CN105406515A - Hierarchically-controlled independent microgrid - Google Patents

Abstract

The invention provides a hierarchically-controlled independent microgrid. According to the microgrid, as for regional energy supply demands, comprehensive utilization of power generated from a plurality of kinds of renewable energy sources is mainly adopted, and power generated by fuel gas/oil and stored energy is adopted auxiliarily. With the microgrid which is practically applicable and is established as the modes mentioned above adopted, the power supplying quality of a distributed power source and the utilization efficiency of clean energy can be improved, and the consumption of fossil resources and environmental pollutant emission can be decreased; distributed power generation accommodating capacity can be enhanced, long-term stable electricity utilization demands can be met, and large-area power blackout can be avoided. The hierarchically-controlled independent microgrid has application and demonstration significances.

Description

Independent Microgrids with Hierarchical Control

technical field

The invention relates to the technical field of power systems, in particular to a hierarchically controlled independent microgrid.

Background technique

Vigorously strengthening the basic theoretical research of renewable energy integrated utilization technology and promoting the large-scale and efficient integrated utilization of renewable energy is a major basic research problem that needs to be solved urgently in the energy field. According to local resource conditions, rationally select and comprehensively utilize multiple renewable energy sources (wind energy, solar energy, ocean energy, biomass energy, backup diesel engines, etc.) to form a distributed renewable energy power supply system and form a microgrid to achieve independent operation or grid connection Operation is the main direction of efficient utilization of renewable energy in the future.

Microgrid is an important part of smart grid, which is an autonomous system capable of self-control, protection and management. Through reasonable power management in the microgrid, the control of power quality is realized, and the change of power exchange between the microgrid and the public grid is controlled, and the problem of sudden changes in distributed generation is overcome. Multi-energy complementary distributed micro-grid technology can realize optimal scheduling and distribution of energy for the micro-grid system, maximize system efficiency, and ensure safe and reliable operation of the system. At present, the research on single renewable energy technology and its control is relatively mature, but for the integrated application of multiple renewable energy technologies and basic theoretical research issues related to microgrids, including the optimal networking technology of distributed renewable energy system microgrids, System structure, research on independent and grid-connected operation control of micro-grid, energy management and dispatching strategy of micro-grid, wireless communication and remote monitoring of micro-grid, impact of micro-grid on grid-connected system, adaptation to distributed renewable energy generation system Research on frequency conversion, commutation, and protection measures needs to be strengthened to solve basic theoretical problems related to distributed renewable energy generation systems and microgrid control, and to promote large-scale and efficient integrated applications of renewable energy.

Renewable energy independent power plants and their distributed power generation microgrid system technology can maximize system efficiency, which is one of the main development directions for the efficient use of renewable energy in the future. Not only can it solve the power supply far away from the power grid and some special areas (mountains, islands), ecological energy projects in rural construction, highway signals and lighting, power supply for users with high power supply costs, etc., it can also be used as an effective supplement to the main power grid to improve transmission The safety and reliability of the substation can reduce the power loss of the line, and its market promotion and application prospect is bright.

Contents of the invention

The purpose of the present invention is to propose a hierarchically controlled independent micro-grid. Aiming at regional energy supply needs, a variety of renewable energy sources (power generation comprehensive utilization is mainly used, gas/oil power generation and energy storage power generation are supplemented. Based on this, the The practically applicable independent micro-grid can improve the power supply quality of distributed power sources and the utilization efficiency of clean energy, reduce the consumption of fossil resources and environmental pollutant emissions; enhance the acceptance capacity of distributed power generation to meet long-term stable power demand, Avoiding large-scale blackout accidents has application demonstration significance.

In order to achieve the above object, the concrete technical scheme that the present invention takes is:

An independent microgrid with hierarchical control, including a superior microgrid and several sub-microgrids;

Each sub-microgrid includes renewable energy generation units, energy storage devices and loads;

Each sub-microgrid includes renewable energy generation units, energy storage devices, and loads. The renewable energy generation units and loads are connected to the AC bus, and the energy storage device is connected to the DC bus. Each sub-microgrid uses a bidirectional converter as a The interface equipment of the upper-level microgrid, the three sets of terminals of the bidirectional converter are respectively connected to the AC bus of the sub-microgrid, the AC bus of the upper-level microgrid, and the DC bus of the energy storage device of the sub-microgrid;

When the sub-microgrid is in the power transmission mode to the upper-level microgrid, the sub-microgrid transmits electric energy to the upper-level microgrid according to the instructions of the upper-level microgrid according to the specified power, and at the same time, the internal power consumption of the sub-microgrid is supplied by the renewable energy generation unit. When the power generated by renewable energy is greater than the load required, the excess electric energy will charge the energy storage device; when the power generated by the renewable energy is less than the load required, the insufficient electric energy will be supplemented by the energy storage device;

Under the mode of obtaining electric energy from the upper-level micro-grid, the sub-micro-grid obtains electric energy from the upper-level micro-grid according to the instruction of the upper-level micro-grid according to the specified power. The electric energy will charge the energy storage device of the sub-microgrid, and the electric energy obtained from the upper-level micro-grid will also charge the energy storage device. When the power generated by the renewable energy is less than the load demand, the insufficient power gap depends on the energy obtained from the upper-level micro-grid. Electric energy replenishment, and at the same time determine charging or discharging the energy storage device according to the power supply and power consumption conditions.

The independent microgrid with hierarchical control of the present invention adopts a two-level control structure. The sub-microgrid uses a bidirectional converter as an interface device with the upper-level microgrid, and the sub-microgrid bidirectional converter operates as a voltage source relative to the sub-microgrid. , determines the voltage of the sub-microgrid bus; compared to the upper-level microgrid, it operates as a grid-connected inverter in the case of power transmission, and operates as a synchronous rectifier when obtaining power from the upper-level microgrid. In this way, the power conversion between the upper-level microgrid and the sub-microgrid is completed, the power supply quality of the distributed power supply and the utilization efficiency of clean energy are improved, the consumption of fossil resources and the discharge of environmental pollutants are reduced; the acceptance capacity of distributed power generation is enhanced, It has application demonstration significance to meet long-term and stable electricity demand and avoid large-scale power outages.

Description of drawings

Fig. 1 is the structure schematic diagram of the independent microgrid of hierarchical control of the present invention;

Figure 2 is the main circuit topology of the self-synchronous bidirectional converter;

Figure 3 is the main circuit topology of the three-port bidirectional converter;

Figure 4 is a flow chart of independent microgrid energy management control for hierarchical control;

Figure 5 is a structural diagram of an independent microgrid intelligent dispatching control system.

detailed description

The present invention will be described in detail below according to the drawings and specific embodiments, but not as a limitation of the present invention.

The independent micro-grid of the present invention includes a super-level micro-grid and several sub-micro-grids.

Each microgrid in this embodiment adopts an AC busbar structure, as shown in Figure 1, all distributed power sources, energy storage, and loads are connected to a 380V low-voltage busbar, and are connected to a 10KV power transmission and transformation system through a transformer. Structurally, the microgrid can be regarded as composed of the main microgrid and several similar sub-microgrids, each sub-microgrid consists of renewable energy generation units (photovoltaic power generation, wind power generation, etc.), energy storage devices and loads. This independent microgrid allows multiple sub-microgrids to exist under the first-level microgrid. By controlling the power exchange between the sub-microgrid and the upper-level microgrid, the sub-microgrid becomes a stable load of the upper-level microgrid, which facilitates the power scheduling of the upper-level microgrid. According to this architecture, many small microgrids can be integrated into a large microgrid framework, and theoretically unlimited expansion is possible.

The sub-microgrid uses a bidirectional converter as the interface device with the upper-level microgrid. The three sets of terminals of the bidirectional converter are respectively connected to the sub-microgrid AC bus, the upper-level microgrid AC bus, and the energy storage device DC bus. Power distribution is fully controlled by bidirectional converters. The sub-microgrid can be mainly divided into two working modes. The first one is to operate when the sub-microgrid transmits power to the upper-level microgrid. In this mode, the sub-microgrid sends power to the upper-level microgrid according to The specified power is used to transmit electric energy, and at the same time, the power inside the sub-microgrid is powered by renewable energy. When the power generated by the renewable energy is greater than the load demand, the excess electric energy will charge the energy storage device of the sub-microgrid. When the renewable energy When the generated power is less than the load required, the insufficient electric energy is supplemented by the energy storage device. The second working mode is the case where the internal power of the sub-microgrid obtains electric energy from the upper-level microgrid. When the power generated by renewable energy is greater than that required by the load, the excess electric energy will charge the energy storage device of the sub-microgrid, and the electric energy obtained from the upper-level microgrid will also charge the energy storage device. When the power generated by renewable energy is less than that required by the load, the insufficient power gap is supplemented by the power obtained from the upper-level micro-grid, and at the same time, the charging or discharging power of the energy storage device must be determined according to the power supply and power consumption conditions. The bi-directional converter of the sub-microgrid operates as a voltage source relative to the interior of the sub-microgrid, and determines the voltage of the busbar of the sub-microgrid; compared with the upper-level microgrid, it operates as a grid-connected inverter under the condition of power transmission. It operates as a synchronous rectifier when extracting power from the grid.

The distributed power generation units in the independent microgrid are mainly photovoltaic power generation units, wind power generation units and backup diesel engine power generation units, supplemented by biomass power generation units and ocean energy power generation units. Biomass power generation units and ocean energy power generation units may be connected depending on the actual resource conditions of the micro-grid site. For example, when there is sufficient biogas supply, biogas power generation units can be connected. When it is close to a sea area with enough wave energy to use, it can be connected to the ocean energy generation unit, and the access method is to connect the "Eagle" wave energy device to the microgrid by supplying power to the shore load (battery) . The configuration ratio of each renewable energy generation unit in the microgrid mainly considers photovoltaic power generation and wind power generation as the first choice of renewable energy power generation in the microgrid, and determines wind power generation and photovoltaic power generation according to actual climate conditions and historical data of photovoltaic power generation and wind power generation. The installed capacity allocation ratios for power generation and their proper proportional relationship with the total installed capacity.

The energy storage devices in the independent microgrid are mainly energy-type battery energy storage devices such as batteries, and power-type energy storage devices such as supercapacitors and flywheels can also be considered as auxiliary devices.

The loads in the independent microgrid include power load, peak load, and sub-microgrid as the stable load of the upper-level microgrid:

1. Electric loads can be divided into sensitive loads, controllable loads and shedable loads according to their importance. Sensitive loads require continuous and uninterrupted power supply, controllable loads can interrupt power supply if necessary, and shedable loads can be cut off at any time;

2. The peak-shaving load adopts the ice-making/cooling-storage peak-shaving load system to cooperate with the power supply and consumption regulation of the independent micro-grid and meet the needs of current load peak-shaving. The main configuration of the system includes an ice maker, a water-cooled cooling tower and a large ice storage. Analyze the demand for domestic energy, and combine the operating parameters of the independent micro-grid, as well as years of meteorological statistics, to effectively predict the future cold storage capacity, thereby fully reducing ineffective cold storage, greatly improving the energy efficiency of the cold storage system, and overall power consumption Reduced by more than 20%;

The power conversion device in the independent microgrid is mainly a bidirectional converter. The bidirectional converter for the microgrid is the key hardware device of the entire system. According to the needs of networking and operation control, it can work in the inverter or rectification state, and can be used to establish a voltage reference signal and realize the bidirectional flow of power. Its topology is shown in the figure 2 shows:

1. Figure 2 shows the topology of the main circuit of the self-synchronous bidirectional converter. The primary side is three single-phase full-bridge circuits, the secondary side adopts Y-shaped connection, and the filter inductor and output transformer adopt an integrated three-column iron core. The structure can ensure that under the balanced/unbalanced, linear/non-linear loads, the control output voltage and current waveforms are good, the harmonics are less, and it is easy to realize.

The control of the converter is mainly divided into two parts, which are phase-locked control and voltage waveform control. Phase a voltage refers to the phase angle difference between the positive zero-crossing point of the sine meter and the rising edge of the synchronous pulse, and adjusts the cycle value of the PWM wave after performing proportional calculations to achieve zero-phase difference phase locking between the two. The reference voltage waveforms of phase b and phase c can be a The phase voltage is obtained by delaying 120 degrees and 240 degrees sequentially with reference to the sine table.

The common synchronous pulse is transmitted by optical fiber, and each bidirectional converter in the microgrid uses the common synchronous pulse as a phase-locking reference to truly realize the modularization and distributed access of the bidirectional converter.

Through the current sharing control of the bidirectional converter, the single machine and multi-machine parallel operation can be realized, and the system capacity can be expanded.

2. Figure 3 shows the topology of the main circuit of the three-port bidirectional converter. It adopts two sets of main circuits separated by inverter and rectifier. On the basis of traditional UPS power supply, four-quadrant high-power frequency conversion technology is used to carry out UPS inverter The secondary transformation can realize the "coupling link" on both sides of the bidirectional converter, so that the distributed power generation units of different frequencies and different voltage levels can be connected through the energy storage system, so that the microgrid can be divided into smaller sub-micro The network accepts upper-level scheduling;

The energy management of the independent microgrid adopts a two-level control structure. Based on the received information, the upper-level control refers to the output forecasting and load forecasting results of the distributed power generation unit, and considers the actual operation of the current micro-grid, and forms control instructions through optimization calculations; the lower-level control mainly includes the control of the power generation unit and the management of energy storage devices. and load management.

1. Prediction of power generation trend. According to the operating status of the microgrid, constantly correct its own operating status, establish an expert system, apply fuzzy technology and BP neural network technology to predict the power of photovoltaic power plants in operation, and pre-estimate the situation of power generation changes. Reasonably dispatch power generation capacity, make full use of solar energy resources, and obtain more economic and social benefits.

2. Load trend forecasting, according to the influence of weather, temperature, day type and other factors on the load, the fuzzy technology is applied to predict the current load.

3. The control of the power generation unit changes the working mode of the power generation unit according to the control instructions of the energy management system, and adjusts the power output of the power generation unit. The energy management system adjusts the output characteristics of the power generation unit according to the monitoring results. When the load demand increases, the power generation unit is ordered to increase the output power or start some micro power sources; when the load demand decreases, the power generation unit is ordered to reduce the output power or shut down some power generation units.

4. The management of energy storage devices, manage the charge and discharge of energy storage devices according to the actual power generation and electricity demand of the microgrid, and conduct real-time detection and management of the state of charge, health and safety performance of energy storage devices.

5. Load management, distribute the output of micro-power sources according to the size of the load, and maintain the balance between the power generation of micro-power sources and the power consumption of loads in the micro-grid. When a fault occurs, the general load is cut off to ensure the power supply of the important load.

The microgrid energy management control strategy adopts "grasp the large and let go of the small", put some control functions at the sub-microgrid or distributed power interface, and let the sub-microgrid or distributed power interface equipment adopt the local "autonomous" method , to reduce the dependence on the superior control system:

In the grid-connected mode, the voltage and frequency of the microgrid are determined by the large grid. The energy storage system mainly plays the role of energy balance adjustment, realizes the dynamic balance of energy inside the microgrid, and maximizes the use of renewable energy. At this time, wind turbines and photovoltaics and other renewable energy power generation all adopt PQ control (also called constant power control) for maximum power tracking. The specific strategy is: when the load is less than the total output power of renewable energy generation in the microgrid, the energy storage converter is controlled to charge the battery until the battery is fully charged, and the microgrid transmits excess electric energy to the large grid; otherwise, when the load is greater than When the output power of renewable energy generation in the microgrid is summed, the battery is discharged by controlling the energy storage converter until the battery can no longer be discharged, and the microgrid absorbs part of the electric energy from the large grid. In addition, relying on the command control of the energy storage converter by the dispatching control system and the two-way rapid power adjustment capability of the energy storage converter, the energy storage system can also perform rapid power adjustment, effectively reducing wind power and photovoltaics. The impact of fluctuations in power generation output on large power grids and loads, so as to ensure the safe operation of the power grid and the reliable power supply of loads.

In the island mode, different from the grid-connected mode, the adjustment of power gap and frequency must be completed by each power generation unit, energy storage and control in the microgrid. Therefore, in order to achieve the energy scheduling goal of optimal system economy, highest power supply reliability, and optimal energy storage distribution, it is necessary to flexibly adjust the feeder power flow in the microgrid, adjust the voltage at the interface of each micro power generation unit, and ensure voltage stability. . The specific control process is shown in Figure 4. First, set the bidirectional converter to V/f mode, and establish the reference voltage and frequency of the microgrid. At this time, the energy is mainly provided by the energy storage system; then, the wind power and photovoltaic systems are connected to the grid, and the microgrid scheduling control system enters the background cycle scheduling In the working mode, the output power of the power generation unit (wind power and photovoltaic system) and load power are continuously monitored. If the output power of the generating unit is greater than the load power, first check whether the fuel generator has been started, and stop its work if it is started. Continue to monitor, if the output power of the generating unit is still greater than the load power, then charge the energy storage system until the charging upper limit is reached, and then start the adjustable load. On the contrary, if it is detected that the output power of the power generation unit is lower than the load power, first check whether there is an adjustable load that can be cut off, if there is, cut it off, if not, start the energy storage system to discharge until the lower limit of discharge is reached, and then start the backup power supply to generate electricity machine to ensure the power supply of the microgrid. As an emergency measure, when entering the island mode, if the energy storage system does not have enough electric energy to support important loads, the backup power fuel generator can be set to V/f mode to establish the reference voltage and frequency of the microgrid. The subsequent control is similar to the control in the grid-connected mode, the difference is that only important loads are supplied with power at this time, and general loads are not started.

The independent micro-grid intelligent dispatching control system monitors the operating status of the entire micro-grid system, and controls and manages the components of the micro-grid according to the multi-objective coordinated control strategy according to the actual situation. The system is designed and developed on the basis of summarizing the advanced control and data acquisition systems at home and abroad. It uses network technology to ensure the real-time performance of the system. All modules use object-oriented programming methods. The system is easy to maintain and expand. The system completely gets rid of the dependence on the specific hardware platform, supports various operating platforms such as WINDOWSNT/2000/XP/2003, and the configuration is convenient and flexible. Its overall structure is shown in Figure 5. The main station layer of the system includes database, SCADA, EMS, and DA subsystems. The sub-station layer includes distributed power supply, energy storage unit, distribution network feeder, classified load and related management equipment (such as Microgrid controller, measurement and control protection device, etc.). The master station layer and the sub-station layer communicate through the 100/1000M optical fiber ring network.

(1) SCADA server

It has the functions of main processor and server, and is the center of monitoring system data collection, processing, storage, distribution and command issuance. The server is also the monitoring center of the entire network. Servers are generally configured with dual-machine redundancy. The main server monitors the startup, shutdown, and network failure of each computer in the network in real time and broadcasts the monitoring results to the entire network, so that any computer in the network can see the operation of the entire network. The standby server monitors the running status of the primary server. When the primary server fails, the secondary server automatically becomes the primary server. The database between the primary and secondary servers remains unified, and two-way data unification or backup can be performed manually.

(2) Operator station

The main man-machine interface of the automation system in the station is used for graph and report display, event record and alarm state display and query, equipment status and parameter query, operation guidance, formation and issuance of operation control commands, etc. Through the operator station, the operation duty personnel can realize the operation monitoring and operation control of the whole equipment.

(3) System maintenance engineer station

For system administrators to maintain the system, it can complete the definition and modification of the system configuration database, the definition and modification of the system configuration graphics, the production and modification of reports, network maintenance, system diagnosis and other work.

(4) Other workstations (optional)

Computers designed for bureau chiefs, chief engineers, livelihood, electricity, maintenance and other departments. These computers can only monitor the system operation screen, and cannot modify the system or send commands such as remote control.

(5) Communication interface equipment

Communication interface equipment, including telecontrol workstations, communication front-end processors, etc., can be selected according to system requirements and networking modes. The active/standby front-end processors are hot standby for each other, with manual/automatic switching. When the two defined front-end processors are running, the machine that runs the front-end processor program first is the main front-end processor; the main front-end processor completes all tasks to be completed by the front-end processor, and the backup front-end processor is timed with the main front-end processor. Carry out simple communication, listen to the running status of the main front-end processor, and for some reason, the communication with the main front-end processor is interrupted, and the standby front-end processor will be upgraded to the main front-end processor (the automatic switching time is not more than 30 seconds). The main/standby channels are hot standby for each other, manual/automatic switching.

The communication front-end processor can be used to access the comprehensive automation system of each substation, and supports Ethernet, serial communication ports, etc. In terms of function, the front-end processor collects information such as system analog quantities, switch quantities, and electricity quantities. After protocol conversion and processing, it is connected to the system station control layer monitoring network through a network interface, or through various telecontrol protocols through analog channels, The digital channel or network transmits the signal to the dispatching terminal.

(6) Network equipment

The system uses a network switch as a network connection device, and other devices such as firewalls, routers, and gateways are also optional.

The network equipment adopts industrial-grade products, and the network cable adopts super-category five shielded twisted-pair wires, and optical fibers can also be used.

(7) Satellite clock calibration equipment

The whole station is equipped with a set of GPS time synchronization equipment, which can track 8 GPS satellites, the start-up satellite capture time is ≤1min, the antenna radio frequency sensitivity is -170dB, the feeder is 1.56GHZ, 0.4dB/m, and RS-232C/RS422/485≥4 , Time error <1ms.

The above detailed description is a specific description of the feasible embodiment of the present invention. This embodiment is not used to limit the patent scope of the present invention. Any equivalent implementation or change that does not deviate from the present invention should be included in the patent scope of this case. middle.

Claims (3)

1. A hierarchically controlled independent microgrid, characterized in that, Including the upper-level microgrid and several sub-microgrids; Each sub-microgrid includes renewable energy generation units, energy storage devices and loads; Each sub-microgrid includes renewable energy generation units, energy storage devices, and loads. The renewable energy generation units and loads are connected to the AC bus, and the energy storage device is connected to the DC bus. Each sub-microgrid uses a bidirectional converter as a The interface equipment of the upper-level microgrid, the three sets of terminals of the bidirectional converter are respectively connected to the AC bus of the sub-microgrid, the AC bus of the upper-level microgrid, and the DC bus of the energy storage device of the sub-microgrid; When the sub-microgrid is in the power transmission mode to the upper-level microgrid, the sub-microgrid transmits electric energy to the upper-level microgrid according to the instructions of the upper-level microgrid according to the specified power, and at the same time, the internal power consumption of the sub-microgrid is supplied by the renewable energy generation unit. When the power generated by renewable energy is greater than the load required, the excess electric energy will charge the energy storage device; when the power generated by the renewable energy is less than the load required, the insufficient electric energy will be supplemented by the energy storage device; Under the mode of obtaining electric energy from the upper-level micro-grid, the sub-micro-grid obtains electric energy from the upper-level micro-grid according to the instruction of the upper-level micro-grid according to the specified power. The electric energy will charge the energy storage device of the sub-microgrid, and the electric energy obtained from the upper-level micro-grid will also charge the energy storage device. When the power generated by the renewable energy is less than the load demand, the insufficient power gap depends on the energy obtained from the upper-level micro-grid. Electric energy replenishment, and at the same time determine charging or discharging the energy storage device according to the power supply and power consumption conditions. 2. The independent microgrid of hierarchical control according to claim 1, characterized in that, Renewable energy power generation units are mainly photovoltaic power generation units, wind power generation units and backup diesel engine power generation units, supplemented by biomass power generation units and ocean energy power generation units. 3. The independent microgrid with hierarchical control according to claim 1 or 2, characterized in that, The bidirectional converter is a three-port bidirectional converter or an energy storage type self-synchronous bidirectional converter; The bidirectional converter operates as a voltage source relative to the sub-microgrid, which determines the voltage of the sub-microgrid bus; compared to the upper-level microgrid, it operates as a grid-connected inverter in the case of power transmission, and obtains power from the upper-level microgrid. operating as a synchronous rectifier.