Sixth, motor drive leakage phenomenon
There are roughly the following reasons:
Seven, current detection program
At present, the use of Hall sensor (HallCurrentSensor) or current transformer (Currenttransformer) to feedback detection of DC bus current on the power converter has many limitations. Because the current through the main switching device is generally relatively large, the rated parameters of the Hall device or current transformer used must also be large, and the solution is large in size and high in cost. In addition, it is inconvenient to achieve a high power density of the power converter.
This paper introduces a novel scheme-based on the current detection circuit composed of semiconductor devices, which can directly arrange the circuit on the control PCB of the power converter, which is not only low in cost, small in size, convenient in installation, but also good in performance. The power converters are solidified together to form an application specific integrated circuit (ASIC).
The working principle of the circuit (as shown in Figure 10):
The drive signal of the lower bridge is.
(1) When it is, the lower bridge MOSFET is turned off, and the right signal point is the diode voltage drop. At this time, the positive input terminal is, the negative input voltage is, and the output is low. The output is also low level, which is the open collector output mode. There is also a problem of conduction voltage drop. Therefore, the signal is subtracted from the signal to eliminate the detection error caused by the conduction voltage drop, thereby eliminating the input error.
(2) When it is, the lower bridge is in the on state, and the right end signal is. At this time, the positive input terminal is, the negative input terminal voltage is, the output is high impedance state, and the voltage is internal resistance. The voltage drop plus the voltage drop of the fast recovery diode, while the output is also high impedance, the voltage is the voltage drop of the diode. The voltage drop across the internal resistance is obtained by subtracting the signal from the subtraction circuit composed of the op amp.
The waveform analysis of the relevant points of the switch tube voltage drop and current detection circuit is shown in Figure 3. In the two-way conduction mode, in the electric or braking state, there is always one lower arm in the working state, so the sum of the conduction voltage drops of the three lower arms is equal to the average current of the motor winding.
The sum is the conduction time, which is the turn-off time, and is the tube voltage drop at the time of conduction, which is the conduction voltage drop. In the detection circuit, it functions as an overcurrent protection, and when the voltage is greater than, the output is low (overcurrent signal).
