阅读说明：本技术 一种基于复合型滤波器的电网同步软件锁相环 (Power grid synchronization software phase-locked loop based on composite filter ) 是由 回楠木 韩晓微 吴宝举 于 2021-05-27 设计创作，主要内容包括：本发明提供一种基于复合型滤波器的电网同步软件锁相环,属于电网电压相位信号检测提取相关技术领域。本发明针对电网电压中基波负序电压、谐波电压和直流偏移电压导致软件锁相环相位估计产生振荡误差,从而锁相精度的问题,提出了一种可消除直流偏移电压的多阶广义积分器,并对将其改进成为可应用于三相并网应用的双多阶广义积分器。将该双多阶广义积分器和滑动平均滤波器组成复合型滤波器并应用在软件锁相环中,利用其可完整消除电网中各次谐波电压和直流偏移电压的优势,从而使本发明具有抗干扰性能好、快速准确锁相等优点。本发明主要用于电网电压发生畸变及直流偏移电压干扰时电网电压同步过程中。(The invention provides a power grid synchronization software phase-locked loop based on a composite filter, and belongs to the technical field of power grid voltage phase signal detection and extraction. The invention provides a multi-order generalized integrator capable of eliminating direct current offset voltage aiming at the problem of phase locking precision caused by oscillation error generated by phase estimation of a software phase-locked loop due to fundamental wave negative sequence voltage, harmonic voltage and direct current offset voltage in power grid voltage, and improves the multi-order generalized integrator into a double multi-order generalized integrator capable of being applied to three-phase grid connection application. The double multi-order generalized integrator and the moving average filter form a composite filter and are applied to a software phase-locked loop, and the advantages of completely eliminating each harmonic voltage and direct-current offset voltage in a power grid are utilized, so that the phase-locked loop has the advantages of good anti-interference performance, rapidness, accuracy and the like. The method is mainly used in the power grid voltage synchronization process when the power grid voltage is distorted and interfered by the direct current offset voltage.)

1. A power grid synchronization software phase-locked loop based on a composite filter is characterized in that: the power grid synchronization software phase-locked loop based on the composite filter comprises a Clark conversion unit of three-phase power grid voltage, the composite filter and a proportional controller k_p1/s of integration link;

three-phase network voltage v_abcThe input end of the coordinate transformation unit is connected, the output end of the Clark transformation unit is connected with the input end of the composite filter, the output end of the composite filter is connected with the input end of the arc tangent operation unit, and the output end of the arc tangent operation unit is connected with the proportional divider controller k_pInput terminal of, proportional controller k_pOutput signal and natural frequency omega_ffAfter adding, the sum is input to the input end of the integration element 1/s, and the output end of the integration element 1/s outputs the phase estimation valueThe output end of the integration element 1/s is connected with the input end of the coordinate transformation unit, and the output end of the integration element 1/s and the output end of the arc tangent operation unit are added to output a phase-locked result

2. A complex filter based grid synchronization software phase locked loop according to claim 1, characterized in that:

the composite filter consists of a double high-order generalized integrator (DMOGI) with a direct current offset elimination function, a park converter and a Moving Average Filter (MAF), wherein the DMOGI is responsible for filtering fundamental negative sequence voltage and direct current offset voltage in power grid voltage in an outer ring (namely an alpha beta coordinate system) of a software phase-locked loop, and the MAF is responsible for filtering each harmonic voltage in the power grid voltage in an inner ring (namely a dq coordinate system) of the software phase-locked loop.

3. A complex filter based grid synchronization software phase locked loop according to claim 2, characterized in that:

the double multi-order generalized integrator (DMOGI) is composed of two multi-order generalized integrators (MOGI) through a parallel interleaving structure, and the transfer function formula of the DMOGI under an alpha beta coordinate system is

In the formula (I), the compound is shown in the specification,for the resonance frequency, s denotes the s domain, and the ξ value usually takes 0.7;

the double multi-order generalized integrator can separate out complete three-phase grid voltage fundamental wave positive sequence voltage under an alpha beta coordinate system, and simultaneously filters out fundamental wave negative sequence voltage and direct current offset voltage.

4. A complex filter based grid synchronization software phase locked loop according to claim 3, characterized in that:

the structure of the multi-order generalized integrator (MOGI) consists of three integrators, three summers, three multipliers and two constant ratio proportional controllers, the structure has the capability of eliminating direct current offset voltage, and the transfer function formula is

And

where u is the input to the multiple-order generalized integrator and v_aAnd v_bTwo outputs of the multi-order generalized integrator are provided.

5. A complex filter based grid synchronization software phase locked loop according to claim 3, characterized in that:

the double multi-order generalized integrator (DMOGI) with the direct current offset elimination function can be obtained by converting an s-domain transfer function of the double multi-order generalized integrator (dqDMOGI) under an alpha beta coordinate system into an equivalent under a dq coordinate system under the dq coordinate system

6. A complex filter based grid synchronization software phase locked loop according to claim 1, characterized in that:

the s-domain transfer function of the complex filter is,

the composite filter can filter fundamental wave negative sequence voltage, direct current offset voltage and each major order harmonic voltage under the working condition that a three-phase power grid contains harmonic voltage and direct current offset voltage, and completely extracts fundamental wave positive sequence voltage of the three-phase power grid voltage, so that the function of accurately and quickly completing three-phase power grid synchronous phase locking is achieved.

Technical Field

The invention belongs to the technical field of related detection and extraction of power grid voltage phase signals, and particularly relates to a power grid synchronization software phase-locked loop based on a composite filter.

Background

Grid-connected power converters need to detect the voltage phase angle and frequency at the Point of Common Coupling (PCC) quickly and accurately to achieve synchronous control. Among the various synchronization methods, the phase-locked loop (PLL) is the most widely used technique, and the most applied software phase-locking technique in the three-phase grid system is the synchronous reference frame phase-locked loop (SRF-PLL). When the three-phase voltage is in a balanced and clean state, the SRF-PLL works well under both steady and dynamic operating conditions due to its high bandwidth. However, the power grid is often disturbed by various faults such as power grid imbalance, distortion, voltage sag, noise, frequency deviation, etc., resulting in a reduced power quality. Conventional SRF-PLLs do not fully address these problems and can thus generate integer multiples of the fundamental frequency oscillation disturbances that cause inaccurate phase lock information and thus phase detection errors.

To overcome this drawback, many filtering techniques will be applied in SRF-PLL. These filtering methods can be generally classified into an outer loop filter and an inner loop filter. An outer loop filter is typically introduced to extract the fundamental positive sequence voltage from the raw voltage signal prior to SRF-PLL. Phase-locked loops based on such filters include phase-locked loops based on multiple reference frame filters (MRF-PLL), biquad generalized integrator-based (DSOGI-PLL), space vector filter-based (SVF-PLL), complex coefficient filter-based phase-locked loops (CCF-PLL), and the like. These methods improve the performance of SRF-PLLs by adjusting the bandwidth of the software phase locked loop. However, when the grid voltage is severely polluted by the harmonic wave, the methods need a plurality of filtering units to obtain the fundamental positive sequence component, thereby resulting in increased algorithm complexity and calculation burden.

While the inner loop filter places the filter unit within the closed control loop of the SRF-PLL. When the grid voltage is unbalanced, the filter trap method (NF) is proposed to eliminate the second harmonic interference. However, this approach is not an effective solution to the problem of grid distortion, since NF requires cascading multiple NFs to suppress major sub-harmonic interference. In addition, a signal delay cancellation method (DSC) is a common inner loop filtering technique under power grid voltage imbalance and distortion, in order to filter different harmonic components in the power grid voltage, the DSC generally employs a method of cascading a plurality of DSC operators with different time delays to complete a specific filtering effect, however, the total phase delay introduced by the cascaded DSC structure is very large, so that the bandwidth of a phase-locked loop is seriously reduced, and the structural complexity is further increased along with the increase of the number of DSCs.

Disclosure of Invention

The invention aims to solve the technical defects and provides a power grid synchronization software phase-locked loop based on a composite filter.

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

the invention providesA power grid synchronization software phase-locked loop based on a composite filter is provided, and comprises a Clark conversion unit of three-phase power grid voltage, a composite filter, a proportional controller k_pAnd an integration link is 1/s.

Three-phase network voltage v_abcThe input end of the coordinate transformation unit is connected, the output end of the Clark transformation unit is connected with the input end of the composite filter, the output end of the composite filter is connected with the input end of the arc tangent operation unit, and the output end of the arc tangent operation unit is connected with the proportional divider controller k_pInput terminal of (1), proportional controller k_pOutput signal and natural frequency omega_ffAfter adding, the sum is input to the input end of the integration element 1/s, and the output end of the integration element 1/s outputs the phase estimation valueThe output end of the integration element 1/s is connected with the input end of the coordinate transformation unit, and the output end of the integration element 1/s and the output end of the arc tangent operation unit are added to output a phase locking result

The composite filter consists of a double high-order generalized integrator (DMOGI) with a direct current offset elimination function, a park converter and a Moving Average Filter (MAF), wherein the DMOGI is responsible for filtering fundamental negative sequence voltage and direct current offset voltage in grid voltage in an outer ring (namely an alpha beta coordinate system) of a software phase-locked loop, and the MAF is responsible for filtering each sub-harmonic voltage in the grid voltage in an inner ring (namely a dq coordinate system) of the software phase-locked loop.

The double multi-order generalized integrator (DMOGI) is formed by two multi-order generalized integrators (MOGI) through a parallel interleaving structure, and the transfer function formula of the double multi-order generalized integrator (DMOGI) under an alpha and beta coordinate system is as follows:

in the formula (I), the compound is shown in the specification,for the resonance frequency, s denotes the s domain, and the ξ value usually takes 0.7;

the double multi-order generalized integrator can separate out complete three-phase grid voltage fundamental wave positive sequence voltage under an alpha beta coordinate system, and simultaneously has the function of filtering fundamental wave negative sequence voltage and direct current offset voltage.

The structure of the multi-order generalized integrator (MOGI) is composed of three integrators, three summers, three multipliers and two constant ratio proportional controllers, the structure has the capability of eliminating direct current offset voltage, and the transfer function formula is as follows:

and

where u is the input to the multiple-order generalized integrator and v_aAnd v_bTwo outputs of the multi-stage generalized integrator.

The double multi-order generalized integrator (DMOGI) with the dc offset cancellation function can be equivalent to a dq coordinate system in an alpha beta coordinate system, and an s-domain transfer function of the double multi-order generalized integrator (dqDMOGI) in the dq coordinate system is as follows:

the s-domain transfer function of the composite filter is as follows:

the composite filter can filter fundamental wave negative sequence voltage, direct current offset voltage and each major order harmonic voltage under the working condition that a three-phase power grid contains harmonic voltage and direct current offset voltage, and completely extracts fundamental wave positive sequence voltage of the three-phase power grid voltage, so that the function of accurately and quickly completing three-phase power grid synchronous phase locking is achieved.

The invention has the beneficial effects that:

the power grid synchronization software phase-locked loop based on the composite filter improves the filtering capability of the phase-locked loop on harmonic waves and direct current offset voltage in power grid voltage, and simultaneously improves the phase-locked precision of the phase-locked loop under the condition of non-ideal power grid voltage working condition. Compared with other phase-locked loop filtering methods, the method has the advantages of faster dynamic time adjustment characteristic and better harmonic interference resistance.

Drawings

FIG. 1 is a block diagram of a multi-order generalized integrator (MOGI) according to the present invention;

FIG. 2 is a diagram of a transfer function Baud of a multi-stage generalized integrator (MOGI) according to the present invention;

FIG. 3 is a block diagram of a Dual Multiple Order Generalized Integrator (DMOGI) according to the present invention;

FIG. 4 is a block diagram of a complex filter provided by the present invention;

FIG. 5 is a diagram of a transfer function Baud for a dual multi-order generalized integrator (DMOGI) according to the present invention;

FIG. 6 is a diagram of a transfer function Baud for a Moving Average Filter (MAF) according to the present invention;

FIG. 7 is a diagram of the transfer function baud of the composite filter provided by the present invention;

fig. 8 is a structure diagram of a phase-locked loop of the grid synchronization software based on the composite filter provided by the invention;

FIG. 9 is a phase estimation diagram of a grid voltage with a 30 ° phase jump according to an embodiment of the present invention;

FIG. 10 is a diagram illustrating phase estimation when a +3Hz frequency jump occurs in the grid voltage in an embodiment of the present invention;

FIG. 11 is a diagram illustrating phase estimation when DC offset voltage mixing occurs in the grid voltage according to an embodiment of the present invention;

fig. 12 is a phase estimation diagram of the grid voltage with voltage distortion in the embodiment of the present invention.

Detailed Description

In order to make the technical problems solved, technical solutions adopted and technical effects achieved by the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some but not all of the matters related to the present invention are shown in the drawings.

The utility model provides a synchronous software phase-locked loop of electric wire netting based on composite filter to the problem that traditional software phase-locked loop filtering link interference killing feature is not enough and dynamic adjustment time is overlength under the condition that three-phase electric wire netting voltage contains harmonic and direct current skew.

The realization principle of the invention is as follows:

the power grid synchronization software phase-locked loop based on the composite filter comprises a Clark conversion unit of three-phase power grid voltage, the composite filter and a proportional controller k_pAnd an integration link is 1/s.

Three-phase network voltage v_abcThe input end of the coordinate transformation unit is connected, the output end of the Clark transformation unit is connected with the input end of the composite filter, the output end of the composite filter is connected with the input end of the arc tangent operation unit, and the output end of the arc tangent operation unit is connected with the proportional divider controller k_pInput terminal of (1), proportional controller k_pOutput signal and natural frequency omega_ffAfter adding, the sum is input to the input end of the integration element 1/s, and the output end of the integration element 1/s outputs the phase estimation valueThe output end of the integration element 1/s is connected with the input end of the coordinate transformation unit, and the output end of the integration element 1/s and the output end of the arc tangent operation unit are added to output a phase locking result

Conventional synchronous reference frame software phase locked loops (SRF-PLLs) suffer from dual frequency oscillations when operating under unbalanced load conditions. In addition, when the grid voltage is polluted by harmonic waves, a simple SRF-PLL is not enough to accurately track the phase of the fundamental voltage in the grid system, so that the loop filtering section needs to be improved. The method can achieve the purpose of correctly tracking the voltage phase of the power grid when the voltage of the power grid is unbalanced and various subharmonics and direct-current offset voltages are mixed by introducing a double multi-order generalized integrator into an SRF-PLL control outer ring (namely under an alpha beta coordinate system) and introducing a moving average filter into an SRF-PLL control inner ring (namely under a dq coordinate system) to form a compound filter consisting of the double multi-order generalized integrator and the moving average filter, and specifically comprises the following implementation steps:

1) multi-order generalized integrator implementation

In order to accurately obtain amplitude and frequency information of a fundamental positive sequence component of a power grid when the power grid is interfered, the influence of fundamental negative sequence voltage and direct current offset voltage on a phase-locked loop needs to be solved. Therefore, the invention provides a multi-order generalized apparatus (MOGI) signal processing module capable of simultaneously filtering out fundamental frequency negative sequence voltage component and direct current offset component, and the structure thereof is shown in FIG. 1;

the transfer function expression of the MOGI from fig. 1 is:

G_a(s) and G_bThe bode plot of(s) is shown in fig. 2, where k takes 1.414. As can be observed from FIG. 2, G_a(s) can be regarded as a band-pass filter, G_a(s) gain values at 0Hz<-50dB, thus G_a(s) the DC offset component at 0Hz can be eliminated. In addition G_b(s) can also be regarded as a high-pass filter, G_b(s) gain values at 0Hz<100dB, thus G_b(s) also the dc offset component at 0Hz can be eliminated. But because ofG as a high pass filter_b(s) insufficient harmonic suppression capability at high frequencies, resulting in insufficient filtering performance of the MOGI, and the addition of an additional high frequency filter to overcome this problem needs to be considered. In addition, near the fundamental frequency G_a(s) and G_bThe phase difference of(s) is 90 degrees, so that a 90-degree phase compensation link needs to be added;

furthermore, according to the formulae (1) and (2), G_a(s) and G_bThe molecules of(s) have two zeros and three zeros, respectively, which means G_a(s) and G_bThe transfer function of(s) can filter out the dc offset component at 0Hz, and also can explain the capability of MOGI to eliminate the dc offset interference.

2) Dual-improved cascaded second-order adaptive notch filter implementation

In the synchronous application of the three-phase-locked loop in grid connection, the fundamental negative sequence voltage of the grid voltage can affect the phase estimation of the phase-locked loop, so that the phase locking precision is deteriorated, and the fundamental negative sequence voltage needs to be filtered while the fundamental positive sequence voltage is accurately extracted. To achieve this, we use 2 MOGIs to make up DMOGI, which is shown in FIG. 3;

from FIG. 3, it can be obtained

Wherein v is_α，v_βRespectively an alpha-axis component and a beta-axis component of the input signal,andan alpha-axis component and a beta-axis component of the output signal containing the fundamental positive sequence voltage component, respectively. In order to extract the fundamental positive sequence component, a symmetric component method can be used in the α β coordinate system, which is implemented by the corresponding structure of the fundamental positive sequence calculator in fig. 3;

the method of the complex filter is one of the main methods for analyzing the lower filter in the alpha beta coordinate system of the three-phase-locked loop, and the method can also be adopted for analyzing the transfer function of the DMOGI filter. The complex filter is represented in FIG. 4, and the transfer function H(s) thereof can be expressed in the following form according to FIG. 4

H(s)＝H^Re(s)+jH^Im(s) (4)

Wherein H^Re(s) and H^Im(s) are the real and imaginary parts of H(s), respectively;

then, in conjunction with fig. 3 and 4, the real and imaginary mathematical expressions of the transfer function of DMOGI can be obtained as

According to the formula (4), the mathematical expression of the transfer function of the DHOGI filtering link in the α β coordinate system is obtained as follows:

from the observation of equation (7), it can be seen that the transfer function of DMOGI(s) has a zero point on the moleculeThe simultaneous existence of another zero point on s-0 indicates that dmogi(s) can be effectively suppressed in the α β coordinate systemThe fundamental negative sequence component and the 0Hz direct current offset component of the corresponding grid voltage are obtained;

according to equation (7), a bode plot of dmogi(s) is plotted as shown in fig. 5. As can be seen from fig. 5, in the α β coordinate system, the amplification value of dmogi(s) at-50 Hz is ∞, and the amplification value at 0Hz is ∞, which indicates that both the fundamental negative sequence component and the dc offset component in the grid voltage can be suppressed by dmogi(s). At 50Hz dmogi(s) amplification is 0 and the corresponding phase is-90 °, which means that dmogi(s) needs to be phase compensated by 90 ° to correct the phase estimation, and thus achieve the task of extracting the fundamental positive sequence component completely.

3) MAF filter implementation

The time-domain form of the in-loop Moving Average Filter (MAF) in dq coordinate system is:

where x (τ) is the signal to be filtered, T_wIn order to have a long time window,is a filtered signal. The frequency domain transfer function corresponding to equation (8) is

T_wThe bode plot of MAF(s) is plotted with the setting of 0.0033s as shown in FIG. 6. from FIG. 6, it can be seen that the MAF can filter out the harmonics of frequencies other than-100 Hz and-50 Hz, i.e., + -300 Hz, + -600 Hz, + -900 Hz, etc., in the dq coordinate system.

4) Power grid synchronization software phase-locked loop implementation based on composite filter

Because the influence of harmonic interference of three-phase power grid input cannot be eliminated by single DMOGI, the phase angle error of software phase-locked loop output is easily caused. In order to solve the problem, DMOGI and MAF are combined into a novel mixed coordinate system composite filter, and the filter is applied to the inside of the structure of an SRF-PLL to form a novel three-phase grid-connected software phase-locked loop, and the structure of the phase-locked loop is shown in FIG. 7;

as shown in fig. 7, DMOGI proposed by the present invention is responsible for eliminating the fundamental negative sequence voltage component and the dc offset component in the outer loop of the pll, and MAF is responsible for eliminating the harmonic components such as-5 th, +7th, -11th, +13th … in the inner loop of the pll;

when the DMOGI needs to be converted into a phase-locked loop inner loop application, the DMOGI needs to be converted into a dq coordinate system to realize the dqDMOGI, and the transfer function of the dqDMOGI can pass throughObtained in place of s in DMOGI(s), i.e.

The transfer function of the complex filter consisting of DMOGI and MAF in dq coordinate system is expressed as

Fig. 8 is a bode diagram of the composite filter according to formula (11). It can be found that the composite filter h(s) can completely filter fundamental negative sequence components, direct current offset components and main harmonic voltages of-5 th, +7th, -11th, +13th and the like in the three-phase voltage of the power grid. Meanwhile, 90-degree phase compensation is required to be added at the rear end of the phase-locked loop, so that fundamental wave positive sequence component information is accurately extracted;

and then, completing the structural design of the power grid synchronization software phase-locked loop based on the composite filter.

The following are specific embodiments:

in order to verify the performance of the software phase-locked loop provided by the invention, MATLAB/Simulink software is adopted to carry out simulation comparison experiments under four faults of phase mutation, frequency mutation, direct current sudden injection and voltage distortion. In simulation, the power grid frequency is 50Hz, the three-phase voltage amplitude is normalized to be 1p.u, and the sampling frequency is 10 kHz. Experimental comparison objects are a traditional trap-based phase-locked loop (NF-PLL) with dc offset cancellation and a moving average filter-based phase-locked loop (MAF-PLL), and the proportional controller k of the present invention_pTaking the value 43. Grid frequency in simulationThe frequency is 50Hz, the amplitude of the three-phase voltage is normalized to 1p.u, and the sampling frequency is 10 kHz.

The concrete implementation effect is as follows:

fig. 9 and fig. 10 are phase estimation diagrams when a phase jump of 30 ° occurs and a frequency jump of +3Hz occurs in the grid voltage in the embodiment of the present invention, respectively, and it can be seen from fig. 9 and fig. 10 that the phase-locked loop proposed by the present invention recovers the accurate estimation of the grid phase faster after the jump occurs, and the phase estimation error is reduced to zero. The phase estimation processes of the NF-PLL and the MAF-PLL are slower than that of the phase-locked loop provided by the invention, which shows that the method provided by the invention has faster dynamic response speed.

Fig. 11 is a phase estimation diagram when the dc offset voltage is mixed in the grid voltage in the embodiment of the present invention, and the time for mixing the dc offset voltage is 0.16s, and it can be seen from fig. 11 that after the dc offset is suddenly injected into the three-phase voltage, the phase estimation error and the frequency estimation value of the three phase-locked loops all fluctuate. The phase-locked loop provided by the invention recovers accurate tracking of phase in the shortest time by taking the frequency deviation less than 0.2Hz as a standard, and the other two PLLs have slower recovery speeds.

Fig. 12 is a phase estimation diagram of the grid voltage when voltage distortion occurs in the embodiment of the present invention, the injected fundamental negative sequence voltage is 0.1p.u, the injected-5, +7, -11, +13 subharmonic voltages are 0.1p.u.,0.05p.u., and the grid has a phase jump of +45 ° while the harmonics are injected. As can be seen from fig. 12, when the power grid is distorted, the frequency and phase estimation curves of the software phase-locked loop proposed by the present invention are smooth, i.e. are not affected by harmonics, which indicates that they have a function of filtering harmonics. The NF-PLL does not have a harmonic elimination function, and the waveform of the NF-PLL greatly oscillates, which may seriously affect the phase locking accuracy. Therefore, when the frequency of the power grid continuously changes, the phase locking precision of the software phase-locked loop provided by the invention is higher.

Through comparison of fig. 9 to fig. 12, it can be seen that the power grid synchronization software phase-locked loop based on the composite filter provided by the invention shows good characteristics in terms of dynamic convergence speed and filtering performance, can quickly and accurately realize the phase-locking function under the condition that the power grid voltage is distorted and mixed with the direct-current offset voltage, and is completely suitable for power grid synchronization application under various complex power grid working conditions.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the preferred embodiments, those skilled in the art should understand that: modifications and equivalents may be made to the disclosed embodiments without departing from the spirit and scope of the present invention.