Neural Network Control for Dynamic Voltage Restorer

This paper describes the medium voltage high power DVR (dynamic voltage restorer) with the new voltage disturbance detection method and the real-time digital voltage control. The new voltage disturbance detector was implemented by using the delta rule of the neural network control. Through the proposed method, we can instantaneously obtain the peak value of each phase voltage even under the single phase input voltage conditions. Compared to the conventional synchronous reference frame method, the proposed one shows the minimum time delay to determine the instance of the voltage sag or voltage swell event. Also real-time digital voltage control technique was adopted, where the inverter output filter capacitance voltage, the filter reactor current and the load current are sampled to calculate the inverter PWM command for the next sampling interval. By using digital control, the disturbance voltage can be compensated to the reference voltage level within two sampling intervals. The proposed disturbance detector and the voltage compensator were applied to the medium voltage high power DVR (22.9 kV/4 MVA) that was developed for the application of semiconductor manufacture plant. The performances of the proposed DVR control were verified through computer simulation and experimental results. Finally, conclusions are given.

Dynamic Voltage Restorer (DVR) is a power electronics device to protect sensitive load when voltage sag occurs. Commonly, sensitive loads are electronic-based devices which generate harmonics. The magnitude and phase of compensated voltage in DVR depend on grounding system and type of fault. If the system is floating, the zero sequence components do not appear on the load side. Meanwhile, in a neutral grounded system, voltage sag is extremely affected by zero sequence components. A blocking transformer is commonly installed in series with DVR to reduce the effect of zero sequence components. This paper proposes a new DVR control scheme that is capable of eliminating the blocking transformer and reducing harmonic distortion. The system uses fuzzy polar controller to replace the conventional PI or FL controller that is commonly used. By taking into account the zero sequence components in the controller design, the effects of zero sequence components can be compensated. Simulated results show the effectiveness of the proposed DVR controller

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.

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.

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.

Power quality is a major concern in electrical power systems. The power quality disturbances such as sags, swells, harmonic distortion and other interruptions have an impact on the electrical devices and machines and in severe cases can cause serious damages. Therefore it is necessary to recognize and compensate all types of disturbances at an earliest time to ensure normal and efficient operation of the power system. To solve these problems, many types of power devices are used. At the present time, one of those devices, Dynamic Voltage Restorer (DVR) is the most efficient and effective device used in power distribution systems. In this paper, design and modeling of a new structure and a new control method of multifunctional DVRs for voltage quality correction are presented. The new control method was built in the stationary frame by combining Proportional Resonant controllers and Sequence-Decouple Resonant controllers. The performance of the device and this method under different conditions such as voltage swell, voltage sag due to symmetrical and unsymmetrical short circuit, starting of motors, and voltage distortion are described. Simulation result show the superior capability of the proposed DVR to improve power quality under different operating conditions and the effectiveness of the proposed method. The proposed new DVR controller is able to detect the voltage disturbances and control the converter to inject appropriate voltages independently for each phase and compensate to load voltage through three single-phase transformers.

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.

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.

The Dynamic Voltage Restorer (DVR) provides an advanced and economical solution for both voltage sag and swell problems. The voltage-restoration process involves real-power injection into the distribution system. The Interline DVR (IDVR) proposed in this paper provides a way to compensate the voltage deviation caused in a feeder. The IDVR consists of several DVRs connected to different distribution feeders in the power system sharing a common energy storage. Here, one DVR in the IDVR system works in voltage-sag/swell compensation mode while the other DVR in the IDVR system operate in power-flow control mode. The single phase model of the IDVR system is illustrated which is operated by Multiple Pulse Width Modulation (PWM). Open-loop and closed-loop control schemes of load voltage for a simple system is modeled and simulated using MATLAB software. The simulation results are presented to demonstrate the effectiveness of the proposed IDVR system.

This paper introduces a control algorithm for generation of reference voltages based on single-phase SOGI (Second Order Generalized Integrator) for DVR (Dynamic Voltage Restorer). The proposed DVR is a series active compensator used for compensation of voltage sag and swell to the desired level. The proposed control algorithm is capable of generating reference voltages in sag, swell and phase jump conditions. The controller is providing the solution for voltage sag and swells with and without phase jump and improving the power quality. In this paper, SOGIPLL (Phase-Locked Loop) is chosen because of its dynamic response, tracking accuracy and faster detection under all varying grid conditions. The control algorithm is tested and evaluated using MATLAB/Simulink and has proved effective.

Dynamic voltage restorers (DVRs) are used to protect sensitive loads from the effects of voltage sags on the distribution feeder. This paper presents and verifies a novel voltage sag detection technique for use in conjunction with the main control system of a DVR. In all cases it is necessary for the DVR control system to not only detect the start and end of a voltage sag but also to determine the sag depth and any associated phase shift. The DVR, which is placed in series with a sensitive load, must be able to respond quickly to a voltage sag if end users of sensitive equipment are to experience no voltage sags. A problem arises when fast evaluation of the sag depth and phase shift is required, as this information is normally embedded within the core of a main DVR control scheme and is not readily available to either users monitoring the state of the grid or parallel controllers. Previous research presented an additional controller, which required phase and sag depth information to manipulate the injection voltage vector returned by the main controller in order to prevent the DVR injection transformers from saturating. Typical standard information tracking or detection methods such as the Fourier transform or phase-locked loop (PLL) are too slow in returning this information, when either applied to the injection voltage vector, or to the supply voltages directly. As a result of this the voltage sag detection method in this paper proposes a new matrix method, which is able to compute the phase shift and voltage reduction of the supply voltage much quicker than the Fourier transform or a PLL. The paper also illustrates that the matrix method returns results that can be directly interpreted, whereas other methods such as the wavelet transform return results that can be difficult to interpret.

In the paper control of series active compensator, particularly dynamic voltage restorer (DVR), is considered. The compensator consists of VSI and an LC filter for smoothing VSI output voltage. Presence of the filter makes control of the compensator more difficult due to dynamics of a second order plant introduced by the filter which results in oscillations during a sudden voltage change. Multiloop controller is able to compensate the effect, however measurement of additional signals is needed. In the paper an estimator of the LC capacitor current is proposed in order to decrease total number of sensor needed for 3-ph DVR controller.

This paper introduces a simple and effective control algorithm for generation of reference voltages based on Three-phase dual SO-SOGI (Second Order-Second Order Generalized Integrator) based Phase Locked Loop (PLL) for DVR (Dynamic Voltage Restorer). The proposed DVR scheme is implemented to achieve faster compensation of voltage sag, swell with and without phase jump and at harmonic conditions. Three-phase PLL is used to extract the phase information and amplitude to control and to inject the required voltage at the load end. The SO-SOGI based QSG (Quadrature Signal Generation) and PLL are found effective in mitigating inter-harmonics, harmonics, DC-Offset and unbalance in the estimated parameters. This enables the DVR with the proposed control algorithm to inject reference voltage accurately under linear/ non-linear load conditions. In this paper, SO-SOGI is chosen because of its dynamic response, tracking accuracy and faster detection under all varying grid conditions within a very short duration of time. The control algorithm is tested and evaluated using MATLAB/Simulink and has proved its effectiveness.

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.

Quality of the power should be effective and error free for the operations of load sensitive, electrical supplies, which may prompt glitch or may bring about hindrance when the power quality worsens. Power Quality deteriorates owing to voltage swells and voltage droop which start in the electrical cables because of load vacillations. Shunt dynamic channels, Dynamic Voltage Restorer (DVR), UPFC and STATCOM are a portion of the alleviation techniques introduced to overcome this power excellence problem. Out of these, DVR is charge effectual with speedy response. Hence this work proposes a 5 level cascaded H-bridge inverter based DVR to guarantee the quality of the power delivered. PSO based MPPT technique is capitalized for tracking the output of the solar system. MCSPWM (Multi Carrier Sinusoidal Pulse Width Modulation) is intended for switching pulses of an inverter. DVR is implemented by using the Neural controller. MATLAB-Simulink is depended upon for activating the system, and results from the simulation demonstrate that the presentation of the new technique is satisfactory.