H. Akagi

Digital control of an integrated series active filter and diode rectifier with voltage regulation

The integration of a series active filter with a 12-pulse diode rectifier can provide a cost-effective and efficient means of supply current harmonic-free AC/DC conversion. Controlling the series active filter as a frequency-selective impedance requires low delays and is not well suited for digital control. This paper suggests a current-mode control strategy to allow full digital control of the active filter. The suggested current-mode control method for supply current balancing and voltage regulation is verified experimentally.

Natural balancing of series-stacked power quality conditioners

This paper develops a systematic and mathematically formal study of the balancing theory of series-stacked multilevel converters. It is shown that the DC bus voltages of these converters balance naturally, provided that the switching frequency is chosen high enough. Two balancing mechanisms, one associated with losses and the other with the load impedance, are identified. A single phase of a 2 MVA series-stacked power quality device was constructed and the theoretical results were verified experimentally.

Design of a Transformerless Shunt Hybrid Filter Integrated into a Three-Phase Diode Rectifier

This paper describes design and performance of a transformerless shunt hybrid filter integrated into a three-phase diode rectifier. The hybrid filter consists of a three-phase passive filter tuned to the 7th-harmonic frequency, and a small-rated active filter based on a three-phase voltage-source PWM converter. The validity of the system design is confirmed by experimental results obtained from a 400-V, 15-kW laboratory system. The experimental results show that the active filter plays an essential role in reducing supply harmonic currents. The THD (total harmonic distortion) of the supply current gets less than 5%. Moreover, the hybrid filter provides satisfactory transient performance as a result of having achieved an optimal design of circuit and control parameters including the dc capacitor voltage and feedback gains of the active filter, along with the cut-off frequency of high-pass filters for harmonic extraction.

DFT-based Repetitive Control of a Series Active Filter Integrated with a 12-pulse Diode Rectifier

This paper considers the transient performance and stability of a recurrent discrete Fourier transform (DFT) based control method for a series active filter integrated with a 12-pulse diode rectifier. The control method targets specific harmonics and/or the negative sequence fundamental component of the supply current, and is intended for use with nonsinusoidal/unbalanced supply voltages. The proposed control method is based on DFTs instead of the dq-method, and a simple approach is used to account for small frequency variations found in practical power systems.

Dynamic performance of a unified power flow controller for stabilizing AC transmission systems

This paper presents dynamic control and performance of a UPFC under a fault condition in a dual-feeder transmission system. The transmission system discussed in this paper consists of two feeders in parallel, which are installed between two power stations. When interruption occurs in one of the two feeders, active and reactive power flow are reduced to half because the line impedance doubles. The UPFC is installed in one power station, and keeps the total amount of active power flowing through the dual feeder constant. In this paper, control stability and power-flow regulation under the single-feeder interrupt are theoretically discussed, and are verified by computer simulation and experiments using a 10-kVA laboratory setup. As a result, it is clarified that a conventional control scheme may cause a large amount of overshoot in active and reactive powers after single-feeder interrupt. On the other hand, advanced control can control the active and reactive power faster than the power fluctuations, and thus make it possible to eliminate the power variation accompanied by single-feeder interrupt.

Magnetic Saturation in Transformers used for a Self-Commutated BTB System with Ride-Through Capability during Voltage Sags

This paper deals with a large-capacity self-commutated BTB(Back-To-Back) system rated at 50 MW for the purpose of power flow control between transmission networks. It focuses on the dynamic behavior of the BTB system during voltage sags such as a single-line-to-ground(1LG) fault. During the 1LG fault, a dc magnetic deviation occurs in the transformers used for the BTB system just after occurrence and restoration of the fault. It is indispensable to understand an amount of deviation because it may bring magnetic saturation as well as a large amount of magnetizing current to the converter-cells. This paper derives theoretical equations related to the deviation during the ILG fault. The theoretical analysis developed in this paper would make significant contributions to designing the transformers.

Digital control of an integrated series active filter and passive rectifier with voltage regulation

The integration of a series active filter with a 12-pulse diode rectifier can provide an effective means for supply current harmonic free AC/DC conversion. Controlling the series active filter as a frequency selective impedance requires low delays and is not well suited for implementation by digital control. This paper suggests two control methods intended for implementation by digital control. The suggested current-mode control method for supply current balancing and voltage regulation is verified experimentally.

Balancing theory of series-stacked power quality conditioners

This paper develops a systematic and mathematically formal study of the balancing theory of series-stacked multilevel converters. It is shown that the DC bus voltages of these converters balance naturally, provided that the switching frequency is chosen high enough. Two balancing mechanisms, one associated with losses and the other with the load impedance, are identified. A 2 MVA series-sacked power quality device was constructed and the theoretical results were verified experimentally.

Current regulation for a series active filter integrated with a diode rectifier

This paper deals with digital control of a series active filter integrated with a diode rectifier where the series active filter is controlled to function as a current source. A predictive current regulator is considered for the series active filter to achieve good ripple characteristics and predictable switching losses. The operating conditions, and the effect there of on the current regulator are considered and oversampling and prediction of the load voltage is suggested to improve the active filtering performance without increasing the switching frequency.

Digital reference generation for a series active filter integrated with a diode rectifier

This paper considers the control of a series active filter integrated with a double-series diode rectifier. It is shown that, as result of delays introduced by digital control, current-mode control is preferred to voltage-mode control for digital implementations. A Fourier-based method for generating balanced current references with optimized power factor is presented. The advantage of current-mode control is illustrated by simulation and the Fourier-based method is verified by experiment.