What are the applications of current sensors in photovoltaic grid-connected inverters?
At present, all aspects of the photovoltaic industry chain are quite complete, with many manufacturers participating, and the photovoltaic market is becoming saturated. Under the situation of fierce competition, reducing production costs and increasing product reliability have become the main ways for manufacturers to seize the market; As the core detection element in photovoltaic grid-connected inverters, the current sensor requires high-precision power metering while requiring product stability.
If classified from the design principles of current sensors, commonly used technologies are open-loop, closed-loop, and fluxgate. Generally, current sensors with different principles are selected to achieve corresponding functions according to different applications.
The open-loop Hall current sensor is based on the direct-measure Hall principle. When the magnetic flux generated by the primary current on the primary side is concentrated in the magnetic circuit by a high-quality magnetic core, the Hall element is fixed in a small magnetic circuit opening air gap space. Here, the change of the magnetic flux is linearly detected. After the Hall voltage output by the Hall device is processed by a special circuit, the secondary side outputs a follow voltage consistent with the waveform of the primary side. This voltage can accurately feedback the change of the current of the primary side.
The closed-loop Hall current sensor is based on the magnetically-balanced Hall principle, that is, the closed-loop principle (also called magnetically-balanced Hall). When the magnetic flux generated by the primary current on the primary side is concentrated in the magnetic circuit through a high-quality magnetic core, the Hall element It is fixed in the air gap to detect the magnetic flux. The multi-turn coil wound around the magnetic core outputs a reverse compensation current to offset the magnetic flux generated by the primary current, so that the magnetic flux in the magnetic circuit is always kept at zero. With special circuit processing, the output end of the sensor can output a signal (current output or voltage output) that accurately reflects the change of the primary current.
As we all know, the topology of a typical distributed photovoltaic inverter (as shown in the figure below) includes a DC input link (string input bus), a DC boost link (Boost MPPT line), and a DC inverter AC link (DC / AC line ), And AC output (leakage current detection), current detection is essential in every link.
DC link open loop current sensor
At present, most manufacturers choose open-loop current sensors on the DC side (string current detection or DC / DC Boost line input current detection), because the DC-side current detection is only for measurement and does not participate in protection, so the accuracy requirements It is not very high, and usually the accuracy of 1% -2% can meet the requirements. As for the lack of temperature characteristics, you can use software algorithms to correct and compensate for hard parameter indicators such as zero temperature drift and accuracy. Contribute to the consistent use of the current sensor. And the cost of the open-loop current sensor is lower than that of the closed-loop current sensor, so the advantages of the open-loop sensor on the DC side are obvious.
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