High-dynamic-response pulse width modulation method at low switching frequency

Abstract

The invention discloses a high-dynamic-response pulse width modulation method at a low switching frequency. The method comprises the steps that (1) in the offline state, an optimization algorithm is adopted for calculation with the modulation ratio as a variable for the purpose of eliminating specific secondary current harmonics, so that switching angles corresponding to all frequency division numbers are calculated; (2) judgment and rejection principles are put forward for the calculated switching angles, wherein if the shape of an obtained stator flux link is a regular hexagon or a regular octadecagon or a regular shape with 30 edges, namely the difference of the numbers of the edges is 12, the switching angles are adopted, and the switching angles are abandoned otherwise; (3) the switching angles corresponding to the modulation ratio are sequentially stored at fixed positions in hardware, or curve fitting is conducted on the switching angles, so that the corresponding relation between the modulation ratio and the switching angles is obtained; (4) in the actual operation process of a system, table look-up or calculation is conducted according to the modulation ratio and the frequency division numbers, so that all the switching angles are obtained. The high-dynamic-response pulse width modulation method at the low switching frequency has the advantages that the specific subharmonics can be effectively eliminated, so that system noise and torque pulsation are lowered, and the dynamic responsiveness of the system can be greatly improved at the same time.

Description

technical field [0001] The invention mainly relates to the field of AC drive systems, in particular to a pulse width modulation method with high dynamic response at low switching frequency suitable for AC drive systems. Background technique [0002] The AC drive system refers to a new type of drive system that takes the AC motor as the control object and adjusts the output torque and speed of the motor. Compared with the DC drive system, the AC drive system has good traction performance, high power factor, small size, light weight and reliable operation. The AC drive system is gradually replacing the DC drive system and is widely used in various fields of industrial production, national life and national defense. [0003] The AC transmission system is generally composed of a control system, a main circuit and a control object, among which the main circuit includes a DC bus, a DC support capacitor, and a converter composed of power switching semiconductor devices; the contro...

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Problems solved by technology

[0024] (1) As the modulation ratio continues to increase, the reference voltage vector will be located in the over-modulation area, which requires special processing to achieve the purpose of modulation, which increases the complexity of program processing to a certain extent, and is difficult to control in the over-modulation area. Guarantee the control performance of the system

[0025] (2) Some specific harmonics that have an important impact on some performance of the system (such as noise, torque fluctuation) cannot be eliminated, and it is difficult to achieve special control requirements

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