A filtering method based on least squares correction for inverter output current

Abstract

The present invention relates to the technical field of inverter output current filtering. The present invention provides a filtering method for inverter output current that incorporates least squares correction. The method comprises: filtering a three-phase sampled current #imgabs0# output by a two-level voltage source inverter through a fixed-period moving mean filter to obtain a filtered three-phase current #imgabs1#; a three-phase sampled current #imgabs2#; and correcting the filtered three-phase current #imgabs3# using a least squares method under the constraint that the sum of the three-phase currents is zero. The present invention can effectively reduce the impact of hardware circuit and measurement noise on the detected current value.

Description

Technical Field

[0001] The present invention relates to the technical field of inverter output current filtering processing, and in particular to a filtering method for inverter output current fused with least squares correction. Background Art

[0002] With the rapid development of renewable energy power generation, electric vehicles, and industrial motor drives, power electronic inverters, as core energy conversion devices, have a direct impact on power quality and system efficiency. Inverters convert DC power to AC power using high-frequency switching devices. However, these switching devices inevitably introduce high-frequency harmonics and pulse noise during the switching process, distorting the output current waveform. This distortion not only reduces power transmission efficiency but can also cause equipment overheating and electromagnetic interference. Although international standards impose strict limits on harmonic content, traditional passive filters, due to their large size, high risk of resonance, and poor dynamic response, struggle to meet the technological trend toward higher frequencies and smaller sizes. In recent years, the emergence of new technologies such as active filtering, three-level topologies, and digital control algorithms has opened up new avenues for harmonic mitigation, but achieving a balance between efficiency, cost, and performance remains a technical challenge.

[0003] Research on inverter output current filtering has multifaceted value. From a power quality perspective, optimizing filtering technology can reduce the negative impact of harmonics on the grid and load devices, for example, improving microgrid connection stability and reducing interference with highly sensitive equipment such as medical devices. In industrial scenarios, it can also extend motor life and reduce maintenance costs. In the renewable energy sector, efficient filtering technology can enhance the dynamic response of inverters under power fluctuations, ensuring the stability of large-scale renewable energy grid integration. Furthermore, with the increasing popularity of high-frequency devices such as silicon carbide (SiC), the development of novel composite filtering solutions (such as passive-active hybrid structures) or high-frequency magnetic integration technology can overcome the size limitations of traditional filters and promote innovative designs of high-density power modules. At the system optimization level, integrating filter parameter design with advanced control algorithms can suppress harmonics while reducing switching losses. This is particularly important in energy- and weight-sensitive sectors such as electric vehicles and aerospace. Therefore, this research is not only a fundamental topic in power electronics technology but also a key breakthrough in achieving energy transformation and equipment upgrades, laying the core foundation for building efficient and intelligent next-generation power conversion systems. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0005] Therefore, the object of the present invention is to propose a filtering method for inverter output current that incorporates least square correction.

[0006] In order to achieve the above-mentioned purpose, the technical solution of the present invention provides a filtering method for the inverter output current by integrating least square correction. The inverter is a two-level voltage source inverter; the two-level voltage source inverter is a three-phase full-bridge circuit, and the power supply of the three-phase full-bridge circuit is a DC power supply. V dc The output end of the three-phase full-bridge circuit is connected to the three-phase motor; the three-phase full-bridge circuit is composed of three independent A, B, and C bridge arms, and the A-phase bridge arm includes an upper switch tube S 1 and anti-parallel diode Z 1. Lower switch tube S 4 and anti-parallel diodes Z 4; Phase B bridge arm includes the upper switch tube S 3 and anti-parallel diodes Z 3. Lower switch tube S 6 and anti-parallel diodes Z 6; The C-phase bridge arm includes the upper switch tube S 5 and anti-parallel diodes Z 5. Lower switch tube S 2 and anti-parallel diodes Z 2; The midpoint of each bridge arm a 、 b 、 c As AC output terminals, they are connected to the corresponding phases of the three-phase motor respectively; the midpoint a 、 b 、 c The output current is i a 、 i b ,and i c ;

[0007] The filtering method comprises:

[0008] Step S1: The three-phase current output by the two-level voltage source inverter The three-phase current is filtered by a fixed-cycle moving average filter to obtain the filtered current. ; Wherein, the three-phase current ;

[0009] Step S2: Under the constraint that the sum of the three-phase currents is zero, the least squares method is used to calculate the filtered three-phase currents. Make corrections.

[0010] Preferably, the step S1 specifically includes:

[0011] Step S1.1: Select the sliding window length as four carrier cycles, and take equal intervals in each carrier cycle. msampling points; there are 4 in a sliding window m points; m is a positive integer;

[0012] Step S1.2: Three-phase current Perform moving average filtering to obtain the filtered three-phase current The corresponding expression is:

[0013] (1)

[0014] In formula (1), is the current value obtained by sliding window through mean filtering, .

[0015] Preferably, the step S2 specifically includes:

[0016] Step S2.1: Set the correction values ​​corresponding to the minimum correction of the three-phase current using the least squares method to be , ,and , the corrected three-phase currents are: , ,and ;

[0017] Among them, the three-phase currents before and after correction satisfy:

[0018] (2)

[0019] Step S2.2: Set the corrected three-phase current to satisfy:

[0020] (3)

[0021] At the same time, the sum of the squares of the corrections to the three-phase currents is minimized, namely:

[0022] (4)

[0023] Step S2.3: Based on equations (2) and (3), the constraints are:

[0024] (5)

[0025] Step S2.4: Define the sum of the three-phase currents after moving average filtering as:

[0026] (6)

[0027] Step S2.5: Based on equations (5) and (6), the constraints of the least squares method are obtained as follows:

[0028] (7)

[0029] Step S2.6: Based on formula (4), the objective function of the least squares method is obtained as follows:

[0030] (8)

[0031] Step S2.7: Introduce the Lagrange multiplier and construct the Lagrange function as follows:

[0032] (9)

[0033] Step S2.8: For the equation (9) , , ,and Find the partial derivatives respectively, and let the , , ,and The partial derivatives of are all zero, and we get equation (10):

[0034] (10)

[0035] Step S2.9: Solve the above equation (10) to obtain the correction value of each phase of the three-phase current:

[0036] (11)

[0037] Step S2.10: Based on equations (2) and (11), the corrected three-phase current is obtained as:

[0038] (12).

[0039] Beneficial effects of the present invention:

[0040] In order to solve the problem that the inherent non-ideal characteristics of the hardware circuit and the random noise introduced during the current measurement process in the fault diagnosis of the inverter open circuit may interfere with the fault feature extraction and reduce the accuracy of the fault diagnosis, the present invention proposes a moving average filtering method integrated with least squares correction. Specifically, the method first uses a moving average filter to perform preliminary smoothing on the collected current signal to suppress the interference of high-frequency noise. Furthermore, in order to reduce the signal delay and amplitude attenuation that may be introduced by the moving average filter, and to more effectively filter out low-frequency noise and baseline drift, the present invention innovatively introduces a least squares correction link. This correction link performs local polynomial fitting on the output result of the moving average filter and optimizes the fitting parameters using the least squares method, thereby more accurately estimating and removing the noise component while retaining the change trend of the original signal. Through this fusion strategy, the noise level in the current detection value can be significantly reduced.

[0041] Additional aspects and advantages of the invention will become apparent from the description which follows, or may be learned by practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A schematic flow chart of a filtering method for inverter output current using a fusion least squares correction according to an embodiment of the present invention is shown;

[0043] Figure 2 A topological diagram of a two-level voltage source inverter according to an embodiment of the present invention is shown;

[0044] Figure 3 The figure shows a principle diagram of a fixed-period integral averaging filter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0046] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0047] Figure 1 FIG1 shows a schematic flow chart of a filtering method for inverter output current fused with least square correction according to an embodiment of the present invention. Figure 2As shown, the inverter is a two-level voltage source inverter; the two-level voltage source inverter is a three-phase full-bridge circuit, and the power supply of the three-phase full-bridge circuit is a DC power supply. V dc The output end of the three-phase full-bridge circuit is connected to the three-phase motor; the three-phase full-bridge circuit is composed of three independent A, B, and C bridge arms, and the A-phase bridge arm includes an upper switch tube S 1 and anti-parallel diode Z 1. Lower switch tube S 4 and anti-parallel diodes Z 4; Phase B bridge arm includes the upper switch tube S 3 and anti-parallel diodes Z 3. Lower switch tube S 6 and anti-parallel diodes Z 6; The C-phase bridge arm includes the upper switch tube S 5 and anti-parallel diodes Z 5. Lower switch tube S 2 and anti-parallel diodes Z 2; The midpoint of each bridge arm a 、 b 、 c As AC output terminals, they are connected to the corresponding phases of the three-phase motor respectively; the midpoint a 、 b 、 c The output current is i a 、 i b ,and i c .

[0048] like Figure 1 As shown, the filtering method for the inverter output current with fusion least square correction includes:

[0049] Step S1: Convert the three-phase current output by the two-level voltage source inverter The three-phase current is filtered by a fixed-cycle moving average filter to obtain the filtered current. ; Wherein, the three-phase current ;

[0050] Step S2: Under the constraint that the sum of the three-phase currents is zero, the least squares method is used to calculate the filtered three-phase currents. Make corrections.

[0051] In this embodiment, with the rapid development of motor drive systems in recent years, in order to solve the problem that the inherent non-ideal characteristics of the hardware circuit and the random noise introduced in the current measurement process in the open-circuit fault diagnosis of the inverter may interfere with the fault feature extraction, resulting in a decrease in the accuracy of fault diagnosis, the present invention proposes a moving average filtering method integrated with least squares correction. Specifically, the method first uses a moving average filter to perform preliminary smoothing on the collected current signal to suppress the interference of high-frequency noise. Furthermore, in order to reduce the signal delay and amplitude attenuation that may be introduced by the moving average filter, and to more effectively filter out low-frequency noise and baseline drift, the present invention innovatively introduces a least squares correction link. This correction link performs local polynomial fitting on the output result of the moving average filter and optimizes the fitting parameters using the least squares method, thereby more accurately estimating and removing the noise component while retaining the change trend of the original signal. Through this fusion strategy, the noise level in the current detection value can be significantly reduced.

[0052] In one embodiment of the present invention, step S1 specifically includes:

[0053] Step S1.1: Select the sliding window length as four carrier cycles, and take equal intervals in each carrier cycle. m sampling points; there are 4 in a sliding window m points; m is a positive integer;

[0054] Step S1.2: Three-phase current Perform moving average filtering to obtain the filtered three-phase current The corresponding expression is:

[0055] (1)

[0056] In formula (1), is the current value obtained by sliding window through mean filtering, .

[0057] In this embodiment, a moving average filter is used to perform preliminary smoothing on the collected current signal to suppress the interference of high-frequency noise. The principle of moving average filtering is as follows: Figure 3 As shown, the sliding window is selected as four carrier cycles, and the m sampling points, so there are 4 in a sliding window m points; is the three-phase current, For the k The current value obtained by averaging the sliding windows is: For the k +1 sliding window current value obtained by mean filtering, ts Represents a carrier cycle, and the time interval between two discrete current points after moving average filtering is .

[0058] In one embodiment of the present invention, step S2 specifically includes:

[0059] Step S2.1: Set the correction values ​​corresponding to the minimum correction of the three-phase current using the least squares method to be , ,and , the corrected three-phase currents are: , ,and ;

[0060] Among them, the three-phase currents before and after correction satisfy:

[0061] (2)

[0062] Step S2.2: Set the corrected three-phase current to satisfy:

[0063] (3)

[0064] At the same time, the sum of the squares of the corrections to the three-phase currents is minimized, namely:

[0065] (4)

[0066] Step S2.3: Based on equations (2) and (3), the constraints are:

[0067] (5)

[0068] Step S2.4: Define the sum of the three-phase currents after moving average filtering as:

[0069] (6)

[0070] Step S2.5: Based on equations (5) and (6), the constraints of the least squares method are obtained as follows:

[0071] (7)

[0072] Step S2.6: Based on formula (4), the objective function of the least squares method is obtained as follows:

[0073] (8)

[0074] Step S2.7: Introduce the Lagrange multiplier and construct the Lagrange function as follows:

[0075] (9)

[0076] Step S2.8: For the equation (9) , , ,and Find the partial derivatives respectively, and let the , , ,and The partial derivatives of are all zero, and we get equation (10):

[0077] (10)

[0078] Step S2.9: Solve the above equation (10) to obtain the correction value of each phase of the three-phase current:

[0079] (11)

[0080] Step S2.10: Based on equations (2) and (11), the corrected three-phase current is obtained as:

[0081] (12).

[0082] The following is a specific embodiment to illustrate the filtering method of the present invention for the inverter output current fusion least square correction. The inverter is a two-level voltage source inverter; the two-level voltage source inverter is a three-phase full-bridge circuit, and the power supply of the three-phase full-bridge circuit is a DC power supply. V dc The output end of the three-phase full-bridge circuit is connected to the three-phase motor; the three-phase full-bridge circuit is composed of three independent A, B, and C bridge arms, and the A-phase bridge arm includes an upper switch tube S 1 and anti-parallel diode Z 1. Lower switch tube S 4 and anti-parallel diodes Z 4; Phase B bridge arm includes the upper switch tube S 3 and anti-parallel diodes Z 3. Lower switch tube S 6 and anti-parallel diodes Z 6; The C-phase bridge arm includes the upper switch tube S 5 and anti-parallel diodes Z 5. Lower switch tube S 2 and anti-parallel diodes Z 2; The midpoint of each bridge arm a 、 b 、 c As AC output terminals, they are connected to the corresponding phases of the three-phase motor respectively; the midpoint a 、 b 、c The output current is i a 、 i b ,and i c .

[0083] The specific implementation steps of the filtering method for inverter output current fusion least square correction of the present invention are as follows:

[0084] (1) Step S1: Convert the three-phase current output by the two-level voltage source inverter The three-phase current is filtered by a fixed-cycle moving average filter to obtain the filtered current. ; Wherein, the three-phase current ;

[0085] The step S1 specifically includes:

[0086] Step S1.1: Select the sliding window length as four carrier cycles, and take equal intervals in each carrier cycle. m sampling points; there are 4 in a sliding window m points; m is a positive integer;

[0087] Step S1.2: Three-phase current Perform moving average filtering to obtain the filtered three-phase current The corresponding expression is:

[0088] (1)

[0089] In formula (1), is the current value obtained by sliding window through mean filtering, .

[0090] (2) Step S2: Under the constraint that the sum of the three-phase currents is zero, the least squares method is used to calculate the filtered three-phase currents. Make corrections.

[0091] The step S2 specifically includes:

[0092] Step S2.1: Set the correction values ​​corresponding to the minimum correction of the three-phase current using the least squares method to be , ,and , the corrected three-phase currents are: , ,and ;

[0093] Among them, the three-phase currents before and after correction satisfy:

[0094] (2)

[0095] Step S2.2: Set the corrected three-phase current to satisfy:

[0096] (3)

[0097] At the same time, the sum of the squares of the corrections to the three-phase currents is minimized, namely:

[0098] (4)

[0099] Step S2.3: Based on equations (2) and (3), the constraints are:

[0100] (5)

[0101] Step S2.4: Define the sum of the three-phase currents after moving average filtering as:

[0102] (6)

[0103] Step S2.5: Based on equations (5) and (6), the constraints of the least squares method are obtained as follows:

[0104] (7)

[0105] Step S2.6: Based on formula (4), the objective function of the least squares method is obtained as follows:

[0106] (8)

[0107] Step S2.7: Introduce the Lagrange multiplier and construct the Lagrange function as follows:

[0108] (9)

[0109] Step S2.8: For the equation (9) , , ,and Find the partial derivatives respectively, and let the , , ,and The partial derivatives of are all zero, and we get equation (10):

[0110] (10)

[0111] Step S2.9: Solve the above equation (10) to obtain the correction value of each phase of the three-phase current:

[0112] (11)

[0113] Step S2.10: Based on equations (2) and (11), the corrected three-phase current is obtained as:

[0114] (12).

[0115] In this specific embodiment, in order to solve the problem that the inherent non-ideal characteristics of the hardware circuit and the random noise introduced during the current measurement process in the fault diagnosis of the inverter open circuit may interfere with the fault feature extraction and reduce the accuracy of the fault diagnosis, the present invention proposes a moving average filtering method that integrates least squares correction. Specifically, the method first uses a moving average filter to perform preliminary smoothing on the collected current signal to suppress the interference of high-frequency noise. Furthermore, in order to reduce the signal delay and amplitude attenuation that may be introduced by the moving average filter, and to more effectively filter out low-frequency noise and baseline drift, the present invention innovatively introduces a least squares correction link. This correction link performs local polynomial fitting on the output result of the moving average filter and optimizes the fitting parameters using the least squares method, thereby more accurately estimating and removing the noise component while retaining the change trend of the original signal. Through this fusion strategy, the noise level in the current detection value can be significantly reduced.

[0116] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A filtering method for inverter output current using a fusion least squares correction, wherein the inverter is a two-level voltage source inverter; the two-level voltage source inverter is a three-phase full-bridge circuit, and the power supply of the three-phase full-bridge circuit is a DC power supply. V dc The output end of the three-phase full-bridge circuit is connected to the three-phase motor; the three-phase full-bridge circuit is composed of three independent A, B, and C bridge arms, and the A-phase bridge arm includes an upper switch tube S 1 and anti-parallel diode Z 1. Lower switch tube S 4 and anti-parallel diodes Z 4; Phase B bridge arm includes the upper switch tube S 3 and anti-parallel diodes Z 3. Lower switch tube S 6 and anti-parallel diodes Z 6; The C-phase bridge arm includes the upper switch tube S 5 and anti-parallel diodes Z 5. Lower switch tube S 2 and anti-parallel diodes Z 2; The midpoint of each bridge arm a 、 b 、 c As AC output terminals, they are connected to the corresponding phases of the three-phase motor respectively; the midpoint a 、 b 、 c The output current is i a 、 i b ,and i c ; It is characterized in that, The filtering method comprises: Step S1: The three-phase current output by the two-level voltage source inverter The three-phase current is filtered by a fixed-cycle moving average filter to obtain the filtered current. ; Wherein, the three-phase current ; Step S2: Under the constraint that the sum of the three-phase currents is zero, the least squares method is used to calculate the filtered three-phase currents. Make corrections; The step S1 specifically includes: Step S1.1: Select the sliding window length as four carrier cycles, and take equal intervals in each carrier cycle. m sampling points; there are 4 in a sliding window m points; m is a positive integer; Step S1.2: Three-phase current Perform moving average filtering to obtain the filtered three-phase current The corresponding expression is: （1） In formula (1), is the current value obtained by sliding window through mean filtering, ; The step S2 specifically includes: Step S2.1: Set the correction values ​​corresponding to the minimum correction of the three-phase current using the least squares method to be , ,and , the corrected three-phase currents are: , ,and ; Among them, the three-phase currents before and after correction satisfy: （2） Step S2.2: Set the corrected three-phase current to satisfy: （3） At the same time, the sum of the squares of the corrections to the three-phase currents is minimized, namely: （4） Step S2.3: Based on equations (2) and (3), the constraints are: （5） Step S2.4: Define the sum of the three-phase currents after moving average filtering as: （6） Step S2.5: Based on equations (5) and (6), the constraints of the least squares method are obtained as follows: （7） Step S2.6: Based on formula (4), the objective function of the least squares method is obtained as follows: （8） Step S2.7: Introduce the Lagrange multiplier and construct the Lagrange function as follows: （9） Step S2.8: For the equation (9) , , ,and Find the partial derivatives respectively, and let the , , ,and The partial derivatives of are all zero, and we get equation (10): （10） Step S2.9: Solve the above equation (10) to obtain the correction value of each phase of the three-phase current: （11） Step S2.10: Based on equations (2) and (11), the corrected three-phase current is obtained as: （12）。

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