This thesis is concerned with the speed control of a brushless DC (BLDC) fan motor by switching its coil currents. Because fans are the most common cooling devices for computers, the demand for a quit and efficient fan that is capable of automatically regulating its speed according to temperature grows with each passing day. A mixed linear and switching control scheme which consists of two loop of feedback compensation for a two-phase BLDC fan motor is presented. Roughly speaking, the linear outer loop is mainly for speed regulation, and the inner loop is to generate a switching control signal while doing plant compensation. This control structure is simple and effective, emphasizing on low power consumption, accurate velocity regulation and low switching noise. The performance and stability requirement can be easily met by tuning several positive coefficients in the controller. The experiment shows an average steady-state regulation error of 0.563% in the range of fan¡¦s speed from 1050 to 2231 r.p.m.

The design and implementation of speed control driver which is applied to three-phase brushless DC fan motor are presented in this thesis. In the back-EMF detection circuit, we use digital filter circuits to obtain commutation to overcome the switch noises which are generated by high frequency PWM, without using traditional capacitor filter circuits which need more volume for additional external capacitor. Because the problems of high frequency magnetizing vibration and dispensable power consumption are generated by open-loop fixed frequency PWM speed control approach, closed-loop speed feedback control methods and closed-loop current feedback control methods are adopted to achieve high efficiency and low vibration of the fan motor drivers.

The design and implementation of speed control driver, which is applied to two-phase brushless DC fan motor is presented in this thesis. In addition, motor coils current limiter, output-stage Snubber circuit, and lock detection and auto-restart circuit are added to the driver for the sake of increasing stability and robustness. Because of high frequency energizing noise and dispensable power consumption problems generated by open-loop fixed frequency PWM speed control approach, several closed-loop speed control methods with speed estimation signal feedback are adopted for improvement. Furthermore, this thesis proposes a sensorless driving control strategy to eliminate Hall sensor in rotor position detection, and similarly has closed-loop speed control methods to achieve the goal of driver cost reduction, size decrease, and good control performance.

Möjligheter att reducera vikten på en hydraulmotor, som tillverkas på Parker Hannifin AB i Trollhättan, har studerats. Målet med arbetet var att ge förslag på hur motorn kan göras lättare för att nå det framtida målet att erbjuda kunder en lättviktsmotor (LWM) lämpad som fläktmotor. För att identifiera komponenterna och deras vikter vägdes alla delar var för sig. Värdena visade att trumhus, lagerhus, axel och lagerpaket stod för ca 75 % av motorns totala vikt. Arbetet koncentrerades därför på att reducera vikten på dessa delar. Flera koncept togs fram med lägre vikt och bibehållen prestanda. Vissa delar kontrollerades mot hållfasthet med handberäkningar och FEM-analyser. Enligt beräkningarna finns möjlighet att reducera vikten med 45 %. Om hydraulmotorn konstrueras enligt koncepten, bör det framtida målet kunna nås, till-verkning av en lättviktsmotor som är betydligt lättare än dagens hydraulmotor. / The weight reducing possibilities for a hydraulic motor, produced by Parker Hannifin AB in Trollhättan, have been investigated. The goal was to provide suggestions for weight optimization to offer customers a light weight motor (LWM) that is well suited as a fan motor. The mass of each part was determined and their functions were identified. The result showed that the housings, shaft and bearings represented 75% of the motor’s total mass. The work was thus concentrated to these parts. Multiple suggestions were generated where weight and performance were taken into consideration. Some parts were analyzed with the aid of FEA-software and hand calculations. The result indicates that a weight reduction of 45% is possible. If the hydraulic motor is redesigned according to the concepts, the goal of a light weight motor can be achieved.

This thesis is about the improved design of small size brushless DC fan motor driving circuit. Two main improvements in the new design are increase the stability and decrease the size of motor fan at the same time. To improve the stability, there are two major parts added to the original driving circuit. The delay circuit that protects the H-bridge and the output low current limit circuit. Furthermore, it is believed that the speed control also can improve the stability. With regard to the rotation speed control, two circuits are attached to the motor, 1) speed feedback controller and 2) speed and current feedback controller. Both controllers are attached in the close loop rotation speed control circuit. They are used to increase the efficiency of drive circuit. In order to make the circuit more efficient, they solve problems such as disturbance in miscellaneous noise; also the power dissipation that occurs in open loop rotation speed control circuit. The second improvement in the new design is to reduce the cost and size of system. The design of sensorless control scheme is proposed to replace the Hall sensor to detect rotor position. This sensorless scheme can also supply fan motor voltage to achieve the speed control.