Your SlideShare is downloading. ×
Canadian space agency technology   increased ripple-free torque, speed in bldc motors
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×

Introducing the official SlideShare app

Stunning, full-screen experience for iPhone and Android

Text the download link to your phone

Standard text messaging rates apply

Canadian space agency technology increased ripple-free torque, speed in bldc motors

242
views

Published on

Canadian space agency technology increased ripple-free torque, speed in bldc motors. …

Canadian space agency technology increased ripple-free torque, speed in bldc motors.
Technology Summary.

Published in: Technology, Business

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
242
On Slideshare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
7
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. Increased Ripple-Free Torque or Speed in BLDC Motors Operating under Current or Voltage Saturation Technology Summary The CSA invention presents a novel electronic commutator of BLDC motors with any backEMF waveform such that the commutator minimizes power dissipation, subject to current and voltage limits of the motor's drivers. When one or more phases reach their voltage and/or current saturation levels, the controller optimally reshapes the stator currents of the remaining phases for continuing accurate, ripple-free torque production -- the controller automatically reshapes the excitation currents in such a way that the motor continues to generate the torque that is requested. A closed-form solution for the optimal phase currents at given angular position, velocity and desired torque, renders the control algorithm suitable for real-time implementation. This innovation allows the motor to operate above the rated speed and torque that would be achieved without current reshaping. This optimal management of the motor's excitation currents can significantly increase the rated speed or torque of the motor in the face of voltage and current limits of the drivers. Experiments show that the maximum torque capability is boosted by 20% when the phase saturation is considered in the phase current shape function. In addition, the torque controller can be used as a remedial strategy to compensate for a phase failure by optimally reshaping the currents of the remaining healthy phases for accurate torque production. The control algorithm allows the motor to optimally generate precise torque, even when operating under a phase failure. Market opportunities for the CSA technology are in applications that require BLDC motors with high efficiency, and those that require BLDC motors with reliable (i.e., fault-tolerant) performance. Of particular commercial interest is the technology's ability to provide ripple-free torque in a BLDC motor that is operating, intentionally, with one or more phases in voltage and/or current saturation. This feature of the technology provides system designers with an opportunity to substantially increase the speed and/or torque from a given BLDC motor.
  • 2. Increased Ripple-Free Torque or Speed in BLDC Motors Page 2 Background to the Technology Brushless DC (BLDC) motors are commonly used as the drives of servo systems in a wide range of industrial applications from robotics and automation to aerospace and military. Accurate and ripple-free torque control of BLDC motors is essential for precision control of such servo systems. In BLDC motors, the electric power is distributed by an electronically controlled commutation system. The conventional electronic commutator incorporates a feedback from the rotor angular position into a control system, which excites the stator coils of the motor in a specific order, in order to rotate the magnetic field generated by the coils to be followed along by the rotor. These conventional drivers of BLDC motors produce sinusoidal (or, alternatively, trapezoidal) current waveforms for smooth motor operation. In practice, however, non-ideal motors do not have a perfect sinusoidal distribution of magneto-motive force, and hence the sinusoidal commutation can result in torque ripple. Suppressing the torque ripple of the motor drive of the servo system can significantly improve system performance by reducing speed fluctuations. The conventional control approach is to assume that the phase currents can be controlled accurately and instantaneously, and therefore the currents can be treated as the control inputs. The waveforms of the motor phase currents are then adequately pre-shaped, so that the generated torque is equal to the requested torque. The limitation of this approach is that the motor's drivers have fixed rated current and voltage limits, and some of them may not be able to deliver the current inputs dictated by the electronic commutator that may occur when the motor operates at high torque or speed. Consequently, the performance of the torque production may significantly deteriorate as a result of the phase current distortions caused by the voltage or current saturation of the amplifiers. When there is a fixed inverter voltage and current, flux weakening allows a BLDC motor to operate above the base speed in constant-power, high-speed regions. Below the rated speed, all of the stator currents can be used to produce torque. Above the rated speed, a part of the stator current must be used to oppose the permanent magnet flux while the remaining portion is used to produce torque. These techniques are adequate only for a BLDC motor with a perfectly shaped, sinusoidal back-EMF waveform, and when, in addition, phase current limits are not taken into account. General Description of the CSA Technology This CSA innovation provides a closed-form solution for optimal excitation currents for accurate torque control of brushless motors with any waveform that minimizes power dissipation subject to current and voltage limits of the motor's drivers. When the motor terminal voltages and/or phase currents reach their saturation levels, the controller automatically reshapes the excitation currents in such a way that the motor generates torque as requested. This optimal management of the motor's excitation currents can significantly increase the rated speed or torque of the motor in the face of the voltage and current limits of the drivers.
  • 3. Increased Ripple-Free Torque or Speed in BLDC Motors Page 3 Another aspect of the innovation is that the torque controller can optimally compensate for the failure of a phase and reshape the currents of the healthy phases for accurate torque production. In the event that an open-circuit or short-circuit of a winding occurs, the torque controller can isolate the faulty phase in order to generate the torque that is requested, given the voltage and current constraints of the healthy phases. A novel aspect of this CSA technology is the optimal non-linear feedback from the rotor's angular position and angular rate (speed) that makes accurate torque production possible when the voltage or current of one or more phases reach their saturation level, or when phase failure occurs. The CSA control algorithm permits torque sharing among phases when some phases saturate. This results in a considerable increase in the attainable maximum motor torque because the torque controller automatically increases the torque contribution of the unsaturated phases when one phase saturates. Experiments show that the maximum torque capability is boosted by 20% when the phase saturation is considered in the phase current shape function. Experimental results, described below, illustrate the capability of the controller to achieve precise torque production during voltage/current saturation of the motor's drivers or a phase failure. Validation of the Technology The performance of this innovative controller has been demonstrated using simulation and experimental data. Experimental results obtained from a brushless servomotor under the proposed torque controller demonstrated accurate torque production under voltage/current saturation of the motor's drivers or failure of one phase. In order to evaluate the performance of the optimal torque controller, experiments were conducted on a three-phase synchronous motor with nine pole pairs. Two tests were set up as follows: Requested torque 10 Nm, speed 21 rad/s. In this test, phase voltages reached their limits, but the phase currents were far from the current limit. Requested torque 25 Nm, speed 2 rad/s. In this test, the phase currents reached their limit, while the terminal voltages were not saturated. These experiments demonstrated that the optimal torque controller can deliver accurate torque production in the face of current and voltage saturation. As described above, the optimal torque controller can produce accurate torque even under operation of a single phase failure. In this experiment, the current circuit of the motor's first phase was virtually broken by sending zero signal to the enable port of the
  • 4. Increased Ripple-Free Torque or Speed in BLDC Motors Page 4 corresponding power amplifier. The objective was to produce the same torque, 10 Nm, as the three phases by using only the remaining two phases. Experimental results show that the motor still produces the desired constant torque when the torque controller is designed based on the two healthy phases. Patent Protection Patent applications have been filed in Canada and USA. Publication The CSA technology is described in the following publication, available from CSA upon request: Aghili, F., "Optimal and Fault-Tolerant Torque Control of Servo Motors Subject to Voltage and Current Limits", accepted for inclusion in a future issue of IEEE Transactions on Control System Technology.