# A Reactive Power Compensated Control Scheme for Solar-Assisted EV Fast-Charging Applications

Authors: Anjanee K Mishra; Saurabh Shukla; Bhim Singh; Ahmad Al Durra
Journal: International Transactions on Electrical Energy Systems
 (2022)

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## Abstract

The main objective of this work is to develop an efficient reactive power compensated control technique for a fast-charging scheme for electric vehicle(s) (i.e., level-3 charging). The developed charging technique has the four-quadrant power flow operation with the simultaneous assurance of the compensated reactive power control. The developed charging infrastructure scheme involves a solar panel and 3-phase grid to charge the E-mobility. A DC-DC boost converter is used to achieve maximum power tracking (MPPT) of a solar PV array, and a 3-phase grid-tied bidirectional voltage source converter (VSC) is utilized to provide the bulk of power to charge the EV. The 3-phase VSC has multiple functionalities including grid side power quality (PQ) improvement with reactive power compensation, seamless flow of power from the grid to EV, and solar to grid or battery to grid (V2G) operation. This scheme also facilitates tariffs earned by discharging solar energy to the grid with additional benefits of reactive power compensation. An arrangement is also made to tackle grid failure conditions during battery discharging mode by connecting a load for ancillary purposes. The effectiveness of this charging scheme is first examined in MATLAB/Simulink environment and then validated on developed hardware.


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## Body

## 1. Introduction

The growing concerns over environmental protection and energy conservation over the past few decades have reinforced stringent regulations on fuel consumption. One of the main sectors that witnessed significant change due to tougher environmental regulations is the transportation sector. Over the past couple of decades, advancements in EV technology have grown significantly [1]. As reported in [2], the deployment of electric vehicles has been growing rapidly over the past few years with the global stock of electric passenger cars reaching over 5 million in 2018 with a huge increase of 63% from the previous years. Extensive research throughout the world is going on to shift our reliance on renewable energy sources, and new technologies are coming up in the field of battery charging [3, 4]. Solar and wind-energy-based systems are quite popular these days. However, these initiatives require more capable power transmission lines with reduced transmission losses. Regarding this, a few easy solutions have been discussed in [5, 6], which emphasize installing a PV array in the vicinity of the charging station. This is considered a local solution with power generation and consumption locally [7]. This does not require up-gradation of power transmission line and saves extra cost incurred in it. This local solution for the charging scheme is independent of the tariff as the power is locally generated for this purpose [8]. Therefore, various solar parks have been developed near the vehicle parking area as reported in the literature [9]. So, the utilization of solar power in charging infrastructure eases the burden on the utility and also reduces the charging cost/miles.The charging stations for E-mobility with solar power have been extensively researched [3, 4], which provides an alternate source for charging stations. However, its intermittency has always been a matter of concern. The grid integration eliminates the complete reliance of the system on solar PV arrays. The storage capacity of the battery can be manifested during the parking hours to feed the utility for additional services for many purposes such as V2G and V2H [10]. In addition, solar power can be fed back to the grid if EV charging is not required, as discussed in [11].The reactive power balance comprises both lagging (inductive) and leading (capacitive) power requirements of the grid. The reactive power balance in V2G mode does not draw any real power from the battery and thereby is independent of battery SOC. Many attempts of research have been made to suggest the merits of reactive power generation and distribution near the load as it reduces the overall losses in the transmission line for long distances [12]. Nowadays, due to the nonlinear nature of most of the loads, distorted phase currents are drawn from the utility. The consequences of these undesirable grid indices on the system performance have been reported in the literature [13] with also the probable solutions to overcome it.Several techniques are reported in the literature based on power quality enhancement of the grid. Among them, synchronous reference frame theory (SRF) [14] and instantaneous reactive power theory (IRPT) [15] are extensively used algorithms. The IRPT technique is based on the transformation of three-phase quantities into two-phase quantities (i.e., voltage and currents) to find active and reactive power. However, the transient response is a bit sluggish due to the utilization of the proportional PI regulator and low-pass filter to control DC link voltage. In addition, it becomes worse when it deals with unbalanced and distorted voltages. Similarly, the SRFT algorithm also suffers from these problems during unbalancing and distortion of voltages. Enhanced PLL (EPLL) [16] overcomes these difficulties and displays excellent tracking capability under these abnormal grid conditions but is computationally more intricate and hence more expensive. The generalized integrator-based algorithms like the second-order generalized integrator (SOGI) [17] based algorithm offer a fast convergence rate and good tracking efficiency in a narrow band of frequency, and the performance deteriorates when the frequency changes. Therefore, it is assisted by a feedback frequency loop to make it frequency adaptive but at the cost of increased computational burden on the processor. The SOGI can be replaced by a notch filter [18]. However, the problem associated with the selection of notch frequency for variable frequency application is very difficult. This problem has been resolved by an adaptive notch filter (ANF) [19], which updates the center frequency by using the feedback signal with the variable frequency. The SOGI FLL offers superior performance to other algorithms but still, the complex computation is its drawback [20].Acknowledging the limitations of previous systems, the proposed system provides an efficient reactive power compensated control method for fast charging of EVs. The schematic of the developed charging scheme is shown in Figure1. This developed charging system provides a unique scheme for the four-quadrant operation of the charger with an improved control algorithm. Solar power is used to feed power into the grid; however, the grid is the main source of charging the EV. Therefore, the power coming from the grid offers a fast-charging infrastructure to the station. The developed system has also the capability to work in V2G mode. In this case, the fully charged battery can feed power to the grid when propulsion mode is not needed. This mode is very effective in peak load hour operations. All four quadrant of P-Q power control is achieved by the proposed control technique. The system acts in a two-stage manner when it operates in G2V or V2G modes. The battery charging is accomplished until it achieves the extreme limit; that is, 80% SOC specifically decided for the present system. After that, the charger starts feeding power to the grid. In case of grid failure or absence condition, the fully charged battery is detached from the charging station and starts supporting ancillary services such as water pumping and lighting.Figure 1
Schematic of developed EV fast-charging infrastructure.A grid-tied VSC performs as a controlled rectifier in the G2V mode, and the converter attached to the battery performs the buck operation to offer energy storage in a battery whereas, in the V2G operation, the same converter on the battery side performs the boost function to match the DC link voltage. The bidirectional power transfer is achieved by the DC link capacitor during different modes of EV charging/discharging modes. Moreover, the bidirectional converter inductor (Lb) suppresses the ripple current into the battery storage. The interfacing inductors (Ls) at the grid side are meant for the mitigation of the harmonics in the grid current caused due to AC-DC conversion.


## 2. Design Configuration

The developed system consists of a solar panel of 4.3 kW and an EV of 4.2 kW power rating. A deviation-free P&O (perturb and observe) MPPT technique is executed using a boost converter for PV panel power optimization. The parameters of the boost and bidirectional DC-DC converter are so selected that it always works in CCM (continuous conduction mode) irrespective of the working mode and battery and PV power. The design configurations of various elements present in the developed system are discussed here.


### 2.1. Estimation of Solar Parameters

The selection of solar panel indices primarily depends on the highest power necessity of the charging station. Here, to charge an EV with a battery bank of voltage and current ratings 240 V and 10 Ah, respectively, a 4.3 kW solar panel is designed with 19 and 13 modules in series and parallel, respectively. The complete electrical specification of the solar panel implemented in the developed system is given in Appendix.


### 2.2. Inductor Calculation for MPPT Converter

The duty ratio (D1) for the MPPT converter is calculated as(1)D1=Vdc−VpvVdc=400−334400≈0.17.Therefore, the calculation of the inductor is done by the governing expression(2)L≥VpvD1ΔiLfsw=334×0.170.25×6.4×10×103≈3.65mH.


### 2.3. Design of Low-Pass Filter for Grid

A series arrangement of RC is attached at the PCC (point of common coupling) to mitigate the switching voltage harmonics. The RC arrangement acts as an LPF (low-pass filter), which attenuates the high-frequency switching harmonics from the main supply and passes only the desired frequency signal to the system [21]. The parameters of the ripple filter are thus designed to achieve the condition, RfCf << Tsw2, where Rf, Cf, and Tsw2 are resistance, capacitance, and switching time, respectively, of the designed LPF.Assuming the value ofRfCf = Tsw2/4, where Tsw2 = 10−4 s and Rf = 5 Ω, the size of the required Cf is estimated as(3)Cf=Tsw24Rf=110000×4×5≅5μF.


### 2.4. Battery Converter Design

The duty ratio (Dbat) for the DC-DC battery converter in boosting operation is expected as(4)Vdc∗=Vbat1−DbatorDbat=Vdc∗−VbatVdc∗=1−240400=0.4.Therefore, the calculation of the inductor is done by the governing expression(5)Lb=Vbat×DbatΔIbat×fs=240×0.40.25×7×10000=5.48mH,where fs (switching frequency) = 10 kHz and ΔIbat (permitted ripple current) = 0.25 A. Similarly, for buck mode, the duty ratio would be 0.6.


## 2.1. Estimation of Solar Parameters

The selection of solar panel indices primarily depends on the highest power necessity of the charging station. Here, to charge an EV with a battery bank of voltage and current ratings 240 V and 10 Ah, respectively, a 4.3 kW solar panel is designed with 19 and 13 modules in series and parallel, respectively. The complete electrical specification of the solar panel implemented in the developed system is given in Appendix.


## 2.2. Inductor Calculation for MPPT Converter

The duty ratio (D1) for the MPPT converter is calculated as(1)D1=Vdc−VpvVdc=400−334400≈0.17.Therefore, the calculation of the inductor is done by the governing expression(2)L≥VpvD1ΔiLfsw=334×0.170.25×6.4×10×103≈3.65mH.


## 2.3. Design of Low-Pass Filter for Grid

A series arrangement of RC is attached at the PCC (point of common coupling) to mitigate the switching voltage harmonics. The RC arrangement acts as an LPF (low-pass filter), which attenuates the high-frequency switching harmonics from the main supply and passes only the desired frequency signal to the system [21]. The parameters of the ripple filter are thus designed to achieve the condition, RfCf << Tsw2, where Rf, Cf, and Tsw2 are resistance, capacitance, and switching time, respectively, of the designed LPF.Assuming the value ofRfCf = Tsw2/4, where Tsw2 = 10−4 s and Rf = 5 Ω, the size of the required Cf is estimated as(3)Cf=Tsw24Rf=110000×4×5≅5μF.


## 2.4. Battery Converter Design

The duty ratio (Dbat) for the DC-DC battery converter in boosting operation is expected as(4)Vdc∗=Vbat1−DbatorDbat=Vdc∗−VbatVdc∗=1−240400=0.4.Therefore, the calculation of the inductor is done by the governing expression(5)Lb=Vbat×DbatΔIbat×fs=240×0.40.25×7×10000=5.48mH,where fs (switching frequency) = 10 kHz and ΔIbat (permitted ripple current) = 0.25 A. Similarly, for buck mode, the duty ratio would be 0.6.


## 3. DPC for Grid Voltage Source Inverter

The power transfer in both directions is executed as per the control technique shown in Figure2. The active and reactive power signals are regulated as per the command signal given by the user as needed. The four-quadrant operation is achieved viz. charging/discharging modes with inductive and capacitive and reactive power compensation. The instant value of active and reactive powers is estimated from the grid parameters.Figure 2
Developed fast-charging control logic with DPC.The expression for the instantaneous magnitude of complex powers(t) is expressed as(6)st=vg×ig∗=ig−α×vg−α+ig−β×vg−β+jig−α×vg−β−ig−β×vg−α.The magnitude of grid current changes by the variation in the VSC voltage, which changes the active and reactive power drawn from the AC mains, and it has to be controlled. For a zero voltage vector, the change observed in active and reactive power is given as(7)Δp0k=vg−αkvg−αk−ig−αk×R+vg−βkvg−βk−ig−βk×RTsL,Δq0k=vg−αkvg−βk−ig−βk×R−vg−βkvg−αk−ig−αk×RTsL.Neglecting resistive power loss, the equation becomes(8)Δp0k=vg−αk×vg−αk+vg−βk×vg−βkTsL,Δq0k=vg−αk×vg−βk−vg−βk×vg−αkTsL.For an instant VSC voltage, the variation in power,P, and Q can be defined by(9)Δpgk=Δp0k−vg−αk×vrec−α+vg−βk×vrec−β×TsL,Δqgk=Δq0k−vg−αk×vrec−β−vg−βk×vrec−α×TsL.In this control scheme, the error signals are made null to attain the optimal voltage. The resultant signals are given as(10)σp=P∗−P=Δp0−vg−α×vrec−α+vg−β×vrec−β×TsL,σq=Q∗−Q=Δq0−vg−α×vrec−β−vg−β×vrec−α×TsL.Thus, equations forΔp0k and Δq0k are used in the aforementioned expression to achieve the subsequent equations as(11)vrec−α=vg−α2+vg−β2−L/Tsσpvg−α+L/Tsσqvg−βvg−α2+vg−β2,vrec−α=vg−α2+vg−β2−L/Tsσpvg−β−L/Tsσqvg−βvg−α2+vg−β2.The resultant error indices are managed by the hysteresis-based controller, resulting in the generation of the switching pulses for VSC namedG1–G6, as shown in Table 1.δ=tan−1vg−β/vg−α.Table 1
DPC switching scenario.
PQδ1δ2δ3δ4δ5δ6δ7δ8δ9δ10δ11δ120n6n7n1n0n2n7n3n0n4n7n5n011n7n7n0n0n7n7n0n0n7n7n0n000n6n1n1n2n2n3n3n4n4n5n5n61n1n2n2n3n3n4n4n5n5n6n6n1n1 (100)n2 (110)n3 (010)n4 (011)n5 (001)n6 (101)n7 (111)n0 (000)


## 4. Charging Control: E-Mobility Battery

Figure3 shows the fast-charging control mechanism of the EV. The battery must discharge through the grid if it is fully charged. However, in this case, if there occurs a grid failure condition, then it must be disconnected and discharged through auxiliary applications. This mode is achieved via. the logic represented by the red line in Figure 3, where the battery current (Ibat) is regulated by a current regulator.Figure 3
Charging control mechanism.On the other side, if the grid is available, the control follows the blue line loop, which follows the reference current input. In the first case, the duty ratio is generated by the current controller to be transformed into the high-frequency switching pulses for the DC-DC converter attached to the battery.(12)Ibat∗k=Ibat∗k−1+KpVerk−Verk−1+KiVerk,where Kp and Ki are termed as proportional and integral gains of PI controller, respectively. In another situation, the desired current for charging purpose relies on the percentage of SOC of the storage system and is generated according to it.


## 5. Simulated Results

The developed charging scheme is simulated and examined under a wide range of operating conditions. The battery terminal voltage is 240 V, and the value of the DC link voltage is set to 400 V. The complete performance is analyzed under all possible situations.


### 5.1. Harmonic Distortion Analysis of Utility Currents

The distortion in grid side current in two working modes viz. G2V and V2G, respectively, is analyzed here. The irradiance level is set at 300 W/m2. The nature of grid current is shown in Figures 4(a)-4(b). In each situation, the current THD is 3.5%, and 3.8%, respectively, which successfully follows the IEEE-519 std.Figure 4
Current THD (a) in G2V mode and (b) in V2G mode.
(a)(b)


### 5.2. Dynamic Behavior under Varying Insolation Level

Figures5(a) and 5(b) show the sudden drop in the solar insolation from 1000 W/m2 to 300 W/m2 at 1.0 s. The system operates in constant charging mode, which draws extra power from the grid, increasing the in-phase grid current (ig). As soon as the battery charge attains its limiting value at 1.5 s, the battery starts discharging through the grid with the PV array at 300 W/m2. The phase displacement of grid current and grid voltage (vg) is π rad. The positive sign of active grid power (P) indicates the G2V operation while the magnitude of “P” below the zero line illustrates the power flow from solar to the grid or V2G operation. Under each situation, Vdc is regulated at 400 V.Figure 5
Dynamic performance of charging system under varying irradiance.
(a)(b)


### 5.3. Battery Discharging during Grid Failure Condition

Figures6(a) and 6(c) show the condition when the battery is discharging and suddenly encounters the grid outage. In this case, a propulsion mode has started, and the battery starts discharging. Figure 6(a) shows this condition and the solar-battery behavior as the storage battery gets discharged at 0.4 s with the rated irradiance level.Figure 6
Mode complying with the utility failure during battery releasing energy. (a) Solar parameters, (b) grid parameters, and (c) propulsion motor behavior.
(a)(b)(c)Both start feeding power to the grid at this moment, as demonstrated in Figure6(b). At 1.0 s, the utility is cut out from the system. Therefore, as in Figure 6(c), the battery initiates feeding a propulsion motor. Moreover, Figure 7 clearly depicts that the proposed DPC approach has effective performance in terms of “% overshoot” and has a minimum settling time as compared to the other control schemes reported in the literature.Figure 7
Comparative analysis of power control algorithms.


## 5.1. Harmonic Distortion Analysis of Utility Currents

The distortion in grid side current in two working modes viz. G2V and V2G, respectively, is analyzed here. The irradiance level is set at 300 W/m2. The nature of grid current is shown in Figures 4(a)-4(b). In each situation, the current THD is 3.5%, and 3.8%, respectively, which successfully follows the IEEE-519 std.Figure 4
Current THD (a) in G2V mode and (b) in V2G mode.
(a)(b)


## 5.2. Dynamic Behavior under Varying Insolation Level

Figures5(a) and 5(b) show the sudden drop in the solar insolation from 1000 W/m2 to 300 W/m2 at 1.0 s. The system operates in constant charging mode, which draws extra power from the grid, increasing the in-phase grid current (ig). As soon as the battery charge attains its limiting value at 1.5 s, the battery starts discharging through the grid with the PV array at 300 W/m2. The phase displacement of grid current and grid voltage (vg) is π rad. The positive sign of active grid power (P) indicates the G2V operation while the magnitude of “P” below the zero line illustrates the power flow from solar to the grid or V2G operation. Under each situation, Vdc is regulated at 400 V.Figure 5
Dynamic performance of charging system under varying irradiance.
(a)(b)


## 5.3. Battery Discharging during Grid Failure Condition

Figures6(a) and 6(c) show the condition when the battery is discharging and suddenly encounters the grid outage. In this case, a propulsion mode has started, and the battery starts discharging. Figure 6(a) shows this condition and the solar-battery behavior as the storage battery gets discharged at 0.4 s with the rated irradiance level.Figure 6
Mode complying with the utility failure during battery releasing energy. (a) Solar parameters, (b) grid parameters, and (c) propulsion motor behavior.
(a)(b)(c)Both start feeding power to the grid at this moment, as demonstrated in Figure6(b). At 1.0 s, the utility is cut out from the system. Therefore, as in Figure 6(c), the battery initiates feeding a propulsion motor. Moreover, Figure 7 clearly depicts that the proposed DPC approach has effective performance in terms of “% overshoot” and has a minimum settling time as compared to the other control schemes reported in the literature.Figure 7
Comparative analysis of power control algorithms.


## 6. Experimental Validation

The experimental validation is carried out with a solar PV array (ETS600 × 17DPVF TerraSAS) of 4.3 kW, 334 V, and 12.4 A. The specification of the battery is 240 V and 10 Ah. A DSP microcontroller dSPACE (1006) is used to execute the control algorithm with the current and voltage signals acquired from voltage and current transducers (LEM LV-25P and LEM LA-55P), respectively. Figure8 shows the photograph of the hardware setup.Figure 8
Photograph of the hardware setup.


### 6.1. Tracking Performance of PV Array

The tracking efficiency of the PV array is almost 100% using a well-known P&O MPPT algorithm at the maximum insolation level, as can be seen from Figure9. The specification of the PV array for experimental work is 4.3 kW.Figure 9
Tracking performance at rated insolation.


### 6.2. Steady-State Response of System

The steady-state response of the system in grid-connected mode is exhibited in Figure10. The power is generated by a solar PV array, which partly feeds it to the grid and partly charges the battery. Figure 10(a) shows three-phase balanced grid voltages and currents with their values given in Figure 10(b).Figure 10
Steady-state response of the grid in terms of grid voltage and grid current (vg and ig).
(a)(b)


#### 6.2.1. Harmonics Analysis of Grid Fed System

Figures11(a) and 11(b) illustrate the behavior of the developed charging system while the grid is being fed by a solar PV array. These results show that the THD of grid currents and grid voltages (igand Vg) of all three phases is less than 5%, which justifies the suitability of the VSC control for not only ensuring MPPT but also compensating the nonlinearity of EV current.Figure 11
Total Harmonics distortion of (a) grid voltage (vg) and (b) grid current (ig) during steady state of the grid-fed system.
(a)(b)


#### 6.2.2. Power Flow Management of PV Fed System

Figure12 shows the solar PV power fed to the grid and the battery. Out of 4.2 kW of power generated by the PV array, 2.6 kW of power is absorbed by the grid, and the rest of the power is used to charge the battery. The negative sign in Figure 12(b) depicts that the battery is being charged.Figure 12
Total harmonics distortion of (a) grid powerP, (b) battery voltage and current (Vbat and Ibat), and (c) charging of the battery with battery power (Pbat).
(a)(b)(c)


### 6.3. Dynamic Performance of System

The dynamic performance of the complete system in terms of insolation change to be followed correspondingly by a change in power flow to the battery and grid to maintain the constancy of power generation and consumption is discussed in this section.


#### 6.3.1. Transient Change in PV Array Power with the Same Rate of Battery Charging

Figure13(a) shows the dynamic behavior of insolation change. As it can be seen, the rated power is delivered by the PV array (Ppv), which is distributed for charging the battery (Pbat) and also feeding the grid (Pg). As the insolation drops down to a lower value, the grid power (Pg) is seen to be positive, which demonstrates that the utility provides power for EV charging. Therefore, the charging of the battery is achieved by drawing power from the PV array and partial power from the grid. Figure 13(b) shows a similar trend in terms of Vdc, Ibat, Ipv, and ig. The zoomed-in version shows the PV current (Ipv) increases in correspondence to insolation increment. The charging rate of the battery is kept constant by maintaining the charging current (Ibat). Therefore, the increased PV power is fed to the grid. As a result, grid current (ig) increases with constant DC link voltage (Vdc).Figure 13
Dynamic performance with constant charging state in terms of (a)Vdc, Pbat, Ppv, and Pg and (b) Vdc,Ibat,Ipv, and ig.
(a)(b)


#### 6.3.2. Changeover in Charging Condition with Constant PV Array Power

Figures14(a) and 14(b) show the dynamic characteristics in terms of Vdc, Ipv, ig, and Ibat. The system is operated with constant rated PV power, as shown by constant PV current (Ipv). The DC link voltage (Vdc) is maintained at a constant value, as shown in both figures. In Figure 14(a), the PV array delivers power for battery charging (presented by negative Ibat) and feeding power to the grid (shown by grid current (ig)). The charging control for the battery is achieved through battery current. The battery is now discharged maintaining the same PV array power. Therefore, both the sources now feed power to the grid, which results in increased grid current (ig). Figure 14(b) shows similar performance.Figure 14
Dynamic response with constant PV power. (a) Changeover from charging to discharging state of the battery. (b) Changeover from discharging to charging state of the battery.
(a)(b)


#### 6.3.3. Dynamic Insolation Condition with Constant Power Fed to Grid

Figures15(a) and 15(b) demonstrate the change in solar PV array insolation well abided by a change in bidirectional power flow of battery to maintain constant grid current. In Figure 15(a), rated power is being fed by the array to the grid with battery in fully charged condition. As soon as PV insolation drops down, the PV power is decreased (shown by Ipv). Therefore, to maintain constant grid input, extra power is delivered by the battery (shown by +Ibat). In Figure 15(b), the reverse case is discussed. Here, the battery along with the PV array with reduced insolation is feeding power to the grid. As soon as the insolation is resumed to its rated value, the battery stops discharging, and the total power is fed by the PV array only.Figure 15
Dynamic performance of insolation change with constant power feeding to the grid. (a) Increment in solar insolation, and (b) decrease in solar insolation.
(a)(b)


#### 6.3.4. Grid Failure Condition

Figure16 shows the blackout condition when the grid is unavailable (shown in the zoomed-in portion). It is noticed that as PV power is available, it quickly starts charging the battery (shown by −Ibat), maintaining the DC link voltage constant.Figure 16
Grid failure condition.


### 6.4. Reactive Power Compensation

Figure17 shows one more capability of the proposed system to be able to compensate for the reactive power. It is seen that as the capacitive reactive power (−Q∗) is changed over to inductive reactive power (+Q∗), it is properly compensated by the proposed control algorithm by regulating the DC link voltage.Figure 17
Reactive power compensation with zero active power.


## 6.1. Tracking Performance of PV Array

The tracking efficiency of the PV array is almost 100% using a well-known P&O MPPT algorithm at the maximum insolation level, as can be seen from Figure9. The specification of the PV array for experimental work is 4.3 kW.Figure 9
Tracking performance at rated insolation.


## 6.2. Steady-State Response of System

The steady-state response of the system in grid-connected mode is exhibited in Figure10. The power is generated by a solar PV array, which partly feeds it to the grid and partly charges the battery. Figure 10(a) shows three-phase balanced grid voltages and currents with their values given in Figure 10(b).Figure 10
Steady-state response of the grid in terms of grid voltage and grid current (vg and ig).
(a)(b)


### 6.2.1. Harmonics Analysis of Grid Fed System

Figures11(a) and 11(b) illustrate the behavior of the developed charging system while the grid is being fed by a solar PV array. These results show that the THD of grid currents and grid voltages (igand Vg) of all three phases is less than 5%, which justifies the suitability of the VSC control for not only ensuring MPPT but also compensating the nonlinearity of EV current.Figure 11
Total Harmonics distortion of (a) grid voltage (vg) and (b) grid current (ig) during steady state of the grid-fed system.
(a)(b)


### 6.2.2. Power Flow Management of PV Fed System

Figure12 shows the solar PV power fed to the grid and the battery. Out of 4.2 kW of power generated by the PV array, 2.6 kW of power is absorbed by the grid, and the rest of the power is used to charge the battery. The negative sign in Figure 12(b) depicts that the battery is being charged.Figure 12
Total harmonics distortion of (a) grid powerP, (b) battery voltage and current (Vbat and Ibat), and (c) charging of the battery with battery power (Pbat).
(a)(b)(c)


## 6.2.1. Harmonics Analysis of Grid Fed System

Figures11(a) and 11(b) illustrate the behavior of the developed charging system while the grid is being fed by a solar PV array. These results show that the THD of grid currents and grid voltages (igand Vg) of all three phases is less than 5%, which justifies the suitability of the VSC control for not only ensuring MPPT but also compensating the nonlinearity of EV current.Figure 11
Total Harmonics distortion of (a) grid voltage (vg) and (b) grid current (ig) during steady state of the grid-fed system.
(a)(b)


## 6.2.2. Power Flow Management of PV Fed System

Figure12 shows the solar PV power fed to the grid and the battery. Out of 4.2 kW of power generated by the PV array, 2.6 kW of power is absorbed by the grid, and the rest of the power is used to charge the battery. The negative sign in Figure 12(b) depicts that the battery is being charged.Figure 12
Total harmonics distortion of (a) grid powerP, (b) battery voltage and current (Vbat and Ibat), and (c) charging of the battery with battery power (Pbat).
(a)(b)(c)


## 6.3. Dynamic Performance of System

The dynamic performance of the complete system in terms of insolation change to be followed correspondingly by a change in power flow to the battery and grid to maintain the constancy of power generation and consumption is discussed in this section.


### 6.3.1. Transient Change in PV Array Power with the Same Rate of Battery Charging

Figure13(a) shows the dynamic behavior of insolation change. As it can be seen, the rated power is delivered by the PV array (Ppv), which is distributed for charging the battery (Pbat) and also feeding the grid (Pg). As the insolation drops down to a lower value, the grid power (Pg) is seen to be positive, which demonstrates that the utility provides power for EV charging. Therefore, the charging of the battery is achieved by drawing power from the PV array and partial power from the grid. Figure 13(b) shows a similar trend in terms of Vdc, Ibat, Ipv, and ig. The zoomed-in version shows the PV current (Ipv) increases in correspondence to insolation increment. The charging rate of the battery is kept constant by maintaining the charging current (Ibat). Therefore, the increased PV power is fed to the grid. As a result, grid current (ig) increases with constant DC link voltage (Vdc).Figure 13
Dynamic performance with constant charging state in terms of (a)Vdc, Pbat, Ppv, and Pg and (b) Vdc,Ibat,Ipv, and ig.
(a)(b)


### 6.3.2. Changeover in Charging Condition with Constant PV Array Power

Figures14(a) and 14(b) show the dynamic characteristics in terms of Vdc, Ipv, ig, and Ibat. The system is operated with constant rated PV power, as shown by constant PV current (Ipv). The DC link voltage (Vdc) is maintained at a constant value, as shown in both figures. In Figure 14(a), the PV array delivers power for battery charging (presented by negative Ibat) and feeding power to the grid (shown by grid current (ig)). The charging control for the battery is achieved through battery current. The battery is now discharged maintaining the same PV array power. Therefore, both the sources now feed power to the grid, which results in increased grid current (ig). Figure 14(b) shows similar performance.Figure 14
Dynamic response with constant PV power. (a) Changeover from charging to discharging state of the battery. (b) Changeover from discharging to charging state of the battery.
(a)(b)


### 6.3.3. Dynamic Insolation Condition with Constant Power Fed to Grid

Figures15(a) and 15(b) demonstrate the change in solar PV array insolation well abided by a change in bidirectional power flow of battery to maintain constant grid current. In Figure 15(a), rated power is being fed by the array to the grid with battery in fully charged condition. As soon as PV insolation drops down, the PV power is decreased (shown by Ipv). Therefore, to maintain constant grid input, extra power is delivered by the battery (shown by +Ibat). In Figure 15(b), the reverse case is discussed. Here, the battery along with the PV array with reduced insolation is feeding power to the grid. As soon as the insolation is resumed to its rated value, the battery stops discharging, and the total power is fed by the PV array only.Figure 15
Dynamic performance of insolation change with constant power feeding to the grid. (a) Increment in solar insolation, and (b) decrease in solar insolation.
(a)(b)


### 6.3.4. Grid Failure Condition

Figure16 shows the blackout condition when the grid is unavailable (shown in the zoomed-in portion). It is noticed that as PV power is available, it quickly starts charging the battery (shown by −Ibat), maintaining the DC link voltage constant.Figure 16
Grid failure condition.


## 6.3.1. Transient Change in PV Array Power with the Same Rate of Battery Charging

Figure13(a) shows the dynamic behavior of insolation change. As it can be seen, the rated power is delivered by the PV array (Ppv), which is distributed for charging the battery (Pbat) and also feeding the grid (Pg). As the insolation drops down to a lower value, the grid power (Pg) is seen to be positive, which demonstrates that the utility provides power for EV charging. Therefore, the charging of the battery is achieved by drawing power from the PV array and partial power from the grid. Figure 13(b) shows a similar trend in terms of Vdc, Ibat, Ipv, and ig. The zoomed-in version shows the PV current (Ipv) increases in correspondence to insolation increment. The charging rate of the battery is kept constant by maintaining the charging current (Ibat). Therefore, the increased PV power is fed to the grid. As a result, grid current (ig) increases with constant DC link voltage (Vdc).Figure 13
Dynamic performance with constant charging state in terms of (a)Vdc, Pbat, Ppv, and Pg and (b) Vdc,Ibat,Ipv, and ig.
(a)(b)


## 6.3.2. Changeover in Charging Condition with Constant PV Array Power

Figures14(a) and 14(b) show the dynamic characteristics in terms of Vdc, Ipv, ig, and Ibat. The system is operated with constant rated PV power, as shown by constant PV current (Ipv). The DC link voltage (Vdc) is maintained at a constant value, as shown in both figures. In Figure 14(a), the PV array delivers power for battery charging (presented by negative Ibat) and feeding power to the grid (shown by grid current (ig)). The charging control for the battery is achieved through battery current. The battery is now discharged maintaining the same PV array power. Therefore, both the sources now feed power to the grid, which results in increased grid current (ig). Figure 14(b) shows similar performance.Figure 14
Dynamic response with constant PV power. (a) Changeover from charging to discharging state of the battery. (b) Changeover from discharging to charging state of the battery.
(a)(b)


## 6.3.3. Dynamic Insolation Condition with Constant Power Fed to Grid

Figures15(a) and 15(b) demonstrate the change in solar PV array insolation well abided by a change in bidirectional power flow of battery to maintain constant grid current. In Figure 15(a), rated power is being fed by the array to the grid with battery in fully charged condition. As soon as PV insolation drops down, the PV power is decreased (shown by Ipv). Therefore, to maintain constant grid input, extra power is delivered by the battery (shown by +Ibat). In Figure 15(b), the reverse case is discussed. Here, the battery along with the PV array with reduced insolation is feeding power to the grid. As soon as the insolation is resumed to its rated value, the battery stops discharging, and the total power is fed by the PV array only.Figure 15
Dynamic performance of insolation change with constant power feeding to the grid. (a) Increment in solar insolation, and (b) decrease in solar insolation.
(a)(b)


## 6.3.4. Grid Failure Condition

Figure16 shows the blackout condition when the grid is unavailable (shown in the zoomed-in portion). It is noticed that as PV power is available, it quickly starts charging the battery (shown by −Ibat), maintaining the DC link voltage constant.Figure 16
Grid failure condition.


## 6.4. Reactive Power Compensation

Figure17 shows one more capability of the proposed system to be able to compensate for the reactive power. It is seen that as the capacitive reactive power (−Q∗) is changed over to inductive reactive power (+Q∗), it is properly compensated by the proposed control algorithm by regulating the DC link voltage.Figure 17
Reactive power compensation with zero active power.


## 7. Conclusion

A 3-phase solar-powered fast-charging station for EV charging has been proposed here. The developed system has been operated for a varied range of working circumstances, and its suitability has been examined by both simulated and experimental results. The system is comprised of a three-phase bidirectional charger with the capability of VAR compensation. The operating conditions such as charging, discharging, inductive, and capacitive reactive power coon have been demonstrated here. The four-quadrant operation has been successfully achieved by the proposed control. The suitability of the system has been justified for all modes of operation. The simple control contributes to fast response and low settling time. The feasibility is enhanced in terms of its capability of a smooth transition in various modes. Since the charger control depends on the direct power measurement and control, therefore, the distortionIist seen in the final charging/discharging modes as well as grid currents. This proves the robustness of the system. The THD of the grid current is within 5% in simulated performance as well as experimental observation.



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*Source: 6723610-2022-06-01.xml*