Broadband impedance measurement disturbance signal generation and optimization method

Abstract

The invention discloses a broadband impedance measurement disturbance signal generation and optimization method so as to meet the requirement for accurate and rapid measurement of broadband impedance in a direct-current power distribution network scene where large-scale photovoltaic and energy storage equipment is connected. According to the method, a DIBS signal of a unit amplitude is generated, and the DIBS signal is finally formed after the amplitude of an injection signal is selected; the spectral characteristics of the DIBS signal are optimized by optimizing the initial phase of each frequency component of the generated signal. The DIBS injection signal has the capability of measuring impedance characteristics under multiple frequency points through one-time injection, so that not only is the measurement efficiency improved, but also stable operation of the system is facilitated. The optimized DIBS signal spectrum is more concentrated, and the measurement accuracy is higher. The method is suitable for the direct-current power distribution network connected with large-scale new energy power generation equipment, provides an effective means for online measurement of system impedance, has practical significance for system stability research, solves the problems of inaccurate impedance measurement and low efficiency in the prior art, and has wide application prospects and practical value.

Description

Technical Field

[0001] The invention discloses a method for generating and optimizing a wide-band impedance measurement disturbance signal, which relates to the technical field of wide-band impedance online measurement in renewable energy power generation, and in particular to a method for generating a discrete interval binary sequence disturbance signal and optimizing its spectrum. Background Art

[0002] After the large-scale access of new energy, the DC distribution network often becomes a system dominated by power electronic equipment and with weak rotational inertia when operating independently. Such system characteristics lead to strong time-varying and diverse operating modes. In addition, factors such as the random fluctuation of photovoltaic power generation and the unpredictability of loads will pose severe challenges to the stable control of system voltage.

[0003] In addition, power electronic loads represented by charging piles often exhibit constant power characteristics during the process of converting electric energy through converters. This characteristic will produce a negative damping effect on the system under closed-loop control, further exacerbating the difficulty of safe and stable operation of DC distribution networks. Therefore, how to effectively respond to these challenges and ensure the stable and efficient operation of DC distribution networks has become an important issue that needs to be solved urgently.

[0004] The impedance method based on frequency domain theory has been widely used in the industry as a common means of analyzing the oscillation problem of grid-connected systems of new energy converters. However, in practical applications, due to the complexity and difficulty in obtaining system parameters and control parameters of new energy devices, it has become a very challenging task to carry out refined impedance modeling of new energy power generation equipment.

[0005] Especially in the context of large-scale renewable energy access to DC distribution networks, the problem of stable control is particularly prominent. Therefore, it is particularly important to use impedance measurement devices suitable for DC distribution systems to obtain the impedance characteristics of power electronic equipment in real time and accurately. Existing impedance measurement devices mainly use a single-frequency disturbance injection signal. Although this method can meet the measurement requirements to a certain extent, it has problems such as long measurement time, large injection signal amplitude, and possible impact on system stability.

[0006] In order to effectively overcome these problems, wideband disturbance injection signals came into being. By injecting a signal covering a wide frequency range at one time, the measurement efficiency can be significantly improved and the measurement time can be shortened. The wideband impedance measurement method can not only obtain the impedance characteristics of the system more comprehensively and quickly, but also provide more accurate and comprehensive data support for system stability analysis, and provide new ideas for the stable control of new energy grid-connected systems. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for generating and optimizing a wide-band impedance measurement disturbance signal in view of the shortcomings of the existing technology, so as to meet the demand for accurate and fast online measurement of wide-band impedance in the scenario of large-scale photovoltaic and energy storage access to DC distribution networks.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a spectrum-optimized discrete interval binary sequence (DIBS, hereinafter referred to as DIBS) disturbance injection signal, including the generation of DIBS signal and spectrum optimization. The DIBS disturbance injection signal generation method of the present invention includes the following five steps:

[0009] Step 1: Target spectrum design: Select N frequencies f to be measured i , and the amplitude A of each frequency component i .

[0010] Step 2: Generate signal construction: According to the frequency selected in step 1 and the amplitude of each frequency component, construct the DIBS generated signal s(t). The construction method is as follows:

[0011]

[0012] Where N is the selected frequency, A i is the amplitude of the ith frequency component, f i is the ith frequency, is the initial phase of the ith frequency. The default initial phase is 0.

[0013] Step 3, unit DIBS signal generation: Generate a unit amplitude DIBS signal h(t) using the DIBS signal generated in step 2. The generation method is as follows:

[0014]

[0015] h(t)=sgn[s(t)]

[0016] Step 4, DIBS amplitude setting: Select the DIBS injection signal amplitude A.

[0017] The amplitude A of the DIBS injection signal is determined according to the actual system (eg, 10% of the system voltage).

[0018] Step 5, DIBS signal generation: Combine the unit amplitude DIBS signal generated in step 3 and the signal amplitude selected in step 4 to generate the final DIBS signal D(t). The generation method is as follows:

[0019] D(t)=A·h(t).

[0021] There are two DIBS spectrum optimization strategies in the present invention. Optimization strategy 1 is convenient and simple, and has good results when the frequencies are selected at equal intervals. Optimization strategy 1 uses a phase optimization formula to calculate the initial phase of each frequency component of the DIBS generated signal. Its expression is as follows:

[0022]

[0023] For the selected N frequencies, the phase of the sinusoidal component of the first frequency is Set to 0. The phases of the remaining N-1 frequency sinusoidal components are calculated using the above formula.

[0024] Optimization strategy 2 uses the downhill simplex algorithm for phase optimization. This method is relatively complex, but it can meet different frequency selection requirements. The specific steps are as follows:

[0025] Step 2.1, parameter setting

[0026] Determine the objective function AF and independent variables

[0027]

[0028] Where s(t) is the signal generated by DIBS, and T is the signal length, that is, a signal of a certain time (such as 1s) is selected for calculation.

[0029] Step 2.2, initial calculation

[0030] Select an initial point (such as [0,0,...,0]), add N linearly independent vectors, and obtain a simplex P containing N+1 vertices. i , note P i The objective function value at is y i . Sort the N+1 function values, and the maximum value point P i Denoted as P h The second largest point is denoted as P h1 , the minimum point is recorded as P l

[0031] Step 2.3, reflection operation

[0032] Remove the maximum point P h , calculate the center point P of the remaining points b , then calculate and define the reflection point P r , the calculation formula is:

[0033]

[0034] P r =(1+α)P b-αP h

[0035] Where α is the reflection coefficient (α>0), if y l ≤y r ≤y h1 , then Ph=Pr, and return to the starting point of step 2.3 for the next iteration.

[0036] Step 2.4, dilation operation

[0037] If the reflection produces a new minimum point, that is, y r <y l , then the reflection point is expanded, and the calculation formula is:

[0038] P e =βP r +(1-β)P b

[0039] Where β is the expansion coefficient (β>1). e <y l , then P e =P h If y e ≥y l , then the expansion fails, let P r =P h , return to step 2.3 for the next iteration.

[0040] Step 2.5, shrink operation

[0041] When h1 <y r ≤y h When P r =P h Then perform the contraction operation. r >y h , then directly perform the contraction operation, the calculation formula is:

[0042] P c =γP h +(1-γ)P b

[0043] Where γ is the contraction coefficient (0<γ<1). c ≤y h , then Ph=Pc, and return to step 2.3 for the next iteration.

[0044] Step 2.6, compression operation

[0045] If y c >y h , the contraction fails. lThe points outside the point are compressed, and the calculation formula is as follows:

[0046] P i =P i +(1-δ)P l

[0047] Where δ is the compression coefficient (0<δ<1). After the compression operation, return to step 2.3 for the next iteration.

[0048] Step 2.7, complete the iteration

[0049] When the number of iterations reaches the specified number (such as 5 times) or the objective function value meets the requirements, the iteration ends and the optimized phase is obtained.

[0050] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and is characterized in that the memory stores the computer program, and when the processor executes the computer program, the method for generating a wide-band impedance measurement disturbance signal is implemented.

[0051] A computer-readable storage medium stores a computer program, wherein the storage medium includes a stored program, wherein when the program is running, the device where the storage medium is located is controlled to execute the method for generating a wide-band impedance measurement disturbance signal.

[0052] Compared with the prior art, the present invention has the following beneficial effects:

[0053] The DIBS injection signal can quickly and accurately measure the system impedance at multiple frequency points; under the condition of the same spectrum energy, the DIBS signal injection amplitude is low, which is beneficial to the stability of the system during the measurement process. The spectrum of the DIBS signal includes multiple frequency components, and the impedance at multiple frequencies can be obtained by one injection, which improves the measurement efficiency, can effectively shorten the impedance measurement time, and provides a basis for the online measurement of impedance characteristics.

[0054] The phase optimization formula has a better spectrum optimization effect when the frequencies are selected at equal intervals, which can make the DIBS signal spectrum more concentrated, and the formula method has a small amount of calculation and is relatively simple. The downhill simplex algorithm can be applied to any frequency selection situation. The optimized DIBS spectrum is more concentrated, making the DIBS signal have a higher signal-to-noise ratio, thereby improving the accuracy of the measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 This is a flow chart of DIBS signal generation and spectrum optimization in an embodiment of the present invention;

[0056] Figure 2This is a schematic diagram of impedance measurement of power electronic equipment in a DC distribution network according to an embodiment of the present invention;

[0057] Figure 3 Time domain and spectrum diagram of DIBS signal generated by an embodiment of the present invention.

[0058] Figure 4 The impedance measurement results of the embodiment of the present invention. DETAILED DESCRIPTION

[0059] The following is attached to the instruction manual Figure 1-4 The present invention is further described in detail:

[0060] Figure 1 The figure shows a flow chart of DIBS signal generation and spectrum optimization in an embodiment of the present invention. The DIBS signal generation and spectrum optimization process is as follows:

[0061] 1) Target spectrum design: Select N frequencies f to be measured i , and the amplitude Ai of each frequency component. 10 frequencies are selected at equal intervals in the frequency range of 10-100 Hz, and the amplitude of each frequency component is set to 1.

[0062] 2) Generation signal construction: Construct DIBS to generate signal s(t).

[0063]

[0064] In the formula, N = 10 is the selected frequency number, A i is the amplitude of the ith frequency component, f i is the ith frequency, is the initial phase of the ith frequency.

[0065] 3) Spectrum optimization: Use the formula method or iterative method to calculate the initial phase of each frequency component.

[0066] 4) Unit DIBS signal generation: construct a DIBS signal h(t) with unit amplitude.

[0067]

[0068] h(t)=sgn[s(t)]

[0069] 5) DIBS amplitude setting: Select the DIBS injection signal amplitude A and set A=10.

[0070] 6) DIBS signal generation: Generate DIBS signal D(t).

[0071] D(t)=A·h(t)

[0072] Figure 2The schematic diagram of impedance measurement principle shows that the power electronic equipment in the DC distribution network includes photovoltaic power generation, energy storage and constant power load. All three are connected to the DC bus through DC / DC converters. Take photovoltaic power generation as an example. The broadband impedance measurement device is connected in series between the photovoltaic power generation equipment to be tested and the DC bus. By injecting a broadband small disturbance voltage into the system, the system to be tested will generate a corresponding current response. The impedance characteristics of the equipment to be tested can be calculated based on the disturbance voltage and the corresponding current response.

[0073] Figure 3 The time domain and spectrum diagrams of the DIBS signal generated according to the above steps are respectively the DIBS signal and spectrum without optimization, the DIBS signal and spectrum optimized by the formula method, and the DIBS signal and spectrum optimized by the iteration method. The spectrum of the DIBS signal includes multiple frequency components, and the impedance at multiple frequencies can be obtained by one injection. The formula method has a better spectrum optimization effect when the frequencies are selected at equal intervals, which can make the DIBS signal spectrum more concentrated. The iteration method can be applied to any frequency selection situation. The DIBS spectrum optimized by the iteration method is more concentrated, and its optimization effect is better than that of the formula method.

[0074] Figure 4 The DIBS impedance measurement simulation results include the impedance measurement results of constant power load, photovoltaic power generation, and energy storage battery. It can be seen from the figure that the impedance characteristics measured by the present invention are well consistent with the theoretical model. The solid line is the theoretical model, and the “×” is the measurement result of the present invention, which proves the effectiveness of the measurement method proposed by the present invention.

[0075] The present invention is suitable for a DC distribution network connected to large-scale renewable energy power generation equipment, provides an effective means for online measurement of system impedance, has practical significance for system stability research, solves the problems of inaccurate impedance measurement and low efficiency in the prior art, and has broad application prospects and practical value.

Claims

1. A method for generating and optimizing a wideband impedance measurement disturbance signal, characterized in that: The steps include: Step 1: Target spectrum design: Select N frequencies f to be measured i , and the amplitude Ai of each frequency component; Step 2, signal generation construction: construct DIBS to generate signal s(t); Step 3, unit DIBS signal generation: construct a unit amplitude DIBS signal h(t); Step 4, DIBS amplitude setting: select the DIBS injection signal amplitude A; Step 5, DIBS signal generation: Generate a DIBS signal D(t).

2. A method for generating and optimizing a wideband impedance measurement disturbance signal according to claim 1, characterized in that: In step 1, the target spectrum is designed according to the actual situation, and N frequencies f to be measured are selected. i , and the amplitude Ai of each frequency component.

3. The method for generating and optimizing a wideband impedance measurement disturbance signal according to claim 1, characterized in that: In step 2, the DIBS generated signal s(t) is constructed according to the frequency selected in step 1 and the amplitude of each frequency component. The construction formula is: Where N is the selected frequency, C i is the amplitude of the ith frequency component, f i is the ith frequency, is the initial phase of the ith frequency. The default initial phase is 0.

4. The method for generating and optimizing a wideband impedance measurement disturbance signal according to claim 1, characterized in that: In step 3, the DIBS signal constructed in step 2 is used to generate a unit amplitude DIBS signal h(t), and its construction formula is: h(t)=sgn[s(t)].

5. The method for generating and optimizing a wideband impedance measurement disturbance signal according to claim 1, characterized in that: In step 4, the DIBS injection signal amplitude A is selected according to the actual system.

6. A method for generating and optimizing a wideband impedance measurement disturbance signal according to claim 1, characterized in that: In step 5, the unit amplitude DIBS signal generated in step 3 and the signal amplitude selected in step 4 are combined to generate the DIBS signal D(t). The generating formula is: D(t)=A·h(t).

7. A method for generating and optimizing a wideband impedance measurement disturbance signal according to claim 3, characterized in that: For the parameters in the formula in step 2 The initial phase can be optimized by: The initial phase of the DIBS generated signal is calculated using the following formula: For the selected N frequencies, the phase of the sinusoidal component of the first frequency is Set to 0; the phases of the remaining N-1 frequency sinusoidal components are calculated using the above formula.

8. The method for generating and optimizing a wideband impedance measurement disturbance signal according to claim 3, characterized in that: The initial phase of the DIBS generated signal is obtained by iterative optimization using the downhill simplex method, including the following steps: Step 2.1, parameter setting; Step 2.2, initial calculation; Step 2.3, reflection operation; Step 2.4, expansion operation; Step 2.5, contraction operation; Step 2.6, compression operation; Step 2.7, complete the iteration.

9. A method for generating and optimizing a wideband impedance measurement disturbance signal according to claim 8, characterized in that: The specific steps include: Step 2.1, parameter setting; determine the objective function AF and independent variables Step 2.2, initial calculation: select an initial point, add N linearly independent vectors, and obtain a simplex P containing N+1 vertices i , note P i The objective function value at is y i ; Sort the N+1 function values, and the P of the maximum value i Denoted as P h The second largest point is denoted as P h1 , the minimum point is recorded as P l ; Step 2.3, reflection operation; Remove the maximum point P h , calculate the center point P of the remaining points b , then calculate the reflection point P r If y l ≤y r ≤y h1 , then P h =P r , and return to the starting point of step 2.3 for the next iteration; Step 2.4, dilation operation. If the reflection produces a new minimum point, that is, y r <y l , then the reflection point is expanded; if y e <y l , then P e =P h If y e ≥y l , then the expansion fails, let P r =P h , return to step 2.3 for the next iteration; Step 2.5, contraction operation; when y h1 <y r ≤y h When P r =P h Then perform the contraction operation. r >y h , then directly perform the contraction operation and return to step 2.3 for the next iteration; Step 2.6, compression operation; if y c >y h , the contraction fails. l After the compression operation, return to step 2.3 for the next iteration; Step 2.7, complete the iteration; when the number of iterations reaches the specified number or the objective function value meets the requirements, the iteration ends and the optimized phase is obtained.

10. A method for generating and optimizing a wideband impedance measurement disturbance signal according to claim 8, characterized in that: In the optimization strategy described above, the objective function AF and the independent variable Where s(t) is the DIBS generated signal and T is the signal length.

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