CN111273093B - Phase sequence identification and phase locking method for three-phase grid-connected inverter - Google Patents
Phase sequence identification and phase locking method for three-phase grid-connected inverter Download PDFInfo
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Abstract
The invention discloses a phase sequence identification and phase locking method for a three-phase grid-connected inverter, which comprises the following steps: configuring a power grid phase sequence identifier and a power grid identifier to lock the phase identifier; the method comprises the steps of configuring switching frequency sampling, interrupting the switching frequency sampling, sampling three-phase power grid voltage, and acquiring three-phase power grid voltage for phase locking according to the three-phase power grid voltage; coordinate conversion is carried out on the three-phase power grid voltage for phase locking to obtain a component U on a Q axis under a rotating coordinate systemqA step (2); a step of configuring a sampling circuit to obtain a power grid zero-crossing signal and judging a power grid identifier; and the step of judging the phase-locked identification through the zero-crossing time of the zero-crossing signal solves the technical problems that a common phase sequence identification method fails in the environment with larger power grid harmonic waves such as a weak power grid and the like, the phase sequence cannot be normally identified and the phase locking cannot be carried out in the prior art, so that the grid-connected inverter can normally operate in the weak power grid and the non-weak power grid, and the applicability of the grid-connected inverter is improved.
Description
Technical Field
The invention belongs to the technical field of grid-connected inverters in power equipment, and particularly relates to a phase sequence identification and phase locking method for a three-phase grid-connected inverter.
Background
Before the grid-connected inverter realizes grid connection, the phase sequence of three-phase sine wave voltage of a power grid needs to be detected, so that the correct phase sequence is used as the premise of correct phase locking of the power grid, and then synchronization with external signals or phases is realized.
In the prior art, since the grid-connected inverter lacks the phase sequence automatic detection function, the phase sequence needs to be confirmed before assembling wiring, so as to prevent the phase sequence from being wrong. Obviously, considering the convenience brought by the application of the phase sequence automatic identification technology in the actual field, adding the phase sequence automatic detection to the grid-connected inverter as the self-contained function thereof is a technology improvement direction of course.
In the prior art, automatic phase sequence identification in a grid-connected inverter mainly comprises machine grid voltage sampling and grid voltage zero crossing point sampling. In the conventional method for judging the phase sequence in the prior art, when one phase of three-phase power grid voltage crosses a zero point, the power grid voltage relationship of the other two phases is judged, so that the positive and negative sequences of the other two phases of power grids are determined. In another method, a voltage phase sequence of a power grid is assumed, the voltage of the power grid is sampled through a sampling modulation circuit to obtain a three-phase power grid voltage ABC, coordinate transformation is carried out on the three-phase voltage to obtain a component Uq on a Q axis, phase locking is carried out on the Uq, whether the error between the Uq component and the voltage component Uq on the actual Q axis is within a set error range or not is judged, if the error exceeds the set error range, the current phase sequence is judged to be wrong, and therefore the phase sequence of the power grid is modified.
When the implementation method in the prior art is applied to an environment such as a large power grid or a laboratory where three-phase voltage is in an ideal state, the automatic identification of the current power grid phase sequence can be normally achieved due to good power grid voltage harmonic. However, in practical field applications, particularly under the condition that the number of distributed energy resources is increased, a field power grid is a weak power grid, the harmonic wave of the power grid is large, multiple zero crossings of the voltage of the power grid may occur, and if the zero crossing of an electric machine on the power grid may occur on a rising edge or a falling edge, the method for judging the phase sequence by using the zero crossing of the voltage of the power grid in the prior art is difficult to accurately identify the phase sequence, so that phase locking cannot be performed. On the other hand, the grid voltage is low, the subharmonic is large, and the error of the Uq component of the grid voltage always exceeds the set error range, so that the phase sequence judgment of the grid voltage is always in an error state. Finally, the judgment result in the grid-connected inverter can directly cause that the machine cannot be connected in a grid-connected mode or drive a given abnormality to cause machine faults or damages in the grid-connected mode.
In view of this, the prior art should be improved to solve the technical problem that the existing grid phase sequence identification is wrong due to multiple zero crossings of the rising and falling edges of the sampling circuit.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a phase sequence identification and phase locking method of a three-phase grid-connected inverter, which can automatically correct phase sequence identification when the current phase sequence identification result is wrong by calculating the harmonic difference of a power grid and is simultaneously suitable for phase sequence identification under a conventional power grid and a weak power grid.
In order to solve the technical problems, the invention provides a phase sequence identification and phase locking method for a three-phase grid-connected inverter, which comprises the following steps: step S1, configuring the phase sequence identification of the power grid and the identification of the power grid to lock the phase; configuring switching frequency sampling, interrupting the switching frequency sampling, sampling the three-phase power grid voltage, and setting the obtained three-phase voltage to be { U }ab、Ubc、UcaAnd obtaining three-phase grid voltage (U) for phase locking according to the three-phase grid voltageab、U*bc、U*caStep S2; coordinate conversion is carried out on the three-phase power grid voltage for phase locking to obtain a component U on a Q axis under a rotating coordinate systemqStep S3; step S4, configuring a sampling circuit to obtain a power grid zero-crossing signal and judging a power grid identifier; and a step S5 of determining the phase lock identification by the zero crossing signal zero crossing time.
Preferably, in step S3, the method further includes the step of phase-locking the component and obtaining the rotation angle of the power grid.
Further preferably, in the step S4, the step of determining the grid identifier includes the following steps: acquiring the time t of zero crossing of any phase zero crossing signal in the three-phase power grid when the rising edge or the falling edge crosses zero each time, and obtaining the time t according to the current zero crossingA step S41 of acquiring a zero-crossing period T at a point time and obtaining a corresponding current zero-crossing frequency F; setting grid-connected zero-crossing frequency F0And each current zero-crossing frequency F and the grid-connected zero-crossing frequency F are combined0A step S42 of comparison; if the current zero-crossing frequency F is continuously greater than the grid-connected zero-crossing frequency F0If the number of times reaches the preset number of times, modifying the grid identifier as a weak grid in step S43.
Still further preferably, in step S43, an accumulation counter is configured, and if the current zero-crossing frequency F is greater than the grid-connection zero-crossing frequency F0The count of the accumulation counter is incremented by one, otherwise the count of the accumulation counter is reset.
Still further preferably, in the step S5, the determining the phase-locked flag by the zero-crossing time of the zero-crossing signal includes the following steps: if the current zero-crossing frequency F is larger than the grid-connected zero-crossing frequency F0Then, for the current zero-crossing time t and the previous zero-crossing time t of the zero-crossing signalpreAccumulating to obtain filtered time tnowStep S51; the filtered time tnowWith said grid zero crossing frequency F0Making a comparison if tnowThe corresponding frequency exceeds the grid zero crossing frequency F0Then t will bepreClearing; if tnowThe corresponding frequency is less than the grid zero-crossing frequency F0And step S52, comparing whether the difference between the current grid rotation angle and the corresponding phase sequence zero-crossing angle is within a preset range.
Still further preferably, in the step S52, the step of comparing the difference between the current grid rotation angle and the corresponding phase-sequence zero-crossing angle includes the following steps: if the difference values of the three continuous current power grid rotation angles and the corresponding phase sequence zero-crossing angles are within a preset range, configuring the phase locking identification to be normal, and completing phase sequence identification; otherwise, configuring the phase locking identification as abnormal, judging the voltages of the remaining two phases, and modifying the phase sequence identification of the power grid.
Still more preferably, in step S52, the step of determining the voltages of the remaining two phases includes: if U is in the set continuous M periodsbcGreater than UcaModifying the phase sequence identifier to be a positive sequence; if U isbcLess than UcaThe modified phase sequence is identified as negative.
Preferably, in step S2, the three-phase grid voltage { U } is usedab、Ubc、UcaAcquiring three-phase grid voltage (U) for phase lockingab、U*bc、U*caIn the process of (1), UabSatisfy Uab＝Uab；U*bcSatisfy Ubc＝(1-P)*Ubc+P*Uca；U*caSatisfy Uca＝(1-P)*Uca+P*Ubc(ii) a And P is a phase sequence, if the current power grid phase sequence is positive, the phase sequence P is 0, and if the current power grid phase sequence is negative, the phase sequence P is 1.
Further preferably, in the step S3, a component U on the Q axis in the rotating coordinate system is obtainedqComprises the following steps: configuring a phase-locked loop and applying a grid voltage { U x } for said phase lockingab、U*bc、U*caExtracting positive sequence (U)aP、U*bP、U*cPStep S31 of taking as a reference voltage; clark conversion is carried out on the reference voltage to obtain a static coordinate system UαAnd UβStep S32; carrying out Park conversion on the static coordinate system to convert a rotating coordinate system UdAnd UqStep S33.
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following advantages:
1. acquiring a three-phase power grid voltage calculation voltage positive sequence component through switching frequency interruption, obtaining a Q-axis component Uq under a rotating coordinate system through coordinate system transformation, phase-locking the component Uq to obtain a coordinate system rotating angle, acquiring a power grid zero-crossing signal for single-phase voltage, and configuring zero-crossing interruption, so that the power grid harmonic environment such as a weak power grid and the like is adapted, and the correct phase sequence identification and the normal operation of equipment of a grid-connected inverter under the weak power grid environment are ensured; the technical problems that in the prior art, a common phase sequence identification method fails in a weak grid and other environments with large power grid harmonic waves, the phase sequence cannot be normally identified, and therefore phase locking cannot be carried out are solved, normal operation of a grid-connected inverter in the weak grid is guaranteed, and applicability of the grid-connected inverter is improved;
2. when the three-phase grid-connected inverter is applied to an environment such as a large power grid or a laboratory where the three-phase voltage is in an ideal state, because the harmonic wave of the power grid voltage is good, the automatic identification of the current power grid phase sequence can be normally realized without modifying the power grid identification, so that the three-phase grid-connected inverter can also be applied to a non-weak power grid state;
3. when the power grid fails or fails, the phase sequence identification, the power grid identification and the phase locking identification of the power grid are recovered, at the moment, the power grid power failure is judged due to the fact that multiple times of signal zero-crossing loss are continuously detected, then the zero-crossing frequency can be continuously monitored through a zero-crossing interruption period, and the current power grid identification is judged again, so that the grid-connected inverter is guaranteed to be normally applicable after the power grid failure or power failure recovery;
4. filtering the zero-crossing signal of the power grid under the weak power grid, when the frequency corresponding to the period of two continuous zero crossings of the zero-crossing signal is greater than the preset frequency, accumulating the two zero-crossing times to be used as the post-filtering time of the power grid, and when the phase locking is abnormal, clearing the filtering to zero to avoid filtering errors. Furthermore, when the phase locking is abnormal, the other two phases of power grid voltages are logically judged to correct the power grid phase sequence, and finally the correct phase locking of the power grid is realized, so that the condition that the phase sequence judgment is misjudged or even fails only by judging the phase sequence through zero crossing under the conventional method due to multiple zero crossing of the power grid under the weak power grid can be avoided, and the phase sequence judgment accuracy is improved;
5. after the phase sequence of the power grid is identified, the positive sequence component of the power grid is extracted in different modes to carry out phase locking, so that the accuracy of phase locking can be further improved, and the applicability of equipment in the unbalanced environment of the power grid can be improved.
Drawings
Fig. 1 is a flow chart illustrating a flow of a phase sequence identification and phase locking method of a three-phase grid-connected inverter in a preferred embodiment of the invention;
FIG. 2 is a diagram illustrating an equivalent circuit structure of the phase-locked loop in the preferred embodiment shown in FIG. 1;
FIG. 3 is a diagram showing the circuit structure of the calculation unit for extracting the positive sequence of the phase-locked loop with respect to the grid voltage for phase locking in the preferred embodiment shown in FIG. 1;
FIG. 4 is a flow chart showing the calculation of the component U on the Q axis in the rotating coordinate system in the preferred embodiment shown in FIG. 1qThe process of (2);
FIG. 5 is a flow chart illustrating the steps of determining grid identification in the preferred embodiment shown in FIG. 1;
fig. 6 is a flow chart showing the steps of determining the phase lock identification by the zero crossing time of the zero crossing signal in the preferred embodiment shown in fig. 1.
Detailed Description
An embodiment of a phase sequence identification and phase locking method of a three-phase grid-connected inverter according to the present invention will be described below with reference to the accompanying drawings. Those of ordinary skill in the art will recognize that the described embodiments can be modified in various different ways, without departing from the spirit and scope of the present invention. Accordingly, the drawings and description are illustrative in nature and not intended to limit the scope of the claims. Furthermore, in the present description, the drawings are not to scale and like reference numerals refer to like parts.
It should be noted that, in the embodiments of the present invention, the expressions "first" and "second" are used to distinguish two entities with the same name but different names or different parameters, and it is understood that "first" and "second" are merely for convenience of description and should not be construed as limitations of the embodiments of the present invention, and the descriptions thereof in the following embodiments are omitted.
Fig. 1 is a flow chart illustrating a flow of a phase sequence identification and phase locking method of a three-phase grid-connected inverter according to a preferred embodiment of the present invention. As shown in fig. 1, the phase sequence identification and phase locking method for the three-phase grid-connected inverter in the preferred embodiment of the present invention includes the following steps: step S1, configuring the phase sequence identification of the power grid and the identification of the power grid to lock the phase; configuring switching frequency sampling, interrupting the switching frequency sampling, sampling the three-phase power grid voltage, and setting the obtained three-phase voltage to be { U }ab、Ubc、UcaAnd according to a three-phase power gridThree-phase grid voltage { U star for voltage acquisition phase lockingab、U*bc、U*caStep S2; coordinate conversion is carried out on the three-phase power grid voltage for phase locking to obtain a component U on a Q axis under a rotating coordinate systemqStep S3; step S4, configuring a sampling circuit to obtain a power grid zero-crossing signal and judging a power grid identifier; and a step S5 of determining the phase lock identification by the zero crossing signal zero crossing time.
Specifically, in step S1, the initialization parameters are set. In this embodiment, the phase sequence identifier includes a phase sequence positive sequence identifier and a phase sequence negative sequence identifier, where the phase sequence positive sequence identifier is 0 and the phase sequence negative sequence identifier is 1; the grid identification is used for marking the grid state of the current grid-connected connection and comprises a weak grid identification and a non-weak grid identification, wherein the weak grid identification is 0, and the non-weak grid identification is 1; the phase locking mark is used for marking the current phase locking state, comprises a phase locking success mark and a phase locking failure mark, and makes the phase locking failure mark be 0 and the phase locking success mark be 1. Certainly, the grid identifier, the phase sequence identifier and the phase-locked identifier may be further subdivided according to grid connection requirements, and corresponding identifier symbols are allocated, which is not expanded here. It should be noted that, in the preferred embodiment, when the parameters are initialized before the system is powered on, the phase sequence of the power grid is set to the positive sequence, the power grid identifier is set to the non-weak power grid identifier, and the phase lock identifier is set to the phase lock failure state. When the power grid fails or has power failure, the phase sequence identifier, the power grid identifier and the phase-locked identifier of the power grid need to be recovered, and the current power grid identifier needs to be judged again, so that the grid-connected inverter is ensured to be normally applicable after the power grid fails or has power failure.
Fig. 2 is a schematic diagram showing an equivalent circuit structure of the phase-locked loop in the preferred embodiment shown in fig. 1. As shown in fig. 2, PI is a PI controller, ω 0 is a synchronous rotation angular frequency of the power grid, 1/s is an integrator, and the three-phase power grid voltage is sampled by an analog-to-digital converter of the micro-control unit to obtain a three-phase power grid voltage { U } Uab、Ubc、UcaAccording to the three-phase grid voltage (U)ab、Ubc、UcaAcquiring three-phase grid voltage (U) for phase lockingab、U*bc、U*caIn the process of (1), UabSatisfy Uab＝Uab；U*bcSatisfy Ubc＝(1-P)*Ubc+P*Uca；U*caSatisfy Uca＝(1-P)*Uca+P*Ubc(ii) a And P is a phase sequence, if the current power grid phase sequence is positive, the phase sequence P is 0, and if the current power grid phase sequence is negative, the phase sequence P is 1. Then extracting positive sequence { U + from grid voltage for phase lockingaP、U*bP、U*cPAs a reference voltage. Fig. 3 is a schematic diagram showing a circuit structure of a computing unit for extracting a positive sequence of a phase-locked loop with respect to a phase-locked grid voltage in the preferred embodiment shown in fig. 1. FIG. 4 is a flow chart showing the calculation of the component U on the Q axis in the rotating coordinate system in the preferred embodiment shown in FIG. 1qThe process of (1). Referring to fig. 3 and 4, where the all-pass filter produces a 90 ° phase shift of the grid voltage signal, then there should be:
then performing clark transformation on the reference voltage to obtain a static coordinate system UαAnd Uβ：
Then, the Park transformation is carried out on the static coordinate system to convert the rotating coordinate system UdAnd Uq：
Thus, the component U of the three-phase voltage on the Q axis is obtainedqThus to UqAnd performing phase locking to obtain the current power grid rotation angle PhaseAngle.
The method comprises the steps that a hardware sampling circuit is configured to obtain a zero-crossing signal of a power grid, the hardware sampling circuit is configured to sample a voltage value of the power grid through a digital-to-analog converter of a micro-control unit, meanwhile, a pulse edge capturing unit of the hardware sampling circuit captures a rising edge or a falling edge zero-crossing point of the power grid, and the micro-control unit is configured with corresponding interruption, namely, the interruption is carried out when the rising edge or the falling edge of the voltage of the power grid crosses the zero-crossing point, so that phase sequence identification and subsequent phase locking judgment are carried out. It should be noted that, when the phase sequence identifier, the grid identifier, and the phase-locked identifier of the grid need to be recovered when the grid fails or power failure occurs, the power failure of the grid can be determined by continuously detecting multiple times of signal zero-crossing loss, and then the zero-crossing frequency can be continuously monitored through the zero-crossing interruption period, and the current grid identifier is determined again, so that the grid-connected inverter is ensured to be normally applicable after the grid failure or power failure is recovered.
In particular, FIG. 5 is a flow chart illustrating the steps of determining grid identification in the preferred embodiment shown in FIG. 1. Referring to fig. 5, first, any phase in a three-phase power grid is selected as a target, for example, U is selectedabTaking the phase as an object, recording the time T of each zero crossing of the phase signal, selecting the current zero crossing time as a node, determining the difference between the current zero crossing time and the last zero crossing time of the phase circuit voltage as a current zero crossing period T, and correspondingly counting down the period T to obtain the current zero crossing frequency F; generally, under different power grid environments in different regions, the power grid frequency does not exceed 70Hz, the grid-connected zero-crossing frequency may be in the range of 70Hz to 100Hz, and considering that the two consecutive zero-crossing frequencies are also high when the power grid harmonic is very large, in this embodiment, the grid-connected zero-crossing frequency F is set0If the frequency is 80Hz, respectively obtaining the zero-crossing period and the zero-crossing frequency for three continuous zero-crossing times, and the frequency value of the three continuous zero-crossing is greater than the grid-connected zero-crossing frequency F0Then the controller controls to modify the grid identity to be a weak grid identity, i.e. the grid identity is 0. In other embodiments, the number of times that the zero-crossing frequency is continuously greater than the grid-connection zero-crossing frequency may be set in a range of 3 to 5, and the embodiment of the invention is not limited thereto. It is worth mentioning that, in the process, an accumulation technologist may be configured to accumulate the times that the current zero-crossing frequency is greater than the grid-connected zero-crossing frequency, that is, if the current zero-crossing frequency F is greater than the grid-connected zero-crossing frequency F0If the counting of the accumulation counter is greater than the preset value, namely the zero-crossing frequency continuously exceeds the preset number of the grid-connected zero-crossing frequency, the counting of the accumulation counter is increased by one, and the counter technology is not reset; and if the current zero-crossing frequency F is not greater than the grid-connected zero-crossing F within the preset times0And when the power grid identification is confirmed, the counting of the accumulation technical device is reset, so that the accuracy of confirming or modifying the power grid identification can be ensured.
And when the power grid identifier is modified into a weak power grid identifier, the current power grid is in a weak power grid environment. Fig. 6 is a flow chart showing the steps of determining the phase lock identification by the zero crossing time of the zero crossing signal in the preferred embodiment shown in fig. 1. Referring to fig. 6, according to the foregoing, when the grid identifier is modified to be a weak grid, it is indicated that the first three zero-crossing frequencies from the current node are all greater than the grid-connected zero-crossing frequency, that is, greater than 80Hz, and if the current zero-crossing frequency F is greater than the grid-connected zero-crossing frequency F0Then, for the current zero-crossing time t and the previous zero-crossing time t of the zero-crossing signalpreAccumulating to obtain filtered time tnow. Normally, in the foregoing process, the time of two consecutive rising edge zero crossings or two consecutive falling edge zero crossings of the signal are selected to be accumulated to obtain tnowHowever, the harmonic ratio of the power grid is large, so that multiple zero-crossing points occur in unit harmonic, and t is acquired at the momentnowThe time of several consecutive zero crossings needs to be accumulated. Then, the time t after filtering is usednowCorresponding frequency and the grid zero crossing frequency F0Making a comparison if tnowThe corresponding frequency exceeds the grid zero crossing frequency F0Then t will bepreClearing; if tnowThe corresponding frequency is less than the grid zero-crossing frequency F0If the difference value between the current grid rotation angle and the corresponding phase sequence zero-crossing angle is within the preset range, and the angle difference value set in the preset range is also the error value between the current grid rotation angle and the corresponding phase sequence zero-crossing angle, in the embodiment of the invention, the range of the error value is within a range of +/-5 degrees, and if the three continuous grid rotation angles obtained through monitoring and calculation and the theoretical value (or the standard value) of the zero-crossing angle under the corresponding phase sequence are within the error range, the controller locks the phase markThe identification configuration is a normal value of 1, i.e., phase sequence identification is completed; otherwise, the controller keeps the phase locking identifier at 0, and considers that the current phase locking state is abnormal/failed.
When the phase lock fails, the remaining two-phase voltage, i.e., U in the preferred embodiment, is determinedbcAnd Uca. If each U in the predetermined periodbcAre all greater than UcaModifying the phase sequence identifier to be positive sequence if each U in the preset periodbcAre all less than UcaThe modified phase sequence is identified as negative. The preset period may be in the range of 80 times to 120 times. In this process, the determination results of the remaining two-phase voltages may be also accumulated by the accumulation counter, specifically, the positive sequence accumulation counter and the negative sequence accumulation counter may be separately provided for separately counting the positive sequence comparison result and the negative sequence comparison result, that is, when U is the casebcGreater than UcaWhen the count of the positive sequence accumulation counter is increased by one, when U is equal to the count of the positive sequence accumulation counterbcIs less than UcaAnd if so, adding one to the count of the negative sequence accumulation counter, and modifying the corresponding identifier when the count of the positive sequence accumulation counter or the negative sequence accumulation counter reaches a preset number.
Compared with the prior art, the invention has the following beneficial technical effects due to the adoption of the technical scheme:
1. acquiring a three-phase power grid voltage calculation voltage positive sequence component through switching frequency interruption, obtaining a Q-axis component Uq under a rotating coordinate system through coordinate system transformation, phase-locking the component Uq to obtain a coordinate system rotating angle, acquiring a power grid zero-crossing signal for single-phase voltage, and configuring zero-crossing interruption, so that the power grid harmonic environment such as a weak power grid and the like is adapted, and the correct phase sequence identification and the normal operation of equipment of a grid-connected inverter under the weak power grid environment are ensured; the technical problems that in the prior art, a common phase sequence identification method fails in the environment with large power grid harmonic waves such as a weak power grid and the like, and the phase sequence cannot be normally identified, so that phase locking cannot be performed are solved, the normal operation of a grid-connected inverter in the weak power grid is guaranteed, and the applicability of the grid-connected inverter is improved;
2. when the three-phase grid-connected inverter is applied to an environment such as a large power grid or a laboratory where the three-phase voltage is in an ideal state, because the harmonic wave of the power grid voltage is good, the automatic identification of the current power grid phase sequence can be normally realized without modifying the power grid identification, so that the three-phase grid-connected inverter can also be applied to a non-weak power grid state;
3. when the power grid fails or fails, the phase sequence identification, the power grid identification and the phase locking identification of the power grid are recovered, at the moment, the power grid power failure is judged due to the fact that multiple times of signal zero-crossing loss are continuously detected, then the zero-crossing frequency can be continuously monitored through a zero-crossing interruption period, and the current power grid identification is judged again, so that the grid-connected inverter is guaranteed to be normally applicable after the power grid failure or power failure recovery;
4. filtering the zero-crossing signal of the power grid under the weak power grid, when the frequency corresponding to the period of two continuous zero crossings of the zero-crossing signal is greater than the preset frequency, accumulating the two zero-crossing times to be used as the post-filtering time of the power grid, and when the phase locking is abnormal, filtering the couple to avoid filtering errors. Furthermore, when the phase locking is abnormal, the other two phases of power grid voltages are logically judged to correct the power grid phase sequence, and finally the correct phase locking of the power grid is realized, so that the condition that the phase sequence judgment is misjudged or even fails only by judging the phase sequence through zero crossing under the conventional method due to multiple zero crossing of the power grid under the weak power grid can be avoided, and the phase sequence judgment accuracy is improved;
5. after the phase sequence of the power grid is identified, the positive sequence component of the power grid is extracted in different modes to carry out phase locking, so that the accuracy of phase locking can be further improved, and the applicability of equipment in the environment of unbalanced power grid can be improved.
The present invention has been described in detail, and the embodiments are only used for understanding the method and the core idea of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and to implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (7)
1. A phase sequence identification and phase locking method for a three-phase grid-connected inverter is characterized by comprising the following steps:
step S1, configuring the phase sequence identification of the power grid and the identification of the power grid to lock the phase;
configuring switching frequency sampling, interrupting the switching frequency sampling, sampling the three-phase power grid voltage, and setting the obtained three-phase voltage to be { U }ab、Ubc、UcaAnd obtaining three-phase grid voltage (U) for phase locking according to the three-phase grid voltageab、U*bc、U*caStep S2;
coordinate conversion is carried out on the three-phase power grid voltage for phase locking to obtain a component U on a Q axis under a rotating coordinate systemqStep S3;
a sampling circuit is configured to obtain a power grid zero-crossing signal, obtain the zero-crossing time T of any phase of zero-crossing signal in a three-phase power grid at each rising edge zero-crossing or falling edge zero-crossing time, obtain a zero-crossing period T according to the current rising edge or falling edge zero-crossing time, obtain a corresponding current zero-crossing frequency F, and set a grid-connected zero-crossing frequency F0And each current zero-crossing frequency F and the grid-connected zero-crossing frequency F are combined0Comparing, if the current zero-crossing frequency F is continuously greater than the grid-connected zero-crossing frequency F0Step S4, if the number of times reaches the preset number of times, modifying the grid identifier as a weak grid; and the number of the first and second groups,
if the current zero-crossing frequency F is larger than the grid-connected zero-crossing frequency F0Then, for the current zero-crossing time t and the previous zero-crossing time t of the zero-crossing signalpreAccumulating to obtain filtered time tnowThe filtered time tnowWith said grid zero crossing frequency F0Making a comparison if tnowThe corresponding frequency exceeds the grid zero crossing frequency F0Then t will bepreClearing; if tnowThe corresponding frequency is less than the grid zero-crossing frequency F0And step S5, comparing whether the difference between the current grid rotation angle and the corresponding phase sequence zero-crossing angle is within the preset range.
2. The phase sequence identification and phase locking method for the three-phase grid-connected inverter according to claim 1, wherein in the step S3, the method further comprises the step of performing phase locking on the components and obtaining the rotation angle of the power grid.
3. The phase sequence identification and phase locking method for the three-phase grid-connected inverter as claimed in claim 2, wherein in step S4, if an accumulation counter is configured, an accumulation counter is configured
If the current zero-crossing frequency F is larger than the grid-connected zero-crossing frequency F0If the count of the accumulation counter is increased by one, otherwise, the count of the accumulation counter is reset.
4. The phase sequence identification and phase locking method for the three-phase grid-connected inverter according to claim 3, wherein in the step S5, the step of comparing the difference between the current grid rotation angle and the corresponding phase sequence zero-crossing angle comprises the following steps:
if the difference values of the three continuous current grid rotation angles and the corresponding phase sequence zero-crossing angles are within a preset range, configuring the phase-locked identification to be normal, and completing phase sequence identification;
otherwise, configuring the phase locking identification to be abnormal, judging the voltages of the remaining two phases, and modifying the phase sequence identification of the power grid.
5. The phase sequence identification and phase locking method for the three-phase grid-connected inverter according to claim 4, wherein in the step S5, the step of judging the voltages of the remaining two phases comprises:
if U is in the set continuous M periodsbcGreater than UcaModifying the phase sequence identifier to be a positive sequence; if U isbcLess than UcaThe modified phase sequence is identified as negative.
6. The phase sequence identification and phase locking method for the three-phase grid-connected inverter according to claim 1, wherein in the step S2, the phase sequence identification and phase locking method is performed according to three-phase grid voltage { U }ab、Ubc、UcaAcquiring three-phase grid voltage (U) for phase lockingab、U*bc、U*caIn the process of (c) },
U*absatisfy Uab＝Uab；
U*bcSatisfy Ubc＝(1-P)*Ubc+P*Uca；
U*caSatisfy Uca＝(1-P)*Uca+P*Ubc；
And P is a phase sequence, if the current power grid phase sequence is positive, the phase sequence P is 0, and if the current power grid phase sequence is negative, the phase sequence P is 1.
7. The phase sequence identification and phase locking method for the three-phase grid-connected inverter according to claim 2, wherein in step S3, a component U on a Q axis in a rotating coordinate system is obtainedqComprises the following steps:
configuring a phase-locked loop and applying a grid voltage { U x } for said phase lockingab、U*bc、U*caExtracting positive sequence (U)aP、U*bP、U*cPStep S31 of taking as a reference voltage;
clark conversion is carried out on the reference voltage to obtain a static coordinate system UαAnd UβStep S32;
carrying out Park conversion on the static coordinate system to convert a rotating coordinate system UdAnd UqStep S33.
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| CN112531784B (en) * | 2020-12-14 | 2022-08-19 | 浙江艾罗网络能源技术股份有限公司 | Phase-sequence self-adaptive phase-locking and inversion control method for three-phase power grid |
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