Search

Increasing installation of photovoltaic (PV) in the distribution power system has resulted in serious voltage rise, limiting grid-connectable power. This scenario becomes significant in the low-voltage resistive feeder. This paper proposes a decentralized control for distributed PV inverters to mitigate voltage rise. Instead of MPPT (maximum power point tracking) mode, the proposed PV inverter is able to curtail its real power and compensate the reactive power according to the impedance at the installation location. The drooped characteristics between the output power and the impedance are developed so that the PV inverters are able to cooperatively suppress voltage rise based on their local voltage measurement only. Therefore, PV inverters are allowed to supply more power to the utility within voltage limitation. Simulations are conducted to guarantee the proposed control on improvement of voltage rise considering different parameter of feeder. A lab-scaled prototype circuit is established to verify effectiveness in a resistive feeder.

Severe voltage distortion, due to power system harmonic resonance, has been reported in recent years. This issue becomes more significant in high penetration of a photovoltaic (PV) network. A conventional voltage detection active filter operates as similar conductance for all harmonic frequencies to resolve this problem whether in a fixed conductance command or in an automatic gain adjustment control. However, its filtering capability is impeded by the mismatch between the active filter and the radial line, and the voltage distortion may still be significant. This paper proposes a discrete frequency tuning active filter to suppress power system harmonics. The active filter operates as variable conductance for each individual harmonic frequency. Each harmonic conductance is dynamically adjusted according to the corresponding harmonic voltage distortion of the active filter installation point in response to increase or decrease of nonlinear loads, or variation of resonant frequency in the power system. The mismatching problem between the feeder impedance and the active filter can be avoided effectively. Therefore, harmonic voltage distortion can be maintained at an allowable level throughout the feeder with lower peak current and lower rms current of the active filter, and loads installed at various locations of the power system receive more uniform voltage waveform. Index Terms--Active power filter, harmonic resonance, harmonic voltage damping.

Distributed generation has attracted great attention in recent years, thanks to the progress in new-generation technologies and advanced power electronics. The Microgrid has been a successful example by integrating various generation sources with the existing power distribution network through power electronic converters. Microgrid converters are required to operate in a decentralized fashion, and power-frequency and reactive-power-voltage droop controls have been adopted for this purpose. In this paper, a droop control technique for imbalance compensation within the three-phase ac distributed generation system is proposed for Microgrid converters. The proposed technique allows even sharing of imbalance current among various converters and can thus be seamlessly integrated with the existing active-power-frequency and reactive-power-voltage droop controls to improve the power quality within the distributed power system. Its control functionalities are discussed, and simulation and laboratory test results are also presented to validate the proposed method. Index Terms--Distributed power system, droop control, voltage imbalance.

The dramatic growth of power electronics applications has led to serious harmonic pollutions in the power system. The phenomenon of harmonic resonance resulting in severe voltage distortion has been reported. Various suppression techniques have been proposed to resolve this problem. The distributed active-filter system (DAFS) is a more effective solution by deploying multiple shunt active filter units (AFUs) in the system to cooperatively damp the harmonic resonance. This paper proposes a dynamic tuning scheme for the DAFS to enhance its filtering performance. Based on the measured voltage harmonic distortion at the installation point, each AFU can dynamically adjust its own filtering volt-ampere (VA) capacity to maintain the total harmonic distortion of the line voltage at an allowable level. The proposed strategy can be integrated with the droop control between the conductance command and VA consumption so that the harmonic-filtering workload is evenly shared among various AFUs. The operation principles and dynamic analyses are presented in this paper, and test results based on simulations and experiments validate the proposed approach. Index Terms--Active filters, distributed active-filter systems (DAFSs), harmonic damping, harmonic resonance.

Increasing demand for premium electric power, in terms of both quality and reliability, and emerging new energy technologies have led to the development of distributed generation systems. Due to rapid penetration of power electronics equipment, many of the loads within distributed generation systems are nonlinear in nature, and the resulting harmonics pollution needs to be addressed. This paper proposes a new cooperative harmonic filtering strategy for the interface converters of distributed generation sources. A droop control method based on the reactive volt-ampere consumption of harmonics of each interface converter is designed and implemented. In this strategy, the overall harmonic filtering workload can be evenly shared without any communications. The operation principle is explained in detail. Computer simulations and laboratory test results validate the distributed harmonic damping capability of the proposed strategy. Index Terms--Distributed generation systems, harmonic damping, harmonic resonance, microgrid.

Increasing demand of electric-power reliability in industrial parks or in urban areas has led to the development of closed-loop distribution power systems. The harmonic resonance between power-factor-correction capacitors and system inductors may cause significant voltage distortion along the feeder. This paper proposes a discrete frequency-tuning active filter installed at the middle point of a closed-loop line for harmonic-resonance suppression. The active filter operates as a variable conductance for individual harmonic frequency according to the corresponding harmonic-voltage distortion. This algorithm allows the damping conductance of each harmonic frequency to be separately and autonomously adjusted in response to variation of both harmonic sources and resonant capacitors. Therefore, the unintentional “whack-a-mole” phenomenon, due to mismatching between the active filter and the line, can be avoided even if the active-filter location deviates from the middle point. Voltage distortion throughout the closed-loop line can be definitely maintained below an allowable level with lower peak current and lower rms current compared to the conventional voltage-detection active filter. Computer simulations based on a 11.4 kV/15 MVA system and a scaled-down platform in the laboratory are developed to validate the effectiveness of the proposed approach. [ABSTRACT FROM PUBLISHER]