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Abstract. An electronic commutator that can drive a PM BLDC motor either in the full bridge or half bridge configuration has been developed. This commutator allows increasing the motor speed over the nominal value, hence the motor is able to operate within a wide constant power speed range. An application of the commutator with a reconfigurable structure for the double drive of a small electric vehicle Elipsa has been presented. The driveline consists of two independent commutators feeding the motors coupled by gears with rear wheels of the vehicle. Both commutators are controlled by a common control system based on a signal microcontroller. The results of road tests indicate new areas of BLCD motor drives application. The fact that the BLCD motor work in the second speed range does not require any changes in the motor construction and at the same time does not significantly deteriorate the drive efficiency is an indisputable advantage of the presented solution.

In practice we often meet with electrical drives, where it is necessary to operate with higher speed, while load torque is less than rated torque. This type of operation is called "constant power operation" and may be defined as second range of natural motor torque-speed characteristic. In case of motors excited with permanent magnets magnetic flux is constant, and while supply voltage remains constant, motor speed is also (approximately) kept constant. In practice, different solutions are attempted in order to achieve increased rotating speed of brushless motors at decreased torque. One of the methods, which make possible PM BLDC motor operation at increased speed and decreased torque, is use of electronic commutator with switchable bridge-half-bridge structure. The investigation presented in the paper has been aimed at estimation of losses and efficiency in the drive consisting of brushless motor operating with variable structure commutator. Results of theoretical analysis, computer simulations and laboratory tests have shown that application of electronic variable structure commutator, which makes possible operation in the second speed range without increasing motor power and supply source power, causes an insignificant decrease in overall drive efficiency.