定子无铁心永磁无刷直流电机驱动拓扑设计方案及对比

Design and Comparison of Drive Topologies for Stator-Ironless Permanent Magnet Brushless DC Motor

单级三相全桥驱动拓扑无法保证力矩控制模式的定子无铁心永磁无刷直流电机在全电流指令范围内电枢电流连续。采用增加电枢回路等效电气时间常数的思路,选取Buck+半桥、全桥串联电感、Buck+全桥三种驱动拓扑,对三种驱动拓扑保证电机正常运行的条件以及不同驱动拓扑的固有属性进行理论分析、说明和对比。在基于数字控制器的三种驱动平台上,使用同一台电机进行实验验证。实验结果表明,三种驱动拓扑均能保证电机的正常运行,实测电流波形证明了关于拓扑特点的理论分析的合理性。对三种驱动拓扑实测稳态运行性能进行了详细的数学分析,为小功率无铁心永磁无刷直流电机的工程应用提供了参考依据。

The ironless permanent magnet brushless DC motor has a very short electrical time constant,and the inductance value of the armature winding is just a few tens of microhenries.When a single-stage,three-phase full-bridge drive topology is used directly to drive an ironless motor in torque control mode,the armature current may be intermittent if the bus input voltage is limited and the average phase current is minimal.The motor may not start correctly in more severe cases.Moreover,the low inductance causes abrupt fluctuations in armature current and torque.The driving characteristics must be examined to improve the motor's performance.Three drive topologies are investigated:Buck cascaded with half-bridge,single-stage full-bridge with inductors in series,and Buck cascaded with full-bridge to ensure normal operation of the ironless motor.Then,the properties of various drive topologies are discussed and contrasted.Initially,the fundamental distinctions between the three types of drive topologies are discussed.Secondly,while operating an ironless brushless DC motor in current continuous mode,the switching frequency conditions of H_PWM-L_PWM chopping mode for a single-stage full-bridge topology circuit are computed.The calculations show that when the bus voltage rises and the average armature current falls,the needed switching frequency rises to the order of GHz.The switching frequency is half when the H_PWM-L_ON chopping mode is used with all other settings maintained constant.The inductance conditions necessary for the three drives to operate in the current continuous mode can be deduced.The single-stage full-bridge topology requires an additional inductor of at least 3.75 mH per phase if the H_PWM-L_PWM control method is used,or at least 1.88 mH per phase if the H PWM-L ON control method is used when the motor is operated at 0.1 A.The power inductors needed for the Buck converters in dual-stage drives are 1.88 mH and 3.75 mH when the rear stage is a half-bridge and a full-bridge,respectively.Thirdly,the bode diagram is provided together with the transfer functions.Compared with the two-stage design,single-stage topology has a higher cutoff frequency,a bigger phase angle margin,and excellent dynamic performance.Fourthly,the same motor is driven subsequently to evaluate the design and functionality of the three drive topologies based on digital controllers.The experimental results show that all three topologies guarantee the motor's dependable running.The highest current fluctuation and current harmonics content are found in the Buck cascaded with half-bridge topology,exhibiting the quickest rate of change with rotational speed.The current fluctuation is lowest when the Buck is cascaded with a full-bridge topology.While the rate of change with rotational speed is the smallest,the fluctuation brought on by the chopping of the full-bridge cascaded with an extra-inductor is noticeable.The single-stage full-bridge's commutation time is the longest among these three topologies since it uses inductors in series in the armature circuit.At 6000 r/min in the experiment,the proportion of the commutation region to each operational section is up to 54.72%,indicating that this topology is unsuitable for high-speed operation.Due to the absence of a channel for the energy of the outgoing phase to discharge,the Buck cascaded with half-bridge topology experiences a voltage spike of 54.4 V.The conclusions are as follows.After the suitable inductor design,all three drive topologies can ensure the normal functioning of the ironless permanent magnet brushless DC motor.Buck cascaded with the three-phase half-bridge topology offers inexpensive cost,simple construction,and control,making it more appropriate for engineering applications of low drive performance.The dynamic response performance of a single-stage full-bridge with inductors in series is superior but unsuitable for high-speed applications.