Direct-driven fan system simulation method based on electromechanical-electromagnetic transient hybrid modeling

Abstract

The invention relates to a power electronic simulation technology, and provides a machine side equivalence method of a direct-drive fan grid-connected system aiming at the contradiction between precision and speed of power system simulation under dense access of new energy. According to the method, a direct-driven fan system is taken as an example, a machine-electricity transient hybrid detailed model (machine-side electromechanical transient and network-side electromagnetic transient) is established, and the core is that a wind turbine, a permanent magnet synchronous generator, a machine-side converter and a control system of the machine-side converter are integrally equivalent to a controlled current source, as shown in figure 1. The equivalent is based on rotor flux linkage directional vector control (id = 0), a power conservation relation and a simplified first-order inertial link current controller transfer function are utilized, the machine side complex dynamic state is mapped to current source output, and the number of simulation nodes is remarkably reduced. The method has the advantages that the control characteristics of the grid-side converter (especially the power grid fault ride-through response) are completely reserved, meanwhile, the simulation efficiency of a large-scale system is improved by more than 66%, the precision error (RMSE) is smaller than 0.45%, and the key problems of new energy simulation precision and speed are effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of power electronics simulation technology, specifically relating to a method for overall equivalent modeling of the turbine side of a direct-drive wind turbine grid-connected system, and particularly to an efficient collaborative simulation technology that combines equivalent modeling on the turbine side with electromagnetic transient modeling on the grid side. Background Technology

[0002] In recent years, the scale of new energy construction, such as wind power and photovoltaic power, has expanded rapidly. However, these new energy power sources generally have characteristics such as weak grid adaptability, low inertia, and a high proportion of power electronic equipment connected, which places higher demands on the accuracy and speed of real-time simulation of large-scale new energy power systems. Unlike AC power systems based on traditional synchronous generators and asynchronous motors, the power electronic converters on which new energy power generation equipment relies have high switching frequencies and fast dynamic response speeds. Their behavioral characteristics require the simulation step size to be shortened to the microsecond or even sub-microsecond level; otherwise, it is difficult to guarantee the accuracy of the simulation.

[0003] Taking a permanent magnet direct-drive wind turbine system as an example, it consists of four parts: a wind turbine, a permanent magnet synchronous generator (PMSG), a turbine-side converter (MSC) and control system, and a grid-side converter (GSC) and control system. A detailed model of a single wind turbine includes 20-30 electrical nodes and complex control system components. The large number of electrical nodes and microsecond-level simulation steps lead to a dramatic increase in computational load, making real-time simulation of power systems with large-scale renewable energy sources difficult to achieve.

[0004] In large-scale system simulations, direct-drive wind turbines require a focus on the response characteristics of the grid-side converter during grid fault ride-through. Research indicates that retaining the grid-side converter and its control model while simultaneously modeling the wind turbine, PMSG, and turbine-side converter using equivalent models can significantly reduce the number of simulation nodes and improve computational efficiency. This approach addresses simulation bottlenecks by reducing computational dimensions while maintaining the accuracy of grid response characteristics. Summary of the Invention

[0005] This invention proposes an equivalent method for grid-connected direct-drive wind turbine systems. By performing equivalent modeling on the turbine side of the grid-connected direct-drive wind turbine system, it achieves hybrid modeling of electromechanical and electromagnetic transients on both the turbine and grid sides, thus resolving the contradiction between speed and accuracy in the full electromagnetic transient simulation of large-scale direct-drive wind turbine systems.

[0006] In a first aspect, the present invention provides an equivalent simplification method for the machine-side converter and control system of a direct-drive wind turbine grid-connected system based on the reduced-order equivalent of the control function.

[0007] The parameter design and order reduction method for the d-axis current controller of the machine-side converter are as follows: the switching gain of the d-axis current controller of the machine-side converter is... Because the R / L ratio on the machine side of the direct-drive fan system is relatively small, the pole of the open-loop gain is s = -R.s / L d Very close to the origin, introducing zero point Achieve pole-zero cancellation. This is achieved through the aforementioned open-loop gain G. i (s) to design the proportional gain k of the proportional integrator p and integral gain k i The transfer function of the system's d-axis control from input to output can be simplified to a first-order inertial element, i.e. At this point, the closed-loop transfer function of the system is Where: τ is the time constant of the closed-loop system. d =L d / k p .

[0008] The parameters of the converter's q-axis current controller are obtained using the same order reduction method as the d-axis controller. After order reduction, the closed-loop transfer function of the system is: Where: τ is the time constant of the closed-loop system. q =L q / k q .

[0009] The equivalent method for the controlled current source of the machine-side converter is based on power conservation. have to Where: The active power output of the PMSG stator; u sq U is the q-axis voltage of the PMSG stator. dc I is the DC bus capacitor voltage; dc This is the DC bus capacitor current; therefore, the permanent magnet synchronous generator and the generator-side converter, among other devices, are collectively equivalent to a controlled current source, and the input signal I of this controlled current source is... dc Depend on The closed-loop transfer function shown is used for equivalent control.

[0010] A second aspect of this invention provides an efficient co-simulation method that employs equivalent modeling on the machine side and electromagnetic transient modeling on the network side, characterized in that:

[0011] The machine side adopts a dynamic controlled current source equivalent model: based on the power conservation principle (P s =U dc I dc By reducing the order of the transfer function of the d / q axis controller, the permanent magnet synchronous generator, machine-side converter, etc. are treated as a controlled current source, reducing the number of simulation nodes by more than 90%.

[0012] The grid side adopts a fully electromagnetic transient refined modeling: retaining the grid-side converter and its control loop, and accurately simulating the current response characteristics under fault ride-through conditions;

[0013] Hybrid interface circuit: The machine-side controlled current source and the grid-side converter are connected through a DC bus, and the machine-side equivalent model (controlled current source) and the electromagnetic transient network are directly coupled at the circuit level;

[0014] Step size coordination mechanism: The electromechanical transient side (machine side) adopts a millisecond-level step size, while the electromagnetic transient side (grid side) adopts a microsecond-level step size. The simulation process on both sides is coordinated through the fundamental voltage / current quantities of the periodic interactive interface (every 1-5 power frequency cycles), balancing efficiency and accuracy. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only illustrate some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a converter model based on a binary resistance model in the existing technology.

[0017] Figure 2 The topology of the direct-drive fan system provided in this application embodiment is configured by the user.

[0018] Figure 3 This is the equivalent circuit of a permanent magnet synchronous motor in the abc coordinate system in the prior art.

[0019] Figure 4 This is the equivalent circuit of a permanent magnet synchronous motor in the dq synchronous coordinate system in the prior art. Figure 4 'a' represents the equivalent circuit along the d-axis. Figure 4 b is the q-axis equivalent circuit.

[0020] Figure 5 The control block diagram of the machine-side converter of the direct-drive wind turbine grid-connected system provided in this application embodiment is configured by the user.

[0021] Figure 6 The equivalent circuit of the grid-side converter provided in the embodiments of this application has parameters set by the user.

[0022] Figure 7 The grid-side converter control block diagram of the direct-drive wind turbine grid-connected system provided in this application embodiment is configured by the user.

[0023] Figure 8 A simplified control block diagram of the machine-side converter of the direct-drive wind turbine grid-connected system provided in this application embodiment.

[0024] Figure 9 The simplified topology of the direct-drive wind turbine grid-connected system provided in this application embodiment.

[0025] Figure 10 An exemplary flowchart of the electromagnetic transient simulation method for the grid-side portion of a direct-drive wind turbine grid-connected system provided in this application embodiment. Detailed Implementation

[0026] 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 embodiments of the present invention, and not all embodiments. 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.

[0027] See Figure 1 This is the two-level converter model used in this invention, which is constructed based on a binary resistor model.

[0028] See Figure 2 This is a topology diagram of the direct-drive wind turbine grid-connected system in this invention. The wind turbine, permanent magnet synchronous motor and turbine-side converter are modeled using electromechanical transients and connected to the grid side through DC bus capacitors. The grid side is modeled using electromagnetic transients.

[0029] The present invention provides an equivalent circuit and control method for a permanent magnet synchronous generator according to an embodiment, see [link to relevant documentation]. Figure 3 The equivalent circuit of the permanent magnet synchronous generator shown in the abc coordinate system shows that there is a coupling relationship between the three phase circuits.

[0030] In the dq rotating coordinate system, permanent magnet synchronous generators can achieve decoupled control of electromagnetic quantities, simplifying the analysis of generator operating characteristics. Assume the dq coordinate system rotates synchronously, with the d-axis leading the q-axis by 90° electrical degrees clockwise, and the d-axis is positioned along the magnetic flux linkage of the rotor permanent magnets. Following the conventional definition of the positive direction for electric motors, the voltage equations and stator flux linkages of the permanent magnet synchronous generator in the dq synchronous rotating coordinate system can be described as follows: and In the formula: ψ d ψ q For stator d-axis and q-axis flux linkages; L d L q For stator d-axis and q-axis inductance; i d i q ψ represents the stator d-axis and q-axis currents. m The flux linkage vector induced in the stator by the rotor permanent magnet; u sd u sq R represents the stator d-axis and q-axis voltages. s ω is the stator resistance; r ω is the rotor's electric angular velocity.

[0031] Combining the voltage equations and stator flux linkages of the permanent magnet synchronous motor described above, we can further derive its voltage equation as follows:

[0032] See Figure 4 , is the d-axis and q-axis equivalent circuit of the permanent magnet synchronous motor used in this invention.

[0033] Furthermore, the active power, reactive power, and electromagnetic torque output from the stator side of the permanent magnet synchronous generator can be obtained as follows: and

[0034] In the rotor flux orientation mode, the electromagnetic torque of the permanent magnet synchronous generator can be further expressed as:

[0035] See Figure 5 This is a control block diagram of the machine-side converter in this invention.

[0036] In a synchronous rotating coordinate system, the permanent magnet synchronous generator employs rotor flux-oriented vector control, achieved by setting the d-axis current component to zero, i.e., i d =0, which realizes both the deterministic mapping relationship between the active power output of the stator and the q-axis current, and the decoupling control between active power and reactive power.

[0037] The active power output of the stator can be rewritten as

[0038] Because there is cross-coupling between the generator and the machine-side converter's dq-axis models, a new control variable u is introduced. d and u q You can get and

[0039] Introducing voltage compensation term Δu sd and Δu sq , for u dref and u qref Cross-coupling voltage compensation is performed, and they satisfy...

[0040] Current controllers in vector control methods all use PI control. Here, we will use the d-axis as an example to illustrate the design method of the current controller. The d-axis current controller can be represented as... In the formula, k p It is the proportional gain, k i It is the integral gain.

[0041] The open-loop gain of the d-axis control system is

[0042] Typically, the R / L ratio on the machine side of a direct-drive wind turbine system is relatively small, and the pole of the open-loop gain is s = -R. s / L d Being very close to the origin causes the amplitude and phase of the open-loop gain to decrease from a relatively low frequency. Therefore, it is necessary to counteract the effect of the poles being close to the origin by zero-pole cancellation, making the zeros...

[0043] This method can be used to design the proportional gain k of a proportional integrator. p and integral gain k i The transfer function of the system's d-axis control from input to output can be simplified to a first-order inertial element. That is, the open-loop transfer function of the system can be simplified to...

[0044] At this point, the closed-loop transfer function of the system is Where: τ is the time constant of the closed-loop system. d =L d / k p .

[0045] The simplified transfer function of the q-axis current controller can be derived using the same method.

[0046] As mentioned earlier, when PMSG employs rotor flux-oriented vector control, it achieves decoupled control of active and reactive power by setting the d-axis current component to zero. From power conservation...

[0047] Therefore, in the equivalent modeling study of the direct-drive wind turbine grid-connected system, in order to accurately reflect the dynamic characteristics of the coordinated operation of the permanent magnet synchronous generator and the converter, through the above series of derivations, the permanent magnet synchronous generator and the generator-side converter are treated as a single controlled current source, and the input signal I of this controlled current source is... dc Depend on The closed-loop transfer function shown is used for equivalent control.

[0048] See Figure 6 This is the equivalent circuit of the grid-side converter in this invention. The grid-side converter adopts... Figure 1 The two-level converter shown is based on a binary resistor model.

[0049] In the dq synchronous rotating coordinate system (the angular velocity of the coordinate system is the synchronous angular velocity ω of the grid voltage), g The mathematical model of the grid-side converter is: In the formula: e gd e gq i gd i gq These are the d-axis and q-axis components of the grid voltage and grid current, respectively; u gd ugq These are the d-axis and q-axis voltage components of the grid-side converter.

[0050] Grid-side converters often employ grid voltage-oriented vector control technology. Here, the comprehensive vector control of the grid voltage is oriented on the d-axis, and the projection of the grid voltage onto the q-axis is 0, i.e. In the formula: U g This is the composite vector of grid voltage.

[0051] The mathematical model of the grid-side converter can be simplified to:

[0052] The active and reactive power input to the power grid can be expressed as:

[0053] See Figure 7 This is a control block diagram of the grid-side converter in this invention.

[0054] See Figure 8 The above equation is the basis of this invention. A simplified control block diagram was constructed.

[0055] See Figure 9 This is the topology obtained by replacing the machine side of the direct-drive wind turbine grid-connected system with an equivalent value using a controlled current source, as described in this invention.

[0056] See Figure 10 The solution framework for the electromagnetic transient side (grid side) includes the solution of electrical components and control components, which respectively include initialization functions and execution functions that iterate by step size.

[0057] The electromagnetic transient side (network side) is calculated and solved using an electromagnetic transient simulation framework based on the main step size Δt1. Following the general Dommel discretization method for electromagnetic transient simulation, the circuit relationships are equivalent to a matrix solved using the nodal voltage method. Its mathematical expression is as follows:

[0058] Y total *V=I source +I hist

[0059] Y total Let I be the system admittance matrix. hist V is the historical current, V is the node voltage, and I is the node voltage. source Inject current into the node.

Claims

1. An equivalent method for a direct-drive wind turbine grid-connected system, characterized in that, include: The grid-side converter module connects the grid interface to the DC bus. A controlled current source module is connected in parallel to the DC bus and is used to equivalently replace the wind turbine, permanent magnet synchronous generator, machine-side converter and its control system of the direct-drive wind turbine. The control signal generation module has its input terminals connected to the voltage signal and power reference value (P) of the DC bus. ref The output terminal is connected to the controlled current source module; The controlled current source module includes: (1) Reference value generation unit, based on power reference value (P) ref ) and DC bus voltage (U dc Generate current reference signal (I) dref ); (2) Transfer function unit, the input terminal of which is connected to the current reference signal (I dref The output terminal generates a controlled current source output value (I). dc ); (3) Current output unit, which outputs the value (I) dc The current is converted into an equivalent current and injected into the DC bus.

2. The equivalent method for a direct-drive wind turbine grid-connected system according to claim 1, characterized in that: (1) The machine side adopts a dynamic controlled current source equivalent model: based on the power conservation principle (P s =U dc I dc By reducing the order of the transfer function of the d / q axis controller, the permanent magnet synchronous generator, machine-side converter, etc. are treated as a controlled current source, reducing the number of simulation nodes by more than 90%. (2) The grid side adopts full electromagnetic transient fine modeling: retain the grid-side converter and its control loop, and accurately simulate the current response characteristics under fault ride-through conditions; (3) Hybrid interface circuit: The machine-side controlled current source and the grid-side converter are connected through a DC bus, and the machine-side equivalent model (controlled current source) and the electromagnetic transient network are directly coupled at the circuit level; (4) Step size coordination mechanism: The electromechanical transient side (machine side) adopts a millisecond step size, and the electromagnetic transient side (grid side) adopts a microsecond step size. The simulation process on both sides is coordinated through the fundamental voltage / current quantities of the periodic interactive interface (every 1-5 power frequency cycles), taking into account both efficiency and accuracy.

Images