International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 10 Issue: 07 | July 2023
p-ISSN: 2395-0072
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Optimal Power Flow Using LQR-Based CCVS Inverter for the GridIntegrated Renewable Energy System Mohamed Jaffer1, Dr. Abdulla Ismail 2 (1) Graduate Student, Dept. of Electrical Engineering and Computing, RIT – Dubai, UAE. (2) Professor of Electrical Engineering, Dept. of Electrical Engineering and Computing, RIT – Dubai, UAE. ---------------------------------------------------------------------***--------------------------------------------------------------------quantities. It eliminates the reactive power in transient Abstract - This paper proposes an effective control method states and harmonic currents. [19]
for the actual and reactive power flow between the renewable energy system (RES) and the grid using a linear quadratic regulator (LQR) to a current-controlled voltage source inverter (CCVSI). Additionally, it makes up for the harmonic current components that the load draws from the grid terminal. The reduced-order state-space model of the three-phase grid-connected renewable energy system is developed using a simplified equivalent circuit. Using fewer weighing variables in LQR makes control law analysis and design simpler. To manage the real and reactive power to the grid and reduce total harmonic distortion (THD), the extension is real-reactive power (p-q) approach implemented in an a-b-c frame is used to generate the reference current.
A control technique is essential to track the reference currents. In literature, many researchers proposed several control techniques to integrate the RES with the grid. The implementation of a hysteresis controller is simple, but its variable switching frequency causes resonance and switching losses. Fixed switching frequency is obtained by comparing the output with the carrier wave in a conventional Proportional Integral (PI) controller with pulse width modulation (PWM). [19,20] But the steady-state error is present in the output if a sinusoidal reference is followed. The steady-state error is eliminated using a proportional Resonant (PR) controller, but its performance depends on the controller which operates in resonant frequency. In terms of response profile, control effort requirement, and robustness concerning system nonlinearities, the optimal Linear Quadratic Regulator (LQR) is superior. Using LQR, the optimal pole placement controller is used in this work to track the sinusoidal references with the fixed switching frequency, good stability margins, and transient response. To prove the supremacy of LQR, the hysteresis controller is compared.[21]
Key Words: Optimal Power Flow, RES, LQR, CCVSI. I INTRODUCTION Due to the enormous increase in power demand, electrical power systems are getting overloaded [1,2]. This leads to an exponential increase in the usage of renewable energy sources (RES). With the advent of power electronic converters, RES is effectively integrated with the electrical power system [3,4]. However, the usage of power electronic devices and non-linear loads deteriorate the quality of power in the electrical system [5,6].
Several current control techniques are proposed in the literature to integrate renewable sources in the grid [22– 31]. The hysteresis controller is simple to implement but results in variable switching frequency causing resonance and more switching losses.
Therefore, an appropriate regulatory framework is to be followed for the distribution system to guarantee the reliable and efficient operation of the system. In addition to the power converter, shunt active power filters [8-12] are used to mitigate power quality issues. This increases the additional hardware cost. Hence, a current-controlled voltage source inverter (CCVSI) is employed in this work for the twofold purpose of power conversion and power quality improvement.[13] The performance of CCVSI is based on the reference current generation.[14]
The switching frequency can be fixed by a carrier wave in a conventional proportional-integral (PI) controller with pulse width modulation (PWM) control. But there exists a steady-state error whenever sinusoidal references are used. This may not be preferable for certain applications. [32] A controller that eliminates the steady-state error while regulating the sinusoidal signals is a proportional resonant (PR) controller, but its performance depends on the resonant frequency at which the controller operates. This frequency has to be adjusted in the method that matches
The generated reference currents compensate for the reactive and harmonic components. Various techniques are presented in the literature [15-18] to generate reference currents. In this work, instantaneous p-q theory is used. It uses instantaneous quantities instead of average
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