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An FPGA-Based Novel Digital
PWM Control
Scheme for BLDC Motor Drives
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS,
VOL. 56, NO. 8, AUGUST 2009
學生:林哲偉
學號:M9920110
指導教授:龔應時
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Outline
 Abstract
 INTRODUCTION
 BRUSHLESS DC MOTOR DRIVE STRATEGIES
 DIGITAL PWM CONTROL OF BLDC DRIVES
 CONTROLLER DESIGN
 DESCRIPTION OF EXPERIMENTAL SETUP
 SIMULATION RESULTS AND EXPERIMENTAL
VERIFICATION
 CONCLUSION
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Abstract
 Development of advanced motor drives has yielded increases
in efficiency and reliability.
 Residential and commercial appliances such as refrigerators
and air conditioning systems use conventional motor drive
technology.
 The machines found in these applications are characterized
by low efficiency and high maintenance.
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 In a market driven by profit margins, the appliance industry is
reluctant to replace the conventional motor drives with the
advanced motor drives (BLDC) due to their higher cost.
 A simple novel digital pulse width modulation (PWM) control
has been implemented for a trapezoidal BLDC motor drive
system.
 The novel controller is modeled and verified using simulations.
Experimental verification is carried out using fieldprogrammable gate arrays to validate the claims presented.
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INTRODUCTION
 An ELECTRIC motor is defined as a transducer that converts
electrical energy into mechanical energy.
 In the case of dc machines, they require more maintenance
due to the presence of brushes.
 Replacing these inefficient motors with more efficient
brushless dc (BLDC) motors will result in substantial energy
savings.
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 In this paper, a novel digital PWM controller has been
proposed for a BLDC motor.
 This controller treats the BLDC motor as a digital system. The
BLDC system is only allowed to operate at a low duty (DL) or
a high duty (DH).
 In addition, this technique utilizes only one current sensor in
the dc link. This helps reduce the cost and complexity of
motor control hardware.
 Computer simulations and experimental results are presented
for proof of concept.
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BRUSHLESS DC MOTOR DRIVE
STRATEGIES
 The typical inverter drive system for a BLDC motor is shown
in Fig. 1.
Fig. 1. Typical inverter drive system for a BLDC motor.
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 In order to get constant output power and, consequently,
constant output torque, current is driven through a motor
winding during the flat portion of the back-EMF waveform.
shown in Fig. 2.
Fig. 2. Back EMF and phase current variation with rotor electrical angle.8
 It is important to know the rotor position in order to follow the
proper energizing sequence.
 A timing diagram showing the relationship between the sensor
outputs and the required motor drive voltages is shown in Fig.
3.
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Fig. 3. Sensor versus drive timing.
 The input sensor state and the corresponding drive state
required for commutation can be put in the form of a state
table as shown in Table I.
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DIGITAL PWM CONTROL OF BLDC
DRIVES
 The general structure of a current controller for a BLDC motor
is shown in Fig. 5.
Fig. 5. Conventional PWM current control.
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 This paper presents the design, simulation, and experimental
verification of a novel constant-frequency digital PWM
controller which has been designed for a BLDC motor drive
system. shown in Fig. 6.
Fig. 6. Flowchart describing the novel digital control.
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 This paper presents a controller with no need of any state
observer. Fig. 7 shows the proposed digital controller. Fig. 8
shows the complete block diagram of the motor drive system.
Fig. 7. Proposed digital control.
Fig. 8. Block diagram for digital PWM
control for a BLDC motor drive system.
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 A proportional controller provides the reference for the current
limit.
 The minimum value of Ilimit decides the steady-state error.
 The proportional constant K for a desired speed ripple can be
calculated as follows. In steady state, Δω ≤ |ωerr ∗ 2|. In the
worst case, Δω = |ωerr ∗ 2|. For the desired speed ripple Δω,
a constant Kset can be defined as
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 Taking the maximum value of the speed ripple
 As long as
 In addition, Ilimit α ωerror
 By using (1)–(3) in (4), it can be shown that
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 In this control strategy, both the high- and low-side switches
are switched simultaneously. Both high- and low-side diodes
conduct. The waveforms for this type of switching are shown
in Fig. 9.
Fig. 9. Gate switching waveforms.
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CONTROLLER DESIGN
 The value of D can be expressed as a function of the motor
parameters. From the torque equation, we have
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DESCRIPTION OF EXPERIMENTAL
SETUP
 The experimental setup is shown in Fig. 12.
Fig. 12. Final experimental setup.
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TABLE II
DATA SHEET FOR BLDC MOTOR FROM POLY-SCIENTIFIC
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 The actual speed was easily calculated as a time between
two Hall effect signals. The schematic of the controller
simulated in the FPGA is shown in Fig. 13.
Fig. 13. Block diagram showing operations and functions implemented
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in FPGA device.
SIMULATION RESULTS AND
EXPERIMENTAL VERIFICATION
 For the verification of the control scheme, several operating
conditions were selected.
Fig. 14. Simulated duty, speed, and current response for a commanded
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speed of 2500 r/min for full-load operation.
Fig. 15. Experimental results for a reference speed of 2500 r/min under
no load condition.
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Fig. 16. Experimental results for a reference speed of 2500 r/min. Load
is 30% of rated value.
Fig. 17. Experimental results for a reference speed of 1500 r/min under
no load condition.
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Fig. 18. Experimental results for a reference speed of 1500 r/min. Load
is 30% of rated value.
Fig. 19. Experimental results for a reference speed of 2100 r/min
under full load.
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Fig. 20. Speed response for
change in load torque and for a
reference speed of 2000 r/min.
Fig. 21. Experimental results for a
change in reference speed from252200
to 1300 r/min under no-load condition.
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CONCLUSION
 The aim of this paper is to develop a low-cost controller for
applications where inefficient single-phase induction motors are
used.
 Due to the simplistic nature of this control, it has the potential to be
implemented in a low-cost application-specific integrated circuit.
 Furthermore, this control strategy does not require a state observer.
Under dynamic load conditions, the proposed controller was found
to be capable of regulating speed without the use of an observer.
 This results in a considerable reduction of size and the cost of the
system.
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