Direct-current power distribution network principal component ripple self-adaptive compensation method

Abstract

The invention provides a direct-current power distribution network principal component ripple self-adaptive compensation method. The method comprises the steps of collecting a to-be-treated bus voltage of a direct-current power distribution network; filtering and extracting the to-be-treated bus voltage of the direct-current power distribution network to obtain a main component ripple frequency of a ripple voltage component; determining a voltage ripple amplification coefficient based on the principal component ripple frequency; and determining control signals of upper and lower bridge arm switch tubes of the converter based on the voltage ripple amplification coefficient. According to the method provided by the invention, the frequency of the principal component ripple is identified by using the short-time discrete Fourier transform, the speed is relatively high, the detection range is relatively large, the extracted principal component ripple frequency is used for modifying the resonant frequency and the ripple voltage peak-to-peak value of the quasi-proportional resonance controller, and the updating frequency is calculated; and the filtering effect of the active filter at the corresponding principal component frequency can be quickly adjusted and improved.

Description

Technical Field

[0001] The present application relates to the technical field of power systems, and in particular to a method for adaptively compensating a main component ripple of a direct current distribution network. Background Art

[0002] In recent years, with the widespread access of distributed renewable energy and the increase in DC load caused by changes in user electricity consumption, the advantages of DC distribution technology in terms of efficiency, economy, and reliability have gradually become prominent, and DC distribution networks have become an important trend in the development of new power systems. In DC distribution networks, there are many factors that can cause voltage ripples in the system, mainly including the randomness of distributed unit power generation, the injection of nonlinear loads, and the resonance of power electronic equipment.

[0003] At present, there are two control schemes for DC voltage ripple suppression: passive and active. Passive filtering uses parallel electrolytic capacitors or LC resonant filters. This scheme is only effective for ripples of specific frequencies, and the effect varies greatly with changes in system load, which is not suitable for the needs of DC distribution networks. Active filtering uses active filters to compensate for ripples, and through corresponding control schemes, it generates a compensation power that is equal to the grid ripple power and opposite in direction to eliminate the voltage ripple of the grid. However, this method requires knowing the frequency, amplitude and phase of the voltage at the grid, and can only filter out the ripple of a specific frequency component of the DC bus. Summary of the invention

[0004] In order to overcome the above technical defects, the present application provides a method for adaptively compensating the main component ripple of a DC distribution network. To achieve the above purpose, the present application is implemented according to the following technical solutions: The present application provides a method for adaptively compensating a main component ripple of a DC distribution network, comprising: Collect the bus voltage to be managed in the DC distribution network; The bus voltage of the DC distribution network to be managed is filtered and extracted to obtain the main component ripple frequency of the ripple voltage component; Determining a voltage ripple amplification factor based on the main component ripple frequency; Based on the voltage ripple amplification factor, determining control signals of the upper and lower bridge arm switches of the converter; Optionally, determining the control signals of the upper and lower bridge arm switches of the converter based on the voltage ripple amplification factor includes: Determining a first current reference value based on the voltage ripple amplification factor and the ripple voltage component; Collect the expected capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor; Determining a second current reference value based on the expected capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor; Based on the first current reference value and the second current reference value, control signals of the upper and lower bridge arm switches of the converter are determined.

[0005] Optionally, the filtering and extraction processing of the bus voltage to be managed in the DC distribution network to obtain the main component ripple frequency of the ripple voltage component comprises: The bus voltage to be managed in the DC distribution network is input into a bandpass filter for processing to obtain a ripple voltage component; The ripple voltage component is transformed and extracted by using a discrete Fourier transform to obtain the main component ripple frequency of the ripple voltage component.

[0006] Optionally, the determining of the voltage ripple amplification factor based on the main component ripple frequency includes: Determining a difference in ripple transformation amount based on the main component ripple frequency; Based on the difference in the ripple variation, a voltage ripple amplification factor is determined.

[0007] Optionally, determining the difference of the ripple transformation amount based on the main component ripple frequency includes: Determining a ripple voltage detection window time length based on the main component ripple frequency; Recording the peak value of the ripple voltage data at the current moment for each ripple voltage detection window time length; Get the peak value of the ripple voltage data at the previous historical moment; The difference in the ripple change amount is determined based on the peak value in the ripple voltage data at the current moment and the peak value in the ripple voltage data at the previous historical moment.

[0008] Optionally, determining the second current reference value based on the expected capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor includes: Determining a capacitor voltage deviation based on the expected capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor; The capacitor voltage deviation is input into a proportional-integral controller to obtain a second current reference value.

[0009] Optionally, determining the control signals of the upper and lower bridge arm switches of the converter based on the first current reference value and the second current reference value includes: Adding the first current reference value and the second current reference value to obtain a total reference current value; Get the inductor current measurement value; Subtracting the total reference current value from the inductor current measurement value to obtain a current deviation value; Based on the current deviation value, control signals of the upper and lower bridge arm switches of the converter are determined.

[0010] Optionally, determining the control signals of the upper and lower bridge arm switches of the converter based on the current deviation value includes: Inputting the current deviation value into a quasi-proportional resonant controller to obtain a duty cycle signal; Based on the duty cycle signal, control signals of the upper and lower bridge arm switches of the converter are determined.

[0011] This application has the following beneficial effects: This application uses short-time discrete Fourier transform to identify the main component ripple frequency, with a faster speed and a larger detection range. The extracted main component ripple frequency is used to modify the resonant frequency of the quasi-proportional resonant controller and the ripple voltage peak-to-peak value calculation update frequency, which can quickly adjust and improve the filtering effect of the active filter at the corresponding main component frequency. During operation, the ripple voltage is observed quickly to quickly update the ripple amplification parameters, and the amplified ripple voltage is output as part of the reference current value. The inductor current of the DC filter can be dynamically adjusted to a higher stable level to achieve a better filtering effect. After the parameter setting is completed, no other operations are required, and the automatic governance effect of the active filter can be achieved when the main component ripple appears or the main component ripple amplitude and frequency change.

[0012] In addition to the above-described purposes, features and advantages, the present application has other purposes, features and advantages. The present application will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings: Figure 1 Schematic diagram of the topological structure of the DC active filter device involved in the embodiment of the present application; Figure 2 It is a control block diagram of the main component ripple adaptive compensation system of the DC distribution network involved in the embodiment of the present application; Figure 3 It is a flow chart of a method for adaptively compensating the main component ripple of a DC distribution network provided in an embodiment of the present application; Figure 4 is a working flow chart of the ripple voltage amplification factor adaptive module involved in the embodiment of the present application; Figure 5 It is a bus voltage waveform diagram before and after the DC distribution network main component ripple adaptive compensation method provided in the embodiment of the present application is treated. DETAILED DESCRIPTION

[0014] The embodiments of the present application are described in detail below with reference to the accompanying drawings; however, the present application can be implemented in many different ways as defined and covered by the claims.

[0015] In order to facilitate the understanding of the method proposed in this application, the topology of the DC active filter device applied in this application is briefly introduced. This application adopts a half-bridge bidirectional buck / boost converter as an active filter. Figure 1 As shown, the topological structure of the DC active filter device used in the method of the present application includes: a DC bus side capacitor C dc , low voltage side energy storage capacitor C s , energy storage inductor L , low voltage side equivalent resistance r, converter upper bridge arm switch tube s1, converter lower bridge arm switch tube s2; DC bus side capacitor C dc The positive electrode of the converter and the source of the upper bridge arm switch tube s1 are both connected to the DC distribution network bus voltage u dc Positive pole; DC bus side capacitor C dc Negative electrode, low voltage side energy storage capacitor C s The negative electrode of the converter and the drain of the lower bridge arm switch tube s2 are both connected to the DC distribution network bus voltage u dc The negative electrode of the converter upper bridge arm switch tube s1 and the converter lower bridge arm switch tube s2 both contain reverse parallel diodes, and the node formed by connecting the drain of the converter upper bridge arm switch tube s1 and the source of the converter lower bridge arm switch tube s2 is A, and the energy storage inductor L One end of the energy storage inductor is connected to node A; L The other end is connected to one end of the low-voltage side equivalent resistor r, and the other end of the low-voltage side equivalent resistor r is connected to the low-voltage side energy storage capacitor C s The positive pole is connected.

[0016] The method proposed in this application adopts Figure 2 The system control block diagram shown in the figure is implemented, and the process is briefly described here: The collected bus voltage of the DC distribution network to be managed u dc , after passing through the BPF bandpass filter, the ripple voltage component is obtained, according to the sampling frequency F s, the ripple voltage component is input into the main component ripple calculation module, and the main component ripple frequency is obtained through discrete fast Fourier transform, and is used to modify the resonant frequency of the quasi-proportional resonant controller in real time, and then the main component ripple frequency is input into the amplification factor adaptive generation module, and the length of the amplification factor adaptive generation module detection window, the amplification factor generated by the amplification factor adaptive generation module, is multiplied with the ripple voltage component to obtain a first reference current value iref1, and the desired capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor are added to the second reference current value iref2 obtained by the proportional integral controller PI to obtain a total reference current value, and the total reference current value is subtracted from the inductor current to obtain a current deviation value, and the current deviation value is input into the quasi-proportional resonant controller PR to generate switch tube control signals s1 and s2 with PWM.

[0017] The method proposed in this application is described in detail below: like Figure 3 As shown, the present application proposes a method for adaptively compensating the main component ripple of a DC distribution network, comprising: Step S301: collecting the bus voltage to be managed in the DC distribution network; Collect the bus voltage to be managed in the DC distribution network u dc , collect bus voltage u dc , the ripple characteristics, such as frequency, amplitude, etc., can be analyzed to provide a basis for selecting appropriate ripple suppression strategies.

[0018] Step S302: filtering and extracting the bus voltage of the DC distribution network to be managed, to obtain the main component ripple frequency of the ripple voltage component; The bus voltage to be managed in the DC distribution network is input into the band-pass filter (BPF) for processing to obtain the ripple voltage component. The bus voltage of the DC distribution network contains DC components and AC components such as ripples. The bandpass filter has the characteristic of allowing signals within a specific frequency range to pass through, while blocking signals of other frequencies from passing through. By properly setting the passband range of the bandpass filter, the ripple voltage component in the bus voltage can be , separated from other components, making it easier to analyze and process the ripple separately later.

[0019] Clearly define the ripple voltage component It is the premise for ripple suppression and other treatment work. Only by extracting the ripple from the bus voltage first can we take appropriate measures to suppress or compensate it according to its characteristics, so as to effectively improve the voltage quality of the DC distribution network.

[0020] In order to obtain the ripple voltage component Finally, the ripple voltage component is transformed and extracted by discrete Fourier transform to obtain the main component ripple frequency of the ripple voltage component. f 0, the process is described in detail below: First, the discrete sampling frequency of the ripple voltage component is set to F s , the main component ripple frequency detection window time length is set to t 1, the construction length is n 1=t1 / F s Array X 1. The ripple voltage component data , At sampling frequency F s After acquisition, the array data is shifted forward by one unit, and the current voltage data array is input X 1 end unit. X 1 Perform discrete fast Fourier transform: (1) Find the array Y The frequency position corresponding to the maximum value k max , the main component ripple frequency is .

[0021] Step S303: determining a voltage ripple amplification factor based on the main component ripple frequency; In determining the main component ripple frequency f After 0, such as Figure 2 and Figure 4 As shown, it is input into the amplification factor adaptive module to determine the voltage ripple amplification factor K ( n ), which explains the process in detail: First, according to the main component ripple frequency f 0, the difference in ripple change can be determined e ( n ), the specific process is as follows: According to the main component ripple frequency, the time length of the ripple voltage detection window is designed to be , which can contain half a cycle of waveform data, and the construction length is n 2= t 2. F s Array X 2. The ripple voltage data , after sampling at sampling frequency Fs, the array X 2 data is shifted forward by one unit, and the current ripple voltage data is inputX 2 end units.

[0022] Then, every time the ripple voltage detection window is used, the peak value of the ripple voltage data at the current moment is recorded, and then the difference in the ripple change amount is determined based on the peak value of the ripple voltage data at the current moment and the peak value of the ripple voltage data at the previous historical moment. It can also be understood as: every t 2 Moment, record the current X The peak-to-peak value of the data in 2 is and the previous moment X The peak-to-peak value of the data recorded in 2 Make a difference and get the difference of ripple transformation .

[0023] It should be noted that when the main component ripple frequency changes, it is necessary to X After the data in 2 is cleared, correct X Array length of 2.

[0024] Secondly, after obtaining the difference in ripple transformation e ( n ) can determine the voltage ripple amplification factor K ( n ), the process is described in detail below: After the active converter is started, K ( n ) value is initially set to 0 and is collected after the first collection is completed. back, K ( n ) value increases to 0.1, and then every t 2. At this moment, according to the current e (n) Whether the absolute value is greater than the set threshold E , to determine the next moment K ( n ) value changes. , then the magnification factor at the next moment is K ( n )constant, K ( n +1)= K ( n ), otherwise judge e (n) is positive or negative, if e (n) is a positive value, indicating that the voltage is disturbed or amplified by the factor K ( n ) changes, and within the corresponding ripple period, the peak value increases, K ( n ) changes in the opposite direction, that is, the directional coefficient d =- d ,d is 1 or -1; if e (n) is a negative value, then K ( n ) The direction of change does not change. The magnification at the next moment becomes: (2) in, is the step size of the K value change this time, and is the arithmetic square root of the absolute value of the ripple transformation difference.

[0025] Step S304: based on the voltage ripple amplification factor, determining control signals of the upper and lower bridge arm switches of the converter.

[0026] like Figure 2 As shown, after passing through the magnification adaptive module, the corresponding voltage ripple magnification factor is obtained K ( n ), the control signals of the upper and lower bridge arm switches of the converter can be determined. The specific process is as follows: Step S401: determining a first reference current value based on the voltage ripple amplification factor and the ripple voltage component; After the voltage ripple amplification factor is obtained, it is multiplied by the ripple voltage component to obtain the first current reference value. i ref1 . i ref1 It can be used as an important basis for system adjustment. According to the actual operation of the system, when the ripple voltage changes, the ripple voltage component and the voltage ripple amplification factor will change accordingly, so that i ref1 The system can also change according to this change. i ref1 To adjust the operating parameters of each part, such as adjusting the output power of distributed power sources or the access status of loads, so as to maintain the stable operation of the entire DC distribution network and ensure the power supply quality.

[0027] Step S402: collecting the expected capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor; like Figure 2 As shown, the expected capacitance reference voltage is collected u sref , and the voltage across the low-voltage side energy storage capacitor u s .

[0028] Step S403: determining a second current reference value based on the expected capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor; Collect the expected capacitance reference voltage u sref, and the voltage across the low-voltage side energy storage capacitor u s After that, the desired capacitor reference voltage u sref , and the voltage across the low-voltage side energy storage capacitor u s The capacitor voltage deviation is obtained by subtracting the capacitor voltage deviation, and then the capacitor voltage deviation is input into Figure 2 In the PI proportional integral controller shown in FIG. 1 , the second current reference value is obtained. i ref2 .

[0029] Step S404: Determine control signals of upper and lower bridge arm switches of the converter based on the first current reference value and the second current reference value.

[0030] After determining and calculating the first current reference value and the second current reference value, the first current reference value and the second current reference value are added to obtain a total reference current value, and the total reference current value is added to the inductor L current measurement value. i L By making a difference, a circuit deviation value is obtained, and the control signals of the upper and lower bridge arm switches of the converter are determined according to the current deviation value; After determining the current deviation value, Figure 2 As shown, it is input into the quasi-proportional resonant controller PR to obtain a duty cycle signal, and the obtained duty cycle signal is used through a pulse width modulation algorithm to obtain control signals of the two switch tubes S1 and S2 of the upper and lower bridge arms of the converter.

[0031] In step S404, before the current deviation value is sent to the quasi-proportional resonant converter, the difference value needs to be processed using a Z transform. It should be noted that the z-domain transfer function of the quasi-proportional resonant controller is specifically: (3) In the above formula, ω 0 is the resonant frequency of the quasi-proportional resonant amplifier, and its value is the main component ripple frequency f 2π times 0, that is ω 0=2π f 0; k p , k r , ω c are the proportional coefficient, resonant gain coefficient and cut-off frequency of the quasi-proportional resonant controller respectively, and z is the result of Z-transformation of the difference signal.

[0032] In this embodiment, since the quasi-proportional resonant controller has a large gain at the resonant frequency, it can achieve zero-static tracking of the AC signal, thereby achieving excellent current tracking control to obtain a duty cycle signal.

[0033] It should be noted that when the above steps are continuously executed, when it is detected that the main component frequency of the DC power distribution network ripple changes, the main component frequency is updated. f 0, modify the resonant frequency parameters of the quasi-proportional resonant controller.

[0034] Experimental verification Taking a 500V DC distribution network as an example, the method provided in this application is used to control the main component of the distribution network ripple. At 0.5s, a 60Hz ripple current is injected into the grid. At 1.1s, the circuit active filter system starts working. At 4s, the current frequency is changed to 100Hz, and the injected ripple current amplitude is increased. At 9s, the active filter system stops working. The bus voltage waveform before and after the control of the main component ripple frequency of the DC distribution network provided by this application is as follows: Figure 5 As shown, it can be seen that after the method provided in the present application starts working and the main frequency and amplitude change, the K value can be adaptively adjusted quickly to reduce the main component ripple frequency level of the DC distribution network, and the main component ripple frequency amplitude reduction effect reaches more than 90%.

[0035] In summary, the present application utilizes short-time discrete Fourier transform to identify the main component ripple frequency, has a faster speed and a larger detection range, and uses the extracted main component ripple frequency to modify the resonant frequency of the quasi-proportional resonant controller and the ripple voltage peak-to-peak value calculation update frequency, which can quickly adjust and improve the filtering effect of the active filter at the corresponding main component frequency. During operation, the ripple voltage is observed quickly to quickly update the ripple amplification parameters, and the amplified ripple voltage is output as part of the reference current value, which can dynamically adjust the inductance current of the DC filter to a higher stability level to achieve a better filtering effect. After the parameter setting is completed, no other operations are required, and the automatic governance effect of the active filter can be achieved when the main component ripple appears or the main component ripple amplitude and frequency change.

[0036] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for adaptively compensating the main component ripple of a DC distribution network, characterized in that: include: Collect the bus voltage to be managed in the DC distribution network; The bus voltage of the DC distribution network to be managed is filtered and extracted to obtain the main component ripple frequency of the ripple voltage component; Determining a voltage ripple amplification factor based on the main component ripple frequency; Based on the voltage ripple amplification factor, determining control signals of the upper and lower bridge arm switches of the converter; Wherein, determining the control signals of the upper and lower bridge arm switches of the converter based on the voltage ripple amplification factor includes: Determining a first current reference value based on the voltage ripple amplification factor and the ripple voltage component; Collect the expected capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor; Determining a second current reference value based on the expected capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor; Based on the first current reference value and the second current reference value, control signals of the upper and lower bridge arm switches of the converter are determined.

2. The method according to claim 1, characterized in that: The method of filtering and extracting the bus voltage of the DC distribution network to be managed to obtain the main component ripple frequency of the ripple voltage component comprises: The bus voltage to be managed in the DC distribution network is input into a bandpass filter for processing to obtain a ripple voltage component; The ripple voltage component is transformed and extracted by using a discrete Fourier transform to obtain the main component ripple frequency of the ripple voltage component.

3. The method according to claim 2, characterized in that The step of determining a voltage ripple amplification factor based on the main component ripple frequency comprises: Determining a difference in ripple transformation amount based on the main component ripple frequency; Based on the difference in the ripple variation, a voltage ripple amplification factor is determined.

4. The method according to claim 3, characterized in that The determining the difference of the ripple transformation amount based on the main component ripple frequency includes: Determining a ripple voltage detection window time length based on the main component ripple frequency; Recording the peak value of the ripple voltage data at the current moment for each ripple voltage detection window time length; Get the peak value of the ripple voltage data at the previous historical moment; The difference in the ripple change amount is determined based on the peak value in the ripple voltage data at the current moment and the peak value in the ripple voltage data at the previous historical moment.

5. The method according to claim 1, characterized in that The determining of the second current reference value based on the expected capacitor reference voltage and the voltage across the low-voltage side energy storage includes: Determining a capacitor voltage deviation based on the expected capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor; The capacitor voltage deviation is input into a proportional-integral controller to obtain a second current reference value.

6. The method according to claim 5, characterized in that: The step of determining control signals of upper and lower bridge arm switches of the converter based on the first current reference value and the second current reference value includes: Adding the first current reference value and the second current reference value to obtain a total reference current value; Get the inductor current measurement value; Subtracting the total reference current value from the inductor current measurement value to obtain a current deviation value; Based on the current deviation value, control signals of the upper and lower bridge arm switches of the converter are determined.

7. The method according to claim 6, characterized in that The step of determining control signals of upper and lower bridge arm switches of the converter based on the current deviation value includes: Inputting the current deviation value into a quasi-proportional resonant controller to obtain a duty cycle signal; Based on the duty cycle signal, control signals of the upper and lower bridge arm switches of the converter are determined.

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