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A Varian of High Performance Boost ConverterSubiyanto#Teknik Elektro, Universitas Negeri Semarang Gd E8 Lt. 1 Kampus Unnes Sekaran Gunungpati Semarang 50229, Indonesiasubiyanto@mail.unnes.ac.id

Abstract This paper presents a new boost converter topology that can be applied to high performance in power conditioning. Boost converter has been designed using a coupled inductor and passive and active snuber. High performance is meant in this case to provide very high gain between the output voltage of the converter input. Coupled inductor very important role in enhance the gain. Snuber serves to minimize losses in the switching converter and also helps increase the gain of the output voltage resulting. Mathematical analysis and simulation results and experiments have shown gains new boost converter is much higher than the conventional boost converter. The experimental results also demonstrate improved efficiency of the boost converter from 81.74% to 90.05% of the conventional.Keywords Boost Converter, gain, snuber, switching, coupled inductorI. IntroductionPower conditioner devices in renewable energy based electric generating is used process and control the flow of electric power by supplying voltage s and currents in a form that is optimally suited for user loads or from side to othe side Castafier & Silvestre 2002(; Schmid & Schmidt 2003). The power conditioners are used depending on the type of Electric power generating system applications. A typical power conditioner which is consist of some DC-DC converters and DC-AC inverter for distributed generation such as PV system Ryu 2009(). In general, the DC-DC converter applied in PV systems is classified into three types: step-up or boost converter, step-down or buck converter and step-up/down or buck-boost converter Kininger 2003(). The most common DC-DC converter used in grid connected PV systems is the boost converter Mekhilef 2008(; Wai & Wang 2008). In this thesis, the boost converter topology is selected considering the voltage ratings of the PV module and the three phase inverter used for grid connected PV system application.

The conventional boost converter operates in hard switching thus making it inefficient where voltages and currents in semiconductor switching devices are changed abruptly from high values to zero and vice versa at turn-on and turn-off times, thus causing switching losses and electromagnetic interference Mohan et al. 2003(; Kazimierczuk 2008). The conventional boost converters can rise reverse recovery problems, electromagnetic interference (EMI) problem so that reduce efficiency the power conversion Mohan et al. 2003(). To overcome the reverse-recovery problem of the output diode in high-level voltage, some voltage-clamped techniques are used in the converter design Duarte & Barbi 2002(; Edelmoser & Himmelstoss 2006). However, there still exists large switching voltage stresses and that the voltage gain is limited by the turn-on time of the switching devices. Moreover, to increase the voltage gain and conversion efficiency of a boost converter, coupled inductors are usually used to make the voltage gain higher referring the turn ratio like as transformer Berkovich & Axelrod 2011

( ADDIN EN.CITE ; Himchi et al. 2002; Laird et al. 2009; Zhao & Lee 2003). However, the use of coupled inductors may cause leakage energy problem in the coupled inductor when the switch is turned off. It will give a high-voltage ripple across the switching device since there is the leakage current which causes a resonant phenomenon. Moreover, the capacity of the magnetic core has to be increased substantially when the demand of high output power is required. To overcome the drawbacks of coupled inductor based boost converter, a small capacitor is placed so as to connect the primary with secondary inductor of the coupled inductor and by adding a passive regenerative snubber circuit Wai & Duan 2005(). However, the use of a snubber circuit is less effective to increase the voltage gain. Considering these facts, a new variant of high gain soft switching DC-DC converter is proposed in this thesis so as to reduce the numbers of connected PV modules in series and to improve the conversion efficiency.

To develop a high performance boost converter, a new converter topology is proposed in this paperby using auxiliary boost circuit which acts as an active snubber to reduce switching losses of the converter. This research focuses on the development of a high performance DC-DC boost converter as the power electronic component of PV systems. The proposed boost converter will reduce the switching losses and enhance the converter voltage gain to meet the needs of the three-phase inverter input in grid connected PV system.

The initial work carried out in this research focused on designing a new coupled inductor based boost converter. The topology of the boost converter circuit is improved by adding active and passive snubber circuits. The snubber circuits provide soft switching operation for the converter in order to reduce the switching losses and consequently increase the conversion efficiency. The active snubber circuit plays the role as an auxiliary boost that improves the gain of the main boost. The switching losses in the main boost are stored by a capacitor in the active snubber. Basically, this capacitor becomes the "power supply" for the active snubber. The performance of the new boost converter is evaluated by making comparisons with the previously designed boost converter circuits.II. Improvement of boost converter circuit configurationA boost converter is a DC to DC power converter with output voltage always greater than the input voltage Skvarenina 2002(). Fig. 1 shows a conventional boost converter, consisting of DC input voltage source Vin, boost inductor L, controlled switch S, diode D, output filter capacitor C, and load RL. During switch S is closed (0 < t < ton) and switch S is opened (ton < t < TS). The voltage gain (Gi) of the ideal boost converter is given as (1)[ Mohan et al. 2003].

(1)

Fig. 1 A simple boost converter circuit [Mohan et al. 2003]To improve efficiency of the power conversion, various topologies of boost converter have been developed. Because the conventional boost converter works in hard switching operation so it makes inefficient where curves of voltages and currents in semiconductor devices are changed abruptly from high values to zero and vice versa at turn-on and turn-off times, thus causing switching losses and electromagnetic interference Kazimierczuk 2008().

Switching losses and electromagnetic interference level in DC-DC converters can be reduced by using soft switching techniques, that is zero-voltage switching and zero-current switching Kazimierczuk 2008(; Pressman et al. 2009).

Bodur and Bakan (2002) proposed a new variant of zero voltage transition for the pulse width modulation boost converter. The switching devices in the boost converter are turned on and off under exact or close to zero voltage switching and/or zero current switching by using active snubber circuit. However, the active snubber acts as a cascade switch boost in which the main switch still has high losses. Zhang and Sen (2003) used an auxiliary inductor and hysteresis current control to achieve zero voltage switching conditions for the boost converter. The main inductor current is kept in continuous conduction mode with small ripple, which allows high output power and small filter parameters. The auxiliary inductor is used for the purpose of commutation. This scheme aims to improve the efficiency of the converter because it is operated under soft-switching conditions. However, the effectiveness of the auxiliary inductor has not been verified and theinductor's magnetic fieldsaffect each other.

Zhao and Lee (2003) developed a high gain boost converter by using a coupled inductor to increase step-up of DC voltage. The topology of the boost is shown in Fig. 2. The function of the coupled inductor is like a transformer. To reduce switching losses, a capacitor snubber is added. However, after the switch is turned on the leakage inductance and the parasitic capacitance of the semiconductor devices rise. Therefore, to eliminate this phenomenon, it is needed a snubber circuit in the boost converter main circuit.

Fig. 2 Zhao and Lee boost converter topology

Wai and Duan (2005) improved the step-up voltage of the coupled inductor based boost converter by replacing capacitor between the primary and secondary inductor and adding snubber circuit as depicted in Fig. 3. To reduce the resonance effect of the coupled inductor, a clamp diode is added in the snubber circuit. The improvement in the voltage gain depends on voltage of the snubber capacitor. The disadvantage of this circuit configuration is that there is resonance effect in the parasitic capacitance of the clamp diode.

Fig. 3 Wai and Duan boost converter topology

A boost converter by using a coupled inductor and two switching devices (MOSFETs) for active clamping has been presented Wu et al. 2005(). The boost converter gives voltage gain higher than conventional boost. A sub circuit of passive clamping is used to reduce undesired resonance between leakage inductor of the coupled inductors and parasitic capacitor of the boost diode for recovering leakage energy. However, the voltage gain is still lower than Wais boost converter. Moreover, the boost very complicate to be applied as MPPT controller, because the two switching need synchronization. The topology of the boost converter is represented in Fig. 4.

Fig. 4 Wus boost converter topology

Santos et al (2006) added a passive snubber circuit in the boost converter and applied to maximum power point tracking for PV systems. Many components are required to develop the snubber circuit and the voltage gain is not very much improved than the conventional boost converter. Selvaganesan et al (2008) proposed a high step-up fly-back DC-DC converter for PV system. The converter used a coupled inductor to increase the turns ratio of the output voltage. However, there are energy losses in the switching process of the converter, because the converter operated in hard switching. In this thesis, a new family of coupled inductor based boost converter has been developed by using active snubber instead of passive snubber. By using an auxiliary boost which acts as an active snubber, the boost converter voltage gain can be enhanced. The active snubber uses a soft switching technique which reduces switching losses of the boost converter so as to increase its performance. This new topology of boost converter is applied for MPPT controller in PV system.

Fig. 5 Santos boost converter topology

III. Development OF A High Performance Boost ConverterA power conditioner for PV system application is designed with MPPT controller to draw maximum power from PV panel. Usually, an MPPT controller is embedded in a front end of the power conditioner which is referred to a DC-DC/ boost converter. This chapter describes the proposed boost converter design that is a new high performance boost converter. Moreover, the circuit operation is also described. The aim of the designing is to provide a high gain of input - output voltage conversion using soft switching technique to alleviate the switching losses and increase the conversion efficiency.A. Design of the new High Performance Boost ConverterThe circuit diagram of the boost converter for the MPPT of PV system is depicted in Fig. 6. It comprises of six parts: a source with input-filter (part 1), a primary side circuit (part 2), a secondary side circuit (part 3), a snubber circuit parts 4a and 4b), an output filter with load (part 5) and a PWM control mechanism (part 6). The detailed components of the converter represented by the respective symbols are described according to the various parts of the circuit.

Fig. 6 Proposed circuit design of the boost converter

The input filter (part 1) and the primary circuit (part 2) with source power are represented:

Vin : DC voltage from PV panel

Iin: DC current from PV panel

Cin : DC capacitor of input filter

L1: coupled inductor of the primary side

Z1: IGBT as a switching device with a diode, DZ1 The secondary side of the coupled inductor sub-circuit (part 3) consists of the following components:

L2: coupled inductor of the secondary side

C3: connecting capacitor

D4 : rectifier diode

DO : rectifier output diode

There are two parts in the snubber circuit, namely, the active regenerative snubber circuit (part 4a) and the passive regenerative snubber circuit (part 4b). The components in the active regenerative snubber circuit are:

Z2: IGBT as a switching device with a diode DZ2C1: input capacitor

C2: output capacitor

D1: input diode to input capacitor, C1D2: input diode to switching device Z2.

LS: snubber inductor

D3: rectifier diode

While the passive regenerative snubber circuit (part 4b) has the following components:

D5, D6: diodesCs : snubber capacitor

The output filter and output side (part 5) is represented by the following components:

Co: filter capacitor

Vo :output voltage of the proposed boost (load terminal)

Io : output current of the proposed boost flows on the load.B. Analysis of the Proposed Boost Converter CircuitThe coupled inductor can be regarded as an transformer with turns ratio, n and coupling coefficient, k Gallagher 2006(; Zhu et al. 2011) as shown in Fig. 7. Hence, the coupled inductor of the proposed boost converter is modeled by a leakage inductance (Lk), a magnetizing inductance (Lm), a primary inductance (L1) and a secondary inductance (L2).

(a) (b)

Fig. 7 Coupled inductor model as (a) schematic diagram and (b) transformer circuit

The mathematical model can be derived from the transformer model by the following equation according to the well-known basic circuit theory Wai & Duan 2005().

(2)

(3)

Where, N1 and N2 denote the primary and secondary sides winding turns of the coupled inductor, respectively. The values of coupling coefficient, k are in the bound of 0 k 1 Zhu et al. 2011(). Lm is the magnetizing inductor and Lk is the leakage inductor.

The inductor, L1 consists of the magnetizing inductor, Lm and leakage inductor, Lk Gallagher 2006(; Zhu et al. 2011). Moreover, the relationship between Lk, Lm and L1 can be expressed as,

(4)

C. Operation Modes of the Proposed Boost Converter

The proposed boost converter is designed to be operated in continuous conduction mode. Moreover, the analysis below considers the steady state condition for the boost operation. Therefore, the capacitors and the inductors were assumed already stored energy.

The theoretical waveforms of PWM triggering signal for the switching device of the proposed boost converter is depicted in Fig. 8. From this waveform, the proposed boost converter circuit analysis is considered in four operation modes in one switching cycle.

Fig. 8 Triggering signal waveform for switching

The triggering signal is in terms of the IGBT gate voltage (VGZ), with a high (H) value to switch on the IGBT and a low value (0) to switch off the IGBT in the boost converter circuit. The converter operating modes in terms of steady state operation based on switching times in Fig. 8, which are considered as mode 1 (t1- t2), mode 2 (t2- t3), mode 3 (t3- t4) and mode 4 (t4- t5). The detailed explanations on modes of operation of the proposed boost converter are described as follows;i. Operation of mode 1 (t1 t2). In this mode of operation, the switches Z1 and Z2 are turned on for a certain time as shown in Fig. 9. At this time, the magnetizing inductor, Lm is charged by the input voltage source, Vin, causing the magnetizing current, ILm to increase gradually and induce current in inductor, L2. In this circuit, the active snubber which consists of capacitor C1, storage inductor Ls, switch Z2, rectifier diode D3 and output filter capacitor C2, acts as an auxiliary its energy and boost. When Z2 switch on, it is formed a loop C1- Ls- Z2. Thus, capacitor, C1 discharges its energy to inductor, Ls. In this mode, the inductor, Ls store energy like as inductor of conventional boost. The passive snubber circuit which consists of diodes, D5 and D6 and capacitor Cs is used to protect the switch Z2 from switching transient. The secondary current that flows through capacitor C2, rectifier diode D4 and inductor L2 will then charge the high-voltage capacitor, C3. As the capacitor voltage, VC3 gradually increases the magnitude of the secondary current, IL2 decreases.

Fig. 9 Current flowing of the proposed boost converter in mode 1 operation

ii. Operation of mode 2 (t2 t3). The boost operation of this mode is shown in Fig. 10. From the figure, switches Z1 and Z2 are turned off under zero voltage switching at time, t2. In this mode the secondary current, IL2 decrease gradually and reach to zero at time t = t2. When the switch voltage of IGBT- Z1 is greater than voltage of the clamped capacitor, VC1, the clamped diode, D1 transfers energy of the primary inductor, L1 toward the capacitor, C1 while clamped diode, D5 transmits the energy of the inductor, Ls into the capacitor, Cs. Hereinafter, two diodes, D3 and D6 transfer energy of the snubber inductor, Ls to the capacitor, C2. In this case, the clamped capacitor, C1 acts as energy storage, with an appropriate response at high frequencies, so its voltage, VC1 can be maintained as a constant DC voltage with low ripple. Here, the clamped diodes, D1 and D5 are assumed as very fast conductive devices. The ultra fast diodes with low power consumption may be a better choice. Capacitors, C1 and Cs act as snubber for switches, Z1 and Z2, respectively.

Fig. 10 Current flowing of the proposed boost converter in mode 2 operation

iii. Operation of mode 3 (t3 t4). Fig. 11 describes the boost operation of this mode. From the figure, at time t = t3, the primary current, IL1 charges the clamped capacitor, C1 and the secondary current, IL2 delivers current to the output terminal through the diode Do. The snubber inductor, Ls releases its energy to charge the auxiliary boost capacitor, C2. The clamped diode, D4 restrains the current from the inductor, IL2 from flowing into the capacitor C2. Thus, the current, IL2 flow into the output terminal and charge the output capacitor, Co.

Fig. 11 Current flowing of the proposed boost converter in mode 3 operation

iv. Operation of mode 4 (t4 t5). Referring to Fig. 12 that decribes this mode, both the switches, Z1 and Z2 are turned on under zero current switching at time, t4. This soft switching property is helpful for reducing the switching losses. Here, while the primary current, IL1 increases, the secondary current, IL2 decreases. Moreover, the output terminal is still energized by flowing current from secondary inductor, L2, though the current magnitude decreased gradually. After t = t5, the operation of the boost converter returns to mode 1.

Fig. 12 Current flowing of the proposed boost converter in mode 4 operation

D. Mathematical Analysis on the Proposed Boost Converter Operation

Operation modes 1 and 3 are called the steady state operation modes while operation modes 2 and 4 are called the transient operation modes. From here, operation modes 1 and 3 for the ON and OFF switching states are considered for the mathematical analysis of the proposed boost converter. Considering the mode 1 operation, when the switch Z1 is turned on, a loop is formed on the primary side, consisting of Vin, L1 and switch-on (Z1). By assuming Z1 is an ideal switch (resistance = 0) and applying the Kirchhoffs voltage law Alexander and Sadiku, 2005() on this loop, the voltages across the primary inductor, L1 can be expressed as,

(5)

By applying the Kirchhoffs voltage law to equation (4), the voltage across the primary inductor (L1), VL1 can be expressed as,

(6)

Besides that, the voltage across the primary inductor (L1), VL1 can also be expressed as,

(7)

While, the voltage across the magnetizing inductor, Lm can be expressed by,

(8)

Considering the current at Lm equals the current at L1 (ILm = IL1), and substituting (7) into (8), resulting equation for the voltage across the magnetizing inductor, Lm as follow,

(9)

By substituting (4) into (9), the voltage across magnetizing inductor, Lm can be rewritten as,

(10)

When the equation (3) is substituted into (10), the voltage across magnetizing inductor, Lm becomes,

(11)

Furtheremore, substituting (5) into (11), the voltage VLm becomes,

(12)

Regarding the voltage across the leakage inductor can be derived by substituting (12) into (6), thus resulting following equation,

(13)

Considering that the coupled inductor acts as a transformer and substituting (11) into (2), the voltage across terminals of the secondary inductor (VL2) is given by,

(14)

The voltage across terminals of the capacitor C3 (VC3), is the summation of voltage across the secondary inductor, L2 (VL2) and voltage across the capacitor, C2 (VC2), which is given by,

(15)

Now consider the mode 3 operation and apply the Kirchhoff's voltage law. The voltage across the primary coupled inductor (VL1) becomes,

(16)

Since in steady state time, the inductor voltage over one time period (TS) which is the summation of voltages during switching on (ton) and switching off (toff) must be zero Mohan et al. 2003().

(17)

(18)

Dividing (18) both sides by TS and rearranging yields,

(19)

where,

TS : switching period (TS = ton + toff),

d : duty cycle of the triggering switching signal d = ton/toff.

From (19), it can be noted that at steady state condition, the switching voltage, Vz1 is greater than Vin. By applying Kirchhoffs voltage law on the primary side of the circuit, the voltage VL1 can be derived as,

(20)

Substituting (19) into (20), VL1 can be rewritten as,

(21)

Furthermore, by substituting (21) into (11) the voltages across the magnetizing inductor, VLm becomes,

(22)

Voltage VC1 is the summation of the voltages VLk, VLm and Vin. Voltage VC1 is the summation of the voltages VLk, VLm and Vin. Assuming that the diode D1 is an ideal diode, the open switch voltage, VZ is equal to the voltage across C1 (VC1) and it is given by

(23)

Substituting (23) into (19), the voltage across C1, VC1 becomes,

(24)

The relationship between the output voltage of auxiliary boost, VC2 and the input voltage of auxiliary boost, VC1 applies the relationship of input-output voltage of the conventional boost converter Mohan et al. 2003() and is given by,

(25)

Substituting (24) into (25), the output voltage of auxiliary boost, VC2 becomes,

(26)

By substituting (26) into (15), the voltage across C3, VC3 becomes,

(27)

Substituting (22) into (14), the secondary inductor voltage, VL2 becomes,

(28)

By applying the Kirchhoffs voltage law, the output voltage of the proposed boost converter, VO is the summation of voltages VC1, VC3 and VL2. Hence, the output voltage is represented as,

(29)

Moreover, substituting (24), (27) and (28) into (29), the output voltage of the proposed boost converter, VO is obtained as follow,

(30)

If both sides of the equation (30) are devided by Vin, it will obtained that the proposed boost converter will provide voltage gain (VO/Vin) as follows,

(31)

By assuming the coupling coefficient, k is ideal (k = 1.0), then the voltage gain, Gi becomes,

(32)

Referring to the equations (31) and (32), it is obvious that the voltage gain of the proposed boost converter is much greater than the voltage gain of the conventional boost converter as discussed in chapter II. Besides, depending on the duty cycle (d), the voltage gain is also influenced by the turns ratio (n) and coupling coefficient of coupled inductor.E. Performance Hypothesis Of The Proposed Boost Converter

Based on operation analysis of the proposed boost converter, it can be hypothesized that the proposed boost converter will give high performance and better than previous studied boost converter.Assuming that k = 1 and n = 1, for d = 0.5 and referring to equation (31) the proposed boost converter gives a voltage gain (Gi) of four times greater than the coupled inductor based high step-up converter introduced by Zhao & Lee (2003). It is also noted that the proposed boost converter results voltage gain (Gi) of 1.333 times the voltage gain of the high step-up boost converter introduced by Wai and Duan (2005). For the various values of the duty cycle d, the voltage gain is calculated and plotted as depicted in Fig. 13. The voltage gain curve of the proposed boost converter is denoted by line labeled star, the pure line represents the conventional boost converter voltage gain curve and the triangle and circle lines represent the other previous topology coupled boost converter voltage gain. It can be seen from Fig. 13, the voltage gain of the proposed boost converter is much greater than the other compared converters.

Fig. 13 Comparison of boost converter voltage gains for k=1 and n=1

IV. Results And DiscussionThis chapter presents the simulation and experimental results of the proposed boost converter and the HFLC based MPPT algorithm of the PV MPPT controller. The converter simulation results compare and evaluate the performance of the four boost converter topologies, namely, the conventional boost converter with R-C-D snubber, boost converter using coupled inductor with C-D snubber, boost converter using coupled inductor with passive snubber and proposed boost converter using coupled inductor with active snubber.The four boost converter topologies as mentioned above are tested using the parameters shown in Table I. The values of these parameters are used in the OrCAD/PSpice simulation and in testing the prototype boost converter hardware. For the experimental testing, the Skytronic 600VA and TR8072AN 6kVA power supplies have been used as the DC supply power. The output waveforms are captured using the Tektronix TDS2024B digital oscilloscope with 200MHz bandwidth. The current and voltage are measured using the ampere meter SK-5000E model and the digital meter DMM3800.

TABLE I Parameter values for boost converter testing

ParameterValue

Switching frequency50 kHz

Input voltage30, 50, 100, 200 V

Resistive load210

Duty cycle0.2, 0.3, 0.4

F. Simulation and Experimental Triggering Signals

To ensure proper synchronization of boost converter operation, the triggering signals, Vpwm for the developed boost converter switching are first considered. Figs. 14 (a) and (b) show the waveforms of the triggering signals obtained from simulation and experiment respectively for the duty cycles of 0.3. From the triggering signals shown in the figures, the simulation and experimental triggering signals are in good agreement as the signals are of square waveform with a lower side voltage, 0V and an upper side voltage, 15 V. The 15 V voltage can turn on the IGBT of the boost converter, whereas, the 0V is used to turn off the IGBT. However, there is slight difference in the wave shape of the triggering signals obtained from experiment. This is due to the parasitic impedance between the gate and emitter ports of the IGBT, which is neglected in the simulation.

(a)

(b)

Fig. 14 Gate triggering signals at duty cycle 0.3 obtained from (a) PSpice simulation and (b) experiment

G. Boost Converter Performance in Terms of Voltage Gain

To evaluate the performance of the proposed boost converter, it is compared with other boost converter topologies. Fig. 15 shows the output voltages of the proposed boost converter and the compared boost converters, obtained from the PSpice simulation for input voltage, 30 V and duty cycle of the triggering signal set at 0.3. From the figure it can be observed that the output voltage of the proposed boost converter (141 V) is the highest compared to the output voltages of the compared boost converters, namely, conventional boost converter (44 V), Zhaos boost converter (71 V) and Wais boost converter (119 V).

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Fig. 15 Output voltages of the boost converters from PSpice Simulation

Figs. 16 (a) and (b) depict the output voltages obtained from experiment for the proposed boost converter and the conventional boost converter, respectively. From the experimental results, it can be observed that the output voltages of the proposed boost converter (140 V) is approximately three times greater than the conventional boost converter (45V).

(a)

(b)

Fig. 16 Output voltages obtained from experiment (a) proposed boost converter and (b) conventional boost converter

Comparing the output voltages obtained from simulation and experiment, it is also noted that there are slight differences in magnitudes of the output voltages of the proposed and the conventional boost converters. This may be due to the fact that the hardware components in the experimental work such as resistors, inductors and capacitors have tolerance value but in the PSpice simulation model they do not have it. Moreover, in the library of the OrCAD/PSpice does not provide all the various components of existing brands on the market. Even so in this research the value of the components in the experiment and simulation has been made equal.H. Effect of Duty Cycle on the Converter Output Voltage

The effect of the duty cycle on the boost converter output voltage was investigated. Fig. 17 shows the simulation results of the output voltages of the proposed boost converter for a 30 V input voltage. From the figure, the output voltages are 113 V, 141 V and 180 V at duty cycles of 0.2, 0.3 and 0.4, respectively. The effect of duty cycle and various input voltages on the simulation output voltages of the various boost converter topologies is summarized as shown in Table II. It can be observed that by increasing the duty cycle, the output voltages of the various boost converters are increased. However, the proposed boost converter produces the highest output voltage among all the compared boost converters.TABLE II Comparison of simulation output voltages of the various boost converters at various input voltages and duty cyclesInput voltage (V)Duty cycleOutput voltage (V) of various boost converters

Conventional.ZhaoWaiProposed

300.23966104113

0.34471119141

0.45278139180

500.265111176191

0.374120201230

0.487132235287

1000.2131224356388

0.3150242412468

0.4176267479584

2000.2263450717870

0.3301487827954

0.43525369551175

Fig. 18 shows the output voltages of the proposed boost converter obtained from experiment at duty cycles of 0.2, 0.3 and 0.4, respectively. At an input voltage of 30 V, the converter output voltages are 116 V, 140 V and 200 V, respectively. It can be observed that by increasing the duty cycle, the output voltages of the boost are increased. I. Result of Conversion Efficiency of the Boost Converter

Fig. 19 shows the plot of the proposed and conventional boost converters efficiency against input power based on observations. From the figure, it is shown that the maximum efficiency of the proposed boost converter is 90.05% at input power of 3.6 kW. It is also noted that the proposed boost converter is able to enhance the efficiency of the conventional boost converter by approximately 8.31%.

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Fig. 17 Output voltages of the proposed boost converter in PSpice simulation

(a)

(b)

(c)

Fig. 18 Effect of duty cycle on output voltage of the proposed boost converter from experiment at 30 V input voltage and duty cycle (a) 0.2, (b) 0.3 and (c) 0.4

Fig. 19 Proposed and conventional boost converter efficienciesV. Conclusions

In this chapter, the simulation and experimental results for the proposed boost converter and MPPT controller have been presented. The high-frequency PWM signal for triggering of gate control signals for the boost converter and the high gain of the proposed boost converter has been validated.This thesis has presented a new MPPT controller for PV generation system using a new coupled inductor based boost converter design with a novel algorithm for the MPPT. Three research objectives have been presented for the development of the new MPPT controller. To accomplish the first objective of the research, an improved high performance boost converter has been designed and implemented using a coupled inductor and an active snubber circuit as an auxiliary small boost for increasing the output voltage gain. A hardware prototype of the proposed boost converter has been developed and tested to verify the new topology. The simulation and experimental results showed that the combined use of coupled inductor and active snubber can produce higher voltage gain in DC-DC conversion. The proposed boost converter gives average voltage gain of 3.26 times the voltage gain of the conventional boost converter. Moreover, the proposed boost converter gives better energy conversion efficiency (90.05%) compared to the efficiency of the conventional boost converter (81.74%).References

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[14] Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification, IEEE Std. 802.11, 1997.PWM

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3

C

-

+

in

V

1

Z

D

o

R

o

C

1

C

3

D

O

D

1

D

1

L

2

L

t1 t2 t3 t4 t5 time

H

0

VGZ

99.97

99.96

99.95

99.94

99.93

Time (ms)

V(input)

Voltage (V)

200

100

0

200.0

199.8

199.6

199.4

199.2

199.0

Time (ms)

Voltage (V)

0

50

100

150

Wais boost converter

Zhaos boost converter

Conventional boost converter

Proposed boost converter

Input voltage of converter

200.0

199.8

199.6

199.4

199.2

Ts = 0.02ms

Ton = 0.006ms

Voltage (V)

15

10

5

0

99.99

99.98

Couple Inductor based boost (Zhao & Lee 2003)

Conventional boost

Couple Inductor based boost (Wai & Duan 2005)

Proposed Boost

Voltage gain (Gi)

Duty cycle (d)

35

30

25

20

15

10

5

0.8

0.7

0.6

0.5

0.4

0.3

0.2

199.0

Time (ms)

V(D 0.2)

V(D 0.3)

V(D 0.4)

50

55

60

65

70

75

80

85

90

95

1st

2nd

3rd

4th

5th

6th

7th

8th

9th

10th

11th

12th

Proposed boost

Conventional boost

Conversion efficiency (%)

Observation (Watt)

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Cin

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