Design of the most popular high-performance full d

Design of high-performance full digital AC spindle servo drive system

this paper introduces a high-performance full digital AC spindle servo drive system. The intelligent power module IPM is used as the switching element of the inverter, and the high-performance DSP admc401 is used as the control core. The control algorithm adopts slip frequency vector control based on rotor field orientation to realize current control, speed control and position control. The operation results show that the system has high speed regulation performance, low-speed load characteristics and good dynamic and static performance, and realizes the functions of spindle positioning and c-axis

slip frequency vector control

when the d-axis of the rotor flux rotation coordinate system is selected in the direction of the rotor flux vector, and the rotor flux is controlled to be constant in the steady state, it is necessary to control the slip angle frequency ω s. Rotor flux linkage ψ Dr, electrical angular frequency ω 1 and rotor flux linkage angle θ e. Respectively:

, where: ω M-rotor mechanical angular frequency

p-pole logarithm

the electromagnetic torque equation of AC asynchronous spindle motor is:

where IDs and IQs are the components of stator current on D and Q axes respectively, L1, L2 and M12 are stator and rotor inductance and mutual inductance respectively, R2 is rotor resistance, ω 1， ω S is the electrical angular frequency and slip angular frequency, and P =d/dt is the differential operator. That is, the linearization control of torque can be realized, but the state equations of IDS and IQs still contain IDS, IQs and ω 1 and product coupling term. From the perspective of current controller design, it is necessary to take decoupling control measures to facilitate the design of the controller. Therefore, it is also necessary to adopt the voltage feedforward compensation method in the d-q coordinate system to realize the independent control of the torque component and excitation component of the motor stator current. Here, the voltage feedforward compensation control is as follows:

Where, is the magnetic flux leakage coefficient, UDS, UQS are the components of the stator voltage on the D and Q axes, and u 'DS and u' QS are the outputs of the magnetic field and torque current controller, In this way, the coupling term of the current component of the stator current in the d-q coordinate system can be removed in the steady state, and the controller can also be designed independently according to the first-order system

the control structure block diagram of the system is shown in Figure 1

system structure

the structure of the full digital AC spindle servo drive system with the digital signal processor as the control core is shown in Figure 2. It can be seen from the figure that the system mainly includes the following parts: control circuit, main circuit (including rectifier power supply and inverter) and switching power supply circuit

control circuit structure

admc401 high performance digital signal processor adopts the core of 16 bit fixed-point DSP adsp2171, and integrates a wealth of peripheral controllers into a single chip. The instruction execution speed is 26m IPS. The main peripherals integrated in the chip include:

· high precision 8-channel a/d converter (ADC)

with 12 bit conversion accuracy, it supports two channel synchronous sampling and sequential sampling, and the conversion time is less than 2 μ s。

· three phase 16 bit PWM generator (PWM)

can be programmed to set the switching cycle, dead time, minimum pulse width limit time, with single refresh and double refresh modes, which can produce symmetrical and asymmetric PWM waveform, space vector PWM waveform, PWM output can be blocked by external pins or software programming, and has strong fault protection ability

· on chip incremental encoder interface unit (EIU)

has a programmable pulse input filter, which can realize frequency doubling, direction discrimination, counting and other functions. With a special encoder event timer, it can easily realize m/t method speed detection, and provide high-precision position and speed feedback for high-performance motor control

admc401 is the core of the whole system. In the system, it is used to realize vector transformation, current loop, speed loop, position loop control, SVPWM signal generation, various fault protection processing, etc. In order to realize the fast real-time control of the system, the system adopts the single-chip microcomputer +dsp Dual CPU structure in the design, so the control tasks of the system are divided: DSP completes the vector control and closed-loop control with high real-time requirements, and the single-chip microcomputer 89c8252 with flash structure completes the management tasks with low real-time requirements, such as control parameter setting, keyboard processing, status display, serial communication, etc, FPGA realizes the parallel data exchange between MCU and DSP, external i/o signal management, position pulse instruction processing and counting, fault signal processing, spindle encoder counting and other functions. The system can support analog speed input, digital speed input, pulse input and control the system through the upper computer

main circuit and switching power supply circuit

the neutral energy of the main circuit of the system is only related to the processing accuracy of the equipment. The circuit adopts modular design. The rectifier power supply part is connected with the AC DC AC voltage source inverter through the common DC bus, so its development is still in an immature stage. The rectifier power supply part adopts the diode rectifier module, At the same time, a soft start circuit is designed to reduce the impact of strong current on the DC smoothing capacitor of the main circuit. The inverter adopts the intelligent power module PM 75cva 120. In the system fault protection link, the main circuit overvoltage, undervoltage, overheating, overload, abnormal braking, photoelectric encoder feedback disconnection, communication fault and other protection are set. The fault signal is detected by the cooperation of software and hardware. Once the protection signal appears, the PWM drive signal is blocked immediately through software or hardware logic. The system adopts magnetic balance Hall current sensor to sample two-phase current feedback IA, IB, and obtain real-time current information. The control power supply of the system adopts switching power supply, and the switching power switching device adopts to p224. For the power supply of the photoelectric encoder of the spindle motor, considering that the voltage drop on the feedback signal line may be relatively large, which will affect the reliability of the feedback signal, the DC DC converter with feedback regulation is used for separate power supply

the total investment of these projects is 327.3 billion yuan. The experimental results and control functions are achieved.

the experiment of the full digital AC spindle servo drive system adopts AC variable frequency spindle motor: rated power 3.7kw/5.5kw; Rated current 9A; Rated synchronous speed 1500r/min; The rated torque is 24.6nm, and the resolution of the photoelectric encoder installed on the motor is 1000p/r. Current control sampling period 100 μ s. PWM switching frequency 10kHz, speed loop and position loop sampling period 500 μ s。 The output limiting amplitude of the speed loop is 1.2 times of the rated current

constant torque control

when the AC spindle servo drive system operates below the base speed, the system should have constant torque characteristics, especially at low speed, the system should output equivalent torque and maintain stable operation. Fig. 3 shows the speed response curve and current waveform when the given speed of the system is 1000r/min. The results show that the response of the system is relatively fast. Figure 4 shows the torque characteristics of the system when it operates below the base speed. It can be seen that the system has a wide range of load torque output capacity

constant power control

when the AC spindle motor operates above the base speed, the system automatically enters the weak magnetic field state. At this time, when operating under the constant power state, the stator voltage should be kept unchanged, the rotor flux linkage should be reduced, and the weak magnetic field control can be realized. According to the slip frequency vector control principle, the stator flux linkage current can be controlled according to the following formula:

, ω Base is the rated synchronous speed of induction motor

when the motor operates in the field weakening range, in order to ensure a considerable electromagnetic torque output, it is necessary to adjust the torque current limit amplitude of the speed PI regulator. The adjustment method is as follows:

where I * qslimit is the output limit amplitude of the speed regulator, IMAX is the maximum allowable output current of the system, K is the adjustment coefficient, which is generally selected to be less than 1, in order to prevent possible stall problems during high-speed start. Figure 5 is the speed response curve when the given speed of the system is 5500r/min

spindle orientation control and c-axis function

using the position encoder installed on the spindle motor, it is convenient to realize the electrical high-speed spindle orientation control, so that the spindle can accurately stop at the specified position, and the spindle orientation position can be conveniently set through communication or manual mode. The experimental results of spindle high-speed orientation control are shown in Figure 6, and the orientation process is completed in 1.2s. The c-axis function can be realized by switching from speed control to position control. Due to the rearrangement of internal grains

the full digital AC spindle servo drive system proposed in this paper makes full use of the high-speed computing ability of DSP admc401 and rich on-chip and off-chip resources, ensures the real-time control, realizes the requirements of high-precision speed regulation and positioning, has a wide speed regulation range, high control accuracy, good dynamic and static performance and perfect protection function, and the speed regulation range of the system reaches 1:1000, The constant power range is 1:4 ~ 12

references

[1] Qin Yi, Li Junyuan Basis of modern AC motor control technology Guangdong science and Technology Press, 1993

[2] D. W. novo TNY, T. a. lipo vector control and dynam ics of ac drives. clarendon press. oxford，1996

[3] b. k. bose. modern power elect ronics and ac drives. Beijing: China Machine Press, 2003

[4] Bi Chengen Modern CNC machine tools Beijing: China Machine Press, 1991 (end)