A Hierarchical Energy Coordination Control Strategy for Multi-Port Power Electronic Equipment

Abstract

The present invention discloses a hierarchical energy coordination control strategy for a multi-port power electronic device. Functionally, it can achieve the flow of energy among solar energy, wind energy, energy storage batteries, the power grid, and loads within the multi-port power electronic device, and through scheduling information, it can achieve the coordinated flow of energy among multiple multi-port power electronic devices. Through the hierarchical energy coordination control of the multi-port power electronic device, the coordinated cooperation of energy within and between devices is realized, enabling the maximum possible power of distributed energy to be fed into the grid, the long-life operation of energy storage batteries, and also improving the operation stability of the multi-port power electronic device.

Description

Technical Field

[0001] The present invention relates to the field of power electronic device control, and particularly to a hierarchical energy coordination control strategy for multi-port power electronic devices. Background Art

[0002] Under the new situation of power development, the main features of the third-generation power grid include: a large proportion of the total power generation comes from renewable energy; multi-port power electronic devices are highly integrated with the backbone grid and local power grids; an environmentally friendly power transmission method with low line losses and large capacity is adopted; the power grid dispatching, protection, and control are intelligent, and an intelligent power distribution and utilization system with two-way interaction between the power grid and users. The future power grid will have the ability to accommodate large-scale renewable energy power, an efficient and flexible energy configuration and a new power supply system, basically eliminate the risk of large-scale power outages, have extremely high power supply reliability, and simultaneously realize an integrated service system of urban and rural power, energy, and information networking. Based on the major requirements of the construction of the third-generation power grid, multi-port power electronic device technology and DC power grid technology will play a major role in promoting the transformation of traditional power grids and the development of future power grids. Multi-port power electronic device technology is an effective way for the sustainable development of the power industry, which provides a flexible and efficient platform for the development and application of DG technologies mainly based on renewable energy such as wind energy, solar energy, and biomass energy. Multi-port power electronic devices can realize the complementary advantages of different types of renewable energy in time and space, meet the load growth demand, and comprehensively improve the energy utilization efficiency and power supply reliability. At the same time, as a small-scale power generation, distribution, and controllable system, DC multi-port power electronic devices can achieve self-control, management, and protection. Therefore, they will surely be widely used in the development of future distribution grids. When DG and multi-port power electronic devices are gradually popularized and account for a large proportion of power generation and supply in the power grid, the management mode, system operation control method, and market operation mechanism of the power grid will surely become important theoretical and practical problems to be solved in the research on power system operation and control. Although existing research enables multi-port power electronic devices to operate stably under certain circumstances, there are problems such as less research on scheduling information from the upper layer of the power grid or between other multi-port power electronic devices and the further optimization of the remaining charge capacity SOC of energy storage. Summary of the Invention

[0003] In order to achieve the stable and efficient operation of power electronic devices, aiming at the deficiencies of the prior art, the present invention proposes a hierarchical energy coordination control strategy for multi-port power electronic devices, comprehensively considering information such as upper-level scheduling and the remaining charge capacity SOC of energy storage, to achieve the longest possible life of energy storage batteries and the coordinated and stable operation between multiple multi-port power electronic devices.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A hierarchical energy coordination control strategy for a multi-port power electronic device, comprising the following steps:

[0006] Step 1: The bottom control layer performs bottom control layer energy coordination control on the multi-port power electronic device according to the operating parameters of each port of the multi-port power electronic device and the bus voltage, and uploads it to the central management layer;

[0007] Step 2: The central management layer optimizes the remaining state of charge (SOC) according to the operating parameters of each port, and performs energy scheduling according to the upper-layer scheduling information, and then issues an instruction to the bottom control layer to perform central management layer energy coordination control;

[0008] Step 3: After a period of time Ts, repeat Steps 1-2 to achieve stable operation of the multi-port power electronic device.

[0009] Furthermore, the specific implementation method of Step 1 is as follows: The AC load and DC load are divided into important loads and unimportant loads according to the load importance degree, and the power emitted or absorbed by each port, the remaining state of charge (SOC) of the energy storage battery, the current control strategy of each port, the grid-connected and off-grid states, the unimportant load power, the important load power, and the bus voltage are transmitted to the central management layer, and the bottom control layer energy coordination control of the multi-port power electronic device is performed according to the above parameters, and the operation of the multi-port power electronic device is defined as 5 modes through different bus voltage levels.

[0010] Furthermore, the 5 modes are:

[0011] (1) Energy balance mode: At this time, the DC bus voltage U dc satisfies 0.975U dc ≤U dc ≤1.025U dc , and the energy storage battery is set to the cut-off state; when the device is in the grid-connected state, the energy of the load, photovoltaic power generation, wind power generation, and the grid is balanced, and the distributed power source composed of photovoltaic power generation and wind power generation operates in the MPPT mode, and the DC bus voltage is controlled by the grid-connected port; when the device is in the off-grid state, the energy required by the load is balanced with the distributed power generation power, and at this time the distributed power source operates in the MPPT mode;

[0012] (2) Energy storage energy absorption mode: At this time, the DC bus voltage U dc satisfies 1.025U dc <U dc <1.05U dc, the energy storage port is in the charging state, the distributed power supply operates in the MPPT mode, and the DC bus voltage is controlled by the energy storage port; when the device is in the off-grid state, under strong light and wind or reduced load, the load power is lower than the output power of the distributed power supply. At this time, the energy storage battery has the ability to absorb energy and enter the charging mode. At this time, the photovoltaic battery operates in the MPPT mode, and the distributed power supply charges the energy storage battery at a constant voltage, absorbing the remaining energy when the energy storage battery has not reached the overcharge state, and the DC bus voltage is controlled by the energy storage port;

[0013] (3) Energy storage discharging mode: At this time, the DC bus voltage U dc satisfies 0.95U dc < U dc <0.975U dc , the energy storage port is in the discharging state, the distributed power supply operates in the MPPT mode, and the DC bus voltage is controlled by the energy storage port; when the device is in the off-grid state, the energy storage battery discharges to supply energy to the load end, maintaining the voltage stable within a certain range; the distributed power supply operates in the MPPT mode, the energy storage battery is in the discharging state, and the bus voltage is maintained stable at a constant voltage;

[0014] (4) Energy surplus mode: At this time, the DC bus voltage U dc satisfies U dc ≥1.05U dc , the excess energy is supplied to the energy storage battery to enter the charging mode, and the energy storage battery is in the idle mode. At this time, the distributed power supply first partially switches to the constant voltage mode to reduce the output power of the distributed power supply. If the bus voltage still cannot be effectively stabilized, then all are switched to the constant voltage mode to ensure the energy balance of the system. At this time, the distributed power supply plays a major control role in the DC bus; when the device is in the off-grid state, the energy provided by the distributed power supply can meet the energy required by the load, and the capacity of the energy storage battery is close to saturation and in the idle mode. At this time, the same as in the grid-connected state, the distributed power supply first partially and then all switches to the constant voltage mode to ensure the energy balance of the system. At this time, the distributed power supply plays a major control role in the DC bus;

[0015] (5) Energy shortage mode: At this time, the DC bus voltage U dc satisfies U dc ≤0.95U dc , at this time, the device is in the grid-connected or off-grid state, the AC grid-connected power is limited to the rated value or in the idle mode, and the energy storage battery has no ability to enter the discharging mode. Unimportant loads are cut off. If the bus voltage still cannot be stabilized after load shedding for a period of time, the device is shut down.

[0016] Furthermore, the specific steps of step 2 include:

[0017] Increase the energy storage protection mode of the battery through central management control. If the SOC value of the energy storage battery is between 30% and 70%, the energy storage battery is in the normal working state; otherwise, the battery enters the energy storage protection mode.

[0018] Increase the dispatching mode through central management control. When receiving the upper-level dispatching information, convert the dispatching power into secondary-important loads. The load importance of the secondary-important loads is between that of the important loads and the unimportant loads: When the power in the device is sufficient, ensure the normal and stable operation of the important loads, unimportant loads, and secondary-important loads in the device; when the power in the device is insufficient, ensure the normal and stable operation of the important loads and secondary-important loads in the device; when the power in the device is not enough to meet the dispatching task, upload the information that the dispatching task cannot be completed. Give priority to ensuring the normal and stable operation of the important loads in the device, exit the central management dispatching mode and resume the control of the bottom control layer. When the power in the device is sufficient and there is a dispatching task, re-enter the dispatching mode.

[0019] Furthermore, the multi-port power electronic device includes six ports: photovoltaic, wind power, energy storage, grid connection, AC load, and DC load. The six ports share a DC bus and operate in parallel; the photovoltaic and wind power ports are connected to the DC bus through Boost converters; the energy storage battery is connected to the DC bus using a bidirectional Buck / Boost converter; the grid connection port and the AC load are connected to the grid using a three-phase AC / DC converter; the DC load is connected to the DC bus using a Buck converter.

[0020] Furthermore, the control methods of the converters of each port are as follows:

[0021] (1) The photovoltaic and wind power Boost converters enable the photovoltaic and wind power generation units to operate in two working modes: maximum power point tracking and DC bus constant voltage control. Among them, the maximum power point tracking uses the perturbation observation method, and the DC bus constant voltage control uses a double-loop control structure with an outer loop of the bus voltage and an inner loop of the current.

[0022] (2) The energy storage bidirectional Buck / Boost converter can freely switch between charging, discharging, and standby modes. During the charging and discharging processes, it uses a constant voltage and current limiting control method. The interface converter uses a double closed-loop control of voltage and current, with the outer loop being the bus voltage and the inner loop being the energy storage battery current. A limiting link is added to the output of the outer loop.

[0023] (3) The grid-connected three-phase AC / DC converter uses a voltage and current double closed-loop control based on feedforward decoupling.

[0024] The beneficial effects of the present invention are:

[0025] 1. A hierarchical energy coordination control strategy for a multi-port power electronic device proposed by the present invention studies and establishes an autonomous switching control strategy for the operating states of each unit converter in the network to meet the requirements of system operation stability and reliability. The autonomous control strategy of the unit converter can achieve rapid and smooth autonomous switching of each unit between different operating states under different operating modes of the multi-port power electronic device.

[0026] 2. When implementing the control strategy, the present invention designs a charge and discharge protection mode for energy storage. When the state of charge (SOC) of the energy storage battery reaches the protection range, this strategy automatically detects and disconnects from the grid. When the protection limit is reached, this strategy can convert the energy storage battery into an idle mode. Through the autonomous charge and discharge regulation of the storage battery and the automatic switching of the protection mode, the power balance of the multi-port power electronic device and the long-life operation of the energy storage battery are ensured.

[0027] 3. When implementing the control strategy, the present invention designs a scheduling mode. It mainly aims to ensure the normal and stable operation of important loads within the device, and realizes the scheduling optimization and power balance inside the multi-port power electronic device and between multiple devices in the on-grid and off-grid states under the condition of having a scheduling task.

[0028] 4. The hierarchical energy coordination control strategy for the multi-port power electronic device proposed by the present invention has very strong universality. The present invention is based on a multi-port power electronic device, and its core lies in considering various operating mode divisions and stable switching, and conducting control for each mode separately. When applied to other power electronic devices with distributed power sources, energy storage, loads, and grid connection ports, the present invention still holds. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 FIG. is a structural diagram of a multi-port power electronic device related to the present invention;

[0030] Figure 2 FIG. is a schematic diagram of the hierarchical energy coordination control strategy of the multi-port power electronic device of the present invention;

[0031] Figure 3 FIG. is a schematic diagram of the voltage level mode of the multi-port power electronic device of the present invention;

[0032] Figure 4 FIG. is a central management layer control flowchart of the multi-port power electronic device of the present invention;

[0033] Figure 5 FIG. is a converter control block diagram of the photovoltaic and wind power units of the multi-port power electronic device of the present invention;

[0034] Figure 6 FIG. is a converter control block diagram of the energy storage unit of the multi-port power electronic device of the present invention;

[0035] Figure 7 This is the converter control block diagram of the grid unit of the multi-port power electronic device of the present invention. Specific embodiments

[0036] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] As Figure 1 shown, the multi-port power electronic device includes a photovoltaic port, a wind power port, an energy storage port, a grid connection port, a DC load, and an AC load; the photovoltaic port and the wind power port provide standardized interfaces for the photovoltaic array and the wind turbine generator set, and are connected to the DC bus through a unidirectional boost converter to convert light energy and wind energy into reliable electric energy and input it into the power electronic device; the energy storage port uses a bidirectional Buck / Boost converter to connect the energy storage battery to the DC bus and can perform charge and discharge control according to the needs of the power electronic device; the grid connection port uses a three-phase AC / DC converter to connect the DC bus to the power grid, and can either choose to connect to the power network according to the needs to realize the bidirectional energy flow between the energy sub-network and the power network, or disconnect according to the operation requirements of the power electronic device to realize the independent operation of the energy sub-network; and a three-phase AC / DC converter is used to connect the DC bus to the AC load to obtain electric energy from the power electronic device; the five ports share a DC bus and operate in parallel.

[0038] As Figure 2 shown, a hierarchical energy coordination control strategy for a multi-port power electronic device of the present invention includes the following steps:

[0039] Step 1: As Figure 3 shown, perform energy coordination control on the multi-port power electronic device at the underlying control layer:

[0040] Classify the AC load and the DC load into important loads and unimportant loads according to the load importance level, and transmit the power generated or absorbed by each port, the remaining state of charge SOC of the energy storage battery, the current control strategy of each port, the on-grid / off-grid state, the power of the unimportant load, the power of the important load, and the bus voltage to the central management layer, and perform energy coordination control on the multi-port power electronic device according to the above parameters. Define the operation of the multi-port power electronic device as 5 modes through different bus voltage levels:

[0041] (1) Energy balance mode: At this time, the DC bus voltage U dc satisfies 0.975Udc ≤U dc ≤1.025U dc Since in the actual working conditions, the system does not have an absolute stable state and the DC bus voltage still fluctuates. Therefore, to avoid frequent operation of the energy storage battery, the energy storage battery is set to the cut-off state. When the device is in the grid-connected state, the energy of the load, photovoltaic power generation, wind power generation, and the power grid is balanced. The distributed power source composed of photovoltaic power generation and wind power generation operates in the MPPT mode, and the DC bus voltage is controlled by the grid-connected port. When the device is in the off-grid state, the energy required by the load is balanced with the power generation power of the distributed power source. At this time, the distributed power source operates in the MPPT mode. Since there is no constant voltage control link in this mode, when the maximum output power of the distributed power source changes slightly due to environmental factors, the DC bus voltage of the device is allowed to fluctuate slightly within the region range.

[0042] (2) Energy storage energy absorption mode: At this time, the DC bus voltage U dc satisfies 1.025U dc <U dc <1.05U dc When the device is in the grid-connected state, at this time, after the distributed power source outputs power to supply the load power, the remaining power is greater than the rated power of the bidirectional DC / AC converter. The bidirectional DC / AC converter operates in the current limiting mode, and the AC grid-connected power is limited to the rated value. It cannot control the bus voltage. Here, the energy storage port is in the charging state, the distributed power source operates in the MPPT mode, and the DC bus voltage is controlled by the energy storage port. When the device is in the off-grid state, in the case of strong light and wind or reduced load, the load power is lower than the output power of the distributed power source. At this time, the energy storage battery still has the ability to absorb energy and enter the charging mode. At this time, the photovoltaic battery operates in the MPPT mode, and the distributed power source charges the energy storage battery at a constant voltage. When the energy storage battery has not reached the overcharge state, it absorbs the remaining energy, and the DC bus voltage is controlled by the energy storage port.

[0043] (3) Energy storage energy release mode: At this time, the DC bus voltage U dc satisfies 0.95U dc <U dc <0.975U dc When the device is in the grid-connected state, due to the limitation of the rated power of the bidirectional DC / AC converter, the bus voltage drops, and it cannot control the bus voltage. Here, the energy storage port is in the discharging state, the distributed power source operates in the MPPT mode, and the DC bus voltage is controlled by the energy storage port. When the device is in the off-grid state, the energy storage battery discharges to supply energy to the load terminal and maintains the voltage stable within a certain range. At this time, the distributed power source operates in the MPPT mode, the energy storage battery is in the discharging state, and the bus voltage is maintained stable at a constant voltage.

[0044] (4) Energy surplus mode: At this time, the DC bus voltage U dc satisfies U dc ≥1.05U dc , when the device is in the grid-connected state, a high DC bus voltage indicates that there is power surplus inside the system. The AC grid-connected power is limited to the rated value, and the energy provided by the distributed power source can meet the energy required by the load. The excess energy can be supplied to the energy storage battery to enter the charging mode. While the capacity of the energy storage battery is nearly saturated and in the idle mode. At this time, the distributed power source can first partially switch to the constant voltage mode to reduce the output power of the distributed power source. If the bus voltage still cannot be effectively stabilized, then all switch to the constant voltage mode to ensure the energy balance of the system. At this time, the distributed power source plays a major control role in the DC bus; when the device is in the off-grid state, the energy provided by the distributed power source can meet the energy required by the load, and the capacity of the energy storage battery is nearly saturated and in the idle mode. At this time, similar to the grid-connected state, the distributed power source first partially and then fully switches to the constant voltage mode to ensure the energy balance of the system. At this time, the distributed power source plays a major control role in the DC bus.

[0045] (5) Energy shortage mode: At this time, the DC bus voltage U dc satisfies U dc ≤0.95U dc , at this time, the device is in the grid-connected or off-grid state, the AC grid-connected power is limited to the rated value or in the idle mode, and the energy storage battery has no ability to enter the discharge mode and cannot provide the energy required for the load to maintain its normal operation. At this time, unimportant loads are cut off to reduce the power required for the normal operation of the device to ensure the normal operation of the device. If the bus voltage still cannot be stabilized after load shedding for a period of time, then the device is shut down to avoid damage to the multi-port power electronic device due to the inability to stabilize the bus voltage for a long time.

[0046] Step 2: As Figure 4 shown, perform SOC optimization according to the operating parameters of each port, etc., and perform central management layer control according to the upper-layer scheduling information. Specifically, it is manifested as:

[0047] (1) The underlying control layer can only extend the working time of important loads by reducing the working time of secondary loads. To better optimize the SOC value of the energy storage battery, the central management layer controls to increase the energy storage protection mode of the battery. If the SOC value of the energy storage battery is between 30% and 70%, the energy storage battery is in a normal working state; otherwise, the battery enters the energy storage protection mode, and the central management layer controls to optimize the SOC value to improve the device's ability to cope with sudden failures: when the SOC value is between 20% and 30% or between 70% and 80%, the device automatically detects whether it is grid-connected every other δTs. When in the grid-connected state and in the energy balance mode, the energy storage battery is charged or discharged through the power grid, and when the SOC value is lower than 20% or higher than 80%, the energy storage battery switches to the idle mode. When the SOC value is lower than 20%, only battery charging is allowed, and when the SOC value is higher than 80%, only battery discharging is allowed to achieve the autonomous protection of the energy storage battery; when the bus voltage rises or falls to the next mode, corresponding load shedding or distributed power source control switching operations are performed to maintain the stable operation of the multi-port power electronic device.

[0048] (2) The underlying control layer can only meet the power balance within the multi-port power electronic device and lacks upper-layer scheduling information, so it cannot ensure the normal and stable operation of the device after receiving the scheduling instruction. Therefore, the central management layer controls to increase the scheduling mode. When receiving the upper-layer scheduling information, the scheduling power is converted into secondary important loads, and the load importance of the secondary important loads is between that of important loads and unimportant loads: when the power in the device is sufficient, it meets the normal and stable operation of the important loads, unimportant loads, and scheduling power (i.e., secondary important loads) in the device; when the power in the device is not very sufficient, it meets the normal and stable operation of the important loads and scheduling power (i.e., secondary important loads) in the device; when the power in the device is not enough to meet the scheduling task, information about the inability to complete the scheduling task is uploaded, mainly to ensure the normal and stable operation of the important loads in the device, exit the central management layer scheduling mode and resume the underlying control layer control, and when the power in the device is sufficient and there is a scheduling task, re-enter the scheduling mode.

[0049] Step 3: After a period of time Ts, repeat Steps 1-2 to achieve the stable operation of the multi-port power electronic device.

[0050] After the instruction is set and issued, each port executes the instruction, and the control methods of each port are as follows:

[0051] Such as Figure 5As shown, the photovoltaic and wind power generation units can operate in two modes: maximum power point tracking (MPPT) and constant voltage control of the DC bus (CVC). Among them, MPPT uses the perturbation observation method. Its working principle is to apply a small perturbation to the voltage of the photovoltaic cell or wind turbine, and observe the change in the photovoltaic output power before and after the perturbation. If the output power increases after the change, it indicates that this change direction can increase the output power, and the output voltage in the next tracking cycle continues to change in this direction; if the output power decreases after the change, it indicates that the change trend is opposite to the given one, and the output voltage in the next tracking cycle changes in the opposite direction to achieve the maximum utilization of solar and wind energy. The constant voltage control adopts a double-loop control with an outer loop of the bus voltage and an inner loop of the current. Among them, U PV and I PV are the voltage and current of the photovoltaic cell or wind turbine; I PV_ref is the bus voltage U dc minus the bus voltage reference value U dc_ref and the current reference value of the photovoltaic cell or wind turbine obtained through PI regulation; PWM modulation is pulse width modulation, which transmits the switching signal to the switch tube.

[0052] As Figure 6 shown, the energy storage bidirectional Buck / Boost converter can freely switch between charging, discharging, and idle modes, avoiding unnecessary actions of power electronic devices caused by small fluctuations in the DC bus voltage, improving the service life of the energy storage battery. The constant voltage and current limiting control method is adopted during the charging and discharging process, and the interface converter adopts a double-loop control of voltage and current. The outer loop is the bus voltage, and the inner loop is the current of the energy storage battery. To prevent overcurrent during discharging, a limiting link is also added to the output of the outer loop; when the energy storage device operates in the charging state, the energy on the bus flows to the energy storage device through the bidirectional conversion circuit at this time, and the bidirectional conversion circuit can be equivalent to a Buck conversion circuit. A double-loop control is used to achieve voltage stabilization control during the charging and discharging process of the energy storage device. The outer loop of the double loop is the voltage loop, and the inner loop is the current loop. The upper limit of the limiting link is set to the value of the constant current charging rated current. In the initial state, the energy stored in the energy storage device is small, and the low voltage causes the output of the voltage loop PI regulator to be too large. The limiting link maintains it at the preset upper limit. As the stored energy continues to increase, the voltage of the energy storage device gradually increases, and the output of the voltage loop PI regulator gradually stabilizes within the range of the limiting link. At this time, the system enters the constant voltage charging state until the stored energy reaches the upper limit of the energy storage device. Among them, I b is the current of the energy storage battery; I b_ref is the bus voltage U dc minus the bus voltage reference value U dc_ref and the current reference value of the energy storage battery obtained through PI regulation; PWM modulation is pulse width modulation, which transmits the switching signal to the switch tube.

[0053] As shown Figure 7 , the grid-connected three-phase AC / DC converter adopts a double closed-loop control of voltage and current based on feedforward decoupling. The DC voltage of the converter is controlled by the outer voltage loop. After comparing the reference voltage value with the actual voltage value, the given current of the d-axis is obtained through PI regulation. After detecting the given current, the inner current loop controls the AC-side current of the converter through relevant regulation. At this time, let i q * = 0, which means that the AC / DC converter rectifies with a power factor of 1. Where i abc is the three-phase current of the AC / DC converter, and its d-axis current i d and q-axis current i q in the dq coordinate system are obtained through park transformation; i d *, i q * represent the reference values of the d-axis and q-axis currents; ω is the rotational angular velocity of the dq coordinate system in the park transformation (usually selected as the grid frequency); L is the inductance value of the AC / DC converter; e d , e q represent the d-axis and q-axis voltages on the grid side; U d , U q are the d-axis and q-axis voltages of the AC / DC converter; SVPWM modulation is space vector pulse width modulation, which transmits the switching signal to the switching tube.

[0054] The present invention aims to cover any variations, uses or adaptations of the present invention, which follow the general principles of the present invention and include common general knowledge or conventional technical means in the technical field not disclosed in the present invention. The description and embodiments are only regarded as exemplary, and the true scope and spirit of the present invention are pointed out by its claims.

[0055] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented in various computer languages. For example, object-oriented programming languages such as Java and interpreted scripting languages such as JavaScript.

[0056] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in one flow Figure 1 one flow or multiple flows and / or blocks Figure 1 or means for implementing the functions specified in one block or multiple blocks.

[0057] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that implement the functions specified in one flow Figure 1 one flow or multiple flows and / or blocks Figure 1 or means for implementing the functions specified in one block or multiple blocks.

[0058] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operational steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one flow Figure 1 one flow or multiple flows and / or blocks Figure 1 or means for implementing the functions specified in one block or multiple blocks.

[0059] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concepts. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0060] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

[0061] It should be understood that the present invention is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims.

Claims

1. A hierarchical energy coordination control strategy for a multi-port power electronic device, characterized in that, It includes the following steps: Step 1: The underlying control layer performs energy coordination control on the multi-port power electronic device according to the operating parameters of each port of the multi-port power electronic device and the bus voltage, and uploads it to the central management layer. The specific implementation method is as follows: Classify AC loads and DC loads into important loads and unimportant loads according to the load importance level, and transmit the power generated or absorbed by each port, the remaining state of charge (SOC) of the energy storage battery, the current control strategy of each port, the grid-connected / off-grid state, the power of unimportant loads, the power of important loads, and the bus voltage to the central management layer. Then, perform energy coordination control on the multi-port power electronic device based on the above parameters, and define the operation of the multi-port power electronic device as 5 modes through different bus voltage levels; Step 2: The central management layer optimizes the remaining state of charge (SOC) according to the operating parameters of each port, performs energy scheduling according to the upper-layer scheduling information, and then issues instructions to the underlying control layer to perform energy coordination control at the central management layer, including: Control the energy storage protection mode of the battery to be increased through the central management layer. If the SOC value of the energy storage battery is between 30% and 70%, the energy storage battery is in a normal working state; otherwise, the battery enters the energy storage protection mode; Control the scheduling mode to be increased through the central management layer. When receiving the upper-layer scheduling information, convert the scheduling power into secondary important loads. The load importance level of secondary important loads is between important loads and unimportant loads: When the power in the device is sufficient, ensure the normal and stable operation of important loads, unimportant loads, and secondary important loads in the device; When the power in the device is insufficient, ensure the normal and stable operation of important loads and secondary important loads in the device; When the power in the device is not enough to meet the scheduling task, upload the information that the scheduling task cannot be completed, and mainly ensure the normal and stable operation of important loads in the device. Exit the scheduling mode at the central management layer and resume control at the underlying control layer. When the power in the device is sufficient and there is a scheduling task, re-enter the scheduling mode; Step 3: After a period of time Ts, repeat Steps 1-2 to achieve the stable operation of the multi-port power electronic device.

2. The hierarchical energy coordination control strategy for a multi-port power electronic device according to claim 1, characterized in that, The 5 modes are: (1) Energy balance mode: At this time, the DC bus voltage meets , and the energy storage battery is set to the cut-off state; when the device is in the grid-connected state, the energy of the load, photovoltaic power generation, wind power generation, and the power grid is balanced. The distributed power supply composed of photovoltaic power generation and wind power generation operates in the MPPT mode, and the DC bus voltage is controlled by the grid-connected port; when the device is in the off-grid state, the energy required by the load is balanced with the power generation power of the distributed power supply. At this time, the distributed power supply operates in the MPPT mode; (2)Energy storage and absorption mode: At this time, the DC bus voltage meets , the energy storage port is in the charging state, the distributed power supply operates in the MPPT mode, and the DC bus voltage is controlled by the energy storage port; when the device is in the off-grid state, under the conditions of strong light, strong wind or reduced load, the load power is lower than the output power of the distributed power supply. At this time, the energy storage battery has the ability to absorb energy and enter the charging mode. At this time, the photovoltaic battery operates in the MPPT mode, and the distributed power supply charges the energy storage battery at a constant voltage. When the energy storage battery has not reached the overcharge state, it absorbs the remaining energy, and the DC bus voltage is controlled by the energy storage port; (3) Energy storage and discharge mode: At this time, the DC bus voltage meets , the energy storage port is in the discharge state, the distributed power supply operates in the MPPT mode, and the DC bus voltage is controlled by the energy storage port; when the device is in the off-grid state, the energy storage battery discharges to supply energy to the load end, maintaining the voltage stable within a certain range; the distributed power supply operates in the MPPT mode, the energy storage battery is in the discharge state, and the constant voltage maintains the stability of the bus voltage; (4) Energy surplus mode: At this time, the DC bus voltage meets , and the excess energy is supplied to the energy storage battery to enter the charging mode. The energy storage battery is in the idle mode. At this time, the distributed power supply first partially switches to the constant voltage mode to reduce the output power of the distributed power supply. If the bus voltage still cannot be effectively stabilized, then all are switched to the constant voltage mode to ensure the energy balance of the system. At this time, the distributed power supply plays a major control role in the DC bus; when the device is in the off-grid state, the energy provided by the distributed power supply can meet the energy required by the load, and the capacity of the energy storage battery is almost saturated and in the idle mode. At this time, as in the grid-connected state, the distributed power supply first partially and then all switches to the constant voltage mode to ensure the energy balance of the system. At this time, the distributed power supply plays a major control role in the DC bus; (5) Energy shortage mode: At this time, the DC bus voltage meets . At this time, the device is in grid-connected or off-grid state. The AC grid-connected power is limited to the rated value or in the idle mode, and the energy storage battery is not capable of entering the discharge mode. Unimportant loads are cut off. If the bus voltage still cannot be stabilized after load shedding for a period of time, the device will be shut down.

3. The hierarchical energy coordination control strategy of a multi-port power electronic device according to claim 2, characterized in that, The multi-port power electronic device includes six ports: photovoltaic, wind power, energy storage, grid connection, AC load, and DC load. The six ports share a DC bus and operate in parallel; The photovoltaic and wind power ports are connected to the DC bus through Boost converters; The energy storage battery is connected to the DC bus through a bidirectional Buck / Boost converter; The grid connection port and the AC load are connected to the grid through a three-phase AC / DC converter from the DC bus; The DC load is connected to the DC bus through a Buck converter.

4. The hierarchical energy coordination control strategy for a multi-port power electronic device according to claim 3, characterized in that, The control methods of the converters of each port are as follows: (1) The photovoltaic and wind power Boost converters enable the photovoltaic and wind power generation units to work in two operating modes: maximum power point tracking and DC bus constant voltage control. Among them, the maximum power point tracking adopts the perturbation and observation method, and the DC bus constant voltage control adopts a double-loop control structure with an outer loop of bus voltage and an inner loop of current; (2) The energy storage bidirectional Buck / Boost converter can freely switch between the charging, discharging, and standby modes. During the charging and discharging processes, a constant voltage and current limiting control method is adopted. The interface converter uses a dual closed-loop control of voltage and current, with the outer loop being the bus voltage and the inner loop being the energy storage battery current. A limiting link is added to the output of the outer loop; (3) The grid-connected three-phase AC / DC converter adopts a dual closed-loop control of voltage and current based on feedforward decoupling.

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