GRID-FORMING ENERGY STORAGE CONVERTER ON/OFF-GRID SWITCHING CONTROL METHOD AND SYSTEM

Abstract

The present invention relates to the technical field of power electronics converters and discloses a grid-forming energy storage converter on/off-grid switching control method and system, where the method includes the following steps: S1: using a single-loop power control strategy in an off-grid state when an on-grid relay of target energy storage drops out; S2: using a parallel virtual impedance loop-based power control strategy in a transient on-grid state when the on-grid relay of target energy storage pulls in; and S3: using a cascaded dual-loop power control strategy with a virtual admittance voltage loop and an inner current loop when a stable on-grid state is established. The present invention solves the problems of large current impact and unstable switching process state in the existing working strategy for on/off-grid switching in the prior art.

Claims

1. A grid-forming energy storage converter on/off-grid switching control method, comprising the following steps: S1: using a single-loop power control strategy in an off-grid state when an on-grid relay of target energy storage drops out; S2: using a parallel virtual impedance loop-based power control strategy in a transient on-grid state when the on-grid relay of target energy storage pulls in, wherein a frequency domain expression of the virtual impedance loop is Rv+sLv, Rv represents a virtual resistance, Lv represents a virtual inductance, s represents the Laplacian operator, and sLv constitutes a differential term of the virtual impedance loop; and S3: using a cascaded dual-loop power control strategy with a virtual admittance voltage loop and an inner current loop when a stable on-grid state is established.

2. The grid-forming energy storage converter on/off-grid switching control method of claim 1, wherein the single-loop power control strategy comprises: an active frequency control loop and a reactive voltage control loop; an implementation manner of the active frequency control loop is as follows: an output of a difference between a reference frequency .sub.ref and a control frequency after passing through a D.sub.p link is superimposed with a difference between a reference active power P.sub.ref and an actual output active power P, and then passes through an inertia integration link 1/Js to generate a control frequency ; a phase reference value of a converter output voltage is generated by integrating , wherein the active frequency control loop simulates a rotor motion equation and a primary frequency modulation process of a synchronous machine, the rotor motion equation comprises an inertia J and a damping D.sub.p, and the primary frequency modulation process comprises a droop D.sub.p; and an implementation manner of the reactive voltage control loop is as follows: an output of a difference between a reference AC voltage amplitude V.sub.ref and an actual AC voltage amplitude V after passing through a D.sub.q link is superimposed with a difference between a reference reactive power Q.sub.res and an actual output reactive power Q, and then passes through an integration link 1/Ks to generate an internal potential amplitude E.

3. The grid-forming energy storage converter on/off-grid switching control method of claim 2, wherein the single-loop power control strategy further comprises: detecting a grid voltage under the single-loop power control strategy, and when a value of the grid voltage is within a preset normal range, carrying out a pre-synchronization algorithm and achieving consistent voltage amplitude and phase between a target converter and the grid in the pre-synchronization algorithm.

4. The grid-forming energy storage converter on/off-grid switching control method of claim 3, wherein an implementation manner of the pre-synchronization algorithm is as follows: a phase angle .sub.g of a grid voltage v.sub.gabc is obtained through a phase-locked loop; the grid voltage v.sub.gabc in an abc coordinate system is transformed according to the phase angle .sub.g to obtain v.sub.gd and v.sub.gq in a dq coordinate system, and a converter output voltage v.sub.abc in the abc coordinate system is transformed according to the phase angle .sub.g to obtain v.sub.d and v.sub.q in the dq coordinate system; an output V of a difference between v.sub.gd and v.sub.d after passing through a PI controller is superimposed into a reactive loop to change V.sub.refV to V.sub.refV+V; and an output of a difference between v.sub.gq and v.sub.q after passing through the PI controller is superimposed onto an output end of an active loop integration link 1/Js.

5. The grid-forming energy storage converter on/off-grid switching control method of claim 1, wherein the parallel virtual impedance loop-based power control strategy comprises: superimposing a current i.sub.sabc flowing through a machine-side inductor L.sub.1 onto a power loop output e.sub.abc through a virtual impedance loop Rv+sL.sub.v to generate a three-phase modulated wave v.sub.mabc.

6. The grid-forming energy storage converter on/off-grid switching control method of claim 1, wherein the cascaded dual-loop power control strategy with a virtual admittance voltage loop and an inner current loop comprises: enabling a difference between a power loop output e.sub.abc and a converter output voltage v.sub.sabc to pass through a virtual admittance voltage loop 1/(R.sub.s+sL.sub.s) to generate a reference current i.sub.refabc, and enabling a difference between the reference current i.sub.refabc and a machine-side current i.sub.sabc to pass through a current controller G.sub.i(s) and get superimposed with control quantities of active damping and grid voltage feedforward links to generate a three-phase modulated wave v.sub.mabc, wherein the current controller G.sub.i(s) comprises a proportional controller, a resonant controller, and a repetitive controller.

7. A grid-forming energy storage converter on/off-grid switching control system, comprising a processor and a non-transitory memory, wherein: the non-transitory memory is configured to store a computer program; and the processor is configured to implement the following method steps when executing the computer program stored on the non-transitory memory: S1: using a single-loop power control strategy in an off-grid state when an on-grid relay of target energy storage drops out; S2: using a parallel virtual impedance loop-based power control strategy in a transient on-grid state when the on-grid relay of target energy storage pulls in, wherein a frequency domain expression of the virtual impedance loop is Rv+sLv, Rv represents a virtual resistance, Lv represents a virtual inductance, s represents the Laplacian operator, and sLv constitutes a differential term of the virtual impedance loop; and S3: using a cascaded dual-loop power control strategy with a virtual admittance voltage loop and an inner current loop when a stable on-grid state is established.

8. The grid-forming energy storage converter on/off-grid switching control system of claim 7, wherein the single-loop power control strategy comprises: an active frequency control loop and a reactive voltage control loop; an implementation manner of the active frequency control loop is as follows: an output of a difference between a reference frequency .sub.ref and a control frequency after passing through a D.sub.p link is superimposed with a difference between a reference active power P.sub.ref and an actual output active power P, and then passes through an inertia integration link 1/Js to generate a control frequency ; a phase reference value of a converter output voltage is generated by integrating , wherein the active frequency control loop simulates a rotor motion equation and a primary frequency modulation process of a synchronous machine, the rotor motion equation comprises an inertia J and a damping D.sub.p, and the primary frequency modulation process comprises a droop D.sub.p; and an implementation manner of the reactive voltage control loop is as follows: an output of a difference between a reference AC voltage amplitude V.sub.ref and an actual AC voltage amplitude V after passing through D.sub.q link is superimposed with a difference between a reference reactive power Q.sub.ref and an actual output reactive power Q, and then passes through an integration link 1/Ks to generate an internal potential amplitude E.

9. The grid-forming energy storage converter on/off-grid switching control system of claim 8, wherein the single-loop power control strategy further comprises: detecting a grid voltage under the single-loop power control strategy, and when a value of the grid voltage is within a preset normal range, carrying out a pre-synchronization algorithm and achieving consistent voltage amplitude and phase between a target converter and the grid in the pre-synchronization algorithm.

10. The grid-forming energy storage converter on/off-grid switching control system of claim 9, wherein an implementation manner of the pre-synchronization algorithm is as follows: a phase angle .sub.g of a grid voltage v.sub.gabc is obtained through a phase-locked loop; the grid voltage v.sub.gabc in an abc coordinate system is transformed according to the phase angle .sub.g to obtain v.sub.gd and v.sub.gq in a dq coordinate system, and a converter output voltage v.sub.abc in the abc coordinate system is transformed according to the phase angle .sub.g to obtain v.sub.d and v.sub.q in the dq coordinate system; an output V of a difference between v.sub.gd and v.sub.d after passing through a PI controller is superimposed into a reactive loop to change V.sub.refV to V.sub.refV+V; and an output of a difference between v.sub.gq and v.sub.q after passing through the PI controller is superimposed onto an output end of an active loop integration link 1/Js.

11. The grid-forming energy storage converter on/off-grid switching control system of claim 7, wherein the parallel virtual impedance loop-based power control strategy comprises: superimposing a current i.sub.sabc flowing through a machine-side inductor L.sub.1 onto a power loop output e.sub.abc through a virtual impedance loop R.sub.v+sL.sub.v to generate a three-phase modulated wave v.sub.mabc.

12. The grid-forming energy storage converter on/off-grid switching control system of claim 7, wherein the cascaded dual-loop power control strategy with a virtual admittance voltage loop and an inner current loop comprises: enabling a difference between a power loop output e.sub.abc and a converter output voltage v.sub.sabc to pass through a virtual admittance voltage loop 1/(R.sub.s+sL.sub.s) to generate a reference current i.sub.refabc, and enabling a difference between the reference current i.sub.refabc and a machine-side current i.sub.sabc to pass through a current controller G.sub.i(s) and get superimposed with control quantities of active damping and grid voltage feedforward links to generate a three-phase modulated wave v.sub.mabc, wherein the current controller G.sub.i(s) comprises a proportional controller, a resonant controller, and a repetitive controller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 is a flowchart of a grid-forming energy storage converter on/off-grid switching control method of an exemplary embodiment of the present invention; and

[0026] FIGS. 2A and 2B is schematic diagram of a grid-forming energy storage converter on/off-grid switching control method of an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some but not all of the embodiments of the present invention. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the common meanings as understood by those skilled in the art to which the present invention belongs. The terms first, second, and the like used in the present invention are not intended to indicate any sequence, amount or importance, but distinguish different components. Also, the terms such as a, an, and the like are not intended to limit the amount, but indicate the existence of at least one. As used herein, connection, connected, and the like are not limited to a physical or mechanical connection but may include a direct or indirect electrical connection. Upper, lower, left, right, and the like are only used to indicate a relative position relationship, and when the absolute position of the described object changes, the relative position relationship may be changed accordingly.

[0029] Referring to FIGS. 1-2, the present invention provides a grid-forming energy storage converter on/off-grid switching control method, including the following steps:

[0030] S1: using a single-loop power control strategy in an off-grid state when an on-grid relay of target energy storage drops out;

[0031] S2: using a parallel virtual impedance loop-based power control strategy in a transient on-grid state when the on-grid relay of target energy storage pulls in, where a frequency domain expression of the virtual impedance loop is Rv+sLv, Rv represents a virtual resistance, Lv represents a virtual inductance, s represents the Laplacian operator, and sLv constitutes a differential term of the virtual impedance loop; and

[0032] S3: using a cascaded dual-loop power control strategy with a virtual admittance voltage loop and an inner current loop when a stable on-grid state is established.

[0033] In the off-grid state, the converter uses the single-loop power control strategy, which corresponds to the three parts of active power control, reactive power control, and off-grid control in FIGS. 2A and 2B. Optionally, the single-loop power control strategy includes:

[0034] an active frequency control loop and a reactive voltage control loop;

[0035] an implementation manner of the active frequency control loop is as follows: an output of a difference between a reference frequency .sub.ref and a control frequency after passing through a D.sub.p link is superimposed with a difference between a reference active power P.sub.ref and an actual output active power P, and then passes through an inertia integration link 1/Js to generate a control frequency ; a phase reference value of a converter output voltage is generated by integrating , where the active frequency control loop simulates a rotor motion equation (including an inertia J and a damping D.sub.p) and a primary frequency modulation process (including a droop D.sub.p) of a synchronous machine; and

[0036] an implementation manner of the reactive voltage control loop is as follows: an output of a difference between a reference AC voltage amplitude V.sub.ref and an actual AC voltage amplitude V after passing through a D.sub.q link is superimposed with a difference between a reference reactive power Q.sub.ref and an actual output reactive power Q, and then passes through an integration link 1/Ks to generate an internal potential amplitude E.

[0037] Optionally, the single-loop power control strategy includes:

[0038] detecting a grid voltage under the single-loop power control strategy, and when a value of the grid voltage is within a preset normal range, carrying out a pre-synchronization algorithm and achieving consistent voltage amplitude and phase between a target converter and the grid in the pre-synchronization algorithm.

[0039] Optionally, an implementation manner of the pre-synchronization algorithm is as follows: a phase angle .sub.g of a grid voltage v.sub.gabc is obtained through a phase-locked loop; the grid voltage v.sub.gabc in an abc coordinate system is transformed according to the phase angle .sub.g to obtain v.sub.gd and v.sub.gq in a dq coordinate system, and a converter output voltage v.sub.abc in the abc coordinate system is transformed according to the phase angle .sub.g to obtain v.sub.d and v.sub.q in the dq coordinate system; an output V of a difference between v.sub.gd and v.sub.d after passing through a PI controller is superimposed into a reactive loop to change V.sub.refV to V.sub.refV+V; and an output of a difference between v.sub.gq and v.sub.q after passing through the PI controller is superimposed onto an output end of an active loop integration link 1/Js.

[0040] Optionally, the parallel virtual impedance loop-based power control strategy includes:

[0041] superimposing a current i.sub.sabc flowing through a machine-side inductor L.sub.1 onto a power loop output e.sub.abc through a virtual impedance loop R.sub.v+sL.sub.v to generate a three-phase modulated wave v.sub.mabc.

[0042] The control with a virtual admittance voltage loop and an inner current loop is a special case of voltage and current dual-loop control. Optionally, the cascaded dual-loop power control strategy with a virtual admittance voltage loop and an inner current loop includes:

[0043] enabling a difference between the power loop output e.sub.abc and a converter output voltage v.sub.sabc to pass through the virtual admittance voltage loop 1/(R.sub.s+sL.sub.s) to generate a reference current i.sub.refabc, and enabling a difference between the reference current i.sub.refabc and the machine-side current i.sub.sabc to pass through a current controller G.sub.i(s) (including a proportional controller, a resonant controller, and a repetitive controller) and get superimposed with control quantities of active damping and grid voltage feedforward links to generate the three-phase modulated wave v.sub.mabc.

[0044] The present invention further provides a grid-forming energy storage converter on/off-grid switching control system, including a processor and a non-transitory memory, where:

[0045] the non-transitory memory is configured to store a computer program; and

[0046] the processor is configured to implement any one of the steps of the grid-forming energy storage converter on/off-grid switching control method when executing the computer program stored on the non-transitory memory.

[0047] The above provides a detailed description of the exemplary embodiments of the present invention. It should be understood that those skilled in the art can make many modifications and changes according to the concept of the present invention without creative efforts. Thus, any technical solution that can be obtained by those skilled in the art on the basis of the concept of the present invention through logical analysis, logical inference, or limited experiments on the basis of the prior art should fall within the scope of protection determined by the claims.