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High-frequency resonances occur frequently and severely disrupt the normal operation of high-speed railways in China. In order to suppress high-frequency resonances in traction power supply systems, a resonant harmonic elimination pulse width modulation (RHEPWM) technology was proposed. With this method, harmonics around the resonant frequency in the harmonic source were eliminated, and thus the resonance formation condition was broken and resonances were suppressed. A real-time simulation of RHEPWM application in high-speed railway system was realised in OP5600 RT-Lab simulator. The real-time simulation results show that the proposed RHEPWM strategy can achieve high-frequency resonance suppression, improve total power factor of traction drive systems, and reduce total harmonic distortion of pantograph currents.

Four-switch three-phase inverters (FSTPIs) are post-fault reconfigured topologies for a two-level inverter with failure of a power switch or a leg, and space vector pulse-width modulation (SVPWM) strategies have been used to control FSTPIs. However, different faulty legs correspond to different topologies of FSTPIs which are controlled by different SVPWM strategies; therefore, three SVPWM strategies need to be prepared for three FSTPIs, respectively, which takes up lots of memory space in the controller and increases the complexity of the control strategy. To overcome these disadvantages, a general SVPWM strategy that can be used to control three FSTPIs is proposed. Experimental results have shown the validity and feasibility of the proposed strategy.Introduction: Two-level inverters are widely applied in various areas, such as motor drives and power quality applications [1, 2]. However, once a power switch or a leg fail, the inverter will not work properly and serious problems will arise regarding the overall system. To solve the problem, two-level inverters can be reconfigured to four-switch three-phase inverters (FSTPIs) which are shown in Fig. 1 by isolating the faulty leg [2]. Space vector pulse-width modulation (SVPWM) is a popular control strategy for FSTPIs. However, there are three legs in a two-level inverter, and different isolated legs correspond to different topologies of FSTPIs, as shown in Figs. 1a-c, which are controlled by different SVPWM strategies [3-6]; therefore, three SVPWM strategies need to be prepared for the three FSTPIs, respectively, which takes up lots of memory space in the controller and increases the complexity of the control strategy. To overcome these disadvantages, this Letter introduces the concept that one of the three SVPWM strategies can be used as a general SVPWM strategy to control the three FSTPIs, because it is shown that the three SVPWM strategies are equivalent to one another, on the basis of analysing the principles of the three SVPWM strategies.

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A significant problem of three-level neutral point clamped converters is the fluctuation of the neutral point voltage. A space vector pulse width modulation (SVPWM) strategy with neutral point voltage balancing for single-phase three-level converters adopted widely in railway traction drive system is proposed in this study. The relationship between the adopted SVPWM and carrier-based pulse width modulation (CBPWM) with an offset voltage injection (OVI) is analysed in details. Theoretical analysis shows that the adopted SVPWM is a special type of CBPWM-OVI methods, and can balance the neutral point voltage effectively. The high-order harmonics of the line current distribute around twice switching frequencies while the SVPWM algorithm is adopted. These performances of the proposed SVPWM are verified by simulation and experimental tests.

This study proposes a speed estimation scheme for the sensorless-vector-controlled linear induction motor (LIM) drives for medium-low-speed maglev applications, which is composed of two parts: (i) a sliding mode model reference adaptive system observer for speed estimation; and (ii) a parallel secondary resistance online identification for achieving the improvements of the proposed speed estimation scheme performance. The sliding mode observer (SMO) is established on the basis of the state space-vector model of the LIM considering the dynamic end effect. Based on SMO, both speed and secondary resistance estimation algorithms are obtained by utilising Popov's hyperstability theory. Moreover, the Lyapunov stability theory is adopted for the stability analysis of the proposed speed estimation scheme. The effectiveness of the proposed speed estimation algorithm has been verified and compared with the performance of the conventional speed estimation scheme based on single-manifold SMO by the simulation and hardware-in-the-loop tests.