Introduction of switching devices in DC brushless motor drive system
Introduction of switching devices in DC brushless motor drive system. From the analysis of the working principle of DC brushless motor, the requirements for its power switching devices are as follows: 1.
Meet the requirements of system voltage, current and current value, and have a certain margin; 2.
The conduction voltage drop and leakage current after shutdown are as much as possible to reduce system loss; 3. Sufficient safe working area 4.
The switching speed as high as possible and the switching loss as low as possible; 5. As small as possible driving efficiency 6.
The driving circuit is as simple as possible, so that the cost of the light tube and the driving circuit is as high as possible.
In this speed regulation system, the power device of DC brushless motor works in the hard switching mode, and the switching frequency is relatively high, so full control power switching device should be selected.
Common power switching devices include GTR, GTO, power MOSFET, IGBT, etc. They differ greatly in withstand voltage, capacity, switching speed, etc.
MOSFET has the characteristics of high-speed light opening, gate voltage control and no secondary breakdown. However, when common MOSFET works at high voltage and high current, the on-resistance is relatively large, the device generates heat seriously, and the output power decreases, therefore, the capacity of a single MOSFET is relatively low, so it is mainly used in low power occasions.
Bipolar high-power transistors have small resistance when large current is on, but DC brushless motors require larger driving power because they are current-driven devices, and their switching speed is not as good as MOSFET.
IGBT is a new type of composite field control device that integrates MOSFET voltage control with the characteristics of high current and low on resistance of bipolar high power transistors, at the same time, it also maintains the characteristics of high speed, low switching loss and insensitivity to temperature.
The maximum output current of IGBT controlled by chip with the same area can be increased by more than 2 times compared with the output current of MOSFET.
In order to meet the requirements of power off devices above the DC brushless motor, and according to the system withstand voltage of 220 V, the rated current of the motor is 7.
57A, switching frequency 50/60HZ requirement, select composite power switch distance Ah IXGH332N60C, internal without freewheeling diode.
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