Current is a commonly used measurement method in industrial equipment, and the detection methods are mainly divided into direct and indirect. The in-line type uses a shunt to enter the circuit. This solution is more suitable for occasions with small currents. If the current is too large, it will be limited by factors such as power supply heating. The indirect type refers to measurement without insertion loss using current transformers or Hall current sensors. Due to its advantages in accuracy, linearity, and bandwidth, the Hall current sensor has become a better choice for precise measurement of AC and DC currents.
Next, let's look at the advantages of domestic Hall current sensors and how to reduce costs and improve efficiency through several typical application scenarios.
Application Scenario 1: Photovoltaic Inverter
Photovoltaic inverters are an important part of the entire photovoltaic system. Although it only accounts for 8%-10% of the total system cost, it directly affects power generation efficiency, operation stability and service life. Since the shipment of inverters is completely related to the number of newly installed photovoltaic machines, with the vigorous development of the photovoltaic power generation market in the future, the shipment of photovoltaic inverters will increase significantly.Cost competition is also becoming more intense.
Typical distributed photovoltaic inverter topology includes DC input link (group input convolution), DC Boost link (Boost MPPT line), DC inverter AC link (DC/AC), AC output link (leakage current detection).
Current sensing is essential in every link.
At present, most manufacturers choose the open-loop Hall current sensor on the DC side, because the current sampled on the DC side is generally only used for measurement and protection, not for control functions, and the measurement accuracy of 1%-2% can meet the requirements of use, and because It is a DC current, and the bandwidth requirements are not high, so a low-cost open-loop Hall current sensor can be selected.
On the AC side, most manufacturers use closed-loop Hall current sensors, because the AC side needs to feed back the sampling current output to the microcontroller for control. The higher the accuracy (0.3%-0.8%), the higher the accuracy of controlling the output current. At the same time, the bandwidth of the closed-loop Hall current sensor is as high as 100-200KHz, and it can also more precisely capture the current disturbance caused by high-frequency modulation.
Application Scenario 2: Inverter
A frequency converter is a variable speed drive system. Adopt variable frequency drive technology to change the frequency and amplitude of the working voltage of the AC motor, so as to control the speed and torque of the AC motor smoothly. The biggest advantage of the frequency converter is that it can provide the required power supply voltage according to the actual needs of the motor, so as to achieve the purpose of energy saving and speed regulation. At the same time, it can also integrate protection functions such as over-current, over-voltage, and overload. With the continuous improvement of industrial automation, frequency converters have been widely used.
As shown in the figure below, a typical voltage source converter main circuit topology includes three-phase rectification (AC/DC), DC part and inverter part (DC/AC).
Similarly, the output of the DC part and the inverter part also needs to be tested for current. The current sampling on the DC side is only used to detect the through fault of the bridge arm, and the accuracy requirement is low, but the response time is long (μs level). Therefore, an open-loop Hall current sensor can be selected. Even for some solutions, the through protection of the bridge arm is realized by intelligently driving the optocoupler, and the current detection can be omitted on the DC side.
AC current detection is used to realize dead zone compensation, non-tripping current closed loop, overload protection, overcurrent protection, phase loss protection and other functions. Current sensing has high demands on accuracy, linearity and response time. In order to prevent misoperation or false protection, a closed-loop Hall current sensor with high precision and high linearity is selected.
Application Scenario 3: Dynamic Var Compensator (SVG)
The reactive power compensation device (SVG) is generally connected in parallel in the power grid system, which is equivalent to a variable reactive current power supply. Its reactive current can change rapidly with the change of load reactive power, and the reactive power required by the automatic compensation system It is an important equipment in the current flexible AC transmission system to increase the power, improve the power factor of the grid, and reduce the network loss. With the development of the power system and the improvement of various technologies, the development of SVG reactive power compensation devices will be better and better.
A typical SVG application block diagram is as follows: the entire system is connected in parallel to the grid and load through an inductor. The system includes a three-phase rectification part, a three-phase inverter part, a main control part and an acquisition part, wherein the acquisition part includes grid side voltage and current acquisition, inverter part output current acquisition and DC side voltage acquisition.
The current acquisition data on the grid side is sent back to the main control part. The main control part uses the harmonic detection algorithm to quickly and accurately calculate the load harmonic current, and forms a closed-loop control through PWM to control the modulation of the three-phase inverter part and the output current of the inverter part. The collected data is controlled to carry out targeted harmonic compensation. Better SVGs can compensate up to 25 harmonics. Therefore, these two current acquisitions have high requirements on accuracy, bandwidth and temperature drift.
At present, some schemes use CT as the choice of current detection due to cost considerations. However, CT generally has higher accuracy at the standard frequency point, and the accuracy decreases after the standard frequency point is exceeded. Therefore, the compensation effect for high harmonics will be reduced.
With the development of domestic closed-loop Hall current sensors, Hall closed-loop current sensors with high precision, high bandwidth, and low temperature drift will gradually become one of the best choices for SVG current sampling.
Application Scenario 4: Medium and High Frequency Heating Equipment
The medium frequency heating equipment uses the thermal effect formed by the induced current (eddy current) generated by the conductor in the alternating electromagnetic field to heat the conductor itself. According to different heating process requirements, induction heating power supply includes different classifications such as working frequency (50/60Hz), intermediate frequency (1-20KHz), high frequency (above 20KHz). Widely used in industrial production processes such as metal smelting, diathermy, heat treatment, welding, etc., it has the advantages of high heating efficiency, fast speed, and good controllability.
The block diagram of a typical medium and high frequency heating scheme is as follows, similar to a frequency converter, including three-phase rectification, DC, inverter and isolated output.
Considering the cost and actual measurement requirements, the DC part can directly use a shunt or an open-loop Hall current sensor. Due to the need for output closed-loop control and partial protection functions to ensure the constant accuracy of the output current, it is necessary to select a high-precision closed-loop Hall current sensor.
Solution: Domestic Hall current sensor
In order to help customers reduce costs and improve efficiency, and optimize the supply chain, Jinshengyang specially launched TL Hall series closed-loop current sensors with high precision, low cost, localization, high bandwidth, low temperature drift, etc., which perfectly meet the needs of current sampling in various industries .
Finally, attach the precautions in the current sensor application:
The through-core conductor of the current sensor can fill the aperture, and the copper bar or copper rod can be reasonably selected according to different sensor apertures;
The through-core conductor must form a closed circuit. In order to avoid the influence of the peripheral current of the iron core on the sensor, the through-core conductor should be closed away from the sensor;
3 There is no strong magnetic field near the sensor installation location, such as transformers, high-current conductors, etc.;
The current to be measured should be close to the standard rated value IPN of the sensor, and the difference should not be too large.
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