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

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

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’.

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

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

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

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

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

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

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

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

MCUs- MCPWM (dsPIC30F) MCPWM Hardware manual http://ww1.microchip.com/downloads/en/DeviceDoc/70062E.pdf MCPWM Hardware manual

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

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

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

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

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

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

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

Conclusion Devices MCUs, FPGAs DC Motor Sensorless PMSM

Motor Control Resources Digi-Key Product Training Modules (49) [Filter for motor control] Stepper Motor Control Fundamentals (Microchip Technology) http://dkc1.digikey.com/us/en/TOD/Microchip/StepperMotorControl/StepperMotorControl.html Control of Magnetic Fields (ST) http://dkc1.digikey.com/us/en/tod/STMicroelectronics/MagneticFields/MagneticFields.html Motor Control Topology and Drivers (ST) http://dkc1.digikey.com/us/en/tod/stmicroelectronics/Motor-Control-Smart/Motor-Control-Smart.html

Additional Resources Suppliers Tutorials and Application Notes: FOC App Note (Microchip) http://ww1.microchip.com/downloads/en/AppNotes/01078B.pdf Maxim Integrated Circuits (Sensing Circuits) http://www.maximintegrated.com/en/app-notes/index.mvp/id/4697 Trapezoidal Control of BLDC Motors (TI) http://www.ti.com/lit/an/sprabq7/sprabq7.pdf Simple Motor Control Library (ST) http://www.st.com/st-web-ui/static/active/en/resource/technical/document/application_note/CD00006812.pdf

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