Design and research of deep slot universal motor for electric power tools
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ORIGINAL ARTICLE
Design and research of deep slot universal motor for electric power tools Huang Qi1 · Luo Ling1 · Cao Jichao2 · Xi Wei2 Received: 5 May 2020 / Revised: 26 July 2020 / Accepted: 1 August 2020 © The Korean Institute of Power Electronics 2020
Abstract In this paper, a deep slot universal motor is designed for electric power tools. The deep slot structure can reduce the cost of universal motor materials and improve production efficiency. A mathematical model of a universal motor is established and a simulation model is established by MagNet finite element software. Then, the static magnetic field distribution and load characteristics of the deep slot universal motor are analyzed. Different methods are adopted to improve the commutation spark of a deep slot universal motor. Finally, three 550-W and 9500-rpm prototype motors are tested. Simulation and experimental results indicate that an uneven air gap, brush offset by a certain angle, as well as different turns of the lead coil and the lag coil can effectively improve the commutation spark of a deep slot universal motor. Keywords Universal motor · Deep slot · Brush · Commutation sparks · Uneven air gap
1 Introduction Universal motors can be used in both AC and DC power [1]. The excitation winding and the armature winding are connected in series by brushes and a commutator. Then they are connected to a single-phase ac power supply. There are two parallel branches after the current flows from the excitation winding to the armature winding. Both the excitation current and the armature current change directions at the same time. The direction of the motor’s torque and speed is constant. A small power universal motor uses a pair of poles and the brush is placed on a neutral line of a commutator to generate the maximum torque [2]. Although universal motors are not as efficient, accurate or long-living as permanent magnet motors, universal motors are simple in structure, low in cost and suitable for short-time with large-torque operations [3, 4]. Universal motors also have the characteristics of high speed, small size and high starting torque, and they are widely used in power tools, household appliances, small machine tools and medical equipment [5]. * Huang Qi [email protected] 1
School of Automation, Northwestern Polytechnical University, Xi’an, China
National Engineering Research Center for Small and Special Precision Motors, Guiyang, China
2
The sales of power tools around the world are growing at a rate of almost 5% a year, and sales of household appliances are growing at an even higher rate. The annual sales of universal motors are more than 200 million units. Thus, the design of low-cost motors suitable for mass production is very important (Fig. 1). With the development of computer technology, motor CAD is becoming more widely used, which greatly reduces the workloads of designers. At the same time, finite element analysis software can help designers perform electromagnetic calculations and simulate motors operation performance more accur
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