CN115864520A - Control method and system for accessing hybrid power grid based on high-proportion photovoltaic energy - Google Patents
Control method and system for accessing hybrid power grid based on high-proportion photovoltaic energy Download PDFInfo
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Abstract
The invention belongs to the technical field of power grid regulation and control, and discloses a control method and a control system for accessing a hybrid power grid based on high-proportion photovoltaic energy, wherein the control method comprises the following steps of; acquiring operating parameters of the synchronous generator, and respectively establishing a phase angle model of the synchronous generator and an active frequency control model of an inverter power supply; acquiring operating parameters of the photovoltaic energy storage inverter in an active state and a reactive state in the microgrid, and establishing a reference voltage model and a reactive voltage control model of the photovoltaic energy storage inverter; and controlling the voltage and frequency fluctuation of a grid connection point caused by accessing the micro-grid into the alternating current-direct current hybrid grid according to the established phase angle model of the synchronous generator, the active frequency control model of the inverter power supply, the reference voltage model of the photovoltaic energy storage inverter and the reactive voltage control model. Through model calculation, the control of grid-connected point voltage and frequency fluctuation caused by the fact that the micro grid is connected into the alternating current-direct current hybrid grid is achieved, and the voltage and frequency fluctuation in the direct current hybrid grid connected into the micro grid is reduced.
Description
Technical Field
The invention belongs to the technical field of power grid regulation and control, and particularly relates to a control method and a control system for accessing a hybrid power grid based on high-proportion photovoltaic energy.
Background
In order to meet the challenges of global climate change and environmental pollution, the realization of sustainable economic development and the reduction of carbon emissions are important measures and strategies. The method has the advantages of constructing a clean, low-carbon, safe and efficient energy system, controlling the total amount of fossil energy, focusing on improving the utilization efficiency, implementing renewable energy source substitution action, deepening electric power system reform and constructing a novel electric power system taking new energy as a main body to become a mainstream trend and a leading direction.
The alternating current-direct current hybrid micro-grid concept is provided aiming at the problems of intermittency and the like of a new energy power generation system and starts to be applied to practical engineering practice, the normal operation of the micro-grid can not be efficiently and reasonably controlled, a large-scale distributed power source has renewable energy with small energy intermittency, volatility and capacity and is merged into a traditional centralized power grid, great threat can be generated on the existing power grid system, and when the intermittent photovoltaic power source and the fluctuating photovoltaic power source are connected into the alternating current-direct current hybrid power grid, the voltage and the frequency of a grid connection point are fluctuated.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a control method and a control system for accessing a hybrid power grid based on high-proportion photovoltaic energy, which can control the voltage and frequency fluctuation of a grid-connected point caused by accessing a micro-grid to an alternating current-direct current hybrid power grid, and reduce the voltage and frequency fluctuation of the micro-grid accessed to a direct current hybrid power grid.
In order to achieve the above purpose, the invention provides the following technical scheme:
a control method based on high-proportion photovoltaic energy access to a hybrid power grid comprises the following steps of;
acquiring operating parameters of the synchronous generator, and respectively establishing a phase angle model of the synchronous generator and an active frequency control model of an inverter power supply;
acquiring operating parameters of the photovoltaic energy storage inverter in an active state and a reactive state in the microgrid, and establishing a reference voltage model and a reactive voltage control model of the photovoltaic energy storage inverter;
and controlling the voltage and frequency fluctuation of a grid connection point caused by accessing the micro-grid into the alternating current-direct current hybrid grid according to the established phase angle model of the synchronous generator, the active frequency control model of the inverter power supply, the reference voltage model of the photovoltaic energy storage inverter and the reactive voltage control model.
Further, the phase angle model of the synchronous generator is
Wherein it is present>
To the phase angle, ω and ω, of a synchronous machine g The angular velocities corresponding to the 0 moment and the t moment in the upper and lower integration limits are respectively.
Further, the inverter power supply active frequency control model of the synchronous generator is
Wherein H is a virtual inertia time constant corresponding to the moment of inertia J, P in For the input power of the inverter, P out The output power of the inverter power supply, omega, is the angular frequency of the inverter power supply, omega g For angular frequency of the common bus, K d Is the damping coefficient. />
Further, the reference voltage model of the photovoltaic energy storage inverter is
Wherein Q is ref And D q Respectively setting an input value and a droop coefficient for the reactive power; t is a Is a delay link time constant; e set And E g Respectively outputting signals for the reference terminal voltage and the reactive power controller of the distributed inverter power supply; k is a radical of p1 And k i1 Are proportional integral coefficients of respective links.
Further, the reactive voltage control model of the photovoltaic energy storage inverter is
Wherein Q is 0 Is rated power; k is a radical of Q Is a reactive power regulation coefficient; q e Instantaneous reactive power for the inverter; e 0 Is a virtual no-load potential; a virtual excitation potential E; k is a radical of U Terminal voltage of generatorAdjusting the coefficient; u is the effective value of the output voltage of the inverter.
Further, said E 0 ＝311V。
Further, when the microgrid enters an off-grid working state, a power supply in the microgrid provides voltage and frequency for a main power grid, and the voltage and frequency generated when the virtual synchronous generator works are adopted to control the photovoltaic inverter to work, so that the photovoltaic system is maintained to operate stably.
A control system based on high-proportion photovoltaic energy access hybrid power grid comprises a power grid, a power grid controller and a power grid controller, wherein the power grid controller is connected with the power grid controller;
the synchronous generator control module is used for acquiring the operating parameters of the synchronous generator and respectively establishing a phase angle model of the synchronous generator and an active frequency control model of the inverter power supply;
the photovoltaic energy storage inverter control module is used for acquiring the operating parameters of the photovoltaic energy storage inverter in the active and reactive states in the microgrid and establishing a reference voltage model and a reactive voltage control model of the photovoltaic energy storage inverter;
and the comprehensive control module is used for realizing control of grid connection point voltage and frequency fluctuation caused by accessing the micro-grid into the alternating current-direct current hybrid grid according to the established phase angle model of the synchronous generator, the inverter power supply active frequency control model, the reference voltage model of the photovoltaic energy storage inverter and the reactive voltage control model.
Compared with the prior art, the invention has the advantages that:
according to the control method for accessing the hybrid power grid based on the high-proportion photovoltaic energy, the phase angle model of the synchronous generator, the active frequency control model of the inverter power supply, the reference voltage model of the photovoltaic energy storage inverter and the reactive voltage control model are established by acquiring the operating parameters of the synchronous generator and the operating parameters of the photovoltaic energy storage inverter in the active state and the reactive state in the microgrid, the voltage and the frequency under the coordination control of the reactive-voltage, the active-frequency and the photovoltaic energy storage in the photovoltaic power grid are analyzed respectively, the control of the voltage and the frequency fluctuation of a grid-connection point caused by accessing the microgrid into the AC-DC hybrid power grid is realized through model calculation, and the fluctuation of the voltage and the frequency in the DC hybrid power grid accessed into the microgrid is reduced.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.
In the drawings:
FIG. 1 is a topological structure diagram of an AC/DC hybrid micro-grid in a control method for accessing a hybrid grid based on high-proportion photovoltaic energy according to the invention;
FIG. 2 is a vector diagram of an equivalent circuit of a synchronous generator in the control method for accessing a hybrid power grid based on high-proportion photovoltaic energy according to the invention;
fig. 3 is a block diagram of active-frequency control of a kungfu system in a control method for accessing a hybrid power grid based on high-proportion photovoltaic energy according to the present invention;
FIG. 4 is a block diagram of the reactive-voltage control of the photovoltaic system in a control method for accessing a hybrid grid based on high-proportion photovoltaic energy according to the present invention;
fig. 5 is a structural diagram of a light storage alternating current-direct current hybrid micro-grid system in an island working mode of a micro-grid in the control method based on the high-proportion photovoltaic energy access hybrid grid of the invention;
fig. 6 is a structural diagram of a hybrid light storage microgrid system in the control method based on the high-proportion photovoltaic energy access hybrid power grid of the invention;
FIG. 7 is a block diagram of a preceding stage control structure of a photovoltaic energy storage system in the control method for accessing a hybrid power grid based on high-proportion photovoltaic energy sources according to the invention;
FIG. 8 is a control flow diagram of a main inverter with VSG control in a preferred embodiment of a control method for accessing a hybrid power grid based on high-proportion photovoltaic energy according to the present invention;
FIG. 9 is a schematic diagram of constant power control of a slave control unit in a preferred embodiment of a control method for accessing a hybrid power grid based on high-proportion photovoltaic energy according to the present invention;
fig. 10 is a schematic flow chart of a control method for accessing a hybrid power grid based on a high-proportion photovoltaic energy source according to the present invention;
Detailed Description
The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The following detailed description is exemplary in nature and is intended to provide further details of the invention. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention.
According to the control method for accessing the hybrid power grid based on the high-proportion photovoltaic energy, a multi-loop control method and a light storage hybrid micro-grid power coordination control method based on a synchronous generator control mode are provided through research and research aiming at the hybrid micro-grid system in a grid-connected mode and an off-grid (island) mode, so that the system is stably operated, and the condition that the system has frequent power conversion among sub-grid systems is avoided.
Example 1
A control method for accessing a hybrid power grid based on high-proportion photovoltaic energy, as shown in fig. 10, includes;
acquiring operating parameters of the synchronous generator, and respectively establishing a phase angle model of the synchronous generator and an active frequency control model of an inverter power supply;
acquiring operating parameters of the photovoltaic energy storage inverter in an active state and a reactive state in the microgrid, and establishing a reference voltage model and a reactive voltage control model of the photovoltaic energy storage inverter;
and controlling the voltage and frequency fluctuation of a grid connection point caused by the access of the micro-grid to the AC/DC hybrid power grid according to the established phase angle model of the synchronous generator, the active frequency control model of the inverter power supply, the reference voltage model of the photovoltaic energy storage inverter and the reactive voltage control model.
In particular, the phase angle model of the synchronous generator is
Wherein it is present>
For the phase angle of the synchronous machine, ω and ω g The angular velocities corresponding to the time 0 and the time t in the upper and lower integration limits are respectively.
Specifically, the active frequency control model of the inverter power supply of the synchronous generator is
Wherein H is a virtual inertia time constant corresponding to the moment of inertia J, P in For the power input of the inverter, P out The output power of the inverter power supply, omega, is the angular frequency of the inverter power supply, omega g For angular frequency of the common bus, K d Is the damping coefficient.
Specifically, the ac/dc hybrid microgrid is a microgrid structure most widely applied in field engineering at present, and is divided into an ac sub-grid system and a dc sub-grid system as shown in fig. 1, which are connected by respective buses, and each sub-grid can directly supply power to an ac load and a dc load. Distributed power supplies, energy storage devices and power electronics are usually connected into the sub-network. According to the invention, on the basis of research on an alternating current-direct current hybrid microgrid, after structural characteristics and advantages of the microgrid are analyzed and researched, the problems that power flow and power reference value selection of a typical control mode of a bidirectional converter under an off-grid condition are insufficient are solved, and a new control mode of the bidirectional converter based on comprehensive droop in an off-grid mode is provided. Meanwhile, the complexity is increased for the system by introducing a complex upper-layer power management system into the energy storage access microgrid to coordinate the photovoltaic system access and the power balance of the energy storage unit, and in order to realize the power coordination control of the hybrid microgrid, the comprehensive control method is adopted to realize the power coordination control of high-proportion photovoltaic energy and energy storage.
According to analysis of the hybrid microgrid, a microgrid formed by distributed power supplies generally has two completely different working modes of grid connection and grid disconnection (isolated island), the grid connection mode is mainly characterized in that the grid connection mode is connected with a power grid system, the power grid system and the microgrid system can generate electric energy exchange, the microgrid can obtain power regulation of the power grid, so that stable operation can be kept, and electric energy generated by new energy sources such as photovoltaic and the like can be effectively utilized in the grid connection operation mode. If the micro-grid is separated from the power grid to independently operate, the micro-grid in an off-grid (island) mode needs to realize power balance and voltage regulation by means of distributed energy sources such as photovoltaic and the like and an energy storage device in the system. In order to ensure the continuity of power supply, the microgrid system is usually regulated by an energy storage device, so as to ensure that important loads can obtain continuous electric energy.
For the alternating current-direct current hybrid micro-grid, if the alternating current-direct current hybrid micro-grid is directly connected with a power grid, the system mainly realizes power exchange through a public connection point connected with the power grid, and therefore internal power balance is realized. Under the state, the photovoltaic and other distributed power supplies can work in a maximum power mode, if the microgrid system has redundant electric energy, the redundant electric energy is directly merged into a large power grid, and if the microgrid system has insufficient power, the power grid can supply power to the microgrid system. The working state of the microgrid can be determined by the energy storage system connected into the microgrid according to the bus voltage on the microgrid, and if the microgrid is found to have power fluctuation, power balance is carried out by controlling charging and discharging modes. The ac/dc power converter for system control needs to be always in a stable working state to ensure that the dc side can exchange electric energy with the grid.
If the hybrid microgrid is separated from the large power grid, the hybrid microgrid enters an off-grid (island) mode, and the alternating current side is not connected with the power grid any more, so that the microgrid cannot realize self power balance through the large power grid. At this time, the distributed power supply is usually required to be set in a constant voltage control working mode, and the energy storage system also needs to release electric energy, so that the microgrid system can be timely adjusted in power to maintain stable operation. The bidirectional alternating current-direct current converter needs to adjust the working mode of the bidirectional alternating current-direct current converter according to the working mode of the power grid, so that the power in the micro-grid can be accurately adjusted, important loads are guaranteed to be stably supplied with power, meanwhile, the stability of a system is maintained, and in addition, the utilization efficiency of the power supply is improved as far as possible.
Specifically, the photovoltaic energy storage system needs to enable the photovoltaic unidirectional inverter to have the working characteristics of the synchronous generator, so that the vector relation principle of the synchronous generator is firstly analyzed. Fig. 2 is a schematic diagram of an operating circuit of a synchronous generator after the synchronous generator is connected to a large power grid, and the following diagram shows the vector relationship between the voltages at two ends of each device in the circuit and the circuit current.
U in the figure s For synchronizing the electromotive force in the generator, R is equivalent to the resistance of the inverter, jX is equivalent to the reactance of the inverter, U g Is terminal voltage, I g In order to be the current flow,
is the phase angle. If the straight axis d of the fixed rotating coordinate system and the network end voltage U are fixed g The directions of the two are the same, and the quadrature axis q and the d axis are mutually vertical. Decomposing the vectors shown in fig. 2 into d-axis and q-axis results in the direct-axis and quadrature-axis output currents shown below, with the specific expressions shown below.
Wherein, admittance Y and U sd 、U sq Are respectively as
Phase angle
For both rotor and system angular velocities ω and ω g Integration of the difference, i.e.
The angular speed omega of a rotor of the synchronous generator is adjusted through a speed regulator, and the angular frequency and the active power of the generator directly determine the angular speed; the internal potential Us of the generator is controlled by an excitation system, and the magnitude of the potential is determined by voltage and reactive power. Therefore, a speed regulator model of the synchronous generator is introduced into the converter control mode, and an excitation system model is also introduced, so that the control method of the photovoltaic energy storage system has the similar characteristic of the synchronous generator.
The control mode under the reactive power-frequency is as follows:
the rotor of the synchronous generator has inertia, so that the condition of sudden change of frequency cannot occur in a short time; therefore, according to the rotor motion equation, virtual inertia control is introduced into the inverter control method, so that the converter has the working characteristics similar to the rotor motion in the synchronous generator, and the active frequency control equation of the inverter is shown as follows.
Wherein H is a virtual inertia time constant corresponding to the moment of inertia J, P in For the input power of the inverter, P out The output power of the inverter, omega, is the angular frequency of the inverter, omega g For angular frequency of the common bus, K d Is the damping coefficient.
When the system is connected to a large power grid, the frequency omega of the photovoltaic unidirectional inverter g And when the clamping is carried out, the frequency of the microgrid is directly determined by the large power grid system, so that the frequency of the microgrid does not need to be adjusted by a distributed inverter. However, if the photovoltaic inverter is connected to a microgrid and the permeability is high, the microgrid needs a distributed power supply to adjust the frequency of the system, so that the system can still keep a normal running state when the load of the system changes. The invention provides a link for adding active-frequency droop control, and a frequency modulation controller is formed in the system, and the adjusting process of the frequency modulation controller is shown as follows.
In the formula, P ref Active power; d p Is the sag factor; omega ref Is a reference angular frequency. In the joint type, a 'speed regulator' model shown as follows is obtained, namely the transfer function of the active-frequency controller is:
the active-frequency control block diagram is shown in fig. 3.
If the photovoltaic inverter is connected with a large power grid at the moment, and the system frequency is the reference frequency, the droop control mode does not work any more at the moment, and the droop control mode has the similar working characteristics with the rotor in the synchronous motor. If the micro-grid is incorporated, the controller can realize droop control on the basis of maintaining the characteristics of the rotor through regulation, so that even if the internal frequency fluctuates, the controller can also play a role in regulating, the fluctuation of the system frequency is reduced, and the system is ensured to be in a stable operation state. And a damping control module K d (ω-ω g ) The frequencies of the microgrid system and the photovoltaic inverter can be kept consistent.
Specifically, the reference voltage model of the photovoltaic energy storage inverter is
Wherein Q is ref And D q Respectively setting an input value and a droop coefficient for the reactive power; t is a Is the delay link time constant; e set And E g Respectively outputting signals for the reference terminal voltage and the reactive power controller of the distributed inverter power supply; k is a radical of formula p1 And k i1 Are proportional integral coefficients of respective links.
Specifically, the reactive voltage control model of the photovoltaic energy storage inverter is
Wherein Q is 0 Is rated power; k is a radical of formula Q Is a reactive power regulation coefficient; q e Instantaneous reactive power for the inverter; e 0 Is a virtual no-load potential; a virtual excitation potential E; k is a radical of U Adjusting a coefficient for a terminal voltage; u is the effective value of the output voltage of the inverter.
Preferably, said E0=311V.
Specifically, when the microgrid enters an off-grid working state, a power supply in the microgrid provides voltage and frequency for a main power grid, and the voltage and frequency generated when the virtual synchronous generator works are adopted to control the photovoltaic inverter to work, so that the photovoltaic system is maintained to operate stably.
The control mode under the reactive power-voltage condition is as follows:
the design of the invention provides a photovoltaic energy storage inverter control system shown in figure 4 through the analysis of the structural operation mode based on the synchronous generator excitation system, which is a reactive-voltage controller model circuit.
Wherein Q is ref And D q Respectively setting an input value and a droop coefficient for the reactive power; t is a Is a delay link time constant; e set And E g Respectively outputting signals for the reference terminal voltage and the reactive power controller of the distributed inverter power supply; k is a radical of p1 And k i1 Are proportional integral coefficients of respective links.
The photovoltaic storage inverter reference voltage can thus be obtained as shown below.
The PI controller has the characteristic of high response speed when controlling the reactive power output by the system, but the reactive power in the synchronous generator needs a period of time when tending to a steady state, if the change is too fast, the active power is caused to fluctuate violently, so that a corresponding delay link needs to be added on the basis of PI control, the reactive power is slowly transited to the steady state value due to the existence of the delay link, and the impact on the system is reduced. The reactive-voltage droop characteristic is mainly determined by Dq.
By simulating the working characteristics of the rotor of the synchronous generator, characteristic change relations can be formed between the output power and the frequency of the inverter power supply in the optical storage system and between the reactive power and the voltage, the distributed inverter power supply also has a virtual moment of inertia similar to that of the rotor of the synchronous motor, and when the distributed inverter power supply is connected to a micro-grid in the control mode, the total moment of inertia of the system is increased, so that the frequency stability of the grid system is further improved.
Specifically, the implementation process of the light storage coordination control method in the preferred embodiment is as follows: because the hierarchical control approach requires communication to manage, the system may crash if the communication device fails. The invention provides a comprehensive control method for realizing coordination control of a light storage alternating current-direct current system, and the specific control process is as follows:
for an optical storage ac/dc hybrid microgrid as shown in fig. 5, two small optical storage dc microgrid systems including units 1 and 2 are provided. A photovoltaic array in the photovoltaic power generation system can output power to a next level of the microgrid through a boost type one-way DC/DC converter, the energy storage system is correspondingly connected with the direct-current sub-microgrid through the two-way DC/DC converter, and the two can exchange electric energy. The direct-current micro-grid is connected with a direct-current load and can be switched according to needs. The direct-current microgrid is also connected to an alternating-current side through an AC/DC bidirectional converter and can provide electric energy for an alternating-current load, and an LC filter is connected into the alternating-current/DC converter, so that output ripples are reduced. The hybrid microgrid is disconnected from the grid, and therefore enters an off-grid (island) mode to operate.
The unit 1 now acts as the main system power supply and the frequencies and voltages of the microgrid are supported by the unit. The unit 2 is used as a slave power supply of the system, the master power bidirectional converter is controlled by a Virtual Synchronous Generator (VSG) when the system works, and the slave power bidirectional converter is controlled by a constant power control method. The direct current bus voltage of the unit 1 and the unit 2 is DC750V, and the load requirement can be changed when the hybrid system works. If the microgrid is separated from a power grid and enters an off-grid (island) working state, the energy storage system plays a key role in regulating voltage, the internal power of the system can be balanced, and the stable operation of the system is maintained. For example, the method can be used for regulating the direct-current side bus voltage and maintaining the system voltage stable. The system can provide stable electric energy for the system, so that the electric energy is supplemented or consumed in time when the load power changes, and the system is ensured to maintain stable operation. The photovoltaic system works at the maximum power point according to the actual working condition.
The energy storage system and the photovoltaic array system can be combined into two groupsThe synthesis method comprises the following steps: the first is to connect the energy storage system and the photovoltaic array system to the next level of the system respectively, and at this moment, the two systems cannot be adjusted mutually, and the photovoltaic system is difficult to be adjusted, which easily causes the system operation to be affected. The second connection mode is that the two are connected in parallel and then are connected to the direct current side together, and the connection method can improve the flexibility of system adjustment. The present invention adopts the connection method shown in fig. 6, and belongs to the second connection method. P pv And P B The power of the photovoltaic array and the power of the energy storage system are respectively, and capacitors Cdc and Cdc2 are connected to the output end of a bidirectional converter in the circuit. The connection mode can completely control the energy storage system and can flexibly select the rated voltage of the energy storage system. The energy storage system can store energy when the power of the photovoltaic power generation system is excessive, and release electric energy when the photovoltaic power generation system is in shortage, so that the stability of the whole system is maintained.
In the above hybrid microgrid, the bidirectional DC/DC converter directly controls the DC bus voltage. And adjusting the photovoltaic system to the maximum power working point through a disturbance observation method (P & O), thereby realizing maximum power tracking (MPPT) control. As shown in fig. 7, in the previous control frame of the optical storage system, the bus voltage Vdc at the dc side, the real-time stored energy current iB, the voltage Vpv and the current ipv of the photovoltaic input are all filtered, so that the switching noise is reduced.
In the control block diagram shown in fig. 7, the reference voltage output by the photovoltaic array can be obtained according to the system state of charge and the photovoltaic system parameters. There is a certain difference in the three modes of normal, off-limit adjustment of the state of charge and off-limit adjustment of the voltage of the direct current bus.
Specifically, the operation of the photovoltaic system is divided into three modes according to whether the voltage of the microgrid in the photovoltaic system participates, namely, the modes of the output voltage of the microgrid in the photovoltaic power grid system, the grid-connected output voltage and the common output voltage of the microgrid and the grid-connected output voltage;
normal operation mode
VMPPT of MPPT and reference voltage V of photovoltaic system when operating in safe range pvref In accordance, the SOC out-of-limit control loops PI0 and PI1 and the bus voltage deviation out-of-limit control loops PI2 and PI3 are all advancedEnter the idle state. And obtaining the photovoltaic output voltage Vpv and the output current ipv through the MPPT algorithm, wherein the photovoltaic system is in a maximum power output state at the moment. And voltage deviation values of the Vpvref and the Vpv are input into a unidirectional DC/DC conversion controller, high power of photovoltaic output is transmitted to a direct current bus, and the energy storage system regulates the bus voltage through a bidirectional DC/DC converter to ensure that the bus voltage reaches a reference voltage Vdcref.
The system can realize the power balance of the circuit through the charging and discharging mode of the energy storage system, at the moment, the charging state of the energy storage system is in a normal range, and the charging and discharging current iB and the voltage fluctuation of the direct current bus are in the normal range. If the SOC is less than the maximum upper limit, the SOC max The positive deviation signal is formed with the actual SOC, and the Pl1 controller with the positive saturation limit has no signal output, so the SOC out-of-limit control loop enters an idle state.
State of charge off-limit regulation mode
When the photovoltaic output power exceeds the load demand, the energy storage system absorbs excess power through charging, the state of charge (SOC) of the energy storage system also rises, but if the energy storage SOC exceeds the SOC max At this point the system will be affected and may enter an unstable state. Photovoltaic systems need to reduce output, ensuring that the system is within safe limits. If the energy storage charge state exceeds the set SOC max When the PI1 control loop starts to work, the SOC max And the deviation of the real-time SOC signal begins to become negative and is finally added to the voltage VMPPT through the PI1 controller, and at the moment, the photovoltaic system does not work at the maximum power point. The power output of the photovoltaic system is reduced because of the PI1 control loop until the energy storage system enters an idle state and the real-time charge state is reduced to the SOC max The following.
DC bus voltage out-of-limit regulation mode
The PI2 control loop enters an idle state when the system works normally, and at the moment, the energy storage system can keep the system in a stable running state through charging and discharging. If the output power of the photovoltaic system is large, the charging current iB is too large and exceeds the bearing range of the energy storage system, the energy storage system is greatly influenced, and the system can enter an unreliable working state at the moment. Therefore, if the output power of the photovoltaic system is large and the load demand of the whole network is small, the charging current iB of the energy storage system exceeds the allowable range, the output of the photovoltaic system cannot be consumed by the energy storage system in a short time, and at the moment, the voltage of the direct-current bus rises, and the power balance cannot be realized inside the system.
In the circuit shown in fig. 6, the deviation of the dc bus voltage is input into the PI2 control loop, and the output value is input into the photovoltaic power controller, so that the photovoltaic system can be prompted to reduce the output power, thereby preventing the dc bus voltage from rising rapidly.
In the control method, a certain voltage safety deviation signal can be set, and the specific value is determined by an application scene and a practical working condition. The specific adjustment process is as follows:
and detecting real-time voltage Vdc of a direct-current bus of the system, if the voltage value exceeds an allowable value, controlling a circuit by PI2 to start working at the moment, subtracting the instantaneous value Vdc of the bus from the allowable upper limit Vdc plus delta V of the voltage, inputting the obtained deviation into a PI2 controller, and outputting a signal to a photovoltaic power generation system so as to reduce the output power of the photovoltaic system. Contrary to the above, if the power output by the photovoltaic system is much lower than the load demand, the dc bus voltage will therefore drop rapidly because the energy storage system cannot provide the necessary power compensation, the PI3 control loop will start to operate at this time, the deviation value obtained by subtracting the instantaneous value Vdc from the bus voltage Vdc- Δ V is input to the PI3 controller, and then the system will cut off part of the load, avoiding the system from collapsing due to the overload.
In the master-slave control of the next-level inverter, when the micro-grid is in coordination work, the master-slave control of the next-level inverter respectively adopts a virtual synchronous generator control mode and a constant power mode, so that the voltage frequency of a system is adjusted and changes along with the load. If the microgrid enters an off-grid (island) working state, part of power supplies are needed to provide voltage and frequency support for the main power grid. When the virtual synchronous generator control mode is adopted, the photovoltaic inverter has certain frequency modulation and voltage regulation capacity in the working process, and the system can be promoted to maintain stable operation. An inverter simulating the working mode of a synchronous generator is called a synchronous inverter, and the active power and the reactive power are automatically distributed by mainly adjusting the frequency and the voltage of a power grid.
The operation of the inverter is analyzed in detail, and the following equation is a reactive voltage control equation under analog synchronous control.
In the formula, Q 0 Is rated power; k is a radical of Q Is a reactive power regulation coefficient; q e Instantaneous reactive power for the inverter; virtual no-load potential E 0 =311V; a virtual excitation potential E; k is a radical of U Adjusting a coefficient for terminal voltage; u is the effective value of the output voltage of the inverter. Fig. 8 is a block diagram showing a structure of the VSG control system.
The inverter adopts constant power control, can output constant power according to a command, and is generally called as a current type inverter. The constant power control comprises two parts of a power outer loop and a current inner loop. P is the rated active power, Q is the rated reactive power, and P and Q are the actual active and reactive powers, respectively, as shown in fig. 9, which is a corresponding control block diagram.
The control method firstly summarizes a virtual synchronous generator control mode, and then provides a comprehensive control method aiming at the problem of power coordination control of the optical storage hybrid microgrid in an off-grid (island) mode. The control mode can avoid the condition that the voltage of the direct current bus is suddenly changed on the basis of maintaining the balance of the power of the previous level, and simultaneously avoid the occurrence of the charge out-of-limit state of the energy storage system. In addition, the main inverter of the next level can be controlled by the control mode of the virtual synchronous generator, and a constant power mode is adopted, so that the internal power of the whole system is kept balanced and a stable operation state is kept.
Specifically, although the typical droop control mode of the bidirectional converter can well realize autonomy, the control method has certain defects, so that different control modes of the bidirectional converter are used under the conditions of off-grid (isolated island) and grid connection, namely, a mode switching mode of the bidirectional converter based on comprehensive droop control is explained. Meanwhile, a comprehensive control mode is provided for realizing power coordination control under different working conditions of the light storage mixed micro-grid in an off-grid mode, the former stage adopts a multi-loop control mode to realize power balance and suppress power fluctuation, and the latter stage adopts a virtual synchronous generator control mode to keep inertia and damping of the system.
According to the invention, specific analysis and research are carried out on the topological structure and characteristics of the alternating current-direct current hybrid micro-grid with high-proportion photovoltaic access to the energy storage system, and modeling analysis is carried out on the energy storage and the photovoltaic. The working principle of the photovoltaic unidirectional converter and the bidirectional energy storage equipment DC/DC converter is researched, and a previous-level system formed by connecting the photovoltaic unidirectional converter and the energy storage equipment with the bidirectional energy storage equipment DC/DC converter can be equivalent to a direct-current voltage source. According to the power distribution principle of the bidirectional converter, the control modes of the bidirectional converter in different modes of the hybrid microgrid are analyzed and researched, the autonomous coordination of power control between the bidirectional converter and the energy storage device is realized through a threshold value method, unnecessary actions of power electronic devices can be avoided, and the loss of electric energy can be reduced. A new bidirectional converter control mode is designed on the basis of the operation of a typical droop control mode: the method is characterized in that a constant direct current bus voltage control mode is adopted in a grid-connected mode, and a comprehensive droop control mode is adopted in an off-grid (island) mode. The simulation result verifies the correctness of the mode: namely, the transmission size and direction of power are determined according to the voltage of a direct-current bus under grid connection; under off-grid conditions, the bidirectional converter works only when one microgrid is in power shortage and the other microgrid is rich in power and has frequency and voltage deviation values exceeding threshold values, and frequent flow of power is reduced. The method ensures that at least one microgrid can be in a normal or near-rated operation state to the maximum extent, and avoids the phenomenon of frequent power conversion among sub-microgrids caused by power fluctuation among networks. The invention designs a comprehensive control mode to realize power coordination control of the light storage alternating current-direct current island microgrid, namely a multi-loop power control mode is constructed in a previous hierarchical structure under the condition that the energy storage charge state and the deviation amount of direct current bus reference voltage are out of limit, so that the previous hierarchical power balance of a system is realized, and the system is operated in a safe range. Simulation results show that the energy storage charge state can be effectively prevented from exceeding the limit and the direct current bus voltage sudden change, and the power balance of the previous layer can be realized. In addition, in the later-level control, a virtual synchronous generator control mode is adopted for the main converter, and a constant power control mode is adopted for the auxiliary converter to realize the coordination control of the whole system and the like.
Example 2
A control system based on high-proportion photovoltaic energy access hybrid power grid comprises a power grid, a power grid controller and a power grid controller, wherein the power grid controller is connected with the power grid controller;
the synchronous generator control module is used for acquiring the operating parameters of the synchronous generator and respectively establishing a phase angle model of the synchronous generator and an active frequency control model of the inverter power supply;
the photovoltaic energy storage inverter control module is used for acquiring operation parameters of the photovoltaic energy storage inverter in an active state and a reactive state in the microgrid and establishing a reference voltage model and a reactive voltage control model of the photovoltaic energy storage inverter;
and the comprehensive control module is used for controlling the voltage and frequency fluctuation of a grid connection point caused by the access of the microgrid to the AC/DC hybrid power grid according to the established phase angle model of the synchronous generator, the active frequency control model of the inverter power supply, the reference voltage model of the photovoltaic energy storage inverter and the reactive voltage control model.
As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention has been described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (8)
1. A control method based on high-proportion photovoltaic energy access to a hybrid power grid is characterized by comprising the following steps of;
acquiring operating parameters of the synchronous generator, and respectively establishing a phase angle model of the synchronous generator and an active frequency control model of an inverter power supply;
acquiring operating parameters of the photovoltaic energy storage inverter in an active state and a reactive state in a microgrid, and establishing a reference voltage model and a reactive voltage control model of the photovoltaic energy storage inverter;
and controlling the voltage and frequency fluctuation of a grid connection point caused by accessing the micro-grid into the alternating current-direct current hybrid grid according to the established phase angle model of the synchronous generator, the active frequency control model of the inverter power supply, the reference voltage model of the photovoltaic energy storage inverter and the reactive voltage control model.
2. The method as claimed in claim 1, wherein the phase angle model of the synchronous generator is
Wherein +>
For the phase angle of the synchronous machine, ω and ω g The angular velocities corresponding to the 0 moment and the t moment in the upper and lower integration limits are respectively.
3. The method for controlling the access of the high-proportion photovoltaic energy to the hybrid power grid as claimed in claim 1, wherein the active frequency control model of the inverter power supply of the synchronous generator is
Wherein H is a virtual inertia time constant, P, corresponding to the moment of inertia J in For the power input of the inverter, P out The output power of the inverter, omega, is the angular frequency of the inverter, omega g For angular frequency of the common bus, K d Is the damping coefficient.
4. An aspect ratio based device as claimed in claim 1The control method for accessing the photovoltaic energy into the hybrid power grid is characterized in that a reference voltage model of the photovoltaic energy storage inverter is
Wherein Q is ref And D q Respectively setting an input value and a droop coefficient for the reactive power; t is a Is the delay link time constant; e set And E g Respectively outputting signals for the reference terminal voltage and the reactive power controller of the distributed inverter power supply; k is a radical of p1 And k i1 Are proportional integral coefficients of respective links.
5. The method for controlling access to a hybrid power grid based on the high-proportion photovoltaic energy source of claim 1, wherein the reactive voltage control model of the photovoltaic energy storage inverter is
Wherein Q is 0 Is rated power; k is a radical of formula Q Is a reactive power regulation coefficient; q e Instantaneous reactive power for the inverter; e 0 Is a virtual no-load potential; a virtual excitation potential E; k is a radical of U Adjusting a coefficient for a terminal voltage; u is the effective value of the output voltage of the inverter.
6. The method as claimed in claim 5, wherein E is the control method for accessing the hybrid power grid based on the high-proportion photovoltaic energy 0 ＝311V。
7. The control method for accessing the hybrid power grid based on the high-proportion photovoltaic energy according to claim 1, wherein when the microgrid enters an off-grid working state, a power supply in the microgrid provides voltage and frequency for a main power grid, and the voltage and frequency generated when the virtual synchronous generator works are used for controlling a photovoltaic inverter to work, so that a photovoltaic system is maintained to operate stably.
8. A control system based on a high-proportion photovoltaic energy access hybrid power grid is characterized by comprising a power grid, a photovoltaic energy storage device, a power grid and a controller, wherein the power grid is connected with the photovoltaic energy storage device;
the synchronous generator control module is used for acquiring the operating parameters of the synchronous generator and respectively establishing a phase angle model of the synchronous generator and an active frequency control model of the inverter power supply;
the photovoltaic energy storage inverter control module is used for acquiring the operating parameters of the photovoltaic energy storage inverter in the active and reactive states in the microgrid and establishing a reference voltage model and a reactive voltage control model of the photovoltaic energy storage inverter;
and the comprehensive control module is used for realizing control of grid connection point voltage and frequency fluctuation caused by accessing the micro-grid into the alternating current-direct current hybrid grid according to the established phase angle model of the synchronous generator, the inverter power supply active frequency control model, the reference voltage model of the photovoltaic energy storage inverter and the reactive voltage control model.
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