Dynamic symmetrical components analysis and compensation for unbalanced distribution systems

Rescent years, some DG (distributed generation) have been introduced in distribution systems, and the voltage violation problem has been at stake for the distribution system. The impact of DG integration on distribution system is studied in this paper, and the transient stability mechanism of DG is analyzed theoretically. This paper investigates the dynamic analysis of a DVR when applied to correct the voltage distortion in distribution system. Then the model of DG is built by Matlab/Simulink. And it is used to study the impact of DG integration on the distribution system. Then the voltage regulation-dynamic voltage restorer (DVR) is introduced to distribution network with distributed generation. A calculation method for DVR in distribution system with distributed generation is proposed, which is based on a semi-period algorithm to extract fundamental component from fault signal then extract the fundamental positive sequence voltage by the decomposition instantaneous link, and then the quantity of voltage compensation can be solved by direct detection algorithm. Simulation results show that the introduction of DVR (dynamic voltage restorer) to the distribution system with distributed generation is good for voltage regulation and making a good guarantee of the voltage quality of sensitive loads; and the algorithm for DVR is simple and effective.

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.

This paper discusses the dynamic voltage restorer (DVR) supported wind power generator connected to the grid to improve the low voltage ride through (LVRT) capability of the grid. The wind power generators are connected to the grid through a feeder to the distribution system and the DVR is connected to the point of common coupling (PCC), where loads are connected. The main aim of the DVR is to regulate the voltage at the load terminal irrespective of sag/swell, distortion, or unbalance in the grid voltage. The proposed DVR structure is operated in such a fashion that it does not supply or absorb any active power during the steady-state operation. Dead beat control algorithm is used for the control of DVR. The DVR supported wind power system operation is verified through extensive simulation study and a prototype experimental setup is built for experimental verification.

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.

In this paper a new control algorithm for self-supported Dynamic Voltage Restorer (DVR) is analysed. DVR is used to mitigate the power quality problems in terminal voltage like voltage sag, swell, harmonics etc. Here two PI (Proportional Integrator) controllers are used for regulating the DC bus voltage and the load voltage. The focus of this paper is to reduce the active power injected by DVR. Synchronous Rotating Frame (SRF) theory is used to extract the fundamentals of terminal voltage and reference voltage is genereted. The error between sensed load voltage and reference load voltage is used to generate the control signal for the DVR. The compensation of voltage sag, swell, harmonics is evaluated using the Self-supported DVR. The DVR has been modelled using MATLAB software with its Simulink and Sim-power system (SPS) block set tool boxes.

In this paper, a Dynamic Voltage Restorer (DVR) control algorithm with battery management features are presented for the protection of sensitive and censorious loads. A simple DVR control scheme based on dual P-Q theory has been presented to obtain the instantaneous reference DVR voltages to compensate the load voltages. The proposed control scheme embraces energy optimized compensation, which results in a reduction of DC energy storage requirement. A DVR battery management scheme, as a part of this control strategy, has been introduced for better battery energy utilization. Each leg of the three-phase three-leg split capacitor inverter is used to inject series DVR compensation voltages explicitly in each phase of the three phase distribution power system. The effectiveness of the proposed control algorithm has been validated by using computer simulation studies.

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 electrical power is transmitted through a high-voltage transmission system to low-voltage consumers on the distribution side. Because of the high R/X ratio, high current, and low voltage in distribution systems, active power loss (TPL) is much higher as compared to transmission systems. The economic incentive for distribution power utilities is to reduce losses in their networks. This inducement is generally the cost differential between actual and standard losses. As a result, when actual losses exceed standard losses, the utilities are economically penalized, while when the reverse happens, they are getting benefitted. As a result, the loss minimization problem in distribution systems is an excellent research subject for academics. All the methods for the loss minimization are different from each other by the means of formulation of the problem, tools used to minimize the losses, constraints taken, solution methods, and results are obtained. In most of the cases, the distribution system is interconnected and due to increment in load demand and limitations of loading capacity of distribution lines, the idea of distribution side generation came to maintain the system parameters like voltage profile, power loss, cost of operation, etc. To minimize losses, several methods are available like distributed generation (DG) using renewable energy sources and combined heat and power systems, capacitor allocation, reconfiguration of the network, and D-FACTS devices like dynamic voltage restorer (DVR), distribution static compensator (D-STATCOM), unified power quality conditioner (UPQC) allocation, etc. In this chapter, 33 and 69 bus mesh distribution system analysis is proposed with implementation of multiple wind turbines (WT) and multiple D-STATCOM. Advantages of WT are cost-effective generation, clean fuel source, sustainability, and less land requirement. Here, the Artificial Bee Colony (ABC) algorithm is used for finding optimal size and location of WG and D-STATCOM. ABC is an optimization technique that offers population-based search procedure in which artificial bees change individual food locations over time, with the aim of the bees being to locate the places of food supply with the most nectar and recognize it as the one with the greatest nectar. Here direct approach-based load flow method is used to find load flow parameters like bus voltage, branch currents, and power loss. The outcome verifies effective improvement in the system voltage profile, reduction in distribution feeder line loss, and increment in cost savings.

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

To enhance the power quality and reliability of electric power delivered to the end users, the electric distribution system is utilising the custom power devices. The power loss and voltage profile evaluates the performance of distribution system. In this paper a heuristic optimisation technique known as firefly algorithm is applied for the optimal location and sizing of dynamic voltage restorer (DVR). The steady state model of DVR is derived to use in forward/backward sweep load flow method. The performance of the proposed method is tested on IEEE 33 bus and 69 bus Radial Distribution systems by using MATLAB software. The obtained results are compared with immune algorithm. The proposed method boost up the voltage profile minimised the power loss and the installation cost of DVR.

Wind technology is one of the fastest developing renewable technologies. Squirrel cage induction generator (SCIG) with back to back fully rated converter used for wind energy conversion systems (WECS) is a meritorious option among its class. SCIG's offer advantages of being robust, suitable for any harsh environment, cheaply available and unsophisticated than the other types available. To enable increased share of wind energy in the grid without compromising power system stability, the generator ought to stay connected and continue to feed the grid even in case of disturbances such as voltage sag. This paper presents a coordinated control scheme to address the fault ride through of SCIG based WECS. A WECS based on SCIG having back to back connected voltage source converters involving Rotor flux oriented vector controlled drive at machine side and hysteresis current controlled inverter for grid interface has been simulated in MATLAB/SIMULINK. Abnormal rise in dc link voltage during symmetrical faults is controlled by de-loading control while positive-negative sequence control is used for real and reactive power control during symmetrical and unsymmetrical faults. During this work, coordinated performance of all the above stated control strategies during most severe symmetrical (LLL) and most frequently occurring unsymmetrical (LG) fault has been examined.

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The design and simulations of a new five-level modular multilevel inverter based Dynamic Voltage Restorer (DVR) to enhance power quality (PQ) in distribution systems is presented in this paper. The load voltage is maintained at desired value while sag, swell, source voltage imbalances etc. occurring in the supply voltage. The proposed modular multilevel inverter topology based DVR require less number of components for the same number of-levels. The synchronous reference frame based control is used to control the DVR. The use of multilevel inverters in medium voltage DVR is a good solution as it reduces the need of filters and improves the injecting voltage quality. The proposed system is simulated in MATLAB software and the results validate the performance of the system.

Sliding mode control based dynamic voltage restorer for voltage sag compensation

Power Quality has always been a major concern ever since the increase in the usage of many power electronic loads such as Personal Computers (PCs), TVs, variable frequency drives in nearly every household. These loads are a major source of harmonics into the distribution system. Unbalanced Three-phase loads or different single-phase loads result in unbalance in the three-phase voltages and currents in the grid. Equipment damage, Loss of data, nuisance tripping, overheating of wires, relay tripping are few of the major issues caused due to power quality. Also, there is an increase in the awareness about the various power quality issues as well as its ill-effects amongst the consumers. Hence, it is essential to improve the quality of the power supplied. Active and Passive filters play a huge role in the mitigation of power quality issues. In recent years, usage of active filters has increased because tuning is possible for various harmonic elimination and active filters when combined with a storage system can provide active as well as reactive power compensation. The fast depletion of non-renewable sources of energy and its effect on the environment has shifted the focus on the usage of non-renewable energy sources such as solar energy, wind energy, etc for the production of electricity. In this research work, solar energy is combined with shunt active filter for the mitigation of various power quality issues occurring in a grid-connected non-linear and unbalanced three-phase load. The active power filter will provide reactive power compensation to the non-linear load and active power delivery for unbalanced loads such the grid current and voltage will remain balanced and the stress on the grid is reduced while meeting the load demand. A battery system is also integrated to store the excess energy that may be generated by the Photo-Voltaic(PV) array and acts as a source of energy when PV array output is low or nil. Conservative Power Theory is used for controlling the power injection into the system by the Voltage Source Converter(VSC). The proposed system is verified using MATLAB/SIMULINK.