Method and apparatus for smooth switching between net following control and net building control

Abstract

The application discloses a kind of smooth switching method and device of follow network control and construct network control, when energy storage converter is in follow network control operating state, the droop constraint consistent with construct network control is introduced in follow network control power outer ring, the active-frequency and reactive-voltage balance steady-state relationship of follow network control is matched with construct network control, and unified steady-state operation reference is formed;According to current operating mode and target switching mode, the initial value of construct network controller or the initial value of follow network controller is calculated and obtained;In switching moment, the initial value of construct network controller is assigned to construct network controller or the initial value of follow network controller is assigned to follow network controller, so that reference coordinate system, equivalent internal potential, reactive-voltage balance relationship, voltage outer loop integral state before and after switching are matched, and smooth switching is completed.The application solves the problems of voltage and current impact and power oscillation in the prior art during switching.

Description

Technical Field

[0001] This invention relates to the field of energy storage grid-connected converter control technology, specifically to a method and apparatus for smooth switching between grid-following control and grid-connected control. Background Technology

[0002] With the large-scale grid connection of new energy sources such as wind power and photovoltaics, the power system is gradually exhibiting characteristics of low inertia, weak damping, and power electronics. Energy storage converters, with their bidirectional energy flow and rapid power regulation capabilities, can provide flexible active, reactive, and voltage / frequency support during new energy fluctuations and grid disturbances. This places higher demands on the grid connection adaptability and stability support capabilities of energy storage converters. Grid-following control typically relies on PLLs to obtain the voltage phase angle at the grid connection point and achieves power tracking in the form of a current source, suitable for strong grid connection scenarios. Grid-building control, on the other hand, establishes voltage and frequency references through active-frequency and reactive-voltage control relationships, providing voltage and frequency support capabilities, and is more suitable for weak grids or islanded operation scenarios.

[0003] Because grid-following control and grid-building control differ in reference coordinate systems, steady-state equilibrium points, and integral states of the control loop, direct mode switching can easily cause voltage and current surges, as well as active and reactive power oscillations. Existing grid-following / grid-building switching methods often reduce switching disturbances through state tracking, pre-synchronization, amplitude and phase synchronization, reference quantity smoothing, or operating point matching. However, in the presence of virtual impedance and multi-loop controller integral states, smoothing only reference quantities or current commands may still lead to problems such as discontinuous internal potential phase angles, shifts in the reactive power-voltage balance, or mismatches in the voltage outer loop integral states after grid-building control takes over.

[0004] Therefore, there is an urgent need for a smooth switching method between grid-following control and grid-building control to solve the problems of voltage and current surges and power oscillations that exist in existing technologies during switching. Summary of the Invention

[0005] To address this, the present invention provides a method and apparatus for smooth switching between grid-following control and grid-building control, solving problems such as voltage and current surges and power oscillations during switching in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for smooth switching between network tracking control and network construction control, comprising:

[0007] When the energy storage converter is in grid-connected control operation, a droop constraint consistent with the grid-connected control is introduced into the outer power loop of the grid-connected control. Based on the droop constraint, the active-frequency and reactive-voltage balance steady-state relationships of the grid-connected control are matched with those of the grid-connected control to form a unified steady-state operation benchmark.

[0008] Based on the unified steady-state operating benchmark, the initial value of the network controller or the initial value of the network controller are calculated according to the current operating mode and the target switching mode.

[0009] At the moment of switching, the initial value of the grid-building controller is assigned to the grid-building controller or the initial value of the grid-following controller is assigned to the grid-following controller, so that the reference coordinate system, equivalent internal potential, reactive power-voltage balance relationship and voltage outer loop integral state before and after switching are matched, thus completing a smooth switching.

[0010] As a preferred method for smoothly switching between grid-following control and grid-building control, during the calculation of the initial values ​​of the grid-building controller or the grid-following controller, before switching from grid-building control to grid-following control, the phase angle of the grid-connected point voltage vector is calculated based on the d-axis and q-axis components of the grid-connected point voltage in the grid-building control reference coordinate system and the phase angle of the grid-building control reference coordinate system, and the output phase angle of the grid-following control PLL is initialized; before switching from grid-following control to grid-building control, the initial values ​​of the reference coordinate system phase angle, the initial values ​​of the reactive power outer loop integrator, and the initial values ​​of the voltage outer loop d-axis and q-axis integrators of the grid-building controller are calculated based on the grid-connected point voltage, current, and virtual impedance parameters in the controller.

[0011] As a preferred method for smoothly switching between grid-following control and grid-building control, a droop constraint consistent with that of grid-building control is introduced into the outer power loop of grid-following control. The expression for the dq-axis current reference value under grid-following control is as follows:

[0012]

[0013] In the formula, i dref,GFL i qref,GFL These are the reference values ​​for the dq-axis current under wire mesh control; P ref Active power command; Q ref This is the reactive power command; ω0 is the rated angular frequency; ω is the angular frequency; D p k is the active damping coefficient. f V is the active-frequency droop factor. ref V is the voltage reference value; k is the voltage amplitude; k is the voltage reference value. q The reactive power-voltage droop factor; v od,GFL The output voltage of the d-axis in the coordinate system of the grid control system.

[0014] As a preferred method for smoothly switching between grid-connected control and grid-connected control, the formula for calculating the phase angle of the grid connection point voltage vector is:

[0015]

[0016]

[0017] In the formula, The phase angle of the voltage vector at the grid connection point is the initial value of the phase angle output by the grid-connected control PLL phase-locked loop. To control the output phase angle of the network; The phase angle deviation of the grid connection point voltage relative to the d-axis of the GFM reference coordinate system; v od,GFM v oq,GFM These are the grid connection point voltages on the dq axis in the GFM reference coordinate system.

[0018] As a preferred method for smoothly switching between network tracking control and network construction control, the initial value of the phase angle of the reference coordinate system of the network construction controller is calculated using the following formula:

[0019]

[0020]

[0021] In the formula, The initial value of the phase angle for the reference coordinate system; To control the output phase angle of the grid; E represents the phase angle deviation of the internal potential of the GFM relative to the GFL coordinate system. d,GFL and E q,GFL These are the internal potentials of the d-axis and q-axis of the network control system under the reference coordinate system for network control, respectively.

[0022] The formula for calculating the initial value of the reactive power outer loop integrator is as follows:

[0023]

[0024] In the formula, This is the initial value for the reactive outer loop integrator;

[0025] The formula for calculating the initial values ​​of the voltage outer loop d-axis and q-axis integrators is as follows:

[0026]

[0027]

[0028] In the formula, , These are the initial output values ​​of the voltage outer loop d-axis and q-axis integrators in the GFM reference coordinate system, respectively; Δθ GFL The phase angle difference between the GFL reference coordinate system and the GFM reference coordinate system; u xd,GFL u xq,GFL These are the initial output values ​​of the voltage outer loop d-axis and q-axis integrators in the GFL reference coordinate system, respectively.

[0029] This invention also provides a smooth switching device for network tracking control and network construction control, employing the above-mentioned smooth switching method for network tracking control and network construction control, including:

[0030] A unified steady-state operating benchmark forming module is used to introduce a droop constraint consistent with the grid-connected control in the outer loop of the grid-connected control power when the energy storage converter is in grid-connected control operation state; based on the droop constraint, the active-frequency and reactive-voltage balance steady-state relationship of the grid-connected control is matched with the grid-connected control to form a unified steady-state operating benchmark.

[0031] The initial value calculation module for the network construction controller and the network follower controller is used to calculate the initial value of the network construction controller or the initial value of the network follower controller based on the unified steady-state operation benchmark and according to the current operation mode and the target switching mode.

[0032] The smooth switching module is used to assign the initial value of the grid-building controller to the grid-building controller or the initial value of the following controller to the following controller at the moment of switching, so that the reference coordinate system, equivalent internal potential, reactive power-voltage balance relationship and voltage outer loop integral state are matched before and after switching, thus completing the smooth switching.

[0033] As a preferred embodiment of a smooth switching device between grid-following control and grid-building control, in the process of calculating the initial value of the grid-building controller and the grid-following controller, before switching from grid-building control to grid-following control, the phase angle of the grid-connected point voltage vector is calculated based on the d-axis and q-axis components of the grid-connected point voltage in the grid-building control reference coordinate system and the phase angle of the grid-building control reference coordinate system, and the phase angle of the output phase angle of the grid-following control PLL is initialized; before switching from grid-following control to grid-building control, the initial value of the phase angle of the grid-connected controller reference coordinate system, the initial value of the reactive power outer loop integrator, and the initial value of the voltage outer loop d-axis and q-axis integrator are calculated based on the grid-connected point voltage, current, and virtual impedance parameters in the controller.

[0034] As a preferred embodiment of a smooth switching device between grid-following control and grid-building control, the unified steady-state operating reference forming module introduces a droop constraint consistent with that of grid-building control in the outer power loop of grid-following control. The expression for the dq-axis current reference value under grid-following control is as follows:

[0035]

[0036] In the formula, i dref,GFL i qref,GFL These are the reference values ​​for the dq-axis current under wire mesh control; P ref Active power command; Q ref This is the reactive power command; ω0 is the rated angular frequency; ω is the angular frequency; D p k is the active damping coefficient. f V is the active-frequency droop factor. ref V is the voltage reference value; k is the voltage amplitude; k is the voltage reference value. qThe reactive power-voltage droop factor; v od,GFL The output voltage of the d-axis in the coordinate system of the grid control system.

[0037] As a preferred embodiment of a smooth switching device between grid-following control and grid-building control, the calculation formula for the phase angle of the grid-connected point voltage vector in the initial value calculation module of the grid-building controller and the grid-following controller is as follows:

[0038]

[0039]

[0040] In the formula, The phase angle of the voltage vector at the grid connection point is the initial value of the phase angle output by the grid-connected control PLL phase-locked loop. To control the output phase angle of the network; The phase angle deviation of the grid connection point voltage relative to the d-axis of the GFM reference coordinate system; v od,GFM v oq,GFM These are the grid connection point voltages on the dq axis in the GFM reference coordinate system.

[0041] As a preferred embodiment of a smooth switching device between network tracking control and network construction control, the calculation formula for the initial value of the reference coordinate system phase angle of the network construction controller in the network construction controller and the initial value calculation module of the network tracking controller is as follows:

[0042]

[0043]

[0044] In the formula, The initial value of the phase angle for the reference coordinate system; To control the output phase angle of the grid; E represents the phase angle deviation of the internal potential of the GFM relative to the GFL coordinate system. d,GFL and E q,GFL These are the internal potentials of the d-axis and q-axis of the network control system under the reference coordinate system for network control, respectively.

[0045] The formula for calculating the initial value of the reactive power outer loop integrator is as follows:

[0046]

[0047] In the formula, This is the initial value for the reactive outer loop integrator;

[0048] The formula for calculating the initial values ​​of the voltage outer loop d-axis and q-axis integrators is as follows:

[0049]

[0050]

[0051] In the formula, , These are the initial output values ​​of the voltage outer loop d-axis and q-axis integrators in the GFM reference coordinate system, respectively; Δθ GFL The phase angle difference between the GFL reference coordinate system and the GFM reference coordinate system; u xd,GFL u xq,GFL These are the initial output values ​​of the voltage outer loop d-axis and q-axis integrators in the GFL reference coordinate system, respectively.

[0052] The present invention has the following advantages:

[0053] First, this invention adaptively adjusts the power outer loop of the grid-following controller and introduces a droop constraint consistent with the grid-building control in the grid-following control, so that the grid-following and grid-building controls have the same steady-state balance relationship before and after the switching, thereby reducing transient impacts and power oscillations during the switching process.

[0054] Secondly, this invention considers the influence of virtual impedance on the phase angle relationship between the grid control reference coordinate system and the grid construction control reference coordinate system. Based on the grid connection point voltage, current and virtual impedance voltage drop, the internal potential of the grid construction control and the initial value of the phase angle of the reference coordinate system are calculated. This can avoid the switching impact caused by only matching the voltage amplitude and ignoring the phase angle deviation, and improve the phase angle continuity when switching control modes.

[0055] Third, based on the steady-state operating data under the grid control state before switching, this invention calculates the initial values ​​of the reactive power outer loop integrator and the voltage outer loop dq-axis integrator of the grid control, and transforms the relevant initial values ​​to the grid control reference coordinate system through coordinate rotation. This can avoid the grid controller from re-establishing the control balance point from zero initial value or default initial value at the moment of switching, reduce voltage outer loop integral sudden change and continuous integral error, and improve the smoothness of the switching process.

[0056] Fourth, when switching from grid-based control to grid-following control, this invention calculates the phase angle of the grid-connected point voltage vector based on the d-axis and q-axis components of the grid-connected point voltage in the grid-based control reference coordinate system and the phase angle of the grid-based control reference coordinate system. This phase angle is then used as the initial value of the output phase angle of the grid-following control PLL, ensuring that the grid-following control reference coordinate system remains consistent with the grid-connected point voltage vector at the moment of switching. This reduces the transient impact caused by sudden changes in the PLL phase angle and improves the smoothness of the switch from grid-based control to grid-following control. Attached Figure Description

[0057] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0058] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0059] Figure 1 This is a flowchart illustrating a smooth switching method between network tracking control and network construction control provided in Embodiment 1 of the present invention.

[0060] Figure 2 This is a schematic diagram of the dual-mode control and switching structure of the energy storage converter and grid / grid construction in one possible embodiment of Embodiment 1 of the present invention;

[0061] Figure 3 This is a schematic diagram of the output power response curve during the network / network switching process in a possible embodiment of the present invention where a smooth switching strategy is not adopted;

[0062] Figure 4 This is a schematic diagram of the output power response curve during the network / network switching process when the smooth switching strategy of the present invention is adopted in one possible embodiment of Embodiment 1 of the present invention;

[0063] Figure 5 This is a schematic diagram of the output power response curve when a smooth switching strategy is adopted under power command disturbance in one possible embodiment of Embodiment 1 of the present invention;

[0064] Figure 6 This is a schematic diagram of the output power response curve when the smooth switching strategy of the present invention is used under grid voltage disturbance in one possible embodiment of Embodiment 1 of the present invention;

[0065] Figure 7 This is a schematic diagram of the output power response curve when the smooth switching strategy of the present invention is used under grid frequency disturbance in one possible embodiment of Embodiment 1 of the present invention;

[0066] Figure 8This is a schematic diagram of the architecture of a smooth switching device for network control and network construction control provided in Embodiment 2 of the present invention. Detailed Implementation

[0067] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0068] Example 1

[0069] See Figure 1 Embodiment 1 of the present invention provides a method for smooth switching between network tracking control and network construction control, comprising the following steps:

[0070] S1. When the energy storage converter is in grid-connected control operation, a droop constraint consistent with the grid-connected control is introduced into the outer power loop of the grid-connected control; based on the droop constraint, the active-frequency and reactive-voltage balance steady-state relationship of the grid-connected control is matched with that of the grid-connected control to form a unified steady-state operation benchmark.

[0071] S2. Based on the unified steady-state operation benchmark, calculate the initial value of the network controller or the initial value of the network controller according to the current operation mode and the target switching mode;

[0072] S3. At the moment of switching, the initial value of the network controller is assigned to the network controller or the initial value of the grid controller is assigned to the grid controller, so that the reference coordinate system, equivalent internal potential, reactive power-voltage balance relationship and voltage outer loop integral state before and after switching are matched, and a smooth switching is completed.

[0073] In this embodiment, in step S1, when the energy storage converter is in the grid-following control operation state, a droop constraint consistent with the grid-building control is introduced into the outer power loop of the grid-following control; based on the droop constraint, the active-frequency and reactive-voltage balance steady-state relationship of the grid-following control is matched with that of the grid-building control, forming a unified steady-state operation benchmark.

[0074] Specifically, energy storage converters mainly include two control modes: grid-connected control and grid-following control. Grid-connected control includes active-frequency control, reactive-voltage control, virtual impedance, voltage control loop, and current control loop. Grid-following control includes SRF-PLL phase-locked loop, power outer loop control, and current control loop.

[0075] In this embodiment, a dq coordinate system is adopted, with the d-axis along the x-axis and the q-axis along the -y-axis. The positive direction of the current is taken as the output direction of the converter to the AC side. P and Q represent the active power and reactive power output by the converter to the AC side, respectively. Under this coordinate system, v odq,GFL and i odq,GFL These are the dq components of the output voltage and output current in the grid control coordinate system, respectively. odq,GFM and i odq,GFM These represent the dq components of the output voltage and output current in the grid control coordinate system. In this embodiment, considering that the filter capacitor current is relatively small compared to the converter output current, to simplify the initial value calculation, the influence of the filter capacitor current on the reactive power calculation is ignored, and the filter inductor current is approximately considered to be consistent with the grid-connected output current. Therefore, the reactive power obtained in grid-following control based on the grid connection point voltage and the filter inductor current can be considered consistent with the reactive power obtained in grid-connecting control based on the grid connection point voltage and the grid-connected output current.

[0076] In this embodiment, since grid-following control typically uses a power command method, while grid-forming control typically uses droop control, the two control methods differ in their steady-state equilibrium point formation mechanisms. To ensure that the steady-state operating point remains consistent before and after the switch, a droop constraint consistent with that of grid-forming control is introduced into the outer power loop of grid-following control. Therefore, the expression for the dq-axis current reference value under grid-following control is:

[0077]

[0078] In the formula, i dref,GFL i qref,GFL These are the reference values ​​for the dq-axis current under wire mesh control; P ref Active power command; Q ref This is the reactive power command; ω0 is the rated angular frequency; ω is the angular frequency; D p k is the active damping coefficient. f V is the active-frequency droop factor. ref V is the voltage reference value; k is the voltage amplitude; k is the voltage reference value. q The reactive power-voltage droop factor; v od,GFL The output voltage of the d-axis in the coordinate system of the grid control system.

[0079] Therefore, under the same operating conditions, grid-connected control and grid-connected control have consistent steady-state grid-connected voltage, grid-connected current, and reactive power-voltage balance relationship, providing a steady-state basis for the initial value matching of the phase angle and integral link of subsequent grid-connected control.

[0080] In this embodiment, in step S2, based on the unified steady-state operating benchmark, the initial value of the network controller or the initial value of the network controller is calculated according to the current operating mode and the target switching mode.

[0081] Specifically, during the switching between the two control modes, the current loop integrator does not require special initial value matching because the current loop has a faster response speed.

[0082] In the process of calculating and obtaining the initial value of the grid-building controller or the grid-following controller, before switching from grid-building control to grid-following control, the phase angle of the grid-connected point voltage vector is calculated based on the d-axis and q-axis components of the grid-connected point voltage in the grid-building control reference coordinate system and the phase angle of the grid-building control reference coordinate system, and the output phase angle of the grid-following control PLL is initialized; before switching from grid-following control to grid-building control, the initial value of the phase angle of the grid-building controller's reference coordinate system, the initial value of the reactive power outer loop integrator, and the initial value of the voltage outer loop d-axis and q-axis integrator are calculated based on the grid-connected point voltage, current, and virtual impedance parameters in the controller.

[0083] When switching from grid-connected control to grid-following control, the function of the PLL phase-locked loop is to align the d-axis of the grid-following control reference coordinate system with the grid-connected point voltage vector. Therefore, the initial value of the PLL phase angle should be the absolute phase angle of the grid-connected point voltage.

[0084] The grid connection point voltage is v in the GFM reference coordinate system. od,GFM v oq,GFM The phase angle of the network control output is θ GFM Then the phase angle deviation of the grid connection point voltage relative to the d-axis of the GFM reference coordinate system is:

[0085]

[0086] In the formula, The phase angle deviation of the grid connection point voltage relative to the d-axis of the GFM reference coordinate system; v od,GFM v oq,GFM These are the grid connection point voltages on the dq axis in the GFM reference coordinate system.

[0087] At the switching time t between GFM and GFL s The phase angle integral state of the PLL phase-locked loop in the GFL control, i.e., the output phase angle of the PLL, is assigned the following value:

[0088]

[0089] In the formula, The phase angle of the voltage vector at the grid connection point is the initial value of the phase angle output by the grid-connected control PLL phase-locked loop. The phase angle is used to control the output phase angle of the network.

[0090] In this embodiment, when switching from grid-following control to grid-building control, it is necessary to ensure the continuity of the phase angle of the potential vector within the grid-building control system at the instant of switching. Based on the virtual impedance relationship, the potential within the GFM in the GFL reference coordinate system can be expressed as:

[0091]

[0092] In the formula, E d,GFL and E q,GFL These are the internal potentials along the d-axis and q-axis of the network control system in the reference coordinate system for network control; v od,GFL and v oq,GFL These represent the d-axis and q-axis voltages of the grid-connected point in the grid control reference coordinate system, respectively; i od,GFL and i oq,GFL These represent the d-axis and q-axis currents of the grid connection point in the grid control reference coordinate system, respectively; R v For virtual resistance; L v This is a virtual inductance.

[0093] Therefore, the phase angle deviation of the internal potential of the GFM relative to the GFL coordinate system is:

[0094]

[0095] In the formula, Δθ GFL This represents the phase angle difference between the GFL reference coordinate system and the GFM reference coordinate system.

[0096] Therefore, the initial phase angle of the GFM reference coordinate system is:

[0097]

[0098] In the formula, The initial value of the phase angle for the reference coordinate system; To control the output phase angle of the network.

[0099] At the switching time t when GFL switches to GFM s The phase angle integral element state in the GFM active-frequency control, i.e., the output phase angle of the network control, is assigned the following value:

[0100]

[0101] In this embodiment, the component E of the internal potential of the GFM in the GFL coordinate system is obtained from the aforementioned calculation. d,GFL E q,GFL Then the potential amplitude within the GFM reactive power control loop is:

[0102]

[0103] In the formula, E GFL Let be the magnitude of the internal potential of the GFM in the GFL reference coordinate system.

[0104] Since reactive power-voltage constraints consistent with those of grid-connected control were introduced into the reactive power loop of the grid-connected control system before the switchover, the PI controller input of the outer reactive power loop of the grid-connected control system can be considered zero at the steady-state operating point before the switchover. At this time, the output of the PI controller in the outer reactive power loop is determined by the steady-state output of the integral element. Defining the steady-state value of the integrator output of the outer reactive power loop of the grid-connected control system as ΔE0, then:

[0105]

[0106] At the switching time t when GFL switches to GFM s The initial value of the reactive power outer loop integrator under GFM control is assigned as follows:

[0107]

[0108] In this embodiment, the equipment has reached equilibrium at the steady-state operating point before switching. At this time, the initial output value of the voltage outer loop dq-axis integrator in the GFL reference coordinate system can be obtained by inverse solving based on the steady-state output relationship of the grid control voltage outer loop:

[0109]

[0110] In the formula, u xd,GFL u xq,GFL These are the initial output values ​​of the voltage outer loop d-axis and q-axis integrators in the GFL reference coordinate system, respectively; i dref,GFL i qref,GFL This is the reference value for the filter current before switching; i od,GFL i oq,GFL This is the grid-connected current before switching; v od,GFL v oq,GFL The output voltage before switching; F is the current feedforward coefficient, C f This is a filter capacitor.

[0111] Since the integrator's initial value is in the grid control reference coordinate system, it is necessary to perform coordinate rotation based on the phase angle difference between the grid control reference coordinate system and the grid control reference coordinate system to obtain the initial value of the voltage outer loop integrator in the grid control reference coordinate system:

[0112]

[0113] In the formula, , These are the initial output values ​​of the voltage outer loop d-axis and q-axis integrators in the GFM reference coordinate system, respectively; Δθ GFL This represents the phase angle difference between the GFL reference coordinate system and the GFM reference coordinate system.

[0114]

[0115] At the switching time t when GFL switches to GFMs The output of the GFM voltage outer loop integrator is assigned the following value:

[0116]

[0117] In the formula, , These are the initial output values ​​of the voltage outer loop d-axis and q-axis integrators in the GFM reference coordinate system, respectively.

[0118] In this embodiment, in step S3, at the moment of switching, the initial value of the network controller is assigned to the network controller or the initial value of the grid controller is assigned to the grid controller, so that the reference coordinate system, equivalent internal potential, reactive power-voltage balance relationship, and voltage outer loop integral state before and after switching are matched, thus completing a smooth switching.

[0119] Specifically, after the assignment is completed, when switching from grid-based control to grid-following control, the phase angle of the PLL phase-locked loop output remains consistent with the phase angle of the voltage vector at the grid connection point before the switch. When switching from grid-following control to grid-based control, the grid-based controller has a reference coordinate system phase angle, internal potential amplitude, reactive power-voltage balance relationship, and voltage outer loop integral state that match the grid-following control operating state before the switch at the moment of takeover, realizing a smooth bidirectional switch between grid-following control and grid-based control.

[0120] In one possible implementation, a verification example is provided as follows:

[0121] like Figure 2 As shown, L f C is the AC side filter inductor of the converter. f For the filter capacitor, L c The inductance is the interconnection inductance between the converter's grid connection point and the power grid, i is the filter inductor current, and v is the inductor current. o i is the voltage at the converter's grid connection point. o For the converter output current, This is the converter voltage modulation command.

[0122] In network control mode, the SRF-PLL phase-locked loop uses v oq,GFL As input, generate angular frequency ω and phase angle θ. GFL Where ω0 is the reference value of the rated angular frequency; the power outer loop is based on the active power command P ref Reactive power command Q ref Voltage reference value V ref And the grid connection point voltage amplitude V, generating the current reference value i in grid-connected mode. dref,GFL and i qref,GFL .

[0123] In network control mode, the active power-frequency control loop operates based on the output active power P and the active power command P. refThe rated angular frequency ω0 generates the angular frequency ω and phase angle θ. GFM , where k f D is the active-frequency droop factor. p J is the active power damping coefficient, and J is the virtual inertia coefficient; the reactive power-voltage control loop is based on the output reactive power Q and the reactive power command Q. ref Output voltage amplitude V and voltage reference value V ref Generate voltage amplitude command E, where k q This is the reactive power-voltage droop factor. The grid voltage control loop is based on v dref,GFM v qref,GFM v od,GFM v oq,GFM i od,GFM and i oq,GFM Current reference value i in the generation network mode dref,GFM and i qref,GFM , where R v For virtual resistance, L v ω0 is the virtual inductance, F is the current feedforward coefficient, and ω0 is the rated angular frequency.

[0124] The GFM / GFL control mode switching module selects the corresponding coordinate transformation angle, voltage feedback quantity, and current reference value according to the current operating mode. When the converter operates in grid-connected control mode, θ is selected. GFL i dref,GFL i qref,GFL v od,GFL and v oq,GFL As the input to the current control loop; when the converter operates in grid control mode, θ is selected. GFM i dref,GFM i qref,GFM v od,GFM and v oq,GFM This serves as the input to the current control loop. The current control loop generates a modulation voltage command in the dq coordinate system based on the selected current reference value and current feedback value. and The three-phase modulation voltage command is obtained after dq / abc coordinate transformation. And the converter switching control signal is generated through the PWM module.

[0125] The control parameters for this embodiment are shown in Table 1:

[0126]

[0127] Table 1 System Parameters

[0128] Grid connection simulation condition 1:

[0129] The power outer loop of the grid-connected control uses the power reference value divided by the voltage amplitude to generate the current reference value. For example... Figure 3 As shown, without any smooth switching strategy, the output reactive power steady-state value changes when switching from grid-based control to grid-following control at 20s. When switching from grid-following control to grid-based control at 30s, both the output active power and reactive power show obvious oscillations.

[0130] Grid connection simulation condition 2:

[0131] like Figure 4 As shown, using the grid-to-grid switching strategy proposed in this invention, the system can directly switch from grid-to-grid control to grid-to-grid control at 20s, and both active and reactive power outputs can achieve a smooth transition. At 30s, the system can also directly switch from grid-to-grid control to grid-to-grid control, and both active and reactive power outputs can be smoothly switched.

[0132] Grid connection simulation condition 3:

[0133] like Figure 5 As shown, the grid-following / grid-building smooth switching strategy proposed in this invention switches from grid-building control to grid-following control at 20s, increases the active power reference value by 0.1pu at 25s, and switches back to grid-building control at 30s. Simulation results show that even when the power command changes, the output active and reactive power can still achieve smooth switching.

[0134] Grid connection simulation condition 4:

[0135] like Figure 6 As shown, using the grid-following / grid-building smooth switching strategy proposed in this invention, the system switches from grid-building control to grid-following control at 20s, the grid voltage drops by 0.1 pu at 25s, and switches back from grid-following control to grid-building control at 30s. Simulation results show that even under grid voltage disturbances, the output active and reactive power can still achieve smooth switching.

[0136] Grid connection simulation condition 5:

[0137] like Figure 7 As shown, using the grid-following / grid-building smooth switching strategy proposed in this invention, the system switches from grid-building control to grid-following control at 20s, the grid frequency drops by 0.1Hz at 25s, and switches back to grid-building control at 30s. Simulation results show that even under grid frequency disturbances, the output active and reactive power can still achieve smooth switching.

[0138] The application scenarios of this invention are as follows:

[0139] In the scenario of grid-connected operation of new energy supporting energy storage converters in a strong power grid, this invention can achieve a smooth switch from grid-based mode to grid-connected mode, reducing power fluctuations caused by the switch.

[0140] In scenarios where wind, solar, and energy storage systems operate under load for extended periods in weak power grids, this invention can match the steady-state operating relationship between two control modes and reduce transient disturbances during mode switching.

[0141] When the energy storage converter switches from islanded operation to grid-connected operation, this invention ensures stable voltage and current during the switching process by matching the coordinate system with the initial integral value.

[0142] In energy storage operation scenarios where grid voltage and frequency experience minor disturbances, this invention can maintain stable power output during mode switching and improve equipment operational reliability.

[0143] In converter operation scenarios where energy storage power commands are dynamically adjusted, this invention adapts to power change conditions and achieves seamless switching between grid connection and grid connection without significant impact.

[0144] It should be noted that the method of this disclosure embodiment can be executed by a single device, such as a computer or server. The method of this embodiment can also be applied to a distributed scenario, where multiple devices cooperate to complete the task. In such a distributed scenario, one of these devices may execute only one or more steps of the method of this disclosure embodiment, and the multiple devices will interact with each other to complete the method described.

[0145] It should be noted that the above description describes some embodiments of this disclosure. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recorded in the claims can be performed in a different order than that shown in the above embodiments and still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0146] Example 2

[0147] See Figure 8 Embodiment 2 of the present invention also provides a smooth switching device for network tracking control and network construction control, comprising:

[0148] The unified steady-state operating benchmark forming module 001 is used to introduce a droop constraint consistent with the grid-connected control in the outer loop of the grid-connected control power when the energy storage converter is in the grid-connected control operation state; based on the droop constraint, the active-frequency and reactive-voltage balance steady-state relationship of the grid-connected control is matched with the grid-connected control to form a unified steady-state operating benchmark.

[0149] The initial value calculation module 002 for the network construction controller and the network follower controller is used to calculate the initial value of the network construction controller or the initial value of the network follower controller based on the unified steady-state operation benchmark and according to the current operation mode and the target switching mode.

[0150] The smooth switching module 003 is used to assign the initial value of the grid-building controller to the grid-building controller or the initial value of the following controller to the following controller at the moment of switching, so that the reference coordinate system, equivalent internal potential, reactive power-voltage balance relationship and voltage outer loop integral state before and after switching are matched to complete the smooth switching.

[0151] In this embodiment, in the initial value calculation module 002 of the grid-building controller and the grid-following controller, during the process of calculating the initial value of the grid-building controller or the initial value of the grid-following controller, before switching from grid-building control to grid-following control, the phase angle of the grid-connected point voltage vector is calculated based on the d-axis and q-axis components of the grid-connected point voltage in the grid-building control reference coordinate system and the phase angle of the grid-building control reference coordinate system, and the phase angle of the output phase angle of the grid-following control PLL is initialized; before switching from grid-following control to grid-building control, the initial value of the reference coordinate system phase angle of the grid-building controller, the initial value of the reactive power outer loop integrator, and the initial value of the voltage outer loop d-axis and q-axis integrator are calculated based on the grid-connected point voltage, current, and virtual impedance parameters in the controller.

[0152] In this embodiment, the unified steady-state operating reference forming module 001 introduces a droop constraint consistent with the grid-based control in the outer loop of the grid-following control power. The expression for the dq-axis current reference value under grid-following control is as follows:

[0153]

[0154] In the formula, i dref,GFL i qref,GFL These are the reference values ​​for the dq-axis current under wire mesh control; P ref Active power command; Q ref This is the reactive power command; ω0 is the rated angular frequency; ω is the angular frequency; D p k is the active damping coefficient. f V is the active-frequency droop factor. ref V is the voltage reference value; k is the voltage amplitude; k is the voltage reference value. q The reactive power-voltage droop factor; v od,GFL The output voltage of the d-axis in the coordinate system controlled by the grid.

[0155] In this embodiment, the calculation formula for the phase angle of the grid connection point voltage vector in the initial value calculation module 002 of the grid-connected controller and the grid-following controller is as follows:

[0156]

[0157]

[0158] In the formula, The phase angle of the voltage vector at the grid connection point is the initial value of the phase angle output by the grid-connected control PLL phase-locked loop. To construct the network control output phase angle; The phase angle deviation of the grid connection point voltage relative to the d-axis of the GFM reference coordinate system; v od,GFM v oq,GFM These are the grid connection point voltages on the dq axis in the GFM reference coordinate system.

[0159] In this embodiment, in the initial value calculation module 002 of the network construction controller and the network tracking controller, the calculation formula for the initial value of the reference coordinate system phase angle of the network construction controller is as follows:

[0160]

[0161]

[0162] In the formula, The initial value of the phase angle for the reference coordinate system; To control the output phase angle of the grid; E represents the phase angle deviation of the internal potential of the GFM relative to the GFL coordinate system. d,GFL and E q,GFL These are the internal potentials of the d-axis and q-axis of the network control system under the reference coordinate system for network control, respectively.

[0163] The formula for calculating the initial value of the reactive power outer loop integrator is as follows:

[0164]

[0165] In the formula, This is the initial value for the reactive outer loop integrator;

[0166] The formula for calculating the initial values ​​of the voltage outer loop d-axis and q-axis integrators is as follows:

[0167]

[0168]

[0169] In the formula, , These are the initial output values ​​of the voltage outer loop d-axis and q-axis integrators in the GFM reference coordinate system, respectively; Δθ GFL The phase angle difference between the GFL reference coordinate system and the GFM reference coordinate system; u xd,GFL u xq,GFL These are the initial output values ​​of the voltage outer loop d-axis and q-axis integrators in the GFL reference coordinate system, respectively.

[0170] It should be noted that the information interaction and execution process between the modules of the above system are based on the same concept as the method embodiment in Embodiment 1 of this application, and the resulting technical effects are the same as those in the method embodiment of this application. For details, please refer to the description in the method embodiment shown above in this application, and it will not be repeated here.

[0171] Example 3

[0172] Embodiment 3 of the present invention provides a non-transitory computer-readable storage medium storing program code for a smooth switching method of network tracking control and network construction control. The program code includes instructions for executing the smooth switching method of network tracking control and network construction control according to Embodiment 1 or any possible implementation thereof.

[0173] Computer-readable storage media can be any available medium that a computer can access, or a data storage device such as a server or data center that integrates one or more available media. The available medium can be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., DVDs), or semiconductor media (e.g., solid-state drives (SSDs)).

[0174] Example 4

[0175] Embodiment 4 of the present invention provides an electronic device, including: a memory and a processor;

[0176] The processor and the memory communicate with each other via a bus; the memory stores program instructions that can be executed by the processor, and the processor can call the program instructions to execute a smooth switching method between network control and network construction control according to Embodiment 1 or any possible implementation thereof.

[0177] Specifically, a processor can be implemented in hardware or software. When implemented in hardware, the processor can be a logic circuit, an integrated circuit, etc. When implemented in software, the processor can be a general-purpose processor that reads software code stored in memory. This memory can be integrated into the processor or located outside the processor and exist independently.

[0178] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable system. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means.

[0179] It is obvious to those skilled in the art that the modules or steps of the present invention described above can be implemented using general-purpose computing systems. They can be centralized on a single computing system or distributed across a network of multiple computing systems. Optionally, they can be implemented using program code executable by a computing system, thereby storing them in a storage system for execution by the computing system. In some cases, the steps shown or described can be performed in a different order than those presented herein, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. Thus, the present invention is not limited to any particular combination of hardware and software.

[0180] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for smoothly switching between network tracking control and network construction control, characterized in that, include: When the energy storage converter is in grid-connected control operation, a droop constraint consistent with the grid-connected control is introduced into the outer power loop of the grid-connected control. Based on the droop constraint, the active-frequency and reactive-voltage balance steady-state relationship of grid control is matched with the grid construction control to form a unified steady-state operation benchmark. Based on the unified steady-state operating benchmark, the initial value of the network controller or the initial value of the network controller are calculated according to the current operating mode and the target switching mode. At the moment of switching, the initial value of the grid-building controller is assigned to the grid-building controller or the initial value of the grid-following controller is assigned to the grid-following controller, so that the reference coordinate system, equivalent internal potential, reactive power-voltage balance relationship and voltage outer loop integral state before and after switching are matched, thus completing a smooth switching.

2. The method for smooth switching between network tracking control and network construction control according to claim 1, characterized in that, In the process of calculating and obtaining the initial value of the grid-connecting controller or the initial value of the grid-following controller, before switching from grid-connecting control to grid-following control, the phase angle of the grid-connecting point voltage vector is calculated based on the d and q axis components of the grid-connecting point voltage in the grid-connecting control reference coordinate system and the phase angle of the grid-connecting control reference coordinate system, and the phase angle of the output phase angle of the grid-following control PLL phase-locked loop is initialized. Before switching from grid-connected control to grid-connected control, the initial values ​​of the phase angle of the reference coordinate system, the initial values ​​of the reactive power outer loop integrator, and the initial values ​​of the voltage outer loop d-axis and q-axis integrators of the grid-connected controller are calculated based on the grid connection point voltage, current, and virtual impedance parameters in the controller.

3. The method for smooth switching between network tracking control and network construction control according to claim 2, characterized in that, In the outer loop of the grid-following control power, a droop constraint consistent with that of the grid-forming control is introduced. The expression for the reference value of the dq-axis current under grid-following control is as follows: ； In the formula, i dref,GFL i qref,GFL These are the reference values ​​for the dq-axis current under wire mesh control; P ref Active power command; Q ref This is the reactive power command; ω0 is the rated angular frequency; ω is the angular frequency; D p k is the active damping coefficient. f V is the active-frequency droop factor. ref V is the voltage reference value; k is the voltage amplitude; k is the voltage reference value. q The reactive power-voltage droop factor; v od,GFL The output voltage of the d-axis in the coordinate system controlled by the grid.

4. The method for smooth switching between network tracking control and network construction control according to claim 3, characterized in that, The formula for calculating the phase angle of the voltage vector at the grid connection point is: ； ； In the formula, The phase angle of the voltage vector at the grid connection point is the initial value of the phase angle output by the grid-connected control PLL phase-locked loop. To construct the network control output phase angle; The phase angle deviation of the grid connection point voltage relative to the d-axis of the GFM reference coordinate system; v od,GFM v oq,GFM These are the grid connection point voltages on the dq axis in the GFM reference coordinate system.

5. The method for smooth switching between network tracking control and network construction control according to claim 4, characterized in that, The formula for calculating the initial phase angle of the reference coordinate system of the network controller is as follows: ； ； In the formula, The initial value of the phase angle for the reference coordinate system; To control the output phase angle of the grid; E represents the phase angle deviation of the internal potential of the GFM relative to the GFL coordinate system. d,GFL and E q,GFL These are the internal potentials of the d-axis and q-axis of the network control system under the reference coordinate system for network control, respectively. The formula for calculating the initial value of the reactive power outer loop integrator is as follows: ； In the formula, This is the initial value for the reactive outer loop integrator; The formula for calculating the initial values ​​of the voltage outer loop d-axis and q-axis integrators is as follows: ； ； In the formula, , These are the initial output values ​​of the voltage outer loop d-axis and q-axis integrators in the GFM reference coordinate system, respectively; Δθ GFL The phase angle difference between the GFL reference coordinate system and the GFM reference coordinate system; u xd,GFL u xq,GFL These are the initial output values ​​of the voltage outer loop d-axis and q-axis integrators in the GFL reference coordinate system, respectively.

6. A device for smoothly switching between network tracking control and network construction control, employing the smooth switching method for network tracking control and network construction control as described in any one of claims 1-5, characterized in that, include: A unified steady-state operating benchmark forming module is used to introduce a droop constraint consistent with the grid-connected control in the outer loop of the grid-connected control power when the energy storage converter is in grid-connected control operation state; based on the droop constraint, the active-frequency and reactive-voltage balance steady-state relationship of the grid-connected control is matched with the grid-connected control to form a unified steady-state operating benchmark. The initial value calculation module for the network construction controller and the network follower controller is used to calculate the initial value of the network construction controller or the initial value of the network follower controller based on the unified steady-state operation benchmark and according to the current operation mode and the target switching mode. The smooth switching module is used to assign the initial value of the grid-building controller to the grid-building controller or the initial value of the following controller to the following controller at the moment of switching, so that the reference coordinate system, equivalent internal potential, reactive power-voltage balance relationship and voltage outer loop integral state are matched before and after switching, thus completing the smooth switching.

7. The smooth switching device for network tracking control and network construction control according to claim 6, characterized in that, In the initial value calculation module of the grid-connected controller and the grid-following controller, during the process of calculating the initial value of the grid-connected controller or the initial value of the grid-following controller, before switching from grid-connected control to grid-following control, the phase angle of the grid-connected point voltage vector is calculated based on the d and q axis components of the grid-connected point voltage in the grid-connected control reference coordinate system and the phase angle of the grid-connected control reference coordinate system, and the phase angle of the output phase angle of the grid-following control PLL phase-locked loop is initialized. Before switching from grid-connected control to grid-connected control, the initial values ​​of the phase angle of the reference coordinate system, the initial values ​​of the reactive power outer loop integrator, and the initial values ​​of the voltage outer loop d-axis and q-axis integrators of the grid-connected controller are calculated based on the grid connection point voltage, current, and virtual impedance parameters in the controller.

8. The smooth switching device for network tracking control and network construction control according to claim 7, characterized in that, In the unified steady-state operating reference formation module, a droop constraint consistent with the grid-based control is introduced into the outer loop of the grid-following control power. The expression for the dq-axis current reference value under grid-following control is: ； In the formula, i dref,GFL i qref,GFL These are the reference values ​​for the dq-axis current under wire mesh control; P ref Active power command; Q ref This is the reactive power command; ω0 is the rated angular frequency; ω is the angular frequency; D p k is the active damping coefficient. f V is the active-frequency droop factor. ref V is the voltage reference value; k is the voltage amplitude; k is the voltage reference value. q The reactive power-voltage droop factor; v od,GFL The output voltage of the d-axis in the coordinate system controlled by the grid.

9. The smooth switching device for network tracking control and network construction control according to claim 8, characterized in that, In the initial value calculation module of the grid-connected controller and the grid-following controller, the calculation formula for the phase angle of the voltage vector at the grid connection point is as follows: ； ； In the formula, The phase angle of the voltage vector at the grid connection point is the initial value of the phase angle output by the grid-connected control PLL phase-locked loop. To construct the network control output phase angle; The phase angle deviation of the grid connection point voltage relative to the d-axis of the GFM reference coordinate system; v od,GFM v oq,GFM These are the grid connection point voltages on the dq axis in the GFM reference coordinate system.

10. A smooth switching device for network tracking control and network construction control according to claim 9, characterized in that, In the initial value calculation module of the network construction controller and the network tracking controller, the calculation formula for the initial value of the phase angle of the reference coordinate system of the network construction controller is as follows: ； ； In the formula, The initial value of the phase angle for the reference coordinate system; To control the output phase angle of the grid; E represents the phase angle deviation of the internal potential of the GFM relative to the GFL coordinate system. d,GFL and E q,GFL These are the internal potentials of the d-axis and q-axis of the network control system under the reference coordinate system for network control, respectively. The formula for calculating the initial value of the reactive power outer loop integrator is as follows: ； In the formula, This is the initial value for the reactive outer loop integrator; The formula for calculating the initial values ​​of the voltage outer loop d-axis and q-axis integrators is as follows: ； ； In the formula, , These are the initial output values ​​of the voltage outer loop d-axis and q-axis integrators in the GFM reference coordinate system, respectively; Δθ GFL The phase angle difference between the GFL reference coordinate system and the GFM reference coordinate system; u xd,GFL u xq,GFL These are the initial output values ​​of the voltage outer loop d-axis and q-axis integrators in the GFL reference coordinate system, respectively.

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