Dayi Li

A high-power active filtering system with fundamental magnetic flux compensation

In this paper, a novel transformer structure is proposed in order to manufacture a high-power active filtering device. The novel transformer structure contains one primary and multiple secondary windings. The system configuration and compensation principle are addressed in detail. The fundamental magnetic flux compensation in the case of the transformer with multiple secondary windings is fulfilled. In addition, a three-phase active power filter topology consisting of three independent transformers with multiple secondary windings is presented so that the filter can run under unbalanced loads. The parameters of hysteresis current control are also analyzed in detail. A simple and practical fundamental detecting approach is discussed. Transient response and fault protection schemes are explained. A set of automatic three-phase active power filtering devices has been constructed and operated in the field. The field test results verify the validity of the novel transformer structure and the active power filtering system.

A Novel Active Power Filter for High-Voltage Power Distribution Systems Application

In this paper, a novel principle of an active power filter based on the harmonic impedance control of a transformer is proposed for high-voltage power distribution systems application. A linear transformer with multiple secondary windings is adopted. The primary winding is shunted with harmonic-producing loads, while the secondary windings are connected with inverters. The primary harmonic current is detected and then tracked by the inverters with fixed compensation coefficient. When the harmonic current compensation condition is satisfied, the transformer can really exhibit nearly zero impedance to harmonic current and primary self-impedance to fundamental current. As a result, the harmonic currents in power systems can be led to flow into the transformer branch. The operation principle, the control scheme, and the harmonic current detection method are discussed in detail. Finally, simulated waveforms and experimental results are presented to verify the effectiveness of the active power filter

A novel power quality conditioner applied to high voltage power systems

A novel principle of parallel hybrid active power filter based on controllable impedance is proposed for high voltage alternate power systems application. The linear parallel transformer can exhibit controllable impedance under the control of power electronic inverters. On the one hand, the transformer can exhibit nearly zero impedance to harmonic current and thus lead harmonic current to flow into the transformer circuit. On the other hand, the transformer can also exhibit continuously adjustable reactance to fundamental current and thus together with the passive power filter compensate reactive power. To increase the capacity of the active power filter, a special transformer structure with multiple secondary compensation windings is adopted. In the mean time, a new reference current operation method is put forward. The simulated results show that the performance in harmonic suppression and reactive power compensation of the proposed scheme is satisfactory

A novel variable reactor based on an inverter-controlled transformer

In the paper, a novel adjustable reactor is proposed. In the novel reactor, a transformer with air gap is chosen and its primary winding is connected in series or parallel to the power system, the primary winding voltage is detected and passed to a phase shift circuit. The output signal of the phase shift circuit functions as the reference signal. A voltage-source inverter (VSI) is applied to produce a controllable voltage source, which is energized across the secondary winding of the transformer. The equivalent impedance of primary winding varies continuously along with the amplitude of the secondary voltage and phase shift angle. Besides this, the stability condition is analyzed. The validity of the theory is proved by the simulation results.

Research on the influence of time delay on fundamental flux controllable reactor

This paper reveals a kind of adjustable reactor. Firstly, it introduces the basic principle of the reactor. The reactor is based on a transformer with air gap. The current signal of primary side is detected and then directly injected into the secondary side. In this paper, the phase difference(caused by time delay) between the detected current signal of primary winding and the injected current signal of secondary winding is taken into consideration. The effect of phase shift on the equivalent impedance of the reactor is analyzed. And its effect on system stability is also analyzed. The validity of the theory is proved by the simulation results.

A multifunctional power quality controller for microgrid

Microgrid power quality has some unique features (harmonic high penetration, frequent voltage fluctuation, overcurrent phenomenon and bidirectional power flow) compared to the conventional power grid, as a result of the intermittence and random of the distributed energy resources. Also it is not cost effective to install various types of power quality controller because of small capacity of the microgrid. In order to cater for the peculiar requirements of microgrid power quality, a novel multifunctional power quality controller (MPQC) suitable for microgrid is proposed and the operational principle is described. The MPQC plays the role of voltage compensation, fault current limiter, power flow control and harmonic isolation. The control scheme is also given. A PSIM simulation model and a prototype of MPQC has been constructed. The simulation and experimental results verify the validity of the MPQC.

A novel Harmonic Suppression and reactive power compensation method

Phased rectifier thyristor commutate circuit has brought serious harmonic pollution to electric power grid. In this paper, a novel power filter method is proposed to solve an actual harmonic problem of a steel factory which was brought by phased rectifier thyristor commutate circuit in ZheJiang province of China. This paper firstly discuss the characteristic of the harmonic source, then introduce the Harmonic Suppression method particularly, including the problems of insulation distance and the protection of the Power Electronic Devices in the conditions of large harmonic current. The actual effect of harmonic suppression was shown at last.

A novel active power filter with shunt transformer

In the paper, a novel active power filter with a shunt transformer and an inverter is proposed. A transformer is chosen and its primary winding is connected in parallel with harmonic source, the primary fundamental voltage is detected and functions as the given signal. A voltage-source inverter is applied to produce a controllable fundamental voltage source, which is energized across the secondary winding of the transformer. When the controlled voltage and the primary winding fundamental voltage satisfy a certain condition, the transformer exhibits a variable reactor to fundamental so as to compensate reactive power; whereas it exhibits primary leakage impedance of the transformer to harmonic so that the harmonic flow through the primary winding. The validity of the theory is proved by the simulation results.