Heya Yang

Study on inverter-fed three-pole active magnetic bearing

The most popular active magnetic bearing (AMB) system has four magnetic pole-pairs. In general, the sensors and the power amplifiers account for the major portion of the cost, and fewer power amplifiers are used for the AMB with fewer magnetic poles. Therefore some researchers proposed the three-pole AMB, and presented two control configurations. Herein the inverter-fed three-pole AMB was further studied. A linear analytical model considering the air gap eccentricity was presented. In this model, the force in the x and y direction are uncoupled and they could be divided into the controlled levitation force, the unilateral magnetic force and the bias force. Its accuracy was verified by the simulation results of Maxwell 2D based on finite element method. Owing to the decoupled analytical model, the traditional PID control method could be used in the three-pole AMB. The inverter-fed three-pole AMB control system with displacement control in the outer loop and hysteresis current control in the inner loop was proposed. Based on the simulator coupling technology, the simulation results of software SIMPLORER verify the performance of the control method.

Comprehensive analysis on carrier-based PWM modulations for advanced composited clamping five-level converter

In order to reduce the total harmonic distortion (THD) of the line-to-line voltage and simplify the circuit structure, an advanced five-level modular multilevel-clamped composited multilevel converter (5L-M-MC2) is proposed [1]. A comprehensive analysis of the level degradation on carrier-based PWM modulation in the 5L-M-MC2 system is analyzed in detail in this paper. The line-to-line voltage levels degrade when the modulation index decreases from 1 to 0. The differences of the degradation in the three classic Carriers Disposition PWM modulation methods are pointed out. Their level degradation points are explored to give a better understanding on this advanced 5L-M-MC2. Finally, the experimental results of three Carriers Disposition PWM modulations are exhibited to verify the validity of the main contributions in this paper.

An equivalent power test scheme for modular multilevel converters (MMCs)

For modular multilevel converters (MMCs), it is important to investigate the electromagnetic and electrothermal performance of sub-modules for design validation and optimization. This paper presents an equivalent test scheme for sub-modules, which has the clear advantages of system simplicity and reduced facility requirements. Firstly, the detailed analysis on the output features of sub-modules demonstrates that submodules working in a real MMC system can be equivalent to a controlled voltage source, which consists of two independent components, the dc and ac components, respectively. Furthermore, the test circuit composed of two identical sub-modules is introduced and the corresponding control strategy is further designed to ensure the equivalence of the test scheme presented. Finally, the simulation and experiment results reveal that the sub-module behaviors under different operating conditions of MMC can be closely emulated with the proposed test scheme, which provides a convenient way to evaluate the reliability of sub-modules.

Average-value model of modular multilevel converters considering capacitor voltage

The average-value model (AVM) of the modular multilevel converters (MMCs) is the simplified one for the average response of switching devices, converters and control. The effect of sub-module capacitor voltage ripple on the MMC dynamic behavior is explored and an accurate average-value model of MMCs is established. Based on the proposed AVM, the equivalent impedances of the DC and AC sides in the MMC converters can be easily extracted and evaluated. Furthermore, the detailed interaction of the AC side voltages/currents and arm voltages and the coupling relationship of AC output current id and iq can be also precisely described by the introduced AVM. The effectiveness of the presented model on the MMC dynamic performance analysis is verified by the simulation.

Phase shift controlled modular DC/DC converter with input voltage auto balance ability

A novel phase shift controlled modular DC/DC converter is proposed in this paper by integrating the full-bridge converters and three-level flying-capacitor circuit. Due to the series connection of the full-bridge modules, the high switch voltage stress in the primary side is effectively reduced. Therefore, the low-voltage rated power devices can be employed to obtain the benefits of low conduction losses. Moreover, the voltage auto-balance ability among the modules is achieved by the inherent flying capacitor, which removes the additional possible active components or control loops. In additional, zero-voltage-switching (ZVS) performance for all the active switches can be provided by the phase shift control scheme, which can reduce the switching losses. The circuit operation and converter performance are analyzed in detail. Finally, the performance of the presented converter is verified by the simulation and experimental results from a 2kW prototype.