CN106018959A - Frequency observation method for droop control of grid-connected inverter - Google Patents

Abstract

The invention discloses a frequency observation method for droop control of a grid-connected inverter, and belongs to the technical field of distributed power generating/micro power grids. The method includes the steps of carrying out Clarke transformation for the three-phase grid voltage, obtaining the voltage value on a two-phase static coordinate system, conducting quadratic differential operation on the value to construct a linear equation group, eliminating negative sequence and second harmonic components by solving the equation, extracting positive sequence components in cooperation with low-pass filtering under a rotating coordinate system calculating real-time grid phase angle accordingly, selecting a shorter calculation window, and fitting the frequency value according to the angle and time sequence in the window by using an improved least squares method. Modified LSM is used to calculate the low-frequency component frequency value in the rotating coordinate system, so as to compensate the phase angle lagging caused by low-pass filtering, and to accurately observe the grid phase angle.

Description

A kind of frequency observation method being applicable to combining inverter droop control

Technical field

The present invention relates to a kind of frequency observation method during distributed power source cutting-in control, can quick and precisely observe electrical network Phase and frequency, belongs to distributed power source/micro-capacitance sensor technical field.

Background technology

At present, the form of increasing new forms of energy power supply in a distributed manner (distributed generation, DG) connects Enter electrical network.For overcoming the DG fluctuation impact on electrical network, generally multiple DG, energy storage device and load are set up into micro-capacitance sensor, then with Main electrical network is connected.Electronic power inverter is as the primary interface of DG Yu micro-capacitance sensor, and its cutting-in control technology is in recent years Individual study hotspot.For the combining inverter of interface in micro-capacitance sensor, frequently with power limitation control (PQ control) and sagging (Droop) Control.Wherein droop control is with its strongly-adaptive, weak communication dependency, obtain the most widely should in micro-capacitance sensor control With.One basic index of new energy grid-connected power is that grid power source will be with line voltage with frequency homophase, it is therefore desirable to quickly accurate Really observe frequency and the phase angle of electrical network, be advantageously implemented the equity control in micro-capacitance sensor of multiple distributed power source.

Current system typically uses the observation of software phase-lock loop frequency and phase angle to realize electrical network, but works as line voltage Because of comprise negative phase-sequence, harmonic wave aliquot and when producing distortion, traditional software phase-lock loop will lose efficacy.In order to carry under non-ideal conditions Take positive-sequence component, have many scholars carry out the research of this respect and propose improvement project, be broadly divided into three major types:

The first kind is to build system of linear equations to carry out phase sequence separation, document " SVENSSON J, BONGIORNO M, SANNINO A.Practical implementation of delayed signal cancellation method for phase-sequence separation[J].IEEE Trans on Power Delivery,2007,22(1):18-26.” Use T/4 (T is power frequency period) related method thereof to build, but this causes to frequency observation delayed；Document " Zhou Peng, He Yikang. electrical network The detection [J] of fundamental voltage synchronizing signal when asymmetrical voltage and harmonic distortion. Chinese journal of scientific instrument, 2010,31 (1): 78- 84. " introducing is differentiated and is ensured real-time, but the differential of high-order can add up and fault in enlargement.

Equations of The Second Kind be design wave filter to filter non-positive-sequence component, document " Wu Xiaobo, Zhao Rende, Hu Chaoran, etc. based on Improve the phase-lock technique [J] of adaptive notch filter. Automation of Electric Systems, 2014,38 (5): 103-108. ", document " once Strive, Yang Jiaqiang. a kind of synchronized method [J] of frequency self adaptation moving average filter. journal of Zhejiang university: engineering version, 2014,48 (9): 1696-1703. " and document " Shen Kaikui, Li Yanlong, Zhao Yuan design etc. Instantaneous Frequency of Power Grid track algorithm [J]. protecting electrical power system and control, 2015,43 (5): 75-80. " separately design adaptive notch filter, moving average Wave filter, finite impulse response filter carry out phase-locked, but parameter designing is complicated, and when mains frequency offsets, need Readjust parameter.

3rd class is the new control algolithm of design, and such as broad sense second order integro point-score and recursive model reference adaptive algorithm, but it is calculated Method is complicated, acquires a certain degree of difficulty in engineer applied.

Said method is while extracting electrical network fundamental positive sequence, and the observation having been achieved with frequency having, have then goes back Frequency values could be obtained after need to calculating further.Traditional cross zero detecting method, fourier transform method and line-of-sight course can not be taken into account The rapidity of frequency detecting and accuracy demand, by introducing the methods such as method of least square (LSM), wavelet analysis, detect performance Increase to a certain extent, but the most also can be restricted because operand is big.The most up to the present, the most still Lack a kind of the phase-locked of combining inverter droop control and frequency observation method of being applicable to so that it is be subject in the application of cutting-in control To limiting.

In view of this, this is studied by the present inventor, develops one specially and is applicable to combining inverter droop control Frequency observation method, this case thus produces.

Summary of the invention

It is an object of the invention to provide a kind of frequency observation method being applicable to combining inverter droop control, make sagging control When making the control of multiple distributed power sources in being applied to micro-capacitance sensor, the advantage that weak communication relies on can be retained, PQ can be inherited again Control the most succinct control structure.

To achieve these goals, the solution of the present invention is:

A kind of frequency observation method being applicable to combining inverter droop control, comprises the steps:

Step 1, first three-phase power grid voltage is carried out Clarke conversion, obtains the magnitude of voltage that biphase static coordinate is fastened, This value is carried out second differential computing, builds and obtain system of linear equations, eliminate negative phase-sequence and second harmonic component by solving equation；

Low-pass filtering under step 2, cooperation rotating coordinate system, extracts positive-sequence component, and calculates real-time grid phase accordingly Angle；

Step 3, choose a shorter calculation window, according to the angle in this window and time series, utilize after improving Least square fitting goes out frequency values, calculates the low frequency component frequency values under rotating coordinate system with LSM equally；

The phase delay that step 4, accurate compensation low-pass filtering are brought, it is achieved the accurate observation of electrical network phase angle.

As preferably, above-mentioned steps 1 specifically includes following sub-step:

Step 101: list the analytical expression of three-phase power grid voltage, comprises positive sequence first-harmonic, negative sequence component, second harmonic divide Amount, three times and above odd harmonics, line voltage U_gExpression formula is:

${\stackrel{\·}{U}}_g={\stackrel{\·}{U}}_1^{+}+{\stackrel{\·}{U}}_1^{-}+{\stackrel{\·}{U}}_2+\underset{i=2k+1}{\overset{k\≥1}{\Σ}}{\stackrel{\·}{U}}_i---\left(1\right)$

If first-harmonic angular frequency is ω, initial phase angle is 0,For other each component initial phase angles, each subscale is shown as the form of three-phase For:

Step 102: the expression formula (1) in step 101 is carried out Clarke conversion, is converted into biphase rest frame (alpha-beta Coordinate system) under analytical expression, according to Clarke conversion character, after this step, the integral frequency harmonizing wave of 3 is filtered out, So under alpha-beta coordinate system, line voltage comprises positive sequence first-harmonic, negative sequence component, second harmonic component and higher harmonic components (5 Secondary above odd harmonics, does not comprise the integral multiple subharmonic of 3), expression formula is:

Wherein M represents higher harmonic components, refers to the odd harmonics of more than 5 times, and the integral multiple subharmonic not comprising 3 divides Amount；

Step 103: expression formula in step 102 (2) is carried out first differential, and angular frequency value ω obtained divided by observation station, Obtaining α axle and each equation of β axle, expression formula is:

Wherein M₁Represent higher harmonic components, comprise 5 times and above odd-order harmonic components；

Step 104: expression formula in step 102 (2) is carried out second-order differential, and the angular frequency value obtained divided by observation station is flat Side ω², obtaining α axle and each equation of β axle, expression formula is:

Wherein, M₂Represent M₁Again divided by income value after ω after first differential.

Step 105: obtain 6 independent equations according to step 102～104 altogether, if the unknown number of equation is positive sequence first-harmonic, bears Order components, second harmonic component and odd-order harmonic components (comprising α axle and beta-axis component respectively), therefore have 8 variablees, logical Cross linear operation and eliminate negative sequence component and these 4 variablees of second harmonic component, obtain comprising positive sequence first-harmonic and higher harmonic components Expression formula, expression formula is:

$\left[\begin{array}{c}{u}_{\mathrm{\α}}^{+}\\ u_{\mathrm{\β}}^{+}\end{array}\right]+M_x=\frac{1}{3}\left[\begin{array}{c}{u}_{\mathrm{\α}}\\ u_{\mathrm{\β}}\end{array}\right]+\frac{1}{2}\left[\begin{array}{c}{u}_{d\mathrm{\β}1}\\ -u_{d\mathrm{\α}1}\end{array}\right]-\frac{1}{6}\left[\begin{array}{c}{u}_{d\mathrm{\α}2}\\ u_{d\mathrm{\β}2}\end{array}\right]---\left(5\right)$

Wherein M_xRepresent higher harmonic components, comprise α axle and beta-axis component equally.

As preferably, above-mentioned steps 2 specifically includes following sub-step:

Step 201: utilize step 1 formula (5) to calculate α axle and the component of voltage of β axle of gained, carry out rotation transformation, in view of Line voltage is generally stabilized at 50Hz effect, and anglec of rotation frequency elects 50Hz as, obtains voltage under d-q coordinate system after rotated conversion D axle and the expression formula of q axle, fundametal compoment, after rotation transformation, obtains being similar to the low frequency component of direct current, and its frequency values is base Wave frequency and the difference of 50Hz；Higher harmonic components, after rotation transformation, obtains 4 times and above even-order harmonic component.Step Expression formula (5) left side of rapid 105 is designated as [u_xα,u_xβ] ', the angular frequency that 50Hz is corresponding₀, then the angle of rotation transformation be θ= ω₀T, so expression is:

$\left[\begin{array}{c}{u}_{xd}\\ u_{xq}\end{array}\right]=\left[\begin{array}{cc}\cos \mathrm{\θ}& \sin \mathrm{\θ}\\ -\sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]\left[\begin{array}{c}{u}_{x\mathrm{\α}}\\ u_{x\mathrm{\β}}\end{array}\right]=\left[\begin{array}{c}{u}_{1d}^{+}\\ u_{1q}^{+}\end{array}\right]+\left[\begin{array}{c}{M}_{xd}\\ M_{xq}\end{array}\right]=U_1^{+}\left[\begin{array}{c}\cos (\mathrm{\ω}-{\mathrm{\ω}}_0)t\\ \sin (\mathrm{\ω}-{\mathrm{\ω}}_0)t\end{array}\right]+\left[\begin{array}{c}{M}_{xd}\\ M_{xq}\end{array}\right]---\left(6\right)$

Step 202: design low pass filter separation low frequency component, by the frequency of identification low frequency component, it is right to complete The accurate compensation of phase place, the expression formula of N rank moving average filter is:

$H\left(z\right)=\underset{r=0}{\overset{N-1}{\Σ}}h\left(r\right)z^{-r},h\left(r\right)=1/N---\left(7\right)$

Make z=exp (j ω T_s), T_sFor the sampling period, the analytical expression trying to achieve moving average filter further is

$H\left(z\right)=\frac{1-z^{-N}}{N(1-z^{-1})}=\frac{1-cos\left({\mathrm{jN\ωT}}_S\right)+jsin\left({\mathrm{jN\ωT}}_S\right)}{N(1-\cos ({\mathrm{j\ωT}}_S)+jsin({\mathrm{j\ωT}}_S\left)\right)}---\left(8\right)$

Step 203: carrying out rotating inverse transformation to the data after after filtering, the frequency of inverse transformation is 50Hz equally, obtains Only comprising the voltage expression of positive-sequence component under alpha-beta coordinate system, voltage now exists delayed, but due to delayed same angle Degree, has no effect on the observation of frequency, and expression formula is:

$\left[\begin{array}{c}{u}_{\mathrm{\α}1}^{+}\\ u_{\mathrm{\β}1}^{+}\end{array}\right]=\left[\begin{array}{cc}\cos \mathrm{\θ}& \sin \mathrm{\θ}\\ -\sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]\left[\begin{array}{c}{u}_{1d}^{+}\\ u_{1q}^{+}\end{array}\right]=\left[\begin{array}{cc}{\mathrm{cos\ω}}_{0}t& -{\mathrm{sin\ω}}_{0}t\\ {\mathrm{sin\ω}}_{0}t& {\mathrm{cos\ω}}_{0}t\end{array}\right]\left[\begin{array}{c}\cos (\mathrm{\ω}-{\mathrm{\ω}}_0)t\\ \sin (\mathrm{\ω}-{\mathrm{\ω}}_0)t\end{array}\right]=U_1^{+}\left[\begin{array}{c}\cos \mathrm{\ω}t\\ \sin \mathrm{\ω}t\end{array}\right]---\left(9\right)$

Calculate the angle values of gained for this voltage, be exactly actual electric network phase angle after overcompensation.

As preferably, step 202 uses finite impulse response (FIR) wave filter, it is ensured that the striction line of filter phases Property.

As preferably, described step 202 specifically selects the adaptive moving average filter of exponent number, selected suitable exponent number, Make its antithesis order harmonic components have complete attenuation ability, if sample frequency is 10kHz, select the moving average filter on 100 rank, Just the integral multiple component of 100Hz can be had complete filter capacity.

As preferably, above-mentioned steps 3 specifically includes following sub-step:

Step 301: based on phase angle and the linear relationship of time, ask for phase angle and time sequence by method of least square (LSM) The linear gradient of row, i.e. frequency, a calculation window (length M=2N+1) of selected appropriate length, it is believed that can be with in window Average frequency substitute the frequency in this window center moment.AngleWith the relational representation of sampling instant t it is:Its InFor initial phase angle, ω is required angular frequency, obtains ω according to method of least square, and solving equation is:

Step 302: time series is carried out translation transformation, shift factor is central instant value t in window_N+1, thus To symmetrical a, sequence and be 0 time series t_i'=t_i-t_N+1, the expression formula after then can being converted is:

$\underset{i=1}{\overset{M=2N+1}{\Σ}}{t}_i^{\′}=T_S\×\underset{i=1}{\overset{M=2N+1}{\Σ}}(i-N-1)=0---\left(12\right)$

Step 303: according to the computing formula of method of least square, solve the coefficient in step 302, after translation Time series and be 0, therefore greatly simplifie cymometer formula, accounting equation is:

Therefore the solution formula of frequency is:

As preferably, above-mentioned steps 4 specifically includes following sub-step:

Step 401: utilize the electrical network positive-sequence component that step 203 is tried to achieve, is calculated an angle according to antitrigonometric function Value, expression formula is:

$\mathrm{\θ}=arctan(u_{\mathrm{\β}1}^{+}/u_{\mathrm{\α}1}^{+})---\left(15\right)$

Step 402: utilize the method for least square described in step 301～303 that the low frequency component under d-q coordinate system carries out frequency Rate is observed, and observation station obtains frequency and is multiplied by a coefficient, it is possible to the phase angle being compensated；

Step 403: two values of gained in step 401 and step 402 are added, i.e. can get the real time phasor of electrical network.

The frequency observation method being applicable to combining inverter droop control of the present invention: electricity can be observed rapidly and accurately Net frequency and phase angle, the more traditional method of least square of operand is significantly improved；Electrical network still can be successfully realized when electrical network distorts Synchronizing signal is extracted and frequency observation, and has dynamic responding speed and higher stable state accuracy faster, and performance is more traditional Software phase-lock loop also has bigger improvement；When being applied to combining inverter droop control, make droop control can retain weak communication The advantage relied on, can inherit again PQ and control the most succinct cutting-in control structure.

Below in conjunction with drawings and the specific embodiments, the present invention is described in further detail.

Accompanying drawing explanation

Fig. 1 is the frequency observation method step flow chart that the present embodiment is applicable to combining inverter droop control；

Fig. 2 is frequency during this enforcement line voltage symmetry and phase angle observed result figure；

Fig. 3 is the frequency during distortion of this enforcement line voltage and phase angle observed result figure；

Fig. 4 is this enforcement line voltage frequency when there is higher hamonic wave and phase angle observed result figure；

Fig. 5 is the schematic diagram of this enforcement droop control；

Fig. 6 is the control structure figure of this enforcement combining inverter；

The dynamic response characteristic figure of combining inverter when Fig. 7 is the change of this enforcement frequency；

Fig. 8 is the inverter output figure under this enforcement grid failure state.

Detailed description of the invention

As it is shown in figure 1, a kind of frequency observation method being applicable to combining inverter droop control, comprise the steps:

Step 101: list the analytical expression of three-phase power grid voltage, comprises positive sequence first-harmonic, negative sequence component, second harmonic divide Amount, three times and above odd harmonics, line voltage U_gExpression formula is:

${\stackrel{\·}{U}}_g={\stackrel{\·}{U}}_1^{+}+{\stackrel{\·}{U}}_1^{-}+{\stackrel{\·}{U}}_2+\underset{i=2k+1}{\overset{k\≥1}{\Σ}}{\stackrel{\·}{U}}_i---\left(1\right)$

If first-harmonic angular frequency is ω, initial phase angle is 0,For other each component initial phase angles, each subscale is shown as the form of three-phase For:

Step 102: the expression formula (1) in step 101 is carried out Clarke conversion, is converted into biphase rest frame (alpha-beta Coordinate system) under analytical expression, according to Clarke conversion character, after this step, the integral frequency harmonizing wave of three is filtered out, So under alpha-beta coordinate system, line voltage comprises positive sequence first-harmonic, negative sequence component, second harmonic component and higher harmonic components (5 Secondary above odd harmonics, does not comprise the integral multiple subharmonic of 3), expression formula is:

Wherein M represents higher harmonic components, refers to the odd harmonics of more than 5 times, and the integral multiple subharmonic not comprising 3 divides Amount；

Step 103: expression formula in step 102 (2) is carried out first differential, and angular frequency value ω obtained divided by observation station, Obtaining α axle and each equation of β axle, expression formula is:

Wherein M₁Represent higher harmonic components, comprise 5 times and above odd-order harmonic components；Each frequency range component after differential Still can retain, the equation left side can be in the hope of in real-time operation, and the first three items on the right can accurately write out analytical expression； Higher harmonic components M₁Representative Section 4 need not write out exact expression, and it comprises 5 times and above odd-order harmonic components Item.

Step 104: expression formula in step 102 (2) is carried out second-order differential, and the angular frequency value obtained divided by observation station is flat Side ω², obtaining α axle and each equation of β axle, expression formula is:

M₂Represent M₁Again divided by income value after ω after first differential, the equation left side equally can be in the hope of in real-time operation , the first three items on the right can accurately write out analytical expression；M₂Representative Section 4 need not write out exact expression, only needs Indicating it is to comprise 5 times and the item of above odd-order harmonic components.

Step 105: obtain 6 independent equations according to step 102～104 altogether, if the unknown number of equation is positive sequence first-harmonic, bears Order components, second harmonic component and odd-order harmonic components (comprising α axle and beta-axis component respectively), therefore have 8 variablees.Though So intangibility, but wherein 4 variablees can be eliminated by linear operation, select to eliminate negative phase-sequence and second harmonic component, then obtain To comprising the expression formula of positive sequence first-harmonic and higher harmonic components, expression formula is:

$\left[\begin{array}{c}{u}_{\mathrm{\α}}^{+}\\ u_{\mathrm{\β}}^{+}\end{array}\right]+M_x=\frac{1}{3}\left[\begin{array}{c}{u}_{\mathrm{\α}}\\ u_{\mathrm{\β}}\end{array}\right]+\frac{1}{2}\left[\begin{array}{c}{u}_{d\mathrm{\β}1}\\ -u_{d\mathrm{\α}1}\end{array}\right]-\frac{1}{6}\left[\begin{array}{c}{u}_{d\mathrm{\α}2}\\ u_{d\mathrm{\β}2}\end{array}\right]---\left(5\right)$

Wherein M_xRepresenting higher harmonic components, comprise α axle and beta-axis component equally, above formula equal sign right-hand component can be accurate Solve.

Step 201: utilize step 1 formula (5) to calculate α axle and the component of voltage of β axle of gained, carry out rotation transformation.In view of Line voltage is generally stabilized at 50Hz effect, and anglec of rotation frequency elects 50Hz as, obtains voltage d under dq coordinate system after rotated conversion Axle and the expression formula of q axle.Fundametal compoment, after rotation transformation, obtains being similar to the low frequency component of direct current, and its frequency values is base Wave frequency and the difference of 50Hz；Higher harmonic components, after rotation transformation, obtains 4 times and above even-order harmonic component.Step Expression formula (5) left side of rapid 105 is designated as [u_xα,u_xβ] ', the angular frequency that 50Hz is corresponding₀, then the angle of rotation transformation be θ= ω₀T, so expression is:

$\left[\begin{array}{c}{u}_{xd}\\ u_{xq}\end{array}\right]=\left[\begin{array}{cc}\cos \mathrm{\θ}& \sin \mathrm{\θ}\\ -\sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]\left[\begin{array}{c}{u}_{x\mathrm{\α}}\\ u_{x\mathrm{\β}}\end{array}\right]=\left[\begin{array}{c}{u}_{1d}^{+}\\ u_{1q}^{+}\end{array}\right]+\left[\begin{array}{c}{M}_{xd}\\ M_{xq}\end{array}\right]=U_1^{+}\left[\begin{array}{c}\cos (\mathrm{\ω}-{\mathrm{\ω}}_0)t\\ \sin (\mathrm{\ω}-{\mathrm{\ω}}_0)t\end{array}\right]+\left[\begin{array}{c}{M}_{xd}\\ M_{xq}\end{array}\right]---\left(6\right)$

Step 202: design low pass filter separation low frequency component, uses finite impulse response (FIR) wave filter, it is ensured that The Strict linear of filter phases: delayed phase place is directly proportional to the frequency of low frequency component.By the frequency of identification low frequency component, The accurate compensation to phase place can be completed.Select the adaptive moving average filter of exponent number (one of FIR filter), selected Suitable exponent number so that it is antithesis order harmonic components has complete attenuation ability.If sample frequency is 10kHz, the slip on 100 rank is selected to put down All wave filter, it is possible to the integral multiple component of 100Hz is had complete filter capacity.The expression formula of N rank moving average filter For:

$H\left(z\right)=\underset{r=0}{\overset{N-1}{\Σ}}h\left(r\right)z^{-r},h\left(r\right)=1/N---\left(7\right)$

Make z=exp (j ω T_s), T_sFor the sampling period, the analytical expression trying to achieve moving average filter further is

$H\left(z\right)=\frac{1-z^{-N}}{N(1-z^{-1})}=\frac{1-cos\left({\mathrm{jN\ωT}}_S\right)+jsin\left({\mathrm{jN\ωT}}_S\right)}{N(1-\cos ({\mathrm{j\ωT}}_S)+jsin({\mathrm{j\ωT}}_S\left)\right)}---\left(8\right)$

Step 203: carrying out rotating inverse transformation to the data after after filtering, the frequency of inverse transformation is 50Hz equally, so that it may To obtain only comprising under alpha-beta coordinate system the voltage expression of positive-sequence component.Voltage now exists delayed, but due to delayed same Individual angle, has no effect on the observation of frequency, and expression formula is:

$\left[\begin{array}{c}{u}_{\mathrm{\α}1}^{+}\\ u_{\mathrm{\β}1}^{+}\end{array}\right]=\left[\begin{array}{cc}\cos \mathrm{\θ}& \sin \mathrm{\θ}\\ -\sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]\left[\begin{array}{c}{u}_{1d}^{+}\\ u_{1q}^{+}\end{array}\right]=\left[\begin{array}{cc}{\mathrm{cos\ω}}_{0}t& -{\mathrm{sin\ω}}_{0}t\\ {\mathrm{sin\ω}}_{0}t& {\mathrm{cos\ω}}_{0}t\end{array}\right]\left[\begin{array}{c}\cos (\mathrm{\ω}-{\mathrm{\ω}}_0)t\\ \sin (\mathrm{\ω}-{\mathrm{\ω}}_0)t\end{array}\right]=U_1^{+}\left[\begin{array}{c}\cos \mathrm{\ω}t\\ \sin \mathrm{\ω}t\end{array}\right]---\left(9\right)$

Calculate the angle values of gained for this voltage, be exactly actual electric network phase angle after overcompensation.

Step 301: based on phase angle and the linear relationship of time, can pass through method of least square (LSM) ask for phase angle and Seasonal effect in time series linear gradient, i.e. frequency.One calculation window (length M=2N+1) of selected appropriate length, it is believed that Ke Yiyong Average frequency in window substitutes the frequency in this window center moment.AngleCan be expressed as with the relation of sampling instant t:WhereinFor initial phase angle, ω is required angular frequency, can obtain ω according to LSM, and solving equation is:

Step 302: time series is carried out translation transformation, shift factor is central instant value t in window_N+1, thus To symmetrical a, sequence and be 0 time series t_i'=t_i-t_N+1, the expression formula after then can being converted is:

$\underset{i=1}{\overset{M=2N+1}{\Σ}}{t}_i^{\′}=T_S\×\underset{i=1}{\overset{M=2N+1}{\Σ}}(i-N-1)=0---\left(12\right)$

Based on step 301 it is assumed that think that frequency is constant in window, and for a window, in window in The heart moment, therefore in above formula bracket, part may be considered constant in a calculation window it is also assumed that be constant.In Be problem be converted into ask for phase angle and translation after seasonal effect in time series linear coefficient.

Step 303: according to the computing formula of LSM, the coefficient in step 302 is solved.Due to the time after translation Sequence and be 0, therefore greatly simplifies cymometer formula, and accounting equation is:

Therefore the solution formula of frequency is:

Step 401: utilize the electrical network positive-sequence component that right step 203 is tried to achieve, be calculated one according to antitrigonometric function Angle value, expression formula is:

$\mathrm{\θ}=arctan(u_{\mathrm{\β}1}^{+}/u_{\mathrm{\α}1}^{+})---\left(15\right)$

Step 402: utilize the improvement LSM described in step 301～303 that the low frequency component under d-q coordinate system is carried out frequency Observation, observation station obtains frequency and is multiplied by a coefficient, it is possible to the phase angle being compensated.

Step 403: two values of gained in step 401 and step 402 are added, i.e. can get the real time phasor of electrical network.

Write corresponding program according to the step described by said method, and set up under Matlab/Simulink environment Phantom, the simulating grid voltage frequency of occurrences/situation such as voltage jump, wave distortion, and with traditional software phase-lock loop (PLL) compare, investigate its phase angle and frequency observation performance.Then, this method making in actual combining inverter controls is given By case, simulation actual frequency bust and the situation of external fault, investigate the performance performance of this method in the case of this.Below in conjunction with Figure of description, elaborates method performance.

As a kind of detailed description of the invention, implementation process has improvement.Owing to system can be reduced after low-pass filtering Dynamic response performance, it is contemplated that negative sequence voltage and secondary, triple-frequency harmonics are the principal elements causing electrical network to distort, and these harmonic waves Separation be not required to carry out low-pass filtering, if there is high fdrequency component, then calculate gained frequency values necessarily lead to larger fluctuation.Choosing Take some neighborhood calculation windows, ask for the difference of frequency observation value in adjacent window apertures, judge degree of convergence.If through several windows Still dissipate after Kou, then there is high fdrequency component in explanation, then starts filtering, until detecting in wave filter dq coordinate system the most single During one low frequency component, just stop filtering.Emulation breaker in middle frequency is 100kHz, a length of 0.4ms, window during the calculation window chosen Width is 41, and the sample frequency of FIR filter elects 10kHz as.

Simulating scenes one: emulation duration altogether 0.12s, starts as normal rating amplitude, the three-phase symmetric voltage of frequency 50Hz, When 0.03s, frequency jumps to 45Hz, and when 0.07s, saltus step occurs in three-phase positive sequence voltage amplitude.Under this scene, voltage waveform The result of (perunit value), mains frequency observed result and phase angle observation is as shown in Figure 2.As seen from the figure, two kinds of methods all can be real The dynamic tracing of existing frequency phase angle.Method described in the present embodiment when frequency discontinuity observed result it is possible that cross punching, but Obviously conventional PLL it is better than on dynamic response time.

Simulating scenes two: emulation duration altogether 0.12s, starts as normal rating amplitude, the three-phase symmetric voltage of frequency 50Hz, Add 20% negative sequence voltage when 0.03s, add the second harmonic voltage of 20% when 0.07s.Under this scene, voltage waveform The result of (perunit value), mains frequency observed result and phase angle observation is as shown in Figure 3.As seen from the figure, when electrical network, negative phase-sequence occurs Or during second harmonic, traditional PLL just loses phase-locked function, although and method described in embodiment exists in mutation process Relatively greater than punching, but the observation to next beat does not impact, remaining time observed result and electrical network actual frequency and Phase place is completely superposed, it is achieved that higher accuracy of observation and faster dynamic responding speed.When there is Sudden Changing Rate, though height can be detected Frequency component, but set in actual algorithm, needs to continue for some time and interior high fdrequency component occurs, just startup low-pass filtering algorithm, This guarantees the dynamic response performance of algorithm.

Simulating scenes three: emulation duration altogether 0.14s, starts as normal rating amplitude, the three-phase symmetric voltage of frequency 50Hz, Be initially added into twice and the quintuple harmonics component of 10% at 0.03s, when 0.09s, fundamental frequency is undergone mutation to 48Hz.This Under scape, the result of voltage waveform (perunit value), mains frequency observed result and phase angle observation is as shown in Figure 4.Owing to high order is humorous The existence of ripple, method described in the present embodiment starts FIR low-pass filtering, has therefore declined in terms of dynamic property, even if Under the most severe power grid environment, the carried algorithm of this case still can realize successfully phase-locked.

Carried for this case algorithm is applied in combining inverter droop control, and the principle of droop control is simulation synchronous motor " frequency-meritorious (f-P) " and " voltage-idle (U-Q) " droop characteristic, it is achieved each DG output from main regulation, as Shown in accompanying drawing 5.In figure, A and B is two operating points, and m is the adjustment factor of f-P, and n is U-Q adjustment factor.Due to microgrid bus electricity Voltage-frequency rate and amplitude are public informations, as long as therefore setting regulation coefficient m, n, each DG can be real according to respective droop characteristic Existing stable operation.According to frequency and voltage, it is calculated meritorious and idle reference value PQ_ref, control inverter accordingly, control Structure is as shown in Figure 6.Main circuit use three phase full bridge voltage source inverter topology, inverter output after LCL filter with Micro-capacitance sensor is connected.Control structure aspect, PQ controls to comprise power and two, electric current controls ring, and other modules are used for machining control institute The input needed and output signal.Phase-locked loop pll is by regulating q shaft voltage U under biphase dq rotating coordinate system_qAnd be allowed to be zero, just Real time phasor θ and the frequencies omega of electrical network can be obtained, provide synchronizing signal to the control of combining inverter.Control through PQ outer shroud, Obtain reference value i that interior circular current controls_ref；Again the voltage modulation signal of electric current loop output is carried out space vector (SVPWM) to adjust System, it is possible to driven signal accordingly.

Based on above control structure, the frequency observation method in this case is substituted phaselocked loop, it is provided that same to grid-connected inverters Step signal；According to the frequency observation result in this case, determine the reference value that PQ controls.Combining inverter rated power in test For 100kW, be provided with the sagging coefficient of merit be 25kW/Hz, idle sagging coefficient be set to 250Var/V, initial launch is at half rated power State.

Grid-connected scene one: electrical network initial launch is in normal voltage and 50Hz rated frequency, and at a time frequency is down to 48Hz, inverter output result is as shown in Figure 7.As seen from the figure, inverter accurately according to sagging relation, declines at mains frequency Time add meritorious output, idle still remain 0, i.e. power factor (PF) still remains 1, and this is grid-connected voltage x current in upper figure Phase relation in (as a example by A phase) also can embody.During frequency discontinuity, meritorious reference value creates of short duration crossing and rushes, But due to the inertia of system itself, actual PQ can not suddenly change, thus the of short duration sudden change of this reference value is not to system stability Influential.

Grid-connected scene two: electrical network initial launch is in normal voltage and 50Hz rated frequency, and a certain moment is due to external short circuit Causing voltage die, produce negative sequence component simultaneously, now the output performance of inverter is as shown in Figure 8.It will be seen that inverter Under grid failure state, provide stable reactive power support, reach to control target.

By above-mentioned l-G simulation test, demonstrate the feasibility of method described in the present embodiment.Being suitable for described in the present embodiment Frequency observation method in combining inverter droop control: can observe mains frequency and phase angle rapidly and accurately, operand relatively passes System method of least square is significantly improved；Synchronized signal extraction and frequency observation still can be successfully realized when electrical network distorts, And there is dynamic responding speed and higher stable state accuracy faster, performance relatively traditional software phaselocked loop also has bigger improvement； When being applied to combining inverter droop control, make droop control can retain the advantage that weak communication relies on, PQ control can be inherited again Make the most succinct cutting-in control structure.

Above-described embodiment and the product form of the graphic and non-limiting present invention and style, any art common Technical staff is suitably changed what it did or modifies, and all should be regarded as the patent category without departing from the present invention.

Claims (7)

1. it is applicable to a frequency observation method for combining inverter droop control, comprises the steps:

Step 1, first three-phase power grid voltage is carried out Clarke conversion, obtain the magnitude of voltage that biphase static coordinate is fastened, to this Value carries out second differential computing, builds and obtains system of linear equations, eliminates negative phase-sequence and second harmonic component by solving equation；

Low-pass filtering under step 2, cooperation rotating coordinate system, extracts positive-sequence component, and calculates real-time grid phase angle accordingly；

Step 3, choose a shorter calculation window, according to the angle in this window and time series, utilize the minimum after improving Square law simulates frequency values, calculates the low frequency component frequency values under rotating coordinate system with method of least square equally；

The phase delay that step 4, accurate compensation low-pass filtering are brought, it is achieved the accurate observation of electrical network phase angle.

A kind of frequency observation method being applicable to combining inverter droop control, step 1 is specifically wrapped Include following sub-step:

Step 101: list the analytical expression of three-phase power grid voltage, comprise positive sequence first-harmonic, negative sequence component, second harmonic component, Three times and above odd harmonics, line voltage U_gExpression formula is:

${\stackrel{\·}{U}}_g={\stackrel{\·}{U}}_1^{+}+{\stackrel{\·}{U}}_1^{-}+{\stackrel{\·}{U}}_2+\underset{i=2k+1}{\overset{k\≥1}{\Σ}}{\stackrel{\·}{U}}_i---\left(1\right)$

If first-harmonic angular frequency is ω, initial phase angle is 0,For other each component initial phase angles, each subscale is shown as the form of three-phase and is:

Step 102: the expression formula (1) in step 101 is carried out Clarke conversion, is converted into biphase rest frame (alpha-beta coordinate System) under analytical expression, according to Clarke conversion character, after this step, the integral frequency harmonizing wave of 3 is filtered out, at alpha-beta Under coordinate system, line voltage comprises positive sequence first-harmonic, negative sequence component, second harmonic component and higher harmonic components, and expression formula is:

Wherein M represents higher harmonic components, refers to the odd harmonics of more than 5 times, does not comprise the integral multiple order harmonic components of 3；

Step 103: expression formula in step 102 (2) is carried out first differential, and divided by angular frequency value ω that observation station obtains, obtains α Axle and each equation of β axle, expression formula is:

Wherein M₁Represent higher harmonic components, comprise 5 times and above odd-order harmonic components；

Step 104: expression formula in step 102 (2) is carried out second-order differential, and the angular frequency value obtained divided by observation station square ω², obtaining α axle and each equation of β axle, expression formula is:

Wherein, M₂Represent M₁Again divided by income value after ω after first differential.

Step 105: obtain 6 independent equations according to step 102～104 altogether, divides if the unknown number of equation is positive sequence first-harmonic, negative phase-sequence Amount, second harmonic component and odd-order harmonic components (comprising α axle and beta-axis component respectively), have 8 variablees, by linear fortune Calculate and eliminate negative sequence component and these 4 variablees of second harmonic component, obtain comprising the expression formula of positive sequence first-harmonic and higher harmonic components, Expression formula is:

$\left[\begin{array}{c}{u}_{\mathrm{\α}}^{+}\\ u_{\mathrm{\β}}^{+}\end{array}\right]+M_x=\frac{1}{3}\left[\begin{array}{c}{u}_{\mathrm{\α}}\\ u_{\mathrm{\β}}\end{array}\right]+\frac{1}{2}\left[\begin{array}{c}{u}_{d\mathrm{\β}1}\\ -u_{d\mathrm{\α}1}\end{array}\right]-\frac{1}{6}\left[\begin{array}{c}{u}_{d\mathrm{\α}2}\\ u_{d\mathrm{\β}2}\end{array}\right]---\left(5\right)$

Wherein M_xRepresent higher harmonic components, comprise α axle and beta-axis component equally.

A kind of frequency observation method being applicable to combining inverter droop control, step 2 is specifically wrapped Include following sub-step:

Step 201: utilize step 1 formula (5) to calculate α axle and the component of voltage of β axle of gained, carry out rotation transformation, rotate angular frequency Rate is 50Hz, obtains voltage d axle and the expression formula of q axle under d-q coordinate system after rotated conversion, and fundametal compoment is through rotation transformation After, obtaining being similar to the low frequency component of direct current, its frequency values is the difference of fundamental frequency and 50Hz；Higher harmonic components is through rotating After conversion, obtain 4 times and above even-order harmonic component, expression formula (5) left side of step 105 is designated as [u_xα,u_xβ] ', 50Hz Corresponding angular frequency₀, then the angle of rotation transformation is θ=ω₀T, so expression is:

$\left[\begin{array}{c}{u}_{xd}\\ u_{xq}\end{array}\right]=\left[\begin{array}{cc}cos\mathrm{\θ}& sin\mathrm{\θ}\\ -sin\mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]\left[\begin{array}{c}{u}_{x\mathrm{\α}}\\ u_{x\mathrm{\β}}\end{array}\right]=\left[\begin{array}{c}{u}_{1d}^{+}\\ u_{1q}^{+}\end{array}\right]+\left[\begin{array}{c}{M}_{xd}\\ M_{xq}\end{array}\right]=U_1^{+}\left[\begin{array}{c}cos(\mathrm{\ω}-{\mathrm{\ω}}_0)t\\ sin(\mathrm{\ω}-{\mathrm{\ω}}_0)t\end{array}\right]+\left[\begin{array}{c}{M}_{xd}\\ M_{xq}\end{array}\right]---\left(6\right)$

Step 202: design low pass filter separation low frequency component, by the frequency of identification low frequency component, completes the standard to phase place Really compensating, the expression formula of N rank moving average filter is:

$H\left(z\right)=\underset{r=0}{\overset{N-1}{\Σ}}h\left(r\right)z^{-r},h\left(r\right)=1/N---\left(7\right)$

Make z=exp (j ω T_s), T_sFor the sampling period, the analytical expression trying to achieve moving average filter further is

$H\left(z\right)=\frac{1-z^{-N}}{N(1-z^{-1})}=\frac{1-cos\left({\mathrm{jN\ωT}}_S\right)+jsin\left({\mathrm{jN\ωT}}_S\right)}{N(1-\cos ({\mathrm{j\ωT}}_S)+jsin({\mathrm{j\ωT}}_S\left)\right)}---\left(8\right)$

Step 203: carrying out rotating inverse transformation to the data after after filtering, the frequency of inverse transformation is 50Hz equally, obtains alpha-beta and sits Only comprising the voltage expression of positive-sequence component under mark system, expression formula is:

$\left[\begin{array}{c}{u}_{\mathrm{\α}1}^{+}\\ u_{\mathrm{\β}1}^{+}\end{array}\right]=\left[\begin{array}{cc}\cos \mathrm{\θ}& \sin \mathrm{\θ}\\ -\sin \mathrm{\θ}& \cos \mathrm{\θ}\end{array}\right]\left[\begin{array}{c}{u}_{1d}^{+}\\ u_{1q}^{+}\end{array}\right]=\left[\begin{array}{cc}{\mathrm{cos\ω}}_{0}t& -{\mathrm{sin\ω}}_{0}t\\ {\mathrm{sin\ω}}_{0}t& {\mathrm{cos\ω}}_{0}t\end{array}\right]\left[\begin{array}{c}\cos (\mathrm{\ω}-{\mathrm{\ω}}_0)t\\ \sin (\mathrm{\ω}-{\mathrm{\ω}}_0)t\end{array}\right]=U_1^{+}\left[\begin{array}{c}\cos \mathrm{\ω}t\\ \sin \mathrm{\ω}t\end{array}\right]---\left(9\right)$

Calculate the angle values of gained for this voltage, be exactly actual electric network phase angle after overcompensation.

A kind of frequency observation method being applicable to combining inverter droop control, step 202 uses Finite impulse response filter.

A kind of frequency observation method being applicable to combining inverter droop control, described step 202 The concrete selection adaptive moving average filter of exponent number.

A kind of frequency observation method being applicable to combining inverter droop control, step 3 is specifically wrapped Include following sub-step:

Step 301: based on phase angle and the linear relationship of time, ask for phase angle by method of least square and seasonal effect in time series is the most oblique Rate, i.e. frequency, a calculation window of selected appropriate length, length M=2N+1, substitute this window with the average frequency in window The frequency of central instant, angleWith the relational representation of sampling instant t it is:WhereinFor initial phase angle, ω is institute Seeking angular frequency, obtain ω according to method of least square, solving equation is:

Step 302: time series is carried out translation transformation, shift factor is central instant value t in window_N+1, thus obtain one Individual symmetry, sequence and be 0 time series t '_i=t_i-t_N+1, the expression formula after then being converted is:

$\underset{i=1}{\overset{M=2N+1}{\Σ}}{t}_i^{\′}=T_S\×\underset{i=1}{\overset{M=2N+1}{\Σ}}(i-N-1)=0---\left(12\right)$

Step 303: according to the computing formula of method of least square, the coefficient in step 302 is solved, due to translation after time Between sequence and be 0, therefore greatly simplifie cymometer formula, accounting equation is:

Therefore the solution formula of frequency is:

A kind of frequency observation method being applicable to combining inverter droop control, step 4 is specifically wrapped Include following sub-step:

Step 401: utilize the electrical network positive-sequence component that step 203 is tried to achieve, is calculated an angle value, table according to antitrigonometric function Reaching formula is:

$\mathrm{\θ}=arctan(u_{\mathrm{\β}1}^{+}/u_{\mathrm{\α}1}^{+})---\left(15\right)$

Step 402: utilize the method for least square described in step 301～303 that the low frequency component under d-q coordinate system is carried out frequency sight Surveying, observation station obtains frequency and is multiplied by a coefficient, it is possible to the phase angle being compensated；

Step 403: two values of gained in step 401 and step 402 are added, i.e. can get the real time phasor of electrical network.