Ekrem Karaman

A Comparative Study of Series and Cascaded Z-Source Matrix Converters

The series Z-source network, an expansion of the popular concept of the Z-source dc link, was originally proposed for boosting the output voltage of power electronic inverters. In this paper, that idea is extended on a three-phase indirect matrix converter. The converter is based on the ultrasparse matrix topology characterized by the minimum number of semiconductor switches. The series Z-source network is placed between the three-switch input rectifier stage and the six-switch output inverter stage in either the positive or the negative rail. A brief shoot-through state produces the voltage boost. An optimal pulsewidth modulation (PWM) technique is developed for higher boosting capability of the converter and minimization of switching losses. A comparison is made between the matrix converters employing series and conventional cascade Z-source networks. The inrush current and Z-source capacitors voltage are reduced in the series Z-source matrix converter. Furthermore, the fast Fourier transform analysis of the output current of the converters suggests superiority of the series Z-source matrix converter over the cascaded Z-source matrix converter.

Indirect Matrix Converters as Generator–Grid Interfaces for Wind Energy Systems

Switched-inductor and quasi-Z-source indirect matrix converters are proposed as generator-grid interface for wind energy systems. Voltage levels of gearless ac generators typical for such systems are low. Thus, power electronic interfaces linking the generator with the grid must provide significant voltage boost. Switched-inductor Z-source network employs a brief shoot-through state to boost the voltage of inverters. The quasi-Z-source network offers other advantages, such as lower component ratings, reduced source stress and switch count, and simpler control strategies. The generator-grid interfaces described in this paper are based on the ultrasparse matrix topology characterized by the minimum number of semiconductor switches. The boosting networks are located between the front-end rectifier and back-end inverter. A space vector modulation technique has been developed to achieve high boosting flexibility and minimum switching losses in the converter. The fast Fourier transform analysis for the input/output currents of the converters with respect to the boost factor is carried out. The simulation and experimental results verify the effectiveness of the proposed topologies and control strategies in providing high boosting capability, while the input/output current quality is maintained within an acceptable range.

Multilayer-Winding Versus Switched-Flux Permanent-Magnet AC Machines for Gearless Applications in Clean-Energy Systems

A variety of clean-energy systems, such as electric and hybrid vehicles or wind-power sources, can appreciably benefit from motors or generators directly connected to the mechanical part of the system. This paper describes the development and experimental investigation of two radically different low-speed permanent-magnet ac machines: a multilayer-winding synchronous machine and a switched-flux machine. The study allows an in-depth comparison of these divergent concepts from the viewpoint of practical applications in the clean-energy infrastructure.

Permanent-magnet synchronous-generator wind-energy systems with boost matrix converters

An idea of wind-energy systems with gearless permanent-magnet synchronous generators and boost matrix converters are presented. The converters combine the indirect sparse-matrix topology with inductive-capacitive-diode networks. Rotor-flux orientation is employed in control of the generatorside rectifier stage of the interface converter. The maximum power point tracking controls the shoot-trough duty ratio of the inverter stage needed for boosting the output voltage. Selected results of experimental investigation of the proposed solutions are provided.

A 3Ф-3Ф quasi Z-source matrix converter for residential wind energy systems

When compared to the Z-source inverter, the quasi Z-source inverter offers several advantages, including lower component ratings, reduced source stress and switch count, and simpler control strategies. In this study, the concept of a quasi Z-source network is extended on a 3Φ-3Φ indirect matrix converter. The converter, destined for residential wind energy systems, is based on the ultra-sparse matrix topology characterized by the minimum number of semiconductor switches. The quasi Z-source network is placed between the three-switch input rectifier stage and the output six-switch inverter stage.

Three-phase to single-phase super-sparse matrix converters

Three novel three-phase to single-phase super-sparse matrix converters are described. It is shown that these converters, based on only seven switches, can function similarly to the twelve-switch conventional direct matrix converter. The Z-source and switched-inductor Z-source circuits have recently been proposed for boosting the voltage of power inverters. Here, these circuits have been adopted in the Z-source and switched-inductor Z-source super-sparse indirect matrix converters. To control them, a new modulation technique has been developed. As an example application, the proposed converters constitute a viable alternative to the existing solutions in residential wind-energy systems, where a low-voltage variable-speed generator feeds power to the higher-voltage fixed-frequency grid.

Matrix converter with a series Z-source

Series Z-source network, an expansion of the popular concept of Z-source dc link, was originally proposed for boosting the output voltage of power electronic inverters. In this paper, that idea is extended onto a three-phase indirect matrix converter. The converter is based on the ultra-sparse matrix topology characterized by the minimum number of semiconductor switches. The series Z-source network is placed between the three-switch input rectifier stage and the six-switch output inverter stage in either the positive or negative rail. A brief shoot-through state produces the voltage boost. The inrush current and Z-source capacitors voltage stress are reduced. An optimal pulse width modulation technique was developed for higher boosting capability of the converter and minimization of switching losses.

Three-phase switched-inductor Z-source matrix converter

Switched-inductor Z-source network, an expansion of the popular concept of Z-source dc link, was originally proposed for boosting the output voltage of power electronic inverters. In this paper, that idea is extended on a three-phase indirect matrix converter. The converter is based on the ultra-sparse matrix topology characterized by the minimum number of semiconductor switches. The switched-inductor Z-source network is placed between the three-switch input rectifier stage and the output six-switch inverter stage. A brief shot-through state produces the voltage boost. An optimal pulse width modulation technique was developed to achieve high boosting flexibility and minimum switching losses in the converter.

Novel modulation schemes and switching pattern for Z-Source ultra-sparse matrix converter

The Z-Source networks are recently being employed in the matrix converters (MCs) to overcome their main drawback, which is the low voltage transfer ratio (VTR). In spite of several Z-Source topologies introduced for the direct and indirect matrix converters, some important issues such as their modulation, operational modes, existing challenges in practical implementation, the design of an optimal switching pattern, and so on, have not been fully addressed in the literature. This paper focuses on cascaded Z-Source ultra-sparse matrix converter (ZSUSMC), where the Z-Source network is inserted between the rectifier stage and inverter stage of an ultra-sparse matrix converter. Provided discussions can be extended to other indirect MC topologies, such as sparse and very-sparse MCs, though. Two space vector modulation (SVM) schemes, with and without considering the zero state in the space vector rectification, are proposed, and then, their advantages and disadvantages are discussed. In addition, an optimal switching pattern, which ensures minimum number of changes in the switches states over the entire switching period, is proposed. Hardware-in-the-loop studies are carried out and performance of the converter under the proposed modulation techniques is evaluated. The proposed modulations are compared with a recent study and its superior performance in terms of input and output currents quality is confirmed.

Speed sensorless instantaneous power control of induction motor drives

A new method of speed sensorless instantaneous power control (IPC) of induction motor drives using an extended Kalman filter (EKF) is presented. The proposed algorithm is based on control of the flow of instantaneous real and reactive powers into the induction motor. The sensorless control method uses EKF-based speed estimation. Unlike the similar methods using the stator or rotor fluxes, the air gap flux is employed to calculate the reference powers needed for IPC. The effectiveness of the proposed control method was verified through computer simulations.