Simple Boost Control Method Optimized with Genetic Algorithm for Z-Source Inverter

Transcription

1 JOURNAL OF ELECTRIC POWER AND ENERGY CONVERSION SYSTEMS (JEPECS) JEPECS VOL. 1, NO. 1, PP , SPRING 2016 ISSN: print/ online Simple Boost Control Method Optimized with Genetic Algorithm for Z-Source Inverter Hamed Hosseinnia, Daryoush Nazarpour and Saeed Sabernia In this paper, Genetic Algorithm (GA) optimization is proposed in order to tune parameters of simple boost control methods for the Z-source inverter. One of the characteristics of a good source is its quality that is measured by its lower harmonic. Impedance source inverter (ZSI) that acts as an interface between source and power grid, has harmonics in its output. GA optimization is used in simple boost control method to minimize these harmonics by setting control parameters on optimized values. The simulation has been carried out using MATLAB/Simulink and results prove that simple boost control method with optimized values has a lower total harmonic distortion (THD). Keywords: Genetic Algorithm, Optimization Problem, Simple Boost Control Method, Z-source Inverter (ZSI). Received March 2015; Revised August 2015; Accepted Feb I INTRODUCTION The voltage-source inverter (VSI) and current-source inverter (CSI) are two types of traditional power inverter typologies (Fig. 1) [1]. These two types of converter have some limitations. In most inverters two switches on the same leg cannot conduct simultaneously, because this will cause a short circuit across the source. One of the advantages of the impedance source converter over other converters is its impedance network that is placed between the source and inverter bridge and prevents input source short circuit and introduces shoot-through zero switching state. Also higher and better output can be expected with equal source conditions. Fig. 2 shows the general structure of z-source inverter [2]. The DC source can be either a voltage or current source. When it is in series with an inductor, it acts as a current source and when it is in parallel with a capacitor it becomes a voltage source. The diode is responsible for preventing the capacitor discharge through the DC input voltage. Z-source inverter performs as buck-boost converter. When the input voltage is not high enough to generate required output voltage, the shoot-through zero state is used to boost the voltage and when the input voltage is enough to make the desired output, shoot-trough zero state is not used and z-source inverter performs the buck conversion [3, 4]. II Z-SOURCE INVERTER A Modified ZSI The modified z-source inverter is shown in Fig. 3. As it can be seen the used element are exactly the same as the traditional type.it has been modified by changing diode and inverter bridge po- Department of Electrical Engineering, Urmia University Iran, Hhosseinnia66@yahoo.com. Department of Electrical Engineering, Urmia University Iran d.nazarpour@urmia.ac.ir, (Crossponding Author) Department of Electrical Engineering, Urmia University Iran Saeed.Sabernia@gmail.com. (a) Voltage source inverter (b) Current source inverter Figure 1: Traditional power inverter typologies. c 2016 Faculty Engineering, Shahed University, P.O.Box: , Tehran, Iran. Published by Shahed University Publishing Center.

2 33 H. HOSSEINNIA et al. OPTIMIZED BOOST CONTROL FOR Z-SOURCE INVERTER Figure 2: Z-source inverter. Figure 3: Improved ZSI. sition.this modified circuit limits inrush current because there is no path for startup current [5, 6]. B Simple boost control method In this section simple boost control method which is used to control the shoot-through duty ratio is introduced.in this method, two straight lines are employed in the usual PWM control method. These two straight lines are equal to the peak value of the three phase reference signals [7, 8]. When the carrier triangular wave is greater than the positive straight line or smaller than the negative line, the inverter works in shoot-through zero state that is prevented in traditional method. From the simple boost control method description, it can be concluded that carrier wave frequency and shoot-through are two main factors in this method and the output waveform is mostly affected by them. So by optimizing these two parameters, the output can be improved compared to that obtained from estimated values. Fig. 4 illustrates the simple boost control method [9, 10]. In simple boost control method, the shoot-through duty ratio decreases with the increasing of modulation index M. The maximum shoot-trough duty ratio of the simple boost control method is limited to (1-M), reaching zero at a modulation index of one. So to generate an output voltage with a high voltage gain, a small modulation index has to be used [11,12]. Because of the important role of M and carrier signal frequency, both of the parameters are used in the optimization problem. In fact, optimization is a trade-off between value of output voltage and total harmonic distortion (THD) [13 15]. In the next section, genetic algorithm is introduced. Figure 4: Simple boost control method. III GENTIC ALGORITHEM (GA) Genetic algorithm (GA) is a search technique used in computing to find true or approximate solutions to optimization and search problems. Genetic algorithms are categorized as global search heuristics. Genetic algorithms are a especial class of evolutionary algorithms that use inspired techniques by evolutionary biology such as inheritance, mutation, selection, and recombination [16]. What do we mean by genetic algorithm? It starts with a set of randomly generated solutions and recombines pairs of them by chance to produce offspring. Only the best offspring and parents are kept to produce the next generation. In Fig. 5 genetic algorithm flowchart has been illustrated. A Simple boost control method with genetic algorithm As described in the previous section, the shoot-trough has an important role in the operation of ZSI. This is because it makes it possible to buck or boost the input voltage. In this paper the genetic algorithm is selected to adjust parameters M and frequency of the carrier signal (f s ) in simple boost control method. Because of the importance of minimizing THD of output voltage [17, 18], the objective function is defined as below: J = t sim 0 t. T HD.dt (1)

3 JEPECS VOL. 1, NO. 1, PP , SPRING Figure 5: GA flowchart. Figure 7: System configuration. Figure 6: Voltage gain and stress versus modulation index. Figure 8: Output voltage with(m = 0.8 and f s = 1800). where, t sim is the simulation time. The output voltage gain (G) is denied as G = v p (2) 0.5v dc in which v p is the peak phase voltage of the inverter output. Based on the simple boost control of the z source inverter, the voltage gain can be obtained as G = M 2M 1 where M is peak of the reference voltage amplitude which is shown in Fig. 4 by V P or V N. The main aim of the optimization is to minimize the objective function in (1) due to constrain: (3) M min M M max f smin f s f smax (4) M min and M max are lower and upper constraints for modulation index. Also, f)min and f max are carrier frequency constraints that are given 2000 and 3000, respectively. In reference [19], the voltage stress across of the inverter switches was introduced for different modulation methods. In the boost control method, this voltage stress is (2G 1)v dc. Fig. 6 shows the variation of voltage gain and stress versus the modulation index. This figure illustrates that the modulation index range for having a gain voltage greater than one is 0.5 M 0.9. Also, upper and lower bounds of the carrier frequency are given f min = 2 khz and f max = 3 khz. The optimal modulation index and carrier frequency which are yielded from genetic algorithm, are M = and f s = 2 khz. IV SIMULATION RESULTS Simulation was conducted with the configuration shown in Fig. 5. The simulation parameters are:v dc = 250 v, L 1 = L 2 = 500 µh, C 1 = C 2 = 1.5 mf, L f = 500µH, C f = 5 µf and R L = 15 Ω. The simulation results with the arbitrarily chosen modulation index (M = 0.8) and carrier frequency (f s = 1.8 khz) are shown in Fig. 8 and Fig. 9. These figures show the output voltage and total harmonic distortion (THD) respectively [21]. Operation of genetic algorithm is shown in Fig. 10. In this figure, the minimum cost versus iteration is plotted. The minimum cost is the minimum objective function in each iteration. The simulation results with modulation index (M = ) and frequency of carrier signal (f s = 2000 khz) optimized by a genetic algorithm, for output voltage and THD analysis are presented in Fig. 11 and Fig. 12, respectively [22, 23]. In order to compare the result of the values obtained from genetic algorithm optimization with default values, output voltage harmonic is considered as the main factor and by using FFT diagrams and comparing them, output voltage harmonic reduction will be provided. As its name suggests, the boost converter output voltage is higher than the input voltage. By comparing the output voltage waveform that

4 35 H. HOSSEINNIA et al. OPTIMIZED BOOST CONTROL FOR Z-SOURCE INVERTER Figure 9: T HD = 5.48 (without optimization). Figure 11: Output voltage with optimized parameters. Figure 10: Operation of GA algorithm. Figure 12: T HD = 3.11 (with optimized parameters). obtained from arbitrarily chosen values and optimized values, it can be concluded that optimization has also had a positive effect on output voltage and it has a better waveform. Because of increased voltage in the optimized case, the voltage stress on the switches (2v c v o ) is decreased compared with normal condition considering optimized parameters (i.e. f s and M [24, 25]. V CONCLUSION As simulation results showed, by tuning carrier signal frequency and modulation index to optimized values, THD of the output is better than arbitrarily chosen values and the quality of ZSI output is improved. This verifies effectiveness of the simple boost control method with GA. Genetic Algorithm can be applied to any problem where optimization is required. Therefore, it can be applied in many usages in power electronics. The comparison of the results in this paper to similar work in the literature shows that the GA approach for the harmonic optimization of Z-Source inverter works properly. REFERENCES [1] M. H. Rashid, Power electronics, 2nd ed. Prentice Hall, [2] F. Z. Peng, Z-Source inverter, IEEE Transactions on Industry Application, vol. 39, no. 2, pp , [3] I. Boldea, R. Antal and N. Muntean, Modified Z-source Single Phase Inverter with Two Switches, presented at the IEEE International Symposium 2008, Industrial Electronics ISIE, Cambridge, [4] P. Chiang and et al. Pulse width modulation of Z-Source Inverters, IEEE Trans. on Power Electronics, vol. 20, no. 5, pp , [5] P. F. Zheng, M. Shen and Z. Qian, Maximum boost control of the current Z-Source inverter, IEEE Transactions on Power Electronics, vol. 20, no. 4, pp , [6] F. Gao, L. Poh Chiang, R. Teodorescu and F. Blaabjerg, Diode-Assisted Buck-Boost Voltage-Source Inverters, IEEE Trans. on Power Electronics, vol. 24, no. 9, pp , [7] B. J. Rabi and R. Arumugam, Harmonic Study and Comparison of Z- Source Inverter with Traditional inverters, ISSN American journal of applied Sciences, vol. 2, no. 10, pp , [8] G. Durgasukumar and M. K. Pathak THD Reduction Performance of Multi-Level Inverter fed Induction Motor Drive, presented at the India International Conference on Power Electronics (IICPE), [9] S. Kouro, P. Lezana, M. Angulo and J. Rodrguez, Multicarrier PWM With Dc-Link Ripple Feed forward Compensation For Multilevel Inverters, IEEE Trans. on Power Electronics, vol. 23, no. 1, pp , January [10] J. Holtz, Puls Width Modulation for Electronic Power Convertion, in proc IEEE, vol. 82, no. 10, pp , 1994.

5 JEPECS VOL. 1, NO. 1, PP , SPRING [11] J. Holtz and B. Beyer, Optimal Pulse Width Modulation for ac Servos and Low- Cost Industrial Drive, IEEE Trans. industry Application, vol. 30, no. 4, pp , [12] C. J. Gajanayake, L. F. Lin, G. Hoay, S. P. Lam and S. L. Kian, Extended Boost Z-Source Inverters, IEEE Trans. on Power Electronics, vol. 25, no. 10, pp , Oct [13] M. S. Shen, J. Wang, A. Joseph, F. Z. Peng, L. M. Tolbert and D. J. Adams, Constant boost control of Z-Source Inverter to minimize current Ripple and voltage stress, IEEE Trans. on Industry Applications, vol.42, no. 3, pp , May-Jun [14] P. C. Loh, F. G.ao, F. Blaabjerg and S. weilim, Operational analysis and modulation control of three-level Z-source inverters with enhanced output waveform quality, IEEE Trans. on Power Electronics, vol. 24, no.7, pp , July [15] F. Gao, P. C. Loh, F. Blaabjerg and C. J. Gajanayake, Operational analysis and comparative evaluation of Embedded Z-source inverter, presented at the IEEE PESC, Rhodes, [16] D. E. Goldberg, Genetic Algorithms in search,optimization and machine learning, Addison Wesley,1989. [17] Z. Du, L. M. Tolbert and J. N. Chiasson, Harmonic elimination for multi level converter with programmed PWM method, presented at the IEEE Industry Applications Soc. Annual Meeting, [18] M. J. Schutten and D. A. Torrey, Genetic algorithm for control of power converters, presented at IEEE Power electronics Speciali, [19] M. Shen and F. Z. Peng, Operation modes and characteristics of the Z-source inverter with small inductance, presented at the Industry Applications Conference, [20] B. J. Rabi, Minimization of harmonics in pwm inverters based on genetic algorithms, Journal of Applied Sciences, vol. 6, no. 9, pp , [21] Y. Tang, S. Xie, C. Zhang and Z. Xu, Improved Z-source inverter with reduced Z-source capacitor voltage stress and soft-start capability, IEEE Trans. on Power Electronics, vol. 24, no. 2, pp , [22] S. Rajakaruna and L. Jayawickrama, Steady state analysis and designing impedance network of Z-source inverters, IEEE Trans. on Industrial Electronics, vol. 57, no.7, pp , July [23] S. Rajakaruna and L. Jayawickrama, Steady-state analysis and designing imedance network of Z-source inverters, IEEE Trans. on industrial electronics, vol. 57, no.7, pp , July [24] S. M. Yousuf, P. Vijayadeepan and D. S. Latha, The Comperative THD Analysis of Neural Clamped Multilevel Z-Source Inverter using Novel Pwm Control Technique, International Journal of Modern Engineering Research (IJMER), vol.2, no. 3, pp , May-June [25] S. Yang, F. Z. Peng, Q. Lei, R. Inoshita and Z. Qian, Current-fed quasi- Z-source inverter with voltage buck-boost and regeneration capability, IEEE Trans. on Industry Applications, vol. 47, no. 2, pp , Hamed Hosseinnia was born in Khoy, Iran in He received his B.S.c degree from Azerbaijan University of Tarbiat Moallem (AUTM), Tabriz, Iran in He is currently M.S.c. student on Electrical engineering in Urmia University, Urmia, Iran. His research interests include power electronics, flexible AC transmission system (FACTS) and Power system Reliability. Daryoush Nazarpour was born in Urmia, Iran in He received his B.Sc. degree from Iran University of Science and Technology, Tehran, Iran in 1982 and the M.Sc. degree from Faculty of Engineering, University of Tabriz, Tabriz, Iran in He received the Ph.D. degree from Tabriz University, in 2005 in Electrical Power Engineering. He is now an assistant professor in Urmia University, Iran. His research interests include power electronics, and flexible AC transmission system (FACTS). Saeed Sabernia was born in Urmia in He received his B.S. in Electrical Engineering from Urmia University, Iran in He is currently pursuing a M.S. in Power (Systems) Engineering. His current research interests are power electronics, FACTS and smart grids.