Browsing by Author "Hegde, Shweta"

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    Control of Single Switch Inverters
    (Office of the Vice Chancellor for Research, 2014-04-11) Hegde, Shweta; Izadian, Afshin
    The single switch inverter was introduced to generate a pure sinusoidal output voltage. The system behaves like a non-minimum phase system in all operating ranges except when it is operating to produce negative half cycle in buck mode. When addressed from a control perspective, the right half plane zeros or the non-minimum phase zeros in the transfer function complicate the control design scheme. The Dual Feed-forward Predictive Control (DFPC) is a method of feed-forward control is used to force the non-minimum phase system to behave like a minimum phase system. The controller successfully isolates the non-minimum phase part of the system from the minimum phase. Both separated minimum phase and non-minimum phase sub-systems were used in the dual feed-forward scheme to generate desired references. The non-minimum phase dynamics are transformed to minimum phase by using an inverse system transfer function as parallel compensator. In this method, the plant is split into two parts to generate two signals. One signal is to make the plant track with a feed-forward control signal that drives the plant to track the reference signal. The signals produced by the feed-forward transfer functions are assumed to contain bounded energy and have no influence on the closed loop stability. For perfect tracking, the error should reach zero which can be accomplished using various types of controller including a simple gain. However, in the new inverter circuit, an adaptive PI controller is required to adjust the gains continuously.
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    SEPIC DC – AC Converter Design and Operation
    (Office of the Vice Chancellor for Research, 2013-04-05) Hegde, Shweta; Izadian, Afshin
    This paper focuses on the design and study of operation of the SEPIC converter which is modified to function as an inverter i.e. converts DC input to AC output. The modified converter consists of reduced number of switches which increases the efficiency and also improves the quality of the waveforms generated. The conventional SEPIC converter consists of two inductors, two capacitors, one transistor switching at high frequency and a diode. The modified SEPIC replaces the diode with a polarity reversing switch component. This component contains two reverse connected transistors T1 and T2 which are synchronized with the polarity of the output waveform. This new inverter is capable of producing pure sinusoidal waveform with only three switches of which only one is switched at high frequency, Q. The new inverter is found to operate in four different modes of operation to produce positive and negative cycles of output voltage. The modes 1 and 2 of operation have the switches Q and T1 operating and produce positive peak and the modes 3 and 4 of operation have the switches Q and T2 operating and produce negative peak. The inductor connected in the input side of the inverter is chosen to be large enough to maintain continuous conduction. State Space Averaging technique is used to model the system where the currents through the inductors and voltages across the capacitors are considered to be the state variables. The state space representation of each mode of operation is obtained and the system is averaged over the positive peak and negative peak separately. The state space model of the inverter is validated using MATLAB/SIMULINK. The inverter model was simulated using SimPowerSystems tool box of MATLAB and found to produce pure sinusoidal waveform. The harmonics were found to be reduced to a great extent.
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    Solar Micro Inverter
    (2014) Hegde, Shweta; Izadian, Afshin; Rizkalla, Maher E.; Li, Lingxi; King, Brian
    The existing topologies of solar micro inverter use a number of stages before the DC input voltage can be converted to AC output voltage. These stages may contain one or more power converters. It may also contain a diode rectifier, transformer and filter. The number of active and passive components is very high. In this thesis, the design of a new solar micro inverter is proposed. This new micro inverter consists of a new single switch inverter which is obtained by modifying the already existing single ended primary inductor (SEPIC) DC-DC converter. This new inverter is capable of generating pure sinusoidal waveform from DC input voltage. The design and operation of the new inverter are studied in detail. This new inverter works with a controller to produce any kind of output waveform. The inverter is found to have four different modes of operation. The new inverter is modeled using state space averaging. The system is a fourth order system which is non-linear due to the inherent switching involved in the circuit. The system is linearized around an operating point to study the system as a linear system. The control to output transfer function of the inverter is found to be non-minimum phase. The transfer functions are studied using root locus. From the control perspective, the presence of right half zero makes the design of the controller structure complicated. The PV cell is modeled using the cell equations in MATLAB. A maximum power point tracking (MPPT) technique is implemented to make sure the output power of the PV cell is always maximum which allows full utilization of the power from the PV cell. The perturb and observe (P&O) algorithm is the simplest and is used here. The use of this new inverter eliminates the various stages involved in the conventional solar micro inverter. Simulation and experimental results carried out on the setup validate the proposed structure of inverter.