Wound Field Synchronous Motor Research Articles

Excitation Control of Brushless Induction Excited Synchronous Motor with Induction Machine Operating in Deep-Plugging Mode

Abstract The popularity of electrified transportation is rising at a sharp pace due to environmental concerns over internal combustion (IC) engines. Researchers are nowadays looking for a brushless and permanent magnet (PM)-less solution for electric vehicle (EV) motors. Wound-field synchronous motor (WFSM) is a potential solution for EVs and is being used in Renault Zoe EV and BMW iX3 e-Drive models. A Brushless Induction excited Synchronous Motor (BINSYM) is a WFSM where the exciter, an induction machine (IM), is embedded inside the synchronous machine (SM) frame. Two machines (SM and IM) are configured for different numbers of poles to achieve magnetic decoupling, which facilitates independent control of both machines. The purpose of IM is to maintain the excitation requirement of SM. The IM is controlled in deep-plugging mode at a constant slip frequency over the entire speed range to minimise its reactive power demand. The maximum torque per ampere (MTPA) and root mean square (rms) current minimisation algorithms are used to control the SM. Simulation of the BINSYM-based system under dynamic conditions (MTPA with varying field current and load transient) has been carried out in MATLAB/Simulink to validate the control strategies. Experimental findings from the laboratory prototype machine closely match the simulation results.

Investigation and Development of the Brushless and Magnetless Wound Field Synchronous Motor Drive System for Electric Vehicle Application

In order to solve the problems of soaring costs and supply fluctuation in permanent magnet materials, this paper investigates and develops a magnetless wound field synchronous motor (WFSM) drive system for electric vehicle (EV) application. As the crucial drive component for EVs, the proposed WFSM in this paper has a two-stage structure which is described as the exciter and the main motor. The excitation characteristics of the exciter that provide power to the rotor field winding are emphatically analyzed. In addition, the discrete time domain armature current regulator and excitation current regulator are designed and analyzed for the high-performance WFSM drive system. A current coordinated control strategy for the full speed range is proposed to expand the constant power region. The experiment shows that the excitation characteristics and torque capability of the WFSM are consistent with the analysis, and proves that the WFSM is a potential solution for the magnetless motor for EV application.

계자권선형 동기전동기의 극 슬롯 조합에 따른 전자계 특성 비교

This paper analyzes the electromagnetic characteristics of wound field synchronous motor (WFSM) for home appliances according to pole slot combination. The analyzed factors are output torque, total harmonic distortion (THD) of back-EMF, cogging torque, efficiency and power factor (PF) which should be considered when designing motors. The pole slot combinations are selected with same number of slots per pole per phase (NSPP) of prototype interior permanent magnet synchronous motor (IPMSM). Because the electromagnetic performances show specific tendencies depending on the number of poles and each performance tends to be different, this study can be a reference in determining pole slot combinations of WFSM.

Robust MTPA Control for Novel EV-WFSMs Based on Pure SM Observer Based Multistep Inductance Identification Strategy

Wound field synchronous motors (WFSMs) without installing slip rings and brushes are drawing increasing attention in the electric vehicle (EV) propulsion systems. To ensure high control performance of the EV-WFSMs, this article proposes a robust maximum torque per ampere (MTPA) control strategy based on a series of new sliding mode (SM) inductance observers. First, after establishing the model of a WFSM based on capacitive coupling, the current control scheme is designed for the MTPA control. Second, to eliminate the impacts of the inductance uncertainties on the MTPA control, the SM mutual inductance observer, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">q</i> -axis inductance observer, and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis inductance observer are designed, which need to be implemented one by one. Then, the Lyapunov stability criterion is used to analyze the stability conditions for the observers. Moreover, considering that the observers are achieved by using the offline inductance information provided by the suppliers, the robustness against parameter mismatch is innovatively discussed at length, and an analytical method that can avoid estimation errors is developed. The proposed inductance identification techniques and MTPA control method are verified by both simulation and experiments, which are conducted on a 580-W three-phase WFSM drive.

Investigation on Time-Varying Behavior of NI HTS Field Coil for Synchronous Motors Considering Armature Reaction and Slotting Effect

This paper presents calculation results of time-varying behavior of no-insulation (NI) high temperature superconductor (HTS) field coil for synchronous motor considering armature reaction and slotting effect. We selected four NI HTS motor models having different stator topologies for confirmation of armature reaction and slotting effect. Also, before NI behavior analysis, we proposed a wound field synchronous motor (WFSM) dq-equivalent circuit which can be considered as a circuit model of insulated (INS) HTS motor. The circuit model used in this paper contains parameters varying with the position of rotor and dq-axes cross-coupling inductance for describing the armature reaction and slotting effect of practical motor. Next, to investigate time-varying behavior of NI field coil during steady-state operation, simulations of a new circuit model combining proposed dq-equivalent circuit and NI lumped circuit were implemented. Turn to turn radial leak current values of selected models were calculated at different armature current density. Also, torque ripple values of the NI and the INS case were obtained by circuit simulations. It can be confirmed that peak to peak radial current occurs by largest value at the topology having the greatest flux linkage harmonics and torque ripple value of NI motor is smaller than that of INS HTS motor.

Electrical Testing for Detection and Classification of Open Damper Bar and Shorted Field Winding Failures in Wound Field Synchronous Motors

Broken damper bars and shorted field winding turns degrade the starting and running performance of industrial wound field synchronous motors (WFSMs), and can lead to a forced outage of the motor and driven process. Testing of WFSM rotor windings mainly relies on offline tests, which cannot be performed frequently and are known to lack reliability. Shorted turns in the field winding can be detected online from the airgap flux measurement, but require a sensor to be installed on the stator bore. In this article, new test methods for detecting and classifying damper and field winding faults based on electrical signals are proposed. The proposed methods can provide remote testing at motor standstill and during the motor starting transient without disassembling the motor. Test results on a 30 kW, salient pole WFSM show that both test methods can provide reliable detection and classification of damper and field winding faults.

Adjustable Speed Drive Capability of Self-Excited Wound-Field Synchronous Motor Utilizing Space Harmonics With 500 W Class Prototype

In this paper, consideration from the viewpoint of the dq-axis current vector locus is reported on the clues for improving the output of wound-field motor utilizing space harmonic for field excitation. It is experimentally verified by visualizing the vector locus on the dq coordinates. First, voltage equation will be explained, and then the offline parameter estimation will be discussed. Then, visualization of the voltage-limit ellipse and vector locus will reveal clues for performance improvement.

High energy efficiency oriented-control and design of WFSM based on driving condition of electric vehicle

The purpose of this paper is to increase the energy efficiency of an electric vehicle (EV) with a wound-field synchronous motor (WFSM). Therefore, methods are proposed to estimate and improve the energy efficiency of the EV as well as the performance of the WFSM. The following contributions are provided: 1) EV model as well as the mathematical model of the electric motor are explained considering the common Artemis driving cycle (CADC); 2) a control method for maximizing the energy efficiency of the electric motor is proposed; 3) analysis methods for calculating the circuit parameters (resistance, inductance, and flux linkage) and losses (ohmic, iron, and mechanical loss) are described. The efficiency of the machine is accurately determined using the proposed analysis method; 4) based on the proposed methods, the design process of the WFSM is proposed to improve the energy efficiency considering the vehicle system and driving cycle; and 5) the proposed methods are verified through tests of the prototype and improved motor. As a result, through the proposed design and control method, even though the volume of the improved motor was 7.8% smaller than that of the prototype, the efficiency of the improved motor was higher than that of the prototype in all regions. In addition, to confirm the effectiveness of the proposed methods, the performance of the electric vehicle considering the driving cycle was analyzed according to the characteristics of the electric motor. The energy loss of the improved motor with the proposed control and design method was 63.3% less than that of the prototype. Accordingly, the energy efficiency of the vehicle system and the energy consumption of the battery increased by 7.8%p and decreased by 2.0 kWh, respectively.

Verification of effect of secondary conductor bar on starting characteristics in line‐start type self‐excited wound‐field synchronous motor

This study clarifies experimentally the effect of the secondary conductor bar on line-start characteristics in a line-start type self-excited wound-field synchronous motor. This motor is based on a brushless wound-field synchronous motor having a rotor winding connected to a diode rectifier circuit. And it has a secondary conductor bar that is independently connected at a pitch of one pole, without end-ring. First, the operation principle of the proposed motor and its magnetic circuit design are described, and then the details of the prototype for principle verification are clarified. Next, when the combination of the connecting of the secondary conductor bar is changed, an experiment of line-starting characteristics and measured rotor field current is demonstrated. Consequently, it was clarified that the influence on the synchronous pull-in, speed ripple, and rotor field current.

Experimental Verification With Loads of Line-Start Type Self-Excited Wound-Field Motor With Three-Phase Concentrated Winding Stators

This article describes a novel line-start type self-excited wound-field synchronous motor with three-phase concentrated winding stator. The unique feature of this proposed motor is that it accelerates by obtaining the starting torque from the slip frequency at the time of starting, and at the time of synchronous pull-in, it is driven synchronously with utilizing the second order space harmonic as the field magnetization power. This driving principle was verified by performing a load test using the prototype with two types of load, fan load and eddy current brake load. Consequently, the synchronization based on the proposed drive principle could be demonstrated on the actual machine, and the line-start characteristics of the proposed motor have been clarified.

A Non-Intrusive Leakage Flux Based Method for Detecting Rotor Faults in the Starting Transient of Salient Pole Synchronous Motors

Damper and field windings are critical components of wound field synchronous motors (WFSM), where failure can lead to forced outage of the motor and industrial process. Due to the relatively rare presence of WFSMs in industry compared to induction motors, research on fault detection techniques for WFSMs is not as active. Rotor fault detection in WFSMs is also difficult, as synchronous operation leaves damper bars inactive during steady state operation while a small number of shorted field windings do not cause noticeable asymmetry. Therefore, most of the field-wide accepted tests rely on off-line testing or visual inspection of the rotor, or require airgap flux measurements, which necessitate motor disassembly and/or installation of sensors. Hence non-intrusive test methods which do not require motor disassembly are sorely needed to guarantee continued operation of the motor and industrial process. In this article, novel test methods based on the use of the leakage flux measured via search coils placed externally on the motor frame are proposed. A non-intrusive method for detecting and distinguishing damper and field winding faults during motor starting is devised from the time and frequency domain analysis of leakage flux and current. The methods are verified via experimental testing on a 30-kW salient pole WFSM.

Wound field synchronous motor with hybrid circuit for neighborhood electric vehicle traction improving fuel economy

Increasing the low mileage associated with electric vehicles is a major requirement. Improving the efficiency of the traction motor is one solution to solve the mileage problem. In this study, we propose a method to improve the efficiency of a wound field synchronous motor (as the traction motor) in case of neighborhood electric vehicles. The wound field synchronous motor is a salient pole machine that generates a negative reluctance torque when operating in the second quadrant, reducing its efficiency. However, second quadrant operation is inevitable due to voltage limitation in the high-speed range. Here, we propose a hybrid circuit comprising U, V, W windings and X, Y, Z windings. The high-speed efficiency of the wound field synchronous motor is improved by changing the connection between the windings. Further, a neighborhood electric vehicle with a wound field synchronous motor was simulated using an advanced vehicle simulator (ADVISOR) to verify the proposal. The hybrid circuit increased the fuel economy of the electric vehicle by up to 3.8%. Finally, a validation experiment was conducted using a fabricated motor prototype.

Proposal of Novel Line-Start Type Self-Excited Wound-Field Synchronous Motor With Three-Phase Concentrated Winding Stator

This paper describes a novel line-start type self-excited wound-field synchronous motor with three-phase concentrated winding stator. The unique feature of this proposed motor is that it accelerates by obtaining the induction torque from the slip frequency at the time of starting, and at the time of synchronous pull-in, it is driven synchronously with the second order space harmonic as the field magnetization power. First, the operation principle and the magnetic circuit design topologies will be described. Then, the prototype for principle verification and experimental setup will be revealed. Next, the result of evaluating the no-load synchronization pull-in characteristics in actual machine evaluation is reported.

Novel Rotor Design of Wound Field Synchronous Motor for Torque Ripple Reduction in ISG System

This paper describes a method to reduce the torque ripple for the Wound Field Synchronous Motor, which does not use a permanent magnet. When a WFSM is used in an Integrated Starter Generator system, it must have a higher power density than other automotive motors in order to satisfy the size constraints and required power. An increase in the power density creates a magnetic flux saturation in the rotor, and this soon becomes the cause of an increase in the torque ripple of motor. An increase in the torque ripple can degrade the Noise Vibration Harshness characteristics of automotive by creating vibration and noise in the engine start-up mode, in which the maximum torque is generated in an ISG system. This paper proposes a method of reducing the torque ripple via a design that uses a flux barrier model in the WFSM’s rotor. The Response Surface Method is used to optimize the flux barrier model, and Finite Element Method is used to to verify the torque ripple reduction.

Design of High Power Density and High Efficiency Wound-Field Synchronous Motor for Electric Vehicle Traction

This paper deals with a design method to improve the power density and energy efficiency of a wound-field synchronous motor (WFSM) using hairpin type rectangular wire for electric vehicle traction. First, the prototype is analyzed via experiments to come up with plans to improve it. In addition, mechanical loss of the prototype including the bearing and brush friction losses is obtained and used for designing the improved motor. After then, an analytical approach is presented for the magnetic circuit design to minimize magnetic resistance in the motor core. Also, the analytical methods are proposed to predict the resistance of the field and armature windings. At this step, rectangular wire is considered for the armature winding to reduce the copper loss. Moreover, the calculation process is presented to estimate the iron loss considering harmonics. The performances such as power density and efficiency of the improved WFSM are analyzed and compared with those of the prototype. In addition, the energy efficiency of the motors in the new European drive cycle (NEDC) is analyzed. Finally, the performances of the improved WFSM are compared with the experimental results to verify the validity of the proposed design process.

Excitation System Technologies for Wound-Field Synchronous Machines: Survey of Solutions and Evolving Trends

WFSM are included in the majority of large power generating units and special high-power motor drives, due to their high efficiency, flexible field excitation and intrinsic flux weakening capability. Moreover, they are employed in a wide range of high-end solutions in the low-to-medium power range. This contribution presents a comprehensive survey of classical and modern methods and technologies for excitation systems (ESs) of (WFSMs). The work covers the fundamental theory, typical de-excitation methods and all the modern excitation equipment topologies in detail. It also includes a description of the state-of-the-art and the latest trends in the ESs of wound-field synchronous motors and generators. The purpose of the paper is to provide a useful and up-to-date reference for practitioners and researchers in the field.

Sensorless Stator Flux Oriented Control for Startup Gas Turbine

This paper proposes a hybrid position estimation method for load commutated inverter (LCI) fed wound field synchronous motor (WFSM) at zero speed up to turbine ignition speed. In this method injection based position estimation method is used at low speed. Then a stator flux observer is applied to firing pulse generation and position estimation.With use of proposed algorithm the problems of other position estimation are reduced and thyristor's commutations at zero up to final speed are well done. In this paper a new structure has been introduced for stator flux oriented control of LCI fed WFSM which improves power factor and dynamic response of speed controller. Moreover, manufacturing cost is reduced. Finally proposed algorithm and structure are simulated in MATLAB Simulink.

Design of High Efficiency Wound Field Synchronous Machine With Winding Connection Change Method

In this paper, a design method for a wound field synchronous motor (WFSM) employing the dual stator winding and the winding connection change circuit is proposed. Through the design method, the WFSM can be operated as two different modes, and each mode is determined by the connection between the stator windings U, V, W and X, Y, Z. By applying the proposed method to the conventional WFSM, the operation mode of the motor is changed at a certain speed. The speed for the mode change is determined to maximize the efficiency of the machine. As a result, through the mode change, the line to line induced voltage, current phase angle, and phase resistance are decreased. In addition, the demand field current is also reduced to achieve the required torque due to the salient pole characteristics of WFSM. Consequently, the efficiency of the WFSM is increased due to the mode change. Finally, the effect of the proposed method and the validity of the simulation results are verified by the load test.

권선형 동기 전동기의 고조파 성분을 저감시키기 위한 연구

Wound-field synchronous motors are currently being heavily researched. These devices are advantageous in that they can flexibly cope with a high-speed control region and their material costs are lower than those of a permanent magnet-type synchronous motor. However, one disadvantage is that mechanical defects occur over long operation, and the control performance and output density become insufficient. Controlling the design of WFSMs by considering volume and weight limitations causes many harmonic components in the current of the stator and field, which are reflected as noise and loss. As a result, harmonics are generated in the current of the DC link capacitor in the inverter, and the lifetime of the capacitor is shortened according to the rms value of the ripple component. In this paper, we propose a vector-control algorithm that compensates the mutual interference components and a vector-control algorithm with high-frequency current injection to reduce the harmonic components of the motor.

Torque Improvement of Wound Field Synchronous Motor for Electric Vehicle by PM-Assist

In order to improve the performance of the wound field synchronous motor (WFSM), the permanent magnet assist (PM-assist) is investigated in this paper. The effect of the PM-assist is dependent on the inserted position of the PMs. Thus, four models whose PMs are inserted at each different position are suggested. Then, the most effective position of the PM is decided by the mean torque per employed amount of the PM. By inserting the PMs into the decided position of a WFSM designed for a small electric vehicle traction, the PM-assisted WFSM is designed. By comparing the torque and the efficiency of the original WFSM and the PM-assisted WFSM, the effectiveness of the PM-assist is figured out. Finally, the validity of this research is verified by the experiment using the manufactured WFSM.