Pulse width modulation.AC to AC, Papers of Electrical Engineering

Download Pulse width modulation.AC to AC and more Papers Electrical Engineering in PDF only on Docsity! AC to AC Voltage Controller Using PWM Technique Without DC Link Y. B. Shukla1, S. K. Joshi2, R. J. Makwana3, A.A.Daiya4 1 E & C Engineering Department, SVIT, Vasad , e-mail : ybshukla2003@yahoo.com 2 Department of Electrical Engineering, The M.S.University of Baroda, e-mail : skjoshi@ieee.org 3 E & C Engineering Department, SVIT, Vasad , e-mail : renuka88@yahoo.com 4 Associate Prof, Electronics Dept, BVM V.V.Nagar, e-mail: daiyaajay@yahoo.in Abstract—The power factor can be improved and more number of harmonics can be reduced using the pulse width modulation techniques of a voltage waveform. This paper discusses various PWM techniques on the AC/AC voltage controller without DC link. The paper also discusses two configurations of PWM technique for harmonics reduction and improvement of power factor and output voltage. Fast switching device, PWM techniques can be applied to AC/AC voltage controllers for producing variable output voltage with a better input Power Factor. The theoretical results are validated through simulation studies using PSIM software package. Keywords-AC to AC voltage converter; PWM; Harmonic; Pulse width control; Carrier frequency; I. INTRODUCTION PWM AC to AC voltage controllers are widely used in UPS and high power flexible AC transmission systems. These systems need switching elements which can bear high voltage. [1-3] AC/AC line-commutated phase angle control or integral cycle control with thyristors technology have been widely used; however, this technique has many drawbacks such as, reduction of power factor at the input side, plentiful lower order harmonics in supplies, and discontinuity of power flow to the load sides.[4] The pulse width control using variable DC based method and the frequency control using carrier frequency based method can theoretically provide high quality output among all PWM methods with simple design approach. In PWM control, the converter switches are turned on and off several times during a half cycle and the output voltage can be controlled by varying width of pulse. The lower order harmonics can be reduced by selecting the number of pulses per cycle.. II. PRINCIPLE OF OPERATION AND PROBLEM FORMULATION Figure 1 shows the circuit configuration of PWM AC to AC voltage converter, which is composed of two bidirectional power switches, one connected in series and the other in parallel with load, the series connected switches S1 & S2 regulate the power delivered to the load and the parallel S1 ' & S2 ' provide a freewheeling path to discharge the stored energy when the series one turned off. The switches are assumed to have bi-directional voltage blocking ability as well as bidirectional current conduction and turn off capability. The present paper uses the switch configuration of inverse parallel connection of two convention IGBT's and two diodes, the two diodes prevent reverse voltage from appearing across switches. Figure 1. Circuit Diagram of AC to AC Voltage Converter 13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India National Conference on Recent Trends in Engineering & Technology Figure 2. Gate signal of AC to AC Voltage Converter When a switching function shown in Figure 2 is applied to AC/AC voltage controller, the output voltage appears in PWM forms at the load terminals. Figure 3. Output Voltage Waveform Fig. 3shows the idealized output voltage waveform from the AC/AC voltage controller. The general Fourier series expression expressed in terms of n switching points variables for the voltage is Where Bn = 0 for n = 1, 2, 3 ….... Due to half wave symmetry of waveform III. OVERVIEW OF CONTROL STRATEGY A. The pulse width control using variable DC method: The gating signals of S1 ' & S2 ' switches shown in Figure 2 can be controlled by DC reference based or control strategy and these signals are used to control S1 & S2 switching duration respectively. In this technique, as the reference DC signal vary, output voltage varies proportionally and reduction in harmonics. B. The frequency control using carrier frequency method: Varying the frequency of clock signal can control the no of pulses in gating signals of S1 & S2 switches shown in Figure 2. In this technique, when the no of pulses vary then harmonics are eliminated/reduced and obtained constant voltage. IV. SIMULATION RESULTS TABLE I. SIMULATED CIRCUIT PARAMETERS Parameter Symbol Value Maximum Supply Voltage Vm 110 Volt Rated power P 1.21 K Watt Load resistance R 100 ohm Load inductance L 6.1 mh A. The pulse width control using variable DC method: Frequency of carrier signal= 250 Hz Simulation summaries of the output voltage and harmonic with DC reference are given in Table II. Figure 4, Figure 6 and Figure 5 shows output voltage with DC reference 1V, 10V and FFT of output voltage, respectively. TABLE II. VARIATIONS OF OUTPUT VOLTAGE AND HARMONIC WITH DC REFERENCE Harmonic Voltage (Volts)Sr. No. DC Reference (Volts) Output voltage (Volts) I ST III RD V TH 1 1 2.08 28.3 6.6 22.4 2 4 2.08 28.3 6.6 22.4 3 6 2.08 28.3 6.6 22.4 4 8 1.8 25.5 2.9 21.3 5 10 1 15.3 3.53 9.75 13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India National Conference on Recent Trends in Engineering & Technology