Lewei Qian

An Improved Adaptive Detection Method for Power Quality Improvement

A new adaptive harmonic selective detection method is proposed in this paper. This adaptive method has better convergence properties compared to previous adaptive or neuron detection methods. The adaptive gains of this method can be relatively large to obtain faster convergence. The stability of the proposed method is guaranteed and its properties are analyzed when compared to its predecessors. This proposed adaptive method is simple and effective in extracting fundamental and harmonic current information from nonlinear load currents. The extracted fundamental or harmonic currents therefore can be used as the reference signals for power quality improvement, harmonic selective cancellation or reactive power compensation. The method is also phase-independent and can thus be easily applied to single- or three-phase unbalanced systems. Simulation and experimental results verify the good performance of this improved adaptive detection method. Moreover, two application cases are built and tested to demonstrate its effectiveness in harmonic selective cancellation and reactive power compensation.

Prony analysis for power system transient harmonics

Proliferation of nonlinear loads in power systems has increased harmonic pollution and deteriorated power quality. Not required to have prior knowledge of existing harmonics, Prony analysis detects frequencies, magnitudes, phases, and especially damping factors of exponential decaying or growing transient harmonics. In this paper, Prony analysis is implemented to supervise power system transient harmonics, or time-varying harmonics. Further, to improve power quality when transient harmonics appear, the dominant harmonics identified from Prony analysis are used as the harmonic reference for harmonic selective active filters. Simulation results of two test systems during transformer energizing and induction motor starting confirm the effectiveness of the Prony analysis in supervising and canceling power system transient harmonics.

Study On Grid Connected Inverter Used in High Power Wind Generation System

In high power wind power generation systems, grid connected voltage source inverters (VSI) are essential devices for power transporting and energy converting. Output currents of inverters increase harmonic distortion due to low switching frequencies. A series inductance usually is used to reduce switching harmonics entering the power distribution network. Another kind of filter, LCL filter, can achieve reduced levels of harmonic distortion at lower switching frequencies. However grid connected inverters with an LCL-filter require more complex control methods to make the system stable. This paper proposes a robust strategy to control grid currents entering a distribution network from a three-phase VSI connected via an LCL filter. This grid connected inverter system is used in high power wind generation systems for reduced current harmonics with low switching frequency. Different from previous control strategies integrating an outer loop grid current regulator with inner capacitor current regulation, this control strategy integrates one bridge current regulation loop with grid current and voltage feed forward (dual feed forwards) to stabilize the system. Therefore, the grid currents are controlled indirectly, and the current sensors number can be reduced. Linear analysis, comparisons with previous methods, simulation and experimental results verify the effectiveness of this control strategy across a range of operating conditions

Multivariable control method in STATCOM application for performance improvement

In this paper, a hybrid PI (proportional integral)/LQR (linear quadratic regulator) control method for STATCOM (static synchronous compensator) control is introduced. The control logic is evaluated in Matlab/Simulink, and the simulation results are compared with those coming from the traditional PI control design. It is shown that the new method is superior to a PI method in both design complexity and response performance. The new method generates less oscillation and has shorter settling time.

Three-Phase Harmonic Selective Active Filter Using Multiple Adaptive Feed Forward Cancellation Method

This paper proposes a three phase harmonic selective active filter with multiple adaptive feed forward cancellation (MAFC) for harmonic reference generation. The MAFC method is derived from previously used adaptive feed forward cancellation (AFC) method used in acoustics. The adaptive law is derived by an SPR (strictly positive real) Lyapunov function. This adaptive method is simple and effective in extracting fundamental and harmonic current information from nonlinear load current. The effectiveness of this method is verified by testing experimentally a nonlinear load current. The extracted harmonic currents are used as the reference signals for the active filter harmonic selective cancellation control. The active filter features harmonic selective ability reduces the active power filter rating, bandwidth requirements and enhances its flexibility. Simulation results are used to validate the control of this harmonic selective active filter system

Experimental Verification and Comparison of MAFC Method and D-Q Method for Selective Harmonic Detection

This paper reviews two popular harmonic detection methods for power electronics applications. One is a d-q method, which dominates the three-phase active filter and STATCOM applications and the other one is a multiple adaptive feed forward cancellation (MAFC) method. The latter one is also called an adaptive neuron method, neural network method or Adaline method. The novelty of this paper is that it presents experimental results, which is rare in the literature. This paper first gives an introduction of MAFC method from adaptive control point of view. Then realtime (RT) implementation of two methods is introduced and realtime hardware in the loop tests (HIL) are fully performed to compare these two methods. Finally, experimental results using these two methods on a diode rectifier front end motor drive and a thyristor rectifier dc drive are presented. Both steady state and dynamic performances of these two methods are compared. The comparison results give guidance for using these two methods for power electronics applications like active filter or STATCOM

A Reconfigurable and Flexible Experimental Footprint for Control Validation in Power Electronics and Power Systems Research

This paper introduces a reconfigurable and flexible experimental footprint for validation of new development in power electronics and power systems research. The system contains six drives with six diode rectifiers, and six IGBT converters, which can be reconfigured as back to back converter or diode rectifier drive systems. The induction motor (IM) and the permanent magnetic synchronous motor (PMSM) in this system provide a platform for research on motor control, fault detection, and diagnosis (FDD), etc. The two thyrisor dc drives with two dc motors work as loads for IM and PMSM. The dc drives also work as nonlinear loads to support research on power quality. Together with the configured diode rectifier drives, one adjustable nonlinear load offers a platform for development of power quality control algorithms. Additionally, the system interacts with real time digital simulator (RTDSreg) for control algorithm verification in controller hardware in the loop (HIL) or power HIL tests. Hence, the entire system is flexible and reconfigurable for different research areas, e.g. motor control, FDD, active filtering, STATCOM and other power electronics or power system research. Three examples are presented in the area of FDD, STATCOM, and power quality to demonstrate the capability of this experimental footprint.

Real time digital simulations augmenting the development of functional reconfiguration of PEBB and universal controller

In this paper, real-time hardware-in-the-loop (HIL) simulation is adopted to augment the development of functional reconfiguration of power electronic building blocks and universal controllers. The simulation environment employs a commercial real-time digital simulator allowing real time simulations of large power systems. Two case studies regarding functional reconfiguration are discussed. The first case is a marine all-electric-ship application to improve system power quality. A novel control algorithm is proposed for an active filter, which is derived from reconfiguring variable speed motor drive. The second case outlines how the HIL simulator is utilized to a static synchronous compensator application where a commercial controller provides firing pulses to a simulated converter and the connected power system. Details of the control scheme, the HIL setup, and test results are given.

A reconfigurable induction motor drive with harmonic cancellation feature

This paper proposes a reconfigurable induction motor (IM) drive with harmonic cancellation ability for shipboard power grids. Power electronic building blocks (PEBBs) and universal controllers (UCs) are used for reconfigurable (multi-function) control. When there are no significant current harmonics in the power grids, the UC controls the IM only. When significant current harmonics are introduced in the power grid, the UC reconfigures the active front end from an active rectifier to an active filter to cancel the harmonics while continuing to control the IM. Therefore, this reconfigurable drive system is universal in applications for harmonic cancellation requirement as well as controlling the existing IM. It supports power quality considerations without adding more equipment to the power system and therefore reduces the shipboard power system cost.

An Extended Adaptive Detection Method and Its Application in Power Quality Improvement

This paper intensively investigates an active noise cancellation methods application in power quality improvement applications. The original algorithm in acoustic area is first introduced and then extended to current harmonic selective detection. The adaptive algorithm identifies amplitudes, phases and frequencies of fundamental and harmonic components from nonlinear load current. The identified results are used to generate control reference for power quality improvement control. The current harmonic selective feature lies in its ability to estimate any specific harmonics. The extended algorithm is fully tested both in simulation and experiment. It is also compared with traditional d-q transformation based harmonic detection method. And this method is found to have advantages such as internal frequency tracking, easy application to single phase and three phase unbalanced systems, simple and flexible. At last, an active filter application example shows the effectiveness of this proposed adaptive method in power quality application.