Zhaoan Wang

A series active power filter adopting hybrid control approach

The series active power filter (APF) is suitable for compensating a voltage type harmonics-producing load, whereas the control approach it adopts may directly influence its compensation characteristics. This paper first discusses the control approach of detecting source current in terms of the basic operation principle of a series APF, then developing a control approach of detecting load voltage. On the basis of these, a hybrid control approach is proposed. In this approach, the reference signal of the compensation voltage needed by the series APF is obtained by detecting both source current and load voltage. Thus, this approach has the advantages of the first and the second control approaches and, at the same time, it can overcome their respective drawbacks. For practical realization, the control methods of the PWM inverter in the series APF and for regulating its DC side voltage are discussed in detail. A prototype of the series APF is manufactured and corresponding experimental investigation is done. The results show that when the series APF, if adopting the hybrid control approach instead of the other two, compensates for the voltage type harmonics-producing load, its performance can be improved greatly.

A new hybrid parallel active filter

This paper presents a new parallel hybrid active filter topology which can reduce the VA rating of the active power filter (APF) greatly. Based on the conventional topology of the hybrid parallel filter, the basic idea of the new topology is to add a small inductor in parallel with APF controlled as a harmonic current source, in order to force the fundamental reactive current to flow through the additional inductor, instead of flowing through APF. Three different control methods and a formula estimating VA rating of APF are proposed for the new topology. Experimental results obtained from a 30 kVA prototype exhibit excellent performance of the new hybrid filter. The required rating of the active filter is approximately only 1% of the harmonic-producing load.

A novel quasiconstant frequency hysteretic current mode control approach

A new quasiconstant hysteretic current mode control is presented by introducing a switching frequency feedback to the normal hysteretic control. The merits of the new control approach are good stability and fast dynamic response. The switching frequency is stabilized within small range around the reference frequency, which makes the design of the filtering circuit become easier. Experiments are carried out to test the stability and the dynamic performance of the new control approach.

A horizontal-winding multi-permeability distributed air-gap inductor

Distributed air-gap inductors have the advantage of reducing winding loss in high switching frequency DC/DC converters. However, they also have the disadvantage of uneven distribution of flux density, which inevitably leads to the incomplete utilization of magnetic material. This paper proposes a horizontal-winding multi-permeability distributed air-gap inductor structure to increase inductance without the increase of inductor volume. To evaluate the proposed method, a two-permeability inductor together with a single permeability inductor is fabricated. The measured results show the two-permeability inductor has higher inductance than the single-permeability one, especially at light load. Both inductors are tested in a 12V input, 1.6V output DC/DC converter to show their performance. The results show the two-permeability inductor could further improve light load efficiency of high frequency DC/DC converters.

A novel control approach to the DC active power filter used in a low ripple and large stable/pulse power supply

In this paper, a hybrid filter structure, which consisting of a passive and a shunt-connected DC active power filter, is proposed for a special high precision, low ripple and large power DC stable/pulse power supply. The main circuit configuration of DC active power filter and its basic concept for suppression harmonics are analyzed in detail. A novel control strategy of DC active power filter with detecting the output ripple voltage, i.e. the reference signal of the DC active power filter is obtained by detecting the output ripple voltage across the DC load, is presented. The advantage of the control approach is that, it is very easy to meet the requirements of low current ripple and fast response in DC stable/pulse power supply, whereas the precision of the circuit transducer and components is not need special request. To validate the proposed concept, a prototype of 12-pulse rectifier system and DC active power filter are manufactured and corresponding experiment investigation is done. Tested by a 120 kW practical industrial application stable/pulse power supply with the DC active power filter and adopting the control approach proposed, its output current ripple factor achieves 8.87/spl times/10/sup -6/ (peak to peak), in addition to others advantages include fast dynamic response, high efficiency and low cost.

A Horizontal-Winding Multipermeability LTCC Inductor for a Low-profile Hybrid DC/DC Converter

Distributed air-gap inductors have the advantage of reducing winding loss in high switching frequency dc/dc converters. However, they also have the disadvantage of uneven distribution of flux density, which inevitably leads to uncompleted utilization of magnetic material. This paper proposes a horizontal-winding multipermeability low-temperature cofired ceramic (LTCC) inductor to increase inductance and improve efficiency without the necessity of increasing inductor volume. For the purpose of simplicity, a two-permeability LTCC inductor is taken as an example for analysis and comparison. Design of such an inductor is demonstrated with the aid of 2-D finite elementary analysis simulation. A two-permeability LTCC inductor together with a single-permeability LTCC inductor is fabricated for measuring and testing. The measured results show the two-permeability inductor has higher inductance than the single-permeability inductor. Both inductors are tested in a 5-V input, 3.3-V output dc/dc converter to test their performances. The testing results show the two-permeability LTCC inductor could further improve the efficiency of high-frequency dc/dc converters compared with the single-permeability LTCC inductor.

A three-phase comprehensive reactive power and harmonics compensator based on a comparatively small rating APF

Focused on harmonics and some other power quality problems caused by variation of reactive power, a three-phase comprehensive compensator composed of a thyristor switched filter and an active power filter (APF) is proposed, in which the rating of APF is comparatively small. Harmonics and reactive power can be compensated dynamically with this compensator. A control method is proposed and is simulated by MATLAB. Then, a prototype is installed and some experiments have been completed. The simulation and experiment results make it clear that the compensation character is very good.

DC-link Pumping-up Voltage Suppression of a Series Active Voltage Regulator With Phase Shift Control

The DC-link voltage pumping-up phenomenon is analyzed for a series active voltage regulator in the paper. In order to avoid DC-link voltage pumping-up, a phase shift compensation strategy is proposed, and the relationship between the source overvoltage ratio, load power factor, phase shift angle and compensation voltage provided by the inverter is presented in detail. Taking a series active voltage regulator used in low voltage distribution for example, the parameters aforementioned are calculated. A group practical design curves for suppressing DC-link voltage pumping-up with phase shift control algorithm are obtained. At last, the validity and the effectiveness of the proposed novel method is verified by some computer simulations and the laboratory experimental results

A novel comprehensive compensator for electrified railway system

Based on the topology consisting of several branch of thyristor switched filters (TSF) and a small rating active power filter (APF), a novel comprehensive compensator is proposed, which compensates for harmonics and reactive power in electrified railways. A cascaded multilevel inverter constructs the main circuit of the APF in the novel compensator. A new method detecting specified order harmonic and a combining control strategy are proposed for the first time. Particular attention has been paid to designing a suitable control law for a TSF bank and its implementation in a real circuit. A digital control system based on double DSPs was designed. Finally, methods of estimating VA rating and designing coupling transformer are provided. Experimental results obtained from a 1 MVA prototype exhibit excellent performance of the new comprehensive compensator.