A microgrid experimental teaching device

Abstract

The present invention provides a microgrid experimental teaching device, which includes a hardware circuit and software. Specifically: The hardware circuit includes a current-controlled converter, a voltage-controlled converter, a current-type converter controller, a voltage-type converter controller, a first DC power supply port, a second DC power supply port, and a host computer. The host computer includes a graphical user interface and an interface. The graphical user interface serves as the software and includes a control parameter adjustment interface for inputting parameters, a control mode adjustment interface for selecting an enabled controller, and a device status display interface for observing the status of the experimental teaching device, so as to realize the control and measurement of the experimental teaching device. The microgrid experimental teaching device of the present invention can flexibly realize the interconnection of multiple devices and expand the load link, and has the characteristics of low cost, small floor area, low power consumption, high flexibility, strong scalability, etc., and can realize the feature reproduction and programming of various microgrid controls.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and more particularly, to a microgrid experimental teaching device. Background Art

[0002] In recent years, with the large-scale application of new energy power generation, the proportion of new energy power generation in the power grid has been increasing. The traditional power grid structure has been unable to adapt to this change. To solve the problem of a large number of new energy grid connections, the concept of a microgrid has been proposed. New energy power generation needs to be connected to the bus in the microgrid through power electronic devices. Therefore, there are a large number of power electronic devices in the microgrid. To achieve the control of these single power electronic devices and the coordinated control between multiple power electronic devices, there is a complex control structure in the microgrid.

[0003] To adapt to the latest scientific research content, the experimental teaching of the microgrid is essential. The typical microgrid experimental teaching uses power hardware in the loop as the experimental equipment. This teaching method has the following limitations:

[0004] 1. High cost. Since power hardware in the loop requires a real-time simulator with powerful computing capabilities and a high-bandwidth linear amplifier, the price is often very high. The excessive price limits the popularization of power hardware in the loop in teaching.

[0005] 2. Large floor area. The real-time simulator often occupies a large floor area, which is not conducive to the development of teaching.

[0006] Therefore, it is necessary to propose a new microgrid experimental teaching device to solve the above problems. Summary of the Invention

[0007] Aiming at the defects in the prior art, the purpose of the present invention is to provide a microgrid experimental teaching device.

[0008] According to one aspect of the present invention, there is provided a microgrid experimental teaching device, including a hardware circuit and software, wherein:

[0009] The hardware circuit includes a current-controlled converter, a voltage-controlled converter, a current-type converter controller, a voltage-type converter controller, a first DC power supply port, a second DC power supply port, and a host computer;

[0010] The DC input end of the voltage-controlled converter is connected to the first DC power supply port; the voltage-controlled converter is used to reproduce the AC bus voltage in the simulated microgrid;

[0011] The DC input terminal of the current-controlled converter is connected to the second DC power supply port; the current-controlled converter is used to reproduce the branch current in the simulated microgrid; the AC output port of the current-controlled converter is connected to the AC output port of the voltage-controlled converter; the AC output ports of the current-controlled converter and the voltage-controlled converter are externally connected to at least one of a load and a device AC output port to achieve function and system expansion;

[0012] The voltage-type converter controller is connected to the host computer and is used to accurately reproduce the control behavior and voltage characteristics of the microgrid system in the experimental teaching device;

[0013] The current-type converter controller is connected to the host computer and is used to accurately reproduce the control behavior and current characteristics of the microgrid system in the experimental teaching device;

[0014] The host computer includes a graphical user interface and an interface for external communication; the interface is used to receive the sampling signals of the experimental teaching device and transmit signals to the voltage-type converter controller and the current-type converter controller respectively; the graphical user interface, as the software, includes a control parameter adjustment interface for inputting parameters, a control mode adjustment interface for selecting the enabled controller, and a device status display interface for observing the status of the experimental teaching device to achieve the control and measurement of the experimental teaching device.

[0015] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0016] The microgrid experimental teaching device of the present invention can flexibly realize the interconnection of multiple devices and expand the load link, and has the characteristics of low cost, small floor area, low power consumption, high flexibility, strong scalability, etc., and can realize the feature reproduction and programming of various typical microgrid controls. The present invention can be used for low-cost microgrid experimental teaching. Description of the Drawings

[0017] By reading the detailed description of the non-restrictive embodiments with reference to the following drawings, other features, purposes and advantages of the present invention will become more obvious:

[0018] Figure 1 It is a schematic structural diagram of the microgrid experimental teaching device according to a preferred embodiment of the present invention;

[0019] Figure 2 It is a schematic structural diagram of the hardware circuit according to a preferred embodiment of the present invention;

[0020] Figure 3 It is a schematic structural diagram of the three-phase DC / AC power electronic converter topology for the voltage-controlled converter according to a preferred embodiment of the present invention;

[0021] Figure 4 Schematic diagram of a three-phase DC / AC power electronic converter topology for a current-controlled converter according to a preferred embodiment of the present invention;

[0022] Figure 5 Schematic diagram of a topology of a passive impedance network for a current-controlled converter according to a preferred embodiment of the present invention;

[0023] Figure 6 Schematic diagram of a topology of a passive impedance network for a voltage-controlled converter according to a preferred embodiment of the present invention;

[0024] Figure 7 Schematic diagram of a topology of a passive impedance network connected to the DC side of a current-controlled converter according to a preferred embodiment of the present invention;

[0025] Figure 8 Schematic diagram of a topology of a passive impedance network connected to the DC side of a voltage-controlled converter according to a preferred embodiment of the present invention;

[0026] Figure 9 Schematic diagram of a secondary control link according to a preferred embodiment of the present invention;

[0027] Figure 10 Schematic diagram of a droop control link according to a preferred embodiment of the present invention;

[0028] Figure 11 Schematic diagram of a closed-loop voltage control link according to a preferred embodiment of the present invention;

[0029] Figure 12 Schematic diagram of a dq-axis current control link according to a preferred embodiment of the present invention;

[0030] Figure 13 Schematic diagram of a dq0-axis current control link according to a preferred embodiment of the present invention;

[0031] Figure 14 Schematic diagram of the structure of impedance network E according to a preferred embodiment of the present invention;

[0032] Figure 15 Schematic diagram of the structure of impedance network F according to a preferred embodiment of the present invention;

[0033] Figure 16 Schematic diagram of a master-slave control link according to a preferred embodiment of the present invention;

[0034] In the figure: 1 - voltage-controlled converter; 2 - converter A; 3 - impedance network B; 4 - DC power supply terminal of converter A; 5 - AC output terminal of converter A; 6 - AC input terminal of impedance network A; 7 - AC output terminal of impedance network A; 8 - first DC power supply port; 9 - impedance network C; 10 - DC input terminal of impedance network C; 11 - DC output terminal of impedance network C; 12 - voltage-source converter controller; 13 - secondary controller; 14 - droop controller; 15 - closed-loop voltage controller; 16 - open-loop voltage controller; 17 - pulse width modulator A; 18 - current-controlled converter; 19 - converter B; 20 - impedance network A; 21 - DC power supply terminal of converter B; 22 - AC output terminal of converter B; 23 - AC input terminal of impedance network B; 24 - AC output terminal of impedance network B; 25 - second DC power supply port; 26 - impedance network D; 27 - DC input terminal of impedance network D; 28 - DC output terminal of impedance network D; 29 - current-source converter controller; 30 - dq-axis current controller; 31 - dq0-axis current controller; 32 - pulse width modulator B; 33 - host computer; 34 - amplitude calculator; 35 - frequency calculator; 36 - amplitude secondary controller; 37 - frequency secondary controller; 38 - active power calculation; 39 - reactive power calculation; 40 - voltage outer loop d-axis controller; 41 - voltage outer loop q-axis controller; 42 - current inner loop d-axis controller; 43 - current inner loop q-axis controller; 44 - Park transformation; 45 - inverse Park transformation; 46 - first current loop d-axis controller; 47 - first current loop q-axis controller; 48 - second current loop d-axis controller; 49 - second current loop q-axis controller; 50 - current loop 0-axis controller; 51 - DC diode; 52 - DC relay; 53 - AC circuit breaker; 54 - DC source; 55 - experimental teaching device; 56 - impedance network E; 57 - impedance network F; 58 - load; 59 - device AC output port; 60 - AC input terminal of impedance network E; 61 - AC output terminal of impedance network E; 62 - AC input terminal of impedance network F; 63 - AC output terminal of impedance network F; 64 - master-slave controller; 65 - dq to abc coordinate transformation; 66 - dq0 to abc coordinate transformation. Specific implementation mode

[0035] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made. These all belong to the protection scope of the present invention. In the description of the embodiments of the present invention, it should be noted that the terms "first", "second", etc. in the specification and claims of the present invention are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here.

[0036] Refer to Figure 1-2, which is a schematic structural diagram of a microgrid experimental teaching device provided by a preferred embodiment of the present invention. The device includes a hardware circuit and software, wherein: the hardware circuit is the design of the main power system, including a current-controlled converter 18, a voltage-controlled converter 1, a current-type converter controller 29, a voltage-type converter controller 12, a first DC power supply port 8, a second DC power supply port 25, and a host computer 33; the ports of the current-controlled converter 18 include a DC input end and an AC output end, and the ports of the voltage-controlled converter 1 include a DC input end and an AC output end; the DC input end of the voltage-controlled converter 1 is connected to the first DC power supply port 8; the voltage-controlled converter 1 is used to reproduce the AC bus voltage in the simulated microgrid; the DC input end of the current-controlled converter 18 is connected to the second DC power supply port 25, and the two DC power supply ports can be connected to the same external power supply or to different external power supplies respectively; the current-controlled converter 18 is used to reproduce the branch current in the simulated microgrid; the AC output port of the current-controlled converter 18 is connected to the AC output port of the voltage-controlled converter 1; the AC output ports of the current-controlled converter 18 and the voltage-controlled converter 1 are externally connected to at least one of a load 58 and a device AC output port 59, and can be connected to other experimental devices to realize function and system expansion; the voltage-type converter controller 12 is connected to the host computer 33 and is used to accurately reproduce the control behavior and voltage characteristics of the microgrid system in the experimental teaching device; the current-type converter controller 29 is connected to the host computer 33 and is used to accurately reproduce the control behavior and current characteristics of the microgrid system in the experimental teaching device; the host computer 33 includes a graphical user interface and an interface for external communication; the interface is used to receive the sampling signals of the experimental teaching device and transmit signals to the voltage-type converter controller 12 and the current-type converter controller 29 respectively; the graphical user interface, as software, includes a control parameter adjustment interface for inputting parameters, a control mode adjustment interface for selecting the enabled controller, and a device state display interface for observing the state of the experimental teaching device to realize the control and measurement of the experimental teaching device.

[0037] In some specific embodiments, the voltage-controlled converter 1 reproduces the AC bus voltage in the simulated microgrid by shaping the voltage amplitude, frequency, and phase of the AC output port of the voltage-controlled converter 1; the voltage-controlled converter 1 includes a converter A2, the converter A2 includes a converter A DC power supply terminal 4 and a converter A AC output terminal 5, and the filter impedance network of the voltage-controlled converter 1 includes at least one of a resistor impedance network A20, a resistor impedance network C9, and a resistor impedance network E56 and at least includes the resistor impedance network A20; where: the resistor impedance network A20 includes a resistor impedance network A AC input terminal 6 and a resistor impedance network A AC output terminal 7, optionally the resistor impedance network C9 includes a resistor impedance network C DC input terminal 10 and a resistor impedance network C DC output terminal 11, and optionally the resistor impedance network E56 includes a resistor impedance network E AC input terminal 60 and a resistor impedance network E AC output terminal 61; where the "optionally" here means that the filter impedance network of the voltage-controlled converter 1 can implement its function without using the resistor impedance network C9 and the resistor impedance network E56; the resistor impedance network A20 is used to filter the voltage harmonics at the converter A AC output terminal 5, the resistor impedance network A AC input terminal 6 is connected to the converter A AC output terminal 5, and the resistor impedance network A AC output terminal 7 is connected to the resistor impedance network E AC input terminal 60 or directly connected to the AC output terminal of the voltage-controlled converter 1; the resistor impedance network C9 is used to suppress the zero-sequence current in the DC loop; the converter A DC power supply terminal 4 can be directly connected to the first DC power supply port 8 or connected to the first DC power supply port 8 through the resistor impedance network C; when using the resistor impedance network C9, the resistor impedance network C DC input terminal 10 is connected to the first DC power supply port 8, and the resistor impedance network C DC output terminal 11 is connected to the converter A DC power supply terminal 4; when using the resistor impedance network E56, the resistor impedance network E56 is used to suppress the zero-sequence current in the AC loop, the resistor impedance network E AC input terminal 60 is connected to the resistor impedance network A AC output terminal 7, and the resistor impedance network E AC output terminal 61 is connected to the AC output terminal of the voltage-controlled converter 1.

[0038] In some specific embodiments, the current-controlled converter 18 reproduces the branch current in the simulated microgrid by shaping the current at the AC output port of the current-controlled converter 18; the current-controlled converter 18 includes a converter B19, the converter B19 includes a converter B DC power supply terminal 21 and a converter B AC output terminal 22, and the filter impedance network of the current-controlled converter 18 includes at least one of a resistor impedance network B3, a resistor impedance network D26, and a resistor impedance network F57 and at least includes the resistor impedance network B3; wherein: the resistor impedance network B3 includes a resistor impedance network B AC input terminal 23 and a resistor impedance network B AC output terminal 24, optionally the resistor impedance network D26 includes a resistor impedance network D DC input terminal 27 and a resistor impedance network D DC output terminal 28, and optionally the resistor impedance network F57 includes a resistor impedance network F AC input terminal 62 and a resistor impedance network F AC output terminal 63; wherein, the "optionally" here means that the filter impedance network of the current-controlled converter 18 can achieve its function without using the resistor impedance network D26 and the resistor impedance network F57; the resistor impedance network B3 is used to filter the current harmonics at the converter B AC output terminal 22, the resistor impedance network B AC input terminal 23 is connected to the converter B AC output terminal 22, and the resistor impedance network B AC output terminal 24 is connected to the resistor impedance network F AC input terminal 62 or directly to the AC output port of the current-controlled converter 18; the resistor impedance network D26 is used to suppress the zero-sequence current in the DC loop; the converter B DC power supply terminal 21 can be directly connected to the second DC power supply port 25 or connected to the second DC power supply port 25 through the resistor impedance network D; when using the resistor impedance network D26, the resistor impedance network D DC input terminal 27 is connected to the second DC power supply port 25, and the resistor impedance network D DC output terminal 28 is connected to the converter B DC power supply terminal 21; when using the resistor impedance network F57, the resistor impedance network F57 is used to suppress the zero-sequence current in the AC loop, the resistor impedance network F AC input terminal 62 is connected to the resistor impedance network B AC output terminal 24, and the resistor impedance network F AC output terminal 63 is connected to the AC output port of the current-controlled converter 18.

[0039] The voltage-controlled converter 1 employs a voltage-source converter controller 12. In some specific embodiments, the voltage-source converter controller 12 includes a pulse-width modulator A17, an optional open-loop voltage controller 16, an optional closed-loop voltage controller 15, an optional droop controller 14, and an optional secondary controller 13, where: "optional" here means that not all of these controllers in the voltage-source converter controller 12 necessarily operate. Some controllers can be selected to operate while others do not. The secondary controller 13 is used to adjust the amplitude reference and frequency reference in the droop control according to the voltage at the AC output port of the voltage-controlled converter, and is used to compensate for the difference between the voltage reference value calculated by the droop control and the standard microgrid voltage. The input of the secondary controller 13 is the given signal from the upper computer 33, and the output is the input of the droop controller 14. The droop controller 14 is used to calculate the voltage reference value of the underlying controller based on the power at the AC output port of the voltage-controlled converter. The input of the droop controller 14 is the given signal from the upper computer 33 and the output of the optional secondary controller 13, and the output of the droop controller 14 is the input of the first underlying controller. The first underlying controller includes a closed-loop voltage controller 15 and an open-loop voltage controller 16, and is used to control the voltage at the AC output port of the voltage-controlled converter. Only one controller operates at the same time, and the other is turned off. The input of the first underlying controller is the voltage reference value, which comes from the output of the optional droop controller 14 or the given signal from the upper computer 33. The output signal of the first underlying controller is the modulation signal of the pulse-width modulator A17. Specifically, the input of the closed-loop voltage controller 15 comes from the output of the droop controller 14 or the given signal from the upper computer 33, and the output of the closed-loop voltage controller 15 is the input of the pulse-width modulator A17. The input of the open-loop voltage controller 16 comes from the output of the droop controller 14 or the given signal from the upper computer 33, and the output of the open-loop voltage controller 16 is the input of the pulse-width modulator A17. The pulse-width modulator A17 has an input that is the output of the closed-loop voltage controller 15 or the open-loop voltage controller 16, and the output of the pulse-width modulator A17 is the switching signal of the voltage-controlled converter 1.

[0040] The current-controlled converter 18 employs a current-mode converter controller 29. In some specific embodiments, the current-mode converter controller 29 includes a pulse-width modulator B32, an optional dq-axis current controller 30, an optional dq0-axis current controller 31, and an optional master-slave controller 64, where: The optional master-slave controller 64 is configured to obtain the current reference value of the underlying controller based on the output current (ig_v) of the voltage-controlled converter 1, the load current (iload), or the current (iout) at the AC output port 59 of the device, and change the given signal of the dq-axis current controller 30 or the dq0-axis current controller 31; the input of the master-slave controller 64 is the output current (ig_v) of the voltage-controlled converter 1, the load current (iload), or the current (iout) at the AC output port 59 of the device, and the output of the master-slave controller 64 is the input of the second underlying controller; the second underlying controller includes a dq-axis current controller 30 and a dq0-axis current controller 31, and is used to control the current at the AC output port of the current-controlled converter. Only one controller works at the same time, and the other is turned off; the input of the second underlying controller is the current reference value, which comes from the optional master-slave control or the given signal of the host computer 33, and the output signal of the second underlying controller is the modulation signal of the pulse-width modulator B32; specifically, the dq-axis current controller 30 is used to control the dq-axis current of the current-controlled converter 18, the input comes from the given signal of the host computer 33 or the output of the master-slave control, and the output is the input of the pulse-width modulator B32; the dq0-axis current controller 31 is used to control the dq0-axis current of the current-controlled converter 18, the input comes from the given signal of the host computer 33 or the output of the master-slave control, and the output is the input of the pulse-width modulator B32; the pulse-width modulator B32, the input of the pulse-width modulator B32 is the output of the dq-axis current controller 30 or the output of the dq0-axis current controller 31, and the output of the pulse-width modulator B32 is the switching signal of the current-controlled converter 18.

[0041] In some specific embodiments, the control mode adjustment interface includes a control mode adjustment interface A and a control mode adjustment interface B; the control mode adjustment interface A is used for enabling the secondary control, droop control, closed-loop voltage control, and open-loop voltage control in the voltage-type converter controller 12, as well as turning on and off the voltage-type converter controller 12; the control mode adjustment interface B is used for enabling the master-slave control, dq-axis current control, and dq0-axis current controller 31 in the current-type converter controller 29, as well as turning on and off the current-controlled converter 18.

[0042] In some specific embodiments, the control parameter adjustment interface includes a control parameter adjustment interface A and a control parameter adjustment interface B; the control parameter adjustment interface A is used to input all the relevant parameters for the control in the voltage source converter controller 12, and the relevant parameters include the given voltage amplitude, the given voltage frequency, the given power, the controller coefficients, etc.; the control parameter adjustment interface B is used to input all the relevant parameters for the control in the current source converter controller 29, and the relevant parameters include the given current, the controller coefficients, etc. For example, the input of the first-level controller comes from the optional droop controller 14 or the given signal of the control parameter adjustment interface A. The input of the droop controller 14 is the input of the control parameter adjustment interface A or the output of the secondary controller 13, and the input of the secondary controller 13 is the input of the control parameter adjustment interface A.

[0043] The parameters that can be input into the control mode adjustment interface A include the enable signals for all control modes of the voltage source converter controller 12. The parameters that can be input into the control parameter adjustment interface A include all the control parameters of the voltage source converter controller 12. These signals are transmitted to the voltage source converter controller 12 through the interface to achieve the state switching and control parameter adjustment of the voltage control type converter 1. The parameters that can be input into the control mode adjustment interface B include the enable signals for all control modes of the current source converter controller 29. The parameters that can be input into the control parameter adjustment interface B include all the control parameters of the current source converter controller 29. These signals are transmitted to the current source converter controller 29 through the interface to achieve the state switching and control parameter adjustment of the current control type converter 18.

[0044] The interface of the host computer 33 sends all the enable signals and parameter signals in the graphical user interface to the voltage source converter controller 12 and the current source converter controller 29 respectively, and transmits the sampling signals to the experimental device status display interface or signal processing. In some specific embodiments, the device status display interface is used to directly display the sampled voltage and current and the signals after signal processing. Among them, the signal processing includes any one or several of amplitude calculation, frequency calculation, coordinate transformation, and power calculation; through the storage and display of the host computer 33, the signals such as the sampled AC output port voltage, current, frequency, and power under different time coordinate axes are displayed on the host computer 33; the sampling signal processing of the host computer 33 is used to perform mathematical processing on the sampled voltage and current signals to obtain signals such as voltage and current amplitudes, voltage frequencies, voltage and current dq-axis components, active power, and reactive power, including amplitude calculation of all sampled voltages, amplitude calculation of all sampled currents, frequency calculation of all sampled voltages, coordinate transformation of all sampled voltages, coordinate transformation of all sampled currents, power calculation of relevant sampled voltages and sampled currents, etc.; the device status display interface can flexibly switch the displayed signals.

[0045] In some specific embodiments, the DC sides of multiple experimental teaching devices are connected to a DC power supply through a DC relay 52 and a DC diode 51 to achieve common power supply for multiple experimental teaching devices 55. The AC sides of multiple experimental teaching devices 55 are connected through an AC circuit breaker 53 to achieve flexible functions and system expansion. The AC circuit breaker 53 is used to control the connection state of the device AC output ports 59 between each experimental teaching device 55, realizing the switching between two working states: multiple experimental teaching devices 55 working in coordination or a single experimental teaching device 55 working alone. The DC relay 52 is used to control the connection state between the experimental teaching device 55 and the DC power source 54 to ensure that the experimental teaching device 55 has no voltage when it is not being operated. The diode circuit is used to restrict the current flow direction between the DC power source 54 and the experimental teaching device 55 to ensure that the current only flows from the DC power source 54 to the experimental teaching device 55, ensuring the safety of the DC power source 54 and the experimental teaching device 55.

[0046] By selecting the control state and control parameters of the experimental teaching device, and through the implementation of different control systems and control objectives by the voltage source converter controller 12 and the current source converter controller 29, various control characteristics of the microgrid can be reproduced, including: control behaviors such as voltage control, current control, master-slave control, droop control, secondary control, and voltage-current characteristics. By selecting the controller of a single experimental teaching device, the reproduction of multiple controllers on the experimental teaching device is realized; by controlling the switch of the AC circuit breaker 53, the connection of multiple experimental teaching devices is achieved, thereby realizing the reproduction of the control structure in a more complex circuit.

[0047] The microgrid experimental teaching device in the embodiments of the present invention will be described in more detail below.

[0048] As Figure 1-2 shown, the microgrid experimental teaching device in the embodiments of the present invention includes: a host computer 33, a voltage source converter controller 12, a current source converter controller 29, a voltage control type converter 1, a current control type converter 18, an impedance network C9, an impedance network D26, a first DC power supply port 8, a second DC power supply port 25, a load 58, and a device AC output port 59; it should be noted that Figure 1 auxiliary circuits and software modules are omitted. Adding conventional circuit modules to the embodiments provided by the present invention also belongs to the essential content of the present invention.

[0049] The current control type converter 18 includes a converter B19 and an impedance network B3. The current control type converter 18 can be but is not limited to such as Figure 4Any DC / AC topology structure, including the three-phase two-level structure shown, the semiconductor devices can be selected but are not limited to fully controlled or semi-controlled power devices such as Si IGBTs. The impedance network B3 is a circuit structure composed of one or more of passive devices such as resistors R, inductors L, and capacitors C, including at least one set of input and output terminals, and is used to cooperate with the converter B19 to reduce the high-order harmonics of the current at the AC test terminal in the system; the passive impedance network adopts, including but not limited to, such as Figure 5 the circuit topology structure shown.

[0050] The voltage-controlled converter 1 includes the converter A2 and the impedance network A20. The voltage-controlled converter 1 can adopt, including but not limited to, such as Figure 3 Any DC / AC topology structure, including the three-phase two-level structure, the semiconductor devices can be selected but are not limited to fully controlled or semi-controlled power devices such as Si IGBTs. The impedance network A20 is a circuit structure composed of one or more of passive devices such as resistors R, inductors L, and capacitors C, including at least one set of input and output terminals, and is used to cooperate with the converter A2 to shape the voltage at the output port of the resistance network and reduce the high-order harmonics of the voltage at the AC test terminal in the system; the passive impedance network adopts, including but not limited to, such as Figure 6 the circuit topology structure shown.

[0051] The impedance network C9 is a circuit structure composed of one or more of passive devices such as resistors R and inductors L, including at least one set of DC input and output terminals, and is used to suppress the common-mode current; the passive impedance network adopts, including but not limited to, such as Figure 7 the circuit topology structure shown, that is, the DC common-mode inductor structure. The impedance network D26 is a circuit structure composed of one or more of passive devices such as resistors R and inductors L, including at least one set of DC input and output terminals, and is used to suppress the common-mode current; the passive impedance network adopts, including but not limited to, such as Figure 8 the circuit topology structure shown, that is, the DC common-mode inductor structure.

[0052] The impedance network E56 is a circuit structure composed of one or more of passive devices such as resistors R and inductors L, including at least one set of AC input and output terminals, and is used to suppress the common-mode current; the passive impedance network adopts, including but not limited to, such as Figure 14 the circuit topology structure shown. The impedance network F57 is a circuit structure composed of one or more of passive devices such as resistors R and inductors L, including at least one set of AC input and output terminals, and is used to suppress the common-mode current; the passive impedance network adopts, including but not limited to, such as Figure 15 the circuit topology structure shown.

[0053] The first DC power supply port 8 includes a positive port and a negative port, which are connected to the positive and negative poles of the converter A2 or the impedance network C9. The power supply methods include but are not limited to DC voltage sources, rectifier circuits, etc. The second DC power supply port 25 includes a positive port and a negative port, which are connected to the positive and negative poles of the converter B19 or the impedance network D26. The power supply methods include but are not limited to DC voltage sources, rectifier circuits, etc. The first DC power supply port 8 and the second DC power supply port 25 can be connected to the same power supply or different power supplies.

[0054] The load 58 can be connected to the AC output terminals of the impedance network E56 and the impedance network F57, or to the AC output terminals of the voltage-controlled converter 1 and the current-controlled converter 18.

[0055] The control system of the microgrid experimental teaching device includes a voltage-type converter controller 12 and a current-type converter controller 29.

[0056] The voltage-type converter controller 12 mainly includes a secondary controller 13, a droop controller 14, a closed-loop voltage controller 15, an open-loop voltage controller 16, and a pulse width modulator A17, where:

[0057] First step, as Figure 9 shown, use the secondary controller 13 to calculate the voltage amplitude compensation amount and the voltage frequency compensation amount in the droop controller 14. First, use the amplitude calculator 34 and the frequency calculator 35 to obtain the voltage amplitude V amp and the voltage frequency f g . Input the obtained voltage amplitude reference V ampref and the voltage amplitude V amp into the voltage amplitude controller, that is, the amplitude secondary controller 36, to obtain the voltage amplitude compensation amount ΔV. Input the obtained voltage frequency reference f gref and the voltage frequency f g into the frequency secondary controller 37 to obtain the voltage frequency compensation amount Δf.

[0058] Second step, as Figure 10 shown, use the droop controller 14 to calculate the voltage reference V and the phase θ. First, use the active power calculation 38 to obtain the active power P g at the AC output port of the impedance network A20, and then calculate the phase θ. The calculation formula is as follows:

[0059] θ = 2π∫(f0 - K P (P0 - P g ))dt (1)

[0060] First, use the reactive power calculation 39 to obtain the reactive power Q at the AC output port of the impedance network A20g , and then the phase θ is calculated, and the calculation formula is as follows:

[0061] V = V0 - K Q (Q g - Q0) + ΔV (2)

[0062] In the third step, through the control mode signal of the host computer 33, the closed-loop voltage controller 15 or the open-loop voltage controller 16 is selected. The input of the closed-loop voltage controller 15 comes from the host computer 33 or the droop controller 14, and the control structure is as Figure 11 shown, and a typical double closed-loop control is adopted.

[0063] V g and the phase θ are respectively transformed by the Park transformation 44 to obtain the d-axis component v of the voltage at the AC output end 24 of the impedance network B gvd and the q-axis component v of the voltage at the AC output end 24 of the impedance network B gvq ; the difference between the output V of the droop control and the d-axis component v of the voltage at the AC output end 24 of the impedance network B gvd is taken, and the obtained difference is the input signal of the voltage outer loop d-axis controller 40. The q-axis component i of the current at the AC output end 24 of the impedance network B gvq is multiplied by ωC and then added to the d-axis component i of the current at the AC output end 24 of the impedance network B gvd , and then added to the output of the voltage outer loop d-axis controller 40 to obtain the given signal i of the current inner loop d-axis controller 42 cd,ref . The given signal i cd,ref is subtracted from the d-axis component i of the inductor current in the impedance network A20 to obtain the input signal of the current inner loop d-axis controller 42. The q-axis component i of the inductor current in the impedance network A20 cd is multiplied by ωL and then added to the d-axis component v of the voltage at the AC output end 24 of the impedance network B cq , and then added to the output of the current inner loop d-axis controller 42 to obtain the d-axis signal e of the inverse Park transformation 45 gvd . The difference between 0 and the q-axis component v of the voltage at the AC output end 24 of the impedance network B vd is taken, and the obtained difference is the input signal of the voltage outer loop q-axis controller 41. The d-axis component i of the current at the AC output end 24 of the impedance network B gvq is multiplied by ωC and then added to the q-axis component i of the current at the AC output end 24 of the impedance network B gvd , and then added to the output of the voltage outer loop q-axis controller 41 to obtain the given signal i of the current inner loop q-axis controller 43 gvq . The given signal i cq,ref . The given signal i cq,refand the q - axis component \(i\) of the inductor current in the impedance network A20 cq is subtracted to obtain the input signal of the q - axis controller 43 of the inner current loop. The d - axis component \(i\) of the inductor current in the impedance network A20 cd after being multiplied by \(\omega L\), is added to the q - axis component \(v\) of the voltage at the AC output terminal 24 of the impedance network B gvq and then added to the output of the d - axis controller 42 of the inner current loop to obtain the q - axis signal \(e\) of the inverse Park transformation 45 vq . Finally, the inverse Park transformation 45 converts the modulation signal in the dq coordinate system into the modulation signal \(e\) in the abc coordinate system v .

[0064] In the fourth step, through the pulse - width modulator A17, the modulation signal \(e\) v is converted into the switching signal of the switching device in the converter A2

[0065] The control system of the current - controlled converter 18 mainly includes the master - slave controller 64, the dq - axis current controller 30, the dq0 - axis current controller 31, and the pulse - width modulator A17, where:

[0066] In the first step, as Figure 16 shown, using the given control signal \(i'\) of the host computer 33 gref , the load current \(i\) load , and the current \(i\) at the AC output port 56 out , the given signal of the dq - axis current controller 30 or the dq0 - axis current controller 31 is calculated

[0067] In the second step, as Figure 12 or Figure 13 shown, using the control - mode signal given by the host computer 33, the dq - axis current controller 30 or the dq0 - axis current controller 31 is enabled

[0068] When using the controller shown in Figure 12 , the d - axis reference \(i\) gid,ref is subtracted from the d - axis component \(i\) of the current at the AC output terminal 24 of the impedance network B, and the obtained difference is the input signal of the first - current - loop d - axis controller 46. The q - axis component \(i\) of the current at the AC output terminal 24 of the impedance network B gid after being multiplied by \(\omega L\), is added to the d - axis component \(v\) of the voltage at the AC output terminal 24 of the impedance network B giq and then added to the output signal of the first - current - loop d - axis controller 46 to obtain the d - axis signal \(e\) of the dq - to - abc coordinate transformation 65 gid . The q - axis reference \(i\) id and the q - axis component \(i\) of the current at the AC output terminal 24 of the impedance network B giq,ref and the q - axis component \(i\) of the current at the AC output terminal 24 of the impedance network B giqTaking the difference, the obtained difference value is the input signal of the q-axis controller 47 of the first current loop. The d-axis component i of the current at the AC output terminal 24 of the impedance network B gid After being multiplied by ωL, it is added to the q-axis component v of the voltage at the AC output terminal 24 of the impedance network B giq Then added to the output signal of the q-axis controller 47 of the first current loop to obtain the q-axis signal e of the dq-to-abc coordinate transformation 65 iq . Finally, the dq-to-abc coordinate transformation 65 converts the modulation signal in the dq coordinate system into the modulation signal e in the abc coordinate system i .

[0069] When using the Figure 13 shown controller, the d-axis reference i gid,ref and the d-axis component i of the current at the AC output terminal 24 of the impedance network B gid Take the difference, and the obtained difference value is the input signal of the d-axis controller 48 of the second current loop. The q-axis component i of the current at the AC output terminal 24 of the impedance network B giq After being multiplied by ωL, it is added to the d-axis component v of the voltage at the AC output terminal 24 of the impedance network B gid Then added to the output signal of the d-axis controller 48 of the second current loop to obtain the d-axis signal e of the dq0-to-abc coordinate transformation 66 id . The q-axis reference i giq,ref and the q-axis component i of the current at the AC output terminal 24 of the impedance network B giq Take the difference, and the obtained difference value is the input signal of the q-axis controller 49 of the second current loop. The d-axis component i of the current at the AC output terminal 24 of the impedance network B gid After being multiplied by ωL, it is added to the q-axis component v of the voltage at the AC output terminal 24 of the impedance network B giq Then added to the output signal of the q-axis controller 49 of the second current loop to obtain the q-axis signal e of the dq0-to-abc coordinate transformation 66 iq . 0 and the q0-axis component i of the current at the AC output port 6 gi0 Take the difference, and the obtained difference value is the input signal of the 0-axis controller 50 of the current loop. The 0-axis component v of the voltage at the AC output terminal 24 of the impedance network B gi0 Is added to the output signal of the 0-axis controller 50 of the current loop to obtain the 0-axis signal e of the dq0-to-abc coordinate transformation 66 i0 . Finally, the dq0-to-abc coordinate transformation 66 converts the modulation signal in the dq0 coordinate system into the modulation signal e in the abc coordinate system i .

[0070] In the third step, through the pulse width modulator B32, the modulation signal e i Is converted into the switching signal of the switching device in the converter B19

[0071] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention. The above preferred features can be used in any combination without conflict.

Claims

1. A microgrid experimental teaching device, characterized in that It includes a hardware circuit and software, where: The hardware circuit includes a current-controlled inverter, a voltage-controlled inverter, a current-type inverter controller, a voltage-type inverter controller, a first DC power supply port, a second DC power supply port, and a host computer; The DC input terminal of the voltage-controlled inverter is connected to the first DC power supply port; the voltage-controlled inverter is used to reproduce the AC bus voltage in the simulated microgrid; The DC input terminal of the current-controlled inverter is connected to the second DC power supply port; the current-controlled inverter is used to reproduce the branch current in the simulated microgrid; the AC output port of the current-controlled inverter is connected to the AC output port of the voltage-controlled inverter; the AC output ports of the current-controlled inverter and the voltage-controlled inverter are externally connected to at least one of a load and a device AC output port to achieve function and system expansion; The voltage-type inverter controller is connected to the host computer and is used to accurately reproduce the control behavior and voltage characteristics of the microgrid system in the experimental teaching device; The current-type inverter controller is connected to the host computer and is used to accurately reproduce the control behavior and current characteristics of the microgrid system in the experimental teaching device; The host computer includes a graphical user interface and an interface for external communication; the interface is used to receive the sampling signal of the experimental teaching device and transmit signals to the voltage-type inverter controller and the current-type inverter controller respectively; the graphical user interface, as the software, includes a control parameter adjustment interface for inputting parameters, a control mode adjustment interface for selecting the enabled controller, and a device status display interface for observing the status of the experimental teaching device to achieve the control and measurement of the experimental teaching device; The voltage-type inverter controller includes: A secondary controller, which is used to adjust the amplitude setting and frequency setting in the droop control according to the voltage of the AC output port of the voltage-controlled inverter. The input of the secondary controller is the given signal of the host computer, and the output is the input of the droop controller; A droop controller, which is used to calculate the voltage reference value of the underlying controller according to the power of the AC output port of the voltage-controlled inverter. The input of the droop controller is the given signal of the host computer and the output of the secondary controller, and the output of the droop controller is the input of the first underlying controller; The first underlying controller includes a closed-loop voltage controller and an open-loop voltage controller, which are used to control the voltage of the AC output port of the voltage-controlled inverter. Only one controller works at the same time, and the other is turned off; the input of the first underlying controller is the voltage reference value, which comes from the droop controller or the given signal of the host computer, and the output signal of the first underlying controller is the modulation signal of Pulse Width Modulator A; Pulse Width Modulator A, the input of Pulse Width Modulator A is the output of the closed-loop voltage controller or the open-loop voltage controller, and the output of Pulse Width Modulator A is the switching signal of the voltage-controlled inverter; The current-type inverter controller includes: The master-slave controller is used to obtain the current reference value of the underlying controller based on the output current of the voltage-controlled converter, the load current, or the current of the AC output port of the device; the input of the master-slave controller is the output current of the voltage-controlled converter, the load current, or the current of the AC output port of the device, and the output of the master-slave controller is the input of the second underlying controller. The second underlying controller includes a dq-axis current controller and a dq0-axis current controller, and is used to control the current of the AC output port of the current-controlled converter. Only one controller works at the same time, and the other is turned off; the input of the second underlying controller is the current reference value, which comes from the given signal of the master-slave control or the upper computer, and the output signal of the second underlying controller is the modulation signal of the pulse width modulator B. The pulse width modulator B, the input of the pulse width modulator B is the output of the dq-axis current controller or the output of the dq0-axis current controller, and the output of the pulse width modulator B is the switching signal of the current-controlled converter. The voltage-controlled converter reproduces the AC bus voltage in the simulated microgrid by shaping the voltage amplitude, frequency, and phase of the AC output port of the voltage-controlled converter; the current-controlled converter reproduces the branch current in the simulated microgrid by shaping the current of the AC output port of the current-controlled converter.

2. The microgrid experimental teaching device according to claim 1, wherein, The voltage-controlled converter includes converter A, and converter A includes a DC power supply end of converter A and an AC output end of converter A; the filter impedance network of the voltage-controlled converter includes at least one of impedance network A, impedance network C, and impedance network E and at least includes impedance network A. Impedance network A includes an AC input end of impedance network A and an AC output end of impedance network A. Impedance network C includes a DC input end of impedance network C and a DC output end of impedance network C. Impedance network E includes an AC input end of impedance network E and an AC output end of impedance network E. The impedance network A is used to filter the voltage harmonics at the AC output end of converter A. The AC input end of the impedance network A is connected to the AC output end of converter A, and the AC output end of the impedance network A is connected to the AC input end of the impedance network E or directly connected to the AC output end of the voltage-controlled converter. The impedance network C is used to suppress the zero-sequence current in the DC loop. The DC power supply end of converter A is directly connected to the first DC power supply port or connected to the first DC power supply port through the impedance network C; when using the impedance network C, the DC input end of the impedance network C is connected to the first DC power supply port, and the DC output end of the impedance network C is connected to the DC power supply end of converter A. When using impedance network E, the impedance network E is used to suppress the zero-sequence current in the AC loop. The AC input end of the impedance network E is connected to the AC output end of the impedance network A, and the AC output end of the impedance network E is connected to the AC output end of the voltage-controlled converter.

3. The microgrid experimental teaching device according to claim 1, characterized in that, The current-controlled converter includes converter B, and converter B includes a DC power supply terminal of converter B and an AC output terminal of converter B; the filter impedance network of the current-controlled converter includes at least one of impedance network B, impedance network D, and impedance network F and at least includes impedance network B. Impedance network B includes an AC input terminal of impedance network B and an AC output terminal of impedance network B. Impedance network D includes a DC input terminal of impedance network D and a DC output terminal of impedance network D. Impedance network F includes an AC input terminal of impedance network F and an AC output terminal of impedance network F; Impedance network B is used to filter out current harmonics at the AC output terminal of converter B. The AC input terminal of impedance network B is connected to the AC output terminal of converter B, and the AC output terminal of impedance network B is connected to the AC input terminal of impedance network F or directly connected to the AC output terminal of the current-controlled converter; Impedance network D is used to suppress zero-sequence current in the DC loop. The DC power supply terminal of converter B is directly connected to the second DC power supply port or connected to the second DC power supply port through impedance network D; when using impedance network D, the DC input terminal of impedance network D is connected to the second DC power supply port, and the DC output terminal of impedance network D is connected to the DC power supply terminal of converter B; Impedance network F is used to suppress zero-sequence current in the AC loop. When using impedance network F, the AC input terminal of impedance network F is connected to the AC output terminal of impedance network B, and the AC output terminal of impedance network F is connected to the AC output terminal of the current-controlled converter.

4. The microgrid experimental teaching device according to claim 1, wherein The control mode adjustment interface includes control mode adjustment interface A and control mode adjustment interface B; Control mode adjustment interface A is used for enabling secondary control, droop control, closed-loop voltage control, and open-loop voltage control in the voltage-type converter controller, as well as turning on and off the voltage-controlled converter controller; Control mode adjustment interface B is used for enabling master-slave control, dq-axis current control, and dq0-axis current controller in the current-type converter controller, as well as turning on and off the current-controlled converter.

5. The microgrid experimental teaching device according to claim 1, characterized in that, The control parameter adjustment interface includes control parameter adjustment interface A and control parameter adjustment interface B; Control parameter adjustment interface A is used to input relevant parameters for all controls in the voltage-type converter controller; control parameter adjustment interface B is used to input relevant parameters for all controls in the current-type converter controller.

6. The microgrid experimental teaching device according to claim 1, wherein, The device status display interface is used to directly display the sampled voltage and current and the signals after signal processing, where the signal processing includes any one or several of amplitude calculation, frequency calculation, coordinate transformation, and power calculation; the device status display interface can flexibly switch the displayed signals.

7. The microgrid experimental teaching device according to any one of claims 1-6, characterized in that, The DC sides of multiple experimental teaching devices are connected to the DC power source through DC relays and DC diodes to achieve the common power supply for multiple experimental teaching devices; the AC sides of multiple experimental teaching devices are connected through AC circuit breakers to achieve flexible functions and system expansion.

8. The microgrid experimental teaching device according to claim 7, characterized in that, By selecting the controller of a single experimental teaching device, the reproduction of multiple controllers on the experimental teaching device is realized; by controlling the switch of the AC circuit breaker, the connection of multiple experimental teaching devices is realized, so as to realize the reproduction of the control structure in a more complex circuit.

Images