D-axis Current Research Articles

Short and long term memory method for predicting the temperature of motor stator based on Harris eagle algorithm optimization

The temperature of a motor significantly affects its control and lifespan. However, due to the influence of motor structure and operating environment, precise temperature measurement of the motor is challenging with temperature sensors. Therefore, machine learning algorithms are often employed to predict the temperature more accurately. To enhance motor control, integrating machine learning algorithm models with the actual motor control terminal is highly beneficial. This paper proposes a Short and Long Term Memory (LSTM) algorithm model based on Harris's hawk optimization to predict the temperature of the motor stator, which is applied in actual motor control. Furthermore, it evaluates the tracking performance of motor control current. Firstly, an experimental platform for temperature measurement is established to acquire the temperature at different positions of the motor as raw data. Subsequently, the raw data is inputted into three algorithms: LSTM, PSO-LSTM, and HHO-LSTM, for comparison. By comparing evaluation metrics, it is demonstrated that HHO-LSTM exhibits excellent predictive performance. Furthermore, utilizing diverse segments of the motor as model input sets enhances the generalization capability and predictive accuracy of the model. Finally, applied in actual motor control, a comparative analysis of q-axis and d-axis currents reveals reduced fluctuation errors, showcasing improved motor control effectiveness.

Investigation of a Parallel Hybrid Excitation Machine With Auxiliary Winding for Loss Reduction in Flux-Weakening Operation

An axial-parallel hybrid excitation machine (APHEM) with an auxiliary winding is proposed and investigated for loss reduction in the flux-weakening operation. The permanent magnet (PM) flux and wound field flux of the APHEM are different and coupled under the armature action. Based on the axial-parallel structure, an auxiliary winding is introduced into the PM part to make better utilization of the distinct PM flux. Because of the coupling of the two fields, this auxiliary winding not only couples the PM flux but also affects the wound field flux. Two major conclusions can be derived from the theoretical analysis. Firstly, the auxiliary winding couples the PM flux and produces extra torque, benefiting a smaller field current. Secondly, the auxiliary winding can suppress the phase voltage because of the larger characteristic current of the PM part than the wound field part. This facilitates a smaller d-axis armature current. The reduced currents favor the reduction in copper loss and core loss. Compared with the original APHEM under the minimum-copper-loss control, the proposed method achieves a 34% reduction in the maximum loss and a 60% decline in the maximum torque ripple ratio. Finally, the measured results verify the analysis.

Stability Improvement of Adaptive Full-Order Observer for Sensorless Induction Motor Drives in Low-Speed Regenerating Mode

In the applications of high power induction motor railway traction systems, the switching frequency of power devices is relatively low. This restriction will severely reduce the accuracy and stability of conventional discrete model for adaptive full-order observer (AFO) in extremely high-speed region. What’s worse, due to the neglect of flux error during speed estimation derivation, the conventional AFO cannot maintain stability under low-speed regenerating mode. The above two reasons limit the application of AFO in rail traction systems for full speed range. To address this problem, this paper utilizes a high-accuracy discretization which is achieved in combined reference frames and feedback gains are designed in z-domain to ensure stability and dynamic performance of AFO. Moreover, a modified speed estimation mechanism with the error of d-axis current is developed to guarantee stability in extremely low-speed regenerating mode. Rigorous simulations and experiments are performed to verify that the proposed AFO model achieves excellent sensorless control performance in full speed range.

Parameter Identification for Maximum Torque per Ampere Control of Permanent Magnet Synchronous Machines under Magnetic Saturation

This paper applies the identified parameters of permanent magnet synchronous machines (PMSMs) for the maximum torque per ampere control (MTPA) under magnetic saturation. The variation in magnet flux with current is determined using a position offset approach while the variation in q-axis inductance with the current is estimated from the d-axis voltage equation afterward. In addition, the d-axis inductance is estimated at standstill by the injection of a small amplitude of high frequency d-axis current. The curve-fitted results of estimated parameters under different saturation conditions are then employed to aid the derivation of MTPA control law. The proposed method is experimentally verified on two prototype PMSMs. Experimental results show that compared with conventional MTPA schemes using fixed values of magnetic parameters, the proposed method can increase maximum output torque by 2.1% and 3.2% on two prototype PMSMs, respectively.

Active-Damping-Based Field-Weakening Control Strategy With Voltage Angle Regulation for High-Speed SPMSM Drive

The field weakening (FW) control strategy with voltage angle regulation has the advantages of fast speed and current response by directly decoupling the voltages. For suppressing the current harmonics, this article proposes a novel active-damping based FW control strategy for high-speed surface-mounted permanent magnet synchronous motor (SPMSM) drives. The resonant issue in the voltage-angle regulated system is analyzed, and the d-axis current is adopted to compensate the voltage angle, which introduces the additional impendence at the resonant frequency to reduce the d-q axis current harmonics. An offline coefficient design method based on the frequency characteristic and step response is proposed to construct the contour map seeking for optimal coefficients, which achieves significant reductions on current harmonics and improves the robustness of the proposed method on mismatches of motor parameters. The damping ratio of the current loop is determined by the integral coefficient with a wider range. Hence, the adaptability of the FW voltage angle regulation can be guaranteed under different speed and load conditions. The effectiveness of the proposed strategy is verified on the 6-kW high-speed SPMSM platform.

Toward Reducing Undesired Rotation Torque in Maglev Permanent Magnet Synchronous Linear Motor

The dq current transformation method can be used to achieve the drive control of the maglev permanent magnet synchronous linear motor (MPMSLM). Specifically, the control of the suspension force Fz can be achieved by controlling the d-axis current, and the control of the thrust force Fx can be achieved by controlling the q-axis current. However, the direct use of the dq current transformation method on traditional MPMSLM structures produces an additional rotation torque around the y-axis. In order to reduce this additional torque, a new MPMSLM structure is proposed in this work. First, the characteristics of additional torque through finite element analysis are analyzed. Second, the Halbach permanent magnet array and coil size are optimized, and the topology of the MPMSLM coil is designed to reduce the additional torque. The decoupling performance and current of the proposed MPMSLM are experimentally verified through open-loop experiments using finite element simulation software. Finally, the decoupling algorithm of the generalized inverse matrix is used to achieve the decoupling between forces Fx and Fz and torque Ty and the d-axis and q-axis currents in each drive unit. Based on this, a three-degree-of-freedom closed-loop control system of the MPMSLM is designed. The LabVIEW 2018 software is used for the simulation analysis of the three-degree-of-freedom MPMSLM motion control system, and the results show that the proposed motor structure has superior closed-loop control performance.

Performance Evaluation of Grid Connected T-Type Multilevel Inverters

This paper deals with performance of three and five level grid-connected T-type inverters. T-Type structure requires fewer power devices than Neutral-Point-Clamped and FlyingCapacitor inverters for the same power level. First, mathematical model of grid connected T-Type inverters is demonstrated. The PI controller is used to control the d-axis and q-axis currents, respectively. The sine Pulse Width Modulation (PWM) technique is used to control the MOSFET switches. The simulation of the complete system has been performed on MATLAB/Simulink.

Optimal Efficiency Control of Wind Mill Induction Generator Using Loss Minimization Technique

Improvement of the operating efficiency of generators used in large wind power generation systems becomes important since such a large machine's power loss is not negligible. In the conventional method integral controller is used to reduce the power loss by up to 25 % at low wind speeds. The proposed PID controller method is based on flux level reduction, where the flux level is computed from the machine model for the optimum d-axis current of the generator. For the vector-controlled induction generator, the d-axis current controls the excitation level to minimize generator loss. In contrast, the q-axis current controls the generator torque, by which the speed of the induction generator is controlled according to the variation of the wind speed in order to produce the maximum output power, thereby improve the efficiency of the induction generator.

Sensorless Control Method of High-Speed Permanent Magnet Synchronous Motor Based on Discrete Current Error

When the Surface-Mounted Permanent Magnet Synchronous Motor (SPMSM) is in the condition of high-speed and low carrier-wave ratio, the performance of sensorless control is more affected by digital control delay, parameter inaccuracy, and other factors. This paper presents a sensorless control method based on the static error between the discrete d-axis current and the corresponding reference value. If there is no error in position angle, the discrete d-axis current should have no static error approximately. In addition, the static error of the d-axis current is related to the speed, so the PI controller with a variable proportional integral coefficient is used to ensure a stable error compensation performance in a wide speed range. The proposed method can accurately compensate the estimated rotor position of the motor under high-speed and low carrier ratio conditions and improve the accuracy of sensorless control. It provides an effective measure for the stable and reliable acceleration of electric vehicles and has specific practical significance for the development of electric vehicle control.

Effect of Grid-Following VSC on Terminal Frequency

Grid-following voltage source converter (GFL-VSC) does not establish frequency like synchronous generator (SG), but follows the frequency of the terminal bus using phase-looked loop (PLL). This letter demonstrates that GFL-VSC also affects the terminal frequency, rather than simply follows it, due to the dynamics of the PLL and outer control loops. The relationship between PLL frequency, d-axis current, and terminal frequency is derived. Both the PLL frequency and the d-axis current affect the terminal frequency in the form of their derivatives, which is completely different from conventional SG and the corresponding frequency divider formula (FDF). Time-domain simulation results validate the derived relationship.

A sensorless stable V/f control of SPMSM based on constant power factor control with a novel MTPA tracking

The paper presents a sensorless stable V/f control strategy of surface permanent magnet synchronous motor (SPMSM), where the maximum torque per ampere (MTPA) condition is satisfied by controlling the d-axis current to zero. However, to directly control the d-axis current, it is necessary to know the exact rotor position, which is not possible in sensorless V/f control. Based on this fact, a constant power factor (CPF) control loop in voltage vector reference frame dvqv with a novel MTPA tracking according to a look-up table (LUT) was developed. The LUT was created based on a set of experimental measurements to store the motor power factor where MTPA is reached. The proposed stable V/f control strategy shows an accurate MTPA tracking of SPMSM in the entire operational range verified by experiments.

Low complexity duty cycle modulation model predictive current control of permanent magnet synchronous motor

This study proposes a model predictive current control algorithm for the synchronous permanent magnet motor with low complexity duty cycle modulation. Three single-phase voltage vectors are simulated to synthesize the target voltage vector that enables the current to achieve deadbeat control. The algorithm can change the amplitude and direction of the synthesized vector and extend the selection range of the synthesized vector to the whole hexagonal region. That is to say, this method can realize the deadbeat control of the d-axis and q-axis currents, and reduce the current pulsation. Moreover, this method only needs one action time operation, which can directly convert the action time of the voltage vector into a three-phase duty cycle after equivalent processing and over-modulation of the action time of the voltage vector. It is not necessary to traverse multiple sectors for optimization, which simplifies the modulation method and reduces the computational complexity. The effectiveness and reliability of the proposed method are verified by theoretical derivation and experimental results.

Maximum efficiency control and predictive-speed controller design for interior permanent magnet synchronous motor drive systems

Improving the efficiency of home appliances is an important area of research these days, especially for global warming and climate change. To achieve this goal, in this paper, a new method to improve the maximum efficiency control of an interior permanent magnet synchronous motor (IPMSM) drive system, which includes an IPMSM and an inverter, is investigated. By suitably controlling the d-axis current, the IPMSM drive system can quickly reach its maximum efficiency. A steepest ascent method is used to obviously reduce the searching steps of the maximum efficiency tracking control for an IPMSM. According to experimental results, by using the traditional fixed step method, 14 steps are required to reach the maximum efficiency operating point. By using the proposed steepest ascent method, however, only 4 steps are needed to reach the maximum efficiency operating point. In addition, according to the experimental results, during the transient dynamics, the predictive controller obtains faster responses and 2% lower overshoot than the PI controller. Moreover, during adding external load, the predictive controller has only a 10 r/min speed drop and 0.1 s recover time; however, the PI controller has a 40 r/min speed drop and 0.3 s recover time. Experimental results can validate theoretical analysis. Several measured results show when compared to the fix-step searching method with a PI controller, the proposed methods provide quicker searching maximum efficiency ability, quicker and better dynamic transient responses, and lower speed drop when an external load is added.

Mathematical Model Derivation and Experimental Verification of Novel Consequent-Pole Adjustable Speed PM Motor

This paper proposes a novel consequent-pole-type PM motor having a structure different from that of conventional consequent-pole-type PM motors. The proposed rotor structure is composed of a magnetic pole pair using a permanent magnet and an image-pole pair using a high permeability core. The windings facing the magnetic pole pair and the image-pole pair are connected in series in the rotor structure, the three-phase synchronous impedance is balanced, and the d-axis inductance is increased. Therefore, compared with the conventional consequent-pole type, the field weakening operation can be performed efficiently with a lower d-axis current. These advantages make it possible to expand the operating range during field weakening. Furthermore, to fix the driving control method of the proposed consequent-pole PM motor, the voltage equation of the proposed motor is derived and verified by analysis and experiment. In addition, the essential characteristics of the proposed motor were compared with that of a standard surface permanent magnet (SPM) motor and a conventional consequent-pole PM motor.

Control research on axial-flux hybrid-excitation generator for offshore vertical axis maglev wind turbine

Vertical axis wind turbines generally have poor starting performance, but in recent years, they have gradually played a great potential in offshore floating wind power generation system. In order to improve the start-up and low wind speed operation capacity of vertical wind turbine, an asymmetric-primary axial-flux hybrid-excitation generator (APAFHG) which can generate an adjustable levitation force for offshore vertical axis maglev wind turbine is proposed. However, the complexity of levitation force characteristic makes it difficult to control the levitation force of the maglev system and output power of the generator independently. In this paper, the levitation force characteristics of APAFHG are analyzed, and a control strategy is proposed to realize the decoupled control of maglev system and generator power. First of all, the topology of AFAPHG is described and operation principle of AFAPHG is expounded. Secondly, the mathematical model of AFAPHG is deduced, and the levitation force performance of AFAPHG under DC excitation, d-axis and q-axis current is obtained by finite element method. Finally, a compensation strategy based on the levitation force mathematical model is proposed. The results show the compensation strategy can effectively realize the decoupled control of levitation force and generator power.

A new Bernard–Praly-like observer for sensorless IPMSMs

A slight extension of the global Bernard–Praly gradient adaptive observer – originally presented for nonsalient-pole surface Permanent Magnet Synchronous Motors (PMSMs) and recently proved to own local exponential convergence properties under well-known observability conditions – is here designed and proposed for Interior Permanent Magnet Synchronous Motors (IPMSMs) (with relatively small saliency) in the case in which the q-axis current is constant. It guarantees local exponential estimation – from stator current and voltage measurements – of both the stator fluxes and the sinusoidal/co-sinusoidal functions of the motor electrical angle, with no modification of the previous persistency of excitation condition requirements. Such an extension complements – at least locally – a previous analysis concerning IPMSMs under constant d-axis current. Applications to the sensorless control of IPMSMs (with realistic simulations) are included.

Optimized OP-FTC for SPMSM Considering Copper Loss Minimization

The traditional fault-tolerant control (FTC) strategy can guarantee that permanent magnet synchronous machine (PMSM) operate stably in open-phase fault (OPF) situation. However, the copper loss minimization is usually out of consideration. Therefore, an optimized open-phase FTC (OP-FTC) method is put forward for surface-mounted PMSM (SPMSM) considering copper loss minimization. First, when an OPF happens, according to the theory that magneto-motive force remains unchanged in normal and faulty situations, the relationships between the remaining two-phase currents and the dq-axis currents are obtained to make SPMSM output the same torque as that before the fault appearance. Then, based on the relationship between dq-axis currents and copper loss, the d-axis current is calculated to make copper loss minimum. Finally, the proposed OP-FTC strategy is presented for SPMSM drive system. The simulation and experiment are studied to test the optimized OP-FTC strategy.

Estimation of the Dynamic Parameters of the Bearings in a Flexible Rotor System Utilizing Electromagnetic Excitation by a Built-In Motor

Estimation of the dynamic parameters of bearings is essential in order to be able to interpret the performance of rotating machinery. In this paper, we propose a method to estimate the dynamic parameters of the bearings in a flexible rotor system. By utilizing the electromagnetic excitation generated by a built-in PM motor and finite element (FE) modeling of the rotor, safe, low-cost, and real-time monitoring of the bearing dynamics can be achieved. The radial excitation force is generated by injecting an alternating d-axis current into the motor windings. The FE model of the rotor and the measured frequency responses at the motor and bearing locations are used to estimate the dynamic parameters of the bearings. To evaluate the feasibility of the proposed method, numerical simulation and experiments were carried out on a flexible rotor system combined with a bearingless motor (BELM) having both motor windings and suspension windings. The numerical simulation results show that the proposed algorithm can accurately estimate the dynamic parameters of the bearings. In the experiment, the estimates made when utilizing the excitation force generated by the motor windings are compared with the estimates made when utilizing the excitation force generated by the suspension windings. The results show that most of the stiffness and damping coefficients for the two experiments are in good agreement, within a maximum error of 8.92%. The errors for some coefficients are large because the base values of these coefficients are small in our test rig, so these coefficients are sensitive to deviations. The natural frequencies calculated from the dynamic parameters estimated from the two experiments are also in good agreement, within a maximum relative error of 3.04%. The proposed method is effective and feasible for turbomachines directly connected to motors, which is highly significant for field tests.

Regression Model-Based Flux Observer for IPMSM Sensorless Control with Wide Speed Range

A new linear regression form is derived for a flux observer and a position observer is designed. In general, the observability of the permanent-magnet synchronous motor is lost at zero speed. In this work, the proposed regressor vector contains current derivative terms in both directions (dq-axis), and it gives the chance for the model-based flux observer to operate at zero speed. When an excitation signal is injected into d and q axes with the proposed flux observer, it helps to satisfy the persistent excitation condition in the low-speed range. Therefore, the sensorless performance of the model-based is improved greatly, even at zero speed. However, it appears with a disturbance term, which depends on the derivative of the d-axis current. Thus, the disturbance does not vanish when an excitation signal is injected. In this work, the disturbance term is also taken care of in constructing an observer. It results in an observer which allows signal injection. Thus, high frequency signal can be injected in the low speed region and turned off when it is unnecessary as the speed increases. This model-based approach utilizes the signal injection directly without recurring to a separate high frequency model. In other words, it provides a seamless transition without switching to the other algorithm. The validity is demonstrated by simulation and experimental results under various load conditions near zero speed.

Improved Voltage Boundary With Model-Based Control Algorithm for Increased Torque in the Field Weakening Region of Induction Machines

At high speed, electric vehicles (EVs) have limited torque when powered by an induction machine (IM). In IM, the high-speed region is called field weakening, and the region is known for torque limitation. This article proposes a control method that increases the torque without applying discontinuous-modulation techniques, which is commonly used. A bespoke model-based voltage control method has been developed, which enables reaching the hexagonal voltage reference trajectory for the field weakening region. So far, all model-based control methods are constrained by the inscribed voltage circle, which lies within the hexagonal voltage boundary. This restriction limits the available inverter output voltage across the motor windings, which, in turn, restricts the output torque of the drive. To achieve the hexagonal voltage trajectory, this article introduces a new calculation of the d-axis current for the entire speed range in the field weakening region. This calculation is based on the hexagonal voltage boundary equations and the stator voltage vector position. This generates a new reference d-axis current that minimizes the difference between the hexagonal voltage boundary and its inscribed voltage circle. As a result, the proposed d-axis current maximizes the output torque and output power in the field weakening region. The proposed method is presented analytically. Simulation and experimentally validated results are presented to confirm its feasibility and effectiveness.