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Self-commutating multilevel current reinjection is a potential alternative to conventional HVDC thyristor technology. An important drawback of the multilevel configurations is the interdependence of the reactive power injections at both ends of the link. This paper describes a new concept applicable to large power converters consisting of two series-connected twelve-pulse groups. It is based on the use of a controllable shift between the firings of the two twelve-pulse groups in opposite directions, a new concept that provides independent reactive power control at the sending and receiving ends. The theory is verified by EMTDC simulation. Index Terms--HVDC transmission, multilevel conversion, reactive power control.

A back to back (BTB) HVdc interconnector consisting of multilevel current reinjection (MLCR) converters is described, based on the parallel converter configuration. Since the MLCR creates a zero current region during the commutations, the proposed BTB configuration permits the continued use of thyristor valves, without loosing the control flexibility of the self-commutating process. Extensive EMTDC simulation is used to demonstrate the satisfactory response of the proposed BTB HVdc interconnector control structure to varying active and reactive power operating conditions. Index Terms--Current source conversion, HVdc, self-commutating conversion.

An old concept proposed to double the pulse number of a line commutated converter and designated 'dc-ripple reinjection,' is made more effective by the use of self-commutating reinjection switches, such as GTO or IGCT. It is shown that the self-commutating reinjection switches can be controlled to force the thyristor valve currents to commutate independently from their respective line voltages. EMTDC-PSCAD simulation is used to verify that this effect adds reactive power controllability, as well as pulse multiplication, to the conventional thyristor converter. Index Terms--Current source conversion, harmonics, self-commutation.

The effectiveness of harmonic state estimation (HSE) in identifying the location and magnitude of harmonic sources is largely dependent on the accuracy of the measurements. Measurement errors (or bad data) can be classified into two groups; measurement noise and gross error. This paper uses a statistical approach (cumulative probability density functions) obtained from five thousand Monte Carlos runs to investigate the impact of measurement noise and gross errors in harmonic state estimation. The Lower South Island of the New Zealand system is used as the test system and the results are probability curves containing the statistics of the estimation error. The effect of additional measurements on an over-determined system to filter noise is also discussed. Index Terms--Error analysis, harmonic analysis, state estimation.

A new self-commutated current source converter is proposed, based on the reinjection of multi-level dc current pulses via a GTO-switched multi-tapped interphase reactor. The ideal reinjection waveform for complete elimination of the harmonic content of the ac system side current is derived and a practical approximation proposed to increase the pulse number of the double-bridge converter to any multiple of twelve. A 48-pulse configuration is analyzed in detail to show the new concept effectiveness on both the ac and dc sides of the converter. Index Terms--AC-DC conversion, current source conversion, harmonics, multilevel.

A widened harmonic power flow algorithm is described capable of determining the interaction between the fundamental, harmonic, and interharmonic frequency components. The algorithm is multiphase and can include any number of nonlinearities. The New Zealand power system is used to illustrate the ability of the algorithm to determine the harmonic interaction between an HVdc link and an aluminum smelter. Index Terms--Converters, harmonics, power flow.

The proposed converter is based on the reinjection of a series of dc voltage pulses, at a frequency multiple of the fundamental, that shape the output voltage waveforms into a multilevel scheme. The reinjection ratio and frequency are chosen to convert the standard 12-pulse into 36-pulse configuration without the assistance of filters or PWM. Thus, the switching losses are greatly reduced. The harmonic current injection can be kept within present standards by an appropriate choice of the interface transformer leakage reactance. Index Terms--Voltage source converter, multi-level voltage reinjection, fundamental switching.

One of the main problems in the area of power quality is voltage flicker, a variation in the root-mean-square (RMS) voltage, that causes flickering of incandescent bulbs. Varying loads can lead to such fluctuations of the supply voltage and for historical reasons, this type of disturbance is viewed as the principal cause of light flicker. With the constant increase of applications that employ power electronic devices, sub- and interharmonics are becoming more prevalent in the power system. These can also vary the instantaneous power supplied to incandescent lamps by beating and, thus, result in visible light flicker. In this paper, the special conditions under which light flicker occurs are derived qualitatively. Computer simulations that are based on a realization of the UIE/IEC flickermeter are then used to produce quantitative data. Index Terms--Electric power quality, flicker, interharmonics, subharmonics, UIE/IEC flickermeter.

The effect of converter impedance is mostly ignored when performing harmonic analysis since it is complicated to calculate and a common assumption is that it has minimal effect. This paper compares the use of simplified techniques against a rigorous calculation of the converter impedance and demonstrates their effect on the frequency response of the system. Index Terms--Converter impedance, harmonics, HV dc.

A recent CIGRE document published in ELECTRA has described the potential benefits of a direct connection of generators to HVdc converters. While many theoretical contributions have been made, no practical test data has become available so far. This paper reports on harmonic tests carried out at the Benmore end of the New Zealand HVdc link operating as a group connected scheme. It was found that the measured harmonic current levels were well below specified generator ratings. Dynamic simulation accurately predicted the harmonic currents whereas the results of a steady state formulation were less reliable. Keywords Unit Connection, Harmonic Tests, Generator Rating

A frequency domain analysis is applied to a controlled HVdc converter interconnecting ac and dc networks. The converter is considered as a three port network, and described using transfer functions. Using ac and dc system frequency dependent impedances an equivalent electrical circuit is constructed. The concept of composite resonance is introduced to emphasise the interaction between the ac and dc systems, and a simplified damping factor derived to predict the dynamics of waveform distortion during transient recovery. The frequency domain analysis is verified by dynamic simulation.

Short-term flicker severity ([P.sub.st]) is an important electric power quality index defined by the International Electrotechnical Commission (IEC). [P.sub.st] results from the statistical evaluation of flicker over short periods of time producing an objective measure for flicker originating from various types of sources. This paper reviews previous methods for computing [P.sub.st] and proposes a new iterative algorithm. The algorithm is computationally efficient and shown to comply with the IEC standard. Index Terms--Electric power quality, flickermeter, flicker severity.

A method for accurate calculation of the harmonics generated by a bipolar HVdc link is described. The method illustrates the importance of including detailed representation of the mutual coupling effects of dc transmission lines, even when smoothing reactors are included. The overall solution is achieved by means of a unified Newton algorithm in the harmonic domain. Index Terms--Bipolar dc, harmonics, HVdc link.