Predictive controller considering electrical constraints: a case example for five‐phase induction machines

Abstract

The modern control of power drives involves the consideration of electrical constraints in the regulator strategy, including voltage/current limits imposed by the power converter and the electrical machine, or magnetic saturation due to the iron core. This issue has been extensively analysed in conventional three-phase drives but rarely studied in multiphase ones, despite the current interest of the multiphase technology in high-power density, wide speed range or fault-tolerant applications. In this paper, a generalised controller using model-based predictive control techniques is introduced. The proposal is based on two cascaded predictive stages. First, a continuous stage generates the optimal stator current reference complying with the electrical limits of the drive to exploit its maximum performance characteristic. Then, a finite-control-set predictive controller regulates the stator current and generates the switching state in the power converter. A five-phase induction machine with concentrated windings is used as modern high-performance drive case example. This is a common multiphase drive that can be considered as a system with two frequency-domain control subspaces, where fundamental and third harmonic currents are orthogonal components involved in the torque production. Experimental results are provided to analyse the proposed controller, where optimal reference currents are generated and steady/transient states are studied.

A Comprehensive Survey on Fault Tolerance in Multiphase AC Drives, Part 1: General Overview Considering Multiple Fault Types

“…In absence of overmodulation, the current references are set following a maximum-torque-per-ampere trajectory taking into account both frequency components. A drawback of this method is that, for simplicity, the phase shifts of the voltage components are assumed to be those of the worst scenario for calculating the conditions of v dc shortage, similarly to [10] (the drive operates within the m 2 = 0 plane from Figure 34 [7]); consequently, the dc-link voltage is not fully exploited [9].…”

“…The latter normally have just two current DOFs, used to set the flux/torque [2], whereas the higher number in the former enables other interesting possibilities [2,4]. This additional versatility can be exploited, among many other purposes, for increased torque density [5][6][7][8][9][10], machine parameter estimation [11], multimotor drives [2,10,[12][13][14][15], integrated battery chargers [16][17][18][19][20][21][22], bearingless machines [23], or, most importantly, for enhanced fault tolerance. In fact, fault tolerance is one of the research topics regarding multiphase drives that has attracted the most attention in recent years.…”

“…Since the machine back-EMF tends to increase with speed, if v dc decreases then the maximum speed and power are reduced as well [141,171]; • If the modulation index increases beyond the linear modulation range, overmodulation occurs. This means that low-order voltage harmonics are introduced, the VSD subspaces become coupled in terms of voltage, and the conventional PWM and control methods are no longer able to work properly [8,9,134,135,[137][138][139]142,143,145,[147][148][149][150][151][152][154][155][156]158,159,167]; • If the VSC ac voltage is reduced, the difference between its magnitude and that of the machine back-EMF may become substantially greater. As a consequence, overcurrent may occur [129,545].…”

“…give rise to large undesired currents [134,135,137,139,487,488,493,494]. Alternative reasons for including multifrequency (multi-subspace) voltages are, e.g., enhancing the torque density by harmonic injection [5][6][7][8][9][10] or driving several machines by a single VSC [2,10,12]. In any of these cases, the output of the multifrequency current control consists of non-zero voltage references in multiple subspaces and frequencies, so as to cancel the effect of the voltage disturbances and/or impose required currents.…”

Predictive current control in electrical drives: an illustrated review with case examples using a five‐phase induction motor drive with distributed windings

“…It is noteworthy that MPC techniques have been widely used to solve control problems in electrical applications with power converters, giving high flexibility and including different control objectives and/or constraints, as stated along with this work. However, electrical limits for multiphase drives have been first considered in [140, 141] using a two‐stage predictive controller (see Fig. 15).…”