Mode switching method and device of network-forming type converter and medium

Abstract

The invention discloses a mode switching method and device for a network-building type current converter and a medium, and the method comprises the steps: introducing any initial working point corresponding to the network-building type current converter, and rewriting a motion equation corresponding to the network-building type current converter, and obtaining a voltage dynamic equation; step analysis is carried out on the voltage dynamic equation to obtain a full response equation corresponding to the network construction type converter; calculating a corresponding target steady-state point after the step disturbance of mode switching is carried out on the network-forming converter; respectively performing steady-state operation analysis on the first mode and the second mode according to the full response equation to obtain a first curve corresponding to the first mode and a second curve corresponding to the second mode, and respectively performing voltage impact analysis on the first curve and the second curve, obtaining a first switching point corresponding to the first curve and a second switching point corresponding to the second curve; and according to the target steady state point, the first switching point and the second switching point, performing mode switching on the network-forming converter. The embodiment of the invention can improve the stability of the direct-current power grid.

Description

Technical Field

[0001] This application relates to, but is not limited to, the field of grid converter technology, and particularly to a mode switching method, device and medium for a grid converter. Background Technology

[0002] Driven by the rapid development of the new energy industry, new power systems require sufficient inertia to maintain stable operation. Fluctuations or collapses in DC bus voltage will adversely affect the absorption of new energy and the stable operation of the DC grid, as inertia is a key factor in maintaining the stability of the DC bus voltage. Current power systems use grid-type converters connected via DC buses to maintain the stability of the DC bus voltage (i.e., the output DC voltage). Grid-type converters mainly stabilize the DC bus voltage through droop control combined with low-pass filters, virtual DC synchronous machine control, and virtual capacitor control. The energy storage characteristics and dynamic energy release characteristics of the simulated DC capacitors in these three existing technologies achieve dynamic power support or inertial support, meaning that the control mechanisms are consistent in principle. However, in actual operation, there are often situations where the operating mode (power / voltage) switches directly, i.e., sudden load changes. The initial full response equation is calculated using the reference operating point corresponding to the rated voltage as a benchmark. However, the sudden load change causes a deviation in the rated voltage, further leading to errors in the initial full response equation of the grid-type converter calculated using the reference operating point corresponding to the rated voltage as the calculation benchmark. This makes it impossible to accurately describe the inertial response process of the grid-type converter under external step disturbances, resulting in DC bus voltage surges and affecting the stable operation of the DC grid. Existing technologies passively adjust the inertia and damping coefficients through preset parameters, which easily induces oscillations and surges in power or DC bus voltage, leading to instability in the DC grid. Summary of the Invention

[0003] This application provides a mode switching method, device, and medium for a grid-type converter, which can improve the stability of the DC power grid.

[0004] In a first aspect, embodiments of this application provide a mode switching method for a grid-connected converter, applied to a power grid control system. The operating modes of the grid-connected converter include a first mode and a second mode. The mode switching method for the grid-connected converter includes: By introducing any corresponding initial operating point of the grid converter, the motion equations corresponding to the grid converter are rewritten to obtain the voltage dynamic equations. A step analysis was performed on the voltage dynamic equation to obtain the full response equation corresponding to the grid-type converter; Calculate the target steady-state point of the grid-type converter after it is subjected to a step disturbance of mode switching; Steady-state operation analysis is performed on the first mode and the second mode according to the full response equation to obtain the first curve corresponding to the first mode and the second curve corresponding to the second mode. Voltage impulse analysis is then performed on the first curve and the second curve to obtain the first switching point corresponding to the first curve and the second switching point corresponding to the second curve. The grid-type converter is switched in mode according to the target steady-state point, the first switching point, and the second switching point.

[0005] Secondly, an electronic device provided according to an embodiment of this application includes: At least one processor; At least one memory for storing at least one program; When at least one of the programs is executed by at least one of the processors, the mode switching method for the grid-type converter according to any one of the first aspects is implemented.

[0006] Thirdly, according to the embodiments of the application, a computer-readable storage medium is provided, storing computer-executable instructions, which are used to execute the mode switching method for implementing any of the grid-type converters described in the first aspect.

[0007] In summary, the mode switching method for a grid-type converter according to the above embodiments of this application is applied to a power grid control system. The operating modes of the grid-type converter include a first mode and a second mode. The mode switching method for the grid-type converter includes: rewriting the motion equation of the grid-type converter by introducing an arbitrary initial operating point corresponding to the grid-type converter to obtain a voltage dynamic equation; performing a step analysis on the voltage dynamic equation to obtain the full response equation corresponding to the grid-type converter; calculating the target steady-state point of the grid-type converter after being subjected to a step disturbance of mode switching; performing steady-state operation analysis on the first mode and the second mode according to the full response equation to obtain a first curve corresponding to the first mode and a second curve corresponding to the second mode, and performing voltage impulse analysis on the first curve and the second curve to obtain a first switching point corresponding to the first curve and a second switching point corresponding to the second curve; and switching the grid-type converter according to the target steady-state point, the first switching point, and the second switching point. This application first introduces an arbitrary initial operating point corresponding to the grid-type converter to rewrite the motion equation of the grid-type converter, obtaining a voltage dynamic equation. This equation can measure the impact of mode switching on the offset of the initial operating point, ensuring that the accurate initial operating point is used to rewrite the motion equation of the grid-type converter, resulting in a voltage dynamic equation that accurately describes the dynamic changes in voltage. Then, a step analysis is performed on the voltage dynamic equation to obtain the full response equation of the grid-type converter. Based on the accurate voltage dynamic equation, a step analysis is performed on the voltage dynamic equation to obtain the full response equation of the grid-type converter, which accurately describes the inertial response process of the grid-type converter under external step disturbances. Next, the target steady-state point of the grid-type converter after being subjected to a step disturbance during mode switching is calculated. Based on the accurate full response equation, the calculation of the grid-type converter's target steady-state point is then performed. The accuracy of the target steady-state point is improved after the step disturbance of mode switching. Then, steady-state operation analysis is performed on the first mode and the second mode according to the full response equation to obtain the first curve corresponding to the first mode and the second curve corresponding to the second mode. Voltage impulse analysis is then performed on the first curve and the second curve to obtain the first switching point corresponding to the first curve and the second switching point corresponding to the second curve. The distance between the first switching point and the second switching point is minimized to provide a basis for reducing voltage impulses in subsequent mode switching. The grid-type converter is switched according to the target steady-state point, the first switching point, and the second switching point. Based on the accurate target steady-state point, the operating point is actively adjusted to switch modes by combining the low-impact first switching point and the second switching point, thereby mitigating the oscillation and impulse of power or DC bus voltage and improving the stability of the DC grid. Attached Figure Description

[0008] Figure 1 This is a flowchart illustrating the steps of a mode switching method for a grid-type converter according to an embodiment of this application; Figure 2 This is a schematic diagram of the topology corresponding to a grid-type converter provided in one embodiment of this application; Figure 3 This is a schematic diagram of the control structure corresponding to a grid-type converter provided in one embodiment of this application; Figure 4 This is a schematic diagram of the capacitor equivalent topology of a grid-type converter provided in one embodiment of this application; Figure 5 This application provides a schematic diagram illustrating the relationship between the output DC voltage and the power variation over time, according to one embodiment. Figure 6 This application provides a schematic diagram of mode switching for a grid-type converter according to one embodiment; Figure 7 This is a hardware schematic diagram of an electronic device provided in one embodiment of this application. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0010] It is understandable that although functional modules are divided in the device schematic diagram and a logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than the module division in the device or the order in the flowchart. The terms "first," "second," etc., in the specification, claims, or the aforementioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0011] Driven by the rapid development of the new energy industry, new power systems require sufficient inertia to maintain stable operation. Fluctuations or collapses in DC bus voltage will adversely affect the absorption of new energy and the stable operation of the DC grid, as inertia is a key factor in maintaining the stability of the DC bus voltage. Current power systems use grid-type converters connected via DC buses to maintain the stability of the DC bus voltage (i.e., the output DC voltage). Grid-type converters mainly stabilize the DC bus voltage through droop control combined with low-pass filters, virtual DC synchronous machine control, and virtual capacitor control. The energy storage characteristics and dynamic energy release characteristics of the simulated DC capacitors in these three existing technologies achieve dynamic power support or inertial support, meaning that the control mechanisms are consistent in principle. However, in actual operation, there are often situations where the operating mode (power / voltage) switches directly, i.e., sudden load changes. The initial full response equation is calculated using the reference operating point corresponding to the rated voltage as a benchmark. However, the sudden load change causes a deviation in the rated voltage, further leading to errors in the initial full response equation of the grid-type converter calculated using the reference operating point corresponding to the rated voltage as the calculation benchmark. This makes it impossible to accurately describe the inertial response process of the grid-type converter under external step disturbances, resulting in DC bus voltage surges and affecting the stable operation of the DC grid. Existing technologies passively adjust the inertia and damping coefficients through preset parameters, which easily induces oscillations and surges in power or DC bus voltage, leading to instability in the DC grid.

[0012] Based on this, embodiments of this application provide a mode switching method, device, and medium for a grid-type converter, which can improve the stability of the DC power grid.

[0013] The mode switching method for a grid-type converter according to this application is applied to a power grid control system. The operating modes of the grid-type converter include a first mode and a second mode. The mode switching method for the grid-type converter includes: introducing an arbitrary initial operating point corresponding to the grid-type converter to rewrite the motion equation corresponding to the grid-type converter to obtain a voltage dynamic equation; performing a step analysis on the voltage dynamic equation to obtain the full response equation corresponding to the grid-type converter; calculating the target steady-state point corresponding to the grid-type converter after being subjected to a step disturbance of mode switching; performing steady-state operation analysis on the first mode and the second mode according to the full response equation to obtain a first curve corresponding to the first mode and a second curve corresponding to the second mode, and performing voltage impulse analysis on the first curve and the second curve to obtain a first switching point corresponding to the first curve and a second switching point corresponding to the second curve; and switching the grid-type converter according to the target steady-state point, the first switching point, and the second switching point. This application first introduces an arbitrary initial operating point corresponding to the grid-type converter to rewrite the motion equation of the grid-type converter, obtaining a voltage dynamic equation. This equation can measure the impact of mode switching on the offset of the initial operating point, ensuring that the accurate initial operating point is used to rewrite the motion equation of the grid-type converter, resulting in a voltage dynamic equation that accurately describes the dynamic changes in voltage. Then, a step analysis is performed on the voltage dynamic equation to obtain the full response equation of the grid-type converter. Based on the accurate voltage dynamic equation, a step analysis is performed on the voltage dynamic equation to obtain the full response equation of the grid-type converter, which accurately describes the inertial response process of the grid-type converter under external step disturbances. Next, the target steady-state point of the grid-type converter after being subjected to a step disturbance during mode switching is calculated. Based on the accurate full response equation, the calculation of the grid-type converter's target steady-state point is then performed. The accuracy of the target steady-state point is improved after the step disturbance of mode switching. Then, steady-state operation analysis is performed on the first mode and the second mode according to the full response equation to obtain the first curve corresponding to the first mode and the second curve corresponding to the second mode. Voltage impulse analysis is then performed on the first curve and the second curve to obtain the first switching point corresponding to the first curve and the second switching point corresponding to the second curve. The distance between the first switching point and the second switching point is minimized to provide a basis for reducing voltage impulses in subsequent mode switching. The grid-type converter is switched according to the target steady-state point, the first switching point, and the second switching point. Based on the accurate target steady-state point, the operating point is actively adjusted to switch modes by combining the low-impact first switching point and the second switching point, thereby mitigating the oscillation and impulse of power or DC bus voltage and improving the stability of the DC grid.

[0014] This application provides a mode switching method for a grid-connected converter, applied to a power grid control system. The operating modes of the grid-connected converter include a first mode and a second mode, as described below. Figure 1As shown, the mode switching method for a grid-type converter may include, but is not limited to, the following steps: Step S100: By introducing any initial operating point corresponding to the grid-type converter, the motion equation corresponding to the grid-type converter is rewritten to obtain the voltage dynamic equation.

[0015] For example, before rewriting the motion equations of the grid-type converter by introducing any corresponding initial operating point to obtain the voltage dynamic equations, the mode switching method of the grid-type converter further includes: determining the control strategy equations of the grid-type converter based on the topology and virtual synchronous machine control strategy; rewriting the control strategy equations into equivalent equations based on the capacitor equivalent topology of the grid-type converter; and introducing the real-time output DC voltage of the grid-type converter to rewrite the equivalent equations to obtain the motion equations.

[0016] For example, the equations of motion can be derived and determined through the following steps: (I) Determine the topology corresponding to the grid-type converter: Understandably, referring to Figure 2 As shown, the topology of a grid-type converter with DC power supply as input is obtained. The topology of the grid-type converter includes the input DC power supply, filter, switching network and physical capacitor.

[0017] Specifically, the input DC voltage first passes through a filter. The filter utilizes the inductive reactance of an inductor or the capacitive reactance of a capacitor to smooth the input DC voltage, filtering out high-frequency noise and ripple, providing a relatively clean input DC voltage for the subsequent switching network. Then, the controller corresponding to the grid-type converter generates a pulse-width modulation signal to drive the power devices in the switching network according to the required output voltage or power command, thereby adjusting the magnitude and waveform of the output voltage. Because the high-frequency operation of the switching network generates current and voltage ripples on the DC bus, when the switching network is on, the physical capacitor absorbs excess energy to prevent excessive voltage; when the switching network is off, the physical capacitor releases energy to the load to maintain voltage stability. This effectively smooths out voltage fluctuations, ensuring that the final output DC bus voltage (i.e., the output DC voltage) is stable and meets the load requirements.

[0018] (II) Determine the control strategy equations corresponding to the grid-type converter: By analogy with synchronous motors, the control method of grid-type converters is applied, introducing a virtual DC synchronous machine control strategy to achieve the construction and networking of DC bus voltage. Specifically, refer to... Figure 3As shown, the virtual DC synchronous machine control strategy includes a DC voltage control loop, an inner loop control loop, a DC network-based control sub-strategy, and a signal modulation loop. Specifically, the DC voltage control loop provides the DC voltage to achieve closed-loop control, ensuring a stable output DC voltage. The control sub-strategy of the DC voltage control loop can be represented by the following expression: ; in, This is the control sub-strategy for the DC voltage control loop. This is the reference value for the output DC voltage of the grid-type converter. This refers to the real-time output DC voltage corresponding to a grid-type converter. These are the gain parameters corresponding to the grid-type converter; The inner loop control uses inductor current to achieve closed-loop control based on the filter structure, accelerating the response of the DC grid-type converter; the signal modulation loop uses pulse width modulation to generate a modulation signal that the grid-type converter can interpret and execute. The DC-networked control sub-strategy can be represented by the following expression: ; in, For DC-networked control sub-strategy, This is the reference value for the output power of the grid-type converter. This refers to the DC-side output power of the grid-type converter. The inertia coefficient corresponding to the grid-type converter. This refers to the DC-side voltage corresponding to a grid-type converter. For time, This is the damping coefficient corresponding to the grid-type converter.

[0019] It is understood that the inner loop control circuit of the current is assumed to have a fast response capability and can stably track the current reference value. Therefore, the embodiments of this application only consider the voltage and power control loops.

[0020] (III) Determine the equivalent equation: Reference Figure 4As shown, the physical capacitors in a grid-connected converter have relatively small capacitance values, and the inertia simulated by the virtual synchronous machine control strategy is also relatively limited. While the damping coefficient has a small impact on the steady-state characteristics of voltage surges during mode switching in a grid-connected converter, the virtual inertia significantly affects both steady-state and dynamic responses. Furthermore, equivalent analysis ignoring the damping coefficient helps in studying the maximization effect of voltage surges during mode switching under undamped conditions. Therefore, by using a control algorithm to simulate capacitor characteristics in the inverter (i.e., introducing virtual capacitors), the output current capability during power response can be enhanced, thereby supporting the virtual inertia characteristics. Based on this principle, introducing virtual capacitors into the control strategy of a grid-connected converter allows for the further derivation of the equivalent capacitor topology of the grid-connected converter, and the rewriting of the control strategy equations into equivalent equations. Specifically, the expression of the equivalent equations is as follows: ; in, For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This refers to the real-time output DC voltage corresponding to a grid-type converter. This refers to the damping coefficient corresponding to the grid-type converter. This refers to the output-side DC current corresponding to a grid-type converter. This refers to the output current corresponding to the grid-type converter.

[0021] Specifically, the virtual and physical capacitances corresponding to a grid-type converter can be represented by the following expressions: ,in, For virtual capacitors, It is a physical capacitor.

[0022] Specifically, the real-time output DC voltage of a grid-type converter satisfies the following expression: ,in, This refers to the real-time output DC voltage corresponding to a grid-type converter. To output the steady-state value of DC voltage in real time.

[0023] (iv) Determine the equations of motion: Combining the equivalent equation with the power equation, the expression for the power equation is as follows: ,in, For power, For voltage, The equation of motion is obtained by multiplying both sides of the equivalent equation by the real-time output DC voltage corresponding to the grid-type converter.

[0024] Specifically, the equation of motion is expressed as follows: ; in, For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This refers to the real-time output DC voltage corresponding to a grid-type converter. For time, This refers to the damping coefficient corresponding to the grid-type converter. This refers to the DC-side output power of the grid-type converter. This refers to the output power of the bus capacitor corresponding to the grid-type converter.

[0025] It is understandable that the control strategy for grid-type converters can be droop control combined with a low-pass filter, virtual DC synchronous machine control, or virtual capacitor control. These control strategies are all based on inertia and damping coefficients. This application, however, uses a control algorithm to simulate capacitor characteristics in the inverter (i.e., introduces a virtual capacitor), which enhances the output current capability during power response, thereby supporting the virtual inertia characteristics. Based on this principle, introducing a virtual capacitor into the control strategy of the grid-type converter allows for the further derivation of the equivalent capacitor topology of the grid-type converter, and the control strategy equations can be rewritten as equivalent equations. Therefore, the embodiments of this application do not limit the control strategy of the grid-type converter.

[0026] For example, the voltage dynamic equation is expressed by the following formula: ; in, For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This refers to the initial output DC voltage of the grid-type converter at its initial operating point, corresponding to steady state. This refers to the real-time output DC voltage corresponding to a grid-type converter. and These are all damping coefficients corresponding to grid-type converters. This refers to the DC-side output power of the grid-type converter. This refers to the output power of the bus capacitor corresponding to the grid-type converter.

[0027] For example, the voltage dynamic equation can be derived and determined through the following steps: Assuming that the step response analysis is performed directly based on the equations of motion, the initial total response equation is obtained.

[0028] Specifically, the initial total response equation can be derived and determined through the following steps: Because the DC-side output power and the bus capacitor output power of the grid-type converter satisfy a constant equation in steady state, the constant equation is expressed as follows: ;in, This represents the DC-side output power of the grid-connected converter under steady-state conditions. This represents the bus capacitor output power of a grid-type converter under steady-state conditions.

[0029] The difference between the equations of motion and the constant equations yields the DC bus voltage characteristic equation, which reflects the bus voltage variation characteristics under conditions of sudden load changes (i.e., mode switching in a grid-type converter). Specifically, the DC bus voltage characteristic equation is expressed as follows: ; in, For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This is the DC bus voltage scalar corresponding to a grid-type converter. This refers to the real-time output DC voltage corresponding to a grid-type converter. This refers to the damping coefficient corresponding to the grid-type converter. This refers to the DC-side output power of the grid-type converter. This refers to the output power of the bus capacitor corresponding to the grid-type converter.

[0030] The DC bus voltage characteristic equation is normalized to obtain the initial total response equation. Specifically, the initial total response equation is expressed as follows: ; in, For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This is the DC bus voltage scalar corresponding to a grid-type converter. This refers to the real-time output DC voltage corresponding to a grid-type converter. This refers to the damping coefficient corresponding to the grid-type converter. For grid-type converters, the power scalar is... This refers to the DC-side output power of the grid-type converter. This refers to the output power of the bus capacitor corresponding to a grid-type converter. The inertia coefficient corresponding to the grid-type converter. for per unit quantity, for per unit quantity, for The per-unit quantity.

[0031] According to the initial total response equation, the initial total response equation only considers the operating point of the DC bus voltage at the rated voltage as the reference operating point. When the load changes (i.e., ... (Changes occur), and there is an error between the actual initial operating point and the reference operating point of the grid-type converter. If the error is ignored and the reference operating point corresponding to the rated voltage is still used as the calculation benchmark, the initial full response equation of the grid-type converter will have an error, and the inertial response process of the grid-type converter under external step disturbance cannot be accurately described.

[0032] Therefore, considering the influence of the initial operating point of the grid converter on the grid converter, we introduce any initial operating point of the grid converter as a reference point, and rewrite the motion equation of the grid converter to obtain the voltage dynamic equation.

[0033] Specifically, the voltage dynamic equation can be derived and determined through the following steps: First of all, with Substituting any initial operating point into the equation of motion, we obtain the following expression: ; in, For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This refers to the initial output DC voltage of the grid-type converter at its initial operating point, corresponding to steady state. This refers to the real-time output DC voltage corresponding to a grid-type converter. This refers to the damping coefficient corresponding to the grid-type converter. This refers to the DC-side output power of the grid-type converter. The output power of the bus capacitor corresponding to the grid-type converter; Then, further substituting the change in the output DC voltage corresponding to the grid-type converter into the above expression, we obtain the following expression: ; in, For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This refers to the initial output DC voltage of the grid-type converter at its initial operating point, corresponding to steady state. The DC bus voltage characteristic equation is given for a grid-type converter. This refers to the damping coefficient corresponding to the grid-type converter. This refers to the DC-side output power of the grid-type converter. The output power of the bus capacitor corresponding to the grid-type converter; Next, the above expression is simplified to obtain the dynamic voltage equation.

[0034] Step S110: Perform step analysis on the voltage dynamic equation to obtain the full response equation corresponding to the grid-type converter.

[0035] For example, the transfer function between the output DC voltage and the output power of the grid converter is calculated based on the voltage dynamic equation; a step disturbance is applied to the grid converter, and a step analysis is performed based on the transfer function to obtain the full response equation of the grid converter.

[0036] For example, the total response equation is expressed by the following formula: ; in, This represents the real-time output DC voltage of the grid-type converter at time t. This refers to the initial output DC voltage of the grid-type converter at its initial operating point, corresponding to steady state. This is the scaling factor corresponding to the step disturbance. This refers to the damping coefficient corresponding to the grid-type converter. This refers to the DC-side output power of the grid-type converter. For the virtual capacitor and physical capacitor corresponding to the grid-type converter. It is a natural constant. For time.

[0037] For example, the total response equation can be derived and determined through the following steps: First, the dynamic voltage equation is subjected to a Laplace transform, resulting in the following expression: ; in, For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This refers to the initial output DC voltage of the grid-type converter at its initial operating point, corresponding to steady state. For Laplace variables, This refers to the damping coefficient corresponding to the grid-type converter. The damping coefficient on the DC side. The equation representing the DC bus voltage characteristic of a grid-type converter in the Laplace domain is given. This refers to the DC-side output power of the grid-type converter. This refers to the output power of the bus capacitor corresponding to the grid converter; Then, the above expression is further simplified to obtain the following expression: ; in, For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This refers to the initial output DC voltage of the grid-type converter at its initial operating point, corresponding to steady state. For Laplace variables, This refers to the damping coefficient corresponding to the grid-type converter. The damping coefficient on the DC side. The real-time output DC voltage of the grid-type converter in the Laplace domain. This refers to the DC-side output power of the grid-type converter. This refers to the bus capacitor output power of the grid converter in the Laplace domain; Next, the transfer function between the real-time output DC voltage and the bus capacitor output power is calculated based on the above expression. The expression for the transfer function is as follows: ; in, For transfer functions, The real-time output DC voltage of the grid-type converter in the Laplace domain. This refers to the bus capacitor output power of the grid converter in the Laplace domain. For Laplace variables, For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This refers to the initial output DC voltage of the grid-type converter at its initial operating point, corresponding to steady state. The damping coefficient corresponding to the grid-type converter; Next, a step disturbance is applied to the grid-type converter, and the expression for the step response is calculated based on the transfer function. The expression for the step response is as follows: ; in, Here is the expression for the step response. For Laplace variables, This is the scaling factor corresponding to the step disturbance. This refers to the DC-side output power of the grid-type converter. For transfer functions, For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This refers to the initial output DC voltage of the grid-type converter at its initial operating point, corresponding to steady state. This is the damping coefficient corresponding to the grid-type converter.

[0038] Next, the expression for the step response is transformed using the inverse pull form, resulting in the following expression: ; in, This represents the real-time output DC voltage of the grid-type converter at time t. This refers to the initial output DC voltage of the grid-type converter at its initial operating point, corresponding to steady state. This is the scaling factor corresponding to the step disturbance. This refers to the damping coefficient corresponding to the grid-type converter. This refers to the DC-side output power of the grid-type converter. For the virtual capacitor and physical capacitor corresponding to the grid-type converter. It is a natural constant. For time.

[0039] Finally, the above expression is further simplified to obtain the full response expression.

[0040] Step S120: Calculate the target steady-state point of the grid-type converter after it is subjected to a step disturbance during mode switching.

[0041] For example, the target steady-state point of the grid-type converter after being subjected to a step disturbance of mode switching is calculated. The mode switching method of the grid-type converter includes: calculating the DC bus voltage change law of the grid-type converter after being subjected to a step disturbance of mode switching according to the full response equation; and determining the target steady-state point of the grid-type converter according to the full response equation and the bus voltage change law.

[0042] For example, the target steady-state point can be expressed by the following formula: ; in, This refers to the target output DC voltage of the grid-type converter at the target steady-state point. This refers to the initial output DC voltage of the grid-type converter at its initial operating point, corresponding to steady state. This is the scaling factor corresponding to the step disturbance. This refers to the DC-side output power of the grid-type converter. This refers to the damping coefficient corresponding to the grid-type converter. This represents the rate of change of the target output DC voltage at the target steady-state point for the grid-type converter.

[0043] For example, the target steady-state point can be determined by the following steps: Reference Figure 5 As shown, based on the full response equation, the change in the output DC voltage of a grid-connected converter with respect to power change and time can be calculated when switching modes (i.e., load abruptly) starting from an arbitrary initial operating point, such as from mode one to mode two. Therefore, by differentiating both sides of the full response equation, the expression for the slope of the target output DC voltage change can be obtained as follows: ; in, The slope This is the scaling factor corresponding to the step disturbance. This refers to the DC-side output power of the grid-type converter. For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This refers to the initial output DC voltage of the grid-type converter at its initial operating point, corresponding to steady state. This refers to the damping coefficient corresponding to the grid-type converter. It is a natural constant. For time.

[0044] Then, based on the slope of the target output DC voltage change, the expression for the initial value of the slope of the target output DC voltage change at t=0 is as follows: ; in, Let be the initial slope of the target output DC voltage corresponding to the grid-type converter at time t=0. This is the scaling factor corresponding to the step disturbance. This refers to the DC-side output power of the grid-type converter. For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This is the initial output DC voltage corresponding to the steady state at the initial operating point of the grid-type converter.

[0045] That is, when a load change occurs (i.e., mode switching), the initial slope value and the load change (i.e.) The slope of the DC bus voltage change gradually approaches 0 as time goes on, determined by the step disturbance generated during mode switching, the initial output DC voltage, and the virtual and physical capacitors corresponding to the grid-type converter, and will stabilize at the target steady-state point.

[0046] For example, the following expression is used to represent the variation law of DC bus voltage: ; in, Let be the initial slope of the target output DC voltage corresponding to the grid-type converter at time t=0. This is the scaling factor corresponding to the step disturbance. This refers to the DC-side output power of the grid-type converter. For the virtual capacitor and physical capacitor corresponding to the grid-type converter. This is the initial output DC voltage corresponding to the steady state at the initial operating point of the grid-type converter.

[0047] Understandably, referring to Figure 5 As shown, when the load changes abruptly (i.e. As a step disturbance generated during mode switching, due to the existence Therefore, the output DC voltage corresponding to the initial operating point will not drop directly, but will decrease smoothly and slowly with an initial slope value, the expression for which is as follows: In other words, the DC bus voltage changes according to the initial slope value. As time progresses, the output DC voltage corresponding to the initial operating point gradually approaches the target output DC voltage corresponding to the target steady-state point, with a settling time of [time value missing]. .

[0048] Step S130: Perform steady-state operation analysis on the first mode and the second mode according to the full response equation to obtain the first curve corresponding to the first mode and the second curve corresponding to the second mode. Perform voltage impact analysis on the first curve and the second curve to obtain the first switching point corresponding to the first curve and the second switching point corresponding to the second curve.

[0049] For example, firstly, the steady-state operating curve of the grid-type converter in the first mode is calculated according to the full response equation, obtaining the first curve corresponding to the first mode. Then, the steady-state operating curve of the grid-type converter in the second mode is calculated according to the full response equation, obtaining the second curve corresponding to the second mode. This accurately describes the first curve of the steady-state operation in the first mode and the curve of the accurate operation in the second mode, providing a foundation for smooth steady-state switching in subsequent modes. Then, the first slope corresponding to each steady-state operating point in the first curve is calculated, reflecting the voltage surge level at that point. Simultaneously, the second slope corresponding to each steady-state operating point in the second curve is calculated, reflecting the voltage surge level at that point. Next, a first switching point with the minimum voltage surge is selected from the steady-state operating points in the first curve based on the first slope, and a second switching point with the minimum voltage surge is selected from the steady-state operating points in the second curve based on the second slope. In this way, both the first switching point and the second switching point in this embodiment are on the steady-state operating curve, and the distance between the first switching point and the second switching point is minimized to reduce voltage surges.

[0050] Step S140: The grid-type converter is switched in mode according to the target steady-state point, the first switching point, and the second switching point.

[0051] For example, refer to Figure 6As shown, taking a grid-type converter in its first mode as an example, with its initial operating point at point A on the first curve, its first switching point on the first curve at point B, its second switching point on the second curve from the first mode to the second mode at point C, and its target steady-state point on the second curve at point D, the grid-type converter returns to a steady-state state. Starting from point A, the output power is actively reduced, and along the first curve, the DC bus voltage slides to point B without overshoot. Then, the converter switches from point B on the first curve to point C on the second curve, reducing the switching impact between modes. Finally, starting from point C, the output power is actively increased, and along the second curve, the DC bus voltage slides to point D without overshoot. Therefore, compared to the prior art where the converter directly switches from point A to point D, the impact of mode switching can be reduced.

[0052] It is understood that the first mode in the embodiments of this application can be a voltage mode or a power mode. This application does not limit the specific mode of the first mode. Similarly, this application does not limit the second mode.

[0053] This application also provides an electronic device, which includes a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the mode switching method of the above-described grid-type converter. This electronic device can be any smart terminal, including tablet computers, in-vehicle computers, etc.

[0054] Please see Figure 7 , Figure 7 The hardware structure of an electronic device according to another embodiment is illustrated. The electronic device includes: The processor 701 can be implemented using a general-purpose CPU (Central Processing Unit), microprocessor, application-specific integrated circuit (ASIC), or one or more integrated circuits, and is used to execute relevant programs to implement the technical solutions provided in the embodiments of this application. The memory 702 can be implemented as a read-only memory (ROM), a static storage device, a dynamic storage device, or a random access memory (RAM). The memory 702 can store the operating system and other application programs. When the technical solutions provided in the embodiments of this specification are implemented through software or firmware, the relevant program code is stored in the memory 702 and is called by the processor 701 to execute the mode switching method of the grid-type converter in the embodiments of this application. The input / output interface 703 is used to implement information input and output; The communication interface 704 is used to enable communication and interaction between this device and other devices. Communication can be achieved through wired means (such as USB, Ethernet cable, etc.) or wireless means (such as mobile network, WIFI, Bluetooth, etc.). Bus 705 transmits information between various components of the device (e.g., processor 701, memory 702, input / output interface 703, and communication interface 704); The processor 701, memory 702, input / output interface 703, and communication interface 704 are connected to each other within the device via bus 705.

[0055] In some embodiments, this application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described mode switching method for a grid-type converter.

[0056] Memory, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs and non-transitory computer-executable programs. Furthermore, memory may include high-speed random access memory, and may also include non-transitory memory, such as at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, memory may optionally include memory remotely located relative to the processor, and these remote memories can be connected to the processor via a network. Examples of such networks include, but are not limited to, the Internet, intranets, local area networks, mobile communication networks, and combinations thereof.

[0057] The embodiments described in this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided by the embodiments of this application. As those skilled in the art will know, with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0058] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of this application, and may include more or fewer steps than shown, or combine certain steps, or different steps.

[0059] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0060] Those skilled in the art will understand that all or some of the steps in the methods disclosed above, as well as the functional modules / units in the systems and devices, can be implemented as software, firmware, hardware, or suitable combinations thereof.

[0061] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0062] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0063] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of the units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0064] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0065] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0066] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes multiple instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this application. The aforementioned storage medium includes various media capable of storing programs, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

Claims

1. A method of mode switching for a meshed converter, characterized in that, The grid control system is applied to the grid-forming converter, the operation mode of the grid-forming converter includes a first mode and a second mode, and the mode switching method of the grid-forming converter includes: The motion equation corresponding to the grid-forming converter is rewritten by introducing any corresponding initial operating point of the grid-forming converter, and a voltage dynamic equation is obtained; The voltage dynamic equation is step analyzed to obtain a full response equation corresponding to the grid-forming converter; A target steady-state point corresponding to the grid-forming converter after the grid-forming converter is subjected to step disturbance of mode switching is calculated; According to the full response equation, steady-state operation analysis is respectively performed on the first mode and the second mode to obtain a first curve corresponding to the first mode and a second curve corresponding to the second mode, and voltage impact analysis is respectively performed on the first curve and the second curve to obtain a first switching point corresponding to the first curve and a second switching point corresponding to the second curve; The grid-forming converter is switched according to the target steady-state point, the first switching point and the second switching point.

2. The mode switching method of the network-forming converter according to claim 1, characterized by, Before the motion equation corresponding to the grid-forming converter is rewritten by introducing any corresponding initial operating point of the grid-forming converter to obtain a voltage dynamic equation, the mode switching method of the grid-forming converter further includes: A control strategy equation corresponding to the grid-forming converter is determined according to a topological structure and a virtual synchronous machine control strategy corresponding to the grid-forming converter; The control strategy equation is rewritten into an equivalent equation based on a capacitance equivalent topological structure corresponding to the grid-forming converter, and the equivalent equation is rewritten by introducing a real-time output direct-current voltage corresponding to the grid-forming converter to obtain the motion equation.

3. The mode switching method of the network-forming converter according to claim 1, characterized by, The voltage dynamic equation is expressed by the following formula: ； wherein, is a virtual capacitance corresponding to the network-forming converter and a physical capacitance, is an initial output direct current voltage corresponding to the network-forming converter at the initial operating point being a steady state, is a real-time output direct current voltage corresponding to the network-forming converter, and are damping coefficients corresponding to the network-forming converter, is a direct current side output power corresponding to the network-forming converter, is an output power corresponding to the network-forming converter.

4. The mode switching method of the network-forming converter according to claim 1, characterized by, The mode switching method of the grid-forming converter includes: A transfer function between an output direct-current voltage corresponding to the grid-forming converter and an output power corresponding to the grid-forming converter is calculated according to the voltage dynamic equation; Step disturbance is applied to the grid-forming converter, and step analysis is performed based on the transfer function to obtain the full response equation corresponding to the grid-forming converter.

5. The mode switching method of the network-forming converter according to claim 4, characterized by, The full response equation is expressed by the following formula: ； wherein, is a real-time output DC voltage corresponding to the network-forming converter at time t, is an initial output DC voltage corresponding to the network-forming converter at a steady state corresponding to the initial operating point, is a proportional coefficient corresponding to the step disturbance, is a damping coefficient corresponding to the network-forming converter, is an output power on a DC side corresponding to the network-forming converter, is a virtual capacitance and a physical capacitance corresponding to the network-forming converter, is a natural constant, is time.

6. The mode switching method of the network-forming converter according to claim 1, characterized by, The mode switching method of the grid-forming converter includes: A direct-current bus voltage variation law after the grid-forming converter is subjected to step disturbance of mode switching is calculated according to the full response equation; A target steady-state point corresponding to the grid-forming converter is determined according to the full response equation and the direct-current bus voltage characteristic equation variation law.

7. The mode switching method of the network-forming converter according to claim 6, characterized by, The target steady-state point is expressed by the following formula: ； wherein, is an initial output DC voltage of the network-forming converter corresponding to the initial operating point being steady state, is an initial output DC voltage of the network-forming converter corresponding to the initial operating point being steady state, is a proportional coefficient corresponding to the step disturbance, is an output power of the network-forming converter corresponding to the target steady state point, is a damping coefficient of the network-forming converter corresponding to the target steady state point, is a rate of change of the target output DC voltage of the network-forming converter corresponding to the target steady state point.

8. The mode switching method of the network-forming converter according to claim 6, characterized by, The direct-current bus voltage variation law is expressed by the following expression: ； wherein, is a slope initial value of a target output DC voltage corresponding to the network-forming converter at t=0, is a proportional coefficient corresponding to the step disturbance, is a DC side output power corresponding to the network-forming converter, is a virtual capacitance and a physical capacitance corresponding to the network-forming converter, is an initial output DC voltage corresponding to the network-forming converter at the initial operating point being a steady state.

9. An electronic device, comprising: It includes: At least one processor; At least one memory for storing at least one program; When at least one program is executed by at least one processor, the method of any one of claims 1 to 8 is implemented.

10. A computer-readable storage medium storing computer-executable instructions, the computer-executable instructions comprising: The computer executable instructions are for performing the method of any one of claims 1 to 8.

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