Harmonic Back Electromotive Force Research Articles

Remedial Direct Torque Control for Dual Three-Phase Permanent-Magnet Motor With Harmonic Torque Suppression

This article proposes a novel remedial direct torque control (RDTC) for the postfault operation of the dual three-phase permanent-magnet (DTP-PM) motor. The DTP-PM motor is configured as a two-neutral points model and fed by an eight-leg voltage source inverter. Also, the harmonic torque induced by the third harmonic back electromotive force and zero-sequence currents is considered at the postfault operation. First, the switching tables for different fault conditions are pre-established. The proposed strategy can be applied to different postfault operations with one phase open by replacing the switching table simply. At the normal operation, the redundant auxiliary legs are disabled. So, the proposed eight-leg voltage inverter is the same as the conventional six-leg one. At the postfault operation, the auxiliary leg in the faulty three-phase windings provides an additional control degree of freedom. Hence, the fault-tolerant capability of the DTP-PM motor with two neutral points can be enhanced. Also, the proposed strategy compensates for the harmonic torque by modifying the reference torque. Based on the proposed RDTC, the postfault operational performance can be significantly improved. Finally, the simulations and experiments are conducted to validate the feasibility of the proposed strategy.

Three-Dimension Space Vector Based Finite Control Set Method for OW-PMSM With Zero-Sequence Current Suppression and Switching Frequency Reduction

The zero-sequence current (ZSC) of open-end winding permanent magnet synchronous motor (OW-PMSM) with common dc bus mainly comes from zero-sequence voltage (ZSV) and third harmonic back electromotive force, so the ZSV levels of voltage vectors in model predictive control (MPC) need to be considered to suppress the ZSC. Different from the conventional MPC methods for OW-PMSM, which usually select the optimal voltage vector under αβ0 coordinate system, this article proposes a three-dimension space vector (TDSV) based MPC method under ABC three-phase coordinate system for OW-PMSM with ZSC suppression and switching frequency optimization strategy. Benefiting from the three-phase voltages decoupling feature of OW-PMSM, TDSVs in ABC coordinate system are regularly distributed in a space cube. A simple optimal TDSV selection method is proposed based on subcubes division. TDSV contains the predicted α-,β-,0 -axis voltages information, so ZSC suppression is achieved automatically. Furthermore, utilizing the switch states redundancy feature of dual-inverter system, a cost function is designed to optimize the switch states change and reduce the switching frequency without affecting the optimal TDSV selection. The performance and switching frequency reduction effect of the proposed method are verified and compared with the existing methods through experiments.

Virtual Third Harmonic Back EMF-Based Sensorless Drive for High-Speed BLDC Motors Considering Machine Parameter Asymmetries

This article investigates the virtual third harmonic back electromotive force (EMF)-based sensorless drive method for high-speed brushless dc (BLDC) motors. Conventional zero-crossing point (ZCP) detection methods of virtual third harmonic back EMF require hardware low-pass filters and voltage comparators, causing serious phase lag. To avoid the undesired phase lag of hardware, the proposed method employs algorithmic oversampling technique to reconstruct the envelope of virtual third harmonic back EMF. Besides, the number of sampling points is dynamically adjusted according to the pulsewidth modulation duty ratio to guarantee the accuracy of ZCP detection. In addition, the influence of asymmetric motor parameters, i.e., phase resistance and inductance, on sensorless commutation is analyzed in depth. With asymmetric impedances, ZCPs of virtual third harmonic will deviate from their ideal positions. Consequently, the commutation events, which are searched based on ZCPs, will also be triggered at inaccurate positions and then the control performance will be deteriorated. In order to suppress the negative influence, a novel phase compensation method is proposed. All the theoretical analyses are validated by experiments at a 60 000 r/min BLDC drive platform.

Drive System With Asymmetrical Power Electronics Devices for Novel Reluctance Machines With DC-Biased Sinusoidal Current

This paper proposes a drive system with asymmetrical power electronics devices for the novel reluctance machines with dc- biased sinusoidal current, which is called as dc- RMs in this paper. The three-phase sinusoidal current with same dc offset is injected into the stator winding in the dc- VMs. Therefore, the power device selection method of the conventional motor drive is no longer suitable for dc- RMs. Because of the dc- biased sinusoidal current, two-quadrant switches with asymmetrical current capacity are proposed for the dc- RMs drive. With the asymmetrical switches, the asymmetrical three-phase H-bridge inverter is further brought out. This paper, detailed, analyzes the influence of modulation strategy on current stress of each device and derive the specific current capacity of asymmetric switches. The effects of harmonic current on the current stress, caused by the harmonic back electromotive force in dc- RMs, are also analyzed. Simulation and experimental verification show that the drive with asymmetrical power electronics devices can ensure the performance of the motor while reducing the cost, increasing the power density, and balancing the temperature of the power devices. The theoretical calculation of the current stress is also proved to be precise. In addition, the two-quadrant switches with asymmetric capacity proposed in this paper can also be applied to other dc- RMs drive structure to improve performance.

An EMF Observer for PMSM Sensorless Drives Adaptive to Stator Resistance and Rotor Flux Linkage

The electromotive force (EMF) observer-based sensorless algorithms are sensitive to temperature rise because it requires the stator resistance ( $R_{s}$ ) or the rotor flux linkage ( $\psi _{r}$ ). The temperature measuring of an operating motor can be difficult, therefore, adaptive sensorless algorithms with online $R_{s}$ and $\psi _{r}$ estimation are appreciated. However, existing methods require extra signal injections, transient operations or estimate $R_{s}$ and $\psi _{r}$ one at a time to overcome the rank-deficient problem. In this paper, an adaptive EMF observer which is able to estimate both $R_{s}$ and $\psi _{r}$ simultaneously without requiring any signal injections or transient operations is proposed. The method exploits the harmonic back EMFs (HBEMF) to serve as a novel reference model and regulates the $R_{s}$ value in the EMF observer accordingly. The rank deficient problem is solved with the extra information provided by the HBEMFs. To make use of the HBEMFs, a parameter insensitive extraction method and an algorithm to calculate the rotor position from them are proposed. With the proposed reference model, an adaptive scheme to regulate $R_{s}$ is proposed. To obtain the rotor flux linkage, a $\psi _{r}$ estimator is also developed. The effectiveness of these proposed methods is verified with experiments and simulations.

Design and Analysis of a Magnetic-Field Modulated Brushless Double-Rotor Machine—Part I: Pole Pair Combination of Stator, PM Rotor and Magnetic Blocks

The magnetic-field modulated brushless double-rotor machine (MFM-BDRM) is a promising candidate for the power splitting device in hybrid electric vehicles. Due to its special operating principle, the magnetic field modulation principle, various harmonic magnetic fields are produced in the MFM-BDRM. Therefore, it is crucial for the design of MFM-BDRM to reduce the influence of nonworking harmonic magnetic fields on the electromagnetic performance of MFM-BDRM, like back electromotive force (EMF) and torque ripple. In this paper, first, the distribution law of permanent-magnet (PM) and armature modulated magnetic fields is analyzed. Second, since the analysis and calculation method of harmonic back EMF in a traditional PM machine is not suitable for the MFM-BDRM, the formation mechanism of harmonic back EMF in the MFM-BDRM is further investigated. Third, combined with the characteristic of modulated magnetic field and formed harmonic back EMF in the MFM-BDRM, the optimal pole pair combination of stator, PM rotor, and magnetic blocks is investigated. Finally, analysis and calculation of a specific MFM-BDRM by analytical and finite- element method shows the MFM-BDRM with the optimal combination can obtain very sinusoidal no-load and load back EMF and quite low torque ripple.

Design and Analysis of a Magnetic-Field Modulated Brushless Double-Rotor Machine—Part II: Winding Configuration

The analysis of Part I shows that the integer-slot winding of the magnetic-field modulated brushless double-rotor machine (MFM-BDRM) can obtain very sinusoidal no-load and load back electromotive force (EMF) and quite small torque ripple under an optimal pole-pair combination of stator, permanent magnet (PM) rotor, and magnetic blocks. In practical applications, however, the integer-slot winding is usually replaced by the fractional-slot concentrated winding (FSCW), which can reduce end windings and easily realize automatic winding. This paper focuses on the influence of the FSCW on the electromagnetic performance of the MFM-BDRM and the application feasibility of the FSCW in the MFM-BDRM. First, the formation mechanism of the harmonic back EMF of FSCW is investigated. Then the pole-pair combination law of stator, PM rotor, and magnetic block for the FSCW of the MFM-BDRM is further investigated. Second, the specific FSCW of the MFM-BDRM with $Q = 2{p_s} \pm 1$ and $Q = 2{p_s} \pm 2$ and the integer-slot MFM-BDRM are comparatively investigated. It shows that the integer-slot winding of the MFM-BDRM is superior to the FSCW of the MFM-BDRM in no-load and load back EMF, torque ripple, maximum torque outputting capability, and power factor. Finally, the optimal winding configuration of the MFM-BDRM is determined. A prototype of the MFM-BDRM with the optimal winding configuration and pole-pair combination is designed and manufactured. The theoretical and finite-element analysis is verified by experiments.

Design and Analysis of a Five-Phase SPM Machine Considering Third Harmonic Current Injection

This paper analytically derives the optimal third harmonic current to improve the output torque in five-phase surface-mounted permanent magnet (SPM) machines under the constraints of the same peak/rms value. The relationship between the output torque and the third harmonic current is established and its optimal value for maximizing the output torque is derived. It is found that the optimal third harmonic current is dependent on the ratio of the third harmonic back electromotive force (EMF) to the fundamental one but it is not 1/6 of the fundamental one as pulse width modulation in an inverter. In order to improve the output torque by increasing the fundamental and third harmonic winding factors and the third harmonic airgap flux density, the unequal width tooth and permanent magnet (PM) segmentation are employed in the 10-slot/8-pole five-phase SPM machine. The optimal unequal tooth dimensions and the number of PM segmentations are analyzed for maximizing the output torque. The airgap flux density, back EMF, cogging torque, and output torque of the machine with equal/unequal tooth width and unsegmented/segmented PM are compared. Finally, the experiments on the prototype 10-slot/8-pole PM machine with unequal tooth width and segmented rotor are given to verify the analytical and finite element analyses.

High-Precision Sensorless Drive for High-Speed BLDC Motors Based on the Virtual Third Harmonic Back-EMF

In order to improve the performance of the high-speed brushless direct current motor drives, a novel high-precision sensorless drive has been developed. It is well known that the inevitable voltage pulses, which are generated during the commutation periods, will impact the rotor position detecting accuracy, and further impact the performance of the overall sensorless drive, especially in the higher speed range or under the heavier load conditions. For this reason, the active compensation method based on the virtual third harmonic back electromotive force incorporating the SFF-SOGI-PLL (synchronic-frequency filter incorporating the second-order generalized integrator based phase-locked loop) is proposed to precise detect the commutation points for sensorless drive. An experimental driveline system used for testing the electrical performance of the developed magnetically suspended motor is built. The mathematical analysis and the comparable experimental results have been shown to validate the effectiveness of the proposed sensorless drive algorithm.

Torque Improvement in Five-Phase Unequal Tooth SPM Machine by Injecting Third Harmonic Current

In order to increase the torque density of the five-phase machines, the third harmonic is commonly employed. In this paper, the optimal and critical ratios for the third harmonic current injection are analytically derived and validated by finite element (FE) analyses. It is found that the optimal and critical injection ratios along with the torque improvement are dependent on the ratio of the third harmonic back electromotive force to the fundamental one. In order to improve the electromagnetic torque contributed by the third harmonic component, this paper employs unequal tooth to increase both the fundamental and third harmonic winding factors. Meanwhile, the optimal unequal tooth width combination is deduced and demonstrated by the FE method. When the third harmonic current is injected under the same amplitude constraint, the output torque can be improved. When the third harmonic current is injected under the same RMS value constraint, for the ten-slot/eight-pole equal tooth machine, the output torque can barely be increased, whilst for the unequal tooth machine, the output torque can be increased by 2.1%. Finally, the ten-slot/eight-pole machine with unequal teeth is prototyped and tested to prove the analyses.

Design and Construction of a Sensorless Circuit for Brushless DC Motor using Third Harmonic back Electromotive Force

In this paper the method of sensorless startup of direct current brushless motor using third harmonic back Electromotive Force (EMF) and motor startup using microcontroller for pulse width modulation, power switch control and motor output analysis is presented which renders RPM control and high speed achievement for motor. The microcontroller is used for processor and MOSFETs are used for power circuit. Besides, the motor does not have any sensors to detect rotor position. Furthermore, the microcontroller modulates pulse width, controls power circuit and analyses motor output. The innovation in this research is that the third harmonic function is used for motor control and is compared with the Back-EMF force to recognize zero crossing. Moreover, N-type MOSFETs are used in power circuit high side and low side which are useful in the current rate of MOSFETs due to their similarities. Also, the IR2101 MOSFET drive is utilized for startup which improves the firing time of MOSFETs. Besides, using tantalum capacitors and putting resistor by the gate route of MOSFETs is efficient. Finally, experimental results are given to verify the validation of the proposed method.

A Novel Zero-Sequence Model-Based Sensorless Method for Open-Winding PMSM With Common DC Bus

This paper proposes a zero-sequence model-based sensorless control strategy for open-winding permanent-magnet synchronous machine (OW-PMSM) with common dc bus. The third harmonic back electromotive force (EMF) in zero-sequence is utilized to estimate the rotor position information. The novelty is that the third harmonic back EMF is reconstructed based on the zero-sequence model together with zero-sequence current, instead of using voltage transducer and three phase resistance network which can be eliminated from the control system. Due to the essence of back EMF, the developed method is appropriate for the applications including wind power generation and motor drives operating above certain speed. Meanwhile, the phase shift-based space vector pulse width modulation method for OW-PMSM is also presented for easier implementation to form zero voltage disturbance in zero-sequence from the inverter side and hence the corresponding influence can be consequently minimized. The torque ripple, loss, and parameter sensitivity analysis are also carried out, as confirmed by predictions of two-dimensional finite element analysis. Due to the essence of decouple, the estimation can be more robust than the conventional fundamental model-based sensorless methods. Finally, the effectiveness of the proposed method is validated experimentally on a 3-kW OW-PMSM drive system with 2.5 kg·m2 total inertia.

Influence of Third Harmonic Back EMF on Modeling and Remediation of Winding Short Circuit in a Multiphase PM Machine With FSCWs

For multiphase open-winding permanent-magnet (PM) machines, both back electromotive force (EMF) and short-circuit current (SCC) contain third harmonic components that interact with each other and produce even-harmonic torque pulsation. This paper investigates the impact of the third harmonic component on SCC prediction, torque pulsation and postfault remediation method in case of a winding short-circuit fault. Analytical modeling of SCC is developed, which shows that the third harmonic SCC increases the maximum value of SCC. It is found that the transient SCC is heavily influenced by the initial phase angle of winding axis and exciting current when the fault is incepted. The braking torque due to the negative q -axis SCC component is investigated, which peaks at low speed as winding inductive impedance goes down. The comparison of two postfault remediation methods for single-phase short-circuit faults shows the importance of considering the third harmonics of SCC and back EMF in terms of torque performance. Finally, the theoretical results of SCC, braking torque, and remediation methods are verified and evaluated with experimental results.

Sensorless control of ultrahigh-speed PM brushless motor using PLL and third harmonic back EMF

Application-specific integrated circuit (ASIC) ML4425 is often used for sensorless control of permanent-magnet (PM) brushless direct current (BLDC) motor drives. It integrates the terminal voltage of the unenergized winding that contains the back electromotive force (EMF) information and uses a phase-locked loop (PLL) to determine the proper commutation sequence for the BLDC motor. However, even without pulsewidth modulation, the terminal voltage is distorted by voltage pulses due to the freewheel diode conduction. The pulses, which appear very wide in an ultrahigh-speed (120 kr/min) drive, are also integrated by the ASIC. Consequently, the motor commutation is significantly retarded, and the drive performance is deteriorated. In this paper, it is proposed that the ASIC should integrate the third harmonic back EMF instead of the terminal voltage, such that the commutation retarding is largely reduced and the motor performance is improved. Basic principle and implementation of the new ASIC-based sensorless controller will be presented, and experimental results will be given to verify the control strategy. On the other hand, phase delay in the motor currents arises due to the influence of winding inductance, reducing the drive performance. Therefore, a novel circuit with discrete components is proposed. It also uses the integration of third harmonic back EMF and the PLL technique and provides controllable advanced commutation to the BLDC motor.

Sensorless Flux-Weakening Control of Permanent-Magnet Brushless Machines Using Third Harmonic Back EMF

The sensorless control of brushless machines by detecting the third harmonic back electromotive force is a relatively simple and potentially low-cost technique. However, its application has been reported only for brushless dc motors operating under normal commutation. In this paper, the utility of the method for the sensorless control of both brushless dc and ac motors, including operation in the flux-weakening mode, is demonstrated.