Construction method for complex proportional-integral current controller in discrete domain

Abstract

The invention discloses a construction method for a complex proportional-integral current controller in a discrete domain. The method comprises the following steps of: directly considering the one-step delay of digital control, and establishing the discrete model of a controlled object in a fundamental positive-sequence rotating coordinate system; constructing the zero points of the controller toachieve the mutual cancellation with the poles of the controlled object so as to eliminate the influence of coupling items; constructing the denominators of the controller, namely the poles of the controller according to the order of the zero points of the controller so as to realize the controller and have the floating adjustment capability on the fundamental positive-sequence component at the same time; adding a delay compensation term to eliminate the influence of the one-step delay of digital control; and obtaining the transfer function of the controller in the discrete domain and converting into a differential equation to realize. According to the construction method for a complex proportional-integral current controller in a discrete domain, the transfer function in the discrete domain is directly obtained, so that the discretization is avoided; and the one-step delay of digital control is directly considered in the controller construction, so that no additional delay compensation is needed, and the performance of a current loop does not reduce due to the reduction in carrier ratio.

Description

technical field [0001] The invention relates to the technical field of power electronics, in particular to a method for constructing a discrete domain complex coefficient vector proportional-integral current controller. Background technique [0002] Grid-connected converters are widely used in power systems, typically including renewable energy (photovoltaic, wind power, etc.) grid-connected power generation, power quality control, energy storage converters, PWM rectification, etc. As far as the grid is concerned, it is an equivalent controllable current source. The focus of the converter is the current quality it can provide for the grid, and currently the voltage source converter (Voltage Source Converter, VSC) dominates . [0003] Since the fundamental positive-sequence AC signal behaves as a DC quantity in the positive-sequence synchronous rotating frame (PS-SRF), intuitively, the infinite gain provided by the proportional-integral (PI) controller to the DC component ca...

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Problems solved by technology

However, it is very cumbersome and difficult to find the most suitable one or several methods from many discretization methods, and no matter what discretization method is used, with the sampling frequency f s , the performance of the controller will inevitably show a downward trend after discretization; on the other hand, even if the sampling frequency remains unchanged, with the control frequency f e The increase of the carrier ratio f s / f e The smaller the value, the performance of the controller after discretization will be further deteriorated. Typically, the damping rate of the system will decrease, the oscillation of the transient response will increase, and the system may even become unstable.

[0005] So far, most of the current loop control of grid-connected converters is carried out in the continuous domain, and all of them need to be discretized for digital realization, and different discretization methods will lead to differences between digital realizations, digital domains and continuous domains. There are performance differences between them, and eventually lead to controller performance degradation or even failure

This situation is particularly prominent for high-power converters. Considering that high-power converters are generally limited to about 3kHz to 4kHz in order to meet the requirements of temperature rise and heat dissipation, the decrease in sampling frequency will further deteriorate the performance of the controller.

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