How to use Hall current sensing to achieve high quality OBC and PV current detection?

In new energy vehicles, the application of current sensors can be roughly divided into five categories: AC charging pile leakage current detection, BMS current detection, PDU current detection, OBC/DCDC current detection and motor controller current detection. The application of Hall sensing in the OBC/DCDC current detection of new energy vehicles generally requires a CMFR of more than 40dB to reduce the impact to less than 1%.

With the spread of automation and intelligence trends, the rapid development of battery cars, industrial automation, photovoltaic energy storage and other fields has increased the demand for high-voltage power systems, whose efficiency characteristics are increasingly regulated. How to operate, monitor and maintain these systems efficiently and accurately is not easy. Current detection is also the most important part.

OBC/DC current detection of new energy vehicles

In new energy vehicles, the application of current sensors can be roughly divided into five categories: AC charging pile leakage current detection, BMS current detection, PDU current detection, OBC/DCDC current detection and motor controller current detection. Among them, OBC car charger, in car DC-DC converter, air conditioning PTC heater and charging pile and other applications, need a kind of current detection sensor - Hall current sensor.

Hall current sensor can be said to be the most traditional current sensor. By using the Hall magnetic balance principle, the measured current is input into the operating current end of the Hall device, and the magnetic field is applied in the normal direction of the Hall device plane, which can accurately reflect the change of the measured current. Hall current sensor converts large current into small current with the same frequency and phase, which is easy to measure or protect.

OBC in /DCDC current detection, the application of chip-level current sensing can be more flexible to achieve high precision detection, not limited to DC or AC, small size, small power loss. In contrast, shunt resistance application detection schemes can lose a large amount of power under current and need to compensate for temperature; The detection scheme using voltage transformer can not measure the weight of DC, and the core is easy to saturate; Even current sensing modules, while accurate, are bulky and costly.

Compared with CMFR, Hall current sensing at chip level attaches great importance to the suppression of common-mode magnetic field. Because it was itself tested by Hall's principle, it is particularly sensitive to interference from external magnetic fields. The application of Hall sensing in the OBC/DCDC current detection of new energy vehicles generally requires a CMFR of more than 40dB to reduce the impact to less than 1%.

In addition to overcurrent protection, current detection also requires the size of the current to be collected for easy operation. Under normal operating conditions, the current of the current is much lower than the maintenance point, so when the small current input, the accuracy of the sensor is very important, the signal-to-noise ratio under the small current input conditions will be relatively poor, so the accuracy of the sensor should be as small as possible (no more than 2%).

Because OBC/DCDC systems require high cost and volume, and therefore high size and performance requirements for sensors, chip-level Hall current sensors are particularly suitable for this application.

Requirements for current detection of photovoltaic systems

First look at the current detection in the photovoltaic inverter. There are many kinds of inverters, such as centralized, distributed, series and small. Microinverters have the lowest voltage rating of nearly 100 volts, while other inverters have voltage ratings of more than 1,000 volts. Therefore, current detection must be carried out in high voltage protection, and the sensor needs to provide fast enough maintenance.

Regardless of the type of inverter, in the junction box or PV series, the sensor requires a high isolation voltage level, so that high side current sampling can be achieved, fast shutdown, and the accuracy requirement is not more than 2%. MPPT operation part of the current detection requirements mainly lie in the bandwidth and response speed, accuracy is not more than 2%. The DCAC operation part of all inverters requires high accuracy of current, preferably less than 1%, DC bias less than 0.5%, and needs to provide a variety of protection functions.

Traditional protective current detection does not require additional vertical components, which is cost advantaging but not necessarily accurate measurement, or additional vertical components can be accurately measured, but the cost will increase. By improving the level of protection, the current sensing chip integrated with electrical shielding can provide excellent common mode suppression and temporary disturbance rejection maintenance, solving the pain points of traditional protection current detection, cost-effective.

Conclusion

Hall current sensing chip with isolation can be used to replace shunt resistance, current mutual induction and isolation devices originally used for current sensing in the field of new energy vehicle OBC and photovoltaic inverter with a very compact solution, which has greater advantages in size and cost