Motorola M68HC08 manual Effect of Mutual Phase Capacitance, Mutual Inductance

Page 111

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

User Guide

Application Suitability Guide

6.2.4.1 Effect of Mutual Phase Capacitance

The effect of the mutual phase capacitances can play an important role in the back-EMF sensing. Usually the mutual capacitance is very small. Its influence is only significant during the PWM switching when the system experiences very high du/dt.The effect of mutual capacitance is described in section 3.2.4.4 Effect of Mutual Phase Capacitance.

NOTE: Note that the configuration of the end-turns of the phase windings has a significant impact. Therefore, it must be properly managed to preserve the balance of the mutual capacity. This is especially important for prototype motors that are usually hand-wound.

CAUTION: Failing to maintain balance of the mutual capacitance can easily disqualify such motors from using sensorless techniques based on the back-EMF sensing. Usually the BLDC motors with windings wound on separate poles show minor presence of the mutual capacitance. Thus, the disturbance is insignificant.

6.2.4.2 Effect of Mutual Inductance

The negative effect on back-EMF sensing of mutual inductance, is not to such a degree as unbalanced mutual capacitance. However, it can be noticed on the sensed phase. The difference of the mutual inductances between the coils which carry the phase current and the coil used for back-EMF sensing, causes the PWM pulses to be superimposed onto the detected back-EMF voltage.

The effect of mutual inductance is described in section 3.2.4.3 Effect of

Mutual Inductance.

NOTE: The BLDC motor with stator windings distributed in the slots has technically higher mutual inductances than other types. Therefore, this effect is more significant. On the other hand, the BLDC motor with windings wound on separate poles, shows minor presence of the effect of mutual inductance.

CAUTION: However noticeable this effect, it does not degrade the back-EMF zero crossing detection, because it is cancelled at the zero crossing point. Additional simple filtering helps to reduce ripples further.

DRM028 — Rev 0		Designer Reference Manual

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Contents Freescale Semiconductor, Inc M68HC08For More Information On This Product Designer Reference Manual Rev Sensorless Bldc Motor Control Using MC68HC908MR32Revision history List of Sections List of Sections Table of Contents Table of Contents Title List of FiguresList of Figures List of Tables List of Tables Application Functionality ContentsBenefits of the Solution IntroductionIntroduction System Concept System DescriptionSystem Description System Specification Software Specifications Software SpecificationSoftware written in C language specifications are listed Software parameter tuning to a customer motorHigh-Voltage Hardware Set Specification Hardware and Drive SpecificationsMotor -Brake Set High Voltage Hardware Set SpecificationsLow-Voltage Evaluation Hardware Set Specification Low Voltage Evaluation Hardware Set SpecificationsLow-Voltage Hardware Set Specification Low Voltage Hardware Set Specifications Bldc Motor Control Brushless DC Motor Control TheoryBldc Motor Targeted by This Application Semiconductor, Inc Bldc Motor Control Brushless DC Motor Control Theory Bldc Motor Back EMF and Magnetic Flux Why Sensorless Control? 2 3-Phase Bldc Power StagePower Stage Motor Topology Indirect Back EMF Sensing Stator Winding EquationsSame expressions can also be found for phase a and B Effect of Mutual Inductance Phase Voltage WaveformMutual Inductance Effect Detail of Mutual Inductance Effect Effect of Mutual Phase CapacitanceMutual Capacitance Model 10. Distributed Back-EMF by Unbalanced Capacity Coupling 11. Balanced Capacity Coupling Back-EMF Sensing Circuit Inc Used Control Technique Sensorless Commutation ControlAlignment Starting Back-EMF Acquisition Running Alignment 14. Commutation Control StagesRunning 15. AlignmentFreescale Semiconductor, Inc Commutation time calculation is shown in Figure Running Commutation Time Calculation17. Bldc Commutation Time with Zero Crossing Sensing Service of received back-EMF zero crossingWhere Starting Back-EMF Acquisition Freescale Semiconductor, Inc 18. Vectors of Magnetic Fields 19. Back-EMF at Start Up Starting Commutation Time Calculation Running Commutation Time Calculation, but the followingComputation coefficients are different Application Control Speed ControlPC Master Software PC Master Software Communication Commands Communication with PC Master Software SpecificationsName Type Representing Description Range PC Master Software API VariablesBIT6 Reserved MotorStatusDef, FailureDefBIT2 Reserved SpeedRangeMaxRPM*PerSpeedMAXRange/PerZCrosFltT2 PerSpeedMAXRange and zero crossing period PerZCrosFltT2Freescale Semiconductor, Inc For High-Voltage Hardware Set cofiguration System Configuration and DocumentationHardware Design MC68HC908MR32 Control BoardComponents will describe the individual boards For Low-Voltage Evaluation Motor Hardware Set configurationEVM Motor Board Phase Low Voltage EVM Bldc Motor Low-Voltage Hardware Set configurationHigh-Voltage Hardware System Configuration High-Voltage Hardware Set ConfigurationDescribed in MC68HC908MR32 Control Board User’s Manual Motorola document order numberSee References Low-Voltage Evaluation Motor Hardware System Configuration Low-Voltage Evaluation Motor Hardware Set ConfigurationSystem configuration for low-voltage hardware set is shown Low-Voltage Hardware Set ConfigurationLow-Voltage Hardware System Configuration All HW Sets Components References1 MC68HC908MR32 Control Board Electrical characteristics in -1apply to operation at 25C 4shows a block diagram of the board’s circuitryElectrical Characteristics of Control Board 1 3-Phase AC/BLDC High Voltage Power StageHigh-Voltage Hardware Set Components Phase AC High Voltage Power Stage Optoisolation Board Electrical Characteristics of Power StageElectrical Characteristics Electrical Characteristics of the Optoisolation Board3 3-phase Bldc High Voltage Motor with Motor Brake Low-Voltage Evaluation Motor Hardware Set ComponentsEVM Motor Board Characteristics of the Bldc motor Electrical Characteristics of the EVM Motor BoardElectrical Characteristics of the EVM Motor Board 2 3-phase Low Voltage EVM Bldc MotorLow-Voltage Hardware Set Components 1 3-Ph AC/BLDC Low Voltage Power StageBlock Diagram Section 2 3-phase Bldc Low Voltage Motor with Motor BrakeData Flow Data Flow Main Software Flowchart State DiagramSoftware Design IntroductionSoftware Variables and Defined Constants Important system variables are listed in TableSoftware Variables Start/Stop Switch Reading and Start/Stop Decision Sys3DefProcess Measurement Process Back, EMF Zero Crossing Sensing Main Data Flow Part1 Process Fault Control Fault StopFreescale Semiconductor, Inc Main Data Flow Part 2 Alignment, Starting Closed Loop Control System Process Desired Speed SettingProcesses Commutation and Zero Crossing Preset and Set Bldc Speed Control and CalculationProcess Alignment Control Bldc Commutation and Zero Crossing Selection Main Software FlowchartMain Software Flowchart Freescale Semiconductor, Inc Main Software Flowchart Main Software Loop Freescale Semiconductor, Inc Freescale Semiconductor, Inc Software Flowchart Interrupts State DiagramApplication State Transitions Stand-By State diagram for this software is shown in FigureInitialize MCU Initialize ApplicationFreescale Semiconductor, Inc Stand-by State Align State Starting Commutation Time Calculation Freescale Semiconductor, Inc 10. Back-EMF Acquisition Service of Commutation SetCommutation Time Calculation Service of Received Back-EMF Zero Crossing Running StateExplained in 5.5.5 Back-EMF Acquisition State Over Current 11. Running State Stop State 12. Stop State Fault StateSoftware files and structure are described in section Implementation NotesSee Figure Software FilesPreset Bldc Commutation and Bemf Zero Crossing Selection Bldc Commutation and Zero Crossing SelectionSet Bldc Commutation and Bemf Zero Crossing Selection PWMValMax = DUTYPWMMAX*MCPWMMODULUS Bldc Speed Control and CalculationDesired Speed Calculation PWM Duty CycleTimer TimersFunction TIMACh3Int Designer Reference Manual DRM028 Rev 108 Software Design Motor’s nominal speed User GuideApplication Suitability Guide Minimal Application SpeedMaximal Application Speed Voltage Closed LoopMotor Suitability Mutual Inductance Designer Reference Manual DRM028 Rev 112 User Guide Application Hardware and Software Configuration Hardware ConfigurationHardware setups are shown in -1, -2, Low-Voltage Evaluation Motor Hardware Set Configuration High-Voltage Hardware Set ConfigurationLow-Voltage Hardware Set Configuration Controller Board Settings EVM Board Settings EVM board settings are the same for all hardware platformsSoftware Setup Application HC08 Software Files \bldczerocros08MR32\sources\bldc08.c, main program Application PC Master Software Control Files Software Execution BuildExecute from Evaluation Board Application Control When the software is built, the S-record fileExecute from Pre-programmed MCU Bldczerocros08mr32MMDS.sx is generatedPC Master Software Remote Operating Mode Manual Operating ModePC Master Software Control Window For More Information On This Product Tuning for Customer Motor User Guide Tuning for Customer Motor Follow-up for Software Customizing to Customer Motor Follow-up for Advanced Software Customizing Start the PC master software parameters tuning application To have PC master software installed on your PC computer11. PC Master Software Parameters Tuning Control Window Software Parameters Setting Follow-up Labels in the File const.h Example of Software Customizing to Hardware Software Customizing to Power StageParameters File Selection \bldczerocros08MR32\sources\constcustlv.h, definitions forVoltage Setting Hardware Customizing Current Setting Hardware CustomizingRange 0,infinity Modified maximal measurable voltage is 55 V, so set Example of Software Customizing to HardwareRange 0,VOLTRANGEMAX Software Customizing to Motor Voltage and Current SettingsMaximal and Minimal Voltage Limits Setting Detailed description starts hereRange 0,CURRENTRANGEMAXA Maximal and Minimal Current Limits SettingAlignment Current and Current Regulator Setting Current during alignment state before motor starts ΑRange 0,8 Parameters Tuning with PC Master Software Project File Set constcustx.hFrom Evaluation Board 12. PC Master Software Current Parameters Tuning Window Designer Reference Manual DRM028 Rev 142 User Guide MUSTCHANGEEXPERnn in file constcustx.h Commutation time period to discharge coil current ∝s Commutation ParametersStart-up Constants and Maximal Commutation Period Start-up Period Maximal commutation period limit ∝sRange -128,127 Ensure Percmtstartus =PERCMTMAXUS /2 Alignment Current and Current Regulator Setting 6.5.4.3Constcustx.h Constcustx.h Set #define Percmtstartus in constcustx.hConstcustx.h file #define Speedpiregigain13. PC Master Software Start Parameters Tuning Window Software Customizing to Motor Speed Control Setting Number of commutations per motor revolutionRange 0,255 Maximal speed range rpm Minimal speed of the drive rpmRange 0,SPEEDRANGEMAXRPM Speedminrpm = 0.07 to 0.5SPEEDMAXRPM User Guide 153 Execute from Evaluation Board Set PC master software control mode and start motor see Remote Operating ModeStart motor see Application Control and PC Master Software PWM Frequency PWM Frequency and Current Sampling Period SettingFor the PWM frequency setting, follow the label PWM frequency setting is provided byPWM Frequency Setting PWM period = Periodpwmus = SETPERPWM*2 EQCurrent Sampling Period Current Sampling Instant Conclusion Software Parameters Setting and TuningCANCHANGEPERCURSAMPn in const.h file PERCST1US = Periodpwmus * Setpercs ∝sUser Guide 159 Designer Reference Manual DRM028 Rev 160 User Guide Appendix A. References AN1627, Motorola Motor using MC68HC705MC4 document order numberSG40N Appendix B. GlossaryGlossary Serial communications interface module SCI a module that Designer Reference Manual DRM028 Rev 166 Glossary Freescale Semiconductor, Inc HOW to Reach US USA/EUROPE/LOCATIONS not Listed