Modulation and Control of Energy Feedback Voltage Source Inverter and Matrix Converter
Type of DegreeDissertation
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In this research work, the modulation and control of energy feedback voltage source inverters and matrix converters are investigated. This paper analyzes the basic principle of the space vector pulse width modulation (SVPWM), and proposes a unified and simplified modulation algorithm as a pulse width modulation method for voltage source inverters and matrix converters. Using the proposed unified model of modulation, several additional contributions are developed for voltage source inverters and matrix converters. Carrier-based discontinuous space vector pulse width modulation (DSVPWM) method for voltage source inverters and matrix converters are proposed. Based on the relationship between SVPWM and carrier based modulation, a simplified DSVPWM method for three-phase inverters and matrix converters is introduced by skillfully arranging two zero voltage vectors. In this method, the conventional space vector modulator with equal division of zero voltage vector time is modified to generate different discontinuous modulating waves. A simple SVPWM scheme for operating three-phase voltage source inverters at higher modulation indexes, including overmodulation region, is proposed. Based on the study of existing overmodulation techniques published in literatures, two two-mode and two single-mode strategies based on simplified SVPWM overmodulation algorithms are proposed which can manage smooth transition from the linear control range to six-step operation. An analysis and uniform compensation of dead-time effect in three-phase multi-level diode clamped voltage source inverters and matrix converters are proposed. This paper analyzes dead-time effects and proposes an approximate solution based on characteristics of simplified SVPWM. The approximation is a result of avoiding the need to determine output current direction. The value of dead time is adjusted online by the magnitude of corresponding phase current. The deviation of voltage vectors caused by dead time effect is directly compensated to three phase reference voltages. A simplified control strategy to balance dc-link capacitor voltage for multi-level diode clamped voltage source inverters based on DSVPWM is proposed. On the basis of a simplified SVPWM algorithm for multi-level inverter and discontinuous modulation, simplified DSVPWM methods are proposed here to balance the dc-link capacitor voltages. The proposed control method changes the path and duration time of the neutral point currents, making the voltages of series connected dc-link capacitors equal. A simplified control scheme is proposed for three-phase voltage source inverters and matrix converters under unbalanced three-phase voltage conditions. On the basis of simplified SVPWM and carrier-based modulation, the concept of voltage modulation by using offset voltage is applied to an unbalanced three-phase grid voltage control method. The control objective is to balance three phase output currents and minimize total harmonic distortion of the output currents without ac current sensors under unbalanced grid voltage conditions. An energy-feedback control scheme of voltage source inverters and matrix converters based on phase and amplitude control and simplified modulation method is proposed, achieves a unity power factor of feedback current and precise control of feedback current. To calculate phase angle $\sigma$ and ratio of modulation $M$, two kinds of determination of feedback current are proposed. Both direct and indirect matrix converters are considered. Computer simulations are used to study feasibility of all algorithms.