A High Step up Boost Converter Using
Coupled Inductor with PI Control

Saurabh; Dr.P.K.Saha; Dr.G.K.P; a

A High Step up Boost Converter Using Coupled Inductor with PI Control

Saurabh¹, Dr.P.K.Saha² and Dr.G.K.Panda³

PG Student [Power Electronics and Drives], Dept. of EE, Jalpaiguri Government Engineering College, Jalpaiguri, West Bengal, India
Professor, Dept. of EE, Jalpaiguri Government Engineering College, Jalpaiguri, West Bengal, India
Professor and HOD, Dept. of EE, Jalpaiguri Government Engineering College, Jalpaiguri, West Bengal, India

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Abstract

The paper proposes a high step up boost converter. The proposed converter has used a coupled inductor with switched capacitors. The capacitors were made to get charged in parallel and were made to get discharged in series by the configuration to achieve high step up voltage gain. And the voltage across the load is maintained constant by using a closed loop control. The operation and steady state analysis of the configuration has been shown in detail. Finally, a circuit with 24-V input, 400-V output, and power of 200W has been implemented in MATLAB software to verify the proper working and performance of the proposed configuration.

Keywords

High step-up Boost Converter, Coupled Inductor, Switched Capacitor, PI Controller.

INTRODUCTION

Boost converter is one of the most important and widely used devices of modern power applications. These converters are electronic devices used to change DC electrical power efficiently from one voltage level to another. They provide smooth acceleration control, high efficiency, and fast dynamic response. There are FOUR main types of converter usually called the buck, boost, buck-boost and Boost converters. The buck converter is used for voltage stepdown/ reduction, while the boost converter is used for voltage step-up. The buck-boost and Cuk converters can be used for either step-down or step-up.

Basically, the DC-DC converter consists of the power semiconductor devices which are operated as electronic switches and classified as switched-mode DC-DC converters. Operation of the switching devices causes the inherently nonlinear characteristic of the DC-DC converters. Due to this unwanted nonlinear characteristics, the converters requires a controller with a high degree of dynamic response. Pulse Width Modulation (PWM) is the most frequently consider method among the various switching control method. In DC-DC voltage regulators, it is important to supply a constant output voltage, regardless of disturbances on the input voltage.

Nowadays, the control systems for many power electronic appliances have been increasing widely. Crucial with these demands, many researchers or designers have been struggling to find the most economic and reliable controller to meet these demands. The idea to have a control system in dc-dc converter is to ensure desired voltage output can be produced efficiently as compared to open loop system. Controller for the PWM switching control is done by Proportional-Integral (PI) controller.

Many different methods have been proposed to improve the efficiency of the converter and to achieve high voltage gain, which can be done by using a switched capacitor and a coupled inductor is used for high gain by adjusting its turns ratio. Voltage spikes may occur due to the coupled inductor. For which we have used an active clamp circuit with coupled inductor which avoids voltage spikes.

Figure 1 shows the block diagram of the proposed converter with closed loop control such that the voltage drift problem is minimized and the desired output is maintained. The output voltage was then taken as feedback and compared with desired value of output voltage and the difference is then fed to PI control which then produces the PWM signal to the switch of the converter.

SYSTEM MODEL AND ASSUMPTIONS

Figure 2 shows the configuration of the proposed circuit. The circuit has a boost converter with coupled inductor, switched capacitor and a clamp circuit. The equivalent circuit of the coupled inductor consists of a magnetizing inductor Lm, leakage Lk, and an ideal transformer. The leakage inductor energy of the coupled inductor is recycled to capacitor C₁, and thus the voltage across the switch S can be clamped. The voltage across the capacitors C₂, and C₃ can be adjusted by the turns ratio of the coupled inductor. For these reasons the voltage of switch is reduced significantly and low conducting resistance Rds(on) of the switch can be used. Thus high step-up voltage gain can be achieved.

To simplify the circuit analysis, these conditions have been assumed.

A. Capacitors C₁, C₂, C₃ and C₀ are very large which makes voltages V_C₁, V_C₂, V_C₃ and V_O to be constant in one switching period.

B. The power devices used are ideal, but the parasitic capacitance of the power switch was considered.

C. The coupling coefficient of the coupled inductor k is equal to L_m/(L_s+L_k ) and the turns ratio of the coupled inductor n is equal to N_s /N_p .

MODES OF OPERATION AND ANALYSIS

There are five operating modes in one switching period.

1) Mode I (t₀, t₁): Mode will start when the switch S is turned ON. Diodes D₁ and D₀ are off, and D₂ and D₃ are on. The current through Lk starts increasing linearly. The inductor Lm starts storing energy from the source voltage. Voltages VC₂ and VC₃ being connected in series to charge the output capacitor CO which will then provide energy to the load. When current through D₀ becomes zero, operating mode ends.

2) Mode II (t₁, t₂): Here S will be kept ON. Diodes D₁, D₂ and D₃ are off and D₀ is on. The Lm starts getting charged due to the source voltage. Capacitors C₂ and C₃ are also get charged due to the source via the coupled inductor. Capacitor C0 discharges to the load to maintain the desired output voltage. Switch S turns off to end the mode.

3) Mode III (t₂, t₃): S is turned OFF in this mode. Diodes D₁, D₂ and D₃ are off, and D₀ is on. Inductors Lk and Lm are discharged to the parasitic capacitor of the switch Cds. Capacitor CO continues to discharge and to provide energy to the load. Now the voltage across C₁ is equal to Vin+Vds, diode D₁ now turned on and the mode ends.

4) Mode IV (t₃, t₄): S is kept OFF. Diodes D₁ and D₀ are turned on and D₂ and D₃ are off. Inductors Lk and Lm are discharged to charge capacitor C₁. Lk gets discharged quickly. No current flows through the secondary side and L2 charges capacitor C0 and maintains the voltage across the load, which makes D₀ to switch off and mode ends.

5) Mode V (t₄, t₅): S is kept OFF. Diodes D₁, D₂ and D₃ are turned on and D₀ is turned off. Inductors Lk and Lm are discharged to charge capacitor C₁. MaK_Ing the voltage across the switch equals Vin+VC₁. And L2 is charging both the capacitors C₂ and C₃. The mode ends when the switch is turned ON and makes the next switching period.

SIMULATION RESULTS AND DISCUSSIONS

Figure 3 shows the MATLAB Simulation diagram of a high step-up boost converter using coupled inductor with PI control. The duty ratio of the switch is adjusted by PI Controller to obtain the require output.

Figure 4 shows the output voltage V₀=400.3V with 18.75% maximum peak overshoot and the output voltage is well controlled by PI controller feedback.

Figure 5 shows the output current of 0.5A which shows the proposed controller was well able to control the output current as desired.

Figure 6 shows the pulse generated and given to the switch for its proper worK_Ing and the maintenance of the desired output.

From Figure 7 it is very much clear and can be calculated that the output voltage VO is not much stable with K_P=0.009 and K_I=1.1, 1.2, 1.3, 1.5 and the maximum peak overshoot, rise time is also more than the output in Figure 4. The output voltage waveform shown in Figure 4 has less settling time. Hence, we have chosen the values for K_P and K_I as in serial number 4 from the table i.e. K_P=0.009 and K_I=1.4. While the converter specifications were kept same.

CONCLUSION

Here a high step-up boost converter using coupled inductor with proportional integral control is simulated. By the capacitor charged in parallel and discharged in series by the coupled inductor, high step-up voltage gain of 400V is achieved. As the output voltage of the converter with PI Control has minimum overshoot and produces a constant output current shown. These studies could solve many types of problems regardless on stability because as we know that proportional integral controller is an intelligent controller to their appliances.

Further it can be simulated with different types of feedback control like fuzzy logic control, artificial neural network, genetic algorithm and others can be used for advanced tuning and to check the constant output voltage with least ripple and to support different appliances with different voltage ratings.

Tables at a glance

Table 1

Figures at a glance


Figure 1	Figure 2	Figure 3	Figure 4

Figure 5	Figure 6	Figure 7

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