CN110365018B - Self-adaptive broadband positive and negative sequence separation method - Google Patents
Self-adaptive broadband positive and negative sequence separation method Download PDFInfo
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- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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Abstract
The invention discloses a self-adaptive broadband positive and negative sequence separation method, which comprises the steps of (1) converting three-phase voltage input quantity into a two-phase static coordinate system by utilizing 3/2 conversion; (2) filtering the two-phase static coordinate components by using an in-phase second-order generalized integrator to obtain in-phase signals; (3) filtering by using an all-pass filter to obtain a quadrature component with the phase delay of 90 degrees; (4) respectively acquiring positive and negative sequence components under a two-phase static coordinate system by adopting a phase lag 90-degree algorithm; (5) performing Park conversion on the positive sequence component to obtain a DQ rotation coordinate component under a synchronous rotation coordinate system; (6) frequency tracking is carried out on the positive sequence component by using a software phase-locked loop to obtain a frequency signal; (7) the obtained frequency signal is subjected to parameter correction on an all-pass filter through fun (f), so that the phase sequence component input signal orthogonalization is realized. The invention introduces frequency negative feedback to dynamically adjust the parameters of the all-pass filter in real time, thereby ensuring the accurate separation of positive and negative sequences.
Description
Technical Field
The invention relates to the field of grid-connected control of a power system, in particular to a self-adaptive broadband positive and negative sequence separation method.
Background
The three-phase grid-connected converter is widely applied to an electric power system, a grid voltage synchronous signal, namely information such as frequency, amplitude, phase and the like of fundamental voltage, needs to be detected for controlling the three-phase grid-connected converter, and the three-phase grid-connected controller can be well adapted to electric change of the electric power system by utilizing the grid information, so that quick electric response is realized.
In an electric power system, the grid voltage asymmetry is a common phenomenon, and if the grid voltage asymmetry is not processed, the grid voltage asymmetry can cause great interference to the operation of a grid-connected converter. In order to meet the requirement of an asymmetric control strategy of the three-phase grid-connected converter, higher requirements are put forward on detection of synchronous signals. The following characteristics are required for the detection of the synchronization signal: under the condition that a power grid is asymmetric, a fundamental wave positive sequence component is rapidly and accurately provided; the frequency adaptability is realized; the control strategy is simple.
In a synchronous signal detection method of a three-phase system, a synchronous reference coordinate phase-locked loop phase-locking technology based on dq coordinate axis system transformation is common, and fundamental wave positive sequence components can be well detected under the condition of symmetrical and ideal grid voltage, so that the method is widely applied. However, under the non-ideal working condition that the voltage of the power grid is asymmetric, when the SRF-PLL algorithm is adopted, 2-frequency multiplication disturbance of 100Hz is generated on the dq-axis component by the negative sequence component, so that the extraction of the positive sequence component is influenced, and errors are caused on phase detection. In order to solve the problem, the 2-time power frequency disturbance can be suppressed by reducing the bandwidth of the SRF-PLL feedback loop filter, but the dynamic response speed is greatly reduced. There is also literature to eliminate the power frequency effect of 2 times of dq axis component when the grid voltage is asymmetric using a specific frequency harmonic filter. However, the filtering effect of the harmonic filter is affected when the frequency changes, and the method cannot detect the amplitude and phase of the negative sequence component of the fundamental wave.
To solve the influence of grid voltage asymmetry on the synchronization signal extraction, many documents propose different solutions. For example, the method based on the space vector filter extracts the fundamental negative sequence component through a low-pass filter or an average filter in dq coordinates, but the use of the filter affects the dynamic performance of the system. The inventor also proposes a method based on an improved Kalman filter to realize the positive and negative sequence separation of the fundamental wave, but the problems of covariance matrix selection and measurement error of the Kalman filter have great influence on the application of the Kalman filter. The inventor also provides a method for decoupling a double synchronous reference coordinate system phase-locked loop, which is characterized in that the separation of positive and negative sequence components of fundamental waves is realized by a positive and negative sequence decoupling network under positive and negative sequence 2 synchronous reference coordinate systems after the asymmetrical power grid voltage is subjected to double dq transformation. Although the method can effectively inhibit the influence of the negative sequence component on the extraction of the synchronous signal, the structure is complex, the calculation amount is large, and the system bandwidth is also reduced in order to ensure the system stability. The conventional separation strategy is a fundamental wave positive and negative sequence separation and extraction method based on delay signal cancellation, and the method is characterized in that a quarter-cycle delay signal of a grid voltage a-b static coordinate system component is utilized to counteract a power frequency fluctuation component of 2 times caused by a voltage negative sequence component. But this scheme cannot be delayed exactly by data buffering alone under the condition of frequency conversion. Nonlinear element adaptive filters (ANF) and generalized integrators of order 2 (SOGI) are also used for the separation of the positive and negative sequence components of the voltage fundamental. The method comprises the steps of extracting fundamental wave components and 90-degree phase shift signals thereof under a power grid voltage abc static coordinate system or ab static coordinate system by utilizing a nonlinear unit, and separating fundamental wave positive and negative sequence components through instantaneous symmetrical component operation.
At present, the conventional positive and negative sequence separation strategy adopts either filter delay or sampling point delay to realize phase lag. The second-order generalized integrator is adopted to realize sequence separation signals, so that the phase can be always orthogonal in a full frequency band range, but the strategy can only realize accurate positive and negative sequence separation of 'point', and the amplitude has attenuation characteristics along with frequency, so that the 'amplitude equality principle' of the accurate positive and negative sequence separation cannot be met.
According to the positive and negative sequence separation theory, the complete and accurate separation of positive and negative sequences is realized, and three conditions must be met simultaneously: 1) the system enters a steady state; 2) the amplitude before and after delay is not attenuated; 3) the phase delay is accurate. At present, the filter schemes (second-order generalized integral, all-pass filter) and the like cannot simultaneously satisfy the conditions 2 and 3 in a wide frequency range.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems, the invention provides a self-adaptive broadband positive and negative sequence separation method, which solves the defect that the conventional positive and negative sequence separation algorithm only has frequency point accurate separation and realizes the broadband frequency positive and negative sequence accurate separation.
The technical scheme is as follows: in order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows: a self-adaptive broadband positive and negative sequence separation method comprises the following steps:
(1) converting the three-phase voltage input quantity into a two-phase static coordinate system by using 3/2 conversion;
(2) filtering the two-phase static coordinate components by using an in-phase second-order generalized integrator to obtain in-phase signals;
(3) filtering by using an all-pass filter to obtain a quadrature component with the phase delay of 90 degrees;
(4) respectively acquiring positive and negative sequence components under a two-phase static coordinate system by adopting a phase lag 90-degree algorithm;
(5) performing Park conversion on the positive sequence component to obtain a DQ rotation coordinate component under a synchronous rotation coordinate system;
(6) frequency tracking is carried out on the positive sequence component by using a software phase-locked loop to obtain a frequency signal;
(7) the obtained frequency signal is subjected to parameter correction on an all-pass filter through fun (f), so that the phase sequence component input signal orthogonalization is realized.
Further, in the step 1, the 3/2 transformation adopts a constant-amplitude CLARK transformation:
wherein a, b and c are three-phase static coordinate systems, and alpha and beta are two-phase static coordinate systems.
Further, in the step 2, a 50Hz in-phase second-order generalized integrator is adopted:
further, in step 3, a 50Hz all-pass filter is adopted:
and k is a self-adaptive adjusting factor of the output frequency of the phase-locked loop.
Further, in step 4, the 90 ° delay sequence is separated into:
wherein p is a positive sequence component and n is a negative sequence component.
Further, in step 5, PARK is converted into:
further, in step 6, the SPLL is:
θ＝∫[PI(q)]dt
wherein, PI is a proportional integral controller.
Has the advantages that: the invention introduces frequency negative feedback to dynamically adjust the parameters of the all-pass filter in real time, thereby ensuring the accurate separation of positive and negative sequences.
Drawings
FIG. 1 is a flow chart of an adaptive wideband positive-negative sequence separation method of the present invention;
FIG. 2 is a Bode diagram of the adaptive broadband positive and negative sequence separation method of the present invention.
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
As shown in fig. 1, the adaptive wideband positive-negative sequence separation method of the present invention is implemented by using an "in-phase generalized second-order integration + all-pass filter" scheme, and specifically includes the steps of:
(1) three-phase voltage input quantity, namely 3-phase static coordinate system acquisition quantity, is converted into a two-phase static coordinate system by utilizing 3/2 coordinates;
3/2 transformation is realized by constant-amplitude CLARK transformation, and the formula is as follows:
wherein a, b and c are three-phase static coordinate systems, and alpha and beta are two-phase static coordinate systems.
(2) Filtering the two-phase static coordinate components by using an in-phase second-order generalized integrator to obtain in-phase signals;
the deep attenuation characteristic of the same-phase generalized second-order integrator to the direct current/low-frequency component is utilized, the problem that the direct current component is contained in the conventional direct feedforward of the negative sequence voltage is solved, and the direct current component is completely eliminated.
The 50Hz second order generalized integrator digital filter is as follows:
(3) filtering the signal passing through the in-phase second-order generalized integrator by using an all-pass filter to obtain a phase delay 90-degree orthogonal component;
the same-phase second-order generalized integrator is connected with the all-pass filter in series to carry out phase lag, the natural advantage that the amplitudes of the delay component and the in-phase component are not attenuated is achieved, and the principle that the amplitudes of a steady-state system are equal is met.
The 50Hz all-pass digital filter is as follows:
and k is a self-adaptive adjusting factor according to the output frequency of the phase-locked loop and is in linear relation with the frequency deviation of the resonance point.
All the above mentioned second-order generalized integrators and all-pass filters are at 4800Hz sampling frequency, using the expression of bilinear transformation.
(4) Respectively acquiring positive and negative sequence components under a two-phase static coordinate according to a phase lag 90-degree algorithm;
the 90 ° delay sequence is separated as follows:
wherein p is a positive sequence component and n is a negative sequence component.
(5) Carrying out Park conversion on the sequential component signal to obtain a DQ rotation coordinate component under a synchronous rotation coordinate system;
PARK is transformed as follows:
(6) frequency tracking is carried out on the positive sequence component by using a software phase-locked loop;
SPLL is as follows:
θ＝∫[PI(q)]dt
wherein PI denotes a proportional integral controller.
(7) The obtained frequency signal is subjected to parameter correction on an all-pass filter through fun (f) so as to adapt to the frequency characteristic of the input signal and realize the orthogonalization of the phase sequence component input signal.
The method is characterized in that amplitude and frequency decoupling is realized by using an SPLL (three-phase-locked loop), the fundamental frequency of an input signal is tracked, and the orthogonalization of a sequence separation input signal is realized by adaptively and dynamically adjusting and revising filter parameters by using the principle of 'equivalence infinitesimal small'.
And (3) phase compensation process:
1) quasi-resonant filter (second order generalized integral filter) transfer function:
the phase-frequency characteristic expression is as follows:
analyzing the frequency characteristic at the resonance point, and making omega be omega-omega0+dω，
It was demonstrated above that the phase frequency of the resonator filter is specified to be equivalent infinitesimally small to-2/kw 0 dw near the resonance point.
2) The first order all-pass filter transfer function is:
the phase-frequency characteristic expression is as follows:
the frequency characteristic at the resonance point is analyzed, and w is w0+ dw,
the above equation demonstrates that the phase frequency characteristic near the resonance point of the first order all-pass filter is equivalent to-1/w 0 × dw to infinitesimally small.
For a first order all-pass filter with resonance points within a small range, the compensation angle is proportional to the resonance frequency. Based on the method, the theoretical basis of the method for realizing the orthogonal positive and negative sequence separation of the angle with the same frequency band and amplitude is found, namely, the parameters of the all-pass filter are dynamically adjusted in real time by introducing frequency negative feedback, and the precise positive and negative separation is ensured.
In summary, the factor k in the third step all-pass filter is linear with the frequency deviation of the resonance point.
FIG. 2 shows Bod of the method of the present inventioneAs can be seen from the figure, the sequence separation strategy has the characteristics of phase orthogonality and equal amplitude at the 50Hz point, namely, precise and accurate separation of positive and negative sequences can be realized at the frequency point. When the frequency point is not at 50Hz, the amplitude-frequency characteristic shows that the sequence separation input components always meet the principle of equal amplitude, but the phase is always orthogonal. The amplitude-frequency characteristic shows that the deep attenuation of the direct current component can be realized at a direct current/low frequency range, and a theoretical basis is provided for realizing the negative sequence direct current voltage feedforward without the direct current component.
At present, the frequency use range of converter equipment is generally required to be 50 +/-5 Hz in an electric power system, and the basic theories are all established in a small frequency conversion range, so that the method can realize accurate and accurate separation of the broadband self-adaptive positive and negative sequences.
Claims (5)
1. A self-adaptive broadband positive and negative sequence separation method is characterized by comprising the following steps:
(1) converting the three-phase voltage input quantity into a two-phase static coordinate system by using 3/2 conversion;
(2) filtering the two-phase static coordinate component by using an in-phase second-order generalized integrator digital filter to obtain an in-phase signal;
(3) filtering by using an all-pass filter to obtain a quadrature component with the phase delay of 90 degrees;
(4) respectively obtaining a positive sequence component and a negative sequence component under a two-phase static coordinate system by adopting a phase lag 90-degree algorithm;
(5) performing Park conversion on the positive sequence component to obtain a DQ rotation coordinate component under a synchronous rotation coordinate system;
(6) frequency tracking is carried out on the positive sequence component by using a software phase-locked loop to obtain a frequency signal;
(7) parameter correction is carried out on the obtained frequency signal through a Fun (f) all-pass filter, and phase sequence component input signal orthogonalization is realized;
wherein the in-phase second order generalized integrator digital filter is represented as:
the digital filter of the in-phase second-order generalized integrator is connected with the all-pass filter in series to carry out phase lag, so that a quadrature component with the phase delay of 90 degrees is obtained;
the all-pass filter is represented as:
and k is a self-adaptive adjusting factor according to the output frequency of the phase-locked loop and is in linear relation with the frequency deviation of the resonance point.
2. The adaptive wideband positive-negative sequence separation method according to claim 1, wherein in step 1, the 3/2 transformation is equal-amplitude CLARK transformation:
wherein a, b and c are three-phase static coordinate systems, and alpha and beta are two-phase static coordinate systems.
3. The adaptive broadband positive-negative sequence separation method according to claim 1, wherein in the step 4, the 90 ° delay sequence separation is:
wherein p is a positive sequence component and n is a negative sequence component.
4. The adaptive wideband positive-negative sequence separation method according to claim 3, wherein in step 5, the PARK transform is:
5. the adaptive wideband positive-negative sequence separation method according to claim 4, wherein in step 6, SPLL is:
θ＝∫[PI(q)]dt
wherein, PI is a proportional integral controller.
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| CN113804958B (en) * | 2021-10-09 | 2024-05-31 | 陕西航空电气有限责任公司 | Alternating current electric quantity positive and negative sequence component extraction method suitable for variable frequency power supply system |
| CN114124085B (en) * | 2021-10-29 | 2024-04-16 | 合肥工业大学 | Construction method of multi-synchronous rotation coordinate system phase-locked loop based on second-order filtering link |
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