Off-grid and grid-connected state switching control method and control system for grid-forming energy storage converter

Abstract

The present invention relates to the technical field of power electronic conversion. Disclosed are an off-grid and grid-connected state switching control method and control system for a grid-forming energy storage converter. The method comprises: S1, when a grid-connected relay for target energy storage is turned off and is in an off-grid state, a converter using a power single-loop control strategy; S2, measuring the voltage of a power grid under the power single-loop control strategy, and when the value of the voltage of the power grid is within a preset normal range, the converter performing a pre-synchronization algorithm; S3, in the pre-synchronization algorithm, realizing the voltage amplitude consistency and phase consistency between a target converter and the power grid; S4, when the grid-connected relay for target energy storage is turned on and is in a grid-connected transient state, the converter using a control strategy of cascading a power loop with a virtual impedance loop; and S5, after a grid-connected steady state, the converter using a control strategy of cascading the power loop with voltage and current double loops. The present invention solves the problems in respect of large current surges and unstable states during switching occuring in existing off-grid and grid-connected state switching operation strategies.

Description

A grid-connected energy storage converter off-grid switching control method and control system Technical Field

[0001] The present invention relates to the technical field of power electronic conversion, and in particular to a grid-connected and off-grid switching control method and control system for a grid-connected energy storage converter. Background Art

[0002] With the rapid development of power electronics conversion technology, three-level energy storage converters are increasingly being used in power grids. As a type of grid-connected energy storage converter, the three-level energy storage converter's off-grid switching operation strategy primarily includes: in the off-grid state, the converter adopts a power unit control strategy; upon detecting that the grid voltage is within the normal range, the converter initiates a pre-synchronization algorithm; the pre-synchronization step ensures voltage amplitude and phase consistency between the converter and the grid; and when the grid-connected relay is engaged, the converter adopts a dual-loop control strategy of cascading power loops, voltage, and current. Currently, when implementing this operation strategy, after the grid-connected relay is engaged, the converter's control strategy immediately switches from a single power loop to a cascaded power loop, voltage, and current loops. This switching method can cause significant current surges, shortening component lifespans and, in severe cases, triggering current transformer protection, leading to shutdown. Therefore, existing off-grid switching operation strategies suffer from significant current surges and unstable switching processes.

[0003] Summary of the Invention

[0004] The present invention provides a grid-connected energy storage converter off-grid switching control method and control system to solve the problems of large current impact and unstable switching process state in the existing off-grid switching operation strategy.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0006] In a first aspect, the present invention provides a method for controlling off-grid and on-grid switching of a grid-connected energy storage converter, comprising:

[0007] S1: When the grid-connected relay of the target energy storage is disconnected and the target energy storage is in an off-grid state, the converter adopts a single-loop power control strategy;

[0008] S2: Detect the grid voltage under the power single-loop control strategy. When the grid voltage is within the preset normal range, the converter performs a pre-synchronization algorithm.

[0009] S3: In the pre-synchronization algorithm, the voltage amplitude and phase of the target converter and the grid are made consistent;

[0010] S4: When the grid-connected relay of the target energy storage is energized and in a grid-connected transient state, the converter adopts a control strategy of cascading a power loop and a virtual impedance loop;

[0011] S5: After being connected to the grid and in steady state, the converter adopts a control strategy of power loop cascade voltage and current dual loops.

[0012] Optionally, the control strategy of the power single loop includes:

[0013] Active power-frequency control loop and reactive power-voltage control loop;

[0014] The active power-frequency control loop is realized as follows: reference frequency ω ref The difference between the control frequency ω and D p The output of the link is related to the reference active power P ref The difference between the actual output active power P is added and then passes through the inertia integral link 1 / Js to generate the control frequency ω. By integrating ω, the phase reference value θ of the converter output voltage is generated. The active-frequency control loop simulates the rotor motion equation of the synchronous machine (inertia J and damping D p ) and a frequency modulation process (droop D p );

[0015] The reactive power-voltage control loop is realized as follows: the reference AC voltage amplitude V ref The difference between the actual AC voltage amplitude V and the actual AC voltage amplitude V is calculated by D q The output of the link is related to the reference reactive power Q ref The difference between it and the actual output reactive power Q is added, and then the internal potential amplitude E is generated through the integration link 1 / Ks.

[0016] Optionally, the pre-synchronization algorithm includes:

[0017] The pre-synchronization algorithm is implemented as follows: the grid voltage v is obtained through a phase-locked loop gabc The phase angle θ g , grid voltage v in abc coordinate system gabc According to the phase angle θ g Transform to get v in dq coordinate system gd and v gq , the converter output voltage v in the abc coordinate system abc According to the phase angle θ g Transform to get v in dq coordinate system d and v q .v gd and v d After the difference is made and passes through the PI controller, the output ΔV is superimposed on the reactive loop, and V ref -V becomes V ref -V+ΔV. v gq and v q After the difference is made and passes through the PI controller, the output Δω is superimposed on the output end of the active loop integral link 1 / Js.

[0018] Optionally, the control strategy of the power loop cascaded virtual impedance loop includes:

[0019] The current i flowing through the machine-side inductor L1 sabc , after R v +sL v Link superimposed on the power loop output e abc On the top, generate three-phase modulation wave v mabc .

[0020] Optionally, the control strategy of the power loop cascade voltage and current dual loops includes:

[0021] Power loop output e abc and the converter output voltage v sabc Make a difference, pass through the virtual admittance loop 1 / (R s +sL s ) generates a reference current i ref , reference current i ref With the machine side current i sabc The difference passes through the current controller G i (s) (including proportional controller, resonant controller, repetitive controller), superimposed with the control quantity of active damping and grid voltage feedforward link to generate three-phase modulation wave v mabc .

[0022] In a second aspect, an embodiment of the present application provides a grid-connected and off-grid switching control system for a grid-connected energy storage converter, including a processor and a memory;

[0023] Memory for storing computer programs;

[0024] The processor is configured to implement any one of the method steps described in the first aspect when executing a program stored in the memory. Beneficial effects:

[0025] The grid-connected switching control method for a grid-storage converter provided by this invention incorporates a virtual impedance component during the grid-connected transient process, resulting in a simple algorithm implementation. Furthermore, the virtual impedance is equivalent to an equivalent impedance connected in series between the converter and the grid, significantly reducing and suppressing grid-connected current surges. This enhances the transient stability of the converter during the off-grid to grid-connected switching process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG1 is a flow chart of a method for controlling off-grid and on-grid switching of a grid energy storage converter according to a preferred embodiment of the present invention;

[0027] FIG2 is a schematic diagram of a method for controlling off-grid and on-grid switching of a grid energy storage converter according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0028] The following is a clear and complete description of the technical solutions of the present invention. It should be understood that the embodiments described are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0029] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one" or "a" do not indicate a quantity limitation, but rather indicate the existence of at least one. Words such as "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship also changes accordingly.

[0030] 1-2 , an embodiment of the present application provides a method for controlling off-grid and on-grid switching of a grid-connected energy storage converter, including:

[0031] S1: When the grid-connected relay of the target energy storage is disconnected and the target energy storage is in an off-grid state, the converter adopts a single-loop power control strategy;

[0032] S2: Detect the grid voltage under the power single-loop control strategy. When the grid voltage is within the preset normal range, the converter performs a pre-synchronization algorithm.

[0033] S3: In the pre-synchronization algorithm, the voltage amplitude and phase of the target converter and the grid are made consistent;

[0034] S4: When the grid-connected relay of the target energy storage is energized and in a grid-connected transient state, the converter adopts a control strategy of cascading a power loop and a virtual impedance loop;

[0035] S5: After being connected to the grid and in steady state, the converter adopts a control strategy of power loop cascade voltage and current dual loops.

[0036] Optionally, the control strategy of the power single loop includes:

[0037] Active power-frequency control loop and reactive power-voltage control loop;

[0038] The active power-frequency control loop is realized as follows: reference frequency ω ref The difference between the control frequency ω and D p The output of the link is related to the reference active power P refThe difference between the actual output active power P is added and then passes through the inertia integral link 1 / Js to generate the control frequency ω. By integrating ω, the phase reference value θ of the converter output voltage is generated. The active-frequency control loop simulates the rotor motion equation of the synchronous machine (inertia J and damping D p ) and a frequency modulation process (droop D p );

[0039] The reactive power-voltage control loop is realized as follows: the reference AC voltage amplitude V ref The difference between the actual AC voltage amplitude V and the actual AC voltage amplitude V is calculated by D q The output of the link is related to the reference reactive power Q ref The difference between it and the actual output reactive power Q is added, and then the internal potential amplitude E is generated through the integration link 1 / Ks.

[0040] Optionally, the pre-synchronization algorithm includes:

[0041] The pre-synchronization algorithm is implemented as follows: the grid voltage v is obtained through a phase-locked loop gabc The phase angle θ g , grid voltage v in abc coordinate system gabc According to the phase angle θ g Transform to get v in dq coordinate system gd and v gq , the converter output voltage v in the abc coordinate system abc According to the phase angle θ g Transform to get v in dq coordinate system d and v q .v gd and v d After the difference is made and passes through the PI controller, the output ΔV is superimposed on the reactive loop, and V ref -V becomes V ref -V+ΔV. v gq and v q After the difference is made and passes through the PI controller, the output Δω is superimposed on the output end of the active loop integral link 1 / Js.

[0042] Optionally, the control strategy of the power loop cascaded virtual impedance loop includes:

[0043] The current i flowing through the machine-side inductor L1 sabc , after R v +sL v Link superimposed on the power loop output e abc On the top, generate three-phase modulation wave v mabc .

[0044] Optionally, the control strategy of the power loop cascade voltage and current dual loops includes:

[0045] Power loop output eabc and the converter output voltage v sabc Make a difference, pass through the virtual admittance loop 1 / (R s +sL s ) generates a reference current i ref , reference current i ref With the machine side current i sabc The difference passes through the current controller G i (s) (including proportional controller, resonant controller, repetitive controller), superimposed with the control quantity of active damping and grid voltage feedforward link to generate three-phase modulation wave v mabc .

[0046] The embodiment of the present application also provides a grid-connected and off-grid switching control system for a grid-connected energy storage converter, comprising a processor and a memory;

[0047] Memory for storing computer programs;

[0048] The processor is configured to implement any one of the method steps described in the method for controlling off-grid and on-grid switching of a grid-connected energy storage converter when executing a program stored in the memory.

[0049] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for controlling off-grid and on-grid switching of a grid-connected energy storage converter, characterized in that: include: S1: When the grid-connected relay of the target energy storage is disconnected and in an off-grid state, the converter adopts a power single-loop control strategy; S2: Detect the grid voltage under the power single-loop control strategy. When the grid voltage value is within the preset normal range, the converter performs a pre-synchronization algorithm. S3: in the pre-synchronization algorithm, the voltage amplitude and phase of the target converter and the power grid are made consistent; S4: When the grid-connected relay of the target energy storage is energized and in a grid-connected transient state, the converter adopts a control strategy of a power loop cascaded virtual impedance loop; S5: After being connected to the grid and in steady state, the converter adopts the control strategy of power loop cascade voltage and current dual loops.

2. The grid-connected and off-grid switching control method of the grid-connected energy storage converter according to claim 1, characterized in that: The control strategy of the power single loop includes: Active power-frequency control loop and reactive power-voltage control loop; The active power-frequency control loop is implemented as follows: reference frequency ω ref The difference between the control frequency ω and D p The output of the link is related to the reference active power P ref The difference between the actual output active power P and the inertia integral link 1 / Js is then used to generate the control frequency ω. By integrating ω, the phase reference value θ of the converter output voltage is generated. The active-frequency control loop simulates the rotor motion equation of the synchronous machine (inertia J and damping D p ) and the primary frequency modulation process (droop D p ); The reactive power-voltage control loop is implemented as follows: Reference AC voltage amplitude V ref The difference between the actual AC voltage amplitude V and the q The output of the link is related to the reference reactive power Q ref The difference between the actual output reactive power Q and the internal potential amplitude E is generated through the integration link 1 / Ks.

3. The grid-connected and off-grid switching control method of a grid-connected energy storage converter according to claim 1, characterized in that: The pre-synchronization algorithm comprises: The pre-synchronization algorithm is implemented as follows: the grid voltage v is obtained through a phase-locked loop gabc The phase angle θ g , grid voltage v in abc coordinate system gabc According to the phase angle θ g Transform to get v in dq coordinate system gd and v gq , the converter output voltage v in the abc coordinate system abc According to the phase angle θ g Transform to get v in dq coordinate system d and v q .v gd and v d After the difference is made, it passes through the PI controller and the output ΔV is superimposed on the reactive loop. ref -V becomes V ref -V+ΔV.v gq and v q After the difference is made and passes through the PI controller, the output Δω is superimposed on the output end of the active loop integral link 1 / Js.

4. The grid-connected and off-grid switching control method of a grid-connected energy storage converter according to claim 1, characterized in that: The control strategy of the power loop cascade virtual impedance loop includes: The current i flowing through the machine-side inductor L1 sabc , after R v +sL v The link is superimposed on the power loop output e abc On the top, generate the three-phase modulation wave v mabc .

5. The grid-connected and off-grid switching control method of a grid-connected energy storage converter according to claim 1, characterized in that: The control strategy of the power loop cascade voltage and current dual loops includes: Power ring output abc and the converter output voltage v sabc The difference is made through the virtual admittance loop 1 / (R s +sL s ) generates a reference current i ref , reference current i ref With the machine side current i sabc The difference passes through the current controller G i (s) (including proportional controller, resonant controller, repetitive controller), superimposed with the control quantity of active damping and grid voltage feedforward link, generates a three-phase modulation wave v mabc .

6. A grid-connected energy storage converter off-grid switching control system, characterized in that: Including processor and memory; Memory, used to store computer programs; A processor, for implementing the method steps described in any one of claims 1 to 5 when executing a program stored in a memory.

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