Hamid Soltani

Effects of Passive Components on the Input Current Interharmonics of Adjustable-Speed Drives

Current and voltage source adjustable-speed drives (ASDs) exert the distortion current into the grid, which may produce some interharmonic components other than the characteristic harmonic components. This paper studies the effects of passive components on the input current interharmonics of ASDs with and/or without motor current imbalance. The investigation is done at different motor operating frequencies and load torque values. It shows that selecting the small filter components (ac choke, dc choke, and dc-link capacitor) results in different performances with respect to those interharmonics issued by motor current imbalance and other noncharacteristic interharmonics. The results are helpful for engineers investigating the effects of drive filters on the input current interharmonic components.

Interharmonic analysis and mitigation in adjustable speed drives

This paper presents the theoretical background and studies on the supply side current interharmonics in a double-stage Adjustable Speed Drive (ASD), when they are initiated by motor current imbalance. Some useful approaches are then proposed to compensate for these interharmonic currents in partially and/or fully controlled ASD, resulting in undistorted grid currents. The simulation studies verify the effectiveness of the proposed schemes.

Harmonic Emissions of Three-Phase Diode Rectifiers in Distribution Networks

Harmonic emissions have been changed in distribution networks, with respect to frequency range and magnitude, due to the penetration of modern power electronics systems. Two new frequency ranges 2–9 and 9–150 kHz have been identified as new disturbing frequency ranges affecting distribution networks. This paper presents the effects of grid-connected three-phase systems with different front-end topologies: conventional, small dc-link capacitor, and electronic inductor. A power converter with a small dc-link capacitor can create a resonant frequency with the line impedance below and above 1 kHz depending on the grid configurations. The resonant effects depend on many factors, such as load power levels, filter types, and the number of parallel drives. These issues can affect the grid current harmonics and power quality of the distribution networks. Analyses and simulations have been carried out for three different topologies and the results have been verified by experimental test at system level. Current harmonic emissions have been considered for 0–2, 2–9, and 9–150 kHz frequency ranges.

Interharmonic mitigation of adjustable speed drives using an active DC-link capacitor

Current and voltage source Adjustable - Speed Drives (ASDs) exert distortion currents in the grid which may lead to some interharmonic components other than the characteristic harmonic components. The frequencies of the line current interharmonics, generated by these ASDs, depend on the motor operating frequency. As there is a growing discussion about the interharmonic effects on the grid and its limitation, the reduction and mitigation of these components is worthwhile especially when more drives are tied to the grid. This paper proposes a new dc-link active capacitor in order to reduce the drive input current interharmonic components. Although the proposed active device is only applied on a voltage source ASD with unbalance load, the concept is general and can also be applied on the multi-pulse thyristor based adjustable speed drives. The study clearly verifies the effectiveness of the proposed dc-link active compensator on the grid current interharmonics reduction.

Sources and Mitigation of Interharmonics in Back-To-Back Controllable Drives

The theme here is to identify the sources of interharmonics that can affect back-to-back controllable drives and make non-characteristic interharmonic components in the grid side currents when the motor currents are unbalanced. A new control methodology then is formulated and proposed to compensate for the sources, leading to undistorted grid currents, which are growingly important as more drives are tied to the grid. It is shown that in the case of back-to-back controllable drives it is possible to reduce the input current interharmonic distortion caused by motor current imbalance.

Input current interharmonics in adjustable speed drives caused by fixed-frequency modulation techniques

Adjustable Speed Drives (ASDs) based on double-stage conversion systems may inject interharmonics distortion into the grid, other than the well-known characteristic harmonic components. The problems created by interharmonics make it necessary to find their precise sources, and, to adopt an appropriate strategy for minimizing their effects. This paper investigates the ASDs input current interharmonic sources caused by applying symmetrical regularly sampled fixed-frequency modulation techniques on the inverter. The interharmonics generation process is precisely formulated and comparative results of different fixed-frequency modulation techniques are presented to evaluate the drive input current interharmonic components. The theoretical analysis and simulation studies are validated with experimental results on a 2.2 kW motor drive system.

Effects of Modulation Techniques on the Input Current Interharmonics of Adjustable Speed Drives

Adjustable speed drives (ASDs) based on a three-phase front-end diode rectifier connected to a rear-end inverter may generate interharmonic distortion in the grid. The interharmonic components can create power quality problems in the distribution networks such as interference with the ripple control signals, and consequently they can hamper the normal operation of the grid. This paper presents the effect of the symmetrical regularly sampled space vector modulation and discontinuous pulse width modulation-30

Effects of DC-link filter on harmonic and interharmonic generation in three-phase adjustable speed drive systems

^{\circ }

Harmonic distortion performance of multi three-phase SCR-fed drive systems with controlled DC-link current under unbalanced grid

lag (DPWM2) techniques, as the most popular modulation methods in the ASD applications, on the drives input current interharmonic magnitudes. Further investigations are also devoted to the cases where the random modulation technique is applied to the selected modulation strategies. The comparative results show how different modulation techniques can influence the ASDs input current interharmonics and consequently may not be a suitable choice of modulation from an interharmonics perspective. Finally, the theoretical analysis and simulation studies are validated with obtained experimental results on a 7.5-kW motor drive system.

Performance evaluation of electronic inductor based adjustable speed drives with respect to line current interharmonics

Harmonic and interharmonic distortions are considered as the main power quality issues especially in the distribution networks. The double-stage Adjustable Speed Drives (ASDs) in which the front-end diode rectifier is connected to a rear-end inverter through an intermediate DC-link filter may inject significant amount of harmonics and interharmonics into the grid and consequently degrade the grid power quality. In this paper, the effect of the DC-link filter — as a key player — on the ASD input current harmonic and interharmonic distortions is investigated. In this respect, the ASD performance is evaluated harmonically based on three different DC-link configurations; the conventional filter (with AC- and/or DC-side chokes, and DC-link capacitor), the Small DC-Link Capacitor (SDLC), and the controlled DC link by using an Electronic Inductor (EI) technique. It shows how employing the small DC-link capacitor will push the harmonics into the higher frequency ranges and it will also give rise to more interharmonic distortions. Moreover, the EI configuration is introduced as an optimal DC-link intermediate circuit within the investigated frequency range of 0–2 kHz. The presented analysis and discussions have been validated by the simulation and experimental results.