A method and apparatus for phase-locked control of a current transformer

Abstract

The embodiment of the present application relates to a kind of converter phase-locked control method and device, the method includes the following steps: S1, simulating synchronous generator no-load operating condition, given the mechanical torque T m Initial value;S2, given excitation electromotive force amplitude E initial value;S3, according to converter grid-connected point instantaneous voltage sampling input value U g ∠θ g And excitation electromotive force amplitude E, by stator electrical equation, electromagnetic power P e Is obtained;S4, according to electromagnetic power P e And mechanical torque T m , by rotor motion equation, rotor speed angle frequency ω is obtained;S5, according to rotor speed angle frequency ω, the rotor phase θ is calculated, and the rotor phase θ is used for stator electrical equation.The technical scheme of the embodiment of the present application is based on the principle of synchronous generator self-synchronization, replaces conventional phase-locked loop with rotor motion equation, replaces converter machine end voltage phase detection with virtual rotor phase, has self-synchronization characteristics, to solve the synchronization stability problem of grid-connected converter based on phase-locked control under weak power grid.

Description

Technical Field

[0001] The present invention relates to the field of converter technology, and in particular to a converter phase-locked control method and apparatus. Background Technology

[0002] Most regions in China with abundant new energy resources are located at the end of the power grid, where the grid structure is relatively weak. This makes it common for new energy generators to operate under weak grid conditions. New energy generators often use power electronic converters as their grid connection interface. The control performance of these converters depends on the voltage characteristics at the connection point. The voltage at the weak grid end is easily disturbed, posing a serious challenge to the safe and stable operation of the grid-connected converter.

[0003] Unlike rotating electrical machines, grid-connected converters typically achieve synchronization with the AC power grid through phase-locked loops (PLLs). The PLL provides synchronization phase by following the terminal voltage; its synchronization performance is closely related to the terminal voltage characteristics. Under weak grid conditions, the terminal voltage is highly sensitive and easily affected by disturbances, posing a challenge to the synchronization stability of the grid-connected converter.

[0004] Studies indicate that in weak power grids, the phase-locked loop (PLL) of a grid-connected converter may lack a steady-state equilibrium point, leading to static instability. Even if a steady-state equilibrium point exists, the PLL may oscillate under small disturbances due to insufficient damping, and under large disturbances, transient stability problems similar to the oscillation instability of a synchronous machine may occur due to the nonlinearity of the PLL's phase detection element.

[0005] To address the small-disturbance synchronization stability problem of grid-connected converters based on phase-locked loop (PLL) control in weak power grids, existing technologies propose increasing damping from the perspective of parameter optimization or adopting PSS-like stability control strategies to improve system synchronization stability. While existing technologies primarily optimize converter operation stability in weak power grids by optimizing PLLs and control parameters, these technologies suffer from several drawbacks. Firstly, the parameter adjustment methods and theories are complex. Secondly, they are affected by actual power grid parameters, requiring adjustments and matching of the designed PLLs and control parameters based on different grid parameters. This makes them particularly prone to instability during large power grid disturbances such as grid fault ride-throughs, thus limiting their applicability. Summary of the Invention

[0006] Based on the above-mentioned situation of the prior art, the purpose of this invention is to provide a converter phase-locked control method and device. This method has self-synchronization characteristics and is used to solve the synchronization and stability problem of grid-connected converters based on phase-locked control under weak power grids. It can be applied to distributed generation, energy storage, microgrids and other fields to realize the stable operation of grid-connected converters connected to weak power grids.

[0007] To achieve the above objectives, according to one aspect of the present invention, a converter phase-locked control method is provided, comprising the steps of:

[0008] S1. Simulate the no-load operation of a synchronous generator, given the mechanical torque T under this condition. m Initial value: T m =1;

[0009] S2. Control the excitation electromotive force and give the initial value of the excitation electromotive force amplitude E: E = 0;

[0010] S3. Based on the instantaneous voltage sampling input value U at the converter grid connection point. g ∠θ g The electromagnetic power P is calculated from the excitation potential amplitude E and the stator electrical equations. e ;

[0011] S4. According to the electromagnetic power P e and mechanical torque T m The rotor speed angular frequency ω is obtained through the rotor motion equation;

[0012] S5. Calculate the rotor phase θ based on the rotor speed angular frequency ω, and use the obtained rotor phase θ in the stator electrical equations in step S3.

[0013] Furthermore, in step S1, the synchronous generator power angle is 0, and the rotor phase is synchronized with the power grid.

[0014] Furthermore, the stator electrical equations include:

[0015]

[0016] Where R is the virtual stator resistance, L is the virtual stator inductance, and I is the virtual stator current; the initial value of θ is θ = 0, and under steady state, P e =T m *ω=0,θ=θ g That is, the rotor phase is synchronized with the power grid.

[0017] Furthermore, the stator electrical equations include:

[0018]

[0019] Where X is the per-unit value of the stator impedance, and θ is calculated according to step S5.

[0020] Furthermore, sinθ g and cosθ g It is obtained through the following formula:

[0021]

[0022] Among them, U a U b Uc These are the instantaneous three-phase grid voltage values, U α U β These are the values ​​of the grid voltage in the two-phase stationary coordinate system, respectively.

[0023] Furthermore, the rotor motion equations include:

[0024]

[0025] Where J is the rotor inertia, T d For the damping torque, K d G is the damping coefficient, ω0 is the rated angular frequency, and G is the damping coefficient. hpf (s) represents the high-pass filter, and ξ represents the damping ratio of the high-pass filter.

[0026] Furthermore, the rotor phase θ is calculated using the following formula:

[0027] θ = ωt.

[0028] According to another aspect of the present invention, a converter phase-locked control device is provided, comprising an active power controller module, an internal electromotive force controller module, a stator electronic equation module, a rotor motion equation module, and a phase calculation module; wherein,

[0029] The active power controller module is used to simulate the no-load operation of a synchronous generator, and to provide a mechanical torque T under this condition. m Initial value: T m =1;

[0030] The internal potential controller module is used to control the excitation potential and to give an initial value of the excitation potential amplitude E: E = 0;

[0031] The stator electronic equation module is used to sample the input value U based on the instantaneous voltage at the converter grid connection point. g ∠θ g The electromagnetic power P is calculated from the excitation potential amplitude E and the stator electrical equations. e ;

[0032] The rotor motion equation module is used to determine the electromagnetic power P. e and mechanical torque T m The rotor speed angular frequency ω is obtained through the rotor motion equation;

[0033] The phase calculation module is used to calculate the rotor phase θ based on the rotor speed angular frequency ω, and use the obtained rotor phase θ for the calculation of the stator electrical equation module.

[0034] Furthermore, the stator electrical equations include:

[0035]

[0036] Where R is the virtual stator resistance, L is the virtual stator inductance, and I is the virtual stator current; the initial value of θ is θ = 0, and under steady state, P e =T m *ω=0,θ=θ g That is, the rotor phase is synchronized with the power grid.

[0037] Furthermore, the rotor motion equations include:

[0038]

[0039] Where J is the rotor inertia, T d For the damping torque, K d G is the damping coefficient, ω0 is the rated angular frequency, and G is the damping coefficient. hpf (s) represents the high-pass filter, and ξ represents the damping ratio of the high-pass filter.

[0040] In summary, the embodiments of the present invention provide a converter phase-locked control method and device. The method includes the following steps: S1, simulating the no-load operation of a synchronous generator and calculating the mechanical torque T under this condition. m S2. Calculate the excitation electromotive force amplitude E; S3. Calculate the instantaneous voltage sampling input value U at the converter grid connection point. g ∠θ g The electromagnetic power P is calculated from the excitation potential amplitude E and the stator electrical equations. e S4. According to the electromagnetic power P e and mechanical torque T m The rotor speed angular frequency ω is obtained through the rotor motion equation; S5, the rotor phase θ is calculated based on the rotor speed angular frequency ω, and the obtained rotor phase θ is used in the stator electrical equation in step S3. The technical solution of this embodiment of the invention is based on the self-synchronization principle of synchronous generators, replacing the conventional phase-locked loop with the rotor motion equation and replacing the converter terminal voltage phase detection with a virtual rotor phase, thus possessing self-synchronization characteristics to solve the synchronization and stability problem of grid-connected converters based on phase-locked control under weak power grids. The technical solution of this embodiment of the invention can be applied to distributed generation, energy storage, microgrids, and other fields to achieve stable operation of grid-connected converters connected to weak power grids. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of a typical converter circuit topology for which the converter phase-locked control method provided in this embodiment of the invention is applied;

[0042] Figure 2 This is a flowchart of the converter phase-locked control method provided in the embodiments of the present invention;

[0043] Figure 3 This is a block diagram of the converter phase-locked control device provided in an embodiment of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0045] The technical solutions of the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. An embodiment of the present invention provides a converter phase-locked control method. Figure 1 This is a schematic diagram of a typical converter circuit topology for the converter phase-locked control method provided in this embodiment of the invention, as shown below. Figure 1 As shown, the DC side is an energy storage battery, and the AC side is a three-phase AC power grid, with DC / AC conversion performed through the converter main circuit. The converter phase-locked control method of this embodiment incorporates the self-synchronization theory of synchronous generators into the converter phase detection algorithm for detection... Figure 1 The phase of the AC voltage position shown.

[0046] The flowchart of this method is as follows Figure 2 As shown, it includes the following steps:

[0047] S1. Simulate the no-load operation of a synchronous generator, given the mechanical torque T under this condition. m Initial value: T m =1. In this step, by setting the active power controller to a set value of 0, the synchronous machine is simulated to operate under no-load conditions. At this time, the power angle of the synchronous machine is 0, and the rotor phase is synchronized with the power grid.

[0048] S2. Initial value of the given excitation potential amplitude E: E = 0. In this step, by setting the internal potential controller to a fixed value of 1pu, the influence of grid voltage disturbances on excitation is ignored, and the internal potential remains stable when large disturbances such as grid fault ride-through occur.

[0049] S3. Based on the instantaneous voltage sampling input value U at the converter grid connection point. g ∠θ g The electromagnetic power P is calculated from the excitation potential amplitude E and the stator electrical equations. e The stator electrical equations are as follows:

[0050]

[0051] Where R is the virtual stator resistance, L is the virtual stator inductance, and I is the virtual stator current; the initial value of θ is θ = 0, and under steady state, Pe =T m *ω=0,θ=θ g That is, the rotor phase is synchronized with the power grid.

[0052] To avoid the impact of amplitude disturbances during grid voltage dips, the stator electrical equations are further simplified, and the relationship between the power angle (the difference between the rotor phase and the grid phase) and the generated power is as follows:

[0053]

[0054] Where X is the per-unit value of the stator impedance.

[0055] Phase detection only considers the relationship between active power and power angle, ignoring the influence of voltage amplitude. Therefore, Ug and E in the above equation can be set to a constant of 1.

[0056]

[0057] Where X is the per-unit value of the stator impedance, and θ is calculated according to step S5. g and cosθ g It can be obtained through the following formula:

[0058]

[0059] Among them, U a U b U c These are the instantaneous three-phase grid voltage values, U α U β These are the values ​​of the grid voltage in the two-phase stationary coordinate system, respectively.

[0060] To simplify the above stator electrical equations, an equivalent method is as follows: U g ∠θ g Projected onto the dq stationary coordinate system oriented with respect to the rotor phase θ, as follows:

[0061]

[0062] In the formula, U d U q These are the values ​​of the grid voltage projected onto the dq stationary coordinate system.

[0063]

[0064] S4. According to the electromagnetic power P e and mechanical torque T m The rotor speed angular frequency ω is obtained through the rotor motion equation. The rotor motion equation is:

[0065]

[0066] Where J is the rotor inertia, T d For the damping torque, K d G is the damping coefficient, ω0 is the rated angular frequency, and G is the damping coefficient. hpf (s) represents the high-pass filter, and ξ represents the damping ratio of the high-pass filter.

[0067] S5. Calculate the rotor phase θ based on the rotor speed angular frequency ω, and use the obtained rotor phase θ in the stator electrical equations of step S3. The rotor phase θ can be calculated according to the following formula:

[0068] θ = ωt.

[0069] The principle of the converter phase-locked control method described in this embodiment of the invention is that, during the grid-connected operation of a traditional synchronous generator, in steady state, its speed is synchronized with the grid, and the relationship between the power angle (the difference between the rotor phase and the grid phase) and the generated power is as follows:

[0070]

[0071] In the formula, U is the terminal voltage, E is the internal potential, and X is the stator impedance.

[0072] Neglecting losses, under steady state, the synchronous generator power Pe is equal to the mechanical power Pm input to the prime mover, that is: P e =P m =T m ·ω.

[0073] When the power generation P e When =0, it can be seen from the previous formula that the power angle is 0, that is, the difference between the rotor phase and the grid phase is 0.

[0074] Based on the above principles, a synchronous machine model is introduced into the converter control, and the active power controller is set with a mechanical torque T. m If the value is 0, the model will automatically adjust the work angle to make P... e =P m =0, after stabilization the power angle is 0, and the rotor phase is the same as the grid phase.

[0075] Traditional synchronous generators possess self-synchronizing voltage source characteristics, enabling them to operate stably in weak grid conditions and serve as parallel units to expand system capacity and enhance grid strength. Based on this principle, the aforementioned converter phase-locked loop (PLL) control method exhibits similar characteristics. In weak grid conditions, compared to conventional PLL control which generates disturbances and negative damping, this method actively supports the grid and provides positive damping, significantly improving the converter's operational stability in weak grid environments.

[0076] On the other hand, when dealing with large disturbances such as grid short-circuit faults, traditional synchronous generators require additional stabilization devices to maintain stable speed, inevitably resulting in significant speed fluctuations. Converters, during grid fault crossings, typically need to provide dynamic reactive power support based on the fault drop depth and meet accuracy requirements; therefore, the converter needs to maintain stable reference frequency and phase during the fault period. The converter phase-locked loop control method provided in this invention sets the internal electromotive force to a fixed value of 1 pu, avoiding the short-circuit excitation problem of traditional synchronous machines; it can flexibly adjust the damping coefficient to increase rotor damping, avoiding significant speed fluctuations during faults and maintaining frequency and phase stability.

[0077] An embodiment of the present invention also provides a converter phase-locked control device, including an active power controller module, an internal potential controller module, a stator electronic equation module, a rotor motion equation module, and a phase calculation module. A block diagram of the device is shown below. Figure 3 As shown.

[0078] The active power controller module is used to simulate the no-load operation of a synchronous generator, given the mechanical torque T under this condition. m The initial value is T m =1;

[0079] The internal electromotive force controller module is used to give the initial value of the excitation electromotive force amplitude E as E=0.

[0080] The stator electronic equation module is used to sample the input value U based on the instantaneous voltage at the converter grid connection point. g ∠θ g The electromagnetic power P is calculated from the excitation potential amplitude E and the stator electrical equations. e ;

[0081] The rotor motion equation module is used to determine the electromagnetic power P. e and mechanical torque T m The rotor speed angular frequency ω is obtained through the rotor motion equation;

[0082] The phase calculation module is used to calculate the rotor phase θ based on the rotor speed angular frequency ω, and use the obtained rotor phase θ for the calculation of the stator electrical equation module.

[0083] The process by which each module in the converter phase-locked control device of this invention realizes its function is the same as the steps in the converter phase-locked control method of the above embodiments, and will not be repeated here.

[0084] In summary, the embodiments of the present invention relate to a converter phase-locked control method and device. The method includes the following steps: S1, simulating the no-load operation of a synchronous generator and calculating the mechanical torque T under this operation. mS2. Calculate the excitation electromotive force amplitude E; S3. Calculate the instantaneous voltage sampling input value U at the converter grid connection point. g ∠θ g The electromagnetic power P is calculated from the excitation potential amplitude E and the stator electrical equations. e S4. According to the electromagnetic power P e and mechanical torque T m The rotor speed angular frequency ω is obtained through the rotor motion equation; S5, the rotor phase θ is calculated based on the rotor speed angular frequency ω, and the obtained rotor phase θ is used in the stator electrical equation in step S3. The technical solution of this embodiment of the invention is based on the self-synchronization principle of synchronous generators, replacing the conventional phase-locked loop with the rotor motion equation and replacing the converter terminal voltage phase detection with a virtual rotor phase, thus possessing self-synchronization characteristics to solve the synchronization and stability problem of grid-connected converters based on phase-locked control under weak power grids. The technical solution of this embodiment of the invention can be applied to distributed generation, energy storage, microgrids, and other fields to achieve stable operation of grid-connected converters connected to weak power grids.

[0085] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A converter phase-locked control method, characterized in that, Including the following steps: S1. Simulate the no-load operation of a synchronous generator, and provide the mechanical torque under this condition. Initial values: ; S2. Control the excitation electromotive force and set the amplitude of the excitation electromotive force. Initial values: ; S3. Sample the input value based on the instantaneous voltage at the converter's grid connection point. and the amplitude of the excitation potential Electromagnetic power is calculated using stator electrical equations. ; S4, based on the electromagnetic power and mechanical torque The rotor speed angular frequency is obtained through the rotor motion equation. The rotor motion equations include: in, For rotor inertia, For damping torque, The damping coefficient is... The rated angular frequency, For high-pass filters, The damping ratio of the high-pass filter; S5, based on the rotor speed angular frequency Calculate rotor phase and the obtained rotor phase Stator electrical equations used in step S3; The stator electrical equations include: in, This is a virtual stator resistance. For virtual stator inductance, This is a virtual stator current; The initial value is Under steady state, , That is, the rotor phase is synchronized with the power grid.

2. The method according to claim 1, characterized in that, In step S1, the synchronous generator power angle is 0, and the rotor phase is synchronized with the power grid.

3. The method according to claim 2, characterized in that, and It is obtained through the following formula: in, , , These are the instantaneous three-phase grid voltage values, , These are the values ​​of the grid voltage in the two-phase stationary coordinate system, respectively.

4. The method according to claim 1, characterized in that, Calculate the rotor phase using the following formula. : 。 5. A converter phase-locked control device, characterized in that, It includes an active power controller module, an internal electromotive force controller module, a stator electronic equation module, a rotor motion equation module, and a phase calculation module; among which, The active power controller module is used to simulate the no-load operation of a synchronous generator and provide the mechanical torque under this condition. Initial values: ; The internal potential controller module is used to control the excitation potential and provide the amplitude of the excitation potential. Initial values: ; The stator electronic equation module is used to sample the input value based on the instantaneous voltage at the converter grid connection point. and the amplitude of the excitation potential Electromagnetic power is calculated using stator electrical equations. ; The rotor motion equation module is used to determine the electromagnetic power. and mechanical torque The rotor speed angular frequency is obtained through the rotor motion equation. The rotor motion equations include: in, For rotor inertia, For damping torque, The damping coefficient is... The rated angular frequency, For high-pass filters, The damping ratio of the high-pass filter; The phase calculation module is used to calculate the rotor speed angular frequency based on the phase calculation module. Calculate rotor phase and the obtained rotor phase Used for calculations in the stator electrical equations module; The stator electrical equations include: in, This is a virtual stator resistance. For virtual stator inductance, This is a virtual stator current; The initial value is Under steady state, , That is, the rotor phase is synchronized with the power grid.

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