Multiobjective Design of a Line-Start PM Motor Using the Taguchi Method

The Line-Start Permanent Magnet Synchronous Motor (LSPMSM) attracted a considerable attention because of the higher value of the product between the power factor and the efficiency. The paper proposes an analytical design method for the LSPMSM, considering the asynchronous starting and the synchronous steady state parameters. Using this theoretical approach, all the synchronous and asynchronous starting characteristics will be calculated. The design of a motor having the following specifications: rated output power 3.5 kW, rated voltage 200 V, rated frequency 50 Hz, rated speed 3000 rpm is presented.

High-efficiency motors are being gradually introduced in many industrial applications because of their positive impacts on the environment by reducing energy consumption and CO2 emission. In this respect, line start permanent magnet synchronous motors (LS-PMSMs) have been introduced recently. Due to their unique configuration, LS-PMSMs allow the obtaining of super premium efficiency levels, accompanied with a high torque and power factor. However, since the use of LS-PMSMs in the industry is in its infancy, no efficient scheme has yet been reported for broken rotor bar (BRB) fault detection in this type of motor. Accordingly, the main aim of this research is to investigate the fault-related feature for BRB faults on LS-PMSMs. In this regard, a simulation model and experimental setup for the investigation of BRB in LS-PMSM are implemented. The detection strategy for BRB in LS-PMSM proposed here is based on the monitoring of the start-up current signal and discrete wavelet transform. The entropy features are used as fault-related features for BRB faults. Finally, the ability of these features is validated for the detection of BRB in LS-PMSM through statistical analysis. In this research, the importance of the starting load is also considered for BRB detection in LS-PMSMs.

In the design process of the existing Line-Start Permanent Magnet Synchronous Motor (LSPMSM), the method to achieve the optimum performance is complicated, and the problem of pull-in synchronization caused by large load inertia is not fully considered. The objective of this research is to introduce a multi-objective optimization technique with efficiency (Eff), power factor (PF), pull-in torque multiple and starting torque multiple as optimization objectives.The impact of parameters such as core length, air gap length, and magnet thickness on efficiency, power factor, pull-in torque, and starting torque are analyzed. To achieve the optimal design outcome, a surrogate model integrating Response Surface Methodology (RSM) and Finite Element Analysis (FEA) for LSPMSM has been developed.The initial scheme based on FEA is analyzed and compared with the optimal scheme in detail, and the prototype manufactured according to the optimal scheme is tested and verified. The results of the optimization analysis show that in the case of a large load inertia, the efficiency, power factor, starting torque multiple and pulse-in torque multiple of the new optimization scheme have all been improved, achieving the collaborative optimization of transient and steady-state performance. Moreover, the results derived from FEA exhibit a high degree of consistency with the experimental data, thereby validating the optimized motor’s superior performance in both transient response and steady-state operation.

Purpose. Analysis of the rotor configuration of line start permanent magnet synchronous motor (LSPMSM) when using 3-bar magnet structure with two cases: one with a separating magnetic steel bridge and one without it. Research results allow selecting the appropriate rotor configuration to obtain the best starting characteristics, current, torque, and performance. Thereby, it is possible to replace high efficiency LSPMSM with low efficiency induction motors used in ventilation and water pumping loads to improve the efficiency of electricity use in mining. Methodology. The article uses analytical methods and simulation methods on Ansys/Maxwell software and conducts a laboratory test evaluation to determine the effect of rotor configuration on the starting characteristics, working current, torque ripple, and working efficiency of an LSPMSM for mining applications. Findings. An LSPMSM model was built based on a 15 kW–3,000 rpm induction motor with two rotor configurations: one with a separating magnetic steel bridge and one without it. The results of the study show that when a rotor configuration has no separating magnetic steel bridge, the LSPMSM reaches its maximum speed in 0.45 seconds, a synchronous speed of 3,000 rpm in around 0.75 seconds, a torque ripple of 23.1 %, a current total harmonic distortion of 14.3 %, and a performance of 93.3 %. In contrast, when a rotor structure has a separating magnetic steel bridge, starting the motor is more difficult, taking 1.14 seconds to reach synchronous speed and having a lower starting torque, a current total harmonic distortion of 16.1 %, and a performance of 92.5 %. Originality. Research rotor configurations of LSPMSM based on the 15 kW–3,000 rpm induction motor with and without a separating magnetic steel bridge. The research results allow choosing the appropriate rotor configuration to obtain the best starting characteristics, current, operating torque and performance efficiency. Practical value. The research results are important scientific guidance in the design and manufacture of LSPMSM for application in underground mining to improve the efficiency of electricity use in mining.

This article presents a design improvement of the dual‐pole, two‐speed line start permanent magnet (LSPM) synchronous motor. For this purpose, the operational performance of the motor with dual‐pole structure is first compared with the conventional single‐pole motor to identify its performance limitations. Next, the structure of the dual‐pole rotor is modified accordingly to address the related limitations. The proposed, modified design reduces the number of PMs in the rotor structure and offers a better steady state and transient performance. The motor is analysed using 2D finite element analysis (FEA), and results are verified by experimental tests on the motor prototype.

The variation of stator winding turns will directly affect the key parameters of a motor, such as winding resistance and winding reactance, which further affect the steady-state performance of the motor. In order to get excellent steady-state performance from line-start permanent magnet synchronous motors (LSPMSMs) under different load powers, taking an 11 kW LSPMSM as an example, the finite element method (FEM), combined with the steady-state phasor diagram and torque angle characteristic, are used in this paper for the optimal design of the stator winding turns of the prototype. The correctness of the model is verified by comparing the experimental data with the calculated data. First, the influences of different stator winding turns on the no-load, back-induced electromotive force (EMF), as well as on inductance and overload ability are studied, and the variation mechanism is obtained. In addition, from the perspective of the torque angle characteristic, the influence of the change in synchronous inductance caused by the number of turns on the steady-state power angle is studied. Second, the variation of the current and power factors with turn number is obtained by studying the steady-state power angle and end voltage. Based on the coupling relationship between the no-load back EMF and the power angle, the mechanism of non-linear variation of current and power factor is revealed. Finally, the variation of the number of turns on the core loss and eddy current loss is analyzed under various operating conditions, and the variation mechanism is revealed, based on the armature reaction theory.

Line-start permanent magnet synchronous motors (LSPMSMs) are of great interest to researchers because of their high energy efficiency, due to the growing interest of manufacturers in energy-efficient units. However, LSPMSMs face some difficulties in starting and synchronization processes. The LSPMSM lumped parameter model is applicable to estimating the successfulness of starting and further synchronization. The parameters of such a model can be determined using computer-aided identification algorithms applied to real motor transient processes’ curves. This problem demands significant computational time. A comparison between two algorithms, differential evolution and Nelder–Mead, is presented in this article. The algorithms were used for 0.55 kW, 1500 rpm LSPMSM parameter identification. Moreover, to increase computational speed, it is proposed to stop and restart the algorithms’ procedures, changing their parameters after a certain number of iterations. A significant advantage of the Nelder–Mead algorithm is shown for the solving of the considered problem.

When the line-start permanent magnet synchronous motor (LSPMSM) operates stably, sudden change of load torque may result in out-of-step and supersynchronous faults. The currents in stator windings and rotor bars will increase under the two faults, so will the strength of demagnetization field, which is likely to cause the irreversible demagnetization of permanent magnets in LSPMSM. This paper adopts two-dimensional finite-element method (2-D FEM) to analyze the demagnetization characteristics of LSPMSM under out-of-step and supersynchronous faults. The operating points of all positions in permanent magnets are not exactly the same, and the variation of magnets' minimum operating point, which is the minimum value of operating points of all positions in permanent magnets, is used to reflect the variation of demagnetization field strength. The influences of initial load condition, load torque change time as well as the load torque after change are studied, and corresponding conclusions are drawn.

A comprehensive comparison of the dynamic and steady state performance characteristics of permanent magnet synchronous motors (PMSM) with interior and surface rotor magnets for line-start operation is presented. The dynamic model equations of the PMSM, with damper windings, are utilized for dynamic studies. Two typical loading scenarios are examined: step and ramp loading. The interior permanent magnet synchronous motor (IPMSM) showed superior asynchronous performance under no load, attaining faster synchronism compared to the surface permanent magnet synchronous motor (SPMSM). With step load of 10 Nm at 2 s the combined effect of the excitation and the reluctance torque forced the IPMSM to pull into synchronism faster than the SPMSM which lacks saliency. The ability of the motors to withstand gradual load increase, in the synchronous mode, was examined using ramp loading starting from zero at 2 s. SPMSM lost synchronism at 12 s under 11 Nm load while the IPMSM sustained synchronism until 41 seconds under 40 Nm load. This clearly suggests that the IPMSM has superior load-withstand capability. The superiority is further buttressed with the steady state torque analysis where airgap torque in IPMSM is enhanced by the reluctance torque within 90° to 180° torque angle.

Pole changing line‐start permanent magnet synchronous motor (LSPMSM) can significantly improve the starting capability of LSPMSM by decreasing the braking torque and pulsating torque during starting process. The fundamental reason for the elimination of braking torque is that there is no generating effect during minor‐pole starting process. That is to say, induced electromotive force (EMF) does not exist when the magnetic field generated by multi‐pole rotor PMs cut the minor‐pole stator winding. Therefore, the induced EMF of pole changing LSPMSM is analysed theoretically and calculated analytically. Considering that the magnetic flux per pole of the coils under the adjacent pole are different, the induced EMFs of a conductor, a full‐pitch coil, a coil group in minor‐pole stator winding are, respectively, calculated, and then the general analytical expression of the induced EMF of a phase winding with different rotor/stator pole ratio is derived. Then, the motors with different rotor/stator pole ratios are simulated based on finite element method to obtain the corresponding EMFs. Meanwhile, a 6/8 pole changing LSPMSM is taken as prototype. The consistency of the simulation, experiment, and the analytical calculation results effectively verify the validity of the derived general analytical expression and theoretical analysis.

Recently, as the request of improvement on efficiency for the household appliances increases, a single-phase line-start permanent-magnet synchronous motor (LSPM) attracts attention. LSPM has the capacitor connected in series with the auxiliary winding and the main winding is connected in parallel with it. For this reason, the elliptic rotating magnetic field is generated by converting single-phase into quasi-two-phase. Because of the negative-sequence component in a capacitor motor, secondary current flows also in steady state. So its numerical analysis is difficult in comparison with three-phase motors. Though analytical methods of starting and synchronous characteristics have been established, the effect of considering squirrel cage into analysis has yet to be discussed. In this paper, the analytical method of considering the positive and negative sequence phase making use of the method of symmetrical coordinates was proposed. And the experimental and analytical results are compared, and we consider the condition of high efficiency operating from them. In addition, we considered the parameter of load angle. Load angle is very important for single-phase LSPM, but few papers consider it. The load angle is measured by the prototype of single phase LSPM

Under the crane's working conditions, a Wound Rotor Line-start Permanent Magnet Synchronous Motor (WRLSPMSM) is designed in this paper. Rotor external resistance can be connected to the prototype, and rotor resistance determines when the maximum torque appears. So this paper puts forward a method to improve the starting performance, which PWM chopping is adopted to control rotor external DC fixed resistance. Because the number of rotor external AC resistance is limited, the starting torque has fluctuation when rotor external AC resistance is switched. Rotor external DC fixed resistance is controlled by PWM chopper technology. Regulate the rotor external DC fixed resistance rapidly to reduce torque ripple and realize speed stepless. Detailed theoretical analysis shows that starting torque is mainly affected by asynchronous torque and generated braking torque, and also according the analysis determines the value of rotor external DC fixed resistance. Meanwhile considering the influence of slots per pole per phase q on cogging torque, which easily disturbs the system's precise controlling during the low speed running, the fraction-slot winding is adopted in the prototype. The PWM chopping control method makes the starting process safer and more convenient than asynchronous motor.

This paper presents a novel 6/8 pole changing line-start permanent magnet synchronous motor (LSPMSM) which can decrease braking torque and pulsating torque fundamentally and improve starting capability effectively. The impedance parameters of 6-pole winding and 8-pole winding are calculated in use of two-dimensional (2D) finite element analysis (FEA). Then the bipolar dynamic simulation model is built based on MATLAB/Simulink. And finally, in use of the simulation model, the influences of switching speeds and phase differences between induced electromotive force of 8-pole winding and applied voltage (Δθ) on impulse currents and synchronization when switching are analyzed, and the results show that the impulse currents are related to Δθ and the synchronization is related to both Δθ and switching speeds.

Starting phase of a motor in general is a very complicated period. Motors draw a large amount of current, several times the normal full-load current when first energized. In starting period of Line Start Permanent Magnet Synchronous Motors (LSPMSM), high current causes saturation in stator and rotor. The effect of saturation on the “q-axis” synchronous inductance, L mq , of LSPMSM is studied in this paper. The paper will proposes a method to calculate the L mq using the Lumped Parameter Method. Comparative results will be carried on using finite element method. Good agreement between results is justified.

Line Start Permanent Magnet Synchronous Motor (LSPMSM) has been proved as an economically feasible, high efficiency alternative to an induction motor where constant speed is desirable. These motors are having the properties of an induction motor during starting and synchronous motor during steady state period. The need of line starting, calls for a cage winding in addition to permanent magnets in the rotor, which increases the complications in rotor design, and restricts the choice of rotor geometries. There is always conflict in the rotor design of this machine. This conflict is in between synchronous and asynchronous performance of the machine which in turn is a conflict between cage and magnet placement in the rotor. This paper reports an attempt in the direction of removing this conflict and optimizes both synchronous and asynchronous performances of the machine. A new two-part rotor geometry is suggested and analyzed using the dynamic model of LSPMSM prepared in Simulink.