A. Fatemi

Single-Phase Dual-Output Inverters With Three-Switch Legs

In this paper, two reduced switch count topologies are introduced for independently supplying two single-phase ac loads with one inverter. Using a new three-switch leg structure recently introduced and implemented in three-phase converters, two types of dual-leg and single-leg topologies are developed which respectively are functionally comparable to two full-bridge and half-bridge inverters working independently though with a less number of semiconductor switches and hence control and gate drive circuit components. The proposed six-switch and three-switch topologies are introduced; two modes of equal frequency and different frequency operation each of its own distinctive characteristics are considered for them and their pulse width modulation schemes are elaborated. Comprehensive analyses of power loss profile and output waveform properties are conducted via simulation for the proposed inverters, and the results are compared with full-bridge and half-bridge inverters. To assess the performance of the proposed inverter topologies, working prototypes are built, and the experimental results are provided.

Integrated Solution for Microgrid Power Quality Assurance

In this paper, a new interface configuration is proposed for connecting a microsource to a weak utility. The proposed configuration simultaneously conditions the quality of the power supplied to the microgrid loads. This system employs a recently introduced reduced switch count dual-output inverter in a so-called equal frequency mode which offers its best operation features such as maximum dc bus voltage utilization and minimum device ratings. Compared to the counterpart system, the proposed configuration enjoys an integrated structure and uses less number of semiconductor switches. Moreover, it retains the desirable features of the conventional system such as ability to compensate unbalanced/sagged utility and to supply three-phase unbalanced loads with balanced and ceaseless voltage. The proposed system is introduced and its carrier-based modulation scheme is elaborated. Subsequently, a detailed study on the maximum achievable modulation index under different working conditions is carried out. The report concludes with a discussion on control of the system and its controller design. The validity of operation of the proposed system is verified through simulation.

Quasi Z-source inverter for photovoltaic system connected to single phase AC grid

A novel photovoltaic system based on quasi Z-source inverter (qZSI) which is connected to a single phase grid is proposed in this paper. Quasi Z-source inverter is a recently developed topology derived from Z-source inverter (ZSI). qZSI is a one-stage power conditioner that employs a capacitor-inductor network for connecting inverter to photovoltaic module. By means of controlling shoot-through duty cycle, the objective of tracking maximum power point can be accomplished. In comparison with ZSI, qZSI benefits some prominent privileges such as lower component ratings and source constant dc current. In this paper, through introducing an appropriate control structure, qZSI is used for connecting photovoltaic system to single phase grid. In the control structure, maximum power with unit power factor and low THD current is delivered to grid by controlling modulation index via PIS controller. Presuming voltage stabilization, the amount of power delivered to grid is regulated through the use of controller of qZSI capacitor voltage. qZSI is also utilized to control the shoot-through duty cycle in order to achieve maximum power point tracking (MPPT). Simulation results are provided to demonstrate the competence of the system.

A novel Z-source four-leg inverter with two independent four-wire outputs

This paper proposes a novel inverter for supplying unbalanced four-wire three-phase loads. The inverter has two three-phase outputs that operate with independent frequencies and amplitudes. Within each output, each phase can have independent voltage magnitude, but the frequency is the same for all phases. The topology is developed by adding an extra leg to a nine-switch converter. Moreover, it benefits from Z-source impedance network which provides more reliability along with voltage boost capability. Two carrier based modulation schemes are developed in the paper; one for the proposed topology and one for the case when Z-source impedance network is added. Simulation results verify the proper operation of the proposed topology.

A minimized switch count single-phase AC/AC converter with active front end

A three-switch single-phase converter is introduced in this paper which is a counterpart to back-to-back half-bridge converters. Introducing the new converter and elaborating its modulation scheme, a single-phase ac/ac converter is proposed based on it. The proposed topology enjoys the benefits of an ideal single-phase ac/ac converter such as low THD input current, unity power factor, fast dynamic response and the ability to compensate input voltage sag/surge when supplying linear or nonlinear loads. The operation of the proposed system is validated through simulation.

A novel single-phase six-switch AC/AC converter for UPS applications

A new reduced-switch-count converter topology is introduced and proposed for UPS applications in this paper. The modulation scheme of this novel converter is developed and a method is devised for calculating the optimal operating point of the converter based on the design specifications in order to maximize dc bus voltage utilization while minimizing the output voltage THD and switching loss. Moreover, a strategy is suggested for battery charging period which increases converter input power and hence accelerates battery charging process. The proposed converter possesses desirable characteristics of an ideal AC/AC converter such as low THD of input current and output voltage and unity power factor. The validity of theoretical issues is confirmed by simulation results.

A novel dual-output six-switch three-phase inverter

A novel dual-output six-switch inverter topology is proposed in this paper for independently supplying two three-phase loads. This inverter employs less number of semiconductor devices compared to former dual-output inverters proposed so far in the literature. Reducing the number of switches and hence drive and control circuits results in reduction in total cost and loss and increases the system efficiency and reliability. The new configuration is introduced and carrier-based PWM schemes for its two defined modes of operation (constant frequency and variable frequency modes) are developed for it. Furthermore, analysis of semiconductor loss is performed and the results are compared with counterpart topologies. Simulation and experimental results will be presented to demonstrate the theoretical knowledge.

A novel reduced switch count single-phase to three-phase AC/AC converter

Recently, reduced-switch-count converters have garnered particular attention in power electronic systems due to the numerous advantages such as low cost, low weight and volume, and high reliability offered by them. In this paper, a new reduced-switch-count converter topology is proposed as a single-phase to three-phase ac/ac converter. This converter employs less number of semiconductor devices compared to former single-phase to three-phase ac/ac converters. The modulation scheme of the novel converter is developed and two methods are devised for enhancing DC bus voltage utilization and hence minimizing the output voltage THD and the switching loss. The proposed converter features sinusoidal input and output, unity input power factor, and more importantly, low manufacturing cost. The validity of theoretical issues is confirmed by simulation results.

A novel fault-tolerant four-leg AC/AC converter capable of compensating unbalanced source/load

A novel reduced switch count AC/AC converter is proposed in this paper which can compensate for unbalanced characteristics of both the input AC source and the output three-phase load. The proposed converter satisfies all the expectations of an ideal robust converter such as unity input power factor, low THD sinusoidal input current and output voltage and fast dynamic response even under serious fault conditions which may occur in one/two phase(s) of the converter source/leg. Being capable of properly supplying the load even under two-phase grid-side fault, the backup batteries do not go into frequent charge/discharge cycling. This increases the battery life considerably. Based on frequency isolation, two modes of operation are defined and the proper control system is designed. The validity of performance of the proposed converter is tested and verified through simulation.

A generalized algorithm for switch reduction in multioutput single-phase inverters: With/without Z-source impedance network

A new algorithm is proposed in this paper for switch reduction in multi-output single-phase converters. The idea is first explained by introducing the dual-output six-switch inverter and then generalized into the switch reduction of m-output topology. Two modes of operation are defined for the proposed converter and the modulation scheme of each mode is devised. To compensate for the reduced dc bus utilization, a general algorithm is also proposed for employing Z-source impedance (ZSI) network in m-output configuration. Simulation results validated the veracity of the proposed algorithm.