The current-limiting strategy for shunt active power filter (SAPF) will be activated automatically, when the compensation-capacity need exceeds the rated capacity. However, the traditional current-limiting strategy cannot realize the comprehensive protection with optimum objectives. The paper firstly reveals the essential of the current-limiting demands for the comprehensive protection of SAPF, namely the limiting control objects: 1) the root mean square (RMS) of the compensation current (mainly for the overheat protection of the IGBT and inductor); 2) the instantaneous wave of compensation current (mainly for the accurate current control and IGBT Icnom specification) and 3) the instantaneous wave of PWM-VSC modulation voltage (for the need of liner close-loop control). Secondly, the paper proposes an improved current-limiting scheme based on particle swarm optimization (PSO) to achieve the two optimization targets: 1) the minimization THD for the grid-side current; 2) the maximization utilization ratio for the capacity of the SAPF. The main advantage lies on the optimum limiting ratios of each harmonic order are calculated in real time respectively to achieve the flexible and liner limiting control. Finally, simulation and experiment verify the effectiveness of the proposed strategy.
- Shunt active power filter
- Current-limiting demands
- Current-limiting strategy
- Particle swarm optimization
Figure. 1. System mechanism diagram of SAPF.
EXPECTED SIMULATION RESULTS:
Traditional current-limiting control
Figure. 2. Simulation results of traditional current-limiting strategy.
(a): Modulation voltage without current limitation, (c)(e):Load current and
spectrum analysis, (b): Modulation voltage with traditional current limitation,
(d)(f):Grid-side current Is, output compensation current Ic and spectrum
analysis of Is.
2) Optimal current-limiting control using PSO
Figure. 3. Simulation results of the proposed current-limiting strategy.
(a)(c)(e)(g): Simulation waves with the optimum-capacity control strategy,
(b)(d)(f)(h): Simulation waves under the optimum-THD control strategy.
An improved current-limiting strategy based on PSO is proposed to optimize the utilization rate of SAPF or the THD of grid-side current. This strategy takes advantages of the two traditional methods: equal-proportion current-limiting control and truncated current-limiting control. Simulation results prove: the proposed current-limiting scheme can reduce the THD of grid-side current and improve the utilization rate of SAPF effectively, and no extra undesired harmonic will be injected into the power system. Future work will focus on further experiment validation for the effectiveness of the proposed method, especially dynamic performance.
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