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Electrolytic capacitors are used in nearly all adjustable-speed drives, and they are one of the components most prone to failure. The main failure mechanisms include loss of electrolyte through outgassing and chemical changes to the electrolyte and oxide layer. All the degradation mechanisms are exacerbated by ripple current heating. Since the equivalent series resistance of electrolytic capacitors is a very strong function of frequency it must be properly modeled to accurately calculate the power loss. In this paper, a method to reduce the ripple current in a constant Volts/Hertz pulse-amplitude-modulation (PAM)/pulsewidth-modulation (PWM) converter driving an induction motor is investigated. The dc-bus voltage amplitude is reduced in proportion to speed by a buck or current stiff rectifier and the PWM modulation index is maintained at a high level to achieve a reduced ripple current below base speed. By comparison with a diode-bridge-fed PWM voltage stiff inverter, it is shown that the PAM/PWM mode of operation can lead to a significant reduction in capacitor power loss leading to increased capacitor lifetime or decreased capacitor size. The capacitor heating is analyzed using numerical and analytical techniques. Experimental results are provided to verify the analytical results. Index Terms--Adjustable-speed drive (ASD), buck rectifier, current ripple, current stiff rectifiers (CSRs), electrolytic capacitor modeling, equivalent series resistance (ESR), industrial drives, pulse amplitude modulation (PAM), pulsewidth modulation (PWM), voltage stiff inverter (VSI).

Paralleling of voltage source converters (VSCs) with a limited maximum output power is essential when the power rating of a system must be increased. Interleaving (ILV) of the switching signals for parallel-connected VSCs provides a better harmonic spectrum than hard paralleling (HP), i.e., applying identical signals to all VSCs. This can be particularly beneficial for grid-tied converters, since a smaller LCL filter can be realized. To investigate the performance limitations and the impact of ILV operation on the LCL filter hardware, a comprehensive optimization procedure for LCL filters and intercell transformers (ICTs) for two paralleled VSCs is presented in this paper. In addition, a comparative evaluation of HP and ILV operation of VSCs is carried out. The developed optimization procedure and the hardware benefits of ILV operation were verified through testing on a 260-kW full-scale system. Compared with the commercial state-of-the-art weight-optimized LCL filter for HP, the developed LCL filter for ILV utilizing an integrated ICT reduces the total filter weight by 30% while guaranteeing harmonic standard compliance and meeting thermal requirements. [ABSTRACT FROM AUTHOR]

For high-power grid-connected voltage source converters (VSC), weight reduction of the LCL filter is one of the main concerns, where a LCL filter can weigh hundreds of kilograms. It is a multidomain optimization issue to find the minimum weight of a LCL filter considering pulse-width modulation (PWM) method, control bandwidth, filter design, and magnetic components with given constraints, such as harmonic standards, semiconductor power losses, and cooling conditions. The comprehensive design procedure and analytical limits of a LCL filter for a 690-V/1.2-MW VSC is provided. In addition, a prototype system of 400 V/40 kW has been built to verify the design methodology and to investigate the impact of different PWM methods on the LCL filter. [ABSTRACT FROM AUTHOR]

Direct model predictive control (MPC) strategies that achieve long prediction horizons with a modest computational complexity are reviewed in this article, focusing on power electronics applications. In many MPC problems, a long prediction horizon is required to ensure an adequate closed-loop performance in steady state and to avoid stability issues. However, the computational effort of solving the optimization problem underlying MPC problems with long prediction horizons is often very great, making the implementation of such schemes in real time a difficult and challenging task. To overcome this difficulty, three established methodologies are surveyed that yield long prediction horizons with a modest computational burden. Case studies are investigated to substantiate the merits of these schemes. More specifically, for dc?dc boost converters, a move blocking strategy is reviewed, and for ac medium-voltage (MV) drives, both an extrapolation and an event-based horizon strategy are examined. [ABSTRACT FROM PUBLISHER]

In this paper, the recently introduced model predictive pulse pattern control (\MP^3\C) strategy is adapted to the ACS 2000 medium-voltage (MV) drive of ABB. The drive system consists of a five-level active neutral-point-clamped (ANPC-5L) rectifier, an inverter, and an induction machine (IM). The inverter is fed with offline-computed optimized pulse patterns (OPPs) that produce minimum harmonic distortion in the stator windings of the ac machine. An optimal stator flux trajectory is calculated from these OPPs, and a trajectory controller tracks it in real time. In the proposed approach, trajectory tracking is based on model predictive control: a constrained optimal control problem is formulated and solved in real time in a computationally efficient manner. An event-based prediction horizon is employed in order to ensure fast tracking of the stator flux trajectory. The advantages of the proposed method are optimal steady-state behavior in terms of harmonic distortion and fast torque response. The method was tested on an MV ANPC-5L inverter coupled to a general-purpose 1.21-MW IM. Experimental results were obtained from this industrial setup, and they are presented in this paper to demonstrate the high performance of \MP^3\C. [ABSTRACT FROM PUBLISHER]

Industrial applications of medium-voltage drives impose increasingly stringent performance requirements, particularly with regard to harmonic distortions of the phase currents of the controlled electrical machine. An established method to achieve very low current distortions during steady-state operation is to employ offline calculated optimized pulse patterns (OPP). Achieving high dynamic performance, however, proves to be very difficult in a system operated by OPPs. In this paper, we propose a method that combines the optimal steady-state performance of OPPs with the very fast dynamics of trajectory tracking control. A constrained optimal control problem with a receding horizon policy, i.e., model predictive control (MPC), is formulated and solved. Results show that the combination of MPC with OPPs satisfies both the strict steady-state as well as the dynamic performance requirements imposed by the most demanding industrial applications. The estimation of the fundamental components of the machine variables separately from their respective harmonic components is not required. As a result, complicated structures such as observers can be avoided, contrary to state-of-the-art methods. A further advantage of the MPC method is the use of a receding horizon policy, which provides feedback and a high degree of robustness. [ABSTRACT FROM AUTHOR]