P. Newman

Design of fast and robust current regulators for high-power drives based on complex state variables

High-power pulsewidth-modulated inverters for medium-voltage applications operate at switching frequencies below 1 kHz to keep the dynamic losses of the power devices at a permitted level. Also, the sampling rate of the digital signal processing system is then low, which introduces considerable signal delays. These have adverse effects on the dynamics of the current control system and introduce undesired cross coupling between the current components i/sub d/ and i/sub q/. To overcome this problem, complex state variables are used to derive more accurate models of the machine and the inverter. From these, a novel current controller structure employing single-complex zeros is synthesized. Experimental results demonstrate that high dynamic performance and zero cross coupling is achieved even at very low switching frequency.

Technical evaluation and practical experience of high-power grinding mill drives in mining applications

Grinding mill drives play an important role in the mining industry. Almost 60% of the electrical energy consumed by modern concentrator plants goes to grinding mill drives. Different technologies are used in grinding systems presenting special characteristics from the electrical and process points of view. This paper presents a technical evaluation and practical experience of two different technologies used in high-power grinding mill drives. The analysis is focused on the static power converter and associated control scheme required to drive the motor. Cycloconverters and load-commutated inverters are analyzed in terms of power grid interaction, motor interaction, and the required control scheme. The evaluation is supported with practical results obtained in different concentrator plant facilities.

Technical evaluation and practical experience of high power grinding mill drives in mining applications

Grinding mill drives play an important role in the mining industry. Close to 60% of the electrical energy consumed by modern concentrator plants goes to grinding mill drives. Different technologies are used in grinding systems presenting special characteristics from the electrical and process points of view. This paper presents a technical evaluation and practical experience of two different technologies used in high power grinding mill drives. The analysis is focused on the static power converter and associated control scheme required to drive the motor. Cycloconverters and load commutated inverters are analyzed in terms of the interaction with the power grid, the motor, and the required control scheme. The evaluation is supported with practical results obtained in different concentrator plant facilities.

Network-Friendly Low-Switching-Frequency Multipulse High-Power Three-Level PWM Rectifier

High-power converters for regenerative drives and distributed generation need a network-friendly operation, low harmonic conductive electromagnetic emission for low electromagnetic interference and high electromagnetic compatibility reaching high reliability and performance. Nevertheless, the converters must be controlled with low switching frequency in order to reduce the commutation losses. These two requirements can be satisfied if an optimal modulation strategy is used. The selective harmonic elimination (SHE) is one of the low-switching-frequency strategies most used today. However, this strategy only eliminates a reduced set of harmonic components from the input current. This paper presents a novel optimal modulation strategy whose objective is to reduce the total harmonic distortion of the input current. Six- and twelve-pulse three-level neutral-point-clamped pulsewidth modulation rectifiers are used in order to implement both modulation techniques. The results confirm the advantages of the proposed strategy, namely, less input current distortion and remarkable reduction of higher order harmonics compared with the SHE method, while keeping a low-switching behavior.

High-power regenerative converter for ore transportation under failure conditions

The use of three-level neutral-point-clamped (3L-NPC) voltage source inverters for drive applications in the megawatt range is becoming a standard solution. In combination with the same converter circuit in rectifier operation as active front end (AFE), four-quadrant operation is also available. An existing plant, which has been in operation with eight converters for several years, has shown some failures, which leads to considerations of failure mechanisms and failure rates. All failures were on the AFE. A first failure of a power semiconductor leads to subsequent breakdowns of others. Some failures are analyzed and failure conditions are described. Some failure reasons can be excluded and a probable reason is pointed out. Finally, a recommended solution is described and its result after its implementation is discussed.

Network friendly low-switching frequency high-power three-level PWM rectifier

High-power converters for regenerative drives and distributed generation need a network-friendly operation with low switching frequency for high reliability and performance. This paper presents a multipulse connection of two three-level NPC PWM rectifiers with the selective harmonics elimination technique (SHE) and a novel optimal method for minimal current distortion

Resonance mitigation and dynamical behavior of systems with harmonic filters for improving reliability in mining plants

Mining systems have complex power networks including high-power equipment, variable configuration and distributed harmonic injections. This paper presents the problem of resonance mitigation and dynamical behavior of a power system with harmonic filters (HF) for improving reliability in mining plants. It is known that the main objective of the harmonic filters is to provide power factor correction and limiting the harmonic distortions. Nevertheless, until now it is not well covered in the literature that HF also provides mitigation of impedance resonances. Simulation results obtained of the transient behavior analysis of industrial electrical system when harmonic filters are switched are presented, with good correlation between steady and transient behavior, supporting the results given by tools intended for stationary analysis of harmonics performance. Different operating conditions of an industrial power system given by variable topology, multiple harmonic injections and loading factor should be taken into account for the proper design of HF systems. The presented methodology supports the risk assessment, failure analysis and reliability improvement of industrial systems as well as the decision making process at the design stage of power systems