Multiphase machines are a suitable choice when high reliability and power are desired. However, the appearance of sensitive secondary subspaces related to harmonic currents has historically hindered the use of direct regulation schemes. In order to leverage the desirable traits of these control algorithms, such as model predictive control, multi-vector solutions have emerged. These control actions allowed direct schemes to accomplish a suitable flux and torque production with low harmonic injection. Nevertheless, many of the proposed multi-vector schemes have failed to address the phenomenon known as average deception, leading to a worse overall performance of the drive. This work presents a set of virtual vectors (VV) which optimizes harmonic injection in the two secondary planes, both in instantaneous and average terms. The quality of this proposal is validated by simulation results, where its performance in a nine-phase permanent magnet synchronous machine is compared to a previously published multi-vector scheme.

Multiphase drives offer certain advantages over conventional three-phase systems, such as improved fault tolerance and efficiency. However, these specialized systems require advanced control schemes to fully exploit their unique features. To this end, model predictive control (MPC) with a variable control period has appeared as a promising approach, but in its standard (single-vector) version current quality still has significant room for improvement. Aiming to enhance the control performance, this work proposes a variable-application-time MPC that employs multi-vector control actions. Simulation results for a six-phase induction motor (IM) drive confirm the effectiveness of the proposed regulation strategy.

To leverage the benefits of model predictive control (MPC) in multiphase drives while addressing its pronounced dependence on the electric machine model, researchers have explored alternative solutions. Recently, interest in the so-called model-free predictive control (MFPC) regulation schemes has increased. Different approaches within MFPC-controllers are shaped by different underlying problems. Solutions such as neural network-based controls and ultra-local models are hindered by high computational demands, heavy reliance on training data, or the need for optimization algorithms. In contrast, approaches based on look-up tables (LUT) that collect measurements of current gradients in a rotating reference frame offer an efficient solution to achieve an MFPC regulator in conventional three-phase systems. However, these LUT-based strategies require a proper updating of the current gradients within the LUT to avoid the stagnation that leads to inadequate performance. To address current gradient stagnation problems and extend these strategies to multiphase systems, this work proposes implementing a stationary reference frame LUT that reduces the stagnation impact on the performance of a nine-phase electric drive. Simulation results confirm that modifying the reference frame to store the current gradients decouples the system behavior from the rotor position, significantly reducing the stagnation effect.

Multiphase open-end-winding (OeW) electric machines offer enhanced capabilities that may find a match in high-performance applications requiring further reliability and efficiency. Nevertheless, the control of this highly complex system requires much attention to avoid the appearance of parasitic currents. In topologies with a single DC source and low homopolar inductances, the proper regulation of zero-sequence currents becomes critical, requiring special attention to common-mode voltages (CMV). This work explores the performance of model predictive control (MPC) to regulate five-phase OeW permanent magnet synchronous motor (PMSM) drives, using both standard (single-vector) and multi-vector MPC. To this end, virtual voltage vectors (VVs) with zero average CMV are proposed for the first time for five-phase systems, making a subsequent comparison of single-vector and VV control actions. Simulation results confirm the capability of MPC to supress current harmonics and successfully regulate the five-phase OeW PMSM.

The use of a single switching state during the whole sampling period in the current regulation of six-phase voltage source converters (VSCs) inevitably generates undesired parasitic x-y currents. Aiming to solve this problem, the creation of virtual/synthetic voltage vectors (VVs) has been recently proposed to ensure zero average x-y voltage production. However, the off-line calculation of VVs makes them static and suboptimal. This paper introduces new approach where the virtual voltages are created on-line within a model predictive control (MPC) based current regulation strategy. Since the selection of the switching states and the dwell times varies each sampling period, the resulting vectors are termed dynamic voltage vectors (DVVs). This new concept allows an online optimization of the output voltage production depending on the operating point at the expense of a higher computational cost. Simulation results confirm that six-phase VSCs can be successfully regulated using DVVs in an MPC-based current control scheme.

Fault-tolerant multiphase drives have received plenty of attention from the research community over the past two decades due to the increased emphasis on reliability of power electronics and drives systems. Among different types of fault, open circuit or open phase faults have been well studied and different fault-tolerant control approaches have been proposed in the past. While fault-tolerant control based on closed-loop approach have been shown to give good performance, it is possible to tolerate open-phase fault using just simple feed-forward voltage compensation. In this paper, the operation of a multiphase induction machine during open phase fault is examined, and the fundamental factors affecting its performance are discussed. Based on the analytical discussion, it is demonstrated that by calculating x-y voltages and adding to the control voltage in feed-forward manner, torque oscillations due to open phase fault can be easily compensated. Compared to the closed-loop approach, the feed-forward method is superior is terms of simplicity and transient response.

High efficiency and reliability are two desirable features for wind energy conversion systems. In this regard, multiphase machines provide inherent fault-tolerance and better power density than conventional three-phase systems. From the point of view of the reliability, multiphase machines can provide a natural/passive fault-tolerance without a mandatory control reconfiguration. For that purpose, the control of the x-y current must be realized in open-loop mode. A recent model predictive control based on virtual voltage vectors (VV-MPC) has satisfactory validated this fact. On the other hand, efficiency can be enhanced with the implementation of a variable-flux control that reduces the copper losses. In order to satisfy the requirements of new wind energy conversion systems, this work proposes an efficient model predictive control based on virtual voltage vectors (EVV-MPC) with a natural fault tolerance for six-phase induction machines (IM). Simulation results confirm the capability of the proposed system to minimize the cooper losses in pre- and post- fault situation without control reconfiguration.

The inherent fault-tolerant capability against open-phase faults (OPFs) of multiphase machines is an appreciated advantage in applications where high-reliability is a main concern. This desirable feature has usually required fault localization and post-fault control reconfiguration to provide a suitable performance in this anomaly situation. However, recent model predictive control (MPC) based on virtual voltage vectors (VVs) has validated the multiphase machine fault-tolerant capability without post-fault control reconfiguration. This fact allows to relax some of the OPF detection methods requirements. On the other hand, incipient faults or damaged connections can generate resistance dissymmetry (RD) situations that produces overheating and control degradation. Although the origin of OPFs and RDs can be of a different nature, the symptoms of both anomalies are common: a current imbalance that generates non-null x-y currents appears. Focusing on this approach, this work suggests new settings for an OPF detection method based on the vector space decomposition (VSD) in order to make it universally valid both in OPF and RD situations. The proposed current imbalance detection (CID) method is implemented together with a natural fault-tolerant direct torque control (DTC) for five-phase induction motor drives. Experimental results are employed to verify the goodness of the proposed method.

The intrinsic high fault tolerant capability of multiple three-phase drives represents an attractive opportunity for critical applications, such as More Electric Aircraft (MEA), in which a high degree of reliability is required. In this paper, a fault tolerant vector control algorithm for quadruple three-phase induction machines, allowing torque and rotor flux regulation, is developed. Four conventional three-phase inverters supply independently the four three-phase stator windings. If a fault prevents one or more three-phase windings from being fed, the machine can continue operating, but the machine power is proportionately reduced. The results of numerical simulations and experimental tests prove the effectiveness of the presented control scheme.

Direct Torque Control (DTC) technique has been applied in recent times in high performance five-phase induction motor drives during the normal operation of the system. The use of DTC in the multiphase area is far from becoming a reality because it has not been used in competitive multiphase applications where the fault operation needs to be considered. The authors have successfully tested the ability of DTC controllers to manage the open-phase fault operation in a five-phase induction motor drive. However, the conclusion of the mentioned study must be completed comparing the obtained results with other mature alternatives based on field oriented controllers. This paper focuses on the comparative analysis of DTC and Rotor Field Oriented Control (RFOC) when an open-phase fault appears in the five-phase induction motor drive. Simulation results are provided to compare the performance of the system using these control alternatives.

Direct torque control (DTC) is extensively used in conventional three-phase drives as an alternative to field-oriented control methods. The standard DTC technique was originally designed to regulate two independent variables using hysteresis controllers. Recent works have extended the procedure for five-phase drives in healthy operation accounting for the additional degrees of freedom. Although one of the main advantages of multiphase machines is the ability to continue the operation in faulty conditions, the utility of DTC after the appearance of a fault has not been covered in the literature yet. This paper analyses the operation of a five-phase induction motor drive in faulty situation using a DTC controller. An open-phase fault condition is considered, and simulation results are provided to study the performance of the drive, comparing with the behavior during healthy state.

Induction motor drives supplied from diode front-end rectifiers are commonly used in industrial applications due to their low cost and reliability. However, the two-quadrant operation of such a topology makes the regenerative braking impossible. Braking resistors can be used to dissipate the braking power and provide enhanced braking capability, but additional hardware is then necessary. Alternatively, the braking power can be dissipated within the inverter/motor by control software reconfiguration. In this scenario, the additional degrees of freedom of multiphase drives can be used to increase the system losses without disturbing the flux and torque production. Simulation results confirm the possibility to enhance the braking capability of the drive with only few changes in the control scheme.

Multiphase energy conversion systems have been recently proposed to achieve simple fault-tolerant operation with no extra hardware. When such multiphase systems are connected to the grid, efficiency is maximized by operating the system in a balanced manner with an equal distribution of the power among phases. However, the situation differs when the multiphase system is connected to different microgrids with individual active and reactive power requirements. In this scenario, unequal power sharing between the different phases of the multiphase machine is mandatory. This work explores the control strategy to operate in speed mode with an independent regulation of the active power contribution of microgrids. Simulation results confirm the capability of the system to operate in unbalanced mode at the expense of some extra copper losses.

Observers are used in relation to several controllers: IFOC, sensor-less drives and for fault detection but they have not been used yet for predictive control of drives. This paper shows the benefits of incorporating a rotor current observer to enhance the predictions needed for predictive control of stator currents in VSI driven IM. The new scheme is compared with the standard one in which non-measurable variables are lumped into one term that is updated using a simple error tracking idea.

Battery energy storage systems (BESSs) have been widely used to minimize wind power fluctuations in microgrids. BESSs control systems are usually based on vector-controlled techniques with inner current control loops and outer control loops. Owing to the complexity of a control system, it is difficult to apply additional functions such as predicting wind power. This paper presents a detailed description of predictive power control in the BESS for smoothing wind power fluctuations. The proposed control system includes the Kalman filter used to predict wind power. Simulation results are provided to confirm the performance of the proposed control system.

Multiphase variable-speed drives' advantages such as fault tolerance and better power-per-phase splitting make these electromagnetic devices suitable for high reliability applications. However, the applied control techniques require accurate knowledge of the electrical parameters of the machine. Although a large number of modulation and control strategies have been proposed, little work has been focused on the estimation of these parameters. This paper proposes an off-line procedure to estimate the parameters of five-phase induction machines. The proposed method is based on standstill time-domain tests and the particle swarm optimization (PSO) technique, and it can be easily extended to any number of phases.

Operation of inverters requires a subsystem to generate the gating signals for the semiconductor switches. In the case of simple modulating schemes such as PWM the gating signals can be obtained from inexpensive analog or digital electronic hardwired logic. In other situations a DSP or other kind of device with high computing power is needed. Then it is usual to have a control program that requires an homogeneous sampling period. In such cases, the actuation signal is kept constant for the whole duration of the sampling period. This is is in sharp contrast with methods that modulate via pulse width. In this paper a geometrical analysis is made over the set of waveforms that can be generated this way. The interest is in the harmonic content of the resulting voltage. The study identifies the key factors regarding harmonic content and provides bounds on the minimum harmonic content achievable by any homogeneous pulse width technique. Other related issues such as commutation losses are also considered.

Multiphase generators in multi-MW wind energy applications can be realized with a variety of possible topologies. Series connection of machine-side converters elevates the dc-link voltage for the same voltage rating of IGBTs, allowing medium voltage generation on the grid-side. On the other hand, parallel connection of machine-side converters provides fault-tolerant capability, enhancing the system reliability. The combination of series and parallel connection of machine-side converters simultaneously elevates the dc-link voltage and provides some fault tolerance to the system. This work discusses the series-parallel topology for six-phase induction generators and analyzes the fault tolerance capability of the topology. Theoretical analysis and simulations confirm that it is possible to obtain additional fault tolerance at the expense of some unbalance on the individual dc-link voltages.

This work proposes a series of activities to promote the motivation and curiosity of engineering students. The activities are designed and coordinated to progressively involve the student in the subject through the use of a dynamic methodology. The proposal includes monitored problem-solving, small application problems, cooperative activities and challenging problems. This methodology is tested in two student groups: second year students (Electric Circuits) and third-year students (Electrical Machines).

This paper presents an investigation of the dc-link voltage balancing control for an asymmetrical six-phase wind energy conversion system, which utilises series-connected two-level machine-side converters and a three-level grid-side neutral point clamped (NPC) converter. In such a topology, the dc-link voltages drift apart if there are asymmetries at the machine-side, so dc-link voltage balancing control is required. The work investigates the capability of the NPC converter to balance the dc-link voltages and examines additional control, provided by the machine-side converters, which can extend the control range. Simulation results confirm that a satisfactory control can be achieved when both converter sets contribute to the dc-link voltage balancing.

Multiphase drives offer interesting advantages against their conventional three-phase counterparts, particularly during the post-fault operation where the higher number of phases allows drive operation under fault conditions. Post-fault performance in multiphase drives can be obtained maintaining a maximum current level and preserving ripple-free operation. Predictive current control techniques have also shown their interest in high performance control application of multiphase drives. However, fault tolerance of conventional and predictive current control methods of multiphase drives have been briefly analyzed although the fault tolerance capability is a demanded feature in industrial applications. This paper analyzes the speed operation of a five-phase drive with an open phase fault condition. The conventional model based predictive current controller is modified to cope with the fault condition, and experimental results are provided to validate the proposed method.

Multiphase electric drives have been recently proposed for applications where the highest overall system reliability and the reduction in the total power per phase are required. This is possible thanks to the extension of modulation and control techniques to the multiphase case. However, the design of techniques to reduce the common-mode voltage (CMV) in multiphase drives is still under development. This work analyzes the CMV of a five-phase drive and proposes two direct torque control (DTC) strategies with reduced CMV. Elimination of certain switching states is proposed to obtain good torque and flux response as well as lower peak-to-peak CMV. The reduction of CMV is achieved at the expense of a small increase of the current distortion. Simulation results are provided to confirm the viability of the proposed schemes which reduce for five-phase induction motor drives the peak-to-peak CMV by 40% and 80% compared to the original DTC scheme.