A Brushless DC Motor Controller
with Current-loop Control
Siyuan Gao
Changchun Institute of Optics, Fine Mechanics and Physics,
Chine Academy of Sciences
Changchun, Jilin Province, China
Abstract—This paper prents a brushless DC motor controller with current loop control. The controller applies a complementary PWM modulation scheme to the power MOSFET. The current processor employed by the controller could detect the current flow through the motor windings accurately and convert the current to a voltage input to the error amplifier. The controller has 100% duty cycle high side conduction capability and "real" four quadrant torque control capability. It is able to implement a tight torque control for a DC brushless motor to satisfy the need of some rvo system which calls for high bandwidth and raid dynamic respon.
Keywords-component; current loop control; four quadrant torque control;complementary PWM; DC brushless motor
I.I NTRODUCTION
The lection of the motor controller plays a key role in order to get the high performance of the electro-mechanic system. Some issues must be take into account so that the proper controller is lected for system.
There are different applications in industrial production and daily life for motors. In application that a fan is ud for ventilation equipment, a simple speed controller with just an over-current limit is all that may be necessary. In application that a rolling system which the torque needs to be controlled, a controller with a current loop control needs to be specified. If the application such as a hard disk calls for a high bandwidth rvo control loop, a full four-quadrant controller must be chon.
This paper prents a brushless DC motor controller with current loop control. It is compod of hall commutation module, PWM generator module, gate driver control module, current processing module and system protection module. The controller has good accuracy around the null torque point. At the same time it has 100% duty cycle high side conduction capability and "real" four quadra
nt torque control capability [1]. The paper is organized into five ctions. Section 2 prents a basic principle of the four quadrant torque control with PWM modulation. Section 3 prents the hardware implementation of the controller. Section 4 shows the experimental results. Finally some conclusion is made in ction 5.
II.F OUR Q UADRANT T ORQUE C ONTROLL
A plot of speed versus torque is showed in figure 1. Quadrant I is forward speed and forward torque. The torque is propelling the motor in the forward direction. Converly, Quadrant III is rever speed and rever torque. Quadrant II is where the motor is spinning in the forward direction, but torque is being applied in rever. Finally, Quadrant IV is exactly the opposite. A DC motor can operate in one of the four quadrant according the motor controller. A speed controller that controls speed in either a clockwi direction or a counterclockwi direction is referred to as a two quadrant controller. The construction of a four-quadrant controller is ex actly the same as the two-quadrant controller. The difference is in the modulation
创新实验
[2] [3]
Figure 1. Four quadrant controll chart.
A.Four Quadrant Current Control in a PWM Cycle
Figure 2. Four quadrant current control in a PWM cycle.
Figure 2 is an example of a full 4 quadrant torque control modulation scheme. This method of modulation is known as “locked anti-pha” PWM. MOSFET Q1 and Q4 get turned on during the first portion of the PWM cycle. At the end of the first portion of the PWM cycle, MOSFET Q1 and Q4 get turned off and MOSFET Q3 and Q2 get turned on. There is a dead-time between Q1 and Q4 off and Q3 and Q2 on to prevent the shoot-through of the bridge. During the first portion, current will flow through R2 and get nd. During the cond portion of the PWM cycle, current flows through R1 and gets nd. Even during the dead-time, current will flow through one of the resistors. Current will be viewed at all times. There is one thing to note that makes this scheme special. At zero current, the modulation is exactly 50% for each transistor pair. There is zero net average current going through the winding of the motor, but there is always current flowing which allows the circuit to n it at all times. The control loop will always be controlling the current even when going through zero [4]. B. Full TorquePoint
Figure 3. True four quadrant current controller near full torque point.
As shown in Figure 3, the voltage waveform across the motor winding has twice the available amplitude as the other examples. This means that the current can be ramped up and down at twice the rate as the others. This figures into the bandwidth equation as twice the available bandwidth. The
two resistors accurately measure the raw current information from the two legs of the bridge. Manipulation of the two waveforms will result in an accurate reprentation of the current going through the motor winding. C. Zero Torque Point
Figure 4. True four quadrant current controller at zero torque point.
Figure 4 shows the various waveforms when zero current is commanded from the bridge. The duty cycle of the PWM is
exactly 50%. This means that there is always current flowing through the motor winding, but the net average of the current is exactly zero. Since there is always current flowing, there is always a feedback signal to u to clo the current loop. The loop is always in control, even exactly at zero [5].
The 3 pha brushless motor torque controllers introduced in this article u the scheme to provide clod loop control through zero and provide high bandwidth becau of the active control of the current at all times. It is for applications requiring tight control of torque continuously regardless of the direction of the motor.
III. T HE
I MPLEMENTATION OF C ONTROLLER
A. Hardware Implementation
The controller is compod of modules as follows: • hall commutation module • PWM generator mod
如果的反义词ule • gate driver control module • current processing module •
鸟语林system protection module
Figure 5. The structure of the controller.
Figure 5 demonstrates the structure of the controller. The 3 pha bridge employ the MOSFET with a low On-Resistance and a fast switching capability. The protection module could generate a control logic to prevent the shoot through of the bridge.
The key components in the controller are gate drive control module and current processor.
Figure 6. Gate drive control module.
As shown in figure 6, the gate drive control module is compod of Hall Commutation Module (HCM) and PWM Distribution Logic Module (PDLM). The HCM generate a control signal according to the hall input and the current command to lect which MOSFET is on. The PLDM implement a complementary modulation by distribute the PWM input signal to the six MOSFET. The function of the gate drive control module is illustrated by the truth table listed below. Table 1 is the truth table when the current command is positive. Table 2 is the truth table when the current command is negative [6] [7].
Table 1. Gate drive control truth table when current command positive
Hall A Hall
B
Hall
C
Q1 Q2 Q3 Q4 Q5 Q6
0 0 1
On cpl cpl On off off
0 1 1 On cpl off Off cpl on
0 1 0 off off on Cpl cpl on
1 1 0 cpl on on Cpl off off 1 0 0 cpl on off Off on cpl 1 0 1 off off cpl On on cpl
0 0 0 off off off Off off off
1 1 1 off off off Off off off Table 2. Gate drive control truth table when current command negative
Hall A Hall
B
Hall
C
Q1 Q2 Q3 Q4 Q5 Q6
1 0 1 off off on Cpl cpl on
1 0 0 On cpl off off cpl on
1 1 0 On cpl cpl on off off
0 1 0 off off cpl on on cpl
0 1 1 cpl on off off on cpl
0 0 1 cpl on on cpl off off
0 0 0 off off off off off off
1 1 1 off off off off off off The structure of the current processor module is showed in Figure 7. To complete a true current loop, both magnitude and direction of current through the load are necessary for correct feedback information. Sensing the current at the bottom of each half bridge allows the paration of current through each half bridge. Becau the n resistors are very low resistance to keep power dissipation low, the voltage developed across them is small. So the current processing module has to amplify the voltage to satisfy the input of the error amplifier. The error amplifier is t up so that both the command input and the feedback input are brought into the summing junction of the amplifier. The voltage feedback signal is t up to be the opposite polarity to the command input, so that negative feedback is achieved. The feedback network is t up as a single pole, integrating feedback network. The resistor ts up the mid-band gain, and the combination of resistor and ries capacitor compensate for the inductance and resistance of the load. The output of the error amplifier network feeds into the input of the PWM generator, and controls the PWM duty cycle
恶梦醒来是早晨
[4] [9]
Figure 7. Current processor module.
Figure 8 is a scope waveform of the current command input and the detected current which flows through the motor winding.
Figure 8. The current command vs current monitor.
笔记本风扇一直嗡嗡响on = switch on 1 = High Level off = switch off 0 = Low Level cpl = switch complementary
IV.T HE R ESULT OF E XPERIMENTS
The controller can provide a rapid dynamic respon. Figure 9 shows the frequency respon of the controller which is tested by the frequency respon analyzer FRA5097. The red curve is a plot of magnitude versus frequency and the blue curve is a plot of pha versus frequency. At the frequency of 1kHz, the attenuation of magnitude is 1.585dB and the pha lag is 26.7e
.
Figure 9. The frequency respon of the controller.
V.C ONCLUTION
This paper prented an DC brushless motor controller with a current loop control. The controller employ a PWM scheme of complimentary modulation. It provide clod loop current control of a brushless motor by nsing the current through the motor, thereby controlling the torque output of the motor.
The controller is able to satisfy the requirement of rvo system which needs to have complete control of motor torque
at all times.
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短发怎么
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