1、直流无刷电机外文资料原文及译文外文资料原文 Commutation Torque Ripple Reduction in BLDC Motor Using PWM_ON_PWM Mode Guangwei Meng, Hao Xiong, Huaishu Li Department of Electrical Engineering, Naval University of Engineering, Wuhan, China. Abstract-The paper analyzes the steady commutation process of the BLDC motor using P
2、WM mode, confirms the commutation time to keep noncommutation phase current amplitude constant during commutation period by way of PWM in the period to implement the compensation control to eliminate commutation torque ripple under both low speed and high speed operation, investigates the effect by
3、PWM mode on a three-phase six-state 120 turn-on BLDC motor, and presents torque ripple compensation control in PWM_ON_PWM mode, which can not only entirelyeliminate torque ripple resulted from the current emerging in the turn-off phase during non-commutation period but also compensate torque ripple
4、caused by the commutation current during commutation period. Index TermsBLDC motor, commutation, PWM, torque ripple.I. INTRODUCTION The BLDC motors have been widely used due to its features a simple structure, good speed adjusting performance,high powerdensity, low noise and simple control, etc. It
5、is a hotspot to suppress the torque ripple and improve the control performance of a BLDC motor with the trapezoidal back emf. BLDC motors usually operate in all kinds of PWM modes, which not only affect the dynamic loss of power switches and radiation uniformity, but also influence the torque ripple
6、. It is an effective way to suppress the torque ripple through changing dc bus chopper control to remain non-commutation phase current amplitude constant, but it results into a more complex topology 1-3. It is just fit for low speed applications to control non-commutation phase current amplitude to
7、regulate the commutation torque ripple 4. It is analyzed about the influence resulted from PWM ON mode on the torque ripple in 5.The ideas in 1-3 are to adopt different suppression methods in different speed interval, but they dont take the effect by PWM modes on the system in account. The predictiv
8、e current, neural network control and active disturbance rejection control etc are introduced to suppress the torque ripple in 9-12, but the control algorithm is more complicated and harder for realization. Depending on the commutation process of BLDC motors and the effect by PWM modes on the system
9、, thepaper presents a torque ripple com-pensation control in PWM_ON_PWM mode at different speeds by seeking different PWM modulation ratios during commutation period as motor runs at low speed and high speed.The method retains the original to-pology, improves the control performance of the system dr
10、amatically,and moreover is easy to realize.II. ELECTROMAGNETIC TORQUE OF BLDC MOTORDURING COMMUTATION PROCESS Assume that the BLDC motor is three-phase symmetrical and Y- connected, and neglect eddy currents and hysteresis losses, its equivalent circuit and main circuit are shown in Figure 1. r, L a
11、re the resistance andinductance of the stator windings respectively; are the counter emfs of the corresponding phase windings respectively; are the corresponding phase currents respectively. (1)The counter emf of every phase winding is a trapezoidal waveform with a flat-top width greater than or equ
12、al to 1200 electrical degree,and its flat-top amplitude is Em. When the motor works in three-phase six-state 1200 turn-on mode, the currents dont commutates instantaneously as a result of the inductanceof the armature winding. Take the power switch and s turn-on to and s turn-on for example. During
13、the commutation, it is gained as follows (2) Suppose that the mechanical angular velocity of the rotor is , the toque can be obtained as follows during the commutation process. (3) It is obvious from (3) that the toque is proportional to the non-commutation phase current during commutation,i.e. the
14、commutation torque ripple can be eliminated so long as non-commutation phase current remains constant during commutation.III. COMMUTATION PROCESS WITHOUT CONSIDERINGEFFECT BY PWM AND ARMATURE WINDING RESISTANT Assume that the circuit status changes from phase A and Cs turn-on to phase B and Cs turn-
15、on, phase A current flows and decays to zero gradually, while phase B current increases to the maximum gradually and reaches its steady-state value.The circuit equation during commutation without considering the effect by PWM can be written as follows. (4) Compared with the winding time constant of
16、a BLDC motor, PWM period can be thought small enough,and then. So the effect of the armature winding resistant can be neglected. Moreover the initial and final values of every phase current equal every phase steady-state current value before and after the commutation. All phase currents during the c
17、ommutation can be obtained from (1), (2) and(4). (5) Then the toque during the commutation can be written (6) From (5), the turn-off time off t of phase A and the turn-on time on t of phase B during the commutation process are (7) (8) From (5)(8), the commutation between two phases cant be completed
18、 in the same time as , i.e. the motor speed is less than a certain value, and as a result has reached its steady-state value before falls to 0, shown in Fig.2(I). Whats more, the commutation leads to an increase in the amplitude of torque. The torque ripple can be obtained (9) The commutation betwee
19、n two phases can be completed in the same time as , i.e. The motor runs at a certain speed, and as a result has exactly reached its steady-state value just as falls to 0, shown in Fig.2(II). In this case, the torque remains constant during the commutation and its value equals the torque during the n
20、on-commutation process (10) As, i.e. the motor speed is greater than a certain value, the commutation between two phases cant be completed in the same time, and as a result doesnt reached its steady-state value when falls to 0,shown in Fig.2(III). The commutation leads to a decrease in the amplitude
21、 of torque. The torque ripple can be obtained (11) IV. COMMUTATION TORQUE RIPPLE COMPENSATIONCONTROL IN PWM MODE It is known based on the previous analysis that the torque ripple caused by commutation can be finally eliminated by two ways-reducing current rate of increase in the turn-on phase to sup
22、press the currentpulsation in the non-commutation phase as the motor speed is less than a certain value; commutation overlapping to keep the turn-on phase constantly on and use PWM mode in the power switches of the turnoff phases to decrease current rate of descend to suppress the current pulsation
23、in the non-commutation phase as the motor speed is greater than a certain value. Assume that is the electric level state variables represents turn-on of power switch or diode in the upper arm of the corresponding phase whie represents turn-on of power switch or diode in the lower arm of the correspo
24、nding phase.As the motor runs at a low speed, PWM is implemented on the turn-on phase, i.e. turn off phase A while PWM on phase B, in order to reduce current rate of increase in the turn-on phase during commutation. The circuit equation during commutation is (12)It can be obtained from (1), (2) and
25、(12) (13)So non-commutation phase current can be got (14) Where is control pulse duty cycle of the turn-on phase during the commutation.From (12) and (13), we can get (15)So (16)The turn-off time of the turn-off phase toff is (17)From (14), the following equation must be satisfied in order to keep t
26、he amplitude of non-commutation phase current unvaried during commutation. (18)Because during commutation, it means that the inequation will be satisfied only if, i.e. the motor runs at a low speed. Furthermore as the machine operates at a low speed, it can be obtained from (14)(1) When , i.e. Under
27、compensated control during commutation, the amplitude of non-commutation phase current decreases during commutation.(2) When , i.e. Overcompensated control during commutation, the amplitude of noncommutation phase current increasesduring commutation. Substitute (18) into (17), we can get the commuta
28、tion time that keeps the amplitude of non-commutation phase current constant during commutation as the machine operates at a low speed. (19)As the motor runs at a high speed, overlapping commutation is adopted to implement PWM on the turn-off phase and turn on the turn-off phase constantly,i.e. PWM
29、on phase A while turn on phase B constantly,in order to reduce non-commutation current ripple during commutation. The circuit equation during commutation is (20)It can be obtained from (1), (2) and (20) (21)So non-commutation phase current can be got (22)Where DAA is control pulse duty cycle of the
30、turn-off phase during the commutation.From (20) and (21), we can get (23)Therefore turn-on phase current can be worked out. (24)The turn-on time of the turn-on phase ton is (25)From (22), the following equation must be satisfied in order to keep the amplitude of non-commutation phase current unvarie
31、d during commutation. (26)Because during commutation, it means that the inequation will be satisfied only if ,i.e. the motor runs at a high speed. Furthermore as the machine operates at a high speed, it can be obtained from (22)(1) When i.e. Undercompensated control during commutation, the amplitude
32、 of non-commutation phase current decreasesduring commutation.(2) When , i.e. Overcompensated control during commutation, the amplitude of non-commutation phase current increases during commutation. Substitute (26) into (25), we can get the commutation time that keeps the amplitude of noncommutation phase cur
