Improvement of AC Power Quality of Three Phase Inverter Using Voltage Drive Mode

Improvement of AC Power Quality of Three Phase Inverter Using Voltage Drive Mode Abstract - The electricity requirements of the world including India are increasing at alarming rate and the power demand has been running ahead of supply renewable. The recent severe energy crisis has forced the world to develop new and alternative methods of power generation. Solar power resources have been increased since last decade. The future visions of Power System contain penetration of inverter which is used to convert power from DC (direct current) to AC (alternating current). The behavior of this device is dependent upon the control algorithm. In particularly the Voltage Drive Mode is used to improve the power quality of the three phase inverter. Sinusoidal current generation provides better effects on power quality. The Voltage Drive Mode aims for perfectly balanced sinusoidal voltage on all the three phases. The three phase inverter can be split into two circuits: power circuit and control circuit. The power circuit consists of fully controlled inverter circuit, which can convert input DC voltage into AC voltage with the help of firing pulses which are being produced by the control circuit. In this project, the Space Vector Pulse Width Modulation (SVPWM) is used to control the switching time of PWM. The harmonic distortion can be reduced by using this. Index Terms Voltage Drive Mode, PI controller, Space Vector Pulse Width Modulation, Power Quality, Total Harmonic Distortion I. INTRODUCTION Now a day the power demand plays a major role in our world due to degradation of the fossil fuels. Recently, renewable energy sources have attracted a great attention in research fields due to the fact that they provide the solution to the power demand problem without creating any pollution. Out of renewable energy sources solar energy based power production is most suitable in India as it lies nearer to the equatorial region and can get solar power mostly throughout the year. The sun is an inexhaustible power supply. It brings more than sufficient energy to our planet every single day to meet a full year s worth of energy for everyone on earth [12]. A. Ramya 1, T.Logeswaran 2. A.Senthil Kumar 3 1 Kongu Engineering College,Perundurai 2 Kongu Engineering College, Perundurai. 3 College of Engineering and Technology, Pollachi 1 ramyaanbu91@gmail.com A solar panel converts only 30-40% of the incident solar radiations into electrical energy. This converted energy has tobe effectively utilized [4]. The output of the solar panel is fed to the three phase inverter [10]. A device which converts DC input to AC output at desired amplitude and frequency is called inverter. The DC input is obtained from a photovoltaic array of solar panels. There are different types of source inverters are used, here Voltage Source Inverter is used [15]. The voltage source inverter has DC voltage source at the input terminal which has small impedance. There are four control modes are obtained for the improvement of Power Quality. From that the voltagedrive mode it provides the good ac power quality but at the expense of high dc bus ripple. The Sinusoidal balanced current mode and dual-sequence controllers provide relatively low dc bus ripple and relatively small effects on power quality. The high-bandwidth dc bus ripple minimization mode works well in the environment of the low grid impedance but it is highly unsuitable within higher impedance at low switching frequencies [16]. Some specialized inverter applications are designed to provide optimum power quality to local sensitive loads within grid environments [5]-[7]. As such inverters become more common place, their combined effect on the ac power network becomes more significant. Thus, their aggregated impact on ac voltage power quality becomes a more significant concern than it has been in the past [11]. The Voltage Drive Mode scheme aims for perfectly balanced, sinusoidal voltage on all the three phases. II. BLOCK CONFIGURATION The output of the solar panel is considered as DC source. The output DC supply of the solar panel is converted to AC supply by means of an inverter circuit i.e. the three phase inverter (VSI). The load (RL) is connected with the three phase inverter. From the three phase inverter harmonics is produced. The harmonics which was produced by the three phase inverter affects the quality of the power. Normally filters are used to reduce the unbalances [9]. The main concept of this paper is to improve power quality. By undergoing the closed loop the harmonics is reduced. The three phase voltage 1363

and the current are taken as the reference sources for the closed loop system of the Voltage Drive Mode. The Voltage Drive Mode balances the current on the all the three phases. The SVPWM generate the gate pulses to the three phase inverter in the case of reduced harmonic distortion. Based on the operating mode signal, the proper control has to choose. Under the closed loop system the quality of the power is improved by reduction of the total harmonic distortion. Fig. 2. Block Diagram of the Voltage Drive Mode Fig. 1.Block Diagram of Improvement of Power Quality III. VOLTAGE DRIVE MODE Among the four control modes in this paper the Sinusoidal Balanced Current Mode is considered for the power quality improvement. The Voltage Drive Mode reduces the DC bus ripple. The output voltage and current of the three phase inverter is taken as references to the closed loop system of Voltage Drive Mode. The line voltage is taken as the reference source to the Phase Locked Loop (PLL). Synchronous Frame PLL (SF-PLL) is widely used in threephase systems. The instantaneous phase angle θ is detected by synchronizing the PLL rotating reference frame to the utility voltage vector. The PLL locks the phase and provide θ value as input to the transformation block. The θ and three phase current are taken as the input to the Park Transformation. The Park Transformation transforms the three variables Ia, Ib, Ic into two variables Id and Iq. By using the PI controller the current is balanced. A proportional controller (Kp) has the effect of reducing the rise time but never eliminate the steady-state error. An integral control (Ki) has the effect of eliminating the steady-state error but it may make the transient response worse. By using PI controller adjustment of each Kp and Ki value until obtaining a desired overall response [13]. The last step requires a transformation from a two-dimensional coordinate space back to the threedimensional space. The output reference voltage obtained by the voltage and current loop is converted into three phase quantity through Clarke s transformation. The Inverse Park Transformation converts the Vdq0 into three phase of Vabc. The transformation is the same for the case of a three phase current; it simply replace the variables of Va, Vb, Vc, Vd, Vq and V0 with the Ia, Ib, Ic, Id, Iq and I0 variables. By using the Clark Transformation the three phase variable is converted into two phase variables. Finally it s given to the SVPWM which provides switching pulses to the inverter [3]. IV. SPACE VECTOR PULSE WIDTH MODULATION There are different types of modulation strategies such as PWM, SVPWM, etc., the Space Vector Pulse width Modulation is specially adapted for good utilization of the DC link voltage, low current ripple and suitable for high voltage, high power applications, such as renewable power generation [8][1]. The Space Vector Pulse Width Modulation is used to give the switching time to the PWM i.e., it act as controller of the PWM. Based on the switching time the PWM generates the gate pulse to the three phase inverter [2]. In a three-level inverter, each space vector diagram is divided into six sectors. For simplicity here only the switching patterns for Sector A will be defined so that calculation for the other sectors will be similar. Sector A is divided into four regions as where all the possible switching states for each region are given as well. SVPWM for three level inverters can be implemented by using the steps of sector determination, determination of the region in the sector, calculating the switching times, T 1, T 2, T 3 and finding the switching states. The complexity is due to the difficulty in determining the location of the reference vector, the calculation of on times and the determination and selection of switching states. 1364

distortion factor and lower order harmonics are reduced significantly. Fig. 3. Sectors of Three level Space Vector The space vector diagram of any three-phase inverter consists of six sectors. The tip of the reference vector can be located within any triangle. Each vertex of any triangle in the SVPWM represents a switching vector. A switching vector which represents one or more switching states depending on its location. The SVPWM is performed by suitable selecting and executing the switching states of the triangle for the respective on-times which is shown in the below Table.I. The performance of the inverter significantly depends on the selection of these switching states. There are six sectors (S1-S6) and a total of six switching states. The principle of SVPWM method is that the command voltage vector is approximately calculated by using three adjacent vectors. Table. 1 Switching Table Of Svpwm The step by step development of a Matlab simulation model for implementing SVPWM. The input given to the three phase inverter is a constant DC link voltage. The Switching time calculation: The switching time and corresponding switch state for each power switch is calculated and a space vector modulation block is created which gives the gating pulse for the switches used in the three phase inverter designed. The three-phase inverter block: This block is built to simulate a voltage source inverter. The input frequency is kept at 50 Hz. The output is seen to be sinusoidal without any ripple except the switching harmonics. In this method, the width of each pulse is varied in proportion to the amplitude of a sine wave evaluated at the centre of the same pulse. The harmonic The gating signals are generated by comparing a sinusoidal reference signal with a triangular carrier wave of frequency. The number of pulses per half cycle depends on the carrier frequency. All the sine triangle modulations are the same in the sense that that the intersection between the carrier triangular waveform and the modulation signal determines the switching instances. The main variations are in the exact shape of the carrier waveform and/or the modulating signal that can be augmented with the third harmonic for increased voltage gain and so on. In three phase sinusoidal pulse width modulation, there are three reference waves each shifted by 120. A carrier signal is compared with the reference signal corresponding to a phase to generate the gating signal for that phase. PWM can be generated by analogue or digital control electronics. The advantage of digital controls over analogue controls is, Stability (no drift, offsets or aging effects).the switching time and corresponding switching state for each power switch is calculated and a space vector modulation block is created which gives the gating pulse for the switches used in the three phase inverter designed. The three phase inverter circuit is designed a using matlab. The design procedure is as follows: The inverter consists of three IGBT arms which forms a three phase inverter. The input is a DC voltage source. The gate pulse is given by the Pulse Width Modulation block. The timing signals, timing generation and the timing calculations, the sequence of switching devices are designed are given by the space vector modulation block. The simulation of the circuit is carried out by matlab. V. SIMULATION RESULTS The results of the three phase inverter circuit and the blocks were simulated by using the MATLAB/Simulink. From the Fig. 6 the output of the solar panel is obtained as the DC Voltage source of about 90.70V which gives the input voltage of the three phase inverter by undergoing closed loop of the Voltage Drive Mode. The simulation is carried out for a cell surface temperature of 40 C and solar irradiation of about 1.22 W/m 2. 1365

Fig. 4. Output Voltage of the Solar Panel Fig. 7. Output of PLL The Phase locked loop locks the three phase and provide the θ value. From PLL the reference voltage is synchronized with the output voltage of the PLL which is shown in the Fig. 8. Fig. 5. Output Voltage of the Three Phase Inverter Fig. 5 shows that the output voltage of the three phase inverter is about 90V by using the Voltage Drive Mode. Fig. 8. Output Power of Three Phase Inverter without SVPWM Fig. 6. Output Current of the Three Phase Inverter Fig. 6 shows that the output of phase current of the three phase inverter. The value is 2.8A through the closed loop system of the Sinusoidal Balanced Current Mode. By using the Voltage Drive Mode the current on all the phases is balanced. Fig. 9. Output Voltage of Three Phase Inverter with SVPWM From the Fig. 9 it can be seen that the quality of the power is improved. 1366

Fig. 13. FFT Analysis showing THD of the Phase Current with SVPWM Fig. 10. FFT Analysis showing THD of the Line Voltage without SVPWM Fig. 12 shows the FFT analysis of the phase current of the three phase inverter without SVPWM and it shows that the THD is about 4.83%. From the Fig. 13, the THD of the phase current of the three phase inverter with SVPWM is about 2.85%. From the FFT analysis it can be shown that the harmonic distortion is reduced by using the SVPWM. Fig. 11. FFT Analysis showing THD of the Line Voltage with SVPWM Fig. 10 shows the FFT analysis of the line voltage of the three phase inverter without SVPWM and it shows that the THD is about 7.03%.From the Fig. 11, the THD of the line voltage of the three phase inverter with SVPWM is about 3.36%. VI.CONCLUSION The paper presented the control s design to improve the power quality by reducing the harmonic distortion. The simulation results of solar panel and three phase inverter are presented. The output Voltage and output power of the PV panel are obtained. All the simulations are performed in matlab/simulink modeling and simulation platform. The improvement of power quality was obtained by the control mode of the Voltage Drive Mode and the Space Vector Pulse Width Modulation is used to reduce the harmonic distortion. Total Harmonic Distortion of the three phase current is reduced to 2.85%. By reducing the total harmonic distortion the quality of the power is improved. REFERENCES Fig. 12. FFT Analysis showing THD of the phase current without SVPWM [1] D.Banupriya, K.Sheela Sobana Rani Space Vector Modulation Based Total Harmonic Distortion Minimization In Induction Motor IEEJ Trans Vol 04 no 01 pp 962-965 [2] Hava.A.M and Un.E, A high-performance PWM algorithm for Common mode voltage reduction in three-phase voltage source inverters, IEEE Trans Power Electronic., vol. 26, no. 7, pp. 1998 2008,2011. [3] Kalpesh H. Bhalodi and Pramod Agarwal, Space Vector Modulation with DC-Link Voltage Balancing Control for Three-Level Inverters, International Journal of Recent Trends in Engineering, vol 1, no. 3,2009. [4] Miguel Castilla, Jaume Miret, Jorge Luis Sosa and Luis Garcia de Vicuna, Grid-Fault Control Scheme for Three-Phase Photovoltaic Inverters with adjustable Power Quality Characteristics, IEEE Trans.Power Electronics, vol. 25, no. 12,2010. 1367

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