AC Brushless Smart Initialization |
| 04-15 00:33:41 来源： 作者： |
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AC Brushless Smart Initialization Inquiry (采购产品): AC Brushless Smart Initialization Hello Motion Control Colleagues, I hope you are doing well there and please pardon me for bothering you. My name is Dr. Alex Ruderman. I am a motion control researcher and a lecturer in University Bar Ilan, Tel Aviv. May I suggest you to consider my Smart Initialization technique for AC brushless motor with incremental (non-commutation) encoder (see below). This Smart Ini is NOT: - Feeding current into two phases (my method induces no rotor movement) - Detection of saturation based (works for ironless motors) - Detection of magnetic anisotropy of the magnets (developed by Mr. Persson of Lausanne Institute for Technology) - Ld-Lq Inductance measurement, in particular, by high-frequency injection (my method makes no use of saliency) - Test pulses and detection of small movements of rotor (my method does not induce any rotor oscillations) - Detection of current phase angle when applying a test sinusoidal waveform (see Beinecke article SPS/IPC/Drives 2003; Korean IEEE paper). Thank you for your time and consideration. Best wishes -Dr. Alex Ruderman ---------------------------- Introduction Here is a typical discussion from one of the motion control Web forums: Question: "I want to know how to initialize AC Brushless motor position when I control it by vector control method - how do I initialize AC Brushless motor?" Answer: "If you have an absolute position sensor on the motor, you just do a "phasing read" to figure out where you are without motion. If you do not have absolute sensor, you must do a "phasing search" requiring some motion to drive you to a known position. Because the phasing search does not require absolute sensor, it can save money, but it is not appropriate for all applications, particularly if there is a significant net load on the motor, as in a vertical axis." The problem – long and rapid oscillating start-up rotor movement of conventional straightforward initialization (phasing search), complexity and defficiencies of other known initialization procedures. For example, that based on magnetic saturation will not work for ironless motrs, is relatively coarse etc. Also the known initialization methods are problematic in the presence of load torque. The solution - our intelligent initialization algorithm called Smart Initialization. Since its invention in 1995, it was purchased by some tens of position control companies. It is now a mature technology that seems today's imperative, especially, for linear motion. And it works fine! It is a matter of few minutes to get Smart Initialization idea. Once you got it you can have it up and running in your lab within some hours. It does not make sense to deliver Smart Initialization software because its implementation requires just adding some tens lines to control code and should be better done by customers themselves. The most recent development is Smart Initialization generalization for unknown position dependent load torque presence. Smart Position Initialization Procedure for Sinusoidal Brushless Motor with Incremental Encoder without Hall Sensors In the Presence of Load Torque Traditionally AC (sinusoidal) brushless motor with incremental encoder employs position Hall sensors. Using them as a coarse position sensor, such a motor starts as BLDC - DC (trapezoidal, or 6 step) brushless or as AC brushless with non-optimal commutation angle until a zero encoder pulse (absolute position) is found. After that, switching to sinusoidal operation mode with optimal commutation angle is possible because absolute electrical rotor position (angle) can be provided to sinusoidal current loop. In the absence of position Hall sensors (or special commutation encoder), a known technique for AC brushless drive to start is first to have motor settled at the predetermined position, for example, by feeding two motor phases (Stepper Motor Method). As constant (DC) current feeds two motor phases, motor torque is a known sinusoidal function of rotor (electrical) angle. Sinusoidal motor torque curve on one electrical revolution has two zero crossing points: one of them represents a stable equilibrium, another – a non-stable one. For the above technique, a worst case “magnetic alignment” movement from a random initial rotor position to a stable state is about one half of electrical revolution. This worst case is achieved if initial rotor position almost coincides with a non-stable equilibrium point (we suppose that a motor is not stuck near or at a non-stable equilibrium position - it is theoretically possible for relatively high Coulomb friction). To summarize, the deficiencies of the known initialization procedure: - may rapidly move the motor up to 180 el.deg; - may make motor oscillating; - is not accurate in the presence of load torque. Such kind of initialization procedure is not intelligent enough and may be unacceptable for certain, say, robotics applications or linear (gearless) brushless motors. Another initialization procedure may be found in US patent No. 5,874,821 "Method and Apparatus for Controlling a Brushless Electro Motor by Determining the Absolute Phase Position of the Rotor Relative to Stator" by Mr. Riccardo Monleone (Switzerland). This initialization technique assumes rotor movements due to applying known test signals. Absolute position is derived from measured position changes and test signal magnitudes. Initialization procedure is comprised of two stages. At coarse initialization stage, a motor is considered DC (trapezoidal) brushless, trapezoidal excitation signals are used and rotor position estimation resolution is 60el.deg. At fine initialization stage, a motor is considered AC (sinusoidal) brushless, sinusoidal excitation signals are used and the absolute rotor position is determined by a binary search routine. We suggest a different sort of initialization procedure for AC (sinusoidal) brushless motor with incremental encoder without position Hall sensors that is smarter than the known initialization techniques. Our no-load Smart Initialization allows identifying exact rotor electrical position while eliminating (long) trial movements, rotor oscillations, test excitation signals and position changes, coarse/fine initialization procedures, search routines etc. We also make no use of saliency and magnetic saturation. Position initialization error is ideally zero for an arbitrary initial rotor position and zero load torque. Any non-zero load torque will cause initialization error that increases motor current (motor and power electronics losses) for the same generated torque. Significant payload and / or cogging may cause unacceptable position initialization errors. In the paper: Doo-Hee Jung, In-Joong Ha "An Efficient Method for Identifying the Initial Position of a PMSM with an Incremental Encoder", IEEE Trans. on Ind. Electronics, Vol. 45, No.4, August 1998, pp. 682-685, the authors suggest initialization procedure for a constant load torque. It is based on providing (small) test sinusoidal torque disturbances and observing motor angle sinusoidal steady-state responses. At least, three test points are required. Test points selection is not that trivial because the close-loop system may become unstable. This approach is too complicated and burdensome (test settling time, steady state trial movement, stability etc.) to gain industry recognition. We suggest a different simple and accurate advanced position initialization technique in the presence of unknown (not necessary constant - time invariant position dependent) load torque (payload, cogging etc) that is an extension of our basic no-load Smart Initialization procedure. Typical questions in connection with Smart Initialization procedure extension to load torque case are: "Can this method handle the following situations: - vertical axis with payload; - motor with brake; - high friction; - linear motor standing against one of the end barriers (mechanical stop) etc?" As opposed to the most known initialization methods, extended Smart Initialization is supposed to work properly also in the presence of position dependent load torque for which |
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