Six-phase Machine Research Articles

Single-Phase On-Board Integrated Battery Chargers for EVs Based on Multiphase Machines

The paper considers integration of multiphase (more than three phases) machines and converters into a single-phase charging process of electric vehicles (EVs) and, thus, complements recently introduced fast charging solutions for the studied phase numbers. One entirely novel topology, employing a five-phase machine, is introduced and assessed jointly with three other topologies that use an asymmetrical nine-phase machine, an asymmetrical six-phase machine, and a symmetrical six-phase machine. In all topologies, both charging and vehicle-to-grid (V2G) mode are viable. Moreover, all are capable of unity power factor operation. A torque is not produced in machines during charging/V2G process so that mechanical locking is not required. Hardware reconfiguration between propulsion and charging/V2G mode is either not required or minimized by using a single switch. Theoretical analysis of operating principles is given, and a control scheme, applicable to all topologies and which includes current balancing and interleaving strategy, is developed. Finally, operation of all topologies is compared by means of experiments in both charging and V2G mode, with a discussion of influence of current balancing and interleaving strategy on the overall performance.

A Nine-Switch-Converter-Based Integrated Motor Drive and Battery Charger System for EVs Using Symmetrical Six-Phase Machines

This paper presents a new configuration for integrated on-board battery chargers of electric vehicles (EVs) incorporating symmetrical six-phase machines. The configuration proposes an exclusive utilization of a nine-switch converter (NSC) along with the machine windings during both propulsion and charging of EVs. The proposed configuration has the advantage of employing a reduced number of components in both the EV (on-board) and charging station (off-board), with the privilege of avoiding machine electromagnetic torque production during charging/vehicle-to-grid (V2G) mode of operation. During charging/V2G mode, the NSC is turned into a conventional three-phase pulse width modulation rectifier and is directly connected to the three-phase mains through the machine windings. Conventional three-phase transformers can be employed for galvanic isolation. Switching between propulsion and charging modes is carried out using a simple hardware reconfiguration. Control schemes for both propulsion and charging/V2G modes are elaborated, along with the principles of operation of the NSC. Experimental results are provided to validate the theoretical deductions for the different operating modes.

Transient Analysis of a Multi-phase Induction Machine Operating as Generator

<em>Multi-phase machines are considered serious contenders as compared to the three phase machines for variable applications in generating mode. </em><em>This paper presents the transient performance analysis of a multi-phase induction machine operating in six-phase mode for power generation. In this paper the simulation and experimental analysis of a six-phase machine in generating mode have been made. The simulations are made and the machine functionality was investigated during no-load and when subjected to different types of loads. Experimental results are provided to confirm the ability of these models to represent during no load as well as during load period and the result were found to be satisfactory for power generation</em>.

Isolated Chargers for EVs Incorporating Six-Phase Machines

This paper considers two isolated solutions for fast charging of electric vehicles (EVs). The isolation is located on the grid side (off board), whereas the rest of the charging apparatus is placed on board the EV, and it entirely consists of the existing power electronics components that would be otherwise used only for propulsion. Thus, substantial savings on space, weight, and cost are achieved. The considered configurations fully incorporate either a symmetrical or an asymmetrical six-phase machine, as well as a six-phase inverter, into the charging process. Due to the nature of the connections, torque production is avoided during the charging/vehicle-to-grid (V2G) modes of operation. Thus, the machines do not have to be mechanically locked, and their rotors naturally stay at standstill. Control schemes for both configurations are elaborated, and theoretical results are validated by experiments for the two configurations in both charging and V2G modes.

Direct vector controlled six-phase asymmetrical induction motor with power balanced space vector PWM multilevel operation

In this paper, a six-phase (asymmetrical) machine is investigated, 300 phase displacement is set between two three-phase stator windings keeping deliberately in open-end configuration. Power supply consists of four classical three-phase voltage inverters (VSIs), each one connected to the open-winding terminals. An original synchronous field oriented control (FOC) algorithm with three variables as degree of freedom is proposed, allowing power sharing among the four VSIs in symmetric/asymmetric conditions. A standard three-level space vector pulse width modulation (SVPWM) by nearest three vector (NTV) approach was adopted for each couple of VSIs to operate as multilevel output voltage generators. The proposed power sharing algorithm is verified for the ac drive system by observing the dynamic behaviours in different set conditions by complete simulation modelling in software (Matlab/Simulink-PLECS) and the results are provided in this paper. Furthermore, harmonic components are shown in each subspace and analysed with Fourier spectrum to confirm the smooth torque propagation with free of harmonic components. The numerical simulation results provided in this paper are closely matching with theoretical developments.

Carrier-Based Pulse Width Modulation for Symmetrical Six-Phase Drives

Modulating the output of a voltage source inverter (VSI) inherently causes current distortions on the load side due to the switching behavior of the inverter. This paper describes a method to reduce these distortions for a drive setup with six phases. The setup consists of a six-phase machine connected to two three-leg two-level VSIs. The phases within the machine are symmetrically arranged and spatially shifted by $60^\circ$ . The phases are grouped so that two conventional three-phase sets are formed, each fed by one inverter. The output of each inverter leg is modulated by comparing a triangle carrier waveform with the desired fundamental wave. Arranged in this way, the drive setup offers an additional degree of freedom, the phase shift of the two carrier waveforms. It is shown that, depending on the machine parameters, there exists an optimal angle, which reduces the harmonic losses of the drive for a certain amplitude of the fundamental wave. The resulting overall current distortion can even be lower compared to a conventional three-phase drive with a two- or three-level inverter topology. For three different modulation techniques, the optimal phase shift angles are derived in an exact form, naturally, symmetrical regular and asymmetrical regular sampled pulse width modulation. An approximation with reasonable accuracy is achieved out of the exact solution. Simulations and experimental tests validate the theoretical considerations.

Current Harmonics Compensation Based on Multiresonant Control in Synchronous Frames for Symmetrical <inline-formula> <tex-math notation="TeX">$n$</tex-math></inline-formula>-Phase Machines

Low-order odd current harmonics arise in practical multiphase drives due to machine and converter nonlinear behavior (e.g., deadtime and flux saturation). If the windings are distributed, some harmonics cause torque ripple, whereas others produce losses. The latter is aggravated by the small impedance in the no-torque subspaces. Current harmonics can be compensated without steady-state error by proportional-integral controllers in multiple synchronous frames (SFs); however, a heavy computational load is required. In three-phase systems, the computational burden of this multiple SF (MSF) scheme is often avoided by implementing instead resonant controllers (RCs) tuned at the harmonics that are multiples of six in an SF rotating with the fundamental frequency. A similar structure has been proposed for nonlinearities compensation in asymmetrical six-phase machines. This paper extends this multiple RC (MRC) strategy to symmetrical machines of any phase number. The optimum frequencies for the RCs and for the SF in each plane, so that the number of RCs is minimized, are established. Then, the computational load of the resulting generic MRC scheme is assessed and compared with that of the MSF structure. The conditions in which the former is particularly preferable over the latter are identified. Experimental results are provided.

Six-Phase Machine Conversion System With Three- and Single-Phase Series Converters

This paper presents two conversion systems based on the association of a six-phase machine (SPM) with an electrical grid by means of three- and single-phase converters. The machine is composed of two three-phase groups. One of them provides the power to the three-phase converter, and the other provides the power to the single-phase converters, in an open-end winding connection (see Fig. 2). The first conversion system is composed of bidirectional switches and can be used with induction or permanent-magnet synchronous machines. The second system is partially reversible since the single-phase converters are also composed of diodes and is more indicated for permanent-magnet synchronous machines. Furthermore, the proposed configurations do not use transformers and generate multilevel voltage at the grid-side converter with amplitude higher than that of the machine side, permitting one to reduce the transmission I 2 R losses. The complete analysis of the systems, including the pulsewidth- modulated techniques, is presented. Simulation and experimental results are also presented.

Design and Experimental Verification of a Short-Circuit Proof Six-Phase Permanent Magnet Machine for Safety Critical Applications

By making use of leakage flux components, a multiphase permanent magnet (PM) machine constructed with fractional-slot concentrated windings can confine winding short-circuit current to rated current to avoid further damage when the stator winding gets short-circuited. However, those high-winding-inductance machines suffer from high PM demagnetization risks. Design principles to avoid PM demagnetization are discussed in this paper to deal with this issue. In addition, mathematical analyses of short-circuit current and torque pulsations are developed, which reveal the physical nature and offer an effective way to investigate the machine performances. Short-circuit fault remediation methods utilizing two-phase symmetry of asymmetric six-phase machine is proposed. Furthermore, a 24 kW prototype machine was fabricated and experimental verification has been conducted.

Full Decoupling Control of Two-Connected Motor Drives with Matrix Converter Supply

Multi-phase converters are required mainly for feeding variable speed multi-phase drive systems. This paper discusses one such solution by using direct ac-ac converter (matrix converter) that can be used to supply a six-phase and three-phase two-connected motor drive system. Matrix converter based two-motor drive system is presented for the first time in this paper. Two stator windings of six-phase and three-phase machines when connected in series while the rotors may be connected to different loads. Appropriate phase transposition is introduced while connecting the series stator winding to obtain decoupled control of the two machines. This paper proposes a scalar modulation scheme with three intervals technique of three-phase to six-phase matrix converter supplying series-connected six-phase and three-phase induction machine drive system. The dynamic decoupling of each machine from the group is obtained using the direct vector control algorithm. Mathematical modeling of the series-connected two-machine showed the possibility of independent control of each machine in the group. The independent control is demonstrated by analyzing the characteristics of the stator current references and speed of each machine under direct vector control scheme. The viability of the proposed control techniques is proved using analytically and simulation approach

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.

Six-Phase Inverter Operation with Space Vector Pulse-width Modulation for a Symmetrical Single Neutral Load

Multi-phase machines with six-phases are preferred due to their inherent advantages. The symmetrical configuration having a single neutral has certain disadvantages over the asymmetrical six-phase machines. Mostly they are supplied with six-phase inverters. The front-end inverter with a different approach in space vector modulation has limitations in utilization of maximum DC bus voltage, as it produces phase voltages with harmonics. These lower-order harmonics in supply also cause de-rating of the machines. Space vector controlled inverters offer a suitable improvement because of multiple choices of the switching states. The single neutral in a six-phase configuration leads to lower-order harmonics, and an attempt was recently made to control these harmonics by varying selection of the switching space vectors. This article presents the comparative analysis of these space vector pulse-width modulation techniques and proposes third harmonic elimination and control of the lower-order harmonics generation in the six-phase inverters. The improved performance of the inverter in space vector controlled mode with 6 and 12 sector selections are compared. The suggested operational method gives the added advantage compared with the asymmetrical six-phase machines. The six-phase inverter operation in space vector pulse-width modulation is investigated with simulation and substantiated with laboratory investigation.

Analysis, Design and Prototyping of a Low-Speed High-Torque Six-Phase Fault-Tolerant Permanent Magnet Synchronous Machine for EVs

This paper deals with a low-speed high-torque six-phase fault-tolerant permanent magnet synchronous machine (PMSM) for wheel-driving electric vehicle (EV) applications. In machine design, winding arrangements and feasible slot/pole combinations are discussed and compared; a 24-slot/22-pole alternate-teeth-wound scheme is analyzed and designed. With reinforced slot-leakage component, the inductance of the machine is increased to restrain the one-phase short-circuit current to nearly 1.0 per unit preventing the machine from deteriorations in condition of that fault. The 24-slot/22-pole alternate-teeth-wound prototype machine is manufactured and the experimental verification is provided.

Direct Torque Control for Double Star Induction Motor

This paper describes a direct torque control (DTC) of dual star induction motor (DSIM). This machine possesses several advantages over conventional three-phase machine and is also known as the six-phase induction machine. The research has been underway for the last two decades to investigate the various issues related to the use of six-phase machine as a potential alternative to the conventional three-phase machine. Though six-phase machines have existed for some time, in the literature very few papers discuss DTC for six-phase motors. Therefore, in this work an investigation is reserved to the application of this type of control to the DSIM. The DTC uses the instantaneous values of voltage vector where each reference voltage vector is computed with a simple DTC algorithm. Finally, simulations results obtained from MatLab/Simulink are presented followed by a discussion.

Experimental Tests of Dual Three-Phase Induction Motor Under Faulty Operating Condition

This paper describes a set of experimental tests on a dual three-phase induction machine for fault-tolerant applications. Both three-phase and six-phase machine operations are considered. Different winding configurations are investigated and compared in case of both open-circuit and short-circuit faults. Experimental tests for each configuration are reported at no-load and under load operating conditions.

Six-Phase Supply Feasibility Using a PM Fractional-Slot Dual Winding Machine

The growing interest in fault-tolerant drives requires new solutions avoiding the adoption of custom and expensive configurations. The machine with a dual three-phase winding is an interesting candidate. It is provided with two windings, each of them fed by one converter of half power. With a proper mechanical and electrical arrangement, the machine can be exactly a six-phase machine, obtaining higher performance during healthy conditions. In the event of a fault, one of the two three-phase windings (the faulty one) is disconnected, and the machine is operated by means of the healthy winding only. This paper analyzes the feasibility of this dual winding configuration applied to a nonoverlapped-coil fractional-slot winding permanent-magnet machine. The star of slots is applied to highlight the proper winding candidates. The more interesting windings are deeply analyzed.

Six-Phase Machine Drive System With Reversible Parallel AC–DC–AC Converters

This paper proposes a reversible six-phase machine drive system. It is composed of two parallel three-phase to three-phase dc-link converters without isolation transformers. The proposed topology permits one to reduce the harmonic distortion in the input converter and decreases the power processed by converter switches. Furthermore, the proposed configuration can guarantee the feasibility of the system when high-power applications are considered. The model and the control strategy have been developed. The simulation and experimental results are presented.

A Two-Frequency Quasi Six-Phase Voltage Source Inverter Based on Space Vector PWM

With development of series multi-phase motor drives and harmonic injection technique to enhance torque for multi-phase motor drives, there is an immense need for multifrequency PWM voltage source inverters (VSI).The PWM techniques used in the previous works are either of ramp-comparison or of hysteresis type. The first suffer from implementation difficulties and the second has the high variable switching frequency drawback (difficulties of LC input EMI filter design). SVM possesses many advantages over the mentioned PWM techniques and it can be used in multiphase drive applications.One of the most popular multi-phase machines is quasi six-phase (QS) machine. The phasor diagram of a QS system and a two level six-phase VSI are depicted in Fig. 1. Despite the three-phase case the numbers of switching vectors are very high (refer to Fig. 2) and the removal of low-order harmonics in SVM six-phase systems is so complicated. In this paper, a two frequency QS SVM VSI is designed and implemented. The approach improves the performance of the system in terms of total harmonic distortion (THD) and DC-bus utilization. The resulted SVM VSI is used to generate two reference vectors for two series QS machines.Some analysis and discussions are given through the development of the SVM technique, computer simulation and practical results.

Modelling and control of six-phase induction machine under special current waveform

A novel strategy for the direct control of the torque and field currents applied to the six-phase induction motor drive was proposed in this paper. This novel current control strategy benefits the developed torque of the motor as well as simplifying the control algorithm by removing the complex transformations used. The main performance of the six-phase machine including the machine modelling is determined with finite element analysis (FE). Furthermore the control strategy proposed is experimentally verified by using the six-phase induction drive system built. All the methods/approaches were proven that the field and torque current components of the six-phase machine can be controlled separately without any coordinate transformation. As such emulation separately excited DC motor control.

Steady-State Modeling of Series-Connected Five-Phase and Six-Phase Two-Motor Drives

Two series-connected two-motor drive systems with a single inverter supply have been proposed recently. The first one consists of two five-phase machines supplied from a single five-phase inverter, whereas the second one comprises one symmetrical six-phase machine, a three-phase machine, and a single six-phase inverter. It has been verified experimentally that, by introducing an appropriate phase transposition in the series connection, completely independent dynamic control of the two machines can be realized using principles of vector control. Detailed dynamic models in the stationary common reference frame have also been reported for the two drive systems. These are taken here as the starting point, and equivalent circuit steady-state representation of the series-connected two-motor drive systems is developed. The equivalent circuits can then be used to evaluate steady-state characteristics of the drives in the same manner as it is done for three-phase induction machines, as well as for the inverter design. The dc-link voltage required for operation of the two series-connected machines is investigated next. It is shown that the specific winding connections lead to a dc voltage requirement that is smaller than it would have been had the windings of the two machines been connected directly in series. Experimental results, obtained during steady-state operation of the series-connected five-phase and six-phase two-motor drives, are presented. Developed equivalent circuit representation is finally verified by comparing calculated and experimentally obtained values for various voltages of the two-motor drives.