Solar PV Battery Integrated UPQC
Design and Simulink Model Explanation
This section covers the design and Simulink model of the PV battery integrated UPQC system.
Solar PV System
The solar PV system consists of 18 series-connected strings and 28 parallel-connected strings, with each panel having a power rating of 213 watts. The voltage at maximum power point is around 29 volts, and the current at maximum power point is 7.35 amps. The total maximum power is around 107.4 kilowatts, and the operating voltage varies between 5 and 22 volts.
Boost Converter
A boost converter is used to maintain the DC link voltage around 700 volts. The input voltage of the solar PV is considered as 552 volts, the output voltage is 700 volts, and the power rating is 1.4 kilowatts. The inductor and capacitor values for the boost converter are calculated as 3 millihenry and 600 microfarad, respectively.
MPPT for Solar PV
Maximum Power Point Tracking (MPPT) is used to extract the maximum power from the PV panel. The MPPT code generates a duty cycle to drive the IGBT, which in turn extracts maximum power from the PV panel.
Battery Converter Control
Battery Specifications
The battery used in this system has a rating of 24 volts with 20 series connections and a capacity of 48 Ah. The initial state of charge is considered to be 50%.
Bidirectional Converter
The battery is connected to the DC link via a bidirectional converter. The inductor and capacitor values for the bidirectional converter are calculated as 0.1164 H and 4.8e-5 F, respectively. The control logic involves measuring the DC link voltage, comparing it with the reference voltage, and processing it via a PI controller to generate the reference current for battery charging and discharging.
Shunt Converter Control
Control Logic
The shunt converter control logic involves measuring the DC voltage, comparing it with the reference voltage, and processing it via a PI controller to generate the power loss. The control strategy uses the PQ theory to generate the reference current components for controlling the shunt active filter.
Reference Current Generation
The reference current is generated based on the real and reactive power calculations. The reference current is then compared with the shunt converter current and processed via a hysteresis controller to generate the pulses for the shunt converter.
Series Converter Control
Series Converter Purpose
The series converter, also known as the series active filter, is used to mitigate voltage sags and swells in the grid system by injecting voltage into the system.
Control Logic
The control logic involves measuring the load voltage and source current, converting them to dq0 components, and comparing the load voltage with the source voltage. The error voltage is processed via a PI controller to generate the compensating voltage, which is then converted back to abc form and processed to generate the pulses for the series converter.
Testing Condition Settings
Grid and Load Settings
The grid voltage is considered as 450 volts with a frequency of 50 Hz. Various sag and swell conditions are created to test the system performance. The system also includes non-linear and unbalanced loads to test the harmonic mitigation capability.
Simulation Results and Discussion
Voltage Sag and Swell Mitigation
The simulation results show that the series converter effectively mitigates voltage sags and swells by injecting the appropriate voltage into the system. The load voltage is maintained at the rated value despite variations in the grid voltage.
Harmonic Mitigation
The shunt converter effectively mitigates harmonics in the source current caused by non-linear loads, ensuring that the grid current remains sinusoidal.
Battery Operation
The battery operates in charging or discharging mode based on the available solar PV power and the power requirements of the grid. The state of charge and current flow are managed effectively by the bidirectional converter.
Conclusion
The three-phase Solar PV Battery Integrated UPQC system effectively mitigates voltage sags, swells, and harmonics, ensuring stable and quality power supply. The system also manages the battery operation efficiently, providing a reliable solution for integrating renewable energy sources into the grid.
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