Virtual damping self-adjustment-based direct-current micro-grid voltage control method and device

Abstract

The invention relates to a virtual damping self-regulation-based direct-current micro-grid voltage control method and device, and the method comprises the steps: taking a condition that a converter is in a voltage conversion control mode as a condition, setting the input power at a steady-state working point to be constant, and obtaining a simplified model of a constant-power load cascade system based on a damping resistance method; defining expression parameters of the model according to the model, and obtaining a mathematical relationship among the expression parameters; after a damping resistor is added in the constant-power cascade system, a characteristic equation of the cascade system is obtained; and deriving a stability constraint condition of the system according to the characteristic equation. According to the method, the stability constraint condition of the system is deduced through the simplified model of the cascade system, the stability of the cascade system is analyzed, and when the filter capacitance of the LC input filter is small, the cascade system generates a resonance phenomenon, so that a passive damping control strategy of a damping resistance method is obtained in order to suppress the resonance phenomenon, and the stability of the cascade system is improved. Therefore, the output control of the voltage is stabilized, and the voltage stability control requirement is met.

Description

Technical Field

[0001] The present invention relates to the technical field of microgrid voltage control, and in particular to a direct current microgrid voltage control method and device based on virtual damping self-regulation. Background Art

[0002] With the continuous development of social economy and the continuous growth of electricity demand, microgrids can give full play to their advantages in the use of new energy, and their development has received more and more attention and attention. In microgrids, due to the existence of power electronic converters and nonlinear loads, the impact of resonance problems on microgrids is becoming increasingly significant, which will also seriously affect the power quality of the power grid.

[0003] In a DC microgrid, in order to ensure the stability of the input side voltage of the constant power load, an LC input filter is usually cascaded in the system, and its access point is between the constant power load and the DC bus. After the input filter is connected, due to the small capacitance value of the LC filter, the negative impedance characteristics of the constant power load will reduce the stability margin of the entire system, thereby triggering the resonance phenomenon of the cascade system, causing fluctuations in the input voltage and output voltage, and failing to meet the system's control requirements for the output voltage. Summary of the invention

[0004] In view of the above problems existing in the prior art, an object of the present invention is to provide a DC microgrid voltage control method and device based on virtual damping self-regulation.

[0005] In order to solve the above technical problems, the first embodiment of the present invention proposes a DC microgrid voltage control method based on virtual damping self-regulation. The present invention provides the following technical solutions: A DC microgrid voltage control method based on virtual damping self-regulation comprises the following steps:

[0006] Step 1: Under the condition that the buck converter is in the voltage conversion control mode and the input power at the steady-state operating point is constant, a simplified model of the constant power load cascade system is obtained based on the damping resistor method;

[0007] Step 2: Define the expression parameters of the model according to the simplified model of the constant power load cascade system, and obtain the mathematical relationship between the various expression parameters;

[0008] Step 3: According to the mathematical relationship between various expression parameters, after adding the damping resistor to the simplified model of the constant power load cascade system, the characteristic equation of the constant power load cascade system is obtained;

[0009] Step 4: According to the characteristic equation of the constant power load cascade system, the stability constraint conditions of the system are derived, and the stability analysis of the constant power load cascade system is performed through the stability constraint conditions. It is determined that the constant power load cascade system suppresses the occurrence of resonance phenomenon with the introduction of damping resistance, thereby stabilizing the output control of the DC microgrid voltage. The resonance suppression of the constant power load cascade system can stabilize the output control of the DC microgrid voltage.

[0010] The mathematical expression relationship in step 2 of the present invention is:

[0011]

[0012] Among them, R d is the damping resistance, i g is the DC bus input circuit, i d is the passive damping current, i C is the capacitor current of the LC filter, i in Input current steady-state value for the buck converter.

[0013] In step 3 of the present invention, the characteristic equation of the cascade system is:

[0014]

[0015] Among them, L f is the LC input filter inductor, R f is the parasitic resistance of the LC input filter, C f is the LC input filter capacitor, V in is the steady-state value of the input voltage of the buck converter, P L is the load power.

[0016] As a preferred solution of the DC microgrid voltage control method based on virtual damping self-regulation described in the present invention, in step 4, the stability constraint condition of the system is:

[0017]

[0018] As a preferred solution of the DC microgrid voltage control method based on virtual damping self-regulation described in the present invention, the simplified model of the constant power load cascade system obtains the input current of the buck converter as follows:

[0019]

[0020] in, is the small signal AC component of the input voltage, and according to this formula, the small signal AC component of the input current is obtained by replacing the curve near the equilibrium point with the tangent line:

[0021]

[0022] When the input voltage changes, the input current changes in the opposite direction, which will affect the stability between the LC input filter and the buck converter and cause resonance.

[0023] As a preferred solution of the DC microgrid voltage control method based on virtual damping self-regulation described in the present invention, the damping resistance method introduced in the simplified model of the constant power load cascade system is the equivalent introduction of virtual resistance damping.

[0024] As a preferred solution of the DC microgrid voltage control method based on virtual damping self-regulation described in the present invention, the optimal value range of the virtual resistance damping is determined, that is, the relevant program is written in MALAB through the m file, the set expression parameters are brought into the program, and the value range of the virtual resistance damping is obtained, thereby determining the critical value of the virtual resistance damping when the system is stable.

[0025] In DC microgrids, switching converters are often used to achieve voltage conversion between the DC bus and the load. To ensure that the load unit works normally at its rated voltage, the converter often has a closed-loop control function. Its instantaneous input power is constant, so it can be regarded as a constant power load. However, considering different working environments, the bus voltage has the characteristics of volatility and randomness. To ensure the input side voltage of the constant power load is stable, an input filter is usually cascaded between the DC bus and the constant power load. At this time, if the parameter value of the filter device is not selected properly, the negative impedance characteristics of the constant power load will reduce the stability margin of the cascade system, induce the resonance phenomenon of the system, and cause fluctuations in the input voltage and output voltage of the converter, thereby affecting the system's control effect on the output voltage.

[0026] The second aspect of the present invention proposes a DC microgrid voltage control device based on virtual damping self-regulation, comprising: a constant power load cascade system simplified model construction module, which is used to obtain a simplified model of the constant power load cascade system based on the damping resistance method under the condition that the input power of the buck converter is constant in the voltage conversion control mode and the steady-state operating point; the simplified model is defined to obtain the mathematical relationship between various expression parameters; a constant power load cascade system characteristic equation determination module, which is used to obtain the characteristic equation of the constant power load cascade system according to the mathematical relationship between the expression parameters after adding the damping resistance to the simplified model of the constant power load cascade system;

[0027] The constant power load cascade system stability analysis module is used to perform stability analysis of the constant power load cascade system through stability constraints, and determine that the constant power load cascade system suppresses the occurrence of resonance phenomenon with the introduction of damping resistance, so as to achieve stable voltage output control of the DC microgrid; wherein the stability constraints are obtained by derivation of the characteristic equation of the constant power load cascade system.

[0028] The third aspect of the present invention proposes an electronic device, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are configured to execute the above-mentioned DC microgrid voltage control method based on virtual damping self-regulation.

[0029] A fourth aspect of the present invention proposes a computer-readable storage medium, characterized in that the computer-readable storage medium stores computer instructions, and the computer instructions are used to enable the computer to execute the above-mentioned DC microgrid voltage control method based on virtual damping self-regulation.

[0030] The present invention provides a DC microgrid voltage control device based on virtual damping self-regulation, which mainly includes the following components:

[0031] 1. Controller: responsible for calculating the control algorithm, achieving stable voltage control, and outputting control instructions. Through real-time monitoring and feedback adjustment of the voltage error, the control algorithm can adjust the control signal of the damping resistor according to the change in the error to achieve the goal of stabilizing the voltage. The controller can use an embedded system, a microcontroller or a digital signal processor. The main control CPU of the device is a domestic industrial-grade chip, with a CPU main frequency of not less than 1GHz, a memory of not less than 1Gbyte, and a data storage device of not less than 4Gbyte.

[0032] 2. Sensor: used to collect data of voltage, current and other parameters in real time and transmit it to the controller

[0033] 3. Damping resistor: The control device controls the connection or disconnection of the damping resistor and the size of the damping resistor, thereby adjusting the voltage stability.

[0034] 4. Power supply and power management module: used to power the device. The main power supply adopts AC 220V, and the backup power supply adopts super capacitor. The backup power supply charging time does not exceed 1 hour. When the main power supply of the device is insufficient or disappears, the backup power supply will automatically and seamlessly start and maintain the normal operation of the device and functional modules for no less than 3 minutes. When the backup power supply is working, the main power supply is restored and the device works normally.

[0035] 5. Communication module: used to communicate with other devices, such as data exchange and coordination with other microgrid nodes. The device has 2 RJ-45 Ethernet communication interfaces for local communication and remote maintenance.

[0036] 6. Protection device: responsible for real-time monitoring of the system's working status and taking corresponding protection measures under abnormal circumstances to ensure the safe operation of the system.

[0037] The present invention provides a DC microgrid voltage control device based on virtual damping self-regulation, which adopts an embedded operating system, is compatible with various APPs and hardware access, and the system occupies 800M storage space. It has the functions of process management, memory management, file system, network management, log management, etc.

[0038] Compared with the prior art, the present invention has the following beneficial effects: the present invention derives the stability constraint conditions of the system based on the simplified model of the cascade system, and then analyzes the stability of the cascade system to obtain the cause of the resonance phenomenon. When the filter capacitance of the LC input filter is small, the cascade system will resonate. In order to suppress the occurrence of the resonance phenomenon, a passive damping control strategy of the damping resistor method is obtained, thereby stabilizing the output control of the DC microgrid voltage and meeting the voltage stability control requirements of the DC microgrid. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0040] Figure 1 A schematic diagram of a simplified model of a medium constant power load cascade system of a DC microgrid voltage control method based on virtual damping self-regulation proposed by the present invention;

[0041] Figure 2 A schematic flow chart of a DC microgrid voltage control method based on virtual damping self-regulation proposed in the present invention. DETAILED DESCRIPTION

[0042] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0043] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0044] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0045] Reference Figure 1-Figure 2 , as an embodiment of the present invention, provides a DC microgrid voltage control method based on virtual damping self-regulation, the method comprising the following steps:

[0046] Step 1: Under the condition that the buck converter is in the voltage conversion control mode, assuming that the input power at the steady-state operating point is constant, a simplified model of the constant power load cascade system is obtained based on the damping resistor method, where the damping resistor method is the equivalent introduction of virtual resistor damping;

[0047] Step 2: Define the expression parameters of the model according to the model. The expression parameters include: R d is the damping resistor, i g is the DC bus input circuit, i d is the passive damping current, i C is the capacitor current of the LC filter, i in Input the steady-state value of the current to the buck converter and obtain the mathematical relationship between various expression parameters;

[0048] i g =i C +i in +i d ;

[0049] Step 3: According to the mathematical relationship between the expression parameters, after adding the damping resistor in the constant power cascade system, the characteristic equation of the cascade system is obtained as follows:

[0050] Among them, L f is the LC input filter inductor, R f is the parasitic resistance of the LC input filter, C f is the LC input filter capacitor, V in is the steady-state value of the input voltage of the buck converter, P L is the load power.

[0051] Among them, according to the simplified model of the constant power load cascade system, the input current of the buck converter is obtained as:

[0052] in, is the small signal AC component of the input voltage, and according to this formula, the small signal AC component of the input current is obtained by replacing the curve near the equilibrium point with the tangent line:

[0053] When the input voltage changes, the input current changes in the opposite direction, which will affect the stability between the LC input filter and the buck converter and cause resonance.

[0054] Step 4: According to the characteristic equation, the stability constraint of the system is derived as follows:

[0055]

[0056] The stability analysis of the cascade system is carried out through constraint conditions, and it is determined that the introduction of damping resistors in the cascade system suppresses the occurrence of resonance, thereby stabilizing the output control of the DC microgrid voltage. The analysis is a common Matlab / Simulink simulation method based on constraint conditions.

[0057] In summary, the optimal value range of the virtual resistance damping is determined, that is, the relevant program is written through the m file in MALAB, the set expression parameters are brought into the program, and the value range of the virtual resistance damping is obtained, so as to determine the critical value of the virtual resistance damping when the system is stable, so as to facilitate the prevention of disturbances and calm the resonant oscillation.

[0058] The present invention derives the stability constraint conditions of the system according to the simplified model of the cascade system, and then analyzes the stability of the cascade system to obtain the cause of the resonance phenomenon. When the filter capacitance of the LC input filter is small, the cascade system will resonate. In order to suppress the occurrence of the resonance phenomenon, a passive damping control strategy of the damping resistor method is obtained to meet the voltage stability control requirements of the DC microgrid.

[0059] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A DC microgrid voltage control method based on virtual damping self-regulation, characterized in that: The following steps are involved: Step 1: Under the condition that the buck converter is in the voltage conversion control mode and the input power at the steady-state operating point is constant, a simplified model of the constant power load cascade system is obtained based on the damping resistor method; Step 2: Define the expression parameters of the model according to the simplified model of the constant power load cascade system, and obtain the mathematical relationship between the various expression parameters; Step 3: According to the mathematical relationship between various expression parameters, after adding the damping resistor to the simplified model of the constant power load cascade system, the characteristic equation of the constant power load cascade system is obtained; Step 4: According to the characteristic equation of the constant power load cascade system, the stability constraint conditions of the system are derived, and the stability analysis of the constant power load cascade system is performed through the stability constraint conditions. It is determined that the constant power load cascade system suppresses the occurrence of resonance phenomenon with the introduction of damping resistance, thereby stabilizing the output control of the DC microgrid voltage.

2. The method for controlling voltage of a DC microgrid based on virtual damping self-regulation according to claim 1 is characterized in that: The mathematical relationship between the various expression parameters in step 2 is: Among them, R d is the damping resistance, i g is the DC bus input circuit, i d is the passive damping current, i C is the capacitor current of the LC filter, i in Input current steady-state value for the buck converter.

3. The method for controlling voltage of a DC microgrid based on virtual damping self-regulation according to claim 2 is characterized in that: In step 3, the characteristic equation of the constant power load cascade system is: Among them, L f is the LC input filter inductor, R f is the parasitic resistance of the LC input filter, C f is the LC input filter capacitor, V in is the steady-state value of the input voltage of the buck converter, P L is the load power.

4. The method for controlling voltage of a DC microgrid based on virtual damping self-regulation according to claim 3 is characterized in that: In step 4, the stability constraint condition of the constant power load cascade system is:

5. The method for controlling voltage of a DC microgrid based on virtual damping self-regulation according to claim 4 is characterized in that: In step 2, based on the simplified model of the constant power load cascade system, the input current of the buck converter when the instantaneous power is constant is obtained, that is, the steady-state value of the buck converter input current is: in, is the small signal AC component of the input voltage, and according to this formula, the small signal AC component of the input current is obtained by replacing the curve near the equilibrium point with the tangent line: When the input voltage changes, the input current changes in the opposite direction, which will affect the stability between the LC input filter and the buck converter and cause resonance.

6. The method for controlling voltage of a DC microgrid based on virtual damping self-regulation according to claim 1 is characterized in that: The method of adding damping resistance in the simplified model of the constant power load cascade system in step three is the equivalent introduction of virtual resistance damping.

7. A DC microgrid voltage control method based on virtual damping self-regulation according to claim 6, characterized in that: Determine the optimal value range of the virtual resistance damping, that is, write the relevant program through the m file in MALAB, bring the set expression parameters into the program, and obtain the value range of the virtual resistance damping, so as to determine the critical value of the virtual resistance damping when the system is stable.

8. A DC microgrid voltage control device based on virtual damping self-regulation, characterized in that: include: A constant power load cascade system simplified model building module is used to obtain a simplified model of the constant power load cascade system based on the damping resistor method under the condition that the input power of the buck converter is constant in the voltage conversion control mode and the steady-state operating point; A mathematical relationship building module defines the expression parameters of the model according to the simplified model of the constant power load cascade system, and obtains the mathematical relationship between the various expression parameters; A constant power load cascade system characteristic equation determination module, used for adding a damping resistor to a simplified model of the constant power load cascade system, and obtaining the characteristic equation of the constant power load cascade system according to the mathematical relationship between the expression parameters; A constant power load cascade system stability analysis module is used to perform stability analysis of the constant power load cascade system through stability constraints, and determine that the constant power load cascade system suppresses the generation of resonance phenomenon with the introduction of damping resistance, so as to achieve stable voltage output control of the DC microgrid; wherein the stability constraints are obtained by derivation of the characteristic equation of the constant power load cascade system.

9. An electronic device, characterized in that: include: at least one processor; And, a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are configured to execute the method described in any one of claims 1 to 7 above.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable the computer to execute the method according to any one of claims 1 to 7.

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