Inertia simulation control method for new energy unit based on super capacitor energy storage

Abstract

The application relates to a new energy unit inertia simulation control method based on super capacitor energy storage, wherein the inertia simulation function is realized by super capacitor energy storage control, the super capacitor is connected to an inverter DC bus through a bidirectional DC / DC converter, the new energy unit power generation efficiency and original control are not affected, and the frequency regulation capacity of a power system is improved. On the basis of simulating the inertia characteristics of a synchronous machine, the method further considers simulating the damping winding characteristics and power transmission characteristics of the synchronous machine, so that the stability of the inertia simulation is guaranteed.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of smart grid control, and relates to a new energy unit inertia simulation control method, in particular to a new energy unit inertia simulation control method based on super capacitor energy storage. BACKGROUND

[0002] The power system in China is accelerating the transition from the traditional power system dominated by traditional synchronous machines to the new power system dominated by wind, light and other new energy. However, the new energy units under the traditional control do not have inertia response capability, which leads to a continuous decline in the system inertia level, bringing serious challenges to the system frequency stability.

[0003] Many studies have been conducted at home and abroad to make new energy units have inertia response characteristics. In terms of energy sources for inertia simulation, existing schemes mainly use rotor kinetic energy (wind turbine) or power reserve after load shedding (wind and photovoltaic units) of new energy units. However, rotor kinetic energy control has the risk of rotor stall and frequency secondary drop, and load shedding control reduces the utilization rate and economic benefit of new energy. Therefore, configuring energy storage devices becomes a more advantageous choice, among which super capacitor energy storage is more suitable for providing energy for inertia simulation due to its high power density and long cycle life.

[0004] On the other hand, based on the energy source for inertia simulation, scholars at home and abroad have proposed many virtual synchronous generator (VSG) schemes. One type of scheme embeds the synchronous machine rotor motion equation into the inverter control to replace the phase-locked loop, changes the inverter operating characteristics to a voltage source, and realizes the simulation of the characteristics of the synchronous machine. However, the large-scale modification of the inverter control is difficult to apply to the modification of existing new energy units. Another type of scheme controls the inverter power output by introducing the grid frequency change rate, which is easier to implement. However, the detection of frequency change will introduce high-frequency noise and interfere with the control, and when simulating a large inertia time constant, the system stability will be significantly weakened, and the stable provision of inertia simulation power cannot be guaranteed. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art and provide a new energy unit inertia simulation control method based on super capacitor energy storage. The method does not need to modify the original control of new energy units, does not affect the power generation efficiency of new energy, and has good compatibility and economy.

[0006] The technical problem of the present application is solved by the following technical scheme:

[0007] A new energy unit inertia simulation control method based on super capacitor energy storage, characterized in that it comprises the following steps:

[0008] Step 1, the super capacitor connected to the new energy unit DC bus through a bidirectional DC / DC converter is used as the energy source for inertia simulation, and the coupling relationship between the super capacitor voltage and the grid frequency is calculated by simultaneously solving the super capacitor power dynamic equation, the synchronous machine rotor motion equation and the power transmission equation;

[0009] Step 2, according to the calculated coupling relationship, the super capacitor capacitance and the rated voltage of the super capacitor are configured according to the required simulated inertia time constant, the simulated damping coefficient, the simulated reactance coefficient, the rated capacity, the allowed super capacitor voltage variation range and the allowed frequency variation range parameters;

[0010] Step 3, the inertia simulation controller is designed according to the calculated coupling relationship;

[0011] Step 4, the phase-locked loop is used to measure the grid frequency information, and the grid frequency, the simulated inertia time constant, the simulated damping coefficient, the simulated reactance coefficient, the rated capacity, the super capacitor capacitance and the super capacitor rated voltage are input into the inertia simulation controller to output the super capacitor voltage reference value;

[0012] Step 5, the bidirectional DC / DC converter controls the super capacitor voltage variation to provide inertia power through voltage and current double-loop control.

[0013] Further, the coupling relationship is:

[0014] (1)

[0015] In the formula, is the super capacitor voltage reference value, is the simulated inertia time constant, is the rated capacity of the new energy unit, is the super capacitor capacitance, is the rated frequency of the grid, is the simulated reactance coefficient, is the simulated damping coefficient, is the grid frequency, is the rated voltage of the super capacitor.

[0016] Further, the derivation method of the coupling relationship is specifically:

[0017] When the grid is disturbed, the rotor motion equation of the synchronous machine is represented as:

[0018] (2)

[0019] In the formula, H is the inertia time constant of the synchronous machine, D is the damping coefficient of the synchronous machine, f is the rotor frequency of the synchronous machine,P m , P e and Δ P 1 represents the mechanical power, electromagnetic power, and rotor absorbed power when the speed changes of the synchronous machine;

[0020] The power angle of a synchronous machine is expressed as:

[0021] (3)

[0022] In the formula, δ The power angle of the synchronizing machine. s It is a differential operator;

[0023] The power transfer equation for a synchronous machine is expressed as:

[0024] (4)

[0025] In the formula, E is the internal electromotive force of the synchronous machine, U is the grid connection point voltage, and X is the stator reactance; due to normal operation δ Smaller, therefore, sin δ ≈ δ .

[0026] Due to the mechanical power of the synchronous machine P m Powered by the prime mover, when only the inertial response of the synchronous machine is considered, P m Treating it as a constant, therefore, combining equations (2) and (4) yields:

[0027] (5)

[0028] Supercapacitors absorb or release energy through a dual-loop voltage and current control of a bidirectional DC / DC converter. Their power dynamic equation is expressed as:

[0029] (6)

[0030] In the formula, Δ P 2 represents the charging power of the supercapacitor. Let Δ P 1=Δ P 2. We can obtain:

[0031] (7)

[0032] In the formula, E v For the simulated internal potential of supercapacitor energy storage, according to the requirements for safe and stable operation of the power system, the grid voltage should not have a significant deviation; therefore, it can be considered that... E v and UApproximately equal to 1pu, integrating both sides of equation (7) simultaneously yields:

[0033] (8)

[0034] Simplifying the above equation, we get:

[0035] (1)

[0036] Furthermore, the principle for configuring the supercapacitor capacitance value is as follows:

[0037] When the power grid frequency reaches the maximum value allowed for variation and minimum value At that time, the supercapacitor voltage also reaches its maximum value. and minimum value Because the time scale of the grid frequency change during the disturbance is much longer than that in the formula... The second-order response coefficient of the term, therefore, from equation (1) we get:

[0038] (9)

[0039] In the formula, H max The maximum simulable inertial time constant is determined by the design. Equation (9) is then combined and the two sub-equations are eliminated. u SC0 The item can be used to obtain the configured supercapacitor value. C SC for:

[0040] (10)

[0041] Combined equations (9) with two sub-equations and eliminated C SC From this, we can obtain the rated voltage of the supercapacitor. u SC0 for:

[0042] (11).

[0043] Furthermore, the inertia simulation controller includes a second-order transfer function, an inverting adder, a forward adder, and a square root operator connected in sequence. The input of the second-order transfer function is the grid frequency, and its output is connected to the positive input of the inverting adder. The positive input of the inverting adder is the rated grid frequency, and its output passes through a gain circuit. The output of the gain circuit is connected to the input of the forward adder. The other input of the forward adder is the square of the rated voltage of the supercapacitor, and its output passes through a square root operator. The output of the square root operator passes through a limiting circuit to output a reference value for the supercapacitor voltage.

[0044] Furthermore, the supercapacitor voltage reference value is input to the controller of the bidirectional DC / DC converter via a limiter.

[0045] The advantages and beneficial effects of this invention are as follows:

[0046] This invention presents a new energy unit inertia simulation control method based on supercapacitor energy storage. This method enables new energy units to provide inertia support to the power grid without requiring the measurement of frequency change rate. It utilizes real-time grid frequency information to drive the inertia simulation controller and generate a supercapacitor voltage reference value. This invention does not require modification of the existing control system for new energy power generation. The energy for the inertia simulation comes from the supercapacitor connected to the DC bus via a bidirectional DC / DC converter, thus not affecting the efficiency of new energy power generation and exhibiting good compatibility and economic efficiency. Based on the simulated synchronous machine inertia characteristics, this invention further considers the simulated synchronous machine damping winding characteristics and power transmission characteristics, ensuring the stability of the inertia simulation. Attached Figure Description

[0047] Figure 1 This is a topology diagram of new energy generating units connected to the power grid in existing technologies;

[0048] Figure 2 This is a topology diagram of a new energy unit connected to a supercapacitor for energy storage on the DC side in an embodiment of the present invention;

[0049] Figure 3 This is a control block diagram for new energy inertia simulation based on supercapacitor energy storage in an embodiment of the present invention. Detailed Implementation

[0050] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0051] like Figure 1 As shown, this is a system where renewable energy units are connected to the AC power grid. The renewable energy unit consists of a front-end renewable energy generator and a back-end grid-side inverter. The front-end renewable energy generator can be a photovoltaic array or a wind turbine-side converter, operating in maximum power point tracking mode to inject captured power into the DC bus. The back-end grid-side inverter uses constant DC voltage control to maintain a constant DC bus voltage.

[0052] like Figure 2 As shown, this is a system where the DC side of a new energy generating unit is connected to a supercapacitor energy storage system. The supercapacitor is connected to the DC bus via a bidirectional DC / DC converter, and energy exchange with the AC system is achieved through a grid-side inverter.

[0053] like Figure 3 As shown, this is a simulation control of inertia in a new energy source based on supercapacitor energy storage.

[0054] First, by combining the synchronous machine rotor motion equation, power transmission equation, and supercapacitor power dynamic equation, the inertial response process of the synchronous machine is simulated. Then, the simulation of the synchronous machine damping winding and power transmission dynamics is further introduced, and the coupling relationship between the supercapacitor voltage and the grid frequency is obtained.

[0055] Secondly, an inertia simulation controller is designed based on the calculated coupling relationship;

[0056] The inertia simulation controller includes a second-order transfer function, an inverting adder, a forward adder, and a square root operator connected in sequence. The input of the second-order transfer function is the grid frequency, and its output is connected to the positive input of the inverting adder. The positive input of the inverting adder is the rated grid frequency, and its output passes through a gain circuit. The output of the gain circuit is connected to the input of the forward adder. The other input of the forward adder is the square of the rated voltage of the supercapacitor, and its output passes through a square root operator. The output of the square root operator passes through a limiting circuit to output the reference value of the supercapacitor voltage.

[0057] Then, the grid frequency information is measured using a phase-locked loop, and the grid frequency, simulated inertia time constant, simulated damping coefficient, simulated reactance coefficient, rated capacity, supercapacitor capacitance, and supercapacitor rated voltage are input into the inertia simulation controller, and the supercapacitor voltage reference value is output.

[0058] Finally, the bidirectional DC / DC converter provides inertial power by controlling the voltage variation of the supercapacitor through a dual-loop voltage and current control.

[0059] The derivation process of the coupling relationship between the supercapacitor voltage and the power grid frequency is as follows:

[0060] When a disturbance occurs in the power grid, the rotor motion equation of the synchronous machine is expressed as:

[0061] (2)

[0062] In the formula, H The inertial time constant of the synchronous machine D This is the damping coefficient of the synchronizing machine. f The frequency of the synchronous machine rotor. P m , P e and Δ P 1 represents the mechanical power, electromagnetic power, and rotor absorbed power when the speed changes, respectively.

[0063] The power angle of a synchronous machine is expressed as:

[0064] (3)

[0065] In the formula,δ The power angle of the synchronizing machine. s It is a differential operator.

[0066] The power transfer equation for a synchronous machine is expressed as:

[0067] (4)

[0068] In the formula, E is the internal electromotive force of the synchronous machine, U is the grid connection point voltage, and X is the stator reactance; due to normal operation δ Smaller, therefore, sin δ ≈ δ .

[0069] Due to the mechanical power of the synchronous machine P m Powered by the prime mover, when only the inertial response of the synchronous machine is considered, P m It can be considered as a constant. Therefore, combining equations (2) and (4) gives:

[0070] (5)

[0071] Supercapacitors absorb or release energy through a dual-loop voltage and current control of a bidirectional DC / DC converter. Their power dynamic equation is expressed as:

[0072] (6)

[0073] In the formula, Δ P 2 represents the charging power of the supercapacitor. Let Δ P 1=Δ P 2. We can obtain:

[0074] (7)

[0075] In the formula, E v This is a simulated internal potential for supercapacitor energy storage. According to the requirements for the safe and stable operation of the power system, the grid voltage should not have a significant deviation; therefore, it can be considered... E v and U Approximately equal to 1 pu. Integrating both sides of equations (21) and (30) simultaneously, we get:

[0076] (8)

[0077] Simplifying the above equation, we get:

[0078] (1)

[0079] Based on the calculated coupling relationship, an inertia simulation controller is designed. The input parameters of the inertia simulation controller are the grid frequency, simulated inertia time constant, simulated damping coefficient, simulated reactance coefficient, rated capacity, supercapacitor capacitance, and supercapacitor rated voltage. The output is the supercapacitor voltage reference value. A bidirectional DC / DC converter provides inertia power by controlling the supercapacitor voltage variation through a dual-loop voltage and current control.

[0080] The specific principles for configuring the capacity of the supercapacitor are as follows:

[0081] To maximize the energy utilization of supercapacitors, when the grid frequency reaches the set maximum allowable variation value... f max and minimum value f min At that time, the supercapacitor voltage also reaches its maximum value. u SCmax and minimum value u SCmin Because the time scale of the grid frequency change during the disturbance is much longer than that in the formula... f g The second-order response coefficient of the term, therefore, can be obtained from equation (1):

[0082] (9)

[0083] In the formula, H max Let this be the maximum simulable inertial time constant. Solve the two sub-equations above simultaneously, eliminating... u SC0 Item and C SC The item can be used to obtain the configured supercapacitor value. C SC The rated voltages of the supercapacitor and the supercapacitor are respectively:

[0084] (10)

[0085] (11)

[0086] Through the aforementioned new energy inertia simulation control based on supercapacitor energy storage, the supercapacitor voltage, under the control of a bidirectional DC / DC converter, tracks the supercapacitor voltage reference value output by the inertia simulation controller, thereby simulating the inertia characteristics of the synchronous machine. This enables the new energy unit to possess inertia simulation capabilities while simultaneously simulating the characteristics of the synchronous machine's damping windings and power transmission characteristics, effectively ensuring the stability of the inertia simulation. Furthermore, this invention provides the capacity configuration principles and rated voltage selection method for the supercapacitor under the aforementioned control, offering a reference for practical engineering applications.

[0087] Those skilled in the art will understand that embodiments of this disclosure can be provided as methods, systems, or computer program products. Therefore, this disclosure can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this disclosure can take the form of one or more computer-usable storage media (including, but not limited to, disk storage, etc.) containing computer-usable program code. CD - ROM It takes the form of a computer program product implemented on (such as optical memory, etc.).

[0088] This disclosure is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create a machine for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0089] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0090] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0091] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

[0092] While the specific embodiments of this disclosure have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of this disclosure. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of this disclosure are still within the scope of protection of this disclosure.

Claims

1. A method for simulating and controlling the inertia of a new energy unit based on supercapacitor energy storage, characterized in that: Includes the following steps: Step 1: Using the supercapacitor connected to the DC bus of the new energy unit via a bidirectional DC / DC converter as the energy source for inertia simulation, the coupling relationship between the supercapacitor voltage and the grid frequency is calculated by simultaneously solving the supercapacitor power dynamic equation, the synchronous machine rotor motion equation, and the power transmission equation. Step 2: Based on the calculated coupling relationship, configure the supercapacitor capacitance and select the supercapacitor rated voltage according to the required parameters such as simulated inertia time constant, simulated damping coefficient, simulated reactance coefficient, rated capacity, allowable supercapacitor voltage variation range, and allowable frequency variation range. Step 3: Design an inertia simulation controller based on the calculated coupling relationship; Step 4: Measure the grid frequency information using a phase-locked loop, and input the grid frequency, grid rated frequency, simulated inertia time constant, simulated damping coefficient, simulated reactance coefficient, rated capacity, supercapacitor capacitance, and supercapacitor rated voltage into the inertia simulation controller, and output the supercapacitor voltage reference value. Step 5: Using the supercapacitor voltage reference value obtained in Step 4, the bidirectional DC / DC converter controls the supercapacitor voltage change through voltage and current dual-loop control to provide inertial power. The derivation of the coupling relationship is as follows: When a disturbance occurs in the power grid, the rotor motion equation of the synchronous machine is expressed as: (2) In the formula, H The inertial time constant of the synchronous machine, D This is the damping coefficient of the synchronizing machine. f The frequency of the synchronous machine rotor. P m , and Δ P 1 represents the mechanical power, electromagnetic power, and rotor absorbed power when the speed changes of the synchronous machine; The power angle of a synchronous machine is expressed as: (3) In the formula, δ The power angle of the synchronizing machine. s It is a differential operator; The power transfer equation for a synchronous machine is expressed as: (4) In the formula, E is the internal electromotive force of the synchronous machine, U is the grid connection point voltage, and X is the stator reactance; due to normal operation δ Smaller, therefore, ; Will P m Treating it as a constant, therefore, combining equations (2) and (4) yields: (5) Supercapacitors absorb or release energy through a dual-loop voltage and current control of a bidirectional DC / DC converter. Their power dynamic equation is expressed as: (6) In the formula, Δ P 2 represents the charging power of the supercapacitor; let Δ P 1=Δ P 2, we get: (7) In the formula, The simulated internal potential for energy storage in a supercapacitor makes and U Both are equal to 1pu. Integrating both sides of equation (7) simultaneously, we get: (8) Simplifying the above equation, we get: (1) In the formula, This is a reference value for the supercapacitor voltage. To simulate the inertia time constant, For the rated capacity of new energy units, This refers to the capacitance value of the supercapacitor. The rated frequency of the power grid. To simulate the reactance coefficient, To simulate the damping coefficient, For the power grid frequency, This refers to the rated voltage of the supercapacitor. The method for configuring the capacitance value of the supercapacitor and selecting the rated voltage of the supercapacitor is as follows: When the power grid frequency reaches the maximum value allowed for variation and minimum value At that time, the supercapacitor voltage also reaches its maximum value. and minimum value Because the time scale of the grid frequency change during the disturbance is much longer than that in the formula... The second-order response coefficient of the term, therefore, from equation (1) we get: (9) In the formula, To determine the maximum simulable inertial time constant, combine the two sub-equations of equation (9) and eliminate... The item can be used to obtain the configured supercapacitor value. for: (10) Combined equations (9) with two sub-equations and eliminated From this, we can obtain the rated voltage of the supercapacitor. for: (11)。 2. The inertia simulation control method for a new energy unit based on supercapacitor energy storage according to claim 1, characterized in that: The inertia simulation controller includes a second-order transfer function, an inverting adder, a forward adder, and a square root operator connected in sequence. The input of the second-order transfer function is the grid frequency, and its output is connected to the positive input of the inverting adder. The positive input of the inverting adder is the rated grid frequency, and its output passes through a gain circuit. The output of the gain circuit is connected to the input of the forward adder. The other input of the forward adder is the square of the rated voltage of the supercapacitor, and its output passes through a square root operator. The output of the square root operator passes through a limiting circuit to output the reference value of the supercapacitor voltage.

3. The inertia simulation control method for a new energy unit based on supercapacitor energy storage according to claim 1, characterized in that: The supercapacitor voltage reference value is input to the controller of the bidirectional DC / DC converter.

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