The protection of the sensitive unbalanced nonlinear loads from sag/swell, distortion, and unbalance in supply voltage is achieved economically using the dynamic voltage restorer (DVR). A simple generalized algorithm based on basic synchronous-reference-frame theory has been developed for the generation of instantaneous reference compensating voltages for controlling a DVR. This novel algorithm makes use of the fundamental positive-sequence phase voltages extracted by sensing only two unbalanced and/or distorted line voltages. The algorithm is general enough to handle linear as well as nonlinear loads. The compensating voltages when injected in series with a distribution feeder by three single-phase H-bridge voltage-source converters with a constant switching frequency hysteresis band voltage controller tightly regulate the voltage at the load terminals against any power quality problems on the source side. A capacitor-supported DVR does not need any active power during steady-state operation because the injected voltage is in quadrature with the feeder current. The proposed control strategy is validated through extensive simulation and real-time experimental studies.

“SRF Theory Revisited” to Control Self-Supported Dynamic Voltage Restorer (DVR) for Unbalanced and Nonlinear Loads

The unified power quality conditioner (UPQC) is a custom power device, which mitigates voltage and current-related PQ issues in the power distribution systems. In this paper, a UPQC topology for applications with non-stiff source is proposed. The proposed topology enables UPQC to have a reduced dc-link voltage without compromising its compensation capability. This proposed topology also helps to match the dc-link voltage requirement of the shunt and series active filters of the UPQC. The topology uses a capacitor in series with the interfacing inductor of the shunt active filter, and the system neutral is connected to the negative terminal of the dc-link voltage to avoid the requirement of the fourth leg in the voltage source inverter (VSI) of the shunt active filter. The average switching frequency of the switches in the VSI also reduces, consequently the switching losses in the inverters reduce. Detailed design aspects of the series capacitor and VSI parameters have been discussed in the paper. A simulation study of the proposed topology has been carried out using PSCAD simulator, and the results are presented. Experimental studies are carried out on three-phase UPQC prototype to verify the proposed topology.

A Modified Three-Phase Four-Wire UPQC Topology With Reduced DC-Link Voltage Rating

In this paper, two new topologies are proposed for three-phase dynamic voltage restorers (DVRs). These topologies are based on direct converters. The proposed topologies do not require dc-link energy storage elements. As a result, they have less volume, weight, and cost. They can also compensate long-time voltage sags and swells. The proposed DVRs can compensate several types of disturbances, such as voltage sags, swells, unbalances, harmonics, and flickers. Moreover, due to the fact that the compensation voltage for each phase is taken from all three phases, the proposed topologies can compensate one-phase outages. In the proposed topologies, three independent three-phase to single-phase direct converters are used. Each converter operates independently and, as a result, the proposed DVRs properly compensate unbalanced voltage sags and swells. The used converters can be constructed by four or six power switches. Depending on the structure of the used converters, the compensation ranges will be different. A new control method is also proposed for using direct ac/ac converters. The experimental and simulation results verify the capabilities of the proposed topologies in compensation of voltage distortions.

Mitigation of Voltage Disturbances Using Dynamic Voltage Restorer Based on Direct Converters

A comprehensive review of dynamic voltage restorers

This paper presents an optimized sliding mode control (SMC) strategy to maximize existence region for single-phase dynamic voltage restorers. It is shown analytically that there exists an optimum sliding coefficient which enlarges the existence region of the sliding mode to its maximum. Also, it is pointed out that the optimum sliding coefficient improves the dynamic response. In addition, a double-band hysteresis control which ensures the switching of a transistor in the voltage source inverter during a half-cycle while it remains either on or off in the other half cycle is used to mitigate the switching frequency. The theoretical considerations and analytical results are verified through computer simulations and experimental results. Simulation and experimental results show that the proposed SMC strategy not only compensates the undesired voltage disturbances and maintains the load voltage at desired level with low total harmonic distortion, but also exhibits fast dynamic response and operates at reasonably low switching frequency.

Optimized Sliding Mode Control to Maximize Existence Region for Single-Phase Dynamic Voltage Restorers

This study presents a novel constant switching frequency band controller for dynamic voltage restorer (DVR) with a proposed filter structure. The switching operation of voltage source inverter (VSI) based on band controller, which restricts the injected voltages within a band, is explored. This control method of the VSI inherits merits such as fast dynamic response, robustness, zero magnitude/phase errors and ease of implementation. The performance of the band controller is improved using a novel filter structure. Quantitative expressions involving the dynamics of DVR and variation of switching frequency are derived. The constancy in the switching frequency is subsequently achieved by an adaptive hysteresis band controller. The proposed filter structure and the adaptive band controller for the DVR are validated by carrying out simulation studies using PSCAD. The performance of the proposed controller in both transient and steady-state conditions has been evaluated and discussed. Based on the proposed design, the performance of the controller is extensively tested with various voltage disturbances on a reduced scale DVR prototype developed in the laboratory.

Constant switching frequency band controller for dynamic voltage restorer

The load side voltage disturbances can be effectively mitigated by connecting a dynamic voltage restorer (DVR), a series compensating device. A DVR is realised by a voltage source inverter with DC storage device and a series injection transformer. Rating and design issues of an injection transformer are of prime concern for the proper voltage compensation using DVR. Voltage underrating of the transformer may lead to its saturation, whereas, overrating increases the cost and size of the DVR. The voltage applied to the primary winding of the transformer is a combination of several components of different frequencies. Considering above aspects, rating and design issues are presented in this paper. A novel method is proposed to find the voltage rating of the transformer as a function of the fundamental frequency. Furthermore, the inrush current due to saturation is avoided during transient period. K factor method is used to account for the effects of current harmonics in the transformer. A PSCAD model is used...

Rating and design issues of DVR injection transformer

This paper presents a filter structure for improving the performance of switching band controlled Dynamic Voltage Restorer (DVR) and a systematic design procedure for the passive filter components. The switching operation of VSI is accompanied by a band controller which restricts the injected voltages within a band, defined about a reference voltage. Switching band control method exhibits merits such as fast dynamic response, robustness, zero magnitude / phase errors and ease in implementation. The performance of the band controller is improved using a novel filter structure. Quantitative expressions involving the dynamics of DVR and variation in switching frequency are also derived. The passive filter components are designed based on switching frequency and inverter rating. The proposed filter structure and design procedure for the DVR filter components are validated by carrying out PSCAD simulation studies.

Design of passive filter components for switching band controlled DVR

The paper describes the design, development, and implementation issues of a digital signal processor-based integrated hardware set-up for a distribution static compensator (DSTATCOM). A detailed documentation revealing all the design aspects of the important building blocks of the set-up is presented. The transducer, signal conditioning, synchronizing, blanking, protection, optoisolation, and power supply circuits are constructed and assembled to form a prototype laboratory model. In the present work, an H-bridge voltage source inverter-based DSTATCOM has been realized. The efficacy of this arrangement is demonstrated by conducting experiments and the results are discussed.

A DSP-based Integrated Hardware Set-up for a DSTATCOM: Design, Development, and Implementation Issues

This paper discusses the power quality survey conducted in the distribution system of Indian Institute of Technology Madras, Chennai, India. Individual power quality parameters measured from the survey are analyzed and presented in detail. To assess the power quality, measured data are compared with various power quality standards including IEEE 519-1992 standard for the measured voltage and current harmonics. The information obtained from this survey will be useful in improving the quality of power in the Institute.

S. Sasitharan

Papers

Constant switching frequency band controller for dynamic voltage restorer

Rating and design issues of DVR injection transformer

Design of passive filter components for switching band controlled DVR

A DSP-based Integrated Hardware Set-up for a DSTATCOM: Design, Development, and Implementation Issues

Power quality survey in a technological institute