Maximum voltage sag compensation using direct converter by modulating the carrier signal

The aim of this paper is to achieve maximum voltage sag compensation of 52% using direct converter based DVR. The DVR topology has only two switches. The DVR is designed to compensate the voltage sag in a phase by taking power from the same phase. A direct converter is connected between the series transformer and the line in which sag compensation is to be achieved. If the actual amplitude of the error signal is used and the amplitude of carrier signal is kept at 1 unit, it is possible to achieve only 22% of sag compensation. If the amplitude of the carrier signal is modulated according to the percentage of existing sag, 52% of the sag is compensated through ordinary PWM technique with the THD less than 5%. Matlab Simulation results are presented for the validating the analysis.

Voltage sag compensation using direct converter based DVR by modulating the error signal

<p class="Text"><span>The aim of this paper is to present a modulation technique to achieve highest voltage sag compensation using direct converter based dynamic voltage restorer (DVR). The DVR topology proposed in this paper, has a direct converter and a series transformer. The direct converter is fabricated using only two bi-directional switches. The DVR is designed to compensate the sag in a phase by taking power from the same phase. The direct converter is connected between the series transformer and the line in which sag compensation is to be achieved. Conventionally, the PWM pulses for the direct converters are produced by comparing the error signal with the carrier signal. The error signal is obtained by comparing the amplitude of voltage in the line with the amplitude of the reference voltage. If the amplitude of the carrier signal is kept constant and the actual amplitude of error signal is used for PWM generation, it is possible to achieve only 22% of voltage sag compensation. But if the error signal amplitude is modulated according to the amplitude of existing voltage sag in the line, 52% of the voltage sag can be compensated with the THD less than 5%. Simulation results are presented for validating the analysis. </span></p>

Modeling and Performance Evaluation of an Electromagnetic Voltage Regulator via Series Compensation

Although there currently exists a wide range of voltage regulators that are commercially available, the search for devices with a simpler physical design remains the focus of research studies. Following this line, an electromagnetic voltage regulator (EVR) arrangement has been proposed. The EVR is constituted of an autotransformer that supplies, via discrete taps, a series transformer that injects voltage for regulating the feeder voltage. Even though its operating principle is shown as being similar to that of other devices on the market, the physical arrangement and operating strategy of EVR show novelties which result in properties such as: economic attractiveness, constructive simplicity, and operational reliability. Moreover, when installing voltage regulators, efficacy studies must be carried out to optimize equipment design. In this context, this paper aims at evaluating the factors that influence the effectiveness of the EVR in restoring voltage variations according to the determinations imposed by regulatory agencies. The ultimate goal of this study is to determine the voltage deviation range that the EVR is able to restore. To achieve this goal, a mathematical modeling of the EVR is given and study cases are computationally carried out to investigate its performance when connected to a typical distribution feeder.

Direct Converter based DVR to Mitigate Single Phase Outage

The aim of this paper is to present a new simplified topology for a Dynamic Voltage Restorer (DVR) which has ability to mitigate single phase outage also. The proposed DVR has a multi-winding transformer, a direct converter and a series transformer for each phase. The multi winding transformer is connected between the direct converter and the grid. Only three bi-directional controlled switches are employed per phase. The direct converter is used to synthesis the required compensating voltage and the series transformer is used to add the compensating voltage in grid. The DVR can compensate balanced voltage sag, balanced swell, unbalanced swell and single phase outage by taking power from the grid. For compensating the voltage sag or outage in any one phase, the other two phase voltages are added using the multi winding transformer. The added voltage is pules-width modulated (PWM) using controlled switches to compensate the sag. Swell is compensated by taking power from the same phase. The simulation results confirm that the proposed topology can mitigate balanced sag of 50%, balanced swell of 100%, unbalanced swell of 100% and single phase outage.