A control method and device for a passive filter and a passive filter

Abstract

The present invention discloses a control method and device of a passive filter and a passive filter, which relate to the field of harmonic processing, including determining the number of converters in a startup state; determining the current of an AC bus when the converter is started; determining the equivalent harmonic frequencies of multiple converters according to the number of converters in a startup state; determining the filter components put into use by the passive filter according to the equivalent harmonic frequencies and the current of the AC bus, and controlling the passive filter to put the determined filter components into use. The filter components put into use, i.e., capacitors, resistors and inductors, are determined according to the number of converters connected to the AC bus and the current of the AC bus, and the filter components themselves are adjusted as the AC bus actually changes, and adjusted as the converter changes, so as to achieve better filtering of harmonics.

Description

Technical Field

[0001] The present invention relates to the field of harmonic processing, and in particular to a control method and device for a passive filter and a passive filter. Background Art

[0002] Due to the modular, standardized, and serialized application of converters, products such as energy storage, wind power, and energy feedback use multiple converters in parallel operation. When the converters are operated in parallel, carrier phase shifting technology can be used to cancel switching harmonics to offset the harmonics generated by the converter itself, and ultimately convert them into higher-order harmonics, so that they can be filtered out using a passive filter with a smaller capacity. When a converter exits operation due to a fault, the carrier phase shift angle will change, and the equivalent high-order harmonic frequency will also change. At this time, it is necessary to adjust the passive filter cutoff frequency and the input ratio of resistance, inductance, and capacitance. In the related technology, the cutoff frequency of the passive filter and the input ratio of resistance, inductance, and capacitance are fixed and cannot be adjusted with changes in the converter, resulting in harmonic amplification. Summary of the invention

[0003] The purpose of the present invention is to provide a control method and device of a passive filter and a passive filter, which determine the filter components, namely, capacitors, resistors and inductors, according to the number of converters connected to an AC bus and the current of the AC bus, adjust the filter components themselves as the AC bus actually changes, and adjust as the converter changes, so as to achieve better filtering of harmonics.

[0004] In order to solve the above technical problems, the present invention provides a control method for a passive filter, wherein the passive filter is connected to an AC bus, the input ends of a plurality of converters are respectively connected to a DC power supply, and the output ends of the plurality of converters are all connected to the AC bus, comprising:

[0005] determining the number of said converters in an activated state;

[0006] determining the current of the AC bus when the converter is started;

[0007] Determining the equivalent harmonic frequencies of a plurality of the converters according to the number of the converters in the startup state;

[0008] Determine the filter device used in the passive filter according to the equivalent harmonic frequency and the current of the AC bus, wherein the filter device includes at least two of a capacitor, a resistor and an inductor;

[0009] The passive filter is controlled to put the determined filter component into operation.

[0010] In another aspect, determining the number of the converters in the startup state includes:

[0011] Determining whether a switch signal sent when a start switch of the converter is closed is received, wherein the start switch corresponds to the converter in a one-to-one manner;

[0012] If the switch signal is received, it is determined that the start switch is closed and the converter is in the start state.

[0013] In another aspect, determining the number of the converters in the startup state includes:

[0014] Sending a first communication signal to each of the converters respectively;

[0015] receiving a second communication signal returned by the converter after receiving the first communication signal;

[0016] The number of the received second communication signals is determined, and the number of the second communication signals is used as the number of the converters in the startup state.

[0017] On the other hand, determining the equivalent harmonic frequencies of a plurality of the converters according to the number of the converters in the startup state comprises:

[0018] Determining the switching frequency of each of the converters;

[0019] Determine the equivalent harmonic frequencies of the plurality of converters according to an equivalent harmonic frequency relationship, the switching frequency of the converter and the number of the converters in a startup state;

[0020] The equivalent harmonic frequency relationship is fs=n×fsw, fs is the equivalent harmonic frequency, n is the number of the converters in the startup state, and fsw is the switching frequency of the converter.

[0021] On the other hand, determining the filter device used in the passive filter according to the equivalent harmonic frequency and the current of the AC bus includes:

[0022] Determining the number of filter components used in the passive filter according to the equivalent harmonic frequency, the current of the AC bus, the input resistance relationship, the input capacitance relationship, and the input inductance relationship;

[0023] Among them, the input resistance relationship is R=Uh / Ih, the input capacitance relationship is C=1 / 2π(fs×R), the input inductance relationship is L=R / 2πfs, Uh is the effective value of the equivalent high-frequency harmonic voltage, Ih is the effective value of the current of the AC bus, fs is the equivalent harmonic frequency, R is the resistance value of the passive filter, C is the capacitance value of the passive filter, and L is the inductance value of the passive filter.

[0024] On the other hand, the passive filter includes a plurality of groups of filter modules, wherein the plurality of groups of filter modules are connected in parallel, and each group of filter modules includes a resistor, b capacitor, c inductor and a+b+c switches, wherein a, b and c are all integers greater than 1, and the a switches are respectively connected in parallel with the a resistors in a one-to-one correspondence, and the b switches are respectively connected in series with the b capacitors in a one-to-one correspondence, and the c switches are respectively connected in parallel with the c inductors in a one-to-one correspondence, and the a switches, the b switches and the c switches are all different switches, and the a resistors in each filter module are connected in sequence, the first end of the first resistor is connected to the AC bus, the second end of the a resistor is respectively connected to the first end of the b capacitors and the first end of the first inductor, and the c inductors are connected in sequence, and the second ends of the b capacitors are all connected to the second end of the c inductor;

[0025] Controlling the passive filter to input the determined filter device comprises:

[0026] Controlling the switch corresponding to the determined resistor to be disconnected, so as to switch the determined resistor on;

[0027] Controlling a switch corresponding to the determined capacitance to close so as to put the determined capacitance into operation;

[0028] Controlling the switch corresponding to the determined inductance to be disconnected to switch the determined inductance on;

[0029] Determining whether a feedback signal after the switch action is received;

[0030] If the feedback signal is received, it is determined that the passive filter is controlled to successfully put the determined filter component into operation.

[0031] In order to solve the above technical problems, the present invention also provides a control device for a passive filter, comprising:

[0032] Memory for storing computer programs;

[0033] A processor is used to implement the steps of the above-mentioned passive filter control method when executing the computer program.

[0034] In order to solve the above technical problem, the present invention further provides a passive filter, including the above passive filter control device and a passive filter body.

[0035] On the other hand, the passive filter body includes a plurality of groups of filter modules, and the plurality of groups of filter modules are connected in parallel. Each group of filter modules includes a resistor, b capacitor, c inductor and a+b+c switches, a, b and c are integers greater than 1, a switches are respectively connected in parallel with a resistor in a one-to-one correspondence, b switches are respectively connected in series with b capacitors in a one-to-one correspondence, c switches are respectively connected in parallel with c inductors in a one-to-one correspondence, and a switch, b switches and c switches are all different switches;

[0036] The a resistors in each filter module are connected in sequence, the first end of the first resistor is connected to the AC bus, the second end of the a resistor is respectively connected to the first end of the b capacitors and the first end of the first inductor, and the c inductors are connected in sequence, and the second ends of the b capacitors are all connected to the second end of the c inductor;

[0037] The resistor, the capacitor and the inductor are used to filter the harmonics on the AC bus. For any resistor, when the switch corresponding to the resistor is disconnected, the resistor is turned on. For any capacitor, when the switch corresponding to the capacitor is closed, the capacitor is turned on. For any inductor, when the switch corresponding to the inductor is disconnected, the inductor is turned on.

[0038] In another aspect, the switch is a relay;

[0039] The power gain and loss control end of the loop where the coil of the relay is located is connected to the processor of the control device of the passive filter, the contacts of a relays are respectively connected in parallel with a resistors in a one-to-one correspondence, the contacts of b relays are respectively connected in series with b capacitors in a one-to-one correspondence, the contacts of c relays are respectively connected in parallel with c inductors in a one-to-one correspondence, and a relay, b relays and c relays are all different relays;

[0040] The coil of the relay a is used to switch the resistor on when power is off, the coil of the relay b is used to switch the capacitor on when power is on, and the coil of the relay c is used to switch the inductor on when power is off.

[0041] The present invention discloses a control method and device of a passive filter and a passive filter, which relate to the field of harmonic processing, including determining the number of converters in a startup state; determining the current of an AC bus when the converter is started; determining the equivalent harmonic frequencies of multiple converters according to the number of converters in a startup state; determining the filter components put into the passive filter according to the equivalent harmonic frequencies and the current of the AC bus, and controlling the passive filter to put the filter components into use. The filter components put into use, i.e., capacitors, resistors and inductors, are determined according to the number of converters connected to the AC bus and the current of the AC bus, and the filter components themselves are adjusted as the AC bus actually changes, and adjusted as the converter changes, so as to achieve better filtering of harmonics. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the prior art and the drawings required for use in the embodiments are briefly introduced below. 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 creative work.

[0043] Figure 1 A flow chart of a control method for a passive filter provided by the present invention;

[0044] Figure 2 A schematic structural diagram of a current conversion module, an AC bus and a passive filter provided by the present invention;

[0045] Figure 3 A schematic diagram of the structure of a passive filter provided by the present invention;

[0046] Figure 4 A schematic structural diagram of a control device for a passive filter provided by the present invention. DETAILED DESCRIPTION

[0047] The core of the present invention is to provide a control method and device of a passive filter and a passive filter, which determines the filter components, namely, capacitors, resistors and inductors, according to the number of converters connected to the AC bus and the current of the AC bus, adjusts its own filter components as the AC bus actually changes, and adjusts as the converter changes, so as to achieve better filtering of harmonics.

[0048] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution 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 described embodiments are 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 creative work are within the scope of protection of the present invention.

[0049] Figure 1 A flowchart of a control method for a passive filter provided by the present invention, Figure 2 A schematic structural diagram of a current conversion module, an AC bus and a passive filter provided by the present invention;

[0050] The passive filter is connected to the AC bus, the input ends of the multiple converters are respectively connected to the DC power supply, and the output ends of the multiple converters are all connected to the AC bus. The control method of the passive filter includes:

[0051] S11: Determine the number of converters in a startup state;

[0052] S12: determining the current of the AC bus when the converter is started;

[0053] Due to the modular, standardized and serialized application of converters, products such as energy storage, wind power and energy feedback mostly use multiple modules in parallel operation. When the modules are operated in parallel, carrier phase shifting technology can be used to cancel switching harmonics to offset the harmonics generated by the converter modules themselves, and ultimately convert them into higher-order harmonics, which can be filtered out using smaller capacity passive filters.

[0054] It should be noted that the passive filter is connected to the AC bus PCC (Point of Common Coupling) grid connection point.

[0055] However, when a module fails and stops running, the carrier phase shift angle will change, and the equivalent high-order harmonic frequency will also change. At this time, it is necessary to adjust the passive filter cutoff frequency and the input ratio of resistance, inductance, and capacitance. In addition, when the load current of the converter module changes, the capacity demand of the passive filter device that needs to be invested will also change.

[0056] Traditional passive filter cutoff frequency designs are calculated based on when all carrier phase-shift converters are fully operational. However, when the converter is switched off, the phase-shift angle needs to change. At this time, the equivalent switching subharmonic frequency has changed, and the RCL ratio of the passive filter needs to be readjusted, otherwise harmonic amplification may occur.

[0057] Therefore, when determining the number of passive filters to be put into operation, it is necessary to consider the number of converters in the startup state and the current of the AC bus.

[0058] S13: determining equivalent harmonic frequencies of a plurality of converters according to the number of converters in a startup state;

[0059] The topology of parallel connection of converters and grid-connected passive filters is as follows Figure 2 As shown. Multiple converters, i.e. converter modules, are operated in parallel, and the switching sub-high frequency harmonic cancellation between the converter modules is achieved through carrier phase shifting technology, so it is necessary to determine the equivalent harmonic frequencies of the multiple converters.

[0060] S14: Determine the filter components used in the passive filter according to the equivalent harmonic frequency and the current of the AC bus, where the filter components include at least two of a capacitor, a resistor and an inductor;

[0061] S15: Control the passive filter to put the determined filter components into operation.

[0062] Specifically, the RCL ratio of the passive filter, that is, the ratio of resistance, capacitance and inductance, needs to be determined according to the current and equivalent harmonic frequency of the AC bus.

[0063] The invention discloses a control method for a passive filter, which relates to the field of harmonic processing, including determining the number of converters in a startup state; determining the current of an AC bus when the converter is started; determining the equivalent harmonic frequencies of multiple converters according to the number of converters in a startup state; determining the filter components put into the passive filter according to the equivalent harmonic frequencies and the current of the AC bus, and controlling the passive filter to put the filter components into use. The filter components put into use, i.e., capacitors, resistors, and inductors, are determined according to the number of converters connected to the AC bus and the current of the AC bus, and the filter components themselves are adjusted as the AC bus actually changes, and adjusted as the converter changes, so as to achieve better filtering of harmonics.

[0064] Based on the above embodiments:

[0065] In some embodiments, determining the number of converters in an activated state includes:

[0066] Determine whether a switch signal sent when a start switch of the converter is closed is received, and the start switch corresponds to the converter one by one;

[0067] If the switch signal is received, it is determined that the start switch is closed and the converter is in the start state.

[0068] Specifically, when detecting the capacitance on the AC bus, it can be determined by setting a current sensor, and the processor obtains the current of the AC bus collected by the current sensor.

[0069] The number of converters in the startup state can be determined based on the startup switch of the converter. It is understandable that when the converter is started, the startup switch of the processor must be in a closed state. When the startup switch is closed, a switch signal is sent, and then the controller can determine that the converter is in the startup state.

[0070] In some embodiments, determining the number of converters in an activated state includes:

[0071] Sending a first communication signal to each converter respectively;

[0072] receiving a second communication signal returned by the converter after receiving the first communication signal;

[0073] The number of the received second communication signals is determined, and the number of the second communication signals is used as the number of the converters in the startup state.

[0074] In addition, the processor can also communicate with the converter. If the converter is in the startup state, the converter can communicate with the processor if there is no failure. Therefore, the processor sends a first communication signal to the converter. If the converter starts normally, it can reply with a second communication signal to the processor.

[0075] When counting the converters in the startup state, the processor only needs to count the number of received second communication signals.

[0076] In some embodiments, determining the equivalent harmonic frequencies of the plurality of converters according to the number of converters in a startup state comprises:

[0077] Determine the switching frequency of each converter;

[0078] Determining equivalent harmonic frequencies of multiple converters according to an equivalent harmonic frequency relationship, a switching frequency of the converter, and the number of converters in a startup state;

[0079] The equivalent harmonic frequency relationship is fs=n×fsw, fs is the equivalent harmonic frequency, n is the number of converters in the startup state, and fsw is the switching frequency of the converter.

[0080] The topology of parallel connection of converters and grid connection of passive filters is shown in the figure below. Multiple converter modules are operated in parallel, and the switching sub-high frequency harmonics between each converter module are cancelled through carrier phase shifting technology. The final switching sub-harmonic equivalent frequency is n×fsw, where fsw is the switching frequency of each converter module and n is the number of modules. The master control system calculates the carrier phase shift value for each converter module according to the number of converter units n put into operation, and the phase shift angle θ=360 / n. For example, when two modules are put into operation, the initial carrier angle difference is 180 degrees; when there are three modules, it is 120 degrees; when there are four modules, it is 90 degrees; and so on; at this time, the equivalent switching sub-high frequency harmonics will also change accordingly; according to the carrier phase shift ratio value and the number of working units n, the equivalent harmonic frequency of the switching sub-harmonics is calculated, fs=n×fsw.

[0081] In some embodiments, determining the filter device to be used in the passive filter according to the equivalent harmonic frequency and the current of the AC bus includes:

[0082] Determine the number of filter components used in the passive filter based on the equivalent harmonic frequency, the current of the AC bus, the input resistance relationship, the input capacitance relationship, and the input inductance relationship;

[0083] Among them, the input resistance relationship is R=Uh / Ih, the input capacitance relationship is C=1 / 2π(fs×R), the input inductance relationship is L=R / 2πfs, Uh is the effective value of the equivalent high-frequency harmonic voltage, Ih is the effective value of the current of the AC bus, fs is the equivalent harmonic frequency, R is the resistance value of the passive filter, C is the capacitance value of the passive filter, and L is the inductance value of the passive filter.

[0084] Through the equivalent harmonic frequency, the appropriate cut-off frequency can be selected. According to the cut-off frequency fs, the formula fs= , combined with the estimated harmonic content, R=Uh / Ih, where Uh is the equivalent high-frequency harmonic voltage effective value, Ih is the equivalent high-frequency harmonic current effective value, and in general, R is 0.1Uh considering the need for harmonic current filtering. In addition, based on R and fs, L and C can be calculated according to the formula, L=R / 2πfs, C=1 / 2π(fs×R). Calculate the inductance, capacitance, and resistance values, and then put them into the corresponding circuit through the relay.

[0085] Figure 3 A schematic diagram of the structure of a passive filter provided by the present invention;

[0086] In some embodiments, the passive filter includes multiple groups of filter modules, which are connected in parallel. Each group of filter modules includes a resistor, b capacitor, c inductor and a+b+c switches, where a, b and c are all integers greater than 1, a switch is respectively connected in parallel with a resistor in a one-to-one correspondence, b switches are respectively connected in series with b capacitors in a one-to-one correspondence, c switches are respectively connected in parallel with c inductors in a one-to-one correspondence, a switch, b switches and c switches are all different switches, a resistor in each filter module is connected in sequence, a first end of the first resistor is connected to the AC bus, a second end of the ath resistor is respectively connected to the first end of the b capacitors and the first end of the first inductor, c inductors are connected in sequence, and the second ends of the b capacitors are all connected to the second end of the cth inductor;

[0087] Controlling the passive filter will determine the filter components input, including:

[0088] Controlling the switch corresponding to the determined resistance to be disconnected, so as to switch the determined resistance on;

[0089] Controlling a switch corresponding to the determined capacitance to close so as to put the determined capacitance into operation;

[0090] Controlling the switch corresponding to the determined inductance to be disconnected so as to switch the determined inductance on;

[0091] Determine whether a feedback signal after a switch action is received;

[0092] If the feedback signal is received, it is determined that the passive filter is controlled to successfully put the determined filter component into operation.

[0093] In order to better realize the fault tolerance and redundancy of the passive filter, the passive filter adopts multiple groups in parallel, and each group can flexibly combine LCR values. The purpose is that multiple groups in parallel can determine the number of combinations required according to different load capacities. Each group of flexible combinations of resistors, capacitors, and inductors can achieve different LCR parameters under different equivalent switching frequencies. In each group, LC is connected in series to form a high-pass filter channel to filter out equivalent high-frequency switching subharmonics. The resistor is connected in series with LC to achieve a better quality factor.

[0094] Each resistor, capacitor and inductor corresponds to a switch, and each switch is only responsible for the input of the corresponding resistor, capacitor or inductor.

[0095] Specifically, the resistance, capacitance or inductance is controlled by closing the contacts of the control relay.

[0096] In actual applications, when the load current changes, the output current of each converter module will also change accordingly. At this time, the high-frequency switching harmonic content will also change. By sampling the load current, the passive filter input capacity requirement is calculated, and then the number of input paths is corrected.

[0097] Scenario 1: When the number of converter modules remains unchanged and the operating current decreases:

[0098] The rated current of the module is 100A, and the rated quantity is 4. When all are put into operation and run at full load, a total of 4 groups of passive filters are put into operation; when the load is reduced, the module only needs to work at 60A, and 4 modules are still put into operation. Since only the capacity changes now, fs does not change, the internal combination of RCL remains unchanged, but only 3 groups need to be put into operation to meet the filtering requirements;

[0099] Scenario 2: When the number of converter modules changes:

[0100] If only three modules are put into operation for energy saving and to reduce module loss, or a module fails, each module will be changed to 80A. In addition to the capacity change, fs also changes. It is necessary to readjust the RCL technical parameters according to the passive filter design formula and select the RCL value to be put into operation.

[0101] Figure 4 A schematic diagram of the structure of a control device for a passive filter provided by the present invention, the control device for the passive filter comprises:

[0102] A memory 41, used for storing computer programs;

[0103] The processor 42 is used to implement the steps of the above-mentioned passive filter control method when executing the computer program.

[0104] For an introduction to the control device of the passive filter provided in the present application, please refer to the above embodiments, which will not be described in detail here.

[0105] The present invention also provides a passive filter, comprising the above-mentioned passive filter control device and a passive filter body.

[0106] For an introduction to the passive filter provided in this application, please refer to the above embodiments, which will not be described in detail here.

[0107] Figure 3 A schematic diagram of the structure of a passive filter provided by the present invention, wherein the passive filter body comprises a plurality of filter modules, wherein the plurality of filter modules are connected in parallel, wherein each filter module comprises a resistor, b capacitor, c inductor and a+b+c switches, wherein a, b and c are integers greater than 1, wherein a switch is connected in parallel with a resistor in a one-to-one correspondence, b switches are connected in series with b capacitors in a one-to-one correspondence, c switches are connected in parallel with c inductors in a one-to-one correspondence, and a switch, b switches and c switches are all different switches;

[0108] The a resistors in each filter module are connected in sequence, the first end of the first resistor is connected to the AC bus, the second end of the ath resistor is respectively connected to the first end of the b capacitors and the first end of the first inductor, and the c inductors are connected in sequence, and the second ends of the b capacitors are all connected to the second end of the cth inductor;

[0109] Resistors, capacitors and inductors are used to filter harmonics on the AC bus. For any resistor, when the switch corresponding to the resistor is disconnected, the resistor is turned on. For any capacitor, when the switch corresponding to the capacitor is closed, the capacitor is turned on. For any inductor, when the switch corresponding to the inductor is disconnected, the inductor is turned on.

[0110] In some embodiments, the switch is a relay;

[0111] The gain and loss power control end of the circuit where the coil of the relay is located is connected to the processor of the control device of the passive filter, the contacts of a relays are respectively connected in parallel with a resistors in a one-to-one correspondence, the contacts of b relays are respectively connected in series with b capacitors in a one-to-one correspondence, the contacts of c relays are respectively connected in parallel with c inductors in a one-to-one correspondence, and a relay, b relays and c relays are all different relays;

[0112] The coil of relay a is used to switch the resistor when power is lost, the coil of relay b is used to switch the capacitor when power is restored, and the coil of relay c is used to switch the inductor when power is lost.

[0113] SR1, SR2, SR3 and SR4 are contacts of a relay for controlling resistance, SC1, SC2, SC3 and SC4 are contacts of a relay for controlling capacitance, and SL1, SL2, SL3 and SL4 are contacts of a relay for controlling inductance.

[0114] Figure 3 Taking a, b and c as 4, the resistance values ​​of the four resistors are R, 2R, 4R and 8R, the capacitance values ​​of the four capacitors are C, 2C, 4C and 8C, and the capacitance values ​​of the four inductors are L, 2L, 4L and 8L. Since the four groups of resistors increase in multiples (1, 2, 4, 8...), the minimum level switching can be achieved, and the precise control of filtering parameters can be improved. The same is true for capacitors and inductors.

[0115] It should also be noted that, in this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0116] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0117] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method for a passive filter, characterized in that: The passive filter is connected to the AC bus, the input ends of the multiple converters are respectively connected to the DC power supply, and the output ends of the multiple converters are connected to the AC bus, including: determining the number of said converters in an activated state; determining the current of the AC bus when the converter is started; Determining the equivalent harmonic frequencies of a plurality of the converters according to the number of the converters in the startup state; Determine the filter device used in the passive filter according to the equivalent harmonic frequency and the current of the AC bus, wherein the filter device includes at least two of a capacitor, a resistor and an inductor; Controlling the passive filter to put the determined filter component into operation; Determining the equivalent harmonic frequencies of a plurality of the converters according to the number of the converters in the startup state comprises: Determining the switching frequency of each of the converters; Determine the equivalent harmonic frequencies of the plurality of converters according to an equivalent harmonic frequency relationship, the switching frequency of the converter and the number of the converters in a startup state; The equivalent harmonic frequency relationship is fs=n×fsw, fs is the equivalent harmonic frequency, n is the number of the converters in the startup state, and fsw is the switching frequency of the converter; Determining the filter device used in the passive filter according to the equivalent harmonic frequency and the current of the AC bus, including: Determining the number of filter components used in the passive filter according to the equivalent harmonic frequency, the current of the AC bus, an input resistance relationship, an input capacitance relationship, and an input inductance relationship; Wherein, the input resistance relationship is R=Uh / Ih, the input capacitance relationship is C=1 / 2π(fs×R), the input inductance relationship is L=R / 2πfs, Uh is the effective value of the equivalent high-frequency harmonic voltage, Ih is the effective value of the current of the AC bus, fs is the equivalent harmonic frequency, R is the resistance value of the passive filter, C is the capacitance value of the passive filter, and L is the inductance value of the passive filter; Determining the capacitance, resistance and inductance invested based on the resistance value, capacitance value and inductance value invested in the passive filter; The passive filter comprises a plurality of filter modules, wherein the plurality of filter modules are connected in parallel, and each filter module comprises a resistor, b capacitor, c inductor and a+b+c switches, wherein a, b and c are integers greater than 1, a switch is respectively connected in parallel with a resistor in a one-to-one correspondence, b switches are respectively connected in series with b capacitors in a one-to-one correspondence, c switches are respectively connected in parallel with c inductors in a one-to-one correspondence, a switch, b switches and c switches are all different switches, a resistor in each filter module is connected in sequence, a first end of the first resistor is connected to the AC bus, a second end of the ath resistor is respectively connected to a first end of the b capacitors and a first end of the first inductor, c inductors are connected in sequence, and second ends of the b capacitors are each connected to a second end of the cth inductor; Controlling the passive filter to input the determined filter device comprises: Controlling the switch corresponding to the determined resistor to be disconnected, so as to switch the determined resistor on; Controlling a switch corresponding to the determined capacitance to close so as to put the determined capacitance into operation; Controlling the switch corresponding to the determined inductance to be disconnected to switch the determined inductance on; Determining whether a feedback signal after the switch action is received; If the feedback signal is received, it is determined that the passive filter is controlled to successfully put the determined filter component into operation.

2. The control method of the passive filter according to claim 1, characterized in that: Determining the number of the converters in an activated state comprises: Determining whether a switch signal sent when a start switch of the converter is closed is received, wherein the start switch corresponds to the converter in a one-to-one manner; If the switch signal is received, it is determined that the start switch is closed and the converter is in the start state.

3. The control method of the passive filter according to claim 1, characterized in that: Determining the number of the converters in an activated state comprises: Sending a first communication signal to each of the converters respectively; receiving a second communication signal returned by the converter after receiving the first communication signal; The number of the received second communication signals is determined, and the number of the second communication signals is used as the number of the converters in the startup state.

4. A control device for a passive filter, characterized in that: include: Memory for storing computer programs; A processor, configured to implement the steps of the passive filter control method according to any one of claims 1 to 3 when executing the computer program.

5. A passive filter, characterized in that: A control device for a passive filter as claimed in claim 4, further comprising a passive filter body; The passive filter body comprises a plurality of filter modules, wherein the plurality of filter modules are connected in parallel, each filter module comprises a resistor, b capacitor, c inductor and a+b+c switches, wherein a, b and c are integers greater than 1, a switch is respectively connected in parallel with a resistor in a one-to-one correspondence, b switches are respectively connected in series with b capacitors in a one-to-one correspondence, c switches are respectively connected in parallel with c inductors in a one-to-one correspondence, and a switch, b switches and c switches are all different switches; The a resistors in each filter module are connected in sequence, the first end of the first resistor is connected to the AC bus, the second end of the a resistor is respectively connected to the first end of the b capacitors and the first end of the first inductor, and the c inductors are connected in sequence, and the second ends of the b capacitors are all connected to the second end of the c inductor; The resistor, the capacitor and the inductor are used to filter the harmonics on the AC bus. For any resistor, when the switch corresponding to the resistor is disconnected, the resistor is turned on. For any capacitor, when the switch corresponding to the capacitor is closed, the capacitor is turned on. For any inductor, when the switch corresponding to the inductor is disconnected, the inductor is turned on.

6. The passive filter according to claim 5, characterized in that The switch is a relay; The power gain and loss control end of the loop where the coil of the relay is located is connected to the processor of the control device of the passive filter, the contacts of a relays are respectively connected in parallel with a resistors in a one-to-one correspondence, the contacts of b relays are respectively connected in series with b capacitors in a one-to-one correspondence, the contacts of c relays are respectively connected in parallel with c inductors in a one-to-one correspondence, and a relay, b relays and c relays are all different relays; The coil of the relay a is used to switch the resistor on when power is off, the coil of the relay b is used to switch the capacitor on when power is on, and the coil of the relay c is used to switch the inductor on when power is off.

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