A High-Power Solar PV-fed TISO DC-DC Converter for Electric Vehicle Charging Applications

Abstract

In this paper, a two-input, single-output (TISO) DC-DC converter for electric vehicle charging applications with solar photovoltaic (PV) as one of the sources is discussed. A novel, simple, and effective control strategy with maximum power point tracking (MPPT) to maximize power from PV while maintaining a constant bus voltage is proposed. A 100 V, 100 W TISO DC-DC converter is designed and comprehensive simulations are conducted under different conditions. The system characteristics are validated by comparing the results with a conventional P&O algorithm and multiple step size P&O algorithm. The proposed control strategy can precisely generate control signals to track MPPT while maintaining the bus voltage by controlling the output of a fixed DC source according to the changes in PV generation. The overall efficiency of the proposed approach is 98.67%, and the average output voltage is 99.09 V under selected conditions. The overall average output voltage ripple is 0.22% with the proposed approach, while it is 2.91% and 1.55% with the conventional P&O and multiple step size P&O MPPT techniques, respectively. Further, a 500 V, 17 kW high-power converter is designed and a simulation is carried out. The high-power converter provides an average output voltage of 496.92 V with an overall efficiency of 98.72%, and the average output voltage ripple is 0.16%. The results obtained from the simulation under the selected conditions lead to the conclusion that the converter has better efficiency and less variation in the output voltage at higher power levels with the proposed control technique.

1. Introduction

Rising fossil fuel costs and new legislation aimed at reducing CO2 emissions in conventional vehicles have increased the interest in electric vehicles (EVs). EVs require effective charging systems to “refuel” their batteries on a regular basis for smooth and continuous operation [1,2]. The simultaneous connection of a number of EVs to the electrical grid for recharging raises the power demand and generates other grid-related issues. Utilizing renewable energy sources (RES) for the recharging of EVs is one of the solutions in resolving the power grid challenges. Solar PV power generation is superior to other renewable energy sources due to the advantages that it presents. Charging stations powered by solar PV may offer pollution-free electricity to EVs, which positively impacts the environment [3,4]. However, EV charging requires a reliable and regulated power supply for efficient charging. The irregular and random output of solar PV systems necessitates the development of hybrid energy systems (HESs) employing a reliable power source with solar PV output to provide a regulated output for EV charging applications. The sources in HES are often connected independently to the load via single- or multi-stage power electronic DC-DC converters, which reduce the overall efficiency and are bulky. Multi-input (MI) DC-DC converters, on the other hand, provide simple circuits with lower costs and greater efficiency, and they integrate multiple energy sources to deliver power at a controlled voltage [5]. A two-input single-output DC-DC converter with solar PV as one of the power sources is discussed in this article. The following section describes the related works proposed in the literature, focusing on multi-input converters. The paper is further subdivided into sections as follows. Section 3 discusses the operation and design of the TISO DC-DC converter; Section 4 analyzes the simulation results, and Section 5 concludes the work.

2. Related Works

A three-level isolated MI converter is introduced in [6], with fewer components and less voltage stress on the power electronic components. When the converter circuit input inductors are selected appropriately, they operate in discontinuous conduction mode (DCM), allowing independent power distribution between the input sources. However, a transformer is required for insulation, resulting in an increased size and cost. Further, the DCM mode of operation requires complicated control schemes. In [7], a bidirectional DC-DC converter with a multi-input transformer for hybrid wind–PV–battery systems is presented. Wind power is captured in the proposed circuit through a half-bridge auxiliary converter coupled to a transformer. In contrast, PV energy is harnessed using a bidirectional buck–boost converter that controls battery charging and discharging. A single-phase, full-bridge bidirectional converter is used to deliver power to the loads and communicate with the grid. However, the system is more expensive because of the inclusion of three converters and a multi-winding transformer. Due to the existence of a transformer, isolated MI converters are only useful in highly demanding situations. As a result, non-isolated MI converters with a simple structure and higher energy density have gained popularity, considering their affordability.

An MI DC-DC boost converter is proposed in [8], which comprises a battery storage device and two boost converters, with an additional capacitor substituted in one of the converters. However, the proposed architecture has more components, a complicated control method, and lower efficiency. A high-voltage-gain MI converter with an inductor in a single-architecture form is presented in [9]. Here, zero voltage switching (ZVS) of two of the four primary switches and the management of the bidirectional power flow between the lower and upper sides of voltage require complex control techniques. In addition, coupled inductors and switches increase both the size and cost. A non-isolated MI DC-DC converter circuit is described in [10], which receives output power from a group of low-powered small wind turbines. The designed circuit architecture consists of two stages with a network of DC-DC converters, which leads to the need for more components and a cumbersome system. Furthermore, numerous steps in operation decrease the overall efficiency of the converter. A modular, non-isolated MI DC-DC converter without a coupled inductor is proposed in [11]. The proposed design uses fewer components to produce the appropriate voltage gain, which can lower the converter’s dimensions, weight, price, and losses while increasing its efficiency. However, significant stress on the power electronic components necessitates complex control schemes for continuous-input-current operation.

Recently, [12] introduced a three-input DC-DC boost converter. It has a standard buck–boost and a boost converter with one bidirectional battery port and two unidirectional power source ports. The large number of passive and semiconductor components in the system has resulted in an increased size and cost with less efficiency. A further MISO step-up converter is introduced in [13], where the load is fed from two sources either separately or simultaneously. This structure is simple and improves the power output, power source utilization, and fault tolerance of the source. However, the switches are subjected to high voltage stress and thus operate with lower efficiency. An MI DC-DC converter based on SEPIC is presented in [14], with an initial stage that connects many input voltage sources and a battery management system (BMS) stage that allows the charging and discharging of the battery. However, during the operation of the proposed converter, the power electronic components and diodes are subject to considerable stress. The large number of components in the system further increases the costs and reduces the efficiency. An MI buck DC-DC converter with a single inductor is proposed in [15]. While there are fewer parts, the suggested architecture may not be acceptable for high-voltage applications since the output voltage is less than the lowest input voltage. Additionally, all input diodes must be changed out for power switches to allow bidirectional operation, practically doubling the switch count, which increases the switching losses and voltage stress on switches and raises the price.

A modified double-input DC–DC converter with a bridge-type configuration, capable of integrating renewable and non-renewable sources and storage systems, is presented in [16]. In the same structure, the suggested converter will work in step-down, step-up, and step-up/down mode. The topology can supply power to the load even if one of the input sources is not available. However, a complex control system is required to drive multiple-input voltage sources simultaneously and for the bidirectional power flow. A transformer-less high-voltage-gain DC-DC MI converter is recommended in [17]. The converter combines the conventional boost and buck–boost converters. It has reduced voltage stress on the power electronic components, and a wide control range of the input sources. However, additional diodes required for the multi-input converter to work continuously increase the cost and component count. A MISO DC-DC power converter described in [18] allows communication between multiple energy sources with different power levels using a dual boost converter connected to the same DC bus. This circuit demands a complex control mechanism for its operations. S. Mohammadi et al. [19] introduced a high-voltage-gain non-isolated MI DC-DC converter, in which the load on the switches can be reduced by adding more input units and selecting a lower duty ratio for each unit. However, the requirement for numerous components makes operation costly and inefficient.

A non-isolated MI boost DC-DC converter with fewer components and higher efficiency is suggested in [20], having input sources that can supply a common load while being completely managed and running concurrently. With this structure, any voltage or current sources can be taken as the converter’s input and plugged into and unplugged from the converter using a plug-and-play interface. The range of suggested converter applications in various low to high voltage and power ranges can be extended by enhancing the converter voltage gains by adding additional input sources. However, the performance of the converter is analyzed with two fixed DC sources. The benefits of this converter topology have prompted further research in the converter to determine the feasibility of incorporating solar PV as one of the sources.

In this paper, the performance of the two-input single-output DC-DC converter proposed in [20] is studied by integrating solar PV as one of the sources with a linear line–slope control technique. The study concentrates on the adoption of photovoltaic solar power to charge electric vehicles. The following are the key contributions of this article.

(i)

Design of a 100 W TISO converter and implementation of a novel control strategy for MPPT tracking and voltage regulation simultaneously.

(ii)

Model development of designed system with proposed controller in MATLAB/Simulink.

(iii)

Analysis of output voltage stability in terms of output voltage ripple using P&O, multiple step size P&O, and proposed control approach.

(iv)

Simulation and analysis of the proposed approach under various conditions.

(v)

Performance analysis of a high-power converter with proposed control technique.

3. Two-Input Single-Output (TISO) DC-DC Converter

The TISO DC-DC converter circuit is shown in Figure 1a, with a variable input voltage source E₁ and a constant DC voltage source E₂. The circuit consists of two switches, S₁ and S₂; two inductors, L₁ and L₂; four capacitors, C₀, C₁, C₂, and C₃; and three diodes, D₁, D₂, and D₃. Despite the fact that the converter may function in both continuous and discontinuous conduction modes depending on the inductor current levels, this work concentrates on the continuous conduction mode of operation. The switching waveforms and inductor current waveforms are shown in Figure 1b.

The operation of the converter circuit in continuous conduction mode (CCM) can be carried out in four different modes. In the first mode, the diodes D₁ and D₃ are reverse-biased, the diode D₂ is forward-biased, and S₁ and S₂ are switched ON, resulting in an increase in current in inductors L₁ and L₂ linearly and the discharge of capacitors C₁ and C₀ via diode D₂, charging the capacitors C₂ and C₃. This mode of operation continues until the diode D₂ is turned off as the current through the capacitor C₃ becomes zero. In the second mode, S₁ and S₂ continue in their conduction states; all diodes are reverse-biased, and switches S₁ and S₂ are conducting, while L₁ and L₂ continue to be in the charging mode, C₂, which discharges to the load. In the third mode, S₂ continues to conduct, whereas S₁ is commutated; D₃ is forward-biased, but D₁ and D₂ are reverse-biased. Due to the energy stored in L₂ and C₃, the capacitors C₁, C₂, and C₀ are charged. S₁ continues to be in the OFF state in the fourth mode, and S₂ is commutated. D₁ and D₃ are forward-biased, whereas D₂ is reverse-biased. As the two inductors and capacitor C₃ discharge, capacitors C₁, C₂, and C₀ are charged.

The TISO converter discussed here is a boost converter that provides the combined output voltage of E₁ and E₂ in the steady state. The operation of the circuit is controlled so as to supply the desired output by supplying voltages from the sources.

When S₁ is ON, V_L1 = E₁, and when S₁ is OFF, V_L1 = E₁ − V_C1.

Likewise, when S₂ is ON, V_L2 = E₂; when S₂ is OFF, V_L2 = E₂ − V_C2.

According to the inductor volt-sec balance, for E₁,

(E₁ × d₁T) + [(E₁ − VC₁) × (1 − d₁)T] = 0

(1)

Similarly,

(E₂ × d₂T) + [(E₂ − VC₂) × (1 − d₂)T] = 0

(2)

From the above equations, we obtain

 E₁ − VC₁ (1 − d₁) = 0 and
E₂ − VC₂ (1 − d₂) = 0

The output voltage is

V₀ = VC₁ + VC₂

Thus, the equation to calculate the converter’s output voltage is given by

$$V_0=\frac{E_1}{1-d_1}+\frac{E_2}{1-d_2}$$

(3)

where d₁ and d₂ are the corresponding switching ratios of the control switches S₁ and S₂, and E₁ and E₂ are the source voltages. Knowing the source voltages E₁ and E₂, by setting the desired output voltage and fixing one of the duty cycles, say d₁, another duty cycle (d₂) can be obtained. For this study, a solar PV module with V_max of 18 V (E₁) and a fixed DC source of 12 V (E₂) are selected. A TISO DC-DC converter is designed for E₁ = 18 V, E₂ = 12 V, output voltage (V₀) = 100 V, output voltage (P₀) = 100 W, and switching frequency f = 15 KHz. The following subsections describe the selection of the load resistance, inductor, and capacitor values.

3.1. Selection of Load Resistance

The load resistance can be obtained from

$$R_L=\frac{V_0{}^2}{P_0}$$

(4)

3.2. Selection of Inductor Values

To ensure the CCM mode of operation, the inductor’s value should be higher than the critical value (L_k), which is given by

$$L_K=\frac{R_L(d_1+2\alpha d_2){(1-d_1)}^2{(1-d_2)}^2}{2f(1+d_2-2d_1{d}_2)(1+\alpha (1-d_1)-d_2)}$$

(5)

where α is the input voltage ratio and is given by $\alpha =\frac{E_2}{E_1}$, and f is the switching frequency.

3.3. Selection of Capacitor Values

The minimum capacitor value can be calculated from

$$C_k=\frac{\lambda V_0}{f{R}_{L\min }{V}_{pp\max }}\hspace{1em}(k = 0,1,2,3)$$

(6)

The effect of the output voltage ripple is included by a factor λ. The range of λ is 1 to 3 and it is regarded as 1.6 in this study. V_ppmax is the output voltage ripple, which is usually assumed to be 2% of V₀. R_Lmin is the minimum load resistance, which is assumed to be 20% of the load resistance [21].

4. Simulation Results and Discussion

4.1. Conventional Circuit

The parameters and designed component values of the converter are listed in

Table 1. Design parameters and component values of TISO DC-DC converter.

Description	Value
Input Voltage (E1)	18 V
Input Voltage (E2)	15 V
Duty Ratio (d1 and d2)	0.7
Switching Frequency (f)	15 kHz
Output Voltage (V0)	100 V
Output Power (P0)	100 W
Boost Inductance (L1 and L2)	200 µH
Capacitance (C0, C1, C2, and C3)	267 µF
Load Resistance (RL)	100 Ω

. Figure 2 illustrates the MATLAB/Simulink simulation model for a basic TISO DC-DC converter with two fixed 18 V and 12 V DC input voltage sources. The duty ratios d₁ and d₂ are maintained at 0.7 throughout the simulation. Figure 3a illustrates the output voltage, while Figure 3b illustrates the converter power.

The average power calculated from the simulated output power curve is 98.49 W; hence, the converter efficiency is 98.49%. Using the simulation results, the voltage ripple and average output voltage are calculated to be 0.21% and 99.195 V, respectively. These figures indicate that the converter has greater efficiency and lower output voltage fluctuation. Losses due to passive components and solid-state switches influence converter efficiency. Power loss in MOSFETs is caused by conduction loss, switching loss, and body diode resistance. However, owing to the CCM mode of operation, body diode resistance losses are disregarded. Power losses due to diodes include threshold voltage loss, conduction loss, switching loss, and reverse recovery current loss, all of which are dependent on the output current, output voltage ripple, and switching frequency [20,22,23]. This study does not evaluate the influence of parasitic components such as trace inductances, parasitic capacitances, and semiconductors on efficiency computation, since this work is primarily focused on the system level rather than the component level.

Figure 4a shows the simulated waveforms of the switching pulses of switches S₁, S₂, the inductor voltage, and the inductor current. The plots show that the results are aligned with the steady−state analysis plots depicted in Figure 1b. In Figure 4b, voltages across the capacitors C₀, C₁, C₂, and C₃ are shown.

4.2. TISO DC−DC Converter with Solar PV Input

4.2.1. MPPT Tracking Algorithms

Solar photovoltaic systems are equipped with MPPT controls to ensure that they operate at MPP for optimal efficiency. A large number of MPPT technologies are proposed in the literature on solar photovoltaic systems [24]. The Perturb and Observe (P&O) method is a popular and widely recognized MPPT approach due to its simple architecture and ease of implementation in comparison to other techniques [25]. A conventional P&O MPPT has a step size of 0.01, and the algorithm gradually increases or decreases the duty ratio until the MPP is attained. The major drawbacks of the P&O method are oscillations around the MPP under steady-state conditions and slow tracking speeds in rapidly changing weather conditions. Variable-step P&O methods are introduced to address the shortcomings of the conventional P&O approach [26]. The improved multi-step P&O approach increases the tracking speed and reduces oscillations because of the multiple step sizes used for tracking. When the operating point is far from the MPP, the algorithm creates a large step value, and when the operating point is close to the MPP, it generates a small step value. Figure 5 depicts the flowchart of the multi-step P&O approach.

4.2.2. Analysis of TISO DC-DC Converter with Solar PV

To investigate the circuit characteristics with a solar PV as one of the sources, the 18 V fixed DC source is replaced with a solar PV module with a maximum peak output voltage of 18 V, and the 12 V fixed DC source is kept as a secondary source of input voltage. Specifications of the solar PV module are listed in

Table 2. Solar PV Module Specifications.

Description	Value
Peak power (Pmax)	100 W
Voltage at peak power (Vmax)	18 V
Current at peak power (IMAX)	5.56 A
Short-circuit current (Isc)	6.06 A
Open-circuit voltage (Voc)	22 V
Temperature coefficient of Isc	(0.06 ± 0.15)%/°C

. The circuit is simulated with P&O and multiple-step size P&O MPPT. Figure 6 shows the MATLAB/Simulink model. Based on the output voltage of the solar PV module, the duty ratio of the switch linked to the PV module is adjusted by an MPPT controller to harvest the maximum power. Simultaneously, the controller will adjust the duty cycle of the switch connected to a fixed DC input source, to keep the output voltage constant.

4.2.3. Analysis under Changing Irradiation at a Constant Temperature

The circuit is simulated under various irradiance levels at a constant temperature (25 °C), as shown in Figure 7. Figure 8 depicts the change in the duty ratio of switch S₁ corresponding to the changes in PV output. Figure 9 shows the duty ratio generated by the control circuit for switch S₂ with respect to the changes. The converter’s output voltage and output power are depicted in Figure 10 and Figure 11, respectively.

Table 3. Performance comparison of the converter with P&O MPPT Algorithms.

Solar Irradiation (W/m2)	Time Delay in Seconds		Average Output Voltage (Vout)		Percentage of Ripple		Average Output Power (Pout)		Efficiency (η)
	Conv P&O	Multi P&O	Conv P&O	Multi P&O	Conv P&O	Multi P&O	Conv P&O	Multi P&O	Conv P&O	Multi P&O
1000	0.73	0.096	98.83	98.64	2.16%	1.34%	99.8	98.95	99.80%	98.95%
500	0.35	0.183	99.24	99.06	2.34%	1.56%	97.22	97.8	97.22%	97.80%
700	0.12	0.098	98.26	98.28	5.20%	1.79%	98.2	98.5	98.20%	98.50%
900	0.07	0.051	96.81	96.81	7.62%	3.26%	99.7	98.9	99.70%	98.90%
800	0.05	0.028	97.68	97.31	6.60%	1.75%	99.65	98.6	99.65%	98.60%
900	0.05	0.027	96.81	96.81	7.62%	3.26%	99.7	98.9	99.70%	98.90%
600	0.2	0.076	98.9	98.97	3.66%	1.77%	98.33	97.9	98.33%	97.90%
Overall Average			98.87	98.81	2.91%	1.55%	99.07	98.43	99.07%	98.43%

displays the average voltage value and ripples in the output voltage estimated from the voltage waveform, the average power value and converter efficiency computed from the power waveform, and the time delay to achieve MPP for each MPPT method. The average voltage, voltage ripple, and overall efficiency with P&O MPPT and multiple-step-size P&O MPPT are also presented in the table. It can be seen that both methods provide almost the same average output voltage and power. However, multi-step P&O is more efficient than conventional P&O in terms of MPP tracking and output voltage ripple. Meanwhile, multiple-step-size P&O also induces ripples in the output due to duty cycle oscillation around the MPP. Since the duty cycle of the fixed source control switch completely depends on the duty cycle and output voltage of the PV modules, this causes an additional ripple in the output. Hence, using the P&O algorithm or its variant for tracking is not ideal to achieve a stable output voltage, even though they assure maximum power extraction.

To overcome the ripple issue and to produce a more stable output, a simple indirect MPPT method with a linear line–slope interpolation algorithm is proposed. Figure 12 depicts the flowchart of the linear line–slope interpolation algorithm approach. The algorithm reads the input(s) and provides a corresponding output based on the preassigned values stored as an array. Duty ratio values are stored for each set of irradiation and temperature values for irradiation values ranging within 500:100:1200 W/m² and temperature values ranging within 15:10:45 °C with a constant period of 10 °C, and duty cycle values are determined. A total of 38 sets of values are stored.

The linear line–slope interpolation algorithm directly provides the duty ratio to the switch from the stored data, if the irradiation and temperature inputs match the stored data; otherwise, the duty ratio is calculated by the algorithm using the linear interpolation formula. The algorithm provides a constant value as output and hence the output ripple is eliminated.

$$v=v_1+\frac{u-u_1}{u_2-u_1}\times (v_2-v_1)$$

(7)

The circuit is simulated with the proposed approach for similar input conditions applied to the P&O and multistep P&O MPPT-based system (Figure 7). Figure 13 depicts the duty ratio generated by the linear line–slope interpolation algorithm given to switch S₁ and the duty ratio produced by the proposed control architecture for switch S₂. The voltage and power output of the converter are depicted in Figure 14 and Figure 15, respectively.

The duty ratios of switch S₁ vary with the variation in irradiation at a constant temperature, causing the duty ratios of switch S₂ to change due to the control topology used to maintain a constant voltage in the converter. Observations of the output power and voltage waveforms indicate that the output is comparatively more stable.

Table 4. Average output voltage, voltage ripple, average output power, and efficiency of the converter with proposed MPPT algorithm.

Solar Irradiation (W/m2)	Average Output Voltage (Vout)	Percentage of Ripple	Average Output Power (Pout)	Efficiency (η)
1000	99.03 V	0.22%	98.3 W	98.30%
500	98.93 V	0.22%	97.49 W	97.49%
700	98.92 V	0.23%	98.85 W	98.85%
900	98.62 V	0.23%	99.34 W	99.34%
800	99.09 V	0.24%	99.08 W	99.08%
900	98.62 V	0.23%	99.34 W	99.34%
600	98.92 V	0.23%	98.39 W	98.39%

displays the average voltage and percentage output voltage ripple calculated from the voltage waveform, the average power value, and converter efficiency computed from the power waveform.

The average voltage and overall efficiency of the converter with the proposed controller are 98.9 V and 98.67%, respectively, and the average voltage ripple is 0.228%. It is evident from the results that the proposed approach is capable of tracking MPP much faster than the P&O tracking approach and the voltage ripple is significantly reduced. The ripple reduction is more than 90% when compared to 2.91% ripple generated by the P&O algorithm, and it is more than 85% when compared to 1.55% voltage ripple in the multiple-step-size P&O algorithm.

4.2.4. Analysis of Rapidly Changing Environmental Conditions with Real-Time Data

The effectiveness of a solar-powered DC-DC converter employing the linear line–slope interpolation technique is examined using real-time data samples where both temperature and irradiance values fluctuate dramatically. Irradiance and temperature on a specific day in the last week of April 2022 from Kollam, India (9.02 N, 76.91 E) are used for the analysis under rapidly changing environmental circumstances and are shown in Figure 16 and Figure 17, respectively. Between 10:00 a.m. and 12:30 p.m., the irradiation varies dramatically. Fourteen data samples are collected at equal intervals between 11 a.m. and 12:20 p.m. for the analysis. Figure 18 and Figure 19 demonstrate the fluctuations in irradiance and temperature across the given time period. Figure 20 and Figure 21 show the changes in temperature and irradiance, which are assumed to be occurring every 10 s for simulation purposes. Figure 22 and Figure 23 illustrate the variation in the duty ratios of switches S₁ and S₂. Figure 24 and Figure 25 depict the generated output voltage and power, respectively.

The duty ratios of switch S₁ vary with respect to the changes in irradiation and temperature, which causes the duty ratios of switch S₂ to shift to keep the output voltage constant. The average voltage, output voltage ripples, average power, and converter efficiency computed from the simulation results are listed in

Table 5. TISO converter analysis under rapidly varying PV inputs.

Irradiation (W/m2)	Temperature (°C)	Average Output Voltage (Vout)	Percentage of Ripple	Average Output Power (Pout)	Efficiency (η)
844.6	32.8	99.21 V	0.22%	98.73 W	98.73%
818.1	32.9	99.25 V	0.23%	98.65 W	98.65%
786.5	33.2	99.4 V	0.22%	98.65 W	98.65%
780.8	33.4	99.39 V	0.23%	98.51 W	98.51%
710.4	33.4	99.87 V	0.22%	98.18 W	98.18%
892.3	33.7	98.92 V	0.22%	98.83 W	98.83%
864.9	33.8	98.95 V	0.23%	98.77 W	98.77%
873.2	33.8	98.91 V	0.22%	98.83 W	98.83%
909.2	33.9	98.78 V	0.22%	98.86 W	98.86%
661.6	33.8	99.72 V	0.24%	97.95 W	97.95%
913.6	34.1	98.74 V	0.22%	98.86 W	98.86%
923.6	34.2	98.69 V	0.22%	98.89 W	98.89%
958.3	34.2	98.57 V	0.2%	98.96 W	98.96%
833.4	34.4	98.91 V	0.22%	98.67 W	98.67%
Overall average		99.09 V	0.22%	98.67 W	98.67%

.

4.2.5. Analysis of High-Power Converter

A 500 V, 17 kW high-power converter with a switching frequency of 20 kHz is designed and simulated with the proposed control approach. Here, a solar PV array with a maximum peak output voltage of 183.95 V and a power output of 11 kWp is used as a primary source. The voltage of the secondary input voltage source of the 12 V fixed DC source is fixed at 96 V. The parameters and values of the designed components of the converter are listed in

Table 6. Specifications of High power TISO DC-DC converter.

Description	Value
Input Voltage (E1)	180 V
Input Voltage (E2)	96 V
Duty Ratio (d1)	0.5
Duty Ratio (d2)	0.314
Switching Frequency (f)	20 kHz
Output Voltage (V0)	500 V
Output Power (P0)	17 kW
Boost Inductance (L1 and L2)	100 µH
Capacitance (C0, C1, C2, and C3)	1359.6 µF
Load Resistance (RL)	14.71 Ω

, and the specifications of the solar PV array are listed in

Table 7. Solar PV array specifications.

Description	Value
Peak power (Pmax)	220 W
Voltage at peak power (Vmax)	36.79 V
Current at peak power (Imax)	5.98 A
Short-circuit current (Isc)	6.31 A
Open-circuit voltage (Voc)	45.31 V
Number of parallel strings	10
Number of series connected per string	5
Temperature coefficient of Isc	(0.06 ± 0.15)%/°C

.

The circuit simulation is performed under the rapidly changing environmental conditions presented in Section 4.2.3 as input for the PV array. Figure 26 and Figure 27 illustrate the variation in the duty ratios of switches S₁ and S₂. Figure 28 and Figure 29 depict the generated output voltage and power, respectively.

The performance of the circuit is found to be satisfactory since the output voltage is almost constant throughout the simulation period, irrespective of the variations in the PV input, and the output power is also very close to the expected value. The average voltage, output voltage ripples, average power, and converter efficiency calculated from the simulation results are given in

Table 8. The average output voltage, voltage ripple, average output power, and efficiency of the high-power converter under rapidly varying PV inputs.

Irradiation (W/m2)	Temperature (°C)	Average Output Voltage (Vout)	Percentage of Ripple	Average Output Power (Pout)	Efficiency (η)
844.6	32.8	496.9 V	0.16%	16.785 kW	98.74%
818.1	32.9	497.1 V	0.16%	16.8 kW	98.82%
786.5	33.2	497.35 V	0.14%	16.815 kW	98.91%
780.8	33.4	497.35 V	0.14%	16.815 kW	98.91%
710.4	33.4	498.3 V	0.16%	16.855 kW	99.15%
892.3	33.7	496.5 V	0.16%	16.755 kW	98.56%
864.9	33.8	496.7 V	0.16%	16.775 kW	98.68%
873.2	33.8	496.6 V	0.16%	16.77 kW	98.65%
909.2	33.9	496.3 V	0.16%	16.745 kW	98.50%
661.6	33.8	498.2 V	0.16%	16.86 kW	99.18%
913.6	34.1	496.3 V	0.16%	16.745 kW	98.50%
923.6	34.2	496.4 V	0.16%	16.735 kW	98.44%
958.3	34.2	495.9 V	0.16%	16.715 kW	98.32%
833.4	34.4	497 V	0.16%	16.795 kW	98.79%
Overall average		496.92 V	0.16%	16.783 kW	98.72%

.

The high-power converter provides an average output voltage of 496.92 V. The overall efficiency of 98.72% and average ripple percentage of 0.16% obtained from the simulation under the selected conditions lead to the conclusion that the converter has better efficiency and less variation in the output voltage under higher power levels with the proposed control technique. When the MPP operation of a solar photovoltaic system is compromised and it is unable to achieve a constant output voltage, the developed converter with the linear line–slope interpolation approach offers better efficiency and less variation in the output voltage. More specifically, the output voltage ripple is significantly reduced, which reduces the filter size of the converter system, the size, and the cost.

5. Conclusions

A two-input single-output DC-DC converter with solar PV as one of the sources is presented and discussed in this paper. A liner line–slope interpolation method is proposed for solar PV power extraction. A detailed analysis of a 100 V, 100 W DC-DC converter circuit with a 12 V fixed DC source and 18 V solar PV module as sources is carried out through simulation studies under various conditions. The circuit characteristics in terms of output voltage, power, efficiency, and voltage stability are evaluated by comparing the converter’s results with the proposed approach against the conventional P&O MPPT and multiple-step-size P&O MPPT algorithms. With the proposed approach, the converter offers overall efficiency of 98.67% and the overall output voltage of the converter is 99.09 V. The proposed approach significantly reduces the ripple generated in the output voltage. The output voltage ripple is 0.22%, which is much lower than with the other approaches. A 500 V, 17 kW TISO DC-DC converter with a 180 V, 11 kWp solar PV array and a 96 V fixed DC source is also designed and simulated under different input conditions by varying the solar PV input. The obtained results are promising as the converter provides an overall average output of 496.92 V at 98.72% efficiency. The output voltage ripple is only 0.16%. The results confirm the feasibility of integrating a solar PV module as one of the sources with the proposed technique for a TISO converter for EV charging applications.