AC-AC Converter Research Articles

A Reduced Switch AC-AC Converter with the Application of D-STATCOM and Induction Motor Drive

In this paper, a reduced switch AC-DC-AC converter is used as a distribution static compensator (DSTATCOM) and induction motor drive. The AC-DC-AC nine switch converter (NSC) is a reduced switch topology of conventional 12-switch back to back converter. With a 25% reduced switch count, NSC has lower losses when operated at constant frequency mode compared to twelve switch converter (TSC). The idea is to operate NSC input terminal as an active front-end rectifier to mimic synchronous generator (SG) operation. The induction motor is connected at the output of the NSC for irrigation application where no speed regulation is required. In distribution generation (DG), a large capacitor bank is used to deliver required reactive power. This may lead to over-voltage at the point of common coupling (PCC) when the load is turned off. To manage reactive power transfer at PCC, a control scheme is developed for NSC such that it can absorb or deliver reactive power with induction motor drive. Similar to SG, V-curve and inverted V-curve is plotted. The simulation and hardware results prove the feasibility of the proposed system.

Bipolar-type Dynamic Voltage Conditioner Using P-Leg and N-Leg Structured AC-AC Converter

The voltage fluctuation caused by the high proportion of residential photovoltaic (PV) grid-connected not only restricts the capacity of network to absorb renewable energy, but also seriously affects the normal operation of electrical equipment. Voltage problems in the low voltage distribution network with high proportion of residential PV are described and a novel bipolar-type dynamic voltage conditioner (B-DVC) is introduced to solve the voltage problem in this paper. The topology of the B-DVC adopts the positive current leg (P-Leg) and the negative current leg (N-Leg). By combining two separation inductors together, the voltage distortion caused by the traditional full-bridge two-way switch converter is overcome. Due to the use of the P-Leg and N-Leg structure, the B-DVC can be short- and open-circuited without damaging the switching devices. Neither lossy RC snubber nor a dedicated soft commutation strategy is required in the proposed B-DVC. Furthermore, B-DVC can not only output the voltage with the same polarity as the grid voltage, but also output the voltage opposite the polarity, which can ensure the stability of the power grid voltage and improve the capacity of grid to absorb renewable energy. A 10-kW prototype of single-phase B-DVC is developed, and its performance is experimentally verified.

Design of an Inductor-less Direct AC-AC Converter Realizing 1/4x and 4x Conversion

In this paper, an inductor-less direct AC-AC converter realizing 1/4x and 4x conversion is designed by using switched-capacitor (SC) techniques. Unlike conventional SC AC-AC converters, the proposed AC-AC converter is synthesized with two converter blocks. By converting an AC input twice by these converter blocks, the 1/4x step-down / 4x step-up conversion is achieved by the proposed converter. The proposed converter has a simple circuit configuration, where each converter block consists of only four bidirectional switches and two capacitors. Hence, the proposed converter can realize smaller circuit components and higher input power factor than conventional converters. The effectiveness of the proposed converter was confirmed by simulation program with integrated circuit emphasis (SPICE) simulations and theoretical analysis. The SPICE simulation revealed that the proposed converter outperforms the conventional AC-AC converter using a flying capacitor.

Single Stage Boost Integrated High-Frequency Full Bridge Inverter for Induction Heating System

This paper proposes a new single-stage boost high frequency ac series resonant power inverter for high frequency induction heating (IH) applications. The proposed ac-ac converter consist of a single stage boost (SSB) converter and full-bridge ac series resonant inverter integrated circuit with a ac source voltage control strategy by controlling the inverter switches. The Simulink model is developed using MATLAB simulation software and the simulated results are examined. The output power is maintained to the required level by using phase shift control strategy and the simulated results are validated.

Dynamic inverse controller with Matrix Converter Drive Feed Three Phase Induction Motor

Dynamic inversion (DI) is a controller technique by which existing undesirable dynamics are cancelled out and changed by desirable dynamics. The application of induction motor drives with sinusoidal input currents a matrix converter combined with DI is used which directly connects a three-phase input voltage source to a three-phase (AC-AC converter) without dc-link components. This paper presents a novelty of using nonlinear dynamic inverse controller with matrix converter topologies on three phase induction motor. The efficiency of the converter and their modulation techniques for the implementation of the strategies is increased. The speed response tracking and torque ripple minimization is achieved. The robustness of the proposed method has been confirmed from simulation and experimental model.

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.

A multistage AC-AC converter designed by using switched capacitor techniques

A multistage AC-AC converter designed by using switched capacitor techniques

Dynamic Voltage Restorer Using Switching Cell Structured Multilevel AC–AC Converter

Dynamic voltage restorer (DVR) technology has become a mature power quality product. In high-power applications, DVR using a multilevel converter is commonly used. However, DVR using a multilevel direct pulse width modulation (PWM) ac–ac converter has not been well studied. This paper presents a new DVR topology using a cascaded multilevel direct PWM ac–ac converter. In the proposed scheme, the unit cell of the multilevel converter consists of a single-phase PWM ac-ac converter using switching cell structure with coupled inductors. Therefore, the multilevel converter can be short- and open-circuited without damaging the switching devices. Neither lossy RC snubber nor a dedicated soft commutation strategy is required in the proposed DVR. This improves the reliability of the DVR system. The output voltage levels of the multilevel converter increase with the number of cascaded unit cells, and a high ac output voltage is obtained by using low-voltage-rating switching devices. Furthermore, a phase-shifted PWM technique is applied to significantly reduce the size of the output filter inductor. A 1-kW prototype of single-phase DVR is developed, and its performance is experimentally verified. Finally, the simulation results are shown for a three-phase DVR system.

Harmonic Reduction in Single Phase AC-AC Converter

Objective: To design the trapezoidal pulse width modulation (TPWM) technique in order to reduce the total harmonic distortions at the output of the converter particularly the AC-AC frequency converter. Methods/Analysis: The proposed scheme of modulation technique is used as a modification as compared to that of an unmodulated converter. Two different parameters, namely frequency of the output from the converter and the frequency of the carrier wave, were varied to obtain the harmonic profile of the output voltage of the converter. Results were verified using MATLAB/SIMULINK software environment. Findings: The generalized 1 ϕ AC-AC frequency converter discussed, can be operated both as cyclo-converter (step down) and cyclo-inverter (step up). The output from these converters contain high THD values at the output. The techniques of filtering cannot be used due to numerous reasons. So the TPWM technique is implemented on the frequency converters. The least THD obtain was 0.983 % at 250 Hz for a step up configuration and THD was about 0.8019 % at 25 Hz in case of a step down converter. In addition to varying the output frequency, carrier frequency, fc, of the carrier wave was also varied to check the THD response of the converter and it was least at 1 kHz of about 0.9316 %. In all case, magnitude of output voltage was on higher side of fundamental frequency component. Novelty/Improvement: Simulation results shows that the THD values have been reduced with the application of modulation techniques as compared to that of the output from an unmodulated converter which can help in various application requiring AC-AC converters.

Harmonic Reduction in Single Phase AC-AC Converter

Harmonic Reduction in Single Phase AC-AC Converter

A Three-Level T-Type Indirect Matrix Converter Based on the Third-Harmonic Injection Technique

An indirect matrix converter (IMC) is a direct ac-ac power converter. As an improvement of the output waveform quality, several types of three-level IMC are proposed and investigated. However, two major problems of these converters still exist. First, in some specific situations, such as wind energy conversion systems and flexible ac transmission systems, these converters’ capabilities of generating input reactive power must be improved greatly. Second, neutral-point voltage balancing is a key challenge to the normal operation of multilevel IMCs, but the control of balancing the neutral-point voltage for multilevel IMCs has not been investigated so far. To address these issues, a three-level T-type indirect MC (3LT2IMC) topology as well as a carrier-based modulation method is proposed. In addition to inheriting the advantages of the third-harmonic injection two-stage MC such as extended input reactive power control range and no need for synchronization in modulation, 3LT2IMC could provide an improved output power quality. Besides, a closed-loop control algorithm for balancing the neutral-point voltage is developed. The presented modulation strategy and control algorithm are generalized and can be extended to other three-level IMCs. Finally, the proposed topology and method are verified by simulation and experimental results.

Simulation study of FACTS devices based on AC–AC modular multilevel hexagonal chopper

This paper proposes a new range of FACTS device based on direct AC-AC conversion, where the modular multilevel AC hexagonal chopper (M2AHC) is employed. The M2AHC is operated in quasitwo-level (Q2L) mode; and the heterodyne modulation is used to decouple voltage amplitude regulation from the phase shift; thus, independent control of active and reactive power is achieved. Then, a family of FACTS devices based on M2AHC that offers voltage, active power and reactive power flow control as both shunt and series compensators is analyzed. The use of AC cell capacitors instead of DC capacitors in M2AHC makes its footprint much smaller and lighter than conventional AC-DC or DC-AC voltage source converter (VSC) based FACTS devices; hence, high reliability and extended service life could be expected. The system modeling and controller design of the proposed FACTS devices are illustrated in a unified reference frame, considering different control modes, transient and unbalanced conditions. Simulation results are used to verify the feasibility of the proposed M2AHC based FACTS device. These FACTS devices will be preferred over conventional counterpart for confined spaced applications such as the grid access of large-scale offshore wind farms and resolution of loop flow in megacities.

Power control in centralized distributed AC load for wind energy system

In electrical power systems, isolated energy system is a more challenging task to fulfill the active power demand as well as reactive power demand under the fluctuating wind at different load conditions. In this paper, a centralized AC load, centralized distributed hybrid system (CDHS), is analyzed. CDHS has the following features in place of the DC centralized grid system, which is focused on controlling of a permanent magnet synchronous generator, a bi-directional DC-AC converter (BDC) with battery energy storage, and a wind energy conversion system with a single-stage, 3-phase 4-wire AC-AC converter connected to a common AC bus. Non-isolation of the input terminals, multi-stage operation, size and cost of the circuits, and efficient working of the AC-AC converter has been resolved using a 3-phase 4-wire AC-AC converter. A specific triggering pattern of variable frequencies to a constant frequency has been generated for the switching devices in the AC-AC converter to achieve a desired polarity of the output voltage. A BDC connects the isolated load using a natural frame instantaneous current control technique to manage the active and reactive load power flow among the parallel connection AC hybrid systems. Different conditions such as a constant load and a variable load for variable source supplies are demonstrated for the architecture of CDHS in MATLAB/Simulink. The modelling of CDHS and performance analysis have been disseminated out that the proposed CDHS is capable of managing the active power demand with reactive power for voltage variations.

A Bipolar High-Voltage Multiplier Using Switched-Capacitor AC-AC Converters

To provide nutritious and fresh processed foods at low cost, an underwater shockwave has been utilized for non-thermal food processing in recent years. In this paper, we propose an efficient high voltage multiplier in order to generate the underwater shockwave. Unlike conventional Cockcroft-Walton voltage multipliers (CWVMs), the proposed multiplier amplifies the input voltage twice by combining a switched-capacitor (SC) ac-ac converter and a bipolar CWVM in series. The proposed multiplier can achieve smaller size than existing multipliers, because the proposed multiplier requires no full-bridge circuits. Furthermore, owing to the series-connected bipolar topology using an SC ac-ac converter, high step-up gain can be realized with a small number of stages. The operation principle and characteristic evaluation are described concerning the proposed multiplier. Simulation program with integrated circuit emphasis (SPICE) simulations demonstrate the feasibility and effectiveness of the proposed multiplier.

Research on Output Voltage Modulation of a Five-Level Matrix Converter

The matrix converter (MC) is a direct ac-ac power converter without an intermediate dc link. It has several attractive features, such as high power density, four-quadrant operation, and bidirectional power flow. However, the application of MCs in high-voltage and high-power systems is still limited by the device voltage levels. It is well known that the multilevel power converter technology can be a solution to enhance the voltage rating and improve harmonic performance in many applications. Therefore, an application of a multilevel topology based on a direct ac-ac power converter is proposed in this paper. This paper first introduce the topology structure, the switching pattern grouping method, and the proposed output voltage modulation method for a five-level capacitor clamped multilevel matrix converter (5LMC). Amplitude coefficient adjustment is also introduced as a part of modulation procedure to simplify the duty cycles calculation. Simulation from MATLAB/Simulink is given to demonstrate the theoretical work. Experimental results from a five-level matrix converter prototype are presented to validate the theoretical findings.

Z–Source Multilevel Inverter Based on Embedded Controller

<p>In this paper Embedded based Z-source multilevel inverter (ZSMLI) is proposed. This work implements a five level cascaded H-bridge Z-source inverter by using embedded control. Switching devices are triggered using embedded controller. In this controller coding is described by using switching table. The presence of Z-source network couples inverter main circuit to the power source that providing special features that can overcome the limitations of VSI (voltage source inverter) and CSI (current source inverter). The Z-source concept can applicable in all dc-ac, dc-dc, ac-dc and ac-ac power conversions. Simulation model of Z-source multilevel inverter based on embedded controller has been built in MATLAB/SIMULINK. The Performance parameters of Z-source MLI such as RMS (root mean square) output voltage, THD (total harmonic distortion) and DC component have been analysed for various inductance (L) and capacitance (C) value.</p>

Design of a Simple Inductor-less AC-AC Converter Realizing High Input Power Factor

Switched capacitor (SC) techniques is used in order to design a simple inductor-less ac-ac converter with small size and high input power factor. Comparing conventional inductor-less ac-ac converters with the proposed converter, an input/ output (I/O) terminal is connected alternately to one of capacitors to achieve ac-ac conversion. To realize the new topology, the new designed converter is composed of two capacitors and four switches in the conversion ratios of 2 and 1/2. For this reason, as well as high input power factor, the proposed converter can achieve small size. To explain how the proposed converter is operated with the conversion ratios of 2 and 1/2, operation’s law, analysis in theory, and results of circuit simulation are written on this paper. The validity of the proposed converter is confirmed by circuit simulations using SPICE simulator.

A Cascaded Switched-capacitor AC-AC Converter with a Ratio of 1/2<sup>n</sup>

Based on the existing AC-AC switched-capacitor (SC) converter, this paper demonstrates a new cascaded AC-AC converter circuit topology with a ratio of 1/2ⁿ, which only consists of power switches and capacitors. The converter consists of multi-stage converters and the pre-and post-stage circuits are independent with each other. The principle of the topology and the formula of related parameters, including equivalent resistance, equivalent capacitance and switching loss, are deduced with the port network theory, thus the equivalent circuit is gained in this paper. After the theoretical analysis, simulation models and experimental prototype were established to validate the correctness of the circuit topology. Both simulation and experimental results have verified the effectiveness of the circuit topology and the correctness of the theoretical derivation.

Аналитическая модель AC-AC преобразователя, входящего в состав авиационной системы генерирования

Аналитическая модель AC-AC преобразователя, входящего в состав авиационной системы генерирования

Single-Phase Direct Boost AC-AC Converter

This paper introduces and studies a boost AC-AC converter circuit that can be used to supply power to the 220V receivers in the 110V grids or to increase and adjust voltage at the end ...