A method and system for selecting a dc side capacitor of an active filter device

Abstract

The application discloses a direct-current side capacitor selection method and system of an active filter device, constructs a direct-current side low-frequency harmonic current model and a direct-current side high-frequency harmonic current effective value model under an active filter application working condition, and selects the direct-current side capacitor of the active filter device based on the direct-current side low-frequency harmonic current model and the direct-current side high-frequency harmonic current effective value model respectively, so that the technical problems that the existing time-domain-based effective value analysis method for analyzing the direct-current side current of a converter does not consider a harmonic compensation current mixed output scene and the existing converter direct-current side current model only considers the sinusoidal condition of the alternating-current side current and cannot accurately analyze the direct-current side current and is difficult to provide a guidance basis for direct-current side capacitor selection are solved.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter technology, and in particular to a method and system for selecting DC-side capacitors in an active filter device. Background Technology

[0002] In the design of DC-side capacitors for active power filters, power loss and voltage ripple are the main considerations. Among these, power loss analysis is directly related to capacitor lifespan and is the most crucial step in the design process. For active power filters, a large number of harmonic current components pass through the DC-side capacitor, generating power loss and voltage ripple, which in turn affect the capacitor's lifespan. Therefore, accurate analysis of the DC-side current is key to DC capacitor design.

[0003] Currently, there are two main methods for analyzing the DC-side current of active power filters or, more broadly, three-phase converters: one is the frequency-domain-based double Fourier transform analysis method, and the other is the time-domain-based RMS analysis method. The frequency-domain-based double Fourier transform analysis method uses a three-dimensional geometric wall structure as its core, obtaining the frequency domain expression of the function through a two-dimensional Fourier transform. However, because different modulation strategies correspond to different modulation signal waveforms, the effective integration interval of the Fourier transform differs, resulting in different frequency domain expressions of the function. Therefore, when using different modulation strategies, the spectrum of the DC-side capacitor needs to be calculated repeatedly and separately, leading to low applicability. The time-domain-based RMS analysis method calculates the average and RMS values ​​of the DC-side current separately during the calculation process, removing the DC component from the RMS value to obtain the RMS value of the DC-side harmonic current. Compared to the frequency-domain-based double Fourier transform analysis method, the time-domain-based RMS analysis method is more efficient, simpler, and can directly analyze extreme cases of the DC-side current. However, current time-domain RMS analysis methods only consider the sinusoidal AC current and do not account for the mixed output of low-order harmonic compensation current and fundamental current in active filter applications. When the AC side outputs both harmonic currents of different orders and the fundamental component, the DC current waveform characteristics change significantly, rendering existing mathematical models inapplicable. Furthermore, the equivalent circuit of the capacitor changes markedly, leading to substantial errors in capacitor loss calculations. Therefore, improving the time-domain RMS analysis method for DC current analysis of active filters and establishing a DC capacitor harmonic analysis model considering the mixed output of low-order harmonic compensation current and fundamental current in active filter applications is a technical problem urgently needing to be solved by those skilled in the art. Summary of the Invention

[0004] This invention provides a method and system for selecting DC-side capacitors in active power filters, addressing the problem that existing time-domain RMS analysis methods for converter DC-side current analysis do not consider the mixed output of harmonic compensation currents. In this scenario, existing converter DC-side current models that only consider the sinusoidal AC-side current are not applicable, cannot accurately analyze the DC-side current, and are difficult to provide guidance for DC-side capacitor selection.

[0005] In view of this, the first aspect of the present invention provides a method for selecting the DC-side capacitor of an active filter device, comprising:

[0006] Construct the RMS model of the DC-side current and the low-frequency harmonic current model under the operating conditions of active filter applications. The RMS model of the DC-side current is as follows:

[0007]

[0008]

[0009]

[0010]

[0011]

[0012]

[0013] Among them, I dcRMS This is the effective value of the DC-side current. Let be the modulation ratio of the fundamental component in the AC side voltage, and k and n be the positive and negative harmonic orders, respectively. Let be the positive-sequence component of the amplitude of the kth harmonic of the target current on the AC side. Let ω1 be the negative-sequence component of the amplitude of the nth harmonic of the target current on the AC side, ω1 be the angular frequency of the fundamental current of the target current on the AC side, and t be the time variable. The positive-sequence phase angle component of the k-th harmonic of the target current on the AC side. This represents the negative sequence phase angle component of the nth harmonic of the target current on the AC side. This represents the effective value of the k-th positive sequence harmonic current on the AC side. This represents the effective value of the nth negative sequence harmonic current on the AC side. This represents the effective value of the interaction between the k-th positive sequence and n-th negative sequence low-frequency harmonic currents at the AC port. The effective value of the interaction between any two negative-order low-frequency harmonic components of different orders on the AC side. It represents the effective value of the interaction between any two positive-sequence low-frequency harmonic components of different orders on the AC side;

[0014] The DC-side low-frequency harmonic current model is as follows:

[0015]

[0016] Among them, I dcLOH This refers to the low-frequency harmonic current on the DC side.

[0017] A model of the effective value of the high-frequency harmonic current on the DC side under the operating conditions of active filtering is constructed. The effective value model of the high-frequency harmonic current on the DC side is as follows:

[0018]

[0019] Among them, I dcSHCRMS I is the effective value of the high-frequency harmonic current on the DC side. dcLOHRMS This represents the effective value of the low-frequency harmonic current on the DC side.

[0020] The selection of DC-side capacitors for active filters is based on the DC-side low-frequency harmonic current model and the DC-side high-frequency harmonic current RMS value model.

[0021] Optionally, a DC-side low-frequency harmonic current model is constructed under active filter application conditions, including:

[0022] Establish an AC side current model for the active filter device;

[0023] The AC side current model of the active filter device after removing high-frequency components is decomposed into positive and negative order to obtain the AC side phase A current, AC side phase B current and AC side phase C current of the active filter device.

[0024] Based on the phase currents of phase A, phase B, and phase C on the AC side of the active filter, a low-frequency harmonic current model on the DC side under the operating conditions of the active filter is established.

[0025] Optionally, the AC side current model of the active filter is:

[0026]

[0027] Among them, i a I is the phase current of phase A on the AC side of the active filter. k Let K be the amplitude of the kth harmonic of the target current on the AC side. Let i be the phase angle of the kth harmonic of the target current on the AC side of the active filter. SW This refers to the high-frequency component of the AC side current.

[0028] Optionally, the positive and negative sequence decomposition of the AC side current model of the active filter after removing high-frequency components yields the following AC side phase A current, AC side phase B current, and AC side phase C current of the active filter:

[0029]

[0030] Among them, i a For the AC side A-phase current of the active filter, i b For the B-phase current on the AC side of the active filter, i c The current in phase C on the AC side of the active filter is given by k, where k and n are the positive and negative harmonic orders, respectively. The positive-sequence phase angle component of the k-th harmonic of the target current on the AC side. This represents the negative sequence phase angle component of the nth harmonic of the target current on the AC side. The positive sequence component of the amplitude of the kth harmonic current on the AC side. It represents the negative sequence component of the amplitude of the nth harmonic current on the AC side.

[0031] A second aspect of the present invention provides a DC-side capacitor selection system for an active filter device, comprising:

[0032] The first model construction module is used to construct the DC-side current RMS model and the low-frequency harmonic current model under active filter application conditions. The DC-side current RMS model is as follows:

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039] Among them, I dcRMS This is the effective value of the DC-side current. Let be the modulation ratio of the fundamental component in the AC side voltage, and k and n be the positive and negative harmonic orders, respectively. Let be the positive-sequence component of the amplitude of the kth harmonic of the target current on the AC side. Let ω1 be the negative-sequence component of the amplitude of the nth harmonic of the target current on the AC side, ω1 be the angular frequency of the fundamental current of the target current on the AC side, and t be the time variable. The positive-sequence phase angle component of the k-th harmonic of the target current on the AC side. This represents the negative sequence phase angle component of the nth harmonic of the target current on the AC side. This represents the effective value of the k-th positive sequence harmonic current on the AC side. This represents the effective value of the nth negative sequence harmonic current on the AC side. This represents the effective value of the interaction between the k-th positive sequence and n-th negative sequence low-frequency harmonic currents at the AC port. The effective value of the interaction between any two negative-order low-frequency harmonic components of different orders on the AC side. It represents the effective value of the interaction between any two positive-sequence low-frequency harmonic components of different orders on the AC side;

[0040] The DC-side low-frequency harmonic current model is as follows:

[0041]

[0042] Among them, I dcLOH This refers to the low-frequency harmonic current on the DC side.

[0043] The second model construction module is used to construct the effective value model of the DC-side high-frequency harmonic current under active filter application conditions. The effective value model of the DC-side high-frequency harmonic current is as follows:

[0044]

[0045] Among them, I dcSHCRMS I is the effective value of the high-frequency harmonic current on the DC side. dcLOHRMS This represents the effective value of the low-frequency harmonic current on the DC side.

[0046] The selection analysis module is used to select the DC-side capacitor of the active filter device based on the DC-side low-frequency harmonic current model and the DC-side high-frequency harmonic current RMS value model.

[0047] Optionally, the construction of the DC-side low-frequency harmonic current model under active filter application conditions includes:

[0048] Establish an AC side current model for the active filter device;

[0049] The AC side current model of the active filter device after removing high-frequency components is decomposed into positive and negative order to obtain the AC side phase A current, AC side phase B current and AC side phase C current of the active filter device.

[0050] Based on the phase currents of phase A, phase B, and phase C on the AC side of the active filter, a low-frequency harmonic current model on the DC side under the operating conditions of the active filter is established.

[0051] Optionally, the AC side current model of the active filter is:

[0052]

[0053] Among them, i a I is the phase current of phase A on the AC side of the active filter. k Let K be the amplitude of the kth harmonic of the target current on the AC side. Let i be the phase angle of the kth harmonic of the target current on the AC side of the active filter. SW This refers to the high-frequency component of the AC side current.

[0054] Optionally, the positive and negative sequence decomposition of the AC side current model of the active filter after removing high-frequency components yields the following AC side phase A current, AC side phase B current, and AC side phase C current of the active filter:

[0055]

[0056] Among them, i a For the AC side A-phase current of the active filter, i b For the B-phase current on the AC side of the active filter, i c The current in phase C on the AC side of the active filter is given by k, where k and n are the positive and negative harmonic orders, respectively. The positive-sequence phase angle component of the k-th harmonic of the target current on the AC side. This represents the negative sequence phase angle component of the nth harmonic of the target current on the AC side. The positive sequence component of the amplitude of the kth harmonic current on the AC side. It represents the negative sequence component of the amplitude of the nth harmonic current on the AC side.

[0057] As can be seen from the above technical solutions, the DC-side capacitor selection method and system for the active filter device provided by the present invention have the following advantages:

[0058] The present invention provides a method for selecting DC-side capacitors in active power filters. It constructs a DC-side low-frequency harmonic current model and a DC-side high-frequency harmonic current RMS model under active power filter application conditions. Based on these two models, the method selects the DC-side capacitors for the active power filter. This solves the problem that existing time-domain RMS analysis methods for converter DC-side current analysis do not consider the mixed output of harmonic compensation currents. In this scenario, existing converter DC-side current models that only consider the sinusoidal AC-side current cannot accurately analyze the DC-side current, making it difficult to provide guidance for DC-side capacitor selection.

[0059] The DC-side capacitor selection system for active filter devices provided by this invention is used to execute the DC-side capacitor selection method for active filter devices provided by this invention. Its principle and the technical effects achieved are the same as those of the DC-side capacitor selection method for active filter devices provided by this invention, and will not be repeated here. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0061] Figure 1 This is a flowchart illustrating a method for selecting the DC-side capacitor of an active filter device provided in this invention.

[0062] Figure 2 This is a topology diagram of the three-phase full-bridge active filter device provided in this invention;

[0063] Figure 3 This is a schematic diagram illustrating the relationship between the equivalent series resistance of a capacitor and frequency provided in this invention.

[0064] Figure 4(a) shows the waveform under the first experimental test condition in the application example provided in this invention;

[0065] Figure 4(b) shows the waveform under the second experimental test condition in the application example provided in this invention;

[0066] Figure 4(c) shows the waveform under the third experimental test condition in the application example provided in this invention;

[0067] Figure 4(d) shows the waveform under the fourth experimental test condition in the application example provided in this invention;

[0068] Figure 4(e) shows the waveform under the fifth experimental test condition in the application example provided in this invention;

[0069] Figure 4(f) shows the waveform under the sixth experimental test condition in the application example provided in this invention;

[0070] Figure 5 This is a comparison chart of experimental results and calculation results in the application examples provided in this invention;

[0071] Figure 6 This is a schematic diagram of the DC-side capacitor selection system for an active filter device provided in this invention. Detailed Implementation

[0072] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0073] For easier understanding, please refer to Figure 1 This invention provides an embodiment of a method for selecting the DC-side capacitor of an active filter device, comprising:

[0074] Step 101: Construct the DC-side current RMS model and low-frequency harmonic current model under active filter application conditions.

[0075] It should be noted that the active filter application is a scenario where harmonic compensation current is mixed and output. In this embodiment of the invention, the DC-side low-frequency harmonic current model for the active filter application is as follows:

[0076]

[0077] Among them, I dcLOH This is the low-frequency harmonic current on the DC side. Let be the modulation ratio of the fundamental component in the AC side voltage, and k and n be the positive and negative harmonic orders, respectively. Let be the positive-sequence component of the amplitude of the kth harmonic of the target current on the AC side. Let ω1 be the negative-sequence component of the amplitude of the nth harmonic of the target current on the AC side, ω1 be the angular frequency of the fundamental current of the target current on the AC side, and t be the time variable. The positive-sequence phase angle component of the k-th harmonic of the target current on the AC side. It represents the negative sequence phase angle component of the nth harmonic of the target current on the AC side.

[0078] The topology of a three-phase full-bridge active filter is as follows: Figure 2 As shown, the AC side current model of the active filter is:

[0079]

[0080] Among them, i a I is the phase current of phase A on the AC side of the active filter. k Let K be the amplitude of the kth harmonic of the target current on the AC side. Let i be the phase angle of the kth harmonic of the target current on the AC side of the active filter. SWThis represents the high-frequency component of the AC-side current. In the AC-side current model of the active filter, the first part on the right-hand side of the equation is the target AC-side current, and the second part is a series of high-frequency harmonic currents generated at the AC port by the PWM modulation process, i.e., ii SW This refers to the high-frequency component of the AC side current. The high-frequency component i of the AC side current. SW Negligible, the target current on the AC side is decomposed into positive and negative sequences to obtain the phase currents of phase A, phase B, and phase C on the AC side of the active filter. The expressions are:

[0081]

[0082] Among them, i a For the AC side A-phase current of the active filter, i b For the B-phase current on the AC side of the active filter, i c The current in phase C on the AC side of the active filter is given by k, where k and n are the positive and negative harmonic orders, respectively. The positive-sequence phase angle component of the k-th harmonic of the target current on the AC side. This represents the negative sequence phase angle component of the nth harmonic of the target current on the AC side. The positive sequence component of the amplitude of the kth harmonic current on the AC side. It represents the negative sequence component of the amplitude of the nth harmonic current on the AC side.

[0083] During any switching cycle, the low-frequency harmonic current I on the DC side dcLOH The unified mathematical model is expressed as:

[0084]

[0085] Where t0 is the starting time of the time variable t, and T s For the switching period, i dc For DC side current, i a Let i be the phase current of phase A. b Let i be the phase current of phase B. c For phase C current, u aref The reference voltage for phase A, u bref The reference voltage for phase B, u cref This is the reference voltage for phase C.

[0086] In a three-phase full-bridge circuit, the reference signal can be simplified to:

[0087]

[0088] Combining equations (2) and (4), the DC-side low-frequency harmonic current model under active filter application conditions can be obtained as follows:

[0089]

[0090] Given a specific amplitude of the low-frequency harmonic current on the AC side, there are infinitely many phase combinations, resulting in an infinite number of effective values ​​for the high-frequency harmonic current on the DC side. This makes it impossible to achieve the maximum design limit for the DC port capacitor. Therefore, this embodiment of the invention establishes an effective value model for the high-frequency harmonic current on the DC side. Figure 3 As shown, the equivalent series resistance of a capacitor decreases significantly with increasing frequency below 1 kHz, while its resistance remains essentially constant with increasing frequency above 1 kHz. Therefore, the capacitor power loss can be expressed as:

[0091]

[0092] Among them, I c,rms R is the effective value of the current flowing through it. ESR f1 is the equivalent series resistance of the capacitor, and f1 is the fundamental frequency. Losses caused by low-frequency harmonic components. This refers to the losses caused by high-frequency harmonic components. Specifically, the harmonic losses caused by low-frequency harmonic currents on the DC side can be calculated individually using each low-frequency harmonic current at the branch port, while the losses caused by high-frequency harmonic currents can be calculated using the total effective value of the high-frequency harmonic currents on the DC side.

[0093] The model for the effective value of the DC side current is:

[0094]

[0095]

[0096]

[0097]

[0098] Where θ0 is the initial phase of the AC side voltage, θ is the phase of the AC side voltage, and u max The maximum value of the three-phase reference voltage, u med u is the median value of the three-phase reference voltage. min i is the minimum value of the three-phase reference voltage. min The minimum DC-side current is given by f1, where f1 is the fundamental frequency and u is the frequency of the DC-side current. aref The reference voltage for phase A, u bref The reference voltage for phase B, u cref This is the reference voltage for phase C.

[0099] Simplifying equation (7), we obtain the effective value of the DC side current, which is divided into 5 parts:

[0100]

[0101] In equation (11), the first term within the square root on the right side comes from the effect of the k-th positive sequence harmonic current on the AC side, where:

[0102]

[0103] In equation (11), the second term inside the square root on the right side comes from the effect of the nth negative sequence harmonic current on the AC side, where:

[0104]

[0105] In equation (11), the fifth term within the square root on the right side originates from the interaction of any two different orders (k1 and k2) of positive-sequence low-frequency harmonic components on the AC side, where:

[0106]

[0107] In equation (11), the fourth term within the square root on the right side originates from the interaction of any two different orders (k1 and k2) of negative-order low-frequency harmonic components on the AC side, where:

[0108]

[0109] In equation (11), the third term within the square root on the right side comes from the interaction between the k-th positive sequence and the n-th negative sequence low-frequency harmonic currents at the AC port, where:

[0110]

[0111] Step 102: Construct a model of the effective value of DC-side high-frequency harmonic current under active filter application conditions.

[0112] It should be noted that, in this embodiment of the invention, the effective value model of the DC-side high-frequency harmonic current is as follows:

[0113]

[0114] Among them, I dcSHCRMS I is the effective value of the high-frequency harmonic current on the DC side. dcRMS I is the effective value of the DC side current. dcLOHRMS This represents the effective value of the low-frequency harmonic current on the DC side.

[0115] In practical engineering applications, in order to reduce the amount of calculation, it is necessary to simplify equations (12)-(16). The specific simplification process is as follows:

[0116] From equations (12)-(16), we can obtain that, except for the cases where k=1 in equation (12) and kn=2 in equation (16), most of the phase angle related terms shown in the equations can be ignored due to the large denominator. Therefore, by eliminating all the terms with phase angles in equations (13)-(15), the simplified total effective value of the low-frequency current component is:

[0117]

[0118] The second term under the radical sign is obtained by simplifying k=1 in the second term of equation (13), and the third term is obtained by simplifying kn=2 in the first term within the curly braces of equation (17).

[0119] By removing the total effective value of the low-order harmonics and the average value of the DC quantity, the total effective value of the high-frequency harmonic current on the DC side can be simplified to the following according to equation (17):

[0120]

[0121] The third term exists only when the low-frequency harmonic components in the alternating current appear in pairs and satisfy kn = 2. For practical applications, only the maximum value of the high-frequency harmonic components needs to be calculated. When the modulation ratio or DC voltage is determined, the third term in equation (18) satisfies... or At this time, the high-frequency harmonic components reach their maximum value. Equation (18) is simplified to:

[0122]

[0123] In practical applications, the above formula can quickly calculate the effective value of the DC side current when AC is mixed with different low-order harmonics, providing a theoretical basis for the selection of DC side capacitors.

[0124] Step 103: Select the DC-side capacitor for the active filter device based on the DC-side low-frequency harmonic current model and the DC-side high-frequency harmonic current RMS value model.

[0125] It should be noted that the effective values ​​of DC-side low-frequency harmonic current and DC-side high-frequency harmonic current are the basis for selecting DC-side capacitors. Therefore, the effective values ​​of DC-side low-frequency harmonic current and DC-side high-frequency harmonic current are calculated based on the DC-side low-frequency harmonic current model and the DC-side high-frequency harmonic current effective value model, and the DC-side capacitors of the active filter are selected based on the calculation results.

[0126] Based on the DC-side low-frequency harmonic current model under active filter application conditions, the impact of low-order harmonic currents on DC-side harmonics can be accurately calculated and analyzed. Based on the DC-side high-frequency harmonic current RMS model under active filter application conditions, the RMS value of the high-frequency harmonic current components can be accurately calculated by solving for the RMS value of the DC-side current and the low-order harmonic components. This solves the problem that existing calculation models cannot accurately calculate DC-side harmonic currents when the AC side contains harmonics.

[0127] The present invention provides a method for selecting DC-side capacitors in active power filters. It constructs a DC-side low-frequency harmonic current model and a DC-side high-frequency harmonic current RMS model under active power filter application conditions. Based on these two models, the method selects the DC-side capacitors for the active power filter. This solves the problem that existing time-domain RMS analysis methods for converter DC-side current analysis do not consider the mixed output of harmonic compensation currents. Furthermore, it addresses the technical problem that existing converter DC-side current models, which only consider the sinusoidal AC-side current, cannot accurately analyze the DC-side current and thus cannot provide guidance for DC-side capacitor selection in this scenario.

[0128] To demonstrate the effectiveness of the DC-side capacitor selection method for the active filter device provided in this invention, the following comparative diagrams illustrating the implementation effects are provided.

[0129] When the AC side of the three-phase active filter contains only the fundamental wave and is balanced, the envelope of the DC side is a waveform with a period of π / 3, as shown in Figure 4(a).

[0130] When the AC side outputs a mixture of low-order harmonics, the envelope has different shapes due to the infinite combinations of harmonic order, amplitude, and phase. This was verified using a 15kW three-phase voltage-source PWM rectifier-inverter experimental platform. Arbitrary low-order harmonic currents of different amplitudes and phases were injected into the AC side to analyze the DC-side current distribution of the three-phase full-bridge active filter. The superscripts "+" and "-" indicate positive and negative sequence, respectively, and the subscripts indicate the harmonic order. The AC-side current input of the three-phase full-bridge active filter is shown in Table 1.

[0131] Table 1 Experimental testing conditions

[0132]

[0133] The waveforms and experimental results corresponding to (a) to (f) are as follows: Figures 4(a) to 4(f) As shown. The final experimental results are compared with the theoretical results, for example... Figure 5 As shown, by Figure 5A comparison of the experimental and calculated results shows that the error in the calculation is within 9%, which is within the safe range of the design margin, verifying the accuracy of the method proposed in this invention. Furthermore, the DC-side current calculated according to this invention provides a theoretical basis for the extreme design of the DC-side capacitor, improving the stability of the active filter system.

[0134] For easier understanding, please refer to Figure 6 This invention provides an embodiment of a DC-side capacitor selection system for an active filter device, comprising:

[0135] The first model construction module is used to construct the DC-side current RMS model and the low-frequency harmonic current model under active filter application conditions. The DC-side current RMS model is as follows:

[0136]

[0137]

[0138]

[0139]

[0140]

[0141]

[0142] Among them, I dcRMS This is the effective value of the DC-side current. Let be the modulation ratio of the fundamental component in the AC side voltage, and k and n be the positive and negative harmonic orders, respectively. Let be the positive-sequence component of the amplitude of the kth harmonic of the target current on the AC side. Let ω1 be the negative-sequence component of the amplitude of the nth harmonic of the target current on the AC side, ω1 be the angular frequency of the fundamental current of the target current on the AC side, and t be the time variable. The positive-sequence phase angle component of the k-th harmonic of the target current on the AC side. This represents the negative sequence phase angle component of the nth harmonic of the target current on the AC side. This represents the effective value of the k-th positive sequence harmonic current on the AC side. This represents the effective value of the nth negative sequence harmonic current on the AC side. This represents the effective value of the interaction between the k-th positive sequence and n-th negative sequence low-frequency harmonic currents at the AC port. The effective value of the interaction between any two negative-order low-frequency harmonic components of different orders on the AC side. It represents the effective value of the interaction between any two positive-sequence low-frequency harmonic components of different orders on the AC side;

[0143] The DC-side low-frequency harmonic current model is as follows:

[0144]

[0145] Among them, I dcLOH This refers to the low-frequency harmonic current on the DC side.

[0146] The second model construction module is used to construct the effective value model of the DC-side high-frequency harmonic current under active filter application conditions. The effective value model of the DC-side high-frequency harmonic current is as follows:

[0147]

[0148] Among them, I dcSHCRMS I is the effective value of the high-frequency harmonic current on the DC side. dcLOHRMS This represents the effective value of the low-frequency harmonic current on the DC side.

[0149] The selection analysis module is used to select the DC-side capacitor of the active filter device based on the DC-side low-frequency harmonic current model and the DC-side high-frequency harmonic current RMS value model.

[0150] The construction of the DC-side low-frequency harmonic current model under active filter application conditions includes:

[0151] Establish an AC side current model for the active filter device;

[0152] The AC side current model of the active filter device after removing high-frequency components is decomposed into positive and negative order to obtain the AC side phase A current, AC side phase B current and AC side phase C current of the active filter device.

[0153] Based on the phase currents of phase A, phase B, and phase C on the AC side of the active filter, a low-frequency harmonic current model on the DC side under the operating conditions of the active filter is established.

[0154] The AC current model of the active filter is as follows:

[0155]

[0156] Among them, i a I is the phase current of phase A on the AC side of the active filter. k Let K be the amplitude of the kth harmonic of the target current on the AC side. Let i be the phase angle of the kth harmonic of the target current on the AC side of the active filter. SW This refers to the high-frequency component of the AC side current.

[0157] The positive and negative sequence decomposition of the AC side current model of the active filter after removing high-frequency components yields the following AC side phase currents: Phase A, Phase B, and Phase C of the active filter:

[0158]

[0159] Among them, i a For the AC side A-phase current of the active filter, i b For the B-phase current on the AC side of the active filter, i c The current in phase C on the AC side of the active filter is given by k, where k and n are the positive and negative harmonic orders, respectively. The positive-sequence phase angle component of the k-th harmonic of the target current on the AC side. This represents the negative sequence phase angle component of the nth harmonic of the target current on the AC side. The positive sequence component of the amplitude of the kth harmonic current on the AC side. It represents the negative sequence component of the amplitude of the nth harmonic current on the AC side.

[0160] The DC-side capacitor selection system for active filter devices provided by this invention is used to execute the DC-side capacitor selection method for active filter devices provided by this invention. Its principle and the technical effects achieved are the same as those of the DC-side capacitor selection method for active filter devices provided by this invention, and will not be repeated here.

[0161] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for selecting the DC-side capacitor of an active filter device, characterized in that, include: Construct the RMS model of the DC-side current and the low-frequency harmonic current model under the operating conditions of active filter applications. The RMS model of the DC-side current is as follows: Among them, I dcRMS This is the effective value of the DC-side current. Let be the modulation ratio of the fundamental component in the AC side voltage, and k and n be the positive and negative harmonic orders, respectively. Let be the positive-sequence component of the amplitude of the kth harmonic of the target current on the AC side. Let ω1 be the negative-sequence component of the amplitude of the nth harmonic of the target current on the AC side, ω1 be the angular frequency of the fundamental current of the target current on the AC side, and t be the time variable. The positive-sequence phase angle component of the k-th harmonic of the target current on the AC side. This represents the negative sequence phase angle component of the nth harmonic of the target current on the AC side. This represents the effective value of the k-th positive sequence harmonic current on the AC side. This represents the effective value of the nth negative sequence harmonic current on the AC side. This represents the effective value of the interaction between the k-th positive sequence and n-th negative sequence low-frequency harmonic currents at the AC port. The effective value of the interaction between any two negative-order low-frequency harmonic components of different orders on the AC side. It represents the effective value of the interaction between any two positive-sequence low-frequency harmonic components of different orders on the AC side; The DC-side low-frequency harmonic current model is as follows: Among them, I dcLOH This refers to the low-frequency harmonic current on the DC side. A model of the effective value of the high-frequency harmonic current on the DC side under the operating conditions of active filtering is constructed. The effective value model of the high-frequency harmonic current on the DC side is as follows: Among them, I dcSHCRMS I is the effective value of the high-frequency harmonic current on the DC side. dcLOHRMS This represents the effective value of the low-frequency harmonic current on the DC side. The selection of DC-side capacitors for active filters is based on the DC-side low-frequency harmonic current model and the DC-side high-frequency harmonic current RMS value model.

2. The method for selecting the DC-side capacitor of the active filter device according to claim 1, characterized in that, Constructing a DC-side low-frequency harmonic current model under active filter application conditions, including: Establish an AC side current model for the active filter device; The AC side current model of the active filter device after removing high-frequency components is decomposed into positive and negative order to obtain the AC side phase A current, AC side phase B current and AC side phase C current of the active filter device. Based on the phase currents of phase A, phase B, and phase C on the AC side of the active filter, a low-frequency harmonic current model on the DC side under the operating conditions of the active filter is established.

3. The method for selecting the DC-side capacitor of the active filter device according to claim 2, characterized in that, The AC current model of the active filter is as follows: Among them, i a I is the phase current of phase A on the AC side of the active filter. k Let K be the amplitude of the kth harmonic of the target current on the AC side. Let i be the phase angle of the kth harmonic of the target current on the AC side of the active filter. SW This refers to the high-frequency component of the AC side current.

4. The method for selecting the DC-side capacitor of the active filter device according to claim 3, characterized in that, The positive and negative sequence decomposition of the AC side current model of the active filter after removing high-frequency components yields the following AC side phase currents: Phase A, Phase B, and Phase C of the active filter: Among them, i a For the AC side A-phase current of the active filter, i b For the B-phase current on the AC side of the active filter, i c The current in phase C on the AC side of the active filter is given by k, where k and n are the positive and negative harmonic orders, respectively. The positive-sequence phase angle component of the k-th harmonic of the target current on the AC side. This represents the negative sequence phase angle component of the nth harmonic of the target current on the AC side. The positive sequence component of the amplitude of the kth harmonic current on the AC side. It represents the negative sequence component of the amplitude of the nth harmonic current on the AC side.

5. A DC-side capacitor selection system for an active filter device, characterized in that, include: The first model construction module is used to construct the DC-side current RMS model and the low-frequency harmonic current model under active filter application conditions. The DC-side current RMS model is as follows: Among them, I dcRMS This is the effective value of the DC-side current. Let be the modulation ratio of the fundamental component in the AC side voltage, and k and n be the positive and negative harmonic orders, respectively. Let be the positive-sequence component of the amplitude of the kth harmonic of the target current on the AC side. Let ω1 be the negative-sequence component of the amplitude of the nth harmonic of the target current on the AC side, ω1 be the angular frequency of the fundamental current of the target current on the AC side, and t be the time variable. The positive-sequence phase angle component of the k-th harmonic of the target current on the AC side. This represents the negative sequence phase angle component of the nth harmonic of the target current on the AC side. This represents the effective value of the k-th positive sequence harmonic current on the AC side. This represents the effective value of the nth negative sequence harmonic current on the AC side. This represents the effective value of the interaction between the k-th positive sequence and n-th negative sequence low-frequency harmonic currents at the AC port. The effective value of the interaction between any two negative-order low-frequency harmonic components of different orders on the AC side. It represents the effective value of the interaction between any two positive-sequence low-frequency harmonic components of different orders on the AC side; The DC-side low-frequency harmonic current model is as follows: Among them, I dcLOH This refers to the low-frequency harmonic current on the DC side. The second model construction module is used to construct the effective value model of the DC-side high-frequency harmonic current under active filter application conditions. The effective value model of the DC-side high-frequency harmonic current is as follows: Among them, I dcSHCRMS I is the effective value of the high-frequency harmonic current on the DC side. dcLOHRMS This represents the effective value of the low-frequency harmonic current on the DC side. The selection analysis module is used to select the DC-side capacitor of the active filter device based on the DC-side low-frequency harmonic current model and the DC-side high-frequency harmonic current RMS value model.

6. The DC-side capacitor selection system for the active filter device according to claim 5, characterized in that, The construction of the DC-side low-frequency harmonic current model under active filter application conditions includes: Establish an AC side current model for the active filter device; The AC side current model of the active filter device after removing high-frequency components is decomposed into positive and negative order to obtain the AC side phase A current, AC side phase B current and AC side phase C current of the active filter device. Based on the phase currents of phase A, phase B, and phase C on the AC side of the active filter, a low-frequency harmonic current model on the DC side under the operating conditions of the active filter is established.

7. The DC-side capacitor selection system for the active filter device according to claim 6, characterized in that, The AC current model of the active filter is as follows: Among them, i a I is the phase current of phase A on the AC side of the active filter. k Let K be the amplitude of the kth harmonic of the target current on the AC side. Let i be the phase angle of the kth harmonic of the target current on the AC side of the active filter. SW This refers to the high-frequency component of the AC side current.

8. The DC-side capacitor selection system for the active filter device according to claim 7, characterized in that, The positive and negative sequence decomposition of the AC side current model of the active filter after removing high-frequency components yields the following AC side phase currents: Phase A, Phase B, and Phase C of the active filter: Among them, i a For the AC side A-phase current of the active filter, i b For the B-phase current on the AC side of the active filter, i c The current in phase C on the AC side of the active filter is given by k, where k and n are the positive and negative harmonic orders, respectively. The positive-sequence phase angle component of the k-th harmonic of the target current on the AC side. This represents the negative sequence phase angle component of the nth harmonic of the target current on the AC side. The positive sequence component of the amplitude of the kth harmonic current on the AC side. It represents the negative sequence component of the amplitude of the nth harmonic current on the AC side.

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