Dynamic Modelling of a Solar Energy System with Vehicle to Home Option for Newfoundland Conditions

DOI: http://dx.doi.org/10.24018/ejers.2021.6.5.2497 Vol 6 | Issue 5 | July 2021 16 Abstract — This paper discusses the dynamic modelling of a solar energy system with vehicle to home (V2H) option for Newfoundland condition. A location was chosen (13 Polina Road) in St. John’s, Newfoundland, Canada. Using BEopt, Homer and MATLAB software, an optimized system was designed for the chosen site to satisfy the house’s energy demand. Furthermore, the concept of V2H is also implemented with aid of smart current sensors installed in the house. When the power provided by the PV panel and the stored energy in the inhouse battery is less than the load’s energy demand, the Nissan Leaf’s battery used to supply home loads in V2H operation mode. The system operates based on the information generated by the sensors. Detailed system dynamic modelling is also presented along with the simulation results. Eight system control modes are proposed and simulated.


I. INTRODUCTION
Electric vehicles (EVs) are a revolutionary development in the global transportation industry. As compared to fossil fuel powered cars, they have more acceleration and emit no pollution, making them a reliable alternative. Renewable energy resources, such as solar energy systems can help meet the fast-growing energy demand in the fast-changing world. Renewables being variable in nature, there is a need for backup support [1]. Hence the need of battery storage comes into play. The inhouse battery is used to supply uninterrupted power to load when the power produced by PV is not sufficient to meet the loads energy demand [2]. Nissan Leaf (40 kW variant) is considered for the Vehicle to Home (V2H) concept implementation [3], [4]. Furthermore, the implemented system, during charging mode has level 1 and level 2 chargers for charging the Nissan Leaf's battery and a converter for simultaneously charging the inhouse battery and powering the load. By default, the designed system uses PV as primary source of power until the produced power is less than the load's energy demand. In this case the inhouse battery is used for powering the loads until it reaches 30% of its State of Charge (SOC). On reaching 30% SOC the system will implement V2H, in this case Nissan leaf's battery will be in discharge mode to meet the load's energy demand [5]- [7].
In this paper, a system is designed, and its control algorithm is presented to address this issue of implementing Vehicle to Home concept along with hybrid PV system. The Submitted Fig. 1 displays a monthly profile of solar radiation and clearness index for the selected site in St. John's, Newfoundland, Canada. The clearness index ranges from 0.20 to 0.30. The solar insolation ranges from 1.28 kW/m 2 /day to 5.14 kWh/m 2 /day, with a mean of 3.15 kWh/m 2 /day.

B. Sites Power Requirement from BEopt
BEopt software was used to estimate the annual power requirement for the chosen site. The house's power requirement amounts to around 21111 kWh per year. This includes all the loads in the home, including heaters, boilers, lightning, ventilation, and other considerations such as plugin loads.

C. Sites Load and Photovoltaic Panel Area Calculation
The site's load requirement comes to 57.8 kWh/day with peak of 11.90 kW. Fig. 2 illustrates the daily load profile (hourly load data) from HOMER, the hourly energy demand is starting to raise around 6 AM and drops by 9PM with an all-time high between 6 PM and 7PM. Fig. 3 illustrates the seasonal load profile (hourly load data) from HOMER, November to April months is having per hour energy demand compared to May to October months.   Including derating factor the number of strings = 24 Strings.

III. SYSTEM SIMULATION
Hybrid Optimization of Multiple Energy Resources (HOMER) software was used for system sizing. Fig. 4 depicts a schematic of the proposed system. The PV panel used is a Canadian Solar CS6U-340M, the battery is a Trojan SAGM 12 105, the inverter is a 20 kW, 10 kW genset which serves only as a backup and has no dynamic implications on the system, Nissan Leaf is added as deferrable load with 9.90 kWh/d with 6.60 kW peak and the home load profile is 57.80 kWh/d with a peak of 11.90 kW.

C. Nissan Leaf -40 kW variant
This concept considers a Nissan Leaf with a 40-kW lithium-ion battery pack and a 6.6 kW onboard charger. Another advantage of the Nissan Leaf is that it has a built-in bidirectional converter for charging and discharging (reeling power to home). Nissan Leaf has two modes of operation: charging and discharging. When the Nissan Leaf is discharging or reeling out power. This is used when the PV panels and battery are unable to satisfy the energy demand of the home load [8], [9]. The following are presumed when the Nissan Leaf is in charging mode. The home loads are met, and the excess energy produced or stored is used to charge the electric vehicle [10].

D. Inverter
Since the peak load is about 18.50kW, a 20kW output power inverter is being considered for the design. The inverter in this case has two outputs: 120V and 240V.

IV. SYSTEM DYNAMIC MODELLING
Simulink was used to carryout simulation of the proposed architecture. It comprises of PV array, MPPT controller, inhouse battery, boost converters, inverter, level 1 charger, level 2 charger, Nissan Leaf battery. Fig. 6 illustrates the overall block diagram of the proposed system. The power produced by PV is used for charging the inhouse battery via a charger, inverter with two outputs 120 V and 240 V is implemented to convert the stored power in battery DC to AC to power the load. Furthermore, Nissan leaf charger with level 1 and level 2 charging feature [11] is implemented, a 10 kW genset is also incorporated which serves only as a backup and has no impact on dynamics of system and a converter is also implemented to stepdown 360 V to 48 V, which is used for simultaneously charging the inhouse battery and powering the house loads [12], [13]. Fig. 7 illustrates the overview of simulated system. The system is simulated for charge and discharge of the inhouse battery, powering the loads using inhouse battery, dual output inverter that gives 120 V and 240 V as output, Nissan leaf charger with level 1 and level 2 charging, Discharge Nissan leaf to charge inhouse battery, discharge inhouse battery during night to charge Nissan leaf and dump load to drain excess power. The implemented system has automatic overrides for state of charge, namely 30% SOC charge ON (inhouse battery) and 40% SOC charge ON (Nissan Leaf battery) for inhouse battery and Nissan Leaf, respectively as shown in Fig. 7. Fig. 7 illustrates the overview of the simulated system.

A. MPPT Algorithm
Maximum power point tracking (MPPT) is a concept that involves modifying PV impedance depending on varying irradiance to get the most power out of a PV panel. The Perturbation & Observation (P&O) algorithm is used by the MPPT controller in this simulation. The voltage is constantly perturbed in the P&O algorithm, and the inverter service cycle is modified depending on the performance observation. Even when there is a significant decrease or spike in irradiance, this algorithm is the best at tracking the maximum point. Fig. 8 illustrates the implemented MPPT algorithm -P&O algorithm. Furthermore, the simulation was carried out incorporating eight modes representing different modes [14] of operation.

B. Mode 1 -Inhouse Battery Charging Mode
In this mode the output from PV is used for charging the inhouse battery and for powering the loads. In this case the loads energy demand is low. The excess energy is used for charging the battery. Fig. 9 illustrates switching control logic of the proposed system. From table 1, switches S1, S2, S3, S8, S9 turns ON and the switches S4, S5, S6, S7, S10, S11 remains OFF. Fig. 10 illustrates the charging design executed in MATLAB. From Fig. 10, the duty cycle from the MPPT block is fed into as the gate pulse for the MOSFET in the boost converter circuit. Fig. 11 and 12 illustrates the low load's current and voltage graph. The load has a voltage of 120 V and current of 12 A.

C. Mode 2 -Inhouse Battery Discharge Mode
In this mode the output from PV is low compared to the load's energy demand. In this case the inhouse battery is used to power the load. From Fig. 9 and Table I, in Mode 2 switches S3, S8, S10 turns ON and the remaining switches stays OFF. Fig. 13 illustrates the inhouse battery in discharge mode. Furthermore, a 2-output inverter is incorporated, that give 120 V and 240 V as output. Fig. 14 and 15 illustrate the high loads current and voltage graph. The load in this case has a voltage of 240 V and 27 A.

A. Mode 3 -Nissan Leaf Charge Mode
In this mode output from PV is higher than the loads energy demand and the inhouse batteries SOC is greater than 60%, the system will charge Nissan Leaf battery [14]. The implemented charger also comprises of level 1 (120V, 14 A) and level 2 (240 V, 20 A) charging. Fig. 16 illustrates the Nissan leaf's charging mode. An inverter is incorporated to supply power for the level 1 and level 2 chargers. Furthermore, the chargers have incorporated boost converters to boost the voltage to 360 V, charging voltage of Nissan Leaf battery. From Fig. 9 and Table I, in mode 3 at level 1 charging, switches S1, S2, S3, S4, S5, S8, S9 turns ON and switches S6, S7, S10, S11 remains OFF. In mode 3 level 2 charging, switches S1, S2, S3, S4, S6, S8, S9 turns ON and switches S5, S7, S10, S11 remains OFF. Fig. 17 and 18 illustrates the charging current graphs for level 1 and level 2 charging, respectively. The SOC of Nissan Leaf battery is illustrated in Fig. 19. The designed system has implemented both level 1 and level 2 charging, the output from level 2 charging can be seen between the time interval of 5 seconds to 10 seconds and the output from level 1 charging can be seen between the time interval of 10 seconds to 15 seconds [15], [16].

B. Mode 4 -Nissan Leaf Discharge Mode
In this mode output from PV is less than the loads energy demand and the inhouse batterie SOC is less than 30%, in this case Nissan Leaf is reels out the stored power to the house to meet the loads energy demand [17], [18]. From Fig. 9 and Table I, in mode 4 switches S7, S8, S10 are turned ON and remaining switches stay OFF. Fig. 20 illustrates the Nissan Leaf's discharge mode. A buck converter is incorporated to convert the high voltage (360 V) from the Nissan Leaf's battery to 48 V to charge the battery and power the load simultaneously [19], [20]. Fig. 21 illustrates the Nissan Leaf's SOC graph. From Fig. 21 the inhouse battery was on discharge cycle between the time intervals of 5 seconds to 15 seconds and then it has started to charge because of Nissan leaf's discharge mode execution.

C. Mode 5 -Inhouse Battery Protection Mode
This mode is incorporated to help in saving the inhouse battery by monitoring the SOC of the battery. When inhouse batteries SOC falls to 30% SOC, the 30%SOC breaker goes HIGH and the 30% SOC charge on breaker goes HIGH to charge the battery. From Fig. 9 and Table I, switches S2, S3 turns ON and the remaining switches are OFF.

D. Mode 6 -System Isolation Mode
In this mode output from PV is less than the loads energy demand, the inhouse batteries SOC is less than 30% and the Nissan leaf SOC is less than 40%, [21] the total cutoff breaker is turned ON. This is executed to isolate the system from the Load so that the system does not fail. From Fig. 9 and Table  I, in mode 6 switch S2 is turned ON to facilitate further charging of battery when PV starts producing power and switches S1, S3, S4, S5, S6, S7, S8, S9, S10, S11 remain OFF.

E. Mode 7 -Excess Power Handling Mode
In this mode the power produced from PV is higher than the loads energy demand, the inhouse battery and Nissan Leaf's battery is charged, a dump load is implemented to dissipate the excess power. From Fig. 9 and Table I, in mode 7 switches S1 and S11 are turned ON and the switches S2, S3, S4, S5, S6, S7, S8, S9, S10 remains OFF.

F. Mode 8 -Nighttime Charging Mode
In this mode is the power stored in the inhouse battery is used to charge Nissan leaf's battery at nighttime when the loads energy demand is considerably less and the inhouse batteries SOC is greater than 60% [22]. From Fig. 9 and Table I, in Mode 8 level 1 charging, switches S3, S4, S5, S8, S9 is turned ON and the remaining switches S1, S2, S6, S7, S10, S11 stays OFF. Mode 8 level 2 charging mode, switches S3, S4, S6, S8, S9 are turned ON and the switches S1, S2, S5, S7, S10, S11 remains OFF. Fig. 22 illustrates the nighttime charging mode. From Fig. 22, the designed system has the option to choose between level 1 and level 2 charging even at nighttime charging mode.

V. CONCLUSION
Dynamic modelling of solar energy system with vehicle to home option for Newfoundland conditions was successfully designed and simulated. The solar insolation for Newfoundland from figure 1 is 3.15 kWh/m 2 /day, PV panels considered are 340 W modules producing 16.3984 kW implemented in 24 strings with 2 panels in each string. A commercially available inverter of 20 kW capacity was incorporated with 80 Trojan SAGM 12 105 batteries each of 12 V and 100 Ah along with a 10kW backup genset, Nissan Leaf is implemented as deferrable load with 9.90 kWh/d with 6.60 kW peak. The implemented simulation consists of eight main operating modes i) Inhouse battery charging modepower produced by PV is used for charging the inhouse battery and for powering the loads simultaneously, ii) inhouse battery discharge mode -The stored power in the inhouse house battery is used to meet the loads energy demand, iii) Nissan Leaf charging mode -The loads energy demand is met and the inhouse battery is charged, the excess power is used for charging Nissan Leaf, iv) Nissan Leaf discharge mode-the loads energy demand is high and the output form PV and inhouse batteries SOC is low [23] Nissan Leaf reels out the stored energy to meet the loads energy demand [24], [25], v) inhouse battery protection modeprevents the inhouse battery from going into degenerative discharge condition, vi) system isolation modeto prevent the system from failing, vii) excess power handing modeto handle the excess power produced, viii) nighttime charging mode -To charge Nissan Leaf to get it ready for next day's use. The implemented system has the scalability factorcan be extended to parking lots, multiple houses can be connected to form a microgrid and can power multiple houses or support the grid (V2G). Further this research would be directed towards V2X and V2G concept where vehicles would be used for sharing power to grid, scheduling loads, powering multiple houses, buildings or locality or an entire city and vehicle to vehicle energy transfers [26]- [30].