1. Digital Motion Control System Design - From the Ground Up

2. Introduction Break Motion Control Design into three parts
Digital Hardware Design
Power Hardware Design
Software Design
Introduce D3 Engineering’s Motor Control Development Kit

3. Control Hardware Choose Feedback Method
Choose Communications interface
Isolation requirements
Isolation between control and power electronics
Isolation between control electronics and outside world
Digital I/O
Analog I/O
Pulse Width Modulation (PWM)
Putting it all together

4. Feedback Incremental or Absolute Resolution requirements
Environmental considerations

5. Incremental Optical Encoder
Code disk with optical transmitter and receiver on either side
Outputs two quadrature signals, A and B, and an index pulse
Multiple options for output configuration
Open collector
Differential Line Driver
5V-24V
Each edge is counted giving 4x resolution
Commutation tracks also available
Available in high resolution (>100K counts per rev)
Easy to interface, no analog hardware

6. Incremental Optical Encoder
Standard products not typically good for harsh environments
No absolute position data

7. Resolver A rotating transformer Input – AC excitation
Output – Sin and Cos of rotor angle modulated at excitation frequency

8. Resolver Typically considered rugged, good for harsh environments
Absolute within 1 revolution

9. Resolver Requires Resolver to Digital Converter (RDC)
Separate ASIC
Implement in DSP
Requires careful analog design
Resolution is a function of RDC

10. Absolute Encoder Serial or Parallel interface
Typically up to 17-bit single turn resolution
Absolute over single or multiple revolutions
12-bit multi-turn resolution typical
Available user memory
Currently popular among commercial industrial servo drives

11. Communications CAN Host Controller External Sensors DeviceNet LIN
Automotive
RS-232
Host PC
Display/Keypad
RS-485
Multi-drop
SPI
Interprocessor
Absolute Encoder
EEPROM
I2C
Display

12. Digital I/O Allow drive to interact with the outside world Sensors
Limit Switches
Relays
Enable Signal
Fault Output

13. Analog I/O To/From the outside world Within the drive Velocity command
Torque command
External sensor
Potentiometer
LVDT
Monitor Output (DAC)
+/-10V
4-20mA
Within the drive
Current sensing
Voltage sensing
Temperature sensing

14. Pulse Width Modulation (PWM)
Modulate the duty cycle of a square wave to generate an output waveform
Generate the switching pattern of power transistors in a motor drive
Regulate Current flow
Generate AC motor voltages

15. High Performance DSP TMS320C28x Family Up to 150MHz
Internal Flash Memory (Up to 512K)
Internal RAM (Up to 68K)
Floating Point Unit (300 MFLOPS)
Includes peripherals needed for motor control

16. High Performance DSP ADC – 12-bit, 12.5 MSPS Current Sensing
Voltage Sensing
Resolver
Analog Inputs

17. High Performance DSP Enhanced Quadrature Encoder Pulse Module (eQEP)
Implement incremental encoder feedback
Use as Pulse/Direction input

18. High Performance DSP Enhanced PWM Module (ePWM)
Control switching of the power hardware
Digital to Analog Conversion (DAC)
Generate resolver excitation signal

19. High Performance DSP
Communications Peripherals
SPI
SCI
I2C
CAN

20. Power Hardware Design DC Bus Inverter Control power High-side supplies
Current Sense

21. DC Bus The DC Bus supplies power to the motor
Supply can be from a DC source or rectified AC
An AC source is typically single or three-phase

22. DC Bus – Single Phase AC Input
Rectifier
Inrush current limiting
DC Bus capacitors
Voltage doubler

23. DC Bus – Rectifier Single-phase for up to 1-2KW
Higher power requires three-phase input and three-phase rectifier

24. DC Bus – Inrush Current Limiter
During a “cold start” DC Bus capacitors initially look like a short circuit
Need to limit inrush current to prevent damage to rectifier and DC Bus capacitors.

25. DC Bus – Inrush Current Limiter
Classic approach is to use a resistor in series with the DC Bus
Once capacitors are charged resistor is shunted by a relay
Resistor doesn’t need to carry full DC Bus current

26. DC Bus – Inrush Current Limiter
Resistor and Relay inrush current limiter is a common failure point in motor drives
Relay can’t be used in some hazardous environments

27. DC Bus Inrush Current Limiter
Alternative – Negative Temperature Coefficient Thermistor (NTC)
Starts out at high resistance when cold, resistance decreases to a few milliohms as current flows and device heats up
No need for shunt relay
Limited range of continuous current ratings
May not work when ambient temperature requirements are high

28. DC Bus – Inrush Current Limiter
Replace relay with a solid state device
OK for hazardous environments
Requires more hardware to turn the device ON

29. DC Bus – Inrush Current Limiter
Need to extensively test whatever method you choose
At max ambient temperature
At max load
Power cycle testing

30. DC Bus – Voltage Doubler
Ability to obtain 300V DC Bus from 110VAC source
Each capacitor charges separately on opposing half cycles of the AC input
Rectified DC Bus is equal to 2 times the peak AC input
Output power must stay the same so max continuous current is cut in half

31. Inverter
A three-phase bridge made of IGBTs or MOSFETs that switch power to the motor
Usually implemented as 6 discrete devices or 1 Intelligent Power Module

32. Inverter - IPM
Intelligent Power Modules are typically designed to directly interface to a DSP or microcontroller
Integrated high and low-side gate drive
Integrated UVLO
Integrated Over-current/Short-circuit protection
Limited packaging options
Limited current/voltage ratings

33. Inverter – Discrete Implementation
More packaging flexability
Greater variety in voltage/current ratings
Need to design external gate drive, UVLO, and over-current detection

34. Control Power Supply Minimum of two supplies
Gate Drive supply
Logic supply
Regulated from DC Bus or separate control power input
Isolated or Non-isolated

35. Non-isolated Buck Converter
Usually used in low-cost designs
Regulate control supplies directly from DC Bus
Digital supply regulated from Gate Drive supply with LDO

36. Isolated Flyback Converter
Powered from DC bus or separate control power input
Generate multiple voltages

37. High-Side Supplies Why do we need separate high-side supplies?
Boot-strap supplies
Separate floating supplies

38. Why High-Side Supplies
IGBT needs VGE > VGEsat to turn completely on
MOSFET needs VGS > VGSsat to turn completely on

39. Why High-Side Supplies
Emitter (or Source) of High-Side device “floats” with motor phase

40. Bootstrap Supplies High-Side Gate Drive powered by bootstrap capacitor
Capacitor charged through diode when low-side device is ON

41. Bootstrap Supplies Can’t run at 100% PWM duty cycle indefinitely
Need some low-side ON-time to charge bootstrap capacitor
Inexpensive

42. Bootstrap Supplies Some considerations for sizing bootstrap components
Minimum Vboot voltage
Gate driver quiescent current
IGBT Gate charge
High-side On-time

43. Separate Floating Supplies
Add three additional windings to flyback transformer
No more limitations on duty cycle
Bigger transformer
More expensive

44. Current Sense Shunt resistor Hall-effect device
Current is measured as voltage drop across a current sense resistor
Hall-effect device
The magnetic field of a current carrying wire is sensed and converted to a voltage

45. Shunt Resistor Place between low-side power device and DC Bus N
Current sense when low-side is ON and high-side is off
Can’t achieve 100% duty cycle, need some OFF time to sense current
Because of power loss, becomes less practical as current gets higher

46. Shunt Resistor Place shunt resistor in motor phase
Need isolated measurement circuitry
Able to sense currents at 100% duty cycle

47. Hall-effect Current Sensor
Inherently and isolated sensor
Usually able to be powered from logic supply
Less power dissipation, able to sense higher currents
Typically more expensive than shunt measurement
Available in fixed sensitivity ranges

48. Motor Control Hardware/Software Interface
Information about the system is acquired through the ADC
The system is controlled by the PWMs
Both information exchanges happen through peripherals in the 28x DSPs
Other feedback is acquired through logical interfaces like GPIO, QEP, Capture and Comm. peripherals

49. ADC Sampling
For a quality motion control algorithm, accurate current information is required
Noise can be reduced by synching current sampling with PWM frequency
Some phase delay between PWM switching edge and ADC sample should be applied to allow for signal to settle
If sampling more than one phase of a motor simultaneous Sampling should be used to acquire signals at same point in time.
Proper capacitance on ADC inputs should be used to allow for good charge transfer. A good rule is 200x the ADC capacitance

50. ADC Sampling for FOC
Current can be sampled in leg of switch or inline with motor phase
If sampled in leg of switch a time when all Switches are switched to ground must be allowed
Leg sampling will not allow for 100% duty cycle operation
Depending on worst case slew rate as much as 10% duty cycle might be lost
Sampling in line with phase requires either a floating reference point or the use of hall or other non intrusive current sensors.

51. PWM Sampling should be synched to PWM frequency
System torque/current loop should also run at PWM frequency and should be able to be processed/executed in the same period
The main control loop should also run at this frequency or some even multiple of this frequency to keep system synchronous.

52. FOC Controls Diagram Sample Custom Designed Blocks
TI DMC Library Blocks

53. More info available at www.ti.com/iqmath
IQ Math Library
Near Floating Point Precision with Fixed Point Performance
TI provided IQ math Library is just one tool available to TI customers.
Library is available in both Mathworks and as a C library.
TI, its customers and 3rd Parties like D3 have worked together to optimize available tools and algorithms like the IQ math Library.
More info available at

54. Digital Filtering For Feedback
Observer Tracking filter
Performance adjusted by changing Alpha and Beta
Possible application as a resolver angle filter
Can be related to basic 2nd order Transfer function (TF)
Alpha and Beta can be expressed in terms of a Damping Coefficient and a Natural Frequency

55. Communications
CAN
SCI
I2C
SPI
I/O

56. Modular Design With Simulink®
Mathworks and TI Tools

57. Motor Control Development Kit
A platform for D3 and our customers to begin development of motor control applications
Include many common features of a motor control application
Allow expansion and flexibility
A two board design, control board and power board
Allows mix and match of control and power boards
Allows control board to be a stand-alone product

58. Motor Development Kit Contol board based on TMS320F2806 DSP
Isolated from power board and outside world
5V input from power board or wall pack
All peripherals come to headers for expansion

59. Motor Development Kit Feedback Communications Digital I/O
Encoder
Resolver
Communications
RS-232
USB
CAN
Digital I/O
Inputs (4)
Outputs (3)
Power Board Interface
PWM (6)
Motor Phase Current Sense (3)
DC Bus Current Sense
DC Bus Voltage Sense
Power Board Fault signal 5V

60. Motor Development Kit
Power board designed to accept Smart Power Modules from 3A to 30A
DC Bus rectified from 110V or 220V AC
Voltage Doubler
Separate control power and DC bus
Isolated from control board
Sense three phase currents and DC bus current through shunt resistors
Bootstrap high-side supplies
DC Bus voltage sense

61. Motor Development Kit
Come see the MDK in action at our booth