Vehicle to Grid and Grid to Vehicle in Single Phase Grid
Explanation of the Simulink Model
This simulation model is developed for Vehicle to Grid (V2G) and Grid to Vehicle (G2V) in a single-phase grid. The grid voltage is approximately 325 volts, which means for a 230-volt RMS, the peak amplitude is always 325 volts. We consider the frequency of a single-phase grid to be 50 Hz.
Model Components
Source Inductance
Single-Phase Bridge Rectifier
DC Link Capacitor
Bi-directional DC-DC Converter: This converter includes two switches, a filter inductor, and a capacitor.
Battery: We use a 120-volt battery with a rated capacity of 48 Ah.
In this model, we need to maintain the voltage across the DC link capacitors at around 380 volts and ensure the source-side power factor is always unity.
Control Methods
We apply two control methods: DC link voltage control and current control. The current control maintains unity power factor on the source side. We measure the DC link voltage and compare it with the reference voltage of 380 volts, processing it via a PI controller. This controller generates the reference peak magnitude for the current control.
Grid Side Voltage and Current Control
The peak magnitude is converted into a sinusoidal nature by measuring the grid voltage and using a Phase Locked Loop (PLL). The PLL generates the omega-t, processed to create a sine wave, which is then multiplied with the reference current. This results in the actual reference current in sinusoidal form, following the nature of the grid voltage.
The reference current combines with the source/grid current and is processed through a PI controller, generating control voltage in sinusoidal form. This control voltage is then fed to a single-phase H-bridge PWM inverter, controlling the power flow from the grid to the battery or vice versa, operating under unity power factor condition with THD always less than 5%.
Battery Side Current Control
We measure the battery current and compare it with the reference current. The error current is processed via a PI controller, whose output is the duty cycle. This duty cycle is processed through a PWM generator to control the bi-directional converter switches, managing the current flow for charging or discharging the battery. This implements the V2G and G2V concepts, where power flows from the vehicle battery to the grid or from the grid to the vehicle to charge the battery.
Simulation Results and Discussion for G2V and V2G Conditions
Using a step input, we change the battery reference current to simulate charging and discharging modes. Initially, with a reference current of -10 amps, the battery charges from the grid (G2V). After 0.2 seconds, the reference current changes to +10 amps, and the battery discharges to the grid (V2G).
Battery Current and Voltage: The battery current and voltage show charging and discharging states, maintaining the DC link voltage around 380 volts.
Source Voltage and Current: The source voltage and current maintain unity power factor, with phase angles in-phase during charging and 180 degrees out-of-phase during discharging.
THD Analysis
The Total Harmonic Distortion (THD) of the source current is measured during both charging and discharging conditions. In both cases, the THD is less than 5%, adhering to IEEE standards.
Conclusion
This simulation demonstrates the V2G and G2V concepts in a single-phase grid, ensuring efficient power management and maintaining grid stability
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