Brushless DC motor is a new type of motor which develops rapidly and is widely used with power electronics technology and high-performance permanent magnet materials. Brushless DC motor not only maintains the good dynamic and static speed regulation characteristics of traditional DC motor, but also has the advantages of simple structure, reliable operation, easy control, convenient maintenance and long service life. Its application has developed rapidly from the initial military industry to the fields of aerospace, medical treatment, information, home appliances and industrial automation. Brushless DC motor does not specifically refer to DC motor with electronic commutation, but generally refers to electronic commutation motor with external characteristics of Brushless DC motor.
1 power drive circuit of Brushless DC motor
Brushless DC motor is generally composed of electronic commutation circuit, rotor position detection circuit and motor body. Electronic commutation circuit is generally composed of control part and driving part, and the detection of rotor position is generally completed by position sensor. During operation, the controller orderly triggers each power tube in the driving circuit according to the motor rotor position measured by the position sensor to conduct orderly commutation to drive the DC motor.
The power drive circuit of Brushless DC motor adopts a three-phase full bridge inverter circuit composed of six n-channel mos-fets centered on the special drive chip IR2130 of IR company. Its input is PWM wave with power ground as the ground, which is sent to the input port of IR2130 to output the power drive MOSFET controlling n-channel, so as to drive the brushless DC motor. This driving mode is mainly due to the ingenious use of the power driving chip IR2130 to form a suspended high-voltage side power supply with “bootstrap” technology, which simplifies the design of the whole driving circuit and improves the reliability of the system. In addition, the IR2130 driving chip has built-in dead band circuit, overcurrent protection and undervoltage protection, which greatly reduces the complexity of circuit design, The reliability of the system is further improved.
2. Characteristics of IR2130 driver chip
IR2130 can be used to drive power MOS gate devices in circuits with bus voltage not higher than 600 v. its maximum forward peak drive current is 250 Ma and reverse peak drive current is 500 mA. Because it is internally designed with overcurrent, overvoltage and undervoltage protection, blocking and indication network, it can be easily used by users to protect the driven MOS gate power transistor. In addition, the ingenious use of internal bootstrap technology to make it used in high-voltage system can also generate 2.5% of the gate driving signal of two power devices above and below the same bridge arm μ S Interlock delay time. Due to its wide working and power supply voltage range (3 ~ 20 V), it is also designed with a current amplifier in linear relationship with the current passed by the driven power device. The circuit design also ensures that the internal three channel high-voltage side driver and low-voltage side driver can be used alone, or only three internal low-voltage side drivers can be used, And the input signal is compatible with TTL and COMS levels.
The motor controlled driver adopts IR2130 chip. IR2130 is a high-voltage, high-speed power MOSFET, IGBT and driver with working voltage of 10 ~ 20 V and three independent high-end and low-end output channels respectively. The logic input is compatible with CMOS or LSTTL output and can reach a minimum logic voltage of 2.5 v. The reference ground operation amplifier in the peripheral circuit provides the analog feedback value of the full bridge circuit current through the external current detection potentiometer. If the set or adjusted reference current value is exceeded, the internal current protection circuit of IR2130 driver starts to turn off the output channel to realize the function of current protection. IR2130 driver reflects the state of high pulse current buffer. The transmission delay is matched with high frequency amplifier. Floating channel can be used to drive n-channel power MOSFET and IGBT, and the maximum voltage can reach 600 v
IR2130 chip can control the on and off sequence of six high-power transistors at the same time, and control the on and off of the upper half bridges Q1, Q3 and Q5 of the three-phase full bridge drive circuit respectively by outputting H01 ~ H03; The outputs L01 ~ L03 of IR2130 respectively control the on and off of the lower half bridges Q4, Q6 and Q2 of the three-phase full bridge drive circuit, so as to control the motor speed and forward and reverse rotation. IR2130 chip has a current comparison circuit, which can set the motor comparison current. The set value can be used as the reference value of the software protection circuit, which can make the circuit suitable for the control of different power motors. The typical circuit of IR2130 is shown in Figure 1.
The three-phase full bridge inverter circuit is composed of six power mosfetrfp40n10, one IR2130 and some resistors and capacitors. Its main features are:
(1) The drive chip IR2130 has built-in 2.5 μ Dead time of S; Prevent the upper and lower MOSFETs of the same bridge arm from conducting at the same time, so that the power supply voltage is short circuited, and the power supply does not pass through the motor. This avoids the false output of IR2130 at the moment when the hardware system is powered on.
(2) The power drive circuit is controlled by PWM modulation with upper bridge arm power MOSFET.
In the modulation process, the bootstrap capacitor is charged only when the high-end device (upper bridge arm MOSFET) is turned off and the potential of VS is pulled to power ground. Therefore, the on time of the lower bridge arm device on the same bridge arm (the off time of the upper bridge arm device) should be long enough to ensure that the charge of the bootstrap capacitor is full. When the upper bridge arm is on, the upper bridge arm has enough time to turn on.
(3) Since the three-way high-voltage side grid driving power supply of the upper bridge arm of the power driving circuit is obtained by charging the bootstrap capacitor, the reverse withstand voltage of the diode connected to the IR2130 power supply must be greater than the peak bus voltage of the driven power MOSFET. In order to prevent the discharge at both ends of the bootstrap capacitor, the diode shall be high-frequency fast recovery diode, and the power driving circuit shall be FR104. Its maximum reverse recovery time is 150 ns and the maximum reverse withstand voltage is 400 V
(4) The capacity of the bootstrap capacitor on the high voltage side of the upper bridge arm depends on the switching frequency of the driven power MOSFET, the on and off duty cycle and the needs of the grid charging current. In order to prevent the voltage at both ends of the bootstrap capacitor from being lower than the threshold voltage of undervoltage protection action after discharge, so as to turn off IR2130, the capacitance value should be large. 10 is selected for this power driving circuit μ F electrolytic capacitor.
(5) The six driving MOS-FET tubes (rfg40n10) inside the power driving chip IR2130 have low output impedance and on output resistance RDS (on) = 0.04 Ω. Directly driving the power MOSFET device may cause oscillation between the drain and source of the device MOSFET.
This will cause RF interference, and may also cause the device MOS-FET to be broken down due to high DV / dt. Therefore, a 30 Ω non inductive resistance is connected in series between the grid of the power tube and the output of IR2130. The resistance between the gate and source mainly provides the discharge circuit to quickly discharge the voltage of the bootstrap capacitor.
The brushless DC motor power drive circuit introduced here is composed of the special drive chip IR2130 of IR company. Because the 1r2130 drive chip has built-in dead time circuit and has the functions of overcurrent protection and undervoltage protection, the complexity of circuit design is greatly reduced, the design of the whole drive circuit is simplified and the reliability of the system is improved