Real and Reactive Power Control of SEIG Systems for Supplying Isolated DC Loads

Abstract

A vector oriented control technique with a two-loop control scheme has been developed for operating a stand-alone three-phase SEIG for supplying DC loads through a three-phase Pulse Width Modulated (PWM) rectifier. The proposed controller maintains constant load voltage with reduced harmonics at the PWM rectifier input terminals. In addition, it controls the real and reactive power flow between the SEIG and converter system. The proposed control scheme has been implemented employing dSPACE 1103 real-time controller. The successful working of the proposed control strategy has been verified for different operating conditions, by modelling the system in MATLAB/Simulink toolbox and the results are presented. A prototype system consisting of an SEIG, PWM rectifier and associated control circuits, has been built in the laboratory environment and a close agreement between the simulated and experimental results has been confirmed.

Appendix

The instantaneous real power at SEIG terminals is given by:

$$p_{g} = v_{sa} i_{Ra} + v_{sb} i_{Rb} + v_{sc} i_{Rc}$$

(5)

where $i_{Ra} ,i_{Rb} ,i_{Rc}$ are the instantaneous rectifier input currents. The steady-state modelling of the system can be represented as

$$\left[ {\begin{array}{*{20}c} {x_{d} } \\ {x_{q} } \\ \end{array} } \right] = \frac{2}{3}\left[ {\begin{array}{*{20}l} {\cos \omega t} \hfill & {\cos \left( {\omega t - \frac{2}{3}\pi } \right)} \hfill & {\cos \left( {\omega t + \frac{2}{3}\pi } \right)} \hfill \\ { - \sin \omega t} \hfill & { - \sin \left( {\omega t - \frac{2}{3}\pi } \right)} \hfill & { - \sin \left( {\omega t + \frac{2}{3}\pi } \right)} \hfill \\ \end{array} } \right]\,\left[ {\begin{array}{*{20}c} {x_{a} } \\ {x_{b} } \\ {x_{c} } \\ \end{array} } \right]$$

where x is instantaneous voltage and currents.

By using above abc to dq transformation matrix, Eq. (2) can be modified as follows,

$$v_{d} = R_{f} i_{Rd} + L_{f} \frac{{di_{Rd} }}{dt} + v_{id} + \omega L_{f} i_{Rq}$$

(6)

$$v_{q} = R_{f} i_{Rq} + L_{f} \frac{{di_{Rq} }}{dt} + v_{iq} + \omega L_{f} i_{Rd}$$

(7)

Further, the equations can be modified as

$$v_{dref} = R_{f} i_{Rd} + L_{f} \frac{{di_{Rd} }}{dt}$$

(8)

$$v_{qref} = R_{f} i_{Rq} + L_{f} \frac{{di_{Rq} }}{dt}$$

(9)

where,

$$v_{dref} = v_{d} - v_{id} - \omega L_{f} i_{Rq}$$

(10)

$$v_{qref} = v_{q} - v_{iq} + \omega L_{f} i_{Rd}$$

(11)

By using abc to dq transformation matrix Eq. (5) can be modified as:

$$P = \frac{3}{2}\left[ {v_{d} i_{d} + v_{q} i_{q} } \right]$$

(12)

$$Q = \frac{3}{2}\left[ {v_{q} i_{d} - v_{d} i_{q} } \right]$$

(13)