A parameter design method of a double-tuned filter with damping

Abstract

The application discloses a parameter design method of a double-tuned filter with damping, and belongs to the technical field of power quality treatment, comprising the following steps: determining the design reactance range of the double-tuned filter under each frequency band according to the harmonic range required to be filtered out by a target power grid area; selecting the optimal parameters of the inductance and the capacitance of the double-tuned filter with the lowest cost as the target; selecting the optimal damping parameters based on the optimization requirements of the load and the energy loss, and determining the final parameter design scheme. The parameter design method of the double-tuned filter with damping can reduce the energy loss as much as possible under the condition of guaranteeing a low harmonic level and a low component cost, realize the parameter design of the double-tuned filter, and has the advantages of low cost, low loss, convenient calculation, high practicability and high reliability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power quality treatment, and particularly relates to a parameter design method of a double-tuned filter with damping. BACKGROUND

[0002] With more and more new energy, electric vehicles and the like being connected to the power grid, the harmonic problem caused by power electronic equipment is becoming more and more serious, wherein the fifth and seventh harmonics in the power grid have a great impact on power quality. From the perspective of economic benefits, there are generally multiple frequencies of harmonics in the power grid, and if a single-tuned filter is used for filtering, a set of single-tuned filters in parallel is required to achieve filtering, which has the disadvantages of large floor area and high cost; and the double-tuned filter can absorb two frequencies of harmonics, and the use of fewer double-tuned filters can meet the requirements, and the floor area is smaller. From the perspective of component cost, when the double-tuned filter is working, one inductance almost bears all the impulse voltages, and the requirements for other components are lower, thereby reducing the cost and increasing the economic benefits. Therefore, the double-tuned filter has a wide application prospect.

[0003] The double-tuned filter is composed of resistors, inductors and capacitors in series and parallel connection, and damping is added to reduce power loss. How to design the parameters of the double-tuned filter under a specific power grid environment to achieve high reliability, low cost and low loss is a difficulty in current research. SUMMARY

[0004] To solve the above problems, the present application provides a parameter design method of a double-tuned filter with damping.

[0005] To achieve the above purpose, the technical scheme of the present application is as follows:

[0006] A parameter design method of a double-tuned filter with damping, comprising,

[0007] Step S1, determining the design reactance range of the double-tuned filter under each frequency band according to the harmonic range required to be filtered out by the target power grid area;

[0008] Step S2, selecting the optimal parameters of the inductance and the capacitance of the double-tuned filter with the lowest cost as the target;

[0009] Step S3, selecting the optimal damping parameters based on the optimization requirements of the load and the energy loss to determine the final parameter design scheme.

[0010] The above-mentioned double-tuned filter with damping includes a series capacitor, a series inductor, a parallel capacitor, a parallel inductor and damping, one end of the series capacitor is connected to a node of a power grid, the other end of the series capacitor is connected to one end of the series inductor, the other end of the series inductor is connected to one end of the parallel inductor, the other end of the parallel inductor is grounded, the damping is connected in parallel across the series inductor, and the parallel capacitor is connected in parallel across the parallel inductor.

[0011] The above-mentioned step S1 includes,

[0012] Step S11, assuming that two harmonic frequencies f1 and f2 need to be filtered in the power grid,

[0013] Step S12, for the harmonic frequency f1, assuming that an equivalent reactance is added at the node where the double-tuned filter with damping is deployed in the power grid, the harmonic current IHD of the power grid under different equivalent reactances is calculated f1 , and the equivalent reactance range when the harmonic current IHD of the power grid is less than the highest limit of the harmonic current is taken as the first design reactance range [0, X f1 ] of the double-tuned filter. f1,max

[0014] Step S13, for the harmonic frequency f2, assuming that an equivalent reactance is added at the node where the double-tuned filter with damping is deployed in the power grid, the harmonic current IHD of the power grid under different equivalent reactances is calculated f2 , and the equivalent reactance range when the harmonic current IHD of the power grid is less than the highest limit of the harmonic current is taken as the second design reactance range [0, X f2 ] of the double-tuned filter. f2,max

[0015] The above-mentioned step S2 includes,

[0016] Step S21, according to the design reactance range of the double-tuned filter under each frequency band, the parameters of two parallel single-tuned filters meeting the requirements are designed, wherein the harmonic frequency filtered by the first single-tuned filter is f1, the harmonic frequency filtered by the second single-tuned filter is f2, and the sum C total of the capacitances of the two parallel single-tuned filters is designed according to the reactive power compensation capacity of the double-tuned filter:

[0017]

[0018] , wherein f b and U b are the fundamental frequency and the fundamental voltage, respectively, and Q is the reactive power compensation demand of the power grid under the fundamental frequency.

[0019] Step S22, setting the initial value of the capacitance, wherein the capacitance C a ​​= 0, the capacitance C of the second single-tuned filter b = C total -C a ;

[0020] Step S23, let C a = C a +dC, C b = C b -dC, wherein dC is a set capacitance change amplitude;

[0021] Step S24, determine whether C a is greater than C total ;

[0022] Step S25, if C a is not greater than C total , according to the impedance design requirements of the single-tuned filter, the inductance value of the single-tuned filter at this time is calculated, and the specific formula is as follows:

[0023]

[0024] Wherein, L a and L b are the inductance values of the first single-tuned filter and the second single-tuned filter respectively;

[0025] Step S26, convert the parameters of the two single-tuned filters into the parameters of the double-tuned filter and return to step S23, and the conversion formula is as follows:

[0026]

[0027] Wherein, C1, C2, L1, L2 are the series capacitance, parallel capacitance, series inductance and parallel inductance in the double-tuned filter respectively;

[0028] Step S27, if C a is greater than C total , take the lowest double-tuned filter cost corresponding parallel capacitance value C2 and the corresponding C1, L1, L2 value in each calculation above as the optimal parameters of the inductance and capacitance of the double-tuned filter.

[0029] The above step S3 includes,

[0030] Step S31, input the optimal parameters C1, C2, L1, L2 of the inductance and capacitance of the double-tuned filter in step S2, and set the initial damping R1 = 0Ω;

[0031] Step S32, let the damping R1 = R1+dR, wherein dR is a damping change amplitude;

[0032] Step S33, under the damping, the grid harmonic rate THD and the grid harmonic current IHD of the double-tuned filter in operation are calculated, if the grid harmonic rate THD and the grid harmonic current IHD exceed the limit, return to step S32;

[0033] Step S34, if the grid harmonic rate THD and the grid harmonic current IHD do not exceed the limit, the energy loss is calculated;

[0034] Step S35, the ratio dZ / dR1 of the change of the overall impedance Z of the double-tuned filter to the change of the damping R1 is analyzed, if dZ / dR1<z, it is determined that the damping change has little effect on the operation level of the double-tuned filter, and the search is ended; otherwise, return to step S32, wherein z is a set value;

[0035] Step S36, in the above calculation, the damping R1 when the unit energy loss can filter out the most harmonics is selected as the optimal damping parameter, and the optimal parameter of the inductance and the capacitance of the double-tuned filter in step S2 is combined to obtain the final parameter design scheme of the double-tuned filter.

[0036] The energy loss is the active loss of the double-tuned filter, and the calculation formula is as follows

[0037]

[0038] Wherein, U is the voltage across the double-tuned filter, and Z is the overall impedance of the double-tuned filter.

[0039] In a specific embodiment, the cost of the double-tuned filter is composed of the inductance cost and the capacitance cost.

[0040] In a specific embodiment, the calculation method of the inductance cost is

[0041]

[0042] Wherein, COST(L i ) is the inductance L i cost, L i is the inductance value, is the current flowing through the inductance.

[0043] In a specific embodiment, the set precision value z is 1%.

[0044] In a specific embodiment, the damping change amplitude dR=2Ω.

[0045] Beneficial effects, the parameter design method of a double-tuned filter with damping, can reduce energy loss as much as possible under the condition of ensuring lower harmonic level and lower component cost, realize the design of the parameters of the double-tuned filter, and has the advantages of low cost, low loss, convenient calculation, high practicability and reliability.

[0046] In order to make the above features and advantages of the application more obvious and easy to understand, the following specific examples are described in detail below, and the accompanying drawings are described as follows. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 The circuit schematic diagram of the double-tuned filter with damping.

[0048] Figure 2 The flow chart of the parameter design method of the double-tuned filter with damping.

[0049] Figure 3 The specific flow chart of step S1 in the method. Figure 2

[0050] Figure 4 The specific flow chart of step S2 in the method. Figure 2

[0051] Figure 5 The specific flow chart of step S3 in the method. Figure 2 DETAILED DESCRIPTION

[0052] In order to make the above features and advantages of the application more obvious and easy to understand, the following specific examples are described in detail below, and the accompanying drawings are described as follows.

[0053] Figure 1 The circuit schematic diagram of the double-tuned filter with damping. As shown in Figure 1 The double-tuned filter with damping includes a series capacitor C1, a series inductor L1, a parallel capacitor C2, a parallel inductor L2 and a damping R1. One end of the series capacitor C1 is connected to a node of a power grid, the other end of the series capacitor C1 is connected to one end of the series inductor L1, the other end of the series inductor L1 is connected to one end of the parallel inductor L2, the other end of the parallel inductor L2 is grounded, the damping R1 is connected in parallel across the series inductor L1, and the parallel capacitor C2 is connected in parallel across the parallel inductor L2.

[0054] Figure 2 ​​​This is a flowchart illustrating the parameter design method for a damped dual-tuned filter according to the present invention. Figure 2 As shown, the present invention provides a parameter design method for a damped dual-tuned filter, specifically including:

[0055] Step S1: Determine the design reactance range of the dual-tuned filter in each frequency band based on the range of harmonics that need to be filtered out in the target power grid area.

[0056] Step S2: Select the optimal parameters for the inductor and capacitor of the dual-tuned filter with the goal of minimizing cost.

[0057] Step S3: Select the optimal damping parameters based on the optimization requirements of load and energy loss, and determine the final parameter design scheme.

[0058] Furthermore, such as Figure 3 As shown, step S1 specifically includes,

[0059] Step S11: Since the dual-tuned filter can filter two harmonic frequencies, let f1 and f2 be the two harmonic frequencies that the power grid needs to filter.

[0060] Step S12: For the harmonic frequency f1, assuming an equivalent reactance is added at the node where the dual-tuned filter is deployed in the power grid, calculate the power grid harmonic current IHD under different equivalent reactances. f1 To reduce grid harmonic current IHD f1 The equivalent reactance range when it is less than the maximum limit of harmonic current is used as the first design reactance range [0, X] of the dual-tuned filter. f1,max ].

[0061] Step S13: For the harmonic frequency f2, assuming an equivalent reactance is added at the node where the dual-tuned filter is deployed in the power grid, calculate the power grid harmonic current IHD under different equivalent reactances. f2 To reduce grid harmonic current IHD f2 The equivalent reactance range when it is less than the maximum limit of harmonic current is used as the second design reactance range [0,X] of the dual-tuned filter. f2,max ].

[0062] Furthermore, in step S2, firstly, the parameters of two single-tuned filters equivalent to the double-tuned filter are designed; secondly, the parameters of the double-tuned filter are calculated according to the parameter equivalence method; and the capacitor and inductor values ​​are optimized using cost considerations, such as... Figure 4 As shown, specifically including,

[0063] Step S21, according to the design reactance range of the double-tuned filter in each frequency band, design the parameters of two parallel single-tuned filters meeting the requirements, wherein the harmonic frequency filtered by the first single-tuned filter is f1, the harmonic frequency filtered by the second single-tuned filter is f2, and the sum of the capacitances of the two parallel single-tuned filters is C total According to the reactive power compensation capacity of the double-tuned filter, design:

[0064]

[0065] Wherein, f b and U b are the fundamental frequency and the fundamental voltage respectively, and Q is the reactive power compensation demand of the power grid under the fundamental frequency.

[0066] Step S22, set the initial value of the capacitance, wherein the capacitance C a of the first single-tuned filter is 0, and the capacitance C b of the second single-tuned filter is C total -C a .

[0067] Step S23, let C a =C a +dC, C b =C b -dC, wherein dC is a set small capacitance change amplitude.

[0068] Step S24, judge whether C a is greater than C total .

[0069] Step S25, if C a is not greater than C total , according to the impedance design requirements of the single-tuned filter, calculate the inductance value of the single-tuned filter at this time, and the specific formula is as follows:

[0070]

[0071] Wherein, L a and L b are the inductance values of the first single-tuned filter and the second single-tuned filter respectively.

[0072] Step S26, convert the parameters of the two single-tuned filters into the parameters of the double-tuned filter and return to step S23, and the conversion formula is as follows:

[0073]

[0074] Wherein, C1, C2, L1, L2 are the series capacitance, parallel capacitance, series inductance and parallel inductance in the double-tuned filter respectively.

[0075] Step S27, if C a greater than C total , comparing the value of parallel capacitor C2 in each calculation, since the value of parallel capacitor C2 is the main factor affecting the cost of the double-tuned filter, taking the minimum parallel capacitor value and the corresponding C1, L1, L2 value as the optimal parameters of the inductance and capacitance of the double-tuned filter.

[0076] Further, as shown in Figure 5 , the step S3 specifically includes,

[0077] Step S31, input the optimal parameters C1, C2, L1, L2 of the inductance and capacitance of the double-tuned filter in the step S2, and set the initial damping R1 = 0Ω.

[0078] Step S32, let the damping R1 = R1 + dR, where dR is a damping change amplitude. In a specific embodiment, dR = 2Ω.

[0079] Step S33, under the damping, calculate the grid total harmonic rate THD and grid harmonic current IHD of the double-tuned filter when working. If the grid total harmonic rate THD and the grid harmonic current IHD exceed the limit, return to step S32.

[0080] Step S34, if the grid total harmonic rate THD and the grid harmonic current IHD do not exceed the limit, calculate the energy loss.

[0081] Where the energy loss is the active loss of the double-tuned filter, and the calculation formula is as follows

[0082]

[0083] Where U is the voltage across the double-tuned filter, and Z is the overall impedance of the double-tuned filter. Where the smaller the parallel resistance, the smaller the energy loss of the double-tuned filter.

[0084] Step S35, analyze the ratio dZ / dR1 of the change of the overall impedance Z of the double-tuned filter to the change of the damping R1 at different dampings R1, if dZ / dR1 < z, it is determined that the damping change has little effect on the working level of the double-tuned filter, and the search is ended. Otherwise, return to step S32. Where z is a set value. In a specific embodiment, z is 1%.

[0085] Step S36, among the above calculations, select the damping R1 when the unit energy loss can filter out the most harmonics as the optimal damping parameter. Combine the optimal parameters of the inductance and capacitance of the double-tuned filter in the step S2 to obtain the final parameter design scheme of the double-tuned filter.

[0086] The working principle of the double-tuned filter with damping according to the present application is described below with a specific example, in which the tuned frequencies are the 5th and 7th harmonics. According to the structure of the power grid, the single and overall harmonic levels at the point of common coupling are calculated, and the design reactance range of the double-tuned filter at the 5th and 7th harmonics is calculated according to the step S1, as shown in Table 1,

[0087] Table 1 Harmonic levels of the power grid before installation of the double-tuned filter and design reactance range

[0088]

[0089] According to the step S2, the single-tuned filter is designed on the basis of the design reactance range, and is equivalent to the corresponding double-tuned filter, and the optimal parameters of the capacitance and inductance of the double-tuned filter at the lowest cost are finally determined, as shown in the following table:

[0090] Table 2 Selection results of the parameters of the double-tuned filter

[0091] [C1 (pF)] [C2 (pF)] [L1(mH)] [L2(mH)] Ht a (5 th )]]> Ht b (7 th )]]> 41.79 241.85 5.63 0.77 4.74 7.11

[0092] wherein Ht a (5 th ) and Ht b (7 th ) are the lower and higher resonance frequency orders of the double-tuned filter.

[0093] On the basis of the determined capacitance and inductance, the optimal damping parameter is selected according to the step S3. The operating results of the double-tuned filter at different dampings are shown in Table 3:

[0094] Table 3 Design results of the double-tuned filter at different dampings

[0095]

[0096]

[0097] wherein V rms , I rms and S rms represent the rated voltage, rated current and rated power effective value of each element, respectively.

[0098] The cost in the above table is mainly composed of the inductance cost and the capacitance cost, wherein the inductance cost calculation method is

[0099] COST(L i ) = 1620 + L i (mH) x 105 + I Li (A) x 15,

[0100] wherein COST(Li L is the inductance i Cost, L i L is the inductance value, I Li L is the current flowing through the inductance.

[0101] The capacitor cost is referenced to the following market statistics.

[0102] Table 4 Capacitor component cost (Yuan)

[0103]

[0104]

[0105] As can be seen from Table 3, as the damping increases, the energy loss and the harmonic distortion rate decrease, and the cost slightly increases, therefore, after comprehensive comparison, the damping R1 is selected as 212Ω.

[0106] Although the present application has been disclosed with reference to the embodiments above, it is not intended to limit the present application, and anyone with ordinary knowledge in the art can make some changes and modifications without departing from the spirit and scope of the present application, and the scope of protection of the present application shall be defined by the appended patent claims.

Claims

1. A parameter design method for a damped dual-tuned filter, characterized in that, include, Step S1: Determine the design reactance range of the dual-tuned filter in each frequency band based on the range of harmonics that need to be filtered out in the target power grid area. Step S2: Select the optimal parameters for the inductor and capacitor of the dual-tuned filter with the goal of minimizing cost. Step S3: Select the optimal damping parameters based on the optimization requirements of load and energy loss, and determine the final parameter design scheme; Step S31: Input the optimal parameters of the dual-tuned filter inductor and capacitor from step S2. C 1. C 2. L 1. L 2. Set the initial damping R 1 = 0Ω; Step S32, set the damping R 1= R 1+dR, where dR is the amplitude of a damping change; Step S33: Under this damping, calculate the combined harmonic power grid rate THD and the harmonic current IHD of the dual-tuned filter when it is working. If the combined harmonic power grid rate THD and the harmonic current IHD of the grid exceed the limit, return to step S32. Step S34: If the combined harmonic rate THD of the power grid and the harmonic current IHD of the power grid do not exceed the limit, then calculate the energy loss. Step S35, analyze the change of the overall impedance Z of the double-tuned filter and the ratio dZ / d R 1 of the damping when R 1 changes. If dZ / d R 1 < z, it is determined that the change of damping has little impact on the working level of the double-tuned filter, and the search ends; otherwise, return to step S32, where z is a set precision value;​​ Step S36: In the above calculation, select the damping that filters out the most harmonics per unit energy loss. R 1. As the optimal damping parameter, combined with the optimal parameters of the inductor and capacitor of the dual-tuned filter in step S2, the final parameter design scheme of the dual-tuned filter is obtained. The energy loss is the active power loss of the dual-tuned filter, and the calculation formula is as follows: ， in, U This is the voltage across the dual-tuned filter. Z The overall impedance of the dual-tuned filter. C 1. C 2. L 1. L 2 represents the series capacitor, parallel capacitor, series inductor, and parallel inductor in a dual-tuned filter, respectively.

2. The parameter design method for a damped dual-tuned filter as described in claim 1, characterized in that, The damped dual-tuned filter includes a series capacitor, a series inductor, a parallel capacitor, a parallel inductor, and a damper. One end of the series capacitor is connected to a node of the power grid, the other end of the series capacitor is connected to one end of the series inductor, the other end of the series inductor is connected to one end of the parallel inductor, the other end of the parallel inductor is grounded, the damper is connected in parallel across the two ends of the series inductor, and the parallel capacitor is connected in parallel across the two ends of the parallel inductor.

3. The parameter design method for a damped dual-tuned filter as described in claim 2, characterized in that, Step S1 includes, Step S11: Assume that the two harmonic frequencies that the power grid needs to filter are f1 and f2, respectively. Step S12: For the harmonic frequency f1, assuming an equivalent reactance is added at the node where a damped dual-tuned filter is deployed in the power grid, calculate the grid harmonic current IHDf1 under different equivalent reactances. The range of equivalent reactance where the grid harmonic current IHDf1 is less than the maximum limit of the harmonic current is taken as the first design reactance range of the dual-tuned filter. ; Step S13: For the harmonic frequency f2, assuming an equivalent reactance is added at the node where a damped dual-tuned filter is deployed in the power grid, calculate the grid harmonic current IHDf2 under different equivalent reactances. The range of equivalent reactance when the grid harmonic current IHDf2 is less than the maximum limit of the harmonic current is taken as the second design reactance range of the dual-tuned filter. .

4. The parameter design method for a damped dual-tuned filter as described in claim 3, characterized in that, Step S2 includes, Step S21: Based on the design reactance range of the dual-tuned filter in each frequency band, design the parameters of two parallel single-tuned filters that meet the requirements. The first single-tuned filter filters the harmonic frequency f1, the second single-tuned filter filters the harmonic frequency f2, and the sum of the capacitances of the two parallel single-tuned filters is... Design based on the reactive power compensation capacity of the dual-tuned filter: ， in, and These are the fundamental frequency and the fundamental voltage, respectively. To meet the reactive power compensation needs of the power grid under the fundamental frequency; Step S22: Set the initial value of the capacitor, wherein the capacitor of the first single-tuned filter... C a =0, the capacitance of the second single-tuned filter C b = C total - C a ; Step S23, let C a = C a +dC, C b = C b -dC, where dC is a set capacitance change amplitude; Step S24, determine Ca Is it greater than Ctotal ; Step S25, if C a Not greater than C total Based on the impedance design requirements of the single-tuned filter, the inductance value of the single-tuned filter is calculated using the following formula: ， in, L a and L b These are the inductance values ​​of the first and second single-tuned filters, respectively. Step S26: Convert the parameters of the two single-tuned filters into the parameters of the double-tuned filter and return to step S23. The conversion formula is as follows: ， in, C 1. C 2. L 1. L 2 represents the series capacitor, parallel capacitor, series inductor, and parallel inductor in a dual-tuned filter, respectively. Step S27, if C a Greater than C total Take all the costs of the dual-tuned filter and the corresponding parallel capacitor C2, series capacitor C1, series inductor L1, and parallel inductor L2 obtained in each calculation after adjusting the capacitance change amplitude dC during the cycle from steps S22 to S26. Determine the lowest cost from all the dual-tuned filter costs, and take the parallel capacitor C2, series capacitor C1, series inductor L1, and parallel inductor L2 corresponding to the lowest cost as the optimal parameters of the inductor and capacitor of the dual-tuned filter.

5. The parameter design method for a damped dual-tuned filter as described in claim 4, characterized in that, The cost of the dual-tuned filter consists of the cost of the inductor and the cost of the capacitor.

6. The parameter design method for a damped dual-tuned filter as described in claim 5, characterized in that, The method for calculating the cost of the inductor is as follows: ， in, Inductor L i cost, This is the inductance value. This represents the current flowing through the inductor.

7. The parameter design method for a damped dual-tuned filter as described in claim 1, characterized in that, The set precision value z is 1%.

8. The parameter design method for a damped dual-tuned filter as described in claim 1, characterized in that, The damping change amplitude is dR = 2Ω.

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