Direct-current component extraction system and applicable direct-current component extraction method thereof

Abstract

A DC component extraction system and a DC component extraction method therefor, the DC component extraction system comprising: an input module for receiving an AC signal; the third-order generalized integrator is electrically connected with the input module and comprises a second-order filter used for filtering the alternating current signal to obtain a first filtering signal; and the third-order filter is used for carrying out operation on the difference between the first filtering signal and the alternating current signal and extracting a first direct current component signal in the alternating current signal according to an operation result.

Description

Technical Field

[0001] This case pertains to the technical field of DC component extraction, and specifically relates to a DC component extraction system and an applicable DC component extraction method. Background Technology

[0002] In existing power electronic systems, AC signals (voltage or current signals) are frequently used as fundamental measurement parameters for control and protection. However, due to factors such as parameter deviations of power devices, dead-zone effects, zero-point drift of current and voltage sensors, and transient responses of capacitors and inductors, the actual measured AC signals often contain a DC component. This DC component can cause magnetic flux deviation in the transformer core, leading to local magnetic saturation of the core, resulting in abnormal vibration, increased noise, and significantly increased iron losses. In severe cases, it can even cause the transformer or related equipment to burn out. Furthermore, when the positive and negative half-cycles of the AC current are asymmetrical due to the DC component, the losses generated by power switching components (such as IGBTs) during conduction will also become unbalanced. Long-term operation will cause localized overheating in some components, accelerating aging and failure.

[0003] To avoid the aforementioned problems, engineering practice typically requires separating the DC component from the AC signal and using it as the basis for compensation or protection control. Existing DC component extraction techniques can be broadly categorized into two types. The first type is the pure hardware extraction method, which uses differential amplifier circuits and hardware filter circuits to extract the DC component. However, the pure hardware extraction method is highly dependent on the design of the hardware circuitry, and once the design is completed, it is not easy to adjust. Furthermore, when the frequency or amplitude of the AC signal changes, the hardware circuitry struggles to maintain the effectiveness of DC component extraction. Even worse, this type of method requires additional sampling and amplification circuitry, increasing not only system cost but also the burden on circuit board layout and size.

[0004] The second type is the hardware-software combined extraction method. This method involves designing simple filtering preprocessing circuits in the hardware, or even without adding any additional hardware. In software, appropriate filters and noise suppression algorithms are designed to filter out or cancel AC components and harmonics, and then a stable DC component is obtained using specific average filtering or low-pass filtering. This type of method has lower hardware costs, as the extraction of the DC component relies entirely on software algorithms within the MCU, offering good portability and adaptability to scenarios with varying AC signal frequency and amplitude. However, this second type of method requires more complex filtering and extraction algorithms in the software, placing higher demands on the MCU's analog-to-digital (ADC) sampling accuracy and computing power. Furthermore, while the hardware-software combined extraction method primarily focuses on improving filtering and noise suppression, its algorithms are only effective for extracting AC signals of specific frequencies. When the DC component is small or the harmonic content in the AC signal is large, it suffers from poor accuracy, insufficient adaptability to variations in AC signal frequency and amplitude, and overly complex algorithms.

[0005] Therefore, how to develop a DC component extraction system and a suitable DC component extraction method that can improve upon the shortcomings of the existing technology is a problem that urgently needs to be solved by those in the relevant technical field. Summary of the Invention

[0006] The purpose of this invention is to provide a DC component extraction system and a suitable DC component extraction method. The DC component extraction system uses a third-order generalized integrator as its core structure, thereby enabling the rapid and accurate extraction of DC components from AC signals using only existing AC signal sampling lines and digital computing resources, thus significantly improving the measurement accuracy and anti-interference capability of DC components.

[0007] To achieve the aforementioned objective, this invention provides a DC component extraction system, comprising: an input module for receiving an AC signal; and a third-order generalized integrator electrically connected to the input module, and comprising: a second-order filter for filtering the AC signal to obtain a first filtered signal; and a third-order filter for calculating the difference between the first filtered signal and the AC signal, and extracting the first DC component signal from the AC signal based on the calculation result.

[0008] To achieve the aforementioned objective, this invention also provides a DC component extraction method, applied to a DC component extraction system. The DC component extraction system includes a third-order generalized integrator, which includes a second-order filter and a third-order filter. The DC component extraction method includes: (S1) receiving an AC signal; (S2) filtering the AC signal using the second-order filter to obtain a first filtered signal; and (S3) performing a calculation on the difference between the first filtered signal and the AC signal using the third-order filter, and extracting the first DC component signal from the AC signal based on the calculation result. Attached Figure Description

[0009] Figure 1A This is a schematic diagram of the architecture of the DC component extraction system in this embodiment.

[0010] Figure 1B for Figure 1A The diagram shows a model of a third-order generalized integrator.

[0011] Figure 2 This is a flowchart illustrating the steps of the DC component extraction method in this embodiment.

[0012] [List of Labels in the Attached Image]

[0013] 1: DC component extraction system

[0014] 2: Input Module

[0015] 3: Third-order generalized integrator

[0016] 30a: Second-order filter

[0017] 31: Third-order filter

[0018] 4: Divider

[0019] 5: Low-frequency SOGI filter

[0020] AC signal

[0021] First DC component signal

[0022] First filtered signal

[0023] Second DC component signal Detailed Implementation

[0024] Some typical embodiments embodying the features and advantages of this invention will be described in detail in the following description. It should be understood that this invention can have various variations in different implementations, all of which do not depart from the scope of this invention, and the descriptions and illustrations herein are for illustrative purposes only and not intended to limit this invention.

[0025] For example, different embodiments in this disclosure may use repeated reference numerals and / or designations. These repetitions are for simplification and clarity and are not intended to limit the relationships between the various embodiments and / or the described appearance structures. Furthermore, when a component is referred to as "connected to" or "coupled to" another component, it may be directly connected to or coupled to the other component, or there may be intervening components. Additionally, it is understood that although terms such as "first," "second," and "third" may be used in the claims to describe different components, these components should not be limited by these terms, and the components described accordingly in the embodiments are represented by different component symbols. These terms are used to distinguish different components. For example, a first component may be referred to as a second component, and similarly, a second component may be referred to as a first component without departing from the scope of the embodiments. The term "and / or" as thus used includes any or all combinations of one or more of the associated listed embodiments.

[0026] Please see Figure 1A and Figure 1B ,in Figure 1A This is a schematic diagram of the architecture of the DC component extraction system in this embodiment. Figure 1B for Figure 1A The diagram shows a model of a third-order generalized integrator. The DC component extraction system 1 in this embodiment can be applied to an off-grid inverter to receive the AC signal provided by the off-grid inverter. For example, the output voltage or inductor current provided by the off-grid inverter, and the AC signal. Extract the first DC component signal The DC component extraction system 1 includes an input module 2 and a third-order generalized integrator (TOGI) 3. The input module 2 receives AC signals. The third-order generalized integrator 3 is electrically connected to the input module 2 and includes a second-order filter 30a and a third-order filter 31. The second-order filter 30a is used to process AC signals. Filtering is performed to obtain the first filtered signal. The third-order filter 31 is used to receive the first filtered signal. With AC signal and the first filtered signal With AC signal The difference is calculated to extract the AC signal based on the calculation result. The first DC component signal in .

[0027] In some embodiments, the model of the third-order generalized integrator 3 is as follows: Figure 1B As shown, the third-order generalized integrator 3 receives AC signals. and angular frequency It includes a second-order filter 30a, an auxiliary second-order filter 30b, and a third-order filter 31. The second-order filter 30a filters the AC signal Ug according to the first transfer function G1 to generate a first filtered signal. The auxiliary second-order filter 30b filters the AC signal Ug based on the auxiliary transfer function Ga to generate an auxiliary filtered signal. The third-order filter 31 generates the first DC component signal based on the second transfer function G2. The second filtered signal With auxiliary filter signal Differential signals can be obtained by performing differential operations. , differential signal It contains no DC component. Traditional third-order generalized integrators are used in grid-connected inverters, typically for grid harmonic detection. A pair of orthogonal first-filter signals are generated by designing a filter. Sum and differential signals The DC component is then filtered out. The DQ-axis components are then obtained through Park transform, which can be used for phase-locked loop (PLL). The purpose is to ensure that the phase angle is unaffected by the DC bias of the grid voltage during PLL.

[0028] In some embodiments, the first transfer function G1 of the second-order filter 30a, the second transfer function G2 of the third-order filter 31, and the auxiliary transfer function Ga of the auxiliary second-order filter 30b are respectively expressed as follows: ; ; ;in, For the Laplace operator, This is the adjustment coefficient for the third-order generalized integrator 3, and the adjustment coefficient is between 0.1 and 2.0, preferably 0.5. AC signal angular frequency.

[0029] Furthermore, from the second transfer function G2 of the third-order filter 31, we can obtain: ; The above formula can be further modified as follows: ; Furthermore, given the first transfer function G1 of the second-order filter 30a, we can obtain: = ; In addition, the AC signal With the first filtered signal Subtracting them, we get: ; again The following is an expression: ; Substitute the above results back The expression is used to obtain the first DC component signal generated by the third-order filter 31. as follows: .

[0030] In the DC component extraction system 1 of the present invention, the third-order generalized integrator 3 can generate a first filtered signal through the operation of the second-order filter 30a. First filtered signal This is the AC component after the DC component has been removed. Further, the DC component extraction system 1 uses a third-order filter 31 to process the AC signal. With the first filtered signal The difference is calculated to obtain the first DC component signal. The first DC component signal Represents an alternating signal The DC component in the signal can be directly used for compensation control of the output voltage of off-grid inverters. Theoretically, if the third-order transfer function of a traditional third-order generalized integrator is used directly for calculation, the computational load is large and the discretization is complex. To simplify the calculation, this invention mathematically decomposes the third-order function into two parts: one is the AC signal. To the first filtered signal The first transfer function, and the other is the first filtered signal. To the first DC component signal The second transfer function. Therefore, it is only necessary to first calculate... The first DC component signal can then be obtained through first-order calculation. It does not require a complete implementation of the third-order discrete function, which can significantly reduce computational complexity and latency.

[0031] In actual operation, when the AC signal frequency When the frequency changes, the third-order generalized integrator 3 can detect the frequency in real time. And correspondingly correct the angular frequency To maintain the DC component extraction system 1 for AC signals of different frequencies The DC component extraction accuracy is high, so the DC component extraction system 1 can adapt to the frequency drift of the off-grid inverter under dynamic operating conditions and ensure the accuracy of DC component detection.

[0032] Since the gain of the third-order generalized integrator 3 at zero frequency is Instead of 1, the extracted first DC component signal actual value Therefore, in order to obtain the actual DC component signal, in some embodiments, the DC component extraction system 1 further includes a divider 4 to divide the first DC component signal output by the third-order filter 31. Divide by adjustment coefficient To output the second DC component signal In this way, after normalization by divider 4, the first DC component signal can be obtained. To obtain the true DC component amplitude, i.e., the second DC component signal. .

[0033] Due to the first DC component signal and the second DC component signal Harmonic components are typically present. Therefore, to suppress harmonics, in some embodiments, the DC component extraction system 1 also includes a low-frequency SOGI (Second-Order Generalized Integrator) filter 5. When the DC component extraction system 1 does not have a divider 4, the low-frequency SOGI filter 5 is electrically connected to the third-order filter 31, or when the DC component extraction system 1 includes a divider 4, such as... Figure 1A As shown, the low-frequency SOGI filter 5 is electrically connected to the divider 4 and is used to process the first DC component signal. Or the second DC component signal Filtering is performed to suppress the first DC component signal. Or the second DC component signal The high-frequency noise or harmonic components in the signal, therefore, the first DC component signal after processing by the low-frequency SOGI filter 5 Or the second DC component signal It can be used as an input signal for subsequent DC flow stabilization processing and control calculations.

[0034] In some embodiments, the DC component extraction system 1 may further include an averaging module (not shown) for averaging the aforementioned first DC component signal. Or the second DC component signal Average value processing is performed to output a stable DC component signal.

[0035] In some embodiments, the low-frequency SOGI filter 5 includes a third transfer function, expressed as follows: ; in, The third transfer function, This is the cutoff angular frequency of the low-frequency SOGI filter 5. In other embodiments, Corresponding to a cutoff angular frequency of approximately 10Hz, it effectively suppresses high-frequency noise without affecting the tracking of DC component changes. Compared to traditional second-order low-pass filters, the low-frequency SOGI filter 5 used in this invention exhibits greater attenuation at the center frequency, more effectively suppressing harmonic components of the AC signal. Furthermore, above the center frequency, its amplitude and phase frequency characteristics attenuate at a faster rate than traditional second-order low-pass filters, resulting in better suppression of high-frequency interference and harmonic components. In other words, the low-frequency SOGI filter 5 of this invention combines the strong suppression characteristics of the TOGI structure for the fundamental frequency component with the rapid attenuation characteristics of a low-pass filter for high-frequency noise, thus significantly improving the system's anti-interference capability and output stability while preserving the DC component.

[0036] As can be seen from the foregoing, the DC component extraction system 1 includes a third-order generalized integrator 3, and the third-order generalized integrator 3 first passes the AC signal through a second-order filter 30a and a third-order filter 31. Decomposed into the first filtered signal With the first DC component signal The true DC component is then restored by divider 4. Finally, the low-frequency SOGI filter 5 outputs a smooth and stable DC signal. Therefore, the overall architecture of the DC component extraction system 1 can achieve accurate extraction without adding a new hardware sampling path. It has low computational load and low latency, making it suitable for implementation with a microcontroller unit (MCU) or a digital signal processor (DSP).

[0037] To verify the effectiveness of the DC component extraction system 1 of this invention in an off-grid inverter, a demonstrative comparative experiment was conducted. The experimental conditions were: AC signal... ,frequency The tests were conducted with and without DC components, and with DC biases of ±0.5V and ±1V. The results were compared with commonly used hardware and software extraction techniques. The comparison results are shown in Table 1.

[0038] (Table 1)

[0039] As shown in Table 1 above, the DC component extraction system 1 used in this invention has a detection error range of approximately ±0.02V to ±0.05V for the extracted DC component signal under the condition of no harmonic interference, which is significantly better than the ±0.06V to ±0.08V error level of the existing scheme.

[0040] Furthermore, to verify the invention's ability to suppress harmonic interference, an AC signal was used... A certain proportion of harmonic components (including low-order harmonics, specifically 15% for the 3rd, 10% for the 5th, 5% for the 7th, 2% for the 9th, and 1% for the 11th) were superimposed on the sample, and compared with commonly used hardware and software extraction techniques. The comparison results are shown in Table 2.

[0041] (Table 2)

[0042] As shown in Table 2 above, the commonly used hardware and software extraction techniques produce serious detection deviations (maximum error exceeding ±0.58V) under harmonic interference conditions, while the DC component extraction system 1 used in this invention significantly reduces the error to within ±0.08V under the same conditions.

[0043] Please see Figure 2 This is a flowchart illustrating the steps of the DC component extraction method in this embodiment. The DC component extraction method of this embodiment can be applied to... Figure 1A The DC component extraction system 1 shown includes the following steps in its DC component extraction method.

[0044] Step S1, Receive AC signal .

[0045] Step S2, the AC signal is filtered by a second-order filter 30a. Filtering is performed to obtain the first filtered signal. .

[0046] Step S3, the first filtered signal is filtered by the third-order filter 31. With AC signal The difference is used for calculation, and the AC signal is extracted based on the calculation result. The first DC component signal in .

[0047] In some embodiments, the DC component extraction method further includes step S4, which involves processing the first DC component signal output by the third-order filter 31. Divide by the adjustment factor to output the second DC component signal. .

[0048] In some embodiments, the DC component extraction method further includes step S5, where the first DC component signal is filtered by a low-frequency SOGI filter 5. (or the second DC component signal) Filtering is performed to suppress high-frequency noise or harmonic components.

[0049] In summary, this invention provides a DC component extraction system and a suitable DC component extraction method. It uses a third-order generalized integrator as its core architecture and, through the coordinated operation of second-order and third-order filters, decomposes the AC signal into a first filtered signal (containing no DC component) and a first DC component signal representing the DC component. This achieves rapid and accurate extraction of the DC component within existing sampling lines and digital computing resources. Furthermore, under pure sinusoidal operating conditions and conditions containing harmonic interference, compared to existing hardware-software combined extraction techniques, this invention significantly reduces the detection error of the DC component and has better suppression capabilities for harmonics and noise disturbances. Therefore, the DC component extraction system and suitable DC component extraction method proposed in this invention are sufficient to effectively improve the problem of DC bias in AC signals in power electronic devices such as off-grid inverters.

Claims

1. A DC component extraction system, comprising: An input module receives an AC signal; and A third-order generalized integrator, electrically connected to the input module, and comprising: A first- or second-order filter is used to filter the AC signal to obtain a first filtered signal; A third-order filter is used to calculate the difference between the first filtered signal and the AC signal, and to extract a first DC component signal from the AC signal based on the calculation result.

2. The DC component extraction system as described in claim 1, wherein the DC component extraction system is applied to an off-grid inverter, and the off-grid inverter outputs the AC signal.

3. The DC component extraction system as described in claim 1, wherein the second-order filter includes a first transfer function, expressed as follows: ； in, This is the first transfer function. For the Laplace operator, This is an adjustment coefficient for the third-order generalized integrator. This refers to one angular frequency of the AC signal; The third-order filter mentioned above includes a second transfer function, expressed as follows: ； in, This is the second transfer function.

4. The DC component extraction system as described in claim 3, wherein the first DC component signal generated by the third-order filter satisfies the following operational relationship: ； in This is the first DC component signal. The AC signal, This is the first filtered signal.

5. The DC component extraction system as described in claim 3, wherein the adjustment coefficient is between 0.1 and 2.0, preferably 0.

5.

6. The DC component extraction system of claim 3, wherein the DC component extraction system includes a divider for dividing the first DC component signal output by the third-order filter by the adjustment coefficient to output a second DC component signal.

7. The DC component extraction system as claimed in claim 1, wherein the DC component extraction system includes a low-frequency SOGI filter electrically connected to the third-order filter for filtering the first DC component signal to suppress high-frequency noise or harmonic components.

8. The DC component extraction system of claim 7, wherein the low-frequency SOGI filter includes a third transfer function, expressed as follows: ； in, The third transfer function, For the Laplace operator, This is an adjustment coefficient for the third-order generalized integrator. This is a cutoff angular frequency of the low-frequency SOGI filter.

9. A method for extracting a DC component, applied in a DC component extraction system, the DC component extraction system comprising a third-order generalized integrator, the third-order generalized integrator comprising a second-order filter and a third-order filter, the DC component extraction method comprising: (S1) Receive an AC signal; (S2) The AC signal is filtered by the second-order filter to obtain a first filtered signal; and (S3) The difference between the first filtered signal and the AC signal is calculated by the third-order filter, and a first DC component signal is extracted from the AC signal based on the calculation result.

10. The DC component extraction method as described in claim 9, wherein the DC component extraction system is applied to an off-grid inverter, and the off-grid inverter outputs the AC signal.

11. The DC component extraction method as described in claim 9, wherein the second-order filter comprises a first transfer function, expressed as follows: ； in, This is the first transfer function. For the Laplace operator, This is an adjustment coefficient for the third-order generalized integrator. This refers to one angular frequency of the AC signal; The third-order filter mentioned above includes a second transfer function, expressed as follows: ； in, This is the second transfer function.

12. The DC component extraction method as described in claim 11, wherein the first DC component signal generated by the third-order filter satisfies the following operational relationship: ； in This is the first DC component signal. The AC signal, This is the first filtered signal.

13. The DC component extraction method as described in claim 11, wherein the adjustment coefficient is between 0.1 and 2.0, and preferably 0.

5.

14. The DC component extraction method as described in claim 11, further comprising: (S4) Divide the first DC component signal output by the third-order filter by the adjustment coefficient to output a second DC component signal.

15. The DC component extraction method of claim 11, wherein the DC component extraction system includes a low-frequency SOGI filter, and the DC component extraction method includes: (S5) The first DC component signal is filtered by the low-frequency SOGI filter to suppress high-frequency noise or harmonic components.

16. The DC component extraction method as described in claim 15, wherein the low-frequency SOGI filter includes a third transfer function, expressed as follows: ； in, The third transfer function, For the Laplace operator, This is an adjustment coefficient for the third-order generalized integrator. This is a cutoff angular frequency of the low-frequency SOGI filter.

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