Conditions for Controlling Brushless DC Machines
Conditions for Controlling Brushless DC Machines
Mar 11, 2019

Brushless DC motor AC servo system is developing rapidly because of its small inertia, large output torque, simple control and good dynamic response. It has broad application prospects. In the field of high performance and high precision servo drive, it will gradually replace the traditional DC servo system. However, the torque ripple still exists in BLDC, which can not achieve more position control and higher performance speed control. Phase current commutation is one of the main reasons for torque ripple.

In AC servo system with non-commutating phase current feedback, low-speed commutating torque ripple can be controlled, but it can not be controlled in high-speed situation, non-commutating phase current is uncontrollable. Therefore, it is necessary to find an optimized commutation scheme to achieve better commutation torque performance.

The effective switching state of the inverter in the commutation process should be selected according to the rules.

Rule 1: Follow the current rotor position, that is, turn off the corresponding switch should disappear, and the corresponding switch should be established.

Rule 2: under Rule 1, single and bipolar controls can be used.

Rule 3: allow the corresponding switch delay to be switched off.

The merits and faults of switch control strategy under commutation state are evaluated by the following two indexes:

1. torque pulsation caused by commutation is as small as possible (non commutation current pulsation as small as possible).

2. shorten the commutation time as far as possible.

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