Efficiency Analysis of BLDC Motor with Delta Connection According to Magnitude of Circulating Current

Abstract

In a delta connection, most of the battery voltage is applied directly to the motor’s phase terminals, resulting in a voltage that is root three times higher than in a wye connection. This characteristic makes delta connections suitable for low-voltage, high-speed systems. However, the presence of 3 n-th harmonic components in the phase back electromotive force (BEMF) of delta-connected motors can induce circulating currents that flow exclusively within the circuit. These circulating currents lead to additional Joule losses and degrade motor performance. This article analyzes the effect of circulating currents on motor efficiency according to different speeds and torques. The presented study models maintain a similar magnitude of the fundamental component of BEMF but differ in the magnitude of the third harmonic component. A six-step circuit was established to compare the currents, losses, and efficiencies of the study models using finite element analysis (FEA). The copper losses were categorized into those caused by the fundamental component of phase current and those caused by the circulating currents. Subsequently, the efficiencies of the study models were compared across different speed and torque ranges, accounting for the separated copper loss components and iron losses. The results show that the improved model achieves an efficiency that is more than 18% higher than that of the basic model in the low-speed and low-torque areas. Finally, the study models were manufactured and evaluated through testing.