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BLDC motor control reference design press presentation

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  • The Sensorless BLDC (Brushless DC) Motor Control Reference Design is a ready to use motor control solution with production-quality hardware and software for quick evaluation and deployment in cost-sensitive applications. The reference design is a vehicle for developers to evaluate and adopt low-cost BLDC Motor Control solutions using the recently launched C8051F85x/6x product family. The C8051F85x/6x has best-in-class analog peripherals:16-channel, 12-bit, 200 ksps or 10-bit, 800 ksps ADC with programmable gain Two analog comparators with programmable hysteresis and response time 3-channel enhanced PWM with 8- to 11-bit or 16-bit resolutionCenter or edge aligned PWMOutput polarity select controlCycle-by-cycle current control for overcurrent or fault detectionComparator clear function
  • The BLDC motor control reference design targets sensorless brushless DC motor control applications.
  • The motor control hardware contains an MCU control board, a powertrain board and Turnigy 450 Series 3800 kV brushless outrunner mounted on a motor mount board.The powertrain board contains the gate drivers, power MOSFETs, current sensing resistor as well as resistor dividers to attenuate motor phase voltages so that they can be measured by the MCUThe MCU board contains C8051F850 MCU, buttons to start/stop and change direction of the motor as well as a button to reset the MCU. The PWM output from the MCU is used to drive the gate drivers on the powertrain board. The MCU board also contains an op-amp to amplify the current sensing voltage so that it can be measured by the MCU.
  • The motor control hardware contains an MCU control board, a powertrain board and Turnigy 450 Series 3800 kV brushless outrunner mounted on a motor mount board.The MCU board consists of the following:C8051F850Motor start/stop, clockwise/anticlockwise direction and MCU reset buttonOne rotary variable resistance potentiometer to control speedOp-amp to amplify and bias the current sense voltageUSB hub to support:C2 USB debug interfaceCP2103 USB-UART bridge operating at 115200 baudThe powertrain board contains:Six IRFH7446 Power MOSFETS for the inverter circuitThree Silicon Labs Si8230 isolated dual drivers50 mohms current sensing resistor rated for 10 WResistor divider to generate attenuated motor voltage supply (VMDC) - allows MCU to determine if motor supply voltage is high enough for safe operationResistor dividers to generate attenuated motor phase voltages with a small positive offset voltage (VMA,VMB, VMC)Resistor network to generate attenuated sum of motor phase voltages with a small positive offset voltage (VMY)
  • A strong value proposition of the Sensorless Brushless DC Motor Control Reference Design is the supporting environment from tools, development kits, software libraries and collateral. The motor control reference design software allows real time control and monitoring of the motor.Silicon Labs offers differentiation in:Motor control source code available which expedites design-insMotor control GUI PC application (Silicon Labs Spinner) offers users flexibility and ease of use when controlling and understanding the BLDC motor operation
  • Specifications of the motor control reference design as well as the motor included in the kit.
  • Advantages of the BLDC Motor Control Reference Design:Achieve 200,000 rpm with Silicon Labs low cost C8051F85x/6x MCU product familyThe C8051F85x/6x MCU architecture features a patented crossbar that enables developers to choose peripherals and pinout placement based on their application needs and layout constraints without worrying about the pre-set limitations and pin conflicts ------ allowing usage of small pinout packages, simplifying PCB routing, minimizing PCB layers and ultimately reducing design time, lowering system cost and most importantly optimal usage of pinsThis design kit implements a technique that takes advantage of some unique features of the C8051F850. The open terminal does not yield any zero crossing information when current flows through that terminal. So, a tracking signal is used to disable a comparator input so that the comparator is effectively not operational when current is flowing in the open terminal. This reduces CPU overhead since there is no need to interrupt PWM cycle for zero crossing detectionThe design kit uses the comparator clear feature to trim the motor PWM duty cycle automatically to ensure that the current does not exceed a predetermined level regardless of the motor load or motor supply voltage.In block commutation driving method, maximum speed is achieved when the motor PWM duty cycle is at 100%. Hyperdrive mode is a technique to further increase this maximum speed. This is done by energizing the open phase after zero crossing has been detected
  • Best-in-class analog peripherals:16-channel, 12-bit, 200 ksps or 10-bit, 800 ksps ADC with programmable gain Two analog comparators with programmable hysteresis and response time The two comparators share a multiplexer with the ADC which helps in saving valuable pins for GPIO’s.Internal precision voltage reference with an absolute accuracy of ±2%
  • Motor control comparator multiplexerFlexible comparator multiplexer to support sensorless BEMF commutationThe two comparators share a multiplexer with the ADC which helps in saving valuable pins for GPIO’s. The three motor terminals can be connected to three pins on the chip and the multiplexer inside can be used to route them to the ADC and the comparators. PWM with hardware fault protection3-channel enhanced PWM with 8- to 11-bit or 16-bit resolutionCenter or edge aligned PWMOutput polarity select controlCycle-by-cycle current control for overcurrent or fault detectionComparator clear function (hardware fault protection)
  • Detecting the back-EMF (BEMF) zero crossing point can be challenging when there is an active PWM signal that interferes with the BEMF signal. Some designs implement a low-pass filter for the terminal signals and the virtual neutral. However, a low-pass filter is not suitable for motors with high commutation frequencies because of the phase shift caused by the filter.This reference design implements a technique that takes advantage of some unique features of the C8051F850. The open terminal does not yield any zero crossing information when current flows through that terminal. So, a tracking signal is used to disable a comparator input so that the comparator is effectively not operational when current is flowing in the open terminal.
  • Zero crossing point (ZCP) cannot be detected reliably when current is flowing in the open terminal because the voltages are dominated by the forward bias voltage of the body diode of the power MOSFETs. Thus, a tracking signal is used to enable the comparator for use at appropriate times during the PWM cycle.When the motor PWM duty cycle is low (inactive period is much longer than the active period), CEX0 is setup to synchronize with the motor PWM signal to observe the BEMF only at the tail end of the inactive part of the PWM cycle as shown in top figure.When the motor PWM duty cycle is high, CEX0 is setup to observe the BEMF at the tail end of the inactive part ofthe PWM cycle and the entire active part of the PWM cycle as shown in the lower figure.
  • In the typical BLDC motor sensorless starting phase, the motor is driven like a stepper motor. The motor is initially commutated very slowly then velocity is increased while the PWM duty cycle is increased to boost the applied motor voltage in an attempt to keep the current constant.However, it is not easy to predetermine PWM duty cycle for constant current level because the motor load may change or the motor supply voltage fluctuates. The design kit uses the comparator clear feature to trim the motor PWM duty cycle automatically to ensure that the current does not exceed a predetermined level regardless of the motor load or motor supply voltage.Using the comparator clear mechanism, the PWM signal is automatically shut off for that cycle when the current sensing voltage exceeds 1.8 V. The firmware programs the MCU to generate a 50% duty cycle PWM signal for motor startup and lets the comparator clear functionality trim the duty cycle to limit the peak current.
  • Hyperdrive Mode:In the block commutation driving method, maximum speed is achieved when the motor PWM duty cycle is at 100%.Hyperdrive mode is a technique to further increase this maximum speed. In the typical block commutation, there is zero current through one motor terminal at any one time because thephase is open for ZCP detection. If the open terminal can be energized, there will be increased electrical torquegenerated to further increase the speed of the motor, but the open terminal is required for ZCP detection. However,the open phase is free to be energized after ZCP has been detected. This technique is the most beneficial formotor designs in which the motor current saturates well before the next commutation event.
  • A strong value proposition of the Sensorless Brushless DC Motor Control Reference Design is the supporting environment from tools, development kits, software libraries and collateral. The motor control reference design contains everything needed to get the motor spinning in under five minutes.Silicon Labs offers differentiation in:Low cost reference design for evaluation purposesMotor control source code available which expedites design-insMotor control GUI PC application (Silicon Labs Spinner) offers users flexibility and ease of use when controlling and understanding the BLDC motor operationCollateral including application notes and knowledge base articles
  • The Sensorless BLDC (Brushless DC) Motor Control reference design is a ready to use motor control solution with production-quality hardware and software for quick evaluation and deployment in cost-sensitive applications. The reference design is a vehicle for developers to evaluate and adopt low-cost BLDC motor control solutions using the recently launched C8051F85x/6x product family.
  • Transcript

    • 1. www.silabs.com C8051F850 Sensorless BLDC Motor Control Reference Design
    • 2. Introducing the BLDC Motor Control Reference Design  Fully featured brushless dc (BLDC) motor control solution     Demonstrates C8051F85x/6x control of sensorless BLDC motors Incorporates motor-driving power electronics with MOSFETs Motor control GUI allows real time motor control and data streaming Contains everything needed to spin motor in less than 5 minutes  Reference design benefits  Highlights motor control features of the C8051F85x/6x MCU family • • • • •   2 12-bit ADC Dual comparators High-speed PWM output Intelligent comparator operation Flexible crossbar architecture Includes production-ready source code that expedites design-in time Provides a competitive, cost-effective solution
    • 3. Target Applications  Small motors     Remote control helicopters, toy cars Electronic speed controllers (ESC) PC fans Electric fans  Electric tools  Cutters, shears, lawn mowers  Staplers  Small appliances     3 Mixers and grinders Electric shavers and toothbrushes Vacuum cleaners Condensers and evaporators
    • 4. Motor Control Reference Design Hardware MCU Board C8051F850 Turnigy 3800 kV Outrunner Helicopter Motor Direction Start/Stop MCU Reset Gate Drivers 3-Phase Inverter Powertrain Board Power Source Option (Bench Power Supply) 4 Power Source Option (AC/DC Adaptor)
    • 5. BLDC Motor Control Board Block Diagram Regulators +3.3V +12V FG 12V +5V 5V J5 MTR_VDC POT +3.3V 3.3V Start/Stop Direction J6 C8051F850 UART_TX UART_RX MTR_VDC MTR_VA Gate Driver +3.3V AH VMA VMB VMC VMY BH USB of PC M MTR_VC AL UART-USB Bridge MTR_VB CH UART_TX BL CL IM_0P UART_RX USB Hub Rx Motor Mount Board MCRD-MMT-1525 C2 USB Debug USB Interfaces Current sense amplifier Three-Phase Inverter +3.3V +3.3V MTR_VA R68 MCU Board MCRD-MCU-C8051F850 R23 VMA MTR_VA VMA VMB C10 R27 MTR_VB VMC VMY MCU_GND MTR_VC +3.3V MTR_VA R31 MTR_VB R32 MTR_VC R33 C14 R72 R34 R35 R73 R74 R36 MCU_GND Zero-Crossing Detect Filter Circuit Powertrain Board MCRD-PWR-NLV Sensorless BLDC Motor Control Hardware Block Diagram 5
    • 6. Motor Control Reference Design Software  Production-ready firmware  Spins a 2-pole motor at 200,000 rpm  Expedites design-in time  Motor control GUI (Silicon Labs Spinner) Features     Start/stop motor Speed control Direction control Real time monitoring • Speed • PWM Duty Cycle • Current  Advanced mode available 6 Silicon Labs Spinner
    • 7. Motor Control Reference Design Specifications Parameter Power supply Motor driver PWM frequency Continuous average output current Speed range (2-pole motor) Speed range (4-pole motor) Speed range (6-pole motor) Min Typ Unit 24 10 Max V kHz A RPM RPM RPM 24 10 200,000 100,000 66,667 Motor Specifications - Turnigy 450 Series 3800 kV Brushless Outrunner Parameter Number of poles Operating voltage range Maximum current Maximum power No-load full-speed average current @ 12 V No-load peak startup current @ 12 V Motor constant Maximum speed @ 12 V 7 Min Typ Max Unit 14.8 35 365 V A W A A RPM/V RPM 6 7.4 3.66 11 3,800 45,600
    • 8. C8051F85x/6x MCUs for Motor Control  Fast, cost-effective 8-bit CPU (25 MIPS)  Designed to support 200,000 RPM for 2-pole BLDC motor  Flexible crossbar  Enables PWM on any of 16 pins  Supports mixed-mode PWM to improve long-term reliability of MOSFETs • Requires MCU to support PWM output to all six MOSFETs  PWM-synchronized comparator blanking  Automatic synchronization of zero crossing detection with motor PWM  Reduces CPU overhead -- no need to interrupt every PWM cycle for zero crossing detection • Enables higher frequency PWM for high-inductance motors  Comparator-clear PWM feature  Enables automatic motor current limit during motor startup  Hyperdrive mode  Technique to increase motor speed beyond rated maximum speed 8
    • 9. C8051F85x/6x Motor Control Enhancements  True 12-bit ADC 1.65V Internal Reference  Programmable sampling rate and resolution • 200 ksps @ 12-bit resolution • 800 ksps @ 10-bit resolution     Up to 16 channels Programmable gain 0.5x or 1x Window compare Temperature sensor Temperature Sensor P0.0 P0.1 P0.7 P1.0 P1.1 A N A L O G 0.5x-1x Gain 12-bit ADC M U X P1.7 VDD ADC Block Programmable Hysteresis MUX + Comparator0  Internal precision voltage reference  Voltage output 1.65 V  ±2% absolute accuracy External Vref (P0.0) VDD MUX Programmable Response Time P0.0 P0.1 P0.7 P1.0 P1.1 MUX 0.5x-1x Gain 12-bit ADC P1.7  Analog comparators  Two analog comparators  Programmable hysteresis and response time • High speed @ 100 ns • Low power @ 1.5 µs 9 Programmable Hysteresis MUX + Comparator1 MUX Programmable Response Time Comparator ADC Multiplexing
    • 10. Motor Control Enhancements Cont’d  Motor Control Multiplexer  Flexible comparator multiplexer to support sensorless BEMF commutation P0.0 P0.1 P0.7 MUX 0.5x-1x Gain 12-bit ADC Programmable Hysteresis MUX + Comparator0 MUX Programmable Response Time  General mux structure supports multiple input pins  Each input pin can be routed to (+) or (-)  Comparator inputs are multiplexed with ADC  Reduces the number of pins needed to perform sensorless BEMF commutation  PWM with Hardware Fault Protection  3-channel 8- to11-bit or 16-bit PWM PWM signal  Cycle-by-cycle current control  Comparator clear function (hardware fault protection) CMP output  Output polarity select control PWM output  Center and edge alignment PWM 10 Comparator clear function
    • 11. Zero Crossing Detection -- Comparators  C8051F850 advantage: synchronized PWM comparator blanking  C8051F850 PWM can force a comparator input low  Reduces CPU overhead to detect zero crossing when PWM is active; no need to interrupt once or many times per PWM cycle CMP0 VMA + VMY - Output = high before ZCP P0.3 = PCA CEX0 Operating as tracking signal P0MDIN.3 = 1 Peripheral configuration for zero crossing detection for rising open phase BEMF voltage CMP0 VMY + VMA - Output = high before ZCP P0.0 = PCA CEX0 Operating as tracking signal P0MDIN.0 = 1 11 Peripheral configuration for zero crossing detection for falling open phase BEMF voltage
    • 12. Zero Crossing Detection CEX1 (motor PWM) CEX0 (tracking signal) Comparator active tracking PCA Cycle Overflow Comparator blanking synchronization with low motor PWM duty cycle CEX1 (motor PWM) CEX0 (tracking signal) Comparator active tracking PCA Cycle Overflow Comparator blanking synchronization with high motor PWM duty cycle 12
    • 13. Motor Startup -- Automatic Current Limit Comparator Output (Red) (Comparator Clear) Comparator Output (Black) (50% duty cycle)  I_meas is op-amp amplified current sensor voltage  Motor PWM signal is automatically switched off by comparator clear feature of PCA peripheral  Firmware can program PWM duty cycle at a constant 50% and allow the comparator clear feature to limit the current automatically  Typical solutions require a table of duty cycles tuned for a specific motor 13
    • 14. Hyperdrive Mode Phase A BEMF waveform Phase A Commutation Instants Phase A Zero Crossings Phase B BEMF waveform Phase B Commutation Instants Phase B Zero Crossings Phase C BEMF waveform Phase C Commutation Instants 0 60 120 180 240 300 360 420 480 540 600 660 720 780 Phase C Zero Crossings  Open phase (shaded regions) terminal after zero crossing detection is free  Hyperdrive mode -- energize open phase AFTER zero crossing detection  Delivers additional torque to increase speed of motor 14
    • 15. Motor Control Reference Design Contents  Contains everything you need to get the motor spinning in five minutes  Evaluation materials     Data sheets Motor control hardware Quick-start guide and user’s guide Silicon Labs Spinner C8051F850-BLDC-RD retails for $164.99  Development collateral  Schematics  BOM  Motor control source code  www.silabs.com/mcu 15 Silicon Labs Spinner
    • 16. Get Your BLDC Motor Control Design Up and Spinning  Fully featured BLDC reference design    Demonstrates C8051F85x/6x MCU control of sensorless BLDC motors Includes all hardware required to spin a motor Motor control GUI allows real-time motor control and data streaming  Highest performance 8-bit solution for motor control     200,000 rpm achieved with 2-pole motor PWM-synchronized comparator blanking Automatic current limit during motor startup Incorporates hyperdrive mode to increase speed  Accelerated design for fast time-tomarket   16 Production-ready source code expedites designin time Development collateral available at www.silabs.com/mcu
    • 17. www.silabs.com Thank You! www.silabs.com/mcu