Texas Instruments MCF8315A Manuale utente

User's Guide

MCF8315A Tuning Guide

ABSTRACT

This Tuning guide provided step by step guidence to setup MCF8315EVM, connect MCF8315A GUI to the EVM

and tune a 3-phase Brushless DC motor using MCF8315A.

Table of Contents

1 Introduction.............................................................................................................................................................................2

1.1 Hardware and GUI Setup...................................................................................................................................................2

2 Essential Controls.................................................................................................................................................................. 5

2.1 Recommended Default Values...........................................................................................................................................5

2.2 Device and Pin Configuration.............................................................................................................................................5

2.3 Control Configuration - Motor Parameters......................................................................................................................... 6

2.4 Control configuration - Closed Loop...................................................................................................................................6

2.5 Testing for Successful Startup into Closed Loop................................................................................................................6

2.6 Fault Handling.................................................................................................................................................................... 8

3 Basic Controls.......................................................................................................................................................................11

3.1 Device and Pin Configuration...........................................................................................................................................11

3.2 System Level Configuration..............................................................................................................................................11

3.3 Control Configurations..................................................................................................................................................... 13

List of Figures

Figure 1-1. Simplified Schematic of MCF8315A..........................................................................................................................2

Figure 1-2. MCF8315EVM Jumper Configuration....................................................................................................................... 3

Figure 1-3. MCF8315EVM External Configuration...................................................................................................................... 4

Figure 2-1. Fault Status............................................................................................................................................................... 7

Figure 2-2. Motor Resistance...................................................................................................................................................... 8

Figure 2-3. Motor Inductance.......................................................................................................................................................8

Figure 2-4. Motor BEMF Constant...............................................................................................................................................9

Figure 2-5. Phase Current Waveform Showing a Spike due to Short Circuit............................................................................ 10

Figure 3-1. Phase current and FFT - Dead time compensation disabled.................................................................................. 12

Figure 3-2. Phase current and FFT - Dead time compensation enabled...................................................................................12

Figure 3-3. Power Supply voltage and phase current waveform when AVS is disabled............................................................13

Figure 3-4. Power Supply voltage and phase current waveform when AVS is enabled............................................................ 13

Figure 3-5. MPET - Phase current.............................................................................................................................................14

Figure 3-6. IPD current waveform during Rand L measurement............................................................................................... 14

Figure 3-7. Reverse Drive Function...........................................................................................................................................15

List of Tables

Table 2-1. Recommended Default Values....................................................................................................................................5

Trademarks

All trademarks are the property of their respective owners.

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MCF8315A Tuning Guide 1

1 Introduction

The MCF8315A provides three half-H-bridge integrated MOSFET drivers with sensorless FOC control to drive

a three-phase brushless DC (BLDC) motor at 12-V/24-V DC rails or battery powered applications. The device

integrates three current-sense amplifiers (CSA) with integrated current sense for sensing the three phase

currents of BLDC motors to achieve optimum FOC control. Simplified schematic of MCF8315A is shown in

Figure 1-1.

MCT8315A

MOSFETs

Buck/LDO Regulator

Integrated Current Sensing

EEPROM

Sensorless

Trap

DIRECTION

BRAKE

I2C

Optional during operation for

I2C speed, diagnostics, or on-

the-fly configuration

PWM, analog, frequency or

commanded over I2C

SPEED

Speed feecback

nFAULT

4.5 to 35 V (40 V abs max)

4 A peak output current,

typically 12 to 24 V

Buck out

3.3 or 5.0 V, up to 170 mA

LDO out

3.3 V, up to 20 mA

Figure 1-1. Simplified Schematic of MCF8315A

This tuning guide provides the steps to tune a 3-phase BLDC motor using the MCF8315A. The tuning process

is classified into two sections: Essential controls and Basic controls. This process is also detailed in the Guided

tuning section in the GUI.

•Essential controls: Tuning steps to successfully spin the motor in closed loop.

•Basic controls: Tuning steps to conform to use-case and explore features in the device.

1.1 Hardware and GUI Setup

Below are the items that are required to run through this tuning guide.

1. MCF8315EVM Board.

2. A computer with the MCF8315A_GUI installed.

3. A motor to be tuned using this process. It is reccomended to have motor data sheet but it is not mandatory.

4. A DC Power Supply rated for the motor.

5. Basic lab equipment such as a Digital Multimeter (DMM), Oscilloscope, current probe and voltage probes.

1.1.1 Jumper Configuration

Confirm the hardware is configured according to the jumper configuration as shown in Figure 1-2. Red boxes

indicate where jumpers are installed on the EVM.

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Figure 1-2. MCF8315EVM Jumper Configuration

1.1.2 External Connections

Connect the motor to J8 (connections A, B, and C). If the motor has a center tap connection or wires for

Hall-effect sensors, leave these wires unconnected. Supply a voltage compliant with the Power Supply Voltage

(VM) range using J7. Recommended voltage range for the device is 4.5 V – 35 V.

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MCF8315A Tuning Guide 3

Figure 1-3. MCF8315EVM External Configuration

1.1.3 Connecting to the GUI

1.1.3.1 Connect to computer

Confirm the EVM is powered on (VM) before connecting USB cable. Plug in the micro-USB, from the computer

that holds the GUI, to the USB Connector (J2) on the EVM.

1.1.3.2 Connect to the GUI

The GUI automatically connects to the EVM, as shown on the status bar located on the bottom of this GUI.

If the GUI doesn't connect automatically, please confirm that the "FTDI" serial port is selected by going to the top

menu "Options -> Serial Port ...". Then click on the chain link icon on the left of the status bar to connect to the

EVM.

1.1.3.3 Verify Hardware Connection

After the GUI establishes connection with the EVM through USB, you can verify the communication with the

MCF8315 device by clicking on the "Read All Registers" button on the top right of this GUI. After a few seconds,

the GUI indicates with a pop-up notification that all registers have been read back successfully.

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2 Essential Controls

The goal of this section is to help customers spin their motor successfully in closed loop. This section provides

standardized steps to tune parameters for successful Motor spin-up in closed loop.

Closed loop is defined as the sensorless closed loop where motor spins at the commanded speed.

2.1 Recommended Default Values

Launch the MCF8315A EVM GUI. Load the recommended default values that are listed in Table 2-1.

Table 2-1. Recommended Default Values

Address Name Address Recommended Value

ISD_CONFIG 0x00000080 0x64738C20

REV_DRIVE_CONFIG 0x00000082 0xA8200000

MOTOR_STARTUP1 0x00000084 0x0B6807D0

MOTOR_STARTUP2 0x00000086 0xA306600C

CLOSED_LOOP1 0x00000088 0x0D3201B5

CLOSED_LOOP2 0x0000008A 0x9BAD0000

CLOSED_LOOP3 0x0000008C 0x00000000

CLOSED_LOOP4 0x0000008E 0x00000000

SPEED_PROFILES1 0x00000094 0x00000000

SPEED_PROFILES2 0x00000096 0x00000000

SPEED_PROFILES3 0x00000098 0x00000000

SPEED_PROFILES4 0x0000009A 0x00000000

SPEED_PROFILES5 0x0000009C 0x00000000

SPEED_PROFILES6 0x0000009E 0x00000000

ALGO_CTRL1 0x000000EA 0x00000000

FAULT_CONFIG1 0x00000090 0xBEC80106

FAULT_CONFIG2 0x00000092 0xF0D00888

PIN_CONFIG 0x000000A4 0x00000000

DEVICE_CONFIG1 0x000000A6 0x00000000

DEVICE_CONFIG2 0x000000A8 0x0000B000

PERI_CONFIG1 0x000000AA 0xC1C01F00

GD_CONFIG1 0x000000AC 0x9C450100

GD_CONFIG2 0x000000AE 0x80200000

INT_ALGO_1 0x000000A0 0xA433407D

INT_ALGO_2 0x000000A2 0x000001A7

MTR_PARAMS 0x000000E6 0x00000000

2.2 Device and Pin Configuration

2.2.1 Speed Input Mode

MCF8315A provides four options to configure the input speed command.

• Analog input on SPEED pin by varying amplitude of input signal

• PWM input on SPEED pin by varying duty cycle of input signal

• Over I2C by configuring [DIGITAL_SPEED_CTRL]

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MCF8315A Tuning Guide 5

• Frequency input on SPEED pin by varying frequency of input signal

Configure the speed input [SPEED_MODE] register to select the desired speed input mode.

If PWM input on SPEED pin is chosen as the speed input, configure [SPEED_RANGE_SEL] to select the PWM

frequency range.

If Frequency input on SPEED pin is chosen as the speed input, configure [INPUT_MAXIMUM_FREQ] to select

the maximum PWM frequency. For example, if 10 kHz is chosen as maximum PWM frequency, 10 kHz PWM

signal on SPEED pin corresponds to 100% speed command.

Note that even when [SPEED_MODE] is configured as Analog input, PWM input, or Frequency input, the

[OVERRIDE] toggle can still be used to override the speed input using the in the I2C Control Section in GUI.

2.3 Control Configuration - Motor Parameters

2.3.1 Maximum Motor Electrical Speed (Hz)

Using the motor’s data sheet, the user can input the maximum motor electrical speed in Hz. If this data is not

available, the user can input the number of pole pairs and motor mechanical speed in RPM. The GUI converts

the motor mechanical speed in RPM to motor electrical speed in Hz using Equation 1 .

fElectrical =nPolePairs ∙ ωMecℎanical

60  (1)

Where:

• ωMechanical is the mechanical speed in units revolutions per minute (RPM)

• fElectrical is the electrical speed in units of hertz (Hz)

• nPolePairs is the number of motor pole pairs

Note

Determining number of motor poles without a motor data sheet:

1. Use a lab power supply and make sure the current limit is set to less than the motor rated current.

Do not turn on the supply

2. Connect V+ of the supply to phase A and V- of the supply to phase B of the motor. Any 2 of the 3

phases can be chosen at random if they are not labeled

3. Turn on supply The rotor settles at one position with the injecting current.

4. Manually rotate the rotor until rotor snaps to another settle position. The rotor has several settle-

down positions around one mechanical cycle

5. Count the number of settle-down positions for one fully mechanical cycle, which is the number of

pole pairs. Multiplying by two calculates the number of poles.

Be careful of gearing systems within a motor. The gearing ratio determines how many rotor revolutions

correlate to the shaft’s mechanical revolution.

2.4 Control configuration - Closed Loop

2.4.1 Current Limit for Torque PI Loop

The current limit for torque PI loop is the same as the rated peak phase current of the motor. Rated peak phase

current is the peak phase current drawn by the motor at rated torque of the motor. Check the motor data sheet

for the rated peak phase current of the motor in Amps. The range of current limit values that can be configured in

MCF8315A is between 0.078125 A and 5 A.

If your motor current rating falls between two dropdown settings, then choose the higher setting.

2.5 Testing for Successful Startup into Closed Loop

1. Apply a nonzero speed command

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a. If the Speed input mode is I2C, change the “I2C Speed Command Percentage” to a non-zero value.

Once the speed command is issued, the device starts commutating and the motor starts spinning that is

proportional to the I2C Speed Command Percentage.

b. If the speed input mode is Analog, rotate the Speed Control potentiometer (R4) clockwise to control the

motor speed. Once the speed command is issued, the device starts commutating and the motor starts

spinning that is proportional to the voltage on the Speed Pin.

c. If the speed input mode is PWM, apply PWM signal to the speed pin with a given duty cycle with a low of

0 V to a high of 2.2 V (min). Once the speed command is issued, the device starts commutating and the

motor starts spinning that is proportional to the duty cycle.

2. Wait for MPET to estimate motor electrical parameters.

The Motor Parameter Extraction Tool (MPET) will attempt to measure the motor resistance, inductance, and

Motor BEMF constant (Ke) and populate these parameters automatically during the initial position detect

(IPD) and open loop stage as the rotor speed attempts to accelerate. It usually takes around 10-15 seconds

to estimate motor resistance, inductance and Motor BEMF constant Ke.

3. Check if motor spins in closed loop at commanded speed.

In closed loop, the motor should spin at the commanded speed and there should not be any faults triggered.

a. Enable the “Auto read fault status” toggle button towards the top right corner of the GUI. Then monitor

the Fault Status in the side panel to the right.

If no fault gets triggered, skip Section 2.6 and proceed to Section 3.

4. Prepare device for fault handling if any fault gets triggered.

If the motor failed to spin successfully in closed loop, check the fault status.

a. Set zero speed command by turning off the PWM, turning the potentiometer completely

counterclockwise, or setting the I2C command percentage to 0%.

b. Clear the fault status registers by clicking on the “Clear” button in the Fault Status side panel to the right

as shown in Figure 2-1

Check Section 2.6 for steps to debug faults.

This completes the essential controls section. At the end of this section, user should be able to spin the motor in

closed loop. Save the register settings by clicking File->Save Registers in the GUI. If there were no faults, skip to

Section 3.

Figure 2-1. Fault Status

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MCF8315A Tuning Guide 7

2.6 Fault Handling

Below are the faults that can possibly get triggered based on the default register configuration specified in Table

2-1.

2.6.1 MPET IPD Fault [MPET_IPD_Fault]

This fault gets triggered when there is no motor connected to the phase pins of the device or when the MPET

IPD Current threshold [MPET_IPD_CURRENT_LIMIT] is set low for motors with high resistance. If this fault is

triggered, then please follow the below suggestions.

Step 1: After confirming this fault triggers consistently from multiple start up attempts, check if all the phases of

the motor are connected to the phase pins of the device.

Step 2: If the fault persists, increase the MPET IPD Current threshold [MPET_IPD_CURRENT_LIMIT]

Step 3: If the fault still persists, check motor data sheet for motor resistance and inductance. Open the “Control

configuration – Motor Parameters” tab in All tuning settings section in the GUI and program motor phase

resistance and motor phase inductance.

Step 4: If the motor does not have a data sheet, then measure the phase to phase resistance across any two

phases using a Digital Multimeter and calculate the phase resistance by dividing the phase to phase resistance

by 2 as shown in equation Equation 2. The motor phase resistance refers to the equivalent phase to center tap

resistance, RPH as shown in Figure 2-2. This measurement holds good for both star wound and delta wound

motors.

RPH Pℎaseresistance  = RPH_PH PℎasetoPℎaseresistance

2(2)

Phase A

Phase B

Phase C

RPH_PH

RPH

Figure 2-2. Motor Resistance

To know the motor inductance, measure the phase to phase inductance at 1 kHz across any two phases using

an LCR meter. Calculate the phase inductance by dividing the phase to phase inductance by 2. Motor phase

inductance refers to the inductance from the phase output to the center tap, LPH as shown in Figure 2-3. For

motors with different phase-phase inductances, measure all three phase to phase inductances and calculate

their average and use this value as the phase to phase inductance. This measurement holds good for both star

wound and delta wound motors.

LPH_PH

Phase A

Phase B

Phase C

LPH_PH

LPH

Figure 2-3. Motor Inductance

2.6.2 MPET BEMF Fault [MPET_BEMF_Fault]

This fault gets triggered when motor stalls while running in open loop for BEMF estimation. If this fault is

triggered, then please follow the below suggestions.

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Step 1: Increase MPET Open loop current reference [MPET_OPEN_LOOP_CURR_REF]

Step 2: Decrease MPET open loop slew rate [MPET_OPEN_LOOP_SLEW_RATE]

Step 3: If this fault persists, check motor data sheet for motor BEMF constant in mV/Hz and program Motor

BEMF Constant [MOTOR_BEMF_CONST] in the “Control configuration – Motor Parameters” tab in All tuning

settings section in the GUI.

Equation 3 and Equation 4 can be used to convert Ke in mV/rpm and torque constant to Ke in mV/Hz.

BEMFConstantinmV

Hz =BEMFConstantmV

rpm ×60

Polepairs (3)

BEMFconstantmV

Hz =Torqueconstant mNm

A×  2π

Polepairs (4)

Step 4: If the motor does not have a data sheet, then measure the voltage across any two phases of the

motor using an oscilloscope by manually spinning the motor. A sinusoidal or trapezoidal voltage appears on the

oscilloscope. Measure the peak voltage EPH in milli-volts and time period TE in seconds as shown in Figure 2-4.

Calculate BEMF constant Ke as shown in Equation 5.

Phase A

Phase B

Phase C

LPH

RPH

EPH_A

LPH

RPH

EPH_C

LPH RPH

EPH_B

EPH

KtPH_N = (1/sqrt(3)) *EPH * TE

LPH

RPH

EPH_A

LPH

RPH

EPH_B

LPH

RPH

EPH_C

Figure 2-4. Motor BEMF Constant

BEMFConstantKe =EPH ×TE

3(5)

2.6.3 Abnormal BEMF Fault [ABN_BEMF]

This fault gets triggered when the difference between estimated and expected back-EMF exceeds the abnormal

BEMF threshold % [ABNNORMAL_BEMF_THR]. For example, if the expected BEMF calculated from Ke is 100

mV and the programmed abnormal BEMF threshold is 40%, this fault gets triggered when the estimated BEMF

is <60 mV or >140 mV. This also means the fault can get triggered when the programmed Ke is inaccurate.

Step 1: Estimated BEMF voltage drops when the motor speed drops. Motor speed can drop due to load

dynamics (sudden change in load). For applications with load dynamics, we expect speed to drop and recover

back. Because the speed drops, the BEMF voltage also drops and can trigger this fault. For such applications,

setting the Abnormal BEMF threshold to 70% is reccomended to avoid triggering this fault.

Step 2: This fault can get triggered if the programmed Ke is inaccurate. Follow steps recommended in Section

2.6.2 to obtain accurate Ke.

2.6.4 Lock Current Limit [LOCK_LIMIT]

This fault gets triggered when the motor is loaded above the stall torque of the motor.

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MCF8315A Tuning Guide 9

We recommend to check the motor data sheet for stall torque and load the motor below the stall torque specified

in the data sheet. If the load torque is still within the stall torque, we recommend to increase the Lock_ILIMIT in

the Control Configuration – Control Fault settings in the All tuning Settings page.

2.6.5 Hardware lock Current Limit [HW_LOCK_LIMIT]

This fault gets triggered when there is a spike in the phase current due to short circuit as shown in Figure 2-5.

Short circuit can be due to phase to phase, phase to GND or Vm to GND short. Another reason to trigger this

fault is incorrect speed loop and current loop PI controller gains.

Figure 2-5. Phase Current Waveform Showing a Spike due to Short Circuit

Step 1: Program Speed loop Kp [SPD_LOOP_KP], Speed loop Ki [SPD_LOOP_KI], current loop Kp

[CURR_LOOP_KP] and current loop Ki [CURR_LOOP_KI] to zero. This enables auto calculation of speed loop

and current loop PI controller gains.

Step 2: If the fault still persists, check the continuity across phase to phase, phase to GND or Vm to GND to

make sure there is no short across these terminals.

2.6.6 No Motor Fault [NO_MTR]

This fault gets triggered when the phase current is below No motor lock threshold % of base current.

Step 1: Make sure the motor phases are connected to J5 or TP9, TP10, or TP11.

Step 2: If the fault persists, set the No-Motor lock current threshold [NO_MTR_THR] to 0.03125A.

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