PEMFC supported dynamic voltage restorer for power quality enhancement

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.

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

Enhancement of DFIG-Wind Turbine’s LVRT capability using novel DVR based Odd-nary Cascaded Asymmetric Multi-Level Inverter

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.

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.

This paper proposes Interline Dynamic Voltage Restorer (IDVR) to mitigate voltage sag, while its DC link energy is restored by phase shifting transformers. The Dynamic Voltage Restorer (DVR) was proposed as a solution to Voltage Sag compensation involving considerable amount of real power injection into the system which entirely depends on the energy storage capacity of DVR thus limiting its capabilities. The extension of the Dynamic Voltage Restorer leads to the concept of IDVR which consists of two DVRs sharing a common DC link. Usually one of the DVR's of IDVR compensates voltage sag while other DVR replenish the energy at DC link. In this paper a new concept of IDVR is proposed where one DVR compensates the Voltage Sag while the energy at the DC link is replenished by other DVR using the phase shifting transformers. The concept is simulated in MATLAB Simulink and performance of IDVR is investigated. Simulation results presented for a three phase example system with voltage sag demonstrates the effectiveness of the proposed method.

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.

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.

One of the major power quality problems in distribution systems are voltage sags. This paper deals with a dynamic voltage restorer (DVR) as one of the different solutions to compensate these sags and protect sensitive loads. However, the quality of DVR output voltage, such as THD, is important. This paper present a new configuration of DVR based on flying capacitor multicell (FCM) converter. The main properties of FCM converter, which causes increase in the number of output voltage levels, are transformer-less operation and natural self-balancing of flying capacitors voltages. To avoid any exchange of active power in compensation process, the proposed DVR is controlled by energy minimized compensation strategy which is explained in details for general unbalanced voltage sags. Also, the proposed voltage sag detection method as well as proposed DVR reference voltage determination method based on synchronous reference frame (SRF) is adopted as the control system. The proposed DVR is simulated using PSCAD/EMTDC software and simulation results are presented to validate its effectiveness.

Power Quality improvement at the distribution level is a demanding requirement these days. The major power quality problems are voltage sag and harmonics. To mitigate the voltage sag, Dynamic Voltage Restorer (DVR) is one of the solutions which involves real power injection into the system which entirely depends on the energy storage capacity of the DVR. This limits the capability of DVR for longer duration of voltage sag. Therefore the DVR in its present form has to be modified and extended to overcome this drawback. The extended device is known as Interline Dynamic Voltage Restorer (IDVR), which consists of two or more DVRs sharing a common DC link. One of the major aspects of IDVR is its controller which modulates the injected voltage to compensate the voltage sag in the system. The other one is being able to replenish energy at DC link for the required compensation. In this paper, a different way of replenishing the energy at the DC link utilizing Phase shifting transformer and differential energy from Photovoltaic system is presented. The simulations are performed using MATLAB SIMULINK software.

The implementation of custom power devices (CUPD) such as dynamic voltage restorer (DVR), distribution static compensator (DSTATCOM) and unified power quality conditioner (UPQC) has become essential for reducing the impact of PQ problems. More specifically, DVR plays vital role for proving solution to the voltage sag problems and to restore the load voltage with in few milliseconds. The performance of the DVR depends on the control strategy adopted with the algorithm. Synchronous reference frame theory (SRFT)-based ANFIS controller is proposed in this paper. The performance of the proposed control strategy is simulated for various conditions like line to ground, double line to ground and three phase fault in MATLAB/Simulink. From the simulation study, it is found that the ANFIS-based DVR helps to mitigate the voltage sag and reduces the harmonics. The proposed ANFIS-based DVR compared with PI, fuzzy and ANN-based controllers.

Voltage sag according to the IEEE standard is a momentary decrease (10% - 90%) in the root mean square (rms) voltage magnitude where the duration is longer than half a cycle and less that one minute. The common causes of voltage sag are faults or short circuit in the system, starting of large loads and faulty wiring. Dynamic voltage restorer (DVR) is a custom power device that is used to compensate voltage sag. The DVR generally consists of voltage source converter (VSC), injection transformers, filters and energy storage (battery). The control strategy and the implementation of the control strategy using DSP board TMS320F2812 will be briefly discussed in the paper. Simulation results of the control strategy for voltage sag and swell will be presented. This paper will focus on the design and the commissioning of a 3 kVa DVR lab prototype. Experimental results of a working DVR lab prototype will be presented.

The overall performance of the electricity distribution network is determined from various parameters. Power quality indices such as drop in voltage, rise in voltage, and harmonics play an essential role in this context. The article introduces a new index called the power quality distortion (DI). This index gives information about the contribution of non-linear load to the harmonic distortion in power. This effect has been observed due to the presence of non-linear component of current drawn by the load. Changes in the supply voltage in the form of dips, over voltages, harmonics, transients, etc., are considered major power quality issues. This has led to deterioration in the quality of the energy delivered to end customers and generates disruptions on the utility side. Load presents at the consumer end also explains the degradation in the quality of the power supply. Initially, penalties were charged for low p.f. consumers, and then, corrective measures were initiated by the consumer. In the same way to control the power quality, penalty is proposed to the consumers who are hampering the quality of power by application of non-linear load without using any mitigation technique. One of the mitigation techniques is custom power devices (CPDs). It is more effective as compared to traditional methods. This article provides various power quality indices such as distortion index as a power quality calculation parameter and the results obtained by application of dynamic voltage restorer (DVR) and hybrid-STATCOM for reducing the effect of the voltage sag and other indices of the quality of power in the electrical network. The proposed concept allows operation in non-linear conditions on the consumer side. The design of the system parameters is proposed based on the compensation parameter as an index of distortion of the distribution network. The simulation is carried out by the MATLAB model, and the results are compared with the analyzed performance of the power distribution system with regards to the index of distortion with injection of DVR and hybrid-STATCOM.KeywordsPower quality (PQ)Custom power devices (CPDs)Dynamic voltage restorer (DVR)Hybrid-STATCOMDistortion index (DI)Total harmonic distortion in voltage (VTHD)Total harmonic distortion in current (ITHD)Active power filters (APFs)Battery energy storage systems (BESSs)

When a sudden load is connected to the distribution system Voltage sag takes place. DVR (Dynamic Voltage Restorer) is one such custom power device which helps in mitigating voltage sag. The DVR injects required volt-ampere to the system in order to maintain nominal balanced sinusoidal voltage at the load. The operation of DVR is depends on the control technique used. In this paper four control techniques are used, the techniques used are pre sag compensation method, in phase compensation method, energy optimization method and in phase advanced compensation method for mitigation of voltage sag. The performance of all the four methods compared. It is observed that in phase advanced compensation method has given better results in magnitude of voltage sag and THD compared to other methods. The simulations are carried out by using MATLAB / SIMULINK software.

Load-side Voltage Compensation of Small Hydropower Grid-connected System Using DVR based on PV Source