Real-Time Implementation of Electric Spring Using a Nine Switch Converter Topology for Combined Power Control in a Hybrid Microgrid System

Abstract

This work proposes an electric spring using a novel nine-switch converter topology (NSC) for power control of an isolated hybrid microgrid system. The hybrid microgrid system comprises a constant power source of a micro-hydro-based self-excited induction generator and a photovoltaic system equipped with battery energy storage. Generally, the ‘generation following load’ (GFL) strategy is used for an isolated system. This suggests the generation be varied according to the load demand. An electric spring works on a ‘load following generation’ (LFG) strategy. Hence, the load demand can be adjusted according to the generation. In this proposed work the loads are segregated into two types, namely sensitive load and non-sensitive load. A nine-switch converter is used in this work, which operates partly as a series and partly as a shunt compensator. The series side of NSC is connected to a non-sensitive load to form an electric spring. The Shunt side of the NSC acts as a power modulator to control the PV side power flow. The proposed isolated hybrid microgrid system is subjected to load and source variation. To study the performance analysis, MATLAB/Simulink is used to simulate the proposed system. The simulation performance is tested with OPAL-RT 5700 system. Typical results are given to prove our claims.

Appendix

1.1 Nomenclature

$V_{ds} ,V_{qs}$::

Direct and quadrature axis stator voltages

$V_{dr} ,V_{qr}$::

Direct and quadrature axis rotor voltages

$R_{s} ,R_{r}$::

Stator side and rotor side resistance

$L_{Ls} ,L_{Lr}$::

Stator and rotor side leakage inductance

$L_{M}$::

Mutual inductance

$i_{ds} ,i_{qs}$::

Direct and quadrature axis stator currents

$i_{dr} ,i_{qr}$::

Direct and quadrature axis rotor currents

$\Psi_{ds} ,\Psi_{qs}$::

Direct and quadrature axis stator flux

$\Psi_{dr} ,\Psi_{qr}$::

Direct and quadrature axis rotor flux

$\omega_{r}$::

Speed of SEIG

$T_{e}$::

Electromagnetic torque

$P$::

Number of poles

$I_{{\text{m}}}$::

Magnetizing current

$a,b,c,d$::

Curve fitting parameters

$V_{as} ,V_{bs} ,V_{cs}$::

SEIG voltages

$i_{ca} ,i_{cb} ,i_{cc}$::

Currents across the delta-connected capacitor bank

$T_{i} ,M_{i} ,B_{i}$::

Top, middle, and bottom set of switches of NSC

$A,B,C$::

Shunt converter terminals of NSC

$X,Y,Z$::

Series converter terminals of NSC

$V_{p0} ,V_{q0}$::

Equivalent three-phase shunt and series voltages concerning the DC midpoint

$V_{d}$::

DC-link voltage

$V_{ia} ,V_{ib} ,V_{ic}$::

Voltages of series converter terminal of NSC

$V_{ca} ,V_{cb} ,V_{cc}$::

Voltages across the capacitors of series side

$i_{fa} ,i_{fb} ,i_{fc}$::

Filter currents of series side

$R_{a} ,R_{b} ,R_{c}$::

Filter resistance

$L_{a} ,L_{b} ,L_{c}$::

Filter inductance

$C_{a} ,C_{b} ,C_{c}$::

Filter capacitance

$i_{{{\text{NSLa}},b,c}}$::

Non-sensitive three-phase load currents

$e_{A} ,e_{B} ,e_{C}$::

Control signal of terminal ABC of NSC

$e_{X} ,e_{Y} ,e_{Z}$::

Control signal of terminal XYZ of NSC

$V_{T}$::

SEIG terminal voltage

$V_{a,b,cNSL}$::

Three-phase non-sensitive load voltage

$U_{a} ,U_{b} ,U_{c}$::

In-phase components

$W_{a} ,W_{b} ,W_{c}$::

Quadrature components