Abstract:Due to the complexity of vector control algorithm for asynchronous motor, in order to achieve high performance, dual DSP must be used to reduce the overall cost-effectiveness of the system. To solve this problem, this paper uses field programmable gate array (GA) to design an intelligent controller to complete a series of complex control algorithms, and implements a dedicated integrated circuit for vector control speed controller of asynchronous motor. This circuit is very important for the development of vector control asynchronous motor special chip with independent intellectual property rights.　　Key word:Asynchronous Motor Vector Control Field Programmable Gate Array Intelligent Controller Control Algorithm
Reliability and real-time are the basic requirements for the control system. The initial motor control is based on analog circuits with discrete components. With the advancement of electronic technology, variable frequency speed control technology based on pulse width modulation (PWM) has been widely used in motor control. In today's digitization trend is widely prevalent, integrated circuits and even special integrated circuits for motor control have been widely used in motor control. Especially in recent years, a new design idea has arisen, that is, hardware implementation technology based on field programmable gate array (field programmable gate array). This technology can be applied to variable frequency speed control system of asynchronous motor based on vector control. As a standard cell array, the function of IC is not available, but users can program their internal through special layout and wiring tools to design their own dedicated integrated circuits in the shortest time, which greatly improves the competitiveness of products. The high performance of the system can be achieved due to the parallel processing of the GA in hardware only and the CPU resource is not consumed. When this design method is applied to vector control variable frequency speed control system of asynchronous motor, current control is generally used as the cooperative processing of DSP, and the algorithm of rotator speed and rotator flux chain is implemented by the host of DSP. Generally, position control is flexible and difficult to achieve versatility, so position control is usually completed by DSP, but speed control and current control are versatile, so they can be integrated into a dedicated chip. In this way, not only speed control but also current control can be achieved separately, but also position control system can be composed with DSP. As shown in Fig. 1, if the CPU core is integrated in the GA, three algorithms of position, speed and current can be implemented by a single chip of the GA to achieve a real on-chip system.^[1][2].

Fig.1 Integrated structure of asynchronous motor speed controller system

Figure 2 Axis setting of three-phase and two-phase windings
Combining the advantages of high logic integration of semi-custom devices with the advantages of short development cycle and low development cost of standard logic devices, GA has the advantages of flexible structure, high density, high performance, advanced development tools, no testing and real-time on-line inspection of finished products after programming. The vector control speed control system of asynchronous motor introduced in this paper is based on the basic idea of modular design. It studies the digital structure of several main function modules, such as current vector control, speed PI adjustment, current PI adjustment, feedback speed measurement, current magnetic chain conversion, SVPWM, Clarke transformation, Park transformation and Park inverse transformation, and completes the layout and wiring of the main modules in a single Xilinx FPA. Special Integrated Circuit for Vector Control Speed Controller of Asynchronous Motor^[3].
1 Basic Principles of Vector Control
Set up asynchronous motor three-phase windings (A, B, C) and two-phase windings ( α、β) The axis of phase A winding is set as shown in Fig. 2. α The phase winding axes are coincident, they are all static coordinates, corresponding AC current is I_A, I_B, I_CAnd I_α, I_β. The magnetic potential F produced by the three-phase AC current in space is equal to that produced by the two-phase AC current by using the transformation of the magnetic potential distribution and the invariant power. That is, if the orthogonal transformation matrix is used, its positive transformation formula is:
　　
The inverse transformation formula is:
　　
By a two-phase stationary coordinate system ( α,β) A transformation to a two-phase rotating coordinate system (d-q) is called a Park transformation. α、β D-q is an arbitrary angular velocity in a stationary coordinate system ω Rotating coordinate system. When α、β When a stationary coordinate system is transformed to a d-q rotating coordinate system, the coordinate axis is set as shown in Figure 3. Figure 3 θ by α Angle between axis and D axis, d, Q windings are placed vertically in space, plus DC ID and iq, and d, Q coordinates to synchronize speed ω When rotating, the resulting magnetic potential and α-β The coordinate system is equivalent. D-q and α-β Angle of axis θ Is a variable that changes with load and speed and has different values at different times. The Park transformation, written as a matrix, is formulated as follows:
　　
Figure 3 α-β coordinate
Vector control, also known as field-oriented control, has the basic idea that the control method of analog DC motor can be used to convert three-phase static coordinates into two-phase static coordinates by orthogonal transformation according to the principle of constant magnetic potential and power (Clarke transformation is 3). Φ/α-β Transform, whose coordinate transformation relationship is shown in Figure 2, the quantitative relationship is like formula (1). Then, through the rotation transformation, the two-phase stationary coordinate is transformed into the two-phase rotational coordinate (Park transformation, that is, (1) α-β/ D-q transformation, coordinate transformation relationship as shown in Figure 3, quantitative relationship as formula (3). stay α-β/ Decomposition of the stator current vector into two DC components I oriented by the rotor magnetic field under d-q transformation_D, I_Q(where I_DFor the excitation current component, I_QAnd control them separately, control I_DIs equivalent to controlling the magnetic flux, while controlling I_QIt is equivalent to controlling the torque.
The two DC component IDs and IQ are transformed by current-voltage transformation and Clarke inverse transformation by speed and current PI regulators respectively (coordinate transformation relation Fig. 2, quantitative relation such as formula (2))), Park inverse transformation (coordinate transformation relation Fig. 3, quantitative relation such as formula (4)) and voltage space vector transformation, respectively. Six PWM signals controlling the inverter are obtained, which enables the variable voltage and frequency control of the asynchronous motor.
Digital Hardware Design of 2 Controller
The digital hardware design of asynchronous motor speed controller mainly includes Clarke transformation and Clarke inverse transformation. Park transformation, Park inverse transformation; Current PI adjustment module, speed PI adjustment module; Voltage space vector module; The calculation module of the rotor magnetic chain and the speed detection module are several different parts. The main circuit and data operation path of the vector control asynchronous motor speed control system are shown in Figure 4.
2.1 Vector Transform Module Design
Vector transformation includes phase coordinates and positive and inverse transformation of coordinate rotation. Formulas (1) ~ (4) give quantitative formulas for the corresponding transformation. One adder and one multiplier can complete the transformation operation. Formulas (3), (4) determine the coordinate rotation positive and inverse transformations, which can be calculated in engineering practice by looking up the sine table or by expanding the Taylor series to complete the corresponding functions.
2.2 PI Regulator Module Design
Figure 4 Data path of speed controller
The inner current loop and the outer speed loop are both regulated according to the PI control strategy. Formula (5) is the iteration formula of the bilinear transformation PI regulator.
O[n]=P[n]+I[n] (5)
Where the iteration formula for scale terms is:
P[n]=Kp.E[n](6)
The iteration formula for integral terms is:
I[n]=I[n-1]+K_H(E[n]+E[n-1]) (7)
In the formula, E[n] is the error input, Kp is the proportional gain, Kh is the integral gain, and the range of Kp and Kh is determined by the motor parameters, and its specific value needs to be determined by experiments. To prevent overflow, the regulator has set a saturation limit. The current PI regulator outputs a voltage instruction which is compensated in the form of a modulation factor and sent to the SVPWM module. The output of the speed PI regulator is the reference current instruction, which is sent directly to the current regulator. Whether it is a current regulator or a speed regulator, if the reference instruction value is large, the integrator may set up a large error value, which will be maintained for a long time due to the inertia of the integrator, resulting in excessive overshoots. Therefore, when designing PI regulators, the integral effect should be switched off immediately when the integrator output exceeds the limit value to reduce the effect of excessive overshoot.
Design of 2.3 M/T Speed Measuring Module
The key problem of vector control variable frequency speed controller for asynchronous motor based on rotor magnetic field orientation is the measurement of the rotor position and feedback speed. In this scheme, an incremental optical code disk and a Hall element are used as position detectors. The initial position of the motor rotator is roughly detected by the Hall element when the power is reset. The location information can be obtained when the Z pulse of the code disk appears. The position counts are performed at 4 times the frequency of the two orthogonal output pulses QEP1 and QEP2 of the code disk, and the pulse waveforms are shown in Figure 5. Rotation speed is measured using the M/T method. M/T method absorbs the advantage of T method on the basis of M method. The process of measuring rotation speed is as follows: starting the timer along the decrease of the output pulse of rotation speed (the timer length is Tc) and recording the number of output pulses of rotation speed M._LAnd number of clock pulses M₂. To measure time, stop counting the number of output pulses of the speed sensor first, and then stop counting the clock pulses when the next output pulse of the speed drops along to ensure that the output pulses of the whole speed sensor are detected. The basic measurement time TC is set to avoid the disadvantage that the T method reduces the measurement time due to the high rotation speed. Reading the clock pulse count value at the same time can avoid the disadvantage of M method worsening due to reduced rotation speed. Its measurement time is:
　　
M in formula (8)_LThe value can no longer have an error of one pulse, so the measurement error of the M/T method can only be caused by the count m₂The value is caused by an error of a pulse whose relative error isThe principle of velocity measurement is shown in Figure 6.
Figure 5 Pulse Waveform

Figure 6 M/T Speed Measuring Principle
2.4 Voltage Space Vector Module Design
Voltage Space Vector Pulse Width Modulation (VSPVWM), also known as flux chain tracing PWM, considers the motor as a whole with the inverter. It focuses on the goal that the motor obtains a circular magnetic field with constant amplitude, and the ideal magnetic chain in the AC motor when it is powered by three-phase symmetric sinusoidal voltage. It approximates the reference circle with the effective vector of the magnetic chain produced by different inverter switching modes. Theoretical analysis and experiments show that SVPWM modulation has low pulsing torque, low noise and high DC voltage utilization (about 15% higher than ordinary SPWM modulation). This control method is widely used in frequency converters and inverters. The voltage space vector structure diagram is shown in Figure 7.
Figure 7 Voltage Space Vector Hardware Structure
The synthesis of symmetric/asymmetric waveform generator, output logic circuit and space vector state machine is controlled by the corresponding bits of the comparative control registers. The working principle can be found in references [5], [6].
In addition to the above main modules, there are communication modules, register heaps, monitoring and protection and other auxiliary modules, where the communication module is mainly used to exchange data with DSP or host (see Figure 1). All these modules form a complete speed followup controller and are implemented in a piece of GA.
3. Implementation and experimental results of hardware design on the basis of GA
All modules in the design circuit of high performance asynchronous motor speed controller based on vector control are described in hardware language VHDL. After the source code is tested by function simulation and time series simulation, the EDF network table file is synthesized by SynPlify software and implemented in Xilinx's field programmable gate device (SpartanIIE-XC2S300E). The layout and wiring of the devices are completed in Xilinx's integrated development environment ISE5.li. The utilization of system resources is shown in Table 1. The equivalent number of gates consumed by the whole design is approximately 350 000, which is nearly saturated. Larger chips are required when future functional extensions are considered, but existing designs can be reused without major modifications^[7].Table 1 Resource utilization of XC2S300E devices
XC2S300E Resource Usage/%GCLK
SLicx
LC
LUT
Flip-Flop
RAM
DLL
LOB5
3074
6 916
6 148
6 148
64Kb
4
1882 (40)
3070 (99)
6 838 (82)
5078 (81)
3 328 (54)
64K
Bits (100)
2(50)
80(41)Note: Numbers in table brackets are%
In this design, the clock frequency of the asynchronous motor speed controller IC system can run at 33.33MHz, and the internal registers can be accessed by the upper computer to set various parameters in the control system. This IC chip can not only form a complete system with TMS320L2812 DSP and other circuits to achieve position servo control, but also can form a speed servo control system separately.
In the experiment to test the performance of speed controller, the drive object is an asynchronous motor with speed of 4 900r/min and encoder line of 4 900 and 1.5 kW, and the switch frequency and sampling frequency are set to 12 kHz. Figures 8 and 9 show the motor rotator speed tracking curves measured under different speed commands and α Axis current response curve. The speed instruction in Figure 8 is a step input from 0 to 1168r/min, with dynamic response time less than 0.5ms, overshoot less than 0.8%, and steady-state error less than 0.02%. The speed instruction in Figure 9 is slope input with acceleration of 0.42 r/min/sampling, target speed of 495 r/min, dynamic tracking error of less than 4%, and steady-state error of about 0.03%. If the switch frequency and sampling frequency are further increased, the operating performance of the control system will be better [8].
Figure 8 Response Curve under Step Speed Instruction

Figure 9 Response Curve under Slope Velocity Instruction
Single-chip integration, hybrid integration and system integration can be viewed as different levels and forms of power electronic integration. At this stage, single-chip integration is limited to a small power range. In the middle power field, hybrid integration or combination of hybrid integration and system integration are often used. System integration is still the main focus in the high power field. Monolithic and hybrid integration are the main directions for future integration technologies due to their higher integration and better performance.^[9].
In this paper, a special IC for variable frequency and speed control of asynchronous motor is designed based on the field programmer. It integrates Clarke transformation, Park transformation, Park inverse transformation, speed PI adjustment, current d-axis PI adjustment, current q-axis PI adjustment, rotor magnetic chain positioning and speed detection, voltage space vector pulse width modulation and PWM waveform generation algorithms. The sampling frequencies of speed outer loop and current inner loop can reach 35 kHz and 20 kHz, respectively. The experimental results show that the dedicated controller has good dynamic and static performance. This dedicated IC has been applied in high performance integrated numerical control system and has achieved good practical results. It is of great reference value for the development of vector control asynchronous motor variable frequency speed special chip with independent intellectual property rights.