CN116914801B - Multiport energy router integrating power quality management function and control method thereof - Google Patents

Multiport energy router integrating power quality management function and control method thereof Download PDF

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Publication number
CN116914801B
CN116914801B CN202311168087.9A CN202311168087A CN116914801B CN 116914801 B CN116914801 B CN 116914801B CN 202311168087 A CN202311168087 A CN 202311168087A CN 116914801 B CN116914801 B CN 116914801B
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China
Prior art keywords
power
energy router
grid
control
energy
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CN202311168087.9A
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CN116914801A (en
Inventor
郑子萱
陈旭林
丁凯
钱一民
陈韵竹
李世杰
肖先勇
汪颖
李长松
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Sichuan University
Electric Power Research Institute of State Grid Hubei Electric Power Co Ltd
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Sichuan University
Electric Power Research Institute of State Grid Hubei Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/28—Arrangements for balancing of the load in a network by storage of energy
    • H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The invention provides a multiport energy router integrating the electric energy quality management function and a control method thereof, comprising the following steps: acquiring grid-connected point voltage of an alternating current power grid, converter output current and alternating load current; positive sequence droop control and negative sequence droop control of the grid-connected converter are performed based on grid-connected point voltage and converter output current; positive sequence sagging control is used for active power control and reactive power control, and negative sequence sagging control is used for grid-connected point three-phase voltage unbalance management; harmonic treatment is carried out based on the output current of the converter and the alternating load current; determining the exchange power of the energy router and the alternating current power grid based on the load power inside the energy router, the output power of the photovoltaic power generation unit and the output power of the energy storage unit by taking the charge state of the battery as a constraint condition; and determining a control mode of the energy router based on the exchange power of the energy router and the alternating current power grid so as to maintain the voltage stability of the direct current bus.

Description

Multiport energy router integrating power quality management function and control method thereof
Technical Field
The invention relates to the technical field of power electronics, in particular to a multiport energy router integrating a power quality management function and a control method thereof.
Background
In order to meet the complexity and diversity requirements of the future power grid on electric energy control, the research of the energy internet and the technology thereof is gradually receiving extensive attention from the academia. The Energy Router (Energy Router) based on the power electronic technology and the operation control strategy thereof are taken as the basis of Energy internet operation, directly relate to the consumption of a distributed power supply and the high-efficiency and flexible conversion of Energy, and determine the flexibility of power system control and the overall stability and high-efficiency of system operation under the background of multi-kind Energy access. Therefore, the circuit topology and coordination control method of the energy router is a necessary research topic for realizing the aim of widely interconnecting and efficiently utilizing energy.
At present, scholars at home and abroad have studied the topology structure, performance characteristics and control mode of the energy router, and have explained that the energy router can have functions of energy coordination, voltage unbalance management, expandable harmonic management and the like. However, the existing research results do not realize the energy coordination, the electric energy quality management and the extensible functions of the energy router at the same time.
Disclosure of Invention
In view of the above, the present invention aims to provide a multiport energy router with integrated power quality control function and a control method thereof, so as to provide a simplified multiport energy router topology structure, which is convenient for the rapid access of new energy power generation units, energy storage units and load units, and design an upper energy management system (Energy Management System, EMS) and a bottom control strategy of each unit, so that the power quality comprehensive control of an ac power grid can be realized while the voltage of a dc bus inside the energy router is maintained constant.
In a first aspect, an embodiment of the present invention provides a method for controlling a multiport energy router integrated with a power quality management function, where the energy router includes: the system comprises an alternating current power grid, a direct current bus, a grid-connected converter, a photovoltaic power generation unit, an energy storage unit and a direct current load; the method comprises the following steps: acquiring grid-connected point voltage of an alternating current power grid, converter output current and alternating load current; positive sequence droop control and negative sequence droop control of the grid-connected converter are performed based on grid-connected point voltage and converter output current; positive sequence sagging control is used for active power control and reactive power control, and negative sequence sagging control is used for grid-connected point three-phase voltage unbalance management; harmonic treatment is carried out based on the output current of the converter and the alternating load current; acquiring load power inside an energy router, output power of a photovoltaic power generation unit and output power of an energy storage unit; determining the exchange power of the energy router and the alternating current power grid based on the load power inside the energy router, the output power of the photovoltaic power generation unit and the output power of the energy storage unit by taking the charge state of the battery as a constraint condition; and determining a control mode of the energy router based on the exchange power of the energy router and the alternating current power grid so as to maintain the voltage stability of the direct current bus.
In an alternative embodiment of the present application, the grid-connected inverter includes an ac-dc converter, and an ac grid is connected to a dc bus through the ac-dc converter; the photovoltaic power generation unit, the energy storage unit and the direct current load are respectively connected with a direct current bus through a plurality of direct current-to-direct current converters; the energy router further comprises: the expansion unit is connected with the direct current bus through a direct current-direct current converter.
In an alternative embodiment of the present application, the control modes of the photovoltaic power generation unit include: maximum power point tracking control and direct current bus voltage control; the control mode of the energy storage unit includes: constant voltage charge and discharge control and constant current charge and discharge control; the control mode of the grid-connected converter comprises the following steps: constant power control and droop control.
In an optional embodiment of the present application, the step of performing positive sequence droop control and negative sequence droop control of the grid-connected inverter based on the grid-connected point voltage and the inverter output current includes: the grid-connected point voltage after alpha beta conversion and the converter output current are sequentially subjected to positive and negative sequence separation by a low-pass filter and delay signal cancellation, so that a positive fundamental wave component and a negative fundamental wave component of the voltage and the current under a two-phase static coordinate system are obtained; converting positive fundamental wave components and negative fundamental wave components of the voltage and the current under the two-phase static coordinate system into two-phase rotation coordinate system, and determining positive sequence active power, positive sequence reactive power, negative sequence active power and negative sequence reactive power based on the positive fundamental wave components and the negative fundamental wave components of the voltage and the current under the two-phase static coordinate system; performing positive sequence droop control of the grid-connected converter based on the positive sequence active power and the positive sequence reactive power; and carrying out negative sequence droop control on the grid-connected converter based on the negative sequence active power and the negative sequence reactive power.
In an optional embodiment of the present application, the step of performing positive sequence droop control of the grid-connected inverter based on positive sequence active power and positive sequence reactive power includes: respectively making differences between the positive-sequence active power and the positive-sequence reactive power and a preset charging and discharging reference positive-sequence active power signal and a reference positive-sequence reactive power signal of the energy router, and then obtaining a positive-sequence reference voltage signal through positive-sequence droop control; the positive sequence reference voltage signal outputs a power control signal of the grid-connected converter through voltage-current double-loop proportional-integral control, and the grid-connected converter is driven to operate based on the power control signal; the step of performing negative sequence droop control of the grid-connected converter based on the negative sequence active power and the negative sequence reactive power comprises the following steps: the negative sequence active power and the negative sequence reactive power are subjected to negative sequence droop control after being subjected to difference with a preset charging and discharging reference negative sequence active power signal and a reference negative sequence reactive power signal of the energy router, so that a negative sequence reference voltage signal is obtained; the negative sequence reference voltage signal outputs a three-phase unbalanced current compensation signal through voltage-current double-loop proportional-integral control, and the three-phase unbalanced current compensation signal and the power control signal are overlapped to drive the grid-connected converter to operate.
In an alternative embodiment of the present application, the step of performing harmonic suppression based on the output current of the converter and the ac load current includes: carrying out low-pass filtering on the output current of the converter after alpha beta conversion to obtain a fundamental wave direct current component under a two-phase static coordinate system; the fundamental wave direct current component after the alpha beta inverse transformation is subjected to the difference with the alternating load current to obtain harmonic current compensation quantity of the energy router; and the obtained harmonic current compensation quantity, the output component controlled by positive sequence sagging and the output component controlled by negative sequence sagging are overlapped and then drive the grid-connected converter to operate.
In an alternative embodiment of the present application, the step of determining the exchange power between the energy router and the ac power grid based on the load power inside the energy router, the output power of the photovoltaic power generation unit, and the output power of the energy storage unit using the state of charge of the battery as a constraint condition includes: if the output power of the photovoltaic power generation unit is 0 and the load power in the energy router is 0, determining the exchange power of the energy router and the alternating current power grid as the output power of the energy storage unit; if the output power of the photovoltaic power generation unit is 0, the load power in the energy router is not 0, the state of charge of the battery is not more than 0.2, and the exchange power of the energy router and the alternating current power grid is determined to be the load power in the energy router; if the output power of the photovoltaic power generation unit is 0, the load power in the energy router is not 0, and the charge state of the battery is larger than 0.2, determining the exchange power of the energy router and the alternating current power grid as the difference value between the load power in the energy router and the output power of the energy storage unit; if the output power of the photovoltaic power generation unit is not 0, the load power in the energy router is not less than the load power in the energy router, the charge state of the battery is less than 0.8, and the exchange power of the energy router and the alternating current power grid is determined as the difference value of the load power in the energy router, which is obtained by subtracting the output power of the photovoltaic power generation unit and then subtracting the output power of the energy storage unit; if the output power of the photovoltaic power generation unit is not 0, the load power in the energy router is not less than the load power in the energy router, and the charge state of the battery is not less than 0.8, determining that the exchange power of the energy router and the alternating current power grid is the difference value of the load power in the energy router and the output power of the photovoltaic power generation unit; if the output power of the photovoltaic power generation unit is not 0, the load power in the energy router is smaller than the load power in the energy router, the charge state of the battery is larger than 0.2, and the exchange power of the energy router and the alternating current power grid is determined as the difference value of the load power in the energy router, the output power of the photovoltaic power generation unit is subtracted, and the output power of the energy storage unit is subtracted; if the output power of the photovoltaic power generation unit is not 0, the load power in the energy router is smaller than the load power in the energy router, the charge state of the battery is not greater than 0.2, and the exchange power of the energy router and the alternating current power grid is determined to be the difference value of the load power in the energy router and the output power of the photovoltaic power generation unit.
In an alternative embodiment of the present application, the step of determining the control mode of the energy router based on the exchange power between the energy router and the ac power grid includes: if the exchange power of the energy router and the alternating current power grid is the output power in the energy router, determining that the control mode of the energy router is a standby mode; if the exchange power of the energy router and the alternating current power grid is the load power in the energy router, determining that the control mode of the energy router is an energy storage constant voltage control mode; if the exchange power of the energy router and the alternating current power grid is the difference value between the load power in the energy router and the output power of the energy storage unit, determining that the control mode of the energy router is an energy storage constant voltage control mode; if the exchange power of the energy router and the alternating current power grid is the difference value of the load power in the energy router subtracted from the output power of the photovoltaic power generation unit and subtracted from the output power of the energy storage unit, determining that the control mode of the energy router is an energy storage constant voltage control mode; and if the exchange power of the energy router and the alternating current power grid is the difference value of the load power in the energy router and the output power of the photovoltaic power generation unit, determining that the control mode of the energy router is a photovoltaic constant voltage control mode.
In an alternative embodiment of the present application, the method further includes: when the expansion unit is connected to the equipment, the exchange power of the energy router and the alternating current power grid is determined based on the load power inside the energy router, the output power of the photovoltaic power generation unit, the output power of the energy storage unit and the output power of the equipment.
In a second aspect, an embodiment of the present application further provides a multiport energy router integrated with a power quality management function, where the multiport energy router integrated with a power quality management function is used in the control method of the multiport energy router integrated with a power quality management function.
The embodiment of the application has the following beneficial effects:
the embodiment of the application provides a multiport energy router integrating an electric energy quality management function and a control method thereof, provides a simplified multiport energy router topological structure, facilitates quick access of a new energy power generation unit, an energy storage unit and a load unit, designs an upper energy management system and a bottom control strategy of each unit, and can realize the comprehensive electric energy quality management of an alternating current power grid while maintaining the constant voltage of a direct current bus in the energy router.
Additional features and advantages of the disclosure will be set forth in the description which follows, or in part will be obvious from the description, or may be learned by practice of the techniques of the disclosure.
The foregoing objects, features and advantages of the disclosure will be more readily apparent from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flowchart of a control method of a multiport energy router integrated with a power quality management function according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a multiport energy router topology according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a topology and a control architecture of a photovoltaic power generation unit according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a battery energy storage converter topology according to an embodiment of the present invention;
FIG. 5 is a constant voltage and constant current control block diagram of a battery energy storage converter according to an embodiment of the present invention;
FIG. 6 is a flow chart of another method for controlling a multiport energy router integrated with power quality management functionality according to an embodiment of the present invention;
fig. 7 is a schematic diagram of a grid-connected inverter topology according to an embodiment of the present invention;
fig. 8 is a block diagram of a multi-objective control strategy of a grid-connected inverter according to an embodiment of the present invention;
FIG. 9 is a schematic diagram of an upper energy management flow of an energy router according to an embodiment of the present invention;
FIG. 10 is a schematic diagram of a DC bus voltage waveform according to an embodiment of the present invention;
fig. 11 is a schematic diagram of an energy storage SoC variation curve according to an embodiment of the present invention;
FIG. 12 is a schematic diagram of a photovoltaic output power curve according to an embodiment of the present invention;
fig. 13 is a schematic diagram of an ac three-phase voltage waveform according to an embodiment of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
At present, scholars at home and abroad have studied the topology structure, performance characteristics and control mode of the energy router, and have explained that the energy router can have functions of energy coordination, voltage unbalance management, expandable harmonic management and the like.
In the existing research, the multi-port energy router comprising photovoltaic power generation, energy storage and direct current load has various possible working states, and how to design a reasonable energy router overall control strategy has certain difficulty. The existing scheme has realized the function of realizing energy exchange between an energy router and an alternating current power grid and maintaining the voltage stability of a direct current bus through controlling power electronic devices, but cannot meet the application requirements of comprehensive treatment of the electric energy quality in the intelligent power distribution network.
In order to realize comprehensive management of electric energy quality, a learner refers to the topological structure of a unified electric energy quality controller and designs a novel energy router integrating electric energy quality management and power optimization functions. However, the basic idea of these schemes is to reduce the complexity of control by increasing the number of power electronic devices and the complexity of circuit topology, and this scheme also results in poor scalability of the energy router, which is not beneficial to flexible capacity expansion of the energy router.
In summary, the existing research results do not realize the energy coordination, the electric energy quality management and the extensible functions of the energy router at the same time.
Based on the above, the embodiment of the invention provides a multiport energy router integrating the power quality control function and a control method thereof, so as to provide a simplified multiport energy router topological structure, facilitate the rapid access of a new energy power generation unit, an energy storage unit and a load unit, design an upper energy management system and a bottom control strategy of each unit, and realize the comprehensive power quality control of an alternating current power grid while maintaining the constant voltage of a direct current bus inside the energy router.
For the convenience of understanding the present embodiment, a detailed description will be given of a control method of a multiport energy router integrated with a power quality management function according to an embodiment of the present invention.
Embodiment one:
the embodiment of the invention provides a control method of a multiport energy router integrating an electric energy quality management function, wherein the energy router comprises the following steps: the system comprises an alternating current power grid, a direct current bus, a grid-connected converter, a photovoltaic power generation unit, an energy storage unit and a direct current load. Referring to a flowchart of a control method of a multi-port energy router integrated with a power quality management function shown in fig. 1, the control method of the multi-port energy router integrated with the power quality management function includes the steps of:
Step S102, grid-connected point voltage of an alternating current power grid, converter output current and alternating load current are obtained; positive sequence droop control and negative sequence droop control of the grid-connected converter are performed based on grid-connected point voltage and converter output current; positive sequence sagging control is used for active power control and reactive power control, and negative sequence sagging control is used for grid-connected point three-phase voltage unbalance management; harmonic remediation is performed based on the converter output current and the ac load current.
In order to ensure that the energy router brings power quality problems to the alternating current power grid when the grid-connected converter rectifies or inverts, the energy router can monitor grid-connected point voltage of the alternating current power grid, converter output current and alternating load current in real time.
When the energy router transmits power to the alternating current power grid and participates in electric energy quality management, in order to reduce the influence of a multi-target control strategy of the grid-connected converter on the direct current bus voltage as much as possible, the grid-connected converter of the quantity router provided by the embodiment adopts droop control in a bottom layer control strategy.
The embodiment can further analyze the generation principle of multi-target compensation current on the premise of not changing the running state of the grid-connected converter of the energy router on the basis of introducing the improved droop control of the virtual impedance, and provides an energy router to participate in the comprehensive compensation control strategy of the electric energy quality of the alternating current power grid, namely, the comprehensive treatment of the three-phase voltage unbalance and harmonic treatment of active power, reactive power control and grid-connected points can be performed, so that the comprehensive treatment of the electric energy quality is realized.
Step S104, obtaining the load power inside the energy router, the output power of the photovoltaic power generation unit and the output power of the energy storage unit; determining the exchange power of the energy router and the alternating current power grid based on the load power inside the energy router, the output power of the photovoltaic power generation unit and the output power of the energy storage unit by taking the charge state of the battery as a constraint condition; and determining a control mode of the energy router based on the exchange power of the energy router and the alternating current power grid so as to maintain the voltage stability of the direct current bus.
In this embodiment, the working mode of the energy router may be determined according to the load, the photovoltaic, and the energy storage overall situation.
The multi-target control strategy of the grid-connected converter is realized based on the improved droop control strategy. Although the control mode better ensures that the energy router transmits controllable active power and controllable reactive power and realizes the control target of three-phase unbalanced regulation and harmonic wave management, the direct current bus voltage is difficult to maintain based on a sagging control strategy, namely the multi-target control strategy of the grid-connected converter cannot realize the control target of maintaining the constant direct current bus voltage.
The control mode of the energy router in the present embodiment includes constant voltage control of the energy storage unit or the photovoltaic power generation unit, and therefore, the control target of maintaining the voltage stability of the direct current bus can be achieved by the constant voltage control of the energy storage unit or the photovoltaic power generation unit.
The embodiment of the invention provides a control method of a multiport energy router integrating an electric energy quality management function, provides a simplified multiport energy router topological structure, facilitates quick access of a new energy power generation unit, an energy storage unit and a load unit, designs an upper energy management system and a bottom control strategy of each unit, and can realize the comprehensive electric energy quality management of an alternating current power grid while maintaining the constant voltage of a direct current bus in the energy router.
Embodiment two:
the present embodiment provides another control method of a multiport energy router integrated with a power quality management function, which is implemented on the basis of the above embodiment. In some embodiments, the grid-connected inverter includes an ac-to-dc converter, and the ac grid is connected to a dc bus through the ac-to-dc converter; the photovoltaic power generation unit, the energy storage unit and the direct current load are respectively connected with a direct current bus through a plurality of direct current-to-direct current converters; the energy router further comprises: the expansion unit is connected with the direct current bus through a direct current-direct current converter.
The multi-port energy router according to this embodiment may be a small DC micro-grid in nature, referring to a schematic diagram of a multi-port energy router topology shown in fig. 2, fig. 2 shows a typical 5-port energy router, which includes a 380V AC power grid, a common DC bus, a photovoltaic power generation unit (i.e., the photovoltaic array in fig. 2), an energy storage unit (i.e., the energy storage battery in fig. 2), and a DC load (i.e., the DC load in fig. 2), where each part of fig. 2 is connected to the DC bus through a DC-to-DC (DC/DC) converter or an AC-to-DC (AC/DC) converter, and receives the schedule of the upper communication controller. In addition, in order to embody the expandability of the multi-port energy router topology and the control method according to the present embodiment, an expansion unit may be disposed at the port 5 in fig. 5, so as to facilitate the detailed description of the control method provided in the present embodiment.
In some embodiments, the control mode of the photovoltaic power generation unit includes: maximum power point tracking control and direct current bus voltage control; the control mode of the energy storage unit includes: constant voltage charge and discharge control and constant current charge and discharge control; the control mode of the grid-connected converter comprises the following steps: constant power control and droop control.
With reference to the control method of the direct current micro-grid, the embodiment can divide the control of the energy router into upper-layer coordination layer control and lower-layer control.
The bottom layer control surface is towards the bottom layer interface converter, the types of energy sources or loads connected to the direct current buses are different, the control targets are different, and the bottom layer control methods are also different. The common control method comprises the following steps: tracking the maximum power point of the photovoltaic power generation system and controlling the voltage of a direct current bus; constant voltage/constant current charge and discharge control of the battery energy storage system; constant Power (PQ) control, droop (Droop) control, etc. of the AC/DC converter.
The upper coordination layer control is oriented to the whole operation target of the energy router, and realizes the energy coordination management by carrying out centralized management on each access energy source and load converter in the energy router, and the bottom control strategies of the photovoltaic power generation unit and the energy storage unit are sequentially described below:
1. Photovoltaic power generation unit bottom layer control strategy
The output control mode of the photovoltaic power generation unit needs to be adjusted according to environmental changes and the power balance requirement of the actual energy router. In this embodiment, the bottom control strategy of the photovoltaic power generation unit is constant voltage control and maximum power point tracking (Maximum Power Point Tracking, MPPT) control, referring to a schematic diagram of a topology and a control architecture of the photovoltaic power generation unit shown in fig. 3, and the basic control architecture is shown in fig. 3. In fig. 3, when the switching signal g=0, the photovoltaic panel is connected to the capacitor C pv And inductance L p Charging; when g=1, L and the photovoltaic cell together supply power to the external circuit.
The constant voltage control principle of the photovoltaic power generation unit is also shown in fig. 3, the voltage of the direct current bus can be compared with the voltage reference value, and the obtained difference value is calculated and output by a PI (proportional integral) controller to generate a Pulse Width Modulation (PWM) signal, so that the control of an Insulated Gate Bipolar Thyristor (IGBT) is realized.
For MPPT control, the present embodiment employs a conductance delta approach to achieve maximum power tracking. The basic idea of the conductivity increment method is as follows: the photovoltaic cell always has a point with the maximum output power under certain illumination and temperature conditions, and when the photovoltaic power generation unit operates at the maximum power point, the slope of the photovoltaic output characteristic curve at the moment is 0, namely dP/dU=0. Whereas the rate of change dP/dU >0 on the left of the maximum power point and the rate of change dP/dU <0 on the right of the maximum power point. The purpose of the conductivity increment method is to find the maximum power point of the change rate and enable the photovoltaic cell to always maintain working at the maximum power point when the environment changes.
2. Energy storage unit bottom layer control strategy
Referring to FIG. 4, a schematic diagram of a battery energy storage converter topology is shown, L in FIG. 4 b For battery converter inductance, C dc And C bat The two ends of the converter are respectively provided with a filter capacitor. During charge and discharge control, the battery is controlled to charge through a switch signal S1, and energy flows into the battery from a direct current bus; when electricity is generatedWhen the cell is discharged, the switch signal S2 controls the discharge of the cell, and energy flows into the direct current bus from the cell.
The battery energy storage system has various control modes, and the embodiment mainly adopts a constant current control mode and a constant voltage control mode. In general, the battery energy storage unit can adopt constant current control to charge and discharge under rated current, so that the SoC (state of charge) is maintained in a normal range while new energy is consumed.
Referring to a constant voltage and constant current control block diagram of a battery energy storage converter shown in fig. 5, constant current control adopts single closed loop control, and is different from a given reference value in a charge-discharge mode, and control signals S1/S2 are output after PI and PWM. When disturbance occurs inside and outside the energy router, the energy storage unit enters a constant voltage control state, and the constant voltage control shown in fig. 5 is adopted to maintain the voltage stability of the direct current bus.
Based on the above description, reference may be made to a flowchart of another control method of a multiport energy router integrated with a power quality control function shown in fig. 6, which includes the following steps:
step S602, grid-connected point voltage of an alternating current power grid, converter output current and alternating load current are obtained; positive sequence droop control and negative sequence droop control of the grid-connected converter are performed based on grid-connected point voltage and converter output current; positive sequence sagging control is used for active power control and reactive power control, and negative sequence sagging control is used for grid-connected point three-phase voltage unbalance management; harmonic remediation is performed based on the converter output current and the ac load current.
For the multi-objective control strategy of the grid-connected inverter, refer to a schematic diagram of a topology of the grid-connected inverter shown in fig. 7, in which the grid-connected inverter in fig. 7 is connected in parallel between an ac load and a power grid after passing through an LC filter, and L abc The filter inductance is the AC side filter inductance of the grid-connected converter, C abc Is a filter capacitor. In order to ensure that the energy router itself brings power quality problems to the AC power grid when the AC/DC converter is rectified or inverted, the energy router needs to monitor the AC load current i in real time Labc Grid current i Gabc Output current i of converter abc Grid-connected point voltage u abc 。
When the energy router transmits power to the alternating current power grid and participates in electric energy quality management, in order to reduce the influence of a multi-target control strategy of the grid-connected converter on the direct current bus voltage as much as possible, the AC/DC converter bottom layer control strategy of the energy router provided by the embodiment adopts droop control. On the premise of not changing the running state of the grid-connected converter of the energy router on the basis of introducing the improved droop control of the virtual impedance, the generation principle of the multi-target compensation current is further analyzed, and the energy router participates in the comprehensive compensation control strategy of the electric energy quality of the alternating current power grid is provided.
1. Three-phase unbalance management control strategy
When the three phases of the power grid are unbalanced, the unbalanced voltage can be decomposed by a symmetrical component method. Since the AC/DC converter adopted in the present embodiment is a three-phase three-wire system, zero-sequence current cannot flow, so zero-sequence components are not considered, and thus the output voltage of the converter can be expressed as:
（1）
in the formula (1):，/>the magnitudes of the positive and negative sequence components, respectively; />Is the initial phase angle of the negative sequence component.
Is provided with，/>The transformation matrix from the αβ coordinate system to the abc coordinate system and the dq coordinate system, respectively, can be expressed as:
（2）
（3）
In the middle of。
The positive and negative sequence components of the output voltage are respectively transformed in a positive and negative sequence rotation coordinate system to obtain the quantities of the positive and negative sequence components of the output voltage in a static coordinate system, and the transformation is shown in the formulas (4-9).
（4）
In the formula (4):、/>、/>、/>the d, q components of the positive and negative sequence components of the output voltage in the synchronous rotating coordinate system, respectively.
The output voltage can be expressed by equation (4):
（5）
and then transforming the positive and negative sequence coordinates of the step (5) into:
（6）
in formula (6):、/>is->The quantities in the coordinate system are rotated synchronously in the positive and negative sequences.
It can be seen that after the three-phase unbalanced voltage is subjected to dq coordinate transformation, the positive sequence component of the output voltage becomes a direct current quantity, and the negative sequence component thereof becomes a double frequency alternating current quantity. In order to realize three-phase unbalance management when the load is unbalanced, positive and negative sequences in the output voltage can be respectively controlled after being separated.
2. Positive and negative sequence separation based on time delay cancellation (DSC)
The delayed signal cancellation method is based on a combination of positive and negative sequence component vectors, allowing accurate information of the sequence components to be obtained with a time delay of one quarter of a period (5 ms at 50Hz of the grid frequency).
In the general case of an asymmetric grid, the voltage vector in a two-phase stationary coordinate system Can be written as:
（7）
wherein,and->The magnitudes of the positive and negative phase sequence voltage vectors, respectively, and the phase shifts thereof. The DSC method applied to the two-phase stationary coordinate system is defined by the formulas (8) and (9).
（8）
（9）
In the middle ofAnd->Estimated positive and negative phase sequence voltages, respectively, ">Is the grid voltage period. Substituting (7) into (8) and (9) to estimate the phase sequence voltage vector as formula (10) and formula (11).
（10）
（11）
Similarly, the method can be used for calculating the output current i of the converter abc Positive and negative sequence components of (a).
For the harmonic current compensation control strategy, the harmonic current can be divided into positive sequence harmonic and negative sequence harmonic by adopting a symmetrical component method, the positive sequence harmonic current component and the negative sequence harmonic current component can be converted into other frequencies due to dq conversion, and the positive sequence unbalanced component and the negative sequence unbalanced component are contained in the harmonic compensation current in the calculation process. Therefore, in order to realize comprehensive compensation of harmonic currents and simplify the design of the controller, the present embodiment adopts αβ transformation for calculation of harmonic compensation currents, transforms three-phase currents in a three-phase rotating coordinate system to two-phase stationary coordinate systems, and the number of times of each current component remains unchanged.
In some embodiments, the grid-connected point voltage after alpha beta transformation and the converter output current are sequentially subjected to positive and negative sequence separation by a low-pass filter and delay signal cancellation, so as to obtain a positive fundamental wave component and a negative fundamental wave component of the voltage and the current under a two-phase static coordinate system; converting positive fundamental wave components and negative fundamental wave components of the voltage and the current under the two-phase static coordinate system into two-phase rotation coordinate system, and determining positive sequence active power, positive sequence reactive power, negative sequence active power and negative sequence reactive power based on the positive fundamental wave components and the negative fundamental wave components of the voltage and the current under the two-phase static coordinate system; performing positive sequence droop control of the grid-connected converter based on the positive sequence active power and the positive sequence reactive power; and carrying out negative sequence droop control on the grid-connected converter based on the negative sequence active power and the negative sequence reactive power.
Referring to a multi-target control strategy block diagram of a grid-connected converter shown in fig. 8, when the energy router performs comprehensive treatment on electric energy quality, the voltage u of a grid-connected point of an alternating current power grid is mainly calculated abc Converter output current i abc And an alternating nonlinear load current i Labc Monitoring is performed.
As shown in fig. 8, the grid-tie point voltage u abc And converter output current i abc After alpha beta transformation, the voltage and current positive and negative fundamental wave components under a two-phase static coordinate system are obtained after the low-pass filter and DSC positive and negative sequence separation are sequentially carried out、、/>、/>After the positive and negative fundamental wave components under the two-phase static coordinate system are further transformed to the two-phase rotating coordinate system, the obtained result can be used for positive and negative sequence sagging control of the converter, and grid-connected point three-phase voltage unbalance management and active and reactive power control are carried out.
As shown in fig. 8, the positive/negative sequence components of the voltage and current in the two-phase rotating coordinate system、/>、/>、The positive sequence active power P is obtained after passing through a power calculation module P Positive sequence reactive power Q P Negative sequence active power P N Negative sequence reactive power Q N 。
In some embodiments, the positive-sequence active power and the positive-sequence reactive power can be respectively differenced with a charging and discharging reference positive-sequence active power signal and a reference positive-sequence reactive power signal of a preset energy router, and then the positive-sequence reference voltage signal is obtained through positive-sequence droop control; the positive sequence reference voltage signal outputs a power control signal of the grid-connected converter through voltage-current double-loop proportional-integral control, and the grid-connected converter is driven to operate based on the power control signal.
As shown in fig. 8, in the converter positive sequence control, P P And Q P Positive sequence active and reactive power signal P referenced with energy router charge and discharge ref-P 、Q ref-P And after the difference is made, the positive sequence reference voltage signal is obtained through positive sequence droop control. And outputting a converter power control signal through voltage-current double-loop PI control to drive the AC/DC converter to operate.
In some embodiments, the negative sequence active power and the negative sequence reactive power can be subjected to negative sequence droop control after being subjected to difference between the negative sequence active power and the reference negative sequence reactive power signal of the charging and discharging reference negative sequence active power signal of the preset energy router, so as to obtain a negative sequence reference voltage signal; the negative sequence reference voltage signal outputs a three-phase unbalanced current compensation signal through voltage-current double-loop proportional-integral control, and the three-phase unbalanced current compensation signal and the power control signal are overlapped to drive the grid-connected converter to operate.
As shown in fig. 8, similarly, in the negative sequence control of the inverter, to achieve three-phase imbalance management, P N And Q N Active and reactive power signal P with reference negative sequence ref-N 、Q ref-N And performing difference making, and obtaining a negative sequence reference voltage signal through negative sequence droop control. And a three-phase unbalanced current compensation signal is output through voltage-current double-loop PI control, and is overlapped with a power control signal output in positive sequence control to drive the AC/DC converter to operate.
In some embodiments, the αβ transformed converter output current may be low pass filtered to obtain a fundamental dc component in a two-phase stationary coordinate system; the fundamental wave direct current component after the alpha beta inverse transformation is subjected to the difference with the alternating load current to obtain harmonic current compensation quantity of the energy router; and the obtained harmonic current compensation quantity, the output component controlled by positive sequence sagging and the output component controlled by negative sequence sagging are overlapped and then drive the grid-connected converter to operate.
As shown in fig. 8, finally, when harmonic suppression is performed, the converter output current i after αβ conversion is first performed abc Low-pass filtering to obtain fundamental wave DC component in two-phase static coordinate system、/>The fundamental wave component is subjected to alpha beta inverse transformation and then is subjected to nonlinear load current i Labc And (5) taking the difference to obtain the harmonic current compensation quantity which is output by the energy router outwards. After the obtained compensation quantity is overlapped with the output components of the positive and negative sequence control of the converter, the comprehensive treatment of the electric energy quality can be realized on the basis of not influencing the normal working state of the energy router.
Step S604, obtaining the load power inside the energy router, the output power of the photovoltaic power generation unit and the output power of the energy storage unit; determining the exchange power of the energy router and the alternating current power grid based on the load power inside the energy router, the output power of the photovoltaic power generation unit and the output power of the energy storage unit by taking the charge state of the battery as a constraint condition; and determining a control mode of the energy router based on the exchange power of the energy router and the alternating current power grid so as to maintain the voltage stability of the direct current bus.
The embodiment also provides an upper layer coordination control method of the energy router, and the multi-target control strategy of the grid-connected converter can be realized based on the improved droop control strategy based on the steps. Although the control mode better ensures that the energy router transmits controllable active power and controllable reactive power and realizes the control target of three-phase unbalanced regulation and harmonic wave management, the direct current bus voltage is difficult to maintain based on a sagging control strategy, namely the multi-target control strategy of the grid-connected converter cannot realize the control target of maintaining the constant direct current bus voltage. Therefore, the control target of maintaining the voltage stability of the dc bus needs to be achieved by constant voltage control by the energy storage unit or the photovoltaic power generation unit.
For the upper-layer energy management flow and operation state division of the energy router, the possible energy management states of the energy router need to be analyzed first, and the energy balance relationship inside the energy router is shown in the following formula (12).
（12）
In the formula (12), P g For exchanging power between the energy router and the AC network, P l P, which is the load power inside the energy router PV For the output power of the photovoltaic power generation unit, P b And outputting power to the energy storage unit. Based on the formula (12), the overall energy management flow of the energy router according to the embodiment can be obtained by using the state of charge (SoC) of the battery as a constraint condition, and a schematic diagram of an upper energy management flow of the energy router shown in fig. 9 can be referred to.
As shown in fig. 9, if the output power of the photovoltaic power generation unit is 0 and the load power inside the energy router is 0, it is determined that the exchange power of the energy router and the ac power grid is the output power of the energy storage unit.
As shown in fig. 9, if the output power of the photovoltaic power generation unit is 0, the load power inside the energy router is not 0, and the state of charge of the battery is not greater than 0.2, the exchange power between the energy router and the ac power grid is determined to be the load power inside the energy router.
As shown in fig. 9, if the output power of the photovoltaic power generation unit is 0, the load power inside the energy router is not 0, and the state of charge of the battery is greater than 0.2, the exchange power between the energy router and the ac power grid is determined as the difference between the load power inside the energy router and the output power of the energy storage unit.
As shown in fig. 9, if the output power of the photovoltaic power generation unit is not 0, the load power inside the energy router is not less than the load power inside the energy router, and the state of charge of the battery is less than 0.8, it is determined that the exchange power of the energy router and the ac power grid is the difference value of subtracting the output power of the photovoltaic power generation unit from the load power inside the energy router and subtracting the output power of the energy storage unit from the load power inside the energy router.
As shown in fig. 9, if the output power of the photovoltaic power generation unit is not 0, the load power inside the energy router is not less than the load power inside the energy router, and the state of charge of the battery is not less than 0.8, it is determined that the exchange power of the energy router and the ac power grid is the difference value of the load power inside the energy router minus the output power of the photovoltaic power generation unit.
As shown in fig. 9, if the output power of the photovoltaic power generation unit is not 0, the load power inside the energy router is smaller than the load power inside the energy router, and the state of charge of the battery is greater than 0.2, it is determined that the exchange power of the energy router and the ac power grid is the difference value of the load power inside the energy router subtracted from the output power of the photovoltaic power generation unit and subtracted from the output power of the energy storage unit.
As shown in fig. 9, if the output power of the photovoltaic power generation unit is not 0, the load power inside the energy router is smaller than the load power inside the energy router, and the state of charge of the battery is not greater than 0.2, it is determined that the exchange power of the energy router and the ac power grid is the difference value of the load power inside the energy router minus the output power of the photovoltaic power generation unit.
The core of the upper energy management flow is that the energy storage unit is fully utilized to absorb photovoltaic electric energy on the basis of ensuring constant voltage of the direct current bus. At night, the photovoltaic output power is 0, so that the energy storage completely bears the control target of maintaining the voltage of the direct current bus. And when the direct current is loaded with the electricity demand When the voltage is higher than the lower limit value of 0.2, the stored energy can supply power to the load, and P is the same as the voltage of the battery g =P l -P b The method comprises the steps of carrying out a first treatment on the surface of the If less than 0.2, the load is supplied mainly by the grid, i.e. P g =P l . When no power is required in the energy router, the whole energy router is in a standby state, and outputs a small amount of power to an external alternating current power grid when required to meet the power quality control requirement. It should be noted that, since energy storage needs enough energy to participate in constant voltage control no matter whether SoC of the energy storage system reaches the lower limit value 0.2, the present embodiment appropriately reduces the charge and discharge depth of the energy storage unit, i.e. the upper limit value and the lower limit value of SoC of the energy storage unit are respectively set to 0.8 and 0.2.
During daytime, the photovoltaic output power P is firstly judged PV Whether or not to be smaller than the load demand power P l Such as P PV >P l Enabling the photovoltaic to maintain the MPPT running state during the period that the energy storage system SoC is smaller than 0.8, wherein P is the same g =P l -P PV -P b . When the charging of the energy storage SoC reaches more than 0.8, the control of the photovoltaic is switched to constant voltage control, and at the moment, P is present g =P l -P PV . When P PV <P l When the energy storage SoC is larger than 0.2, the energy storage system is in a constant voltage control state, the photovoltaic is in an MPPT running state, and after the SoC is smaller than 0.2, the control of the photovoltaic is converted from MPPT to constant voltage control.
Based on the above analysis, the dominant unit for performing constant voltage control can be determined from the energy management flowchart of the energy router, and thus the control strategy design of each unit of the energy router can be simplified into three types as shown in fig. 9: photovoltaic constant voltage control mode, energy storage constant voltage control mode, standby mode, specifically:
if the output power of the photovoltaic power generation unit is 0 and the load power in the energy router is 0, determining the exchange power of the energy router and the alternating current power grid as the output power of the energy storage unit;
if the output power of the photovoltaic power generation unit is 0, the load power in the energy router is not 0, the state of charge of the battery is not more than 0.2, and the exchange power of the energy router and the alternating current power grid is determined to be the load power in the energy router;
if the output power of the photovoltaic power generation unit is 0, the load power in the energy router is not 0, and the charge state of the battery is larger than 0.2, determining the exchange power of the energy router and the alternating current power grid as the difference value between the load power in the energy router and the output power of the energy storage unit;
if the output power of the photovoltaic power generation unit is not 0, the load power in the energy router is not less than the load power in the energy router, the charge state of the battery is less than 0.8, and the exchange power of the energy router and the alternating current power grid is determined as the difference value of the load power in the energy router, which is obtained by subtracting the output power of the photovoltaic power generation unit and then subtracting the output power of the energy storage unit;
If the output power of the photovoltaic power generation unit is not 0, the load power in the energy router is not less than the load power in the energy router, and the charge state of the battery is not less than 0.8, determining that the exchange power of the energy router and the alternating current power grid is the difference value of the load power in the energy router and the output power of the photovoltaic power generation unit;
if the output power of the photovoltaic power generation unit is not 0, the load power in the energy router is smaller than the load power in the energy router, the charge state of the battery is larger than 0.2, and the exchange power of the energy router and the alternating current power grid is determined as the difference value of the load power in the energy router, the output power of the photovoltaic power generation unit is subtracted, and the output power of the energy storage unit is subtracted;
if the output power of the photovoltaic power generation unit is not 0, the load power in the energy router is smaller than the load power in the energy router, the charge state of the battery is not greater than 0.2, and the exchange power of the energy router and the alternating current power grid is determined to be the difference value of the load power in the energy router and the output power of the photovoltaic power generation unit.
Step S606, when the expansion unit is connected to the device, determining the exchange power between the energy router and the ac power grid based on the load power inside the energy router, the output power of the photovoltaic power generation unit, the output power of the energy storage unit, and the output power of the device.
For expansion of the energy router, in order to ensure flexible expansion of the energy router, the multiport energy router not only needs to meet the standard plug and play interface and routing protocol requirements, but also puts forward a requirement on whether the upper energy management system allows the expansion of the energy router. Based on the analysis of the foregoing steps, the main basis for determining the system operation state is to compare the output power of the photovoltaic with the load demand power, and consider the SoC state of the stored energy at the same time. On the basis of the analysis of the above steps, if a new device is connected to the expansion unit of the port 5 in fig. 2, the energy balance relationship of the equation (12) is updated to the following equation (13).
（13）
It can be seen that, whether the load or the distributed power is connected to the port 5, the scenario and the working condition corresponding to the formula (13) still conform to the upper energy management flowchart shown in fig. 9 under the condition that the underlying control strategy is unchanged. Therefore, it can be considered that the energy router has scalability within the range allowed by the maximum transmission power of the energy storage and grid-connected inverter.
In the embodiment, a simulation result is also provided, when the simulation starts, the direct current load is 14kW, the alternating current load is 6kW, the grid-connected converter outputs 6kW of active power to the power grid, the photovoltaic is under MPPT control, the output power is 28.7kW, the energy storage system is charged at a constant voltage, and redundant electric energy output by the photovoltaic is absorbed.
Referring to a schematic diagram of a dc bus voltage waveform shown in fig. 10, a schematic diagram of an energy storage SoC variation curve shown in fig. 11, a schematic diagram of a photovoltaic output power curve shown in fig. 12, and an ac three-phase voltage waveform schematic diagram shown in fig. 13, the obtained simulation waveforms are as shown in fig. 10-13, when t=0.5 s, the energy storage SoC reaches the upper limit of 0.8, charging is stopped, and at the same time, the photovoltaic power generation unit is converted from MPPT control to constant voltage control, the output power is reduced to 20kW, i.e., the photovoltaic power is supplied to the dc load, and the ac load is supplied through the grid-connected inverter.
It can also be seen from fig. 10 that the dc bus voltage remains constant throughout the change in the internal operating state of the energy router. Meanwhile, as can be seen from fig. 13, at t=0.6 s, the inverter starts to perform three-phase imbalance control, and the imbalance of the three-phase ac voltage is improved.
The embodiment of the invention provides a multiport energy router control method integrating an electric energy quality management function. Specifically, positive and negative sequence components of grid-connected point voltage and grid-connected converter output current are obtained through a delay cancellation method, different control targets of the energy router grid-connected converter are considered, active and reactive power control of the energy router is achieved through positive sequence sagging control, three-phase imbalance treatment is achieved through negative sequence sagging control, and harmonic treatment is achieved through filtering control of load current under a two-phase static coordinate system. Meanwhile, an upper-layer energy coordination control strategy of the energy router is designed, and the voltage stability of the direct-current bus can be maintained at any time while the energy router exchanges power with an alternating-current power grid, so that the coordination capacity and expandability of the energy router are improved.
The method provided by the embodiment of the invention provides an upper energy management strategy of the energy router, solves the problem that the voltage of the direct current bus cannot be maintained constant when the grid-connected converter transmits power and treats the quality of electric energy, can avoid instability of the system caused by improper control, and improves coordination capacity and expandability of the energy router. In addition, the multi-target control strategy of the bottom grid-connected converter provided by the embodiment solves the defect that the conventional scheme cannot treat the electric energy quality of the alternating current power grid, and comprehensively improves the steady-state electric energy quality of the alternating current/direct current system under different operation conditions.
Embodiment III:
corresponding to the above method embodiments, the embodiments of the present invention provide a multiport energy router integrated with a power quality management function, and the multiport energy router integrated with a power quality management function is used to execute the control method of the multiport energy router integrated with a power quality management function provided in the foregoing embodiments.
The embodiment of the invention provides a multiport energy router integrating an electric energy quality management function, provides a simplified multiport energy router topological structure, facilitates quick access of a new energy power generation unit, an energy storage unit and a load unit, designs an upper energy management system and a bottom control strategy of each unit, and can realize comprehensive electric energy quality management of an alternating current power grid while maintaining constant voltage of a direct current bus inside the energy router.
It will be clearly understood by those skilled in the art that, for convenience and brevity of description, the specific working process of the above-described multiport energy router integrated with the power quality management function may refer to the corresponding process in the foregoing embodiment of the control method of the multiport energy router integrated with the power quality management function, which is not described herein again.
Finally, it should be noted that: the above examples are only specific embodiments of the present invention, and are not intended to limit the scope of the present invention, but it should be understood by those skilled in the art that the present invention is not limited thereto, and that the present invention is described in detail with reference to the foregoing examples: any person skilled in the art may modify or easily conceive of the technical solution described in the foregoing embodiments, or perform equivalent substitution of some of the technical features, while remaining within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention, and are intended to be included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (10)

1. A method of controlling a multiport energy router integrated with a power quality management function, the energy router comprising: the system comprises an alternating current power grid, a direct current bus, a grid-connected converter, a photovoltaic power generation unit, an energy storage unit and a direct current load; the method comprises the following steps:
acquiring grid-connected point voltage of the alternating current power grid, converter output current and alternating load current; performing positive sequence droop control and negative sequence droop control of the grid-connected converter based on the grid-connected point voltage and the converter output current; the positive sequence droop control is used for performing active power control and reactive power control, and the negative sequence droop control is used for performing grid-connected point three-phase voltage unbalance management; harmonic remediation based on the converter output current and the ac load current;
acquiring load power inside the energy router, output power of the photovoltaic power generation unit and output power of the energy storage unit; determining the exchange power of the energy router and the alternating current power grid based on the load power inside the energy router, the output power of the photovoltaic power generation unit and the output power of the energy storage unit by taking the charge state of the battery as a constraint condition; a control mode of the energy router is determined based on the exchange power of the energy router with the ac power grid to maintain the voltage of the dc bus stable.
2. The method for controlling a multiport energy router integrated with a power quality management function according to claim 1, wherein the grid-connected inverter comprises an ac-to-dc converter, and the ac grid is connected to the dc bus through the ac-to-dc converter;
the photovoltaic power generation unit, the energy storage unit and the direct current load are respectively connected with the direct current bus through a plurality of direct current-direct current converters;
the energy router further comprises: the expansion unit is connected with the direct current bus through a direct current-direct current converter.
3. The method for controlling a multiport energy router integrated with a power quality management function according to claim 1, wherein the control mode of the photovoltaic power generation unit comprises: maximum power point tracking control and direct current bus voltage control; the control mode of the energy storage unit comprises the following steps: constant voltage charge and discharge control and constant current charge and discharge control; the control mode of the grid-connected converter comprises the following steps: constant power control and droop control.
4. The method for controlling a multiport energy router integrated with a power quality management function according to claim 1, wherein the step of performing positive sequence droop control and negative sequence droop control of the grid-connected inverter based on the grid-connected point voltage and the inverter output current comprises:
Sequentially separating positive and negative sequences of the grid-connected point voltage after alpha beta conversion and the converter output current through a low-pass filter and delay signal cancellation to obtain a positive fundamental wave component and a negative fundamental wave component of the voltage and the current under a two-phase static coordinate system;
converting positive fundamental wave components and negative fundamental wave components of the voltage and the current under the two-phase static coordinate system into two-phase rotation coordinate system, and determining positive sequence active power, positive sequence reactive power, negative sequence active power and negative sequence reactive power based on the positive fundamental wave components and the negative fundamental wave components of the voltage and the current under the two-phase static coordinate system;
performing positive sequence droop control of the grid-connected converter based on the positive sequence active power and the positive sequence reactive power;
and carrying out negative sequence droop control on the grid-connected converter based on the negative sequence active power and the negative sequence reactive power.
5. The method for controlling a multiport energy router integrated with a power quality control function according to claim 4, wherein the step of performing positive sequence droop control of the grid-connected inverter based on the positive sequence active power and the positive sequence reactive power comprises:
respectively differencing the positive-sequence active power and the positive-sequence reactive power with a preset charging and discharging reference positive-sequence active power signal and a reference positive-sequence reactive power signal of the energy router, and then obtaining a positive-sequence reference voltage signal through positive-sequence droop control; the positive sequence reference voltage signal outputs a power control signal of the grid-connected converter through voltage-current double-loop proportional-integral control, and the grid-connected converter is driven to operate based on the power control signal;
And performing negative sequence droop control of the grid-connected converter based on the negative sequence active power and the negative sequence reactive power, wherein the negative sequence droop control comprises the following steps:
the negative sequence active power and the negative sequence reactive power are subjected to negative sequence droop control after being subjected to difference between the negative sequence active power and the negative sequence reactive power and a preset charging and discharging reference negative sequence active power signal and a reference negative sequence reactive power signal of the energy router, so that a negative sequence reference voltage signal is obtained;
and the negative sequence reference voltage signal outputs a three-phase unbalanced current compensation signal through voltage-current double-loop proportional-integral control, and the three-phase unbalanced current compensation signal and the power control signal are overlapped to drive the grid-connected converter to operate.
6. The method of controlling a multiport energy router integrated with a power quality control function according to claim 1, wherein the step of performing harmonic control based on the converter output current and the ac load current comprises:
carrying out low-pass filtering on the output current of the converter after alpha beta conversion to obtain a fundamental wave direct current component under a two-phase static coordinate system;
the fundamental wave direct current component after the alpha beta inverse transformation is subjected to the difference with the alternating load current to obtain harmonic current compensation quantity of the energy router;
And the obtained harmonic current compensation quantity, the output component of the positive sequence droop control and the output component of the negative sequence droop control are overlapped and then drive the grid-connected converter to operate.
7. The method for controlling a multiport energy router integrated with a power quality management function according to claim 1, wherein the step of determining the exchange power of the energy router with the ac power grid based on the load power inside the energy router, the output power of the photovoltaic power generation unit, and the output power of the energy storage unit with the state of charge of the battery as a constraint condition comprises:
if the output power of the photovoltaic power generation unit is 0 and the load power in the energy router is 0, determining that the exchange power of the energy router and the alternating current power grid is the output power of the energy storage unit;
if the output power of the photovoltaic power generation unit is 0, the load power in the energy router is not 0, and the state of charge of the battery is not more than 0.2, determining that the exchange power of the energy router and the alternating current power grid is the load power in the energy router;
if the output power of the photovoltaic power generation unit is 0, the load power in the energy router is not 0, and the charge state of the battery is greater than 0.2, determining that the exchange power of the energy router and the alternating current power grid is the difference value between the load power in the energy router and the output power of the energy storage unit;
If the output power of the photovoltaic power generation unit is not 0, the load power in the energy router is not less than the load power in the energy router, and the charge state of the battery is less than 0.8, determining that the exchange power of the energy router and the alternating current power grid is the difference value of the load power in the energy router minus the output power of the photovoltaic power generation unit and minus the output power of the energy storage unit;
if the output power of the photovoltaic power generation unit is not 0, the load power in the energy router is not less than the load power in the energy router, and the charge state of the battery is not less than 0.8, determining that the exchange power of the energy router and the alternating current power grid is the difference value of the load power in the energy router minus the output power of the photovoltaic power generation unit;
if the output power of the photovoltaic power generation unit is not 0, the load power in the energy router is smaller than the load power in the energy router, and the charge state of the battery is larger than 0.2, determining that the exchange power of the energy router and the alternating current power grid is the difference value of the load power in the energy router minus the output power of the photovoltaic power generation unit and minus the output power of the energy storage unit;
And if the output power of the photovoltaic power generation unit is not 0, the load power in the energy router is smaller than the load power in the energy router, and the charge state of the battery is not greater than 0.2, determining that the exchange power of the energy router and the alternating current power grid is the difference value of the load power in the energy router minus the output power of the photovoltaic power generation unit.
8. The method of controlling a multiport energy router integrated with a power quality management function according to claim 7, wherein the step of determining a control mode of the energy router based on an exchange power of the energy router with the ac power grid comprises:
if the exchange power of the energy router and the alternating current power grid is the output power inside the energy router, determining that the control mode of the energy router is a standby mode;
if the exchange power of the energy router and the alternating current power grid is the load power in the energy router, determining that the control mode of the energy router is an energy storage constant voltage control mode;
if the exchange power of the energy router and the alternating current power grid is the difference value between the load power inside the energy router and the output power of the energy storage unit, determining that the control mode of the energy router is an energy storage constant voltage control mode;
If the exchange power of the energy router and the alternating current power grid is the difference value of the load power in the energy router subtracted by the output power of the photovoltaic power generation unit and subtracted by the output power of the energy storage unit, determining that the control mode of the energy router is an energy storage constant voltage control mode;
and if the exchange power of the energy router and the alternating current power grid is the difference value of the load power in the energy router minus the output power of the photovoltaic power generation unit, determining that the control mode of the energy router is the photovoltaic constant voltage control mode.
9. The method of controlling a multiport energy router integrated with power quality check functions of claim 2, further comprising:
when the expansion unit is connected to a device, the exchange power of the energy router and the alternating current power grid is determined based on the load power inside the energy router, the output power of the photovoltaic power generation unit, the output power of the energy storage unit and the output power of the device.
10. A multiport energy router integrating power quality control functions, characterized in that the multiport energy router integrating power quality control functions is used for executing the control method of the multiport energy router integrating power quality control functions according to any one of claims 1 to 9.
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