Medium Voltage Dynamic Voltage Restorer with Neural Network Controlled Voltage Disturbance Detector

Dynamic voltage restorers (DVRs) are now becoming more established in industry to reduce the impact of voltage sags to sensitive loads. However, DVRs spend most of their time in standby mode, since voltage sags occur very infrequently, and hence their utilization is low. In principle, it would be advantageous if the series-connected inverter of a DVR could also be used to compensate for any steady-state load voltage harmonics, since this would increase the power quality "value-added" benefits to the grid system. However, before this can be done, consideration must be given to the control of steady-state power through the DVR, the increased losses, and the low modulation depths at which the scheme must operate to achieve acceptable harmonic compensation performance. This paper presents a selective harmonic feedback control strategy that can be easily added to medium-voltage DVR systems to provide voltage harmonic compensation capabilities with minimal effect on the sag compensation performance of the basic DVR. The proposed controller has been experimentally verified on a medium-voltage (10 kV) three-phase DVR prototype under a range of conditions, including distorted supply voltages, nonlinear loads, and operation during distorted voltage sags.

Problem statement: ANRPC is a refinery based in Alexandria, Egypt. The plant was subjected to several shutdowns due to tripping of large induction motors, either by under voltage or by over current relays, sometimes by the mechanical protection. The main cause for such unplanned shutdowns was voltage sags. The Dynamic Voltage Restorer (DVR) has recently been introduced to protect the industrial facilities from voltage sags and other voltage disturbances. Existing configurations and control techniques for the DVR aim at protecting industries of high-tech, loads with adjustable speed drives and other power-electronic based loads. Industries with induction motors loads require a complete different approach for the design and control of a suitable DVR. Owing to the inherit inertia of the induction motors and their capability to withstand short-duration, shallow sags, in addition to its tolerance to phase jumps, a DVR with low cost, fast response and simple controller could be configured to fulfill the voltage restoration requirements. Approach: In this study, a simple DVR was proposed, which utilized the classical Fourier Transform (FT) for sag detection and quantification, a controller based on feed-foreword technique which utilized the error signal (difference between the reference voltage and actual measured voltage) to trigger the switches of an inverter using a Pulse Width Modulation (PWM) scheme. The proposed DVR utilized energy from other available feeder or from energy storage unit through a rectifier. Modeling and simulation of the proposed DVR was implemented in the Matlab/Simulink workspace. Results: Simulation results showed that the proposed DVR was efficient in mitigating balanced, unbalanced, multistage and consecutive sags, as well as swells (over-voltages). The main shortcoming of the DVR, being a series device, is its inability to mitigate complete interruptions. Conclusion: The DVR should be configured with respect to the load requirements. With respect to induction motors loads with inherit inertia and insensitivity to phase jumps, the proposed DVR would be of lower cost, simpler controller and faster response.

Dynamic voltage restorers (DVR) have gained popularity as a cost-effective solution for protecting sensitive loads from balanced and unbalanced voltage sags. DVR implementation has been proposed at medium voltage (MV) levels to safeguard downstream or sensitive loads from such disturbances. This paper presents a case study of a DVR implemented on a medium voltage (11 kV) system, modelled in MATLAB/Simulink environment. The impact of the DVR was evaluated under both unbalanced and balanced conditions for linear loads, where voltage sags of varying durations and depths were applied. The analysis focuses on voltage restoration capability and the resulting waveshape at the load side. The results demonstrate that the DVR compensates for the balanced sags up to 0.5 p.u. For sags where the retained voltage was lower than 0.5 p.u., partial compensation was achieved by the DVR. Under unbalanced conditions, particularly during single-phase-to-ground faults, the DVR helps maintain a stable voltage above 0.9 p.u. These findings validate the DVR's capability as a viable solution for voltage sag mitigation in MV networks and highlight design considerations for optimal performance under diverse fault conditions.

Highly automated production processes are particularly susceptible to voltage disturbances in the power system. Series compensation in the form of dynamic voltage restorer (DVR) is used to mitigate these voltage disturbances. The compensation capability of a particular DVR topology depends on its voltage injection ability and maximum energy storage. This paper presents a new DVR circuit topology which has the ability to mitigate long duration voltage sags with comparatively small energy storage capacitors. The proposed DVR is equipped with a line-side current forced reversible rectifier that helps to maintain the DC-link voltage under voltage sag conditions. A closed loop controller that consists of an inner current loop and an outer voltage loop has been incorporated into the DVR inverter to maintain the load voltage at a desired level. Simulation and experimental results are presented to demonstrate the efficacy of proposed DVR multiloop controller for various voltage sags.

The dynamic voltage restorer (DVR), a custom power device, has been proposed to mitigate voltage sags, thereby protecting sensitive loads. The maximum amount of real power that the DVR can provide to the load is a deciding factor in determining the capability of the restorer. This paper proposes a concept of interline dynamic voltage restoration (IDVR) in which several DVRs in different feeders are connected to a common DC-link energy storage. The cost of installation of a group of DVRs protecting various parts of a power system can be reduced by the sharing of a common energy storage system. While one of the DVRs carries out voltage compensation during sags, the other DVRs can replenish energy to the DC-link to maintain the DC-link voltage at a specific level. A closed-loop controller that consists of an inner current loop and an outer voltage loop is incorporated into the IDVR system in both the voltage control and the power flow control modes. Simulation results are presented to verify the efficacy of the proposed IDVR design.

The dynamic voltage restorer (DVR) is one of the modern devices used in distribution systems to protect consumers against sudden changes in voltage amplitude. It is a custom power device used in power distribution networks to protect consumers from sudden sags (and swells) in grid voltage. Implemented at medium voltage level, the DVR can be used to protect a group of medium voltage or low voltage consumers. In this paper, the controller using the P+Resonant controller and charge regulator is proposed in order to eliminate the steady-state error in DVR response and to stabilize the system, respectively. The current limitation will restore the point of common coupling (PCC) voltage and protect the DVR itself. The innovation here is that the DVR with the fifteen level inverter systems protects the PCC voltage during a voltage sag condition without any real power injection into the DVR. Simulation results show the capability of the DVR to control the emergency conditions of the distribution systems.

Voltage disturbances which affect the stability of electrical networks are the most important power quality problems. The most known voltage disturbances are voltage sag and swell in distribution systems. Dynamic Voltage Restorer (DVR) is the most effective device to compensate these voltage disturbances among the custom power devices. The basic structure of a conventional DVR consists of an inverter, dc link capacitor, injection transformer and filter. The major component in DVR is inverter that generates controlled voltage to compensate voltage sag/swell and other problems such as flicker, interruption and harmonics. Each inverter implemented in DVR has individual properties such as voltage level, unbalanced compensation capability and/or dc link capacitor requirement. This paper aims a comprehensive review on different inverter topologies according to the number of phases, size, voltage level and structure of DVR. In addition, individual properties of inverters are presented in this study.

Power quality (PQ) is an important issue in power systems that reflects a measure of quality of energy supply to the consumers. Power electronics-based equipment is increasing in power systems that cause voltage distortions which may damage a sensitive appliance in the distribution grid. Besides, many electrical and electronic equipment is susceptible to power supply disturbances in modern industrial establishments. The most vital power quality issues affecting large commercial and industrial customers are momentary power interruptions and voltage sags. Usually, these PQ issues are associated with the faults that occur in the supplying power systems. Voltage sags are very common since they can be associated with the faults that happen remotely to the customer. Further, these PQ problems with about 4–5 cycles may cause an extensive malfunction to the sensitive equipment. Therefore, an appropriate solution is necessary to handle this problem. A Dynamic voltage restorer (DVR) is a custom power device (CPD) that can protect sensitive equipment against voltage disturbances and improve power quality in electrical distribution systems. In recent years, many CPDs have been developed to meet the need of the industries and their critical load establishment. The DVR is one of the most promising CPDs used to improve the power quality before feeding it to the sensitive load to protect electric appliances from damage. DVR is the combination of a voltage source inverter (VSI), which can impose the voltage in series through a series injection transformer (SIT) with the power distribution system during voltage sag. The required voltage compensation can be achieved by adopting the pulse width modulation (PWM) technique for VSI. The DVR's performance mainly depends upon the control system that includes voltage disturbance detection, reference generation, voltage & current control and PWM switching strategy. The main objective of the control system is to compensate for the disturbance at the earliest using a fast detection technique, optimum control variables for the control circuit and a suitable PWM switching methodology. Many such compensation methods and control techniques are proposed in the literature along with various DVR topologies which are analysed and studied in this chapter.KeywordsPower qualityDynamic voltage restorerVoltage source inverterPI controllerHarris hawk’s optimization (HHO) algorithm

This paper presents frequency feedback loop based Cascaded Delayed Signal Cancellation PLL employed for dynamic voltage restorer (DVR) application to compensate grid voltage disturbances. The primary and key function of PLL is continuous tracking of grid voltage angle in a precise manner and feed it to DVR control. The conventional CDSC-PLL performance during frequency variation is poor which affects the estimation of grid voltage angle and thereby leads to maloperation of DVR control. Thus in this paper FFL is added to the CDSC-PLL to adapt for frequency variations for effective operation of DVR control. The performance analysis of FFL based CDSC-PLL is presented for various disturbances. Finally, FFL based CDSC-PLL is incorporated in the 10 kV, DVR system and the simulation results of the system for different voltage disturbances by using MATLAB/SIMULINK.

In the present electric power grids, power quality issues are recognized as a crucial concerns and a frequently occurring problem possessing significant costly consequence such as sensitive load tripping and production loss. Consequently, demand for high power quality and voltage stability becomes a pressing issue. Dynamic voltage restorer (DVR), as a custom power device, is one of the most effective solutions for “restoring” the quality of voltage at its load-side terminals when the quality of voltage at its source-side terminals is disturbed. In this paper, a new DVR topology based on double flying capacitor multicell (DFCM) converter for medium-voltage application has been proposed. The advantage of the proposed DVR is that it does not need any line-frequency step-up isolation transformer, which is bulky and costly, to be connected to medium-voltage power grid. The proposed DVR topology obtains the required active power from the energy storage feeding the dc link of the DFCM converter. The pre-sag compensation method, which is explained in detail, is used to restore amplitude and angle of the sensitive load voltage. Moreover, an approach based on d-q synchronous reference frame to determine DVR reference voltages is utilized. The proposed DVR topology is simulated and results to illustrate its performance under various conditions of voltage sag compensation are provided.

Energy quality problems can cause diverse failures of sensitive equipment. Dynamic voltage restorers (DVRs) are devices that have been proposed to protect sensitive loads from voltage sag effects. However, the compensation capacity of DVRs is limited by the amount of energy stored in the restorer. One way to overcome this limitation is to use the interline DVR (IDVR) structure in which two or more DVRs connected to different feeders share a common DC-link. This paper proposes a new IDVR topology based on two three-phase input matrix converters (TTI-MC) without a capacitor in the dc-link. The TTI-MC integrates the power from two feeders and synthesizes the dc-link voltage. The inverters take the dc-link voltage and generate the appropriate compensation voltages to keep the load voltages stable. Each one of the inverters has its own modulation algorithm which are synchronized with the TTI-MC control. Inverter control is carried out in the reference frame dq and a modified space vector pulse width modulation (MSV-PWM) technique is used. TTI-MC control is performed in the dq reference frame with proportional-integral controllers and the modulation is based on the carrier-based pulse width modulation (MCB-PWM) technique. The proposed Two Input Interline DVR (TI-IDVR) extends its compensation range and has multifunctional capabilities. The efficiency of the proposed TI-IDVR is corroborated by simulations on MATLAB/Simulink.

In this paper the detail description of Flexible AC Transmission devices in distribution network are presented so as to mitigate the voltage sag at the network buses. Two FACTS devices are implemented in this paper namely Distributed Static Compensator (D-STATCOM) and Dynamic Voltage restorer (DVR). D-STATCOM provides injection of shunt current into the system and DVR provides injection of series voltage into the system to solve the problem of short term reduction in the root mean square voltage of the system. These two devices are very effectual devices working on the principle of Voltage Source Inverter. This paper elaborates the performance of the DVR and D-STATCOM during voltage sag problems. Simulation studies have been carried out to affirm the consequences. DVR and D-STATCOM are modeled and simulated using the MATLAB/Simulink and simpower system toolboxes.

The dynamic voltage restorer is a power electronic device which has demonstrated its ability to protect sensitive loads from the effects of voltage sags. This compensator is connected in series with the distribution feeder. A neural network control is proposed. Simulation results are shown to validate these control methods.

Real coded GA optimized fuzzy logic controlled PEMFC based Dynamic Voltage Restorer for reparation of voltage disturbances in distribution system

The wind power plant is one of the fastest growing electrical power sources. The integration of wind turbine into the power grid originates various power quality problems. Low-voltage ride through (LVRT) capability improvement is impregnating exigency in recent power quality issue, which is acquainted with various renewable power generation resources like solar PV and wind power plant. Dynamic voltage restorer (DVR) is a custom power device (CPD), which is connected in series with the electrical system, and it is a contemporary and efficient CPD expended in the distribution system to curb the power quality problems. In this paper, LVRT capability of doubly fed induction generator (DFIG) wind turbine system connected to a power grid is enhanced by means of DVR. LVRT capability is improved by the introduction of neural network controller. This controller fulfils the various grid code requirements. Thus, the performance of the DVR becomes far superior by the robust control technique. The simulation results were compared with conventional PI controller and the proposed artificial neural network (ANN) controller. It is proved that the proposed system raises the reliability of grid-connected DFIG wind turbine system.