# Browsing by Subject "Matrix converter"

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Item Design and Comparison of passive component requirements of a matrix converter and voltage-source based back-to-back converter(2013-09) Sahoo, Ashish KumarShow more A filter is required to eliminate the high frequency switching ripple present in the input current of AC/AC pulse-width modulated (PWM) converters. Design of such filters requires an estimation of the higher harmonic components present in various voltages and currents. Due to pulse-width modulation (PWM), the matrix converter generates switched currents at its input and the back-to-back converter generates switched input voltages which flows distorted currents. This dissertation presents simple closed form analytical expressions for the RMS input current ripple of the matrix converter and RMS input voltage ripple of a DC-link based back-to-back converter. The design of DC-link capacitor in a back-to-back converter requires the estimation of ripple current flowing through it which is also analytically computed. The expressions evaluated are independent of variation of load frequency, output alignment angle, switching frequency, etc. and is a function of known parameters like the modulation indices of the converters, the load and its power factor, DC-link voltage, etc. A systematic step-by-step procedure is presented to design various input filter components from the specifications of allowable THD in the grid current, permissible distortion in the input voltage, allowable inverter current ripple and reactive current drawn by filter capacitor. The converters are modeled for the grid frequency component in order to evaluate the design for input power factor, voltage drop across the filter, maximum possible real power transfer, etc. A damping resistance has been designed ensuring minimum ohmic loss. The analytical estimation of the ripple quantities and the proposed design procedure have been validated by simulations in MATLAB/Simulink and experiments on a laboratory prototype. A comprehensive comparison between the passive filter component requirements of a matrix converter and a DC-link based back-to-back converter is studied under different operating conditions. An input L-C filter of matrix converter is compared with an LCL filter and DC-link capacitor of a back-to-back converter. To compare size, volume and lifetime of passive components, the analysis with a quantitative and qualitative comparison of the passive component values along with their current and voltage ratings is also presented under different load power rating and variation of switching frequency.Show more Item Dynamic power flow control for a smart micro-grid by a power electronic transformer.(2011-05) Shah, Jalpa KaushilShow more A novel strategy, for control of the power flow for a smart micro-grid is proposed. The utility grid power is dynamically controlled by a Power Electronic Transformer (PET). A 60 Hz, step-down transformer is generally used at the point of common coupling (PCC), to connect the micro-grid to the power system grid. Substitution of the conventional 60Hz transformer, by a PET, results in enhanced micro-grid power management system, during grid-connected operation. The smart micro-grid is a set of controllable loads and distributed energy resources (DER); both renewable and non-renewable; that supply demand of a group of customers. The proposed dynamic power limiter (also referred to as PET) is a high-frequency, isolated power-converter system, comprised of a highfrequency step-down transformer and three-phase to single-phase matrix converters. The matrix converters are modulated with a novel pulse width modulation (PWM) strategy for a bi-directional power flow control. The output of the matrix converter generates a high frequency (few kHz) pulsating single phase AC at the primary and secondary of the transformer, which are phase shifted for active power control. The PET also allows voltage regulation by control of reactive power. The entire system; represented as two, three-phase AC systems with an intermediate high-frequency transformer; is simulated using Matlab/Simulink. The equivalent system has utility grid at the input side and a micro-grid on the output side. The micro-grid is modeled as an interconnected system consisting of set of DERs and smart loads. The simulation analyzes the change in micro grid’s power generation and consumption in response to the change in its local grid frequency, upon limiting the utility grid power. The PET hence restores the system frequency by adjusting supply and demand at the PCC. The micro-grid can now participate in frequency regulation for the main grid. The simulation results are obtained to verify the operation and claims of the dynamic power limiter as stated below: 1. Restricted active power flow to the micro-grid, at a desired value determined by the main utility grid. 2. Utilization of the change in local grid frequency, to dynamically control the active power generation or consumption within the micro-grid. 3. Decentralized control of the DERs as well as the controllable loads, which operate synchronously, to supply the demand within the micro-grid. 4. Bi-directional active-power flow capability at the PCC. 5. Voltage regulation by control of reactive power. 6. Contribution of the micro-grid components in frequency regulation of the main grid. 7. Smooth transition from islanding to grid-connected mode of the micro-grid, without the need of grid synchronization. 8. Extra degree of freedom due to the presence of active-power controller in a possible deregulation and market strategy within the micro-grid.Show more Item Matrix converter fed power electronic transformer with enhanced features.(2012-08) Nath, ShabariShow more Power transformers are an integral part of power systems. In many applications, like wind energy conversion and electric ship, the large weight and volume of present 60 Hz power transformer is a limitation. The size of transformers can be reduced by replacing the power transformers with high frequency transformers. For use of high frequency transformer in power systems, first the low frequency voltages are converted to high frequency by a power electronic converter and then it is stepped up or down by the high frequency transformer and finally the high frequency voltage is converter to low frequency by a second power electronic converter. The whole system is termed as power electronic transformer (PET). Matrix converter(MC) based power electronic transformers are the focus of this doctoral research. Direct AC to AC conversion using matrix converters have the major advantage of absence of storage capacitors over AC-DC-AC based conversion systems. A matrix converter based PET with open ended primary is described in this thesis. It has the salient features of controllable output voltage frequency, controllable input power factor, bi-directional power flow, zero common mode voltage and voltage transfer ratio of 1.5. The described PET is analyzed and simulation results are presented. Commutation of current in the leakage inductance is one of the challenges in the matrix converter based PET. The effect on voltage regulation due to increase in leakage inductance is studied using extensive simulation. An alternative path is needed for change of direction of current during commutation time. One of the ways to provide alternative path is use of clamp circuits. But use of clamp circuits lead to energy loss unless efficient energy recovery systems are designed. A source based commutation method is proposed to eliminate the use of clamp circuits. Depending on the direction of current in the HF transformer, the matrix converters on primary side of the transformer are switched such that natural commutation takes place in the leakage inductances. The overall efficiency of the PET is significantly improved. The commutation time is dependent on the value of leakage inductance. So, higher the leakage inductance, larger the commutation time and therefore, lower is the switching frequency. The nano-crystalline materials used for making HF transformers have very low core losses at very high frequencies as compared to 60 Hz power transformers. Also, power devices made of SiC devices are available which can operate at very high switching frequencies with very low switching losses. Therefore, leakage inductance is the only factor that limits the switching frequency. To solve the above mentioned problem, three novel PET topologies are proposed in which the switching frequency is independent of the value of leakage inductance. The first one is sinusoidal input output three phase HF transformer. It has a three phase low pass filter and a matrix converter on both primary and secondary side of the HF transformer. Three square wave voltages at switching frequency, phase shifted by 120◦ are produced by the primary side MC. The square wave voltages are filtered by the primary side filter to give three sine waves at high frequency shifted by 120◦. The switched currents at the input of secondary side MC are filtered by the secondary side low pass filter. The HF transformer works like a three phase power transformer. The second topology proposed is sinusoidal input output three winding HF transformer. In this topology, the supply voltages are first converted to square wave voltage at high frequency by a three phase to single phase MC and then filtered to a sine wave by a low pass filter connected to primary of the HF transformer. Two opposite sine voltages at high frequency are produced by the three winding transformer, on the secondary side, which is further connected to two capacitors. The switched currents on the input of MC, connected to load, are filtered by these two capacitors. The transformer again sees sinusoidal voltages and currents as in the first topology. Zero common mode voltage is achieved in this topology by use of a modified pulse density modulation(PDM) strategy proposed. The third one proposed is sinusoidal current HF transformer. Unlike the first two, it does not has a filter on the primary side. A high frequency square wave voltage is produced by a three phase to single phase MC. A MC is connected between the secondary terminals and the load. PDM is used for secondary side MC. A low pass filter is formed with the transformer by connecting a capacitor at the secondary terminals. Both, the switched currents at input of secondary side MC and the square wave voltages across the primary windings are filtered by the low pass filter. Thus, only sinusoidal currents flow through the HF transformer. In all the above three mentioned topologies, the leakage inductance is used to form the low pass filter, minimizing the amount of reactive elements required. As these low pass filters are required to filter very high frequency voltages, the size of reactive elements are reduced. For the sinusoidal current HF transformer only one additional capacitor is needed. Also because of use of PDM, zero voltage switching is possible for the sinusoidal three winding and sinusoidal current transformers. All the proposed topologies are analyzed and simulated in MATLAB/ SIMULINK environment and the simulation results are presented. Mathematical model for filter design is provided. A laboratory prototype is built for sinusoidal current HF transformer and the experimental results are presented.Show more