CN114552600A - Frequency adjusting method for photovoltaic grid-connected power generation participation system - Google Patents

Frequency adjusting method for photovoltaic grid-connected power generation participation system Download PDF

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CN114552600A
CN114552600A CN202210149908.3A CN202210149908A CN114552600A CN 114552600 A CN114552600 A CN 114552600A CN 202210149908 A CN202210149908 A CN 202210149908A CN 114552600 A CN114552600 A CN 114552600A
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energy storage
frequency
power
storage battery
photovoltaic
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孙建聿
孙双魁
王鹏
李书山
吕钧章
刘小兵
马宏霞
赵修文
赖丽
陈永超
董朝辉
马鸿翔
王玲
张强
张存朝
周冰雁
张玮
蒋秀婷
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PowerChina Qinghai Electric Power Engineering Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H02J3/241—The oscillation concerning frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00006—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment
    • H02J13/00028—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment involving the use of Internet protocols
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/28—Arrangements for balancing of the load in a network by storage of energy
    • H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/466—Scheduling the operation of the generators, e.g. connecting or disconnecting generators to meet a given demand
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
    • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin

Abstract

The invention belongs to the field of control and stable operation of a photovoltaic power generation system, and particularly relates to a method for regulating the frequency of a photovoltaic grid-connected power generation participation system. The method comprises the following steps: detecting the voltage of a photovoltaic direct-current bus, and adjusting and controlling the voltage to be in a maximum output state by adopting an MPPT algorithm; detecting the regulated voltage, controlling and regulating the duty ratio of a Boost circuit, and maintaining the stability of the direct-current voltage of a Boost bus; detecting whether the SOC of the energy storage battery is maintained at a normal level, and if not, controlling energy storage charging and discharging to adjust active storage when the frequency of a power grid is stable; and detecting whether the frequency of the power grid deviates, controlling the energy storage battery to charge and discharge to adjust the frequency of the power grid under the condition that the SOC of the energy storage battery meets the condition, and stopping the operation of the energy storage battery after the frequency deviation is eliminated or the SOC of the energy storage battery does not meet the condition. The method provided by the invention can keep the photovoltaic system stably running in the maximum output state, and can also participate in the frequency modulation of the power system by means of the energy storage battery, thereby not only ensuring the economic benefit, but also enhancing the frequency supporting capability of the power grid.

Description

Frequency adjusting method for photovoltaic grid-connected power generation participation system
Technical Field
The invention belongs to the field of control and stable operation of a photovoltaic power generation system, and particularly relates to a method for adjusting the frequency of a photovoltaic grid-connected power generation participation system.
Background
Under the background that fossil energy is gradually exhausted and environmental problems are increasingly highlighted, the technology of clean and harmless new energy generators is rapidly developed in the world, and the electric power system in China is gradually changed into a double-high electric power system with high proportion of clean energy and high proportion of power electronic devices. However, power generation by new energy sources such as photovoltaic and the like has strong volatility and randomness, a current grid-connected new energy source unit does not contain rotational inertia or is hidden, and as an electric power system is gradually transformed and upgraded to a power grid form dominated by new energy sources such as photovoltaic and wind power, the proportion of thermal power units with inertial response capability and frequency modulation capability is gradually reduced, which will certainly weaken the frequency stability capability of the power grid, so that reasonably arranging the new energy source unit such as photovoltaic and wind power to supplement part of inertia, and assuming a primary frequency modulation task of the electric power system is an inevitable trend of future electric power industry development.
In order to enable the photovoltaic generator set to have inertial response capability and primary frequency modulation capability, numerous scholars at home and abroad focus on the improvement of a new energy grid-connected converter control strategy. Because the photovoltaic unit does not contain a rotating element, the hidden inertia of the photovoltaic unit cannot be decoupled with a power grid through control and regulation, and the frequency regulation capability can be provided only by using active standby under the load shedding operation or the energy storage configuration mode, however, the photovoltaic operation is carried out on a suboptimal curve through the load shedding operation, the photovoltaic power generation efficiency is damaged, and the economy is poor, so that the invention focuses on the photovoltaic configuration energy storage frequency modulation mode. According to research on a large number of documents in recent years, the types of energy storage elements configured in the current photovoltaic system comprise storage battery energy storage, super capacitor energy storage, flywheel energy storage and the like, and at present, the storage battery energy storage is mature and is popularized and applied in practical engineering, so that the method for providing active standby by adopting storage battery energy storage is considered.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a frequency adjusting method of a photovoltaic grid-connected power generation participation system, which can improve the frequency stability of a double-high power system while ensuring the maximum output benefit of a photovoltaic system.
In order to achieve the purpose, the invention adopts the following technical scheme:
a frequency adjusting method of a photovoltaic grid-connected power generation participation system comprises the following steps:
s1: the photovoltaic array is connected to a power grid through a direct current boost converter and a grid-connected converter, the direct current boost converter is matched with a corresponding measurement and calculation element and a communication part, the direct current boost converter detects the output voltage and current of the photovoltaic array, and the voltage is adjusted through an MPPT algorithm to ensure the maximum output of photovoltaic;
s2: the direct current Boost converter is matched with a corresponding measuring and calculating element to detect the output voltage of the photovoltaic array, and the duty ratio is adjusted through a Boost circuit to ensure the stability of the voltage at the Boost side when the output voltage of the photovoltaic array changes;
s3: the storage battery energy storage system is merged into a direct current boost bus through a direct current bidirectional converter and then merged into a power grid through a grid-connected converter, the direct current bidirectional converter is matched with a corresponding measuring and calculating element to detect the SOC of the energy storage battery, if the SOC does not meet the condition, namely 20% < SOC < 90%, the energy storage battery is controlled to be charged and discharged to store active power for later use when the frequency of the power grid is stable;
s4: the DC bidirectional converter is matched with corresponding measurement and calculation elements and communication parts to detect the frequency f of the power gridprWhen the frequency of the power grid is increased or reduced, starting communication to detect the SOC of the energy storage battery, and controlling the energy storage battery to charge and discharge to adjust the frequency of the power grid if the SOC meets the condition (the SOC is less than 20% or the SOC is more than 90%);
s5: the detection element respectively detects the frequency deviation of the power grid or the SOC of the energy storage battery, and when the frequency deviation is eliminated or the SOC does not meet the condition (20% < SOC < 90%), the control element is started to control the energy storage battery to quit operation.
Further, in the step S1, the voltage adjustment method by the MPPT algorithm is as follows: according to the P-V curve characteristic of the photovoltaic array, when the output voltage of the photovoltaic array is adjusted, the output power of a photovoltaic system is correspondingly changed, a control part algorithm adopts a conductance incremental method, namely when the derivative of transmitted active power and direct-current voltage is 0, the photovoltaic output power is maximum, and the principle is as follows:
Figure RE-GDA0003613476400000031
obtainable from formula (1):
Figure RE-GDA0003613476400000032
the formula (2) is transformed to obtain:
Figure RE-GDA0003613476400000033
if the condition of the formula (3) is not met, accumulating the generated difference value in a PI regulator in the direct current boost converter and outputting an error signal, changing the output voltage of the photovoltaic array until the error is eliminated, and outputting the maximum power by the photovoltaic array after the condition of the formula (3) is met; the photovoltaic output power is maximum when the derivative of the transmitted active power with the dc voltage is 0.
Further, in the step S2, the regulation principle of the Boost circuit is as follows:
according to Boost circuit, its output voltage VOutAnd the output voltage V of the photovoltaic array direct current businThe relation is as follows:
Figure RE-GDA0003613476400000034
wherein D is the duty cycle;
the selection of parameters of inductance and capacitance elements in the Boost circuit needs to satisfy the following relational expression:
Figure RE-GDA0003613476400000035
Figure RE-GDA0003613476400000036
in the formula, C1F is the frequency of the DC boost converter, L is the parameter of the inductance element, Delta I is the ripple current value, and Delta VOutAs ripple voltage value, RLoadIs a load resistor with a magnitude equal to VOut/IOut。
Further, when the photovoltaic bus voltage changes under the control of the MPPT algorithm in the step S3, the voltage of the boost-side circuit is stabilized by adjusting the duty ratio to ensure that the voltage of the operating environment of the dc bidirectional converter connected to the energy storage battery is stable, and the calculation method of the SOC of the energy storage battery is as follows:
Figure RE-GDA0003613476400000041
in the formula, SOCi(t) is the current chargeability, SOC, of each energy storage celli_iniFor the initial chargeability, i, of the respective energy storage celli-bat(t) is the magnitude of the discharge current of the energy storage battery, Qi-batThe capacity of the energy storage battery is obtained;
when the source side of the direct current bidirectional converter is configured with a plurality of energy storage batteries, the output power of the direct current bidirectional converter is obtained according to the proportional relation of the output power among the energy storage batteries as follows:
Figure RE-GDA0003613476400000042
in the formula, PDThe difference between the total power of photovoltaic power generation and the total power of load in the system, N is the number of energy storage battery blocks, mpiCorresponding power coefficients of the SOC to different energy storage batteries in the system;
neglecting the self loss of the converter, the output power on both sides is equal, and the combination formulas (7) and (8) can obtain:
Figure RE-GDA0003613476400000043
and the estimation of the SOC state among the multiple energy storage batteries is realized, and the energy storage batteries are controlled to be charged and discharged through the SOC calculated value so as to adjust the frequency of the power grid. The setting condition (20% < SOC < 90%) of the energy storage battery SOC selects the factor, not only considers that the energy storage battery can greatly reduce the service life by charging and discharging for many times when the energy storage battery is too low and too high in electric quantity, but also considers that the energy storage battery can have certain frequency regulation capacity when a high-frequency or low-frequency fault occurs at any time in a power grid.
Further, in the step S4, the grid frequency is detected through a control algorithm of the energy storage battery participating in the frequency adjustment of the power system, which includes two parts, namely, virtual inertia control and active-frequency droop control, and the two parts are respectively used for simulating a power output curve of the inertia response and the primary frequency modulation control of the synchronous generator:
the expression of the virtual inertia control is:
Figure RE-GDA0003613476400000051
in the formula, HBESSFor the set virtual inertia constant, df/dt is the detected grid frequency change rate;
the expression of active-frequency droop control is:
ΔPBESS-t＝P0-k(fpr-fref)Pn (11)
in the formula, P0As sag factor, fprFor detected grid frequency, frefTo set a frequency reference (typically 50Hz, line frequency), PnRated power output for the energy storage battery;
under the coordination of virtual inertia control and active-frequency droop control, the energy storage battery simulates a power response curve of the synchronous generator to realize stable adjustment of the power grid frequency.
Further, after the power grid frequency deviation is eliminated in the step S5, the frequency modulation element is required to stop operating immediately, and a time-efficient power grid frequency detection and communication channel is required to send a stop instruction to control the energy storage battery to immediately exit from operation; when the SOC of the energy storage battery does not meet the condition, the control element also needs to rapidly act to control the energy storage battery to immediately quit the operation.
According to the invention, the MPPT tracking and fast frequency response control algorithm of a communication part corresponding to the control of the photovoltaic array and the energy storage battery has timeliness, the controlled unit and the control unit establish an Ethernet network, and GOOSE, Ethercat and the like are adopted to support a fast communication protocol, so that the controlled unit has the capability of rapidly receiving signals and rapidly finishing target output power and SOC regulation according to the self state. The capacity and the charge-discharge performance of the energy storage battery participating in the system frequency regulation are key factors influencing the frequency regulation capability of the photovoltaic system, so that the energy storage battery needs to have the characteristics of higher energy density, higher terminal voltage and higher power density.
Compared with the prior art, the method has the following advantages: the maximum output of the photovoltaic unit is ensured by fully utilizing the charge-discharge characteristics of the energy storage battery, and the photovoltaic unit has power grid frequency regulation capability, so that the anti-interference capability and the frequency support capability of the new energy power grid are improved.
Drawings
FIG. 1 is a diagram of an example of a three-machine nine-node system with photovoltaic grid connection according to the present invention;
FIG. 2 is an overall structure diagram of the photovoltaic power generation grid-connected system according to the invention;
FIG. 3 is a logic flow diagram of a photovoltaic array MPPT algorithm according to the present invention;
FIG. 4 is a diagram of an example of photovoltaic output power control under varying environmental conditions in accordance with the present invention
Fig. 5 is a structure diagram of a Boost circuit of the dc Boost converter according to the present invention;
FIG. 6 is a diagram illustrating a virtual inertia control structure of the energy storage battery according to the present invention;
fig. 7 is a diagram of a power-frequency droop control architecture for an energy storage battery according to the present invention;
fig. 8 is a logic flow diagram of the energy storage battery frequency adjustment algorithm of the present invention.
Fig. 9 is a diagram illustrating an example of energy storage charging and discharging control under the change of the grid frequency according to the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, the present invention will be further described in detail with reference to the accompanying drawings and specific examples, which are only used for illustrating the present invention and are not used for limiting the scope of the present invention.
Example 1
The embodiment provides a new method for realizing photovoltaic grid-connected power generation participation system frequency regulation by using an energy storage battery, which comprises the following steps:
s1: the direct current boost converter detects the output voltage and current of the photovoltaic array, adjusts the voltage through a corresponding MPPT algorithm, and ensures the maximum output of photovoltaic.
According to the P-V curve characteristic of the photovoltaic array, when the output voltage of the photovoltaic array is adjusted, the output power of a photovoltaic system is changed correspondingly, and the control part of the algorithm adopts a conductance incremental method, which has the following principle: when the photovoltaic output power is maximum, the derivative of the transmitted active power and the direct-current voltage is 0, namely:
Figure RE-GDA0003613476400000071
then, it can be obtained from formula (1):
Figure RE-GDA0003613476400000072
then transforming equation (2) can obtain:
Figure RE-GDA0003613476400000073
if the condition of the formula (3) is not satisfied, accumulating the generated difference value in a PI regulator in the direct current boost converter and outputting an error signal, changing the output voltage of the photovoltaic array until the error is eliminated, and outputting the maximum power by the photovoltaic array after the condition of the formula (3) is achieved.
And S2, detecting the output voltage of the photovoltaic array by the direct current Boost converter, and adjusting the duty ratio by the Boost circuit to ensure the stability of the voltage at the Boost side when the output voltage of the photovoltaic array changes.
According to Boost circuit, its output voltage VOutAnd the output voltage V of the photovoltaic array direct current businThe relation is as follows:
Figure RE-GDA0003613476400000074
wherein D is the duty cycle.
The selection of parameters of inductance and capacitance elements in the Boost circuit needs to satisfy the following relational expression:
Figure RE-GDA0003613476400000075
Figure RE-GDA0003613476400000081
in the formula, C1F is the frequency of the DC boost converter, L is the parameter of the inductance element, Delta I is the ripple current value, and Delta VOutAs ripple voltage value, RLoadIs a load resistor with a magnitude equal to VOut/IOut。
S3: and detecting the SOC of the energy storage battery, and controlling the energy storage battery to charge and discharge to store proper active power for later use when the frequency of the power grid is stable if the SOC does not meet the condition (20% < SOC < 90%).
When the source side of the direct current bidirectional converter is configured with a plurality of energy storage batteries, the output power of the direct current bidirectional converter is obtained according to the proportional relation of the output power among the energy storage batteries as follows:
Figure RE-GDA0003613476400000082
in the formula, PDThe difference between the total power of photovoltaic power generation and the total power of load in the system, N is the number of energy storage battery blocks, mpiAnd corresponding the power coefficients of the SOC of different energy storage batteries in the system.
The method for calculating the SOC of the energy storage battery comprises the following steps:
Figure RE-GDA0003613476400000083
in the formula, SOCi(t) is the current chargeability, SOC, of each energy storage batteryi_iniFor the initial chargeability, i, of the respective energy storage celli-bat(t) is the magnitude of the discharge current of the energy storage battery, Qi-batThe capacity of the energy storage battery is.
Neglecting the self loss of the converter, the output power on both sides is equal, and the combination formulas (7) and (8) can obtain:
Figure RE-GDA0003613476400000084
therefore, the estimation of the SOC state among the multiple energy storage batteries can be realized, and the output speed of each energy storage battery can be correspondingly distributed when the energy storage batteries participate in the frequency modulation of the power system under different SOC conditions.
S4: detecting the frequency f of the networkprAnd when the frequency of the power grid is increased or reduced, starting communication to detect the SOC of the energy storage battery, and controlling the energy storage battery to charge and discharge to adjust the frequency of the power grid if the SOC meets the condition.
The energy storage battery participating in the frequency regulation of the power system comprises a virtual inertia control part and an active-frequency droop control part, which are respectively used for simulating a power output curve of the inertia response and the primary frequency modulation control of the synchronous generator:
the expression of the virtual inertia control is:
Figure RE-GDA0003613476400000091
in the formula, HBESSDf/dt is the detected rate of change of grid frequency for the set virtual inertia constant.
The expression of active-frequency droop control is:
ΔPBESS-t＝P0-k(fpr-fref)Pn (11)
in the formula, P0Is the sag factor, fprFor detected grid frequency, frefTo set a frequency reference (typically 50Hz, power frequency), PnThe rated power output by the energy storage battery.
Under the coordination of the virtual inertia and the droop control, the energy storage battery can simulate a power response curve of the synchronous generator to realize stable adjustment of the frequency of the power grid.
S5: the energy storage battery is in the charge-discharge participation frequency modulation process, the detection element detects the power grid frequency deviation or the energy storage battery SOC respectively, and when the frequency deviation is eliminated or the energy storage battery SOC does not meet the conditions, the control element is started to control the energy storage battery to quit the operation.
Example 2
As shown in figure 1, the three-machine nine-node system comprises two thermal power generating units and one hydroelectric generating unit, the output power is 150MW, the inertia time constants are set to be 5s, a photovoltaic system provided with an energy storage battery with the capacity of 20MW & h is connected to BUS5, and the transmission power of the photovoltaic system can reach 10 MW.
Fig. 2 is a diagram of the overall structure of the photovoltaic power generation grid-connected system provided by the method, and the overall system is composed of a photovoltaic array, a direct-current boost converter, a storage battery energy storage system, a corresponding direct-current bidirectional converter, a grid-connected converter, corresponding measurement calculation elements and a communication part.
The method comprises the following steps that the ambient temperature and the illumination intensity of a photovoltaic system are constantly changed, a boost transformer starts an MPPT control algorithm after detecting that the voltage of a photovoltaic direct-current bus is changed, a conductance increment method is adopted for realizing, and the control flow is shown in the attached figure 3 and specifically comprises the following steps: 1. detecting a current photovoltaic output voltage VkAnd IkAnd V detected in the previous stepk-1And Ik-1Performing difference comparison; 2. if it is poorIf the value delta V is 0, detecting delta I, indicating that the photovoltaic power generation device operates at the maximum power point, and if the value delta I is greater than or less than 0, correspondingly reducing or increasing the photovoltaic output voltage; 3. if the difference value Δ V is not 0, detecting whether 1+ (dI/dV) × V ═ 0 is satisfied, indicating that the photovoltaic output voltage is operated at the maximum power point, and if 1+ (dI/dV) is greater than or less than 0, decreasing or increasing the photovoltaic output voltage accordingly. In the example, the control effect of the MPPT algorithm is shown in fig. 4, and the photovoltaic system can always keep in the maximum active output state along with the change of the illumination intensity and the temperature.
In the process of controlling the voltage change of the photovoltaic bus by the MPPT algorithm, the boosting transformer needs to stabilize the voltage at the side of the boosting bus and provide a good working environment with stable voltage for the charging and discharging operating conditions of the energy storage battery, therefore, a Boost boosting circuit shown in the attached figure 5 needs to be configured, and under the condition that the voltage at the input side changes, the duty ratio is changed by a control element to adjust the voltage of the boosting bus to be unchanged.
The energy storage battery participates in frequency modulation control of the power system, receives control signals of the direct-current bidirectional converter, the frequency modulation control strategy of the energy storage battery comprises virtual inertia control and frequency-active droop control, control block diagrams are respectively shown in the attached drawings 6 and 7, and under the coordination of the virtual inertia control and the droop control, the energy storage battery can simulate a power response curve of the synchronous generator to achieve stable adjustment of the power grid frequency.
In this example, the three-machine nine-node system starts the detection element to detect the SOC of the energy storage battery under the initial condition of stable frequency, and starts the control element to control the energy storage battery to charge and discharge to the power grid if the SOC of the energy storage battery is less than 20% or greater than 90% until the condition is satisfied.
At 60s, the BUS6 suddenly cuts in/cuts off 40MW load to cause sudden change of the grid frequency, at this time, the detection element detects that the grid frequency changes, the frequency regulation control action of the photovoltaic system is shown in fig. 8, and the action flow algorithm specifically comprises the following steps: 1. detecting whether a difference value exists between the power grid frequency and the power frequency, normally setting threshold change frequency, and detecting the SOC of the energy storage battery when the absolute value of the difference value is greater than the threshold; 2. if the current power grid frequency is less than the power frequency and the SOC of the energy storage battery is more than or equal to 20%, controlling the energy storage battery to discharge until the SOC of the energy storage battery is less than 20% or the power grid frequency returns to the power frequency to stop, and if the initial SOC is less than 20%, charging the energy storage battery; 3. and if the current power grid frequency is greater than the power frequency and the SOC of the energy storage battery is less than 90%, controlling the energy storage battery to charge until the SOC of the energy storage battery is greater than 90% or the power grid frequency returns to the power frequency and stops.
The control effect of the frequency adjustment algorithm in the embodiment is shown in figure 9, when the frequency of the power grid deviates, after the SOC of the energy storage battery meets the condition, the control element controls energy storage charging and discharging to provide frequency support for the power grid, then the primary and secondary frequency modulation control actions of the thermoelectric and hydroelectric generating set in the system are carried out, the frequency of the power grid is recovered to be normal, and after the frequency deviation of the power grid is eliminated, the control element is operated, and the energy storage battery is stopped from running.
Aiming at the stability problem of the new energy power grid, the charging and discharging characteristics of the energy storage battery are fully utilized, the economy of the maximum output of the photovoltaic system is guaranteed, and meanwhile, the power grid frequency adjusting capacity is achieved, so that the anti-jamming capacity and the frequency supporting capacity of the new energy power grid are improved.
It should be noted that the above-mentioned embodiments are only used 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-mentioned embodiments, a person skilled in the art can make modifications or equivalent substitutions to the specific embodiments of the present invention, and any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the scope of the claims of the appended claims.

Claims (5)

1. A frequency adjusting method of a photovoltaic grid-connected power generation participation system is characterized by comprising the following steps: the method comprises the following steps:
s1: the photovoltaic array sequentially passes through a direct current boost converter and a grid-connected converter and then is connected into a power grid, the direct current boost converter detects the output voltage and current of the photovoltaic array, the voltage is adjusted through an MPPT algorithm, and the maximum photovoltaic output is guaranteed;
s2: the direct current Boost converter is matched with a corresponding measuring and calculating element to detect the output voltage of the photovoltaic array, and the duty ratio is adjusted through a Boost circuit to ensure the stability of the voltage at the Boost side when the output voltage of the photovoltaic array changes;
s3: the storage battery energy storage system is merged into a direct current boost bus through a direct current bidirectional converter and then merged into a power grid through a grid-connected converter, the direct current bidirectional converter is matched with a corresponding measurement and calculation element to detect the SOC of the energy storage battery, and if the SOC is less than 20% and less than 90%, the energy storage battery is controlled to be charged and discharged to store active power for later use when the frequency of the power grid is stable;
s4: detecting the frequency f of the networkprWhen the frequency of the power grid is increased or reduced, starting communication to detect the SOC of the energy storage battery, and if the SOC is less than 20% or the SOC is more than 90%, controlling the energy storage battery to charge and discharge so as to adjust the frequency of the power grid;
s5: the detection element detects the frequency deviation of the power grid or the SOC of the energy storage battery respectively, and when the frequency deviation is eliminated or 20% of the SOC is less than 90%, the control element is started to control the energy storage battery to quit the operation.
2. The frequency regulation method of the photovoltaic grid-connected power generation participation system according to claim 1, characterized in that: in the step S1, the voltage adjustment method by the MPPT algorithm is as follows: according to the P-V curve characteristic of the photovoltaic array, when the output voltage of the photovoltaic array is adjusted, the output power of a photovoltaic system is correspondingly changed, a control part algorithm adopts a conductance incremental method, and the principle is as follows:
Figure RE-FDA0003613476390000011
obtainable from formula (1):
Figure RE-FDA0003613476390000021
the formula (2) is transformed to obtain:
Figure RE-FDA0003613476390000022
if the condition of the formula (3) is not met, accumulating the generated difference value in a PI regulator in the direct current boost converter and outputting an error signal, changing the output voltage of the photovoltaic array until the error is eliminated, and outputting the maximum power by the photovoltaic array after the condition of the formula (3) is met; the photovoltaic output power is maximum when the derivative of the transmitted active power with the dc voltage is 0.
3. The frequency regulation method of the photovoltaic grid-connected power generation participation system according to claim 1, characterized in that: the regulation principle of the Boost circuit in the step S2 is as follows:
according to Boost circuit, its output voltage VOutAnd the output voltage V of the photovoltaic array direct current businThe relation is as follows:
Figure RE-FDA0003613476390000023
wherein D is the duty cycle;
the selection of parameters of inductance and capacitance elements in the Boost circuit needs to satisfy the following relational expression:
Figure RE-FDA0003613476390000024
Figure RE-FDA0003613476390000025
in the formula, C1F is the frequency of the DC boost converter, L is the parameter of the inductance element, Delta I is the ripple current value, and Delta VOutAs ripple voltage value, RLoadIs a load resistor with a magnitude equal to VOut/IOut。
4. The frequency regulation method of the photovoltaic grid-connected power generation participation system according to claim 1, characterized in that: the method for calculating the SOC of the energy storage battery in the step S3 comprises the following steps:
Figure RE-FDA0003613476390000031
in the formula, SOCi(t) is the current chargeability, SOC, of each energy storage batteryi_iniFor the initial chargeability, i, of the respective energy storage celli-bat(t) is the discharge current of the energy storage battery, Qi-batThe capacity of the energy storage battery is obtained;
when the source side of the direct current bidirectional converter is configured with a plurality of energy storage batteries, the output power of the direct current bidirectional converter is obtained according to the proportional relation of the output power among the energy storage batteries as follows:
Figure RE-FDA0003613476390000032
in the formula, PDThe difference between the total power of photovoltaic power generation and the total power of load in the system, N is the number of energy storage battery blocks, mpiCorresponding power coefficients of the SOC to different energy storage batteries in the system;
neglecting the self loss of the converter, the output power of the two sides is equal, and by combining the formulas (7) and (8), the following results are obtained:
Figure RE-FDA0003613476390000033
and the estimation of the SOC state among the multiple energy storage batteries is realized, and the energy storage batteries are controlled to be charged and discharged through the SOC calculated value so as to adjust the frequency of the power grid.
5. The frequency regulation method of the photovoltaic grid-connected power generation participation system according to claim 1, characterized in that: in the step S4, the power grid frequency is detected by a control algorithm in which the energy storage battery participates in the frequency adjustment of the power system, and the control algorithm includes two parts, namely virtual inertia control and active-frequency droop control, which are respectively used for simulating a power output curve of the inertia response and primary frequency modulation control of the synchronous generator:
the expression of the virtual inertia control is:
Figure RE-FDA0003613476390000041
in the formula, HBESSFor the set virtual inertia constant, df/dt is the detected grid frequency change rate;
the expression of active-frequency droop control is:
ΔPBESS-t＝P0-k(fpr-fref)Pn (11)
in the formula, P0As sag factor, fprFor detected grid frequency, frefTo set the frequency reference value, PnRated power output for the energy storage battery;
under the coordination of virtual inertia control and active-frequency droop control, the energy storage battery simulates a power response curve of the synchronous generator to realize stable adjustment of the power grid frequency.
CN202210149908.3A 2022-02-18 2022-02-18 Frequency adjusting method for photovoltaic grid-connected power generation participation system Pending CN114552600A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
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CN117154900A (en) * 2023-10-30 2023-12-01 荣耀终端有限公司 Charging control method and electronic equipment
CN117424267A (en) * 2023-10-24 2024-01-19 上海勘测设计研究院有限公司 Power system peak shaving method and device for energy storage capacity optimal configuration

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117424267A (en) * 2023-10-24 2024-01-19 上海勘测设计研究院有限公司 Power system peak shaving method and device for energy storage capacity optimal configuration
CN117424267B (en) * 2023-10-24 2024-05-07 上海勘测设计研究院有限公司 Power system peak shaving method and device for energy storage capacity optimal configuration
CN117154900A (en) * 2023-10-30 2023-12-01 荣耀终端有限公司 Charging control method and electronic equipment
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