DIGITAL SIMULATIO OF A DY AMIC VOLTAGE RESTORER SYSTEM P. USHA RA I, S. RAMA REDDY

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1 ELECTROTECHNICS, ELECTRONICS, AUTOMATIC CONTROL, INFORMATICS DIGITAL SIMULATIO OF A DY AMIC VOLTAGE RESTORER SYSTEM P. USHA RA I, S. RAMA REDDY Department of Electrical and Electronics Enineerin, Jerusalem Collee of Enineerin,Centre for collaboratie research with Anna Uniersity, Chennai, India. pusharani7@yahoo.com Abstract: The Dynamic Voltae Restorer (DVR), a custom power deice, has been used to protect sensitie loads from the effect of oltae sas / swells on the distribution feeder. The DVR s main function is to inject the difference in oltae to the power line and thus maintain the load side oltae at the optimum alue. This paper presents the modelin and closed loop control aspects of the DVR system with an H bride inerter workin aainst oltae sas / swells by simulation. The power circuit of the DVR system with an H bride inerter with the control techniques used for compensation is explained. The proposed DVR is modeled and simulated usin MATLAB/ SIMULINK software. The simulation results show that the control approach performs ery effectiely and yields excellent compensation for compensatin oltae sas / swells. Keywords: Dynamic Voltae Restorer (DVR), Voltae Source Conerter (VSC), Total Harmonic Distortion (THD) INTRODUCTION A common characteristic of most electronics is that they are sensitie to oltae ariations. Computers and other sensitie loads can lower their performance or een shutdown the process they are in control due to those ariations. Voltae ariations can be classified as disturbances that produce oltaes below the nominal alue, which are called oltae sas, and disturbances that produce oltaes aboe the nominal alue, which are called oltae swells. Voltae sa is defined as a sudden reduction of supply oltae down 9% to % of nominal, followed by a recoery after a short period of time. A typical duration of sa is ms to minute. Voltae sa can cause loss of production in automated processes since oltae sa can trip a motor or cause its controller to malfunction. Voltae swell is defined as sudden increasin of supply oltae up % to 8% in RMS oltae at the fundamental frequency with duration from ms to minute. Switchin off a lare inductie load or enerizin a lare capacitor bank is atypical system eent that causes swells. Durin power disturbances Dynamic Voltae Restorer (DVR) installed in front of a critical load will appropriately proide correction to that load only. Also DVR cannot proide compensation durin full power interruptions. Voltae sa is a momentary decrease in RMS oltae lastin between half a cycle to a few seconds. It is enerally caused by faults in the power system and is characterized by its manitude and duration. Voltae sa manitude is defined as the net RMS oltae durin oltae sa, which is usually in per unit of the nominal oltae leel. The oltae sa manitude depends on arious factors like the type of fault, the location of the fault and the fault impedance. The This paper was recommended for publication by Emil Rosu 64

2 duration of the oltae sa depends on how fast the fault is cleared by the protectie deice. In short, oltae sa will last till the fault is cleared (Aileswari, et al., 5). The structures and control of a dynamic oltae restorer that injects in series with a distribution feeder is described (Arindam and Ledwich, ). A detailed analysis of the load oltae compensation for the DVR that is used for enhancin power quality is presented (Boonchiam, et al., 6) A fast dynamic control scheme for a capacitorsupported sinle phase dynamic oltae restorer for inductie loads are described (Naiman Ho., et al., 8). A new matrix method, which is able to compute the phase shift and a reduction of the supply oltae much quicker than the Fourier transform or phase locked loop is presented (Fitzer, et al., 4). A feed forward and state feedback based controller structure for DVR systems is described (Hyosun and Seun Ki Sul, 5). A new DVR circuit topoloy which has the ability to mitiate lon duration oltae sas with comparatiely small enery storae capacitors are presented (Mahinda Vilathamuwa and Wijekoon, ). The modelin aspects of seeral types of DVR workin aainst arious oltae sas by simulation in PSCAD/EMTDC are presented (Nuyen and Tapan, 4). A fast detection method for oltae disturbances is explored. The alorithm is based on the theory that allows a set of three phase oltaes be represented as dc oltaes in a dq synchronous rotatin frame.(monterohernandez and Enjeti, 5). The application of the DVR on power distribution systems for mitiation of oltae sas/ swells at critical loads is presented (Boonchiam and Mithlananthan, 6). A control system based on a repetitie controller to compensate for power quality disturbances is presented (Roncero, et al., 9). to the prefault leel durin a oltae sa as depicted in Fi.. To restore the load oltae, the DVR should inject the equialent of the dropped oltae, which represents the difference between the prefault and fault oltae throuh a series connected transformer. Voltae restoration of the DVR inoles the injection of actie power and enery from the DVR to the distribution system. Howeer, the capability of the enery storae capacitors in the DVR is limited. The DVR Power Circuit can be diided into four main blocks as shown in Fi.. They are the Enery storae deice, the PWM inerter unit, the Filter Circuit and the Series injection transformer. 3.CONTROL STRATEGY The control stratey is desined usin the inphase compensation technique. Voltae sa is detected as a sudden chane in the manitude of the load oltae. Power Circuit of DVR Fi.. Basic Operation of DVR In this paper, the modelin and control of the DVR for protection aainst oltae sa / swell is described usin the MATLAB packae. Simulation results are presented to show the effectieness of the proposed control method. This paper is oranized as follows: A eneral description of the DVR circuit topoloy is presented in section. Section 3 presents a control stratey of the DVR, while section 4 presents the DVR system with an H bride inerter power circuit. The effectieness of the proposed DVR closed loop control system is ealuated and the simulation results are ien in section 5. Fi.. Power Circuit of DVR. DVR IN SAG MITIGATION The Dynamic Voltae Restorer, installed between the supply and a critical load can restore the load oltae Fi.3. Block Diaram of Control Stratey 65

3 To rectify the oltae dip, the difference between the presa oltae and the sa oltae has to be injected into the distribution line. Fi.3. shows the basic blocks used for the control stratey. 4. DVR POWER CIRCUIT IN SIMULATION DVR system is simulated usin MATLAB and the results are presented here. 4.. Closed Loop Controlled DVR system with an H bride inerter A typical Closed Loop Controlled DVR with an H bride inerter is used in a simple power system to protect a sensitie load in a lare distribution system as presented in Fi.4. Its control system block diaram is shown in Fi.5. The inerter is a fourpulse switch controlled bride. The currents follow different directions at outputs dependin on the control scheme, eentually supplyin AC output power to the critical load durin power disturbances. The control of this bride lies in the control of the switch firin anles. The time to open and close ates will be determined by the control system. To model a DVR protectin a sensitie load aainst oltae sas a simple method of usin the measurement of a sinle phase RMS output oltae for controllin sinals can be applied. The amplitude modulation is then used. In addition to proide appropriate firin anles to switches, a switchin control usin the PWM technique is employed. Subsystem is shown in Fi.6. It consists of a full bride inerter with a filter. Pulse Width Modulation technique was used to control the H bride inerter. Subsystem consists of a rectifier with a capacitor filter as shown in Fi SIMULATION RESULTS The simulation is done usin MATLAB and the results are presented here. Initially the system was subjected to sa of 33 % manitude and.3s duration. Simulation is done and transient performance at sa front and recoery was obsered. Fi.8. shows the simulation result for the closed loop DVR system response to the oltae sa. 5ohm 3mH.ohm.mH 3e8 5, 44.35e3..8, 44.35e / 6/ ohm mh 65 Constant In Gain3 delay >= AND. ohm 35 S S3.H.uf.H.uf ohm Conn Conn 4V In Conn Conn Subsystem 8 ohm 8mH Conn Out Conn Gain s Interator ms delay AND S4 S Subsystem Scope Fi.4. Closed loop DVR with an HBride inerter Fi.6. Sub System of closed loop DVR with an H Bride inerter Diode Diode3 Conn Conn Diode Diode UF ohm Out Fi.5. Block diaram of Control system Fi.7. Sub System of closed loop DVR with an H Bride inerter 66

4 The first raph shows the input supply oltae. The second raph indicates the injected oltae and the third raph shows the compensated load oltae after oltae injection. The system was subjected to swell of 6 % manitude and.3s duration. Simulation is done and transient performance at swell front and recoery was obsered. Fi.9. shows the response of the closed loop DVR system to the oltae swell. The first raph shows the sa in oltae. The second raph indicates the injected oltae and the third raph shows the compensated load oltae after oltae injection. The driin pulses of the inerter switches are shown in Fi.. The output of the inerter with and without filter is shown in Fi.. The Fi.. shows the FFT analysis of closed loop DVR system. The THD alue is 4.93%. uncompensatedolt (V) injectedolt (V) p p p3 p Fi.. Driin pulses of inerter switches V before filter(v) V after filter(v) Fi.. Inerter output with & without filter compensatedolt (V) Fi.8. DVR response to oltae sa uncompensated olt(v) injected olt(v) compensated olt(v) Fi.9. DVR response to oltae swell Fi.. FFT analysis for the output of DVR CONCLUSION The modellin and simulation of a DVR system usin MATLAB has been presented. DVR is an effectie custom power deice for oltae sa / swell mitiation. The impact of oltae sa on sensitie equipment is seere. Therefore, DVR is considered to be an efficient solution due to its low cost, small size and fast response. 67

5 The simulation results indicate that the implemented control stratey compensates for oltae sas / swells with hih accuracy. The results show that the control technique is simple and efficient method for oltae sa / swell compensation. REFERENCES Aileswari Ramaswany, K., K.R. Renan and R.N. Mukherjee (5). Dynamic Voltae Restorer for Voltae Sa Compensation. Conference on Power Electronics and Drie Systems, Vol., pp Arindam, G. and G. Ledwich (). Structures and Control of a Dynamic Voltae Reulator. Proceedins of the IEEE Industrial Electronics Conference, pp 73. Boonchiam, P., P.Apiratikul and N. Mithulanathan(6). Detailed Analysis of Load Voltae Compensation for Dynamic Voltae Restorer. IEEE Transactions on Power Deliery. Boonchiam, P. and N. Mithlananthan (6). Understandin of dynamic oltae restorers throuh MATLAB simulation. Thammasat Ins.J.Sc.Tech., Vol., No.3.,pp.6. Naiman Ho, C., H.S.H. Chun and T.K. Keith (8). Desin and Implementation of a Fast Dynamic Control Scheme for Capacitor Supported Dynamic Voltae Restorers. IEEE Transactions on Power Electronics, Vol.3, No., pp Fitzer, C., M. Barnes and P. Green (4). Voltae sa detection technique for a dynamic oltae restorer. IEEE transactions on industry applications, Vol.4.No.. Hyosun, K. and S. SeunKi (5). Compensation Voltae Control in Dynamic Voltae Restorers by Use of Feed Forward and State Feedback Scheme. IEEE transactions on power electronics. Vol., No.5, pp Mahinda Vilathamuwa, D. and H.M. Wijekoon (). Control and Analysis of a New Dynamic Voltae Restorer Circuit Topoloy for Mitiatin Lon Duration Voltae Sas. Proceedins of the IEEE Industrial Electronics Conference. pp 5. Nuyen, P.T. and K.S., Tapana (4). DVR aainst Balanced and Unbalanced Load Proceedins of the IEEE Industrial Electronics Conference. pp.6. MonteroHernandez, O.C., and P.N., Enjeti (5).A fast Detection Alorithm Suitable for Mitiation of Numerous Power Quality Disturbances. IEEE transactions on industry applications. Vol.4, No.6, pp Roncero, P., J., Enrique and A. Garcia (9). A Versatile Control Scheme for a Dynamic Voltae Restorer for Power Quality Improement. IEEE transactions on power deliery, Vol.4, No., pp