Augmented ASC Network for Photo Voltaic Applications

Augmented ░ ABSTRACT - This work uses a DC-DC converter that employs an Active Switched Capacitor (ASC) to provide high gain that makes it appropriate for the Photo Voltaic (PV) system. The transformer less converter with an ASC network consists of a capacitor and a diode that boosts voltage effectively. The well-liked converter operates effectually on both Continuous Conduction Mode (CCM) and Discontinuous Conduction Modes (DCM). The suggested topology of converter is easy to design, and it renders a less stress on auxiliary diode and capacitors. This preferred converter scheme is validated through MATLAB Simulink and the outcomes are confirmed using hardware prototype.

Step up gain converters are the class of converters that lifts the voltage to high value. Photovoltaic (PV) panels and battery sources generate low voltage outputs which should be increased to high voltages for grid-tied and standalone applications [1]. High gain converters are essential for renewable energy applications like photo voltaic systems, fuel cells etc. [2]. In [3], boost converter designed with switched inductor configuration is described. In order to boost voltage gain, Active Switched Inductor (ASL) converters are combined with Active Switched Capacitor (ASC) and Voltage Lift (VL) boosting techniques. Currently, renewable energy has wide application due to the energy crisis. By using the ASC based converter circuit, a higher gain can be achieved with high efficacy and less stress on the switches [4]. By utilizing split inductors, boost converters achieve a voltage increase. The converter that has low energy consumption, lesser-voltage stresses on switches and less control complexity is normally preferred in many applications. The high gain voltage conversion feature is more attractive, and it is employed for harnessing energy from renewable energy sources like fuel cells and photo voltaic. There is a new DC-DC high gain converter published in [5] that provides steady current and can be applied to DC microgrids. An improved DC-DC converter that is non-isolated and has low switching stress is described in [6]. A capacitor and inductor are utilized to maintain the converter voltage gain. This is achieved via a multi-cell arrangement as well. This paper introduces a switched capacitor DC-DC converter for boosting the voltage generated by solar panels to a higher level. Several works are reported in the literature for high gain DC-DC converters. With photovoltaic cell as the supply, this paper explains the multiplier topology SEPIC converter employed for renewable energy sources as the converter can provide high voltage gain [7]. The renewable energy sources provide intermittent output power. Flow of power can be controlled with the help of stepup DC-DC power converter that gives rise to efficient management of energy [8]. We present the active switched inductor [ASL] network with two capacitor cells for obtaining the desired voltage gain for PV and grid-tied applications. [9]. According to [10], DC converter output voltage can be adjusted by a fuzzy logic controller. The boosting power stage of converter is employed via current-fed voltage multiplier for distributed energy applications [11]. The high gain voltage conversion feature is more attractive, and it is employed for harnessing energy from renewable energy sources like fuel cells, photo voltaic. Based on experiments, the suggested converter can meet the converter performance requirements with an efficiency of around 95.5% [12]. Normal boost converters never provide the sufficient gain hence the transformer less high gain converter is preferred in this scope. Here the single stage conversion with ASL and a passive SC network is accomplished which makes this topology more attractive for renewable applications [13]. As a result of high output voltage, it is crucial to reduce the voltage stress across each conducting diode and switch. Thus, for boosting the gain, quasi ASL configuration is proposed. In [14], numerous SL and SC circuits are compared, and the voltage gain is boosted. The proposed DC-DC converter offering high gain uses fuzzy logic controller for uplifting the voltage obtained from solar panel [15]. In this scope, a novel H-SLC (Hybrid Switched inductor and capacitor) network is analyzed and implemented to enhance the voltage gain with high efficiency [16]. In [17], a new stepup converter of n stage is presented that find its application in integrating low voltage from solar PV. An active coupled inductor comprises of two coupled inductors for a renewable energy system is proposed in [18]. A transformer less three switched capacitor network that attains high gain with lesser duty ratio is elaborated in [19]. The literature review reveals there is a need to introduce high gain converters that prevail over the shortcomings like switching stress, high component count and high duty ratio. One such converter that overcomes the above said drawbacks is proposed in this paper.

░ 2. MATERIALS AND METHODS
There is a constant rise in energy demand worldwide, and scientists are still searching for ways to address these needs by exploiting alternative sources of energy. In terms of alternate sources of energy, solar energy offers the most advantages since it is abundant and clean. The schematic representation of PV system is portrayed in Figure 1. The converter serves as an integrating platform for harvesting energy from renewable sources. Here the interface between solar and load is ASC based DC-DC converter. It is possible to utilize the energy acquired from the PV for a variety of applications. Because it offers high gain in voltage, the proposed system is ideal for grid-connected applications.

Active Switched Capacitor Based Exalted Convolution
The proposed converter topology has a conventional ASL converter. Along with the existing ASL network, a diode and a capacitor are included to ensure that the power switch is under low stress and therefore provides enhanced gain. The proposed converter circuit is presented in Figure 2. This active switched capacitor-based converter is made to increase the output of a solar PV system. The traditional ASL network contains inductors L1 and L2 and switches S1 and S2. Diode D1 and capacitor C1 share a common switch S1 in the existing circuit.

Proposed Power Converter Operation
There exist two operating modes. The converter is made to operate under CCM. It is taken that all the devices used in the converter are in ideal state. The current flow path under CCM of converter is picturized in Figures 3(a) and 3(b).

Mode 1
In this mode, switches S1 and S2 are turned ON so that inductors L1 and L2 are charged parallelly and capacitors C1 and C0 are being discharged. In this condition diodes D1 and D0 remains off due to reverse bias. Capacitor C0 is feeding the load and L2 is getting charged via load. Equation (1) and (2)

Mode 2
The diodes (D1 and D0) are ON, when switches S1 and S2 are OFF. The inductors L1 and L2 now deliver stored energy to charge the capacitor C0. Meanwhile, capacitor C1 is charged through inductor L1. The inductor voltages are derived as in equations (3) and (4).

Converter Design Equation
Assume the converter is operated in CCM and the design equations are given in equations (5) to (10).

Converter Switching Waveforms
The customary switching waveform in CCM mode is depicted in figure 4.

Open Loop Simulation Results of the Proposed Converter
The simulations are performed in open loop and the waveforms obtained from simulation are displayed in figure 5 and figure 6.

Closed Loop Simulation Outcomes of the Proposed Converter with Solar MPPT technique
The closed loop simulation of the proposed converter is then performed with solar MPPT and the results are analyzed. The specifications of the solar PV panel are mentioned in table 2.
░  Table 3 summarizes the results of the converter for quick changes in load under 1000 W/m 2 of irradiation and 25°C of temperature. The voltage waveform attained is depicted in Figure 7 (a).

Type 1: For 1000W/m 2 Irradiation and Temperature of 25°C
░    Table 4 displays the simulation outcomes achieved with 850 W/m 2 irradiation and 20 ˚C temperature for different loads.

Comparative Results of Proposed Converter
The analogies of various converter topologies are displayed in Table 9 to justify that the suggested converter exhibits the high gain. Figure 9 portrays the representation of propounded converter's performance with other topologies of the converters. The voltage gain obtained from suggested converter is high compared to other traditional converters.

Hardware Results
The real time implementation of proposed converter of 100 W power rating with 120V rated supply voltage is designed with the derived parameter values as shown in table 5. Figure 10 shows the hardware arrangement of the proposed converter offering high gain. Figures 11 and 12 portrays the gating signal and output voltage observed with the prototype.  The gate signal generation is done using TL294 IC to drive the MOSFET switches.

░ 5. CONCLUSION
ASC-based converters with a higher gain are proposed here in order to harness energy from a PV panel. By operating the converter with optimal duty cycle, desired gain value of output voltage is obtained. This converter is compact as it has lesser number of elements. An illustration of the preferred converter's response to constant insolation level and temperature was presented. A Proportional Integral controller keeps a steady output voltage under load modifications. Perturb and Observation MPPT method is employed for acquiring maximum power from the solar PV panel. The efficacy achieved is 80-90% in simulation.
With the MATLAB/Simulink platform the findings are substantiated. At rated condition the converter efficiency achieved with the experimental prototype is 85%. The proposed converter is suitable for use with renewable energy and all drive applications. The work can be further extended by implementing the proposed work with intelligent controllers.
Funding: "This research received no external funding"