In order to automatically detect and display the current, and with automatic protection and more advanced intelligent control in the event of overcurrent, overvoltage, etc., it is necessary to use a Hall current sensor with high speed and high precision detection, sampling and protection. Hall current sensor module, is the development of the past decade to measure the control current and voltage of a new generation of industrial electricity sensors.
Today, the new power semiconductor devices into the field of power electronics , AC variable frequency speed control, inverter, switching power supply and other increasingly popular, the original current and voltage detection components, have not adapted to the detection of high-frequency current waveform. In order to automatically detect and display the current, and with automatic protection and more advanced intelligent control in the event of overcurrent, overvoltage, etc., it is necessary to use a Hall current sensor with high speed and high precision detection, sampling and protection. Hall current sensor module, is the development of the past decade to measure the control current and voltage of a new generation of industrial electricity sensors.
1, the basic working principle and structure of the inverter
Inverter described in this article refers to the general-purpose industrial inverter and variable frequency general-purpose inverter. Such drives have become the mainstream of inverters due to their widespread use in the industrial field.
General asynchronous motor speed and synchronous speed there is a slip relationship, speed control method can change the motor stator frequency f, the motor stator winding pole pairs P, slippage rate S of either one of the best method of induction motor Is to change the frequency f, to achieve speed control. As long as the slip is not too large, you can approximate the speed n and f is proportional to, which means that continuous smooth change the power frequency, AC motor can achieve a wide range of continuous smooth speed.
It can be seen from the above analysis that when the general frequency converter controls the speed of the asynchronous motor, the output frequency and voltage are changed according to a certain rule. Under the rated frequency, the output current of the inverter keeps unchanged, and the output voltage increases with the output frequency The so-called variable frequency speed control (VVVF). Above the rated frequency, the voltage does not change, and the change in frequency is proportional to the output current.
The inverter is more and more widely used, inverter protection device is more and more important. Inverter generally has over-current, over-voltage, overload, lack of equal protection, mainly by the different functions of the sensor sampling to different analog values, converted by the conversion circuit into a microcontroller for the signal by the microcontroller to complete a variety of protection. Current sensor in the role of the most important in the inverter, through which you can accurately determine the current inverter current, the inverter overcurrent, overload protection is very important.
2, Hall current sensor in the inverter application
A magnetic field is induced around the wire through which the current flows, and then the magnetic field induced by the current is detected by the Hall device to measure the amount of current that generates this magnetic field. From this we can form a Hall current and voltage sensor. Because the output voltage of a Hall device is proportional to the product of the magnetic flux density applied to it and the operating current flowing in it, it is a multiplier-enabled device that can interface directly with various logic circuits and can be directly driven Various types of loads. Because Hall device application principle is simple, signal processing convenience, the device itself has a series of unique advantages, so the inverter has also played a very important role.
In the frequency converter, Hall current sensor's main role is to protect expensive high-power transistors. Due to the Hall-effect current sensor response time of less than 1s, so in the event of overload short circuit, the transistor can not cut off the power supply before the limit temperature has been reached, the transistor is reliably protected.
Hall current sensor according to their working mode can be divided into direct measurement and zero flux, in the inverter due to the need for accurate control and calculation, so the choice of zero flux method. Hall device output voltage amplification, and then amplified by the current, so that the current through the compensation coil, and make the compensation coil and the magnetic field generated by the measured current direction opposite magnetic field, if the condition IoN1 = IsN2, then the core In the flux is 0, then the following formula holds:
Io = Is (N2 / N1)
Where, I1 is the measured current, that is, the current in the primary winding of the magnetic core, N1 is the number of turns of the primary winding, I2 is the current in the compensation winding, and N2 is the number of turns in the compensation winding. It can be seen from the above equation that when magnetic equilibrium is reached, Io can be obtained from Is and turns ratio N2 / N1.
Hall current sensor is characterized by the current can be achieved without potential detection. Namely the measuring circuit can realize the current detection without connecting to the circuit under test, and they are coupled by the magnetic field. Therefore, the detection circuit input and output circuits are completely isolated. During the test, the detection circuit and the circuit under test each other.
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