Taking MOS tube inverter bridge as an example to analyze the interference source characteristics of the driver

0. Introduction

With the industrial control industry's pursuit of energy efficiency and control accuracy, and based on the application of wide bandgap semiconductor devices, the switching speed and control frequency of motor controllers (drivers) are getting higher and higher, making EMI a difficult problem in the industry. This article takes the MOS tube inverter bridge as an example to analyze the interference source characteristics of the driver, hoping to bring help and thinking to everyone!

1. Relationship between inverter bridge waveform and common mode current

• The schematic diagram of the inverter bridge DC-AC is as follows:

• The common mode current is the largest when the open tube state is 000 or 111, and is generated by the superimposed dV/dt of the three tubes;

Upper bridge falling edge waveform example (vector 000/vector 111)

• When the open tube is in other states, the common mode current is generated by the superposition of dV/dt of the two tubes;

Upper bridge falling edge waveform example (vector 001 to vector 110)

2. Relationship between load and edge time

• The heavier the load (the higher the output current), the steeper the edge time;

3. Relationship between load current and common mode current

• The larger the load current, the common mode current Icm-min basically shows a trend of increasing with the increase of current;

• The larger the load current, the common mode current Icm-max basically shows a flat trend;

• When the load current is 0, Icm-min is the minimum and Icm-max is the maximum;

4. Common mode voltage

• The open tube is in 000 or 111 state;

Common mode voltage waveform in vector 000/vector 111 state

• Open pipe for other states

Common mode voltage waveform in vector 001~vector 110 state

5. Noise source spectrum distribution

• The common mode voltage spectrum distribution when the open tube is vector 001~vector 110;

The common mode voltage spectrum distribution in the open tube state vector 000/vector 111 state:

6. Thoughts and inspirations

• The three-phase bridge arm voltage is not zero, which is the essential reason for the common mode interference of the driver;

• The driver's high-frequency EMI suppression is called dv/dt suppression;

• Understanding the characteristics of interference sources can help you better design suppression;