Although the concept of variable-speed drives, based on utilization of multiphase machines, dates back to the late 1960s, it was not until the mid- to late 1990s that multiphase drives became serious contenders for various applications. These include electric ship propulsion, locomotive traction, electric and hybrid electric vehicles, ldquomore-electricrdquo aircraft, and high-power industrial applications. As a consequence, there has been a substantial increase in the interest for such drive systems worldwide, resulting in a huge volume of work published during the last ten years. An attempt is made in this paper to provide a brief review of the current state of the art in the area. After addressing the reasons for potential use of multiphase rather than three-phase drives and the available approaches to multiphase machine designs, various control schemes are surveyed. This is followed by a discussion of the multiphase voltage source inverter control. Various possibilities for the use of additional degrees of freedom that exist in multiphase machines are further elaborated. Finally, multiphase machine applications in electric energy generation are addressed.

Multiphase Electric Machines for Variable-Speed Applications

The area of multiphase variable-speed motor drives in general and multiphase induction motor drives in particular has experienced a substantial growth since the beginning of this century. Research has been conducted worldwide and numerous interesting developments have been reported in the literature. An attempt is made to provide a detailed overview of the current state-of-the-art in this area. The elaborated aspects include advantages of multiphase induction machines, modelling of multiphase induction machines, basic vector control and direct torque control schemes and PWM control of multiphase voltage source inverters. The authors also provide a detailed survey of the control strategies for five-phase and asymmetrical six-phase induction motor drives, as well as an overview of the approaches to the design of fault tolerant strategies for post-fault drive operation, and a discussion of multiphase multi-motor drives with single inverter supply. Experimental results, collected from various multiphase induction motor drive laboratory rigs, are also included to facilitate the understanding of the drive operation.

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Multiphase induction motor drives - : a technology status review

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Design Of Analog Cmos Integrated Circuits

The solid-state transformer (SST), which has been regarded as one of the 10 most emerging technologies by Massachusetts Institute of Technology (MIT) Technology Review in 2010, has gained increasing importance in the future power distribution system. This paper presents a systematical technology review essential for the development and application of SST in the distribution system. The state-of-the-art technologies of four critical areas are reviewed, including high-voltage power devices, high-power and high-frequency transformers, ac/ac converter topologies, and applications of SST in the distribution system. In addition, future research directions are presented. It is concluded that the SST is an emerging technology for the future distribution system.

Review of Solid-State Transformer Technologies and Their Application in Power Distribution Systems

This paper investigates the capacitor-current-feedback active damping for the digitally controlled LCL-type grid-connected inverter. It turns out that proportional feedback of the capacitor current is equivalent to virtual impedance connected in parallel with the filter capacitor due to the computation and pulse width modulation (PWM) delays. The LCL-filter resonance frequency is changed by this virtual impedance. If the actual resonance frequency is higher than one-sixth of the sampling frequency (fs/6), where the virtual impedance contains a negative resistor component, a pair of open-loop unstable poles will be generated. As a result, the LCL-type grid-connected inverter becomes much easier to be unstable if the resonance frequency is moved closer to fs/6 due to the variation of grid impedance. To address this issue, this paper proposes a capacitor-current-feedback active damping with reduced computation delay, which is achieved by shifting the capacitor current sampling instant towards the PWM reference update instant. With this method, the virtual impedance exhibits more like a resistor in a wider frequency range, and the open-loop unstable poles are removed; thus, high robustness against the grid-impedance variation is acquired. Experimental results from a 6-kW prototype confirm the theoretical expectations.

Capacitor-Current-Feedback Active Damping With Reduced Computation Delay for Improving Robustness of LCL-Type Grid-Connected Inverter

SiC MOSFETs have the capability to handle large di/dt and dv/dt. This can be used to reduce the switching losses, and thereby increase efficiency of the converter. But, even moderate amount of layout parasitic inductance and capacitance can cause significant detrimental effects on reliability and EMI of the power device. Present paper proposes a di/dt feed back based, current controlled active gate driver mechanism. It allows the device to operate at desired di/dt as well as dv/dt level, even under moderate layout parasitic. Proposed gate driver also tries to exploit certain benefits offered by the layout parasitic to further reduce the switching losses. Active damping and over shoot arresting features of the proposed gate driver can ensure fast switching speeds without compromising on the reliability and EMI of the device.

Closed loop analog active gate driver for fast switching and active damping of SiC MOSFET

A comparative evaluation of three different three-phase Dual Active Bridge (DAB) topologies with a 15-kV Si-IGBT based three-level converter at the high-voltage side and 1200-V SiC-MOSFET based converters in three different arrangements at the low-voltage side are compared. The proposed DABs are an integral part of a solid state transformer which connects a 13.8-kV distribution grid and a 480-V utility grid. The three-level converters connected at the high-voltage side in each topology with 30° zero-enforcing and proposed arrangements at low-voltage side of the high frequency-link transformer help to reduce dominant harmonic currents. Thus harmonic-free currents in the high frequency link transformer are achieved without pulse-width modulation which can be utilized for D-Q Mode smooth-control.

A comparative study of three-phase dual active bridge topologies and their suitability for D-Q mode control

1200V SiC MOSFETs have superior characteristics compared to silicon (Si) IGBTs. However due to parasitic inductances in the converter layout, one to one replacement of Si IGBT with SiC MOSFET may result in higher overshoot in the device voltage and current. Active gate driving mechanism can control these unwanted stresses on the device without compromising its switching speed. The limited bandwidth of OP-AMP used in a conventional closed loop active gate driver poses a major hindrance to drive fast switching SiC MOSFET. To address this issue a new current controlled Active Gate Driver mechanism is proposed. The proposed AGD can be realized with cheaper electronic components with sufficient bandwidth to drive a SiC MOSFET. The proposed technique ensures better controllability on the device by directly controlling the injected gate current. The proposed AGD has been experimentally verified in a double pulse test set up with a 1200 V, 35 A SiC MOSFET (ROHM make: SCH2080KE).

Current controlled active gate driver for 1200V SiC MOSFET

The ability of an electrical drive to continue operation without tripping in spite of short-duration voltage sags or power supply interruptions is known as power failure ride-through capability. Critical production processes in industries require the drives to smoothly ride-through during momentary power interruptions. The reliability of the drive is dependent on the maximum duration for which a total power supply failure can be tolerated without process interruption. This paper presents a method to extend the duration of the ride-through in voltage-source-inverter-fed vector-controlled induction motor drives with a front-end diode bridge rectifier. The proposed method minimizes the losses in the system during the ride-through, thereby enabling a longer ride-through duration. The method only requires a modification of the control software and hence is easy to implement. This paper also briefly describes two conventional methods used for ride-through and compares the proposed method with the conventional methods to clearly bring out its advantage. Simulation study using MATLAB/PLECS verifies the effectiveness of the proposed method. Hardware implementation of the method on a 30-kW induction machine indicates an extension of up to 34% in the ride-through duration with the proposed method, as compared with the conventional method.

An improved scheme for extended power loss ride-through in a voltage source inverter fed vector controlled induction motor drive using a loss minimisation technique

In this study, design considerations of gate driver for silicon carbide (SiC) power devices is discussed. The work is focused in minimizing the common-mode current injection into the control circuit, thereby adapting the gate circuit to operate at higher dv/dt of fast switching transients. By reducing the common-mode interference with the control circuit, the signal integrity can be increased, spurious faults in the converter can be minimized and the reliability of the converter operation can be enhanced. The effect of the coupling capacitance of the isolation transformer in the gate driver design is taken into account. The shoot-through protection of the device is ensured based on device voltage measurement. The operation of the designed gate driver is validated through double pulse switching as well as continuous operation of various converters. All the corresponding test results are reported.

Kamalesh Hatua

Papers

Closed loop analog active gate driver for fast switching and active damping of SiC MOSFET

A comparative study of three-phase dual active bridge topologies and their suitability for D-Q mode control

Current controlled active gate driver for 1200V SiC MOSFET

An improved scheme for extended power loss ride-through in a voltage source inverter fed vector controlled induction motor drive using a loss minimisation technique

Gate driver design considerations for silicon carbide MOSFETs including series connected devices