Voltage-controlled electrode boiler load frequency modulation system and method based on virtual synchronous machine

Abstract

The invention belongs to the field of electrode boiler load frequency modulation, and provides a voltage-controlled electrode boiler load frequency modulation system and method based on a virtual synchronous machine. The system comprises a voltage control type electrode boiler, an AC / DC converter and a DC / AC converter. An electrode bar of the voltage control type electrode boiler is connected with a power grid through the DC / AC converter and the AC / DC converter in sequence; the voltage-controlled electrode boiler is used as a load for power grid frequency regulation; the power of the voltage-controlled electrode boiler is changed according to the change of the input voltage; the input voltage is the output voltage of the DC / AC converter; the DC / AC converter is connected with the virtual synchronous machine controller; and the virtual synchronous machine controller is used for adaptively calculating rotational inertia according to a comparison result of the angular frequency change rate of the output voltage of the DC / AC converter and an angular frequency change rate threshold value, and determining a d / q axis given reference voltage required by double closed loops of the DC / AC converter by combining the reactive power-voltage droop characteristic of the virtual synchronous machine.

Description

Technical Field

[0001] The present invention belongs to the field of electrode boiler load frequency modulation, and particularly relates to a voltage-controlled electrode boiler load frequency modulation system and method based on a virtual synchronous machine. Background Technique

[0002] The statements in this part merely provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] The rapid and precise regulation of the power grid frequency is an important factor in ensuring the stability of the power system. Due to factors such as geography, lifespan, cost, and the working conditions of loads, traditional frequency modulation resources such as energy storage and loads are difficult to be widely used. Immersion electrode boilers have unique advantages of stepless regulation ability from 0% to 100%, almost 100% electro-thermal conversion efficiency, fast response rate, low cost, and clean and pollution-free.

[0004] The power regulation methods of traditional immersion electrode boilers are all achieved by adjusting the water level in the inner cylinder or adjusting the isolation shield. This method has a slow adjustment speed, requires the installation of a complex transmission structure, and is difficult to meet the rapidly changing power of the power system. Moreover, the electrodes are not fully immersed, presenting certain safety hazards. Summary of the Invention

[0005] In order to solve the technical problems in the above background technique, the present invention provides a voltage-controlled electrode boiler load frequency modulation system and method based on a virtual synchronous machine, which can achieve inertia damping support during the transient process and grid frequency regulation at steady state through the electrode boiler load.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] The first aspect of the invention provides a voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine.

[0008] A voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine includes: a voltage-controlled electrode boiler, an AC / DC converter, and a DC / AC converter; the electrode rods of the voltage-controlled electrode boiler are connected to the power grid through the DC / AC converter and the AC / DC converter in sequence;

[0009] The voltage-controlled electrode boiler serves as a load for power grid frequency regulation; the power of the voltage-controlled electrode boiler changes according to the change of the input voltage; the input voltage is the output voltage of the DC / AC converter;

[0010] The DC / AC converter is connected to the virtual synchronous machine controller; the virtual synchronous machine controller is configured to: adaptively calculate the moment of inertia according to the comparison result between the angular frequency change rate of the output voltage of the DC / AC converter and the angular frequency change rate threshold, and then combine the reactive power-voltage droop characteristic of the virtual synchronous machine to obtain the d / q axis given reference voltage required for the voltage-current double closed loop of the DC / AC converter.

[0011] As an implementation manner, the calculation process of the power of the voltage-controlled electrode boiler is as follows:

[0012]

[0013] Wherein, P is the power of the voltage-controlled electrode boiler; U is the input voltage; R is the resistance value of the solution of the voltage-controlled electrode boiler, which changes with the solution conductivity.

[0014] As an implementation manner, the calculation process of the resistance value of the solution of the voltage-controlled electrode boiler is as follows:

[0015]

[0016] Wherein, L is the length of the electrode rod of the voltage-controlled electrode boiler; ρ is the resistivity of the solution of the voltage-controlled electrode boiler; b is the distance between the electrode axis and the center of the voltage-controlled electrode boiler; d is the cross-sectional diameter of the electrode of the voltage-controlled electrode boiler; r is the radius of the cylindrical container of the voltage-controlled electrode boiler.

[0017] As an implementation manner, in the virtual synchronous machine controller, the process of adaptively calculating the moment of inertia is as follows:

[0018]

[0019] Wherein, J is the moment of inertia; J0 is the basic value of the moment of inertia; M is the threshold of the angular frequency change rate; μ represents the state of the voltage-controlled electrode boiler; ω and ω0 are respectively the angular frequency and the rated angular frequency of the output voltage of the DC / AC converter.

[0020] As an implementation manner, in the virtual synchronous machine controller, the reactive power-voltage droop characteristic of the virtual synchronous machine is as follows:

[0021]

[0022] In the formula: u n , u0 are respectively the rated value and the actual value of the output voltage of the DC / AC converter; Q ref and Q e are respectively the given reactive power and the actual reactive power; K i is the integral coefficient; K q is the reactive power droop coefficient; E mE0 and E0 are the virtual potential and no-load potential respectively.

[0023] As an implementation, in the virtual synchronous machine controller, the angular frequency of the output voltage of the DC / AC converter is calculated through the rotor motion equation of the virtual synchronous machine.

[0024] As an implementation, the rotor motion equation of the virtual synchronous machine is:

[0025]

[0026] where P m , P e and P ref are the mechanical power, electromagnetic power and given active power respectively; ω and ω0 are the angular frequency of the output voltage of the DC / AC converter and the rated angular frequency respectively; J and D are the moment of inertia and damping coefficient respectively; K p is the active droop coefficient.

[0027] As an implementation, in the virtual synchronous machine controller, the virtual potential is calculated through the reactive power-voltage droop characteristic of the virtual synchronous machine, and it is multiplied by the three-phase signals converted from the angular frequency of the output voltage of the DC / AC converter to obtain the d / q-axis given reference voltage required for the voltage-current double closed loop of the DC / AC converter.

[0028] As an implementation, the AC / DC converter is connected to a pulse controller, and the pulse controller is configured to control the power switching tubes in the AC / DC converter according to the set pulse adjustment method.

[0029] The second aspect of the present invention provides a method for a voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine.

[0030] A method for a voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine includes:

[0031] According to the comparison result between the angular frequency change rate of the output voltage of the DC / AC converter and the angular frequency change rate threshold, the moment of inertia is adaptively calculated and fed back to the DC / AC converter;

[0032] Based on the adaptively calculated moment of inertia, the angular frequency corresponding to the output voltage of the DC / AC converter is calculated through the rotor motion equation of the virtual synchronous machine;

[0033] The virtual potential is calculated through the reactive power-voltage droop characteristic of the virtual synchronous machine, and it is multiplied by the three-phase signals converted from the angular frequency of the output voltage of the DC / AC converter to obtain the d / q-axis given reference voltage required for the voltage-current double closed loop of the DC / AC converter to control the output voltage of the DC / AC converter;

[0034] Take the real-time output voltage of the DC / AC converter as the real-time input voltage of the voltage-controlled electrode boiler, and then calculate the corresponding power of the voltage-controlled electrode boiler.

[0035] The beneficial effects of the present invention are as follows:

[0036] When the DC / AC converter of the present invention adopts virtual synchronous machine control, the output angular frequency corresponds to the frequency of the AC side, that is, the frequency of the electrode boiler. The invention adjusts the input voltage of the load according to the change of the grid frequency, and then adjusts the power value of the load to stabilize the grid frequency, realizing the inertia damping support in the transient process and the frequency regulation in the steady state.

[0037] Compared with the traditional electrode boiler, the present invention overcomes the problems of slow and complex power regulation, and realizes the inertia damping support in the transient process and the grid frequency regulation in the steady state through the electrode boiler load, achieving the active support of the electrode boiler load for the grid frequency and reducing the harmonic impact on the grid.

[0038] The advantages of the additional aspects of the present invention will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings forming a part of this specification are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation of the present invention.

[0040] Figure 1 is the schematic diagram of the load frequency modulation system of the voltage-controlled electrode boiler based on the virtual synchronous machine in the embodiment of the present invention;

[0041] Figure 2 is the change situation of the output voltage frequency of the DC / AC converter in the embodiment of the present invention;

[0042] Figure 3 is the change situation of the moment of inertia in the virtual synchronous machine controller in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] The present invention will be further described below in conjunction with the drawings and embodiments.

[0044] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0045] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0046] The present invention is based on virtual synchronous machine control technology and regulates the frequency by controlling the load of a voltage-controlled electrode boiler. A rectification and inversion link is added to the power input end of the electrode boiler, and a virtual synchronous machine is used for control in the inversion link to simulate virtual damping and inertia to stabilize the frequency of the power grid system.

[0047] According to Figure 1 , an embodiment of the present invention provides a load frequency modulation system for a voltage-controlled electrode boiler based on a virtual synchronous machine, including: a voltage-controlled electrode boiler, an AC / DC converter, and a DC / AC converter; the electrode rods of the voltage-controlled electrode boiler are connected to the power grid through the DC / AC converter and the AC / DC converter in sequence;

[0048] The voltage-controlled electrode boiler serves as a load for power grid frequency regulation; the power of the voltage-controlled electrode boiler changes according to the change of the input voltage; the input voltage is the output voltage of the DC / AC converter;

[0049] The DC / AC converter is connected to a virtual synchronous machine controller; the virtual synchronous machine controller is configured to: adaptively calculate the moment of inertia according to the comparison result between the angular frequency change rate of the output voltage of the DC / AC converter and the angular frequency change rate threshold, and then combine the reactive power-voltage droop characteristic of the virtual synchronous machine to obtain the d / q axis given reference voltage required for the voltage-current double closed loop of the DC / AC converter.

[0050] In this embodiment, the voltage-controlled electrode boiler includes electrode rods, an inner cylinder, an outer cylinder, water level control, pressure control, pressure safety, and pressure safety valves, a processing feed water valve, conductivity control, a circulation pump, and trisodium phosphate solution, etc.

[0051] Among them, the water level control is only used to ensure that the water levels of the inner and outer cylinders are detected and do not exceed the warning value, and the processing feed water valve and the circulation pump are controlled to ensure the stability of the water level in the inner cylinder at all times, so that the electrode rods are fully immersed in water.

[0052] The electrode boiler does not require an electrode rod up-and-down adjustment device or a shielding shield adjustment device, greatly simplifying the structure of the electrode boiler.

[0053] In the specific implementation process, the calculation process of the power of the voltage-controlled electrode boiler is as follows:

[0054]

[0055] Among them, P is the power of the voltage-controlled electrode boiler, for example, in kilowatts; U is the input voltage, for example, in kilovolts; R is the resistance value of the solution of the voltage-controlled electrode boiler, which varies with the solution conductivity, for example, in ohms.

[0056] Among them, the calculation process of the resistance value of the solution of the voltage-controlled electrode boiler is:

[0057]

[0058] Among them, L is the length of the electrode rod of the voltage-controlled electrode boiler, for example, in meters; ρ is the resistivity of the solution of the voltage-controlled electrode boiler, for example, in ohm-meters; b is the distance between the electrode axis and the center of the voltage-controlled electrode boiler; d is the cross-sectional diameter of the electrode of the voltage-controlled electrode boiler; r is the radius of the cylindrical container of the voltage-controlled electrode boiler. The units of b, d, and r are the same.

[0059] Specifically, in the virtual synchronous machine controller, the process of adaptively calculating the moment of inertia is:

[0060]

[0061] Among them, J is the moment of inertia; J0 is the base value of the moment of inertia; M is the threshold value of the angular frequency change rate; μ represents the state of the voltage-controlled electrode boiler; ω and ω0 are the angular frequency and rated angular frequency of the output voltage of the DC / AC converter respectively.

[0062] In the virtual synchronous machine controller, the reactive power-voltage droop characteristic of the virtual synchronous machine is:

[0063]

[0064] In the formula: u n , u0 are the rated value and actual value of the output voltage of the DC / AC converter respectively; Q ref and Q e are the given reactive power and actual reactive power respectively; K i is the integral coefficient; K q is the reactive power droop coefficient; E m and E0 are the virtual electromotive force and no-load electromotive force respectively.

[0065] In the virtual synchronous machine controller, the angular frequency of the output voltage of the DC / AC converter is calculated through the rotor motion equation of the virtual synchronous machine. Among them, the rotor motion equation of the virtual synchronous machine is:

[0066]

[0067] Among them, P m , P e and P ref are mechanical power, electromagnetic power, and given active power respectively; ω and ω0 are the angular frequency and rated angular frequency of the output voltage of the DC / AC converter respectively; J and D are the moment of inertia and damping coefficient respectively; K p is the active droop coefficient.

[0068] In the virtual synchronous machine controller, the virtual electromotive force is calculated through the reactive-voltage droop characteristic of the virtual synchronous machine, and it is multiplied by the three-phase signals converted from the angular frequency of the output voltage of the DC / AC converter to obtain the d / q-axis given reference voltages required for the voltage-current double closed-loop of the DC / AC converter.

[0069] In this embodiment, the AC / DC converter is connected to the pulse controller, and the pulse controller is configured to control the power switch tubes in the AC / DC converter according to the set pulse adjustment method.

[0070] In this embodiment, the DC / AC inverter adopts a virtual synchronous machine control method based on adaptive moment of inertia. The AC / DC rectifier adopts a multi-pulse rectification method suitable for high-power occasions, which can ensure that the harmonics generated by the electrode boiler load have the least impact on the power grid. The AC / DC rectifier is relatively flexible. When the electrode boiler is directly connected to the DC bus through the inverter, the rectification device can be omitted.

[0071] In one or more embodiments, a method for a voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine is also provided, including:

[0072] Step 1: According to the comparison result between the angular frequency change rate of the output voltage of the DC / AC converter and the angular frequency change rate threshold, adaptively calculate the moment of inertia and feedback it to the DC / AC converter;

[0073] Step 2: Based on the adaptively calculated moment of inertia, calculate the angular frequency corresponding to the output voltage of the DC / AC converter through the rotor motion equation of the virtual synchronous machine;

[0074] Step 3: Calculate the virtual electromotive force through the reactive-voltage droop characteristic of the virtual synchronous machine, and multiply it by the three-phase signals converted from the angular frequency of the output voltage of the DC / AC converter to obtain the d / q-axis given reference voltages required for the voltage-current double closed-loop of the DC / AC converter to control the output voltage of the DC / AC converter;

[0075] Step 4: Take the real-time output voltage of the DC / AC converter as the real-time input voltage of the voltage-controlled electrode boiler, and then calculate the corresponding power of the voltage-controlled electrode boiler.

[0076] In an island mode embodiment of the present invention, at 0.4 s, the load of the electrode boiler is increased by approximately 0.4 WM while the power given command remains unchanged. Figure 2 The change of the system frequency is shown. Compared with the fixed moment of inertia, the fluctuations of the adaptive moment of inertia become slower at 0 s, 0.4 s, and 0.7 s respectively. Figure 3 The change of the moment of inertia is shown. At 0 s, 0.4 s, and 0.7 s, the moment of inertia increases to varying degrees. The moment of inertia at 0 s is larger because Δω has an overshoot of first increasing and then decreasing at the initial moment, resulting in a relatively large change in the angular frequency. After passing the peak point, it decreases relatively slowly. Figure 2 The frequency value at steady state in [the figure] is approximately 56.6 Hz, which is caused by the given power command being greater than the actual power of the load.

[0077] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine, characterized in that, Including: A voltage-controlled electrode boiler, an AC / DC converter, and a DC / AC converter; the electrode rods of the voltage-controlled electrode boiler are successively connected to the power grid through the DC / AC converter and the AC / DC converter; The voltage-controlled electrode boiler serves as a load for power grid frequency regulation; the power of the voltage-controlled electrode boiler varies according to the change of the input voltage; the input voltage is the output voltage of the DC / AC converter; The DC / AC converter is connected to a virtual synchronous machine controller; the virtual synchronous machine controller is configured to: adaptively calculate the moment of inertia according to the comparison result between the angular frequency change rate of the output voltage of the DC / AC converter and the angular frequency change rate threshold, and then combine the reactive power-voltage droop characteristic of the virtual synchronous machine to obtain the d / q axis given reference voltage required for the voltage-current double closed loop of the DC / AC converter.

2. The voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine according to claim 1, wherein The calculation process of the power of the voltage-controlled electrode boiler is: Where P is the power of the voltage-controlled electrode boiler; U is the input voltage; R is the resistance value of the solution of the voltage-controlled electrode boiler, which changes with the solution conductivity.

3. The voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine according to claim 2, characterized in that The calculation process of the resistance value of the solution of the voltage-controlled electrode boiler is: Where L is the length of the electrode rods of the voltage-controlled electrode boiler; ρ is the resistivity of the solution of the voltage-controlled electrode boiler; b is the distance between the electrode axis and the center of the voltage-controlled electrode boiler; d is the cross-sectional diameter of the electrode of the voltage-controlled electrode boiler; r is the radius of the cylindrical container of the voltage-controlled electrode boiler.

4. The voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine according to claim 1, characterized in that In the virtual synchronous machine controller, the process of adaptively calculating the moment of inertia is: Where J is the moment of inertia; J0 is the base value of the moment of inertia; M is the threshold of the angular frequency change rate; μ represents the state of the voltage-controlled electrode boiler; ω and ω0 are respectively the angular frequency and the rated angular frequency of the output voltage of the DC / AC converter.

5. The voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine according to claim 1, characterized in that, In the virtual synchronous machine controller, the reactive power-voltage droop characteristic of the virtual synchronous machine is: where: u n , u0 are the rated value and the actual value of the output voltage of the DC / AC converter respectively; Q ref and Q e are the given reactive power and the actual reactive power respectively; K i is the integral coefficient; K q is the reactive droop coefficient; E m and E0 are the virtual electromotive force and the no-load electromotive force respectively.

6. The voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine according to claim 1, characterized in that, In the virtual synchronous machine controller, the angular frequency of the output voltage of the DC / AC converter is calculated through the rotor motion equation of the virtual synchronous machine.

7. The voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine according to claim 6, wherein The rotor motion equation of the virtual synchronous machine is: Among them, P m , P e and P ref are mechanical power, electromagnetic power, and given active power respectively; ω and ω0 are the angular frequency and rated angular frequency of the output voltage of the DC / AC converter respectively; J and D are the moment of inertia and damping coefficient respectively; K p is the active droop coefficient.

8. The voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine according to claim 1, characterized in that, In the virtual synchronous machine controller, the virtual electromotive force is calculated through the reactive power-voltage droop characteristic of the virtual synchronous machine, and it is multiplied by the three-phase signal converted from the angular frequency of the output voltage of the DC / AC converter to obtain the d / q axis given reference voltage required for the voltage-current double closed loop of the DC / AC converter.

9. The voltage-controlled electrode boiler load frequency modulation system based on a virtual synchronous machine according to claim 1, characterized in that, The AC / DC converter is connected to a pulse controller, and the pulse controller is configured to control the power switch tubes in the AC / DC converter according to the set pulse adjustment method.

10. A method for a voltage-controlled type electrode boiler load frequency modulation system based on a virtual synchronous machine according to any one of claims 1-9, characterized in that, Including: According to the comparison result between the angular frequency change rate of the output voltage of the DC / AC converter and the angular frequency change rate threshold, adaptively calculate the moment of inertia and feedback it to the DC / AC converter; Based on the adaptively calculated moment of inertia, calculate the angular frequency corresponding to the output voltage of the DC / AC converter through the rotor motion equation of the virtual synchronous machine; The virtual electromotive force is calculated through the reactive power-voltage droop characteristic of the virtual synchronous machine, and it is multiplied by the three-phase signal converted from the angular frequency of the output voltage of the DC / AC converter to obtain the d / q axis given reference voltage required for the voltage and current double closed-loop of the DC / AC converter, so as to control the output voltage of the DC / AC converter; The real-time output voltage of the DC / AC converter is used as the real-time input voltage of the voltage-controlled electrode boiler, and then the corresponding power of the voltage-controlled electrode boiler is calculated.

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