Three-level inverter optimization modulation method based on VSVPWM

Abstract

The invention discloses an optimization modulation method suitable for a three-level inverter. The method comprises the following steps of 1, redefining a virtual middle vector in a voltage space vector, 2, dividing a vector region, 3, calculating the action time of the synthesized three vectors, 4, calculating the quantity of electric charges flowing out of the midpoint under the action of the virtual middle vector when k and k1 are different in value, 5, determining values of k and k1 according to the maximum and minimum values of the quantity of charges flowing out of the midpoint generated by the virtual middle vector, 6, determining a basic vector sequence and an action sequence according to the values of k and k1, and 7, carrying out balance control on the midpoint potential. High-precision and high-speed control of midpoint balance can be realized based on virtual space vector modulation and by taking compensation of the maximum charge quantity in a unit switching period as a principle.

Description

technical field [0001] The invention relates to the technical field of power electronics, in particular to a VSVPWM-based three-level inverter optimization modulation method. Background technique [0002] With the continuous deepening of inverter technology research, the modulation technology of three-level inverter has also been developed rapidly. As an important control component of three-level inverter, PWM modulation technology directly affects the quality of its modulation technology. performance of the inverter. Compared with the traditional two-level inverter, the NPC three-level inverter has the advantages of small output voltage harmonic component, low device stress, and strong pressure bearing capacity, so it is widely used in the field of medium-high voltage and high-power inverters. However, for NPC three-level inverters, there is always a problem of midpoint potential imbalance. The imbalance of the midpoint potential will not only lead to uneven pressure on t...

AI Technical Summary

Problems solved by technology

However, for NPC three-level inverters, there is always the problem of midpoint potential imbalance

The unbalanced midpoint potential will not only lead to uneven pressure on the upper and lower capacitors and switch tubes on the DC side, but also increase the harmonic content of the output current and reduce the life of the switch devices.

[0003] In the case of high modulation degree and low power factor, the traditional SVPWM modulation strategy has weak midpoint adjustment ability, and there is an area that cannot be completely balanced

Especially when the angle of the reference voltage is similar to that of the mid-vector, the resultant vector is almost entirely occupied by the mid-vector. At this time, the effect of using a small vector to balance the mid-point is not ideal, which will cause low-frequency oscillation of the mid-point potential in practice.

Although the traditional VSVPWM modulation strategy can realize the midpoint balance in the whole range, in some specific areas, because the small vector does not participate in the synthesis, it is impossible to use the small vector balance factor to control the midpoint, so that the dynamic speed of the midpoint balance slower

Images