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This paper investigates the open-circuit faults of switching devices in the three-level T-Type inverter and proposes a new tolerant control method. The three-phase current and variation of the neutral-point voltage are detected to determine the fault switch. A carrier-based pulse width modulation is developed to tolerate switch fault by transiting from three-level to two-level switching. This makes the modulation scheme easier to be implemented compared to space vector modulation. For the neutral-point fault, the fault phase is operated by two-level modulation to produce the same rating voltage. On the other hand, the inverter is able to produce balanced voltage with reduced rating by keeping the phase of half-bridge fault to the neutral-point voltage. The neutral-point voltage is also able to be balanced by using two-level modulation since it does not contribute the neutral-point current. The performance and effectiveness of the proposed tolerant control are verified by a laboratory build. [ABSTRACT FROM AUTHOR]

Unintentional series and/or parallel resonances, due to the tuned passive filter and the line inductance, may result in severe harmonic distortion in the industrial power system. This paper presents a hybrid active filter to suppress harmonic resonance and to reduce harmonic distortion. The proposed hybrid filter is operated as variable harmonic conductance according to the voltage total harmonic distortion; therefore, harmonic distortion can be reduced to an acceptable level in response to load change or parameter variation of the power system. Since the hybrid filter is composed of a seventh-tuned passive filter and an active filter in series connection, both dc voltage and kVA rating of the active filter are dramatically decreased compared with the pure shunt active filter. In real application, this feature is very attractive since the active power filter with fully power electronics is very expensive. A reasonable tradeoff between filtering performances and cost is to use the hybrid active filter. Design consideration are presented, and experimental results are provided to validate effectiveness of the proposed method. Furthermore, this paper discusses filtering performances on line impedance, line resistance, voltage unbalance, and capacitive filters. [ABSTRACT FROM PUBLISHER]

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]