The motor protector improves the reliability of the motor operation and the requirements of system intelligence, so the reliable operation of the protector plays an important role, and it also puts forward more realistic requirements for the protector against external interference. Use Freescale's high-performance processor MC9S08AW60 ($3.8740). MC9S08AW60 is a highly energy-efficient processor based on the S08 core from Freescale, and is the first microcontroller approved for the automotive market. It can be used in home appliances, automobiles, industrial control and other occasions, with the industry's best EMC performance. Power filter processing Using electromagnetic principles to filter hardware circuits is an effective way to improve the EMC of the protector. The circuit is as shown in the figure below. After the two-stage filtering process composed of the thermistor t, varistor RV1, inductor L1, L2, differential mode capacitor C1, common mode inductor L3, common mode capacitor C2 and C3, the power supply is well isolated. Terminal input and output interference. The PTC thermistor is mainly used for overcurrent and overheat protection. It is directly connected in the load circuit. When abnormal conditions occur in the circuit, it can automatically limit overcurrent or block current. When the fault is removed, it will return to the original state. Secondary fuse". Determine the selection according to the maximum operating current of the line. Varistors are mainly used to absorb various operating surges and induced lightning surge overvoltage protection to prevent such overvoltage interference or damage to various circuit components. According to the surge voltage that the design withstands, choose according to the maximum allowable use voltage and current capacity. Among them, L1, L2, C1 are used to suppress differential mode interference, and L3, C2, and C3 are used to suppress common mode interference. L1 and L2 cores should be made of materials that are not easily saturated and materials with excellent MF characteristics. According to the recommendation of IEC-380 safety technical indicators, the selection range of the component parameters in the figure is: C1=0.1~2uF; C2, C3=2.2~33uF; L3 is a few or tens of millihenries, depending on the working current. Parameter value. Figure 1 Power-side processing diagram Figure 2 Experimental results of unfiltered processing at the power supply terminal Figure 3 Experimental results after filtering on the power supply terminal The above picture shows whether a filter is used on the power supply terminal, using the Swiss TRANSIENT 2000 electromagnetic compatibility tester 1000V 100KHZ 0.75mS condition EFT group pulse experiment, from the signal comparison captured by TEXtronix TDS1012B, the power supply output without filtering processing has a spike , It will cause the microprocessor to reset or even crash. Signal end processing Harmonic and electromagnetic radiation interference will cause the protector to malfunction, making the electrical meter inaccurate or even unable to work normally. The sources of this type of interference in the motor control loop are frequency converters and on-site walkie-talkies. The solutions are as follows: First, the signal input line is glued. The glued double glue line can reduce the common mode interference, because the magnetic flux direction of the electromagnetic induction of the wire is changed, so that the induction cancels each other. The second is internal circuit processing. As shown in the figure below, a differential amplifier with dual differential inputs has a high common-mode rejection ratio. Connect the RC filter in the input loop, use special devices at the signal input and output ends, reduce input and output impedance, reliable grounding, and reasonable shielding. Figure 4 Signal processing circuit Protection output processing The input and output terminals adopt photoelectric isolation method, which can also eliminate common mode interference. At the same time, the varistor is connected in parallel to the output terminal of the protection relay, which effectively improves the life of the relay and reduces the internal interference due to the action of the external contactor. . Considering the uncertainty of the customer's use of the control voltage and the capacity of the contactor coil, confirm the use of MYG14D821. Figure 5 Protection output circuit External storage technology and watchdog protection circuit Use external memory chip X25043, SPI interface. The microprocessor has a built-in SPI control module, which is convenient to interface with the chip, and the external storage technology ensures the recording of running status and events. Low voltage reset and external watchdog improve the reliability of the protector. Figure 6 External memory and watchdog circuit The main body and the display unit are connected through RS485 Taking into account the particularity of the use environment and the diversity of requirements, the connection between the main body and the display unit also adopts the RS485 Modbus-Rtu protocol connection, which improves the reliability of display and control. The protector plays an important role in protecting the motor. The requirement for it is that it cannot be moved by mistake or refused to move, and it must be fast. Real-time multi-task scheduling actually achieves macro-multitasking effects through time slice rotation. For the protector, there are three important tasks: AC sampling at equal intervals to obtain steady-state and transient power data according to the algorithm; judging the fault according to the obtained data, fault timing, resetting and tripping output; man-machine user-interface. The following figure takes a cycle T=20mS, 32-point sampling as an example (taking into account fast division), the total time of 32 sampling is 3.2mS, the data calculation time is 9.72mS, and the timing is 0.36mS, then the human-computer interaction time is 6.72mS . Such task scheduling not only meets the real-time protection requirements, but also responds to the parameter settings quickly. Figure 7 Task execution relationship On the basis of sampling the signal multiple times, the software algorithm extracts the data that is closest to the true value. This algorithm calculates continuous periodic AC signals with high accuracy and strong ability to resist waveform distortion. When using this algorithm, digital filtering such as continuous average method and median algorithm can also be used to improve the anti-interference ability of the protector. Aiming at various electromagnetic compatibility problems encountered in the actual use of low-voltage intelligent motor protectors, this paper proposes anti-interference methods from two aspects of hardware and software according to the characteristics of the microprocessor system, and obtains good EMC performance. We are Tugboat Vape distributor and manufacturer in China, welcome to order.
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