A method and device for parameter setting and seamless switching of a grid-connected energy storage VSG

Abstract

This disclosure relates to a method and apparatus for parameter tuning and seamless switching of a grid-connected energy storage VSG. The method includes: designing control parameters for the grid-connected energy storage VSG and establishing a control circuit for the VSG; establishing a virtual synchronizer small-signal model and optimizing the control parameters of the VSG based on the virtual synchronizer small-signal model to complete the parameter tuning of the VSG; and determining pre-synchronization control based on preset pre-synchronization logic by judging the voltage difference between the inside and outside of the AC switch, thereby achieving seamless switching of the grid-connected energy storage PCS for grid connection / networking. This method has advantages such as simple structure and ease of design.

Description

Technical Field

[0001] This disclosure relates to the field of power electronics, and more specifically, to a method and apparatus for VSG parameter tuning and seamless switching in grid-connected energy storage systems. Background Technology

[0002] With the application and development of renewable energy and the large-scale integration of power electronic converters into the grid, new power systems are gradually exhibiting characteristics of "low inertia" and "low damping," which have become key factors hindering the penetration of new energy sources. Grid-based energy storage is expected to become one of the effective control methods for friendly interaction between the source, grid, and load in the future, improving the stability of new power systems and achieving 100% penetration of new energy sources. Grid-based algorithms include Virtual Oscillator Control (VOC), Droop Control, and Virtual Synchronous Generator (VSG). The Virtual Synchronous Generator algorithm provides inertia and damping to the system by mimicking a synchronous generator, making it a grid-friendly power source that can actively support system voltage / frequency and is widely used in energy storage converters.

[0003] Virtual synchronous generators have spawned various control structures, including single-loop RMS control, dual-loop control, adaptive inertia and damping, additional decoupling terms, and additional virtual impedance. National standards have provided design guidelines and specifications for VSG parameter tuning and testing, specifying that virtual synchronous generators in grid-connected energy storage converters must have grid-connected / off-grid switching capabilities. The transition from off-grid to grid-connected VSGs in grid-connected energy storage requires pre-synchronization technology to mitigate the impact of instantaneous current during grid connection. During the grid-connected to off-grid transition, the VSG itself possesses voltage source characteristics, enabling seamless switching. Therefore, the key to seamless switching technology for grid-connected energy storage VSGs lies in implementing reasonable pre-synchronization control. Pre-synchronization control in grid-connected energy storage consists of three parts: ① phase pre-synchronization; ② frequency pre-synchronization; ③ amplitude pre-synchronization. Existing technologies use a phase-angle compensation-based phase-locked loop (PLL) pre-synchronization method, which reduces one PI controller compared to traditional pre-synchronization. Following the approach of virtual synchronous machines in the stator circuit, virtual damping is added to the rotor circuit, using two PI controllers to complete the pre-synchronization control, increasing the complexity of pre-synchronization control. Using the grid voltage amplitude / frequency as the reference value for the VSG output voltage / frequency greatly simplifies the pre-synchronization algorithm, but the pre-synchronization logic is not designed. An islanding / grid-connected mode switching strategy is proposed, but the frequency pre-synchronization stage is not considered, and pre-synchronization results for grid frequency deviations from the rated value are not provided.

[0004] Therefore, one or more methods are needed to solve the above problems.

[0005] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this disclosure is to provide a method and device for VSG parameter tuning and seamless switching in grid-connected energy storage, thereby overcoming, to at least to some extent, one or more problems caused by the limitations and defects of related technologies.

[0007] According to one aspect of this disclosure, a method for VSG parameter tuning and seamless switching in grid-connected energy storage is provided, comprising:

[0008] Based on the grid-connected / networked circuit of the grid-connected energy storage PCS based on the virtual synchronous generator control VSG, the control parameters of the grid-connected energy storage VSG are designed respectively, and the grid-connected energy storage VSG control circuit is established.

[0009] Based on the aforementioned grid-connected energy storage VSG control circuit, a virtual synchronous machine small-signal model is established, and the control parameters of the grid-connected energy storage VSG are optimized based on the virtual synchronous machine small-signal model to complete the grid-connected energy storage VSG parameter tuning.

[0010] The grid-connected energy storage VSG control circuit, tuned according to the parameters of the grid-connected energy storage VSG, uses preset pre-synchronization logic to determine the pre-synchronization control by judging the voltage difference between the inside and outside of the AC switch, thereby achieving seamless switching of the grid-connected energy storage PCS to the grid / network.

[0011] In one exemplary embodiment of this disclosure, the control parameters of the grid-connected energy storage VSG include voltage and current loop parameters, Pf loop parameters, and Qv loop parameters.

[0012] In one exemplary embodiment of this disclosure, the method further includes:

[0013] The design of the Pf loop parameters includes the active power frequency regulation coefficient K. f Parameter design of virtual synchronous machine rotational inertia J and damping control D;

[0014] The design of the Qv loop parameters includes the reactive power regulation coefficient K. v Excitation regulator K e Parameter design.

[0015] In one exemplary embodiment of this disclosure, the method for establishing a virtual synchronizer small-signal model further includes:

[0016] The active and reactive power outputs of the grid-connected energy storage VSG are obtained by calculating the apparent power output of the VSG to the point of common coupling (PCC).

[0017] The steady-state operating point is calculated based on the output active and reactive power of the grid-connected energy storage VSG, and a small-signal disturbance is introduced near the steady-state operating point.

[0018] After introducing a small-signal disturbance near the steady-state operating point, a VSG small-signal model is generated by removing the steady-state and nonlinear components.

[0019] In one exemplary embodiment of this disclosure, the method further includes:

[0020] The natural oscillation frequency ω in the Pf loop parameters is calculated based on the virtual synchronizer small-signal model. ωo-ωn And damping ratio ξ ωo-ωn The Pf loop parameters are optimized based on the preset first constraint and the preset second constraint.

[0021] The reactive power closed-loop transfer function in the Qv loop parameters is calculated based on the virtual synchronous machine small-signal model, and the Pf loop parameters are optimized based on the preset third constraint and the preset fourth constraint.

[0022] In one exemplary embodiment of this disclosure, the method further includes a pre-synchronization logic:

[0023] When the system starts in VSG mode and operates independently, there is no voltage on either side of the switch, the AC switch is closed, the voltage difference between the inside and outside of the AC switch is 0V, the pre-synchronization output module is 0, and the angular frequency is the rated angular frequency ω. n The Qv loop reference voltage is the rated voltage. VSG starts to build up the output voltage until the voltage outside the switch is sampled (V). g If the value exceeds the first preset threshold, the normal Pf loop is enabled, and the system begins to operate normally.

[0024] When the system starts in VSG mode and operates in grid-connected mode, there is a voltage difference between the inside and outside of the switch. The AC switch is open, and the system starts pre-synchronization. The Pf loop of VSG is not enabled, and the reference voltage of the Qv loop is the grid voltage. When the voltage difference between the inside and outside of the switch is less than the second preset judgment value, it is considered that the pre-synchronization is completed, the AC switch can be closed, the pre-synchronization is exited, and the Pf loop is enabled.

[0025] In one exemplary embodiment of this disclosure, the method further includes:

[0026] The pre-synchronization control uses an integral controller to achieve the pre-synchronization function. The integral controller and the subsequent angular velocity integral module form PI control, thereby achieving phase synchronization.

[0027] In one aspect of this disclosure, a device for VSG parameter tuning and seamless switching in grid-connected energy storage is provided, comprising:

[0028] The parameter design module is used to design the control parameters of the grid-connected energy storage VSG based on the grid-connected / networked circuit of the grid-connected energy storage PCS based on the virtual synchronous generator control VSG, and to establish the grid-connected energy storage VSG control circuit.

[0029] The parameter tuning module is used to establish a virtual synchronous machine small-signal model based on the grid-connected energy storage VSG control circuit, and to optimize the control parameters of the grid-connected energy storage VSG based on the virtual synchronous machine small-signal model, thereby completing the parameter tuning of the grid-connected energy storage VSG.

[0030] The seamless switching module is used to adjust the grid-connected energy storage VSG control circuit according to the grid-connected energy storage VSG parameters. Based on the preset pre-synchronization logic, it determines the pre-synchronization control by judging the voltage difference between the inside and outside of the AC switch, thereby realizing the seamless switching of the grid-connected energy storage PCS to the grid / network.

[0031] An exemplary embodiment of this disclosure discloses a method for tuning and seamlessly switching grid-connected energy storage VSG parameters. The method includes: designing control parameters for the grid-connected energy storage VSG based on the grid-connected / networked circuit of the grid-connected energy storage PCS using a virtual synchronous generator-controlled VSG, thus establishing a grid-connected energy storage VSG control circuit; establishing a virtual synchronous generator small-signal model based on the grid-connected energy storage VSG control circuit, and optimizing the control parameters of the grid-connected energy storage VSG based on the virtual synchronous generator small-signal model, thereby completing the tuning of the grid-connected energy storage VSG parameters; and, based on the tuned grid-connected energy storage VSG control circuit, determining pre-synchronization control by judging the voltage difference between the inner and outer sides of the AC switch using preset pre-synchronization logic, thereby achieving seamless switching of the grid-connected energy storage PCS for grid connection / networking, and possessing advantages such as simple structure and ease of design.

[0032] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0033] The above and other features and advantages of this disclosure will become more apparent from the detailed description of exemplary embodiments thereof with reference to the accompanying drawings.

[0034] Figure 1 A flowchart is shown below illustrating a method for VSG parameter tuning and seamless switching in grid-connected energy storage according to an exemplary embodiment of this disclosure;

[0035] Figure 2 A schematic diagram of PCS grid connection is shown for a method of VSG parameter tuning and seamless switching in grid-connected energy storage according to an exemplary embodiment of the present disclosure;

[0036] Figure 3 A block diagram of a grid-connected energy storage VSG control system is shown, illustrating a method for VSG parameter tuning and seamless switching according to an exemplary embodiment of this disclosure.

[0037] Figure 4 A flowchart illustrating the VSG parameter design process for grid-connected energy storage according to an exemplary embodiment of the present disclosure is provided.

[0038] Figure 5 A block diagram of a grid-connected energy storage VSG dual-closed-loop control method for VSG parameter tuning and seamless switching according to an exemplary embodiment of the present disclosure is shown.

[0039] Figure 6 A block diagram of a dual-closed-loop system control for grid-connected energy storage VSG is shown, illustrating a method for tuning and seamlessly switching VSG parameters according to an exemplary embodiment of this disclosure.

[0040] Figures 7A-7B A schematic diagram of a small-signal model of a grid-connected energy storage VSG is shown, illustrating a method for VSG parameter tuning and seamless switching according to an exemplary embodiment of the present disclosure.

[0041] Figures 8A-8B A schematic diagram showing the design results of the current loop proportional coefficient for a method of VSG parameter tuning and seamless switching in grid-connected energy storage according to an exemplary embodiment of the present disclosure is shown.

[0042] Figures 9A-9B A schematic diagram of the dual-closed-loop design results of a method for VSG parameter tuning and seamless switching in grid-connected energy storage according to an exemplary embodiment of the present disclosure is shown.

[0043] Figure 10 A schematic diagram of the J / D coordination range values ​​of a method for VSG parameter tuning and seamless switching in grid-connected energy storage according to an exemplary embodiment of the present disclosure is shown.

[0044] Figure 11 A schematic diagram of a pre-synchronization algorithm for a method of VSG parameter tuning and seamless switching in grid-connected energy storage according to an exemplary embodiment of the present disclosure is shown.

[0045] Figure 12 A pre-synchronization logic diagram of a method for VSG parameter tuning and seamless switching in grid-connected energy storage according to an exemplary embodiment of the present disclosure is shown.

[0046] Figure 13 A schematic block diagram of a grid-connected energy storage VSG parameter tuning and seamless switching device according to an exemplary embodiment of the present disclosure is shown. Detailed Implementation

[0047] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0048] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of the specific details described, or other methods, components, materials, apparatuses, steps, etc., can be employed. In other instances, well-known structures, methods, apparatuses, implementations, materials, or operations are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0049] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in software, or in one or more software-hardened modules, or in different network and / or processor devices and / or microcontroller devices.

[0050] In this example embodiment, a method for VSG parameter tuning and seamless switching in grid-connected energy storage is first provided; refer to Figure 1 As shown, the method for VSG parameter tuning and seamless switching in grid-connected energy storage can include the following steps:

[0051] Step S110: Based on the grid-connected / networked circuit of the grid-connected energy storage PCS based on the virtual synchronous generator control VSG, design the control parameters of the grid-connected energy storage VSG and establish the grid-connected energy storage VSG control circuit.

[0052] Step S120: Based on the grid-connected energy storage VSG control circuit, establish a virtual synchronous machine small-signal model, and optimize the control parameters of the grid-connected energy storage VSG based on the virtual synchronous machine small-signal model to complete the grid-connected energy storage VSG parameter tuning;

[0053] Step S130: Based on the parameters of the grid-connected energy storage VSG, the grid-connected energy storage VSG control circuit determines the pre-synchronization control by judging the voltage difference between the inside and outside of the AC switch, thereby realizing seamless switching of the grid-connected energy storage PCS to the grid / network.

[0054] An exemplary embodiment of this disclosure discloses a method for tuning and seamlessly switching grid-connected energy storage VSG parameters. The method includes: designing control parameters for the grid-connected energy storage VSG based on the grid-connected / networked circuit of the grid-connected energy storage PCS using a virtual synchronous generator-controlled VSG, thus establishing a grid-connected energy storage VSG control circuit; establishing a virtual synchronous generator small-signal model based on the grid-connected energy storage VSG control circuit, and optimizing the control parameters of the grid-connected energy storage VSG based on the virtual synchronous generator small-signal model, thereby completing the tuning of the grid-connected energy storage VSG parameters; and, based on the tuned grid-connected energy storage VSG control circuit, determining pre-synchronization control by judging the voltage difference between the inner and outer sides of the AC switch using preset pre-synchronization logic, thereby achieving seamless switching of the grid-connected energy storage PCS for grid connection / networking, and possessing advantages such as simple structure and ease of design.

[0055] The following will further explain a method for VSG parameter tuning and seamless switching in grid-connected energy storage in this example embodiment.

[0056] Example 1:

[0057] In step S110, the control parameters of the grid-connected energy storage VSG can be designed according to the grid-connected / networked circuit of the grid-connected energy storage PCS based on the virtual synchronous generator control VSG, and the grid-connected energy storage VSG control circuit can be established.

[0058] In this example embodiment, the control parameters of the grid-connected energy storage VSG include voltage and current loop parameters, Pf loop parameters, and Qv loop parameters.

[0059] In this example embodiment, the method further includes:

[0060] The design of the Pf loop parameters includes the active power frequency regulation coefficient K. f Parameter design of virtual synchronous machine rotational inertia J and damping control D;

[0061] The design of the Qv loop parameters includes the reactive power regulation coefficient K. v Excitation regulator K e Parameter design.

[0062] In step S120, a virtual synchronous machine small-signal model can be established based on the grid-connected energy storage VSG control circuit, and the control parameters of the grid-connected energy storage VSG can be optimized based on the virtual synchronous machine small-signal model to complete the grid-connected energy storage VSG parameter tuning.

[0063] In this example embodiment, the method for establishing a virtual synchronizer small-signal model further includes:

[0064] The active and reactive power outputs of the grid-connected energy storage VSG are obtained by calculating the apparent power output of the VSG to the point of common coupling (PCC).

[0065] The steady-state operating point is calculated based on the output active and reactive power of the grid-connected energy storage VSG, and a small-signal disturbance is introduced near the steady-state operating point.

[0066] After introducing a small-signal disturbance near the steady-state operating point, a VSG small-signal model is generated by removing the steady-state and nonlinear components.

[0067] In this example embodiment, the method further includes:

[0068] The natural oscillation frequency ω in the Pf loop parameters is calculated based on the virtual synchronizer small-signal model. ωo-ωn And damping ratio ξ ωo-ωn The Pf loop parameters are optimized based on the preset first constraint and the preset second constraint.

[0069] The reactive power closed-loop transfer function in the Qv loop parameters is calculated based on the virtual synchronous machine small-signal model, and the Pf loop parameters are optimized based on the preset third constraint and the preset fourth constraint.

[0070] In step S130, the grid-connected energy storage VSG control circuit, which is tuned according to the grid-connected energy storage VSG parameters, can determine the pre-synchronization control by judging the voltage difference between the inside and outside of the AC switch based on the preset pre-synchronization logic, thereby realizing the seamless switching of the grid-connected energy storage PCS to the grid / network.

[0071] In this example embodiment, the pre-synchronization logic in the method further includes:

[0072] When the system starts in VSG mode and operates independently, there is no voltage on either side of the switch, the AC switch is closed, the voltage difference between the inside and outside of the AC switch is 0V, the pre-synchronization output module is 0, and the angular frequency is the rated angular frequency ω. n The Qv loop reference voltage is the rated voltage. VSG starts to build up the output voltage until the voltage outside the switch is sampled (V). g If the value exceeds the first preset threshold, the normal Pf loop is enabled, and the system begins to operate normally.

[0073] When the system starts in VSG mode and operates in grid-connected mode, there is a voltage difference between the inside and outside of the switch. The AC switch is open, and the system starts pre-synchronization. The Pf loop of VSG is not enabled, and the reference voltage of the Qv loop is the grid voltage. When the voltage difference between the inside and outside of the switch is less than the second preset judgment value, it is considered that the pre-synchronization is completed, the AC switch can be closed, the pre-synchronization is exited, and the Pf loop is enabled.

[0074] In this example embodiment, the method further includes:

[0075] The pre-synchronization control uses an integral controller to achieve the pre-synchronization function. The integral controller and the subsequent angular velocity integral module form PI control, thereby achieving phase synchronization.

[0076] Example 2:

[0077] In this example embodiment, the present invention establishes an active / reactive small-signal model of the grid-connected energy storage VSG based on a dual closed-loop control VSG scheme, proposes a detailed parameter design process for the grid-connected energy storage VSG, and ensures that the grid-connected energy storage VSG provides the grid with damping, inertia, response time, and power control error that meet the standard requirements. Based on the improvement of the pre-synchronization control loop and related logic, a novel pre-synchronization strategy is proposed, which has the advantages of simple structure and easy industrial implementation.

[0078] In this example embodiment, the basic principle of the grid-connected / networked circuit of the grid-connected energy storage PCS based on the virtual synchronous generator-controlled VSG includes:

[0079] Grid connection / networking of VSG for grid-connected energy storage, such as Figure 2 As shown. The system as a whole consists of a battery, DC switch, intelligent power module and corresponding drive module, LC filter, and AC switch. i represents the bridge arm current sampling; i o Sample the output current; v o For sampling the voltage inside the AC switch; v g The voltage outside the switch is sampled. The output voltage of the grid-connected energy storage VSG control is denoted as V. o ∠0; The power grid passes through the line impedance Z line Upon reaching the grid connection point, the grid voltage is denoted as V. g ∠0.

[0080] according to Figure 2 It can be concluded that when the voltage at the PCC point and the output voltage of the grid-connected energy storage VSG are out of sync in terms of amplitude and phase, a voltage drop ΔV exists between the inner and outer sides of the AC switch, resulting in a near short circuit at the moment of grid connection and generating a huge current surge. Therefore, the voltages between the inner and outer sides of the AC switch should be synchronized before the grid-connected energy storage VSG is connected to the grid.

[0081] like Figure 3 The block diagram of the grid-connected energy storage VSG control with pre-synchronization function is shown. The grid-connected energy storage VSG control algorithm consists of power calculation and filtering, phase-locked loop, pre-synchronization and related logic, Pf loop, Qv loop, dual closed loop, virtual impedance and PWM wave generation module.

[0082] In the Pf loop, primary frequency regulation is achieved by simulating the characteristics of a synchronous generator governor (active frequency droop characteristic), and the mathematical expression is:

[0083] P m =P ref +K f (ω n -ω o (1)

[0084] P m P represents the mechanical power of the virtual synchronous generator. ref It is the reference active power; K f ω is the active power-frequency droop factor. n and ω o These represent the rated angular frequency and output angular frequency of the VSG, respectively.

[0085] In the Pf loop, the inertia and damping functions are achieved by referencing the rotor motion equations of a synchronous generator set. The mathematical expression of the first-order transfer function used is:

[0086]

[0087] T m T e Let the mechanical torque and electromagnetic torque of the VSG be represented respectively, and their expressions be as follows:

[0088]

[0089] In the Pf loop, the expressions for the VSG output angular velocity and angle are as follows:

[0090] dθ / dt=ω o (4)

[0091] In the Qv loop, the primary voltage regulation function is achieved by simulating the reactive voltage droop characteristics of a synchronous generator. m The total reactive power reference of the VSG is expressed mathematically as follows:

[0092] Q m =Q ref +K V (V ref -V o (5)

[0093] In the Qv loop, the output voltage is controlled by an excitation regulator that simulates a synchronous generator. The mathematical expression is:

[0094] E p =K Q ∫(Q m -Q e )dt (6)

[0095] Qv loop output reference electromotive force amplitude E pThe Pf loop output angle θ, after coordinate transformation, generates the VSG internal reference voltage, which is then used to generate the modulation wave signal e through virtual impedance and dual closed-loop control. abc The signal is fed into the PWM waveform generation module and compared with the carrier wave to generate a pulse signal, which is then applied to the IPM.

[0096] The VSG pre-synchronization stage of the grid-connected energy storage system consists of four modules: frequency pre-synchronization, phase pre-synchronization, amplitude pre-synchronization, and pre-synchronization judgment logic. The judgment module outputs command signals from SW1, SW2, SW3, and the AC switch. When the system is in pre-synchronization (about to be connected to the grid or at the moment of grid formation), the AC switch outputs a command signal of 0, SW1 to SW3 output a signal of 1, and modules 1 to 3 are connected to the control system; when the system is not in pre-synchronization (islanding operation or already connected to the grid), SW1 to SW3 output a signal of 0, and modules 1 to 3 are bypassed.

[0097] In this example embodiment, the VSG control parameter tuning for grid-connected energy storage includes:

[0098] This invention adopts Figure 3 This design is based on an example. The advantage of this design is that it can serve as a foundational framework, facilitating further expansion into subsequent designs. Since there are numerous control parameters for grid-connected energy storage VSG, its design process can be referenced... Figure 4 A complete design should follow the three-step process of stand-alone operation, pre-synchronization, and grid connection.

[0099] The dual closed-loop control block diagram is as follows: Figure 5 Consider the system control block diagram of the controlled object as follows: Figure 6 .

[0100] Open-loop transfer function of the current loop:

[0101]

[0102] Based on the relationship between the typical Type I system's following performance index and frequency domain index and parameters in the principles of automatic control, it can be seen that the system at k... pi K PWM L -1 *1.5T s At time 0.5, the optimal damping ratio of 0.707 is obtained, and the current loop proportionality coefficient k pi The calculation formula is as follows:

[0103]

[0104] To simplify the design, the influence of sampling delay / wave generation is ignored in the voltage loop proportional-integral coefficient design, thus simplifying it to a first-order inertial element. The closed-loop transfer function of the inner current loop can be simplified as follows:

[0105]

[0106] Depend on Figure 6 The open-loop transfer function of the voltage loop is obtained from equation (9) as follows:

[0107]

[0108] The open-loop transfer function and mid-bandwidth of a typical Type II system are defined as follows:

[0109]

[0110] From equations (10)(11)(12), we can obtain

[0111]

[0112] Where h is the system bandwidth determined using the oscillation index method, and this invention selects 5.

[0113] In this example embodiment, the Pf loop parameter design includes:

[0114] (1) Active frequency regulation coefficient K f

[0115] The active power frequency regulation factor of a virtual synchronous machine is clearly defined in GB / T 38983.1-2020 "Virtual Synchronous Machines Part 1: General Principles". The active power frequency regulation factor characterizes the rate of change of active power with frequency, and the factor is usually expressed as K. f The formula is as follows:

[0116]

[0117] The sign of the above formula determines the direction of the converter current sampling. For energy storage converters, the current sampling direction is generally assumed to be positive when the converter is inverting, and the power supplied to the grid is positive power. This invention follows the positive sign. ΔP represents the change in active power of the virtual synchronous machine, and Δf represents the change in frequency of the virtual synchronous machine. n with f n These are the rated power and frequency of the virtual synchronizer, respectively, with default units of kW and Hz. The standard specifies K... f The range should ideally be between 20 and 50, when K f When K is 20, and the grid frequency changes by 0.05 pu, the system outputs 1 pu of active power; f With a power grid frequency change of 0.02 pu, the system outputs 1 pu of active power. The Pf loop design should follow the dead-zone setting, that is, when the power grid frequency change is within the range of 0.033-0.1 Hz, the Pf loop should not play a regulating role.

[0118] (2) Moment of inertia J of the virtual synchronous machine

[0119] The People's Republic of China Electric Power Industry Standard, Technical Specification for Grid-Connected Operation and Control of Electrochemical Energy Storage Power Stations, Part 7: Inertia Support and Damping Control, defines inertia (J) as a characteristic parameter characterizing the rotational inertia of an electrochemical energy storage power station simulating a traditional synchronous generator, with units of kilograms squared. It also defines T as a characteristic parameter characterizing the time constant of an electrochemical energy storage power station simulating a traditional synchronous generator. j The calculation parameters are as follows:

[0120]

[0121] It is worth noting that the rated power P here n The unit is W. The standard "Virtual Synchronous Generator Part 1: General Principles" specifies the inertial time constant T of a virtual synchronous generator. j It is advisable to keep the time within the range of 3 to 12 seconds.

[0122] (3) Damping control D: Since the damping coefficient of the virtual synchronous generator should be equal to the inertial time constant T j The tuning is designed to ensure that the virtual inertia and primary frequency regulation active power overshoot meet the grid connection requirements, but no clear design specifications are given. This parameter will be discussed in the optimization control section.

[0123] In this example embodiment, the Qv loop parameter design includes:

[0124] (1) Reactive power voltage regulation coefficient K v

[0125] The reactive power regulation coefficient of a virtual synchronous machine is clearly defined in GB / T 38983.1-2020 "Virtual Synchronous Machines Part 1: General Principles". The reactive power regulation coefficient characterizes the rate of change of reactive power with voltage variation, and the coefficient is usually represented by K. v The formula is described as follows:

[0126]

[0127] The signs of the above equation have been explained above. ΔQ represents the change in reactive power of the virtual synchronous machine, and ΔU represents the change in voltage of the virtual synchronous machine. n with U n These are the rated power and frequency of the virtual synchronizer, respectively, with default units of kvar and V. The standard specifies Kvar. v The range should preferably be between 12.5 and 33.3, when K v When the voltage is 12.5, a grid voltage change of 0.08 pu results in a system output of 1 pu of reactive power; when the voltage is 50, a grid voltage change of 0.03 pu results in a system output of 1 pu of reactive power.

[0128] (2) Excitation regulator K e This parameter does not have a design specification; it will be discussed in the section on optimization control.

[0129] In this example embodiment, the VSG parameter optimization design for grid-connected energy storage includes:

[0130] To better analyze the dynamic characteristics of the VSG under small disturbances and select appropriate parameters, a small-signal model needs to be established. The basic principle of the virtual synchronous machine small-signal model is to use a single-input single-output (SISO) system to evaluate the system's following performance under different parameters, neglecting power coupling. The angle difference between the bridge arm voltage of the energy storage converter and the voltage at the PCC point is defined as the power angle, and its mathematical expression is as follows:

[0131] δ=δ o -δ PCC =∫ω o -ω g dt (17)

[0132] The apparent power S output by VSG to PCC point is...

[0133]

[0134] From (18), the active and reactive power outputs of VSG are respectively

[0135]

[0136] Ignoring the effect of parasitic resistance R, simplifying (19) yields...

[0137]

[0138] From (18), the steady-state operating point (with the grid frequency at the rated value and the VSG output active and reactive power both at 0) is derived:

[0139]

[0140] By introducing a small-signal perturbation near the steady-state operating point, the variables of VSG are expressed as follows:

[0141]

[0142] Combining (1)-(5), (17) and (19) and removing the steady-state and nonlinear components, we obtain the VSG small-signal model:

[0143]

[0144] Perform a Laplace transform on the above equation and substitute it into (19).

[0145]

[0146] The VSG small signal model is as follows: Figures 7A-7B As shown:

[0147] In this example embodiment, the design and optimization of Pf loop parameters includes:

[0148] Depend on Figure 6 The small-signal transfer function of the VSG output active power and the grid angular frequency is:

[0149]

[0150] Natural oscillation frequency ω pe-ωg And damping ratio ξ pe-ωg for

[0151]

[0152] The small-signal transfer function of the VSG output active power and the reference power is:

[0153]

[0154] The natural oscillation frequency ω of system (27) pe-pm And damping ratio ξ pe-pm for

[0155]

[0156] The small-signal transfer function of the VSG output angular frequency and the reference angular frequency is:

[0157]

[0158] Natural oscillation frequency ω ωo-ωn And damping ratio ξ ωo-ωn for

[0159]

[0160] Where A = V n 2 / X.

[0161] According to national standards, the VSG output active power curve can be set to the optimal damping or overdamped state, thus obtaining constraint condition 1:

[0162] 0.707≤ζ pe-pm <1 (31)

[0163] The national standard specifies the active response time t s <500ms, and combined with the second-order system response time (often represented by 4 times the time constant to indicate that the system output has reached 98% of its steady-state value), we obtain constraint condition 2.

[0164]

[0165] In this example embodiment, the Qv loop parameter design and optimization includes:

[0166] The reactive power closed-loop transfer function is

[0167]

[0168] The reactive power closed-loop transfer function is a first-order inertial element, X / (K Q V n K is the inertial time constant. Q The larger the value, the shorter the response time. Since the response time of the reactive power regulation system is specified to be no more than 500ms, then 3X / (K Q V n If 0.5s < 0.5s, then constraint condition 3 can be obtained:

[0169]

[0170] The reactive open-loop gain is G Q (s)=1 / X / (K Q V n Let the open-loop cutoff frequency of reactive power be fq, and the open-loop gain at the cutoff frequency be 0dB. Therefore...

[0171]

[0172] Organizing can yield

[0173]

[0174] To ensure that fq is sufficiently small to suppress the influence of the second harmonic fluctuation in instantaneous reactive power on the reference voltage amplitude, a value of 10Hz is typically chosen, thus yielding constraint condition 4:

[0175]

[0176] In this example embodiment, the pre-synchronization principle and logic include:

[0177] like Figure 11-12 As shown, the pre-synchronization control strategy proposed in this invention automatically determines whether pre-synchronization control needs to be enabled by judging the pressure difference (instantaneous pressure difference) between the inside and outside of the AC switch, and defines AC switch 1 as closed and 0 as open.

[0178] When the system starts in VSG mode and is operating independently (islanded), there is no voltage on either side of the switch, the AC switch is closed, the voltage difference between the inside and outside of the AC switch is 0V, the pre-synchronization output module is 0, and the angular frequency is the rated angular frequency ω. n The Qv loop reference voltage is the rated voltage. VSG starts to build up the output voltage until V... gWhen the voltage is >30V, the normal Pf loop is enabled, and the system starts to operate normally. When the system starts VSG mode and operates in grid-connected mode, there is a voltage difference between the inside and outside of the switch. The AC switch is disconnected, and the system starts pre-synchronization. The Pf loop of VSG is not enabled, and the reference voltage of the Qv loop is the grid voltage. When the voltage difference between the inside and outside of the switch is less than 3V, it is considered that the pre-synchronization is completed. The AC switch can be closed, the pre-synchronization is exited, and the Pf loop is enabled.

[0179] The pre-synchronization control proposed in this invention uses an integral controller K. I It can achieve pre-synchronization function, K I This forms a PI control with the subsequent angular velocity integral module, thereby achieving phase synchronization. The phase angle difference is segmented to eliminate sign jumps; the phase angle jump elimination module follows equation (38). This invention K I When the value is selected as 0.02, and the AC switch is closed, the VSG reference angular frequency is the rated angular frequency ω. n When the AC switch is in the open state, the VSG reference angular frequency is the grid angular frequency ω. g The proposed solution reduces design complexity compared to traditional pre-synchronization, can automatically adapt to grid-connected / off-grid conditions, and does not require the issuance of pre-synchronization commands.

[0180]

[0181] Example 3:

[0182] In this example embodiment, the parameter calculation of a 300VA grid-connected energy storage VSG is used as an example.

[0183] This invention uses a 300VA PCS as an example to perform parameter tuning, with the discretization method being "ZOH" and the discrete time T. s It is 1 / 10k. The main loop parameters of the system are shown in Table 1.

[0184] Table 1 Main circuit parameters of the 300VA experimental platform

[0185]

[0186] The voltage and current loop parameters are calculated. The current loop kp-i is calculated to be 3.33 by (7). The step response curve and stability margin of the current closed loop controller are shown in Figure 8.

[0187] Figure 8A This indicates that the designed current inner loop proportional coefficient has a good ability to track the reference signal. The current proportional controller tracks the step signal quickly, reaching steady state in about 1ms. The system has a certain overshoot, with a peak value of about 1.04, which indicates that the system has a high response speed. The system gradually returns to steady state, indicating that there is a certain damping ratio to reduce oscillation. Figure 8BThis indicates that the designed current proportional controller has good stability, a phase margin of about 65°, and a control bandwidth of about 514Hz.

[0188] Substituting the values ​​into (10), the voltage loop proportional controller coefficient k is solved. pu The integral controller coefficient k is 0.02. iu The value is 13.33. Under dual closed-loop control, the system step response curve and stability margin are as follows: Figures 9A-9B As shown.

[0189] Figure 9A (a) indicates that the designed voltage proportional-integral coefficient has good tracking ability of the reference signal, the rise time of the step response is fast, the system reaches steady state in about 4ms, there is a certain overshoot, the peak value is about 1.3, indicating that the system has a high response speed; (b) indicates that the designed voltage proportional-integral coefficient can be well stable and has a phase margin of about 45°, and the control bandwidth is about 311Hz.

[0190] In this example embodiment, the Pf loop optimization calculation yields the virtual synchronous machine active power frequency regulation coefficient K from (11). f The range value is 19.099~47.746. From (12), the range of the virtual synchronizer's moment of inertia J is 0.00913~0.0365; the range of the virtual synchronizer's damping D is also obtained. Finally, the range values ​​of the moment of inertia J and damping D that make the system stable are as follows: Figure 10 As shown.

[0191] In this example embodiment, the Qv loop optimization calculation, based on the formula above, yields the virtual synchronous machine excitation regulator K. Q The coefficient ranges from 0.06 to 0.6, and the reactive power regulation coefficient (Kv) ranges from 120.97 to 322.58.

[0192] Based on the above analysis, the range of control parameters for the virtual synchronous machine, with a rated capacity of 300VA-PCS, is shown in Table 2.

[0193] Table 2 VSG Control Parameters

[0194]

[0195] In this example embodiment, the present invention designs the VSG parameters for grid-connected energy storage according to national standards, and designs parameters not yet specified in the standards through VSG small-signal modeling. The designed parameters have been experimentally proven to have grid-connection capability and meet current standard requirements. This design can provide a feasibility reference for industrial and commercial grid-connected energy storage. The adaptive moment of inertia, damping scheme, and other additional functions (such as harmonic suppression, adaptive virtual impedance, power limiting circuitry, etc.) can use this design as their rated values.

[0196] This invention achieves seamless switching of VSG (Variable Relay Station) in grid-connected energy storage systems by improving the pre-synchronization algorithm. Simulations and experiments have demonstrated that the designed pre-synchronization algorithm has advantages such as simple structure and ease of design.

[0197] This invention selects three pairs of SCRs for grid-connected energy storage VSG testing. The design of virtual impedance is not discussed. If the SCRs are at different levels, the virtual impedance value needs to be changed to adapt to different grid strengths and meet the grid construction requirements.

[0198] It should be noted that although the steps of the method in this disclosure are described in a specific order in the accompanying drawings, this does not require or imply that the steps must be performed in that specific order, or that all the steps shown must be performed to achieve the desired result. Additional or alternative steps may be omitted, multiple steps may be combined into one step, and / or a step may be broken down into multiple steps.

[0199] Furthermore, this example embodiment also provides a device for VSG parameter tuning and seamless switching in grid-connected energy storage. (Refer to...) Figure 13 As shown, the VSG parameter tuning and seamless switching device 200 for grid-connected energy storage may include: a parameter design module 210, a parameter tuning module 220, and a seamless switching module 230. Wherein:

[0200] The parameter design module 210 is used to design the control parameters of the grid-connected energy storage VSG according to the grid-connected / networked circuit of the grid-connected energy storage PCS based on the virtual synchronous generator control VSG, and to establish the grid-connected energy storage VSG control circuit.

[0201] The parameter tuning module 220 is used to establish a virtual synchronous machine small-signal model based on the grid-connected energy storage VSG control circuit, and to optimize the control parameters of the grid-connected energy storage VSG based on the virtual synchronous machine small-signal model, thereby completing the parameter tuning of the grid-connected energy storage VSG.

[0202] The seamless switching module 230 is used to adjust the grid-connected energy storage VSG control circuit according to the grid-connected energy storage VSG parameters. Based on the preset pre-synchronization logic, it determines the pre-synchronization control by judging the voltage difference between the inside and outside of the AC switch, thereby realizing the seamless switching of the grid-connected energy storage PCS to the grid / network.

[0203] The specific details of each of the above-mentioned grid-connected energy storage VSG parameter tuning and seamless switching device modules have been described in detail in the corresponding grid-connected energy storage VSG parameter tuning and seamless switching method, so they will not be repeated here.

[0204] It should be noted that although several modules or units of a grid-connected energy storage VSG parameter tuning and seamless switching device 200 have been mentioned in the detailed description above, this division is not mandatory. In fact, according to the embodiments of this disclosure, the features and functions of two or more modules or units described above can be embodied in one module or unit. Conversely, the features and functions of one module or unit described above can be further divided and embodied by multiple modules or units.

[0205] Furthermore, the above figures are merely illustrative of the processes included in the method according to exemplary embodiments of the present invention, and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0206] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0207] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method for VSG parameter tuning and seamless switching in grid-connected energy storage, characterized in that, The method includes: Based on the grid-connected / networked circuit of the grid-connected energy storage PCS based on the virtual synchronous generator control VSG, the control parameters of the grid-connected energy storage VSG are designed respectively, and the grid-connected energy storage VSG control circuit is established. Based on the aforementioned grid-connected energy storage VSG control circuit, a virtual synchronous machine small-signal model is established. Based on this model, the control parameters of the grid-connected energy storage VSG are optimized, completing the VSG parameter tuning. The control parameters of the grid-connected energy storage VSG include voltage and current loop parameters. P - f Loop parameters, Q - v Loop parameters; The grid-connected energy storage VSG control circuit, tuned according to the VSG parameters, uses preset pre-synchronization logic to determine pre-synchronization control by judging the voltage difference between the inside and outside of the AC switch, thereby enabling the switching of the grid-connected energy storage PCS to the grid / network. The preset pre-synchronization logic further includes: when the system starts VSG mode and is operating independently, the AC switch is closed, the voltage difference between the inside and outside of the AC switch is 0V, the pre-synchronization output module is 0, and the angular frequency is the rated angular frequency. ω n , Q - v The loop reference voltage is the rated voltage. The VSG starts to build up the output voltage until the voltage outside the switch is sampled. V g Greater than the first preset judgment value, normal P - f The loop is enabled, and the system operates; when the system starts in VSG mode and operates in grid-connected mode, the AC switch is disconnected, the system starts pre-synchronization, and the VSG... P - f Loop circuit disabled. Q - v The loop reference voltage is the mains voltage. When the voltage difference between the inside and outside of the switch is less than the second preset judgment value, it is considered that the pre-synchronization is completed, the AC switch can be closed, and the pre-synchronization is terminated. P - f Loop enable.

2. The method as described in claim 1, characterized in that, The method further includes: The P - f The design of loop parameters includes the active frequency regulation coefficient. K f Moment of inertia of virtual synchronizer J Damping control D Parameter design; The Q - v The design of loop parameters includes the reactive power regulation coefficient. K v Excitation regulator K e Parameter design.

3. The method as described in claim 1, characterized in that, The method for establishing a virtual synchronizer small-signal model also includes: The active and reactive power outputs of the grid-connected energy storage VSG are obtained by calculating the apparent power output of the VSG to the point of common coupling (PCC). The steady-state operating point is calculated based on the output active and reactive power of the grid-connected energy storage VSG, and a small-signal disturbance is introduced near the steady-state operating point. After introducing a small-signal disturbance near the steady-state operating point, a VSG small-signal model is generated by removing the steady-state and nonlinear components.

4. The method as described in claim 3, characterized in that, The method further includes: Calculation based on the virtual synchronizer small-signal model P - f Natural oscillation frequency in loop parameters ω ωo-ωn Damping ratio ξ ωo-ωn And based on the preset first constraint and the preset second constraint, the P - f The loop parameters were optimized.

5. The method as described in claim 4, characterized in that, The method further includes: Calculation based on the virtual synchronizer small-signal model Qv The closed-loop transfer function of reactive power in the loop parameters, and based on the preset third constraint and preset fourth constraint, the following conditions are considered. Qv The loop parameters were optimized.

6. The method as described in claim 1, characterized in that, The method further includes: The pre-synchronization control uses an integral controller to achieve the pre-synchronization function. The integral controller and the subsequent angular velocity integral module form a PI control to achieve phase synchronization.

7. A device for VSG parameter tuning and seamless switching in grid-connected energy storage, characterized in that, The device includes: The parameter design module is used to design the control parameters of the grid-connected energy storage VSG based on the grid-connected / networked circuit of the grid-connected energy storage PCS based on the virtual synchronous generator control VSG, and to establish the grid-connected energy storage VSG control circuit. The parameter tuning module is used to establish a virtual synchronous machine small-signal model based on the grid-connected energy storage VSG control circuit, and to optimize the control parameters of the grid-connected energy storage VSG based on the virtual synchronous machine small-signal model, thereby completing the parameter tuning of the grid-connected energy storage VSG; the control parameters of the grid-connected energy storage VSG include voltage and current loop parameters, P - f Loop parameters, Q - v Loop parameters; The seamless switching module is used to adjust the grid-connected energy storage VSG control circuit according to the grid-connected energy storage VSG parameters. Based on preset pre-synchronization logic, it determines the pre-synchronization control by judging the voltage difference between the inside and outside of the AC switch, thereby realizing seamless switching of the grid-connected energy storage PCS to the grid / network. The preset pre-synchronization logic also includes: when the system starts VSG mode and is operating independently, the AC switch is closed, the voltage difference between the inside and outside of the AC switch is 0V, the pre-synchronization output module is 0, and the angular frequency is the rated angular frequency. ω n , Q - v The loop reference voltage is the rated voltage. The VSG starts to build up the output voltage until the voltage outside the switch is sampled. V g Greater than the first preset judgment value, normal P - f The loop is enabled, and the system operates; when the system starts in VSG mode and operates in grid-connected mode, the AC switch is disconnected, the system starts pre-synchronization, and the VSG... P - f Loop circuit disabled. Q - v The loop reference voltage is the mains voltage. When the voltage difference between the inside and outside of the switch is less than the second preset judgment value, it is considered that the pre-synchronization is completed, the AC switch can be closed, and the pre-synchronization is terminated. P - f Loop enable.

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