Electronic Nonlinearity of Full-Bridge PWM Inverter for Zero-Power PEMS System

Abstract

The permanent-electro magnetic suspension (PEMS) technology takes advantage of the attractive magnetic force between the magnet and the iron core and reduces the power consumption eventually to zero. However, the active current in the electromagnet of the zero-power PEMS system fluctuates around zero due to external disturbances and suffers from the electronic nonlinearity of the driving circuit, such as the full-bridge pulse-width-modulation (PWM) inverter. This work presents that the 2 μs turn-off delay (one electronic defect) of the integrated circuit L298N (one commercial full-bridge PWM inverter produced by STMicroelectronics) leads to the nonlinear current-duty cycle characteristic, which undermines the control stability and limits the PWM frequency of the zero-power PEMS system. Moreover, the nonlinear mechanism is experimentally and theoretically analyzed for the critical PWM frequency and the sensitivity transition with respect to the 2 μs turn-off delay. Besides, the critical PWM frequency is of great significance for the energy efficiency and the dynamic performance of the high-speed PEMS transportation system.

Close-Loop Current Control With Current-Sensing Resistor for Electromagnet Driven by Full-Bridge PWM Inverter

“…As reported in the previous work [10], Fig. 1 shows the circuit of the L298N full-bridge PWM inverter that is controlled by the PWM signal.…”

“…Equation ( 3) indicates that 𝑈 𝑀 and 𝑈 𝑁 may potentially fluctuate between 0 V and 𝑈 if 𝑅 𝑙𝑒𝑓𝑡 = 0 or 𝑅 𝑟𝑖𝑔ℎ𝑡 = 0 [10]. In order to minimize the voltage fluctuation of 𝑈 𝑀 and 𝑈 𝑁 , the electromagnet is separated into two equal halves, i.e., 𝑅 𝑙𝑒𝑓𝑡 = 𝑅 𝑟𝑖𝑔ℎ𝑡 ≫ 𝑅 𝑐𝑢𝑟𝑟 and 𝐿 𝑙𝑒𝑓𝑡 = 𝐿 𝑟𝑖𝑔ℎ𝑡 , so that we can derive 𝑈 𝑀 and 𝑈 𝑁 by symmetry,…”

“…• When the current signal is lower than the associated setpoint, i.e., 𝑈 𝑄 < 𝑈 𝑆 , 𝑈 𝐵𝐵 ′ will decrease by (10), 𝐷 will increase by (12), 𝑖 𝑀𝑁 will increase by (3), which results in the increase of 𝑈 𝑄 by (9). Therefore, the proposed approach can stabilize the current signal at the associated setpoint, i.e., 𝑈 𝑄 ≈ 𝑈 𝑆 .…”

“…Since 𝑓 𝑃𝑊𝑀 = 10 kHz , the high-frequency switching of L298N results in ripples on 𝑈 𝑃 [10,20]. Fig.…”

“…The current through the electromagnet plays an important role [8] in the robustness of AMB [9] and PEMS [4,8]. However, the electromagnet possesses a large inductance that leads to the large time constant; besides, the tiny turn-off delay of the full-bridge PWM inverter results in the nonlinear current-duty cycle characteristic around the zero current [10]. Both the large time constant and the current-duty cycle nonlinearity challenge the timely and accurate control on the current through the electromagnet [11].…”