Development of a Proportional + Resonant (PR) Controller for a Three-Phase AC Micro-Grid System

ABSTRACT:

This document presents a Proportional + Resonant (PR) controller design for regulating the active and reactive power output of a three-phase AC Micro-Grid inverter system. The system employs a Voltage Sourced Inverter (VSI). The VSI is configured to operate as a current source through an interface L-filter. The power is controlled indirectly by controlling the inverter’s output current. The stationary reference frame strategy is adopted for the design of the PR controller. A model of a grid connected AC inverter and a detailed design of the inverter’s PR based control scheme are presented. The control scheme is developed and simulated in MATLAB/Simulink software environment. The control algorithm code is generated for a target device. Using Processor In-the Loop (PIL) simulation, functional equivalence testing is performed between the simulated control algorithm and the compiled algorithm code on the target device. Results in both normal and PIL simulations are discussed from the viewpoint of steady state and dynamic performance of the controller.

KEYWORDS:

  1. Stationary Reference Frame
  2. Processor In-the Loop
  3. Feedback Control
  4. Voltage Sourced Inverter
  5. Alpha-Beta transformation
  6. Proportional Resonant controller

SOFTWARE: MATLAB/SIMULINK

SCHEMATIC DIAGRAM:

Figure 1 Schematic diagram for a three-phase grid connected VSI

EXPECTED SIMULATION RESULTS

Figure.2 Three-Phase grid voltages (Vabc)

Figure 3 Normal simulation α-axis current tracking due to a step change in Pref at t = 0.5s

Figure 4 Normal simulation system’s response tracking active power reference signal due to a step change in Pref at t = 0.5s

 

Figure 5 PIL simulation α-axis current tracking due to a step change in Pref at t = 0.5s

Figure 6 PIL simulation system’s response tracking active power reference signal due to a step change in Pref at t = 0.5s

CONCLUSION:

This paper has presented the effectiveness of using the Proportional Resonant (PR) control strategy to control active and/or reactive power transfer between the Micro-Grid and the transmission grid system. The PR controller tracks stationary frame reference currents calculated from the active (PC(t)) and reactive (QC(t)) PI controller actuating power outputs using d-q frame power equations. Consequently this improves the performance of the control loop as opposed to reference currents calculated directly from αβ frame power equations. The PR controller tracks reference currents with a very small steady-state error and reduced harmonic distortion. Model development and simulations were done using the MATLAB/Simulink software environment. Functional equivalence testing was performed between the simulated control algorithm and the compiled algorithm code on the real hardware target device. Same results were obtained for both normal and PIL simulation modes.

REFERENCES:

[1] A Yazdani and R Iravani, Voltage-Sourced Converters in Power Systems. New Jersey: John Wiley & Sons, Inc, 2010.

[2]  S. Meshram, G. Agnihotri, and S. Gupta, “A Modern Two DOF Controller for Grid Intergration with Solar Power Generator,” International Journal of Electrical Engineering and Technology, vol. 3, no. 3, pp. 164-174, December 2012.

[3] X. Wang, J. M. Guerrero, F. Blaabjerg, and Z. Chen, “A Review of Power Electronics Based Microgrids,” Journal of Power Electronics, vol. 12, no. 1, pp. 181-192, January 2012.

[4] J. J. V. Cardona, J. C. A. Gil; F. J. G. Sales, S. Segui-Chilet, S. O. Grau, and N. M. Galeano, “Improved Control of Current Controlled Grid Connected Inverters in Adjustable Speed Power Energies,” Universidad Politecnica de Valencia and Universidad de Antioquia,.

[5] R. Teodorescu, M. Liserre, and P. Rodríguez, Grid Converters for Photovoltaic and Wind Power Systems.: John Wiley & Sons, Ltd, 2011.

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