Network construction energy storage VSG parameter setting and seamless switching method and device

Abstract

The invention relates to a network construction energy storage VSG parameter setting and seamless switching method and device. The method comprises the following steps: designing control parameters of a network construction energy storage VSG respectively, and establishing a network construction energy storage VSG control circuit; establishing a small signal model of the virtual synchronous machine, and performing optimization design on the control parameters of the network construction energy storage VSG based on the small signal model of the virtual synchronous machine to complete parameter setting of the network construction energy storage VSG; based on preset pre-synchronization logic, pre-synchronization control judgment is achieved by judging the voltage difference between the inner side and the outer side of the alternating current switch, seamless switching of grid connection / networking of the network construction energy storage PCS is achieved, and the system has the advantages of being simple in structure, easy to design and the like.

Description

Technical Field

[0001] The present disclosure relates to the field of power electronics, and in particular to a method and device for parameter setting and seamless switching of a grid-connected energy storage device (VSG). Background Art

[0002] With the application and development of renewable energy, large-scale power electronic converters are connected to the power grid, and new power systems are gradually showing "low inertia" and "low damping" characteristics, which have become key factors hindering the penetration of new energy. Grid energy storage is expected to become one of the effective control means for the friendly interaction of "source-grid-load" in the future, improve the stability of new power systems, and achieve 100% new energy penetration. The grid-building algorithm includes virtual oscillator control (Virtual Oscillator Control, VOC), droop control (Droop), and virtual synchronous generator control (Virtual Synchronous Generator, VSG). The virtual synchronous generator algorithm provides inertia and damping for the system by imitating the synchronous generator. It is a grid-friendly power supply that can actively support the system voltage / frequency and is widely used in energy storage converters.

[0003] Virtual synchronous generators have derived a variety of control structures, including single-loop effective value control, double closed-loop control, adaptive inertia and damping, additional decoupling terms, and additional virtual impedance. The national standard has made design guidelines and specifications for VSG parameter setting and testing, which points out that the virtual synchronous generator in the grid-connected energy storage converter must have the function of on-grid / off-grid switching. The off-grid to grid-connected VSG of the grid-connected energy storage requires pre-synchronization technology to alleviate the impact of the instantaneous current of the grid connection; when the grid-connected energy storage VSG is on-grid to off-grid, it has the characteristics of a voltage source and can achieve seamless switching. Therefore, the key to the seamless switching technology of the grid-connected energy storage VSG lies in the implementation of reasonable pre-synchronization control. The pre-synchronization control of the grid-connected energy storage is divided into three parts: ① phase pre-synchronization; ② frequency pre-synchronization; ③ amplitude pre-synchronization. In the prior art, the phase-locked loop-free pre-synchronization method based on phase angle compensation reduces one PI controller compared with the traditional pre-synchronization. Following the idea of ​​the virtual synchronous machine in the stator circuit, virtual damping is added to the rotor circuit, and two PI controls are used to complete the pre-synchronization control, which increases the complexity of the pre-synchronization control. The grid voltage amplitude / frequency is used as the reference value of the VSG output voltage / frequency. This design greatly simplifies the pre-synchronization algorithm, but does not design the pre-synchronization logic. An island / grid-connected mode switching strategy, but does not consider the frequency pre-synchronization link, and does not give the pre-synchronization result when the grid frequency deviates from the rated value.

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

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

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

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

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

[0009] Based on the VSG control circuit, a small signal model of a virtual synchronous machine is established, and based on the small signal model of the virtual synchronous machine, the control parameters of the VSG are optimized and designed to complete the parameter setting of the VSG;

[0010] The grid-connected energy storage VSG control circuit is set according to the grid-connected energy storage VSG parameters. Based on the preset pre-synchronization logic, the pre-synchronization control is determined by judging the pressure difference between the inside and outside of the AC switch, thereby realizing seamless switching of the grid-connected energy storage PCS / networking.

[0011] In an exemplary embodiment of the present disclosure, in the method, 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 an exemplary embodiment of the present disclosure, the method further includes:

[0013] The design of the Pf loop parameters includes the active frequency modulation coefficient K f , parameter design of virtual synchronous machine moment of inertia J and damping control D;

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

[0015] In an exemplary embodiment of the present disclosure, the method of establishing a virtual synchronous machine small signal model further includes:

[0016] The output active power and reactive power of the grid energy storage VSG are obtained by calculating the output apparent power of the grid energy storage VSG to the common connection point PCC;

[0017] Calculating a steady-state operating point based on the output active power and reactive power of the grid-connected energy storage VSG, and introducing a small signal disturbance 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 with the steady-state component and the nonlinear component removed.

[0019] In an exemplary embodiment of the present disclosure, the method further includes:

[0020] Calculate the natural oscillation frequency ω in the Pf loop parameters based on the virtual synchronous machine small signal model ωo-ωn and damping ratio ξ ωo-ωn , and optimizing the Pf loop parameters based on the preset first constraint condition and the preset second constraint condition;

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

[0022] In an exemplary embodiment of the present disclosure, the method of presetting the pre-synchronization logic further includes:

[0023] When the system starts the VSG mode and is in independent operation, there is no voltage on both sides 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 , Qv loop reference voltage is rated voltage, VSG starts to build output voltage until the switch outer voltage sampling V g is greater than the first preset judgment value, the normal Pf loop is enabled, and the system starts to operate normally;

[0024] When the system starts the VSG mode and runs in grid connection, there is a voltage difference between the inside and outside of the switch, and the AC switch is disconnected. At this time, the system starts pre-synchronization, the Pf loop of the VSG is not enabled, and the Qv loop reference voltage 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 an exemplary embodiment of the present disclosure, the method further includes:

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

[0027] In one aspect of the present disclosure, a VSG parameter setting and seamless switching device is provided, comprising:

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

[0029] A parameter setting module is used to establish a virtual synchronous machine small signal model based on the grid-building energy storage VSG control circuit, and optimize the control parameters of the grid-building energy storage VSG based on the virtual synchronous machine small signal model to complete the parameter setting of the grid-building energy storage VSG;

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

[0031] A method for parameter setting and seamless switching of a grid-connected energy storage VSG in an exemplary embodiment of the present disclosure comprises: designing control parameters of the grid-connected energy storage VSG according to a grid-connected energy storage PCS grid-connected / networked circuit based on a virtual synchronous generator to control the VSG, and establishing a grid-connected energy storage VSG control circuit; establishing a virtual synchronous machine 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 machine small signal model to complete parameter setting of the grid-connected energy storage VSG; based on the grid-connected energy storage VSG control circuit with parameter setting of the grid-connected energy storage VSG, judging the pressure difference between the inside and outside of the AC switch based on a preset pre-synchronization logic to realize the determination of pre-synchronization control, thereby realizing seamless switching of the grid-connected energy storage PCS grid-connected / networked, and having the advantages of simple structure and easy design.

[0032] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and other features and advantages of the present disclosure will become more apparent by describing in detail example embodiments thereof with reference to the attached drawings.

[0034] Figure 1 A flow chart of a method for parameter setting and seamless switching of a grid-connected energy storage VSG according to an exemplary embodiment of the present disclosure is shown;

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

[0036] Figure 3 A control block diagram of a grid-connected energy storage VSG according to a method for parameter setting and seamless switching of a grid-connected energy storage VSG is shown;

[0037] Figure 4 A grid energy storage VSG parameter design flow chart of a grid energy storage VSG parameter setting and seamless switching method according to an exemplary embodiment of the present disclosure is shown;

[0038] Figure 5 A dual closed-loop control block diagram of a grid-connected energy storage VSG according to a parameter setting and seamless switching method of a grid-connected energy storage VSG is shown;

[0039] Figure 6 A control block diagram of a grid-connected energy storage VSG dual closed-loop system of a grid-connected energy storage VSG parameter setting and seamless switching method according to an exemplary embodiment of the present disclosure is shown;

[0040] Figure 7A-7B A schematic diagram of a small signal model of a grid-connected energy storage VSG according to a parameter setting and seamless switching method of a grid-connected energy storage VSG according to an exemplary embodiment of the present disclosure is shown;

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

[0042] Figures 9A-9B A schematic diagram of a double closed-loop design result of a grid-connected energy storage VSG parameter setting and seamless switching method according to an exemplary embodiment of the present disclosure is shown;

[0043] Fig.10 A schematic diagram of the J / D coordination range value of a grid-connected energy storage VSG parameter setting and seamless switching method according to an exemplary embodiment of the present disclosure is shown;

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

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

[0046] Fig.13 A schematic block diagram of a parameter setting and seamless switching device for grid-connected energy storage VSG according to an exemplary embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0047] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be comprehensive and complete and will fully convey the concepts of the example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar parts, and thus their repeated description will be omitted.

[0048] In addition, the described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced without one or more of the specific details, or other methods, components, materials, devices, steps, etc. may be adopted. In other cases, known structures, methods and devices, implementations, materials or operations are not shown or described in detail to avoid blurring the various aspects of the present 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 may be implemented in software form, or these functional entities or parts of functional entities may be implemented in one or more software hardened modules, or these functional entities may be implemented in different networks and / or processor devices and / or microcontroller devices.

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

[0051] Step S110, according to the PCS grid-connected / networked circuit of the grid-building energy storage based on the virtual synchronous generator control VSG, the control parameters of the grid-building energy storage VSG are designed respectively, and the grid-building energy storage VSG control circuit is established;

[0052] Step S120, based on the control circuit of the grid-building energy storage VSG, a virtual synchronous machine small signal model is established, and based on the virtual synchronous machine small signal model, the control parameters of the grid-building energy storage VSG are optimized and designed to complete the parameter setting of the grid-building energy storage VSG;

[0053] Step S130, according to the grid energy storage VSG control circuit set according to the grid energy storage VSG parameters, based on the preset pre-synchronization logic, the pre-synchronization control is determined by judging the pressure difference between the inside and outside of the AC switch, thereby realizing seamless switching of the grid energy storage PCS grid connection / networking.

[0054] A method for parameter setting and seamless switching of a grid-connected energy storage VSG in an exemplary embodiment of the present disclosure comprises: designing control parameters of the grid-connected energy storage VSG according to a grid-connected energy storage PCS grid-connected / networked circuit based on a virtual synchronous generator to control the VSG, and establishing a grid-connected energy storage VSG control circuit; establishing a virtual synchronous machine 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 machine small signal model to complete parameter setting of the grid-connected energy storage VSG; based on the grid-connected energy storage VSG control circuit with parameter setting of the grid-connected energy storage VSG, judging the pressure difference between the inside and outside of the AC switch based on a preset pre-synchronization logic to realize the determination of pre-synchronization control, thereby realizing seamless switching of the grid-connected energy storage PCS grid-connected / networked, and having the advantages of simple structure and easy design.

[0055] Next, a parameter setting and seamless switching method of a grid-connected energy storage VSG in this example embodiment will be further described.

[0056] Embodiment 1:

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

[0058] In the embodiment of this example, 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 the embodiment of this example, the method further includes:

[0060] The design of the Pf loop parameters includes the active frequency modulation coefficient K f , parameter design of virtual synchronous machine moment of inertia J and damping control D;

[0061] The design of the Qv loop parameters includes the reactive voltage 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-building energy storage VSG control circuit, and the control parameters of the grid-building energy storage VSG can be optimized based on the virtual synchronous machine small signal model to complete the parameter setting of the grid-building energy storage VSG.

[0063] In the embodiment of this example, the method of establishing a virtual synchronous machine small signal model further includes:

[0064] The output active power and reactive power of the grid energy storage VSG are obtained by calculating the output apparent power of the grid energy storage VSG to the common connection point PCC;

[0065] Calculating a steady-state operating point based on the output active power and reactive power of the grid-connected energy storage VSG, and introducing a small signal disturbance 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 with the steady-state component and the nonlinear component removed.

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

[0068] Calculate the natural oscillation frequency ω in the Pf loop parameters based on the virtual synchronous machine small signal model ωo-ωn and damping ratio ξ ωo-ωn , and optimizing the Pf loop parameters based on the preset first constraint condition and the preset second constraint condition;

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

[0070] In step S130, the grid energy storage VSG control circuit can be adjusted according to the grid energy storage VSG parameters, based on the preset pre-synchronization logic, and the pre-synchronization control is determined by judging the pressure difference between the inside and outside of the AC switch, thereby realizing seamless switching of the grid energy storage PCS grid connection / networking.

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

[0072] When the system starts the VSG mode and is in independent operation, there is no voltage on both sides 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 , Qv loop reference voltage is rated voltage, VSG starts to build output voltage until the switch outer voltage sampling V g is greater than the first preset judgment value, the normal Pf loop is enabled, and the system starts to operate normally;

[0073] When the system starts the VSG mode and runs in grid connection, there is a voltage difference between the inside and outside of the switch, and the AC switch is disconnected. At this time, the system starts pre-synchronization, the Pf loop of the VSG is not enabled, and the Qv loop reference voltage 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 the embodiment of this example, the method further includes:

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

[0076] Embodiment 2:

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

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

[0079] The grid connection / networking of VSG Figure 2 As shown in the figure, the system consists of a battery, a DC switch, an intelligent power module and a corresponding drive module, an LC filter, and an AC switch. i is the bridge arm current sampling; i o is the output current sampling; v o is the voltage sampling inside the AC switch; v g The voltage outside the switch is sampled. The output voltage of the VSG control grid energy storage is recorded as V o ∠0; the power grid passes through the line impedance Z line Arriving at the grid connection point, the grid voltage is V g ∠0.

[0080] according to Figure 2 It can be concluded that when the PCC voltage and the grid-connected energy storage VSG control output voltage amplitude and phase are not synchronized, there is a voltage drop ⊿V inside and outside the AC switch, and the grid-connected moment is close to a short circuit, resulting in a huge current shock. Therefore, before the grid-connected energy storage VSG is connected to the grid, the voltage inside and outside the AC switch should be synchronized.

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

[0082] In the Pf loop, the primary frequency regulation function is realized by simulating the synchronous generator speed regulator characteristics (active frequency droop characteristics). The mathematical expression is:

[0083] P m =P ref +K f (ω n -ω o ) (1)

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

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

[0086]

[0087] T m , T e Represent the mechanical torque and electromagnetic torque of VSG respectively, and the expression is

[0088]

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

[0090] dθ / dt=ω o (4)

[0091] In the Qv loop, the primary voltage regulation function is realized by simulating the reactive voltage droop characteristics of the synchronous generator. m Represents the total reactive power reference of VSG, and the mathematical expression is

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

[0093] In the Qv loop, the output voltage is controlled by simulating the excitation regulator of the 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 generates the internal reference voltage of VSG through coordinate change, and then generates the modulation wave signal e through virtual impedance and double closed-loop control. abc , sent to the PWM wave generation module for comparison with the carrier, and finally a pulse signal is generated to act on the IPM.

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

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

[0098] The present invention adopts Figure 3 The advantage of this design is that it can be used as the underlying framework to facilitate further expansion of subsequent designs. Since there are many control parameters for VSG, its design process can be referred to Figure 4 The complete design should be carried out according to the three steps of stand-alone machine / pre-synchronization / grid connection.

[0099] Among them, the double 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] The open-loop transfer function of the current loop is:

[0101]

[0102] According to the typical type I system following performance index and frequency domain index and parameter relationship in automatic control principle, the system is pi K PWM L -1 *1.5T s = 0.5, the best damping ratio is 0.707, and the current loop proportional coefficient k pi The calculation formula is as follows

[0103]

[0104] To simplify the design, in the design of the voltage loop proportional integral coefficient, the influence of the sampling delay / wave generation link is ignored, and then simplified to the first-order inertia link. The closed-loop transfer function of the current inner loop can be abbreviated as

[0105]

[0106] Depend on Figure 6 The voltage loop open-loop transfer function is obtained by equation (9):

[0107]

[0108] The open-loop transfer function and intermediate frequency bandwidth of a typical type II system are defined as

[0109]

[0110] From formula (10), (11), (12), we can get

[0111]

[0112] Wherein, h is the bandwidth in the system determined by the oscillation index method, and the present invention selects 5.

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

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

[0115] The active frequency modulation coefficient of the virtual synchronous machine is clearly defined in GB / T 38983.1-2020 "Virtual Synchronous Machine Part 1: General Principles". The active frequency modulation coefficient represents the rate of change of active power with frequency. The coefficient is usually expressed as K. f The formula is as follows

[0116]

[0117] The positive and negative in the above formula are used to determine the current sampling direction of the converter. For energy storage converters, the default current sampling direction is reverse to positive, and the power provided to the grid is positive power. The present invention uses the positive sign. ⊿P is the change in the active power of the virtual synchronous machine, ⊿f is the change in the frequency of the virtual synchronous machine, P n With f n The default units are kW and Hz respectively. f The range should be between 20 and 50. f is 20, the grid frequency changes by 0.05pu, and the system outputs 1pu of active power; when K f When the grid frequency changes by 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 grid frequency changes within the range of 0.033-0.1 Hz, the Pf loop should not play a regulating role.

[0118] (2) Virtual synchronous machine moment of inertia J

[0119] The Electric Power Industry Standard of the People's Republic of China on the Grid-connected Operation and Control Technical Specifications for Electrochemical Energy Storage Power Stations Part 7: Inertia Support and Damping Control states: Inertia (J) is defined as the characteristic parameter that characterizes the rotational inertia of the electrochemical energy storage power station simulating the traditional synchronous generator, and the unit is kilograms squared. The characteristic parameter T that characterizes the time constant of the electrochemical energy storage power station simulating the traditional synchronous generator is defined. j , the calculation parameters are as follows:

[0120]

[0121] It is worth noting that the rated power P n The unit is W. The standard "Virtual Synchronous Machine Part 1: General Principles" points out that the inertia time constant of the virtual synchronous generator is T j It should be within the range of 3 to 12 seconds.

[0122] (3) Damping control D: Since the damping coefficient of the virtual synchronous generator should be proportional to the inertia time constant T j Through coordinated setting, the virtual inertia and primary frequency regulation active overshoot meet the grid connection requirements, but no clear design indicators are given. This parameter is discussed in the optimization control.

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

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

[0125] The reactive voltage regulation coefficient of virtual synchronous machine is clearly defined in GB / T 38983.1-2020 "Virtual Synchronous Machine Part 1: General Principles". The reactive voltage regulation coefficient represents the rate of change of reactive power with voltage change. The coefficient is usually expressed as K v Indicates that the formula is described as follows:

[0126]

[0127] The positive and negative of the above formula have been explained above. ⊿Q is the change in reactive power of the virtual synchronous machine, ⊿U is the change in voltage of the virtual synchronous machine, and Q n with U n They are the rated power and frequency of the virtual synchronous machine, and the default units are kvar and V respectively. The standard gives K v The range should be between 12.5 and 33.3. v When Kv is 12.5, the grid voltage changes by 0.08pu, and the system outputs 1pu reactive power; when Kv is 50, the grid voltage changes by 0.03pu, and the system outputs 1pu reactive power.

[0128] (2) Excitation regulator K e :No design indicator is given for this parameter, which is discussed in the optimization control.

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

[0130] In order to better analyze the dynamic characteristics of 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 following performance under different parameters, and ignore the power coupling phenomenon. The angle difference between the bridge arm voltage of the energy storage converter and the PCC point voltage is defined as the power angle. 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), we can get the active and reactive power output of VSG as follows:

[0135]

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

[0137]

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

[0139]

[0140] By introducing a small signal disturbance 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 component and nonlinear component, we get the VSG small signal model:

[0143]

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

[0145]

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

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

[0148] Depend on Figure 6 , the small signal transfer function of VSG output active power and 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 VSG output active power and 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 between 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 over-damping state, and constraint condition 1 can be obtained:

[0162] 0.707≤ζ pe-pm <1 (31)

[0163] The national standard stipulates that the active power response time t s <500ms, and combined with the second-order system response time (4 times the time constant is usually used to indicate that the system output reaches 98% of the steady-state value), constraint 2 is obtained.

[0164]

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

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

[0167]

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

[0169]

[0170] The reactive open loop gain is G Q (s)=1 / X / (K Q V n ), assuming the reactive open-loop cutoff frequency is fq, the open-loop gain at the cutoff frequency is 0dB, so

[0171]

[0172] Arrangement available

[0173]

[0174] Let fq be small enough to suppress the influence of the double frequency fluctuation in instantaneous reactive power on the reference voltage amplitude. It is generally selected as 10Hz, and constraint 4 can be obtained:

[0175]

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

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

[0178] When the system starts the VSG mode and is in independent operation (island), there is no voltage on both sides 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, and VSG starts to build up the output voltage until V g>30V, the normal Pf loop is enabled and the system starts to operate normally; when the system starts the VSG mode and runs in grid connection, there is a voltage difference between the inside and outside of the switch, and the AC switch is disconnected. At this time, 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 exits, and the Pf loop is enabled.

[0179] The presynchronization control proposed in the present invention uses an integral controller K I Can realize pre-synchronization function, K I The PI control is formed with the angular velocity integral module of the subsequent stage to achieve phase synchronization. The phase angle difference is processed in sections to eliminate the sign jump. The phase angle jump elimination module follows formula (38). I Selected as 0.02, when the AC switch is closed, the VSG reference angular frequency is the rated angular frequency ω n , when the AC switch is disconnected, the VSG reference angular frequency is the grid angular frequency ω g ; Compared with traditional pre-synchronization, the solution proposed in the present invention reduces the design complexity and can automatically adapt to grid-connected / off-grid working conditions without issuing pre-synchronization instructions.

[0180]

[0181] Embodiment three:

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

[0183] The present invention takes 300VA PCS as an example, and sets its parameters. The discretization mode is "ZOH", and the discrete time T s The system main circuit parameters are shown in Table 1.

[0184] Table 1 300VA test platform main circuit parameters

[0185]

[0186] Calculation of voltage and current loop parameters. 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] Fig. 8A It shows 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 and reaches a steady state in about 1ms. The system has a certain overshoot, with a peak value of about 1.04, which shows that the system has a high response speed. The system gradually returns to a steady state, indicating that there is a certain damping ratio to reduce oscillation; Figure 8BIt shows 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), we can solve for the voltage loop proportional controller coefficient k: pu is 0.02; the integral controller coefficient k iu is 13.33. Under double closed-loop control, the system step response curve and stability margin are as follows Figures 9A-9B shown.

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

[0190] In the embodiment of this example, the Pf loop is optimized and calculated, and the active frequency modulation coefficient K of the virtual synchronous machine is obtained by (11): f The range value is 19.099~47.746. From (12), we can get the range of virtual synchronous machine moment of inertia J is 0.00913~0.0365; the range of virtual synchronous machine damping D can be obtained, and finally the range of inertia J and damping D that make the system stable is as follows Fig.10 shown.

[0191] In the embodiment of this example, the Qv loop is optimized and calculated. According to the above formula, the virtual synchronous machine excitation regulator K can be obtained. Q Coefficient 0.06~0.6, reactive voltage regulation coefficient Kv range 120.97~322.58

[0192] From the above analysis, we can see that with a rated capacity of 300VA-PCS, the range of virtual synchronous machine control parameters is shown in Table 2:

[0193] Table 2 VSG control parameters

[0194]

[0195] In the embodiment of this example, the present invention designs the VSG parameters for grid-building energy storage according to the requirements of national standards, and designs the parameters that are not given in the standards through VSG small signal modeling. The designed parameters have been proven through experiments to have the ability to build a grid and meet the current standard requirements. This design can provide a feasibility reference for industrial and commercial grid-building energy storage; adaptive moment of inertia, damping schemes and other additional functions (such as harmonic suppression, adaptive virtual impedance, power limiting link, etc.) can use this design as the rated value;

[0196] The present invention realizes seamless switching of VSG for energy storage by improving the pre-synchronization algorithm. The designed pre-synchronization algorithm has been proved by simulation and experiment to have the advantages of simple structure and easy design.

[0197] The present invention selects SCR as 3 pairs of grid-building energy storage VSG for testing, and does not discuss the design of virtual impedance. If the SCR is at different levels, the virtual impedance value needs to be changed to adapt to different grid strengths to meet the grid-building requirements.

[0198] It should be noted that, although the steps of the method in the present disclosure are described in a specific order in the drawings, this does not require or imply that the steps must be performed in this specific order, or that all the steps shown must be performed to achieve the desired results. Additionally or alternatively, some steps may be omitted, multiple steps may be combined into one step, and / or one step may be decomposed into multiple steps, etc.

[0199] In addition, in this exemplary embodiment, a VSG parameter setting and seamless switching device is also provided. Fig.13 As shown, the VSG parameter setting and seamless switching device 200 may include: a parameter design module 210, a parameter setting module 220 and a seamless switching module 230. Among them:

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

[0201] A parameter setting module 220 is used to establish a virtual synchronous machine small signal model based on the grid-building energy storage VSG control circuit, and optimize the control parameters of the grid-building energy storage VSG based on the virtual synchronous machine small signal model to complete the parameter setting of the grid-building energy storage VSG;

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

[0203] The specific details of each of the above-mentioned grid-building energy storage VSG parameter setting and seamless switching device modules have been described in detail in a corresponding grid-building energy storage VSG parameter setting 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 setting and seamless switching device 200 are mentioned in the above detailed description, this division is not mandatory. In fact, according to the embodiment of the present 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 into multiple modules or units for embodiment.

[0205] In addition, the above-mentioned figures are only schematic illustrations of the processes included in the method according to an exemplary embodiment of the present invention, and are not intended to be limiting. It is easy to understand that the processes shown in the above-mentioned figures do not indicate or limit the time sequence of these processes. In addition, it is also easy to understand that these processes can be performed synchronously or asynchronously, for example, in multiple modules.

[0206] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include common knowledge or customary technical means in the art that are not disclosed in the present disclosure. The specification and examples are to be considered as exemplary only, and the true scope and spirit of the present disclosure are indicated by the claims.

[0207] It should be understood that the present disclosure is not limited to the exact structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A method for parameter setting and seamless switching of VSG for grid energy storage, characterized in that: The method comprises: According to the PCS grid-connected / networked circuit of grid-connected energy storage based on virtual synchronous generator control VSG, the control parameters of grid-connected energy storage VSG are designed respectively, and the control circuit of grid-connected energy storage VSG is established; Based on the VSG control circuit, a virtual synchronous machine small signal model is established, and based on the small signal model, the control parameters of the VSG are optimized and designed to complete the parameter setting of the VSG; The grid-connected energy storage VSG control circuit is set according to the grid-connected energy storage VSG parameters. Based on the preset pre-synchronization logic, the pre-synchronization control is determined by judging the pressure difference between the inside and outside of the AC switch to achieve the switching of the grid-connected energy storage PCS / networking.

2. The method according to claim 1, characterized in that In the method, the control parameters of the grid-connected energy storage VSG include voltage and current loop parameters, Pf loop parameters, and Qv loop parameters.

3. The method according to claim 2, characterized in that The method further comprises: The design of the Pf loop parameters includes the active frequency modulation coefficient K f , parameter design of virtual synchronous machine moment of inertia J and damping control D; The design of the Qv loop parameters includes the reactive voltage regulation coefficient K v , Excitation regulator K e Parameter design.

4. The method according to claim 1, characterized in that The method for establishing a virtual synchronous machine small signal model further includes: The output active power and reactive power of the grid energy storage VSG are obtained by calculating the output apparent power of the grid energy storage VSG to the common connection point PCC; Calculating a steady-state operating point based on the output active power and reactive power of the grid-connected energy storage VSG, and introducing a small signal disturbance 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 with the steady-state component and the nonlinear component removed.

5. The method according to claim 4, characterized in that The method further comprises: Calculate the natural oscillation frequency ω in the Pf loop parameters based on the virtual synchronous machine small signal model ωo-ωn and damping ratio ξ ωo-ωn , and optimize the Pf loop parameters based on the preset first constraint condition and the preset second constraint condition.

6. The method according to claim 5, characterized in that The method further comprises: The reactive power closed-loop transfer function in the Qv loop parameter is calculated based on the virtual synchronous machine small signal model, and the Pf loop parameter is optimized based on the preset third constraint condition and the preset fourth constraint condition.

7. The method according to claim 1, characterized in that The method further includes presetting the pre-synchronization logic: When the system starts the VSG mode and is in independent operation, 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 , Qv loop reference voltage is rated voltage, VSG starts to build output voltage until the switch outer voltage sampling V g If the value is greater than the first preset judgment value, the normal Pf loop is enabled and the system operates.

8. The method according to claim 7, characterized in that The method further comprises: When the system starts the VSG mode and runs in grid connection, the AC switch is disconnected, the system starts pre-synchronization, the Pf loop of the VSG is not enabled, and the Qv loop reference voltage 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 exits, and the Pf loop is enabled.

9. The method according to any one of claims 7 or 8, characterized in that The method further comprises: The pre-synchronization control uses an integral controller to implement the pre-synchronization function. The integral controller and the subsequent angular velocity integral module form PI control to achieve phase synchronization.

10. A VSG parameter setting and seamless switching device for grid energy storage, characterized in that: The device comprises: The parameter design module is used to design the control parameters of the grid-building energy storage VSG according to the grid-building energy storage PCS grid-connected / networking circuit based on the virtual synchronous generator control VSG, and establish the grid-building energy storage VSG control circuit; A parameter setting module is used to establish a virtual synchronous machine small signal model based on the grid-building energy storage VSG control circuit, and optimize the control parameters of the grid-building energy storage VSG based on the virtual synchronous machine small signal model to complete the parameter setting of the grid-building energy storage VSG; The seamless switching module is used to control the grid-connected energy storage VSG control circuit according to the grid-connected energy storage VSG parameters. Based on the preset pre-synchronization logic, the pre-synchronization control is determined by judging the pressure difference between the inside and outside of the AC switch, thereby realizing the seamless switching of the grid-connected energy storage PCS / networking.

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