Voltage Sag Mitigation of DVR using Matlab Simulation

Transcription

1 Voltage Sag Mitigation of DVR using Matlab Simulation Ms.T.D.Paunikar, Prof. C.M.Bobde Abstract One of power quality problem is Voltage sag. Voltage sag becomes severe to industrial customers. Voltage sag can cause miss operation to several sensitive electronic equipment. That problem can be mitigating with voltage injection method using custom power device, Dynamic Voltage Restorer (DVR). This paper presents modelling and analysis of a DVR with pulse width modulation (PWM) based controller using Matlab/Simulink. Dynamic voltage restorer (DVR) can provide the most commercial solution to mitigation voltage sag by injecting voltage as well as power into the system. The performance of the DVR depends on the efficiency of the control technique involved in switching the inverter. This paper represented by the control techniques which is Proportional-integral Controller (P) which give the result to assess the performance of controller and capability of DVR for the best power quality solution. The modelling and simulation of DVR controlled by PI has been developed using Matlab/Simulink. Index Terms Dynamic Voltage restorer, PI Controller, SVPWM. I. INTRODUCTION 1 Recently, power quality problems become a major concern of industries due to massive loss in terms of time and money. Hence, there are always demands for good power quality, which positively resulting in reduction of power quality problems like voltage sag, harmonic and flicker. Voltage sag is always considered as one of the major power quality problems because the frequency of occasion is so high. The common causes of voltage sag are faults or short circuit in the system, starting of large loads and faulty wiring. This will lead to increase in both production and financial loss for industries. Therefore, it is vital to mitigate voltage sag. Two main characteristics that explain the voltage sag are depth/magnitude and duration of voltage sag itself to mitigate the voltage sag in the power distribution system. There are various types of voltage sag mitigation equipment that available nowadays such as Uninterrupted Power Supply (UPS), flywheel, and the flexible ac technology (FACTS) devices which have been widely used in the power system due to the reliability to maintain power quality control. One of the most FACTS devices that have been created in improvement the performance of power quality is Dynamic Voltage Restorer (DVR) also known as custom power devices. II. CONFIGURATION AND OPERATION 1. Dynamic voltage restorer (DVR) This is the series connected device that has the same structure as that of an SSSC. The main purpose of this device is to protect sensitive load from sag/swell, interruption in the supply side. This is accomplished by rapid series voltage injection to compensate for the drop/rise in the supply voltage. Since this is the series device, it can also be used as a series active filer. Even though this device has the same structure as that of an SSSC the operating principles of the two devices differ significantly[2]. While the SSSC injects a balance voltage in series, the DVR may have to inject unbalance voltages to maintain the voltage at the load terminal in case of an unbalance sag in the supply side. Furthermore when there is distortion in source voltage, the DVR may also have to inject a distorted voltage to counteract the harmonic voltage Final Stage. 2. Power quality Power quality can be defined as the measure, analysis, and improvement of bus voltage, usually a load bus voltage, to maintain that voltage to be a sinusoidal at rated voltage and frequency. quality may also be defined as the provision of voltage and system design so that the user of electric power can utilize electric energy from distribution system successfully without interface or interruption 2.1 Power Quality Problems Power quality problem can be defined as the nonstandard voltage, current or frequency that results in a failure of end use equipment. The power quality problems are increasingly felt by felt by customers industrial, commercial and residential. The power quality problems are classified as bellow Short Duration Voltage Variation Any variation in supply voltage for duration not exceeding one minute is called a short duration voltage variation. Usually such variations are caused by fault, energization of load that requires large inrush current and 1

2 intermittent loose connection in the power wiring. Short duration variations are further classified as following. When the supply voltage is zero for a period of a period of time in excess of 1 minute, the long duration voltage variation is called sustained interruption. a) Voltage sag Sag can be defined as the momentary decrease in RMS ac voltage (10%-90% of nominal voltage) at the power frequency of duration from 0.5 cycles to few seconds. Voltage sag is normally caused by a short-circuit fault such as single line to ground fault, L-L fault, double line to ground fault, three phase to ground fault and startup of induction motor of large rating. b) Voltage swell Voltage swell is defined as short duration increase in RMS voltage of supply having range from1.1 p.u to 1.8 p.u of nominal supply. The main reason for voltage swell is switching large capacitor or removal of large load [2]. c) Interruption If the supply voltage or load current decreases to less than 0.1 p.u for a period of time not more than one minute is known as interruption. Interruption can be caused either by system faults, equipment failures or control mal functions. d) Spikes Spikes are a sudden, short surge in voltage. Voltage spikes can be caused by lightning, power outages, short circuits, or power transitions in large equipment on the same power line Long duration voltage variations These are defined as the RMS variation in the supply voltage at fundamental frequency for periods exceeding 1 minute. These variations are classified into following [1] a) Under voltage Under voltage is defined as 10% or more decrease in RMS voltage for more than 1 minute. The switching off of large capacitor bank or energization of large load may results in an under voltage. b) Over voltage Overvoltage is defined as 10% or more increase in RMS voltage for more than 1 minute. In a weak system the switching off of a large load or the energization of a large capacitor bank may results in an overvoltage. c) Sustained interruption Transient Transient is the part of change in a system variable that disappears during transition from one steady-state operating condition to another. Transient can be classified into two categories Impulsive transients Oscillatory transients a) Impulsive transients It is a type of transient disturbance that may enter the power system. It is defined by IEEE 1159 as a sudden, non power frequency change in the steady-state condition of voltage, current, or both that is unidirectional in polarity either primarily positive or negative. It is normally a single, very high impulse like lightning. Impulsive transients are not usually transmitted far from the source of where they enter the power system. However, in some cases, they may propagate for some distance along distribution utility lines. Also, it may considerably have different characteristics b) Oscillatory transients Oscillatory Transient is described as a sudden, non power frequency change in the steady-state condition of voltage, current, or both that has both positive and negative polarity values (bidirectional). The oscillatory transient is subdivided into three classes which are as follows: 3. Solution on power quality problems There are two general approaches to mitigate power quality problems. One approach is to ensure that the process equipment is less sensitive to disturbances, allowing it to ride-through the disturbances [6]. The other approach is to install a custom power device to suppress or counteract the disturbances. Many CUPS devices are commercially available in the market today such as, active power filters (APF), battery energy storage systems (BESS), distribution static synchronous compensators (DSTATCOM), distribution series capacitors (DSC), dynamic voltage restorer (DVR), power factor controller (PFC), surge arresters (SA), super conducting magnetic energy storage systems (SMES), static electronic tap changers (SETC), solid-state transfer switches (SSTS), solid-state circuit breaker (SSCB), static Var 2

3 compensator (SVC), thyristor switched capacitors (TSC) and uninterruptible power supplies (UPS). Focusing on the compensation of voltage dips the number of devices can be narrowed down, and in three types of devices have been compared, they are: - PI controller UPS: Uninterruptible Power Supply. This could be a static converter with double conversion to mitigate most type of power quality disturbances. DVR: Dynamic Voltage Restorer is a series-connected device, which corrects the voltage dip and restore the load voltage in case of a voltage dip. SSTS: Solid State Transfer Switch to change from a faulted feeder to a healthy feeder. 4. PI controller based system - In order to mitigate the simulated voltage sags in the test system of each compensation technique, also to compensate voltage sags in practical application, SPWMbased control scheme is implemented, with reference to DVR.Voltage sag is created on transmission line by a LG fault Load voltage is sensed and passed through a sequence analyser. The magnitude is compared with reference voltage (V ref ) [9].Sinusoidal Pulse width modulated (SPWM) control technique is applied for inverter switching so as to produce a three phase 50 Hz sinusoidal voltage at the load terminals. Chopping frequency is in the range of a few KHz. The IGBT inverter is controlled with PI controller in order to maintain 1 p.u. voltage at the load terminals i.e. considered as base voltage =1p.u. A proportional-integral (PI) controller shown in figure 5.1 drives the plant to be controlled with a weighted sum of the error (difference between the actual sensed output and desired set-point) and the integral of that value. An advantage of a proportional plus integral controller is that its integral term causes the steady-state error to be zero for a step input. PI controller input is an actuating signal which is the difference between the V ref and V in. Output of the controller block is of the form of an angle δ, which introduces additional phase-lag/lead in the three-phase voltages. The output of error detector is V ref - V in. V ref equal to 1 p.u. voltage V in voltage in p.u. at the load terminals. Fig.4.1 Schematic diagram of PI controller The controller output when compared at SPWM Signal generator results in the desired firing sequence. The sinusoidal voltage V control is phase-modulated of the angle δ or delta and the modulated three-phase voltages are given by V A = Sin (ωt +δ) V B = Sin (ωt+δ-2π/3) V C = Sin (ωt +δ+2π/3) The modulated angle is applied to the SPWM generators in phase A. The angles for phases B and C are shifted by 120 o and 240 o. In this PI controller, only voltage magnitude is taken as a feedback parameter in the control scheme. Figure4.2:Simulink model of test system for PI ontroller Actuating RESULT signal + Vref output of PI controller 3

4 constant voltage maintaining the continuity of production. Fig 2.3: Simulation of PI controller without fault for Voltage and Current CONCLUSION In this paper, the modelling and simulation of DVR controlled by PI Controller has been developed using Matlab/Simulink. For this controller, the simulation result shows that the DVR compensates the sag quickly (70μs) and provides excellent voltage regulation. DVR handles all types, balanced and unbalanced fault without any difficulties and injects the appropriate voltage component to correct any fault situation occurred in the supply voltage to keep the load voltage balanced and constant at the nominal value. However, the performance of DVR needs to be addressed for enhancement of the output voltage. Fig 2.4: Simulation of PI controller with fault for Voltage and Current Fig 2.5: Simulation of PI controller after compensation for Voltage and Current APPLICATION 1. In DVR parameters of the design of the PLL controller are not only dependent on the steady state and dynamic state, but also on practical conditions such as utility unbalance, voltage sag/swell magnitude, voltage harmonics, phase jumps and frequency variations 2. PI Controller based DVR to mitigate power quality and reduce the harmonics distortion of sensitive load 3. It is series connected power electronic based device that can quickly mitigate the voltage sag in the system and restore the load voltage to the pre fault value. the primary advantage of the DVR is keeping the users always online with high quality References 1. Woodley N.H., Senior Member, IEEE, Morgan L., Member, IEEE, Sundaram A., Member, IEEE, Experience with an Inverter-Based Dynamic Voltage Restorer, IEEE Transaction on Power delivery, Vol. 14, No. 3, July Chang C.S., Ho Y.S., The Influence of Motor Loads on the Voltage Restoration Capability of the Dynamic VoltageRestorer, PowerCon,International Conference, Vol. 2, pp , Zhan Changjiang, Ramachandaramurthy Vigna, Arulampalam Atputharajah, Fitzer Chris, Kromlidis Stylianos, Barnes Mike, Jenkins Nicholas, Dynamic Voltage Restorer Based on Voltage SVPWM Control, IEEE Transactions on Industry Applications, Vol. 37, No. 6, Nov-Dec Jurado Francisco, Member, IEEE, Manuel Valverde, University of Jaen, Fuzzy Logic Control of a Dynamic Voltage Restorer IEEE-ISIE, Vol. 2, pp , Jowder Al. Fawzi, Modeling and Simulation of Dynamic Voltage Restorer Based on Hysteresis Voltage Control 33 rd Annual Conference of the IEEE Industrial Electronics Society (IECON), Nov. 5-8, 2007, Taipei, Taiwan. 6. Kumar Ravi, Nagaraju Siva, J.N.T.U. College of Engineering, Kakinada, A.P, India, Simulation of D-STATCOM and DVR in Power APRN Journal of Engineering and Applied Sciences, ISSN , Vol. 2, No. 3, June Ashari M., Hiyama T., Pujiantara M., Suryoatmojo H., Purnomo M.H., A Novel Dynamic Voltage Restorer with Outage Handling Capability Using Fuzzy Logic Controller Innovative Computing, Information and Control, pp.51, 5-7 Sept Margo P., Heri P.M., Ashari M., Hendrik M., Hiyama T., Compensation of Balanced and Unbalanced 4

5 Voltage Sags using DVR Based on Fuzzy Polar Controller International Journal of Applied Engineering Research, ISSN , Vol. 3, No.3, pp , JayaPrakash P., Member, IEEE, Singh bhim, Senior Member, IEEE, Kothari D.P., Senior Member, IEEE, Chandra Ambrish, Senior Member, IEEE, Al-Haddad Kamal, Fellow, IEEE, Control of Reduced Rating DVR with Battery ESS IEEE, Chellali Benachaiba, Brahim Ferdi, Voltage Quality Improvement Using DVR, Electrical Power Quality and Utilisation, Vol. 14, No. 1, pp ,