阅读说明：本技术 一种光伏并网逆变器直流母线电压的鲁棒控制方法 (Robust control method for DC bus voltage of photovoltaic grid-connected inverter ) 是由 周雪松 刘乾 马幼捷 潘俊清 于 2021-09-07 设计创作，主要内容包括：本发明公开了一种基于改进型自抗扰的光伏并网逆变器直流母线电压控制方法,涉及光伏发电领域。本发明包括以下步骤：建立并网逆变器和直流母线上的功率平衡模型；基于并网逆变器和直流母线上的功率平衡模型,构建ESO和反馈控制律,其中ESO负责估计系统动态中的总扰动,反馈控制律对总扰动进行实时补偿。本发明对传统ESO的内部结构做出了变更以提升对扰动的估计能力,进而使整个控制器补偿扰动更为充分。(The invention discloses a photovoltaic grid-connected inverter direct-current bus voltage control method based on improved active disturbance rejection, and relates to the field of photovoltaic power generation. The invention comprises the following steps: establishing a power balance model on a grid-connected inverter and a direct current bus; and constructing an ESO (electronic stability and safety) and a feedback control law based on a power balance model on the grid-connected inverter and the direct-current bus, wherein the ESO is responsible for estimating the total disturbance in the system dynamic state, and the feedback control law carries out real-time compensation on the total disturbance. The invention changes the internal structure of the traditional ESO to improve the estimation capability of disturbance, thereby enabling the whole controller to compensate the disturbance more fully.)

1. A photovoltaic grid-connected inverter direct current bus voltage control method based on improved active disturbance rejection is characterized by comprising the following steps:

establishing a power balance model on a grid-connected inverter and a direct current bus;

and constructing an ESO (electronic stability and safety) and a feedback control law based on a power balance model on the grid-connected inverter and the direct-current bus, wherein the ESO is responsible for estimating the total disturbance in the system dynamic state, and the feedback control law carries out real-time compensation on the total disturbance.

2. The method according to claim 1, wherein the grid-connected inverter model comprises the following steps:

in the formula u_*，i_*And e_*Respectively representing inverter output phase voltage, grid-connected current and grid phase voltage.

3. The method according to claim 2, wherein the grid-connected inverter model is converted into dq coordinate system synchronously rotating at grid angular frequency, and the following model is obtained:

in the formula u_·、i_·And e_·The components of the inverter output phase voltage, the grid-connected current and the grid phase voltage on the dq axis are respectively; ω represents the grid voltage angular frequency.

4. The method according to claim 1, wherein the power balance model is as follows:

wherein u is_dcIs a DC bus voltage, C₂Is a DC bus capacitor i_sIs the input current of the DC bus, e_dIs the component of the inverter output phase voltage on the d-axis, i_dIs the component of the inverter output phase voltage on the d-axis.

5. The method according to claim 4, wherein the differential equation of the power balance model is as follows:

6. the method for controlling the voltage of the direct-current bus of the photovoltaic grid-connected inverter based on the improved active disturbance rejection of claim 5, wherein the current inner loop is simplified into an inertial link of a transfer function 1/(3Ts +1), and a differential equation of a controlled object model is simplified into:

7. the method for controlling the voltage of the direct-current bus of the photovoltaic grid-connected inverter based on the improved active disturbance rejection of claim 6, wherein the specific steps for constructing the ESO are as follows:

will be provided withDescribed in standard fashion:

wherein, b₀To control the gain, f is the total interference, which includes the internal interference of the systemAnd external disturbance i_s(ii) a Will be provided withDefined as the first state variable x₁And f is defined as the expanded state x₂Then, thenThe state space expression of (a) is:

corresponding reduced-order ESO:

in the formula I₁，l₂Represents the observed gain of the ESO; z is a radical of₁，z₂Respectively estimating the direct current bus voltage and the total disturbance; e.g. of the type₁Tracking error of the DC bus voltage;

from equationObtaining:

due to the fact thatRewritten as: :

will be provided withESO was constructed as a regulatory basis:

8. the method according to claim 1, wherein the feedback control law is as follows:

wherein k is_pAnd k_dRespectively control parameters of the PD controller; r and y respectively represent a reference value and an output value of the direct current bus voltage; b₀To control the gain.

Technical Field

The invention relates to the field of photovoltaic power generation, in particular to a robust control method for direct-current bus voltage of a photovoltaic grid-connected inverter.

Background

For a two-stage photovoltaic grid-connected power generation system widely applied in industry, in addition to realizing maximum power tracking and current protection, the voltage on a direct current side capacitor connected with a front stage and a rear stage must be controlled within a reasonable range. Too high a voltage triggers the action of the protection device, and too low a voltage causes power to flow from the grid side to the dc side. Therefore, effective control of the dc bus voltage has been a research focus.

Generally, the dc bus voltage is regulated by an inverter control system, which typically employs a dual closed loop control architecture of a voltage outer loop and a current inner loop. The voltage outer ring has the task of keeping the voltage of the direct current bus constant, and the current inner ring is responsible for power factor correction and harmonic compensation on the alternating current side. The presence of various disturbances in the system (e.g., grid voltage fluctuations and environmental uncertainties) makes it difficult for conventional PI control to achieve the desired control effect. In addition, PI control may cause the system to oscillate or overshoot severely due to excessive initial control forces. Therefore, the invention discloses a strong robust outer loop control scheme to enhance the immunity of the DC bus voltage.

In recent years, an emerging control technology, Active Disturbance Rejection Control (ADRC), has prevailed in the field of engineering application, and is widely used as an optimized version of a conventional PI controller. ADRC does not need an accurate model of a controlled object, and has the characteristics of high control precision, strong anti-interference capability and the like. The core idea of the method is that an integral series connection type is used as a standard type of a controlled object, all parts in system dynamics different from the standard type are classified as generalized disturbance, an Extended State Observer (ESO) is constructed to estimate the disturbance, and finally the disturbance is compensated through a feedback control law. Therefore, the ADRC has strong immunity and is widely applied to control of various motor speed regulation systems, photovoltaic systems, wind power systems and the like.

Disclosure of Invention

For the control system generated by ADRC, the overall performance depends mainly on the accuracy of the estimate of the generalized disturbance by the ESO. Therefore, the internal structure of the traditional ESO is changed to improve the estimation capability of the disturbance, so that the disturbance is more fully compensated by the whole controller.

In view of the above, the present invention provides a method for controlling a dc bus voltage of a photovoltaic grid-connected inverter based on improved active disturbance rejection.

In order to achieve the purpose, the invention adopts the following technical scheme:

a photovoltaic grid-connected inverter direct current bus voltage control method based on improved active disturbance rejection is characterized by comprising the following steps:

establishing a power balance model on a grid-connected inverter and a direct current bus;

and constructing an ESO (electronic stability and safety) and a feedback control law based on a power balance model on the grid-connected inverter and the direct-current bus, wherein the ESO is responsible for estimating the total disturbance in the system dynamic state, and the feedback control law carries out real-time compensation on the total disturbance.

Preferably, the grid-connected inverter model is as follows:

in the formula u_*，i_*And e_*Respectively representing inverter output phase voltage, grid-connected current and grid phase voltage.

Preferably, the grid-connected inverter model is converted into a dq coordinate system synchronously rotating at the grid angular frequency, so as to obtain the following model:

in the formula u_·、i_·And e_·The components of the inverter output phase voltage, the grid-connected current and the grid phase voltage on the dq axis are respectively; ω represents the grid voltage angular frequency.

Preferably, the power balance model is as follows:

wherein u is_dcIs a DC bus voltage, C₂Is a DC bus capacitor i_sIs the input current of the DC bus, e_dIs contrary toComponent of the converter output phase voltage on the d-axis, i_dIs the component of the inverter output phase voltage on the d-axis.

Preferably, the differential equation of the power balance model is as follows:

preferably, the current inner loop is simplified into an inertia link of a transfer function 1/(3Ts +1), and the differential equation of the controlled object model is simplified as follows:

preferably, the specific steps for constructing the ESO are as follows:

will be provided withDescribed in standard fashion:

wherein, b₀To control the gain, f is the total interference, which includes the internal interference of the systemAnd external disturbance i_s(ii) a Will be provided withDefined as the first state variable x₁And f is defined as the expanded state x₂Then, thenThe state space expression of (a) is:

corresponding reduced-order ESO:

in the formula I₁，l₂Represents the observed gain of the ESO; z is a radical of₁，z₂Respectively estimating the direct current bus voltage and the total disturbance; e.g. of the type₁Tracking error of the DC bus voltage;

from equationObtaining:

due to the fact thatRewritten as: :

will be provided withESO was constructed as a regulatory basis:

preferably, the feedback control law is as follows:

wherein k is_pAnd k_dRespectively control parameters of the PD controller; with r and y representing dc bus voltage, respectivelyA reference value and an output value; b₀To control the gain.

Compared with the prior art, the invention discloses and provides the photovoltaic grid-connected inverter direct-current bus voltage control method based on the improved active disturbance rejection, and the method has the following beneficial effects:

the first aspect of the present invention: disturbance estimation capability comparison before and after ESO improvement

By applying the Laplace transform, the disturbance estimation transfer functions before and after the ESO improvement can be solved, which are respectivelyAnd ω_o/(s+ω_o). Bode plots at the same bandwidth are plotted for both transfer functions as shown in fig. 5 a-5 b. It can be seen that the improved ESO has a considerable gain in amplitude in the mid-to-high frequency range and improves to some extent the phase lag disadvantage. It is noted that although the estimation of certain types of high frequency disturbances is enhanced, the noise sensitivity is also increased. In practical applications, a filter may be collocated before the ESO to solve the noise problem.

The 2 nd aspect: to verify the theoretical analysis of the above technique, the estimated curves of conventional and improved ESOs with respect to generalized disturbances were analyzed during system startup, as shown in fig. 6 a-6 b. In the framework of the improved ESO, the estimated curve is more consistent with the actual curve, and the disturbance elimination time is significantly shortened. The increase in ESO performance provides the controller with faster and more adequate disturbance information, thereby speeding up the disturbance compensation process.

Aspect 3: compared with the simulation control effect of the traditional ADRC and the improved ADRC, a simulation model of the photovoltaic grid-connected system is established by using SIMULINK, the voltage waveforms of the direct current bus of the two control methods are analyzed and compared under various working conditions, and the selected bandwidth parameters are consistent.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

Fig. 1 is a topology structure diagram of a two-stage photovoltaic grid-connected system according to the present invention;

FIG. 2 is a diagram of a conventional dual closed loop control architecture for an inverter according to the present invention;

FIG. 3 is a simplified control block diagram of the voltage outer loop of the present invention;

FIG. 4 is a schematic diagram of the structure of ADRC of the present invention;

FIGS. 5 a-5 b are Bode plots of two observers of the present invention with respect to disturbance estimation;

fig. 6 a-6 b are dynamic curves of two observers estimating generalized disturbances according to the invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The embodiment of the invention discloses a photovoltaic grid-connected inverter direct-current bus voltage control method based on improved active disturbance rejection, which comprises the following steps:

step 1: establishing a power balance model on the grid side inverter and the direct current bus:

fig. 1 depicts a topology structure of a two-stage photovoltaic grid-connected system, in which a front stage controls a photovoltaic array through an MPPT algorithm, and a rear stage maintains a stable dc bus voltage and converts dc power into ac power to implement grid connection.

Modeling a grid-connected inverter in a three-phase static coordinate system:

in the formula u_*，i_*And e_*Respectively representing inverter output phase voltage, grid-connected current and grid phase voltage. Since each variable is an alternating current quantity which is difficult to control, the formula (1) is converted into a dq coordinate system synchronously rotating at the angular frequency of the power grid through Park conversion, and the design of a control system is simplified:

wherein u, i and e are components of the inverter output phase voltage, the grid-connected current and the grid phase voltage on the dq axis respectively; ω represents the grid voltage angular frequency.

To achieve separate control of the grid-side active and reactive power, the d-axis direction is usually aligned with the grid voltage vector, with e_q0. Thus, the active power injected into the grid by the inverter can be expressed according to the instantaneous power theory as:

if the loss of the alternating current side filter and the loss of the switching device are not considered, the power of the direct current side terminal of the inverter is equal to the power of the power grid side, and then a power balance model on the power grid side inverter and the direct current bus is established:

wherein u is_dcIs a DC bus voltage, C₂Is a DC bus capacitor i_sIs the dc bus input current. From equation (4), it can be seen that the dynamics of the dc bus voltage is related to the power balance across the capacitor.

Equation (4) is reduced to a standard differential equation:

it can be seen that the dc bus voltage u of the inverter_dcCan be adjusted by controlling the d-axis component i of the grid-connected current_dTo be implemented. Therefore, in the inverter dual closed-loop control structure shown in fig. 2, the control output signal of the outer loop can be used as the reference value of the inner loop currentIn addition, a great deal of research shows that the current inner loop can be simplified into an inertia loop with a transfer function of 1/(3Ts + 1). Thus, a control block diagram of the voltage outer loop can be plotted, as shown in FIG. 3, where i_sAs an external disturbance, the controlled object model can be simplified as follows:

step 2: design of improved active disturbance rejection control strategy

As shown in fig. 4, ADRC is composed of ESO and feedback control law. The ESO is responsible for estimating the total disturbance in the system dynamics, which the feedback control law compensates for in real time. In the figure, r is a DC bus voltage reference valueu is d-axis current reference valuey is the system output u_dc。

The first step before the construction of the ESO is to describe the model (6) in a standard paradigm:

wherein, b₀To control the gain, f is the total interference, which includes the internal interference of the systemAnd external disturbance i_s. For second order objects, a third order ESO is typically designed to estimate the total disturbance. However, when the dc bus voltage can be measured, reduced-order ESO can be employed to ease the estimation burden. Therefore, willDefined as the first state variable x₁And f is defined as the expanded state x₂And then the state space expression of the controlled object (7) is as follows:

designing corresponding reduced-order ESO:

in the formula I₁，l₂Represents the observed gain of the ESO; z is a radical of₁，z₂Respectively estimating the direct current bus voltage and the total disturbance; e.g. of the type₁The tracking error of the DC bus voltage. From the formula (9), z is shown₁And z₂All are tracked by the deviation e₁To negative feedback control. If this mechanism is mapped to the principle of deviation regulation in classical control, it is found that the dynamic estimation of the total disturbance is regulated by the deviation of other state variables. Under this premise, when z is₁After the good tracking is realized, the reason e₁At this moment, very small, the observer will be aligned with z₂The regulation of (c) appears to be debilitating. For this reason, the process of ESO estimating the total disturbance, as analyzed from the principle of deviation control, is more worth the z-pass₂And x₂Error between to make feedback adjustments.

As can be seen from equation (9):

due to the fact thatEquation (10) can be rewritten as: :

will be provided withAs a basis for regulation, improved ESO was constructed:

by pole allocation method, observer gain l is selected₁＝ω_o，l₂＝ω_oThe roots of the characteristic equations are all located in the left half plane. Where ω is_oAlso called observer bandwidth, by choosing the appropriate bandwidth the observer can track the defined state variables in real time.

The following control laws were designed to compensate for the generalized disturbances:

wherein k is_pAnd k_dRespectively control parameters of the PD controller; r and y respectively represent a reference value and an output value of the direct current bus voltage; b₀To control the gain.

In the formulak_d＝2ω_cIs a parameter of the feedback controller. Where ω is_cAnd may also be the controller bandwidth. If equation (13) is substituted into equation (7), the closed loop transfer function of the system is obtained:

the expression is a second-order standard transfer function with a damping ratio of 1, which illustrates that ADRC can achieve fast overshoot-free tracking of a given value.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.