High-Efficiency Converter Applied to DC Microgrid

Abstract

This application relates to the technical field of converter design, and particularly to a high-efficiency converter applied to a DC microgrid, including a conversion circuit module and a control module; the conversion circuit module is used to connect to the DC microgrid and provide power for it; the control module is used to collect the DC bus voltage, generate a switching control signal according to the DC bus voltage and the virtual inertia damping control strategy, and output the switching control signal to the first switch and the second switch to control the conversion circuit module to work in different modes to achieve stable high-voltage output. The high-efficiency converter applied to the DC microgrid obtains a high voltage conversion ratio through the improvement of the converter topology structure, that is, obtains a high output voltage, improves the conversion efficiency of electric energy, and has a stable and reliable output voltage, strong anti-interference ability, and improves the overall efficiency and reliability.

Description

Technical Field

[0001] The present application relates to the technical field of converter design, and particularly to a high-efficiency converter applied to a DC microgrid. Background Art

[0002] Due to the non-renewability of traditional fossil energy and environmental pollution problems, the development of renewable energy has received extensive attention, and the importance of distributed generation technology with renewable energy as the main body and DC microgrids composed of distributed generations has become increasingly obvious. As a key link in the DC microgrid, the power electronic converter plays a role in power conversion. Usually, a Boost converter is used to boost the voltage to solve the problem of the relatively low output voltage of distributed generation. However, the traditional Boost converter usually relies on a high duty cycle condition to achieve a large output voltage, and has large power losses, so the output voltage is limited. In addition, the output voltage is easily affected by power fluctuations and has poor anti-interference ability, and is not suitable for occasions with high energy efficiency requirements and high stability requirements in the DC microgrid. Summary of the Invention

[0003] Based on this, it is necessary to provide a high-efficiency converter applied to a DC microgrid, which obtains a high voltage conversion ratio, that is, a high output voltage, improves the power conversion efficiency, and has a stable and reliable output voltage and strong anti-interference ability through the improvement of the converter topology structure.

[0004] The above object of the present application is achieved by the following technical solutions.

[0005] An embodiment of the present application provides a high-efficiency converter applied to a DC microgrid, including a conversion circuit module and a control module; the conversion circuit module is used to connect to the DC microgrid and provide power for it.

[0006] The conversion circuit module includes: a DC input power supply, a first inductor L1, a second inductor L2, a first switch S1, a second switch S2, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, an output capacitor C5, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, and an output diode D5.

[0007] The first end of the first inductor L1 is connected to the positive pole of the DC input power supply, and the second end of the first inductor L1 is connected to the first end of the first capacitor C1, the anode of the second diode D2, and the first signal terminal of the first switch S1; the second end of the first capacitor C1 is connected to the anode of the first diode D1 and the first signal terminal of the second switch S2; the second signal terminal of the second switch S2 is connected to the first end of the second inductor L2, the anode of the third diode D3, and the first end of the fourth capacitor C4; the cathode of the second diode D2 is connected to the second end of the second inductor L2 and the first end of the second capacitor C2; the cathode of the third diode D3 is connected to the anode of the output diode D5 and the first end of the third capacitor C3; the cathode of the output diode D5 is connected to the first end of the output capacitor C5 and forms a DC output terminal; the DC output terminal is used to connect to the DC bus; the negative pole of the DC input power supply is connected to the cathode of the first diode D1, the second signal terminal of the first switch S1, the second end of the second capacitor C2, the second end of the third capacitor C3, and the cathode of the fourth diode D4; the anode of the fourth diode D4 is connected to the second end of the fourth capacitor C4 and the second end of the output capacitor C5; the controlled terminals of the first switch S1 and the second switch S2 are respectively connected to the output terminal of the control module.

[0008] The control module is used to collect the DC bus voltage, generate a switch control signal according to the DC bus voltage and the virtual inertia damping control strategy, and output the switch control signal to the first switch S1 and the second switch S2 to control the conversion circuit module to work in different modes to achieve stable high-voltage output.

[0009] The present application has the following beneficial effects: a high voltage conversion ratio is obtained through the improvement of the converter topology structure, that is, a high output voltage is obtained, and the conversion efficiency of electric energy is improved; a virtual inertia coefficient and a virtual damping coefficient are introduced in the converter control to improve the stability of the DC microgrid. When the system is disturbed by power fluctuations and the like, the capacitance virtualized on the DC side of the converter is much larger than the actual capacitance, and the virtualized capacitance can store more electric energy, thereby reducing the DC voltage change speed and keeping the DC voltage output stable, thereby enhancing the anti-interference ability and stability of the system, and helping to improve the power quality and reliability of the DC microgrid. Description of the Drawings

[0010] Figure 1 It is a schematic structural diagram of a high-efficiency converter provided by an embodiment of the present application.

[0011] Figure 2 It is a schematic topological structure diagram of a conversion circuit module provided by an embodiment of the present application.

[0012] Figure 3 It is an equivalent schematic diagram of the conversion circuit module provided in an embodiment of the present application when operating in Mode 1.

[0013] Figure 4 It is an equivalent schematic diagram of the conversion circuit module provided in an embodiment of the present application when operating in Mode 2.

[0014] Figure 5 It is a waveform diagram of the main devices of the conversion circuit module provided in an embodiment of the present application. Specific Embodiments

[0015] To make the above objects, features, and advantages of the present application more obvious and understandable, the specific embodiments of the present application will be described in detail below. Many specific details are set forth in the following description to fully understand the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

[0016] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present application, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the specification of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0018] In a new energy power generation system, a DC power supply obtains electrical energy and outputs it. The DC electrical energy is boosted by a converter and then transmitted to a DC microgrid, and the DC microgrid supplies power to the backend load. Since the structure of the DC microgrid is complex and the power fluctuation is large, that is, the DC microgrid belongs to an application scenario with high energy efficiency requirements and high stability requirements. To enable the converter to meet the needs of this special scenario, it is necessary to consider from two aspects: high electrical energy conversion efficiency and strong stability.

[0019] Please refer to Figure 1 , a high-efficiency converter applied to a DC microgrid, includes: a conversion circuit module 10 and a control module 20; the output end of the conversion circuit module 10 is a DC output end DC out, for connecting to the DC microgrid 30 and providing a DC power supply therefor.

[0020] The conversion circuit module 10 includes: a DC input power supply DC in , a first inductor L1, a second inductor L2, a first switch S1, a second switch S2, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, an output capacitor C5, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, and an output diode D 5。

[0021] From the topological structure of the conversion circuit module 10, the first end of the first inductor L1 is connected to the positive pole of the DC input power supply DC in , the second end of the first inductor L1 is connected to the first end of the first capacitor C1, the anode of the second diode D2, and the first signal terminal of the first switch S1; the second end of the first capacitor C1 is connected to the anode of the first diode D1 and the first signal terminal of the second switch S2; the second signal terminal of the second switch S2 is connected to the first end of the second inductor L2, the anode of the third diode D3, and the first end of the fourth capacitor C4; the cathode of the second diode D2 is connected to the second end of the second inductor L2 and the first end of the second capacitor C2; the cathode of the third diode D3 is connected to the anode of the output diode D5 and the first end of the third capacitor C3; the cathode of the output diode D5 is connected to the first end of the output capacitor C5, and a DC output terminal DC out is formed; the DC output terminal DC out is used to connect to the DC bus; the negative pole of the DC input power supply DC in is connected to the cathode of the first diode D1, the second signal terminal of the first switch S1, the second end of the second capacitor C2, the second end of the third capacitor C3, and the cathode of the fourth diode D4; the anode of the fourth diode D4 is connected to the second end of the fourth capacitor C4 and the second end of the output capacitor C5; the controlled terminals of the first switch S1 and the second switch S2 are respectively connected to the output terminal of the control module 20.

[0022] As Figure 1 shown, it can be understood that the first switch S1 and the second switch S2 can be field effect transistors or other switching devices. When the voltage between the gate and the source of the field effect transistor satisfies the conduction condition of the field effect transistor, the field effect transistor conducts; otherwise, it turns off.

[0023] Among them, the third capacitor C3, the fourth capacitor C4, the third diode D3, and the fourth diode D4 form a voltage doubler unit 12, which can double the DC input voltage Boost to a preset multiple to obtain a high-voltage output and avoid the converter operating under high-duty-cycle conditions. The voltage multiplier unit 12 has the advantages of simple control, high voltage gain, high efficiency, good input current continuity, and few inductors and capacitors.

[0024] The control module 20 is used to collect the DC bus voltage , and generate a switching control signal PWM according to the DC bus voltage and the virtual inertia damping control strategy, and output the switching control signal PWM to the first switch S1 and the second switch S2 to control the conversion circuit module 10 to flexibly change the topological structure to operate in different modes, obtain the corresponding high voltage gain, and thus obtain a stable high-voltage signal output to the DC microgrid; at the same time, the system has a fast dynamic response, a small output voltage deviation, and a small response overshoot.

[0025] The embodiments of the present application have the following beneficial effects: By improving the topological structure of the conversion circuit module, a high voltage conversion ratio is obtained, that is, a high output voltage is obtained, and the conversion efficiency of electric energy is improved; A virtual inertia coefficient and a virtual damping coefficient are introduced in the converter control to improve the stability of the DC microgrid. When the system is disturbed by power fluctuations, etc., the virtual capacitor on the DC side of the converter is much larger than the actual capacitor, and the virtual capacitor can store more electric energy, thereby reducing the DC voltage change speed and keeping the DC voltage output stable, thus enhancing the anti-interference ability and stability of the system, and helping to improve the power quality and reliability of the DC microgrid.

[0026] In an optional embodiment, as Figure 1 shown, the method for generating the switching control signal includes: determining an intermediate voltage variable based on the virtual inertia control equation according to the virtual inertia coefficient and the virtual damping coefficient; based on the intermediate voltage variable , the DC bus voltage value of the conversion circuit module 10, and the output current value of the conversion circuit module 10, a switching control signal is generated by adopting a double-loop PI control strategy.

[0027] The intermediate voltage variable obtains the switching control signal after double-loop PI control, adjusts the duty cycle of the switching tube in the converter module in real time, stabilizes the DC voltage, enhances the anti-interference ability of the system, and improves the system response characteristics.

[0028] In the virtual inertia damping control of the DC microgrid, the virtual inertia coefficient and the virtual damping coefficient are both virtual parameters, so the virtual inertia coefficient and the virtual damping coefficient can be adjusted in real time according to the change of the virtual angular frequency .

[0029] Preferably, the virtual inertia damping control strategy is as follows: introducing a virtual inertia coefficient and a virtual damping coefficient in the control of the conversion circuit module, and determining a virtual inertia control equation in combination with a preset virtual angular frequency reference value, the virtual voltage angular frequency of the common coupling point of the DC microgrid measured in real time, and the output power of the conversion circuit module; then, determining the output voltage change rate according to the DC bus voltage, and adjusting the virtual inertia coefficient and the virtual damping coefficient , when the output voltage change rate is greater than 0, increasing the virtual inertia coefficient , and increasing the virtual damping coefficient ; when the output voltage change rate is less than 0, decreasing the virtual inertia coefficient , and increasing the virtual damping coefficient ; when the output voltage change rate tends to be stable, increasing the virtual inertia coefficient , and decreasing the virtual damping coefficient .

[0030] The virtual inertia control equation is: , where , is the virtual angular frequency, is the reference value of the virtual angular frequency, represents the virtual voltage angular frequency of the common coupling point, is the frequency modulation coefficient; is the active power on the source side, is the reference value of the active power, is the virtual inertia coefficient, is the virtual damping coefficient, is the exchange power between the system and the power grid, is the reference voltage value, is the DC bus voltage value.

[0031] Adopting the virtual inertia damping control strategy can improve the dynamic performance of the converter, enhance the anti-interference ability and stability of the whole system, help to improve the power quality and reliability of the DC microgrid, and reduce the disturbances caused by power supply fluctuations and load changes.

[0032] Based on the topology structure and control method of the conversion circuit module, the voltage gain of the conversion circuit module is:

[0033] , where is the voltage gain of the conversion circuit module, is the duty cycle of the first switch S1 and the second switch S2, that is, the duty cycle of the switch control signal PWM.

[0034] Among them, the method for determining the voltage gain of the conversion circuit module is as follows: when the conversion circuit module is in a stable operating state, apply the volt-second balance principle to the first inductor L1 and the second inductor L2 to determine the relationship between each capacitor voltage and the switching duty cycle: , where is the DC input voltage, is the voltage of the first capacitor, is the voltage of the second capacitor, is the voltage of the third capacitor, is the voltage of the fourth capacitor; then derive the voltages of the first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4: ; and then determine the voltage gain of the conversion circuit module according to the above formula.

[0035] Combined with Figure 3 , Figure 4 , Figure 5 viewed, based on the above control method, the conversion circuit module 10 can switch between two operating modes.

[0036] When the converter is in a steady state, assume that the operating period of the switch is T S , and the duty cycles of the first switch S1 and the second switch tube S2 are .

[0037] In the first mode (t0 - t1), the first switch S1, the second switch S2, and the output diode D5 are turned on, and the first diode D1, the second diode D2, the third diode D3, and the fourth diode D4 are turned off; the DC input power supply DC in supplies energy to the first inductor L1, and the first inductor L1 stores energy; the first capacitor C1 and the second capacitor C2 supply energy to the second inductor L2 through the first switch S1 and the second switch S2, and the second inductor L2 stores energy; the currents flowing through the first inductor L1 and the second inductor L2 increase; the third capacitor C3 and the fourth capacitor C4 supply energy to the output capacitor C5 and the DC load Ro through the output diode D5; when the first switch S1 and the second switch S2 are turned off, mode 1 ends.

[0038] In the second mode (t1 - t2): the first diode D1, the second diode D2, the third diode D3, and the fourth diode D4 are turned on, and the first switch S1, the second switch S2, and the output diode D5 are turned off; the DC input power supply DC inThe first inductor L1 supplies energy to the first capacitor C1 and the second capacitor C2 through the first diode D1 and the second diode D2, and the first capacitor C1 and the second capacitor C2 store energy; the second inductor L2 supplies energy to the third capacitor C3 and the fourth capacitor C4 through the third diode D3 and the fourth diode D4, and the third capacitor C3 and the fourth capacitor C4 store energy; the currents flowing through the first inductor L1 and the second inductor L2 decrease; the output capacitor C5 supplies energy to the DC load Ro; when the first switch S1 and the second switch S2 are turned on, Mode 2 ends.

[0039] The high-efficiency converter applied to the DC microgrid described in the above embodiments obtains a high voltage conversion ratio through the improvement of the converter topology structure, that is, a high output voltage is obtained, and the conversion efficiency of electric energy is improved; a virtual inertia coefficient and a virtual damping coefficient are introduced in the converter control to improve the stability of the DC microgrid. When the system is disturbed by power fluctuations and the like, the capacitance virtualized on the DC side of the converter is much larger than the actual capacitance, and the virtualized capacitance can store more electric energy, thereby reducing the DC voltage change speed and keeping the DC voltage output stable, thereby enhancing the anti-interference ability and stability of the system, contributing to improving the power quality and reliability of the DC microgrid, and reducing the disturbances caused by power supply fluctuations and load changes.

[0040] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0041] The above embodiments only represent several implementation manners of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims, and the specification can be used to explain the content of the claims.

Claims

1. A high-efficiency converter applied to a DC microgrid, characterized in that, It includes a conversion circuit module and a control module; The conversion circuit module is used to connect to a DC microgrid and provide power for it; The conversion circuit module includes: a DC input power supply, a first inductor L1, a second inductor L2, a first switch S1, a second switch S2, a first capacitor C1, a second capacitor C2, a third capacitor C3, a fourth capacitor C4, an output capacitor C5, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, and an output diode D5; The first end of the first inductor L1 is connected to the positive pole of the DC input power supply, and the second end of the first inductor L1 is connected to the first end of the first capacitor C1, the anode of the second diode D2, and the first signal terminal of the first switch S1; the second end of the first capacitor C1 is connected to the anode of the first diode D1 and the first signal terminal of the second switch S2; the second signal terminal of the second switch S2 is connected to the first end of the second inductor L2, the anode of the third diode D3, and the first end of the fourth capacitor C4; the cathode of the second diode D2 is connected to the second end of the second inductor L2 and the first end of the second capacitor C2; the cathode of the third diode D3 is connected to the anode of the output diode D5 and the first end of the third capacitor C3; the cathode of the output diode D5 is connected to the first end of the output capacitor C5 and forms a DC output terminal; the DC output terminal is used to connect to a DC bus; the negative pole of the DC input power supply is connected to the cathode of the first diode D1, the second signal terminal of the first switch S1, the second end of the second capacitor C2, the second end of the third capacitor C3, and the cathode of the fourth diode D4; the anode of the fourth diode D4 is connected to the second end of the fourth capacitor C4 and the second end of the output capacitor C5; the controlled terminals of the first switch S1 and the second switch S2 are respectively connected to the output terminal of the control module; The control module is used to collect the DC bus voltage, generate a switch control signal according to the DC bus voltage and the virtual inertia damping control strategy, and output the switch control signal to the first switch S1 and the second switch S2 to control the conversion circuit module to work in different modes to achieve stable high-voltage output; The conversion circuit module can switch between two working modes: In the first mode, the first switch S1, the second switch S2, and the output diode D5 are turned on, while the first diode D1, the second diode D2, the third diode D3, and the fourth diode D4 are turned off. The DC input power supply provides energy to the first inductor L1 to store energy in the first inductor L1. The first capacitor C1 and the second capacitor C2 provide energy to the second inductor L2 through the first switch S1 and the second switch S2 to store energy in the second inductor L2. The currents flowing through the first inductor L1 and the second inductor L2 increase. The third capacitor C3 and the fourth capacitor C4 provide energy to the output capacitor C5 and the DC microgrid through the output diode D5. When the first switch S1 and the second switch S2 are turned off, the first mode ends and the second mode begins. In the second mode, the first diode D1, the second diode D2, the third diode D3, and the fourth diode D4 are turned on, while the first switch S1, the second switch S2, and the output diode D5 are turned off. The DC input power supply and the first inductor L1 provide energy to the first capacitor C1 and the second capacitor C2 through the first diode D1 and the second diode D2 to store energy in the first capacitor C1 and the second capacitor C2. The second inductor L2 provides energy to the third capacitor C3 and the fourth capacitor C4 through the third diode D3 and the fourth diode D4 to store energy in the third capacitor C3 and the fourth capacitor C4. The currents flowing through the first inductor L1 and the second inductor L2 decrease. The output capacitor C5 provides energy to the DC microgrid. When the first switch S1 and the second switch S2 are turned on, the second mode ends and the first mode of the next working cycle begins. The voltage gain of the conversion circuit module is , where is the voltage gain of the conversion circuit module, is the duty cycle of the first switch S1 and the second switch S2.

2. The high-efficiency converter applied to a DC microgrid according to claim 1, wherein The virtual inertia damping control strategy is as follows: Introduce a virtual inertia coefficient and a virtual damping coefficient in the control of the conversion circuit module, and combine the preset virtual angular frequency reference value, the virtual voltage angular frequency of the point of common coupling of the DC microgrid measured in real time, and the output power of the conversion circuit module to determine the virtual inertia control equation. Determine the output voltage change rate according to the DC bus voltage, and adjust the virtual inertia coefficient and the virtual damping coefficient according to the output voltage change rate. When the output voltage change rate is greater than 0, increase the virtual inertia coefficient and increase the virtual damping coefficient. When the output voltage change rate is less than 0, decrease the virtual inertia coefficient and increase the virtual damping coefficient. When the output voltage change rate tends to be stable, increase the virtual inertia coefficient and decrease the virtual damping coefficient.

3. The high-efficiency converter applied to a DC microgrid according to claim 2, characterized in that, The virtual inertia control equation is: ， Among them, , is the virtual angular frequency, is the reference value of the virtual angular frequency, represents the virtual voltage angular frequency of the common coupling point, is the frequency modulation coefficient; is the active power on the source side, is the reference value of the active power, is the virtual inertia coefficient, is the virtual damping coefficient, is the exchanged power between the system and the power grid, is the reference voltage value, is the DC bus voltage value.

4. The high-efficiency converter applied to a DC microgrid according to claim 2, wherein, The method for determining the voltage gain of the conversion circuit module is: When the conversion circuit module is in a stable operating state, the volt-second balance principle is applied to the first inductor L1 and the second inductor L2 to determine the relationship between each capacitor voltage and the switch duty cycle: , wherein, is the DC input voltage, is the voltage of the first capacitor, is the voltage of the second capacitor, is the voltage of the third capacitor, is the voltage of the fourth capacitor; Derive the voltages of the first capacitor C1, the second capacitor C2, the third capacitor C3, and the fourth capacitor C4: ; Determine the voltage gain of the conversion circuit module according to the above formula.

5. The high-efficiency converter applied to a DC microgrid according to claim 2, wherein The method for generating the switch control signal includes: Determine the intermediate voltage variable based on the virtual inertia control equation according to the virtual inertia coefficient and the virtual damping coefficient. Based on the intermediate voltage variable, the DC bus voltage value of the conversion circuit module, and the output current value of the conversion circuit module, a double-loop PI control strategy is adopted to generate the switching control signal.

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