output voltage 48[V] was constantly controlled in dynamic state in case while the load is suddenly changed (50 [Ω]→100 [Ω]). From the above result, we could know that the quasi Z-source AC-AC converter can act as a power electronic transformer with a low DC voltage distribution capability.

전 영역의 전압보상을 위한 단상 직렬형 Quasi Z-소스 전압 Sag-Swell 보상기

Conventional single-phase series quasi Z-source voltage compensator can not compensate for voltage sag less than 50% that frequently occurs in the industrial field. In this study, single-phase series quasi Z-source voltage sag-swell compensator which can compensate the voltage variation of entire range is proposed. The proposed system is composed of two quasi Z-source AC-AC converters connected in series with output terminal stage. Voltage sag less than 50% could be compensated by the intersection switching control of the upper converter duty ratio and of the upper converter duty ratio. Also the compensation voltage and its flowchart for each compensation mode are presented for entire sag-swell region. To confirm the validity of the proposed system, a DSP(DSP28335) controlled experimental system was manufactured. As a result, the proposed system could compensate for the voltage sag/swell of 20% and 60%. Finally, voltage compensation factor and THD(Total Harmonic Distortion) according to voltage variation and load change were measured, and voltage quality shows a good results.

두 개의 Quasi Z-소스 AC-AC 컨버터에 의한 6.6[kV]/60[Hz] 배전계통의 동적 전압 보상기(DVR)

This paper proposes a quasi Z-source DVR(Dynamic Voltage Restorer) system with a series connection of the output terminals, to compensate the voltage variations in the 6.6[kV]/60[Hz] power distribution system. The conventional DVR using one quasi Z-source AC-AC converter has the advantage which it can compensate the voltage variations without the need for the additional energy storage device such as a battery, but it is impossible to compensate for the 50[%] under voltage sags. To solve this problem, a DVR system using two quasi Z-source AC-AC converters with the series connection of the output terminals is proposed. By controlling the duty ratio D in the buck-boost mode, the proposed system can control the compensation voltage. For case verification of the proposed system, PSIM simulation is achieved. As a result, in case that the voltage sags-swells occur 10[%], 20[%], 60[%] in power distribution system, and, in case that the 50[%] under voltage sags-swells continuously occur, all case could compensate by the proposed system. Especially, the compensated voltage THD was examined under the condition of the 10[%]∼50[%] voltage sags and the 20[Ω]∼100[Ω] load changes. The compensated voltage THD was worse for the higher load resistances and more severe voltage sags. Finally, In case of the voltage swells compensation, the compensation factor has approached nearly 1 regardless of the load resistance changes, while the compensation factor of voltage sags was related to the load variations.

A Modified Single-Phase Quasi-Z-Source AC–AC Converter

A modified single-phase quasi-Z-source ac-ac converter is proposed in this paper. The proposed converter has the main features in that the output voltage can be bucked or boosted and be both in-phase and out-of-phase with the input voltage. The input voltage and output voltage share the same ground, the size of a converter is reduced, and it operates in a continuous current mode. A safe-commutation strategy for the modified single-phase quasi-Z-source ac-ac converter is used instead of a snubber circuit. The operating principles and a steady-state analysis are presented. A laboratory prototype, tested using a resistive load, a passive load, and a nonlinear load, was constructed that used an input voltage of 70 Vrms /60 Hz in order to verify the performance of the modified single-phase quasi-Z-source ac-ac converter. The experimental results verified that the converter has a lower input current total harmonic distortion, a higher input power factor, and a higher efficiency in comparison to a conventional single-phase Z-source ac-ac converter. In addition, the experimental results show that the use of the safe-commutation strategy is a significant improvement, as it makes it possible to avoid voltage spikes on the switches.

출력이 직렬 결합된 단상 Quasi Z-소스 AC-AC 컨버터

본 연구에서는 출력이 직렬 연결된 단상 quasi Z-소스 AC-AC 컨버터를 제안하였다. 제안된 시스템은 단상quasi Z-소스 AC-AC 컨버터 2대의 입력 단을 병렬로 연결하고 출력 단을 직렬로 연결한 구조로 되어 있으며, 역상 모드와 동상 모드 별 전류 흐름과 출력전압의 형성 과정을 나타내었다. DSP로 제어되는 실험 시스템을 제작하여 PSIM시뮬레이션 결과와 비교 분석하였다. 그 결과 각 모드별로 듀티 비를 제어하여 원하는 출력 전압을 벅-부스트 할 수 있었다. 컨버터 1대가 단독으로 운전한 경우에 비하여, 각각의 모드에 대하여 부하 저항의 증가에 따른컨버터 효율과 입력 역률을 제안된 방법에 의하여 개선할 수 있었다. 또한 역상 모드의 경우, 일정 부하에서 컨버터의 효율과 입력 역률을 각각 10[%]와 35[%]정도 개선하였으며, 특히 부하 저항이 변동하는 과도상태에서도 일정한 출력 전압을 유지할 수 있었다. In this study, a single-phase quasi Z-source AC-AC converters with a series connection of the output terminals is proposed. The proposed system has configuration that the input terminals of two quasi Z-source AC-AC converters are connected in parallel and its output terminals are connected in series. The out of phase mode and in phase mode of the proposed system are presented. To verify the validity of the proposed converter, a DSP controlled hardware was made and PSIM simulation was executed. As a result, controlling the duty ratio of the converter, the desired buck-boost output voltages could be generated. For each modes, as compared with the single converter operation, the proposed converter could enhance the efficiency and input power factor according to different loads. Also, in case of the out of phase mode under the constant load, the efficiency and input power factor of the proposed system are increased 10[%], 35[%] respectively in compared with the single converter. And, the output voltage is constantly controlled in dynamic state in case while the load is suddenly changed.

A New Quasi Z-Source Dynamic Voltage Restorer

Abstract –This paper deals with a new quasi Z-source Dynamic Voltage Restorer(DVR). The proposed system based on single-phase quasi Z-source AC-AC converter which has features such as the input voltage and output voltage are sharing ground, and the input current operates in continuous current mode. Also the proposed system is able to compensate voltages sags and swells. For the detection of voltage sag-swell, the fast detection of an instantaneous value detection algorithm is applied. The operating principles of the proposed quasi Z-source AC-AC converter are described and PSIM simulation is presented to verify the proposed concept and theoretical analysis. Keywords : Quasi Z-Source AC-AC Converter, Dynamic Voltage Restorer, Voltage Sag-Swell Compensator 1. Introduction Some decades, the power quality did not cause any problems, because it had no effect on most of the loads connected to the electric distribution system. In recent years, power quality issues have been received much attention. With the increased use of the sophisticated electronics, high efficiency variable speed drive, and power electronics controller, power quality has become an increasing concern to utilities and customers and huge economical losses due to the interruption of production processes[1]. Among these problems, voltages sag and swell are the most common type of power quality disturbance in the distribution system. In order to increase the reliability of a power distribution system, many methods of solving quality problems, especially voltage sag, have been suggested. Many voltage sag mitigation schemes are based on inverter systems consisting of energy storage and power switches. Also, the Dynamic Voltage Restorer (DVR) and Uninterrupted Power Supply (UPS) developed and they are able to compensate voltage sags and swells, harmonics maintaining a regulated voltage at critical load[2]. But some of them are based on energy storage devices such as large capacitors or batteries bank. If the power is increased, the size of these devices will increase and make them more expensive[3]. In this paper, we propose a new quasi Z-source dynamic voltage restorer. The proposed topology employs a single-phase quasi Z-source AC-AC Converter[4] along with an autotransformer. During the voltage sags or swells, the proposed system regulates the adding or missing voltage and maintaining the rated voltage at the terminals of the critical load. The proposed system is able to compensate up to over 50% voltage sag and it is able to compensate voltage swell. In addition, it is possible to use an AC-AC converter instead of a power inverter in the topology of a dynamic voltage restorer avoiding the energy storage devices[2]. This paper also proposes the control method of the fast detection of an instantaneous value detection algorithm. The operating principle, analysis, simulation results are presented.

Z-소스 교류 컨버터 토폴로지의 동적 전압 보상기

This paper proposes a new type of voltage sag-swell compensator based on a Z-source AC-AC converter. The proposed topology employs a pulse width modulation (PWM) Z-source AC-AC converter along with a injection transformer. A safe commutation strategy is used to eliminate voltage spikes on switches without snubber circuit. During a voltage sag or swell, the proposed system controls the adding or missing voltage and maintains the rated voltage of sinusoidal waveform at the terminals of the critical loads. The proposed system is able to compensate 20[%] voltage swell and is also able to compensate 60[%] voltage sag. In order to control and detect the voltage sag and swell, the peak voltage detection method is applied. Also, the operating principles of the proposed system are described, and a circuit analysis is provided. Finally, PSIM simulation and experimental results are presented to verify the proposed concept and theoretical analysis.

Single-Phase AC–AC Converter Based on Quasi-Z-Source Topology

This paper deals with a new family of single-phase ac-ac converters called single-phase quasi-Z-source ac-ac converters. The proposed converter inherits all the advantages of the traditional single-phase Z-source ac-ac converter, which can realize buck-boost, reversing, or maintaining the phase angle. In addition, the proposed converter has the unique features that the input voltage and output voltage share the same ground and the operation is in the continuous current mode. The operating principles of the proposed converter are described, and a circuit analysis is provided. In order to verify the performance of the proposed converter, a laboratory prototype was constructed with a voltage of 84 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> /60 Hz. The simulation and experimental results verified that the converter has a lower input current total harmonic distortion and higher input power factor in comparison with the conventional single-phase Z-source ac-ac converter.

Z-Source AC–AC Converters Solving Commutation Problem

A new family of Z-source ac-ac converters with buck-boost ability are proposed, including four switches single-phase structure and six switches three-phase structure. New commutation strategies for these converters are proposed and safe commutation can be achieved without snubber circuit. The commutation strategies are easily to realize by sampling only voltage signals, and two switches are always turned on, so switching loss can be reduced. Analysis based on state-space averaging reveals the relationship between Z-source inductor current and filter inductor current as well as voltage ratio. The design considerations of voltage-fed single-phase topology are given as an example. Simulation results on the voltage-fed topologies and experimental results on voltage-fed single-phase topology verified the unique features of Z-source ac-ac converters and the proposed commutation strategies. These converters have merits such as less conduction and switching loss, less devices, therefore high efficiency and reliability can be achieved.

Single-phase Z-source PWM AC-AC converters

The letter proposes a new family of simple topologies of single-phase PWM ac-ac converters with a minimal number of switches: voltage-fed Z-source converter and current-fed Z-source converter. By PWM duty-ratio control, they become solid-state transformers with a continuously variable turns ratio. All the proposed ac-ac converters in this paper employ only two switches. Compared to the existing PWM ac-ac converter circuits, they have unique features: providing a larger range of output ac voltage with buck-boost, reversing or maintaining phase angle, reducing in-rush and harmonic current, and improving reliability. The operating principle and control method of the proposed topologies are presented. Analysis, simulation, and experimental results are given using the voltage-fed Z-source ac-ac converter as an example. The analysis can be easily extended to other converters of the proposed family. The proposed converters could be used in voltage regulation, power regulation, and so on.