Distributed power grid-connected converter control method based on improved adaptive observer

Abstract

The application discloses a kind of based on the control method of improved adaptive observer's distributed power grid-connected converter, input the AC power grid voltage signal collected in improved adaptive observer, the phase of power grid voltage is tracked, the phase angle of output power grid voltage is transferred to the converter control structure as feedback, for the coordinate transformation of converter control system, then obtain dq axis voltage signal, by the double-loop control system of current inner loop and voltage outer loop of converter control system, the accurate control of distributed power grid-connected converter output voltage is realized.Effectively improve the control performance of grid-connected converter, quickly and accurately track grid point voltage frequency.

Description

Technical Field

[0001] This invention belongs to the field of converter control technology, specifically relating to a distributed power grid-connected converter control method based on an improved adaptive observer. Background Technology

[0002] In recent years, with the large-scale integration of distributed generation sources into the power grid, the application of power electronic converters in the power grid has increased significantly. Distributed generation sources are connected to the grid using voltage source converters, and by controlling the output voltage quality of the converter, friendly interaction between the distributed generation source and the upstream grid can be achieved. Therefore, ensuring the output voltage quality of the voltage source converter through effective control methods is crucial, and achieving precise and stable converter control requires accurate tracking of the voltage and frequency at the grid connection point. In AC power grids, a common phase information tracking method is the phase-locked loop (SRF-PLL) control strategy based on a synchronous rotating coordinate system, which is now widely used in practical engineering.

[0003] During normal grid operation, the SRF-PLL phase-locked loop can quickly, accurately, and stably track the phase and frequency of the grid voltage. By properly adjusting the control parameters of the SRF-PLL, good dynamic and steady-state performance can be achieved. However, when a grid fault occurs, the SRF-PLL cannot achieve fast and accurate grid voltage phase tracking.

[0004] Please see Figure 1 The main drawback of traditional SRF-PLL-based converter grid-connected control structures is their inability to accurately lock onto the phase-locked loop (PLL) under fault conditions such as grid voltage fluctuations. This is because, to improve the dynamic response speed of the PLL, its bandwidth is increased through parameter tuning. However, excessively high bandwidth leads to decreased PLL stability. Conversely, reducing the PLL bandwidth fails to meet grid voltage tracking requirements. Balancing these two factors significantly complicates PLL parameter tuning. Furthermore, the performance of the SRF-PLL directly impacts the grid-connected control effect of the converter. When the grid voltage phase tracked by the SRF-PLL has a large steady-state error, all voltage and current dq-axis components in the converter control system will exhibit significant errors, degrading the converter's control performance and potentially causing instability in the entire grid-connected system. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a distributed power grid-connected converter control method based on an improved adaptive observer, which addresses the shortcomings of the prior art and solves the technical problems of slow dynamic response and large steady-state error of traditional phase-locked loops under grid faults.

[0006] The present invention adopts the following technical solution:

[0007] The distributed power grid-connected converter control method based on an improved adaptive observer is characterized by inputting the collected AC grid voltage signal into an improved adaptive observer to track the grid voltage phase. The output grid voltage phase angle is then fed back to the converter control structure for coordinate transformation of the converter control system, thereby obtaining the dq-axis voltage signal. Through a dual-loop control system of the converter control system consisting of an inner current loop and an outer voltage loop, precise control of the output voltage of the distributed power grid converter is achieved.

[0008] Specifically, the collected AC grid voltage signal is input into an improved adaptive observer to obtain the unknown variable x. s and θ s The estimated value and Based on the estimated value Calculate the positive and negative sequence components of the three-phase power grid voltage, based on the estimated values. Calculate the power grid voltage frequency The improved adaptive observer control loop is as follows:

[0009]

[0010] Where A, L, and C are the 2m+1 order coefficient matrices of the collected three-phase AC power grid voltage system; y s Let x represent the input of the system, α and β represent the α and β coordinate system of the grid voltage system, and x represent the input of the system. s This represents the variables related to the collected three-phase power grid voltage. Represents the unknown parameter x s The estimate, ζ s The state variables represent the filter; λ represents the adaptive update rate of the system, and λ is the adaptive gain of the system.

[0011] Furthermore, based on the estimated value The positive and negative sequence components of the three-phase power grid voltage are calculated as follows:

[0012]

[0013] Where i = 1, 2, ..., m, and These are the positive and negative sequence harmonic components of the grid voltage in the αβ coordinate system, where the subscript p represents the positive sequence component, the subscript n represents the negative sequence component, and the subscript i represents the harmonic order.

[0014] Furthermore, based on the estimated value Calculate the power grid voltage frequency as follows:

[0015]

[0016] Where, ω r It is the nominal value of the grid voltage and frequency.

[0017] Specifically, the grid voltage phase angle δ is:

[0018]

[0019] in, These are the components of the fundamental frequency of the grid voltage in the αβ coordinate system.

[0020] Specifically, the grid voltage phase angle δ is fed back to the coordinate transformation stage in the converter control system, transforming the grid voltage signal u... α u β Transform into u d u q The specific conversion is as follows:

[0021]

[0022] Specifically, the state equation expression for the outer voltage loop is as follows:

[0023]

[0024]

[0025] Where x1 and x2 are intermediate variables in the state equation; v dc , These are the acquired DC bus voltage of the converter and its setpoint, respectively; Q, Q * These represent the measured reactive power output of the converter; These are the setpoint values ​​for the converter output current; k pvdc k ivdc k pv k iv These are the PI control parameters for the outer voltage loop.

[0026] Specifically, the state equation expression for the inner current loop is:

[0027]

[0028]

[0029] Where x3 and x4 are intermediate variables in the state equation; These are the setpoint values ​​for the converter output current, u and u, respectively. d u q i d i q These represent the voltage value at the grid connection point after coordinate transformation and the current value flowing into the grid connection point, respectively; vd v q These are the voltage modulation signals output by the inner current loop controller; k pi k ii These are the PI controller parameters for the inner current loop, ω c The voltage frequency input to the controller by the adaptive observer.

[0030] Specifically, the circuit equations for the DC bus link of the distributed generation grid-connected converter are as follows:

[0031]

[0032] Among them, C dc It is the DC-side capacitor, v dc DC side voltage, P in The active power flowing into the grid-side converter, u d u q These are the dq-axis voltages at the grid connection point, i d i q These are the dq-axis currents flowing into the grid connection point, respectively.

[0033] Specifically, the grid equivalent circuit of the distributed generation grid-connected converter is as follows:

[0034]

[0035] Among them, i gd i gq These are the d-axis and q-axis currents flowing out of the grid connection point of the converter, respectively; R g The equivalent resistance of the power grid; L g It is the equivalent inductance of the power grid; E d E q These are the dq-axis voltages of the AC power grid; ω s Indicates the nominal frequency of the power grid voltage; u d u q These are the voltage values ​​at the grid connection point after coordinate transformation.

[0036] Compared with the prior art, the present invention has at least the following beneficial effects:

[0037] This invention presents a distributed power grid-connected converter control method based on an improved adaptive observer, which enables grid-friendly grid connection of the converter even in the presence of disturbances. Because the improved adaptive observer possesses good robustness and can accurately estimate grid voltage parameters even when disturbances exist in the grid voltage, the control method using the improved adaptive observer enables the grid-connected converter to achieve grid-friendly connection.

[0038] Furthermore, the improved adaptive observer control loop has good anti-interference capability and can accurately estimate various parameters of the grid voltage under interference.

[0039] Furthermore, using estimated values Calculating the positive and negative sequence components of the three-phase grid voltage can transform the grid voltage parameters into variables to be estimated.

[0040] Furthermore, using estimated values Calculate the power grid voltage frequency It can convert estimated values ​​into per-unit values.

[0041] Furthermore, the estimated grid voltage phase angle δ can be used for coordinate transformation of the controller to realize the phase-locked loop function of a traditional phase-locked loop.

[0042] Furthermore, the grid voltage signal u α u β Transform into u d u q Transforming the grid voltage onto a rotating coordinate system converts the AC quantity into a DC quantity, making it easier to estimate its parameters using an improved adaptive observer.

[0043] Furthermore, the setting of the voltage outer loop can achieve a constant DC bus voltage and a constant power factor, ensuring that the system DC bus voltage is stable and the converter output power is unity power factor.

[0044] Furthermore, the setting of the inner current loop can achieve stable current control.

[0045] Furthermore, the circuit equations for the DC bus link of the distributed power grid-connected converter provide circuit relationship expressions for the DC bus link, which can be used to control the DC bus voltage stability.

[0046] Furthermore, the grid equivalent circuit of the distributed power grid-connected converter provides the equivalent circuit expression of the AC grid, which is an important link in the connection between the converter system and the AC grid.

[0047] In summary, this invention proposes a distributed power grid-connected converter control method based on an improved adaptive observer, which can effectively control the grid-connected converter to achieve grid-friendly connection even under interference conditions. The improved adaptive observer has good anti-interference management capabilities and can accurately estimate grid voltage parameters even when interference exists in the grid voltage. Therefore, the control method using the improved adaptive observer enables the grid-connected converter to achieve grid-friendly connection.

[0048] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0049] Figure 1 This is a control structure diagram of a traditional phase-locked loop;

[0050] Figure 2 Diagram of the improved adaptive observer architecture;

[0051] Figure 3 This is a structural diagram of a distributed power converter grid-connected system.

[0052] Figure 4 This is a structural diagram of a converter grid-connected control system based on an improved adaptive observer.

[0053] Figure 5 The figures show the simulation results of frequency tracking for the two methods. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "one side," "one end," and "one side," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0056] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0057] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0058] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0059] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0060] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0061] Because adaptive observers can achieve accurate and rapid tracking of grid voltage, they maintain good dynamic and steady-state performance even in the event of grid faults. Therefore, applying them to the grid-connected control structure of distributed generation converters can effectively improve the converter's accurate and efficient control of grid voltage.

[0062] This invention provides a distributed power source grid-connected converter control method based on an improved adaptive observer. Based on the adaptive observer principle, a grid-connected control strategy is designed to effectively improve the dynamic and steady-state performance of the converter control system. Furthermore, an improved adaptive observer grid-connected control system based on distributed power sources is designed. Theoretically, this control system can be applied under various grid fault conditions, and its dynamic performance is significantly improved compared to the traditional phase-locked loop (PLL)-based control structure. Based on the adaptive observer principle, the distributed power source-based grid-connected control structure is designed, and a Simulink simulation model is built to verify the overall converter control system through simulation. Simulation results show that under fault conditions, the improved adaptive observer-based control system designed in this invention can effectively improve the control performance of the grid-connected converter. It can quickly and accurately track the grid connection point voltage frequency, demonstrating significant application advantages and practical value compared to the traditional PLL-based grid-connected control system.

[0063] This invention discloses a distributed power grid-connected converter control method based on an improved adaptive observer. The method involves inputting the acquired AC grid voltage into an improved adaptive observer algorithm to accurately track the grid voltage phase. The output grid voltage phase is then fed back to the converter control structure for coordinate transformation, resulting in the dq-axis voltage signal. Through a dual-loop control system of the converter control system (current inner loop and voltage outer loop), precise control of the distributed power grid converter's output voltage is achieved.

[0064] Please see Figure 2 The grid-connected converter control structure is adopted, and the improved adaptive observer element is applied to the grid-connected control system of the distributed power source converter. This control structure has good dynamic and steady-state performance, and can achieve precise control of the distributed power source grid-connected converter under various grid voltage fault conditions.

[0065] By inputting the acquired grid voltage signal into the improved adaptive observer control loop, the expression is as follows:

[0066]

[0067] Where s = α, β, A, L, and C are the 2m+1 order coefficient matrices of the collected three-phase AC power grid voltage system; y s Let x represent the input of the system, α and β represent the α and β coordinate system of the grid voltage system, and x represent the input of the system. s This represents the variables related to the collected three-phase power grid voltage. Represents the unknown parameter x s The estimate, ζ s The state variables represent the filter; Let λ represent the adaptive update rate of the system, and λ be the adaptive gain of the system. This observer can be used to obtain the unknown variable x. s and θ s The estimated value.

[0068] Based on the estimated values ​​of the state variables obtained from the observer Calculate the positive and negative sequence components of the three-phase power grid voltage:

[0069]

[0070] Where i = 1, 2, ..., m, and These are the positive and negative sequence harmonic components of the grid voltage in the αβ coordinate system, where the subscript p represents the positive sequence component, the subscript n represents the negative sequence component, and the subscript i represents the harmonic order.

[0071] Based on the estimated value obtained by the observer Calculate the grid voltage frequency:

[0072]

[0073] Where s = α, β, It is an estimate of the grid voltage frequency ω, ω r It is the nominal value of the grid voltage and frequency.

[0074] Calculate the grid voltage phase angle based on the positive and negative sequence components of the fundamental voltage obtained above:

[0075]

[0076] in, These are the components of the fundamental frequency of the grid voltage in the αβ coordinate system.

[0077] Finally, the grid voltage phase angle output by the improved adaptive observer is fed back to the coordinate transformation stage in the converter control system, transforming the grid voltage signal u... α u β Transform into u d u q The rotation transformation expression used is:

[0078]

[0079] Please see Figure 3 The distributed power grid-connected converter control system includes the grid-side converter, filters, grid equivalent circuits, and AC grid. The controller components include coordinate transformation, an improved adaptive observer, an outer voltage loop, and an inner current loop. Figure 4As shown, by employing an improved adaptive observer method to obtain the voltage phase at the converter's grid connection point, fast and accurate control of the controller is achieved. The modulated voltage signal is then fed into the PWM converter to realize overall closed-loop control of the converter.

[0080] First, the circuit equations for the DC bus link of the grid-side converter are expressed as follows:

[0081]

[0082] Among them, C dc It is the DC-side capacitor, v dc DC side voltage, P in The active power flowing into the grid-side converter, u d u q These are the dq-axis voltages at the grid connection point, i d i q These are the dq-axis currents flowing into the grid connection point, respectively.

[0083] An LC filter element is represented as follows:

[0084]

[0085]

[0086] Among them, v d v q These are the dq axis terminal voltages output by the converter, and R... f L f C f ω represents the equivalent resistance, filter inductance, and filter capacitor of the converter, respectively. s Indicates the nominal frequency of the power grid voltage.

[0087] The equivalent circuit of the power grid is represented as follows:

[0088]

[0089] Among them, i gd i gq These are the dq-axis currents flowing out of the grid connection point of the converter, L g It is the equivalent impedance of the power grid, E d E q These are the dq-axis voltages of the AC power grid.

[0090] The converter control structure proposed in this invention adopts a voltage outer loop and a current inner loop control method. The voltage outer loop mainly maintains a constant DC bus voltage and unity power factor control, and its expression is:

[0091]

[0092]

[0093] Furthermore, the state equation expression for the inner current loop is:

[0094]

[0095]

[0096] Where x1, x2, x3, and x4 are intermediate variables in the state equation; v dc , These are the acquired DC bus voltage of the converter and its setpoint, respectively; Q, Q * These represent the measured reactive power output of the converter; These are the setpoint values ​​for the converter output current, u and u, respectively. d u q i d i q These represent the voltage value at the grid connection point after coordinate transformation and the current value flowing into the grid connection point, respectively; v d v q These are the voltage modulation signals output by the inner current loop controller; k pvdc k ivdc k pv k iv These are the PI control parameters for the outer voltage loop; k pi k ii These are the parameters of the PI controller for the inner current loop.

[0097] Furthermore, the voltage signal v output by the inner current loop controller d v q After undergoing Park and Clark transformations, the modulation signal v of the three-phase grid voltage is obtained. abc This enables the overall closed-loop control process of the distributed power converter.

[0098] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0099] To further verify the effectiveness of the proposed improved adaptive observer control based on grid-connected control of distributed power converters, simulation verification was performed by establishing a distributed power converter control system model based on the improved observer in MATLAB / Simulink.

[0100] Table 1 Circuit parameters based on distributed power grid-connected converter

[0101]

[0102]

[0103] Table 2 PI controller parameters in voltage loop and current loop

[0104]

[0105] The parameters of the converter grid-connected system are shown in Table 1, and the parameters of the converter control system are shown in Table 2.

[0106] Simulations were performed using a traditional phase-locked loop and an improved adaptive observer, respectively. The simulation waveforms for both cases are shown below. Figure 5 As shown.

[0107] from Figure 5 The results show that when a grid voltage fault occurs, the grid frequency fluctuates. The dynamic response of a traditional phase-locked loop (PLL) converges to a steady-state value within 0.052 seconds, while the dynamic response of the frequency tracked by the improved adaptive observer converges to a steady-state value within 0.031 seconds. Furthermore, the traditional PLL exhibits an overshoot of 5.516 Hz after frequency fluctuations, while the overshoot of the frequency tracked by the improved adaptive observer is only 2.143 Hz.

[0108] In summary, the present invention provides a distributed power grid-connected converter control method based on an improved adaptive observer, which can achieve faster and more accurate parameter estimation performance during grid voltage faults, enabling the distributed power grid-connected converter to achieve good grid connection.

[0109] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A distributed power grid-connected converter control method based on an improved adaptive observer, characterized in that, The collected AC grid voltage signal is input into the improved adaptive observer to track the grid voltage phase. The output grid voltage phase angle is used as feedback to transmit to the converter control structure for coordinate transformation of the converter control system, thereby obtaining the dq axis voltage signal. Through the dual-loop control system of the current inner loop and voltage outer loop of the converter control system, the output voltage of the distributed power converter is precisely controlled. The collected AC grid voltage signal is input into an improved adaptive observer to obtain the unknown variables. and The estimated value and According to the estimated value Calculate the positive and negative sequence components of the three-phase power grid voltage, based on the estimated values. Calculate the power grid voltage frequency The improved adaptive observer control loop is as follows: in, , and These are the 2m+1 order coefficient matrices of the collected three-phase AC power grid voltage system; Indicates the system input, , Represents the voltage system of the power grid coordinate system This represents the variables related to the collected three-phase power grid voltage. Represents unknown parameters The estimate, The state variables represent the filter; Represents the adaptive update rate of the system. It is the system's adaptive gain; Grid voltage phase angle for: in, , These are the fundamental frequency of the grid voltage at... Components in the coordinate system.

2. The distributed power grid-connected converter control method based on an improved adaptive observer according to claim 1, characterized in that, Based on the estimated value The positive and negative sequence components of the three-phase power grid voltage are calculated as follows: in, , , , and These are the grid voltages at Harmonic positive and negative sequence components in coordinate system, subscript p Represents the ordinal component, subscript n Represents the negative order component, subscript i Represents the harmonic order.

3. The distributed power grid-connected converter control method based on an improved adaptive observer according to claim 1, characterized in that, Based on the estimated value Calculate the power grid voltage frequency as follows: in, It is the nominal value of the grid voltage and frequency.

4. The distributed power grid-connected converter control method based on an improved adaptive observer according to claim 1, characterized in that, Phase angle of grid voltage The coordinate transformation element in the converter control system feeds back the grid voltage signal. , Transform into , The specific conversion is as follows: 。 5. The distributed power grid-connected converter control method based on an improved adaptive observer according to claim 1, characterized in that, The state equation expression for the outer voltage loop is: in, These are intermediate variables in the state equation; , These are the collected DC bus voltage of the converter and its setpoint, respectively; , These represent the measured reactive power output of the converter; , These are the setpoint values ​​for the converter output current; , , , These are the PI control parameters for the outer voltage loop.

6. The distributed power grid-connected converter control method based on an improved adaptive observer according to claim 1, characterized in that, The state equation for the inner current loop is expressed as follows: in, These are intermediate variables in the state equation; , These are the setpoint values ​​for the converter output current; , , , These are the voltage value at the grid connection point and the current value flowing into the grid connection point after coordinate transformation, respectively. , These are the voltage modulation signals output by the inner current loop controller; , These are the PI controller parameters for the inner current loop. The voltage frequency input to the controller by the adaptive observer.

7. The distributed power grid-connected converter control method based on an improved adaptive observer according to claim 1, characterized in that, The DC bus circuit equations for a distributed generation grid-connected converter are as follows: in, It is a DC-side capacitor. DC side voltage, The active power flowing into the grid-side converter, , These are the dq-axis voltages at the grid connection point. , These are the dq-axis currents flowing into the grid connection point, respectively.

8. The distributed power grid-connected converter control method based on an improved adaptive observer according to claim 1, characterized in that, The grid equivalent circuit of the distributed generation grid-connected converter is as follows: in, , These are the dq-axis currents flowing out of the grid connection point of the converter, respectively. The equivalent resistance of the power grid; It is the equivalent inductance of the power grid; , These are the dq-axis voltages of the AC power grid, respectively. Indicates the nominal frequency of the power grid voltage; , These are the voltage values ​​at the grid connection point after coordinate transformation.

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