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This paper deals with the protection of critical loads from voltage-related power quality issues using a dynamic voltage restorer (DVR). A generalized control algorithm based on instantaneous space phasor and dual $P$ - $Q$ theory has been proposed to generate the instantaneous reference voltages to compensate the load voltages with direct power flow control. The proposed algorithm adapts energy-optimized series voltage compensation, which results in a reduction of energy storage requirement. The proposed DVR control scheme can support the load from voltage-related power quality issues irrespective of the load current profile. Each leg of the three-phase three-leg split capacitor inverter is used to inject series compensation voltage in respective phases of the system. Model-based computer simulation studies and real-time experimental results validate the effectiveness of the proposed control algorithm. [ABSTRACT FROM AUTHOR]

This paper presents a predictive voltage control scheme for the effective control of a transformerless dynamic voltage restorer (TDVR). This control scheme utilizes the discrete model of a voltage source inverter and an interfacing filter for the generation of the switching strategy of inverter switches. Predictive voltage control algorithm-based TDVR tracks the reference voltage effectively and maintains load voltages sinusoidal during various voltage disturbances as well as load conditions. Moreover, this scheme does not require any linear controller or modulation technique. Simulation and experimental results are presented to verify the performance of the proposed scheme. [ABSTRACT FROM PUBLISHER]

This paper proposes an improved hybrid distribution static compensator (DSTATCOM) topology to address some practical issues such as power rating, filter size, compensation performance, and power loss. An $LCL$ filter has been used at the front end of a voltage source inverter (VSI), which provides better switching harmonics elimination while using much smaller value of an inductor as compared with the traditional $L$ filter. A capacitor is used in series with an $LCL$ filter to reduce the dc-link voltage of the DSTATCOM. This consequently reduces the power rating of the VSI. With reduced dc-link voltage, the voltage across the shunt capacitor of the $LCL$ filter will be also less. It will reduce the power losses in the damping resistor as compared with the traditional $LCL$ filter with passive damping. Therefore, the proposed DSTATCOM topology will have reduced weight, cost, rating, and size with improved efficiency and current compensation capability compared with the traditional topology. A systematic procedure to design the components of the passive filter has been presented. The effectiveness of the proposed DSTATCOM topology over traditional topologies is validated through both simulation and experimental studies. [ABSTRACT FROM PUBLISHER]

This paper presents a detailed study on the design and analysis of user-defined constant switching (UDCS) frequency current-control-based four-leg distribution static compensator (DSTATCOM). The three phase legs of its voltage source inverter are operated in hysteresis current tracking mode whereas the fourth leg is controlled by a square switching pulse of user-defined frequency. Consequently, the switches of the other three legs also get tuned to this user-defined frequency. Analytical expressions are derived that prescribe the range of frequencies for which the scheme works effectively. Design procedure is also suggested for the selection of the parameters of the four-leg inverter such as dc-link voltage, dc-link capacitor, interface inductor, and hysteresis band. Simulation and experimental studies are conducted to validate the proposed design procedure for a UDCS-controller-based DSTATCOM. Its performance is compared with a conventional hysteresis-controlled DSTATCOM. [ABSTRACT FROM AUTHOR]

In this paper, design aspects of various passive components and switching dynamics of a voltage source inverter (VSI) for compensating unbalanced and nonlinear load are presented. The design method for VSI to track desired reference currents smoothly, is illustrated. By using the proposed method, it is possible to design the passive components of different VSI topologies used for load compensation. The results are supported by detailed simulation studies on a three-phase four-wire compensated system using PSCAD 4.2.1. The design steps are also verified by conducting experiments using a prototype model developed in the laboratory. [ABSTRACT FROM AUTHOR]

Abstract-In this paper, an optimization-based control algorithm for the compensation of steady-state load under distorted supply voltages is presented. For balanced and sinusoidal supply voltages, load compensation using shunt active filter produces perfect harmonic cancellation (PHC) and unity power factor (UPF) source currents. However, when the supply voltages are distorted, compensation for PHC will not provide UPF, as the harmonics in the supply voltages are not utilized for delivering the average power. In the same way, to achieve UPF source currents, the compensated source currents should have the same harmonics, unbalance, shape, and be in phase with the respective supply voltages, thereby violating the perfect harmonic cancellation objective. Hence, there should be an optimal operation between these two important compensation characteristics. The optimization-based control algorithm presented in this paper gives the best power factor while satisfying the constraints such as total harmonic distortion limits and average power balance of source currents. It is also flexible to adopt different compensation characteristics based upon the supply voltage conditions. MATLAB and its optimization toolbox are used for simulation studies and solving the nonlinear optimization problem, respectively. The algorithm is validated by using a prototype of digital signal processor (TMS320F2812PGFA)-based shunt active power filter. Detailed experimental results are presented. [ABSTRACT FROM AUTHOR]

In this paper, load compensation techniques under unbalanced and distorted voltages have been discussed. Two kinds of compensation methods are considered. In the first category, synchronous detection and modified equal current strategies are used under the unbalanced but sinusoidal source voltages. In the second method, load compensation based on instantaneous symmetrical component theory with positive sequence extraction is proposed and is shown to work under unbalanced and the non-sinusoidal source voltages. To support the proposed method, a 440 V (L-L) three-phase, four-wire distribution system is considered. The compensator is realized using a three-phase voltage source inverter (VSI) operated in the current control mode. Detailed digital simulation and experimental results are presented to validate the approach. [ABSTRACT FROM AUTHOR]

This paper proposes a modified four-leg distribution static compensator (DSTATCOM) topology for compensation of unbalanced and nonlinear loads in three-phase four-wire distribution system. DSTATCOM, connected in parallel to the load, supplies reactive and harmonic powers demanded by unbalanced nonlinear loads. In this proposed topology, the voltage source inverter (VSI) of DSTATCOM is connected to point of common coupling (point of interconnection of source, load, DSTATCOM) through interface inductor and series capacitance, unlike the conventional topology which consists of interface inductor alone. Load compensation with a lower value of input DC link voltage of VSI is possible in this modified topology compared to conventional topology. A comparative study on modified and conventional topologies in terms of voltage rating of inverter power switches, switching losses in VSI and power rating of input DC capacitor of VSI is presented. The detailed design aspects of DC link capacitor and interface series capacitor are also presented. The reference filter currents are generated using instantaneous symmetrical component theory and are tracked using hysteresis current control technique. A detailed simulation study is carried out, to compare the compensation performances of conventional, modified topologies using PSCAD simulator and experimental studies are done to validate the simulation results. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes the effective utilization of unified power quality conditioner (UPQC) for interconnecting the PV modules to the grid using power angle control (PAC) method. A shunt active power filter (APF) is used to evacuate the power from the photovoltaic module in addition to compensating the current harmonics, load unbalance and reactive power. To accomplish this the series APF in the UPQC is used for supplying a part or whole reactive power required by the load in addition to compensating the sag, swell, supply voltage unbalance and distortions. This is made possible by controlling the phase angle and magnitude of series injected voltage called power angle control method. The reactive power and voltage compensation technique introduces a phase shift between the load terminal voltage and source voltage. The transient due to sudden phase shift is minimized using step by step introduction of series compensation voltage. The proposed method effectively utilizes the shunt APF and series APF in the UPQC for interconnecting the PV module to the grid. The simulation results from MATLAB/SIMULINK are discussed to validate the developed method. [Copyright &y& Elsevier]

The unified power-quality conditioner (UPQC) is used to mitigate the current and voltage-related power-quality (PQ) problems simultaneously in power distribution systems. Among all of the PQ problems, voltage sag is a crucial problem in distribution systems. In this paper, a new methodology is proposed to mitigate the unbalanced voltage sag with phase jumps by UPQC with minimum real power injection. To obtain the minimum real power injection by UPQC, an objective function is derived along with practical constraints, such as the injected voltage limit on the series active filter, phase jump mitigation, and angle of voltage injection. Particle swarm optimization (PSO) has been used to find the solution of the objective function derived for minimizing real power injection of UPQC along with the constraints. Adaptive neuro-fuzzy inference systems have been used to make the proposed methodology online for minimum real power injection with UPQC by using the PSO-based data for different voltage sag conditions. The proposed method has been validated through detailed simulation and experimental studies. [ABSTRACT FROM AUTHOR]

The theory of instantaneous symmetrical components is used for the detection of insulation faults in a three-phase induction motor. Based on the experimental data of motor intake currents and the system voltages, the loci of positive- and negative-sequence components of currents are plotted. These loci overlap with each other under healthy winding conditions as their major and minor axes coincides. When an inter-turn short circuit occurs, these axes do not coincide with each other and displacement angle ϕ appears between two major axes. Thereby, the non-overlapping area comes into existence. The proposed system considers the effects due to unbalance in voltages, asymmetry in stator winding design, and measurement errors. Experimental results are reported to demonstrate the effectiveness of the proposed technique at different load conditions. [ABSTRACT FROM AUTHOR]