Sewing machine with a brushless DC motor controller of torque ripple
Introduction
Industrial sewing machine did not prepare as a mechanical and electrical integration, power drive system is the core of its technology is one of the sewing machine with brushless DC motor controller and compared to previous products, has a great advantage in performance. This article will focus on brushless DC motor torque ripple caused some problems for analysis.
Brushless DC motor commutation by a small spark of its free, reliable operation, easy maintenance, simple structure, no excitation loss of the many advantages on many occasions been more widely used.
l brushless DC motor torque characteristics
Brushless DC motor equivalent circuit shown in Figure l. Torque characteristics are important indicators of motor performance, the most important is the average torque and torque smoothness. Brushless DC motor average torque than high, but the existence of brushless DC motor torque ripple, and this is affecting the application of brushless DC motor as a main reason.
Sewing machine with a brushless DC motor controller of torque ripple
Brushless DC motor induced electromagnetic torque ripple There are 3 main reasons: cogging torque ripple, caused by non-ideal back EMF commutation torque ripple and torque ripple. Which produced the first two with the motor rotor magnet manufacturing process or the magnetization is not satisfactory, can the transformation of the motor body to contain.
2 for the theoretical analysis of torque ripple
During the set of commutation, motor speed is, the ideal trapezoidal back EMF motor wave (flat top width is 120 °), and that the commutation of each phase winding during the back-EMF amplitude unchanged.
Phase change to the current flow to C from B-phase (upper leg commutation), A non-commutation phase windings of the commutation process as an example.
Pre-S1 and S6 commutation conduction current from the A and B by two-phase windings; commutation is S1 and S2 after the turn, S6 off, A and C two-phase power, B winding up of the current through the diode freewheeling. DC voltage to the midpoint as a reference point, you can write during the three-phase commutation voltage equations:
Sewing machine with a brushless DC motor controller of torque ripple
Type in: Vsa = (Sa-1 / 2) Vdc, Vse = (Sc-1 / 2) Vdc, respectively A and C phase windings on the voltage between the reference point N0, Sa and Sc as the switching capacity, such as Sa S1 = 1 is open, S4 off; Sa = O, said the shutdown S1, S3 open.
Vsa = (Sa-1 / 2) Vdc for the A-phase winding on the voltage between the reference point N0; Vsc = (Sc-1 / 2) Vdc for the C-phase winding on the voltage reference point N0, VNN0 the mid-point for the motor the voltage between the reference point. Taking into account the three-phase motors connected in Y there: ia + ib + ic = 0, from (1) of the voltage balance equation can be obtained
Sewing machine with a brushless DC motor controller of torque ripple
And the winding time constant L / R compared to PWM cycle can be considered small enough, then the sewing machine controller with a brushless DC motor torque ripple of ignoring the impact of three-phase winding resistance, there
Sewing machine with a brushless DC motor controller of torque ripple
Type in: Ka, Kb, Kc, said the convenience to the introduction of variables.
Solution of this differential equation, there
Sewing machine with a brushless DC motor controller of torque ripple
Commutation torque during the two parts, part for the steady component in front of the back part of the phase change is caused by fluctuation component can be seen, commutation torque ripple caused by the parameters of the motor windings, commutation electromotive force during the three opposite variation of motor speed and DC voltage, modulation methods are involved. According to previous assumptions, the three opposite electromotive force of the ideal trapezoidal waveform, there
Sewing machine with a brushless DC motor controller of torque ripple
Available under the ideal back-EMF waveform caused by commutation torque ripple for the
Sewing machine with a brushless DC motor controller of torque ripple
3 Torque Ripple
This paper is a kind of sewing machine controllers for brushless DC motor, as sewing machines correct characteristics and requirements of motor shutdown. High precision down, because the exact parking location is directly related to the sewing machine performance and peer evaluation on the overall aircraft.
In the controller design, in the braking torque applied before the motor has a predetermined minimum speed is transferred, while the motor drive system load can be approximated in the shutdown process that is constant and every time - like, in the this case, that each stop, the braking torque imposed by the duration and amplitude are constant, that is, that each stop braking torque imposed by the average power is constant. By adjusting the average braking power to ensure the motor stops at the specified location accuracy: Once the parameters adjust braking power after the shutdown in each subsequent process, the same rules imposed on the average braking power can be shut down to ensure a more accurate location.
However, the actual process of debugging drive system found during the motor braking torque in the event of commutation, will affect the accuracy of downtime. This is because the phase change to a predetermined average torque was changed, making downtime accuracy affected. Therefore, when we must stop this situation commutation torque ripple suppression.
Introduction of a lag for the first phase (overlap commutation) method, phase delay that is off for some time off to compensate for the phase current. In order to be able to delay the DC bus during the shutdown of non-commutation phase reflects the current (total current), the commutation to take off during the commutation phase and non-phase synchronous PWM modulation and phase Hengtong opening measures, shown in Figure 2 below.
Sewing machine with a brushless DC motor controller of torque ripple
As can be seen from Figure 2, if the only method by overlapping commutation, commutation overlap time as more difficult to determine, and many factors affect the torque ripple, torque ripple suppression therefore not ideal. In order to avoid overlapping commutation method of conventional shortcomings of current regulation better performance, literature fixed-frequency current into the stator current regulation sampling techniques, to form the current fixed-frequency sampling and overlapping commutation technology combined with the current control methods, such as Figure 3. Is this paper, torque ripple suppression.
Sewing machine with a brushless DC motor controller of torque ripple
In this method, do not overlap, as for conventional lag phase in the commutation, as Zhi Shi Ke Shi Guan Duan began with a Shi Jian Tong Yan Zhang lead interval; Ershi in the commutation period, sampling points in Dianliu current feedback signal right Genju phase to wither off the system. Shown in Figure 3, in the A phase current volatile than the threshold is set off when the C phase, so the current decrease: the A-phase current fluctuation is less than the negative threshold setting phase when the opening of C, so that current.
Simulation experiments show that in the current when the sampling frequency of 200 kHz, and compared to the conventional overlap commutation, torque ripple coefficient reduced from 43% to 23%.
4 results
According to the development of high-speed sewing machine brushless motor drive system down situation, a series of experiments. The results obtained in Figure 4 and Figure 5 below. Bottom two graphs with the amplification curve for the upper waveform details, for the DC bus current waveform.
Sewing machine with a brushless DC motor controller of torque ripple
Sewing machine with a brushless DC motor controller of torque ripple
Figure 4 and Figure 5 shows that during braking, to a certain commutation compensation, the DC bus current sag in the degree of the compensation, with no phase change occurs, the DC bus current (Figure omitted) approximately equal to the power , thus ensuring the proper reverse torque to stop running within the precision. It is worth noting that the leg for the next phase, and negative DC bus current, but in compensation the Bank of China did not take measures to eliminate the negative current, this is because the delay through the off-phase conduction, the compensation has been the reverse torque can guarantee the precision in running down the range, there is no progress to take compensatory measures.
5 Conclusion
This high-speed sewing machine brushless DC motor drive system, for example, mainly discussed the process of change in braking torque ripple on motor downtime accuracy, and made according to actual situation of current fixed-frequency sampling and overlap commutation phase technique combination of commutation current compensation method to reduce commutation torque ripple effect on the accuracy of downtime. The design of the system and the use of compensation, after the actual system operation prove, show that it can use a good Deman Zu Yao Qiu, system requirements Yezai Jishujingduo within the scope of the provisions of.