CN106972536B - Control method and device for virtual synchronous generator of photovoltaic power station - Google Patents

Abstract

The invention discloses a control method and device for a virtual synchronous generator of a photovoltaic power station. First, each photovoltaic power generation unit participating in the control of the virtual synchronous generator in the photovoltaic power station is subjected to load reduction control; and then the voltage at the grid connection point of the photovoltaic power station is collected. , current and frequency signals; use the virtual synchronous generator controller to realize the virtual synchronous generator control of the photovoltaic power station, and obtain the active and reactive power reference values of each photovoltaic power generation unit; pass the power command obtained by the virtual synchronous generator controller through the optical fiber The network is sent to each photovoltaic power generation unit; each photovoltaic power generation unit receives the power command, tracks the power reference value, and realizes the power control of the photovoltaic power station. The above method realizes the virtual synchronous generator function of the photovoltaic power station, enhances the safe and stable operation capability of the photovoltaic power station, and at the same time can exert the voltage and frequency control capabilities of the photovoltaic power station.

Description

A control method and device for a virtual synchronous generator of a photovoltaic power station

technical field

The invention relates to the technical field of photovoltaic power generation systems, in particular to a control method and device for a virtual synchronous generator of a photovoltaic power station.

Background technique

With the continuous development of new energy power generation technology, in recent years, the proportion of new energy power generation (photovoltaic power generation, wind power generation, etc.) based on power electronic inverter interface in the power system is increasing. Major countries in the world have formulated their own new energy power generation development plans. However, compared with the traditional synchronous generator power supply, the new energy power generation system based on the power electronic inverter interface has a fast response speed, and the decoupling of the response of the power generation system and the dynamic response of the power system has almost no rotational inertia that is conducive to maintaining the stable operation of the system. And damping, its large number of access will inevitably affect the dynamic characteristics of the power system, cannot provide the necessary voltage and frequency support for the power system, bring changes to the power system, and bring challenges to the stable operation and control of the power system.

For the new energy power generation system with grid-connected inverters, the control strategy generally adopted is the current mode control based on the rotating coordinate system. This control method can realize the decoupling control of active and reactive power. The energy power generation system does not have the characteristics of rotational inertia and damping, which is not conducive to the stable operation of the system. Using the virtual synchronous generator control method can make the new energy power generation system based on the inverter grid-connected to have characteristics similar to the synchronous generator. However, the photovoltaic grid-connected system in the prior art does not have the characteristics of a virtual synchronous generator. It is time-consuming and laborious to retrofit the existing photovoltaic unit inverters one by one, and since the inverters of each photovoltaic unit operate independently, its The mutual influence needs further research to ensure the operation performance of the entire photovoltaic power station.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a control method and device for a virtual synchronous generator of a photovoltaic power station, the method realizes the function of a virtual synchronous generator of a photovoltaic power station, enhances the safe and stable operation capability of the photovoltaic power station, and can exert the voltage of the photovoltaic power station at the same time. and frequency control capability.

A control method for a virtual synchronous generator of a photovoltaic power station, the method comprising:

Step 1. Perform load shedding control on each photovoltaic power generation unit participating in the virtual synchronous generator control in the photovoltaic power station;

Step 2, collecting voltage, current and frequency signals at the grid connection point of the photovoltaic power station;

Step 3, using the virtual synchronous generator controller to realize the virtual synchronous generator control of the photovoltaic power station, and obtain the active and reactive power reference values of each photovoltaic power generation unit;

Step 4, sending the power command obtained by the virtual synchronous generator controller to each photovoltaic power generation unit through the optical fiber network;

Step 5: Each photovoltaic power generation unit receives a power command, tracks a power reference value, and realizes power control of the photovoltaic power station.

In the step 1, the process of performing load reduction control on each photovoltaic power generation unit participating in the virtual synchronous generator control in the photovoltaic power station is as follows:

By changing the power reference value of each photovoltaic power generation unit, the active power output of the photovoltaic power generation unit deviates from its maximum power tracking value.

In the step 2, the voltage, current and frequency signals at the grid connection point of the photovoltaic power station are collected by using a current transformer and a voltage transformer.

In the step 3, obtaining the active and reactive power reference values of each photovoltaic power generation unit specifically includes: obtaining the active power and reactive power of each photovoltaic unit through a virtual synchronous generator control algorithm according to the measured voltage, current and frequency signals. Power reference value.

In the step 4, the power command is the power command of each photovoltaic power generation unit controlled by the virtual synchronous generator.

A control device for a virtual synchronous generator of a photovoltaic power station, the device includes:

The load shedding control module is used to perform load shedding control on each photovoltaic power generation unit participating in the virtual synchronous generator control in the photovoltaic power station;

a measurement module for collecting voltage, current and frequency signals at the grid-connected point of the photovoltaic power station;

The virtual synchronous generator control module is used to realize the virtual synchronous generator control of the photovoltaic power station by using the virtual synchronous generator controller, and obtain the active and reactive power reference values of each photovoltaic power generation unit;

The communication module is used to send the power command obtained by the virtual synchronous generator controller to each photovoltaic power generation unit through the optical fiber network.

It can be seen from the technical solutions provided by the present invention that the above method realizes the virtual synchronous generator function of the photovoltaic power station, enhances the safe and stable operation capability of the photovoltaic power station, and can exert the voltage and frequency control capabilities of the photovoltaic power station at the same time.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

1 is a schematic flowchart of a control method for a virtual synchronous generator of a photovoltaic power station according to an embodiment of the present invention;

2 is a block diagram of an inverter topology and its equivalent virtual synchronous generator in the example of the present invention;

3 is a schematic control block diagram of a virtual synchronous generator controller in an embodiment of the present invention;

FIG. 4 is a schematic diagram of a power system model in an example according to an embodiment of the present invention;

5 is a schematic diagram of the output power of the photovoltaic unit in the example of the present invention;

6 is a schematic diagram of the output power of the photovoltaic power station in the example of the present invention;

7 is a schematic diagram of the frequency comparison of the power system in the example of the present invention;

FIG. 8 is a schematic diagram of a frequency-controlled power output of a photovoltaic unit in an embodiment of the present invention;

9 is a schematic diagram of frequency control power output of a photovoltaic power station in an embodiment of the present invention;

FIG. 10 is a schematic diagram of a control device of a virtual synchronous generator of a photovoltaic power station provided by an embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

The embodiments of the present invention provide a more effective and concise control method for a virtual synchronous generator of a photovoltaic power station, which can easily establish a virtual synchronous generator control function of the photovoltaic power station, improve the stable operation ability of the photovoltaic power station and the control of frequency and voltage. control ability. The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. FIG. 1 is a schematic flowchart of a control method for a virtual synchronous generator of a photovoltaic power station provided by an embodiment of the present invention, and the method includes:

Step 1. Perform load shedding control on each photovoltaic power generation unit participating in the virtual synchronous generator control in the photovoltaic power station;

In this step 1, the process of performing load shedding control on each photovoltaic power generation unit is as follows:

By changing the power reference value of each photovoltaic power generation unit, the active power output of the photovoltaic power generation unit deviates from its maximum power tracking value (the maximum power that the photovoltaic unit can emit according to the current light intensity), so as to participate in the virtual synchronous generator for the photovoltaic power generation unit Controls setting aside spare capacity.

Step 2, collecting voltage, current and frequency signals at the grid connection point of the photovoltaic power station;

In this step, a current transformer and a voltage transformer are specifically used to collect the voltage, current and frequency signals at the grid connection point of the photovoltaic power station.

Step 3, using the virtual synchronous generator controller to realize the virtual synchronous generator control of the photovoltaic power station, and obtain the active and reactive power reference values of each photovoltaic power generation unit;

In this step, the process of obtaining the active and reactive power reference values of each photovoltaic power generation unit specifically includes: obtaining the active and reactive power of each photovoltaic unit through a virtual synchronous generator control algorithm according to the measured voltage, current and frequency signals Reference.

The following describes the control principle of the virtual synchronous generator in detail with a specific example:

Figure 2 shows the inverter topology structure and its equivalent virtual synchronous generator block diagram in the example of the present invention. The mechanical equation of the synchronous generator is:

In the formula, J is the moment of inertia of the synchronous generator, in kg m ² T _m , _Te and T _d are the mechanical, electromagnetic and damping torques of the synchronous generator, in N m, and D is the damping coefficient , the unit is N·m·s/rad, ω ₀ is the grid synchronous angular velocity, the unit is rad/s. The electromagnetic torque Te of the generator is calculated from the virtual synchronous generator potential e _abc and output current i _abc , as shown in formula (2):

T _e =P _e /ω=(e _a i _a +e _b i _b +e _c i _c )/ω (2)

In the formula, P _e is the electromagnetic power output by the virtual synchronous generator.

The virtual synchronous generator control of the inverter introduces the control of formula (1) into its active power loop, and realizes the mechanical characteristics of the synchronous generator by means of control. Due to the introduction of the moment of inertia J, the grid-connected inverter has inertia in the dynamic process of active power and frequency, and the introduction of the damping parameter D makes the inverter have the ability to damp the power oscillation of the grid. The introduction of these two variables is The inverter has the performance of a synchronous generator, which is of great significance for improving the operating characteristics of the inverter.

From Figure 2, the electromagnetic equation of the virtual synchronous generator can be obtained as:

In the formula, L is the synchronous reactance of the synchronous generator, R is the synchronous resistance of the synchronous generator, u _abc is the terminal voltage of the synchronous generator, i _abc is the terminal current of the synchronous generator, and e _abc is the synchronous generator potential.

The terminal current of the virtual synchronous generator can be obtained from the electromagnetic equation of the virtual synchronous generator, so that the power command can be calculated from the terminal current and voltage, and the power command is the total power command of each photovoltaic power generation unit controlled by the virtual synchronous generator.

Further, in the virtual synchronous generator control, frequency control and voltage control can be realized at the same time. FIG. 3 is a schematic diagram of the control block diagram of the virtual synchronous generator controller in the embodiment of the present invention. Use its deviation from the system's rated frequency to adjust the total active power:

ΔP=K _f (f _ref -f _meas ) (3)

In the formula, K _f is the frequency modulation coefficient, f _ref is the rated frequency of the system, and f _meas is the measured grid-connected point frequency.

The voltage control is located in the reactive power control loop, and the voltage deviation is used to adjust the potential of the virtual synchronous machine

ΔE=K _v (V _ref -V _meas ) (4)

The active and reactive power reference values are obtained by the virtual synchronous generator controller, and then the power distribution unit distributes the power command to each photovoltaic power generation unit proportionally according to the rated capacity of each photovoltaic power generation unit, as shown in formula (5) shown

In the formula, P _refi is the active power command of the ith photovoltaic unit, S _i is the rated capacity of the ith photovoltaic unit, N is the total number of photovoltaic power generation units controlled by the virtual synchronous generator, and P _Total is the power generated by the virtual synchronous generator. The total power reference value obtained by the machine control, the allocation method for reactive power is the same as that for active power.

Step 4, sending the power command obtained by the virtual synchronous generator controller to each photovoltaic power generation unit through the optical fiber network;

Since the virtual synchronous generator controller and each photovoltaic power generation unit are distributed in different geographical locations, in order to ensure the speed of signal transmission, an optical fiber network can be used to issue power commands to each photovoltaic power generation unit.

The power command is the power command of each photovoltaic power generation unit controlled by the virtual synchronous generator.

Step 5: Each photovoltaic power generation unit receives a power command, tracks a power reference value, and realizes power control of the photovoltaic power station.

Here, the general photovoltaic power generation unit can accept external power commands, so it is relatively easy to implement, and the embodiment of the present invention does not involve the modification of the internal control system of the photovoltaic power generation unit.

The control of the present invention will be described in detail below with reference to a specific embodiment. Matlab/Simulink is used to build a power system model as shown in Figure 4 to simulate and verify the control method. The power system includes a synchronous generator G1 and a photovoltaic system. The power station, the photovoltaic power station is represented by 2 photovoltaic inverter units with a capacity of 30kW, and the rated capacity of the synchronous generator G1 is 300kW.

According to the light conditions, the maximum output power of the photovoltaic power station is 50kW. In order to control the virtual synchronous generator of the photovoltaic power station, 20% of the spare capacity is reserved for the load reduction control of the photovoltaic power station (which is realized by directly giving the photovoltaic power generation unit a load reduction power command). Control The total output power is 40kW, the output power of photovoltaic power generation units 1 and 2 are the same as about 20kW, the output power of the synchronous generator is 150kW, and the load is 190kW. The control parameters of the virtual synchronous generator of the photovoltaic power station are J=4, D=20. Since the photovoltaic unit 1 and the photovoltaic unit 2 have the same capacity, the power command of the virtual synchronous generator is evenly distributed. In order to verify the control effect of the virtual synchronous generator of the photovoltaic power station, a step signal is given to the virtual synchronous generator controller at 2s to control the output power of the virtual synchronous generator to step from 40kW to 45kW. A schematic diagram of the output power of the photovoltaic unit, as shown in FIG. 6 is a schematic diagram of the output power of the photovoltaic power station in the example of the present invention.

The simulation results show that through the virtual synchronous generator control, the output power of the photovoltaic power station has inertia and damping characteristics similar to those of the synchronous generator. Further, to verify the effect of the virtual synchronous generator control of the photovoltaic power station on the system frequency control, the frequency controller parameter K _{f is} set to 1000. At 5s, the load is increased by 20kW, causing the system frequency to drop. Figure 7 is a schematic diagram of the frequency comparison of the power system in the example of the present invention. When the virtual synchronous generator control is adopted and the virtual synchronous generator control is not adopted (the photovoltaic power generation unit does not respond to the system frequency change), the obtained system frequency is as follows: shown in Figure 7.

Further, FIG. 8 is a schematic diagram of the frequency control power output of the photovoltaic unit in the embodiment of the present invention, and FIG. 9 is a schematic diagram of the frequency control power output of the photovoltaic power station in the embodiment of the present invention. The photovoltaic power station controlled by the synchronous generator can increase the output of active power to participate in the system frequency control, which is beneficial to the safe and stable operation of the system.

It can be seen from the above embodiments that the control method for a virtual synchronous generator of a photovoltaic power station provided by the embodiment of the present invention enables the photovoltaic power station to have the function of a virtual synchronous generator, which can provide inertia and damping for the system, effectively cope with changes in the system frequency, and improve the security system. The ability to operate safely and stably.

In view of the above method flow, the embodiment of the present invention also provides a control device for a virtual synchronous generator of a photovoltaic power station, and the specific content of the device can be implemented with reference to the above method. Schematic diagram of the control device of the synchronous generator, the device mainly includes:

The load shedding control module 101 is used to perform load shedding control on each photovoltaic power generation unit participating in the virtual synchronous generator control in the photovoltaic power station;

a measurement module 102, configured to collect voltage, current and frequency signals at the grid connection point of the photovoltaic power station;

The virtual synchronous generator control module 103 is used to realize the virtual synchronous generator control of the photovoltaic power station by using the virtual synchronous generator controller, and obtain the active and reactive power reference values of each photovoltaic power generation unit;

The communication module 104 is configured to send the power command obtained by the virtual synchronous generator controller to each photovoltaic power generation unit through the optical fiber network.

In addition, a power control module is arranged inside the photovoltaic power generation unit, and the power control module is used for receiving power commands, tracking the power reference value, and realizing the power control of the photovoltaic power station.

For the specific implementation process of the above functional modules, reference may be made to the description in the method embodiments.

As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, or as a 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, etc.) having computer-usable program code embodied therein.

The present invention is 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 in the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to the processor of a general purpose computer, special purpose computer, embedded processor or other programmable data processing device to produce a machine such that the instructions executed by the processor of the computer or other programmable data processing device produce Means for implementing the functions specified in a flow or flow of a flowchart and/or a block or blocks of a block diagram.

These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory result in an article of manufacture comprising instruction means, the instructions The apparatus implements the functions specified in the flow or flow of the flowcharts and/or the block or blocks of the block diagrams.

These computer program instructions can also be loaded on a computer or other programmable data processing device to cause a series of operational steps to be performed on the computer or other programmable device to produce a computer-implemented process such that The instructions provide steps for implementing the functions specified in the flow or blocks of the flowcharts and/or the block or blocks of the block diagrams.

The above is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. Any person skilled in the art can easily think of changes or Substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (4)

1. A control method of a virtual synchronous generator of a photovoltaic power station is characterized by comprising the following steps:

step 1, load reduction control is carried out on each photovoltaic power generation unit participating in virtual synchronous generator control in a photovoltaic power station, and the specific process is as follows: the active power output of each photovoltaic power generation unit deviates from the maximum power tracking value thereof by changing the power reference value of each photovoltaic power generation unit;

step 2, collecting voltage, current and frequency signals at the grid-connected point of the photovoltaic power station;

step 3, realizing virtual synchronous generator control of the photovoltaic power station by using the virtual synchronous generator controller, and obtaining the active power reference value and the reactive power reference value of each photovoltaic power generation unit, wherein the method specifically comprises the following steps: obtaining total active and reactive power reference values by a virtual synchronous generator controller according to the measured voltage, current and frequency signals, and then obtaining the active and reactive power reference values of each photovoltaic power generation unit according to the rated capacity of each photovoltaic power generation unit in a proportional distribution manner;

step 4, issuing the power instruction obtained by the virtual synchronous generator controller to each photovoltaic power generation unit through an optical fiber network;

and 5, each photovoltaic power generation unit receives the power instruction, tracks the active power reference value and the reactive power reference value and realizes power control of the photovoltaic power station.

2. The control method according to claim 1, characterized in that in step 2, voltage, current and frequency signals at the grid-connected point of the photovoltaic power plant are collected by using a current transformer and a voltage transformer.

3. The control method according to claim 1, wherein in the step 4, the power command is a power command of each photovoltaic power generation unit controlled by a virtual synchronous generator.

4. A control device for a virtual synchronous generator of a photovoltaic power plant, characterized in that the device comprises:

the load reduction control module is used for carrying out load reduction control on each photovoltaic power generation unit participating in virtual synchronous generator control in the photovoltaic power station, and the specific process is as follows: the active power output of each photovoltaic power generation unit deviates from the maximum power tracking value thereof by changing the power reference value of each photovoltaic power generation unit;

the measuring module is used for collecting voltage, current and frequency signals at the grid-connected point of the photovoltaic power station;

the virtual synchronous generator control module is used for realizing the virtual synchronous generator control of the photovoltaic power station by utilizing the virtual synchronous generator controller, obtaining the active and reactive power reference values of each photovoltaic power generation unit, and the specific process is as follows: obtaining total active and reactive power reference values by a virtual synchronous generator controller according to the measured voltage, current and frequency signals, and then obtaining the active and reactive power reference values of each photovoltaic power generation unit according to the rated capacity of each photovoltaic power generation unit in a proportional distribution manner;

and the communication module is used for issuing the power instruction obtained by the virtual synchronous generator controller to each photovoltaic power generation unit through an optical fiber network.

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