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Industrial/Appliance Consumer Ceiling Sensorless field-oriented control for ceiling fan sinusoidal BLDC motor with PFC

Introduction Figure 1: Sensorless Sinusoidal BLDC/PMSM FOC + PFC Brushless direct current (BLDC) motors are readily gaining popularity DC Bus Voltage (VDC) where energy savings are required. BLDC fans offer several advantages Rectified AC Voltage (Vac) over traditional brushed DC motor and induction motors, including more Rectifier PFC Ceiling torque per weight, more torque per FAN AC watt (increase efficiency), high dynamic Input response, increased reliability, reduced noise, longer lifetime, more power and overall reduction in electromagnetic interference (EMI). This article covers PFC Vdc a typical ceiling fan application with PWM cost-effective smart electronics along PWM FOC and Feedback with the advantages of BLDC motors PFC Generation Processing Feedback BEMF as mentioned above. The reduced Control Observer energy consumption in this application Speed Command makes it an excellent choice for the energy efficiency initiative. 8 kHz current control loop frequency Application Concept This article is dedicated to the is used to gain excellent performance, FOC sensorless sinusoidal BLDC/PMSM low noise and high efficiency. In order to run the motor properly, FOC for the ceiling fan application. Features of Ceiling Fans five stages are taken to start the fan, including sector detection, start, open System Overview • Speed range 140–320 RPM loop, merge and closed loop. Front-end power factor circuit (PFC) • Input power factor > 0.95 from followed by three-phase inverter with minimum speed of 90 RPM Sector detection stage: The motor Freescale DSCs is used to drive a must start with a relatively large initial • Direction can be reversed when three-phase sinusoidal back EMF torque position, otherwise there fan is running BLDC/PMSM motor. The three shunt will be oscillation or failure when • Start-up even if the vanes are still resistors cascaded in the lower leg starting the fan. Consider dividing rotating (due to inertia) of the inverter are required to obtain the rotor position of 0–360 electrical three-phase current. The power • 45 seconds to deceleration/ degrees into six sectors, and the configuration is shown in figure 1. A acceleration from 90 to 320 RPM sectors can be identified using stator firmware observer is applied to obtain • 25 watt total power consumption magnet’s B-H characteristics. the rotor’s magnetic axis position • Speed control in five steps through Start stage: Because there are current which is crucial for the vector field- IR remote pulses in the windings when detecting oriented control (FOC) algorithm. The the rotor’s initial position, these current sensorless vector control algorithm pulses may cause a bit of mechanical with 16 kHz PWM frequency and vibration. This stage is designed Beyond Bits Motor Control Edition

Figure 2: Sensorless Sinusoidal BLDC/PMSM FOC, Software Blocks

d-current PI Control Required Inverse Park Compensated d-current Transformation Voltage SVM PWM u u α α d, q DC Bus u Ripple u β Elimination β

α, β Inverter

Required Three-Phase Speed Sector DC Bus From Speed PI Control q-current Voltage Remote PI Control Control

Extended BEMF Estimation and Tracking Observer

i i i d-current d α α, β a d, q i i b q-current iq β ic Current

α, β a, b, c Sensing Sensors Processing Feedback Park Clarke Two Transformation Transformation Currents

to add some delay before actually smoothly in the merge stage, now the cascaded in the lower legs of the starting the fan. output of the speed control loop is inverter. When calibration is complete, used as IQ reference instead of using the stop task then positions the Open loop stage: When the rotor’s a given reference value. detection task to be executed. The magnetic axis has been detected, position detection task is intended to the open loop control for speed is PFC Control realize the function mentioned in the used. During open loop operation, Boost circuitry in a discontinuous sector detection stage. The start stage the observer for position and speed conduction mode is used to realizes the function mentioned in the estimation is enabled and the speed implement the PFC inner current mode start stage and the run state realizes loop is also enabled to obtain control. Outer voltage loop controls the functions mentioned in the open reference IQ which will be used in the the DC bus and provides constant loop stage, merge stage and close close loop. voltage with input and speed of fan loop stage. Merge stage: Once a desired speed changes. Inner current loop controls is achieved, the control transfer from the input current and corrects the Sensorless Driving with PFC speed open loop runs to speed close input power factor > 0.95 and input To read the speed and position in loop. In close loop, the estimated current THD. rotor position is used to perform park sensorless control, it is necessary and inverse park transformation and Software Design to know the motor parameters well to calculate its model observer. The use the speed loop’s output as the The software is designed using a parameters are programmed into quadrature current reference. There state machine so that the software the BEMF observer algorithm. This could be a shift between the estimated is easy to understand and control. observer’s function is to calculate the position and simulated position during The fault task deals with overcurrent, position of the BEMF, which is needed open loop running. overvoltage and undervoltage. The to drive the motor. The position is then Closed loop stage: Since the rotor’s initial task initializes all variables used passed through the tracking observer position used in the algorithm has in the algorithm. The calibration task to be filtered, and as a side product, been transferred from simulated rotor gets the DC offset of currents passing determines the actual speed. The PFC position to estimated rotor position through the three shunt resistors Motor Control Edition Beyond Bits Motor Control Edition

current loop algorithm is three times Performance PFC: Has two main control loops: faster than FOC and the voltage loop The application uses two system current and voltage. The slow moving is at much lower speed. control loops. voltage loop keeps the DC bus voltage constant. The current loop is critical as At this point, we see that this solution FOC: Has two main control loops: it controls the input current waveform. requires a powerful controller from the current and speed loops. The current Freescale 56800E/Ex family of DSCs. loop is critical and is calculated on the Freescale Enablement PWM frequency at 16 kHz. The loop Implementation • Application based on FSLESL has several tasks: Freescale offers a selection of DSCs freescale.com/motorcontrol for this important task. The following is • Reading of measured currents and • Embedded software and motor a list of what is mandatory for such voltage, and reconstruction of the control libraries an application: current from two values into three freescale.com/fslesl • BEMF + tracking observer • PWM: Two PWM configurations • FreeMASTER visualization tool • Clarke and Park transformation freescale.com/FreeMASTER One for FOC should offer a center-aligned mode, • D and Q current controllers and • Application support from Freescale complementary switching their limitation depending on the motor control experts capability with the deadtime DC bus voltage insertion, and three-phase • DC bus ripple compensation orientation • Space vector modulation One for PFC and PWM • PWM update of three-phase inverter synchronization with the ADC • ADC configuration for the next step • ADC: Simultaneously measures two FOC currents and PFC current, with two channels working in parallel • SCI: Necessary for the communication with FreeMASTER to allow application debugging • Interrupt controller: Must be priority controlled to avoid disintegrity of the control technique. The interrupt latency should be short. • Core: Must have great computation potential in terms of mathematical operation Beyond Bits Motor Control Edition

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