1. Implementing Motor Control Designs with MCUs and FPGAs
Class 3: Device Features and Functions
3/11/2015
Warren Miller

2. This Week’s Agenda
3/9/15 An Introduction to Motor Control 3/10/15 Motor Control Algorithms 3/11/15 Device Features and Functions 3/12/15 Software Tools 3/13/15 Dev Kits and Reference Designs

3. Course Description
Motor control is one of the most common MCU applications and over the years MCUs have continue to add new features and capabilities to make motor control easier to implement.
Even FPGAs have evolved to address this application area.
This class provides the beginner a comprehensive introduction to motor control and the experienced engineer a refresher and update on the newest devices, software tools and development kits.
Students wanting to extend their knowledge are encouraged to do an optional final hands-on ‘class project’.

4. Today’s Topics Types of Devices Motor Control Algorithms Reminder
Example Implementations Using
Standard Products, Drivers, Sensors
MCUs, FPGAs
Examples: Brushless DC, AC Induction, Sensorless PMSM
Resources

5. Motor Control Algorithms
All about controlling voltage and current
All about timing and waveform generation
Feedback loop- the main concept
Can be very simple or very complex
Simple- low efficiency, fixed load
Complex- multiple speed, dynamic load, high efficiency, low noise, low vibration, low wear, no sparks, no electrical noise, etc.
Renesas Motor Control Algorithm Site

6. Brushed DC Motors- Example Devices
MCU, Supervisor
Sensors
Gate Driver, MOSFET Switch
ADC, Op Amp
Voltage Converter
Display Panel
UART, Isolation, Transceiver

7. Brushed DC Motors- Example Devices
MCU, Supervisor
Sensor
Voltage Converter
DC Motor Controller
Display Panel
UART, Isolation, Transceiver TI
DRV8837

8. Brushless DC Motors- Example Devices
MCU, Supervisor
Sensor
Voltage Converter
DC Motor Controller
Display Panel
UART, Isolation, Transceiver
MOSFET H-Bridge
ADCs

9. AC Induction Motors- Example Devices
MCU, Supervisor
UART, Isolation, Transceiver
Sensors
Voltage Converters
IGBT, Drivers
ADCs
Display Panel
IGBT- Insulated Gate Bipolar Transitor

10. Motor Control Algorithms- MCUs
MCU Key Features
Computation
DSP, Transforms
PID Control Loops
Encoders
Timing
PWM
ADC
Sensors
Measure Current
DAC
Voltage Control
Interface
UART, CAN, LIN
Ethernet, USB
Renesas Motor Control Algorithm Site

11. MCUs- Timing Pulse Width Modulation Number of Channels Waveform Shape
Period, Duty Cycle
Timer
Compare Registers
Period
Duty Cycle
Frequency vs. Resolution
IGBT- Insulated Gate Bipolar Transitor

12. MCUs- MCPWM (dsPIC30F) MCPWM Hardware manual
MCPWM Hardware manual

13. Sensorless FoC of a PMSM
Permanent Magnet Synchronous Motor (PMSM)
Common for Appliance motor control
Washing machines
HVAC compressors
Device used- Microchip dsPIC
PWM capable timers
Analog to Digital converter
Quadrature Encoder Interface (QEI)
DSP computation (1 cycle)
MAC
Fractional operations
Microchip app note

14. Sensorless Control of a PMSM
1: Measure stator currents (ia, ib, ic)
-They sum to 0
2: Convert to two axis system (ialpha, ibeta)
-As viewed from the stator
3: Rotate to align with the rotor flux (id and iq)
-Constant in steady state
-id controls rotor flux, Iq controls torque
4: Use control loop to generate Vd and Vq voltage vectors
5: Estimate new transformation angle
6: Rotate Vq and Vd back to stationary reference with new angle
7: Transform new voltages back to Va, Vb and Vc
- Create new PWM duty cycle values
Key Concept- Change of Reference
Stator Perspective (Fixed)
Rotating Flux
Speed = f( Flux vector)
Rotor Perspective (Rotating)
Stationary Flux
Stator currents constant
(in steady state)
Goal: control the stator currents for desired rotor currents
Can’t measure rotor currents directly!
With a reference change the stator currents can be controlled like DC values
Use a standard control loop
Microchip app note

15. Clarke and Park Transforms
Clarke Transform
Moves a 3-axis, 2-dimensional coordinate system, referenced to the stator, into a 2-axis system
Keeps the same frame of reference
Ia, ib, ic (120o from each other) and sum to zero
Transformed into ialpha and ibeta
Stator current is now represented in a two axis orthogonal system
Axis is alpha/beta
Park Transform
Transform into 2-axis system rotating with the rotor flux
Use the rotor theta
Results in values on the d/q axis
Microchip app note

16. PID Control Background
Proportional Integral Derivative (PID) Control
Responds to an error signal to adjust the controller quantity
Uses periodic sampling interval of sufficient frequency
Error = Desired – Measured
Sign indicates direction of change
Proportional Term = Error * P Gain
Results in small steady state error
Integral Term = Sum of Error * I Gain
Eliminates ‘running’ errors
Differential Term = Error Difference * D Gain
Needed for fast response
Not typically needed in motors
Select P gain for overall system control
Increase I gain to reduce error to 0
I should be small wrt P
Some experimenting is useful…
Microchip app note

17. PI Control Microchip app note Three PI control loops are used
Rotor speed, flux and torque
Outer Loop- Motor speed
Inner Loops- iq (torque) and id (flux)
The Kc.Excess term is used to limit integral windup
Excess = Unlimited output – Limited Output
Kc term limits Excess and thus Sum
Microchip app note

18. And the Rest… Inverse Park and Clarke Field Weakening Faster speed
Position and Speed Estimation
Back EMF Estimation

19. FPGAs Computationally Intensive High Reliability
Industrial Connectivity
RTOS
Multiple Motors
5us Performance Closed Loops
High-level Algorithm Development
Fast Prototype Development and Application Exploration
Function Library
Altera Motor Control

20. Conclusion
Devices MCUs, FPGAs DC Motor Sensorless PMSM

21. Motor Control Resources
Digi-Key Product Training Modules (49) [Filter for motor control] Stepper Motor Control Fundamentals (Microchip Technology) Control of Magnetic Fields (ST) Motor Control Topology and Drivers (ST)

22. Additional Resources
Suppliers Tutorials and Application Notes: FOC App Note (Microchip) Maxim Integrated Circuits (Sensing Circuits) Trapezoidal Control of BLDC Motors (TI) Simple Motor Control Library (ST)

23. This Week’s Agenda
3/9/15 An Introduction to Motor Control 3/10/15 Motor Control Algorithms 3/11/15 Device Features and Functions 3/12/15 Software Tools 3/13/15 Dev Kits and Reference Designs