There is a certain amount of current harmonics in interior permanent magnet synchronous motor. In order to accurately control the current harmonic, this article focuses on three aspects: establishing current harmonic calculation model, extracting current harmonic, and designing current harmonic regulator. A current harmonic calculation model, which considers the effect of voltage harmonics induced by current controllers and digital control delay on the initial phase angle of voltage harmonics, is established for the first time. With the help of multiple synchronous rotating frame transformation, a current harmonic extraction method more suitable for motor drive field, which aims to extract the current harmonic characteristics of d -axis and q -axis currents, is proposed. On this basis, the controlled quantity and control quantity are unified in d–q coordinate frame for analyzing the coupling relationship of current harmonic characteristics. And then a PI current harmonic regulator, including current harmonic decoupling and voltage harmonic initial phase angle compensation, is constructed, so as to realize the effective control of current harmonics. Finally, the effectiveness and superiority of the proposed method are verified by simulation and experiments.

A method of current reference setting for interior permanent magnet synchronous motor based on virtual constant signal injection is proposed. Unlike traditional methods, the partial derivative of torque to d-aixs, q-axis currents is obtained by injecting a virtual constant signal into d-axis, q-axis currents, then the derivative of torque to current angle is obtained through the full differential equation. A scheme of current reference setting, which is applicable to constant torque region and flux-weakening region, is established by means of the derivative information. The difference between the voltage output by the current controller and the actual voltage applied to the motor is also analyzed. Filters that are essential in the virtual sinusoidal signal injection scheme are avoided. Moreover, the acquisition of partial derivative information avoids the influence of neglecting high-order partial derivative term from which the method of injecting virtual square wave signal along the current angle suffers. This method not only realizes maximum torque per ampere control, accurately, but also guarantees the speed range of constant torque region by the setting of q-axis current reference, which is parameter independent. Meanwhile, the torque output capacity is assured in the flux-weakening region. Finally, the proposed method is verified by experiments.

The variable dc-link voltage control methods can effectively improve the operation efficiency of the permanent magnet synchronous motor (PMSM) drive system. At present, the reported variable dc-link voltage control methods applied in the PMSM driven by a quasi-Z-source inverter (qZSI) are limited to the analytical calculation methods (ACMs) based on the system model. The ACMs demand measurement of qZSI's input voltage and usually need a larger margin index due to the inaccurate model to calculate the reference dc-link voltage. To overcome the restriction, this article proposes a novel variable dc-link voltage control method that can indirectly adjust the dc-link voltage with an extra proportional-integral (PI) regulator. Basic principle of the method is introduced and two design rules of the PI regulator are illustrated. Besides, necessary conditions that need to be met when obtaining the feedback signal of the PI regulator are analyzed. Finally, experiments are performed to validate the feasibility and effectiveness of the proposed method. In comparison with the ACMs, the proposed method gets rid of the dependence on an extra voltage sensor to measure the input voltage and can reserve less margin for the dc-link voltage, which contributes to less cost and higher efficiency of the drive system. Besides, the proposed method is easy and convenient to apply.

Rolling bearings are key components that support the rotation of motor shafts, operating with a quite high failure rate among all the motor components. Early bearing fault diagnosis has great significance to the operation security of motors. The main contribution of this paper is to illustrate Gaussian white noise in bearing vibration signals seriously masks the weak fault characteristics in the diagnosis based on the Teager–Kaiser energy operator envelope, and to propose improved TKEO taking both accuracy and calculation speed into account. Improved TKEO can attenuate noise in consideration of computational efficiency while preserving information about the possible fault. The proposed method can be characterized as follows: a series of band-pass filters were set up to extract several component signals from the original vibration signals; then a denoised target signal including fault information was reconstructed by weighted summation of these component signals; finally, the Fourier spectrum of TKEO energy of the resulting target signal was used for bearing fault diagnosis. The improved TKEO was applied to a vibration signal dataset of run-to-failure rolling bearings and compared with two advanced diagnosis methods. The experimental results verify the effectiveness and superiority of the proposed method in early bearing fault detection.

The fast and stable inner current loop in the permanent magnet synchronous motor control system is the key factor that ensures the torque control performance of the motor. The deadbeat predictive current control has good dynamic response performance, but it depends heavily on the precise mathematical model of the controlled object. The parameter mismatch will degrade the control performance. A deadbeat predictive current control method based on online parameter identification is proposed in this study. This method does not need to inject additional d ‐axis current to identify the parameters during the operation of the motor; it only needs to make full use of the inherent phenomenon that the q ‐axis current changes when the load of the motor changes during operation, and perform parameter identification. Aiming at the problem that the effect of parameter identification is easily affected by motor speed, a new variable step‐size neural network algorithm is designed in this study. The speed factor is introduced into step function to ensure the performance of the identification algorithm at a different speed. Finally, based on the new online parameter identification algorithm, the deadbeat predictive current control method is used to verify the experiment.

Compared with other topologies, the modular multilevel converter (MMC) has the advantages of higher scalability and lower harmonic distortion. When carrier-based pulse-width modulation approaches are used for the MMC, the number of carriers increases for more sub-modules, and the complexity of the control and the memory required increases as a result. In addition, the synchronization of several carriers is another issue. Due to the unique constructional characteristics of the MMC, circulating currents will be generated internally, causing distortions in the arm currents and, thus, unnecessary converter losses. In this paper, an improved 2N+1 pulse-width modulation approach with low control complexity and a circulating current suppression strategy are proposed. Firstly, the conventional carrier phase-shifted 2N+1 pulse-width modulation approach is improved so that the number of carrier signals adopted in each arm is always two. Secondly, the redundant switching states are used to suppress the circulating current. Finally, the effectiveness of the proposed strategy is verified experimentally. The results show that the proposed method reduces the control complexity while retaining the output performance. Meanwhile, the circulating current can be suppressed.