An adaptive compensation method for main component ripple of DC distribution network

Abstract

The present application provides a method for adaptively compensating the main component ripple of a DC distribution network, including: collecting the bus voltage to be managed in the DC distribution network; filtering and extracting the bus voltage to be managed in the DC distribution network to obtain the main component ripple frequency of the ripple voltage component; determining the voltage ripple amplification factor based on the main component ripple frequency; determining the control signal of the upper and lower bridge arm switches of the converter based on the voltage ripple amplification factor. The method proposed in the present application uses short-time discrete Fourier transform to identify the frequency of the main component ripple, has a faster speed and a larger detection range, uses the extracted main component ripple frequency to modify the resonant frequency and the peak-to-peak value of the ripple voltage of the quasi-proportional resonant controller, calculates the update frequency, and can quickly adjust and improve the filtering effect of the active filter at the corresponding main component frequency.

Description

Technical Field

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

[0002] In recent years, with the wide access of distributed new energy and the increase in DC loads caused by the change of user power consumption forms, the advantages of DC power distribution technology in terms of efficiency, economy, reliability, etc. have gradually emerged, 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 power generation of distributed units, the injection of nonlinear loads, and the resonance of power electronic devices.

[0003] At present, the ripple suppression of DC voltage is divided into two control schemes: passive and active. Passive filtering is achieved by shunting electrolytic capacitors or LC resonance filters. This scheme is only effective for specific frequency ripples, and the effect will vary greatly with the change of system load, which does not meet the requirements of DC distribution networks; active filtering uses an active filter to compensate for the ripple, and through a corresponding control scheme, it generates a compensation power with the same magnitude and opposite direction as the grid ripple power to eliminate the voltage ripple of the grid. However, this method requires knowledge of the frequency, amplitude, and phase of the voltage at the grid, and can only filter out the ripples of specific frequency components on 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 object, the present application is implemented according to the following technical solutions:

[0005] The present application provides a method for adaptively compensating the main component ripple of a DC distribution network, including:

[0006] Collect the voltage of the bus to be treated in the DC distribution network;

[0007] Filter and extract the voltage of the bus to be treated in the DC distribution network to obtain the main component ripple frequency of the ripple voltage component;

[0008] Based on the main component ripple frequency, determine the voltage ripple amplification factor;

[0009] Based on the voltage ripple amplification factor, determine the control signals of the upper and lower bridge arm switching tubes of the converter;

[0010] Wherein, optionally, the determining the control signals of the upper and lower bridge arm switching tubes of the converter based on the voltage ripple amplification factor includes:

[0011] Based on the voltage ripple amplification factor and the ripple voltage component, determine the first current reference value;

[0012] Collect the desired capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor;

[0013] Determine a second current reference value based on the desired capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor;

[0014] Determine the control signals of the upper and lower bridge arm switching tubes of the converter based on the first current reference value and the second current reference value.

[0015] Optionally, the step of subjecting the bus voltage to be regulated in the DC distribution network to filtering and extraction processing to obtain the main component ripple frequency of the ripple voltage component includes:

[0016] Input the bus voltage to be regulated in the DC distribution network into a band-pass filter for processing to obtain a ripple voltage component;

[0017] Use discrete Fourier transform to perform transformation and extraction processing on the ripple voltage component to obtain the main component ripple frequency of the ripple voltage component.

[0018] Optionally, the step of determining the voltage ripple amplification factor based on the main component ripple frequency includes:

[0019] Determine the difference in the ripple transformation amount based on the main component ripple frequency;

[0020] Determine the voltage ripple amplification factor based on the difference in the ripple change amount.

[0021] Optionally, the step of determining the difference in the ripple transformation amount based on the main component ripple frequency includes:

[0022] Determine the length of the ripple voltage detection window time based on the main component ripple frequency;

[0023] Record the peak value in the ripple voltage data at the current moment every time the length of the ripple voltage detection window time;

[0024] Obtain the peak value in the ripple voltage data at the previous historical moment;

[0025] Determine the difference in the ripple transformation amount 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.

[0026] Optionally, the step of determining the second current reference value based on the desired capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor includes:

[0027] Determine the capacitor voltage deviation based on the desired capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor;

[0028] Input the capacitance voltage deviation into a proportional-integral controller to obtain a second current reference value.

[0029] Optionally, determining control signals for the upper and lower bridge arm switching tubes of the converter based on the first current reference value and the second current reference value includes:

[0030] Add the first current reference value and the second current reference value to obtain a total reference current value;

[0031] Obtain an inductor current measurement value;

[0032] Subtract the inductor current measurement value from the total reference current value to obtain a current deviation value;

[0033] Determine control signals for the upper and lower bridge arm switching tubes of the converter based on the current deviation value.

[0034] Optionally, determining control signals for the upper and lower bridge arm switching tubes of the converter based on the current deviation value includes:

[0035] Input the current deviation value into a quasi-proportional-resonant controller to obtain a duty cycle signal;

[0036] Determine control signals for the upper and lower bridge arm switching tubes of the converter based on the duty cycle signal.

[0037] The present application has the following beneficial effects:

[0038] The present application uses short-time discrete Fourier transform to identify the main component ripple frequency, which has a fast speed and a large detection range. The extracted main component ripple frequency is used to modify the resonant frequency of the quasi-proportional-resonant controller and calculate the updated frequency of the ripple voltage peak-to-peak value, which can quickly adjust and improve the filtering effect of the active filter at the corresponding main component frequency. During operation, the ripple voltage can be observed quickly to update the ripple amplification parameter, and the amplified ripple voltage is used as part of the reference current value for output, which can dynamically adjust the inductor current of the DC filter 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 control effect of the active filter when the main component ripple appears or the amplitude and frequency of the main component ripple change can be realized.

[0039] In addition to the objectives, features, and advantages described above, the present application has other objectives, features, and advantages. The following will refer to the accompanying drawings for a further detailed description of the present application. Description of the Drawings

[0040] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0041] Figure 1 It is a schematic diagram of the topological structure of the DC active filter device involved in the embodiments of the present application;

[0042] Figure 2 It is a control block diagram of the main component ripple adaptive compensation system of the DC distribution network involved in the embodiments of the present application;

[0043] Figure 3 It is a schematic flow diagram of a method for adaptive compensation of the main component ripple of a DC distribution network provided for the embodiments of the present application;

[0044] Figure 4 It is a working flow diagram of the ripple voltage amplification factor adaptive module involved in the embodiments of the present application;

[0045] Figure 5 It is a waveform diagram of the bus voltage before and after the treatment of the method for adaptive compensation of the main component ripple of the DC distribution network provided for the embodiments of the present application. Detailed implementation manners

[0046] The following will describe the embodiments of the present application in detail with reference to the accompanying drawings. However, the present application can be implemented in many different ways defined and covered by the claims.

[0047] For the convenience of understanding the method proposed in the present application later, the topological structure of the DC active filter device applied in the present application will be briefly introduced here. The present application uses a half-bridge bidirectional buck / boost converter as the active filter, as Figure 1 shown, the topological structure of the DC active filter device applied in the method of the present application includes: a DC bus side capacitor C dc , a low-voltage side energy storage capacitor C s , an energy storage inductor L , a low-voltage side equivalent resistance r, an upper-bridge arm switch tube s1 of the converter, and a lower-bridge arm switch tube s2 of the converter;

[0048] The positive electrode of the DC bus side capacitor C dc and the source electrode of the upper-bridge arm switch tube s1 of the converter are both connected to the positive electrode of the DC distribution network bus voltage u dc ; the negative electrode of the DC bus side capacitor C dc , the negative electrode of the low-voltage side energy storage capacitor C s , and the drain electrode of the lower-bridge arm switch tube s2 of the converter are all connected to the DC distribution network bus voltage u dcThe negative electrode; both the converter upper-bridge-arm switch tube S1 and the converter lower-bridge-arm switch tube S2 contain anti-parallel diodes. 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 is connected to node A; the energy storage inductor 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 positive electrode of the low-voltage side energy storage capacitor C s Is connected.

[0049] The method proposed in this application is implemented by using the system control block diagram as shown in Figure 2 As shown, a simple description of this process is as follows:

[0050] The collected bus voltage of the DC distribution network to be treated u dc , after passing through the BPF band-pass filter, the ripple voltage component is obtained. According to the sampling frequency F s , the ripple voltage component is input into the principal component ripple calculation module. Through discrete fast Fourier transform, the principal component ripple frequency is obtained and is used in real time to modify the resonant frequency of the quasi-proportional resonant controller. Then, the principal component ripple frequency is input into the amplification factor adaptive generation module. With the length of the detection window of the amplification factor adaptive generation module, the amplification factor generated by the amplification factor adaptive generation module is multiplied by the ripple voltage component to obtain the first reference current value iref1. The second reference current value iref2 obtained by the proportional-integral controller PI with the desired capacitor reference voltage and the voltages at both ends of the low-voltage side energy storage capacitor are added together to obtain the total reference current value. After subtracting the inductor current from the total reference current value, the current deviation value is obtained. The current deviation value is input into the quasi-proportional resonant controller PR to generate the switch control signals S1 and S2 of the PWM.

[0051] The method proposed in this application is described in detail below:

[0052] As shown in Figure 3 As shown, a principal component ripple adaptive compensation method for a DC distribution network proposed in this application includes:

[0053] Step S301: Collect the bus voltage of the DC distribution network to be treated;

[0054] Collect the bus voltage of the DC distribution network to be treated u dc , collect the bus voltage u dc , and the ripple characteristics such as frequency and amplitude can be analyzed, providing a basis for selecting an appropriate ripple suppression strategy.

[0055] Step S302: Filter and extract the voltage of the bus to be regulated in the DC distribution network to obtain the main component ripple frequency of the ripple voltage component;

[0056] Input the voltage of the bus to be regulated in the DC distribution network into a band-pass filter (BPF) for processing to obtain the ripple voltage component . The DC distribution network bus voltage contains DC components and AC components such as ripples. The band-pass filter has the characteristic of allowing signals within a specific frequency range to pass through while blocking signals of other frequencies. By reasonably setting the passband range of the band-pass filter, the ripple voltage component in the bus voltage can be separated from other components, facilitating subsequent separate analysis and processing of the ripple.

[0057] Identifying the ripple voltage component is a prerequisite for performing governance work such as ripple suppression. Only by first extracting the ripple from the bus voltage can appropriate measures be taken to suppress or compensate it according to its characteristics, effectively improving the voltage quality of the DC distribution network.

[0058] After obtaining the ripple voltage component , use the discrete Fourier transform to extract and process the ripple voltage component to obtain the main component ripple frequency of the ripple voltage component f 0 , and the following is a detailed description of this process:

[0059] First, set the discrete sampling frequency of the ripple voltage component to F s , and set the time length of the main component ripple frequency detection window to t 1 , construct an array n 1 = t 1 / F s of length X 1 , and input the ripple voltage component data , After collecting at the sampling frequency F s , shift the array data forward by one unit, and input the current voltage data array into X 1 the end unit. Perform discrete fast Fourier transform on X 1 :

[0060] (1)

[0061] Find the arrayY The frequency position corresponding to the maximum value k max to obtain the main component ripple frequency as .

[0062] Step S303: Determine the voltage ripple amplification factor based on the main component ripple frequency;

[0063] After determining the main component ripple frequency f 0 , as Figure 2 and Figure 4 shown, input it into the magnification adaptive module to determine the voltage ripple amplification factor K ( n ), and the process will be described in detail as follows:

[0064] First, according to the main component ripple frequency f 0 , the difference in the ripple transformation amount can be determined e ( n ), and the specific process is as follows:

[0065] According to the main component ripple frequency, design the time length of the ripple voltage detection window as , which can include half-cycle waveform data, and construct an array with a length of n 2 = t 2 · F s of X 2 . After collecting the ripple voltage data at the sampling frequency Fs, shift the data in the array X 2 forward by one unit, and input the current ripple voltage data into X 2 the last unit.

[0066] Then, record the peak value in the current ripple voltage data every time the time length of the ripple voltage detection window elapses, and then determine the difference in the ripple transformation amount based on the peak value in the current ripple voltage data and the peak value in the ripple voltage data of the previous historical moment. It can also be understood as: every t 2 moment, record the peak-to-peak value of the data in the current X 2 as , and subtract it from the peak-to-peak value X 2 of the data recorded in the previous moment to obtain the difference in the ripple transformation amount .

[0067] It should be noted that when the main component ripple frequency changes, it is necessary to clear the data in X 2 and then correct X 2 the array length.

[0068] Secondly, after obtaining the difference of the ripple transformation amount e ( n ), the voltage ripple amplification factor K ( n ) can be determined. The following is a detailed description of this process:

[0069] After the active converter starts, K ( n ) has an initial value of 0 and, after the first acquisition is completed , K ( n ) increases to 0.1. Subsequently, at every t 2 moment, according to whether the absolute value of the current e (n) is greater than the set threshold E , it is determined whether the value of the next moment K ( n ) changes. When , the amplification factor of the next moment K ( n ) remains unchanged, K ( n + 1) = K ( n ). Otherwise, it is judged whether e (n) is positive or negative. If e (n) is positive, it indicates that the voltage increases at the peak within the corresponding ripple period due to disturbance or the change of the amplification factor K ( n ). The change direction of K ( n ) is reversed, that is, the direction coefficient d = - d , d is 1 or -1; if e (n) is negative, then K ( n ) does not change the direction of change. The amplification factor of the next moment becomes:

[0070] (2)

[0071] Among them, is the change step of the current K value and is the arithmetic square root of the absolute value of the ripple transformation amount difference.

[0072] Step S304: Determine the control signals of the upper and lower bridge arm switching tubes of the converter based on the voltage ripple amplification factor.

[0073] As Figure 2 shown, after passing through the amplification factor adaptive module to obtain the corresponding voltage ripple amplification factor K ( n ), the control signals of the upper and lower bridge arm switching tubes of the converter can be determined. The specific process is as follows:

[0074] Step S401: Determine a first reference current value based on the voltage ripple amplification factor and the ripple voltage component;

[0075] After obtaining the voltage ripple amplification factor, multiply it 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 regulation. According to the actual operating conditions of the system, when the ripple voltage changes, both the ripple voltage component and the voltage ripple amplification factor will change accordingly, so that i ref1 also changes. The system can adjust the operating parameters of each part according to this changed i ref1 to maintain the stable operation of the entire DC distribution network and ensure the power supply quality, such as adjusting the output power of the distributed power source or the connection status of the load.

[0076] Step S402: Collect the desired capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor;

[0077] As Figure 2 shown, collect the desired capacitor reference voltage u sref , and the voltage across the low-voltage side energy storage capacitor u s .

[0078] Step S403: Determine a second reference current value based on the desired capacitor reference voltage and the voltage across the low-voltage side energy storage capacitor;

[0079] After collecting the desired capacitor reference voltage u sref , and the voltage across the low-voltage side energy storage capacitor u s , subtract the voltage across the low-voltage side energy storage capacitor u sref , from the desired capacitor reference voltage u s to obtain the capacitor voltage deviation, and then input the capacitor voltage deviation into asFigure 2 In the PI proportional-integral controller shown, a second current reference value is obtained i ref2 .

[0080] Step S404: Based on the first current reference value and the second current reference value, determine the control signals for the upper and lower bridge arm switching tubes of the converter.

[0081] After determining and calculating the first current reference value and the second current reference value, add the first current reference value and the second current reference value to obtain a total reference current value, and subtract the measured value of the current of inductor L from the total reference current value i L to obtain a circuit deviation value, and based on this current deviation value, determine the control signals for the upper and lower bridge arm switching tubes of the converter;

[0082] After determining the current deviation value, as Figure 2 shown, input it into the quasi-proportional-resonant controller PR to obtain a duty cycle signal, and through the pulse width modulation algorithm, obtain the control signals for the two switching tubes S1 and S2 of the upper and lower bridge arms of the converter.

[0083] In step S404, before the current deviation value is sent to the quasi-proportional-resonant converter, it is necessary to process the difference using the Z-transform. It should be noted that the z-domain transfer function of the quasi-proportional-resonant controller is specifically:

[0084] (3)

[0085] In the above formula, ω 0 is the resonant frequency of the quasi-proportional-resonant amplifier, and its value is taken as 2π times the main component ripple frequency f 0 , that is ω 0 =2π f 0 ; k p , k r , ω c are respectively the proportional coefficient, resonant gain coefficient and cut-off frequency of the quasi-proportional-resonant controller, and z is the result after the Z-transform of the difference signal.

[0086] In this embodiment, because the quasi-proportional-resonant controller has a large gain at the resonant frequency, it can achieve static-error-free tracking of the AC signal, and further achieve excellent current tracking control to obtain a duty cycle signal.

[0087] It should be noted that when continuously executing the above steps, when it is detected that the main component frequency of the DC distribution network ripple changes, the main component frequency is updated. f 0 , and the resonant frequency parameter of the quasi-proportional resonant controller is modified.

[0088] Experimental verification

[0089] Taking a 500V DC distribution network as an example, using the method provided in this application to control the main component of the distribution network ripple. At 0.5s, a 60Hz ripple current is injected into the power grid. At 1.1s, the active power filter system of the circuit starts to work. At 4s, the current frequency is changed to 100Hz, and the amplitude of the injected ripple current is increased. At 9s, the active power filter system stops working. The waveforms of the bus voltage before and after the control by the adaptive compensation method for the main component ripple frequency of the DC distribution network provided in this application are as Figure 5 shown. It can be seen that after the method provided in this application starts to work and after the main frequency and amplitude change, it can quickly adjust adaptively through the K value, reduce the level of the main component ripple frequency of the DC distribution network, and the reduction effect of the amplitude of the main component ripple frequency reaches more than 90%.

[0090] In summary, this application uses the short-time discrete Fourier transform to identify the main component ripple frequency, which has a fast speed and a large detection range. The extracted main component ripple frequency is used to modify the resonant frequency of the quasi-proportional resonant controller and calculate and update the frequency of the peak-to-peak ripple voltage, 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 update the ripple amplification parameter, and the amplified ripple voltage is used as part of the reference current value for output, which can dynamically adjust the inductor current of the DC filter to a relatively high stable level to achieve a good filtering effect. After the parameter setting is completed, no other operations are required, and the automatic control effect of the active filter when the main component ripple appears or the amplitude and frequency of the main component ripple change can be achieved.

[0091] The above are only the preferred embodiments of this application and are not used to limit this application. For those skilled in the art, this application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of this application shall be included within the protection scope of this 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; 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, determining control signals of the upper and lower bridge arm switches of the converter; 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.

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 transformation amount, 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.

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