Since the power capacity needed for the propulsion of large ships is very large, a multiphase AC induction propulsion mode is generally adopted to meet the higher requirements of reliability, redundancy and maintainability. This paper gives a detailed description of the development of a 20MW fifteen-phase PWM driver for advanced fifteen-phase propulsion induction motors with a special third-harmonic injection in terms of the main circuit hardware, control system design, experiments, etc. The adoption of the modular design method for the main circuit hardware design can make the enclosed mechanical structure simple and maintainable. It can also avoid the larger switch stresses caused by the multiple turn on of the IGBTs in conventional large-capacity converter systems. The use of the distributed controller design method based on a high-speed fiber-optic ring net for the control system can overcome such disadvantages as the poor reliability and long maintenance times arising from the conventional centralized controller which is designed according to point-to-point communication. Finally, the performance of the 20MW PWM driver is verified by experimentation on a new fifteen-phase induction propulsion motor.
Planetary reducer box undertakes the vibration transmitted from gear transmission system to bearing, and further transmits the vibration to the base. Research on the transmission path contribution of reducer box has an important guiding role in reducing vibration. This paper first analyzed the contribution of each vibration path of the gearbox based on the velocity intervention loss, so as to identify the main transmission path of the gearbox vibration; then the vibration test of the gearbox is carried out to verify the correctness of the transmission path model. The results show that the vibration transmission path of the right bearing of the gearbox is the main transmission path, and the established vibration transmission path dynamics model of the gearbox can well reveal the contribution law of the vibration transmission path of the gearbox.
Abstract.One of the main problems of the Modular Multilevel Converter (MMC) for ship electric propulsion applications is the significant magnitude of capacitor voltage ripple at low speed operation. The commonly used solution is harmonic injection. In this paper, the injection rules are explored through the dynamic relationship of MMC in a comprehensive way, and the harmonic characteristics of injection current are derived. Furthermore, the circulating current controller is modified according to the harmonics of injected current with changing frequency, which reduces the ripple of capacitor voltage effectively in a wide speed range. Simulation results are shown to demonstrate the effectiveness of the proposed method. IntroductionThe Modular Multilevel Converter (MMC) has been widely used in the field of high voltage direct current (HVDC) transmission [1,2], and has attracted increasing attention for the application of medium-voltage adjustable-speed motor drive [3,4,5]. The great potential of MMC for ship electric propulsion has been mentioned in [6]. The main challenge of the application of MMC-based drive system is the suppression of capacitor voltage ripple at low speed operation.In order to suppress the voltage ripples of submodule (SM) capacitor which increase significantly as the output frequency decreases, several schemes have been adopted. Harmonic injection is the most mature method at present. The values of injected components are usually derived from MMC's arm energy relations. Several components are neglected in the derivation process which make the derivation result lack of comprehensiveness.The injected circulating current is regulated by the circulating current controller which also controls the even harmonics caused by MMC's mechanism. The performance of the circulating current controller is related to the control accuracy of the injected current. Many control strategies have been used in the design of current controller, such as repetitive control [7], model predictive control [8], and multiple quasi-resonant control [9], but they are only designed to regulate the even harmonics at the rated frequency. Meanwhile some other literatures like [10], [11] put emphasis on the control of the injected current but neglect the even harmonics which needs to be regulated at the same time. In [12], the current controller contains six resonant controllers to regulate the second harmonic and injected harmonics at low speed operation, but it is not suitable with the changing frequency.In this paper, the injection rules are explored through the relations of mathematical model, and the proposed formula of harmonic injection is derived from the rules. The circulating current controller is
After active neutral point clamped(ANPC) adopts SiC-MOSFETs, SiC-MOSFETs are easily damaged due to the excessive peak voltage. This paper establishes a single-phase parasitic inductance model of ANPC based on the SiC-MOSFET half-bridge modules. Then, based on this model, the cause of peak voltage on SiC-MOSFETs during ANPC commutation is analyzed. Finally, a short-loop commutation modulation strategy is proposed under the full working conditions of ANPC. The modulation strategy considers the influence of modulation carriers selection and dead time on ANPC commutation and optimizes the ANPC commutation loop to suppress the overvoltage on SiC-MOSFETs during ANPC commutation.
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