Photovoltaic inverter control method based on preset time

Abstract

The invention relates to the field of photovoltaic inverter control, and particularly discloses a photovoltaic inverter control method based on preset time. Aiming at the problems of slow response, complex model and insufficient control precision of a traditional method under a complex power grid and a dynamic load, the method comprises the following steps: firstly, establishing an accurate model of a three-phase photovoltaic inverter based on a Kirchhoff's law, and designing a preset time control algorithm based on a scaling function, so that convergence time can be independently preset without being influenced by an initial state; and the control flexibility and precision are obviously improved. Meanwhile, a dynamic surface method is introduced to construct a novel first-order filter, complexity explosion is effectively avoided, and stability and reliability of the system are guaranteed. According to the method, the dynamic response capability and the grid-connected electric energy quality of the photovoltaic inverter are effectively improved, and the method is suitable for various photovoltaic grid-connected power generation systems and has a good application value.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power electronic control and new energy grid-connected technology, and particularly relates to a preset time control method for a photovoltaic inverter, which is particularly suitable for accurate time constraint control of a three-phase photovoltaic grid-connected inverter under complex power grid conditions, including dynamic response optimization, grid-connected power quality improvement, and system stability enhancement. TECHNICAL BACKGROUND

[0002] With the growth of global energy demand and the emphasis on environmental protection, photovoltaic grid-connected power generation systems, as a clean and renewable energy utilization method, have been widely used. The photovoltaic inverter, as the core component of the photovoltaic grid-connected power generation system, directly affects the power generation efficiency and power quality of the system. In actual operation, the power grid environment is complex and changeable, and the load is often in dynamic change, which puts high requirements on the control of the photovoltaic inverter.

[0003] Traditional photovoltaic inverter control methods, such as those based on PI control, have many shortcomings when facing complex power grid environments and dynamic load changes. Firstly, it is difficult to quickly and accurately control the inverter output, resulting in slow dynamic response of the inverter output voltage and current, low tracking accuracy, and difficulty in meeting the high requirements for power quality in different scenarios. Secondly, the model complexity is high, which not only increases the difficulty of controller design and implementation, but also makes the system sensitive to parameter changes and poor in adaptability. Thirdly, error control is poor, and it is difficult to effectively suppress the influence of power grid interference and load disturbance, which can easily lead to system performance degradation and even instability.

[0004] Therefore, developing a new photovoltaic inverter preset time control method to solve the problem of accurate time constraint control of traditional methods under complex and variable conditions and improve the performance and reliability of photovoltaic inverters has become a research hotspot and a problem to be solved in this field. SUMMARY

[0005] In view of the defects of the traditional photovoltaic inverter control method in uncontrollable convergence time and explosive calculation complexity, the present application provides a photovoltaic inverter control method based on preset time, which realizes: 1) strict convergence of system state within user-set time T p , which is independent of initial value and design parameters; 2) elimination of repeated differentiation of virtual control quantity through a new first-order dynamic surface filter.

[0006] To achieve the above purpose, the technical solution of the present application is as follows:

[0007] 1. A photovoltaic inverter control method based on preset time, characterized in that it comprises the following steps:

[0008] Step one: In the three stationary ABC coordinate system, according to Kirchhoff's voltage law (KVL), the dynamic differential equation relationship between the three-phase photovoltaic grid-connected inverter AC side output voltage, current and grid voltage is established. Then through coordinate transformation, the state vector in the three-phase stationary ABC coordinate system is converted into the synchronous rotating DQ coordinate system, and the internal relationship between the inverter output voltage, inductor current and grid voltage in the synchronous rotating coordinate system is clarified;

[0009] Step two: The voltage tracking error between the component of the inverter output voltage on the DQ axis and its expected reference value, and the current tracking error between the component of the grid-connected current on the DQ axis and its expected reference value are defined respectively, and the error dynamic system model representing the performance of the three-phase photovoltaic grid-connected inverter control system is constructed;

[0010] Step three: A time-varying scaling function is introduced to establish a scaling coordinate transformation, and based on the scaled error variables, a control algorithm with a clear preset convergence time parameter is designed combined with the preset time stability theory. No matter the grid voltage fluctuation, load mutation or environmental temperature change, etc. Complex working conditions, this algorithm can ensure that the inverter output voltage and current can quickly and accurately track the expected value within the preset time, greatly improving the flexibility and accuracy of the control, effectively solving the problem that the control time is difficult to guarantee when the traditional control method faces complex and variable working conditions.

[0011] Step four: The Lyapunov theory is used to analyze the global stability of the system to ensure its stable performance under complex and severe working conditions. By optimizing the controller parameters, the system can be reliably converged within the preset time, taking into account the speed and stability, providing a guarantee for the efficient and reliable operation of photovoltaic grid-connected inverters.

[0012] 2. The preset time-based photovoltaic inverter control method according to claim 1, wherein the step one specifically comprises:

[0013] In the three-phase stationary ABC coordinate system, according to Kirchhoff's voltage law, the dynamic differential equation between the three-phase photovoltaic grid-connected inverter AC side output voltage, current and grid voltage is established as follows:

[0014]

[0015] wherein k a , k b , k c represent the input switching signals; u s represents the three-phase photovoltaic grid-connected inverter DC side voltage; v a , v b , v ca-phase, b-phase, c-phase voltage representing the three-phase photovoltaic grid-connected inverter AC side output, the size and phase will change with the inverter state and control strategy and other factors, is one of the important indicators to measure the inverter output power quality, in volts (V) units; i a , i b , i c represents the output current flowing through the three-phase photovoltaic grid-connected inverter AC side a-phase, b-phase, c-phase, reflecting the load on the consumption of electrical energy and the inverter to the grid current size of the electrical energy delivered, with the output voltage together determine the output power of the inverter, units of amperes (A); L represents the filter inductance connected between the inverter AC side and the grid, units are henry (H); R represents the resistance in the inverter AC side output line and filter circuit, units of ohms (Ω).

[0016] Then, using the coordinate transformation, the state vector under the three-phase stationary ABC coordinate system is converted to the synchronous rotating DQ coordinate system, which can be obtained as follows:

[0017]

[0018] Among them, v d , v q are the D-axis and Q-axis components of the inverter output voltage; i d , i q are the D-axis and Q-axis components of the grid-connected current; v d , v q are the D-axis and Q-axis components of the grid voltage; L is the filter inductance; R is the equivalent resistance of the line; is the grid angular frequency.

[0019] 3. The preset time-based photovoltaic inverter control method according to claim 1, wherein the step two specifically comprises:

[0020] Based on the current-voltage relationship under the synchronous rotating DQ coordinate system, let x1=u s -u s0 , x2=i d -i d0 and x3=i q -i q0

[0021]

[0022] The system model constructed above adopts a double closed-loop control architecture: 1. D-axis control loop: taking the DC bus voltage u s and the AC side D-axis current i d as the direct control object. Among them, u sThe control of the direct current bus voltage directly relates to the active power regulation of the photovoltaic power generation system, and the corresponding control variable is u d ; 2. Q-axis control loop: taking the alternating current side Q-axis current i q as the control object, responsible for the control and design of the system reactive power, and the corresponding control variable is u q . u s0 is the expected steady-state operating point of the set direct current bus voltage; i d0 and i d0 respectively represent the expected steady-state operating points of the D-axis current and the Q-axis current.

[0023] 4. The preset time-based photovoltaic inverter control method according to claim 1, wherein the step three specifically comprises:

[0024] Firstly, the coordinate transformation is defined as follows:

[0025]

[0026] wherein, is the output signal of the first-order filter as follows:

[0027]

[0028] Meanwhile, l2 is a positive design parameter, and α1 is a virtual controller. The filtering error is a time-varying scaling function, satisfying and In addition, the first derivative satisfies and T p is the preset time. λ1=2+m, λ2=1+m, λ3=m and λ0=3+m, wherein m is a positive integer.

[0029] Secondly, the scaling coordinate transformation is designed as

[0030]

[0031] wherein, i=1, 2, 3.

[0032] The derivatives of r1 and E f are taken and a suitable Lyapunov function is selected as:

[0033]

[0034] The derivative of V1 is taken, and the form of the virtual controller α1 is as follows:

[0035]

[0036] wherein, k1 is a positive design parameter.

[0037] The derivative of r2 is taken and a suitable Lyapunov function is selected as:

[0038]

[0039] The derivative of V2 is taken to obtain the form of the controller u d as follows:

[0040]

[0041] where k2 is a positive design parameter.

[0042] The derivative of r3 is taken and a suitable Lyapunov function is selected as:

[0043]

[0044] The derivative of V3 is taken to obtain the form of the controller u d as follows:

[0045]

[0046] where k3 is a positive design parameter.

[0047] 5. The preset time-based photovoltaic inverter control method according to claim 1, wherein step four uses Lyapunov stability theory to comprehensively analyze the stability of the entire control system, ensuring that the system can maintain stable performance under various complex and harsh working conditions. At the same time, by reasonably designing the controller parameters, the system can reliably converge within the preset time, not only achieving rapid control, but also ensuring the stability and reliability of the system, thereby providing a solid guarantee for the efficient and stable operation of the photovoltaic grid-connected power generation system.

[0048] Compared with the prior art, the present application has the following advantages:

[0049] 1. Accurate dynamic response and rapid tracking capability: The preset time control algorithm based on the scaling function is designed in the DQ rotating coordinate system, which can ensure that the inverter output voltage and current can quickly and accurately track the expected value within the preset time. No matter the complex working conditions such as grid voltage fluctuation, load mutation, or environmental temperature change, the system can achieve rapid and stable dynamic response, effectively solving the problem that the control time is difficult to guarantee under complex and variable working conditions in traditional control methods, and greatly improving the rapidity and stability of the system.

[0050] 2. Flexible control time: Unlike traditional control methods, the application can realize independent presetting of control time, which is not limited by initial conditions and design parameters. Users can flexibly adjust the control time according to specific requirements in actual application scenarios, meet the diversified needs of different photovoltaic grid-connected power generation systems for control timeliness, and improve the flexibility and adaptability of control.

[0051] 3. Reduce system complexity and ensure stability: The first-order filter carefully constructed by the dynamic surface method successfully solves the "complexity explosion" problem in the control process, simplifies the system structure, and expands the applicability of the designed algorithm to complex systems. At the same time, the filter can effectively ensure the boundedness of the "virtual error", simplify the system, and ensure the stability and reliability of the control process, avoiding the risk of system performance degradation and instability caused by high complexity. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 The flowchart of the first embodiment of the photovoltaic inverter control method based on preset time of the application process is shown in the figure.

[0053] Figure 2 The response curve change curve of the error variable s1 in the specific embodiment of the application is shown in the figure.

[0054] Figure 3 The response curve change curve of the error variable s2 in the specific embodiment of the application is shown in the figure.

[0055] Figure 4 The response curve change curve of the error variable s3 in the specific embodiment of the application is shown in the figure.

[0056] Figure 5 The response curve change curve of the controller u d in the specific embodiment of the application is shown in the figure.

[0057] Figure 6 The response curve change curve of the controller u q in the specific embodiment of the application is shown in the figure. DETAILED DESCRIPTION

[0058] In order to further illustrate the technical solutions of the application, in combination with the drawings of the specification, the specific embodiments of the application are as follows:

[0059] 1. A photovoltaic inverter control method based on preset time, characterized in that it specifically comprises the following steps:

[0060] Step one: In the three-phase static ABC coordinate system, the dynamic differential equation relationship between the output voltage, current and grid voltage of the three-phase photovoltaic grid-connected inverter is established according to the Kirchhoff voltage law (KVL). Then, through coordinate transformation, the state vector in the three-phase static ABC coordinate system is converted into the synchronous rotating DQ coordinate system, and the internal relationship between the inverter output voltage, inductor current and grid voltage in the synchronous rotating coordinate system is determined.

[0061] Step two: The voltage tracking error between the component of the inverter output voltage on the DQ axis and its expected reference value, and the current tracking error between the component of the grid-connected current on the DQ axis and its expected reference value are defined respectively, and the error dynamic system model representing the performance of the three-phase photovoltaic grid-connected inverter control system is constructed.

[0062] Step three: A time-varying scaling function is introduced to establish a scaling coordinate transformation, and based on the scaled error variables, a control algorithm with a clear preset convergence time parameter is designed combined with the preset time stability theory. Regardless of complex working conditions such as grid voltage fluctuation, load sudden change or environmental temperature change, this algorithm can ensure that the inverter output voltage and current quickly and accurately track the expected value within the preset time, greatly improving the flexibility and accuracy of the control, and effectively solving the problem that the control time is difficult to guarantee in the traditional control method when facing complex and variable working conditions.

[0063] Step four: The Lyapunov theory is used to analyze the global stability of the system to ensure its stable performance under complex and severe working conditions. By optimizing the controller parameters, the system is strictly guaranteed to converge reliably within the preset time, taking into account the speed and stability, and providing protection for the efficient and reliable operation of the photovoltaic grid-connected inverter.

[0064] 2. The preset time-based photovoltaic inverter control method of claim 1, wherein the step one specifically comprises:

[0065] In the three-phase static ABC coordinate system, the dynamic differential equation between the output voltage, current and grid voltage of the three-phase photovoltaic grid-connected inverter is established according to the Kirchhoff voltage law as follows:

[0066]

[0067] wherein k a , k b , k c represent the input switching signals; u s represents the DC side voltage of the three-phase photovoltaic grid-connected inverter; v a , v b , v ca-phase, b-phase and c-phase voltages representing the three-phase PV grid-connected inverter AC side output, whose size and phase will change with the inverter working state and control strategy, etc., are one of the important indicators to measure the inverter output power quality, in units of volts (V); i a b c i d a-phase, b-phase and c-phase output currents flowing through the three-phase PV grid-connected inverter AC side, reflecting the load consumption of electrical energy and the current size of the inverter delivering electrical energy to the grid, together with the output voltage to determine the output power of the inverter, in units of amperes (A); L represents the filter inductance connected between the inverter AC side and the grid, in units of henries (H); R represents the resistance in the inverter AC side output line and the filter circuit, in units of ohms (Ω).

[0068] Then, the state vector in the three-phase stationary ABC coordinate system is converted to the synchronous rotating DQ coordinate system by coordinate transformation, and the following can be obtained:

[0069]

[0070] wherein v d and v q are the D-axis and Q-axis components of the inverter output voltage, respectively; i d and i q are the D-axis and Q-axis components of the grid-connected current, respectively; v d and v q are the D-axis and Q-axis components of the grid voltage, respectively; L is the filter inductance; R is the equivalent resistance of the line; and ω is the grid angular frequency.

[0071] 3. The preset time-based PV inverter control method according to claim 1, wherein the step two specifically comprises:

[0072] Based on the current-voltage relationship in the synchronous rotating DQ coordinate system, let x1=u s -u s0 , x2=i d -i d0 and x3=i q -i q0

[0073]

[0074] The system model constructed above adopts a double closed-loop control architecture: 1. D-axis control loop: taking the DC bus voltage u s and the AC side D-axis current i d as the direct control objects. Among them, u s ​The control of the active power regulation of the photovoltaic power generation system, and the corresponding control variable u q The Q-axis control loop: taking the AC-side Q-axis current i q as the control object, responsible for the control and design of the system reactive power, and the corresponding control variable u q The DC bus voltage setpoint u s0 The desired steady-state working points of the D-axis current and the Q-axis current i d0 and i q0 respectively.

[0075] 4. The preset time-based photovoltaic inverter control method according to claim 1, wherein the step three specifically comprises:

[0076] First, define the coordinate transformation as follows:

[0077]

[0078] wherein, is the output signal of the first-order filter as follows:

[0079]

[0080] Meanwhile, l2 is a positive design parameter, and α1 is a virtual controller. Define the filtering error as a time-varying scaling function, satisfying and In addition, the first derivative of satisfies and T p is the preset time. λ1 = 2 + m, λ2 = 1 + m, λ3 = m, and λ0 = 3 + m, wherein m is a positive integer.

[0081] Second, design the scaling coordinate transformation as

[0082]

[0083] wherein, i = 1, 2, 3.

[0084] Derive r1 and E f and select an appropriate Lyapunov function as:

[0085]

[0086] Derive V1 to obtain the form of the virtual controller α1 as follows:

[0087]

[0088] wherein, k1 is a positive design parameter.

[0089] Differentiating r² and choosing a suitable Lyapunov function, we get:

[0090]

[0091] Taking the derivative of V2, we can obtain the controller u. d The format is as follows:

[0092]

[0093] Where k2 is the positive design parameter.

[0094] Differentiating r3 and choosing a suitable Lyapunov function, we get:

[0095]

[0096] Taking the derivative of V3, we can obtain the controller u. d The format is as follows:

[0097]

[0098] Where k3 is the positive design parameter.

[0099] 5. The photovoltaic inverter control method based on a preset time as described in claim 1, wherein step four utilizes Lyapunov stability theory to conduct a comprehensive stability analysis of the entire control system, ensuring that the system maintains stable performance under various complex and harsh operating conditions. Simultaneously, by rationally designing controller parameters, reliable convergence of the system within the preset time is guaranteed, achieving not only rapid control but also ensuring the stability and reliability of the system, providing a solid guarantee for the efficient and stable operation of the photovoltaic grid-connected power generation system.

[0100] To demonstrate the effectiveness of this embodiment, the following simulation verification was performed:

[0101] like Figure 1 The control block diagram of the algorithm proposed in this invention is shown below. To further illustrate the technical effects of the invention, the simulation experiment verification process of the photovoltaic inverter control method based on a preset time provided by this invention is as follows:

[0102] In the simulation experiment, the system parameters of the three-phase photovoltaic grid-connected inverter model are: R = 0.5Ω, L = 2.5mH. C s =4.4mF, v d =270V, v q =0V,u s0 =500V, i d0 =0A, i q0=0A. Control parameters are set as: k1=15, k2=15, k3=15, l2=50, T p =1. By using MATLAB software, the mathematical model established in the control method of the embodiment is simulated to obtain simulation Figures 2-6 . Figure 2 is the response curve change curve of the error variable s1 in the embodiment of the application; Figure 3 is the response curve change curve of the error variable s2 in the embodiment of the application; Figure 4 is the response curve change curve of the error variable s3 in the embodiment of the application; Figure 5 is the response curve change curve of the controller ud in the embodiment of the application; Figure 6 is the response curve change curve of the controller uq in the embodiment of the application; it can be known from the simulation results above that the photovoltaic grid-connected inverter can quickly converge and remain stable within the preset time T=1s under the preset time control algorithm.

[0103] The above is only the preferred embodiment of the application, and does not limit the patent scope of the application, and any equivalent structure or equivalent flow transformation using the content of the specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the application.

Claims

1. A photovoltaic inverter control method based on a preset time, characterized in that, Specifically, it includes the following steps: Step 1: In the three-term static ABC coordinate system, based on Kirchhoff's Voltage Law (KVL), establish the dynamic differential equation relationship between the AC output voltage and current of the three-phase photovoltaic grid-connected inverter and the grid voltage; then, through coordinate transformation, transform the state vector in the three-phase static ABC coordinate system to the synchronous rotating DQ coordinate system, and clarify the intrinsic relationship between the inverter output voltage, inductor current and grid voltage in the synchronous rotating coordinate system. Step 2: Define the voltage tracking error between the inverter output voltage component on the DQ axis and its expected reference value, and the current tracking error between the grid-connected current component on the DQ axis and its expected reference value, respectively, and construct an error dynamic system model characterizing the performance of the three-phase photovoltaic grid-connected inverter control system. Step 3: Introduce a time-varying scaling function and establish a scaling coordinate transformation. Based on this scaling error variable and combined with the preset time stability theory, design a control algorithm with a clearly preset convergence time parameter. Regardless of complex operating conditions such as grid voltage fluctuations, load abrupt changes, or ambient temperature changes, this algorithm can ensure that the inverter output voltage and current quickly and accurately track the expected value within a preset time, greatly improving the flexibility and accuracy of control and effectively solving the problem that traditional control methods cannot guarantee control time when facing complex and variable operating conditions. Step 4: Analyze the global stability of the system using Lyapunov theory to ensure its stable performance under complex and harsh working conditions; optimize controller parameters to strictly guarantee reliable convergence of the system within a preset time, balancing speed and stability, and providing a guarantee for the efficient and reliable operation of photovoltaic grid connection.

2. The photovoltaic inverter control method based on a preset time as described in claim 1, characterized in that, Step one specifically includes: In the three-phase stationary ABC coordinate system, based on Kirchhoff's voltage law, the dynamic differential equations between the AC side output voltage and current of the three-phase photovoltaic grid-connected inverter and the grid voltage are established as follows: Where, k a k b k c Indicates the input switch signal; u s This indicates the DC-side voltage of a three-phase photovoltaic grid-connected inverter; v a v b v c , , and , respectively, represent the a-phase, b-phase, and c-phase voltages output from the AC side of a three-phase photovoltaic grid-connected inverter. Their magnitudes and phases vary depending on factors such as the inverter's operating state and control strategy, and are one of the important indicators for measuring the power quality of the inverter's output, expressed in volts (V); i a i b i c The output current flowing through phases a, b, and c of the AC side of the three-phase photovoltaic grid-connected inverter represents the load's energy consumption and the current supplied by the inverter to the grid. Together with the output voltage, it determines the inverter's output power, measured in amperes (A). L represents the filter inductance connected between the inverter's AC side and the grid, measured in Henrys (H). R represents the resistance in the inverter's AC output lines and filter circuit, measured in ohms (Ω). Then, using coordinate transformation, the state vector in the three-phase stationary ABC coordinate system is transformed to the synchronously rotating DQ coordinate system, specifically: Among them, v d v q These are the D-axis and Q-axis components of the inverter output voltage, respectively; i d i q These are the D-axis and Q-axis components of the grid-connected current, respectively; v d v q These represent the D-axis and Q-axis components of the grid voltage, respectively; L is the filter inductance; and R is the line equivalent resistance. This is the angular frequency of the power grid.

3. The photovoltaic inverter control method based on a preset time as described in claim 1, characterized in that, Step two specifically includes: Based on the current-voltage relationship in the synchronously rotating DQ coordinate system, let x1 = u s -u s0 x2 = i d -i d0 and x3=i q -i q0 The system model constructed above adopts a dual closed-loop control architecture:

1. D-axis control loop: based on the DC bus voltage u s and AC side D-axis current i d For directly controlled objects; where u s The control of this is directly related to the active power regulation of the photovoltaic power generation system, and the corresponding control quantity is u. d 2. Q-axis control loop: based on the AC side Q-axis current i q As the controlled object, it is responsible for the control and design of the system's reactive power, and its corresponding control variable is u. q ;u s0 To set the desired steady-state operating point of the DC bus voltage; i d0 and i q0 These represent the desired steady-state operating points of the D-axis current and the Q-axis current, respectively.

4. The photovoltaic inverter control method based on a preset time as described in claim 1, characterized in that, Step three specifically includes: First, the coordinate transformation is defined as follows: in, The output signal of the following first-order filter is: at the same time, The design parameters are positive, α1 is the virtual controller; the filter error is defined. For time-varying scaling functions, satisfying and In addition, its first derivative satisfy and T p The preset time; λ1=2+m, λ2=1+m, λ3=m and λ0=3+m, where m is a positive integer; Secondly, design the scaling coordinate transformation as follows: Where i = 1, 2, 3; For r1 and E f Differentiating and choosing a suitable Lyapunov function yields: Taking the derivative of V1, we obtain the form of the virtual controller α1 as follows: Where k1 is the positive design parameter; Differentiating r² and choosing a suitable Lyapunov function, we get: Taking the derivative of V2, we can obtain the controller u. d The format is as follows: Where k2 is the positive design parameter; Differentiating r3 and choosing a suitable Lyapunov function, we get: Taking the derivative of V3, we can obtain the controller u. d The format is as follows: Where k3 is the positive design parameter.

5. The photovoltaic inverter control method based on a preset time as described in claim 1, wherein step four utilizes Lyapunov stability theory to conduct a comprehensive stability analysis of the entire control system, ensuring that the system maintains stable performance under various complex and harsh operating conditions. Simultaneously, by rationally designing controller parameters, reliable convergence of the system within the preset time is guaranteed, achieving not only rapid control but also ensuring the stability and reliability of the system, providing a solid guarantee for the efficient and stable operation of the photovoltaic grid-connected power generation system.

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