In this thesis, a ZCP (Zero Crossing Point) filter scheme is studied together with a slow start initial control method for sensorless 3-phase sinusoidal BLDC (Brush-Less DC Motor) controller. ZCP filter is a key IP block to detect the rotor position of the BLDC motor and control the drive transistors of an inverter. A traditional 3-phase sinusoidal BLDC motor uses 3 saddle sensors to detect the rotor position to control the motor speed.
But it often causes reliability issues in automotive applications due to sensor failure. Therefore, a sensorless BLDC motor becomes more desirable and a position sensing scheme replacing the Hall sensor is a key area of โโresearch. The proposed ZCP digital filter for self sensing rotor position with slow start drive is implemented with digital logic designed using Verilog HDL.
Also, the SPWM (Sinusoidal Pulse Width Modulation) sensorless BLDC motor controller is designed by Verilog HDL. KEYWORDS: Automotive IC, BLDC Motor, SPWM Sensorless, Position Sensing ZCP Digital Filter, Slow Start Starter Driver.
Introduction
Basic Operation of Sinusoidal PWM BLDC Motor Controller
Design of SPWM BLDC Motor Controller
- Bipolar SPWM Control Condition
- Bipolar SPWM Control with Digital Logic
The second is the frequency modulation ratio, ๐๐, which describes the quality of the current waveform [11]. The closer the amplitude of the triangle wave and the amplitude of the sine wave are, the closer the MI approaches 1. If the frequency of the fundamental wave is higher than that of the carrier wave, the quality of the voltage waveform can be improved [11]. .
Secondly, there is a sine wave generator that creates an address based on the position and speed of the motor and a sine wave that will be used as a fundamental wave based on this address. A period detector is a block that reads the speed of the rotor from Hall sensor signals. The three hall sensors produce constant signals and a constant step, called 6-step, depending on the direction of rotation of the rotor.
The period detector uses the counter to indicate the frequency of the hall sensor signal in relation to time. After that, the period detector sends the obtained period value of cycle and period set indicating the change of the step of hall sensor signals to the sine wave generator. This block produces a 10-bit address depending on the RPM and the location of the rotor.
The input block affects the frequency of the triangular wave, and amplitude clipping affects amplitude. Also in this digital logic, the amplitude of the fundamental wave is fixed, so that the MI can be modulated by adjusting the amplitude of the triangular wave. After deriving the location of the rotor from saddle sensor signals built into the BLDC motor, determine the rotation cycle of the BLDC motor.
However, bipolar SPWM control is only possible when there are hall sensor signals used as rotor position information from the hall sensor of the BLDC motor. In the case of the sensorless BLDC motor, the rotor position information must be acquired without the hall sensor. In this design, virtual hall sensor signals indicating the position of the rotor are generated from the phase voltages.
The Problem of SPWM Sensor-less Control of BLDC Motor
Proposed Design of Position-sensing ZCP Filter
- Design of Position-sensing Digital ZCP Filter for Modulation
- Design of Position-sensing Digital ZCP Filter for Overmodulation and Six-step
- Schematic of Position-sensing Digital ZCP Filter
- Design of Slow Start-up Initial Driving
- Initial Driving 1 st Stage: Alignment Stage
- Initial Driving 2 nd Stage: Acceleration Stage
- Initial Driving TOP Block Diagram
- TOP Block Diagram of SPWM Sensor-less BLDC Controller
Since it is difficult to calculate ๐ก๐๐ using the natural sampling method, we used the symmetric sampling method calculation method using the characteristics of digital logic. With the algorithm, it is possible to obtain signals that will be used as virtual hall sensor signals. In addition, in the case of six-step control, the connection voltage has noise due to the commutation section where the body MOS diode is turned on.
Therefore, the design of the digital ZCP filter to achieve the virtual hall sensor is necessary without expressing the ๐ก๐๐ equation. This digital ZCP filter mainly removes the noise from the signal caused by the terminal voltage passing through the comparator. Then measure the edge interval of the section using the counter from the rising edge of the input signal to the next rising edge.
When the detection pulse is ON, the output signal follows the current state of the input signal. In sensorless control, starting is one of the main problems that are mainly based on EMF estimation techniques. Another solution is to paralyze the rotor in the specified position by exciting every two phases of the motor for a certain time [23].
Most popular techniques to estimate the rotor position are based on the inductance variation, which varies with the rotor position, arising from the saturation effect of the stator iron core due to the permanent magnet [24]โ[28]. Since the initial position of the rotor is unknown when the BLDC motor is started from standstill, the 3-phase inverter switches cannot be operated normally according to the position of the rotor. By increasing the duty ratio so linearly, the magnetic field intensity and angular velocity of the motor can be increased so linearly.
Also, since motor speed is related to voltage, the RPM of the motor can be expressed as equation (23). This operation increases the RPM of the motor linearly according to the increase in duty ratio. If the rotor turns on slowly and if the RPM of the motor reaches the reference RPM through this process, the acceleration stage begins.
Afterwards, while the 3-phase inverter is switched to a constant frequency, ๐๐ต๐ด๐ changes and the speed of the motor is controlled. Each of the adjustment stage blocks and the acceleration stage blocks produces a gate control signal that goes into the 3-phase inverter.
Simulation and Experiment Results
Simulation Results
2.6, the output signals are made from the phase signal, which can be seen in fig. 3.2, it can be seen that the virtual hall sensor signals are made from the counting interval graph. By comparing the counting interval and the filtering interval, the detection pulse is activated and the output signal follows the current state of the phase signal.
The steps of virtual hall sensor signal also follow the steps of original hall sensor signals. It also shows that the signals generated by position-sensing digital ZCP filter for overmodulation can also be used for sensorless driving in SPWM overmodulation. The simulation results come out as designed, and the designed circuits are verified to actually work normally through experiments.
Experiment Setup
Experiment Results
As shown in the figure, it can be seen that the virtual hall sensor signal is created using the phase signal generated from the phase voltage. The virtual hall sensor signal can be obtained by filtering the noise generated by the freewheeling diode. As shown in the figure, virtual hall sensor signal is created using the phase signal generated from the phase voltage.
Since the filtering interval varies according to the VBAT and the dead time control interval, the shorting of the ZCP digital filter with position sensor must be adjusted. As shown in the figure, the high gate control signals have the form of a PWM signal depending on the duty ratio. From these experiment results, it can be seen that the SPWM sensorless BLDC motor controller works as designed.
Conclusion
Future Works
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