A band-pass filter with no fundamental loss low parallel resonance

Abstract

This invention relates to the field of power grid harmonic mitigation technology, and particularly to a bandpass filter with low parallel resonance and no fundamental loss. It includes a first single-tuned filter Hn1 and a second single-tuned filter Hn2 connected in parallel. The series resonant frequencies of the first single-tuned filter Hn1 and the second single-tuned filter Hn2 are different, and a resistor R1 is connected across the first single-tuned filter Hn1 and the second single-tuned filter Hn2. The first single-tuned filter Hn1 includes a first capacitor C11, a second capacitor C12, and a first reactance L1, which are connected in series. The second single-tuned filter Hn2 includes a third capacitor C2 and a second reactance L2, which are connected in series. This invention features a simple structure, low cost, and no fundamental loss across resistor R1, which helps improve the energy conversion efficiency of the entire power system, reduces energy loss during transmission and processing, and has excellent energy-saving effects.

Description

Technical Field

[0001] This invention relates to the field of power grid harmonic control technology, and in particular to a bandpass filter with low parallel resonance and no fundamental loss. Background Technology

[0002] With the rapid development of power electronics technology, converter equipment, including rectifier equipment, inverter equipment, chopper equipment, etc., is constantly progressing towards high efficiency, reliability and intelligence. However, it generates a lot of harmonic pollution during application. These harmonics can harm other equipment in the power grid and affect the safe operation of the power grid.

[0003] To reduce the harm of harmonics to the power grid, users who generate harmonics need to manage the harmonics flowing into the public power grid. Currently, passive harmonic filters composed of capacitors, reactors, and resistors are widely used to suppress harmonics in the power system. However, passive harmonic filters are prone to parallel resonance in practical applications. At the resonant frequency, the impedance of the passive harmonic filter interacts with the impedance of the power system, causing a sharp increase in current or voltage in the power supply and passive harmonic filter circuits, damaging power components and affecting the safe operation of the power system.

[0004] For example, in a power system with a fundamental frequency of 50Hz, the main harmonics of a 24-pulse rectifier are the 23rd and 25th harmonics, corresponding to harmonic frequencies of 1150Hz and 1250Hz respectively. However, in actual operation, a small number of lower harmonics such as the 5th, 7th, 11th, 13th, 17th, and 19th harmonics will also be generated. A single-tuned filter is a type of passive harmonic filter that has a high efficiency in filtering harmonics of specific frequencies. If only a 23rd harmonic filter is installed, it may easily cause parallel resonance, leading to the amplification of lower harmonics. Currently, in order to prevent parallel resonance in the filter circuit, the conventional approach is to suppress it starting from the lower harmonics, that is, to install 5th, 7th, and 11th harmonic filters. Although this avoids lower harmonic resonance, the filtering effect on the main 23rd and 25th harmonics is relatively small. If more passive harmonic filters are installed in the power system, the equipment installation cost is high. If multiple passive filters are connected in parallel, it is difficult to quickly locate the problem if it occurs, resulting in high maintenance costs.

[0005] In the prior art, a single-tuned filter can be extended into a bandpass filter by combining multiple sets of capacitors and reactors or cascading with other filters, allowing harmonics within a certain frequency range to pass through. For example, the utility model patent with publication number CN201898336U discloses a double-tuned filter based on a smoothing resistor, which can reduce the impedance at the parallel resonant point. However, the loss on the resistor of this filter is large, which increases the cost of the resistor itself and wastes a lot of electrical energy. Summary of the Invention

[0006] The purpose of this invention is to provide a bandpass filter with no fundamental loss and low parallel resonance, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A bandpass filter with low parallel resonance and no fundamental frequency loss includes a first single-tuned filter Hn1 and a second single-tuned filter Hn2 connected in parallel. The series resonant frequencies of the first single-tuned filter Hn1 and the second single-tuned filter Hn2 are different, and a set of resistors R1 is connected between the first single-tuned filter Hn1 and the second single-tuned filter Hn2. The first single-tuned filter Hn1 includes multiple capacitors connected in series, and the second single-tuned filter Hn2 includes one capacitor.

[0009] Preferably, the first single-tuned filter Hn1 includes a first capacitor C11, a second capacitor C12 and a first reactance L1, wherein the first capacitor C11, the second capacitor C12 and the first reactance L1 are connected in series, and the second single-tuned filter Hn2 includes a third capacitor C2 and a second reactance L2, wherein the third capacitor C2 and the second reactance L2 are connected in series.

[0010] Preferably, the series resonant frequency of the first single-tuned filter Hn1 is n1f1, and the series resonant frequency of the second single-tuned filter Hn2 is n2f1, where f1 is the fundamental frequency, and n1 and n2 are both natural numbers greater than 1. <n2。

[0011] Preferably, the capacitance of the first capacitor C11 is C 11 The capacitance of the second capacitor C12 is C 12 The inductance of the first reactance L1 is L1; the fundamental impedance of the first capacitor C11 is XC. 11 =-1 / (2πf1C) 11 The fundamental impedance XC of the second capacitor C12 12 =-1 / (2πf1C) 12 The fundamental impedance of the first reactance L1 is XL1 = 2πf1L1, XC 11 XC 12 XL1 and XL1 satisfy the following relationship:

[0012] (XC 11 +XC 12 ) / n1=-n1*XL1.

[0013] Preferably, the capacitance of the third capacitor C2 is C2, the inductance of the second reactance L1 is L2, the fundamental impedance of the third capacitor C2 is XC2 = -1 / (2πf1C2), and the fundamental impedance of the second reactance L1 is XL2 = 2πf1L2. XC2 and XL2 satisfy the following relationship:

[0014] XC2 / n2=-n2*XL2.

[0015] Preferably, the total fundamental impedance of the first capacitor C11 and the second capacitor C12 in the first single-tuned filter Hn1 remains unchanged. Based on the total fundamental impedance, the fundamental impedance values ​​of the first capacitor C11 and the second capacitor C12 are adjusted, and the fundamental voltage across resistor R1 is 0. At this time, the fundamental loss on resistor R1 is 0. 11 XC 12 XL1, XC2, and XL2 satisfy the following relationship:

[0016] XC 11 / (XL1+XC 12 ) = XC2 / XL2.

[0017] Preferably, one end of the first reactance L1 is connected to one end of the second reactance L2, one end of the first capacitor C11 is connected to one end of the third capacitor C2, the other end of the first capacitor C11 is connected to one end of the second capacitor C12 and one end of the resistor R1, the other end of the first reactance L1 is connected to the other end of the second capacitor C12, and the other end of the second reactance L2 is connected to the other end of the second capacitor C2 and the other end of the resistor R1.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] This invention provides a bandpass filter with low parallel resonance and no fundamental frequency loss. It features a simple structure and low cost. Compared to two sets of conventional single-tuned filters connected in parallel, the harmonic current amplification factor is significantly reduced due to the resistor R1 bridging the first single-tuned filter Hn1 and the second single-tuned filter Hn2, thus lowering the possibility of parallel resonance. Compared to a double-tuned filter based on a smoothing resistor, although a resistor R2 is also bridging the two parallel first and second sub-filters in a double-tuned filter, the fundamental frequency voltage across resistor R2 in the double-tuned filter is not zero, resulting in significant fundamental frequency loss and wasted energy. The filter of this invention has no fundamental frequency loss across resistor R1, which helps improve the energy conversion efficiency of the entire power system, reduces energy loss during transmission and processing, and enables the system to achieve the same filtering effect with less input energy, resulting in excellent energy-saving performance. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a bandpass filter structure with low parallel resonance and no fundamental wave loss, as described in an embodiment of the present invention.

[0021] Figure 2 This is a schematic diagram of the structure of two sets of conventional single-tuned filters connected in parallel in the prior art;

[0022] Figure 3 This is a schematic diagram of the structure of a dual-tuned filter based on a smoothing resistor, as referenced in the background section of this invention.

[0023] Figure 4 This is a schematic diagram illustrating the application of the bandpass filter with no fundamental loss and low parallel resonance described in this invention in engineering.

[0024] Figure 5 This is a schematic diagram illustrating the application of two sets of conventional single-tuned filters connected in parallel in an engineering context.

[0025] Figure 6 This is a schematic diagram illustrating the application of a dual-tuned filter based on a smoothing resistor in engineering.

[0026] Figure 7 The diagram shows the current multiples of harmonics flowing into the system after the application of the bandpass filter with low parallel resonance and no fundamental loss described in this invention.

[0027] Figure 8 A diagram showing the current multiples of harmonics flowing into the system after applying two sets of conventional single-tuned filters in parallel.

[0028] Figure 9 A diagram showing the current multiples of harmonics flowing into the system after applying a dual-tuned filter based on a smoothing resistor. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0030] In the following description of the invention, it should be noted that the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation. The term "connection" simply indicates a connection between devices and has no special meaning.

[0031] Furthermore, the technical fields and installation methods involved in the embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] For specific implementation examples, please refer to: Figure 1A bandpass filter with low parallel resonance and no fundamental loss includes a first single-tuned filter Hn1 and a second single-tuned filter Hn2 connected in parallel. The series resonant frequencies of the first single-tuned filter Hn1 and the second single-tuned filter Hn2 are different, and a set of resistors R1 is connected between the first single-tuned filter Hn1 and the second single-tuned filter Hn2.

[0033] The first single-tuned filter Hn1 includes multiple capacitors connected in series. The first single-tuned filter Hn1 includes a first capacitor C11, a second capacitor C12, and a first reactance L1. The first capacitor C11, the second capacitor C12, and the first reactance L1 are connected in series, with a series resonant frequency of n1f1, where f1 is the fundamental frequency. The first single-tuned filter Hn1 filters the n1th harmonic, where n1 is a natural number greater than 1. The capacitance of the first capacitor C11 is C... 11， The fundamental impedance of the first capacitor C11 is XC 11 The capacitance of the second capacitor C12 is C 12 The fundamental impedance of the second capacitor C12 is XC. 12 The inductance of the first reactance L1 is L1, and the fundamental impedance of the second capacitor C12 is XL1.

[0034] Among them, the fundamental impedance XC of the first capacitor C11 11 The calculation formula is:

[0035] XC 11 =-1 / (2πf1C) 11 )

[0036] The fundamental impedance XC of the second capacitor C12 12 The calculation formula is:

[0037] XC 12 =-1 / (2πf1C) 12 )

[0038] The formula for calculating the fundamental impedance XL1 of the first reactance L1 is:

[0039] XL1=2πf1L1

[0040] When the series resonant frequency is n1f1, XC 11 XC 12 XL1 and XL1 satisfy the following relationship:

[0041] (XC 11 +XC 12 ) / n1=-n1*XL1

[0042] The second single-tuned filter Hn2 includes a third capacitor C2 and a second reactance L2. The third capacitor C2 and the second reactance L2 are connected in series, and the series resonance frequency is n2f1, where f1 is the fundamental frequency. The second single-tuned filter Hn2 filters the n2th harmonic, n2 is a natural number greater than 1, and n1 < n2; One end of the first reactance L1 is connected to one end of the second reactance L2, one end of the first capacitor C11 is connected to one end of the third capacitor C2, the other end of the first capacitor C11 is connected to one end of the second capacitor C12 and one end of the resistor R1, the other end of the first reactance L1 is connected to the other end of the second capacitor C12, and the other end of the second reactance L2 is connected to the other end of the second capacitor C2 and the other end of the resistor R1.

[0043] The capacitance value of the third capacitor C2 is C2, the fundamental impedance of the third capacitor C2 is XC2, the inductance of the second reactance L1 is L2, and the fundamental impedance of the second reactance L1 is XL2.

[0044] Among them, the fundamental impedance XC2 of the third capacitor C2 is:

[0045] XC2 = -1 / (2πf1C2)

[0046] The fundamental impedance XL2 of the second reactance L1 is:

[0047] XL2 = 2πf1L2

[0048] When the series resonance frequency is n2f1, XC2 and XL2 satisfy the following relationship:

[0049] XC2 / n2 = -n2*XL2

[0050] When XC 11 / (XL1 + XC 12 ) = XC2 / XL2, the fundamental voltage across the resistor R1 is 0, and at this time the fundamental loss on the resistor R1 is 0.

[0051] The total fundamental impedance value of the first capacitor C11 and the second capacitor C12 in the first single-tuned filter Hn1 remains unchanged. Based on the total fundamental impedance value, the distribution of the fundamental impedance values of the first capacitor C11 and the second capacitor C12 is adjusted. The change in the fundamental impedance values of the first capacitor C11 and the second capacitor C12 will affect the voltage distribution between the first capacitor C11 and the second capacitor C12, thereby changing the fundamental voltage and fundamental loss of the resistor R1. When the fundamental impedance values of the first capacitor C11 and the second capacitor C12 satisfy a specific relationship, the fundamental voltage across the resistor R1 is 0, and at this time the fundamental loss on the resistor R1 is 0.

[0052] Such as Figure 2This represents two sets of conventional single-tuned filters connected in parallel in the prior art. One set of conventional single-tuned filters includes capacitor C3 and reactance L3 connected in series to filter the n1st harmonic. The other set of conventional single-tuned filters includes capacitor C4 and reactance L4 connected in series to filter the n2th harmonic. One end of reactance L3 is connected to one end of reactance L4, and one end of capacitor C3 is connected to one end of capacitor C4. The capacitance values ​​of capacitor C3 and capacitor C4 are C3 and C4, respectively, and C3 and C4 are different. The inductance values ​​of reactance L3 and reactance L4 are L3 and L4, respectively. The fundamental impedance of capacitor C3 is represented by XC3, the fundamental impedance of capacitor C4 is represented by XC4, and the fundamental impedances of reactance L3 and reactance L4 are represented by XL3 and XL4, respectively.

[0053] like Figure 3 This represents a dual-tuned filter based on a smoothing resistor, comprising capacitor C5, capacitor C6, reactance L5, and reactance L6. C5 and L5 are connected in series to form the first sub-filter, used to filter the n1st harmonic. C6 and L6 are connected in series to form the second sub-filter, used to filter the n2th harmonic. The series circuit of C5 and L5 is connected in parallel with the series circuit of C6 and L6. A resistor R2 is connected across the series circuit of C5 and L5 and the series circuit of C6 and L6. The capacitance values ​​of C5 and C6 are C5 and C6, respectively, and C5 and C6 are different. The fundamental impedance of C5 is denoted as XC5, the fundamental impedance of C6 is denoted as XC6, and the fundamental impedances of L5 and L6 are denoted as XL5 and XL6, respectively.

[0054] like Figures 4-6 As shown, the bandpass filter with low parallel resonance and no fundamental wave loss, two sets of conventional single-tuned filters in parallel, and a dual-tuned filter based on a smoothing resistor described in this invention are respectively applied to a power system. The power system includes a harmonic current source and a fundamental voltage source U, which are connected in parallel. The harmonic current source and the fundamental voltage source U provide AC power to the system. The two ends of the harmonic current source are respectively connected to the bandpass filter with low parallel resonance and no fundamental wave loss, two sets of conventional single-tuned filters in parallel, or a dual-tuned filter based on a smoothing resistor described in this invention. In this embodiment, the voltage of the fundamental voltage source U is set to 5774V, and a series reactor LS is connected in series at the output terminal of the fundamental voltage source U. The inductance value of the series reactor LS is L. S The fundamental impedance of the line where the fundamental voltage source U is located is XL. S In the present invention, the resistor R1 in the bandpass filter with low parallel resonance and no fundamental wave loss and the resistor R2 in the dual-tuned filter based on the smoothing resistor are both set to 60Ω.

[0055] set up Figures 4 to 6 In the middle, XC 11 With XC 12 The sum of XC3 and XC5 is equal to that of XC2, XC4 and XC6. The inductances of reactance 5 L5 and reactance 6 L6 are L5 and L6 respectively. XL1, XL3 and XL5 are equal to that of XL2, XL4 and XL5.

[0056] Specifically, such as Figure 4 As shown, the fundamental impedance XC of the first capacitor C11 in the filter described in this invention 11 =-j83.12, the fundamental impedance XC of the second capacitor C12 12 = -j3.28, the fundamental impedance of the first reactor L1 is XL1 = j3.53, the fundamental impedance of the third capacitor C2 is XC2 = -j129.6, the fundamental impedance of the second reactor L1 is XL2 = j0.25, and the impedance of the fundamental voltage source U is XL S =j1.1;

[0057] like Figure 5 As shown, in the two sets of parallel conventional single-tuned filters, the impedance of capacitor C3 is XC3 = -j86.4, the fundamental impedance of capacitor C4 is XC4 = -j129.6, the fundamental impedance of reactance L3 is XL3 = j3.53, the fundamental impedance of reactance L4 is XL4 = j0.25, and the impedance of the fundamental voltage source U is XL. S =j1.1;

[0058] like Figure 6 As shown, in the dual-tuned filter based on smoothing resistors, the fundamental impedance of capacitor C5 is XC5 = -j86.4, the fundamental impedance of capacitor C6 is XC6 = -j129.6, the fundamental impedance of reactance L5 is XL5 = j3.53, the fundamental impedance of reactance L6 is XL6 = j0.25, and the impedance of the fundamental voltage source U is XL. S =j1.1.

[0059] Figure 7-9 Under the above parameter conditions, the filter of the present invention, two sets of parallel conventional single-tuned filters, and a double-tuned filter based on smoothing resistors are applied to the current multiple diagram of the above power system. A harmonic analyzer or power quality analyzer is connected to the test point of the power system to continuously record voltage or current signals. The harmonic analyzer automatically performs a fast Fourier transform to convert the collected signals into frequency domain data, thereby identifying each harmonic component. Based on the analysis results, the current multiple diagram of harmonics flowing into the system is plotted with the harmonic order as the abscissa and the multiple relationship between the harmonic current after the filter is put into operation and the harmonic current before the filter is put into operation as the ordinate.

[0060] like Figure 7 As shown, under the same parameter conditions, the filter of this invention exhibits peak values ​​at the 4th and 11th harmonic frequencies, with current multiples corresponding to 2.4 and 2.0, respectively, which is significantly better than... Figure 8 The current factor is much smaller, and also smaller than... Figure 9 The slightly smaller maximum current multiple indicates that the parallel resonance in the power system is not significant, and it has good safety.

[0061] like Figure 8 As shown, under the same parameter conditions, the current multiples of two sets of parallel conventional single-tuned filters are 13.0 and 36.5 at the 4th and 11th harmonic frequencies, respectively. After the filters are put into operation, the ratio of each harmonic current to the harmonic current before the filters are put into operation reaches a local maximum value, which amplifies the harmonic current at that frequency. At this time, the power system experiences obvious parallel resonance, which amplifies the harmonic current and poses a great threat to the equipment of the power system, easily causing burn-out accidents.

[0062] like Figure 9 As shown, the harmonic current amplification factor of the dual-tuned filter based on the smoothing resistor is approximately the same as that of the filter of this invention. Peak values ​​appear at the 4th and 11th harmonic frequencies, respectively, with current multiples of 2.5 and 2.0, respectively, indicating that parallel resonance in the power system is not obvious.

[0063] but, Figure 9 In the dual-tuned filter based on a smoothing resistor, the fundamental current flowing through resistor R2 is 4A, and its fundamental loss is 960W. This increases the loss and operating temperature of resistor R2, which is detrimental to energy conservation in the power system. Figure 7 The filter of this invention has a slightly smaller current amplification factor and a lower harmonic current content at the 4th harmonic frequency. Furthermore, based on the configuration of each capacitor and reactance, the fundamental current flowing through resistor R1 in this invention is 0A, and its fundamental loss is 0W, resulting in good energy-saving effect.

Claims

1. A bandpass filter with no fundamental loss and low parallel resonance, characterized in that: The filter includes a first single-tuned filter Hn1 and a second single-tuned filter Hn2 connected in parallel. The series resonant frequencies of the first single-tuned filter Hn1 and the second single-tuned filter Hn2 are different, and a set of resistors R1 is connected across the first single-tuned filter Hn1 and the second single-tuned filter Hn2. The first single-tuned filter Hn1 includes multiple capacitors connected in series, and the second single-tuned filter Hn2 includes one capacitor. The first single-tuned filter Hn1 includes a first capacitor C11, a second capacitor C12 and a first reactance L1, with the first capacitor C11, the second capacitor C12 and the first reactance L1 connected in series. The second single-tuned filter Hn2 includes a third capacitor C2 and a second reactance L2, with the third capacitor C2 and the second reactance L2 connected in series. The series resonant frequency of the first single-tuned filter Hn1 is n1f1, and the series resonant frequency of the second single-tuned filter Hn2 is n2f1, where f1 is the fundamental frequency, and n1 and n2 are both natural numbers greater than 1. <n2; In the first single-tuned filter Hn1, the total fundamental impedance of the first capacitor C11 and the second capacitor C12 remains unchanged. Based on the total fundamental impedance, the fundamental impedance values ​​of the first capacitor C11 and the second capacitor C12 are adjusted, and the fundamental voltage across resistor R1 is 0. At this time, the fundamental loss on resistor R1 is 0. 11 XC 12 XL1, XC2, and XL2 satisfy the following relationship: 。 2. The bandpass filter of claim 1, wherein: The capacitance of the first capacitor C11 is C 11 The capacitance of the second capacitor C12 is C 12 The inductance of the first reactance L1 is L1; the fundamental impedance of the first capacitor C11 is XC. 11 =-1 / (2πf1C) 11 The fundamental impedance XC of the second capacitor C12 12 =-1 / (2πf1C) 12 The fundamental impedance of the first reactance L1 is XL1 = 2πf1L1, XC 11 XC 12 XL1 and XL1 satisfy the following relationship: 。 3. The bandpass filter of claim 2, wherein: The capacitance of the third capacitor C2 is C2, the inductance of the second reactance L1 is L2, the fundamental impedance of the third capacitor C2 is XC2 = -1 / (2πf1C2), and the fundamental impedance of the second reactance L1 is XL2 = 2πf1L2. XC2 and XL2 satisfy the following relationship: 。 4. The bandpass filter of claim 2, wherein: One end of the first reactor L1 is connected to one end of the second reactor L2, one end of the first capacitor C11 is connected to one end of the third capacitor C2, the other end of the first capacitor C11 is connected to one end of the second capacitor C12 and one end of the resistor R1, the other end of the first reactor L1 is connected to the other end of the second capacitor C12, and the other end of the second reactor L2 is connected to the other end of the second capacitor C2 and the other end of the resistor R1.

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