Design and Controlling of Proposed Efficient Boost-Inverter Implemented using Boost DC-DC Converter

Transcription

1 Design and Controlling of Proposed Efficient Boost-Inverter Implemented using Boost DC-DC Converter Mohit Bajaj and V. K. Dwivedi, Student Members IEEE, Anurag Bansal, P. R. Sarkar and Rahul Kumar Abstract:- Mostly the boost inverters are planned to be used in system when the average output voltage is required to be larger than the input dc voltage, like uninterruptible power supply (UPS) and PV systems, unlike single-phase voltage source inverter(vsi) which uses buck topology and average output voltage is always found lower than the dc input voltage. Such kind of inverters need two stages of power conversion and more number of switches with a boost dc-dc converter in between dc source and inverter depending upon the voltage and power levels. This work proposes a novel dc to ac boost inverter based on sinusoidal-pulse-width-modulation (SPWM) control to generate the output in single stage of conversion and whose peak value will be greater than the dc input one depending on the duty cycle of converters. The proposed inverter reduces the switching losses and has much higher efficiency with respect to conventional boost inverter, due to much reduction in the number of switches. The strategy of modulation of new proposed boost inverter will reduce the harmonics and the energy loss in the output of proposed inverter, thereby allowing the proposed inverter to become a new sufficient solution for many applications like automotive electronics, PV systems, solar home applications and other power supply systems. Keywords:- Boost inverter, inverter and sinusoidal-pulsewidth-modulation. I. INTRODUCTION The single phase voltage source inverter (VSI) shown in figure 1, which uses the buck topology, has the characteristic that the instantaneous average output voltage is always lower than the input dc voltage irrespective of any PWM technique being used. Hence as a consequence, when an output voltage larger than the input one is compulsory, a boost dc-dc converter must be used between dc source and inverter as shown in figure 2. On the basis of the voltage and power levels, this can almost certainly result in high volume, weight, cost and reduced efficiency. Mohit Bajaj, V. K. Dwivedi, P.R. Sarkar, and Rahul Kumar are Research Scholars with the Department of Electrical Engineering, Motilal Nehru National Institute of Technology, Allahabad , India (mob In this Paper, a new VSI has been proposed, referred to as boost inverter, which generates an output ac voltage larger than the input dc voltage depending on the instantaneous duty ratio [1-4]. The classic solution for this kind of conversion is a boost converter coupled with a pulse width modulated voltage source inverter [5]. II. BASIC PRINCIPLE OF THE NEW PROPOSED INVERTER Let us consider two boost dc-dc converters feeding any resistive load R as shown in figure 3. The two converters produce a dc-component and a sinusoidal component at the output such that each source only produces a unipolar voltage as shown in figure 4. If the modulation of each converter is made 180 out of phase with respect to the other then the voltage excursion across the load will be maximized. Thus, the output voltages of the converters are described by, V1(t) = Vdc + Vmsinwt (1) V2(t) = Vdc + Vmsinwt (2) Thus, the output voltage is sinusoidal as given by, Vo(t) = V1(t) V2(t) = 2Vmsinwt (3) Thus the output voltage of the inverter is the difference between the outputs of the two converters and a dc component of voltage appears at each end of the load with respect to ground, but the differential dc voltage across the load is zero. The generation of the bipolar voltage at the output is solved by a push-pull arrangement [12]. Thus, the dc-dc converters need to be current bidirectional. Figure 4 shows the output voltage of the each converter alone. 589

2 Fig. 1 The conventional VSI Fig4. Output voltage characteristics of the converters Fig. 2 Conventional boost inverter The current bidirectional boost dc dc converter is shown in Figure 5. A circuit implementation of the boost dc ac converter is shown in Figure 6. Fig 3. The proposed boost inverter block diagram Fig5. The current bidirectional boost dc dc converter III. PRINCIPLE OPERATION OF THE PROPOSED INVERTER Each converter is a current bidirectional boost converter as shown in figure 5. The boost inverter consists of two boost converters as shown in figure 6. The output of the inverter can be controlled by one of the two methods either by using a duty cycle K for converter A and a duty cycle of (1-K) for converter B or using a different duty cycle for each converter such that each converter produces a dc-biased sine wave output. The second method is preferred and it uses controllers A and B to make the capacitor voltages V1 and V2 follow a sinusoidal reference voltage. 590

3 L1 + Vo - IL1 à R Vin C1 + - V1 V2 S1à ON S2 à OFF Fig 8(a). Modes of operation Mode 2: Fig6. The proposed boost inverter For the condition, switch S1 is open and S2 is closed, as shown in figure 8(b), the inductor current il1 flows through capacitor C1 and load. The current il1 decreases while capacitor C1 is recharged. The operation of the inverter can be explained by considering one converter A only as shown in figure7. Now there are two modes of operation. L1 IL1 à + Vo - R Vin C1 + _ V1 V2 S1 à OFF S2 à ON Fig 8(b). Modes of operation A. DC Gain Characteristic of the Proposed Boost Inverter The average output voltage of converter A, which operates under the boost mode, is given by, Mode 1: Fig7. Equivalent circuit for the boost inverter The average output voltage of converter B, which operates under the buck mode, is given by, For the condition, switch S1 is closed and S2 is open as shown in figure 8(a), the inductor current il1 raises quite linearly, diode D2 is reversed biased, capacitor C1 supplies energy to the load, and Voltage V1 decreases. Therefore, the average output voltage is given by, which gives DC gain of the boost inverter as 591

4 Where K is the duty cycle. It should be noted that Vo becomes zero at K = 0.5. If the duty cycle K is varied around the quiescent point of 50 % duty cycle, there is an ac voltage across the load. B. AC Gain Characteristic of the Proposed Boost Inverter Since output voltage in equation (3) is twice the sinusoidal component of converter A, the peak output voltage equals to Because a boost converter cannot produce a output voltage lower than the input voltage, the dc component must satisfy the condition, the boost inverter output voltage and power ratings are selected, inductances L1 and L2 are designed from output current ripples and capacitors C1 and C2 are designed so as to limit the output voltage ripple. Further maximum switching frequency is selected from the converter ratings and switch type. Let we want to design the inverter for resistive load of Po = 500Watt, switching frequency = 3 KHz, Vin =150V and Vo = 220Vrms. The selection of the value of inductor and capacitor is based on the minimum ripples in output current and voltage. Now for output voltage Vo=311sin314t, first the DC component of the capacitor voltage is calculated from the equation (8), This implies there are many possible values of Vdc. However, equal term produces the least stress on the devices. From the equation (4), (7) and (8), we get Here Vdc comes out 305.5V, hence duty ratio of the converter is given by, Solving, K(opr.) Which gives the ac voltage gain as Thus Vo (peak) becomes Vin at K equal to 0.5. The ac and dc gain characteristics of the boost inverter are shown in figure 9. The inductor current IL that depends on the load resistance R and duty cycle K, can be found from, The voltage stress of the boost inverter depends on the ac gain Gac, the peak output voltage Vm and the load current IL. V. SPWM CONTROLLER Sliding mode (SM) controllers are known for their stability and robustness. Most of the previously proposed SM controllers for switching power converters are hysteresis modulation (HM) based [1] [7]. That modulation method of the SM controllers for switching power converters can be the SM controllers for switching power converters can be replaced by pulse-width modulation (PWM) [8]. At a high switching frequency, the controlling of a sliding mode controller is equivalent to the duty cycle controlling of a PWM controller. Hence, the movement of a sliding mode controller from being HM based to PWM based is possible [9]. Modulation Index: (1 Where, Amplitude Modulation Index: (12) Ar Amplitude of sinusoidal reference signal Ac Amplitude of triangular carrier wave signal Fig 9. Gain characteristic of the boost inverter IV. INVERTER DESIGN METHODOLOGY A. PWM Generator Circuit :- While designing the inverter, power switches are assumed to be ideal and operating at high-switching frequency. Once PWM generator circuit produces gating signal for the switches S1-S4.It is generated by comparing the sinusoidal 592

5 reference signal with triangular carrier wave signal.pwm generator circuit is shown in figure 10. shows the output current waveform and Figure17 shows the voltage across each converter side capacitor and R- load. For the above circuit parameters, THD is measured using FFT analysis and the THD value is 7.18% Figure 10. PWM Generator Circuit The complete operation of the SPWM control is as follows: When Vc < Vr, S1,S4 = ON and S2,S3 = OFF. When Vc > Vr, S2,S3 = ON and S1,S4 = OFF. Vc Voltage amplitude of triangular carrier wave signal. Vr Voltage amplitude of sinusoidal reference signal. The theoretical waveforms of SPWM control is shown in figure 11. Figure 12. Simulation circuit of Boost inverter Figure 11. Theoretical waveforms of SPWM control VI. SIMULATION RESULTS The performance of the proposed boost inverter is verified via computer simulation. The simulations are conducted using MATLAB SIMULINK software package. The simulated circuit for resistive load is shown in Figure 12. Figure show simulation waveforms of the converter for resistive load of R=97Ω. The circuit parameters in the S1, S4 S2, S3 Figure13. Switch pulses waveforms of SPWM control simulation are given as follows: Vin =150V, V0= 220Vrms, L1=L2=0.325 H, C1=C2=150μF, R=97Ω. Figure 14 shows the waveforms of converter1 and Figure 15 shows the waveforms of converter2. The wave forms of converter shows current through the inductor & diode, voltage across the capacitor and collector current and collector to emitter voltage of switch IGBT. Figure16 (IL1) 593

6 Figure 14. Waveforms of Converter 2 (ID1) Figure 15. Output current (IC1) Voltage across capacitor C1 (V1) (Vce1) Figure 13. Waveforms of Converter 1 Voltage across capacitor C2 (V2) Voltage across load (Vo) (IL2) Figure 16. Voltage across each converter side Capacitor and Load (ID2) (IC2) VII. CONCLUSION This study has proposed a novel boost DC-AC converter topology, which is designed by the DC-DC boost converter. As a result, it offers the advantages of ease in implementation and reduced complexity of the circuit. The other advantages of proposed boost inverter over conventional boost inverter scheme are, reduced switching loss, improved efficiency and reliability, simplified PWM control scheme, reduced cost, size and weight compared to conventional systems etc. Therefore, the proposed boost inverter circuit is a good choice for many applications such as PV systems, automotive electronics, solar home applications and other power supply systems. (Vce2) 594

7 REFERENCES [1]. R. C aceres and I. Barbi, A boost dc ac converter: Operation, analysis, control and experimentation, in Proc. Int. Conf. Industrial Electronics, Control and Instrumentation (IECON 95), Nov. 1995, pp [2]. R.C aceres and I. Barbi A boost dc ac converter: Analysis, design, and experimentation IEEE Trans. Power Electronics, vol. 14, pp , Jan [3]. Nimrod Vázquez, Carlos Aguilar, Jaime Arau, Ramón O. Cáceres, Ivo Barbi, Jaime Alvarez Gallegos, A Novel Uninterruptible Power Supply System With Active Power Factor Correction IEEE Transactions on Power Electronics, vol. 17, no. 3, May [4]. R. C aceres and I. Barbi, Sliding mode control for the boost inverter, in Proc. 5th IEEE Int. Power Electron. Conf. (CIEP 96), Cuernavaca, Mexico, pp ,Oct ,1996. [5]. Vazquez N, Almazan J,Alvarez J, Aguilar C. Arau J. Analysis and experimental study of the buck, boost and buckboost inverters[j]. Power Electronics, 2: , [6]. P. Malesani, L. Rossetto, G. Spiazzi, and P. Tenti, General purpose sliding mode controller for dc dc converter applications, in Proc. Power Electronic Specialist Conf. (PESC 93), pp [7]. P. Malesani, L. Rossetto, G. Spiazzi, and P. Tenti, Performance optimization of Cuk converter by sliding mode control, in Proc. Applications Power Electronic Conf. (APEC 92), pp Mr. Vinay Dwivedi was born in Banaras. His B-tech was completed from Ideal Institute of Technology, Ghaziabad and M-tech from MNNIT Allahabad. His area of research includes power quality improvement using Custom Power Devices. Mr. Anurag Bansal was born in Bulandshahar. His B-tech was completed from NIIT Noida and M-tech from MNNIT Allahabad. His area of research includes power quality improvement using Custom Power Devices. Mr. P.R. Sarkar was born in Deoria. His B-tech was completed from SRMS Bareilly and M-tech from MNNIT Allahabad. His area of research includes specifically power electronics converters. Mr. Rahul Kumar was born in Patna. His B-tech was completed from COER Roorkee and M-tech from MNNIT Allahabad. His area of research includes specifically power electronics converters and power quality improvement using Custom Power Devices. [8]. Yuen-Haw Chang and Ming-Zong Wu, High-Conversion- Ratio Switched- Capacitor Boost DC-AC Inverter Using Sinusoidal PWM Control, in Proc. International Multi Conference of Engineers and Computer Scientists.( IMECS 2010),Hong Kong,Mar 17-19,2010 [9]. H. Sira-Ramirez and M. Ilic, A geometric approach to the feedback control of switch mode DC-to-DC power supplies, IEEE Transactions on Circuits and Systems, vol. 35 no. 10, pp ,Oct [10]. Muhammad H.Rashid, Power Electronics, Circuits, Devices and application-third Edition., Prentice-Hall of India, Mr. Mohit Bajaj was born in Roorkee. His B-tech was completed from Faculty of Engineering and Technology GKV Haridwar and M-tech from MNNIT Allahabad. He is Student Member of IEEE and has published numerous numbers of International Research Journals and Conference Papers. His area of research includes specifically power electronics converters and power quality improvement using Custom Power Devices. 595