Ranjan Kumar Gupta

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 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.

Space vector PWM for a direct matrix converter based open-end winding ac drives with enhanced capabilities

This paper introduces a space vector PWM technique for a direct matrix converter based three-phase open-end winding ac machine drive. With the proposed PWM technique, the following simultaneous capabilities of the open-end winding drive system are achieved: 1) Machine phase voltage up to 1.5 times the input phase voltage in the linear modulation, 2) Controllable grid power factor, and 3) Elimination of the high-frequency common-mode voltage at the machine terminals. Elimination of the high-frequency common-mode voltage results in elimination of the high-frequency bearing current and reduced conducted EMI. The proposed modulation scheme is implemented on a dSPACE and FPGA based control platform. Experimental results on a hardware prototype verify the abovementioned capabilities of the drive system.

A novel three-phase switched multi-winding power electronic transformer

In this paper, a novel topology for a three-phase high-frequency power electronic transformer is proposed. In each phase, there are two mutually-coupled primary windings and one secondary winding. On the high-voltage side of the transformer, only two controlled switches are required to create a three-phase high frequency ac link. This is a significant reduction in the required number of controlled high voltage semiconductor switches as compared to the present state-of-the-art, leading to simplicity, reliability and reduced system cost. A 3×3 matrix converter is used on the low-voltage side of the transformer. The matrix converter is modulated with the proposed space vector PWM to achieve the following features simultaneously: 1) grid power factor control, 2) load voltage of adjustable amplitude and frequency and 3) elimination of common-mode voltage at the load terminals. The simulation results of a 2 MVA system demonstrating the abovementioned capabilities of the proposed topology are presented.

Power management with a dynamic power limit by a power electronic transformer for micro-grid

In this paper, a dynamic power limiter at the point of common coupling (PCC) of a micro-grid is proposed. A 60 Hz, step-down transformer is generally used at the PCC to connect the micro-grid to the power system grid. Substitution of the conventional 60Hz transformer by a dynamic power limiter has the following advantages: 1) Bi-directional active-power control capability at the PCC which results in enhanced micro-grid power management system during grid-connected operation, 2) Smooth transition from islanding to the grid-connected mode without the need of grid frequency synchronization, and 3) Extra degree of freedom due to the presence of active-power controller in a possible deregulation and market strategy within the micro-grid. The proposed dynamic power limiter is a high-frequency isolated power-converter system comprised of a high-frequency step-down transformer and three-phase to single-phase matrix converters. The matrix converters are modulated with a new PWM strategy for bi-directional active and reactive power flow control. Simulation results presented verify the operation of the proposed dynamic power limiter.

A Modular Stacked DC transmission and distribution system for long distance subsea applications

A new power transmission and distribution concept-Modular Stacked DC (MSDC) - architecture is described. Its main application is subsea oil and gas processing, where marinization of system components, their reliability and retrieval are the most critical requirements. In contrast to conventional HVDC systems, the proposed MSDC technology achieves the required DC transmission voltage by stacking a number of power converter building blocks in series that are easy to marinize. Since each building block is similar to a standard VFD, the MSDC technology has potentially much lower cost and higher reliability. Moreover, the modular architecture renders the system fault-tolerant and capable of operating in a degraded mode. The architecture is also highly reconfigurable as the field matures and the loads evolve over time. A generic subsea field scenario for oil and gas has been designed and analyzed. The MSDC architecture and associated system control strategy are developed and tested using a real-time simulation platform together with an experimental scaled down prototype of 160 kVA.

Three-level indirect matrix converter based open-end winding AC machine drive

A new space vector PWM technique for an indirect matrix converter based open-end winding drive is presented in this paper — The presented drive achieves the advantages of direct conversion, viz. 1) Machine phase voltages up to 1.5 times the grid voltage, 2) controllable grid power factor, and 3) zero instantaneous common mode voltage; and further achieves, 4) lower number of switching transitions and 5) simpler protection clamp circuit, owing to two-stage conversion. A detailed analysis of the PWM technique is presented along with the simulation results. Further, commutation strategies for the matrix converters of the presented drive have been developed and the simulation results are included.