Indian Journal of Science and Technology, Vol 8(S2), 278 283, January 2015 ISSN (Online) : 0974-5645 ISSN (Print) : 0974-6846 DOI:.10.17485/ijst/2015/v8iS2/71717 Implementation of Fuzzy Logic Controller for Cascaded Multilevel Inverter with Reduced Number of Components K. Yamini *, B. Vasudha, Avinash Sharma and P. Ponnambalam School of Electrical Engineering, VIT University, Vellore, Tamil Nadu; yaminieng@gmail.com, b.vasudha250@gmail.com, avinash_sharma3824@yahoo.in, ponnambalam.p@vit.ac.in Abstract In this paper, cascaded multilevel inverter with fuzzy closed loop control is proposed. The proposed cascaded multilevel inverter needs lower number of dc voltage sources, power semiconductor switches hence the complexity and the cost of the overall system decreases. Pulses for the switches are generated by using sinusoidal pulse width modulation. Procedure to generate voltage levels is developed. Closed loop control using fuzzy logic is used to improve the RMS output voltage. Simulation results are observed for seven level inverter with fuzzy logic. Keywords: Cascaded Multi Inverter, Fuzzy Logic, Power Semiconductor Switches 1. Introduction Recently the demand for multilevel inverters is increasing because of their high performance like quality of power and minimum harmonics, low switching losses and good EMI on low and medium levels of voltage. These inverters can generate an output voltage waveform in the form of steps with the less number of direct current voltage sources as the input and proper arrangement of semiconductor switches. Generally, there are three different types of multilevel inverters: Neutral clamped MLI, capacitor-mli and cascaded MLI. Further in cascaded multilevel two different varieties are there symmetric MLI and asymmetric MLI. In symmetric type the magnitude of dc voltage of all inverters are equal. Where as in asymmetric type magnitudes are different with this we can generate more voltage levels. Various varieties of cascaded multilevel inverters are presented 1. The major factor using these structures is because of lower number of dc voltage sources and switches so cost of the inverter will decrease. In case of conventional one it uses only one voltage source and four power switches. Disadvantage with the use of conventional one is of low output voltage levels. In this paper to avoid the drawbacks with use of conventional one, a cascaded multilevel inverter is proposed to get more levels of output voltage with lower dc voltages and lower number of switches. Procedure to obtain output voltage levels is also presented. This proposed one is compared with the conventional one on various aspects. Fuzzy logic control can provide solution to the system even where there is no mathematical model. Fuzzy logic works on the rules given by the user. So the user can modify the rules to get better performance. Fuzzy logic is flexible it can be model for any number of inputs and outputs as it is based on the rules. 2. System Configuration In Figure 1, two different types of seven levels inverter is proposed. This one we can obtain with use of extra two switches and one voltage source compared to the conventional one 2. It consists of six switches and (SP1, *Author for correspondence
K. Yamini, B. Vasudha, Avinash Sharma and P. Ponnambalam SP2, SQ1, SQ2, SU, SV), and two voltage sources of VP1 and VQ1. From Figure 1 each switch consists (IGBT) and one body diode across it, so that it can block voltage in one direction and can conduct current in two directions. Turn-on of switches SP1, SP2 at the same time will cause the short circuit. So it should be avoided. Similarly for SQ1, SQ2 and SU, SV. Connections of these topologies with different voltage polarity are shown in Figure. Table shows the switching states. If the two voltage sources are equal we can get only three levels, if we use different sources voltage levels increases with the same number of switches. The voltages of VP1 and VQ1 should be 3pu and 1pu for Figure 1 and it should be 2pu and 1pu for Figure 2. From the Figure 1 terminals of the voltage VP1 and VQ1 are same. Procedure for generating voltage levels is shown in Table 1 From the Figure 2 terminals of the voltage VP1 and VQ1 are opposite. Procedure for generating voltage levels is shown in Table 2. Figure 1. Seven level inverter configuration 1. Table 1. Output voltage levels of seven level inverter configuration 1 SNO SP1 SP2 SQ1 SQ2 SU SV V0 1 1 0 0 1 0 1 VP1 2 1 0 0 1 1 0 VQ1 3 1 0 1 0 0 1 VP1-VQ1 4 1/0 0/1 1/0 0/1 1/0 0/1 0 5 0 1 1 0 1 0 VP1 6 0 1 1 0 0 1 VQ1 7 0 1 0 1 1 0 (VP1 V1) Table 2. Output voltage levels of seven level inverter configuration 2 SNO SP1 SP2 SQ1 SQ2 SU SV V0 1 1 0 0 1 0 1 VP1 2 1 0 0 1 1 0 VQ1 3 1 0 1 0 0 1 VP1-VQ1 4 1/0 0/1 1/0 0/1 1/0 0/1 0 5 0 1 1 0 1 0 VP1 6 0 1 1 0 0 1 VQ1 7 0 1 0 1 1 0 (VP1 V1) From this seven level inverter we can generate thirty one level inverter is shown in Figure 3. For thirty-one level inverter it requires ten switches and four voltage sources. As the number of levels and switches increases the procedure to obtain voltage levels is different. From Figure 3 if the switches SP1, SP2, SP3 and SP4 are turned at the same time short circuit will occur on the voltage sources VP1, VP2, VQ1 and VQ2. Hence it should be avoided. Procedure for generating voltage levels is shown in Table 3. From Figure 3 with the help of thirty-one level inverter one twenty seven level inverter can be developed. It requires 14 switches and six voltage sources. 3. Procedure to Obtain Output Voltage Levels To have maximum number of output voltage levels, voltage sources magnitude should be different 3. (A) Seven level Inverter V P1 =V DC V Q1 =2V DC. Figure 2. Seven level inverter configuration 2. It can produce V DC, 2V DC, 3V DC, 0, V DC, 2V DC, 3 V DC. Vol 8 (S2) January 2015 www.indjst.org Indian Journal of Science and Technology 279
Implementation of Fuzzy Logic Controller for Cascaded Multilevel Inverter with Reduced Number of Components Table 3. Output voltage levels of 31level inverter SNO T1 T2 T3 T4 K1 K2 K3 K4 TU TV Output Voltage 1 ON OFF ON OFF ON OFF ON OFF OFF ON VA2+VB2 2 ON OFF ON OFF OFF ON ON OFF OFF ON VA2+VB2-VA1 3 OFF ON ON OFF ON 0 ON OFF OFF ON VA2+VB2-VB1 4 OFF ON ON OFF OFF ON ON OFF OFF ON VA2+VB2-VA1-VB1 5 ON OFF ON OFF ON OFF OFF ON OFF ON VA1+VB2 6 ON OFF ON OFF OFF ON OFF ON OFF ON VB2 7 OFF ON ON OFF ON OFF OFF ON OFF ON VA1 VB1+VB2 8 OFF ON ON OFF OFF ON OFF ON OFF ON VB2 VB1 9 ON OFF OFF ON ON OFF ON OFF OFF ON VA2+VB1 10 ON OFF OFF ON OFF ON ON OFF OFF ON VA2+VB1 VA1 11 OFF ON OFF ON ON OFF ON OFF OFF ON VA2 12 OFF ON OFF ON OFF ON ON OFF OFF ON VA2 VA1 13 ON OFF OFF ON ON OFF OFF ON OFF ON VA1+VB1 14 ON OFF OFF ON OFF ON OFF ON OFF ON VB1 15 OFF ON OFF ON ON OFF OFF ON OFF ON VA1 16 OFF OFF OFF OFF OFF OFF OFF OFF OFF OFF 0 17 ON OFF ON OFF OFF ON ON OFF ON OFF VA1 18 OFF ON ON OFF ON OFF ON OFF ON OFF VB1 19 OFF ON ON OFF OFF ON ON OFF ON OFF (VA1+VB1) 20 ON OFF ON OFF ON OFF OFF ON ON OFF (VA2 VB1) 21 ON OFF ON OFF OFF ON OFF ON ON OFF VB2 22 OFF ON ON OFF ON OFF OFF ON ON OFF (VA2+VB1 VA1) 23 OFF ON ON OFF OFF ON OFF ON ON OFF (VA2+VB1) 24 ON OFF OFF ON ON OFF ON OFF ON OFF (VB2 VB1) 25 ON OFF OFF ON OFF ON ON OFF ON OFF (VA1 VB1+VB2) 26 OFF ON OFF ON ON OFF ON OFF ON OFF VB2 27 OFF ON OFF ON OFF ON ON OFF ON OFF (VA1+VB2) 28 ON OFF OFF ON ON OFF OFF ON ON OFF (VA2+VB2 VA1 VB1) 29 ON OFF OFF ON OFF ON OFF ON ON OFF (VB2+VA2 VB1) 30 OFF ON OFF ON ON OFF OFF ON ON OFF (VA2+VB2 VA1) 31 OFF ON OFF ON OFF ON OFF ON ON OFF (VA2+VB2) (B) Thirty one level Inverter V P1 =V DC (C) One twenty seven Level Inverter V P1 =V DC V Q1 =2V DC V P2 =5V DC V Q1 =2V DC V Q2 =10V DC It can produce all positive and negative levels of output from 0 to15 V DC. V P2 =5V DC V Q2 =10V DC 280 Vol 8 (S2) January 2015 www.indjst.org Indian Journal of Science and Technology
K. Yamini, B. Vasudha, Avinash Sharma and P. Ponnambalam Figure 3. Thirty-one level inverter. Fuzzy controller contains three parts 1. Fuzzification 2. Rules 3. Defuzzification For fuzzification to be performed membership functions for input and output along with rules are used. To get proper output defuzzification is done on fuzzy input membership functions and rules. Rules are given from an inference using mamdani algorithm. Inputs are entered into the fuzzification block using preprocessor. Fuzzification block converts the input variables to the membership functions which match with the rules. Rms output voltage of the seven level inverter is taken and is compared with the reference value. From this Figure 5. Error Membership functions. Figure 4. One-twenty-seven Level Inverter. V P3 =25V DC Figure 6. Differential error Membership function. V Q3 =50V DC It can produce all positive and negative levels of output from 0 to 63 V DC. 4. Closed Loop Control Using Fuzzy Logic Closed loop control of fuzzy logic is used to get the error as zero by comparing actual voltage with the reference voltage. Two inputs error and differential error are given to the fuzzy controller. Table 4. Rules for fuzzy logic controller SNO Error Differential error Output 1 Ne Ne Z 2 Ne Z Pe 3 Ne Pe Z 4 Z Ne Z 5 Z Z Pe 6 Z Pe Ne 7 Pe Ne Ne 8 Pe Z Z 9 Pe Ne Ne Vol 8 (S2) January 2015 www.indjst.org Indian Journal of Science and Technology 281
Implementation of Fuzzy Logic Controller for Cascaded Multilevel Inverter with Reduced Number of Components Figure 7. Output Membership function. Figure 10. PWM Pulses. Figure 8. Simulink diagram for seven level inverter. Figure 11. Output Current. Figure 9. Simulink diagram for seven level inverter with fuzzy logic controller. error is generated, with the help of d/dt block change in error is calculated. The error and the change in error are given as inputs to the fuzzy controller. Output of the fuzzy controller is given to the saturation block for limiting the maximum and minimum values. Output from the saturation block is given as inputs to the sine wave amplitude. Figure 12. Output Voltage. 5. Simulation Results VP1=150V VQ1=50V Figure 13. Total Harmonic Distortion for output voltage. 282 Vol 8 (S2) January 2015 www.indjst.org Indian Journal of Science and Technology
K. Yamini, B. Vasudha, Avinash Sharma and P. Ponnambalam 7. References Figure 14. 6. Conclusion Output voltage for Vref=105V. Simulation results for the seven levels MLI with closed loop Fuzzy Logic Controller (FLC) is designed and observed. Root Mean Square voltage of the inverter can be controlled from 97V to 122V using FLC by changing the amplitude of the sine wave from 4.3V to 7V. 1. Ebrahimi J, Babaei E, Gharehpetian GB. A new topology of cascaded multilevel converters with reduced number of components for high-voltage applications. Journal of IEEE Trans on Power Electronics. 2011; 26(11):3109 18. 2. Farhadi M, Kangarlu, Babaei E. A generalized Cascaded multilevel inverter using series connection of sub multilevel inverters. Journal of IEEE Trans on Power Electronics. 2013; 28(2):625 36. 3. Babaei E, Farhadi M, Najaty Mazgar F. MLI topologies with reduced switching devices. Journal of Elect Power Syst. 2012; 86:122 30. 4. Babaei E, Hosseini SH. New cascaded multilevel inverter topology with reduced switches. Journal of Energy Converges Manage. 2009; 50(11):2761 7. Vol 8 (S2) January 2015 www.indjst.org Indian Journal of Science and Technology 283