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无感BLDC变电感启动算法应用文档.pdf

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    Application Note, V1.0, Oct 2006 AP08018 XC866 Start-up Control Algorithm for Sensorless and Variable Load BLDC Control Using Variable Inductance Sensing Method Microcontrollers
    Edition 2006-11-24 Published by Infineon Technologies AG 81726 München, Germany © Infineon Technologies AG 2006. All Rights Reserved. LEGAL DISCLAIMER THE INFORMATION GIVEN IN THIS APPLICATION NOTE IS GIVEN AS A HINT FOR THE IMPLEMENTATION OF THE INFINEON TECHNOLOGIES COMPONENT ONLY AND SHALL NOT BE REGARDED AS ANY DESCRIPTION OR WARRANTY OF A CERTAIN FUNCTIONALITY, CONDITION OR QUALITY OF THE INFINEON TECHNOLOGIES COMPONENT. THE RECIPIENT OF THIS APPLICATION NOTE MUST VERIFY ANY FUNCTION DESCRIBED HEREIN IN THE REAL APPLICATION. INFINEON TECHNOLOGIES HEREBY DISCLAIMS ANY AND ALL WARRANTIES AND LIABILITIES OF ANY KIND (INCLUDING WITHOUT LIMITATION WARRANTIES OF NON-INFRINGEMENT OF INTELLECTUAL PROPERTY RIGHTS OF ANY THIRD PARTY) WITH RESPECT TO ANY AND ALL INFORMATION GIVEN IN THIS APPLICATION NOTE. Information For further information on technology, delivery terms and conditions and prices please contact your nearest Infineon Technologies Office (www.infineon.com). Warnings Due to technical requirements components may contain dangerous substances. For information on the types in question please contact your nearest Infineon Technologies Office. Infineon Technologies Components may only be used in life-support devices or systems with the express written approval of Infineon Technologies, if a failure of such components can reasonably be expected to cause the failure of that life-support device or system, or to affect the safety or effectiveness of that device or system. Life support devices or systems are intended to be implanted in the human body, or to support and/or maintain and sustain and/or protect human life. If they fail, it is reasonable to assume that the health of the user or other persons may be endangered.
    AP08018 Start-up Control Algorithm for Sensorless and Variable Load BLDC Control Using Variable Inductance Sensing Method 2006-10 none V1.0 AP08018 Revision History: Previous Version: We Listen to Your Comments Any information within this document that you feel is wrong, unclear or missing at all? Your feedback will help us to continuously improve the quality of this document. Please send your proposal (including a reference to this document) to: mcdocu.comments@infineon.com Application Note 3 V1.0, 2006-10
    AP08018 Start-up Control Algorithm for Sensorless and Variable Load BLDC Control Using Variable Inductance Sensing Method Table of Contents 1 Page INTRODUCTION.................................................................................................................................................. 5 1.1 RAMP UP METHOD........................................................................................................................................ 5 VARIABLE INDUCTANCE SENSING METHOD.......................................................................................... 6 HARDWARE IMPLEMENTATION WITH XC866 MICROCONTROLLER............................................ 8 SOFTWARE IMPLEMENTATION WITH DAVE AND KEIL COMPILER ............................................. 9 4.1 MAIN PROGRAM ........................................................................................................................................... 9 4.2 VARIABLE INDUCTANCE SENSING METHOD .............................................................................................. 12 CURRENT SENSING CIRCUIT ...................................................................................................................... 15 EVALUATE YOUR OWN VARIABLE INDUCTANCE SENSING BLDC CONTROL.......................... 16 OTHER RELATING REFERENCES .............................................................................................................. 16 2 3 4 5 6 7 Application Note 4 V1.0, 2006-10
    AP08018 Start-up Control Algorithm for Sensorless and Variable Load BLDC Control Using Variable Inductance Sensing Method Introduction 1 One of the main concerns of running a BLDC motor is its startup operation. The initial rotor position should be known so that the corresponding motor phases are energized. If the energized phases are incorrect, the rotor will not be able to rotate. There are several ways to startup a BLDC motor. One way is to use the hall sensor to detect the initial position of the rotor and then startup up the motor by energizing the 3 phases according to an energizing pattern. This pattern corresponds to the pair of motor phases that should be energized so that the motor rotates properly. Figure 1 shows this pattern and is labeled as commutation states. After a stable speed, the hall sensor is removed to switch to sensorless mode via detection of the back-emf zero crossing. This method is not commonly used since it is not advisable to use hall sensors because of its cost. phase B phase B phase B phase A phase A phase A phase C STATE 1 phase C STATE 3 phase C STATE 2 phase B phase B phase B phase A phase A phase A phase C STATE 5 phase C STATE 4 phase C STATE 6 Figure 1. Commutation Pattern 1.1 Ramp up Method Another method is to initialize the rotor to a certain position by energizing a phase pair and waiting for the rotor to be aligned with the created stator flux. The motor phases are then energized according to a certain coil energizing pattern. The motor speed is gradually increased by slowly decreasing the commutation period. The values used for the commutation period are stored in a ramp up table. The values of the ramp up table must be tuned according to the inertia, back-emf constant, speed constant, voltage applied, and initial load of the motor to be used. http://www.infineon.com Published by Infineon Technologies AG
    AP08018 Start-up Control Algorithm for Sensorless and Variable Load BLDC Control Using Variable Inductance Sensing Method When the motor has reached the speed where the back-emf can be detected, the operation will switch to sensorless mode via detection of back-emf zero crossing. The commutation period will now depend on the time between the zero crossings. Although hall sensors are not required for this method of startup, the use of ramp up table makes it ineffective since a change in the motor characteristics, like the initial load, will hinder the motor from starting up correctly. A motor with different characteristics will not start properly using the same values in the ramp table tuned for a different motor. The folder HOT5 Project 1 Demo 2 - Full sensorless operation with ramp up contains all the source codes for the sensorless operation using ramp up method. Variable Inductance Sensing Method 2 A much more effective method uses variable inductance to detect the initial rotor position. It does not depend on any motor specific characteristics, which allows it to work on any BLDC motor. Even changing the initial load would not be a problem with this method. This method relies on the fact that if voltage is applied across an inductor which is in the presence of a permanent magnet, the resulting current will either add or subtract to the external field created by the permanent magnet, which leads to a further decrease or increase in the inductance. In the case of a BLDC motor, the inductor is the stator while the permanent magnet is the rotor. The implementation of this method requires that a voltage is applied for a fixed time such that it creates a magnetic field in the direction of only one winding. Two magnetic fields of opposite directions should be created for each winding. In order to do this, two phases are held to ground and one is switched to high, creating the forward magnetic field. Then two are switched to high and one is held to ground, creating the opposing magnetic field. This procedure is shown in Figure 2 where phase A is energized in the forward direction. Figure 2. Energizing of Motor Windings http://www.infineon.com Published by Infineon Technologies AG
    AP08018 Start-up Control Algorithm for Sensorless and Variable Load BLDC Control Using Variable Inductance Sensing Method The two peak currents created from the two opposing magnetic fields are then measured and compared. The larger peak will indicate the current that is in the same direction as the magnetic field caused by the permanent magnet (rotor). Therefore, the polarity of the permanent magnet can be obtained, i.e. the rotor position is found within 180 degrees. Figure 3 shows the current peaks produced when the procedure was done with phase A, given that the rotor is in the position shown in Figure 4. The first current peak which is generated from the forward magnetic field is higher than the one generated from the reverse direction. This means that the magnetic field in the forward direction is in the same direction as that of the magnetic field of the rotor. Thus, the north pole of the rotor is known within 180 degrees. Figure 3. Current Pulses phase B phase A phase C Figure 4. Rotor Position within 180° http://www.infineon.com Published by Infineon Technologies AG
    AP08018 Start-up Control Algorithm for Sensorless and Variable Load BLDC Control Using Variable Inductance Sensing Method By repeating the entire procedure for the other two phases, the rotor position can be narrowed down to within 60 degrees, which is sufficient enough for proper commutation (Figure 5). There is also the possibility that the rotor is right on the edge of one of the semicircles but it does not matter since the phase that should be energized is the same whether the rotor is on one half of the boundary or the other. Figure 5. Rotor Position within 60° Hardware Implementation with XC866 Microcontroller 3 In order to implement the variable inductance sensing method, a current sensor circuit is required. The motor driver board contains an op amp in a current sensor configuration and is capable of detecting and amplifying the current peaks. The output of this current sensor circuit is read by the ADC peripheral of the XC866. Figure 6 shows the block diagram of the hardware implementation of this method. The ADC peripheral will also measure the back-emf after the motor startup has finished. The ADC will look for the back-emf zero crossing, the moment when the back-emf has reached half of the motor power supply level. The ADC adjusts the zero crossing level accordingly by periodically sampling the power supply thru a voltage divider feedback circuit. This allows the power supply to vary within a certain range, without affecting the motor operation. The back-emf zero crossing is crucial in the sensorless operation of a BLDC motor since the time between the zero crossings is used to calculate the commutation period throughout the motor operation. The Capture/Compare Unit 6 (CCU6) produces the coil energizing pattern and PWM which is fed to the 3 phase bridge driver IC. The IC will then drive the switches composing the inverter bridge circuit. The inverter bridge is made up of Infineon Optimos® N-channel power transistors. These switches will control the current flow in the stator windings. There is a specific pattern at which the inverter bridge switches must be activated so that the motor rotates properly. If the motor is stalled while running or the startup did not run properly, an emergency stop will be activated by the CTRAP of the microcontroller. This CTRAP will force the CCU6 outputs into a passive state and no active modulation is possible. http://www.infineon.com Published by Infineon Technologies AG
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