Pulse Width Modulation is widely used in measurement, communications, industrial control, etc.
In AC charging pile communication, the monitoring of the interaction between the car and the charging pile is completed through the CP signal. The CP signal is the handshake signal between the car and the AC charging pile. The communication method uses pulse width modulation amplitude alternating.
Information interaction between electric vehicles and charging piles is carried out by adjusting the PWM duty cycle. The so-called duty cycle refers to the proportion of high-level time in the entire cycle within a pulse cycle, ranging from 0% to 100%. Among them, the period is the time occupied by a complete pulse signal, including high level and low level, and the pulse width time refers to the high-level time. For example, if the pulse period is 10ms and the pulse width is 7ms, then the duty cycle is 7/10 = 70%, which is a pulse signal with a duty cycle of 70%.
During the charging process, the CP signal amplitude changes:
1. Before inserting the gun: the CP signal is 12V.
2. After inserting the gun: due to the voltage-dividing resistor connected to the car charger, the CP signal jumps to 9V.
3. After the charging pile detects that the CP signal is 9V, the switching level is PWM output.
4. The PWM duty cycle reflects the maximum output current of the charging pile.
5. When the car confirms the charging signal, it will switch the voltage dividing resistor in the car charger so that the signal jumps to 6V.
6. After the charging pile detects that the CP signal jumps to 6V, the relay closes, and charging starts.
7. During the charging process, the PWM signal amplitude is monitored in real-time. When it jumps to a value other than 6V, the power is cut off in time.
The AC charging pile detects the voltage between the CP line and PE to determine the duty cycle of the PWM wave emitted by the AC charging pile. According to different duty cycles, the maximum charging current between the AC charging pile and the car can be confirmed.
The corresponding states of different duty cycles are as follows:
Mapping relationship between charging facility duty cycle and charging current limit
| PWM duty cycle D | Maximum charging current I/A |
| D=0%, continuous -12V | The charging station is not available |
| D=5% | A 5% duty cycle indicates the need for digital communication, and communication needs to be established between the charging station and the electric vehicle before power is supplied. |
| 10%≤D≤85% | I=D×100×0.6 |
| 85%＜D≤90% | I=(D×100-64) ×2.5；I≤63 |
| 90%＜D≤97 | reserved |
| D=100%, continuous positive voltage | not allowed |
The mapping relationship between duty cycle and charging current limit of electric vehicle detection
| PWM duty cycle D | Maximum charging current I/A |
| D<3% | No charging allowed |
| 3%≤D≤7% | A 5% duty cycle means digital communication is required and needs to be established between the charging station and the electric vehicle before charging. No charging is allowed without digital communication |
| 7%<D<8% | No charging allowed |
| 8%≤D＜10% | I=6 |
| 10%≤D≤85% | I=(D×100)×0.6 |
| 85%＜D≤90% | I=(D×100-64)×2.5；I≤63 |
| 90%<D≤97% | reserved |
| D>97% | No charging allowed |