Active rectification resonance detection and suppression method and system under weak power grid system

Abstract

The invention discloses an active rectification resonance detection and suppression method and system under a weak power grid system, and belongs to the technical field of electronic power systems. The method comprises the following steps: collecting a direct current bus voltage and a three-phase output current of active rectification, and carrying out resonance detection calculation; when the difference value of the filtered direct-current voltage continuously exceeds a first threshold value for a set duration time and the change rate of the amplitude of the output current exceeds a second threshold value, judging that resonance occurs, and setting a resonance mark; inputting a resonance controller, generating a compensation voltage by the resonance controller based on the harmonic component of the power grid voltage, and limiting the amplitude of the output current; and when the input time of the resonance controller reaches the set time, the direct-current voltage difference value is lower than a first threshold value, and the output current amplitude change rate is lower than a second threshold value, the resonance controller is quitted. The problems of low resonance suppression efficiency and poor adaptability in the prior art can be solved. Resonance can be quickly and accurately detected by monitoring the change of the direct-current voltage and the output current in real time.

Description

Technical Field

[0001] This invention relates to the field of electronic power system technology, and more specifically to a method and system for detecting and suppressing active rectifier resonance in a weak power grid system. Background Technology

[0002] In industrial power supply systems, distributed generation grid connection, and microgrids, active rectifiers are widely used in motor drives, energy storage systems, and other fields due to their advantages such as adjustable power factor and low input current harmonic content. In practical engineering, to meet the power supply needs of multiple loads, a topology of a single distribution transformer connected in parallel with multiple active rectifiers is often adopted. The capacity of the transformer is smaller than the total capacity of the multiple active rectifiers. The small-capacity transformer has a relatively large winding inductance, and its equivalent impedance is significantly higher than that of the large-capacity transformer, resulting in a significant reduction in grid strength when it is under load, forming a typical weak grid operating environment. The power supply line between the transformer and the active rectifier is too long. Long-distance power supply lines introduce non-negligible distributed inductance and parasitic resistance. These parameters will superimpose with the original system impedance, significantly changing the equivalent parameters of the resonant circuit. The active rectifier is equipped with an LCL filter at the front end. In a weak grid environment, the grid impedance formed by the equivalent impedance of the transformer and the impedance of the long line will couple with the LCL filter.

[0003] Under the combined effects of a single transformer connected in parallel with multiple active rectifiers, small transformer capacity, long power supply lines, and LCL filter configuration, the system resonance mechanism exhibits characteristics of "multi-factor coupling and high suppression difficulty." While traditional passive damping methods can suppress resonance, they reduce system efficiency due to resistive energy consumption; active damping methods are susceptible to grid impedance fluctuations and struggle to guarantee stable damping characteristics under weak grid conditions. Therefore, a highly efficient and adaptive resonance suppression method is urgently needed. Summary of the Invention

[0004] In view of the above problems, the present invention is proposed to provide a method for detecting and suppressing active rectifier resonance in a weak power grid system that overcomes or at least partially solves the above problems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, embodiments of the present invention provide a method for detecting and suppressing active rectifier resonance in a weak power grid system, comprising the following steps: Step S1: Collect the DC bus voltage and three-phase output current of the active rectifier, and perform resonance detection calculation based on the difference between the DC bus voltage and the set DC voltage, and the rate of change of the output current amplitude. Step S2: When the filtered DC voltage difference continues to exceed the first threshold for a set duration, and the rate of change of the output current amplitude exceeds the second threshold, resonance is determined to have occurred, and the resonance flag is set. Step S3: When the resonance flag is set, the resonance controller is activated. The resonance controller generates a compensation voltage based on the harmonic components of the grid voltage and limits the output current. Step S4: When the resonant controller is engaged for a set time, and the DC voltage difference is lower than the first threshold and the output current amplitude change rate is lower than the second threshold, the resonant controller is deactivated.

[0006] Furthermore, in step S1, the DC voltage difference is processed by a first-order low-pass filter.

[0007] Furthermore, the cutoff frequency of the first-order low-pass filter is set to 40Hz.

[0008] Furthermore, in step S2, the set duration is adjustable from 0.2 seconds to 5 seconds.

[0009] Furthermore, in step S2, the second threshold is set based on the percentage of the rated current of the active rectifier.

[0010] Further, in step S3, the resonant controller generates a compensation voltage through the following steps: A second-order bandpass filter is applied to the DQ-axis component of the grid voltage to obtain the filtered voltage. The harmonic voltage component is obtained by subtracting the original DQ axis voltage component from the filtered voltage. The compensation voltage is obtained by multiplying the harmonic voltage component by the resonance coefficient.

[0011] Furthermore, the resonance coefficient gradually increases from 0 to a set value when the resonance flag is set.

[0012] Furthermore, in step S3, the resonant controller also outputs a given current limit value for the D-axis, limiting the output current to within 100% of the rated current.

[0013] Furthermore, in step S4, the set time is adjustable from 0.1 seconds to 5 seconds.

[0014] In a second aspect, embodiments of the present invention provide an active rectification control system, including a resonance detection module and a resonance control module, for performing the method as described in any one of the embodiments of the first aspect.

[0015] As can be seen from the above technical solution, compared with the prior art, the present invention has the following technical advantages: 1) By monitoring changes in DC voltage and output current in real time, the resonance can be detected quickly and accurately; 2) The active damping method based on voltage harmonic compensation is adopted, which does not require additional hardware and does not affect the system efficiency; 3) The resonant controller is only activated when resonance occurs and automatically deactivated when the system is normal, thus balancing suppression effect and operating efficiency; 4) It is suitable for complex working conditions such as weak power grids, multiple machines in parallel, and long lines, and has strong engineering applicability. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] Figure 1 This is a flowchart of the active rectifier resonance detection and suppression method provided in the embodiments of the present invention for a weak power grid system; Figure 2 This is a waveform diagram of resonance occurring as provided in an embodiment of the present invention; Figure 3 This is a control principle diagram provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the resonant controller provided in an embodiment of the present invention; Figure 5 The waveform diagram of the resonance detection input resonance controller provided in the embodiment of the present invention is shown. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention discloses a method for detecting and suppressing active rectifier resonance in a weak power grid system, referring to... Figure 1 As shown, it includes the following steps: Step S1: Collect the DC bus voltage and three-phase output current of the active rectifier, and perform resonance detection calculation based on the difference between the DC bus voltage and the set DC voltage, and the rate of change of the output current amplitude. Step S2: When the filtered DC voltage difference continues to exceed the first threshold for a set duration, and the rate of change of the output current amplitude exceeds the second threshold, resonance is determined to have occurred, and the resonance flag is set. Step S3: When the resonance flag is set, the resonance controller is activated. The resonance controller generates a compensation voltage based on the harmonic components of the grid voltage and limits the output current. Step S4: When the resonant controller is engaged for a set time, and the DC voltage difference is lower than the first threshold and the output current amplitude change rate is lower than the second threshold, the resonant controller is deactivated.

[0020] In weak power grid conditions, the number of active rectifiers operating under the same transformer increases. Due to the influence of LCL parameters, changes in other loads at the common point of contact of long power lines can easily trigger active rectifier resonance, leading to the failure of all active rectifier devices. Even with active damping algorithms based on the voltage and current across the filter capacitor in the active rectifier control, resonance can still occur when other loads change at the common point, such as... Figure 2 As shown, the DC voltage and current of the active rectifier oscillate, causing the active rectifier to report a fault.

[0021] This invention detects resonance in advance by detecting changes in the DC voltage and output current of the active rectifier exceeding a threshold. For example, when the resonance flag is set to 1, the resonance controller is activated to adjust the given voltage. When the changes in the DC voltage and output current are detected to be within the threshold, the resonance flag is set to 0, and the resonance controller is deactivated.

[0022] like Figure 3 The control schematic diagram shown includes a DC voltage loop (inputs are the DC voltage setpoint VDC_SET and the actual DC bus voltage VDC), a D-axis current loop (inputs are the D-axis current setpoint ID_SET and the actual D-axis current ID), a Q-axis current loop (inputs are the Q-axis current setpoint IQ_SET and the actual Q-axis current IQ), coordinate transformation, and an SVPWM module (inputs are...). shaft and The given voltages Valpha_set and Vbeta_set of the shaft together form the basic control algorithm for active rectification. This invention adds a resonance detection algorithm and a resonance control algorithm to the basic control algorithm for active rectification resonance detection and suppression in weak power grid systems. The steps include: Step one: First, sample the DC bus voltage VDC and three-phase output currents (Ia, Ib, Ic) of the active rectifier based on hardware analog signals, and then perform resonance detection calculations. The principle of resonance detection is: subtract the set DC voltage VDC_SET from the sampled actual DC bus voltage VDC, and then perform a first-order low-pass filter on the voltage difference to obtain the filtered difference. Sample the three-phase output currents (Ia, Ib, Ic), and calculate the output current amplitude I and the rate of change of the output current amplitude. .

[0023] Step two, resonance detection and judgment. The difference in the filtered DC voltage is greater than the set threshold. Duration Exceeding the set time And the rate of change of current amplitude Exceeding the threshold Set the resonance flag to 1.

[0024] Step 3: Activate the resonant controller. For example... Figure 4 The principle of the resonant controller shown is as follows: It detects the three-phase grid voltage, performs a second-order bandpass filter on the DQ-axis components of the grid voltage, and obtains the filtered voltage. Subtract the filtered voltage from the original DQ axis voltage component. The harmonic voltage components are obtained, and the harmonic voltage components multiplied by the resonance coefficient K are the output of the resonant controller. At the same time, the resonant controller also outputs a given current limit value ID_LIMIT to limit the current.

[0025] Step 4: Once the resonant controller has been engaged for the set time, and the filtered DC voltage difference is less than the set threshold, and the current amplitude change rate is less than the threshold, then the resonant controller is deactivated.

[0026] In this embodiment, resonance detection is based on the values ​​from steps one and two. The specific calculation formula for resonance detection is as follows:

[0027] in, This is the actual DC voltage value. DC voltage setting value, This is a first-order low-pass filter function, where the angular frequency Wc = 2πfc, and fc is the filter frequency, which can be set to 40Hz. The threshold for determining duration can be modified through parameter settings. The value is settable (0.2~5s). The rate of change of the current amplitude within the sampling period Ts. This represents the change in current within one sampling period. The threshold for determining the rate of change of current is also specified. This is a settable value, set as a percentage of the rated current. The resonance detection flag is set to 1 when both conditions in the above formula are met.

[0028] In this embodiment, the resonance controller participates in control after the resonance detection flag is set to 1. The inputs of the resonance controller are the D and Q axis voltage components. ,Will After passing through a second-order bandpass filter The filtered voltage is obtained. The compensation voltage is obtained by subtracting the filtered voltage from the voltage before filtering and then multiplying it by the resonance coefficient K. The specific calculation formula for the resonant controller is as follows:

[0029]

[0030] The output voltages of the active rectifier current loop, VD_SET and VQ_SET, minus the compensation voltage. To suppress resonance, the resonance detection flag is set to 1, and the resonance coefficient K is increased from 0 to 100%; at the same time, the D-axis output current limit value ID_LIMIT is reduced from more than 150% to 100%, limiting the output current. Figure 5 The waveform used by the resonance controller to detect resonance is the waveform that triggers the resonance controller.

[0031] In this embodiment, after the resonant controller is put into control, it starts timing. After the time reaches the set value (0.1~5s), it detects that the difference of the filtered DC voltage is less than the set threshold and the rate of change of the current amplitude is less than the threshold. The resonance detection flag is set to 0 and the resonant controller exits control.

[0032] Based on the same inventive concept, this invention also provides an active rectification control system, including a resonance detection module and a resonance control module, for executing an active rectification resonance detection and suppression method for a weak power grid system as described in any of the above embodiments.

[0033] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0034] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for active rectification resonance detection and suppression under a weak grid system, characterized in that, The method comprises the following steps: Step S1: Collecting the DC bus voltage and three-phase output current of the active rectifier, and performing resonance detection calculation based on the difference between the DC bus voltage and the set DC voltage, and the output current amplitude change rate; Step S2: When the filtered DC voltage difference continuously exceeds the first threshold for a set duration, and the output current amplitude change rate exceeds the second threshold, it is determined that resonance occurs, and a resonance flag is set; Step S3: When the resonance flag is set, the resonance controller is turned on, and the resonance controller generates a compensation voltage based on the harmonic component of the grid voltage and limits the output current; Step S4: When the resonance controller is turned on for a set time, and the DC voltage difference is lower than the first threshold, and the output current amplitude change rate is lower than the second threshold, the resonance controller is turned off.

2. The method of claim 1, wherein, In step S1, the DC voltage difference is processed by a first-order low-pass filter.

3. The method of claim 2, wherein, The cutoff frequency of the first-order low-pass filter is set to 40 Hz.

4. The method of claim 1, wherein, In step S2, the set duration is adjustable between 0.2 seconds and 5 seconds.

5. The method of claim 1, wherein, In step S2, the second threshold is set based on the rated current percentage of the active rectifier.

6. The method of claim 1, wherein, In step S3, the resonance controller generates a compensation voltage by the following steps: Second-order band-pass filtering the DQ axis component of the grid voltage to obtain a filtered voltage; Subtracting the original DQ axis voltage component from the filtered voltage to obtain a harmonic voltage component; Multiplying the harmonic voltage component by a resonance coefficient to obtain a compensation voltage.

7. The method of claim 6, wherein, The resonance coefficient gradually increases from 0 to a set value when the resonance flag is set.

8. The method of claim 1, wherein, In step S3, the resonance controller also outputs a D-axis given current limiting value to limit the output current within 100% of the rated current.

9. The method of claim 1, wherein, In step S4, the set time is adjustable between 0.1 seconds and 5 seconds.

10. An active rectification control system characterized by, The method comprises a resonance detection module and a resonance control module for executing the method as claimed in any one of claims 1 to 9.

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