Guochun Xiao

Novel load ripple voltage-controlled parallel DC active power filters for high performance magnet power supplies

The cooling storage ring of the heavy ion research facility in Lanzhou (HIRFL-CSR) is one of the five mega-science projects undertaken by Chinese Academy of Science within its ninth and tenth five-year plan period. The HIRFL-CSR facility can providing heavy ion beams in wide energy range, manifold and with high quality. This paper presents a hybrid filter structure consisting of a passive filter and a parallel dc active power filter (DCAPF) for a sample magnet power supply in HIRFL-CSR. The configuration of the power system with the DCAPF is introduced. Then a novel feedback control scheme for the DCAPF is proposed with detecting the output ripple voltage across the magnet load. For detailed discussion, a simple model of the whole system has been derived and the stability characteristic is analyzed. Through simulation and experiment investigation, the DCAPF is successfully applied in a 120-kW magnet power supply in HIRFL-CSR finally. The ripple factor and tracking accuracy of the output current through the load achieve 8.87 ppm and 100 ppm, respectively. Therefore, the rigor requirements of low output current ripple and fast ramp rate are both satisfied with the DCAPF proposed.

DC-Link Voltage Pumping-up Analysis and Phase Shift Control for a Series Active Voltage Regulator

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. The effectiveness of this novel control strategy is also verified by some simulation results.

Insertion sort correction of two-way merge sort algorithm for balancing capacitor voltages in MMC with reduced computational load

The Modular Multilevel Converter (MMC) is very suitable for high-power applications like High-Voltage Direct Current (HVDC) transmission system, in which the number of submodules is commonly very large to reach high voltage. Therefore, the sorting algorithm of the conventional voltage balancing strategy causes too much computational load, greatly increasing the hardware cost and challenging the controller design. This paper introduces a two-way merge sort that evidently reduces computation weight and accelerates the sorting, combining with the prediction of capacitor voltages in ideal conditions. Furthermore, to solve the issue of non-ideal conditions in practical applications, this paper proposes an insertion sort correction algorithm with little and controllable computational load on the basis of the two-way merge sort. The proposed sorting algorithm takes advantage of the features of MMC control strategy, and consequently is much faster than conventional sorting such as quicksort. 401-level MMC simulation results in PSCAD/EMTDC show the validity of the proposed sorting algorithms, and the reduced computational load with shorter execution time is verified by DSP controller TMS320F28335.

The experimental studies on active power filter for HVDC system

The main circuit configuration of an active power filter for an HVDC transmission system and its basic concept for th suppression of harmonics are analyzed in detail in this paper and on the basis of these, an experimental device is developed. The experimental results show that the hybrid filter, consisting of a passive fitter and active filter can further increase the filter performance on the DC side in an HVDC system.

A Research on the Application of Phase Shift Control for Active Voltage Quality Regulator

The relationship between overvoltage ratio, power factor, phase shift angle and compensation voltage is first analyzed in this paper. Then the investigation into the DC-link voltage pumping-up from the viewpoint of active power flow is conducted and a novel closed-loop phase shift control method based on the DC-link voltage is proposed. The experiment conducted in the laboratory examines the feasibility of the proposed idea, the results show that AVQR based on the proposed idea performs well in sustaining DC-link voltage, and it also ensures the progressive phase shift of load voltage. Two AVQRs with a respective rating of 50 kVA and 100 kVA are also developed afterwards, they have been successfully integrated into a realistic power system environment and have a good performance of mitigating voltage disturbances.

An Active Voltage Quality Regulator with variable dc-bus voltage topology

The active voltage quality regulator (AVQR) is an equipment designed to mitigate the long-term voltage disturbance, such as undervoltage, overvoltage and voltage harmonics etc. For the existing AVQR topology, the dc-bus voltage is either uncontrolled or controlled to a constant value, and it can not vary with the missing voltage variation. When the missing voltage is small, the corresponding and required dc-bus voltage should be small as well. But in the existing topology, the dc-bus voltage usually keep very high. Therefore, the duty ratio of the inverter is very small and then the efficiency is very low. In order to overcome its drawbacks, a new AVQR topology is proposed in which the diode-rectifier is replaced by the thyristor-rectifier in this paper. Then for the sake of show the advantage of the proposed topology, the dc-bus voltage in the both topologies (uncontrolled or controlled) are compared by simulations. Through comparative analysis, the proposed topology is proven to be better than the existing topology, especially on a large missing voltage variation. At last, the validity and effectiveness of the proposed topology and control strategy are also verified by the laboratory experimental results. In a case, under the same supply voltage and load conditions, the efficiency increases from 89.1% of uncontrolled dc-bus voltage to 96.1% of controlled dc-bus voltage on a 2 kVA prototype, so the efficiency is increased significantly.

Analysis of Transformerless Voltage Quality Regulator with Load Current Feed-Forward and Dual-Loop Control

The transformerless voltage quality regulator is a new power electronic equipment designed to mitigate the voltage disturbance. Performance of the voltage quality regulator in improving the quality of power supply is examined. In order to improve the performance, a combined load current feed-forward and dual-loop(outer voltage loop and inner filter inductor current loop) control scheme is proposed in this paper. This paper analyzes the control scheme that with and without load current feed forward in detail. This paper also adopts the phase shift control to deal with DC link voltage pumping-up phenomenon when source voltage is long duration overvoltage. Through comparative analysis, the proposed scheme is verified to be better than traditional dual-loop control methods. At last, the validity and effectiveness of the proposed control scheme are verified by the computer simulation and laboratory experimental results.

Performance Improvement for a Series Active Voltage Quality Regulator with Source Voltage Feed-forward and Load Voltage Feed-back Control

The series active voltage quality regulator is a new power electronic equipment designed to mitigate the voltage disturbance in forms of voltage swell, voltage sag, distorted voltage waveforms, harmonics, transient interruption, frequency deviation on sensitive loads. Performance of the series active voltage quality regulator in improving the quality of power supply is examined. It is shown that the existing open-loop control strategy used in the series active voltage quality regulator to regulate load voltage can produce poorly damped response due to the presence of the switching harmonic filter in the regulator. Also, the load voltage feedback method called closed-loop control is still inadequate because the bad load regulating characteristic and the poor dynamic response. In order to improve the performance, a composite control method that combined feed-forward of source voltage and feed-back of load voltage is proposed in this paper. Furthermore, this paper firstly presents two criterions that should be satisfied when the load voltage is properly tracking the reference voltage for active voltage quality regulator. Aimed at these two criterions, three control methods are comparative analyzed in detail. Through comparative analysis, the proposed scheme is verified to be better than the previous methods. At last, the validity and effectiveness of the proposed control scheme are verified by the computer simulation and laboratory experimental results.

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