Chi-Jui Wu

Effect of battery energy storage system on load frequency control considering governor deadband and generation rate constraint

Since a battery energy storage system (BES) can provide fast active power compensation, it also can be used to improve the performance of load-frequency control. In this paper a new incremental model of a BES is presented and merged into the load-frequency control of a power system. A comprehensive digital computer model of a two-area interconnected power system including governor deadband and generation rate constraint is employed for a realistic response. Computer simulations show that the BES is very effective in damping the oscillations caused by load disturbances. The BES model is suitable for charging mode and discharging mode operations. Optimization of controller gains is obtained by the second method of Lyapunov. >

Application of superconducting magnetic energy storage unit to improve the damping of synchronous generator

A systematic approach to the design of a controller for superconducting magnetic energy storage (SMES) units to improve the dynamic stability of a power system is presented. The scheme employs a proportional-integral (PI) controller to enhance the damping of the electromechanical mode oscillation of synchronous generators. The parameters of the PI controller are determined by the pole assignment method based on modal control theory. Eigenvalue analysis and nonlinear computer simulations show that SMES with the PI controller can greatly improve the damping of the system under various operating conditions. Although the PI controller is designed for a special load condition, it can also provide good damping under other load conditions. >

Investigation and mitigation of harmonic amplification problems caused by single-tuned filters

This paper investigates the harmonic amplification problems in a plastics plant and the appropriate mitigation methods. Four single-tuned filters (LC filters) were installed to eliminate the harmonic currents from three 6-pulse rectifiers. However, after the capacitance reduction of some filter capacitors, the driving point impedance at the frequency of 8th order harmonic increased severely and the harmonic current of this order was amplified. There were many failures of the power filter capacitors. Field measurements and computer simulations are used to verify the disturbance problems. Finally, two high-pass damped filters are recommended to replace the original single-tuned filters. The amplification problems at some even-order harmonics can be avoided.

Optimal multiobjective planning of large-scale passive harmonic filters using hybrid differential evolution method considering parameter and loading uncertainty

This paper is used to investigate the optimal multiobjective planning of large-scale passive harmonic filters for a multibus system under abundant harmonic current sources using the hybrid differential evolution (HDE) method. The migrant and accelerating operations embedded in HDE are used to overcome traps of local optimal solutions and problems of time consumption. The design purposes are to minimize the total demand distortion of harmonic currents and total harmonic distortion of voltages at each bus. Filters loss, fundamental reactive power compensation, and constraints of individual harmonics are also considered. The search for the global optimal solution is applied to the harmonic problems in a steel plant, where both ac and dc arc furnaces are used and a static var compensator is installed. Three design schemes are compared to demonstrate the performance of HDE. Finally, expectations of objective function are used to present the effects of filter parameter detuning and furnace loading uncertainty.

Damping of power system oscillations with output feedback and strip eigenvalue assignment

This paper presents a modified optimal controller for an interconnected power system. The design method does not need the specification of weighting matrices. The eigenvalues of electromechanical and exciter modes would be shifted to a prespecified vertical strip. For practical implementation, the design method only uses partial output feedback. For demonstrating the effectiveness of damping enhancement, eigenvalue analysis and nonlinear simulation results are used to show that the proposed controller gives significant improvement in the dynamic performance of the interconnected power system. >

On-line reactive power compensation schemes for unbalanced three phase four wire distribution feeders

A new reactive power compensation method is developed to reduce the negative and zero sequence components of load currents and to improve the load bus power factor of unbalanced three-phase four-wire distribution feeders. Negative and zero sequence currents may cause additional losses and damage to power systems. Load compensation at the load bus is an effective method to eliminate those undesired sequence currents. The compensation technique uses a Y-connected and a Delta -connected static reactive power compensators (SVCs) to give a different amount of reactive power compensation to each phase. The compensation formulas are very suitable for on-line control by measurement of phase voltages and currents in real time. The compensation effect can also be achieved even if one leg of the SVCs is out of service. In addition to balancing effect and power factor improvement at the load bus, the SVCs can also be used to support the load bus voltage and to maintain the substation feeder at unity power factor. Digital simulations are made with the load data measured from an 11.4 kV secondary substation feeder. >

A compact control algorithm for reactive power compensation and load balancing with static Var compensator

Abstract A compact control algorithm for reactive power compensation and load balancing with the static Var compensator (SVC) in three-phase three-wire systems is developed in this paper. The required compensation susceptance of each SVC phase can be obtained from a very simple function of voltage and power signals which are measured by a three-phase voltage transducer and two single-phase active and reactive power (P–Q) transducers at the load bus. The calculation of compensation susceptances is based on the criterion of a unity power factor and zero negative-sequence currents after compensation. A simulation is made, as the first stage, to show the validity of the proposed compensation algorithm. Then, a laboratory size microcomputer-based SVC, which consists of thyristor-controlled reactors (TCRs) and fixed capacitors (FCs), is designed and implemented. Simulation and experiment results show that the algorithm is very suitable for on-line control of the SVC which is designed for phase balancing and power factor correction.

A flexible voltage flicker teaching facility for electric power quality education

A voltage flicker teaching facility is developed for electric power quality education. The facility consists of a single and three-phase voltage flicker generator, measurement devices, and a lamp test system. The modulation amplitudes and frequencies based on the UIE 10 Hz equivalent voltage flicker value (/spl Delta/V/sub 10/) can be arbitrarily assigned by software with high accuracy. Three experiments can be offered to students, including the introduction of voltage flicker with finite or infinite frequency components and the effect of voltage flicker on lamps. This hardware teaching facility can give students a realistic and practical concept about voltage flicker.

Design of PID static VAr controllers for the damping of subsynchronous oscillations

Damping of subsynchronous resonance using static VAr compensator (SVC) is investigated. To damp the various unstable torsional modes, a proportional-integral-derivative (PID) controller is used to modulate the reactive power output feedback controller with only one feedback signal (generator speed deviation), the proposed controller is relatively simple for practical implementation. Eigenvalues analysis of the closed-loop system reveals that the PID controller is quite effective over a wide range of operating conditions. Digital simulations using a nonlinear system model are also performed to demonstrate the effectiveness of the proposed controller under disturbance conditions. >

A novel algorithm for precise voltage flicker calculation by using instantaneous voltage vector

A novel approach has been presented in this paper to calculate voltage flicker components precisely by using instantaneous voltage vectors. After the voltage waveform of a phase is recorded, the smart discrete Fourier transform can be used to obtain the system frequency and magnitude. Then, the other two phases are assumed perfectly sinusoidal to construct a virtual three-phase system. The instantaneous voltage vectors are calculated from the virtual three-phase voltages. Finally, the fast Fourier transform is used to obtain the voltage flicker components from instantaneous voltage vectors. The flicker components of the other two phases can be calculated by repeating the procedure. The flicker values of three phases are calculated individually and separately. The effects of jump-sampling, harmonics, power frequency shifting, and sampling rates are investigated. The calculation ability of this approach is compared with the traditional indirect demodulation method. Some given waveforms and field measured waveforms of arc furnace loads with voltage flicker disturbances are used to show the goodness of this approach. From the results, this approach could calculate flicker components accurately with short calculation time by using small size data. It also avoids the frequency leakage effect.