An apparatus for a microgrid and an operation method thereof

Abstract

The present invention discloses a device for a microgrid, which microgrid includes a DC bus connected to at least one DC power source, an AC bus connected to the main grid and providing power to the microgrid, and a DC / AC converter coupling the DC bus and the AC bus, wherein the DC / AC converter can be a unidirectional DC / AC inverter or a bidirectional DC / AC converter. The device includes a control system configured to control a plurality (at least one) of DC power converters, wherein each DC power converter is configured to couple a corresponding controllable DC load to the DC bus and control the power flowing from the DC bus to each of the plurality of controllable DC loads, thereby controlling each of the plurality of controllable DC loads to achieve its function and the control of the DC bus voltage.

Description

Technical Field

[0001] The present invention mainly relates to power systems in renewable energy systems, particularly solar photovoltaic power generation systems and wind power generation systems, as well as micro power networks or microgrids. Background Art

[0002] Recently, there has been an increasing interest in distributed and embedded renewable energy generation systems, such as wind power generation systems and solar photovoltaic power generation systems, built independently or in a building / community environment. Renewable energy resources such as wind energy and solar energy are usually intermittent, uncontrollable, and even unpredictable, thus having a significant impact on the distribution network. For distributed renewable energy generation systems, it is necessary to improve the power quality of the distribution network and reduce the capacity demand for connecting to the grid; for building / community renewable energy generation systems, it is necessary to increase the on-site or local consumption of renewable energy generation, so that the distribution network can accommodate more renewable energy generation. Summary of the Invention

[0003] On the one hand, the present invention describes a device for a microgrid, which includes a DC (direct current) bus connecting at least one DC power source, an AC bus connected to the main grid and providing power for the microgrid, and a DC / AC converter coupling the DC bus and the AC bus, wherein the DC / AC converter can be a unidirectional DC / AC inverter or a bidirectional DC / AC converter. The device includes a control system configured to control a plurality (at least one) of DC power converters, wherein each DC power converter is configured to couple its corresponding controllable DC load to the DC bus and control the power flowing from the DC bus to each of the plurality of controllable DC loads, so as to control each of the plurality of controllable DC loads to achieve its function and the control of the DC bus voltage.

[0004] The control system can be configured to balance the power flowing in and out of the DC bus by cooperatively controlling the power flowing to the at least two controllable DC loads through the corresponding coupled DC power converters, thereby controlling the voltage of the DC bus.

[0005] The controllable DC load can be a resistor, and the corresponding coupled DC power converter can be configured as a DC / DC converter.

[0006] The controllable DC load can be a DC motor, and the corresponding coupled DC power converter can be configured as a DC / DC converter.

[0007] The controllable DC load can be an induction motor, and the corresponding coupled DC power converter can be configured as a DC / AC frequency converter.

[0008] The controllable DC load can be the battery of an electric vehicle (EV), and the corresponding coupled DC power converter can be configured as a DC charger for an electric vehicle (EV).

[0009] The control system can be configured to balance the power flowing in and out of the DC bus and thus control the voltage of the DC bus by co - controlling the power flowing to the plurality of controllable DC loads and the power flowing through the DC / AC converter, wherein the power flowing to the plurality of controllable DC loads is controlled by the corresponding coupled DC power converter.

[0010] The device can further include at least one energy storage battery configured to be connected to the DC bus.

[0011] The control system can be configured to balance the power flowing in and out of the DC bus and thus control the voltage of the DC bus by co - controlling the power flowing in and out of the at least one energy storage battery and the power flowing to the plurality of controllable DC loads via the corresponding coupled DC power converter.

[0012] The control system can be configured to balance the power flowing in and out of the DC bus and thus control the voltage of the DC bus by co - controlling the power flowing in and out of the at least one energy storage battery, the power flowing to the plurality of controllable DC loads, and the power flowing through the DC / AC converter, wherein the power flowing to the plurality of controllable DC loads is controlled by the corresponding coupled DC power converter.

[0013] The device can further include at least one bi - directional energy storage charger configured to couple a specific energy storage device to the DC bus and control the charge and discharge of the specific energy storage device.

[0014] The control system can be configured to balance the power flowing in and out of the DC bus and thus control the voltage of the DC bus by co - controlling the power flowing in and out of the at least one energy storage device and the power flowing to the plurality of controllable DC loads; wherein the power flowing in and out of the at least one energy storage device is controlled by its coupled bi - directional energy storage charger, and the power flowing to the plurality of controllable DC loads is controlled by the corresponding coupled DC power converter.

[0015] The control system can be configured to balance the power flowing in and out of the DC bus and thus control the voltage of the DC bus by co - controlling the power flowing in and out of the at least one energy storage device, the power flowing to the plurality of controllable DC loads, and the power flowing through the DC / AC converter; wherein the power flowing in and out of the at least one energy storage device is controlled by its coupled bi - directional energy storage charger, and the power flowing to the plurality of controllable DC loads is controlled by the corresponding coupled DC power converter.

[0016] The control system can be configured to balance the power flowing in and out of the DC bus and thus control the voltage of the DC bus by coordinately controlling the power flowing in and out of the at least one energy storage battery, the power flowing in and out of the at least one energy storage device, the power flowing to the plurality of controllable DC loads, and the power flowing through the DC / AC converter; wherein, the power flowing in and out of the at least one energy storage device is controlled by the coupled bi-directional energy storage charger, and the power flowing to the plurality of controllable DC loads is controlled by the corresponding coupled DC power converter.

[0017] The at least one energy storage device can be configured as an energy storage battery, and the coupled bi-directional energy storage charger can be configured as a bi-directional DC / DC battery charger.

[0018] The at least one energy storage device can be configured as the battery of an electric vehicle (EV), and the coupled bi-directional energy storage charger can be configured as an intelligent bi-directional DC / DC EV charger or an intelligent electric vehicle charger.

[0019] The control system can be configured to balance the power flowing in and out of the DC bus and thus control the voltage of the DC bus by coordinately controlling the power flowing to a part (but not all) of the plurality of controllable DC loads.

[0020] The device can include a plurality (at least one) of DC power converters.

[0021] A second aspect of the present invention describes a method for controlling a microgrid, the microgrid including a DC bus connected to at least one DC power source, an AC bus connected to the main grid and providing power to the microgrid, and loads, wherein the loads include at least one controllable DC load and a DC / AC converter coupling the DC bus and the AC bus; the method includes controlling a plurality (at least one) of DC power converters, wherein each DC power converter is configured to couple a corresponding controllable DC load to the DC bus and control the power flowing from the DC bus to each controllable DC load so as to control each of the plurality of controllable DC loads to achieve its function and control of the voltage of the DC bus.

[0022] The microgrid can further include at least one energy storage device, and the method can include periodically updating the power demand prediction of the loads and the power generation prediction of the at least one DC power source, and periodically scheduling the power flow distribution flowing in and out of the DC bus required to meet a first-level control target set within a defined time window at least partially based on the power demand prediction of the loads and the power generation prediction of the at least one DC power source.

[0023] The method may include periodically updating the average power demand of the load monitored during the previous time period and the average power generation of the at least one DC power source monitored, and periodically determining the power flowing through the DC / AC converter and into and out of the at least one energy storage device (if any) required to meet a second-level control objective set, based at least in part on the power flow distribution scheduled into and out of the DC bus during the current time period and the average power demand of the load and the average power generation of the at least one DC power source during the previous time period.

[0024] Controlling the power flowing from the DC bus to each of the plurality of controllable DC loads may include continuously controlling the power flowing to each of the plurality of controllable DC loads based at least in part on the power flowing through the DC / AC converter determined during the current time period and the power flowing into and out of the at least one energy storage device (if any) determined, so as to balance the power flowing into and out of the DC bus and control the voltage of the DC bus, and continuously controlling the power flowing through the DC / AC converter and the power flowing into and out of the at least one energy storage device (if any) based at least in part on the power flowing through the DC / AC converter determined during the current time period and the power flowing into and out of the at least one energy storage device (if any) determined, as well as the instantaneous change in the power generation of the at least one DC power source and the instantaneous change in the power flowing to the plurality of controllable DC loads, so as to meet a third-level control objective set.

[0025] The microgrid may further include AC loads connected to the AC bus and / or uncontrollable DC loads directly or indirectly connected to the DC bus through corresponding DC power converters, wherein the average power demand of the monitored load may also include the power demand of the AC loads and / or uncontrollable DC loads, and the power flow distribution into and out of the DC bus may include the power flowing into and out of the at least one energy storage device, the power flowing to the plurality of controllable DC loads, and the power flowing through the DC / AC converter.

[0026] Updating the power demand prediction of the load and the power generation prediction of the at least one DC power source and scheduling the power flow distribution into and out of the DC bus may be performed for at least two consecutive time periods within a defined time window.

[0027] Updating the average power demand of the load and updating the average power generation of the at least one DC power source and determining the power flowing through the DC / AC converter and the power flowing into and out of the at least one energy storage device (if any) may be performed for at least two consecutive time periods within the current time period.

[0028] The first - level control target set may at least partially include maximizing the on - site consumption of power generated from the at least one DC power source through loads in the micro - grid, minimizing the reverse power flowing from the micro - grid to the main grid, maximizing the economic benefits of micro - grid end - users, and minimizing the power taken from the main grid to the micro - grid during high electricity price periods.

[0029] The second - level control target set may at least partially include stabilizing the power flowing through the DC / AC converter, stabilizing the power flowing in and out of the at least one energy storage device (if any), and stabilizing the power flowing to the controllable DC loads, which depends at least partially on the power controllability, power capacity, and function of each of the plurality of controllable DC loads.

[0030] The third - level control target set at least partially includes balancing the power flowing in and out of the DC bus and stabilizing the voltage of the DC bus.

[0031] The method may further include continuously controlling the power flowing to the plurality of controllable DC loads by following a priority order, which is determined at least partially based on the power controllability, power capacity, and function of each of the plurality of controllable DC loads.

[0032] The method may further include, when the power balance flowing in and out of the DC bus is at least partially interrupted by a relatively large DC load and / or DC power source and / or an energy storage device connected or disconnected from the DC bus each time, updating the determined power flowing through the DC / AC converter and / or the determined power flowing in and out of the at least one energy storage device (if any).

[0033] The device according to the first aspect may further include a control device configured to execute the method according to the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] To more comprehensively understand the device and method of the present invention, the following drawings are provided for reference, wherein:

[0035] Figure 1A An example of a directly - grid - connected solar photovoltaic power generation system in a building environment is shown;

[0036] Figure 1B An example of a directly - grid - connected solar photovoltaic power generation system in a distribution network is shown;

[0037] Figure 1C and 1D shows for Figure 1A and 1B An example of a renewable energy power generation system for the directly - grid - connected renewable energy power generation system shown;

[0038] Figure 2A and 2B shows an example of an apparatus for a microgrid with a DC / AC converter for direct grid connection;

[0039] Figure 2C shows an example of a renewable energy power generation system for Figure 2A and 2B the microgrid shown;

[0040] Figure 3A and 4A shows an example of a storage battery for Figure 2A and 2B the apparatus shown;

[0041] Figure 3B and 4B shows an example of a storage battery for an apparatus for a microgrid with a bidirectional DC / AC converter; and

[0042] Figures 5A to 5D shows examples of various control methods that can be executed by a control system of an apparatus for a microgrid. DETAILED DESCRIPTION

[0043] Throughout the specification and all the figures, the same reference numerals always denote the same elements.

[0044] Figure 1A Describes an example of a solar photovoltaic power generation system for direct grid connection in a building environment or an embedded solar photovoltaic power generation system in a building environment. The embedded solar photovoltaic power generation system includes a parallel string 7 of a plurality of solar photovoltaic modules, which is connected to an AC bus 2 through a central DC / AC converter 30 or a plurality of parallel DC / AC converters forming the central DC / AC converter. A plurality of AC loads in the building environment are connected to the AC bus 2 through a switchgear, and the AC bus 2 is connected to the main grid. After meeting the power demand of the AC loads in the building environment, the remaining power of the parallel string of the plurality of solar photovoltaic modules is output to the main grid through the DC / AC converter.

[0045] Figure 1B Describes an example of a distributed solar photovoltaic power generation system directly connected to a distribution grid. The distributed solar photovoltaic power generation system includes a parallel string 7 of a plurality of solar photovoltaic modules, which is connected to an AC bus 2 through a central DC / AC converter 30. The AC bus 2 is connected to a distribution grid powered by the main grid. If the voltage of the distribution grid is higher than the voltage of the AC bus 2, a transformer is generally configured to couple the AC bus 2 and the distribution grid. A plurality of AC load centers (not shown) can be directly or indirectly connected to the distribution grid through a transformer. The power from the string of the solar photovoltaic modules is directly output to the distribution grid through the central DC / AC converter.

[0046] Figure 1C describes a second type of solar photovoltaic power generation system, which includes a parallel string 7 of multiple solar photovoltaic modules, and each string of solar photovoltaic modules is connected to the AC bus 2 through a string DC / AC converter 73. The solar photovoltaic power generation system can replace Figure 1A and 1B the solar photovoltaic power generation systems shown.

[0047] Figure 1D describes an example of a wind power generation system, which includes multiple wind turbines 9, and each wind turbine 9 is connected to the AC bus 2 through a power electronic converter 10. The wind power generation system can replace Figure 1A and Figure 1B the solar photovoltaic power generation systems shown. This grid connection method can be applied to most wind turbines; however, for wind turbines equipped with induction generators, the power electronic converter can be omitted.

[0048] For Figures 1A to 1D each renewable energy power generation system shown, all grid connection devices, including the DC / AC converter 30 for the solar photovoltaic module string 7 (as shown in Figure 1A , 1B and 1C) and the power electronic converter 10 for the wind turbine 9 (as shown in Figure 1D ), the cables for the AC bus 2 and the transformer coupling the AC bus 2 and the distribution network (as shown in Figure 1B ), usually have the same power capacity as the renewable energy power generation system.

[0049] For Figure 1A and 1B the grid-connected renewable energy power generation systems shown, whether for the building environment (as shown in Figure 1A ), or directly connected to the distribution network (as shown in Figure 1B ), the common problems they face include: 1) The fluctuating power from the renewable energy generators (such as wind turbines and / or photovoltaic modules) is directly transmitted to the AC bus 2, which may have a significant impact on the power quality of the main grid (as shown in Figure 1A ) or the distribution network (as shown in Figure 1B ); 2) The power generation of the renewable energy generators may not match the AC load in the building environment (as shown in Figure 1A ) or the AC load center connected to the distribution network (as shown in Figure 1Bthe power demand shown), and such mismatch requires more backup power stations based on traditional fuels, especially natural gas and diesel; 3) The main grid and distribution grid are generally designed for one-way power flow, and the reverse power flow capacity may be limited; and 4) The grid-connected equipment of direct grid-connected renewable energy power generation systems generally has a low power capacity factor. For example, the power capacity factor of a solar photovoltaic power generation system is about 8% - 12%, and that of a wind power generation system is about 25% - 35%.

[0050] The present invention will hereinafter introduce equipment for a microgrid, which enables end-users, grid operators, and the public of the microgrid to benefit more from Figures 1A to 1D the direct grid-connected renewable energy power generation system shown, while avoiding the above problems.

[0051] Figure 2A and 2B An example of the device 100 for a microgrid is described.

[0052] As Figure 2A shown, the microgrid includes a DC bus 1, at least one DC power source 21, which is configured to be connected to the DC bus 1 and supply power from the at least one DC power source 21 to the DC bus 1, an AC bus 2 configured to be connected to the main grid 20, a DC / AC converter 3 configured to couple the DC bus 1 and the AC bus 2 and supply power from the DC bus 1 to the AC bus 2, and the device 100.

[0053] As Figure 2B shown, the microgrid may include (at least one) AC load 9 connected to the AC bus 2 through a switchgear 91.

[0054] It should be noted that many different types of DC power sources 21 can be configured to be connected to Figure 2A and 2B the DC bus 1 of the microgrid shown, especially renewable energy DC power sources. A renewable energy DC power source can be, for example, an array of solar photovoltaic modules, a wind turbine or multiple wind turbines, a solar photovoltaic and wind hybrid power generation system, but not limited thereto.

[0055] It should be noted that in Figure 2A and 2B the microgrid shown, there are many different ways to connect a solar photovoltaic power generation system or a wind power generation system or a solar photovoltaic and wind hybrid power generation system to the DC bus 1. For example, through the method shown in Figure 2C shown, but not limited thereto.

[0056] As Figure 2C shown, the solar photovoltaic module string 7 can be configured to be connected to the DC bus 1 through an MPPT (maximum power point tracking) DC / DC converter 8.

[0057] As Figure 2C shown, a wind turbine having a synchronous generator 9 can be configured to be connected to a DC bus 1 through an AC / DC power converter 11, which is often configured with an MPPT control algorithm.

[0058] As Figure 2A and 2B shown, the DC / AC converter 3 can be configured to control the power flow from the DC bus 1 to the AC bus 2.

[0059] As Figure 2A and 2B shown, a microgrid may include (at least one) controllable DC load. The controllable DC load may have different meanings in different contexts. However, in the present invention, the controllable DC load refers to the controllability of the power input to the DC load. The controllability of the power input to the DC load refers to the time (i.e., when) the power source is input to the DC load and / or the magnitude (i.e., value) of the power input to the DC load. While the function of the DC load is realized, the power input to the DC load can be controllable in terms of time (i.e., when to supply power) and value (i.e., power magnitude).

[0060] The controllable DC load can be controlled to meet the management purpose of power demand response while realizing the function of the controllable DC load. In other words, the power flow to the controllable DC load can be controlled in response to, for example, the availability of at least one DC power source or the electricity price from the main grid (i.e., the price per degree of electricity) (as Figure 2A and 2B shown), while the function of the controllable DC load is realized or not affected or not significantly affected (i.e., in the case where such an impact is allowed), but not limited thereto.

[0061] There are many types of controllable DC loads. For example, a resistor or a DC motor or an AC motor, and even the battery of an electric vehicle can be a controllable DC load, but not limited thereto.

[0062] A resistor can be a DC load and be powered by a DC power supply. The resistor can be configured as an electric heater or an immersion heater for heating water, for heating, or for other heating purposes. As a heater, while the resistor performs its function, i.e., heating, it generally has excellent flexibility and controllability in terms of electric power input. For example, in a building environment, an electric heater or an immersion heater used for heating or water heating usually has flexibility in terms of the power supply time (i.e., when) and the power supply power (i.e., the magnitude of the power) for the electric heater or the immersion electric heater, and the power is proportional to V2, where V is the voltage applied across the resistor. In other words, as long as the required total heat can be provided over a period of time, the voltage applied across the electric heater or the immersion heater in the building environment can vary between 0 and its nominal voltage. Therefore, the voltage applied across the resistor can be controlled by a DC / DC converter while the function of the resistor is achieved, unaffected, or not significantly affected.

[0063] A DC motor can be a DC load and be powered by a DC power supply. The DC motor has strong controllability in terms of speed (i.e., rotational speed), and thus is widely used as a driver for electrical appliances and machines in a building environment. The speed control of the DC motor is achieved by controlling the voltage applied across the DC motor, i.e., the power. In some applications, on the premise that its function is satisfied, the DC motor can have flexibility or controllability in terms of the power supply time (i.e., when to supply power). In other applications, on the premise that its function is satisfied, the DC motor generally can have flexibility or controllability in terms of the input power supply power (i.e., the magnitude of the power). For example, the compressor of a heat pump can be driven by a DC motor. By changing the voltage applied across the DC motor, the speed of the DC motor and the compressor changes accordingly. In addition, since the power is proportional to the speed, the power input to the DC motor and the heat pump compressor also changes accordingly. Heat pumps are widely used for heating, cooling, and refrigeration. Heat pumps generally have strong flexibility or controllability in terms of the power supply time (i.e., when to supply power) and the power supply power (i.e., the magnitude of the power). Therefore, the voltage applied across the DC motor can be controlled between a pair of low and high values by a DC / DC converter while the function of the DC motor (i.e., the functions of the compressor and the heat pump) is achieved, unaffected, or not significantly affected. Fans and pumps in air-conditioning and ventilation systems can also be driven by DC motors, and the DC motors can be powered by a DC power supply through a DC / DC converter and have flexibility or controllability in terms of the power supply time (i.e., when) and the power supply power (i.e., the magnitude of the power) to the DC motors.

[0064] An induction motor (i.e., an AC motor) can be a DC load powered by a DC power supply through a DC / AC inverter. Induction motors are widely used as drives for electrical appliances and machines in the building environment, mostly driven by frequency converters. A frequency converter is a back-to-back power converter that includes an AC / DC converter and a DC / AC inverter. The speed control of an induction motor is achieved by controlling the frequency of the AC power supply applied to the induction motor, and the power input to the induction motor is generally proportional to the speed of the induction motor. Therefore, the power of the AC power supply applied to the induction motor is also proportional to its frequency. This is the case in the vast majority of applications when the load torque applied to the rotor shaft of the induction motor is constant. In some applications, subject to the satisfaction of its functions, the induction motor has great flexibility or controllability in terms of the power supply time (i.e., when to supply power) and the power supply power (i.e., the magnitude of the power). For example, the compressor of a heat pump can be driven by an induction motor, and the induction motor can be driven by an AC power supply (i.e., the main power grid) through a back-to-back power converter, where the back-to-back power converter includes a grid-side AC / DC converter and a machine-side DC / AC inverter used as a frequency converter. When there is a DC power supply, the grid-side AC / DC converter can be omitted, and the DC / AC inverter can be used as a frequency converter to supply power to the induction motor. In other words, the induction motor can be a DC load and be powered by a DC power supply through a DC / AC frequency converter. By changing the frequency of the alternating current output by the DC / AC frequency converter, the speed and input power of the induction motor can be controlled. Therefore, for the heat pump compressor driven by an induction motor, the frequency and power applied to the induction motor can be controlled between a pair of low and high values through the DC / AC frequency converter, while the functions of the AC motor (i.e., the functions of the compressor and the heat pump) are achieved or not affected or not significantly affected. Similar to the analysis of DC motors, the fans and pumps in air-conditioning and ventilation systems can also be driven by induction motors, and the induction motors can be powered by a DC power supply through a DC / AC frequency converter and have flexibility or controllability in terms of the power supply time (i.e., when) and the power supply power (i.e., the magnitude of the power) to the induction motor.

[0065] The battery of an electric vehicle (EV) can be charged by a DC power source through an EV DC charger. In other words, when the EV is connected to an EV DC charger powered by a DC power source for charging, the battery of the EV can be configured as a DC load. By industry convention, the charging power (i.e., charging current) of an EV battery is controllable and variable, including fast charging with a large charging power (i.e., large charging current) or slow charging with a low charging power (i.e., small charging current). The charging of an EV battery generally has excellent flexibility and controllability in terms of charging power (i.e., charging current), and can complete the charging of a specific charge amount (in kWh) of the EV battery within a defined time. Therefore, by controlling the charging current of the EV battery through the EV DC charger, the EV battery can be configured as a controllable DC load. In other words, as long as a specific charge amount of the EV battery can be completed within the defined time, the charging power (i.e., charging current) flowing into the EV battery can vary between 0 and the nominal value of the EV DC charger.

[0066] As Figure 2A and 2B shown, device 100 includes a plurality (at least one) of DC power converters and a control system. Among them, each of the plurality of DC power converters is configured to couple its corresponding controllable DC load to DC bus 1, and the control system is configured to control the power flowing from DC bus 1 to each of the plurality of controllable DC loads through the corresponding coupled DC power converter to achieve its function.

[0067] A resistor can be a controllable DC load, which can be configured to be connected to DC bus 1 through a specific DC power converter. The specific DC power converter can be configured as a DC / DC converter, and this DC / DC converter can be configured to control the power flowing from DC bus 1 to the controllable DC load (i.e., the resistor) to achieve its function (i.e., as an electric heater).

[0068] A DC motor can be a controllable DC load, which can be configured to be connected to DC bus 1 through a specific DC power converter. The specific DC power converter can be configured as a DC / DC converter, and this DC / DC converter can be configured to control the power flowing from DC bus 1 to the controllable DC load (i.e., the DC motor) to achieve its function (i.e., as a variable speed drive).

[0069] An AC motor (i.e., an induction motor) can be a controllable DC load, which can be configured to be connected to DC bus 1 through a specific DC power converter. The specific DC power converter can be configured as a DC / AC frequency converter, and this DC / AC frequency converter can be configured to control the power flowing from DC bus 1 to the controllable DC load (i.e., the AC motor) to achieve its function (i.e., as a variable speed drive).

[0070] An electric vehicle (EV) battery can be a controllable DC load, which can be configured to be connected to DC bus 1 through a specific DC power converter. The specific DC power converter can be configured as a DC / DC charging converter (i.e., an EV DC charger), and the EV DC charger can be configured to control the power flowing from DC bus 1 to the controllable DC load (i.e., the EV battery) to achieve its function (i.e., charge the EV battery).

[0071] As Figure 2A and 2B shown, the control system is configured to control each of the plurality of DC power converters. The control system is configured to control each of the plurality of DC power converters to control the voltage of DC bus 1 by the method that: if the corresponding controllable DC load has sufficient power capacity, the power flowing from DC bus 1 to its corresponding controllable DC load is controlled to balance the power flowing in and out of DC bus 1.

[0072] For example, Figure 2A the microgrid shown can be used in a residence, and there may be only one immersion heater as a controllable DC load in the residence, which is connected to DC bus 1 through a DC / DC converter as the corresponding DC power converter. The DC power source can be one or two strings of solar photovoltaic modules, but is not limited thereto. The immersion heater has a fixed (i.e., defined) rated power (i.e., power capacity), and the maximum power that can be obtained from the solar photovoltaic modules may be higher than the fluctuation range of the power output of the solar photovoltaic modules during a certain period. In this case, the immersion heater can be configured to control the power flowing from DC bus 1 to the immersion heater, so that the power flowing out of the solar photovoltaic modules is balanced by flowing to the immersion heater and the power scheduled to flow to the AC bus through the DC / AC converter 3 (described in the control method), thereby controlling the voltage of DC bus 1.

[0073] As Figure 2A and 2B shown, a specific controllable DC load and its coupled DC power converter may not have sufficient controllable power capacity to balance the power flowing in and out of DC bus 1 and control the voltage of DC bus 1. However, some or all of the plurality of controllable DC loads may have sufficient power capacity to achieve this, and the control system can be configured to control the power flowing to some or all of the controllable DC loads through the corresponding coupled DC power converters in cooperation to balance the power flowing in and out of DC bus 1, thereby controlling the voltage of DC bus 1.

[0074] For example, Figure 2AThe microgrid shown can be used in a building, and there may be an immersion heater and an electric vehicle EV in the building, which are connected to the DC bus 1 as two controllable DC loads through a DC / DC converter (for the immersion heater) and an electric vehicle DC charger (for the electric vehicle battery) as the corresponding DC power converters. The DC power supply 78 can be multiple strings of solar photovoltaic modules 7 (as Figure 2C shown), but is not limited thereto. The immersion heater may not have sufficient controllable power capacity to balance the power fluctuations of multiple strings of solar photovoltaic modules 7, but together with the electric vehicle battery, the two controllable DC loads may have sufficient power capacity to do so. In this case, the priority order determined based on the power controllability, power capacity, and function of each of the two controllable DC loads can be used to control the order and / or mode of the power flowing to the immersion heater and the electric vehicle battery. Therefore, the control system can be configured to balance the power flowing in and out of the DC bus 1 by coordinately controlling the power flowing to the immersion heater via the DC / DC converter and the power flowing to the electric vehicle battery through the electric vehicle DC charger, thereby controlling the voltage of the DC bus 1.

[0075] It should be noted that any appropriate priority control order and / or mode can be used to coordinately control the power flowing to some or all of the controllable DC loads through the corresponding coupled DC power converters.

[0076] It should be noted that in Figure 2A and 2B the microgrid shown, a low-voltage DC network (not shown) with a low-voltage battery and low-voltage DC loads connected thereto can be regarded as a controllable DC load and is configured to be connected to the DC bus 1 (not shown) through a DC power converter (i.e., a DC / DC converter). The low-voltage DC loads can be, for example, computers, laptops, and multimedia devices, but are not limited thereto. The low-voltage DC loads can be configured to be directly or indirectly connected to the low-voltage DC network through a low-voltage DC power converter.

[0077] As Figure 2A and 2BAs shown, multiple controllable DC loads and their corresponding coupled DC power converters may not have sufficient controllable power capacity to balance the power flowing in and out of DC bus 1 and control the voltage of DC bus 1. The DC / AC converter 3 can be configured to receive an external control signal to control the power flowing from DC bus 1 to AC bus 2. For example, the DC / AC converter 3 can be configured to receive a control signal from a control system (i.e., a power signal from DC bus 1 to AC bus 2), but is not limited thereto. Therefore, the control system can be configured to control the voltage of DC bus 1 by coordinately controlling the power flowing to the multiple controllable DC loads through the corresponding coupled DC power converters and the power flowing from DC bus 1 to AC bus 2 by controlling the DC / AC converter 3 to balance the power flowing in and out of DC bus 1.

[0078] It should be noted that when the DC / AC converter 3 participates in balancing the power flowing in and out of DC bus 1, it will cause power fluctuations in the power output from the microgrid to the main grid 20. In other words, the power flowing from DC bus 1 to AC bus 2 will fluctuate and is no longer under control. In this case, an energy storage battery can be introduced to buffer the power fluctuations to the main grid 20.

[0079] As Figure 3A and 3B shown, the device 100 can further include at least one energy storage battery, which can be configured to be directly connected to DC bus 1.

[0080] As Figure 3A shown, the DC / AC converter 3 in the microgrid is a DC / AC inverter (i.e., the power flow is only from DC bus 1 to AC bus 2). Charging of the energy storage battery will only occur when the at least one DC power source is generating electricity and the voltage of DC bus 1 is higher than the open-circuit voltage of the energy storage battery 51. When the voltage of DC bus 1 is lower than the open-circuit voltage of the energy storage battery 51, the energy storage battery will discharge.

[0081] As Figure 3B shown, the microgrid can include a bidirectional DC / AC converter, which is configured to operate in an inverter mode (i.e., conversion from DC power source to AC power source) and a rectifier mode (i.e., conversion from AC power source to DC power source). When the voltage of DC bus 1 is higher than the open-circuit voltage of the energy storage battery, charging of the energy storage battery will occur, and the power source required for charging can come from the at least one DC power source and / or from the main grid 20 through the bidirectional DC / AC converter (when it operates as a rectifier). When the voltage of DC bus 1 is lower than the open-circuit voltage of the energy storage battery, the energy storage battery will discharge.

[0082] As Figure 4A and 4BAs shown, the device 100 may further include at least one bidirectional DC / DC battery charger, which may be configured as a bidirectional DC / DC converter to couple the energy storage battery and the DC bus 1 together and control the charging and discharging of the energy storage battery 51. The control system may be configured to control at least one bidirectional DC / DC battery charger.

[0083] As Figure 4A shown, the DC / AC converter 3 in the microgrid may be a DC / AC inverter, which is similar to Figure 3A the DC / AC converter 3 shown.

[0084] As Figure 4B shown, the microgrid may include a bidirectional DC / AC converter 31, which is similar to Figure 3B the bidirectional DC / AC converter 31 shown.

[0085] Using the bidirectional DC / AC converter 31 (as Figure 3B and 4B shown), the control system 10 may be configured to control the power flowing from the AC bus 2 to the DC bus 1 to charge the at least one energy storage battery 51 and meet the power requirements of a plurality of controllable DC loads and other DC loads connected to the DC bus 1.

[0086] It should be noted that Figure 3B and 4B the bidirectional DC / AC converter 31 shown may be implemented by a DC / AC inverter and an AC / DC converter, and the DC / AC inverter and the AC / DC converter may be interlocked by a pair of interlock switches (not shown).

[0087] As Figure 3A 、 3B 、4A and 4B shown, by controlling the charging and discharging current, the controllability of the charging and discharging of the at least one energy storage battery 51 is excellent. The at least one energy storage battery 51 may be configured to charge (i.e., the current flows from the DC bus 1 to the energy storage battery 51) or discharge (i.e., the current flows from the energy storage battery 51 to the DC bus 1), and the charging and discharging of the at least one energy storage battery 51 may be configured to balance the power flowing in and out of the DC bus 1 and control the voltage of the DC bus 1. The at least one bidirectional DC / DC battery charger 5 may be configured to control the charging and discharging of the energy storage battery 51 (as Figure 4A and 4B shown), or the charging and discharging of the at least one energy storage battery 51 may be controlled by controlling the voltage of the DC bus 1 (as Figure 3A and 3BAs shown). In other words, the control system 10 can be configured to balance the power flowing in and out of the DC bus 1 by controlling the power flowing in and out of the at least one energy storage battery 51, thereby controlling the voltage of the DC bus 1.

[0088] The control system 10 can be configured to cooperate in controlling the power flowing to the plurality of controllable DC loads by controlling the corresponding coupled DC power converters 4 to balance the power flowing in and out of the DC bus 1, thereby controlling the voltage of the DC bus 1, as described above with reference to Figure 2A and 2B described.

[0089] As Figure 3A , 3B , 4A and 4B show, using at least one energy storage battery 51, the cooperative control and balancing of the power flowing in and out of the DC bus 1 may further include the power flowing in and out of the at least one energy storage battery 51. In other words, the control system 10 can be configured to cooperate in controlling the power flowing in and out of the at least one energy storage battery 51 and controlling the power flowing in and out of the plurality of controllable DC loads through the corresponding coupled DC power converters 4 to balance the power flowing in and out of the DC bus 1, thereby controlling the voltage of the DC bus 1.

[0090] It should be noted that the control system 10 can be configured to balance the power flowing in and out of the DC bus 1 by controlling the at least one energy storage battery 51 to achieve control of the voltage of the DC bus 1. However, when there are multiple controllable DC loads available, the capacity of the at least one energy storage battery 51 can be greatly reduced. In other words, the cost of the device 100 and the microgrid can be significantly reduced.

[0091] As Figure 3A and 3B shown, when at least one energy storage battery 51 is directly connected to the DC bus 1, controlling the power flowing in and out of the at least one energy storage battery 51 is achieved by controlling the voltage of the DC bus 1. As Figure 4A and 4B shown, when the at least one energy storage battery 51 is connected to the DC bus 1 through a specific bidirectional DC / DC battery charger 5, controlling the power flowing in and out of the at least one energy storage battery 51 is achieved by controlling the specific bidirectional DC / DC battery charger 5.

[0092] It should be noted that directly connecting at least one energy storage battery 51 to the DC bus 1 may be a very economical solution because it saves the cost of the specific bidirectional DC / DC battery charger 5 and may have a very high power conversion efficiency for the at least one energy storage battery 51 because there is no power conversion loss caused by the specific bidirectional DC / DC battery charger 5.

[0093] It should be noted that forFigure 3A and 3B the control system 10 of the device 100 shown may be more complex than that for Figure 4A and 4B the control system 100 of the device 100 shown.

[0094] The control system 10 may be configured to balance the power flowing in and out of the DC bus 1 by co - controlling the power flowing to the plurality of controllable DC loads (by controlling the corresponding coupled DC power converters 4) and the power flowing from the DC bus 1 to the AC bus 2 through the DC / AC converter 3, thereby controlling the voltage of the DC bus 1, as described above with reference to Figure 2A and 2B stated.

[0095] As Figure 3A and 4A shown, using at least one energy storage battery 51, co - controlling and balancing the power flowing in and out of the DC bus 1 may further include the power flowing from the DC / AC converter 3 to the AC bus 2.

[0096] As Figure 3B and 4B shown, using at least one energy storage battery 51, co - controlling and balancing the power flowing in and out of the DC bus 1 may further include the power flowing in and out of the AC bus 2 through the bidirectional DC / AC converter 31.

[0097] As Figure 3A , 3B , 4A and 4B shown, using at least one energy storage battery 51, the control system 10 may be configured to balance the power flowing in and out of the DC bus 1 by co - controlling the power flowing in and out of the at least one energy storage battery 51, the power flowing to the plurality of controllable DC loads via the corresponding coupled DC power converters 4, and the power flowing to the AC bus 2 via the DC / AC converter 3 (as Figure 3A and 4A shown) or the power flowing in and out of the AC bus 2 via the bidirectional DC / AC converter 31 (as Figure 3B and 4B shown), thereby controlling the voltage of the DC bus 1.

[0098] It should be noted that in some applications, the device 100 may have to limit the capacity of the at least one energy storage battery 51 to reduce system costs. In this case, the DC / AC converter 3 may be configured to participate in balancing the power flowing in and out of the DC bus 1, even if it will cause fluctuations in the power output from the micro - grid to the main grid 20. It is worth mentioning that the fluctuations in the power output from the micro - grid to the main grid 20 are generally smaller than those of a directly grid - connected solar photovoltaic power generation system outputting to the main grid 20 (as Figure 1A and 1Bis much better controlled as shown.

[0099] The battery of an electric vehicle (EV) can be configured as a plug-and-play energy storage battery to Figure 2A 、 2B support the microgrids shown in 3A, 3B, 4A, and 4B. Figure 4A and 4B At least one energy storage battery 51 shown in and can be replaced by an EV battery, and the at least one bidirectional DC / DC battery charger 5 can be configured as a smart bidirectional DC / DC EV charger (i.e., a smart EV charger). For example, the smart EV charger (5) and the EV battery (51) can be configured to provide frequency support to the main power grid 20, provide voltage support to the DC bus 1 (i.e., participate in balancing the power flowing in and out of the DC bus 1 by controlling the power flowing in and out of the EV battery), and support the main power grid 20 (i.e., supply power to the main power grid 20 by discharging the EV battery through the DC / AC converter 3), but not limited to this.

[0100] It should be noted that Figure 4A and 4B At least one energy storage battery 51 shown in and can be replaced by any other type of energy storage device, and the coupled bidirectional DC / DC battery charger 5 can be replaced by a corresponding bidirectional energy storage charger or charging controller of another type. For example, a flywheel and its associated power converter can be configured to replace the at least one energy storage battery 51 and the coupled bidirectional DC / DC battery charger 5, and pumped storage and its associated power converter can be configured to replace the at least one energy storage battery 51 and the coupled bidirectional DC / DC battery charger 5, but not limited to this.

[0101] In a building environment, there may be some electrical loads that can be powered by a DC power supply but may be uncontrollable in terms of power supply (i.e., the time and power of power supply), such as computers without embedded batteries, lights, multimedia and entertainment devices without embedded batteries, but not limited to this.

[0102] It should be noted that in the microgrids shown in Figure 2A 、 2B 、3A, 3B, 4A, and 4B, uncontrollable DC loads (not shown) can be configured to be directly or indirectly connected to the DC bus 1 through a specific DC power converter (not shown); and the uncontrollable DC loads can be configured to be equipped with an on / off type switch. For example, a light or a group of lights connected in series and / or parallel can be regarded as an uncontrollable DC load and can be configured to be directly or indirectly connected to the DC bus 1 through a specific DC / DC converter, and a computer can be regarded as an uncontrollable DC load and can be configured to be connected to the DC bus 1 through a specific DC / DC converter, but not limited to this.

[0103] The following will refer to Figures 5A to 5E in detail the various operations performed by the control system 10 of the device 100 of the microgrid shown in Figure 2A , 2B , 3A, 3B, 4A, and 4B.

[0104] As Figure 5A shown, the control system 10 is configured to update the power demand prediction of the loads in the microgrid (S5.1), where the loads include the AC loads 9 connected to the AC bus 2 and the DC loads connected to the DC bus 1, and the DC loads include all controllable DC loads and all uncontrollable DC loads connected to the DC bus 1. The control system 10 is configured to update the power generation prediction of the at least one DC power source 21 (S5.2), and the DC power source 21 may be, for example, a string of solar photovoltaic modules 7 coupled to an MPPT DC / DC converter 212 (as Figure 2C shown) and / or a wind turbine 9 coupled to an AC / DC power converter 11 (as Figure 2C shown), but not limited thereto. Any suitable method for the power demand prediction of the loads (S5.1) and the power generation prediction of the at least one DC power source 21 (S5.2) can be adopted.

[0105] The control system 10 may be further configured to schedule the power flow distribution in and out of the DC bus 1 (S5.3), including the power in and out of the at least one energy storage device 51 (as Figure 3A , 3B , 4A, and 4B shown), the power flowing to the plurality of controllable DC loads (as Figure 2A , 2B , 3A, 3B, 4A, and 4B shown), and the power flowing through the DC / AC converter 3 (as Figure 2A , 2B , 3A, and 4A shown) or the bidirectional DC / AC converter 31 (as Figure 3B and 4B shown). The power flow distribution scheduling module (S5.3) is at least partially based on the power generation prediction (S5.2) from the at least one DC power source 21 and the power demand prediction (S5.1) from the loads.

[0106] Figure 5A The functions of the three modules (S5.1, S5.2, and S5.3) shown in Figure 5E are to periodically repeat at least two consecutive time periods T6.2 within a defined time window, such as 24 hours T6.1, for example, one hour or two hours or three hours, but not limited thereto, as

[0107] The scheduling of the power flow distribution (S5.3) can be further based on a single objective or multiple objectives. For example, the objectives of scheduling the power flow distribution (S5.3) can include, for example, maximizing the in-situ consumption of power generated from the at least one DC power source 21 through the loads of the microgrid; minimizing the reverse power flowing from the microgrid to the main grid 20; maximizing the economic benefits of the microgrid end-users; and minimizing the power taken from the main grid 20 to the microgrid during high (peak) electricity price periods, but not limited thereto. The power flow distribution in and out of the DC bus 1 is scheduled based on the following information, for example, the main grid electricity price, time-of-use electricity price, feed-in tariff and grid-connected electricity price of renewable energy, the operating cost and technical information of the at least one energy storage device 51, but not limited thereto. Any suitable scheduling optimization algorithm for scheduling the power flow distribution (S5.3) can be adopted.

[0108] Figure 5A The control method shown also helps to extend the life of the at least one energy storage battery 51 through the scheduling measures set in the power flow distribution scheduling module (S5.3), and these scheduling measures may be, for example, slowly charging and discharging the at least one energy storage battery 51 and avoiding overcharging and over-discharging of the at least one energy storage device 51 (i.e., the energy storage battery), but not limited thereto.

[0109] As Figure 5B shown, during the current time period T6.3 (as Figure 5E shown), the control system 10 is configured to update the monitored average power demand of the load (S5.4) and the monitored average power generation of the at least one DC power source 21 (S5.5), where the load includes the AC load 9 connected to the AC bus 2 and all DC loads connected to the DC bus 1.

[0110] The control system 10 is further configured to periodically determine the power in and out of the at least one energy storage device 51 and the power flowing through the DC / AC converter 3 (as Figure 5E shown), for example but not limited to every 5 minutes or every 10 minutes, within at least two consecutive time periods T6.3 of the current time period T6.2 (as Figure 2A 、 2B 、3A and 4A shown) or the power flowing through the bidirectional DC / AC converter 31 (as Figure 3B and 4B shown) (S5.6). The power flow determination module (S5.6) is at least partially based on the scheduled power flow distribution (S5.3) within the current time period T6.2 and the monitored average power demand of the load (S5.4) and the monitored average power generation prediction of the at least one DC power source 21 (S5.5) in the previous time period T6.3. Figure 5BThe functions of the three modules shown (S5.4, S5.5, and S5.6) are repeatedly executed in at least two consecutive time periods of the current time cycle T6.2.

[0111] Determining the power flow (S5.6) can be further based on a single objective or multiple objectives. The objectives of determining the power flow (S5.6) can include, for example, stabilizing the power flowing in and out of the at least one energy storage battery 51, as stabilizing the power flowing in and out of the at least one energy storage battery 51 helps extend the life of the at least one energy storage battery 51; stabilizing the power flowing through the DC / AC converter 3 (as shown in Figure 2A , 2B , 3A, and 4A) or the bidirectional DC / AC converter 31 (as shown in Figure 3B and 4B ) to provide a high-quality power flow from the DC bus 1 to the AC bus 2 and the main power grid 20; and stabilizing the power flowing to the plurality of controllable DC loads at least partially based on the power controllability, power capacity, and function of each of the plurality of controllable DC loads.

[0112] As shown in Figure 5C , when at least one controllable DC load is connected to the DC bus 1 (S5.7) and the controllable DC load has a power demand (S5.8), the control system 10 is configured to, at least partially based on the power flowing in and out of the at least one energy storage device 51 determined in the current time period T6.3 and the power flowing through the DC / AC converter 3 (as shown in Figure 2A , 2B , 3A, and 4A) or the bidirectional DC / AC converter 31 (as shown in Figure 3B and 4B ) determined in (S5.6), continuously control the power flowing to the plurality of controllable DC loads (S5.9) to balance the power flowing in and out of the DC bus 1 in the microgrid and control the voltage of the DC bus 1.

[0113] When at least two controllable DC loads are available for continuous power flow control purposes, the control system 10 can be configured to call the above-described (refer to Figure 5CA continuous power flow control module (S5.9) as shown controls the power flowing to the multiple controllable DC loads, and the priority order depends at least in part on the power capacity and controllability (but not limited to this) of each of the multiple controllable DC loads. For example, an immersion heater for hot water storage usually has excellent controllability. Therefore, when an immersion heater can be used as a controllable DC load, it can be called with the highest priority, followed by other electric heaters, then a heat pump, and then the battery of an electric vehicle (if any). Any cooperative / intelligent control algorithm at least partially based on computing / artificial intelligence can be used for the continuous power flow control module (S5.9) to call the priority order of the multiple controllable DC loads.

[0114] As Figure 5C shown, when no controllable DC load is available (S5.7) or when the power capacity of the multiple controllable DC loads is insufficient to balance the power flowing in and out of DC bus 1 and control the voltage of DC bus 1 (S5.8), the control system 10 is further configured to, at least partially based on the power flowing in and out of the at least one energy storage device 51 determined at T6.3 within the current time period and the determined power flowing through the DC / AC converter 3 (as Figure 2A , 2B , 3A and 4A shown) or the bidirectional DC / AC converter 31 (as Figure 3B and 4B shown), continuously control the power flowing through the DC / AC converter 3 (as Figure 2A , 2B , 3A and 4A shown) or the bidirectional DC / AC converter 31 (as Figure 3B and 4B shown) and the power flowing in and out of the at least one energy storage device 51 (S5.11), so as to balance the power flowing in and out of DC bus 1 and control the voltage of DC bus 1 in the microgrid.

[0115] For example, within an arbitrarily defined time period T6.3, when the power flowing in and out of the at least one energy storage device 51 and the power flowing through the DC / AC converter 3 (as Figure 2A , 2B , 3A and 4A shown) or the bidirectional DC / AC converter 31 (as Figure 3B and 4BWhen the power (S5.6) (but not limited to this) shown in the figure is determined and stable, when the water temperature in the hot water tank reaches the upper limit, there is no heat demand for the immersion heater (as a controllable DC load), or when the immersion heater is too small, the immersion heater does not have enough power capacity to balance the power flowing in and out of the DC bus 1 (S5.10). For example, the power capacity of the immersion heater may be lower than the fluctuation range of the power output of the DC power supply 21 (such as a solar photovoltaic power generation system), but not limited to this. In this case, the continuous power flow control module (S5.11) can be called alone or together with the continuous power flow control module (S5.9) to balance the power flowing in and out of the DC bus 1 and control the voltage of the DC bus 1. Any at least partially calculation / AI-based collaborative / intelligent control algorithm can be used for the continuous power flow control modules (S5.9) and (S5.11).

[0116] As Figure 5D shown, when the power balance of the DC bus 1 is broken by, for example but not limited to, a relatively large DC load (S5.12) or a DC power supply (such as a renewable energy generator) (S5.13) or an energy storage device (S5.14), that is, the connection to the DC bus 1 is interrupted or disconnected from the DC bus 1, the control system 10 can be configured to update the determined power flowing in and out of the at least one energy storage device 51 and the determined power flowing through the DC / AC converter 3 (such as Figure 2A , 2B shown in Figures 3A and 4A) or the determined power flowing through the bidirectional DC / AC converter 31 (such as Figure 3B and 4B shown) (S5.6). In other words, the control system 10 can be configured to re-determine the power flowing in and out of the at least one energy storage device 51 and the power flowing through the DC / AC converter 3 (such as Figure 2A , 2B , Figures 3A and 4A) or the bidirectional DC / AC converter 31 (such as Figure 3B and 4B shown) (S5.6), and then continue to continuously control the power flowing to the multiple controllable DC loads (S5.9) and the power flowing through the DC / AC converter 3 (such as Figure 2A , 2B , Figures 3A and 4A) or the bidirectional DC / AC converter 31 (such as Figure 3B and 4B shown) and the power of the at least one energy storage device 51 (S5.11).

[0117] A rather large DC load may be a controllable or uncontrollable DC load and may have a rather large power capacity. During the process of continuously controlling the power flowing to the plurality of controllable DC loads (S5.9), with a determined and stable power flowing in and out of the at least one energy storage device 51 and a determined and stable power flowing through the DC / AC converter 3 (as shown in Figure 2A , 2B , 3A and 4A) or the power flowing through the bidirectional DC / AC converter 31 (as shown in Figure 3B and 4B ) (S5.6), when a rather large DC load or a DC power source (such as a renewable energy generator) or an energy storage device is suddenly connected to or disconnected from the DC bus 1, the power flowing in and out of the DC bus 1 may not be able to maintain balance, and the voltage of the DC bus 1 may become unstable. In this case, the power flow determination module (S5.6) can be recalled.

[0118] Although several aspects of the present invention are listed in the independent claims, other aspects of the present invention include combinations of the features of the independent claims with the features of the embodiments and / or the dependent claims, rather than just the combinations explicitly specified in the claims.

[0119] It should also be noted that although the above detailed description describes various embodiments, these descriptions should not be considered limiting. On the contrary, several variations and modifications can be made to the embodiments without departing from the scope of the present invention defined by the appended claims.

Claims

1. An apparatus for a microgrid comprising a DC bus connected to at least one DC power source, an AC bus connected to a main power grid and providing microgrid power, and a DC / AC converter coupling the DC bus and the AC bus, the apparatus comprising: A control system, which is configured to: Control n DC power converters, where n is a positive integer and at least n = 1, and each DC power converter is configured to couple its corresponding controllable DC load to a DC bus; and Control the power flowing from the DC bus to each of the n controllable DC loads, thereby controlling: Each of the n controllable DC loads to achieve its function; and Control the voltage of the DC bus; The device further includes at least one energy storage battery directly connected to the DC bus; Wherein: the control system is configured to jointly control the power flowing in and out of the at least one energy storage battery and the power flowing to the n controllable DC loads to balance the power flowing in and out of the DC bus, thereby controlling the voltage of the DC bus, wherein the power flowing to the n controllable DC loads is controlled by the corresponding coupled DC power converters; Wherein, the control system is further configured to: Periodically update the power demand prediction of the load and the power generation prediction of the at least one DC power source; Periodically schedule the power flow distribution flowing in and out of the DC bus required to meet a set of first-level control target sets at least partially based on the power demand prediction of the load and the power generation prediction of the at least one DC power source within a defined time window; Periodically update the average power demand of the load monitored in the previous time period and the average power generation of the at least one DC power source monitored; Periodically determine the power flowing through the DC / AC converter and flowing in and out of the at least one energy storage device required to meet a set of second-level control target sets at least partially based on the power flow distribution flowing in and out of the DC bus scheduled in the current time period and the average power demand of the load and the average power generation prediction of the at least one DC power source in the previous time period; Wherein, controlling the power flowing from the DC bus to each of the n controllable DC loads includes: Continuously controlling the power flowing to each of the n controllable DC loads at least partially based on the power flowing through the DC / AC converter and flowing in and out of the at least one energy storage device determined in the current time period, thereby balancing the power flowing in and out of the DC bus and controlling the voltage of the DC bus; and Continuously controlling the power flowing through the DC / AC converter and flowing in and out of the at least one energy storage device at least partially based on the power flowing through the DC / AC converter and flowing in and out of the at least one energy storage device determined in the current time period, the instantaneous change in the power generation of the at least one DC power source, and the instantaneous change in the power flowing to the n controllable DC loads to meet a set of third-level control target sets.

2. The apparatus according to claim 1, characterized in that: The control system is configured to jointly control the power flowing in and out of the at least one energy storage battery, the power flowing to the n controllable DC loads, and the power flowing through the DC / AC converter to balance the power flowing in and out of the DC bus, thereby controlling the voltage of the DC bus, wherein the power flowing to the n controllable DC loads is controlled by the corresponding coupled DC power converters.

3. The apparatus according to claim 1, characterized in that: The device further includes at least one bidirectional energy storage charger configured to couple its corresponding energy storage device and the DC bus and control the charge and discharge of the corresponding energy storage device.

4. The apparatus according to claim 3, characterized in that: The control system is configured to coordinately control the power flowing in and out of the at least one energy storage device and the power flowing to the n controllable DC loads to balance the power flowing in and out of the DC bus, thereby controlling the voltage of the DC bus, wherein the power flowing in and out of the at least one energy storage device is controlled by its coupled bidirectional energy storage charger, and the power flowing to the n controllable DC loads is controlled by the corresponding coupled DC power converter.

5. The apparatus according to claim 3, characterized in that: The control system is configured to coordinately control the power flowing in and out of the at least one energy storage device, the power flowing to the n controllable DC loads, and the power flowing through the DC / AC converter to balance the power flowing in and out of the DC bus, thereby controlling the voltage of the DC bus, wherein the power flowing in and out of the at least one energy storage device is controlled by its coupled bidirectional energy storage charger, and the power flowing to the n controllable DC loads is controlled by the corresponding coupled DC power converter.

6. The apparatus according to claim 3, characterized in that: The control system is configured to coordinately control the power flowing in and out of the at least one energy storage battery, the power flowing in and out of the at least one energy storage device, the power flowing to the n controllable DC loads, and the power flowing through the DC / AC converter to balance the power flowing in and out of the DC bus, thereby controlling the voltage of the DC bus; wherein the power flowing in and out of the at least one energy storage device is controlled by its coupled bidirectional energy storage charger, and the power flowing to the n controllable DC loads is controlled by the corresponding coupled DC power converter.

7. The apparatus according to any one of claims 3 to 6, characterized in that: The corresponding energy storage device is configured as an energy storage battery, and at least one bidirectional energy storage charger is configured as a bidirectional DC / DC battery charger.

8. The apparatus according to any one of claims 3 to 6, characterized in that: The at least one energy storage device is configured as a battery of an electric vehicle (EV), and at least one bidirectional energy storage charger is configured as a smart bidirectional DC / DC EV charger or a smart electric vehicle charger.

9. The apparatus according to claim 1, characterized in that: When a certain coupled controllable DC load is a resistor, its corresponding coupled DC power converter is configured as a DC / DC converter.

10. The apparatus according to claim 1, characterized in that: When a certain coupled controllable DC load is a DC motor, its corresponding coupled DC power converter is configured as a DC / DC converter.

11. The apparatus according to claim 1, characterized in that: When a certain coupled controllable DC load is an induction motor, its corresponding coupled DC power converter is configured as a DC / AC frequency converter.

12. The apparatus according to claim 1, characterized in that: When a certain coupled controllable DC load is a battery of an electric vehicle (EV), its corresponding coupled DC power converter is configured as an electric vehicle DC charger.

13. The device according to claim 1, characterized in that: The DC / AC converter is a unidirectional DC / AC converter or a bidirectional DC / AC converter.

14. The device according to claim 1, characterized in that: The control system is configured to balance the power flowing in and out of the DC bus by coordinately controlling the power flowing to some but not all of the n controllable DC loads, thereby controlling the voltage of the DC bus.

15. A system, comprising: n DC power converters, and The device according to any one of claims 1 to 13.

16. A method for controlling a microgrid including a DC bus connected to at least one DC power source, an AC bus connected to the main power grid and providing microgrid power, a load including at least one controllable DC load, a DC / AC converter coupling the DC bus and the AC bus, and at least one energy storage device, the method comprising: Control n DC power converters, where n is a positive integer and at least n = 1, and each DC power converter is configured to couple its corresponding controllable DC load to a DC bus; and Control the power flowing from the DC bus to each of the n controllable DC loads, thereby controlling: Each of the n controllable DC loads to perform its function; and Control the voltage of the DC bus; Wherein, the method further includes: Periodically update the power demand prediction of the load and the power generation prediction of the at least one DC power source, and periodically schedule the power flow distribution in and out of the DC bus required to meet a set of first-level control objectives at least partially based on the power demand prediction of the load and the power generation prediction of the at least one DC power source within a defined time window; and Periodically update the average power demand of the load monitored in the previous time period and the average power generation of the at least one DC power source monitored, and periodically determine the power flowing through the DC / AC converter and in and out of the at least one energy storage device required to meet a set of second-level control objectives at least partially based on the power flow distribution in and out of the DC bus scheduled in the current time period and the average power demand of the load and the average power generation prediction of the at least one DC power source in the previous time period; Wherein, controlling the power flowing from the DC bus to each of the n controllable DC loads includes continuously controlling the power flowing to each of the n controllable DC loads at least partially based on the power flowing through the DC / AC converter and the power in and out of the at least one energy storage device determined in the current time period, thereby balancing the power in and out of the DC bus and controlling the voltage of the DC bus, and continuously controlling the power flowing through the DC / AC converter and the power in and out of the at least one energy storage device at least partially based on the power flowing through the DC / AC converter and the power in and out of the at least one energy storage device determined in the current time period, as well as the instantaneous change in the power generation of the at least one DC power source and the instantaneous change in the power flowing to the n controllable DC loads, so as to meet a set of third-level control objectives.

17. The method according to claim 16, characterized in that: Updating the power demand prediction of the load and the power generation prediction of the at least one DC power source and scheduling the power flow distribution in and out of the DC bus can be executed for at least two consecutive time periods within a defined time window.

18. The method according to claim 17, characterized in that: Updating the average power demand of the load and updating the average power generation of the at least one DC power source and determining the power flowing through the DC / AC converter and the power in and out of the at least one energy storage device can be executed for at least two consecutive time periods within the current time period.

19. The method according to claim 16, characterized in that: The set of first-level control objectives at least partially includes: Maximize the in-situ consumption of the power generated by the at least one DC power source by the loads in the microgrid; Minimize the reverse power flowing from the microgrid to the main grid; Maximize the economic benefits of the microgrid end-users; and Minimize the power taken from the main grid to the microgrid during high electricity price periods.

20. The method according to claim 17, characterized in that: The set of second-level control objectives at least partially includes: Stabilize the power flowing through the DC / AC converter; Stabilize the power flowing into and out of the at least one energy storage device; and Stabilize the power flowing to the controllable DC loads at least in part based on the power controllability, power capacity, and function of each of the n controllable DC loads.

21. The method according to claim 16, characterized in that: The third-level control target set at least partially includes: Balance the power flowing into and out of the DC bus; and Stabilize the voltage of the DC bus.

22. The method according to claim 16, wherein: Further includes: Continuously control the power flowing to the n controllable DC loads by following a priority order that at least partially depends on the power controllability, power capacity, and function of each of the n controllable DC loads.

23. The method according to claim 16, wherein: Further includes: When the power balance flowing into and out of the DC bus is at least partially interrupted by the connection or disconnection of a relatively large DC load and / or DC power supply and / or energy storage device to / from the DC bus each time, update the determined power flowing through the DC / AC converter and / or the determined power flowing into and out of the at least one energy storage device.

24. The apparatus according to any one of claims 1 to 14, wherein: Further includes a control device for performing the method according to any one of claims 16 to 23.

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