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Table 1. PWM sequence for rotating motor in clockwise direction.

Table 1 PWM sequence for rotating motor in clockwise direction.

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BLDC motor consists of permanent magnetic rotor and stator windings. Depending on stator winding BLDC moto may be single phase or three phase. Figure 1 shows internal structure of three phase BLDC motor and star connectet three phase stator winding[1]. The numbers one to six on stator winding represents the commutation sequence. Eacl commutation sequence has one of the windings energized to positive power, the second winding is negative and th third is in a non-energized condition. Torque is produced because of the interaction between the magnetic fielc generated by the stator coils and the permanent magnets. Ideally, the peak torque occurs when these two fields are a 90° to each other and falls off as the fields move together. In order to keep the motor running, the magnetic fiel produced by the windings should shift position, as the rotor moves to catch up with the stator field.
BLDC motor consists of permanent magnetic rotor and stator windings. Depending on stator winding BLDC moto may be single phase or three phase. Figure 1 shows internal structure of three phase BLDC motor and star connectet three phase stator winding[1]. The numbers one to six on stator winding represents the commutation sequence. Eacl commutation sequence has one of the windings energized to positive power, the second winding is negative and th third is in a non-energized condition. Torque is produced because of the interaction between the magnetic fielc generated by the stator coils and the permanent magnets. Ideally, the peak torque occurs when these two fields are a 90° to each other and falls off as the fields move together. In order to keep the motor running, the magnetic fiel produced by the windings should shift position, as the rotor moves to catch up with the stator field.
The commutation sequence is generated based on the hall sensor output (rotor position) and required phase voltage. For continuous rotation phase sequence numbered 1 to 6 should be followed to energize respective phases based on hall sensor outnut.
The commutation sequence is generated based on the hall sensor output (rotor position) and required phase voltage. For continuous rotation phase sequence numbered 1 to 6 should be followed to energize respective phases based on hall sensor outnut.
Table 2. PWM sequence for rotating motor in counter-clockwise direction. BLDC MOTOR DRIVE SYSTEM:
Table 2. PWM sequence for rotating motor in counter-clockwise direction. BLDC MOTOR DRIVE SYSTEM:
Sa Se a ee ee SS ee SSS SE ee ee ee ee. Typical three phase BLDC motor drive system is similar to three phase induction motor drive system as shown in fig. 3. DC voltage source may be a battery, fuel-cell stack, diode rectifier and capacitor. DC source gives 5V, 12V and 24V output for operation of controller, driver and the main inverter circuit respectively. Three phase inverter circuit consists of six switches connected in three legs. PIC Microcontroller 18f452 has High Performance RISC architecture, with in built four 16 bit timers, eight channel-10 bit configurable analog to digital controller, 10 bit PWM generator, capture/compare module and many other advanced features. These advanced features make it useful in all types of control system applications. Microcontroller is used to generate PWM pulses to control on/off time of switching devices in a proper sequence based on hall sensor feedback signal. Driver circuit is used to amplify PWM signal and to provide isolation between microcontroller and inverter circuit. A display device such as LCD display is used to display speed and duty ratio of PWM signals and provides interaction between user and the system. LEDs are also used to indicate status such as ON/OFF, forward direction, reverse direction etc. Here PIC microcontroller 18f452 used to generate PWM pulses at PORTD using its internal TIMERO. The potentiometer, connected to one of the analog-to-digital converter channel in PIC microcontroller, is used to set reference speed. Based on this reference input voltage, the PWM duty cycle is calculated. PWM output of PIC microcontroller is applied to the respective gate terminals of inverter switches through gate drive circuit. The hall sensor feedback signal is applied to the PORTE of microcontroller to sense the rotor position.
Sa Se a ee ee SS ee SSS SE ee ee ee ee. Typical three phase BLDC motor drive system is similar to three phase induction motor drive system as shown in fig. 3. DC voltage source may be a battery, fuel-cell stack, diode rectifier and capacitor. DC source gives 5V, 12V and 24V output for operation of controller, driver and the main inverter circuit respectively. Three phase inverter circuit consists of six switches connected in three legs. PIC Microcontroller 18f452 has High Performance RISC architecture, with in built four 16 bit timers, eight channel-10 bit configurable analog to digital controller, 10 bit PWM generator, capture/compare module and many other advanced features. These advanced features make it useful in all types of control system applications. Microcontroller is used to generate PWM pulses to control on/off time of switching devices in a proper sequence based on hall sensor feedback signal. Driver circuit is used to amplify PWM signal and to provide isolation between microcontroller and inverter circuit. A display device such as LCD display is used to display speed and duty ratio of PWM signals and provides interaction between user and the system. LEDs are also used to indicate status such as ON/OFF, forward direction, reverse direction etc. Here PIC microcontroller 18f452 used to generate PWM pulses at PORTD using its internal TIMERO. The potentiometer, connected to one of the analog-to-digital converter channel in PIC microcontroller, is used to set reference speed. Based on this reference input voltage, the PWM duty cycle is calculated. PWM output of PIC microcontroller is applied to the respective gate terminals of inverter switches through gate drive circuit. The hall sensor feedback signal is applied to the PORTE of microcontroller to sense the rotor position.
The three phase inverter to drive the BLDC motor is shown in the Fig. 4. Q1 to Q6 are the power switches controlled by the PIC18F452 micro-controller. Based on the motor voltage and current ratings, these switches can be MOSFETs, or IGBTs, or simple bipolar transistors. The BLDC motor is connected at the output terminals A, B, C. If the signals marked by PWMx are switched ON or OFF according to the sequence, the motor will run at the rated speed, provided DC bus voltage is equal to the motor rated voltage, plus any losses across the switches.
The three phase inverter to drive the BLDC motor is shown in the Fig. 4. Q1 to Q6 are the power switches controlled by the PIC18F452 micro-controller. Based on the motor voltage and current ratings, these switches can be MOSFETs, or IGBTs, or simple bipolar transistors. The BLDC motor is connected at the output terminals A, B, C. If the signals marked by PWMx are switched ON or OFF according to the sequence, the motor will run at the rated speed, provided DC bus voltage is equal to the motor rated voltage, plus any losses across the switches.
Test is carried out in open loop with manual control. By varying pot resistance the analog voltage at channel 0 get varied. ADC module converts this analog voltage in to equivalent 10 bit digital data. The range of output of ADC is limited 0 to 255, by connecting a resistance in series with pot. Hardware results are taken for both full load and no load. At no load motor runs at full speed more than rated one with very small current 0.19A. When load is connected, the motor current increases with increase in load. Motor speed is found to vary smoothly from zero to rated speed with increase in PWM duty cycle. The motor hall sensor signals are obtained as shown in the fig.8. The hardware setup is shown the fig.7. The PWM signals generated by microcontroller as illustrated in fig.6 are used to control the speed of BLDC motor. BLDC motor specifications are shown table 3.
Test is carried out in open loop with manual control. By varying pot resistance the analog voltage at channel 0 get varied. ADC module converts this analog voltage in to equivalent 10 bit digital data. The range of output of ADC is limited 0 to 255, by connecting a resistance in series with pot. Hardware results are taken for both full load and no load. At no load motor runs at full speed more than rated one with very small current 0.19A. When load is connected, the motor current increases with increase in load. Motor speed is found to vary smoothly from zero to rated speed with increase in PWM duty cycle. The motor hall sensor signals are obtained as shown in the fig.8. The hardware setup is shown the fig.7. The PWM signals generated by microcontroller as illustrated in fig.6 are used to control the speed of BLDC motor. BLDC motor specifications are shown table 3.
The reference hall sensor signals are 120° phase shifted from each other. So those signals can be generated using three phase supply module, Op-amp comparator and diode combination. The generated signals are equivalent to the Hall sensor signals as shown in fig. 5. These signals are applied to the PORTE of microcontroller. The microcontroller is programmed to generate six PWM switching signals based on these hall sensor signals. The PWM output signals PWMA, PWMB, PWMC corresponding to the reference hall sensor signals are shown in the fig.6. PWM signals of lower switches are not shown in this figure, but are similar to upper switches and occur when respective hall sensor signal switches to low level.
The reference hall sensor signals are 120° phase shifted from each other. So those signals can be generated using three phase supply module, Op-amp comparator and diode combination. The generated signals are equivalent to the Hall sensor signals as shown in fig. 5. These signals are applied to the PORTE of microcontroller. The microcontroller is programmed to generate six PWM switching signals based on these hall sensor signals. The PWM output signals PWMA, PWMB, PWMC corresponding to the reference hall sensor signals are shown in the fig.6. PWM signals of lower switches are not shown in this figure, but are similar to upper switches and occur when respective hall sensor signal switches to low level.
Fig.10. Motor input voltage. (Scale: 20V/div) The PWM signals corresponding to the upper switches in inverter (fig.4) are shown in the fig.9. The hall sensor signals and PWM signals are similar to the one observed in Proteus simulation. The driver circuit inverts these PWM signals, which are then applied to MOSFET gate. Thus 0 levels in PWM signal indicates ON state of MOSFET and 1 level indicates OFF state. The output voltage of inverter is found trapezoidal in nature as shown in the fig.10. The output voltages of three phase inverter are 120° phase shifted from each other. BLDC motor can be also controlled by sensing back emf of the motor.
Fig.10. Motor input voltage. (Scale: 20V/div) The PWM signals corresponding to the upper switches in inverter (fig.4) are shown in the fig.9. The hall sensor signals and PWM signals are similar to the one observed in Proteus simulation. The driver circuit inverts these PWM signals, which are then applied to MOSFET gate. Thus 0 levels in PWM signal indicates ON state of MOSFET and 1 level indicates OFF state. The output voltage of inverter is found trapezoidal in nature as shown in the fig.10. The output voltages of three phase inverter are 120° phase shifted from each other. BLDC motor can be also controlled by sensing back emf of the motor.
Fig.7. Hardware setup
Fig.7. Hardware setup
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