Search

Harmonic pollution is considered to be one of the major power-quality problems in electric power systems. Correct identification of the dominant source of harmonic pollution is an essential step towards solving this problem. The total harmonic power (THP) method is one of the methods proposed in the literature for this purpose. However, the method is still debatable as its complete success has been questioned by some researchers. This paper tries to answer some concerns regarding the success of the THP method in radial systems by using several comprehensive case studies. Then, a modification to the method is proposed to generalize its application to nonradial systems. Moreover, to increase the reliability and applicability of the method, a new time-domain algorithm is proposed for measuring the harmonic, subharmonic and interharmonic powers for single-phase and three-phase four-wire systems. Index Terms--Harmonics, harmonic pollution, harmonic powers, point of common coupling (PCC).

STATCOM is a FACTS controller that is used in power systems to regulate the line voltage, enhance the power transmission capacity and extend the transient stability margin. STATCOM is conventionally realized by a voltage-source converter; however, being a current injection device, its performance can be improved when realized by a current-source converter (CSC) that can generate a controllable current directly at its output terminals. In this paper, a STATCOM based on the current-source converter topology is proposed. The nonlinear model of the current-source converter, which is the source of the difficulties in the controller design, has been modified to a linear model through a novel modeling technique. The proposed modeling technique is not based on the linearization of a set of nonlinear equations around an operating point. Instead, the power balance equation and a nonlinear input transformation are used to derive a linear model independent of the operating point. This model acts as the basis for the design of a decoupled state-feedback controller. The proposed STATCOM has been simulated using the PSCAD/EMTDC package. The simulation results show that a CSC-based STATCOM can result in excellent current and voltage waveforms as well as very short response time while operating at a low switching frequency. This makes the proposed scheme suitable for high power applications. Index Terms--CSC, decoupled state-feedback control, FACTS, linear model, STATCOM, VSC.

The control methodology of the active power-line filter is the key element for its successful performance in mitigating the line current harmonics. The control system processes the distorted line current signal and forces the converter to inject the proper compensating current. At the same time, it regulates the dc term, i.e., the dc current in the current source converter topology and the dc voltage in the voltage source converter topology. in this paper, a new intelligent control scheme for a modular single-phase active power filter based on the current source converter (CSC) topology is proposed. The intelligent controller utilizes two adaptive linear neurons (ADALINEs) to process the signals obtained from the power-line. The first ADALINE (the Current ADALINE) extracts the harmonic components of the distorted line current signal and the second ADALINE (the Voltage ADALINE) estimates the fundamental component of the line voltage signal. The outputs of the two ADALINEs are used to construct the modulating signals of a number of CSC modules, each dedicated to eliminate a specific harmonic. The proposed controller is also responsible for activating selected CSC filter module(s) to the electric grid. The automated activation of the corresponding filter module(s) is based on the decision-making rules in accordance with the current total harmonic distortion (TH[D.sub.i]) and the harmonic factor (HF) levels set by the IEEE 519-1992 standard. A special 3-level PWM switching strategy is proposed for the filter modules which results in a 50% reduction in the overall switching losses compared with the 2-level method. The proposed controller adjusts the [I.sub.dc] in each CSC module based on the present magnitude of the corresponding harmonic current which results in optimum dc-side current value and minimal converter losses. The high speed, accuracy, efficiency and flexibility offered by the proposed controller, combined with the fast response and low dc energy storage requirement of CSC topology, are the main advantages of the proposed active filter system. The analytical expectations are verified by digital simulation using EMTDC simulation package. Index Terms--Harmonic mitigation, ADALINE, active power filter, 3-level PWM technique, CSC, EMTDC.

This paper shows that the voltage-source matrix converter has all the features of an asynchronous intertie, namely: (1) frequency changing capability, (2) 360 [degrees] phase shift range, and (3) bi-directional real power transfer. In addition, it has the capabilities for: (4) series line reactance compensation using a complex conjugate property, and (5) static VAR compensation. Series reactance compensation gives rise to high synchronization power which improves transient stability. The matrix converter also has the flexibility to control both the transmitted real power and, independently, the reactive power flows at the sending-end and receiving-end of the transmission line. Keywords: AC transmission, FACTS, power flow controller, line compensation, phase shifter, asynchronous link, GTO, matrix converter.

Active power filtering is performed by detecting the line current and voltage signals, generating a current equal-but-opposite to the distortion current using a power converter and injecting the compensating current into the power line. In such applications, it is desirable to combine high power and high switching frequency while minimizing the losses. This asks for special converter topologies and control techniques. In this paper, a multi-converter active power-line filter, based on current-source converter (CSC) modules, is proposed. The power rating and switching frequency of each CSC module is equal to those required for the filtering job divided by the number of modules. The control system utilizes two linear adaptive neurons (ADALINE's) to process the signals obtained from the line. The first ADALINE (the Current ADALINE) extracts the harmonic components of the distorted line current signal and the second ADALINE (the Voltage ADALINE) estimates the fundamental component of the line voltage signal. The outputs of both ADALINE's are used to construct the modulating signals of the filter modules. The proposed modular active filter offers the following advantage: 1) high efficiency due to low conduction and switching losses; 2) high reliability and 3) high serviceability. The proposed active power-line filter treats the ac system on a per-phase basis, has fast response and adapts to the load variations. Theoretical expectations are verified by digital simulation using EMTDC simulation package. Index Terms--Active filter, ADALINE, modular, PWM converter.

Active power-line filtering is conventionally performed by injecting equal-but-opposite of the distortion into the line. The power converter used for this purpose is rated based on the magnitude of the distortion current and operated at the switching frequency dictated by the desired filter bandwidth. Fast switching at high power, even if technically possible, causes high switching losses. In this paper, a new modular approach to active harmonic filtering is proposed. The method utilizes two linear adaptive neurons (ADALINEs) to process the signals obtained from the line. The first ADALINE (the Current ADALINE) extracts the harmonic components of the distorted line current signal and the second ADALINE (the Voltage ADALINE) estimates the fundamental component of the line voltage signal. The outputs of both ADALINEs are used to construct the modulating signals of a number of current-source inverter (CSI) modules, each dedicated to eliminate a specific harmonic. The power rating of the modules will decrease and their switching frequency will increase as the order of the harmonic to be filtered is increased. The overall switching losses are minimized due to the selected harmonic elimination and balanced 'power rating'-'switching frequency' product. Power losses are also reduced by adjusting the [I.sub.dc] in each CSI module according to the present magnitudes of the individual harmonics to be filtered. Speed and accuracy of ADALINE, self-synchronizing harmonic tracking, optimum [I.sub.dc] value and minimal converter losses, high reliability and flexibility and speed and low dc energy requirement of the CSI, result in superb performance of the proposed active conditioner. The theoretical expectations are verified by digital simulation using EMTDC simulation package. Index Terms--Active power filter, ADALINE, CSI, EMTDC.

STATCOM is a FACTS controller that is used in power systems to regulate the line voltage, enhance the power transmission capacity and extend the transient stability margin. STATCOM is conventionally realized by a voltage-source converter; however, being a current injection device, its performance can be improved when realized by a current-source converter (CSC) that can generate a controllable current directly at its output terminals. In this paper, a STATCOM based on the current-source converter topology is proposed. The nonlinear model of the current-source converter, which is the source of the difficulties in the controller design, has been modified to a linear model through a novel modeling technique. The proposed modeling technique is not based on the linearization of a set of nonlinear equations around an operating point. Instead, the power balance equation and a nonlinear input transformation are used to derive a linear model independent of the operating point. This model acts as the basis for the design of a decoupled state-feedback controller. The proposed STATCOM has been simulated using the PSCAD/EMTDC package. The simulation results show that a CSC-based STATCOM can result in excellent current and voltage waveforms as well as very short response time while operating at a low switching frequency. This makes the proposed scheme suitable for high power applications. [ABSTRACT FROM PUBLISHER]