Chuanjing Hou

The reduced switch count three-level inverter (RSC TLI) can reduce the number of power switches, but the conventional space vector modulation (SVM) method generates the large dc-link current ripple and reduces the dc-link capacitor reliability. This article proposes a novel dc-link current ripple reduction method, which is applicable to both balanced and unbalanced neutral-point (NP) voltage (NPV) conditions. Firstly, the duty cycles calculation of the conventional SVM method is introduced. To realize the dc-link current ripple reduction, the region division method is optimized by analyzing the range of the duty cycle distribution factor and combining the magnitude of output current. Doing so, the calculating complexity of duty cycles is reduced. Secondly, a deadbeat control method is designed for accurate and fast separate control of capacitor voltages. At last, appropriate switching sequences are arranged. Compared with the conventional SVM method, the dc-link current ripple of the proposed method is reduced by one-fourth and two-fifths in the high and low modulation indices, respectively, and maintains the rewarding quality of output currents with balanced and unbalanced NPVs. The feasibility and effectiveness of the proposed method are verified by simulations and experiments.

Tower cranes are typical underactuated systems, characterized by high-state coupling and lack of available control inputs, resulting in major challenges for the dynamics analysis. A dynamic model of tower cranes without simplifications is established, where the nonlinearities, unknown frictions, and wind disturbances are emphatically considered. Based on the developed model, an adaptive robust sliding mode control (ARSMC) scheme is proposed, which can achieve accurate payload positioning and sufficient swings suppression, even in the presence of unknown frictions and wind disturbances. Specifically, a sliding mode surface and a suppression function are designed to eliminate payload swings; a sliding mode convergence law is constructed to alleviate the chattering problem; the robustness of the controller is enhanced by designing an estimation strategy of wind disturbances; an effective parameter estimation is presented to improve the adaptive ability of unknown parameters. The stability of the closed-loop system is proved by utilizing the Lyapunov technique and LaSalle’s invariance principle. Finally, the effectiveness of the tower crane model and the superiority of the ARSMC are verified by multiple comparative simulations.

The impedance-source (IS) three-level inverter has been put forward to implement buck-boost operation and obtain multi-level output waveforms. The virtual space vector modulation (VSVM) can balance the neutral-point voltage (NPV) in full power factors and modulation indices. This article further proposes a fast-processing implementation method of VSVM for IS three-level inverter. According to the relationship of three-phase modulation waves, a proper differential-mode voltage injection scheme is developed to control the NPV balance actively. In order to boost the dc input voltage, the maximum and minimum modulation waves are further moved upwards and downwards, and the shoot-through (ST) states are properly generated without affecting the normal ac output voltage. Doing so, the VSVM strategy for IS three-level inverter is simply implemented by carrier-based modulation (CBM) approach. The effectiveness of the proposed method is verified by experiments.