Design Techniques for Power-Efficient Motor Control Ravi Pragasam Senior Manager, Fusion Product Marketing April 2008 Agenda Need for power-efficient motor control Improving motor efficiencies using Programmable System Chips Integrated Pulse Width Modulation Power efficiency schemes Quadrature encoder interface Load matching and variable speed control Slip control Summary Design Techniques for Power-Efficient Motor Control Feb 29 08 Motor Control Power Consumption Profile Electronic motors have become increasingly ubiquitous With this growth comes increasing requirements for improved performance, efficiency and flexibility Electric motors use half of all US electricity consumed In 2005, US consumed 4,055 billion KWh of electrical power More than 50% of this was consumed by electric motors Design Techniques for Power-Efficient Motor Control Feb 29 08 The Need for Power-efficient Motor Control High cost of control and power electronics has been a major barrier to deployment of intelligent power management solutions Implemented broadly, efficient electronic motor control could result in savings of as much as 15% of the power consumed in the U.S. An annual reduction of as much as 300 billion kWh and $15 billion saved Design Techniques for Power-Efficient Motor Control Feb 29 08 Motors, Motors Everywhere Consumer Applications Type of Motor and Applied Control Algorithm Toys Model Aircrafts DVD/CD Players BLDC Trapezoidal Stepper Half/Full Step Micro Step Conventional Shunt Wound Control Scheme Open-Loop Appliance (White Goods) Refrigerators Washers/Dryers Dish Washers PMSM FOC Trapezoidal ACIM V/F Slip Optimization Conventional Shunt Wound Open-Loop Close-Loop Sensorless Design Techniques for Power-Efficient Motor Control Industrial/HVAC Pumps Conveyers Compressors Inverters Meters PMSM FOC Trapezoidal ACIM FOC V/F Slip Optimization Stepper Industrial Servo Material Handler Robot Instrumentation Office Equipment PMSM FOC Trapezoidal ACIM FOC Slip Optimization Stepper Half/Full/Micro Step Half/Full/Micro Step Open-Loop Close-Loop Sensor Sensorless Close-Loop Sensor Sensorless Feb 29 08 Agenda Need for power-efficient motor control Improving motor efficiencies using Programmable System Chips Integrated Pulse Width Modulation Power-efficiency schemes Quadrature encoder interface Load matching and variable speed control Slip control Summary Design Techniques for Power-Efficient Motor Control 4/29/2008Feb 29Feb 08 29 08 6 Traditional Motor Control Implementation Design Techniques for Power-Efficient Motor Control Feb 29 08 Traditional Motor Control Design Component selection process Selection depends on application needs and type of motor being controlled ADC – how many bits of resolution, accuracy, sampling rate, conversion time… Interface – number of input channels, signal conditioning, amplifiers, filters… Sensors – hall effect, back EMF,… CPU – processor cores (ARM, 8051, State Machines,…) Network Interfaces – connectivity needs, what is the interface, how fast is the data rate transfer, any protocols,… Traditional solutions offer one or more function, but not all Determine if some of the above functions can be achieved with a microcontroller Designer will need to make a decision based on the following Power needs Performance needs Overall system cost Design environment knowledge Design cycle Once selection made, use the design environment to generate the application When design complete, debug and validate to ensure that the specification is met Design Techniques for Power-Efficient Motor Control 4/29/2008 8 Changing Motor Control Design Component selection process Ideal solution will integrate several functions into one Several benefits can be obtained with an integrated solution Lower overall power Lower system cost Less design complexity Better signal integrity Single platform that can be scaled Optional functions can be included based on needs Platform needs to be flexible to accommodate different needs Use design environment to generate the application When design complete, debug and validate to ensure that the specification is met Design Techniques for Power-Efficient Motor Control 4/29/2008 9 Programmable System Chips - PSCs Incorporate analog functions, embedded flash memory and FPGA fabric in a single chip Flexible platform for scalability Offers benefits of monolithic design environment Design Techniques for Power-Efficient Motor Control PSC Offers Analog Integration Up to 12 bit or 600 Ksps Better than 1% total channel accuracy with calibration Internal reference voltage GPIO Analog Inputs Ana Mux MOSFET Outputs A/D FPGA Fabric (incl. SRAM, CCC/PLL, IO) Successive Approximation Register (SAR) ADC Built in sample and hold Increases accuracy of dynamic signals Analog I/O ± 12 V Tolerant Up to 30 channels input Current monitor block FLASH Memory Xtal OSC, RC OSC, RTC, Vreg 2 mV resolution Temperature monitor block + 3o C accuracy + 5O C Offset MOSFET Gate driver output JTAG Port Programmable drive strength P and N channel devices 4/29/2008Feb 29 08 11 PSC Analog Quad – I/O Structures Essence of Motor Control Offers the analog interface, sensing with signal conditioning functions required System management and motor control benefit from Integrated current, temperature and voltage monitoring Supports up to 30 channels FET gate driver output to drive H-Bridge Unique positive and negative polarity support Pre-scaler ranges: 1, 2, 4, 8, 12, 16 Volts Selectable ADC reference (internal vs external) 8/10/12-bit selectable resolution Design Techniques for Power-Efficient Motor Control Feb 29 08 Methodology For Flexible Functionality Graphical productivity tools ADC sampling Digital low-pass filtering Threshold comparisons State filtering Analog input High current output Flash memory access Automatically connects FPGA, flash and analog block with required functions 4/29/2008Feb 29 08 13 Using PSCs for Motor Control PSC can integrate multiple functions into a single platform Take analog inputs from motor with the analog interface and ADC Leverage CPU for processing and control (Cortex-M1, 8051) Utilize flash memory to store the program and embedded SRAM blocks to store data Use clock circuitry for generating signals needed for control (RC Oscillator) Interface to external components with network and peripheral interface Utilize soft PWM cores to generate current or voltage for gate drivers Design Techniques for Power-Efficient Motor Control Programmable System Chip PSC Feb 29 08 PSCs versus Discrete Solutions Features Programmable System Chip (PSC) PWM Frequency Control On-board PLL and clock generators can target a wide range of motors Software-generated PWM; Use of internal timers to generate PWM frequencies; Algorithm/computing resources stressed Sensing & Protection Internal threshold flags control and protect; Drive over-current, overtemperature … External implementation results in increased BOM cost Real Time Monitoring System Internal real-time counter (RTC) to log/record drive parameters and characteristics Would require RTC and NVM On-board NVM to store configuration data for fast and efficient drive operation Reprogrammable in H/W and S/W Need external NVM and hardware to store configuration data Damping Dedicated on-board PWM IP coasting/braking possible Timer based; Software overhead BEMF – Zero Crossing Sensorless operation using internal ADCs possible with minimal external components External comparator circuit required for sensorless operation Multiple Drive support Rich I/O features and flexibility to drive multiple motors on single platform Would require additional devices Configuration Storage Design Techniques for Power-Efficient Motor Control Discrete Solutions (Microcontroller/DSP) Pulse Width Modulation (PWM) - Basics PWM control works by switching the power supplied to the motor on and off very rapidly DC voltage is converted to a square-wave signal, alternating between fully on and zero, giving the motor a series of power "kicks" If switching frequency is high enough, the motor runs at steady speed due to fly-wheel momentum By adjusting the signal’s duty cycle, the average power and motor speed can vary Used to implement closed loop control of motors Can be implemented by discrete components Design Techniques for Power-Efficient Motor Control Feb 29 08 Integrated Pulse Width Modulation in PSC Programmable System Chip Standard PWM solutions offer very little flexibility Not a “one size fits all” for all motor control apps Number of windings, voltage/current ratings, torque profiles and other parameters widely vary PSC implementation allows the designer to customize PWM instead of “making do” with MCU or DSP capabilities Design Techniques for Power-Efficient Motor Control Feb 29 08 Pulse Width Modulation IP with PSC 8 PWM digital outputs Edge control based on configurable 8bit PWM period 8-bit pre-scaler value Duty cycle – 0% to 100% Can perform closed-loop control Combined with processor or simple state machine Design Techniques for Power-Efficient Motor Control Feb 29 08 PWM Implementation Methodology Allows designer to define parameters based on need Number of outputs Negative or positive edge of each output Interrupt mask Enable PWM Duty cycle Effectively provides power-sensitive motor control based on environmental need Design Techniques for Power-Efficient Motor Control Feb 29 08 Agenda Need for power-efficient motor control Improving motor efficiencies using Programmable System Chips Integrated Pulse Width Modulation Power-efficiency schemes Quadrature encoder interface Load matching and variable speed control Slip control Summary Design Techniques for Power-Efficient Motor Control Feb 4/29/2008 29 08 20 Quadrature Encoder - Background A B Light Source Code Track on Disk Channel A Channel B Quadrature Encoder Output Channel A 10 11 01 00 01 11 10 00 Channel B 90o Counter Clockwise Clockwise Quadrature encoder is composed of a light source, wheel and receptor Technique uses sinusoidal signal generated from light source to represent position in BLDC motors Information is communicated to other machine interfaces Receptor output can be in the form of pulses based on wheel position Benefits Simpler to implement Improved reliability Immune to noise 4/29/2008 21 Implementing Quadrature Encoder Interface CCC/PLL QEA Filter ChA Index Filter ChB Quadrature Decoder DIR(U/D) Reset Up/Down Counter CNT QEB Filter FPGA Fusion Block FPGA Logic Most high-precision motors, like the servo-type stepper motors, support quadrature-encoder interfaces Control system must provide quadrature-encoder interface logic to determine accurate speed, position and acceleration of the motion rotors With a PSC, accuracy and dynamic speed can be adjusted, depending on the characteristics of the motor Design Techniques for Power-Efficient Motor Control Feb 29 08 Traditional Quadrature Encoder Interface Implementation CCC/PLL QEA Filter ChA Index Filter ChB Quadrature Decoder DIR(U/D) Reset Up/Down Counter CNT QEB Filter FPGA Fusion Block FPGA Logic Uses discrete components DSP chips (filters) Timers (clocks) Quadrature encoder block (Schmitt Triggers or pulse generators) Logic (counters) Not optimized for efficiency and power Higher design complexity with little flexibility Design Techniques for Power-Efficient Motor Control Feb 29 08 PSC Quadrature Encoder Interface Implementation CCC/PLL Filter QEA ChA Filter Index ChB Quadrature Decoder DIR(U/D) Reset Up/Down Counter CNT Filter QEB FPGA Fusion Block FPGA Logic PSC used to implement all the above functions in a single integrated solution Can be optimized for application to deliver a power-efficient solution Each function customized to address the application need Highly flexible and less design complexity Design Techniques for Power-Efficient Motor Control Feb 29 08 Load Matching and Variable Speed Control For applications that need to be operated at a constant speed, intelligent load matching is a great way to deliver an efficient solution Load sensed and matched with the proper input power, maximizing efficiency and minimizing power consumption and operating costs Variable-Frequency Drives (VFD) For low-cost drives suitable for applications with known loading, VFDs used to vary the motor's rotational speed to match current load condition Vector Control Schemes (Field oriented) Use real world feedback (speed or torque) to adjust to load variations Deals with varying operating conditions and allows responsive and accurate speed control with a changing load Offers optimum efficiency even during motor transition Traditional solutions use microcontrollers and DSPs to implement the closed loop control for speed and torque Using PSCs allow a single device to be used to control a range of motor types, including permanent-magnet AC and brushless DC motors Design Techniques for Power-Efficient Motor Control Feb 29 08 Slip Control Actual Current Desired Torque Commanded Current Current & Slip Tables PI Controller Slip Frequency (fs) Current Magnitude Calculation ia Current ib Sensor va Volts Frequency ADC V/F to 3φ vb Voltage to Hightime PWM Power Stage vc + + Motor Frequency (fr) Speed Calculator Speed Sensor Bottleneck Area A slip is a percentage of synchronous speed When none of the motors run with a fixed level of loading, the load can set a “slip” in the motor and determine the actual speed of the motor shaft The slip affects the torque and operation of the motor In the control algorithm, slip frequency is often the key variable Design Techniques for Power-Efficient Motor Control Feb 29 08 Efficiencies from Slip Control An optimized slip control mechanism is the key factor in getting the required torque and efficiency An optimized slip control compensation system can benefit power saving in typical AC motors, according to U.S. Environmental Protection Agency 160 Power Reduction due to Slip Control Compensation (Input Power = 8477W) Reduction in Input Power 140 120 100 80 60 40 20 0 40:16 50:25 60:36 70:49 80:64 90:81 95:90 Speed:Torque Design Techniques for Power-Efficient Motor Control Feb 29 08 Slip Control Using Mixed-signal PSCs Iq SRAM NVM Id Ia S/H Park Transformation Clark Transformation ADC Ib S/H + _+ ID PID Controller Vq PID Controller Vd Slip Slip Freq Frequency Calculator (fs) + Desired torque Power Stage Modulator CPU _ IQ PWM Gate Drive PMSM ACIM Encoder Frequency + Motor Frequency (fr) Encoder Interface Soft IP Function Option in PSC PSC Hard Function SW on CPU (option in PSC) The slip frequency calculator implemented as software running on CPU The other functions needed can be optional soft IP on PSC This scheme will provide an efficient slip control method and deliver a power-optimized motor Design Techniques for Power-Efficient Motor Control Feb 29 08 Agenda Need for power-efficient motor control Improving motor efficiencies using Programmable System Chips Integrated Pulse Width Modulation Power-efficiency schemes Quadrature encoder interface Load matching and variable speed control Slip control Summary Design Techniques for Power-Efficient Motor Control 4/29/2008Feb Feb 29 08 29 Summary Increasing demand for energy savings and lower power puts pressure on designers to use more efficient motors Traditional solutions may not offer the best solution for efficient motors Highly integrated, flexible PSCs allow designers to implement the most efficient design for their application and also use the same device across motor applications Implemented broadly, electronic motor control could result in savings of as much as 15% of the power used in the U.S. Design Techniques for Power-Efficient Motor Control Feb 29 08