Direct-current active filtering method and system based on three-level topological connection low-voltage direct-current power supply system

Abstract

The invention relates to the technical field of low-voltage direct-current power supply, and discloses a direct-current active filtering method and system based on a three-level topological connection low-voltage direct-current power supply system. Firstly, a three-level topological active filter is connected with the low-voltage direct-current power supply system in parallel, so that the voltage stress of a switching tube is reduced; reference voltages under different working conditions are dynamically generated through a preset working condition proportionality coefficient, the compensation capacitor voltage can be more accurately adjusted, the compensation precision is improved, a processing mode of firstly adopting a proportional resonance controller and then adopting a proportional controller is adopted, so that the active filter more effectively suppresses various ripple components, and finally, the active filter can be effectively controlled. The three-level topological active filter can drive the switching tube to be switched on and switched off according to different modulation results, the filter inductor is flexibly controlled to generate the compensation current, finally, the compensation current injected into the low-voltage direct-current power supply system can be more effectively subjected to ripple filtering, and the ripple suppression capacity in the system is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of low-voltage direct current (DC) power supply, and in particular to a DC active filtering method and system for connecting a low-voltage DC power supply system based on a three-level topology. Background Art

[0002] "Solar-storage-direct-flexible" buildings are a key path to achieving zero-carbon operation. Low-voltage DC power supply systems, with their advantages of fewer power conversion steps, low line losses, and high power quality, have become the core infrastructure for such buildings. However, in residential buildings, sensitive electronic equipment (such as data center servers) and emergency power systems place extremely high demands on DC bus voltage quality. Single-phase / three-phase AC loads and nonlinear loads connected to the system introduce ripple on the DC bus, leading to voltage distortion and deteriorating power quality. Therefore, this ripple problem urgently needs to be addressed.

[0003] Existing ripple control solutions are primarily categorized as passive filtering and active filtering. Passive filters utilize a combination of inductors, capacitors, and resistors to create a low-impedance shunt path for specific sub-ripples. While they offer advantages such as simple structure and low cost, they suffer from significant drawbacks: First, they can only filter out ripple within a preset frequency band and cannot dynamically adapt to spectrum changes; second, the filtering effect is easily affected by grid impedance and load characteristics; and third, the size and weight of the components required for low-frequency ripple increase significantly. In contrast, active filters utilize power electronics circuits and control algorithms to generate dynamic compensation signals, suppressing ripples with varying frequency and amplitude. Their performance is unaffected by system impedance, making them more suitable for low-voltage DC power supply scenarios with uncertain disturbance sources.

[0004] Currently, existing DC active filtering solutions mostly use a two-level bidirectional DC / DC (also known as buck-boost) circuit topology. For example, invention patent CN119009920A proposes a hybrid DC active filtering method for low-voltage DC power supply systems. However, this hybrid DC active filtering method can experience significant fluctuations in the compensation capacitor voltage when the bus voltage fluctuates or the system is subject to external interference. In complex grid scenarios, this method cannot accurately compensate for individual ripples, reducing its ripple suppression capability. Furthermore, the active filter topology uses a two-level bidirectional DC / DC circuit. While this two-level bidirectional DC / DC can also meet the basic requirement of bidirectional power transmission in DC systems, it suffers from high voltage stress on the switching tubes. Summary of the Invention

[0005] The present invention provides a DC active filtering method and system based on a three-level topology connected to a low-voltage DC power supply system, which solves the technical problems of insufficient ripple suppression capability and high voltage stress of the switch tube in the existing DC active filtering scheme using a two-level bidirectional DC / DC circuit topology.

[0006] A first aspect of the present invention provides a DC active filtering method based on a three-level topology connected to a low-voltage DC power supply system, wherein the three-level topology active filter is connected in parallel with the low-voltage DC power supply system, comprising:

[0007] detecting a DC bus voltage of the low-voltage DC power supply system, filtering the DC bus voltage, and determining a DC bus voltage ripple based on a filtering result and the DC bus voltage;

[0008] When the DC bus voltage ripple is not equal to zero, determining a first current command value according to the DC bus voltage ripple in combination with a proportional resonant controller;

[0009] Performing a multiplication operation on the DC bus voltage and a preset operating condition proportional coefficient to generate a reference voltage;

[0010] Detecting a compensation voltage of a compensation capacitor in the three-level topology active filter, and determining a second current command value based on the compensation voltage and the reference voltage in combination with a proportional-integral controller;

[0011] detecting an inductor current of a filter inductor in the three-level topology active filter, and determining a switch duty cycle signal according to the inductor current, the first current command value, and the second current command value in combination with a proportional controller;

[0012] Pulse width modulation is performed on the switch tube duty cycle signal, and based on the modulation result, the switch tube in the three-level topology active filter is driven to be turned on and off, and the filter inductor is controlled to inject a compensation current for ripple filtering into the low-voltage DC power supply system.

[0013] Optionally, the detecting a DC bus voltage of the low-voltage DC power supply system, filtering the DC bus voltage, and determining a DC bus voltage ripple based on a filtering result and the DC bus voltage includes:

[0014] Detecting the DC bus voltage of the low-voltage DC power supply system;

[0015] Filtering the DC bus voltage through a low-pass filter to obtain a filtered voltage;

[0016] A difference operation is performed between the DC bus voltage and the filtered voltage to obtain a DC bus voltage ripple.

[0017] Optionally, when the DC bus voltage ripple is not equal to zero, determining the first current command value according to the DC bus voltage ripple in combination with a proportional resonant controller includes:

[0018] When the DC bus voltage ripple is not equal to zero, performing a difference operation between the DC bus voltage ripple and a preset voltage ripple reference value to obtain a first difference;

[0019] The first difference is input into a proportional resonant controller to perform ripple compensation to obtain a first current command value.

[0020] Optionally, detecting the compensation voltage of the compensation capacitor in the three-level topology active filter, and determining the second current command value according to the compensation voltage and the reference voltage in combination with a proportional-integral controller, includes:

[0021] Detecting a compensation voltage of a compensation capacitor in the three-level topology active filter;

[0022] performing a difference operation on the reference voltage and the compensation voltage to obtain a second difference;

[0023] The second difference is input into a proportional-integral controller for proportional-integral processing to obtain a second current command value.

[0024] Optionally, detecting the inductor current of the filter inductor in the three-level topology active filter and determining the switch tube duty cycle signal according to the inductor current, the first current command value, and the second current command value in combination with a proportional controller includes:

[0025] Detecting the inductor current of the filter inductor in the three-level topology active filter;

[0026] performing a sum operation on the first current command value and the second current command value to obtain a first sum value;

[0027] performing a difference operation on the first sum and the inductor current to obtain a third difference;

[0028] The third difference is input into the proportional controller for proportional processing to obtain a switch tube duty cycle signal.

[0029] Optionally, the switching tubes include a first switching tube, a second switching tube, a third switching tube, and a fourth switching tube. The pulse width modulation of the switching tube duty cycle signal is performed, and based on the modulation result, the switching tubes in the three-level topology active filter are driven to be turned on and off, and the filter inductor is controlled to inject a compensation current for ripple filtering into the low-voltage DC power supply system. The method includes:

[0030] Performing pulse width modulation on the switch tube duty cycle signal to obtain a modulation result;

[0031] When the modulation result shows that the first switch tube and the fourth switch tube are turned on, and the second switch tube and the third switch tube are turned off, a voltage is applied to the filter inductor via the first high-side voltage-dividing capacitor, the second high-side voltage-dividing capacitor and the compensation voltage in the three-level topology active filter to generate a compensation current;

[0032] When the modulation result is that the first switch tube and the fourth switch tube are turned off, and the second switch tube and the third switch tube are turned on, applying a voltage to the filter inductor through the compensation voltage to generate a compensation current;

[0033] When the modulation result shows that the first switch tube and the third switch tube are turned on, and the second switch tube and the fourth switch tube are turned off, a voltage is applied to the filter inductor through the first high-side voltage divider capacitor and the compensation voltage until the inductor current reaches a preset command current, and the inductor current is used as the compensation current;

[0034] When the modulation result shows that the first switch tube and the third switch tube are turned off, and the second switch tube and the fourth switch tube are turned on, a voltage is applied to the filter inductor through the second high-voltage side voltage divider capacitor and the compensation voltage until the inductor current reaches a preset command current, and the inductor current is used as the compensation current;

[0035] The compensation current is injected into the low-voltage DC power supply system to perform ripple filtering.

[0036] A second aspect of the present invention provides a DC active filter system connected to a low-voltage DC power supply system based on a three-level topology, wherein the three-level topology active filter is connected in parallel with the low-voltage DC power supply system, comprising:

[0037] a first processing module, configured to detect a DC bus voltage of the low-voltage DC power supply system, filter the DC bus voltage, and determine a DC bus voltage ripple based on a filtering result and the DC bus voltage;

[0038] a second processing module, configured to determine a first current command value according to the DC bus voltage ripple in combination with a proportional resonant controller when the DC bus voltage ripple is not equal to zero;

[0039] a third processing module, configured to perform a multiplication operation on the DC bus voltage and a preset operating condition proportional coefficient to generate a reference voltage;

[0040] a fourth processing module, configured to detect a compensation voltage of a compensation capacitor in the three-level topology active filter, and determine a second current command value based on the compensation voltage and the reference voltage in combination with a proportional-integral controller;

[0041] a fifth processing module, configured to detect an inductor current of a filter inductor in the three-level topology active filter, and determine a switch duty cycle signal based on the inductor current, the first current command value, and the second current command value in combination with a proportional controller;

[0042] The sixth processing module is used to perform pulse width modulation on the switch tube duty cycle signal, and drive the switching of the switch tube in the three-level topology active filter based on the modulation result, and control the filter inductor to inject a compensation current for ripple filtering into the low-voltage DC power supply system.

[0043] A third aspect of the present invention provides an electronic device, comprising a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor performs the steps of the DC active filtering method for connecting a low-voltage DC power supply system based on a three-level topology as described in any one of the above items.

[0044] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed, the method for active DC filtering of a low-voltage DC power supply system connected based on a three-level topology as described in any one of the above items is implemented.

[0045] It can be seen from the above technical solutions that the present invention has the following advantages:

[0046] (1) The present invention connects a three-level topology active filter in parallel with a low-voltage DC power supply system. In the three-level topology, the voltage borne by the switch tube is only half of the DC bus voltage. Compared with the two-level topology where the switch tube bears the entire DC bus voltage, this greatly reduces the voltage stress of the switch tube, allowing the switch tube to select a device with a lower withstand voltage rating, thereby improving the reliability of the system and reducing the cost and difficulty of heat dissipation design.

[0047] (2) The present invention dynamically generates reference voltages under different working conditions by presetting the working condition proportional coefficient. Compared with the traditional method of using a fixed reference voltage, the present invention can be applied to complex and changeable grid working conditions. At the same time, the deviation between the compensation voltage of the sampled compensation capacitor and the reference voltage is processed by the proportional-integral controller, which can more accurately adjust the compensation capacitor voltage, improve the compensation accuracy, and thus effectively reduce the ripple content in the grid.

[0048] (3) The present invention firstly processes the input signal accurately through a proportional resonant controller, which can better track and control different ripples independently without static error, more accurately extract and process the signal components related to the ripple, and then perform appropriate scaling adjustment through the proportional controller, so that the final output control signal is more accurate. While improving the compensation accuracy of ripple and reactive power, it can also enable the active filter to more effectively suppress various ripple components, significantly improving the ripple suppression capability. In addition, the present invention first processes the input signal through a proportional resonant controller. The proportional resonant controller itself has good anti-interference ability and can suppress the interference in the input signal to a certain extent. Then, it passes through the proportional controller. The proportional controller makes adjustments based on the relatively stable control signal, making the system more stable when facing external interference or parameter changes.

[0049] (4) Based on the scenario where the three-level topology active filter is connected to the low-voltage DC power supply system, the three-level topology active filter of the present invention can drive the switching of the switch tube according to different modulation results, flexibly control the filter inductor to generate compensation current, and finally make the compensation current injected into the low-voltage DC power supply system more effectively filter the ripple, significantly improving the ability to suppress the ripple in the system. In addition, the three-level topology active filter of the present invention also involves a freewheeling control, which can ensure that the inductor current stably and efficiently tracks the preset instruction current, reduce current fluctuations and energy loss in the transition process, and improve the working efficiency of the three-level topology active filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0051] Figure 1 A flowchart of a method for active DC filtering connected to a low-voltage DC power supply system based on a three-level topology provided in the first embodiment of the present invention;

[0052] Figure 2 A topological diagram of a low-voltage DC power supply system provided by the present invention;

[0053] Figure 3 Schematic diagram of the three-level topology active filter provided by the invention connected in parallel with the low-voltage DC power supply system;

[0054] Figure 4 A schematic diagram of a three-level topology active filter provided by the present invention;

[0055] Figure 5 This is the block diagram of active filter control strategy;

[0056] Figure 6 A schematic diagram showing the DC bus voltage waveform of the three-level topology active filter simulation effect provided by the present invention;

[0057] Figure 7 A block diagram of a DC active filter system connected to a low-voltage DC power supply system based on a three-level topology provided in the second embodiment of the present invention;

[0058] Figure 8 This is a structural block diagram of a computer device provided in Example 3 of the present invention. DETAILED DESCRIPTION

[0059] Embodiments of the present invention provide a DC active filtering method and system based on a three-level topology connected to a low-voltage DC power supply system, which is used to solve the technical problems of insufficient ripple suppression capability and high voltage stress of switching tubes in existing DC active filtering solutions using a two-level bidirectional DC / DC circuit topology.

[0060] In order to make the purpose, features, and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0061] Currently, existing DC active filtering solutions mostly use two-level bidirectional DC / DC (also known as buck-boost) circuits. However, while two-level bidirectional DC / DCs can also meet the basic requirement of bidirectional power transmission in DC systems, compared with three-level bidirectional DC / DCs, they have disadvantages such as high switching tube voltage stress, high losses, large output ripple, and smaller capacity.

[0062] As can be seen from the above, the passive filters widely used in DC systems in existing technologies have significant drawbacks: First, they are limited by a fixed resonant frequency design and can only attenuate specific secondary ripples, resulting in poor frequency domain adaptability. Second, their filtering performance is significantly affected by grid impedance parameters and load fluctuations, resulting in insufficient robustness under operating conditions. Third, to suppress the dominant secondary low-frequency ripple in DC systems, large-capacity capacitor banks are required, which exponentially increases the size and weight of the passive filter and reduces its economic efficiency. Furthermore, the two-level bidirectional DC / DC topology used in existing DC active filtering solutions suffers from high voltage stress on the topology switch, high losses, large output ripple, and relatively small capacitance.

[0063] Compared with the existing DC system ripple control solutions that widely use passive filters, active power filters (APFs) generate dynamic compensation signals through power electronic circuits and control algorithms, which can suppress ripples with changing frequency and amplitude. Their performance is not affected by system impedance and is more suitable for low-voltage DC power supply scenarios with uncertain disturbance sources.

[0064] Therefore, the present invention proposes a DC active filtering method and system based on a three-level topology connected to a low-voltage DC power supply system. A non-isolated bidirectional three-level DC / DC circuit is selected as the topology of the DC active filtering device, and the ripple suppression of the DC bus voltage is achieved through a corresponding control strategy. First, the three-level topology reduces the voltage stress of the switching device to half of the DC bus voltage, significantly reducing the difficulty of selecting the switching device and the switching loss in the low-voltage system; second, its multi-level output characteristics can generate a step voltage that is closer to the ideal waveform, greatly reducing the high-frequency ripple content of the output voltage. In addition, the reduction in switching loss means higher efficiency and switching frequency, which increases the bandwidth of ripple suppression at the same switching loss.

[0065] Figure 1 This is a flowchart of the steps of a DC active filtering method based on a three-level topology connected to a low-voltage DC power supply system provided in Example 1 of the present invention.

[0066] The present invention provides a DC active filtering method based on a three-level topology connected to a low-voltage DC power supply system. The three-level topology active filter is connected in parallel with the low-voltage DC power supply system, comprising:

[0067] See also Figure 2 The present invention mainly targets low voltage DC power supply system, filters the DC bus voltage of low voltage DC power supply system to improve power supply quality and protect sensitive equipment. Figure 2 In the DC bus voltage V dc The DC load and harmonic source load are connected in parallel to the DC bus.

[0068] See also Figure 3 The three-level topology active power filter (DC-APF) proposed in this invention adopts a non-isolated three-level bidirectional DC / DC circuit as the topology, which is connected in parallel to the DC bus of the low-voltage DC power supply system. The APF (Active Power Filter) is connected in parallel at both ends of the DC bus. The DC bus voltage is V dc . Figure 3 The APF is connected in parallel between the interface converter and the DC load. In fact, the APF can be connected in parallel at any position on the DC bus, such as between harmonic source 1 and harmonic source 2.

[0069] See also Figure 4 , Figure 4 A schematic diagram of a three-level topology active filter provided by the present invention. Figure 4 In the figure, the left side of the three-level topology active filter is connected in parallel to the DC bus. C2 is the first high-voltage side voltage divider capacitor, C3 is the second high-voltage side voltage divider capacitor, S1, S2, S3, and S4 are four IGBTs (Insulated Gate Bipolar Transistors) with anti-parallel diodes, namely the first, second, third, and fourth switching tubes. L1 is the filter inductor, C1 is the compensation capacitor, and i apf is the inductor current, and the circuit connection relationship of the three-level topology active filter is as follows:

[0070] The first high-voltage side voltage-dividing capacitor C2 is connected in series with the second high-voltage side voltage-dividing capacitor C3;

[0071] One end of the first high-voltage side voltage-dividing capacitor C2 away from the second high-voltage side voltage-dividing capacitor C3 is respectively connected to the high-potential output end and the first switch tube S1;

[0072] One end of the first switch tube S1 away from the first high-voltage side voltage-dividing capacitor C2 is respectively connected to the second switch tube S2 and the filter inductor L1;

[0073] The filter inductor L1 is connected in series with the compensation capacitor C1;

[0074] The second switch tube S2 and the third switch tube S3 are connected in series;

[0075] One end of the second high-voltage side voltage-dividing capacitor C3 away from the first high-voltage side voltage-dividing capacitor C2 is respectively connected to the low-potential output end and the fourth switch tube S4;

[0076] One end of the fourth switch tube S4 away from the second high-side voltage-dividing capacitor C3 is respectively connected to the third switch tube S3 and the compensation capacitor C1 .

[0077] Taking the first switch S1 as an example, when the system is operating normally, the maximum voltage across the first switch S1 is the potential difference from the potential at which it is connected to the connection point between the first high-voltage side voltage divider capacitor C2 and the second high-voltage side voltage divider capacitor C3. dc The maximum voltage that the first switch tube S1 can withstand is 2V. dc The same applies to the other switch tubes (the second switch tube S2, the third switch tube S3 and the fourth switch tube S4). This is different from the traditional two-level topology where the switch tube bears the entire DC bus voltage V dcCompared to conventional MOSFETs, voltage stress is reduced to half. In low-voltage systems, lower voltage stress allows for the selection of switching devices with relatively low withstand voltage ratings, thus simplifying the selection process. Furthermore, lower voltage stress reduces losses during the switching device turn-on and turn-off processes.

[0078] The three-level topology has a multi-level output characteristic, which can output three states: high potential, zero potential, and low potential. When different combinations of switch tubes are turned on, a step voltage that is closer to the ideal waveform can be generated. For example, when the first switch tube S1 and the fourth switch tube S4 are turned on, a high potential is output; when the second switch tube S2 and the third switch tube S3 are turned on, a low potential is output; when the first switch tube S1 and the third switch tube S3 or the second switch tube S2 and the fourth switch tube S4 are turned on, a zero potential is output. Compared with the two-level topology with only high potential and low potential states, this multi-level output method can more closely approximate the ideal smooth voltage waveform, significantly reducing the high-frequency ripple content of the output voltage.

[0079] Because the three-level topology reduces the voltage stress on the switching devices, it also reduces losses during the turn-on and turn-off phases. In traditional two-level topologies, higher voltage stress results in greater switching losses. The reduced switching losses in the three-level topology mean that the system can operate at a higher switching frequency without excessive losses, thereby improving system efficiency. With equivalent switching losses, a higher switching frequency can increase the ripple suppression bandwidth. For example, in PWM modulation with carrier phase-shift control, a higher switching frequency allows the inductor current to more quickly track the preset command current, providing better suppression of high-frequency ripple. This further enhances the power quality improvement effect of the three-level active filter on low-voltage DC power supply systems.

[0080] See also Figure 5 , Figure 5 This is a block diagram of the active filter control strategy, specifically the specific control logic of steps 101 to 106 as shown below:

[0081] Step 101: Detect a DC bus voltage of a low-voltage DC power supply system, filter the DC bus voltage, and determine a DC bus voltage ripple based on the filtering result and the DC bus voltage.

[0082] Furthermore, step 101 may include the following sub-steps:

[0083] S11. Detect the DC bus voltage of the low-voltage DC power supply system.

[0084] In the embodiment of the present invention, the DC bus voltage V at the grid connection point between the three-level topology active filter and the low-voltage DC power supply system is detected. dc .

[0085] S12. Filter the DC bus voltage through a low-pass filter to obtain a filtered voltage.

[0086] In the embodiment of the present invention, the DC bus voltage is filtered by a low-pass filter to obtain a filtered voltage.

[0087] S13, performing a difference operation on the DC bus voltage and the filtered voltage to obtain a DC bus voltage ripple.

[0088] In a specific implementation, to facilitate the implementation of the method, the process of step 101 above can be converted into a formula encapsulation form, wherein the expression of the DC bus voltage ripple can be as follows:

[0089]

[0090] Where, It is the frequency domain expression of the first-order RC low-pass filter (Resistor-Capacitor First-order Low-pass Filter).

[0091] In the embodiment of the present invention, the DC bus voltage V dc Subtract the DC bus voltage ripple to get the DC bus voltage ripple Δu dc .

[0092] It should be noted that the DC bus voltage is detected to obtain voltage ripple information. The voltage ripple is determined by filtering the DC bus voltage and comparing the filtered result with the original DC bus voltage.

[0093] Step 102 : When the DC bus voltage ripple is not equal to zero, determine a first current command value according to the DC bus voltage ripple in combination with a proportional resonant controller.

[0094] Furthermore, step 102 may include the following sub-steps:

[0095] S21 . When the DC bus voltage ripple is not equal to zero, perform a difference operation between the DC bus voltage ripple and a preset voltage ripple reference value to obtain a first difference.

[0096] In an embodiment of the present invention, when the DC bus voltage ripple is not equal to zero, it means that there is a ripple component in the DC bus voltage and the ripple needs to be eliminated. The preset voltage ripple reference value is preferably 0, and the DC bus voltage ripple and the preset voltage ripple reference value are used to perform a difference operation to obtain a first difference.

[0097] S22 . Use the first difference input proportional resonant controller to perform ripple compensation to obtain a first current command value.

[0098] In the embodiment of the present invention, a first difference input proportional resonant (PR) controller is used to perform ripple compensation to obtain a first current command value i ref1 The purpose of this process is to convert the DC bus voltage V dc The ripple is controlled to 0.

[0099] In a specific implementation, to facilitate the implementation of the method, the process of step 101 to step 102 can be converted into a formula encapsulation form, wherein the expression of the first current command value can be as follows:

[0100]

[0101] Where, For the characteristic angular frequency, the low-pass filter can select filters of different orders and types according to the actual accuracy requirements; is the frequency domain expression of the proportional resonant controller, is the proportional gain; is the resonator gain, for Since the main ripple frequency in the low-voltage DC power supply system is ripple frequency below 12, a proportional resonant controller of 12 and below can be selected here. The frequency domain expression of the above proportional resonant controller takes 12 ripple frequency as an example. A proportional resonant controller with high ripple frequency can also be used. There is no restriction here. represents the complex frequency, symbol It is the basic variable in the frequency domain: complex frequency; it can be compared to the basic variable in the commonly used time domain: time. In the time domain, voltage and current change with time, so they are expressed using expressions related to time. Similarly, in the frequency domain, variables such as voltage, current, or transfer functions can be expressed using expressions related to complex frequency, such as the PI transfer function expression G here. PI , the complex frequency s = σ + jω, σ is the real part, representing the exponential decay or growth factor, j is the imaginary unit, ω is the imaginary part, representing the angular frequency (in radians per second, rad / s), and the relationship between ω and the ordinary frequency f is ω = 2πf.

[0102] In a specific implementation, the proportional resonant controller includes multiple parallel resonant links and proportional links. The first difference is input into the multiple parallel resonant links and proportional links respectively to obtain the superposition value of the outputs of the multiple resonant links and the fundamental frequency amplitude correction amount. The superposition value and the fundamental frequency amplitude correction amount are used to perform a sum operation to obtain the first current command value.

[0103] It should be noted that when the first difference is input to each resonant link ( ), each resonant link will respond to the component of the corresponding ripple frequency in the difference signal according to its own characteristics and generate a corresponding output. Since there are multiple resonant links corresponding to ripples from 2nd to 12th order (multiple resonant links corresponding to multiple ripples are set according to actual conditions, and this is not limited here. Only ripples from 2nd to 12th order are used as an example here), the outputs of these resonant links are added together to obtain the superposition value of the outputs of multiple resonant links. Then, the first difference is input to the proportional link. The proportional link will perform a proportional operation on the difference according to its set proportional gain to obtain the fundamental frequency amplitude correction amount. The superposition value and the fundamental frequency amplitude correction amount are then summed. The final result is the first current command value. The first current command value comprehensively considers the resonant control of different ripple components and the overall proportional control to achieve control and regulation of the system.

[0104] It is worth mentioning that compared with the traditional proportional resonant controller which only controls a specific single frequency or a few specific frequencies, has the problem of limited compensation capability, and is difficult to achieve comprehensive and accurate ripple suppression when facing ripple interference of multiple frequencies and complex working conditions, the proportional resonant controller of the present invention takes into account the control of multiple ripples and can independently and accurately adjust ripples of multiple frequencies at the same time. In a low-voltage distribution network containing complex ripple components, by setting the appropriate resonator gain for each ripple separately, the total ripple content in the system can be more effectively reduced, the ripple control accuracy is greatly improved, and the power quality of the system is improved.

[0105] Step 103 : Perform multiplication operation on the DC bus voltage and the preset operating condition proportional coefficient to generate a reference voltage.

[0106] It should be noted that according to the characteristic that the midpoint potential of the three-level topology active filter should be half of the DC bus in an ideal situation, the preset working condition proportional coefficient is initially set to 0.5. Because in an ideal situation, when the reference voltage of the compensation capacitor C1 is set to the DC bus voltage V dc Half of V dc *D, D=0.5), the voltages of the upper and lower series capacitors can be more balanced, which helps to reduce the voltage stress of the switching devices and maintain the basic stable operation of the system.

[0107] However, there are multiple operating conditions during the operation of the low-voltage DC power supply system. In order to better maintain the voltage stability of the compensation capacitor C1 under different operating conditions, different preset operating condition proportional coefficients D will be selected according to different operating conditions. The preset operating condition proportional coefficient D corresponding to the light load condition is 0.55, the preset operating condition proportional coefficient D corresponding to the large inertia load condition is 0.4-0.5, the preset operating condition proportional coefficient D corresponding to the pulse load condition is 0.45-0.55, and the preset operating condition proportional coefficient D corresponding to the parallel operating condition of multiple active inverter devices is 0.45-0.5.

[0108] In the embodiment of the present invention, by obtaining the current operating condition of the low-voltage DC power supply system, determining the preset operating condition proportional coefficient corresponding to the operating condition, and multiplying the DC bus voltage by the preset operating condition proportional coefficient to generate a reference voltage, the preset operating condition proportional coefficient can be used to determine the DC bus voltage V dc The size of the compensation capacitor is adjusted in real time to adjust the reference voltage.

[0109] Step 104: Detect the compensation voltage of the compensation capacitor in the three-level topology active filter, and determine a second current command value based on the compensation voltage and the reference voltage in combination with a proportional-integral controller.

[0110] Furthermore, step 104 may include the following sub-steps:

[0111] S31. Detecting the compensation voltage of the compensation capacitor in the three-level topology active filter.

[0112] In the embodiment of the present invention, the compensation voltage U of the compensation capacitor in the three-level topology active filter is detected. c1 .

[0113] S32: Perform a difference operation on the reference voltage and the compensation voltage to obtain a second difference.

[0114] In the embodiment of the present invention, a difference operation is performed between the reference voltage and the compensation voltage to obtain the second difference.

[0115] S33: Use the second difference value to input a proportional-integral controller to perform proportional-integral processing to obtain a second current command value.

[0116] In the embodiment of the present invention, the second difference is input into the proportional-integral (PI) controller to perform proportional-integral processing to obtain the second current command value i ref2 The purpose of this step is to control the voltage of the compensation capacitor in the three-level topology active filter to be stable at a given reference voltage U c1ref= V dc *D.

[0117] In a specific implementation, to facilitate the implementation of the method, the process of step 103 to step 104 can be converted into a formula encapsulation form, wherein the expression of the second current command value can be as follows:

[0118]

[0119] Where, represents the second current command value, represents the compensation voltage, represents the proportionality coefficient, represents the integral coefficient, is the frequency domain expression of the proportional-integral controller.

[0120] It is worth noting that the proportional-integral (PI) controller provided by the present invention has a proportional coefficient that can quickly adjust the output of the controller according to the current deviation of the system, and the integral part is used to accumulate past deviations. and The value of can adjust the stability of the system. Due to its simple structure and good control performance, it is suitable for the low-voltage DC power supply system of the present invention.

[0121] Step 105 : Detect the inductor current of the filter inductor in the three-level topology active filter, and determine the switch duty cycle signal according to the inductor current, the first current command value, and the second current command value in combination with the proportional controller.

[0122] Furthermore, step 105 may include the following sub-steps:

[0123] S41. Detect the inductor current of the filter inductor in the three-level topology active filter.

[0124] In the embodiment of the present invention, the inductor current i of the filter inductor in the three-level topology active filter is detected. apf .

[0125] S42: Perform a sum operation on the first current command value and the second current command value to obtain a first sum.

[0126] In the embodiment of the present invention, the first current command value and the second current command value are used to perform a sum operation to obtain a first sum value i ref .

[0127] S43 , performing a difference operation on the first sum and the inductor current to obtain a third difference.

[0128] In the embodiment of the present invention, a difference operation is performed on the first sum and the inductor current to obtain a third difference.

[0129] S44: Use the third difference to input the proportional controller to perform proportional processing to obtain a switch tube duty cycle signal.

[0130] In the embodiment of the present invention, the third difference input proportional controller is used for proportional processing. The purpose of this step is to make the inductor current follow the current command value (i.e., the first sum value i ref = i ref1 +i ref2 ) changes, and the switch tube duty cycle signal d is obtained.

[0131] In a specific implementation, to facilitate the implementation of the method, the process of step 105 can be converted into a formula encapsulation form, wherein the expression of the switch tube duty cycle signal can be as follows:

[0132]

[0133] Where, Indicates the duty cycle signal of the first switch tube S1, is the size of the proportional coefficient, represents the inductor current.

[0134] Step 106 : Pulse width modulation is performed on the switch duty cycle signal, and based on the modulation result, the switch in the three-level topology active filter is driven to be turned on and off, thereby controlling the filter inductor to inject a compensation current for ripple filtering into the low-voltage DC power supply system.

[0135] Furthermore, the switch tube includes a first switch tube, a second switch tube, a third switch tube, and a fourth switch tube. Step 106 may include the following sub-steps:

[0136] S51. Perform pulse width modulation on the switch tube duty cycle signal to obtain a modulation result.

[0137] It should be noted that in a three-level active filter, the on-off relationship of the four switches is as follows: d represents the duty cycle of the first switch S1, 1-d represents the duty cycle of the fourth switch S4, the second switch S2 and the first switch S1 are turned on in a complementary manner, and the third switch S3 and the fourth switch S4 are turned on in a complementary manner. Once the duty cycle d of the first switch S1 is determined, PWM modulation can be used to generate the four modulation waves that control the on and off of the four switches.

[0138] In the embodiment of the present invention, the proportional controller K of the inner current loop is used. p After that, d is obtained and the duty cycle signal of the switch tube is pulse-width modulated, using the PWM modulation process of carrier phase shift control:

[0139] The first switch tube S1 and the second switch tube S2 are disconnected

[0140] The duty cycle signal d of the first switch S1 is compared with the periodic triangular carrier 1 (the period is the switching frequency). If the duty cycle signal d of the first switch S1 is greater than the triangular carrier 1, the first switch S1 is turned on. Because the second switch S2 is complementary to the first switch S1, when the first switch S1 is turned on, the second switch S2 is turned off.

[0141] The third switch tube S3 and the fourth switch tube S4 are disconnected

[0142] The aforementioned 1-d represents the duty cycle of the fourth switch S4. This control can be achieved through carrier phase-shift control. Similarly, the duty cycle signal d of the first switch S1 is compared with the periodic triangular carrier 2, but here the phase of triangular carrier 2 is opposite to that of triangular carrier 1. If the duty cycle signal d of the first switch S1 is greater than the phase of triangular carrier 2, the fourth switch S4 is turned on. Because the third and fourth switches S3 and S4 are complementary, when the fourth switch S4 is turned on, the third switch S3 is turned off.

[0143] S52. When the modulation result shows that the first switch tube and the fourth switch tube are turned on and the second switch tube and the third switch tube are turned off, a voltage is applied to the filter inductor through the first high-side voltage-dividing capacitor, the second high-side voltage-dividing capacitor and the compensation voltage in the three-level topology active filter to generate a compensation current.

[0144] In an embodiment of the present invention, a PWM modulated signal is input into a three-level topology active filter to drive the first switch tube and the fourth switch tube to turn on, and the second switch tube and the third switch tube to turn off. In the Buck working state, a voltage is applied to both ends of the filter inductor through the high-potential output end of the first high-voltage side voltage divider capacitor, the second high-voltage side voltage divider capacitor and the compensation capacitor, thereby causing the inductive current of the filter inductor to change, thereby generating a compensation current. In the Boost working state, a voltage is also applied to both ends of the filter inductor through the first high-voltage side voltage divider capacitor, the second high-voltage side voltage divider capacitor and the compensation voltage, thereby causing the inductive current of the filter inductor to change, thereby generating a compensation current. However, at this time, the compensation current is continued through the anti-parallel diode of the first switch tube and the fourth switch tube.

[0145] S53 . When the modulation result shows that the first switch tube and the fourth switch tube are turned off and the second switch tube and the third switch tube are turned on, apply a voltage to the filter inductor through the compensation voltage to generate a compensation current.

[0146] In an embodiment of the present invention, a PWM modulated signal is input into a three-level topology active filter to drive the first switch tube and the fourth switch tube to be turned off, and the second switch tube and the third switch tube to be turned on. In the Boost working state, a voltage is applied to both ends of the filter inductor through the low-potential output end where the compensation voltage is located, thereby causing the inductive current of the filter inductor to change, thereby generating a compensation current. In the Buck working state, a voltage is also applied to both ends of the filter inductor through the compensation capacitor, thereby causing the inductive current of the filter inductor to change, but at this time, the compensation current is freewheeling through the anti-parallel diodes of the second switch tube and the third switch tube.

[0147] A voltage is applied to the filter inductor through the compensation capacitor in the three-level topology active filter, which causes the inductor current of the filter inductor to change, thereby generating a compensation current. The change trend of the compensation current at this time is that the negative current increases or the positive current decreases.

[0148] S54. When the modulation result shows that the first switch tube and the third switch tube are turned on and the second switch tube and the fourth switch tube are turned off, a voltage is applied to the filter inductor through the first high-voltage side voltage divider capacitor and the compensation voltage until the inductor current reaches the preset command current, and the inductor current is used as the compensation current.

[0149] In an embodiment of the present invention, a PWM modulated signal is input into a three-level topology active filter, driving the first and third switches to conduct, and the second and fourth switches to shut down. In the Boost operating mode, the first and third switches form a path for freewheeling through the anti-parallel diodes. At this time, the second switch is turned off, so the current can only pass through the anti-parallel diode of the first switch, then through the first high-voltage side voltage divider capacitor, the compensation capacitor, and the anti-parallel diode of the third switch to complete a freewheeling loop until the inductor current reaches the preset command current, at which point the inductor current is used as the compensation current. In the Buck operating mode, the current is initially in the forward direction, and the first switch is turned on, so the current flows from the first switch. However, when the fourth switch is turned off, the current flows to the anti-parallel diode of the third switch, then through the first high-voltage side voltage divider capacitor to the left end of the first switch, completing a freewheeling loop until the inductor current reaches the preset command current, at which point the inductor current is used as the compensation current.

[0150] S55. When the modulation result is that the first switch tube and the third switch tube are turned off and the second switch tube and the fourth switch tube are turned on, a voltage is applied to the filter inductor through the second high-voltage side voltage divider capacitor and the compensation voltage until the inductor current reaches the preset command current, and the inductor current is used as the compensation current.

[0151] In an embodiment of the present invention, a PWM modulated signal is input into a three-level topology active filter to drive the first and third switch tubes to turn off, and the second and fourth switch tubes to turn on. In the Buck working state, the fourth switch tube, the second high-voltage side voltage-dividing capacitor and the anti-parallel diode of the second switch tube form a freewheeling path. At this time, the fourth switch tube is turned on, and the current flows into the anti-parallel diode of the fourth switch tube. Since the first switch tube is turned off, the current can only pass through the second high-voltage side voltage-dividing capacitor, pass through the compensation capacitor, and then pass through the anti-parallel diode of the second switch tube to complete a freewheeling path. A freewheeling loop is formed until the inductor current reaches the preset command current, at which point the inductor current is used as the compensation current. In the Boost working state, the second switch tube, the second high-voltage side voltage-dividing capacitor, and the anti-parallel diode of the fourth switch tube form a freewheeling path. At this time, the second switch tube is turned on, and current flows from the second switch tube. Since the third switch tube is turned off, the current flows in through the anti-parallel diode of the fourth switch tube. After passing through the second high-voltage side voltage-dividing capacitor, the current flows through the anti-parallel diode of the second switch tube to complete a freewheeling loop until the inductor current reaches the preset command current, at which point the inductor current is used as the compensation current.

[0152] S56. Inject the compensation current into the low-voltage DC power supply system to filter the ripple.

[0153] In the embodiment of the present invention, a compensation current is injected into the low-voltage DC power supply system to interact with the ripple component to filter the ripple and improve the power quality of the system.

[0154] It should be noted that by adjusting the on / off states of switches S1-S4 in real time, the three-level active filter can output a compensation current. Once injected into the low-voltage DC power supply system, this compensation current offsets the ripple in the DC bus, making the low-voltage DC power supply system current closer to a sine wave and in phase with the low-voltage DC power supply system voltage, thus achieving the active filtering purpose of filtering out ripple.

[0155] It is worth mentioning that through the control of the above process, the DC bus voltage V dc The effect of controlling the ripple to zero is essentially to transfer the ripple fluctuation of the DC bus voltage to the APF. It is worth mentioning that both the ripple generated by the DC bus due to the distortion of the upstream AC grid and the ripple current of the load-side harmonic source can be filtered out by the active DC filtering method of the present invention.

[0156] The following is a simulation test example:

[0157] See also Figure 6, build a simulation model of a low-voltage DC power supply system and a three-level topology active filter. In the simulation model, the AC grid voltage contains 5 positive and negative sequence harmonics at 1s, and the load-side harmonic source generates 2nd ripples. At 2s, the three-level topology active filter is added, and the simulation waveform of the DC bus voltage is as follows: Figure 6 As shown in the figure, it can be seen that when the ripple current is generated by the distortion of the AC power grid and the harmonic source load at the previous stage, it will cause large ripple fluctuations on the DC bus voltage. After adding the DC active filter device designed by the present invention, the ripple fluctuations of the DC bus voltage are basically filtered out.

[0158] The present invention has the following advantages:

[0159] (1) The present invention connects a three-level topology active filter in parallel with a low-voltage DC power supply system. In the three-level topology, the voltage borne by the switch tube is only half of the DC bus voltage. Compared with the two-level topology where the switch tube bears the entire DC bus voltage, this greatly reduces the voltage stress of the switch tube, allowing the switch tube to select a device with a lower withstand voltage rating, thereby improving the reliability of the system and reducing the cost and difficulty of heat dissipation design.

[0160] (2) In some industrial scenarios, when the load changes significantly, the bus voltage will fluctuate accordingly. If the reference voltage of the compensation capacitor cannot keep up with the change, there will be a certain deviation between the actual voltage of the compensation capacitor and the expected reference value, which will affect the ripple compensation accuracy of the active filter. The present invention dynamically generates reference voltages under different working conditions by presetting the working condition proportional coefficient. Compared with the traditional method of using a fixed reference voltage, the present invention can be applied to complex and changeable power grid working conditions. At the same time, the deviation between the sampled compensation voltage of the compensation capacitor and the reference voltage is processed by the proportional-integral controller, which can more accurately adjust the compensation capacitor voltage, improve the compensation accuracy, and thus effectively reduce the ripple content in the power grid.

[0161] (3) The existing DC active filtering scheme adopts a structure that first passes through a proportional controller and then enters a proportional resonant controller. Since the proportional controller is in front, it will amplify or reduce the signal input to the proportional resonant controller. When the system is subject to external interference or the parameters change to a certain extent, this signal scaling may cause the output of the proportional resonant controller to fluctuate greatly, thereby affecting the stability of the entire system. The present invention first processes the input signal through a proportional resonant controller, which itself has good anti-interference ability and can suppress the interference in the input signal to a certain extent. After that, it passes through the proportional controller, which makes adjustments based on a relatively stable control signal, so that the system is more stable when facing external interference or parameter changes. At the same time, the existing structure that first passes through the proportional controller and then enters the proportional resonant controller may change the original characteristics of the ripple signal when processing complex ripple components, so that the subsequent proportional resonant controller’s ripple suppression effect is affected, reducing the ripple suppression capability. The present invention first performs precise processing through the proportional resonant controller, which can better perform separate zero-static tracking and control for different ripples, more accurately extract and process the signal components related to the ripple, and then perform appropriate scaling adjustment through the proportional controller, so that the final output control signal is more accurate, improving the ripple compensation accuracy, and also enabling the active filter to more effectively suppress multiple ripple components, significantly improving the ripple suppression capability.

[0162] (4) Based on the scenario where the three-level topology active filter is connected to the low-voltage DC power supply system, the three-level topology active filter of the present invention can drive the switching of the switch tube according to different modulation results, flexibly control the filter inductor to generate compensation current, and finally make the compensation current injected into the low-voltage DC power supply system more effectively filter the ripple, significantly improving the ability to suppress the ripple in the system. In addition, the three-level topology active filter of the present invention also involves a freewheeling control, which can ensure that the inductor current stably and efficiently tracks the preset instruction current, reduce current fluctuations and energy loss in the transition process, and improve the working efficiency of the three-level topology active filter.

[0163] See also Figure 7 , Figure 7 This is a structural block diagram of a DC active filter system connected to a low-voltage DC power supply system based on a three-level topology provided in the second embodiment of the present invention.

[0164] The present invention provides a DC active filter system based on a three-level topology connected to a low-voltage DC power supply system. The three-level topology active filter is connected in parallel with the low-voltage DC power supply system, comprising:

[0165] The first processing module 701 is configured to detect a DC bus voltage of a low-voltage DC power supply system, filter the DC bus voltage, and determine a DC bus voltage ripple based on the filtering result and the DC bus voltage;

[0166] The second processing module 702 is configured to determine a first current command value based on the DC bus voltage ripple in combination with a proportional resonant controller when the DC bus voltage ripple is not equal to zero;

[0167] The third processing module 703 is configured to perform a multiplication operation on the DC bus voltage and a preset operating condition proportional coefficient to generate a reference voltage;

[0168] The fourth processing module 704 is configured to detect a compensation voltage of a compensation capacitor in the three-level topology active filter, and determine a second current command value based on the compensation voltage and a reference voltage in combination with a proportional-integral controller;

[0169] a fifth processing module 705 configured to detect an inductor current of a filter inductor in a three-level topology active filter, and determine a switch duty cycle signal based on the inductor current, the first current command value, and the second current command value in conjunction with a proportional controller;

[0170] The sixth processing module 706 is configured to perform pulse width modulation on the switch duty cycle signal, and drive the switching of the switch in the three-level topology active filter based on the modulation result, thereby controlling the filter inductor to inject a compensation current into the low-voltage DC power supply system for ripple filtering.

[0171] Furthermore, the first processing module 701 includes:

[0172] DC bus voltage submodule, used to detect the DC bus voltage of the low-voltage DC power supply system;

[0173] The filter voltage submodule is used to filter the DC bus voltage through a low-pass filter to obtain a filtered voltage;

[0174] The DC bus voltage ripple submodule is used to perform a difference operation between the DC bus voltage and the filtered voltage to obtain the DC bus voltage ripple.

[0175] Furthermore, the second processing module 702 includes:

[0176] A first difference submodule is configured to perform a difference operation between the DC bus voltage ripple and a preset voltage ripple reference value to obtain a first difference when the DC bus voltage ripple is not equal to zero;

[0177] The first current command value submodule is used to use the first difference input proportional resonant controller to perform ripple compensation to obtain a first current command value.

[0178] Furthermore, the fourth processing module 704 includes:

[0179] The compensation voltage submodule is used to detect the compensation voltage of the compensation capacitor in the three-level topology active filter;

[0180] A second difference submodule, configured to perform a difference operation on the reference voltage and the compensation voltage to obtain a second difference;

[0181] The second current command value submodule is used to use the second difference value to input the proportional-integral controller to perform proportional-integral processing to obtain the second current command value.

[0182] Furthermore, the fifth processing module 705 includes:

[0183] The inductor current submodule is used to detect the inductor current of the filter inductor in the three-level topology active filter;

[0184] A first sum submodule, configured to perform a sum operation using the first current command value and the second current command value to obtain a first sum;

[0185] a third difference submodule, configured to perform a difference operation on the first sum and the inductor current to obtain a third difference;

[0186] The switch tube duty cycle signal submodule is used to use the third difference input proportional controller to perform proportional processing to obtain the switch tube duty cycle signal.

[0187] Furthermore, the switch tube includes a first switch tube, a second switch tube, a third switch tube, and a fourth switch tube, and the sixth processing module 706 includes:

[0188] The pulse width modulation submodule is used to perform pulse width modulation on the switch tube duty cycle signal to obtain a modulation result;

[0189] a first modulation result output submodule, configured to apply a voltage to the filter inductor via the first high-side voltage-dividing capacitor, the second high-side voltage-dividing capacitor, and the compensation voltage in the three-level topology active filter to generate a compensation current when the modulation result indicates that the first and fourth switching tubes are turned on and the second and third switching tubes are turned off;

[0190] a second modulation result output submodule, configured to apply a voltage to the filter inductor via a compensation voltage to generate a compensation current when the modulation result indicates that the first switch tube and the fourth switch tube are turned off and the second switch tube and the third switch tube are turned on;

[0191] a third modulation result output submodule, configured to, when the modulation result indicates that the first and third switching tubes are turned on and the second and fourth switching tubes are turned off, apply a voltage to the filter inductor via the first high-voltage side voltage divider capacitor and the compensation voltage until the inductor current reaches a preset command current, and then use the inductor current as the compensation current;

[0192] a fourth modulation result output submodule, configured to, when the modulation result indicates that the first and third switching tubes are turned off and the second and fourth switching tubes are turned on, apply a voltage to the filter inductor via the second high-voltage side voltage divider capacitor and the compensation voltage until the inductor current reaches a preset command current, and then use the inductor current as the compensation current;

[0193] The injection submodule is used to inject the compensation current into the low-voltage DC power supply system for ripple filtering.

[0194] See also Figure 8 , Figure 8 This is a structural block diagram of a computer device provided in Example 3 of the present invention.

[0195] An electronic device according to an embodiment of the present invention includes: a memory 801 and a processor 802, wherein the memory 801 stores a computer program; when the computer program is executed by the processor 802, the processor 802 executes a DC active filtering method for connecting a low-voltage DC power supply system based on a three-level topology as described in any of the above embodiments.

[0196] Memory 801 can be an electronic memory such as flash memory, EEPROM (Electrically Erasable Programmable Read-Only Memory), EPROM, hard disk, or ROM. Memory 801 has storage space 803 for program code 813 for executing any of the method steps described above. For example, storage space 803 for program code can include individual program codes 813 for implementing various steps in the method described above. These program codes can be read from or written to one or more computer program products. These computer program products include program code carriers such as hard disks, compact disks (CDs), memory cards, or floppy disks. The program codes can be compressed, for example, in a suitable format. When executed by a processing device, these codes cause the processing device to execute the various steps in the method described above. These program codes can be read from or written to one or more computer program products. These computer program products include program code carriers such as hard disks, compact disks (CDs), memory cards, or floppy disks. The program codes can be compressed, for example, in a suitable format. When these codes are executed by a computing and processing device, they cause the computing and processing device to execute the steps of the above-described DC active filtering method for connecting a low-voltage DC power supply system based on a three-level topology.

[0197] Embodiment 4 of the present invention further provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method for active DC filtering of a low-voltage DC power supply system connected based on a three-level topology as described in any of the above embodiments is implemented.

[0198] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0199] In the several embodiments provided in this application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely schematic. For example, the division of units is only a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interface, device or unit, which can be electrical, mechanical or other forms.

[0200] Units described as separate components may or may not be physically separate, and components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0201] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0202] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the various embodiments of the method of the present invention. The aforementioned storage medium includes various media that can store program code, such as USB flash drives, mobile hard drives, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical disks.

[0203] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A DC active filtering method based on a three-level topology connected to a low-voltage DC power supply system, characterized in that: The three-level topology active filter is connected in parallel with the low-voltage DC power supply system and includes: detecting a DC bus voltage of the low-voltage DC power supply system, filtering the DC bus voltage, and determining a DC bus voltage ripple based on a filtering result and the DC bus voltage; When the DC bus voltage ripple is not equal to zero, determining a first current command value according to the DC bus voltage ripple in combination with a proportional resonant controller; Performing a multiplication operation on the DC bus voltage and a preset operating condition proportional coefficient to generate a reference voltage; Detecting a compensation voltage of a compensation capacitor in the three-level topology active filter, and determining a second current command value based on the compensation voltage and the reference voltage in combination with a proportional-integral controller; detecting an inductor current of a filter inductor in the three-level topology active filter, and determining a switch tube duty cycle signal in combination with a proportional controller according to the inductor current, the first current command value, and the second current command value; Pulse width modulation is performed on the switch tube duty cycle signal, and based on the modulation result, the switch tube in the three-level topology active filter is driven to be turned on and off, and the filter inductor is controlled to inject a compensation current for ripple filtering into the low-voltage DC power supply system.

2. The DC active filtering method based on a three-level topology connection low-voltage DC power supply system according to claim 1, characterized in that: The detecting the DC bus voltage of the low-voltage DC power supply system, filtering the DC bus voltage, and determining the DC bus voltage ripple based on the filtering result and the DC bus voltage includes: Detecting the DC bus voltage of the low-voltage DC power supply system; Filtering the DC bus voltage through a low-pass filter to obtain a filtered voltage; A difference operation is performed between the DC bus voltage and the filtered voltage to obtain a DC bus voltage ripple.

3. The DC active filtering method based on a three-level topology connection low-voltage DC power supply system according to claim 1, characterized in that: When the DC bus voltage ripple is not equal to zero, determining the first current command value according to the DC bus voltage ripple in combination with a proportional resonant controller includes: When the DC bus voltage ripple is not equal to zero, performing a difference operation between the DC bus voltage ripple and a preset voltage ripple reference value to obtain a first difference; The first difference is input into a proportional resonant controller to perform ripple compensation to obtain a first current command value.

4. The DC active filtering method based on a three-level topology connection low-voltage DC power supply system according to claim 1, characterized in that: The detecting the compensation voltage of the compensation capacitor in the three-level topology active filter and determining the second current command value according to the compensation voltage and the reference voltage in combination with a proportional-integral controller includes: Detecting a compensation voltage of a compensation capacitor in the three-level topology active filter; performing a difference operation on the reference voltage and the compensation voltage to obtain a second difference; The second difference is input into a proportional-integral controller for proportional-integral processing to obtain a second current command value.

5. The DC active filtering method based on a three-level topology connection low-voltage DC power supply system according to claim 1, characterized in that: The detecting the inductor current of the filter inductor in the three-level topology active filter and determining the switch tube duty cycle signal in combination with a proportional controller according to the inductor current, the first current command value, and the second current command value include: Detecting the inductor current of the filter inductor in the three-level topology active filter; performing a sum operation on the first current command value and the second current command value to obtain a first sum value; performing a difference operation on the first sum and the inductor current to obtain a third difference; The third difference is input into the proportional controller for proportional processing to obtain a switch tube duty cycle signal.

6. The DC active filtering method for connecting a low-voltage DC power supply system based on a three-level topology according to any one of claims 1 to 5, characterized in that: The switching tubes include a first switching tube, a second switching tube, a third switching tube, and a fourth switching tube. Pulse width modulation is performed on the switching tube duty cycle signals, and based on the modulation results, the switching tubes in the three-level topology active filter are driven to be turned on and off, thereby controlling the filter inductor to inject a compensation current for ripple filtering into the low-voltage DC power supply system. The method includes: Performing pulse width modulation on the switch tube duty cycle signal to obtain a modulation result; When the modulation result shows that the first switch tube and the fourth switch tube are turned on, and the second switch tube and the third switch tube are turned off, a voltage is applied to the filter inductor via the first high-side voltage-dividing capacitor, the second high-side voltage-dividing capacitor and the compensation voltage in the three-level topology active filter to generate a compensation current; When the modulation result is that the first switch tube and the fourth switch tube are turned off, and the second switch tube and the third switch tube are turned on, applying a voltage to the filter inductor through the compensation voltage to generate a compensation current; When the modulation result shows that the first switch tube and the third switch tube are turned on, and the second switch tube and the fourth switch tube are turned off, a voltage is applied to the filter inductor through the first high-side voltage divider capacitor and the compensation voltage until the inductor current reaches a preset command current, and the inductor current is used as the compensation current; When the modulation result shows that the first switch tube and the third switch tube are turned off, and the second switch tube and the fourth switch tube are turned on, a voltage is applied to the filter inductor through the second high-voltage side voltage divider capacitor and the compensation voltage until the inductor current reaches a preset command current, and the inductor current is used as the compensation current; The compensation current is injected into the low-voltage DC power supply system to perform ripple filtering.

7. A DC active filter system based on a three-level topology connected to a low-voltage DC power supply system, characterized in that: The three-level topology active filter is connected in parallel with the low-voltage DC power supply system and includes: a first processing module, configured to detect a DC bus voltage of the low-voltage DC power supply system, filter the DC bus voltage, and determine a DC bus voltage ripple based on a filtering result and the DC bus voltage; a second processing module, configured to determine a first current command value according to the DC bus voltage ripple in combination with a proportional resonant controller when the DC bus voltage ripple is not equal to zero; a third processing module, configured to perform a multiplication operation on the DC bus voltage and a preset operating condition proportional coefficient to generate a reference voltage; a fourth processing module, configured to detect a compensation voltage of a compensation capacitor in the three-level topology active filter, and determine a second current command value based on the compensation voltage and the reference voltage in combination with a proportional-integral controller; a fifth processing module, configured to detect an inductor current of a filter inductor in the three-level topology active filter, and determine a switch duty cycle signal based on the inductor current, the first current command value, and the second current command value in combination with a proportional controller; The sixth processing module is used to perform pulse width modulation on the switch tube duty cycle signal, and drive the switching of the switch tube in the three-level topology active filter based on the modulation result, and control the filter inductor to inject a compensation current for ripple filtering into the low-voltage DC power supply system.

8. An electronic device, characterized in that: The method comprises a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor performs the steps of the DC active filtering method for connecting a low-voltage DC power supply system based on a three-level topology according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed, the method for active DC filtering of a low-voltage DC power supply system connected based on a three-level topology is implemented as described in any one of claims 1 to 6.

10. A computer program product, characterized in that The computer program product includes a computer program stored on a non-transitory computer-readable storage medium, wherein the computer program includes program instructions. When the program instructions are executed by a computer, the computer is caused to perform the DC active filtering method for connecting a low-voltage DC power supply system based on a three-level topology according to any one of claims 1 to 6.

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