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    2016 Microchip Technology Inc.DS90003152A-page 1 TB3152 INTRODUCTION The motor control industry has been focusing ondesigning low-cost motor control drives for variousapplications. The consumer demand for low-cost motor control applications is driving this trend. Microchip has recently introduced the PIC32MM familyof microcontrollers, which is capable of addressing thelow-cost motor control requirements. The low-costsolution benefits from the capability of the MultipleCapture/Compare/PWM (MCCP) module available inMicrochip’s PIC32MM controllers. This documentillustrates the usage of the MCCP module in thePIC32MM0064GPL036 controller, from MicrochipTechnology, to deliver a development platform for motor drive applications.MCCP implementation, similar to the motor controlsolution discussed in this document, can also beextended to Microchip’s PIC24 and dsPIC33 family of devices which feature MCCP. SIX-STEP COMMUTATION FOR THREE-PHASE BLDC MOTOR CONTROL This document describes the algorithm for running asensorless Brushless DC (BLDC) motor using a six-steptrapezoidal or 120° commutation. Figure1 shows how the six-step commutation works. Each step, or sector, isequivalent to a 60° electrical and six sectors make up a360° electrical or one electrical revolution.In Figure1:ãThe arrows in the winding diagram show the direction in which the current flows through the motor windings in each of the six steps. ãThe graph shows the potential applied at each lead of the motor during each of the six steps. Sequencing through these steps moves the motor through one electrical revolution. FIGURE 1:SIX-STEP COMMUTATION  Author:Naresh Tummalapalli Microchip Technology Inc. A C B 154623 60° 123456 Blue WindingGreen WindingRed Winding Sector  +V DC GND+V DC GNDGND+V DC Multiple Capture/Compare/PWM (MCCP): Extending the Functionality for Low-Cost Motor Control Applications  TB3152 DS90003152A-page 2    2016 Microchip Technology Inc. Table1 shows a typical commutation sequence. TABLE 1:COMMUTATION SEQUENCE For every sector, two windings are energized and theother winding is not energized. The fact that one of thewindings is not energized during each sector is animportant characteristic of the six-step control thatallows the measurement of the Back-EMF (BEMF) inthat phase, and thereby, enables the sensorless com-mutation scheme. Figure2 shows the PWM signalsapplied to each winding during the six-step trapezoidalcommutation. FIGURE 2:SIX-STEP TRAPEZOIDAL BLDC COMMUTATION   Sector MOSFET StatusPhase CurrentA TOP A BOTTOM B TOP B BOTTOM C TOP C BOTTOM ABC 1PWMOFFOFFOFFOFFPWM+OFF—2PWMOFFOFFPWMOFFOFF+—OFF3OFFOFFOFFPWMPWMOFFOFF—+4OFFPWMOFFOFFPWMOFF—OFF+5OFFPWMPWMOFFOFFOFF—+OFF6OFFOFFPWMOFFOFFPWMOFF+—    2016 Microchip Technology Inc.DS90003152A-page 3 TB3152 Bipolar Independent PWM The three-phase voltages are controlled by applying aPWM-based voltage to the top and bottom MOSFETs/Insulated-Gate Bipolar Transistors (IGBTs). The six-stepcommutation in this document employs bipolar indepen-dent PWM switching. This kind of commutation requiresswitching the top and bottom MOSFETs diagonally, butthe complementary switching on the same phase is notrequired. Figure3 shows an instance of diagonal switching inwhich Phase A top side (Q1) and Phase B bottom side(Q4) MOSFETs are switched. FIGURE 3:DIAGONAL SWITCHING Q6Q5Q3Q4Q1 Q2 V DC GND  TB3152 DS90003152A-page 4    2016 Microchip Technology Inc. The advantage of this switching scheme is that theBEMF signal is cleaner, and avoiding the complemen-tary switching makes the switching pattern simpler andthe dead-time insertion is not needed. The disadvantageof this scheme is the higher switching losses (due toswitching both diagonal MOSFETs). However, it isobserved that in low-cost solutions, the switching lossesare significantly low in magnitude when compared toother losses. Details of the technique are shown inFigure4.In Figure4, the signals are gate driver inputs withHigh= On and Low = Off.The signal conventions followed here are: ãPWM1H for Phase A Top (Q1), PWM1L for Phase A Bottom (Q2)ãPWM2H for Phase B Top (Q3), PWM2L for Phase B Bottom (Q4)ãPWM3H for Phase C Top (Q5), PWM3L for Phase C Bottom (Q6) FIGURE 4:BIPOLAR INDEPENDENT PWM  

2016 All is Energy

Jul 11, 2019

12. Misc. Subjects

Jul 11, 2019
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