Texas Instruments MCF8316A Manuale utente

User’s Guide

MCF8316A Tuning Guide

ABSTRACT

This Tuning guide provided step by step guidence to setup MCx8316AEVM, connect MCF8316A GUI to the

EVM and tune a 3-phase Brushless DC motor using MCF8316A.

Table of Contents

1 Revision History......................................................................................................................................................................2

2 Introduction.............................................................................................................................................................................3

2.1 Hardware and GUI Setup...................................................................................................................................................3

3 Essential Controls.................................................................................................................................................................. 6

3.1 Recommended Default Values...........................................................................................................................................6

3.2 Device and Pin Configuration.............................................................................................................................................6

3.3 Control Configuration - Motor Parameters......................................................................................................................... 7

3.4 Control configuration - Closed Loop...................................................................................................................................7

3.5 Testing for Successful Startup into Closed Loop................................................................................................................7

3.6 Fault Handling.................................................................................................................................................................... 9

4 Basic Controls.......................................................................................................................................................................12

4.1 Device and Pin Configuration...........................................................................................................................................12

4.2 System Level Configuration............................................................................................................................................. 12

4.3 Control Configurations..................................................................................................................................................... 14

List of Figures

Figure 2-1. Simplified Schematic of MCF8316A..........................................................................................................................3

Figure 2-2. MCx8316A EVM Jumper Configuration.................................................................................................................... 4

Figure 2-3. MCx8316A EVM External Configuration................................................................................................................... 5

Figure 3-1. Fault Status............................................................................................................................................................... 8

Figure 3-2. Motor Resistance...................................................................................................................................................... 9

Figure 3-3. Motor Inductance.......................................................................................................................................................9

Figure 3-4. Motor BEMF Constant.............................................................................................................................................10

Figure 3-5. Phase Current Waveform Showing a Spike due to Short Circuit.............................................................................11

Figure 4-1. Phase current and FFT - Dead time compensation disabled.................................................................................. 13

Figure 4-2. Phase current and FFT - Dead time compensation enabled...................................................................................13

Figure 4-3. Power Supply voltage and phase current waveform when AVS is disabled............................................................14

Figure 4-4. Power Supply voltage and phase current waveform when AVS is enabled............................................................ 14

Figure 4-5. MPET - Phase current.............................................................................................................................................15

Figure 4-6. IPD current waveform during Rand L measurement............................................................................................... 15

Figure 4-7. Reverse Drive Function...........................................................................................................................................16

List of Tables

Table 3-1. Recommended Default Values....................................................................................................................................6

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MCF8316A Tuning Guide 1

1 Revision History

NOTE: Page numbers for previous revisions may differ from page numbers in the current version.

Changes from Revision * (August 2021) to Revision A (January 2022) Page

• RTM updates...................................................................................................................................................... 1

Trademarks

All trademarks are the property of their respective owners.

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2 Introduction

The MCF8316A 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 MCF8316A is shown in

Figure 2-1.

4.5 V to 35 V

MCF8316A

Three Phase Integrated

FET driver

Built-In Protection OUTC

nFAULT

BRAKE

DIR

SPEED

Buck Regulator

OUTB

OUTA

Optional I2C

Sensorless FOC

Control

Figure 2-1. Simplified Schematic of MCF8316A

This tuning guide provides the steps to tune a 3-phase BLDC motor using the MCF8316A. 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.

2.1 Hardware and GUI Setup

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

1. MCx8316AEVM Board.

2. A computer with the MCF8316A_GUI installed.

3. A motor to be tuned using this process. It will be good to have motor datasheet 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.

2.1.1 Jumper Configuration

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

indicate where jumpers should be installed on the EVM.

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MCF8316A Tuning Guide 3

Figure 2-2. MCx8316A EVM Jumper Configuration

2.1.2 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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Figure 2-3. MCx8316A EVM External Configuration

2.1.3 Connecting to the GUI

2.1.3.1 Connect to computer

Ensure 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.

2.1.3.2 Connect to the GUI

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

If the GUI doesn't connect automatically, please ensure 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.

2.1.3.3 Verify Hardware Connection

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

MCx8316 device by clicking on the "Read All Registers" button on the top right of this GUI. After a few seconds,

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

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MCF8316A Tuning Guide 5

3 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.

3.1 Recommended Default Values

Launch the MCF8316A EVM GUI. Load the recommended default values that are listed in Table 3-1.

Table 3-1. Recommended Default Values

Address Name Address Recommended Value

ISD_CONFIG 0x00000080 0x44638C20

REV_DRIVE_CONFIG 0x00000082 0x283AF064

MOTOR_STARTUP1 0x00000084 0x0B6807D0

MOTOR_STARTUP2 0x00000086 0x23066000

CLOSED_LOOP1 0x00000088 0x0C3181B0

CLOSED_LOOP2 0x0000008A 0x1AAD0000

CLOSED_LOOP3 0x0000008C 0x00000000

CLOSED_LOOP4 0x0000008E 0x0000012C

SPEED_PROFILES1 0x00000094 0x00000000

SPEED_PROFILES2 0x00000096 0x00000000

SPEED_PROFILES3 0x00000098 0x00000000

SPEED_PROFILES4 0x0000009A 0x00000000

SPEED_PROFILES5 0x0000009C 0x00000000

SPEED_PROFILES6 0x0000009E 0x00000000

FAULT_CONFIG1 0x00000090 0x5FE80206

FAULT_CONFIG2 0x00000092 0x74000000

PIN_CONFIG 0x000000A4 0x00000000

DEVICE_CONFIG1 0x000000A6 0x00000000

DEVICE_CONFIG2 0x000000A8 0x0000B000

PERI_CONFIG1 0x000000AA 0x40000000

GD_CONFIG1 0x000000AC 0x00000100

GD_CONFIG2 0x000000AE 0x00200000

ALGO_CTRL1 0x000000EA 0x00000000

INT_ALGO_1 0x000000A0 0x00B3407D

INT_ALGO_2 0x000000A2 0x000001A7

3.2 Device and Pin Configuration

3.2.1 Speed Input Mode

MCF8316A provides four options to configure the input speed command.

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

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

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

• Over I2C by configuring SPEED_CTRL

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Configure the speed input [SPEED_MODE] register to select the appropriate 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 will correspond to 100% speed command.

To command the speed via I2C, toggle the “Enable Speed Control via I2C” in the I2C Control Section in GUI.

3.3 Control Configuration - Motor Parameters

3.3.1 Maximum Motor Electrical Speed (Hz)

Using the motor’s datasheet, 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 will convert

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 datasheet:

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 should have settled at one position with the injecting current.

4. Manually rotate the rotor until rotor snaps to another settle position. It will have 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 will determine how many rotor

revolutions correlate to the shaft’s mechanical revolution.

3.4 Control configuration - Closed Loop

3.4.1 Current Limit for Torque PI Loop

The current limit for torque PI loop will be 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 datasheet for

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

MCF8316A is between 0.125 A and 8 A.

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

3.5 Testing for Successful Startup into Closed Loop

1. Apply a nonzero speed command

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 will start commutating and the motor should start

spinning that is proportional to the I2C Speed Command Percentage.

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MCF8316A Tuning Guide 7

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 will start commutating and the motor

should start 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 will start commutating and

the motor should start 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 3.6 and proceed to Section 4.

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 3-1

Check Section 3.6 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 4.

Figure 3-1. Fault Status

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3.6 Fault Handling

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

3-1.

3.6.1 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 datasheet 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 datasheet, 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 3-2. 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 3-2. 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 3-3. 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 3-3. Motor Inductance

3.6.2 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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MCF8316A Tuning Guide 9

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 datasheet 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 datasheet, then measure the voltage across any two phases of the motor

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

oscilloscope. Measure the peak voltage EPH in milli-volts and time period TE in seconds as shown in Figure 3-4.

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 3-4. Motor BEMF Constant

BEMFConstantKe =EPH ×TE

3(5)

3.6.3 Abnormal BEMF Fault [ABN_BEMF]

This fault gets triggered when the estimated BEMF voltage drops below the programmed Abnormal

BEMF threshold % [ABNNORMAL_BEMF_THR] of the programmed or MPET estimated BEMF constant

Ke [MOTOR_BEMF_CONST] which is programmed as 40% (default value). For example, if the estimated /

measured Ke is 5 mV/Hz and programmed Abnormal BEMF threshold is 40%, this fault gets triggered when the

estimated Ke drops below 2 mV/Hz. This fault can also 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 will also drop and can trigger this fault. For such applications,

it is recommended to set the Abnormal BEMF threshold to 10% to avoid triggering this fault.

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

3.6.2 to obtain accurate Ke.

3.6.4 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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