Impedance measurement method based on PRBS broadband disturbance injection

Abstract

The invention discloses an impedance measurement method based on PRBS broadband disturbance injection. The method comprises the following steps: determining broadband disturbance signal basic parameters; generating a PRBS signal according to the broadband disturbance signal basic parameter; the PRBS signal is used as a voltage loop instruction value of a single-phase H-bridge DC / AC converter at the rear stage side in the broadband impedance measurement device, and the on and off of a power device of the single-phase H-bridge converter are controlled through bipolar SPWM multi-level modulation, so that the broadband impedance measurement device provides disturbance voltage for a system to be measured; the broadband impedance measuring device is connected between the to-be-measured system and the bus in series; and sampling the voltage and current response of the to-be-tested system in the stable operation time period of the disturbance voltage, and calculating the impedance of the to-be-tested system according to the sampled voltage and current response. According to the scheme, PRBS signals are adopted, the spectral range is wider, the amplitude is more uniform, and the impedance measurement effect is better.

Description

Technical Field

[0001] The present invention relates to the technical field of impedance measurement, and in particular to an impedance measurement method based on PRBS broadband disturbance injection. Background Art

[0002] As the global consensus on reducing carbon emissions and responding to climate change grows, the development and utilization of renewable energy such as wind and solar energy has become the trend of the times. However, the oscillation characteristics (such as frequency and damping) of the grid-connected renewable energy power generation system are affected by the aggregation effect of multiple converters and many parameters of the power grid, wind, solar, load and storage and other external conditions. These influencing factors have the characteristics of complexity, large-scale time-varying and strong nonlinearity, which further enhances the uncertainty of the oscillation phenomenon and poses a serious threat to the stable operation of the system. Therefore, stability analysis of the renewable energy power generation system is the key to ensure reliable power supply of the power grid, and establishing the impedance model of the renewable energy power generation system is an important part of stability analysis. The premise of establishing the impedance model is to obtain the impedance characteristics of the system, and the impedance characteristics of the system at different frequencies can be obtained through impedance measurement. Therefore, the continuous innovation and development of impedance measurement technology will provide a better technical route for broadband oscillation suppression and control characteristic optimization of renewable energy power generation systems.

[0003] At present, there are two main methods for impedance measurement. The first is the non-disturbance measurement method, which uses the inherent harmonics generated by the port to be measured as a disturbance signal, and estimates the impedance characteristics of the object to be measured by measuring the amplitude and phase relationship of these harmonic signals. However, the disadvantage of this method is that due to the uncontrollable injected harmonics, there will be problems with uneven distribution of the amplitudes of each harmonic, and it is impossible to inject full-band harmonics, so the measurement accuracy is lacking. The second is the external disturbance injection measurement method, which injects an external disturbance signal into the system to be measured and measures the system's response to the disturbance to calculate the impedance of the system. The advantage of this method is that the disturbance signal can be selected independently. In impedance measurement, the rapidity of measurement is an important performance indicator, and the selection of a wide-band disturbance signal for impedance measurement can achieve the fastest injection to obtain the impedance characteristics of the system to be measured. Among the existing disturbance signals, the most used are single sine signals and square wave signals. Among them, the single sine signal sweep frequency method has the highest accuracy, but the disadvantage is low measurement efficiency. A square wave signal can be decomposed into an infinite number of single sinusoidal signals. However, the spectrum information of a square wave signal is unevenly distributed over the entire frequency band and has a high-frequency attenuation characteristic, that is, the frequency band with a higher amplitude is narrower, which makes it lack measurement accuracy when used for impedance measurement.

[0004] That is, among many disturbance injection signals, the single sine frequency sweep method has the highest measurement accuracy, but the measurement efficiency is low. In contrast, multi-sine signals have better spectral characteristic design capabilities, but their peak constraints are more difficult, and the frequency band with high measurement accuracy of square wave signals is relatively narrow. When the measurement frequency band is wide, it may be difficult to ensure sufficient measurement accuracy in the entire measurement frequency band through a set of square wave signals. Therefore, in order to make up for the limitations of using more disturbance signals for impedance measurement, the use of a new type of pseudo-random binary sequence with a wide bandwidth and sufficient disturbance amplitude on each frequency component for impedance measurement is of great significance to improve measurement accuracy and measurement efficiency. Summary of the invention

[0005] In order to solve the technical problem that the measurement efficiency is low when a single sinusoidal signal is used as a disturbance signal for impedance measurement, and the square wave signal has uneven distribution of spectrum information in the entire frequency band and has high-frequency attenuation characteristics, which makes it lack measurement accuracy when used for impedance measurement, an embodiment of the present invention provides an impedance measurement method based on PRBS broadband disturbance injection.

[0006] The technical solution of the embodiment of the present invention is achieved as follows:

[0007] An embodiment of the present invention provides an impedance measurement method based on PRBS broadband disturbance injection, the method comprising:

[0008] Determine basic parameters of broadband disturbance signal;

[0009] A PRBS signal is generated according to the basic parameters of the broadband disturbance signal; the PRBS signal is used as a voltage loop instruction value of a single-phase H-bridge DC / AC converter at the rear stage in the broadband impedance measuring device, and is used to control the on and off of the power device of the single-phase H-bridge converter through bipolar SPWM multi-level modulation, so that the broadband impedance measuring device provides a disturbance voltage to the system to be measured; the broadband impedance measuring device is connected in series between the system to be measured and the bus;

[0010] During the period of time when the disturbance voltage is running stably, the voltage and current responses of the system to be measured are sampled, and the impedance of the system to be measured is calculated according to the sampled voltage and current responses.

[0011] In one embodiment, the basic parameters of the broadband disturbance signal include the order and initial sequence of the broadband disturbance signal and two initial values ​​of the shift register that need to be subjected to an exclusive OR logic operation.

[0012] In one embodiment, generating a PRBS signal according to the broadband disturbance signal basic parameters includes:

[0013] A PRBS signal is generated by using a linear shift register according to the basic parameters of the broadband disturbance signal according to the following rules:

[0014] The order of the broadband disturbance signal is used as the number of bits of the initial sequence to set the initial sequence; the initial sequence is a binary sequence composed of 0 and 1;

[0015] The values ​​of the last bit and the second to last bit of the linear shift register are selected for exclusive OR logic operation to obtain a new input bit of the linear shift register and right shift it, and iterate repeatedly until a PRBS signal of the order is generated.

[0016] In one embodiment, the signal period sequence length of the PRBS signal is 2 raised to a power of 1 minus 1.

[0017] In one embodiment, the PRBS signal is specifically used as the AC side voltage command value of the single-phase H-bridge DC / AC converter on the rear side of the wide-band impedance measuring device, and is subtracted from the actual AC voltage measured by the single-phase H-bridge DC / AC converter to obtain a voltage error; the voltage error is obtained by controlling the voltage loop, and then multiplied by the gain index after passing through a limiting link, and then subjected to bipolar sinusoidal pulse width modulation to obtain a single-phase H-bridge switch tube control signal on the rear side of the wide-band impedance measuring device; the single-phase H-bridge switch tube control signal on the rear side of the wide-band impedance measuring device is used to control the conduction and shutdown of the single-phase H-bridge power device.

[0018] In one embodiment, the transfer function of the voltage loop control is:

[0019]

[0020] Among them, K p is the proportional coefficient of the quasi-voltage loop control, K i is the integral coefficient of voltage loop control, and S is the complex variable in Laplace transform.

[0021] In one embodiment, calculating the impedance of the system under test according to the sampled voltage and current responses includes:

[0022] The impedance of the system to be measured is calculated according to the sampled voltage and current values ​​using the following calculation formula:

[0023]

[0024] Among them, f p is the disturbance frequency, Z[f p ] is the impedance at the corresponding frequency component, V p [f p ] is the voltage response V p The frequency components obtained after fast Fourier transform, I p [fp ] is the voltage response I p The frequency components obtained after fast Fourier transform.

[0025] This embodiment has the following beneficial effects:

[0026] This embodiment uses a PRBS signal. The PRBS signal is a pseudo-random binary sequence whose spectrum is similar to white noise, with widely distributed spectrum components and uniform amplitude distribution in a wider frequency band. Using the PRBS signal as a disturbance signal and combining it with a wide-band impedance measurement device to perform impedance measurement, on the one hand, the amplitude of the disturbance signal is large enough to weaken the influence of noise interference; on the other hand, the wide-band characteristic of the PRBS signal enables it to measure the impedance characteristics at multiple frequencies at one time when used as a disturbance signal for impedance measurement, meeting the requirements of high efficiency and accuracy of wide-band impedance measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of an impedance measurement method based on PRBS broadband perturbation injection according to an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the system structure of an embodiment of the present invention;

[0029] Figure 3 It is a time domain diagram and spectrum diagram of the 12th order PRBS signal of an embodiment of the present invention; wherein, Figure 3 (a) is the time domain diagram of the 12th order PRBS signal; Figure 3 (b) is the spectrum diagram of the 12th order PRBS signal;

[0030] Figure 4 A schematic diagram of a control method for a single-phase H-bridge and a PRBS signal injection position in a wide-band impedance measurement device according to an embodiment of the present invention;

[0031] Figure 5 Schematic diagram of impedance measurement results according to an embodiment of the present invention; wherein, Figure 5 (a) is a schematic diagram of the impedance measurement results of the energy storage converter; Figure 5 (b) is a schematic diagram of the results of measuring the impedance of the photovoltaic converter; Figure 5 (c) is a schematic diagram of the constant power load impedance measurement results. DETAILED DESCRIPTION

[0032] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0033] The embodiment of the present invention provides an impedance measurement method based on PRBS broadband disturbance injection, such as Figure 1 As shown, the method includes:

[0034] Step 101: Determine basic parameters of broadband disturbance signal;

[0035] Step 102: Generate a PRBS signal according to the basic parameters of the broadband disturbance signal; the PRBS signal is used as a voltage loop command value of a single-phase H-bridge DC / AC converter at the rear stage in the broadband impedance measurement device, and is used to control the on and off of the power device of the single-phase H-bridge converter through bipolar SPWM multi-level modulation, so that the broadband impedance measurement device provides a disturbance voltage to the system to be measured; the broadband impedance measurement device is connected in series between the system to be measured and the bus;

[0036] Step 103: within the time period when the disturbance voltage is running stably, sampling the voltage and current responses of the system to be measured, and calculating the impedance of the system to be measured according to the sampled voltage and current responses.

[0037] This embodiment proposes a novel PRBS signal with a wide frequency band and sufficient disturbance amplitude on each frequency component for impedance measurement, so as to improve the measurement accuracy and efficiency of impedance measurement.

[0038] PRBS: Pseudo Random Binary Sequence, which is a signal composed of a digital sequence. It is similar to a random signal in statistical characteristics. Its data stream is random within a cycle, but the entire data stream appears cyclically, so it is called pseudo-random.

[0039] like Figure 2 As shown, the system of this embodiment includes a bus, a wide-band impedance measuring device and a system to be measured; wherein the wide-band impedance measuring device is connected in series between the system to be measured and the bus, and the wide-band impedance measuring device is composed of a DC source module, a single-phase H-bridge and an LC filtering circuit, and the output is directly connected to the system to be measured through the LC filtering circuit to provide a voltage disturbance source.

[0040] Based on the above system, the impedance measurement method based on PRBS broadband perturbation injection in this embodiment includes the following steps:

[0041] Step 1: Determine the basic parameters of the wideband disturbance signal, that is, determine the order of the disturbance injection PRBS signal, and obtain the time domain diagram and spectrum diagram of the PRBS signal under this order. The generation of PRBS signal depends on the linear shift register, and its generation rule is: taking the generation of 12-order PRBS signal as an example, first determine the order N=12 of the PRBS signal, and set the initial sequence to [1 00 0 0 0 0 0 0 0 1 1], where the number of bits of the initial sequence is equal to the PRBS signal order, then select the last bit and the second to last bit of the initial sequence for XOR logic operation to obtain the new input bit of the shift register and right shift it, and iterate repeatedly to finally generate a 12-order PRBS signal, and the sequence length of one signal cycle is 2 12 -1=4095. Figure 3 The time domain diagram and spectrum diagram of a 12-order PRBS signal generated by an embodiment.

[0042] Step 2: Use the PRBS signal as the AC side voltage command value U of the single-phase H-bridge DC / AC converter on the rear side of the broadband impedance measurement device ref , and the broadband impedance measurement device is used to measure the actual voltage u of the single-phase H-bridge DC / AC converter at the rear stage o Subtract and get the voltage error ΔU o .

[0043] Step 3: Voltage error ΔU o The value obtained by voltage loop PI control is limited by the gain index k pwm Multiply, where the transfer function of PI control is: K p is the proportional coefficient of quasi-PI control, K i is the integral coefficient of PI control. After bipolar SPWM multi-level modulation, the single-phase H-bridge switch control signals S1, S2, S3, and S4 of the broadband impedance measurement device are obtained, thereby controlling the on and off of the single-phase H-bridge power device. Figure 4 shown.

[0044] Step 4: The time domain voltage response V generated by the system under test after the disturbance injection p The time domain current response I p Sampling and V p and I p Perform FFT to obtain the corresponding frequency components, and then obtain the impedance measurement value Z of the system to be measured. The calculation formula of Z is: Among them, f p is the disturbance frequency.

[0045] Based on the above process, see Figure 5 The impedance measurement effect of the method of this embodiment is as follows: Figure 5As shown, the impedance of the energy storage converter, photovoltaic converter and constant power load is measured, and the impedance measurement value is compared with the theoretical value to verify the effectiveness of the method described in this proposal. The results show that compared with traditional injection signals such as single sine signals and square wave signals, the scheme of this embodiment has a simple structure, low complexity, and balanced spectrum energy distribution, and has higher measurement accuracy and measurement efficiency.

[0046] This embodiment is combined with a wideband impedance measurement device. The single-phase H-bridge DC / AC converter on the back-stage side of the device adopts voltage loop PI control, takes PRBS as the command value of the voltage loop, and controls the power device of the single-phase H-bridge converter to be turned on and off through bipolar SPWM multi-level modulation. The wideband impedance measurement device is connected in series between the system to be measured and the bus, provides a disturbance source, samples the voltage and current response of the system to be measured during the relatively stable operation period after the disturbance voltage is injected, and calculates the impedance of the system to be measured.

[0047] Compared with the prior art, it has the following differences:

[0048] 1) Impedance measurement based on disturbance injection method, using different disturbance signals;

[0049] 2) The disturbance signal injection method is different.

[0050] Protection points of this embodiment:

[0051] 1. PRBS signal generation method and its injection method in a wideband impedance measurement device.

[0052] 2. A method for providing a disturbance source for a wideband impedance measurement device.

[0053] 3. When impedance measurement is performed in combination with a wide-band impedance measurement device, the device is connected between the system to be measured and the bus.

[0054] 4. A control method for a single-phase H-bridge DC / AC converter at the rear stage of a wide-band impedance measurement device.

[0055] 5. A method for obtaining the voltage response and current response of the system under test after disturbance injection to calculate the impedance.

[0056] This embodiment uses a PRBS signal. The PRBS signal is a pseudo-random binary sequence whose spectrum is similar to white noise, with widely distributed spectrum components and uniform amplitude distribution in a wider frequency band. Using the PRBS signal as a disturbance signal and combining it with a wide-band impedance measurement device to perform impedance measurement, on the one hand, the amplitude of the disturbance signal is large enough to weaken the influence of noise interference; on the other hand, the wide-band characteristic of the PRBS signal enables it to measure the impedance characteristics at multiple frequencies at one time when used as a disturbance signal for impedance measurement, meeting the requirements of high efficiency and accuracy of wide-band impedance measurement.

[0057] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0058] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.

Claims

1. An impedance measurement method based on PRBS broadband disturbance injection, characterized in that: The method comprises: Determine basic parameters of broadband disturbance signal; A PRBS signal is generated according to the basic parameters of the broadband disturbance signal; the PRBS signal is used as a voltage loop instruction value of a single-phase H-bridge DC / AC converter at the rear stage in the broadband impedance measuring device, and is used to control the on and off of the power device of the single-phase H-bridge converter through bipolar SPWM multi-level modulation, so that the broadband impedance measuring device provides a disturbance voltage to the system to be measured; the broadband impedance measuring device is connected in series between the system to be measured and the bus; During the period of time when the disturbance voltage is running stably, the voltage and current responses of the system to be measured are sampled, and the impedance of the system to be measured is calculated according to the sampled voltage and current responses.

2. The impedance measurement method based on PRBS broadband disturbance injection according to claim 1 is characterized in that: The basic parameters of the broadband disturbance signal include the order and initial sequence of the broadband disturbance signal and the initial values ​​of two bits in the selected shift register that need to be subjected to an exclusive OR logic operation.

3. The impedance measurement method based on PRBS broadband disturbance injection according to claim 2 is characterized in that: Generating a PRBS signal according to the basic parameters of the broadband disturbance signal includes: A PRBS signal is generated by using a linear shift register according to the basic parameters of the broadband disturbance signal according to the following rules: The order of the broadband disturbance signal is used as the number of bits of the initial sequence to set the initial sequence; the initial sequence is a binary sequence composed of 0 and 1; The values ​​of the last bit and the second to last bit of the linear shift register are selected for exclusive OR logic operation to obtain a new input bit of the linear shift register and right shift it, and iterate repeatedly until a PRBS signal of the order is generated.

4. The impedance measurement method based on PRBS broadband disturbance injection according to claim 3 is characterized in that: The signal period sequence length of the PRBS signal is 2 raised to a power of 1 minus 1.

5. The impedance measurement method based on PRBS broadband disturbance injection according to claim 1, characterized in that: The PRBS signal is specifically used as the AC side voltage command value of the single-phase H-bridge DC / AC converter at the rear stage of the wide-band impedance measuring device, and is subtracted from the actual AC voltage measured by the single-phase H-bridge DC / AC converter to obtain a voltage error; the voltage error is obtained by controlling the voltage loop, and then multiplied by the gain index after passing through a limiting link, and then subjected to bipolar sinusoidal pulse width modulation to obtain a single-phase H-bridge switch tube control signal at the rear stage of the wide-band impedance measuring device; the single-phase H-bridge switch tube control signal at the rear stage of the wide-band impedance measuring device is used to control the conduction and shutdown of a single-phase H-bridge power device.

6. The impedance measurement method based on PRBS broadband disturbance injection according to claim 5, characterized in that: The transfer function of the voltage loop control is: Among them, K p is the proportional coefficient of the quasi-voltage loop control, K i is the integral coefficient of voltage loop control, and S is the complex variable in Laplace transform.

7. The impedance measurement method based on PRBS broadband disturbance injection according to claim 1, characterized in that: Calculating the impedance of the system under test according to the sampled voltage and current responses includes: The impedance of the system to be measured is calculated according to the sampled voltage and current values ​​using the following calculation formula: Among them, f p is the disturbance frequency, Z[f p ] is the impedance at the corresponding frequency component, V p [f p ] is the voltage response V p The frequency components obtained after fast Fourier transform, I p [f p ] is the voltage response I p The frequency components obtained after fast Fourier transform.

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