Angular position detection system based on AD2S83 and its application in electric power steering system[Copy link]
1 Introduction The resolver based on the principle of electromagnetic induction, sometimes also called a resolver, is a precision control motor that completes the detection function of shaft angular displacement information in the electric power steering system. Since it is an analog electromechanical component, when it is used in a digital system, it requires a certain interface circuit, namely a resolver-digital converter (RDC), to realize the conversion of analog signals to digital quantities of the control system. With the rapid development of electronic technology, the American AD company has developed it into a series of monolithic integrated circuits, thus making up for the shortcomings of the RDC built by discrete components in the past, which was large in size and low in reliability, and brought great convenience to engineering applications. The resolver and AD2S83 can form a high-precision electric power steering angular position detection system, and the analog speed signal output by AD2S83 can also be used as a speed feedback signal to form a speed loop in the electric power steering system. 2 Resolver
The resolver is a component that works according to the principle of electromagnetic induction. There are windings on its stator and rotor, which are arranged concentrically and coupled to each other. The resolver uses orthogonal two-phase windings. It is mainly used in angle position control systems as an angle position detection component. If the excitation voltage of the rotary transformer is E=Esinwt, the electromotive force induced in the orthogonal A and B phase windings is:
Among them, θ is the rotor angle of the rotary transformer, which is the absolute position. 3 Introduction to AD2S83 AD2S83 is a monolithic integrated circuit launched by AD Company of the United States, which is manufactured with BiMOS II process and combines advanced CMOS logic circuit with high-precision bipolar linear circuit. It has low power consumption (300mW), and its digital output resolution can be set by the user to 10, 12, 14 or 16 bits, and has a speed output signal that can be used by the user as a speed feedback signal of the speed loop to replace speed measuring components such as tachometer generators, thereby reducing the size of the system. After AD2S83 is connected as shown in Figure 1, it constitutes a tracking RDC working in a type II servo loop. Its digital output can automatically track the shaft angle input at the selected maximum tracking rate without static error. Because it uses a ratio tracking method when converting the resolver signal to binary, the output digital angle is only related to the ratio of the SIN and COS input signals, but not to their absolute values. Therefore, AD2S83 is insensitive to the amplitude and frequency changes of the input signal, and does not need to use a stable and accurate oscillator to generate the reference signal, while still ensuring accuracy. The presence of a phase-sensitive detector in the conversion loop ensures a high suppression capability for the orthogonal components in the reference signal. In addition, it has a strong ability to suppress noise and harmonics. The outstanding advantage of AD2S83 is that it allows users to select the corresponding parameters to optimize the performance of the entire system. Figure 1
4 Design of angular position detection circuit The key to the design of position detection circuit is to correctly select the peripheral components of AD2S83. The following introduces the selection of peripheral components of AD2S83. It should be noted that the components with quantities close to the ideal values should be selected and operate within the allowable temperature range. The selection of components with an error level of 5% will not reduce the performance of the converter. See Figure 1. 4.1 Selection of high-frequency filter components R1, R2, C1, C2 The role of the high-frequency filter is to eliminate DC bias and reduce the noise entering the AD2S83 signal because they affect the output of the phase-sensitive detector. Its role is particularly important when there is noise from the switching power supply and brushless motor. The selection of component parameters is as follows: C1=C2=15k ≤R1=R2≤56k (3)
Where, is the reference frequency. When R2＝R3, C1＝C3, only R1 and C2 can be omitted. Note: Since the high-frequency filter has a 3-fold attenuation on the signal input to the phase-sensitive detector, it will affect the gain of the loop. 4.2 Selection of gain proportional resistor R4 If C1 and C2 satisfy equations (3) and (4), then
When the reference frequency is 400Hz, the typical value of the bandwidth is 100Hz, and when the reference frequency is 5kHz, the typical value of the bandwidth is 500Hz to 1000Hz. C4, C5, R5 are selected as follows:
The drift of the integrator input and the bias current will cause additional position drift at the converter output. If the drift can be ignored, R8 and R9 can be omitted. Otherwise, R8 = 4.7M and R9 = 1M (potentiometer) should be used. In order to reduce the zero drift, first select the peripheral components of AD2S83 and disconnect the connection between AD2S83 and the resolver. Then connect the COS and REFERENCE INPUT pins, the SIN and SIGNAL GROUND pins, add power and reference signals, and adjust the potentiometer R9 to make the output all "0". Figure 2
5 Application of AD2S83 in EPS system The electric power steering system must meet very high real-time and high precision requirements, while ensuring its high reliability. Based on the advantages of brushless rotary transformer and AD2S83 integrated circuit, the high-reliability brushless rotary transformer and AD2S83 are selected to form the EPS system angular position detection system, and the analog speed output signal of AD2S83 is used as the speed feedback signal to form the speed loop of the EPS system. This is a good choice when designing these EPS systems. See Figure 2 for the system block diagram. 5.1 Position detection unit hardware circuit design and implementation According to the system performance indicators, the resolution is 12bit, the excitation frequency is 5KHz, the maximum tracking frequency is 260rps, and the bandwidth is 520Hz. After selecting the peripheral components of AD2S83 according to the above calculation method, the speed feedback and position detection circuit can be designed. The hardware connection diagram is as follows:
When implementing this circuit, you should pay attention to the parallel connection of 100uF (ceramic) and 10uF (tantalum) decoupling capacitors between Vs, -Vs and ANALOG GROUND, and between +VL and DIGITAL GROUND. They should be placed as close to the AD2S83 converter as possible, and each converter should have its own separate decoupling capacitor. The two signal ground terminals of the resolver should be connected to the SIGXAL GROUND pin of the converter to reduce the coupling between the positive and cosine signals. In addition, the positive and cosine signals of the resolver and the reference signal should preferably use twisted shielded wires. 5.2 Connection between AD2S83 and MCU The following introduces the operation of the MCU on the AD2S83 RDC. Before that, the control signal of the AD2S83 converter is briefly explained:
The signal only prohibits the reversible counter from transmitting data to the output latch and does not interrupt the operation of the tracking loop. Releasing the signal will automatically generate a BUSY and refresh the output latch.
The signal determines the state of the output data. When it is high, the output data pin remains in a high-impedance state. When it is low, the data in the output latch is allowed to be transferred to the output pin. BYTESELECT input: Regardless of the state of the signal, when it is low, the low-order byte will appear on the data output lines DB9-DBl6. When BYTE SELECT is high, the high 8-bit byte will appear on the data output lines DBl-DB8; when BYTE SELECT is low, the low 8-bit byte will appear on the data output lines DBl-DB8. They also appear on DB9-DBl6 at the same time. Speed signal: The speed signal is a DC signal proportional to the speed output by the integrator. In many cases, this signal can be used instead of the traditional speed measuring engine. 5.3 The process of the microcontroller reading data from AD2S83: First, apply to AD2S83
6 Conclusion This paper introduces the application of AD2S83RDC integrated circuit, and designs the position detection system in EPS system composed of this integrated circuit and rotary transformer, which has been successfully applied to the EPS project of Municipal Science and Technology Commission in Automobile College. Practice shows that the system has the advantages of small error, good real-time performance, high reliability and strong anti-interference ability.
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
600)this.width=600" border=0>
提升卡
变色卡
千斤顶
京公网安备 11010802033920号
