CLOSED LOOP CONTROL OF HIGH STEP UP CONVERTER TOPOLOGIES 1 MEERA BALARAMAN, 2JYOTHI G K 1 Student (FISAT, MG university, Kerala), 2Associate professor (FISAT, MG university, Kerala) Abstract- In recent years, with the increasing development of power electronics technology, the boost DC-DC converters are more widely for the electricity-supply applications .In this paper, a new step up (boost) converter with closed loop control is proposed, It is analyzed, designed, simulated with MATLAB Simulink. Conventional DC-DC boost converters are not able to provide high step-up voltage gains. This paper presents transformerless dc-dc converters with closed loop control to achieve high step-up voltage gain without an extremely high duty ratio. Moreover closed loop control methodology is used for voltage drift problems. In the proposed converters, two inductors with the same level of inductance are charged in parallel during the switch-on period and are discharged in series during the switch-off period. The structures of the proposed converters are very simple. Index Terms- DC-DC converter, high step up converter, closed loop control, PI controller. as they possess attractive switching capabilities, especially in terms of switching frequency and power ratings. I. INTRODUCTION In recent years, with the increasing development of power electronics technology, the boost DC-DC converters are more widely for the electricity-supply applications. In general, these power converters are always required for a small volume, a light weight, a high efficiency, and a better regulation capability. At present the most widely used approach to do DC to DC conversions is inductor-based DC-DC converters, which contains at least one inductor. For low-power and highly integrated electronic systems, inductor-based converters have the switches integrated with the controller. High step up (Boost) converter is used in many applications such as discharge lamp for automobile, fuel cell energy conversion systems, and solar energy conversion system. In this thesis closed loop control of high step up boost converter topology is presented which will remove the disadvantage of high step up boost converter with open loop control. II. LITERATURE SURVEY DC–DC converter with a high step-up voltage gain is used for many applications, such as high-intensity discharge lamp ballasts for automobile headlamps, fuel-cell energy conversion systems, solar-cell energy conversion systems, and battery backup systems for uninterruptible power supplies. Theoretically, a dc–dc boost converter can achieve a high step-up voltage gain with an extremely high duty ratio [1]–[3]. However, in practice, the step-up voltage gain is limited due to the effect of power switches, rectifier diodes, and the equivalent series resistance (ESR) of inductors and capacitors. Moreover, the extremely high duty-ratio operation will result in a serious reverse-recovery problem. Many topologies have been presented to provide a high step-up voltage gain without an extremely high duty ratio. A dc–dc fly back converter is a very simple structure with a high step-up voltage gain and an electrical isolation, but the active switch of this converter will suffer a high voltage stress due to the leakage inductance of the transformer. Figure 1: The typical configuration of inductor-based DC-DC converter A DC-to-DC converter is a device that accepts a DC input voltage and produces a DC output voltage which is-typically- at a different voltage level than the input. Apart from voltage level conversion, DC-to-DC converters are used to provide noise isolation, power bus regulation. The typical usage of DC-DC converters is to convert unregulated dc voltage to regulated or variable dc voltage at the output. The output voltage in DC-DC converters is generally controlled using a switching concept. In fact, early DC-DC converters were known as choppers with silicon-controlled rectifiers (SCRs) used as the switching mechanism. Modern DC-DC converters employ insulated gate bipolar transistors (IGBTs) and metal oxide silicon field effect transistors (MOSFETs) III. NEWTOPOLOGIES Figure 2 shows the three proposed topologies. These three proposed dc–dc converters utilize the switched inductor technique, in which two inductors with same International Conf. on Electrical, Electronics, Mechanical & Computer Engineering, 06th July-2014, Cochin, India, ISBN: 978-93-84209-34-6 30 Closed Loop Control of High Step Up Converter Topologies level of inductance are charged in parallel during the switch-on period and are discharged in series during the switch-off period, to achieve high step-up voltage gain without the extremely high duty ratio. The operating principles and steady-state analysis are discussed in the following sections. To analyze the proposed converters, some conditions are given as follows: waveforms for the proposed converter I.CCM operation. i. Mode 1 [t0, t1]. During this time interval, switches S1 and S2 are turned on. The equivalent circuit is shown in Fig. 4(a). Inductors L1 and L2 are charged in parallel from the dc source, and the energy stored in the output capacitor Co is released to the load. Thus, the voltages across L1 and L2 are given as VL1 = VL2 = Vin (1) ii. Mode 2 [t1, t2]. During this time interval, S1 and S2 are turned off. The equivalent circuit is shown in Figure 4(b). The dc source, L1, and L2 are series connected to transfer the energies to Co and the load. Thus, the voltages across L1 and L2 are derived as All components are ideal and the ESRs of the inductors and capacitors are ignored all capacitors are sufficiently large, so that voltages across the capacitors can be assumed as Constant Figure 2(b): new converter 1 Figure 2(a): new converter 2 . Figure 3: waveforms of converter 1 Figure 2(c): new converter 3 A. NEW CONVERTER 1 Figure 2(a) shows the circuit configuration of the proposed converter I, which consists of two active switches (S1 and S2), two inductors (L1 and L2) that have the same level of inductance, one output diode Do, and one output capacitor Co. Switches S1 and S2 are controlled simultaneously by using one control signal. Figure 3 shows some typical waveforms obtained during continuous conduction mode (CCM). By using the volt–second balance principle on L1 and L2, the following equation can be obtained: dt = 0 (3) ∫ Vin dt + ∫ . CCM Operation The operating modes can be divided into two modes, defined as modes 1 and 2. Figure 3 shows typical Voltage across S1 and S2 and diode is given by: VL1 = VL2 = Vin -Vo/2 (2) By simplifying (3), the voltage gain is given by Vo (1 D) /(1 D ) Vin Vs1=Vs2 = VD1 = Vo/2 (4) (5) International Conf. on Electrical, Electronics, Mechanical & Computer Engineering, 06th July-2014, Cochin, India, ISBN: 978-93-84209-34-6 31 Closed Loop Control of High Step Up Converter Topologies source, L1, C1, and L2 are series connected to transfer the energies to Co and the load. Thus, the voltages across L1 and L2 are derived as VL1 = VL2 = (Vin-Vo)/2 (11) By using the volt–second balance principle on L1 and L2, the following can be obtained: Figure 4(a); mode 1 So the voltage gain is given by Vo 2 /(1 D) Vin Figure 4(b): mode 2 (12) (13) The voltage stress on switches and diodes is given by: B. NEW CONVERTER 2 Figure 2(b) shows the circuit configuration of the proposed converter II, which is the proposed converter I with one voltage-lift circuit. Thus, two inductors (L1 and L2) with the same level of inductance are also adopted in this converter. Switches S1 and S2 are controlled simultaneously by one control signal. VS1 =VS2=VD1= VDo = Vo (14) Figure 6(a): mode1 Figure 5: typical waveforms of proposed converter operating in CCM. . CCM Operation The operating modes can be divided into two modes, defined as modes 1 and 2. i. Mode 1 [t0, t1]. During this time interval, S1 and S2 are turned on. The equivalent circuit is shown in Fig. 6(a). L1 and L2 are charged in parallel from the dc source, and the energy stored in Co is released to the load. Moreover, Figure 6(b): mode 2 Capacitor C1 is charged from the dc source. Thus, the voltages across L1, L2, and C1 are given as VL1 = VL2 = VC1 = Vin C. NEW CONVERTER III Figure. 2(c) shows the circuit configuration of the proposed converter III, which is the proposed converter I with two voltage lift circuits. Thus, two inductors (L1 and L2) with the same level of inductance are also adopted in this converter. Switches S1 and S2 are controlled simultaneously by on control signal. (10) ii. Mode 2 [t1, t2]. During this time interval, S1 and S2 are turned off. The equivalent circuit is shown in Figure 6(b). The dc International Conf. on Electrical, Electronics, Mechanical & Computer Engineering, 06th July-2014, Cochin, India, ISBN: 978-93-84209-34-6 32 Closed Loop Control of High Step Up Converter Topologies Figure 8(a): mode 1 Figure 7: typical wave forms of proposed converter3 operating in CCM Figure 8(b):mode 2 CCM Operation The operating modes can be divided into two modes, defined as modes 1 and 2. i. Mode 1 [t0, t1]. During this time interval, S1 and S2 are turned on. The equivalent circuit is shown in Fig. 8(a). L1 and L2 are charged in parallel from the dc source, and the energy stored in Co is released to the load. IV. CLOSED LOOP CONTROL Controller is a device that produces an output signal based on the input signal it receives. The input signal is actually an error signal, which is the difference between the measured variable and the desired value, or set point. This input error signal represents the amount of deviation between where the process system is actually operating and where the process system is desired to be operating. The characteristic of this output signal is dependent on the type, or mode, of the controller. Four modes of controller commonly used for most applications are: Moreover, capacitors C1 and C2 are charged from the dc source. Thus, the voltages across L1, L2, C1, and C2 are given as VL1 = VL2 = VC1 = VC2 =Vin (15) ii. Mode 2 [t1, t2]. During this time interval, S1 and S2 are turned off. The equivalent circuit is shown in Figure 8(b). The dc source, L1, C1, C2, and L2 are series connected to transfer the energies to Co and the load. Thus, the voltages across L1 and L2 are derived as VL1=VL2= = (16) By using the volt–second balance principle on L1 and L2, the following can be obtained: =0 (17) ∫ Vin dt + ∫ Voltage gain of the circuit is given by Vo (3 D ) /(1 D) Vin Proportional (P) Proportional plus integral (PI) Proportional plus derivative control (PD) Proportional plus Reset plus derivative (PID) Figure 9: pi control (18) Among this PI control is widely used for industrial applications. PI controller Proportional PI control is a combination of the proportional and integral control modes, combining Voltage stress across switches and diodes is given by: VS1=VS2=VD1=VD2= (19) VD0 = V0 –Vin International Conf. on Electrical, Electronics, Mechanical & Computer Engineering, 06th July-2014, Cochin, India, ISBN: 978-93-84209-34-6 33 Closed Loop Control of High Step Up Converter Topologies the two modes results in gaining the advantages and compensating for the disadvantages of the two individual modes. The PI controller is considered a fast-acting device the main disadvantage of the proportional control mode is that a residual offset error exists between the measured variable and the set point for all but one set of system conditions. The main advantage of the integral control mode is that the controller output continues to reposition the control element until the error is reduced to zero. This results in the elimination of the residual offset error allowed by the proportional mode. The main disadvantage of the integral mode is that the controller output does not immediately direct the signal control element to a new position in response to an error signal. The combination of the two control modes is called the proportional plus reset (PI) control mode. It combines the immediate output characteristics of a proportional control mode with the zero residual offset Characteristics of the integral mode. B.PROPOSED CONVERTER 2 Figure 12: simulation block diagram Figure 13: output waveforms (CCM) V. SIMULATION RESULT C. PROPOSED CONVERTER 3 This section carry simulation result of the improved topology by using MATLAB Simulink the parameter values that are used are For continuous conduction mode: L1= L2=100µH Fs(switching frequency)=100kHZ Co=33µF C1=C2=47µF Ro=250 VO/Vin = (1+D)/(1-D) = 100/12 So D= 78.57% Figure 14: simulation block diagram A. PROPOSED CONVERTER1 Simulation block diagram Figure 15: Output waveforms (CCM) Figure10: Simulation block diagram VI. EXPERIMENTAL RESULT In order to verify the performance prototype of third converter is built. Input voltage is 12V and output is 100v.control is applied through dspic controller. Figure 11: Output waveforms (CCM) Figure 16: circuit of converter3 International Conf. on Electrical, Electronics, Mechanical & Computer Engineering, 06th July-2014, Cochin, India, ISBN: 978-93-84209-34-6 34 Closed Loop Control of High Step Up Converter Topologies CONCLUSION This paper studied three Transformerless topologies with simple structures to reduce the power losses by decrease the switch voltage stress. The structures of the proposed converters are very simple. And a closed loop control strategy is adopted to avoid voltage drift problems. Also the hardware of third converter is built, which has lower voltage stress than the other two. Figure17: output current REFERENCES [1] B. Bryant and M. K. Kazimierczuk, “Voltage-loop power-stage transfer functions with MOSFET delay for boost PWM converter operating in CCM,” IEEE Trans. Ind. Electron., vol. 54, no. 1, pp. 347–353, Feb. 2007. [2] X. Wu, J. Zhang, X. Ye, and Z. Qian, “Analysis and derivations for a family ZVS converter based on a new active clamp ZVS cell,” IEEE Trans. Ind. Electron., vol. 55, no. 2, pp. 773–781, Feb. 2008. [3] D. C. Lu, K. W. Cheng, and Y. S. Lee, “A single-switch continuous conduction- mode boost converter with reduced reverse-recovery and switching losses,” IEEE Trans. Ind. Electron., vol. 50, no. 4, pp. 767–776, Aug. 2003. [4] B. Axelrod, Y. Berkovich, and A. Ioinovici, “Switched-capacitor/ switched-inductor structures for getting transformerless hybrid DC–DC PWM converters,” IEEE Trans. CircuitsSyst. I, Reg. Papers, vol. 55, no. 2, pp. 687–696, Mar. 2008. Figure18: output voltage Figure19: inductor current International Conf. on Electrical, Electronics, Mechanical & Computer Engineering, 06th July-2014, Cochin, India, ISBN: 978-93-84209-34-6 35