FCS-MPC-Based Current Control of a Five-Phase Induction Motor and its Comparison with PI-PWM Control

This paper presents an investigation of the finite-control-set model predictive control (FCS-MPC) of a five-phase induction motor drive. Specifically, performance with regard to different selections of inverter switching states is investigated. The motor is operated under rotor flux orientation, and both flux/torque producing (d-q) and nonflux/torque producing (x-y) currents are included into the quadratic cost function. The performance is evaluated on the basis of the primary plane, secondary plane, and phase (average) current ripples, across the full inverter's linear operating region under constant flux-torque operation. A secondary plane current ripple weighting factor is added in the cost function, and its impact on all the studied schemes is evaluated. Guidelines for the best switching state set and weighting factor selections are thus established. All the considerations are accompanied with both simulation and experimental results, which are further compared with the steady-state and transient performance of a proportional-integral pulsewidth modulation (PI-PWM)-based current control scheme. While a better transient performance is obtained with FCS-MPC, steady-state performance is always superior with PI-PWM control. It is argued that this is inevitable in multiphase drives in general, due to the existence of nonflux/torque producing current components. © 1982-2012 IEEE

A Fault-Tolerant Two-Motor Drive With FCS-MP-Based Flux and Torque Control

Independently controlled multi-motor drives are typically realized by using a common dc link and independent sets of three-phase inverters and motors. In the case of an open-circuit fault in an inverter leg, one motor becomes single-phase. To enable continued controllable operation by eliminating single-phasing, the supply for the motor phase with the faulted inverter leg can be paralleled to a healthy leg of another inverter, using hardware reconfiguration. Hence, the two motors are now supplied from a five-leg inverter, which has inherent voltage and current limitations. Theoretically, violating the voltage limit leads to inverter over-modulation and large torque oscillations. It is shown here that the finite-control-set model predictive control (FCS-MPC), designed to control the machines’ stator flux and torque, can consider the inherent voltage limit dynamically in the control loop. Apart from preserving the independent control of the two machines, the additional constraint consideration significantly widens the operating speed ranges of the machines. In particular, it is shown that whenever the voltage limit is entered, the controller reduces the stator flux level automatically, without requiring external flux reference change. The obtained performance is illustrated using experimental results and is also compared to the conventional two-motor field-oriented control scheme. The control concept is thus fully experimentally verified

Current Control Methods for an Asymmetrical Six-Phase Induction Motor Drive

Using the vector space decomposition approach, the currents in a multiphase machine with distributed winding can be decoupled into the flux and torque producing α-β components, and the loss-producing x-y and zero-sequence components. While the control of α-β currents is crucial for flux and torque regulation, control of x-y currents is important for machine/converter asymmetry and dead-time effect compensation. In this paper, an attempt is made to provide a physically meaningful insight into current control of a six-phase machine, by showing that the fictitious x-y currents can be physically interpreted as the circulating currents between the two three-phase windings. Using this interpretation, the characteristics of x-y currents due to the machine/converter asymmetry can be analyzed. The use of different types of x-y current controllers for asymmetry compensation and suppression of dead-time-induced harmonics is then discussed. Experimental results are provided throughout the paper, to underpin the theoretical considerations, using tests on a prototype asymmetrical six-phase induction machine. © 1986-2012 IEEE

A Comparative Study of Synchronous Current Control Schemes Based on FCS-MPC and PI-PWM for a Two-Motor Three-Phase Drive

A two-motor drive, supplied by a five-leg inverter, is considered in this paper. The independent control of machines with full dc-bus voltage utilization is typically achieved using an existing pulsewidth modulation (PWM) technique in conjunction with field-oriented control, based on PI current control. However, model predictive control (MPC), based on a finite number of control inputs [finite-control-set MPC (FCS-MPC)], does not utilize a pulsewidth modulator. This paper introduces three FCS-MPC schemes for synchronous current control in this drive system. The first scheme uses all of the available switching states. The second and third schemes are aimed at reducing the computational burden and utilize a reduced set of voltage vectors and a duty ratio partitioning principle, respectively. Steady-state and transient performances are analyzed and compared both against each other and with respect to the field-oriented control based on PI controllers and PWM. All analyses are experimental and use the same experimental rig and test conditions. Comparison of the predictive schemes leads to the conclusion that the first two schemes have the fastest transient response. The third scheme has a much smaller current ripple while achieving perfect control decoupling between the machines and is of low computational complexity. Nevertheless, at approximately the same switching loss, the PI-PWM control yields the lowest current ripple but with slower electrical transient response. © 1982-2012 IEEE

Operation of a Six-Phase Induction Machine Using Series-Connected Machine-Side Converters

This paper discusses the operation of a multiphase system, which is aimed at both variable-speed drive and generating (e.g., wind energy) applications, using back-to-back converter structure with dual three-phase machine-side converters. In the studied topology, an asymmetrical six-phase induction machine is controlled using two three-phase two-level voltage source converters connected in series to form a cascaded dc link. The suggested configuration is analyzed, and a method for dc-link midpoint voltage balancing is developed. Voltage balancing is based on the use of additional degrees of freedom that exist in multiphase machines and represents entirely new utilization of these degrees. The validity of the topology and its control is verified by simulation and experimental results on a laboratory-scale prototype, thus proving that it is possible to achieve satisfactory dc-link voltage control under various operating scenarios. © 1982-2012 IEEE

Postfault Operation of an Asymmetrical Six-Phase Induction Machine With Single and Two Isolated Neutral Points

The paper presents a study of postfault control for an asymmetrical six-phase induction machine with single and two isolated neutral points, during single open-phase fault. Postfault control is based on the normal decoupling (Clarke) transformation, so that reconfiguration of the controller is minimized. Effect of the single open-phase fault on the machine equations under this control structure is discussed. Different modes of postfault operation are analyzed and are further compared in terms of the achievable torque and stator winding losses. Validity of the analysis is verified using experimental results obtained from a six-phase induction motor drive prototype

Perceived exertion influences pacing among ultramarathon runners but post-race mood change is associated with performance expectancy

Objectives. This study investigated whether post-race mood changes among ultramarathon runners are associated with perceived exertion or the discrepancy between their actual and predicted performance times.Methods. Eight runners completed the Puffer ultramarathon, which is a challenging 73 km mountainous race across Table Mountain National Park in South Africa. Each runner completed a series of profile of mood state questionnaires (POMS) 2 days before the race (baseline), on the morning of the race (pre-race) and immediately after the race (post-race). Ratings of perceived exertion (RPE) were measured at 13 points during the race using the Borg 6-20 scale. The accuracy of performance expectationswas measured as the difference between runners’ actual and predicted race times.Results. Average completion time was 11:31:36±00:26:32 (h :mm:ss), average running speed was 6.4±2.2 km.hr-1 and averageRPE was 14.1±2.0. Increased POMS confusion was found before the race (33.30.7 v. 37.1±5.2, p=0.014; baseline v. pre-race). Post-race increases in POMS total mood disturbance (TMD) were found (168.3±20 v. 137.5±6.3, p=0.001; post race v. baseline) characterised by decreased vigour (43.3±4.0 v. 33.5±7.0, p=0.008; baseline v. post race), increased confusion (33.3±0.7 v. 38.5±4.8, p=0.006; baseline v. post race) and increased fatigue (37.8±4.8 v. 53.8±7.3, p=0.0003; baseline v. post race). A linear increase in RPE was found during the race (r=0.737, p=0.002).The magnitude of their post-race mood change (r=-0.704, p=0.026) was not found to be associated with runners’ average RPE but was found to be negatively correlated with accuracy of the performance predictions. A time series analysis indicated that POMS TMD would have taken 142±89 min to recover. Conclusions. The results show that RPE influences the wayultramarathon runners pace themselves more than performance expectancy but performance expectations have a greater influence on post-race mood. The magnitude of post-race mood change is associated with the extent of discrepancy between runners’ predicted and actual performance. This has implications for designing appropriate goals and pacing strategies for ultraendurance athletes.

The prevalence of injection-site reactions with disease-modifying therapies and their effect on adherence in patients with multiple sclerosis: an observational study

<p>Abstract</p> <p>Background</p> <p>Interferon beta (IFNβ) and glatiramer acetate (GA) are administered by subcutaneous (SC) or intramuscular (IM) injection. Patients with multiple sclerosis (MS) often report injection-site reactions (ISRs) as a reason for noncompliance or switching therapies. The aim of this study was to compare the proportion of patients on different formulations of IFNβ or GA who experienced ISRs and who switched or discontinued therapy because of ISRs.</p> <p>Methods</p> <p>The Swiss MS Skin Project was an observational multicenter study. Patients with MS or clinically isolated syndrome who were on the same therapy for at least 2 years were enrolled. A skin examination was conducted at the first study visit and 1 year later.</p> <p>Results</p> <p>The 412 patients enrolled were on 1 of 4 disease-modifying therapies for at least 2 years: IM IFNβ-1a (n = 82), SC IFNβ-1b (n = 123), SC IFNβ-1a (n = 184), or SC GA (n = 23). At first evaluation, ISRs were reported by fewer patients on IM IFNβ-1a (13.4%) than on SC IFNβ-1b (57.7%; <it>P </it>< 0.0001), SC IFNβ-1a (67.9%; <it>P </it>< 0.0001), or SC GA (30.4%; <it>P </it>= not significant [NS]). No patient on IM IFNβ-1a missed a dose in the previous 4 weeks because of ISRs, compared with 5.7% of patients on SC IFNβ-1b (<it>P </it>= 0.044), 7.1% of patients on SC IFNβ-1a (<it>P </it>= 0.011), and 4.3% of patients on SC GA (<it>P </it>= NS). Primary reasons for discontinuing or switching therapy were ISRs or lack of efficacy. Similar patterns were observed at 1 year.</p> <p>Conclusions</p> <p>Patients on IM IFNβ-1a had fewer ISRs and were less likely to switch therapies than patients on other therapies. This study may have implications in selecting initial therapy or, for patients considering switching or discontinuing therapy because of ISRs, selecting an alternative option.</p