A direct current micro-grid control method based on virtual-real combined direct current motor

Abstract

The application provides a DC micro-grid control method based on a virtual and real DC motor, which comprises the following steps: setting a virtual DC motor connected with a DC bus and a real DC motor connected with the DC bus; maintaining the stability of the low-frequency component of the DC bus voltage by using the real DC motor; and maintaining the stability of the high-frequency component of the DC bus voltage by using the virtual DC motor. The DC micro-grid control method can stabilize the DC bus voltage, improve the anti-disturbance capability of the DC micro-grid, and ensure the safe and stable operation of the DC micro-grid system.

Description

Technical Field

[0001] This invention belongs to the field of power equipment technology and relates to a DC microgrid control method based on a virtual-real combined DC motor. Background Technology

[0002] Microgrids are small-scale power systems composed of distributed power sources, energy storage, and loads. They can operate autonomously independently of the main power grid and are an important technology for building new power systems. Compared to AC microgrids, DC microgrids can more efficiently and reliably accommodate distributed renewable energy generation systems such as wind and solar power, energy storage units, electric vehicles, and other DC loads. They also do not have inherent problems such as power angle synchronization and reactive power coupling, and have broader application prospects compared to AC distribution networks.

[0003] In DC microgrids, power generation and energy storage devices are typically connected to the DC bus via power electronic equipment. Due to the rapid speed of this equipment, the DC bus changes drastically after being disturbed. To address this issue, the external characteristics of a DC motor can be simulated in the energy storage converter control, making its ports exhibit inertia and damping characteristics similar to a DC motor. This improves the disturbance rejection capability of the DC microgrid and, consequently, enhances the voltage stability of the microgrid's DC bus. This is the Virtual DC Motor (VDM) control method.

[0004] This virtual DC motor control method can provide the energy storage converter with a certain degree of inertia and damping support. However, the frequency response characteristics of the virtual control system are fixed, making it difficult to adapt to various sudden changes in the microgrid. It is also difficult to design a control strategy that balances stability and parameter change rate. Furthermore, the virtual DC motor control method needs to be combined with the energy storage unit's power allocation strategy, and the control effect depends on the effectiveness of the battery energy storage device. In summary, using a single virtual DC motor control method for DC microgrids is insufficient to achieve ideal results. A more effective control method is needed to improve the inertia and damping characteristics of the DC microgrid, thereby enhancing the stability of the bus voltage during operation. Summary of the Invention

[0005] The purpose of this invention is to at least solve one of the problems existing in the prior art.

[0006] Therefore, this invention provides a DC microgrid control method based on a virtual-real combined DC motor. The method uses a physical DC motor to maintain the stability of the low-frequency components of the DC bus voltage and a virtual DC motor to maintain the stability of the high-frequency components of the DC bus voltage. This method can stabilize the DC bus voltage, improve the anti-disturbance capability of the DC microgrid, and ensure the safe and stable operation of the DC microgrid system.

[0007] The technical solution of the present invention is as follows:

[0008] A control method for a DC microgrid based on a virtual-physical DC motor is provided. The control method involves setting up a virtual DC motor connected to the DC bus and a physical DC motor connected to the DC bus. The physical DC motor is used to maintain the stability of the low-frequency components of the DC bus voltage, while the virtual DC motor is used to maintain the stability of the high-frequency components of the DC bus voltage.

[0009] Furthermore, the control method is as follows:

[0010] During microgrid operation, the DC bus voltage is monitored in real time. A virtual-real scheduling algorithm is used to decompose the DC bus voltage fluctuations, extracting the high-frequency component ΔU1 and the low-frequency component ΔU2 of the DC bus voltage difference. The virtual inertia coefficient Cvir and the virtual damping coefficient D are then calculated. Based on the high-frequency component ΔU1, the virtual inertia coefficient Cvir, and the virtual damping coefficient D, a virtual DC motor is controlled to exhibit the characteristics of a DC motor, minimizing the high-frequency component ΔU1 of the DC bus voltage difference to achieve high-frequency voltage stability. Similarly, the physical DC motor is controlled based on the low-frequency component ΔU2 of the DC bus voltage difference to minimize the low-frequency component ΔU2, thus stabilizing the low-frequency voltage of the DC bus.

[0011] Furthermore, the electrical interfaces of both the virtual DC motor and the physical DC motor are connected to the DC bus. The other side of the virtual DC motor is connected to the battery energy storage device, while the physical DC motor is connected to the flywheel of the flywheel energy storage device through its output shaft. The battery energy storage device is used to provide energy storage and electrical energy exchange for the virtual DC motor during operation. The flywheel energy storage device is used to provide energy storage and electrical energy and kinetic energy exchange for the physical DC motor during operation.

[0012] Furthermore, the electrical connections between the virtual DC motor and the physical DC motor are as follows:

[0013] The virtual DC motor includes: capacitor C1, capacitor C2, inductor L1, and a single-phase bridge composed of switching transistors S1 and S2; the two ends of capacitor C2 are connected in parallel to the two ends of the DC bus; the series-connected switching transistors S1 and S2 are connected in parallel to the two ends of capacitor C2, wherein switching transistor S1 is connected to the positive line of the DC bus, and switching transistor S2 is connected to the negative line of the DC bus; the series-connected capacitor C1 and inductor L1 are connected in parallel to the two ends of switching transistor S2, wherein capacitor C1 is connected to the negative line of the DC bus; a battery energy storage device is connected in parallel to the two ends of capacitor C1;

[0014] The physical DC motor includes: capacitor C3, inductor L2, a single-phase bridge composed of switching transistors S3 and S4, and the DC motor body; the two ends of capacitor C3 are connected in parallel to the two ends of the DC bus, and the series-connected switching transistors S3 and S4 are connected in parallel to the two ends of capacitor C3, wherein switching transistor S3 is connected to the positive line of the DC bus, and switching transistor S4 is connected to the negative line of the DC bus; one end of inductor L2 is connected to the wire between switching transistors S3 and S4, and the other end of inductor L2 is connected to the input terminal of the electrical interface of the DC motor body, and the output terminal of the electrical interface of the DC motor body is connected to the negative line of the DC bus; the output shaft of the DC motor body is connected to the flywheel energy storage device.

[0015] Furthermore, the process of controlling the virtual DC motor and the physical DC motor in the control method is implemented through a control module;

[0016] The control module includes: a VDM controller, a DM controller, a scheduling controller, a voltage sampling module, a current sampling module one, a current sampling module two, a PWM modulation module one, a PWM modulation module two, and a speed sampling module;

[0017] The VDM controller is used to control the virtual DC motor, the DM controller is used to control the physical DC motor, and the scheduling controller has an embedded virtual-physical scheduling algorithm for scheduling and controlling the VDM controller and the DM controller.

[0018] The voltage sampling module is used to acquire the DC bus voltage signal Udc and transmits the DC bus voltage signal Udc as the input of the virtual-real scheduling algorithm to the scheduling controller. The scheduling controller uses the virtual-real scheduling algorithm to calculate and obtain the high-frequency component ΔU1 of the DC bus voltage difference, the low-frequency component ΔU2 of the DC bus voltage difference, the virtual inertia coefficient Cvir, and the virtual damping coefficient D. Then, the high-frequency component ΔU1 of the DC bus voltage difference, the virtual inertia coefficient Cvir, and the virtual damping coefficient D are transmitted as the input of the VDM controller to the VDM controller, and the low-frequency component ΔU2 of the DC bus voltage difference is transmitted as the input of the DM controller to the DM controller.

[0019] The current sampling module 1 is used to collect the current signal I1 of the virtual DC motor and transmit the current signal I1 to the VDM controller. The VDM controller calculates the control output Kout1 based on the received current signal I1, the high-frequency component ΔU1 of the DC bus voltage difference, the virtual inertia coefficient Cvir, and the virtual damping coefficient D through the control algorithm inside the VDM controller. The control output Kout1 is then transmitted to the PWM modulation module 1. The PWM modulation module 1 modulates the control output Kout1 to obtain two PWM signals, namely PWM1 and PWM2. PWM1 is used to drive the switching transistor S1 in the virtual DC motor to turn on and off, and PWM2 is used to drive the switching transistor S2 in the virtual DC motor to turn on and off, so that the virtual DC motor exhibits the characteristics of a DC motor and suppresses the high-frequency component ΔU1 of the DC bus voltage difference to the minimum.

[0020] The second current sampling module is used to acquire the current signal I2 of the physical DC motor and transmit it to the DM controller. The speed sampling module is used to acquire the speed signal ω of the output shaft of the physical DC motor and transmit it to the DM controller. The DM controller calculates the control output Kout2 based on the received current signal I2, speed signal ω, and low-frequency component ΔU2 of the DC bus voltage difference through its internal control algorithm. Then, it transmits the control output Kout2 to the second PWM modulation module. The second PWM modulation module modulates the control output Kout2 to obtain two PWM signals, namely PWM3 and PWM4. PWM3 is used to drive the switching transistor S3 in the physical DC motor to turn on and off, and PWM4 is used to drive the switching transistor S4 in the physical DC motor to turn on and off, thus suppressing the low-frequency component ΔU2 of the DC bus voltage difference to the minimum.

[0021] Furthermore, the process by which the dispatch controller uses its internal virtual-real scheduling algorithm to control the virtual DC motor and the physical DC motor is as follows:

[0022] In this virtual-real scheduling algorithm, three reference values ​​are pre-set: the DC bus voltage reference value Uref, the virtual inertia coefficient reference value Cvir_ref, and the virtual damping coefficient reference value Dref. The algorithm first subtracts the DC bus voltage reference value Uref from the DC bus voltage signal Udc to obtain the DC bus voltage difference ΔU. This ΔU is then passed through a low-pass filter to obtain the low-frequency component ΔU2 of the DC bus voltage difference. Subtracting ΔU from ΔU2 yields the high-frequency component ΔU1 of the DC bus voltage difference. After ΔU2 passes through PI regulator one, the regulator output PIout1 is obtained. The virtual inertia coefficient reference value Cvir_ref is then subtracted from PIout1 to obtain the virtual inertia coefficient Cvir. After ΔU2 passes through PI regulator two, the regulator output PIout2 is obtained. The virtual damping coefficient reference value Dref is then subtracted from PIout2 to obtain the virtual damping coefficient D. Finally, the virtual-real scheduling algorithm calculates the high-frequency component ΔU1 of the DC bus voltage difference, the low-frequency component ΔU2 of the DC bus voltage difference, the virtual inertia coefficient Cvir, and the virtual damping coefficient D.

[0023] Furthermore, the process by which the DM controller controls the physical DC motor using its internal control algorithm is as follows: The DM controller inputs the low-frequency component ΔU2 of the DC bus voltage difference calculated by the virtual-real scheduling algorithm. After the PI regulator performs three operations, the regulator output PIout3 is obtained. PIout3 is then subtracted from the speed signal ω obtained by the speed sampling module to obtain the speed error Δω. The speed error Δω is then processed by the PI regulator performs four operations to obtain the regulator output PIout4. PIout4 is then subtracted from the current signal I2 obtained by the current sampling module performs two operations to obtain the current error ΔI2. The current error ΔI2 is then processed by the PI regulator performs five operations to obtain the regulator output Kout2. The regulator output Kout2 is then processed by the PWM modulation module. After modulation, two PWM signals are obtained, namely PWM3 and PWM4. PWM3 is used to drive the switching transistor S3 inside the physical DC motor to turn on and off, and PWM4 is used to drive the switching transistor S4 inside the physical DC motor to turn on and off. When the low-frequency component ΔU2 of the DC bus voltage difference shows an increasing trend, the DM controller controls the switching transistors S3 and S4 to increase the speed of the output shaft of the DC motor body, thereby increasing the speed of the flywheel energy storage device, so as to convert the remaining electrical energy of the DC bus into kinetic energy and store it in the flywheel. When the low-frequency component ΔU2 of the DC bus voltage difference shows a decreasing trend, the DM controller controls the switching transistors S3 and S4 to decrease the speed of the output shaft, thereby decreasing the speed of the flywheel, so as to convert the kinetic energy stored in the flywheel into electrical energy and feed it back to the DC bus.

[0024] Furthermore, the process of the VDM controller controlling the virtual DC motor using its internal control algorithm is as follows: The input of the outermost loop of the VDM controller comes from the high-frequency component ΔU1 of the DC bus voltage difference calculated by the virtual-real scheduling algorithm. After the PI regulator performs the operation, the regulator output PIout6 is obtained. The difference between PIout6 and the current signal I1 obtained by the current sampling module is calculated to obtain the current error ΔI1. The current error ΔI1 is subtracted from the output Mpy1 of the multiplier to obtain the virtual torque error ΔT. Among them, the multiplication coefficient of the multiplier is the virtual damping coefficient D, and the output Mpy1 of the multiplier is obtained by multiplying the virtual voltage Uvir by the virtual damping coefficient D.

[0025] When the virtual torque error ΔT passes through multiplier two, it is multiplied by the multiplication coefficient of multiplier two. Then, the output Mpy2 of multiplier two is obtained; after the multiplier two output Mpy2 is integrated, the virtual electromotive force error ΔE is obtained; the virtual electromotive force error ΔE is added to the reference value Uref of the DC bus voltage to obtain the virtual voltage Uvir; the virtual voltage Uvir is divided into two paths, one path is multiplied with the multiplication coefficient D of multiplier one to output Mpy1; the other path is used as the input of PI regulator seven, and after calculation, the regulator output Kout1 is obtained; the regulator output Kout1 is modulated by PWM modulation module one to obtain two PWM signals, namely PWM1 and PWM2. PWM1 is used to drive the switching transistor S1 in the virtual DC motor to turn on and off, and PWM2 is used to drive the switching transistor S2 in the virtual DC motor to turn on and off; when the DC bus voltage is subjected to high-frequency disturbance, the virtual inertia coefficient Cvir and virtual damping coefficient D of the virtual DC microgrid are input to the VDM controller, and then the VDM controller controls the switching transistors S1 and S2 to control the virtual DC motor.

[0026] By applying the above technical solution, the present invention has the following beneficial effects:

[0027] (1) Compared with the traditional virtual DC motor DC microgrid control method, this invention adopts a combination of physical DC motor and virtual DC motor. That is, a physical DC motor is introduced into the microgrid, and the output shaft of the physical DC motor is connected to a flywheel energy storage device. On the one hand, the energy storage characteristics of the flywheel energy storage device are used to realize the energy peak shaving and valley filling function in the microgrid; on the other hand, the inherent inertia and damping characteristics of the motor rotor and flywheel rotor can effectively improve the stability of the DC bus voltage, thereby enhancing the safety and stability of the microgrid. Therefore, this invention overcomes the shortcomings of using only a virtual DC motor control method, such as fixed frequency response characteristics and difficulty in balancing stability and parameter change rate; in addition, by adding a flywheel energy storage device, the shortcomings of traditional control effects relying solely on battery energy storage devices are solved.

[0028] (2) During the operation of the microgrid, the present invention monitors the DC bus voltage in real time, decomposes the fluctuation of the DC bus voltage using the "virtual-real scheduling algorithm", extracts the high-frequency component and the low-frequency component, and outputs the two parameters required in the virtual DC motor control algorithm through two PI regulators based on the voltage fluctuation: virtual inertia coefficient Cvir and virtual damping coefficient D; thereby realizing the generation of parameters for the control of the physical DC motor and the virtual DC motor using the virtual-real scheduling algorithm. This control method uses two independent control algorithms to control the high-frequency and low-frequency disturbances of the bus respectively. The algorithm is simple and the effect is direct.

[0029] (3) When the bus voltage fluctuation of the present invention contains low-frequency components, the physical DC motor relies on the inertia and damping characteristics of its own rotor (output shaft) and the connected flywheel, and suppresses the low-frequency components in the bus voltage fluctuation through the control of the DM controller; when the bus voltage fluctuation contains high-frequency components, the virtual DC motor uses the armature circuit equation to adjust the virtual electromotive force and reference current, uses the integral link to simulate the inertia characteristics, and uses the proportional feedback link to simulate the damping characteristics, providing an energy buffer for the DC bus voltage, thereby improving the DC bus's resistance to high-frequency disturbances; therefore, the present invention uses a physical DC motor to eliminate low-frequency fluctuations in the bus voltage and a virtual DC motor to eliminate high-frequency fluctuations in the bus voltage, which can effectively improve the stability of the DC bus voltage across the entire frequency band. Attached Figure Description

[0030] The accompanying drawings, which form part of this specification, are provided to further illustrate embodiments of the invention and, together with the textual description, explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0031] Figure 1 This is a diagram of the overall topology of a DC microgrid;

[0032] Figure 2 It is a block diagram of a DC motor that combines virtual and real principles;

[0033] Figure 3 This is a block diagram illustrating the principle of the virtual-real scheduling algorithm;

[0034] Figure 4 This is a block diagram of the DM controller.

[0035] Figure 5 This is a block diagram of the VDM controller. Detailed Implementation

[0036] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0038] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0039] Example 1:

[0040] This embodiment provides a DC microgrid control method based on a virtual-physical hybrid DC motor. The method involves setting up a virtual DC motor (VDM) connected to the DC bus and a physical DC motor (DM) connected to the DC bus. The physical DC motor is used to maintain the stability of the low-frequency components of the DC bus voltage, while the virtual DC motor is used to maintain the stability of the high-frequency components of the DC bus voltage. Specifically:

[0041] During microgrid operation, the DC bus voltage is monitored in real time. A virtual-real scheduling algorithm is used to decompose the DC bus voltage fluctuations, extracting the high-frequency component ΔU1 and the low-frequency component ΔU2 of the DC bus voltage difference. The virtual inertia coefficient Cvir and the virtual damping coefficient D are then calculated. Based on the high-frequency component ΔU1, the virtual inertia coefficient Cvir, and the virtual damping coefficient D, a virtual DC motor is controlled to exhibit the characteristics of a DC motor, minimizing the high-frequency component ΔU1 of the DC bus voltage difference to achieve high-frequency voltage stability. Similarly, the physical DC motor is controlled based on the low-frequency component ΔU2 of the DC bus voltage difference to minimize the low-frequency component ΔU2, thus stabilizing the low-frequency voltage of the DC bus.

[0042] Example 2:

[0043] This embodiment provides a DC microgrid control method based on a virtual-real hybrid DC motor, building upon Embodiment 1.

[0044] See appendix Figure 1 The overall topology of the microgrid includes: a DC bus, photovoltaic panels, DC / DC converter 1 (i.e., DC / DC 1), DC / DC converter 2 (i.e., DC / DC 2), DC loads, wind turbines, AC / DC converters (i.e., AC / DC), DC / AC converters (i.e., DC / AC), AC loads, and virtual-physical DC motor components.

[0045] The DC bus is the center of the overall topology. The DC power generated by the photovoltaic panels is converted into stable DC power by DC / DC converter 1 and connected to the DC bus. The AC power generated by the wind turbine is converted into stable DC power by AC / DC converter and connected to the DC bus. DC / DC converter 2 converts the DC power from the DC bus into voltage and supplies it to DC loads. The DC / AC converter converts the DC power from the DC bus into AC power and supplies it to AC loads.

[0046] See appendix Figure 2 The virtual-physical hybrid DC motor assembly includes: a virtual DC motor (VDM), a physical DC motor (DM), a battery energy storage device, a flywheel energy storage device, and a control module;

[0047] The electrical interfaces of both the virtual DC motor and the physical DC motor are connected to the DC bus. The other side of the virtual DC motor is connected to the battery energy storage device, while the physical DC motor is connected to the flywheel of the flywheel energy storage device through a mechanical interface, i.e., the output shaft. The battery energy storage device is used to provide energy storage and electrical energy exchange for the virtual DC motor during operation; the flywheel energy storage device is used to provide energy storage and exchange of electrical and kinetic energy for the physical DC motor during operation.

[0048] The positive wires of both the virtual and physical DC motors are connected to the positive wires of the DC bus, and the negative wires are connected to the negative wires of the DC bus. The specific electrical connections are as follows:

[0049] The virtual DC motor includes: capacitor C1, capacitor C2, inductor L1, and a single-phase bridge composed of switching transistors S1 and S2; the two ends of capacitor C2 are connected in parallel to the two ends of the DC bus (i.e., one end of capacitor C2 is connected to the positive line of the DC bus, and the other end of capacitor C2 is connected to the negative line of the DC bus); the series-connected switching transistors S1 and S2 are connected in parallel to the two ends of capacitor C2, wherein switching transistor S1 is connected to the positive line of the DC bus, and switching transistor S2 is connected to the negative line of the DC bus; the series-connected capacitor C1 and inductor L1 are connected in parallel to the two ends of switching transistor S2, wherein capacitor C1 is connected to the negative line of the DC bus; the battery energy storage device is connected in parallel to the two ends of capacitor C1;

[0050] The physical DC motor includes: capacitor C3, inductor L2, a single-phase bridge composed of switching transistors S3 and S4, and the DC motor body; the two ends of capacitor C3 are connected in parallel to the two ends of the DC bus (i.e., one end of capacitor C3 is connected to the positive line of the DC bus, and the other end of capacitor C3 is connected to the negative line of the DC bus), and the series-connected switching transistors S3 and S4 are connected in parallel to the two ends of capacitor C3, wherein switching transistor S3 is connected to the positive line of the DC bus, and switching transistor S4 is connected to the negative line of the DC bus; one end of inductor L2 is connected to the wire between switching transistors S3 and S4, and the other end of inductor L2 is connected to the input terminal of the electrical interface of the DC motor body, and the output terminal of the electrical interface of the DC motor body is connected to the negative line of the DC bus; the output shaft of the DC motor body is connected to a flywheel energy storage device;

[0051] The control module includes: a VDM controller, a DM controller, a scheduling controller, a voltage sampling module, a current sampling module one, a current sampling module two, a PWM modulation module one, a PWM modulation module two, and a speed sampling module;

[0052] The VDM controller is used to control the virtual DC motor, the DM controller is used to control the physical DC motor, and the scheduling controller has an embedded virtual-physical scheduling algorithm for scheduling and controlling the VDM controller and the DM controller.

[0053] The voltage sampling module is used to acquire the DC bus voltage signal Udc and transmits the DC bus voltage signal Udc as the input of the virtual-real scheduling algorithm to the scheduling controller. The scheduling controller uses the virtual-real scheduling algorithm to calculate and obtain the high-frequency component ΔU1 of the DC bus voltage difference, the low-frequency component ΔU2 of the DC bus voltage difference, the virtual inertia coefficient Cvir, and the virtual damping coefficient D. Then, the high-frequency component ΔU1 of the DC bus voltage difference, the virtual inertia coefficient Cvir, and the virtual damping coefficient D are transmitted as the input of the VDM controller to the VDM controller, and the low-frequency component ΔU2 of the DC bus voltage difference is transmitted as the input of the DM controller to the DM controller.

[0054] The current sampling module 1 is used to acquire the current signal I1 of the virtual DC motor and transmit the current signal I1 to the VDM controller. The VDM controller calculates the control output Kout1 based on the received current signal I1, the high-frequency component ΔU1 of the DC bus voltage difference, the virtual inertia coefficient Cvir, and the virtual damping coefficient D through its internal control algorithm. Then, the control output Kout1 is transmitted to the PWM modulation module 1. The PWM modulation module 1 modulates the control output Kout1 to obtain two PWM signals, namely PWM1 and PWM2. PWM1 is used to drive the switching transistor S1 in the virtual DC motor to turn on and off, and PWM2 is used to drive the switching transistor S2 in the virtual DC motor to turn on and off, so that the virtual DC motor exhibits the characteristics of a DC motor and suppresses the high-frequency component of the DC bus error, namely the high-frequency component ΔU1 of the DC bus voltage difference, to the minimum, so as to achieve the stability of the high-frequency voltage of the DC bus.

[0055] The current sampling module 2 is used to acquire the current signal I2 of the physical DC motor and transmit it to the DM controller. The speed sampling module is used to acquire the speed signal ω of the output shaft of the physical DC motor and transmit it to the DM controller. The DM controller calculates the control output Kout2 based on the received current signal I2, speed signal ω, and low-frequency component ΔU2 of the DC bus voltage difference through its internal control algorithm. Then, it transmits the control output Kout2 to the PWM modulation module 2. The PWM modulation module 2 modulates the control output Kout2 to obtain two PWM signals, namely PWM3 and PWM4. PWM3 is used to drive the switching transistor S3 in the physical DC motor to turn on and off, and PWM4 is used to drive the switching transistor S4 in the physical DC motor to turn on and off, so as to suppress the low-frequency component of the DC bus error, that is, the low-frequency component ΔU2 of the DC bus voltage difference, to the minimum, so as to achieve the stability of the low-frequency voltage of the DC bus.

[0056] In a preferred embodiment, see Appendix Figure 3The process by which the dispatch controller controls the virtual and physical DC motors using its internal virtual-real scheduling algorithm is as follows: Three reference values ​​are pre-set in the algorithm: the DC bus voltage reference value Uref, the virtual inertia coefficient reference value Cvir_ref, and the virtual damping coefficient reference value Dref. The algorithm first subtracts the DC bus voltage reference value Uref from the DC bus voltage signal Udc to obtain the DC bus voltage difference ΔU. This DC bus voltage difference ΔU is then passed through a low-pass filter to obtain the low-frequency component ΔU2 of the DC bus voltage difference. Subtracting ΔU2 from ΔU2 yields the high-frequency component ΔU1 of the DC bus voltage difference. ΔU2 passes through PI regulator one (i.e., PI 1) to obtain the regulator output PIout1. Subtracting PIout1 from the virtual inertia coefficient reference value Cvir_ref yields the virtual inertia coefficient Cvir. ΔU2 then passes through PI regulator two (i.e., PI 1...) 2) After that, the regulator output PIout2 is obtained. Then, the virtual damping coefficient reference value Dref is used to calculate the difference between PIout2 and the virtual inertia reference value Dref to obtain the virtual damping coefficient D. Finally, after the virtual and real scheduling algorithm is calculated, the high-frequency component ΔU1 of the DC bus voltage difference, the low-frequency component ΔU2 of the DC bus voltage difference, the virtual inertia coefficient Cvir, and the virtual damping coefficient D are obtained.

[0057] In a preferred embodiment, see Appendix Figure 4The purpose of the DM controller is to achieve the control objective of bringing the low-frequency component ΔU2 of the DC bus voltage difference close to zero through three closed-loop control (i.e., voltage loop, speed loop, and current loop). Therefore, the process of the DM controller controlling the physical DC motor using its internal control algorithm is as follows: The input of the outermost loop of the DM controller comes from the low-frequency component ΔU2 of the DC bus voltage difference calculated by the virtual-real scheduling algorithm. This low-frequency component ΔU2 of the DC bus voltage difference is processed by PI regulator three (i.e., PI 3) to obtain the regulator output PIout3. PIout3 is then subtracted from the speed signal ω obtained by the speed sampling module to obtain the speed error Δω. The speed error Δω is processed by PI regulator four (i.e., PI 4) to obtain the regulator output PIout4. PIout4 is then subtracted from the current signal I2 sampled by current sampling module two to obtain the current error ΔI2. The current error ΔI2 is then processed by PI regulator five (i.e., PI 4) to obtain the current error ΔI2. 5) After the calculation, the regulator output Kout2 is obtained. This output Kout2 is modulated by the PWM modulation module to obtain two PWM signals, PWM3 and PWM4. PWM3 is used to drive the switching transistor S3 inside the physical DC motor, and PWM4 is used to drive the switching transistor S4 inside the physical DC motor. When the low-frequency component ΔU2 of the DC bus voltage difference shows an increasing trend, the DM controller controls the switching of transistors S3 and S4 to increase the speed of the output shaft of the DC motor, thereby increasing the flywheel speed of the flywheel energy storage device to dissipate the remaining DC bus voltage. Electrical energy is converted into kinetic energy and stored in the flywheel. When the low-frequency component ΔU2 of the DC bus voltage difference shows a decreasing trend, the DM controller controls the switching of switching transistors S3 and S4 to reduce the output shaft speed, thereby reducing the flywheel speed. This allows the kinetic energy stored in the flywheel to be converted into electrical energy and fed back to the DC bus. Through the above control, the low-frequency component in the fluctuation of the bus voltage is suppressed by the DM controller, utilizing the inertia and damping characteristics of the physical DC motor relying on its own rotor (i.e., output shaft) and the flywheel energy storage device connected to it. This achieves the purpose of stabilizing the low-frequency component in the DC bus voltage.

[0058] In a preferred embodiment, see Appendix Figure 5The purpose of the VDM controller is to achieve the control objective of bringing the high-frequency component ΔU1 of the DC bus voltage difference close to 0 through dual closed-loop control (i.e., voltage loop and current loop). Therefore, the process of the VDM controller controlling the virtual DC motor using its internal control algorithm is as follows: The input of the outermost loop of the VDM controller comes from the high-frequency component ΔU1 of the DC bus voltage difference calculated by the virtual-real scheduling algorithm. After the high-frequency component ΔU1 of the DC bus voltage difference is processed by PI regulator six (i.e., PI 6), the regulator output PIout6 is obtained. Then, the difference is calculated with the current signal I1 obtained by current sampling module one to obtain the current error ΔI1. The current error ΔI1 is subtracted from the output Mpy1 of multiplier one to obtain the virtual torque error ΔT. Among them, the multiplication coefficient of multiplier one is the virtual damping coefficient D, and the output Mpy1 of multiplier one is obtained by multiplying the virtual voltage Uvir by the virtual damping coefficient D.

[0059] When the virtual torque error ΔT passes through multiplier two, it is multiplied by the multiplication coefficient of multiplier two. After (Cvir is the virtual inertia coefficient), the output Mpy2 of multiplier two is obtained; after the output Mpy2 of multiplier two is integrated by the "∫" element, the virtual electromotive force error ΔE is obtained; the virtual electromotive force error ΔE is added to the reference value Uref of the DC bus voltage to obtain the virtual voltage Uvir; this virtual voltage Uvir is divided into two paths, one of which is multiplied by the multiplication coefficient D of multiplier one to output Mpy1; the other path is used as the input of PI regulator seven (i.e., PI 7), and after calculation, the regulator output Kout1 is obtained; the regulator output Kout1 is modulated by PWM modulation module one to obtain two PWM signals, namely PWM1 and PWM2. PWM1 is used to drive the switching transistor S1 in the virtual DC motor to turn on and off, and PWM2 is used to drive the switching transistor S2 in the virtual DC motor to turn on and off; wherein, the high-frequency component ΔU1 of the DC bus voltage difference, the virtual damping coefficient D in multiplier one, and the virtual inertia coefficient Cvir in multiplier two are all output by the virtual-real scheduling algorithm; when the DC bus voltage is subjected to high-frequency disturbance, through the virtual The virtual inertia coefficient Cvir and virtual damping coefficient D of the DC microgrid are input into the VDM controller. The VDM controller then controls the on / off state of switches S1 and S2 to control the virtual DC motor, enabling the DC bus voltage to suppress voltage surges and dampen voltage oscillations. Specifically, the virtual DC motor uses the armature circuit equation to adjust the virtual electromotive force and reference current. The essence of its control is to use the integral link to simulate inertia characteristics and the proportional feedback link to simulate damping characteristics, providing an energy buffer for the DC bus voltage, thereby improving the DC bus's resistance to high-frequency disturbances.

[0060] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0061] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0062] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A DC microgrid control method based on a virtual-real hybrid DC motor, characterized in that, The control method is as follows: set up a virtual DC motor connected to the DC bus and a physical DC motor connected to the DC bus. Use the physical DC motor to maintain the stability of the low-frequency components of the DC bus voltage and use the virtual DC motor to maintain the stability of the high-frequency components of the DC bus voltage. The control method is as follows: During microgrid operation, the DC bus voltage is monitored in real time. A virtual-real scheduling algorithm is used to decompose the DC bus voltage fluctuations, extracting the high-frequency component ΔU1 and the low-frequency component ΔU2 of the DC bus voltage difference. The virtual inertia coefficient Cvir and the virtual damping coefficient D are then calculated. Based on the high-frequency component ΔU1, the virtual inertia coefficient Cvir, and the virtual damping coefficient D, a virtual DC motor is controlled to exhibit the characteristics of a DC motor, minimizing the high-frequency component ΔU1 of the DC bus voltage difference to achieve stability of the high-frequency DC bus voltage. Similarly, the physical DC motor is controlled based on the low-frequency component ΔU2 of the DC bus voltage difference to minimize the low-frequency DC bus voltage, thus stabilizing the low-frequency DC bus voltage. The process of controlling the virtual DC motor and the physical DC motor in the control method is implemented through a control module; The control module includes: a VDM controller, a DM controller, a scheduling controller, a voltage sampling module, a current sampling module one, a current sampling module two, a PWM modulation module one, a PWM modulation module two, and a speed sampling module; The VDM controller is used to control the virtual DC motor, the DM controller is used to control the physical DC motor, and the scheduling controller has an embedded virtual-physical scheduling algorithm for scheduling and controlling the VDM controller and the DM controller. The voltage sampling module is used to acquire the DC bus voltage signal Udc and transmits the DC bus voltage signal Udc as the input of the virtual-real scheduling algorithm to the scheduling controller. The scheduling controller uses the virtual-real scheduling algorithm to calculate and obtain the high-frequency component ΔU1 of the DC bus voltage difference, the low-frequency component ΔU2 of the DC bus voltage difference, the virtual inertia coefficient Cvir, and the virtual damping coefficient D. Then, the high-frequency component ΔU1 of the DC bus voltage difference, the virtual inertia coefficient Cvir, and the virtual damping coefficient D are transmitted as the input of the VDM controller to the VDM controller, and the low-frequency component ΔU2 of the DC bus voltage difference is transmitted as the input of the DM controller to the DM controller. The current sampling module 1 is used to collect the current signal I1 of the virtual DC motor and transmit the current signal I1 to the VDM controller. The VDM controller calculates the control output Kout1 based on the received current signal I1, the high-frequency component ΔU1 of the DC bus voltage difference, the virtual inertia coefficient Cvir, and the virtual damping coefficient D through the control algorithm inside the VDM controller. The control output Kout1 is then transmitted to the PWM modulation module 1. The PWM modulation module 1 modulates the control output Kout1 to obtain two PWM signals, namely PWM1 and PWM2. PWM1 is used to drive the switching transistor S1 in the virtual DC motor to turn on and off, and PWM2 is used to drive the switching transistor S2 in the virtual DC motor to turn on and off, so that the virtual DC motor exhibits the characteristics of a DC motor and suppresses the high-frequency component ΔU1 of the DC bus voltage difference to the minimum. The second current sampling module is used to acquire the current signal I2 of the physical DC motor and transmit it to the DM controller. The speed sampling module is used to acquire the speed signal ω of the output shaft of the physical DC motor and transmit it to the DM controller. The DM controller calculates the control output Kout2 based on the received current signal I2, speed signal ω, and low-frequency component ΔU2 of the DC bus voltage difference through its internal control algorithm. Then, it transmits the control output Kout2 to the second PWM modulation module. The second PWM modulation module modulates the control output Kout2 to obtain two PWM signals, namely PWM3 and PWM4. PWM3 is used to drive the switching transistor S3 in the physical DC motor to turn on and off, and PWM4 is used to drive the switching transistor S4 in the physical DC motor to turn on and off, thus suppressing the low-frequency component ΔU2 of the DC bus voltage difference to the minimum.

2. The DC microgrid control method based on a virtual-real combined DC motor as described in claim 1, characterized in that, The electrical interfaces of both the virtual DC motor and the physical DC motor are connected to the DC bus. The other side of the virtual DC motor is connected to the battery energy storage device, while the physical DC motor is connected to the flywheel of the flywheel energy storage device through its output shaft. The battery energy storage device is used to provide energy storage and electrical energy exchange for the virtual DC motor during operation. The flywheel energy storage device is used to provide energy storage and electrical energy and kinetic energy exchange for the physical DC motor during operation.

3. The DC microgrid control method based on a virtual-real combined DC motor as described in claim 2, characterized in that, The electrical connections between the virtual DC motor and the physical DC motor are as follows: The virtual DC motor includes: capacitor C1, capacitor C2, inductor L1, and a single-phase bridge composed of switching transistors S1 and S2; the two ends of capacitor C2 are connected in parallel to the two ends of the DC bus; the series-connected switching transistors S1 and S2 are connected in parallel to the two ends of capacitor C2, wherein switching transistor S1 is connected to the positive line of the DC bus, and switching transistor S2 is connected to the negative line of the DC bus; the series-connected capacitor C1 and inductor L1 are connected in parallel to the two ends of switching transistor S2, wherein capacitor C1 is connected to the negative line of the DC bus; a battery energy storage device is connected in parallel to the two ends of capacitor C1; The physical DC motor includes: capacitor C3, inductor L2, a single-phase bridge composed of switching transistors S3 and S4, and the DC motor body; the two ends of capacitor C3 are connected in parallel to the two ends of the DC bus, and the series-connected switching transistors S3 and S4 are connected in parallel to the two ends of capacitor C3, wherein switching transistor S3 is connected to the positive line of the DC bus, and switching transistor S4 is connected to the negative line of the DC bus; one end of inductor L2 is connected to the wire between switching transistors S3 and S4, and the other end of inductor L2 is connected to the input terminal of the electrical interface of the DC motor body, and the output terminal of the electrical interface of the DC motor body is connected to the negative line of the DC bus; the output shaft of the DC motor body is connected to the flywheel energy storage device.

4. The DC microgrid control method based on a virtual-real combined DC motor as described in claim 3, characterized in that, The process by which the dispatch controller uses its internal virtual-real scheduling algorithm to control the virtual DC motor and the physical DC motor is as follows: In this virtual-real scheduling algorithm, three reference values ​​are pre-set: the DC bus voltage reference value Uref, the virtual inertia coefficient reference value Cvir_ref, and the virtual damping coefficient reference value Dref. The algorithm first subtracts the DC bus voltage reference value Uref from the DC bus voltage signal Udc to obtain the DC bus voltage difference ΔU. This ΔU is then passed through a low-pass filter to obtain the low-frequency component ΔU2 of the DC bus voltage difference. Finally, the difference between ΔU and ΔU2 is used to obtain the high-frequency component ΔU1 of the DC bus voltage difference. After ΔU2 passes through PI regulator one, the regulator output PIout1 is obtained. The virtual inertia coefficient reference value Cvir_ref is then subtracted from PIout1 to obtain the virtual inertia coefficient Cvir. After ΔU2 passes through PI regulator two, the regulator output PIout2 is obtained. The virtual damping coefficient reference value Dref is then subtracted from PIout2 to obtain the virtual damping coefficient D. Finally, the virtual-real scheduling algorithm calculates the high-frequency component ΔU1 of the DC bus voltage difference, the low-frequency component ΔU2 of the DC bus voltage difference, the virtual inertia coefficient Cvir, and the virtual damping coefficient D.

5. The DC microgrid control method based on a virtual-real combined DC motor as described in claim 3, characterized in that, The process by which the DM controller controls the physical DC motor using its internal control algorithm is as follows: The DM controller inputs the low-frequency component ΔU2 of the DC bus voltage difference calculated by the virtual-real scheduling algorithm. After the PI regulator performs three operations, the regulator output PIout3 is obtained. PIout3 is then subtracted from the speed signal ω obtained by the speed sampling module to obtain the speed error Δω. The speed error Δω is then processed by the PI regulator four operations to obtain the regulator output PIout4. PIout4 is then subtracted from the current signal I2 obtained by the current sampling module two operations to obtain the current error ΔI2. The current error ΔI2 is then processed by the PI regulator five operations to obtain the regulator output Kout2. The regulator output Kout2 is then processed by the PWM modulation module two operations. Two PWM signals are obtained after processing, namely PWM3 and PWM4. PWM3 is used to drive the switching transistor S3 inside the physical DC motor to turn on and off, and PWM4 is used to drive the switching transistor S4 inside the physical DC motor to turn on and off. When the low-frequency component ΔU2 of the DC bus voltage difference shows an increasing trend, the DM controller controls the switching transistors S3 and S4 to increase the speed of the output shaft of the DC motor body, thereby increasing the speed of the flywheel energy storage device, so as to convert the remaining electrical energy of the DC bus into kinetic energy and store it in the flywheel. When the low-frequency component ΔU2 of the DC bus voltage difference shows a decreasing trend, the DM controller controls the switching transistors S3 and S4 to decrease the speed of the output shaft, thereby decreasing the speed of the flywheel, so as to convert the kinetic energy stored in the flywheel into electrical energy and feed it back to the DC bus.

6. The DC microgrid control method based on a virtual-real combined DC motor as described in claim 3, characterized in that, The process by which the VDM controller controls the virtual DC motor using its internal control algorithm is as follows: The input of the outermost loop of the VDM controller comes from the high-frequency component ΔU1 of the DC bus voltage difference calculated by the virtual-real scheduling algorithm. This high-frequency component ΔU1 of the DC bus voltage difference is processed by the PI regulator to obtain the regulator output PIout6, which is then subtracted from the current signal I1 obtained by the current sampling module to obtain the current error ΔI1. The current error ΔI1 is subtracted from the output Mpy1 of the multiplier to obtain the virtual torque error ΔT. Here, the multiplication coefficient of the multiplier is the virtual damping coefficient D, and the output Mpy1 of the multiplier is obtained by multiplying the virtual voltage Uvir by the virtual damping coefficient D. When the virtual torque error ΔT passes through multiplier two, it is multiplied by the multiplication coefficient of multiplier two. Then, the output Mpy2 of multiplier two is obtained; after the multiplier two output Mpy2 is integrated, the virtual electromotive force error ΔE is obtained; the virtual electromotive force error ΔE is added to the reference value Uref of the DC bus voltage to obtain the virtual voltage Uvir; the virtual voltage Uvir is divided into two paths, one path is multiplied with the multiplication coefficient D of multiplier one to output Mpy1; the other path is used as the input of PI regulator seven, and after calculation, the regulator output Kout1 is obtained; the regulator output Kout1 is modulated by PWM modulation module one to obtain two PWM signals, namely PWM1 and PWM2. PWM1 is used to drive the switching transistor S1 in the virtual DC motor to turn on and off, and PWM2 is used to drive the switching transistor S2 in the virtual DC motor to turn on and off; when the DC bus voltage is subjected to high-frequency disturbance, the virtual inertia coefficient Cvir and virtual damping coefficient D of the virtual DC microgrid are input to the VDM controller, and then the VDM controller controls the switching transistors S1 and S2 to control the virtual DC motor.

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