Supercapacitor Based Energy Storage System in STATCOM Application
A supercapacitor based static synchronous compensator, STATCOM, is proposed to control both reactive and active power exchange with the grid side. It aims to provide a comprehensive control for a distributed network, and improve the stability. However, due to its low cell voltage, long time constant, and voltage dependent energy storage, applying the supercapacitor to grid level applications is challenging. This paper examines the steady state performance of three types of supercapacitor based energy storage system, which used as the DC link capacitor part in STATCOM application. The simulation results shown that, even at steadystate, the dc link has a high ripple current. In order to tolerate the high ripple current, the supercapacitor based energy storage system should be carefully designed. Two types of parallel hybrid capacitor systems are developed in comparison with the pure supercapacitor system, which provide an improved performance in terms of efficiency, volume, thermal, cost, and lifetime under the same STATCOM operating condition.
- Capacitor storage
- Energy storage
Figure 1. STATCOM topology in Simulink.
EXPECTED SIMULATION RESULTS:
Figure 2. Current waveform during normal conditions.
Figure 3. DC link current generation mathematical model
The steady state performance analysis indicates a positive bias for using the supercapacitor as an energy storage system for a STATCOM. The proposed SC based STATCOM has a similar topology as the conventional STATCOM, with the capacitor bank replaced by a SC based energy storage system. As shown in the simulations, the proposed SC based STATCOM retains the same reactive power capability as the conventional system. The simulation results shows that, even at steady-state, the dc link has a high ripple current, 830A rms. For available SCs, the maximum current rating is 210A, so SC parallel connection is required. However, the SC-only system requires a large number of SCs, operating at maximum current ratings. The SCEC and SCFC systems, as the simulation results shown, the SC rms current of the two hybrid capacitor systems has been effectively reduced, with only one SC string sufficient to withstand the ripple current. As a result, system volume, power loss, efficiency, temperature performance, cost and life expectation can be improved by using the hybrid parallel capacitor system.
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