Analysis of overcurrent protection circuit of electric vehicle on-board charger

Abstract: This article uses BYD's patents to understand electric vehicles, on-board chargers and their overcurrent protection circuits. The on-board charger includes an AC/DC converter and a DC/DC converter. Both the AC/DC converter and the DC/DC converter use SiC switch tubes driven by optocouplers. The overcurrent protection circuit includes: a current detection unit that outputs a current detection value by detecting the output current of the DC/DC converter; an overcurrent protection unit that outputs an overcurrent protection signal; and a control unit that closes the control signal output channel of the SiC switch tube when receiving the overcurrent protection signal, so that the AC/DC converter and the DC/DC converter stop working. The overcurrent protection circuit can quickly trigger the overcurrent protection function when an overcurrent fault occurs in the on-board charger, thereby improving the safety of the on-board charger. At the same time, the use of SiC switch tubes can increase the charging rate of the on-board charger and reduce the control difficulty and cost.

Technical Field

The utility model relates to the technical field of electric vehicles, in particular to an overcurrent protection circuit of an on-board charger, an on-board charger and an electric vehicle.

Background Art

As the exhaust gas produced by traditional fuel vehicles aggravates environmental pollution and the earth's oil resources are becoming increasingly scarce, the global market demand for electric vehicles is growing rapidly. At present, on-board chargers mostly use a two-stage conversion structure, the specific structure of which is shown in Figure 1. The on-board charger first rectifies the AC power through the AC/DC converter 100, then connects the rectified DC power to the DC/DC converter 200 to adjust the DC voltage, and finally inputs the adjusted DC power to the load (i.e., the battery pack). The specific circuit topology is shown in Figure 2. The DC/DC converter 200 mostly uses BOOST (boost chopper circuit) and BUCK (buck chopper circuit) circuits to achieve DC/DC conversion. The switch tube generally uses IGBT (Insulated Gate Bipolar Transistor, insulated gate bipolar transistor), and the on and off of the IGBT is controlled by the driver chip. The model of the driver chip is generally 1ED020I12FA.

In order to ensure the safety of the on-board charger, an overcurrent protection circuit is generally required. Some on-board chargers can close the PWM (Pulse Width Modulation) output channel through software or hardware circuits according to the collected IPM (Intelligent Power Module) overcurrent protection signal to achieve overcurrent protection.

However, most car chargers use MOS tubes and do not have IPM (Intelligent Power Module) overcurrent protection signals. It is necessary to detect the current signal of the car charger to construct an overcurrent protection signal. However, the maximum switching frequency of some car chargers can reach 100KHz. If the above method is used to implement the overcurrent protection function of the car charger, the action delay time of the overcurrent protection circuit is large, and the overcurrent protection function has the risk of failure, which seriously affects the safety of the car charger.

Utility Model Content

The utility model aims to solve one of the technical problems in the related art at least to a certain extent. To this end, one purpose of the utility model is to propose an overcurrent protection circuit for a vehicle charger, which can quickly trigger the overcurrent protection function when an overcurrent occurs in the vehicle charger, thereby improving the safety of the vehicle charger. At the same time, the vehicle charger adopts SiC (Silicon Carbide) switching tube, which can increase the charging rate of the vehicle charger and reduce the control difficulty and cost. The second purpose of the utility model is to propose a vehicle charger. The third purpose of the utility model is to propose an electric vehicle.

To achieve the above-mentioned purpose, the utility model proposes, on one hand, an overcurrent protection circuit of an on-board charger, the on-board charger comprising an AC/DC converter and a DC/DC converter, both of which use SiC switch tubes driven by optocouplers, and the overcurrent protection circuit comprising: a current detection unit, the current detection unit outputs a current detection value by detecting the output current of the DC/DC converter; an overcurrent protection unit, the overcurrent protection unit is connected to the current detection unit, and the overcurrent protection unit is used to output an overcurrent protection signal when the current detection value is greater than a preset current threshold; a control unit, the control unit is connected to the overcurrent protection unit, and the control unit closes the control signal output channel of the SiC switch tube when receiving the overcurrent protection signal, so that the AC/DC converter and the DC/DC converter stop working.

According to the overcurrent protection circuit of the on-board charger of the utility model, the current detection unit outputs the current detection value by detecting the output current of the DC/DC converter, and the overcurrent protection unit outputs the overcurrent protection signal when the current detection value is greater than the preset current threshold value, and the control unit closes the control signal output channel of the SiC switch tube when receiving the overcurrent protection signal, so that the AC/DC converter and the DC/DC converter stop working. Therefore, the overcurrent protection circuit can quickly trigger the overcurrent protection function when an overcurrent fault occurs in the on-board charger, thereby improving the safety of the on-board charger. At the same time, the on-board charger adopts the SiC switch tube, which can improve the charging rate of the on-board charger and reduce the control difficulty and cost.

The overcurrent protection circuit of the vehicle charger according to the utility model may also have the following additional technical features:

The current detection unit includes a current Hall sensor, which is connected to the output end of the DC/DC converter. The DC/DC converter is a resonant full-bridge isolation converter, which includes a first bridge conversion unit, a second bridge conversion unit and an isolation transformer, wherein the input end of the first bridge conversion unit is connected to the DC end of the AC/DC converter, the output end of the first bridge conversion unit is connected to the primary side of the isolation transformer, the secondary side of the isolation transformer is connected to the input end of the second bridge conversion unit, the output end of the second bridge conversion unit is connected in parallel with a DC side capacitor and serves as the output end of the DC/DC converter, and the current Hall sensor is connected to the positive terminal of the DC side capacitor.

The AC/DC converter is a three-phase bridge converter, the AC end of the three-phase bridge converter is used to connect to the power grid or drive the motor, and the DC end of the three-phase bridge converter is connected in parallel with a bus capacitor. The SiC switch tube is a SiC power field effect tube. The overcurrent protection unit includes: a first resistor, a second resistor and a third resistor connected in series between the reference voltage power supply and the ground, and a first node is provided between the second resistor and the third resistor; a comparator, the negative input end of the comparator is connected to the output end of the current detection unit, and the positive input end of the comparator is connected to the first node; a fourth resistor, one end of the fourth resistor is connected to the first preset power supply, and the other end of the fourth resistor is connected to the output end of the comparator; a fifth resistor, one end of the fifth resistor is connected to the output end of the comparator; a sixth resistor, one end of the sixth resistor is connected to the other end of the fifth resistor, and the other end of the sixth resistor is grounded; a first capacitor, the first capacitor is connected in parallel with the sixth resistor.

The overcurrent protection unit also includes: an amplifier, wherein the positive input terminal of the amplifier is respectively connected to the other end of the fifth resistor and one end of the sixth resistor, the negative input terminal of the amplifier is connected to the output terminal of the amplifier, and the power supply terminal of the amplifier is connected to the first preset power supply; a second capacitor, wherein one end of the second capacitor is connected to the power supply terminal of the amplifier, and the other end of the second capacitor is grounded; a seventh resistor, wherein one end of the seventh resistor is connected to the output terminal of the amplifier, and the other end of the seventh resistor is connected to the control unit; and a third capacitor, wherein one end of the third capacitor is connected to the other end of the seventh resistor, and the other end of the third capacitor is grounded.

The overcurrent protection unit also includes: a first clamping diode, an anode of the first clamping diode is grounded; a second clamping diode, an anode of the second clamping diode is connected to a cathode of the first clamping diode, a second node is provided between the anode of the second clamping diode and the cathode of the first clamping diode, a cathode of the second clamping diode is connected to the first preset power supply, and the second node is connected to the other end of the seventh resistor.

To achieve the above-mentioned object, a second aspect of the present invention provides a vehicle charger, which includes the overcurrent protection circuit of the vehicle charger described in the first aspect of the present invention.