To reduce the harmonics injected by non-linear loads, power quality improvement devices like shunt active power filters (SAPFs) are commonly employed. This study presents a digital signal processor (DSP) TMS320LF2407A based hardware implementation of current error space phasor-based hysteresis controller for SAPF. The proposed controller-based SAPF allows precise compensation of harmonic currents. Design considerations for practical implementation of the proposed space phasor-based current error hysteresis controller for SAPF are explained here. Performance analysis of space phasorbased current error hysteresis controller for SAPF is explained in the study. The controller's self-adaptive nature is studied for different logics of necessary sector changes. Here, the versatile nature of the controller is proved by analysing its performance for different reference compensating current generation methods. The proposed controller works on the principle of switching voltage vectors adjacent to the desired output voltage vector of SAPF (voltage vector at the point of common coupling). This strategy helps in restricting the current error within the desired hexagonal boundary. A comparative study of DSP-based implementation for two different schemes of reference compensating currents generation is presented in this study. Instantaneous reactive power theory and Fryze current computation methods are chosen for this comparative study. Experimental results of reference compensating currents generated by different strategies using DSP are presented in this study.
A current-error space-vector-based PWM hysteresis controller is proposed for three-level voltage source inverter fed induction motor drive applications. A hexagonal boundary for the current-error space vector is formed by sensing the current-error space vector along three different axes, which are 1201 apart and are orthogonal to machine phase axes. Only the adjacent inverter voltage vectors forming a triangular sector, in which tip of the machine voltage vector lies, are switched to keep the current-error space vector within the hexagonal boundary. Selection amongst the three nearest voltage vectors is done by a simple region detection logic in all the sectors. Calculation of the machine voltage vector is not needed and information of the same is indirectly derived from the direction of current-error space vector. The controller uses a self-adaptive sector identification logic, which provides smooth transition between sectors (voltage levels), including over modulation region up to 12-step mode of operation. Inherent advantages of current hysteresis controller are retained with the added advantage of adjacent voltage vector selection for hysteresis PWM control. Simple look-up tables are only needed for sector and vector selection, based on the hysteresis controller output, for the proposed hysteresis PWM controller. Experimental verification is provided by implementing the proposed controller on a 1.5 kW open-end winding induction motor drive. The proposed controller can be extended for further levels of multi-level inverters for high-performance drives by constructing suitable look-up tables.
A scheme for a three-level voltage space phasor generation with common-mode voltage elimination is proposed. An open-end-winding induction motor, fed from both ends by two threelevel inverters, which are realised by a cascading two two-level inverter, is used in this configuration. The voltage space vectors of individual three-level inverters, which generate the same commonmode voltage in the inverter pole voltage, are variously grouped. When these voltage space vectors are used to switch individual three-level inverters, it results in zero common-mode voltage across the motor windings. In the proposed scheme, voltage space phasors from individual inverters with zero common-mode voltage in the inverter pole voltage are used for PWM control. For the proposed drive configuration, the DC link voltage requirement is only half when compared to the DC link voltage of a conventional neutral-point-clamped (NPC) three-level inverter. The proposed inverter configuration offers reduced circuit and control complexity when compared to similar schemes with NPC or H-bridge inverter configurations.
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