DC motors are increasingly popular because of their performance advantages over ac motors for applications ranging from high-speed automation to electric motorbikes.
Three-phase ac induction motors are the most common motors in industrial application, mainly due to their simple design, low purchase cost, high reliability and wide choice of sizes and specifications. Nonetheless, for applications where speed needs to be various or torque requires for high control accuracy, brushed dc motors are popular. Under circumstances that even higher performance and/or reliability are desired, brushless dc motors overcome the disadvantages typically associated with brushed dc motors.
As well as industrial applications, brushed and brushless dc motors are also used in smaller machines and equipment where speed control is critical – such as computer hard disk drives – or in battery-powered, automotive and other applications where a dc supply is readily available. It should also be marked that brushless dc motors are sparkless and therefore do not produce ozone, which makes them suitable for use in medical applications. Compared with brushed dc motors, brushless motors have the advantage of further reducing motor noise.
Today there are several factors behind the increase in demand for dc motors. For instance, cars are being provided with more powered equipment. Besides, designers are looking to improve the performance of their designs, which often require upgrading from an ac motor to a dc motor. Particularly, coreless (ironless) dc motors have low inertia so are useful and require high accelerations. Interest in alternative energy sources often leads to a high-efficiency dc motor being used for the final drive.
Giving an example, the prototype ENV motorbike from Intelligent Energy features a fuel cell that generates electrical energy from hydrogen and oxygen. In order to take full advantage of the limited supply of electrical energy, the bicycle is equipped with a highly efficient Lynch axial-gap dc motor. The other two motors can be coupled together to drive a single output shaft, hence increasing the available power. Illustrated by the motors’ capability, the LEM 130 model 95s has a rated power of 3.02kW, rated torque of 4.35Nm and rated speed of 6624rpm. Peak efficiency is 87 per cent. For more demanding applications, the LEM 200 model D135 is with a rated power of 14.39kW, rated torque of 36.4Nm and rated speed of 3780rpm. The motor has peak efficiency of 90 per cent.