M. Azizi

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.

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 New Family of Multi-Input Converters Based on Three Switches Leg

Multiterminal converters eliminate using several single-input-single-output converters and simplify their topologies and reduce their cost. In this paper, a new family of multi-input converters based on three switches leg is introduced. Inputs of the proposed converters are similar and they are topologically interchangeable and have boost or buck operation modes. The proposed converter has one output that operates as an inverter. Here, all operating modes of the proposed converters and their effects on each other are investigated, in details. Also, an appropriate switching technique for the converters is given. A detailed comparison between conventional and proposed two-input converters is also presented. A two-input, one-output prototype converter has been implemented to validate the given analyses and to verify the proposed converters performance. The experimental results are in good agreement with the theoretical and simulated analyses.

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.

Dual-output four-leg inverter

A novel dual-output four-leg inverter topology is proposed in this paper. The proposed inverter which is able to provide two three-phase voltage sets of independent magnitudes and frequencies is operationally equivalent to two four-leg inverters working independently though with a reduced number of semiconductor switches and hence gate drive and control circuits. The structure of the new topology is developed and the carrier based PWM scheme is elaborated for its two subsequently defined different frequency and equal frequency operation modes. The proposed converter is compared with conventional topology in terms of characteristics of output waveforms, rating of devices and power loss. A prototype of the system is built and tested. The simulation and experimental results confirmed the validity of operation of the proposed topology.

Cost-effective solution for microgrid power quality assurance

In this paper, an optimum interface configuration is proposed which can be used for connecting a microsource to a weak utility. The proposed configuration simultaneously conditions the quality of the power delivered to the supplied loads in the microgrid. This system employs a recently introduced reduced switch count dual-output inverter in a mode of operation named Equal Frequency which offers the 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 less number of semiconductor switches while possessing the same principal characteristics such as ability to compensate unbalanced and distorted utility or the ability to supply three-phase unbalanced loads with balanced and ceaseless voltage. The proposed system is developed, its carrier based modulation scheme is elaborated and a simple control strategy is devised for it. The validity of operation of the proposed system is verified through simulation.