Sustainable Development Goals
Abstract/Objectives
This thesis discusses the development of a network-enabled permanent magnet synchronous motor (PMSM) drive system for an electric scooter. A bidirectional DC-DC single-arm interface converter is used to connect the battery and supercapacitor to the DC link of the motor drive system, which can improve the driving performance of the motor in a wide range of speeds. The proposed current management strategy ensures steady allocation of battery and supercapacitor currents, increasing mixed energy conversion efficiency. Design details of the motor drive system are discussed, including rotor position and commutation current sensing, frequency converter commutation shift, space vector modulation switching, current control, and external motion control. A dynamic braking arm is also included to prevent overvoltage due to regenerative braking failure. A power level of the battery and supercapacitor with a bidirectional DC-DC converter, dynamic mode, and coordination control is also described, and experimental results test the operation performance of the system with variable DC-linked voltage. Finally, a charging system using a single-phase boost-switching rectifier is discussed, and good charging performance with power factor correction is achieved.
Results/Contributions

This thesis develops an electric scooter (E-scooter) permanent-magnet synchro- nous motor (PMSM) drive with grid connected function. Both the battery and super-capacitor (SC) are connected to the motor drive DC-link through a bidirec- tional DC-DC one-leg interface conver- ter, respectively. The boosted and vari- able DC-link voltage can be established to improve the motor driving perfor- mance over wide speed range. In addi- tion, the power type energy storage device, SC, can assist the battery in quick discharging and charging operations. With the proposed current management strategy, the currents of the battery and the SC can be smoothly distributed to improve the hybrid energy conversion performance.

First, the fixed DC-link voltage fed surface-mounted PMSM (SPMSM) drive is designed and implemented. The pro- perly treated affairs include: (i) necessary rotor position and armature current sen- sing schemes; (ii) inverter commutation scheme; (iii) space-vector pulse-width modulation switching scheme; and (iv) current control scheme. As to the outer motion control schemes, both the speed and torque control modes are arranged with their properly designed controllers. Additionally, a dynamic brake leg is added at the DC-link to prevent the over-voltage due to the failure of regenerative braking.

Next, the battery and SC power stages are constructed, including their interface  DC-DC converters, dynamic modeling and control schemes. The coordinated control for the two energy storage devices is made. And the battery/SC powered E-scooter motor drive with varied voltage DC-link is evaluated experimentally.

Finally in idle mode, the isolated grid-to-vehicle (G2V) charging operation is performed. The power circuit includes a single-phase boost switch-mode rectifier (SMR) formed by the embedded compo- nents of the SPMSM drive, an isolated half-bridge CLLC (HBCLLC) resonant converter, and the battery with its inter- face converter. Good charging perfor- mance with isolation and power factor correct (PFC) function from the mains is achieved.

Keywords
E-scooterPMSMcontrolbatterysuper-capacitorCLLC resonant converterswitch-mode rectifiergrid-to-vehicle operation