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.

Dual $P$ - $Q$ Theory Based Energy-Optimized Dynamic Voltage Restorer for Power Quality Improvement in a Distribution System

Power quality is a pressing concern and of the utmost importance for advanced and high-tech equipment in particular, whose performance relies heavily on the supply’s quality. Power quality issues like voltage sags/swells, harmonics, interruptions, etc. are defined as any deviations in current, voltage, or frequency that result in end-use equipment damage or failure. Sensitive loads like medical equipment in hospitals and health clinics, schools, prisons, etc. malfunction for the outages and interruptions, thereby causing substantial economic losses. For enhancing power quality, custom power devices (CPDs) are recommended, among which the Dynamic Voltage Restorer (DVR) is considered as the best and cost-effective solution. DVR is a power electronic-based solution to mitigate and compensate voltage sags. This paper provides a thorough discussion and comprehensive review of DVR topologies based on operations, power converters, control methods, and applications. The review compares the state-of-the-art in works of literature, and comparative study on power quality issues, the DVR principle along with its operation modes, the DVR components, the DVR topologies based on energy storage, the DVR topologies based on single-/three-phase power converters, and the DVR topologies based on control units that have different control processing stages. Furthermore, modified and improved configurations of the DVR, as well as its integration with distributed generations, are described. This work serves as a comprehensive and useful reference for those who have an interest in researching DVRs.

https://www.mdpi.com/1996-1073/13/16/4152/pdf

Dynamic Voltage Restorer (DVR): A Comprehensive Review of Topologies, Power Converters, Control Methods, and Modified Configurations

A novel dual-dc-port dynamic voltage restorer (DDP-DVR) is proposed. One low-voltage dc port is directly connected to the energy storage, while the other high-voltage dc port is connected to the intermediate dc bus. An integrated dc–dc converter is interfaced with these two dc ports which is aimed at providing a high-dc-link voltage and maintaining the voltage injection capability even if the energy-storage voltage is lower than the peak value of the injected ac-line voltage. Compared with the traditional DVR that uses the dc–dc converter for all voltage sag compensation, the proposed DDP-DVR can compensate shallow voltage sags without using the dc–dc converter, and for deep voltage sags, only partial active power needs to be processed by the dc–dc converter. Therefore, the power rating of the dc–dc converter can be reduced significantly. Meanwhile, much lower power losses can be achieved by the proposed DDP-DVR due to reduced power conversion stages. The operation principles, modulation strategies, and characteristics of the proposed DDP-DVR are analyzed in detail and verified with experimental results.

A Novel Dual-DC-Port Dynamic Voltage Restorer With Reduced-Rating Integrated DC–DC Converter for Wide-Range Voltage Sag Compensation

In this paper, an improved control scheme is proposed to improve the voltage quality of sensitive loads using dynamic voltage restorer. The existing control strategies either put emphasis on the optimal control during steady operation stage of compensation or correct the phase angle jump in the initial stage of compensation. In current researches, the impact of phase jump characteristic of voltage sag on the load side after voltage sag recoveries is widely ignored, further, there are still drawbacks in existing energy self-recovery strategies of DVR. Therefore, to improve the overall voltage compensation time while correcting the phase jump and accelerate the energy recovery of dc link side, this paper aims to 1) Propose the strategies to minimum active power consumption during voltage compensation stage and maximum active power absorption during energy self-recovery stage. 2) Deliver smooth transition in dynamic process to ensure the flexible switching between two stages. Theoretical analysis of proposed strategy is been validated through simulation and experimental results.

/pdf/dynamic-voltage-restorer-with-an-improved-strategy-to-z638895ic7.pdf

Dynamic voltage restorer with an improved strategy to voltage sag compensation and energy self-recovery

This article presents a super twisting sliding-mode control (ST-SMC) for single-phase dynamic voltage restorers (DVRs). Unlike the conventional first-order sliding-mode controller, the proposed ST-SMC technique eliminates the need for differentiating the compensation voltage in the sliding surface function while keeping the merits of first-order SMC. As a consequence of employing ST-SMC, a continuous control signal is achieved from which the pulsewidth modulation (PWM) signals can be generated. In this case, the inverter operates at a constant switching frequency. The stability analysis of ST-SMC is also presented. The reference compensation voltage needed in ST-SMC is estimated by using Brockett oscillator-based frequency-locked loop. Theoretical considerations are verified through experimental results under ideal and distorted grid voltage conditions. The obtained results show that the ST-SMC has good dynamic performance and can maintain the load voltage at a desired level under voltage sag, swell, and harmonically distorted grid voltages.

/pdf/super-twisting-sliding-mode-control-of-dvr-with-frequency-1mvu835yke.pdf

Super Twisting Sliding-Mode Control of DVR With Frequency-Adaptive Brockett Oscillator

This paper introduces a series compensation philosophy to improve the voltage property of loads using three-phase voltage ellipse parameters intended for optimal utilization of a dynamic voltage restorer. The proposed approach relies on the instantaneous magnitude of voltage signals and functions by inserting a virtual equivalent impedance in series with the distribution feeder during voltage sags, compensating for the difference between faulty and nominal voltages. In addition, the definite mathematical derivations using iterative processes are properly used as an identification mark of the resultant rotating vector tracing an ellipse. The ellipse parameters including major axis, minor axis, and inclination angle are utilized to develop the proposed algorithm and hence, a set of generalized VA loading formulations calculating an optimal sizing with the minimum possible rating are presented. The uniqueness of dual VSCs connected with common dc-side is an attempt to formalize the topological structure keeping a higher level of compensation accuracy. A novel design and the corresponding algorithm are proposed and all possible scenarios concerning sag depth and phase jump are taken into consideration. MATLAB-based simulation results are discussed in detail to support the concept and the test is also performed to verify the effectiveness through real-time experimental laboratory.

A New Voltage Compensation Philosophy for Dynamic Voltage Restorer to Mitigate Voltage Sags Using Three-Phase Voltage Ellipse Parameters

In this paper, a novel decentralized control for a dynamic voltage restorer is proposed to deal with its captivity by improving the voltage quality of loads. The proposed technique controls the magnitude and the phase angle of the injected voltage to accomplish low-voltage ride-through based on the instantaneous calculations of voltages and currents and the application of elliptical compensation properly demonstrated at first. A set of generalized equations based on symmetric-sequence components are represented, aiming to separately control active and reactive powers with two individually adaptable parameters. Moreover, this approach can also describe a theoretical methodology by regulating the status parameters so that the multiple alternatives can be provided. The two parameters are an external voltage contribution of this work utilized to raise and equalize the phase voltage for a particular purpose of positive- and negative-sequence injected powers. Furthermore, a control algorithm for reference generators that provide flexible voltage support is proposed simultaneously to improve ride-through ability. Results of the simulation in the MATLAB indicate that the proposed control strategies can compensate voltage sags in a considerable short-time period. Finally, the laboratory test is performed to verify the effectiveness of the proposed approach that preserves flexible controllability.

Shilin Pang

Papers

A New Voltage Compensation Philosophy for Dynamic Voltage Restorer to Mitigate Voltage Sags Using Three-Phase Voltage Ellipse Parameters

New Decentralized Control Scheme for a Dynamic Voltage Restorer Based on the Elliptical Trajectory Compensation