A grid-connected converter parameterized control method based on all-drive system theory

Abstract

The present application relates to power electronics, in particular to a grid-connected converter parameterized control method based on all-wheel drive system theory, which establishes an energy function based on the observed angular velocity of the grid-connected converter phase-locked loop and the PCC axis q-axis voltage component; the energy function is processed by using Lagrange equation to obtain a control law; and the operation state of the grid-connected converter is characterized based on the control law. The method obtains the grid-connected control method that meets the lowest system energy, i.e. the most stable one, by constructing the energy function that can describe the system state of the grid-connected converter and taking the variation, the control method can generally obtain the control method of the grid-connected converter containing more system state variables, and the control effect of multiple state optimization is realized. The observed angular velocity and q-axis voltage component are considered in the energy function and processed based on Lagrange equation, the reconstruction of the control structure of the grid-connected converter can be realized, and the state optimization of the control is realized.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and specifically relates to a parameterized control method for grid-connected converters based on the theory of all-drive systems. Background Technology

[0002] With the development of new energy technologies, the control characteristics of grid-connected converters are of great significance to the safe grid-connected operation of wind power, photovoltaics, etc. However, due to the complex nonlinear characteristics of grid-connected converters, the control method based on phase-locked loops is prone to instability, which brings great difficulties to stability analysis and optimized control. It is also difficult to identify the internal parameters of grid-connected converters through their operating status.

[0003] Due to the multiple control loops and the interaction between the control loops and the power grid, the grid-connected converter system can be equivalent to a second-order or higher-order nonlinear system. Traditional nonlinear control design methods for nonlinear systems, such as the Lyapunov method, have difficulty in constructing a suitable Lyapunov function for the system. Feedback linearization and other methods can be implemented for systems under special conditions, but there are few general theoretical methods.

[0004] In order to establish the feedback structure of the grid-connected converter, it is necessary to characterize the operating state of the grid-connected converter to obtain an accurate operating state. However, the existing operating state characterization methods still have the drawback of being relatively crude. Summary of the Invention

[0005] To address the problems existing in the background technology, this invention provides a parameterized control method for grid-connected converters based on the theory of all-drive systems.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a parameterized control method for grid-connected converters based on the theory of all-drive systems, comprising:

[0007] An energy function is established based on the observed angular velocity and the q-axis voltage component of the PCC axis of the grid-connected converter phase-locked loop.

[0008] The energy function is processed using the Lagrange equation to obtain the control law;

[0009] The operating state of the grid-connected converter is characterized by the control law.

[0010] In the above-mentioned parameterized control method for grid-connected converters based on the theory of all-drive systems, the energy function includes the energy of the grid-connected converter phase-locked loop observed angular velocity and the energy of the q-axis voltage.

[0011] In the above-mentioned parameterized control method for grid-connected converters based on the theory of all-drive systems, the energy function is:

[0012]

[0013] Where ω is the observed angular velocity of the grid-connected converter's phase-locked loop, and V pccq K represents the q-axis voltage component at the PCC point of the system grid connection, and k1 and k2 are energy distribution coefficients.

[0014] In the above-mentioned parameterized control method for grid-connected converters based on the theory of all-drive systems, the method of obtaining the control law by processing the energy function using the Lagrange equation is as follows:

[0015]

[0016] Where, q k In grid-connected converter systems, the generalized coordinates characterizing the system's operating state are represented by ω and V. pccq ω is the observed angular velocity between the grid-connected converter and the power grid, V pccq The voltage at the grid-connected PCC point of the grid-connected converter passes through d q The q-axis component obtained after coordinate transformation.

[0017] In the above-mentioned parameterized control method for grid-connected converters based on the theory of all-drive systems, V pccq for:

[0018] V pccq =V g sin(-δ)+ω g L g I g

[0019] Among them, V g ω represents the magnitude of the grid voltage. g L is the angular frequency of the power grid. g For the equivalent line inductance, I g It outputs grid-connected current to the grid-connected converter.

[0020] Compared with the prior art, the present invention constructs an energy function that can describe the state of the grid-connected converter system (grid-connected converter angular velocity and q-axis component of PCC point voltage). Since the energy function considers the observed angular velocity and q-axis voltage component and is processed based on the Lagrange equation, it can accurately characterize the operating state of the grid-connected converter.

[0021] By taking the variation of the energy function, we obtain the grid-connected control method that satisfies the requirement of the lowest system energy, i.e. the most stable system. This control method can be used to obtain a control method for grid-connected converters that includes more system state variables in a general sense, and achieve optimal control effects in multiple states. Attached Figure Description

[0022] Figure 1This is a schematic flowchart of a parameterized control method for a grid-connected converter based on the theory of all-drive systems, according to an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the overall topology of a grid-connected inverter access system according to an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the topology of the feedback circuit of a grid-connected inverter access system according to an embodiment of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0027] The present invention will be further described below with reference to specific embodiments, but these are not intended to limit the scope of the invention.

[0028] This embodiment establishes an energy function based on the observed angular velocity and q-axis voltage component of the phase-locked loop (PLL) of the grid-connected converter; it then processes the energy function using the Lagrange equation to obtain a control law; and finally, it characterizes the operating state of the grid-connected converter based on the control law. Because this embodiment considers the observed angular velocity and q-axis voltage component in the energy function and processes it using the Lagrange equation, it can accurately characterize the operating state of the grid-connected converter.

[0029] This embodiment is achieved through the following technical solution: a parameterized control method for grid-connected converters based on the theory of all-drive systems, comprising:

[0030] An energy function is established based on the observed angular velocity and the q-axis voltage component of the PCC axis of the grid-connected converter phase-locked loop.

[0031] The energy function is processed using the Lagrange equation to obtain the control law;

[0032] The operating state of the grid-connected converter is characterized by the control law.

[0033] Furthermore, the energy function includes the energy of the grid-connected converter phase-locked loop observed angular velocity and the q-axis voltage energy.

[0034] Furthermore, the energy function is:

[0035]

[0036] Where ω is the observed angular velocity of the grid-connected converter's phase-locked loop, and V pccq K represents the q-axis voltage component at the PCC point of the system grid connection, and k1 and k2 are energy distribution coefficients.

[0037] Furthermore, the control law is obtained by processing the energy function using the Lagrange equation, specifically as follows:

[0038]

[0039] Where, q k In grid-connected converter systems, the generalized coordinates characterizing the system's operating state are represented by ω and V. pccq ω is the observed angular velocity between the grid-connected converter and the power grid, V pccq The voltage at the grid-connected PCC point of the grid-connected converter passes through d q The q-axis component obtained after coordinate transformation.

[0040] Furthermore, V pccq for:

[0041] V pccq =V g sin(-δ)+ω g L g I g (3)

[0042] Among them, V g ω represents the magnitude of the grid voltage. g L is the angular frequency of the power grid. g For the equivalent line inductance, I g It outputs grid-connected current to the grid-connected converter.

[0043] In specific implementation, such as Figure 1 As shown, a parameterized control method for grid-connected converters based on the theory of all-drive systems is proposed. First, an energy function is established based on the observed angular velocity of the phase-locked loop of the grid-connected converter and the q-axis voltage component of the PCC (Point of Common Coupling) axis. Second, the energy function is processed using the Lagrange equation to obtain the control law. Finally, the operating state of the grid-connected converter is characterized based on the control law.

[0044] In this embodiment, Figure 2 A schematic diagram of the overall topology of a grid-connected inverter access system is shown. As can be seen from the diagram, the converter circuit includes the grid-connected inverter main circuit, the grid-connected inverter LC filter, the line impedance formed by the line, and the power grid. Figure 3 A schematic diagram of the feedback circuit topology of a grid-connected inverter connected to a system is shown, such as... Figure 3The diagram first constructs the energy function T, where q1 and q2 are the angular velocities ω and q-axis voltages of the grid-connected converter, respectively, and t is time. k The control law, i.e., the control strategy signal u. ref .

[0045] A feedback circuit is provided between the main circuit of the grid-connected converter and the power grid. This feedback circuit includes a phase-locked loop (PLL), a power loop, a voltage loop, a current loop, and a PWM circuit connected in sequence. The PLL receives the induced current i from the circuit entering the power grid. abc and induced voltage u abc To achieve control over the induced current i abc and induced voltage u abc Phase locking and outputting i to the power loop. dq and u dq The power loop is based on the received P set Q set The process is then performed. In this embodiment, a virtual synchronization control strategy can be used to obtain the phase and voltage amplitude reference of the inner loop using PQ. The control law is shown in the following equation:

[0046]

[0047] Q ref -Q e =-k q (U N -U * (5)

[0048] Among them, P ref Q is the active reference power. ref U is the reactive power reference power. N U is the rated voltage amplitude. * For the d-axis voltage reference, k q Q is the droop coefficient. e For the converter to output reactive power, P e The converter outputs active power. A virtual synchronous machine obtains the phase θ, and a phase-locked loop obtains the grid's fundamental frequency phase θ. g The difference between the two is the power angle δ. The voltage amplitude signal is directly given to the positioning d-axis voltage reference, and the q-axis voltage reference is 0. The processed u... * d and u * q The input is fed into the voltage loop. The voltage loop output is i. * d and i * q The reference voltage u is output to the PWM circuit through current loop processing. ref The PWM circuit is based on this reference voltage u. ref Control the converter.

[0049] The processed u * d and u * q The input is fed into the voltage loop. The voltage loop output is i. * d and i * q The reference voltage u is output to the PWM circuit through current loop processing. ref The PWM circuit is based on this reference voltage u. ref Control the converter.

[0050] In this disclosure, the part of the feedback circuit other than the PWM circuit is optimized. In the method for characterizing the operating state of the grid-connected converter of the all-drive system, an energy function that can characterize the operating state of the grid-connected converter is first established.

[0051] The energy function characterizing the system's operating state can be established as follows, where ω is the angular velocity observed by the phase-locked loop of the grid-connected converter, and V pccq For the q-axis voltage component of the PCC point of the system grid connection

[0052]

[0053] Secondly, the variational function of the energy function is obtained to establish the Lagrange equation for the state model of the grid-connected converter;

[0054] The Lagrange equation can be expressed as

[0055]

[0056] Where q k In grid-connected converter systems, generalized coordinates representing the system's operating state can be expressed as ω and V. pccq ω is the angular velocity between the grid-connected converter and the power grid, V pccq Let q be the voltage at the grid-connected PCC point of the grid-connected converter after undergoing dq coordinate transformation. Its steady-state solution can be expressed as follows:

[0057] V pccq =V g sin(-δ)+ω g L g I g (8)

[0058] Where V g ω represents the magnitude of the grid voltage. g L is the angular frequency of the power grid. g For the equivalent line inductance, I g It outputs grid-connected current to the grid-connected converter.

[0059] Finally, the control law of the grid-connected converter system is obtained by solving the established Lagrange equations. The control law u... ref By performing parameterization, a large-signal nonlinear model is established as an example, resulting in a high-order full-drive system model of the grid-connected converter that includes line parameters and system state variables, which can provide all degrees of freedom in the control system design.

[0060] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the content of this specification should be included within the protection scope of the present invention.

Claims

1. A parameterized control method for grid-connected converters based on all-drive system theory, characterized in that, include: Based on the observed angular velocity and PCC point of the grid-connected converter phase-locked loop q The energy function is established based on the axis voltage components; The energy function is processed using the Lagrange equation to obtain the control law; The operating state of the grid-connected converter is characterized by the control law. The energy function includes the energy of the grid-connected converter phase-locked loop observed angular velocity and the energy of the phase-locked loop. q Axis voltage energy; specifically, the energy function is: in, V g The voltage amplitude of the power grid. ω g The angular frequency of the power grid. L g For the equivalent line inductance, I g Output grid-connected current for the grid-connected converter; ω The observed angular velocity between the grid-connected converter and the power grid. V pccq The voltage at the grid-connected PCC point of the grid-connected converter passes through d q obtained after coordinate transformation q Axial components, k1 and k2 are the energy distribution coefficients, where k1 is the power angle and k2 is the energy distribution coefficient. The control law is obtained by processing the energy function using the Lagrange equation, specifically as follows: in, q k In grid-connected converter systems, a generalized coordinate system characterizing the operating state is expressed as: ω and V pccq , ω The observed angular velocity between the grid-connected converter and the power grid. V pccq The voltage at the grid-connected PCC point of the grid-connected converter passes through d q obtained after coordinate transformation q Axial components.

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