Active power distribution network stability control method based on intelligent soft switch

Abstract

The application relates to a kind of active power distribution network stability control methods based on intelligent soft switch, comprising: the AVSG control equation of direct current power distribution network is established: capacitor in boost converter in direct current side in direct current power distribution network is analogized as rotor in virtual synchronous generator, when power fluctuates, absorbs or discharges electric energy, to achieve the effect of stabilizing voltage, analogize the relationship between frequency and power when rotor speed changes in alternating current system, the kinetic energy of rotor in motor is analogized as the reactive power of capacitor, and the AVSG control equation of direct current power distribution network is obtained;For the boost converter used in AVSG control, the state average equation of boost converter running in a switching cycle is obtained, and the transfer function calculation formula is given;Through the analysis of proportional coefficient and integral coefficient in PI control, AVSG control is combined with PI control, and its bode diagram and zero-pole diagram are made, to judge control stability.

Description

Technical Field

[0001] This invention belongs to the field of active distribution network system stability control, and specifically relates to an active distribution network stability control method based on intelligent soft switching. Background Technology

[0002] With the development of industry over the past century, the energy demand of various countries has been rising continuously. However, the reserves of fossil fuels on Earth are limited, and their use has a huge impact on the environment. After nearly a century of massive fossil fuel use, climate change has become an important factor that cannot be ignored in energy consumption. Under increasing pressure from energy security and climate change, my country has proposed the strategic goal of "peak carbon and carbon neutrality." This strategy aims to accelerate my country's energy transformation and speed up the transition from fossil fuels to renewable energy. Renewable energy sources such as wind power and photovoltaic energy have developed rapidly in recent decades. The grid connection of these distributed energy storage units is inevitable, but a series of problems arise when they are integrated into the power grid.

[0003] Active distribution networks contain numerous distributed power sources such as photovoltaics, wind power, and energy storage devices. When conducting power system operation planning and stability analysis, the instability caused by renewable energy sources significantly increases the difficulty of stability analysis. Furthermore, with the integration of renewable energy into the grid, the significant structural differences between active distribution networks and traditional power grids amplify these differences. For example, distributed power sources in active distribution networks cannot directly transfer energy; instead, they require power electronic converters as intermediaries. While power electronic converters are easy to control and highly flexible in use, DC distribution networks composed of power electronic converters suffer from low inertia. When faced with unstable voltage sources such as wind and solar power, the bus voltage of the active distribution network experiences drastic changes. These voltage fluctuations not only affect power quality but also cause significant losses to power electronic components. With the rapid development of active distribution networks, the poor grid stability caused by the low inertia and low damping characteristics of distributed power sources is becoming increasingly apparent. Moreover, as the distribution of active distribution networks expands, the stability problems caused by the lack of inertia and damping in active distribution network systems with distributed power sources as the primary energy source become particularly prominent. Among these, frequency stability is a significant issue in active distribution networks, and the main problem in the active distribution network with intelligent soft switching, which is the focus of this invention, is stability. DC bus voltage is the sole indicator of stable distribution network operation and the only basis for judging power quality.

[0004] In summary, given the widespread integration of distributed energy resources, in order to improve the stability of DC power distribution systems and fully leverage their advantages, it is necessary to propose an active distribution network stability control method based on intelligent soft switching. Summary of the Invention

[0005] To address the stability issues in DC power distribution systems, this invention proposes a stability control method for active distribution networks based on intelligent soft switching. This method is applicable to active distribution networks and can improve the stability, safety, and reliability of active distribution network operation, achieving efficient and high-quality stable power supply. The technical solution is as follows:

[0006] Step 1: Establish the AVSG control equations for the DC distribution network

[0007] The capacitors in the DC-side boost converter of a DC distribution network are analogous to the rotors in a virtual synchronous generator. When power fluctuates, they absorb or release electrical energy to stabilize the voltage. Analogous to the relationship between frequency and power when the rotor speed changes in an AC system, the current relationship is as follows:

[0008]

[0009] In the formula: It is an inertial current; i in For input current; For resistance current; u dc This refers to the DC-side bus voltage. i dc For output current; C vir Let be the virtual inertia time constant; and using the reactive power of the capacitor as an analogy to the rotor kinetic energy in the motor, the following AVSG control equations for the DC distribution network are obtained:

[0010]

[0011] In the formula: k droop for IU Sag coefficient; k D It is the voltage damping coefficient; The rated voltage is analogous to the rated voltage of the rated angular velocity in the rotor inertial element of a virtual synchronous motor; the DC bus voltage is... As a feedback signal, it is introduced into the primary voltage regulation and damping stage, using IU Droop control; Reference value for DC side bus voltage As a reference value for the outer voltage loop in AVSG control, the DC-side bus voltage of the converter is... Reference value for tracking DC-side bus voltage ;

[0012] Step 2: For the boost converter used in AVSG control, based on small-signal model analysis, the state-average equation of the boost converter operating within one switching cycle is obtained, and the transfer function calculation formula is given under the following conditions: the switching device is ideal and can switch between on and off states instantaneously; the boost converter operates under continuous conduction; the frequency of the AC small signal and the inherent corner frequency of the boost converter are less than the switching frequency; the amplitude of the AC component of each variable in the DC distribution network is less than its DC component. Based on the switching state of the switching device, a small-signal model is established to obtain the state-average equation of the boost converter operating within one switching cycle:

[0013]

[0014] In the formula, L It's an inductor. R It is the load resistor. C It is a filter capacitor; d For duty cycle, <> indicates the averaging sign for the corresponding physical quantity; inductor current is represented by <>. i L Indicates capacitor voltage v o Indicates input power supply voltage v in express;

[0015] Obtain the duty cycle-capacitor voltage transfer function G vd (s) Duty cycle—inductor current transfer function G id (s) and the transfer function of inductor current-output voltage G P (s) :

[0016]

[0017]

[0018]

[0019] In the formula, D It is the duty cycle of the boost converter in steady state. V o It is the output voltage of the boost converter in steady state;

[0020] Step 3: By analyzing the proportional and integral coefficients in PI control, AVSG control and PI control are combined. Bode plots and pole-zero plots are generated using MATLAB to determine the control stability.

[0021] After the DC distribution network is connected to AVSG control, the closed-loop transfer function of the system is obtained. G(s) as follows:

[0022]

[0023] G id (s) The duty cycle-inductor current transfer function; G P (s) It is the transfer function of inductor current versus output voltage; G i (s) It is the transfer function of the inner loop of the PI control current; G v (s) This is the outer loop transfer function of the PI control voltage. The outer loop transfer function is: , These are the proportional control parameters for the voltage loop. The voltage loop integral control parameters are used; the inner current loop also uses PI control, and its transfer function is... , These are the proportional control parameters for the current loop. Bode plots and pole-zero plots are generated for the integral control parameters of the current loop. Simulation verification under resistive load is performed based on actual operating parameters to determine the control stability of the DC distribution network connected to AVSG control. Attached Figure Description

[0024] Figure 1 The transfer function block diagram after adding dual closed-loop control to AVSG control.

[0025] Figure 2 This is the topology of the boost converter.

[0026] Figure 3 for G(s) The Bird diagram.

[0027] Figure 4 for G(s) Pole-zero plot. Detailed Implementation

[0028] The following will describe in detail the power allocation strategy of the hybrid energy storage system based on intelligent soft switching proposed in this invention, with reference to the accompanying drawings and specific implementation.

[0029] (1) By analyzing the VSG control of the AC distribution network, the AVSG control of the DC distribution network is derived. The AVSG control equation of the DC distribution network is derived by combining the VSG control equation, and the transfer function of the system is derived.

[0030] VSG control directly transforms the circuit equations into mechanical motion equations based on the rotor rotation by simulating the operating state of a synchronous motor.

[0031]

[0032] In the formula: It is the input mechanical power; To output electromagnetic power; The damping power reflects the damping characteristics; ω is the angular frequency of the rotor in a synchronous generator; It is the virtual inertial time constant, and the rotor's moment of inertia. Correspondingly, J This demonstrates the relationship between the total kinetic energy of the motor and the rotor angular frequency. H and J The relationship is as follows:

[0033]

[0034]

[0035] In the formula: ω N This is the rated angular frequency; P N This refers to the rated power of the synchronous generator; ω g The common bus angular frequency is the difference between the rated angular frequency and the common bus angular frequency, i.e. ( ω N - ω g ), serving as a damping element and a feedback signal used as a reference in primary frequency modulation; k d It is the frequency damping coefficient, which reflects the ability of the system's damping to suppress frequency oscillations; k yes P-ω The droop coefficient of droop control represents the primary frequency regulation capability of the system.

[0036] VSG control simulates the control of rotational inertia. J The energy released through simulation control is used to prevent sudden changes in system frequency, thereby controlling and increasing the overall system's inertia. The released energy is stored in the corresponding virtual synchronous generator rotor, whose rotor contains energy... W v as follows

[0037]

[0038] It can be seen that synchronous generators control the energy contained in the entire system through rotor inertia and rotor rotation angular frequency. However, DC systems differ from AC systems in that AC distribution networks contain angular frequencies, allowing the system energy to be considered as the energy of a virtual rotor, and all parameters in the system except for the rotor angular frequency to be uniformly considered as the inertia of the virtual rotor. But in DC distribution network systems, the bus frequency parameter does not exist. Therefore, to approximate the expression of synchronous generators to DC distribution networks, the bus voltage is chosen as the parameter. u dc Analogous to the rotor angular frequency in a synchronous generator ω Virtual capacitors in DC distribution networks C vir Analogous to the moment of inertia in a synchronous generator J .

[0039] In AC distribution networks, the stability of the system frequency is the key indicator for system stability. However, in DC distribution networks, the stability of the DC bus voltage is used to measure system power stability. This is because DC grids contain numerous power electronic devices with isolation functions, preventing the power supply voltage from directly affecting the bus voltage. However, the capacitors in the DC-side boost converter of a DC distribution network can be analogized to the rotor in a virtual synchronous generator. When power fluctuates, they absorb or release electrical energy, thus stabilizing the voltage. The current relationship is shown below, and by analogy between the reactive power of the capacitor and the rotor kinetic energy in a motor, the following expression can be obtained.

[0040]

[0041] In the formula: It is an inertial current; i in For input current; For resistance current; u dc The output voltage of the AVSG; i dc For output current; C vir This is the virtual inertial time constant.

[0042] By analogy between the reactive power of a capacitor and the rotor kinetic energy in a motor, we can obtain:

[0043]

[0044] In the formula: k droop for IU Sag coefficient; k D It is the voltage damping coefficient; The rated voltage is analogous to the rated angular velocity in the rotor inertial element of a virtual synchronous motor, and is the DC bus voltage. As a feedback signal, it is introduced into the primary voltage regulation and damping stage, using IU Droop control. Output voltage. As a reference value for the outer voltage loop in AVSG control, the DC-side bus voltage of the converter is... Reference value for tracking DC-side bus voltage .

[0045] It can be observed that energy is stored in a DC grid through a virtual capacitor, similar to the function of the rotor in a synchronous generator. The energy contained in its virtual rotor is as follows:

[0046]

[0047] In the formula: C vir This is a virtual capacitor connected in parallel on the DC distribution network side; W c The energy stored in the capacitor; u This is the voltage across the capacitor.

[0048] Corresponding parameters of synchronous generator and AVSG control

[0049]

[0050] It can be seen that not only resistors are used R d As a droop factor, it is used for primary voltage regulation; variable inductance L PI This indicates a PI controller for the outer voltage loop; capacitor. C vir This indicates the inertial support of the virtual rotor to the distribution network in AVSG control; controllable current source - k D u D This indicates that AVSG provides damping support for the system. u D The voltage of the controllable current source. According to Kirchhoff's current law for circuits, under traditional droop control, the output current... Only by The magnitude of the current is determined by the AVSG control. Under AVSG control, the output current... i dc Depend on R d , C vir as well as k D u DThe current on the bus is determined by the AVSG control, which improves the low inertia and low damping characteristics of the system, giving the system a better coping strategy when facing DC bus voltage fluctuations, thereby improving voltage quality.

[0051] A dual closed-loop control method using voltage and current can address system stability issues caused by sudden load changes. To effectively eliminate deviations, accelerate system response, control system overshoot, increase system damping, and ultimately improve steady-state characteristics, a suitable compensator should be selected. Common compensators include lead compensators and lag compensators. Both have the following transfer function form:

[0052]

[0053] The former has the following characteristics: This can make the system more stable and converge faster; the latter has the following characteristics: This can reduce steady-state error. To improve the stability of the power system and reduce errors, the selected voltage and current dual-loop controllers are all PI controllers with lag compensation devices. Transfer function , For proportional control parameters, These are integral control parameters; the inner current loop also uses PI control, with the transfer function... , These are integral control parameters used to eliminate errors.

[0054] proportionality coefficient k p It is the mainstay and indispensable component of PI control. Proportional control is an immediate control mechanism; once a deviation is detected, it immediately outputs a control quantity. Proportional coefficient. k p Increasing the value of PI control can speed up the system's response, reduce static and steady-state errors, and thus improve the accuracy of PI control. However, if the value is too large, it will result in excessive control and a large overshoot, which will affect the stability of the control. Conversely, if the value is too small, it can reduce the overshoot and increase the system's stability margin, but it will reduce the speed of control, thus prolonging the transition time and reducing the efficiency of PI control. k p The larger the value, the faster the response.

[0055] Integral coefficient k i Integral control is the mainstay of PI control, used to eliminate static errors. It's a control method with corrective properties; once a deviation is detected, it aims to eliminate that deviation. It's suitable for systems capable of automatic balancing. Increasing the integral coefficient... ki This is beneficial for reducing system steady-state error, but if the integral control is too large, it will increase the overshoot, causing system instability and even oscillation; the integral coefficient k i Reducing the overshoot can decrease the overshoot and enhance the stability of the system, but it is not conducive to eliminating static errors in the system.

[0056] The block diagram of the transfer function after connecting the voltage and current dual closed-loop PI controller is attached. Figure 1 In the picture u dc This is the reference value for the bus voltage, which is used as the set output voltage value. i dc This is a reference value for the bus current. V o That is, the output voltage; G id (s) The transfer function from duty cycle to inductor current; G P (s) It is the transfer function from inductor current to output voltage; G i It is the transfer function of the inner loop of the PI control current. G v It is the outer loop transfer function of the PI control voltage.

[0057] Therefore, its double closed-loop transfer function can be derived. G(s) for:

[0058]

[0059] Based on its open-loop transfer function of the inner current loop G id (s) The Bode plot is plotted and analyzed. A suitable phase-crossover frequency is selected to ensure that the switching frequency does not interfere with the system. Simultaneously, by combining the phase margin and gain margin, the damping of the system can be roughly determined; generally, a damping value of 0.707 is taken. This allows for a preliminary assessment of the system's stability.

[0060] (2) For the boost converter used in AVSG control, based on the small signal model analysis, its relevant model is established, and its transfer function is derived and calculated.

[0061] Appendix Figure 2 This is a basic topology diagram of a boost converter. Among them,V in It is the power input voltage; S It is a switching element of the boost converter, whose switching state is controlled by a PWM current switching signal; L It's an inductor. R It is the load resistor. C It is a filter capacitor; VD is a freewheeling diode. Assume an inductor... L The current is in continuous operating mode, depending on the switching device. S By observing the switching states, the equivalent circuits of the boost converter under two operating states can be obtained.

[0062] State 1: When the switching element S is turned off, because of the inductor current i L Because it is continuous, there will be no abrupt changes; therefore, the freewheeling diode VD conducts, and in the adjacent... Figure 2 When the switch is in the off state, the capacitor C Simultaneously inducted L With power supply voltage V in Charging, and load resistance R When powered, the capacitor voltage is the output voltage. v o The inductor current gradually increases. i L Gradually decreasing; the following inductance current can be established. i L and output voltage v o The mathematical model.

[0063]

[0064] Status 2: According to the appendix Figure 2 The topology diagram shows that when the switching element S is turned on, the freewheeling diode VD is reverse-biased and the input power supply is connected to the inductor. L During charging, the inductor current i L Gradually increase, while capacitance C Discharge the load. According to Kirchhoff's laws, an inductor current can be established. i L and output voltage v o The dynamic mathematical model.

[0065]

[0066] DC-DC converters are power electronic devices with switching functions and are highly nonlinear dynamic systems. Currently, common methods for mathematical modeling DC-DC converters include small-signal modeling, large-signal modeling, switching averaging, and state-space averaging. Among these, the small-signal modeling method is widely applicable due to its good and broad applicability; therefore, this paper will employ the small-signal modeling method to model and analyze the boost converter and derive its relevant transfer function. In the modeling process, a series of reasonable assumptions are first set, and then combined with the small-signal equivalent circuit. Specifically, based on the switching states of the switching elements, a small-signal model that meets practical requirements is established. Then, based on the small-signal characteristics, steady-state and transient analyses are performed through analytical analysis of the model, and these are combined to further establish the steady-state model of the converter, as well as dynamic mathematical models in the time and frequency domains. The following reasonable assumptions are introduced for the boost converter in this invention:

[0067] Assumption 1: The switching device is ideal and can switch between on and off states instantaneously;

[0068] Assumption 2: The converter operates under continuous conduction;

[0069] Assumption 3: The frequency of the AC small signal and the inherent corner frequency of the converter are much smaller than the switching frequency;

[0070] Assumption 4: The amplitude of the AC component of each variable in the system must be much smaller than that of its DC component.

[0071] Define the average value of the system state variables over the switching cycle as:

[0072]

[0073] In the formula, x ( t ) represents the system's state variables. T Given the switching duty cycle, the state-average equation for the boost converter's operation over one switching cycle is obtained:

[0074]

[0075] In the formula, d For duty cycle, <> indicates the averaging sign over the corresponding physical quantity. In inductor current... i L capacitor voltage v o Input power supply voltage v in and duty cycle d To introduce interference signals into the average value, the average value is divided into the sum of its DC and AC components:

[0076]

[0077] In the formula: It is the AC component of the inductor current. I L It is the DC component of the inductor current; It is the AC component of the capacitor voltage. V o It is the DC component of the capacitor voltage; It is the AC component of the input power supply voltage. V in It is the DC component of the input power supply voltage; It is the AC component of the duty cycle. D It represents the DC component of the duty cycle. The AC component represents the instantaneous value, and the DC component represents the steady-state value.

[0078]

[0079] Steady-state analysis: Removing the AC component from the above equation and retaining the DC component, we have

[0080]

[0081] Let the left side of the equation be zero, that is

[0082]

[0083] Therefore, in steady-state conditions, the boost converter exhibits the following algebraic relationships:

[0084]

[0085] Transient analysis: Remove the DC component from the equation, retain the AC component, and ignore the second-order component d. and d Then there is

[0086]

[0087] Applying a Laplace transform to both sides of the above equation and rearranging them, we can obtain the duty cycle-capacitor voltage transfer function. G vd (s) Duty cycle—inductor current transfer function G id (s) and the transfer function of inductor current-output voltage G P (s) :

[0088]

[0089]

[0090]

[0091] In the formula, D It is the duty cycle of the boost converter in steady state. V o It is the output voltage of the boost converter in steady state, and is related to the input voltage. V in There exists a steady-state relationship, namely:

[0092]

[0093] (3) By analyzing the proportional coefficient and integral coefficient in PI control, AVSG control and PI control are combined, and Bode plot and zero-pole plot are generated using MATLAB to prove the stability of the system control.

[0094] Based on the system transfer function diagram, assuming the DC input power supply voltage is 375V, and a constant power load is connected after the boost converter, the IU droop control coefficient is selected. k droop The damping coefficient is 2. k D The value is 0.01, the switching frequency is 1kHz, and the system inductance and resistance are... R The inductance is 0.5Ω. L The capacitance is 0.002H. C The value is 0.00188F. Simulation verification under resistive load was performed using PLECS software.

[0095] System parameters

[0096]

[0097] Table V Rated voltage u N .

[0098] Default control parameters

[0099]

[0100] To select appropriate phase and gain margins, a crossover frequency of 100Hz is chosen. Based on the formula from the previous step, the value of the inner-loop PI controller is calculated. k pi and k ii Parameters. Connect it to its inner loop PI controller and form it into a closed-loop transfer function to obtain its transfer function.G ii (s)

[0101]

[0102] Obtain the outer loop open-loop voltage transfer function G vdc (s)

[0103]

[0104] By connecting a voltage outer-loop PI controller and forming its closed-loop transfer function, the outer-loop voltage closed-loop transfer function is obtained. G viv (s)

[0105]

[0106] By integrating AVSG control, the closed-loop transfer function of the system can be obtained. G(s) as follows

[0107]

[0108] After connecting to AVSG control, stability is determined based on the Bode plot criterion, according to the attached... Figure 3 It can be seen that both its phase margin and gain margin are positive; similarly, according to its pole-zero plot... Figure 4 Since all its poles are located in the left half-plane of the s-plane, the system can be preliminarily determined to be stable. Therefore, it was found that the system remains stable after combining AVSG control and PI control.

[0109] In summary, the research on the active distribution network stability control method based on intelligent soft switching proposed in this invention can provide theoretical and technical support for improving the stability, security and reliability of active distribution network operation and realizing efficient, high-quality and stable power supply.

[0110] The following is a summary of the technical solution of the present invention:

[0111] Step 1: Establish the AVSG control equations for the DC distribution network

[0112] The capacitors in the DC-side boost converter of a DC microgrid are analogous to the rotor in a virtual synchronous generator. When power fluctuates, they absorb or release electrical energy to stabilize the voltage. Analogous to the relationship between frequency and power when the rotor speed changes in an AC system, the current relationship is as follows:

[0113]

[0114] In the formula: It is an inertial current;i in For input current; For resistance current; u dc The output voltage of the AVSG; i dc For output current; C vir Let be the virtual inertia time constant. And, analogous to the rotor kinetic energy in a motor with the reactive power of a capacitor, the following AVSG control equations for a DC distribution network are obtained:

[0115]

[0116] In the formula: k droop for IU Sag coefficient; k D It is the voltage damping coefficient; The rated voltage is analogous to the rated voltage of the rated angular velocity in the rotor inertial element of a virtual synchronous motor; the DC bus voltage is used as an analogy. As a feedback signal, it is introduced into the primary voltage regulation and damping stage, using IU Droop control. Output voltage. As a reference value for the outer voltage loop in AVSG control, the DC-side bus voltage of the converter is... Reference value for tracking DC-side bus voltage .

[0117] Step 2: For the boost converter used in AVSG control, based on small-signal model analysis, the state-average equation of the boost converter operating within one switching cycle is obtained, and the formula for calculating the transfer function is given.

[0118] Conditions: The switching devices are ideal and can switch between on and off states instantaneously; the converter operates under continuous conduction; the frequency of the AC small signal and the converter's inherent corner frequency are less than the switching frequency; the amplitude of the AC component of each variable in the system is less than its DC component. Combined with the small-signal equivalent circuit, a small-signal model is established based on the switching states of the switching elements, yielding the state-average equations of the boost converter operating within one switching cycle.

[0119]

[0120] In the formula, L It's an inductor. R It is the load resistor. C It is a filter capacitor; d For duty cycle, <> indicates the averaging sign for the corresponding physical quantity; inductor current is represented by <>. i LIndicates capacitor voltage v o Indicates input power supply voltage v in express.

[0121] Then the duty cycle-capacitor voltage transfer function is obtained. G vd (s) Duty cycle—inductor current transfer function G id (s) and the transfer function of inductor current-output voltage G P (s) :

[0122]

[0123]

[0124]

[0125] In the formula, D It is the duty cycle of the boost converter in steady state. V o It is the output voltage of the boost converter in steady state.

[0126] Step 3: By analyzing the proportional and integral coefficients in PI control, AVSG control and PI control are combined. Bode plot and pole-zero plot are generated using MATLAB to determine the stability of the system control.

[0127] After the DC distribution network is connected to AVSG control, the closed-loop transfer function of the system is obtained. G(s) as follows:

[0128]

[0129] G id (s) The transfer function from duty cycle to inductor current; G P (s) It is the transfer function from inductor current to output voltage; G i (s) It is the transfer function of the inner loop of the PI control current. G v (s) It is the outer loop transfer function of the PI control voltage. , These are the proportional control parameters for the voltage loop. The voltage loop integral control parameters are used; the inner current loop also uses PI control, and its transfer function is... , These are the proportional control parameters for the current loop. These are the integral control parameters for the current loop.

[0130] Finally, Bode plots and pole-zero plots were generated using MATLAB; based on actual operating parameters, PLECS software was used to perform simulation verification under resistive loads to determine the stability of the DC distribution network system connected to AVSG control.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An active distribution network stability control method based on intelligent soft switching, comprising the following steps: Step 1: Establish the AVSG control equations for the DC distribution network The capacitors in the DC-side boost converter of a DC distribution network are analogous to the rotors in a virtual synchronous generator. When power fluctuates, they absorb or release electrical energy to stabilize the voltage. Analogous to the relationship between frequency and power when the rotor speed changes in an AC system, the current relationship is as follows: In the formula: It is an inertial current; i in For input current; For resistance current; u dc This refers to the DC-side bus voltage. i dc For output current; C vir Let be the virtual inertia time constant; and using the reactive power of the capacitor as an analogy to the rotor kinetic energy in the motor, the following AVSG control equations for the DC distribution network are obtained: In the formula: k droop for IU Sag coefficient; k D It is the voltage damping coefficient; The rated voltage is analogous to the rated voltage of the rated angular velocity in the rotor inertial element of a virtual synchronous motor; the DC bus voltage is... As a feedback signal, it is introduced into the primary voltage regulation and damping stage, using IU Droop control; Reference value for DC side bus voltage As a reference value for the outer voltage loop in AVSG control, the DC-side bus voltage of the converter is... Reference value for tracking DC-side bus voltage ; Step 2: For the boost converter used in AVSG control, based on small-signal model analysis, the state-average equation of the boost converter operating within one switching cycle is obtained, and the transfer function calculation formula is given under the following conditions: the switching device is ideal and can switch between on and off states instantaneously; the boost converter operates under continuous conduction; the frequency of the AC small signal and the inherent corner frequency of the boost converter are less than the switching frequency; the amplitude of the AC component of each variable in the DC distribution network is less than its DC component. Based on the switching state of the switching device, a small-signal model is established to obtain the state-average equation of the boost converter operating within one switching cycle: In the formula, L It's an inductor. R It is the load resistor. C It is a filter capacitor; d For duty cycle, <> indicates the averaging sign for the corresponding physical quantity; inductor current is represented by <>. i L Indicates capacitor voltage v o Indicates input power supply voltage v in express; Obtain the duty cycle-capacitor voltage transfer function G vd (s) Duty cycle—inductor current transfer function G id (s) and the transfer function of inductor current-output voltage G P (s) : In the formula, D It is the duty cycle of the boost converter in steady state. V o It is the output voltage of the boost converter in steady state; Step 3: By analyzing the proportional and integral coefficients in PI control, AVSG control and PI control are combined. Bode plots and pole-zero plots are generated using MATLAB to determine the control stability. After the DC distribution network is connected to AVSG control, the closed-loop transfer function of the system is obtained. G(s) as follows: G id (s) The duty cycle-inductor current transfer function; G P (s) It is the transfer function of inductor current versus output voltage; G i (s) It is the transfer function of the inner loop of the PI control current; G v (s) This is the outer loop transfer function of the PI control voltage. The outer loop transfer function is: , These are the proportional control parameters for the voltage loop. The voltage loop integral control parameters are used; the inner current loop also uses PI control, and its transfer function is... , These are the proportional control parameters for the current loop. Bode plots and pole-zero plots are generated for the integral control parameters of the current loop. Simulation verification under resistive load is performed based on actual operating parameters to determine the control stability of the DC distribution network connected to AVSG control.

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