MATLAB/SIMULINK based simulations of KY converter for PV panels powered led lighting system

Received Feb 19, 2019 Revised Mar 1, 2019 Accepted Jul 18, 2019 The main objective of this research work is to develop KY conveter topology for renewable energy sources.Solar energy is the readily available and is the cheapest form of energy. It is non-polluting and environment friendly. The development of high static gain DC-DC converters is an important research area due to the crescent demand of this technology for several applications supplied by low DC output voltage power sources. It is used to provide the uninterruptable power supply and battery powered to the system. So here, step-up DC-DC converters based on the KY converter are proposed for LED lighting systems. The proposed topologies present high voltages and high efficiency for low input voltage and high output voltage applications. The simulation results of the proposed topology have been presented using MATLAB/SIMULINK software.


INTRODUCTION
The growth of power systems emphasizes all aspects of electrical energy, innovation in power generation, distribution and Utilization , alternative resources, and efficient power electronic devices. Latest power electronic devices plays vital role for the power conversion, delivery, and usage of energy in the power system network. The activity ranges from controls for large utility systems to energy harvesting devices for micro-sensors. Electrical energy continues to be the foundation of the modern economy. The growth of solar energy, wind energy, and other resources, combined with trends such as electric and hybrid vehicles will a have profound impact on global society. Large number of the simulation study of power systems and power electronics converters were reported . The Photo Voltaic (PV) power generation system is gaining more and more visibility, while the worlds power demand is increasing and awareness of the importance of protecting the global environment has been growing. The PV systems are modular, hence the major advantage of these systems is that they can be simply adopted in existing buildings and can be installed anywhere. In addition, manufacturers have designed various models, which can be placed in different types of houses or buildings to achieve better performance.
An interesting work [33], derives the voltage loop gain and the closed loop transfer function from reference voltage to output voltage for the voltage-loop of a pulse width modulated (PWM) dc-dc converter operating in continuous-conduction mode (CCM) with peak current-mode control (PCM). In PV system topology, a series connected to PV module is used to create a high voltage string connected to the DC-DC converter [34][35][36][37]. However, under real conditions the performance of this scheme is negatively affected if all its modules are in homogeneously illuminated. All the modules in a series array are forced to carry the same current even though a few modules, under shade, produce less photocurrent. The shaded modules may get reverse biased, acting as loads, and dissipating power from fully illuminated modules in the form of heat. On the other hand, the inhomogeneous illuminated part makes PV array have multiple power peaks. To avoid thermal overload, substrings of cells inside the interconnection circuit of modules are bridged by bypass diodes. Although it is possible for string circuits to reduce the influence of partial shadow to some extent, they could not solve the maximum power point tracking (MPPT) problem in the shaded string circuit because the presence of the PV array has multiple power peaks due to the existing MPPT schemes which are unable to discriminate between the local and global power peaks [38]. To overcome this problem a series string of the DC-DC converter with corresponding string current diverter circuits based on buck-boost converter is used. The string current diverter circuit is independently utilized to balance the output voltage of the DC-DC converter under shadow conditions. The proposed circuit enables the individual PV modules to operate effectively at the MPPT by imposing an optimum ratio under any conditions. An interesting work on KY Converter is presented in [39]. In this research paper the authors have proposed the boundary for the DCM operation region, DCM dc voltage and small-signal transfer functions. Another work on KY converter is proposed by K. I. Hwu et.al in [40]. This work focuses on KY Converter and Its Derivatives. Latest works on KY converter has been reported in [41][42][43].

THE PROPOSED SOLUTION: PROPOSED KY CONVERTER MODEL
The proposed block diagram of the system is shown in Figure 1. The designed KY converter is implemented in standard 0.18-μm CMOS technology, consisting three power transistors, a filter network, and a current mode control network, demonstrating excellent performance. This paper is organized as follows. Section II presents the study of an integrated KY converter in both system and circuits level, including operating modes, effects of parasitic resistances, transistor sizes, power loss, output voltage ripples, design of power components, and the load and line regulations [44]. In addition, various aspects of the KY converter are also theoretically analyzed to compare with boost converter to show its advantages. Section III presents the circuit implementation details of the proposed integrated KY converter, based on the analysis developed in Section II. The measurement results and comparison with recent works are provided in Section IV. Finally, Section V concludes this paper.

PV panel
The Monocrystalline PV panels are used. 40 cells are connected in series to form a single module. Voltage of single cell is 0.6V so the voltage of a single module is 24V. In this proposed method 3 modules are used.

MPPT (Incremental Conductance)
The incremental conductance algorithm is based on the fact that the slope of the curve power vs.

KY CONVERTER CIRCUIT DIAGRAM
The circuit diagram of the KY Convereter is represented in Figure 3. The KY buck-boost converter reported in has many good features when compared to other DC-DC converters for portable applications. The KY buck-boost converter uses only two switches, which are operated in synchronous way. This reduces the cost and size of the circuit and can operate in bidirectional mode. The polarity of the output voltages of buckboost, Zeta, SEPIC, Cuk, and single-switch buck-boost converters are opposite in polarity with input voltage whereas the KY buck -boost converter provides the output voltage of same polarity with input voltage. The KY buck boost converter does not have RHP zero that increases stability and transient response. A simple voltage mode analog controller is proposed in this work for the KY buck-boost converter to regulate the output voltage.

Mode 1(S1 ON, S2 OFF):
In Figure 4, the input voltage provides energy for C1 and L1 making C1 getting charged and L1 to be magnetized as shown in equivalent circuit diagram, At the same moment, the input voltage along with capacitor C2 supplies the energy for inductor L2 and to the output which causes C2 to be discharged and L2 getting magnetized.

Mode 2(S1 OFF, S2 ON):
The equivalent circuit diagram during this mode of operation as show in Figure 5. The energy stored in inductor L1 and capacitor C1 are released to capacitor C2 and to the output via inductor L2 causing C1 to be discharged and L1 to be demagnetized. At the same moment, the voltage across L2 is vC2 minus Vo, thus making C2 to be charged and L2 being demagnetized.

PV panel
In electronics, a driver is an electrical circuit or other electronic component used to control the KY converter. They are usually used to regulate current flowing through a circuit or to control other factors such as other components, some devices in the circuit. The term is often used, for example, for a specialized integrated circuit that controls high-power switches in switched-mode power converters.

SIMULATION DIAGRAM OF PROPOSED KY CONVERTER CIRCUIT
The simulation diagram of KY converter is shown in the Figure 6. The KY buck-boost converter with the PI controller is simulated in MATLAB/SIMULINK as shown in Figure 4. The output voltage when operated in buck and boost mode in MATLAB simulation are shown in Figure 5 respectively.

Simulation diagram of PV panel
The subsystem of PV panel is shown in the Figure 7. The solar cell is a physical system it cannot be directly connected to the Simulink model so a converter is used in between them to connect the two systems.

Simulation diagram of MPPT technique
The simulation diagram of MPPT technique is show in the Figure 8. In the proposed method Incremental Conductance Algorithm is used to track the MPPT. In this MPPT the maximum power is tracked by comparing the previous value of voltage, current and power with the recent values and the duty cycle is given accordingly.

Simulation diagram of KY converter
The simulation diagram of KY converter is shown in the Figure 9. The KY buck-boost converter with the PI controller is simulated in MATLAB/SIMULINK. The output voltage when operated in buck and boost mode in MATLAB simulation are shown in Figure 5 respectively.

Simulation diagram of string current diverter
The simulation diagram of String Current Diverter is shown in the Figure 10. The String Current Diverter diverters back the output current of the DC-DC converter in order to maintain the output voltage of the DC-DC converters constant. String current diverter is switched ON or OFF according to balance or imbalance of output currents of PV modules. With the existing measures of output currents of PV modules, an error calculation is carried out and compared with a threshold value ε and the SCD is switched ON or OFF accordingly.

RESULTS AND DISCUSSIONS
The output current of PV panel is shown in Figure 11. Figure 11. PV panel current (X-axis 1 div=0.5s Y-axis 1 div=1A) The output voltage of KYconverter is shown in Figure 12 and Figure 13.

Drawbacks in this system
If the input power is higher than the required one, then the circuit components may lead to fault.

Advantages of Proposed System
a. KY boost converter has higher voltage ratio than the traditional boost converter does. b. Besides, the input and output inductor currents are continuous, different from the traditional boost converter. c. Hence this converter is very suitable for low ripple applications.

CONCLUSIONS
This paper presents design and implementation of the KY buck boost converter. A simple PI controller is proposed and designed to regulate the output voltage of the converter. Exclusive Simulation results are presented to verify the functionality of the converter with the controller under steady state and dynamic conditions.The proposed conveter design and simulation results will be useful for power system and power electronics Engineers to explore the possibilities of developing hardware and suitable for real time high voltage power transmission. KY conveter will play a vital role in integrating intermittent renewable energy sources effectively in to the existing power grid.