High-frequency clamp carrier provides good support

   High-frequency clamp carrier provides good support
   High-frequency clamp carrier  signal and phase voltage of each phase bridge arm power device of the high frequency clamp carrier are increased from 2 to 3, the line voltage level is compared with the ordinary two-level PWM inverter. The number is increased from 3 to 5, the amplitude of each level is relatively reduced, and the DC bus voltage is changed to half of the entire DC bus voltage. Under the premise of the same switching frequency, the output waveform quality can be greatly improved. .
   Compared with the two-level inverter, High-frequency clamp carrier can reduce the required withstand voltage of the power device by half under the same output voltage condition, and each phase always turns on two adjacent switching devices. The other two devices are turned off, resulting in different combinations of switching states and corresponding output voltages, the driving signals of which are complementary.
   When the medium vector and the small vector are applied, there is a difference in phase or amplitude between the currents on the two capacitors, and the charging and discharging transient process is asymmetrical. In the high-frequency clamp carrier, the two capacitors on the DC side cannot be exactly the same, resulting in an inherent offset of the midpoint voltage; the smaller the value of the DC-side capacitor, the more severe the fluctuation, so the capacitor should be as large as possible, but subject to Cost and DC side high voltage.
     High-frequency clamp carrier of the high frequency clamp carrier, the more severe the fluctuation, and the midpoint current is a direct reflection of the stator current, so the larger the load torque, the more severe the fluctuation; High-frequency clamp carrier load power factor and the midpoint current The phase relationship is close, so it is also an important factor affecting the midpoint potential.
     High-frequency clamp carrier alternates between positive and negative small vectors in a series of switching cycles. This method is only used in the case of good load balance, and is a simple and popular closed-loop midpoint potential control strategy. Using this method requires knowing the direction of the current in each phase and selecting a small vector that tends to balance the midpoint potential.