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Brushless Motor Fuzzy Control by using ST52x301

Authors: G. Grasso, M. Di Guardo

AN1113 APPLICATION NOTE
Brushless Motor Fuzzy Control by using ST52x301
Authors: G. Grasso, M. Di Guardo
INTRODUCTION
AN OUTLINE OF BRUSHLESS MOTORS
The Brushless motor has the physical appearance of a 3-phase permanent magnet synchronous machine. The brushes and commutator have been eliminated and the windings are connected to the control electronics. Electronics replaces the function of the commutator and energizes the proper winding. The energized stator winding leads the rotor magnet and switches just as the rotor aligns with the stator. In synchronous motor drives, the stator is supplied with a set of balanced three-phase currents, whose frequency is f. If p is the number of the poles in the motor, then:
where s (rad / s) is the flux synchronous speed or, that is the same, the rotor speed. This equation links the rotor speed to the phases switching frequency of the electronic drive. The above currents produce a constant amplitude flux s in the air gap, which rotates at the synchronous speed s. Since the flux amplitude is proportional to the current amplitude, it is enough to manage winding current level to control the rotor torque. From Brushless theory 3-4 it is possible to demonstrate that
where kt is a constant, f is the field-flux, is called torque angle. represents the angle between the phase linked flux fph1 and the relative stator current Iph1.
January 1999
AN1113 - APPLICATION NOTE
In the diagram, three position sensors (Hall sensors) are placed around the rotor in order to detect the shaft position. Fig. 2 reports motor data sheet supplied by the motor builder. Figure 2. Motor Data Sheet
Linked Voltage for Counterclockwise direction
Brushless Motor Fuzzy Control by using ST52x301
By observing the motor data sheet, these concepts become clear. In fact, it is possible to see the relation between shaft position, hall sensors response and voltage profile to be supplied. This way to supply the stator phases is very complex because it is necessary to produce a sine wave with a proper period and delay with respect to the sensors information. As we will show later on, a simpler method is possible.
INVERTER DRIVER TOPOLOGY
turned off, the current it was carrying is immediately diverted to the diode in parallel with T4. This diode re-circulates the instantaneous current of the winding until it decreases to zero. Once the phase current reverses direction is carried by T4. In term of voltage it is easy to draw the phases voltages by conceiving the transistors as switches. Due to the triangular connection of the phases, each phase voltage depends by the status of two legs of the bridge. Figure 4 shows one real phase star voltage and one phase current. Six voltage steps are evident in the look like sine wave. The same happens in the other legs of the bridge in different times. This topology drives the windings for the whole period, avoiding the phase to be "floating" (Six-Steps Continuous Mode Inverter).
FUZZY CONTROLLER
AN1113 - APPLICATION NOTE
Figure 4. Phase voltage and current
The aim of the control is to maintain the desired Speed regardless of the applied load to the shaft. When a resistance torque is applied to the shaft, a reduction of the speed takes place. This implies an increment in the wave period of the Hall sensors signals and then a decrement of the sine frequency in the phases, to follow sensors information. In this case, the only way to lead the rotor at the previous speed is to increase the winding current in order to balance the load torque. Fuzzy Controller, in fig. 6, performs this task. ST52x301 reads the speed
Figure 5. Control topology
Error
FUZZY CONTROLLER
MOTOR DRIVER
Speed
Brushless Motor Fuzzy Control by using ST52x301
"Ref" value from AD Channel0 and the instantaneous Hall signal period by means of a digital port. A software task performs the "error" calculation
Figure 6. Fuzzy algorithm
HARDWARE DESCRIPTION
AN1113 - APPLICATION NOTE
Speed REF VCC 15K Torque REF
Isense
RST 22pF 20MHz
S1 RPM VCC
TRES TCTRL TCLK
VPP OSCOUT OSCIN BG
AVDD AVSS
MODE TEST RESET TIMEROUT
INT TRIACOUT
AIN0 AIN1 AIN2 AIN3 READY P8
MAIN2 MAIN1
ST52x301
TXD RXD
Isense
IN3 10
Brushless Motor
2.2uF 10K
IN1 H3
3.9 2W
74LS00
Brushless Motor Fuzzy Control by using ST52x301
fact, a high frequency PWM wave produces, in a coil, a voltage whose amplitude value is the mean value of the square wave. The motor data sheet displayed in fig. 2, clearly shows that "U-W" phase must be supplied positive when sensor "H1" is high, "W-V" when sensor "H2" is high and so on. This is true because the triangular connection was preferred in the coils arrangement. AND output is, then, a Pulse train whose duration is the same of the Hall signal. This pulses train is used to drive each leg of the bridge L298. L298 is a monolithic dual full-bridge driver designed to accept standard TTL logic levels and drive inductive loads such as relays, solenoids, DC and stepping motors. Enable input signals are available to allow a software protection. Internal circuitry provides the appropriate dead-time in order to avoid a "cross-conduction" along the leg. ST52x301 provides, by means of an internal peripheral, a PWM wave that can be varied by software. ST52x301 PWM frequency is chosen as compromise between acoustic noise in the motor and losses in the power stages of the bridge. A 19 KHz wave frequency was used in the implemented application.
SOFTWARE DESCRIPTION
Before to discuss about ST52x301 software configuration, it is important to note some HW connections in the schematic. Bit "0" (pin 9) of the parallel port is used to enable the power stage only after power-on reset, then parallel port must be configured in OUT mode. The analog input AIN0 (pin 43) is used to read the voltage reference. A voltage between 0 + 2.5 V present on this pin, is converted in the range 0 + 255. External INTerrupt pin (27) is used to read one Hall sensor signal period in order to calculate the instantaneous speed. This digital input will be configured both in negative or positive edge trigger to produce an internal software interrupt. Fig. 8 displays how to configure A / D peripheral with 3 inputs, TRIAC peripheral in PWM mode at 19 KHz, the used global variables. The following figure reports the main program in term of graphical programming. The appendix at the Figure 8 . Peripheral configuration
AN1113 - APPLICATION NOTE
Brushless Motor Fuzzy Control by using ST52x301
Figure 10 . Arithmetic blocks
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CONCLUSIONS AND RESULTS
By using ST52x301 Fuzzy Controller it is easy to implement a real time control with few components.The brushless motor control described in this application note represents a good compromise between system costs and motor performances. The graphical programming environment reduces the development time also for not expert programmers. Fig. 12 displays a phase current and the star voltage Vu-o. PWM square wave is filtered by the oscilloscope. From this picture it is possible to observe the six steps on the current wave that yields a distortion of the theoretical sine wave. At higher speed rates the distortion becomes lower, although at low speed, motor performance does not degrade. To evaluate acceleration characteristics and control goodness, some trials were made during the softwa-
Figure 12 . Phase current
Brushless Motor Fuzzy Control by using ST52x301
Figure 13.
Dynamical performances
REFERENCES
1 Paul C. Krause "Analysis of Electric Machinery" - McGraw-Hill 2 "Power Products- Application Manual", STMicroelectronics 3 Mohan, Undeland, Robbins "Power Electronics: Converters, Applications and Design" John Wiley & Sons 4 Yasuhiko Dote, Sakan Kinoshita "Brushless Servomotors - Fundamentals and Applications" Oxford Science Publications 5 FUZZYSTUDIO 3.0 - User Manual, STMicroelectronics, 1998
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APPENDIX: ST52X301 ASSEMBLER CODE
Brushless Motor Fuzzy Control by using ST52x301
AN1113 - APPLICATION NOTE
Brushless Motor Fuzzy Control by using ST52x301
AN1113 - APPLICATION NOTE
Brushless Motor Fuzzy Control by using ST52x301
AN1113 - APPLICATION NOTE
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