Krushna K. Mohapatra

Direct-Matrix-Converter-Based Drive for a Three-Phase Open-End-Winding AC Machine With Advanced Features

This paper describes how matrix converters (MCs), one at each side of a three-phase open-end-winding ac machine, achieve the following features simultaneously: 1) machine phase voltage up to 1.5 times the input phase voltage in the linear modulation mode, therefore extending the rated torque operation region to 150% of the rated speed of the machine; 2) peak voltage stress across the slot insulation which is limited to the peak of input phase voltage, i.e., a factor of at least √3 lower as compared to the conventional back-to-back converter; 3) controllable grid power factor to be leading, lagging, or unity; and 4) elimination of the instantaneous common-mode voltage at the machine terminals, therefore eliminating the bearing current due to switching common-mode voltage and reduction in the conducted electromagnetic interference. To simultaneously achieve the aforementioned capabilities, a space vector pulsewidth modulation technique is described in which the MCs are modulated using only rotating space vectors. A hardware prototype of the drive system is built. Experimental results from this hardware prototype verify the operation and claims of the drive system.

On the Causes of Circulating Currents in PWM Drives With Open-End Winding AC Machines

Electric drives with open-end winding ac machines offer certain advantages over drives with star- or delta-connected machines. Such drives have been recently considered for some applications such as electric vehicles. Circulating currents have been experimentally observed in such open-end winding ac drives. These currents have the effect of increasing conduction losses in the stator winding resistance of the ac machine. Two major causes for these currents have been identified as device voltage drops in power semiconductor devices and dead time used for shoot-through current protection. These effects are analyzed, and a mathematical description for predicting their severity is provided. Experimental results are presented that support the theory. The theory developed should be useful for devising solutions for this problem such as the design of common-mode filters. Two methods of suppressing the circulating currents are also outlined, and their experimental results are presented.

A Novel Carrier-Based PWM Scheme for Matrix Converters that is Easy to Implement

Since the inception of matrix converter concept, various modulation schemes have been proposed for its control. But the explanation of matrix converter operation is complex, and so is the control methodology of it. In this paper a 3-phase to 3-phase matrix converter is explained from the point of view of multi-level inverter topology, and a novel modulation scheme is proposed where the need for sector information and corresponding look-up tables is avoided

Open-End Winding Induction Motor Driven With Matrix Converter For Common-Mode Elimination

In this article a novel scheme using matrix converter is proposed for control of three phase machines. The analysis shows that the scheme has several benefits. By eliminating the common mode voltage from the three phases of the machine the motor bearing current is entirely removed. The maximum insulation stress in the motor winding is limited to the peak value of input phase voltage. The power factor at the utility end is controllable. By using matrix converters for power conversion bulky capacitors are eliminated from the drive.

Universal utility interface for Plug-in Hybrid electric vehicles with vehicle-to-grid functionality

This paper proposes a novel topology for Electrical Vehicles and Plug-in Hybrid Electrical Vehicles with controllable power factor with 3-phase input and unity power factor with single phase input. The proposed on-board topology provides bidirectional power flow to/from the grid, low weight, low volume, and isolation. A control scheme is devised and a complete simulation of power control is performed over varying loads, varying input voltages, three phase or single phase input, and switching schemes. Simulation results are presented that demonstrate the ability to control power flow and synthesize the grid currents to be sinusoidal.

Matrix converter fed open-ended power electronic transformer for power system application

A matrix converter controlled 3-phase power electronics transformer is proposed for power system application. The proposed system uses three matrix converters and a three phase high frequency transformer in order to achieve isolation and, voltage and current transformation from primary to secondary. The primary side of the transformer is open-ended and two matrix converters connected to both sides of the opened primary side control the voltage by use of high frequency switching. By use of high frequency switching the size of the transformer is reduced. Another matrix converter connected to the star connected secondary side of the transformer converts back the high frequency chopped voltage at the output of the transformer to normal line frequency voltage by synchronized switching with primary side converters. By applying phase shift control to the forward rotating and backward rotating vectors the input power factor and output power factor are decoupled and unity power factor operation is achievable at the input.

A novel integrated three-phase, switched multi-winding power electronic transformer converter for wind power generation system

In this paper, a novel wind power generation system is proposed which uses an intermediate high frequency (few kHz) ac link for power conversion. The high frequency ac link is achieved by using a reduced switch-count three-phase power electronic transformer (PET). There are two primary windings and one secondary winding in each phase of the PET. The primary windings are coupled in exact phase opposition. A 3×3 matrix converter is used to convert the high frequency secondary voltage to the desired low frequency voltage to be applied at the generator terminals. Two modulation modes as a part of the PWM of the matrix converter are described. In the first mode of operation, the common-mode voltage is eliminated at the generator terminals however, the output voltage transfer ratio of the matrix converter is limited to 0.75. The other modulation mode has higher output voltage transfer ratio equal to 0.866 with finite high-frequency common-mode voltage at the generator terminals. A method for smooth transition between the two modes of operation is described.

Research in matrix-converter based three-phase power-electronic transformers

This paper presents a review of the current research in the area of ac/ac power conversion with power electronic transformer. The topologies considered have the following features: 1) generation of adjustable frequency and magnitude PWM ac voltage waveform from a balanced three-phase ac voltage source with a high frequency ac link, 2) bidirectional power flow capability, and 3) single stage power conversion without any storage elements. All of these topologies provide power factor correction. Based on the operation and control, these topologies have been classified into three groups. The operation, advantages and drawbacks of each of these topologies have been presented along with a comparison of their performance in the presence of leakage inductance, complexity to control and reliability.

Modulation strategies for direct-link drive for open-end winding AC machines

Switching common-mode voltages generated by conventional pulse-width modulated inverters are known to cause bearing currents in ac machines. These undesirable currents may result in bearing damage. A direct-link drive for open-end winding ac machines has recently been proposed. Some advantages of the drive include: 1) common-mode voltage suppression, 2) no storage elements, and 3) ability to achieve up to 1.5 times the peak input phase voltage across the machine phase windings. In this paper, pulsewidth modulation strategies for the drive are proposed. Two strategies are based on space vector modulation and suppress common-mode voltage at the machine terminals. One carrier-based strategy achieves 1.5 times the peak input phase voltage across the machine phase windings but causes switching common-mode voltage at the machine terminals. Simulation and experimental results are presented to verify the operation of the drive.

Matrix converter over-modulation using carrier-based control: Maximizing the voltage transfer ratio

This paper presents a comprehensive solution for over-modulation of direct matrix converter using carrier- based control. The over-modulation operating region is classified, based on the choice of duty-ratios (input/output) and the maximum achievable output voltage amplitude, into three different modes named as input-side over- modulation (ISO), output-side over-modulation (OSO) and simultaneous input and output-side over-modulation (SIOSO). The boundaries for operation of the matrix converter in each of the above three operating modes are established. The ISO is sub-divided into two modes based on the capability to control the power factor of input phase currents. The two regions are named as input-side over-modulation with power factor control (ISO with PFC) and input-side over-modulation without power factor control (ISO without PFC) respectively. A modulation algorithm for the choice of duty-ratios to allow a smooth transition between linear modulation and the ISO operating modes is proposed. A modification to the choice of the reference output voltage modulating signals for OSO that forces the converter into square wave mode operation with peak amplitude of the reference signal that is only twice the peak amplitude in linear modulation, is proposed. The SIOSO is used to obtain the maximum possible voltage transfer ratio of 105.3% from the matrix converter with over-modulation. The total harmonic distortion (THD) of the output voltages and input currents are presented for all over- modulation operating modes. Theoretical calculations are verified with experiments on a laboratory prototype of the direct matrix converter.