Maximum torque per ampere control strategy of a 5-phase PM generator in healthy and faulty modes for tidal marine turbine application

Abstract

The work presented in this paper aims to propose a control strategy being able to extract efficiently energy from a fixed-pitch marine current turbine associated with a 5-phase Permanent Magnet Synchronous Generator (PMSG) in healthy mode and in faulty mode. The considered faults are opened phases. For each tidal current speed, the control strategy aims to extract the maximum power with respect of the maximum values of currents and voltage s related to the converter. The maximum power is directly related to the Maximum Torque per Ampere (MTPA) control strategy characteristics (all the points which are below the MTPA torque VS rotating speed characteristic can be reached by the converter/generator set). This paper proposes a methodology to establish MTPA characteristics and calculate the corresponding current references in healthy mode and in faulty mode (one or two opened phases) for a 5-phase generator. The studied strategy includes flux weakening operations in the both modes.

Modelling, control and frequency domain analysis of a tidal current conversion system with onshore converters

“…This ability is defined as fault tolerance and fault tolerant control (FTC) can be a very useful application in tidal current systems, where the generator is difficult to access, so that the operation of the system does not stop but operate at reduced power output until maintenance. Fault tolerant generators in tidal current systems have been explored by other researchers as well in [54], [55]. In [54] authors compare conventional 3-phase PMSG with a 5-phase PMSG with faulttolerant capabilities.…”

Performances comparison of different concentrated-winding configurations for 5-phase PMSG in normal and faulty modes in flux weakening operation for fixed pitch tidal turbines

“…In [15] a flux weakening strategy for a 5-phase PM synchronous machine has been presented for healthy mode. In [7] a control strategy which allows flux weakening operation both in healthy and fault modes has been presented. With this strategy, it should be noticed that if the back-EMF has a negligible third harmonic, i q1 and i d1 can be controlled to be constant in steady state (i d1 is controlled to be non-null in flux weakening operations) as presented in [7] in healthy mode and fault mode.…”

“…The experimental results of this control strategy has been given in [16]. Nevertheless, if the back-EMF has a significant part of the third harmonic, a pulsating torque is introduced by the control method proposed in [7] in fault mode, because i q3 cannot be maintained as constant if both i d1 and i q1 are controlled as constant. To solve this problem, a 5-H-bridge converter instead of a 5-leg inverter can be used to add one supplementary degree of freedom (zero sequence current is non null).…”

“…|i a,b,c,d;e |<I max and |v a,b,c,d;e |<V max ). As described in [7] this optimization is carried out by using fmincon function, from Matlab.…”

“…This strategy has been adapted by the authors in [7] to flux weakening operations of 5-phase PM synchronous machines by taking into account the voltage and current limit related to machine and drive association. The method proposed in [7] is based on Maximum Torque Per Ampere control strategy (MTPA) under the base speed and flux weakening operation over the base speed with objective to maximize the available torque (and harnessed power) in a wider range of speed as much as possible in healthy and fault cases.…”