Investigation of the influence of the number of poles on the external characteristic of a brushless DC machine in the generator mode

The article presents the results of a study on the generator mode of operation of a brushless DC machine (BLDC) when operating under active load. For analysis, two models were created with the number of permanent magnets on the rotor differing by a factor of two. The relevance of the research is due to the wide range of applications of BLDC in various fields. One of the key advantages of BLDC is the absence of a brush-commutator unit, which is replaced by a controller with semiconductor elements. This increases the reliability of BLDC and expands the range of operating modes. The main objective of this study is to determine the impact of the number of permanent magnets on the external characteristic of BLDC in generator mode. To achieve this goal, computer modeling was performed using ANSYS Maxwell software. This software is designed to study and calculate the magnetic field pattern using the finite element method in electromechanical devices, providing accurate results for analysis. For each BLDC model, the degree of saturation of the magnetic system elements was determined, and graphs of voltage, current, and braking torque at the generator shaft over time were obtained. Analysis of the calculation results for BLDC models with 46 and 92 permanent magnets demonstrated an impact on the voltage and current waveforms, leading to some slight distortion of their shape. The obtained calculation results allowed determining the efficiency and constructing the external characteristic for both BLDC models. Higher efficiency was obtained for the BLDC model with 92 permanent magnets on the rotor. The external characteristic for the generator mode of BLDC operation demonstrated a change in voltage when transitioning from idle to nominal current operation within the range of 15% and 21%, indicating the stiffness of the characteristic. The conclusions of the study indicate the potential for improving the efficiency of BLDC through optimization of the magnetic system design and cooling conditions, and can be useful for engineers and developers of electromechanical systems aiming to improve the performance of their products.