Nine-phase Machine Research Articles

Detection of incipient faults in nine-phase machines: Impact of the star winding configuration

Two approaches are commonly used for modelling and control of nine-phase (triple star) fault-tolerant machines with symmetrical and asymmetrical star winding configurations: The Vector Space Decomposition (VSD) and the decentralized d-q modelling. In this paper, it will be shown how the VSD approach used for machines with an Asymmetrical Star Winding Configuration (ASWC), unlike the decentralized d-q one used for machines with a Symmetrical Star Winding Configuration (SSWC), can be helpful for non-intrusive Fault Detection and Diagnosis (FDD) purposes. Supporting MATLAB/Simulink simulations are discussed.

Symmetrical Nine-Phase Drives with a Single Neutral-Point: Common-Mode Voltage Analysis and Reduction

Power converters generate switching common mode voltage (CMV) through the pulse width modulation (PWM). Several problems occur in the drive systems due to the generated CMV. These problems can be dangerous to the insulation and bearings of the electric machine windings. In recent years, many modulation methods have been developed to reduce the CMV in multiphase machines. Symmetrical nine-phase machines with single-neutral are considered in this paper. In this case, conventional PWM uses eight active vectors of different magnitudes in combination with two zero states in a switching cycle, and this generates maximum CMV. This paper proposes two PWM schemes to reduce the CMV in such a system. The first scheme is called active zero state (AZS). It replaces the zero vectors with suitable opposite active vectors. The second scheme uses ten large active vectors during switching and is called SVM-10L. Compared with conventional strategies, the AZS reduces the peak CMV by 22.2%, and the SVM-10L reduces the peak CMV by 88.8%. Moreover, this paper presents a carrier-based implementation of the proposed schemes to simplify the implementation. The proposed schemes are assessed using simulations and experimental studies for an induction motor load under different case studies.

Arbitrary Power Sharing Among Three-Phase Winding Sets of Multiphase Machines

The paper develops a technique for arbitrary power sharing among three-phase winding sets of a multiphase generator. Multiple d - q modeling is commonly used when independent control of the winding sets is required. This paper utilizes instead the vector space decomposition modeling as the starting point and combines it with a multiple d - q approach to preserve the advantages of the vector space decomposition, while still enabling independent control over each winding set. The power sharing is achieved by imposing appropriate x - y currents at the fundamental frequency so that the flux and average torque are not affected. The theory is developed initially for the nine-phase machine. A general expression for arbitrary current sharing is derived further for any multiphase machine with multiple three-phase windings. The obtained equations are valid for any possible machine topology (asymmetrical/symmetrical, with single or multiple neutral points). The theory is validated experimentally using an asymmetrical nine-phase induction generator with indirect rotor field oriented control.

Efficiency Evaluation of Fully Integrated On-Board EV Battery Chargers With Nine-Phase Machines

A fully integrated on-board battery charger for future electric vehicles (EVs) has been recently introduced. It reutilizes all the propulsion components of an EV in charging/vehicle-to-grid (V2G) modes, it does not require any additional components or hardware reconfiguration, and charging/V2G modes are realized with zero electromagnetic torque production. Both fast (three-phase) and slow (single-phase) chargings are possible, with unity power factor operation at the grid side. The solution is based on the use of a triple three-phase machine and a nine-phase inverter/rectifier. This paper reports on the results of efficiency evaluation for the said system. Testing is performed using both a nine-phase induction machine and a nine-phase permanent magnet machine for a range of operating conditions in charging/V2G modes, with both three-phase and single-phase grid connection. Additionally, the impact of converter interleaving on the losses and efficiency is also studied. Losses are separated for different subsystems, thus providing an insight into the importance of optimization of different EV power train components from the efficiency point of view. Promising efficiencies, in the order of 90%, are achieved although none of the system components have been optimized.

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.

Onboard Integrated Battery Charger for EVs Using an Asymmetrical Nine-Phase Machine

This paper considers an integrated onboard charger for electric vehicles that incorporates an asymmetrical nine-phase machine and an inverter into the charging process. The charging is from three-phase mains, and it employs exclusively the power electronic components that already exist on board the vehicle and that are mandatory for the propulsion. No new elements are introduced. Moreover, the charging is achieved without any hardware reconfiguration since the existing elements and their connections are not altered during the transfer from propulsion to the charging mode. Instead, the operating principle is based on additional degrees of freedom that exist in nine-phase machines. These degrees of freedom are employed to avoid electromagnetic torque production in the machine during the charging process, although currents flow through its stator windings. The configuration operates with a unity power factor and is capable of vehicle to grid (V2G) operation as well. A detailed theoretical analysis is given, and the control for the charging/V2G and propulsion modes is discussed. Theoretical analysis is validated by experiments for charging, V2G, and propulsion operating regimes.

The modeling and position sensor-less estimation technique for a nine-phase interior permanent magnet machine using high frequency injections

This paper presents a sensorless method to estimate the rotor angle and speed of a nine-phase interior permanent-magnet (IPM) machine. The major contributions of this work include the injection of high-frequency voltage signals into a nontorque-producing circuit of the machine in which the rotor angle is estimated without generating any high-frequency torque ripple. The inductances of the third sequence of the nine-phase machine are used to modulate the high-frequency injected voltage signals from which the third-sequence currents are extracted. Using a heterodyning method and the Luenberger observer, the rotor position is estimated. The requirement of only one low-pass filter in the angle estimation algorithm is another novelty. This rotor estimation method can be used for a wide speed range including the zero speed. The proposed method has been tested using the coupled full-order model of the nine-phase IPM machine including all the higher order magnetomotive force (MMF) harmonics. Simulation and experimental results for the motor operating under open-loop constant volts per hertz are presented to validate the estimation technique.

A Simplified Model of a Nine-phase Synchronous Machine Using Vector Space Decomposition

This article describes the use of vector space decomposition for development of a simplified model of a nine-phase synchronous machine. It is shown that the nine-phase machine can be reduced to the usual d-q equivalent circuit model plus seven additional non-torque-producing circuits. These additional components are shown to provide additional current paths for both zero-sequence components as well as negative-sequence components.