Ashish Kumar Sahoo

Systematic Input Filter Design of Matrix Converter by Analytical Estimation of RMS Current Ripple

A filter is required to eliminate the high-frequency switching ripple present in the input current of a matrix converter (MC). Design of such a filter requires an estimation of the higher harmonic components present in the input current. This paper presents a simple closed-form analytical expression for the RMS input current ripple injected by the MC. The expression shows the variation with load power factor and is independent of the output frequency. This is used in a step-by-step procedure to design various input filter components from the specifications of allowable total harmonic distortion in the grid current and distortion in the input voltage. The MC is modeled for the grid frequency component in order to evaluate the design for input power factor and voltage drop across the filter. A damping resistance has been designed ensuring minimum ohmic loss. The analytical estimation of the ripple current and the proposed design procedure have been validated by simulations in MATLAB/Simulink and experiments on a laboratory prototype.

A Single-Stage Solid-State Transformer for PWM AC Drive With Source-Based Commutation of Leakage Energy

A solid-state transformer is a three-phase ac/ac converter with a high-frequency transformer. Due to advanced features like high power density, on demand var support and frequency regulation, solid-state transformer is an enabling technology for the modern power distribution system. It can also find application in high-power-density motor drives. The single-stage solid-state transformer considered in this paper is capable of bidirectional power flow and open loop power factor correction. This topology uses a minimum amount of copper and has relatively few semiconductor switches. One major problem in this converter is the commutation of leakage energy which results in power loss, reduction in switching frequency, loss of output voltage, and additional common-mode voltage switching. This paper presents a source-based commutation strategy along with a novel modulation technique resulting in elimination of additional snubber circuits, minimization of the frequency of leakage inductance commutation, recovery of the leakage energy, and soft switching of the output converter. The topology and its proposed control have been analyzed. Simulation and experimental results confirm the operation.

New 3-level submodules for a modular multilevel converter based HVDC system with advanced features

Modular multilevel converters have emerged as a viable solution over conventional voltage source converters (VSC) for applications in high voltage direct current (HVDC) transmission. Due to modular structure, the converter can reach high number of voltage levels resulting in low switching frequency and near sinusoidal voltage waveforms. This paper proposes new submodule topologies which can result in even higher voltage levels with reduced voltage stress across some switches and lower semiconductor losses. A modified modulation scheme and voltage balancing algorithm is proposed for the new topology and is validated by MATLAB/Simulink simulations. A comprehensive comparative analysis with other available submodule topologies is presented to show the added benefits.

Grid-Side AC line filter design of a current source rectifier with analytical estimation of input current ripple

This paper presents a systematic step-by-step design procedure for the input filter of a current source rectifier (CSR). The design is based on the specifications of allowable ripple in the input voltage of the CSR and high-frequency harmonic components in the grid current. Analytical techniques have been developed to estimate the ripple present in the input current and to model the converter for fundamental or grid frequency. The analysis is done for carrier-based and space-vector modulation of the current source rectifier and the model at grid frequency is used to evaluate the design of the filter for grid power factor, voltage drop across filter, etc. A damping resistance is designed ensuring a minimum power loss. The analysis and design of the input filter have been verified by simulations in MATLAB/Simulink and experimental tests on a laboratory prototype.

LCL filter design for grid-connected inverters by analytical estimation of PWM ripple voltage

LCL filter is becoming an attractive choice over conventional L filters for grid-connected voltage source inverters (VSI) due to smaller inductor size and better attenuation of the ripple components in the grid current. The modulation of the VSI generates switched voltages which results in distorted currents. In this paper, a simple closed form analytical expression is derived for the higher order switching components present in the inverter voltage. This is used in a systematic design procedure to design the LCL filter components for allowable grid current harmonics. A passive damping resistor is designed ensuring minimum power loss. The design is validated by simulations in MATLAB/Simulink and experiments on a laboratory prototype.

High frequency link multi-winding power electronic transformer using modular multilevel converter for renewable energy integration

Grid integration of multiple renewable energy sources using a power electronic transformer (PET) topology is presented in this paper. A modular multilevel converter (MMC) is proposed as the power converter on the high voltage grid side to generate high frequency sinusoidal voltages. A single multi-winding high frequency transformer (HFT) interfaces different wind generators/photovoltaic arrays using many H-bridge converters and PWM inverters. The leakage inductance of the transformer acts as the smoothening filter for the current through the HFT. With sinusoidal voltages and smooth currents through the transformer, there is significant reduction in transformer losses and also natural commutation of leakage energy is obtained. The operating principle, modulation and control of the proposed PET is validated by simulations in MATLAB/Simulink.

A power electronic transformer with sinusoidal voltages and currents using modular multilevel converter

Power electronic transformer consisting of power converters and a high frequency transformer (HFT) can be used to interface a low voltage machine to a high voltage grid. A modular multilevel converter (MMC) is proposed as the power converter on the high voltage side to generate high frequency, adjustable magnitude sinusoidal voltages. A matrix converter (MC) is used on the low voltage side to synthesize three-phase adjustable frequency PWM AC at the machine terminals. With the leakage inductance of the transformer, a capacitor bank forms an LC filter to result in sinusoidal currents through the HFT. With sinusoidal voltages and currents through the transformer, there is significant reduction in transformer losses and also natural commutation of leakage energy is obtained. The magnitude of the output voltage requirement by the machine is met by controlling the output voltage of the MMC on the primary of the HFT, to result in reduced voltage stress and losses in the transformer, secondary side converter and the machine. The operating principle, modulation and control of the proposed PET is validated by simulations in MATLAB/Simulink.

Review of modular multilevel converters for teaching a graduate-level course of power electronics in power systems

With rapid advancements in power semiconductor technologies, Forced Commutated Converter systems are taking the market in high voltage, high power transmission and distribution applications. The Modular Multilevel Converters have become an attractive choice for future HVDC transmission projects because of their easy scalability, full real and reactive power flow control, dynamic voltage regulation, black start capability, smaller space requirements, etc. Graduate students in universities should be made aware of these newer converters to be able to apply them in industry and research. This paper presents an overview of the different fundamental concepts of Modular Multilevel Converters and a roadmap to teaching it in a graduate level course of Power Electronics in Power Systems.

Comparison of filter components of back-to-back and matrix converter by analytical estimation of ripple quantities

This paper presents an analysis and comprehensive comparison between the passive filter component requirements of a matrix converter and a DC-link based back-to-back converter. Proper design of the filter components requires the estimation of the switching frequency components present in various voltages and currents. An accurate estimation of different ripple quantities is presented by simple analytical expressions and verified by MATLAB/Simulink simulations. The filters are designed and a quantitative comparison of the passive components is done.

SVPWM technique with varying DC-link voltage for common mode voltage reduction in an indirect matrix converter

This paper discusses a modified space vector technique applied to an indirect matrix converter (IMC) which results in the reduction of common mode voltages and other advanced features. The conventional indirect space vector pulse-width modulation (SVPWM) method of controlling matrix converters involves the usage of two adjacent active vectors and one zero vector for both rectifying and inverting stages of the converter. By suitable selection of space vectors, the rectifying stage of the matrix converter can generate different levels of virtual DC-link voltage. This capability can be exploited for operation of the converter in different ranges of modulation indices for varying machine speeds. This results in lower common mode voltage and improves the harmonic spectrum of the output voltage, without increasing the number of switching transitions as compared to conventional modulation. The effectiveness of the algorithm is substantiated by simulations in MATLAB/Simulink and experiments on a laboratory prototype.