A flexible dynamic voltage stabilization control method for medium frequency electric heating energy storage

Abstract

The present invention relates to a flexible dynamic voltage stabilization control method for medium-frequency electric heating energy storage, the method comprising: constructing an impedance model of a medium-frequency electric heating energy storage system; identifying the medium-frequency electric heating energy storage system as an inductive or capacitive operating mode based on the Hope bifurcation theory; converting the 3n+2 dimensional Newton iterative equation of the impedance model into an n+2 dimensional linear equation group through a dimensionality reduction algorithm, and calculating the Hope bifurcation point in real time; determining an optimized trigger angle based on the calculation result of the Hope bifurcation point; and adjusting the operating mode of the medium-frequency electric heating energy storage system to an inductive or capacitive mode based on the optimized trigger angle. The beneficial effect is that the dynamic stability of the medium-frequency heating system is effectively improved, the stable operation of the IGBT full-bridge inverter circuit is ensured, and the output range of the medium-frequency heating system power is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of cast iron electric heating energy storage, and in particular to a flexible dynamic voltage stabilization control method applied to medium-frequency electric heating energy storage. Background Art

[0002] The cast iron electric heating energy storage system uses electromagnetic induction heating technology to send the medium-frequency alternating current generated by the rectification, filtering, and inverter circuits in the heating power supply into the load composed of a resonant capacitor and an induction coil, so that the load generates eddy currents under the action of the induced electromotive force, thereby heating the cast iron heat storage body. The controller can realize the energy storage power control function for the abandoned wind and solar power of new power systems. However, due to the poor stability of emerging power systems such as photovoltaic and wind power, the use of a direct power input circuit is likely to cause damage to the insulated gate bipolar transistor (IGBT), resulting in failure of power heating of the cast iron.

[0003] As one of the most widely used components in flexible AC transmission systems (FACTS), thyristor-controlled series capacitors (TCCs) can smoothly adjust impedance over a wide range by adjusting the thyristor's trigger angle. Due to their control sensitivity, the DC power they output can be used through IGBTs for frequency control in medium-frequency heating systems, improving system stability and raising the circuit's output power limit. During power control, the accuracy of the correspondence between the modulation signal and line impedance is crucial for stable energy output. When analyzing circuit impedance characteristics, the thyristors and three-phase AC sinusoidal power supply in a three-phase bridge controlled rectifier circuit are typically considered ideal. That is, when the thyristor is in a conducting state, its voltage drop is negligible. However, in practical applications, both the controller and the thyristor valve resistance affect the impedance characteristics of the medium-frequency heating system, thereby affecting the accuracy of power output. Summary of the Invention

[0004] Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a flexible dynamic voltage stabilization control method applied to medium-frequency electric heating energy storage, which solves the technical problem of how to effectively improve the dynamic stability of medium-frequency heating.

[0006] Technical solution:

[0007] In order to achieve the above objectives, the main technical solutions adopted by the present invention include:

[0008] In a first aspect, the present invention provides a flexible dynamic voltage stabilization control method for medium frequency electric heating energy storage, comprising:

[0009] Construct an impedance model of a medium-frequency electric heating energy storage system with a three-phase bridge rectifier circuit including thyristor on-resistance and equivalent resistance;

[0010] Based on the Hopkin bifurcation theory, the medium frequency electric heating energy storage system is identified as an inductive or capacitive operating mode;

[0011] The 3n+2-dimensional Newton iterative equations of the impedance model are converted into an n+2-dimensional linear equation system through a dimensionality reduction algorithm, and the Hope bifurcation point is calculated in real time;

[0012] Determine the optimized trigger angle based on the calculation results of the Hope bifurcation point;

[0013] The working mode of the medium frequency electric heating energy storage system is adjusted to inductive or capacitive according to the optimized trigger angle.

[0014] Optionally, the dimensionality reduction algorithm specifically includes:

[0015] Decompose the 3n+2 dimensional Newton iterative equation into a matrix block form;

[0016] Construct the linear equation system after dimensionality reduction based on the matrix block form;

[0017] The Broyden quasi-Newton method is used to accelerate the iterative convergence to obtain the n+2 dimensional linear equations.

[0018] Optionally, if convergence fails after three consecutive iterations, an alternative linearization control strategy is enabled;

[0019] Under the backup strategy, the trigger angle α is fixed to the critical value of 45°, and the output power is reduced to 80% of the rated value.

[0020] Optionally, determining the optimized trigger angle according to the calculation result of the Hope bifurcation point includes:

[0021] When the system impedance characteristic is located on the left side of the Hope bifurcation point, the optimal trigger angle is determined to adjust the working mode of the medium frequency electric heating energy storage system to the inductive working mode;

[0022] When the system impedance characteristic crosses the Hope bifurcation point, the optimized trigger angle is determined to adjust the working mode of the medium frequency electric heating energy storage system to the capacitive working mode.

[0023] Optionally, the trigger angle α and the modulation frequency f are dynamically corrected during the switching of the working mode of the medium frequency electric heating energy storage system.

[0024] Optionally, the method further includes:

[0025] When the working mode of the medium frequency electric heating energy storage system is switched to the inductive mode, α increases in steps of Δα = 0.5°;

[0026] When the working mode of the medium frequency electric heating energy storage system is switched to the capacitive mode, α decreases in steps of Δα=0.3°.

[0027] Optionally, the method further includes:

[0028] Real-time monitoring of the voltage fluctuation rate δV and current harmonic distortion rate THDi of the medium frequency heating system;

[0029] When δV>10% or THDi>5%, the emergency protection mode is triggered and the working mode of the medium frequency electric heating energy storage system is forced to switch to a low power output state.

[0030] In a second aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements a flexible dynamic voltage stabilization control method for medium-frequency electric heating energy storage as described in any one of the first aspects above.

[0031] In a third aspect, the present invention provides a storage device comprising a storage medium and a processor, wherein the storage medium stores a computer program, and when the program is executed by the processor, a flexible dynamic voltage stabilization control method for medium-frequency electric heating energy storage as described in any one of the first aspects above is implemented. Beneficial effects

[0032] The beneficial effects of the present invention are as follows: a flexible dynamic voltage stabilization control method for medium-frequency electric heating energy storage is provided. When optimizing the relationship between the trigger angle and the thyristor conduction, the on-resistance and equivalent resistance of the thyristor are introduced into the control system, thereby achieving a better control effect. Compared with related technologies, this application can effectively improve the dynamic stability of the medium-frequency heating system, ensure the stable operation of the IGBT full-bridge inverter circuit, and increase the power output range of the medium-frequency heating system. This provides an effective control method for stabilizing the power grid and enabling new power systems such as wind and solar power generation to have primary frequency modulation capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A flow chart of a flexible dynamic voltage stabilization control method for medium-frequency electric heating energy storage provided by an embodiment of the present invention;

[0034] Figure 2 Bifurcation diagram of Us under different initial values ​​provided by the embodiment of the present invention;

[0035] Figure 3 Another bifurcation diagram of Us under different initial values ​​provided by the embodiment of the present invention;

[0036] Figure 4 The projection of PH provided in the embodiment of the present invention on planes a1 and a3. DETAILED DESCRIPTION

[0037] To better explain the present invention and facilitate understanding, the present invention is described in detail below with reference to the accompanying drawings and through specific embodiments. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0038] In fundamental frequency impedance solutions, two solution curves corresponding to the same trigger angle exist within most steady-state operating regions of three-phase bridge controlled rectifier circuits: one for inductive loads and the other for capacitive loads. By varying the trigger angle, the impedance of the medium-frequency heating system changes solely according to the original impedance curve, with no switching between them. This bifurcation phenomenon is known as a Hopkins bifurcation. This dual-solution bifurcation introduces random perturbations to the control of the PWM input power supply. Switching between different control methods under varying total load conditions is crucial for maintaining the stability of the medium-frequency heating system's power output. Because the dimension of the parameter space subset where the bifurcation occurs decreases with bifurcation degeneration, bifurcations with high codimension are difficult to measure and control. However, in many cases, the bifurcation set with codimension n serves as the organizing center of the bifurcation set with codimension n - 1, as it is the intersection of the lower codimension set. Finding the most degenerate saddle-node branch offers significant advantages in mapping regions of steady-state multiplicity.

[0039] However, due to the existence of this dual impedance phenomenon, it is impossible to switch the control mode simply by changing the size of the trigger angle. This control method can automatically switch the control mode according to the specific actual solution. The characteristic of this method is that it reduces a (3n+2)-dimensional Newton iterative equation to a (n+2)-dimensional linear equation system to describe the system. Compared with the traditional direct calculation method, it can reduce the computational burden and avoid dimensionality explosion. Therefore, it is suitable for the power output analysis of the medium frequency heating system and the calculation of dynamic voltage stability. The actual control output shows that this control method is more accurate than the conventional linearization method when performing dynamic stability analysis near the critical point of the power system and medium frequency heating signal control.

[0040] First, refer to Figure 1 This embodiment provides a flexible dynamic voltage stabilization control method for medium-frequency electric heating energy storage, including:

[0041] S1, construct an impedance model of the medium-frequency electric heating energy storage system including the thyristor on-resistance and equivalent resistance of the three-phase bridge rectifier circuit.

[0042] S2, based on the Hopkins bifurcation theory, identifies whether the medium-frequency electric heating energy storage system is inductive or capacitive working mode.

[0043] S3, through the dimensionality reduction algorithm, converts the 3n+2-dimensional Newton iterative equations of the impedance model into an n+2-dimensional linear equation system and calculates the Hope bifurcation point in real time.

[0044] S4, determining the optimized trigger angle according to the calculation result of the Hope bifurcation point.

[0045] S5, adjusting the working mode of the medium frequency electric heating energy storage system to inductive or capacitive according to the optimized trigger angle.

[0046] Constructing an impedance model that includes the thyristor on-resistance and equivalent resistance makes the analysis of the medium-frequency electric heating energy storage system closer to reality and can more accurately consider the impact of the actual circuit device characteristics on the system; identifying the working mode based on the Hope bifurcation theory can enable targeted control according to the different characteristics of the system; calculating the Hope bifurcation point and determining the optimized trigger angle through the dimensionality reduction algorithm provides an accurate basis for subsequent adjustment of the working mode; adjusting the working mode can improve the dynamic stability of the system, ensure the stable operation of the IGBT full-bridge inverter circuit, and increase the power output range.

[0047] Optionally, the dimensionality reduction algorithm specifically includes:

[0048] Decompose the 3n+2 dimensional Newton iterative equation into a matrix block form;

[0049] Construct the linear equation system after dimensionality reduction based on the matrix block form;

[0050] The Broyden quasi-Newton method is used to accelerate the iterative convergence to obtain the n+2 dimensional linear equations.

[0051] The dimensionality reduction algorithm simplifies the complex 3n + 2-dimensional Newton iterative equations into an n + 2-dimensional linear system of equations, reducing the computational burden, avoiding dimensionality explosion, and improving computational efficiency, enabling faster and more accurate results to meet real-time control requirements. The Broyden quasi-Newton method is used to accelerate iterative convergence, further improving the speed and efficiency of the computational process and rapidly obtaining accurate results to serve system control.

[0052] Optionally, if convergence fails after three consecutive iterations, an alternative linearization control strategy is enabled;

[0053] Under the backup strategy, the trigger angle α is fixed to the critical value of 45°, and the output power is reduced to 80% of the rated value.

[0054] If convergence fails after three consecutive iterations, the backup linearization control strategy is activated to ensure that the system can maintain a certain working state when the calculation fails to converge as expected, thereby guaranteeing the basic operation of the system. The trigger angle α is fixed to the critical value of 45° and the output power is reduced to 80% of the rated value. When calculation anomalies occur, the system can be operated with relatively stable and reliable parameters to prevent system failure or instability caused by calculation anomalies.

[0055] Optionally, determining the optimized trigger angle according to the calculation result of the Hope bifurcation point includes:

[0056] When the system impedance characteristic is located on the left side of the Hope bifurcation point, the optimal trigger angle is determined to adjust the working mode of the medium frequency electric heating energy storage system to the inductive working mode;

[0057] When the system impedance characteristic crosses the Hope bifurcation point, the optimized trigger angle is determined to adjust the working mode of the medium frequency electric heating energy storage system to the capacitive working mode.

[0058] The optimized trigger angle is determined based on the positional relationship between the system impedance characteristics and the Hope bifurcation point, thereby rationally adjusting the working mode so that the system can flexibly switch working modes according to actual operating characteristics, thereby improving the system's adaptability and performance, and helping to improve the accuracy and stability of the system's power output.

[0059] Optionally, the trigger angle α and the modulation frequency f are dynamically corrected during the switching of the working mode of the medium frequency electric heating energy storage system.

[0060] Dynamically correcting the trigger angle α and modulation frequency f during the working mode switching process helps the system achieve a smooth transition when switching between different working modes, avoids unstable factors caused by switching, and ensures continuous and stable operation of the system.

[0061] Optionally, the method further includes:

[0062] When the working mode of the medium frequency electric heating energy storage system is switched to the inductive mode, α increases in steps of Δα = 0.5°;

[0063] When the working mode of the medium frequency electric heating energy storage system is switched to the capacitive mode, α decreases in steps of Δα=0.3°.

[0064] The changing step size of the trigger angle α when switching between different working modes is clarified, providing precise control parameters for mode switching, making the mode switching process operational and controllable, and contributing to more precise control and optimization of system operation.

[0065] Optionally, the method further includes:

[0066] Real-time monitoring of the voltage fluctuation rate δV and current harmonic distortion rate THDi of the medium frequency heating system;

[0067] When δV>10% or THDi>5%, the emergency protection mode is triggered and the working mode of the medium frequency electric heating energy storage system is forced to switch to a low power output state.

[0068] Real-time monitoring of the voltage fluctuation rate δV and current harmonic distortion rate THDi of the medium frequency heating system and setting thresholds to trigger the emergency protection mode can promptly detect abnormal conditions in system operation. When the system becomes unstable or abnormal fluctuations exceed the specified range, the system is promptly switched to a low-power output state to protect the safety of system equipment and personnel, while preventing greater adverse effects on surrounding power systems, thereby improving the reliability and safety of the system.

[0069] Direct solution method for the Hope bifurcation point:

[0070] The control expression of the medium frequency heating system is: , , (1)

[0071] is the single-parameter steady-state solution of equation (1), and the single-parameter real matrix is , so the bifurcation point of the Hopse bifurcation can be calculated inversely If there is a pure imaginary characteristic root of The sufficiency function and , and the branch conditions H1, H2 and H3 are met, then , ,and is the system (e) for a given and Hope bifurcation point.

[0072] in yes The characteristic root of .

[0073]

[0074]

[0075] for characteristic root The eigenvector of .

[0076] Traditional direct algorithm:

[0077] Expanding equation (1) yields:

[0078]

[0079] Where: and express and of Component, the Newton iteration equation of its linear equation is:

[0080]

[0081] in:

[0082]

[0083]

[0084] Formula (3) is reduced to a (n+2)-dimensional linear system by using the Newton iterative equation. This reduces the (3n+2)-dimensional Newton iterative equation to a (n+2)-dimensional linear system to describe the control system. Compared with traditional direct calculation methods, this conversion can reduce the computational burden and avoid dimensionality explosion. It is suitable for the analysis, calculation, and control of voltage stability in medium-frequency electric heating systems. When analyzing the dynamic stability near the critical point of the control system, the bifurcation method is more accurate than the linearization method. The specific solution process is as follows. Formula (3) is expanded:

[0085]

[0086]

[0087]

[0088]

[0089]

[0090] make

[0091] You can get:

[0092]

[0093]

[0094] Take the pth row of equation (5):

[0095]

[0096] in yes The row vector of and Indicates the OK and vector.

[0097] The following set of equations can be obtained from equations (6)-(8).

[0098]

[0099]

[0100]

[0101]

[0102] in:

[0103] Combining equations (2) and (8), we can obtain:

[0104]

[0105] in: ,

[0106] Will Substituting into equation (17), we get:

[0107]

[0108] So we can calculate 、 ,and and:

[0109] , ,

[0110]

[0111] Right now: ,

[0112] ;

[0113] Combining equations (5) and (6), we can obtain:

[0114]

[0115] Therefore, from formula (21) we can calculate , substituting it into formula (6) we can get

[0116]

[0117] Therefore, we can get , , , ,

[0118] use Correction ,Right now:

[0119]

[0120] Iterate formula (20) until , and obtain the bifurcation point of the trigger curve of the medium frequency heating control system.

[0121] The control output calculation shows that in the medium frequency heating IGBT system with controllable three-phase bridge controlled rectifier control, the differential state variable is , the control variable (bifurcation parameter) is , when the control variable When the initial value of the differential state variable is , and its bifurcation point is When the control variable When the initial value of the differential state variable is , and its bifurcation point is .

[0122] Figure 2 Shown when When, with The stable limit cycle (solid line) generated by the change of , compared with its control output (dashed line). Figure 3 The actual bifurcation diagram (solid line) is shown compared to the approximate bifurcation diagram (dashed line). Figure 3 Given the bifurcation parameter The change of , the comparison between the real limit cycle and the approximate limit cycle of the controller output.

[0123] Figure 4 Shows that the bifurcation point is in the plane The projection on , and the path followed by the system during bifurcation control. Start by changing ,until . Supercritical Hope bifurcation in Then, the system moves along a straight line and reaches the origin of the plane. .

[0124] This paper proposes a new method for determining the Hope bifurcation point in dynamic voltage stability and applies it to medium-frequency electric heating energy storage control systems. This method, applied to control systems with controlled series three-phase bridge rectifiers and IGBT variable-frequency output, can reduce the computational burden and avoid the curse of dimensionality. The control method based on Hope bifurcation theory is more accurate than linearization methods.

[0125] In a second aspect, an embodiment of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed, implements a flexible dynamic voltage stabilization control method for medium-frequency electric heating energy storage as described in any one of the first aspects above.

[0126] In a third aspect, an embodiment of the present invention provides a storage device comprising a storage medium and a processor, wherein the storage medium stores a computer program, and when the program is executed by the processor, a flexible dynamic voltage stabilization control method for medium-frequency electric heating energy storage as described in any one of the first aspects above is implemented.

[0127] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROMs, optical storage, etc.) containing computer-usable program code.

[0128] Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations fall within the scope of the claims and their equivalents, the present invention shall also include such modifications and variations.

[0129] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may alter, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A flexible dynamic voltage stabilization control method for medium frequency electric heating energy storage, characterized in that: include: Construct an impedance model of a medium-frequency electric heating energy storage system with a three-phase bridge rectifier circuit including thyristor on-resistance and equivalent resistance; Based on the Hopkin bifurcation theory, the medium frequency electric heating energy storage system is identified as an inductive or capacitive operating mode; The 3n+2-dimensional Newton iterative equations of the impedance model are converted into an n+2-dimensional linear equation system through a dimensionality reduction algorithm, and the Hope bifurcation point is calculated in real time; The optimized trigger angle is determined based on the calculation results of the Hope bifurcation point, which specifically includes: When the system impedance characteristic is located on the left side of the Hope bifurcation point, the optimal trigger angle is determined to adjust the working mode of the medium frequency electric heating energy storage system to the inductive working mode; When the system impedance characteristic crosses the Hope bifurcation point, the optimal trigger angle is determined to adjust the working mode of the medium frequency electric heating energy storage system to the capacitive working mode; Dynamically correct the trigger angle α and modulation frequency f during the working mode switching process of the medium frequency electric heating energy storage system; Adjust the working mode of the medium frequency electric heating energy storage system to inductive or capacitive according to the optimized trigger angle; The method further comprises: When the working mode of the medium frequency electric heating energy storage system is switched to the inductive mode, α is increased in steps of Δα = 0.5°; When the working mode of the medium frequency electric heating energy storage system is switched to the capacitive mode, α decreases in steps of Δα=0.3°.

2. A flexible dynamic voltage stabilization control method for medium frequency electric heating energy storage according to claim 1, characterized in that: The dimensionality reduction algorithm specifically includes: Decompose the 3n+2 dimensional Newton iterative equation into a matrix block form; Construct the linear equation system after dimensionality reduction based on the matrix block form; The Broyden quasi-Newton method is used to accelerate the iterative convergence to obtain the n+2 dimensional linear equations.

3. A flexible dynamic voltage stabilization control method for medium frequency electric heating energy storage according to claim 2, characterized in that: If convergence fails after three consecutive iterations, the backup linearization control strategy is activated; Under the backup strategy, the trigger angle α is fixed to a critical value of 45°, and the output power is reduced to 80% of the rated value.

4. A flexible dynamic voltage stabilization control method for medium frequency electric heating energy storage according to claim 3, characterized in that: The method further comprises: Real-time monitoring of the voltage fluctuation rate δV and current harmonic distortion rate THDi of the medium frequency heating system; When δV>10% or THDi>5%, the emergency protection mode is triggered and the working mode of the medium frequency electric heating energy storage system is forced to switch to a low power output state.

5. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the flexible dynamic voltage stabilization control method for medium-frequency electric heating energy storage as described in any one of claims 1 to 4 is implemented.

6. A storage device comprising a storage medium and a processor, wherein the storage medium stores a computer program, wherein: When the processor executes the computer program, it implements the flexible dynamic voltage stabilization control method applied to medium frequency electric heating energy storage as described in any one of claims 1 to 4.

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