An adaptive control system and control method for off-grid loads of a photovoltaic storage microgrid

Abstract

The present invention provides an off-grid load adaptive control system and control method for a photovoltaic and energy storage microgrid. The control method detects the operating parameters of AC load, photovoltaic cells and energy storage batteries, optimizes the switching state, working order and working mode of photovoltaic access converters, energy storage converters and inverters in the photovoltaic and energy storage microgrid system, removes unnecessary converter losses, and enables the system to operate in a range with higher overall efficiency, thereby solving the problem of excessive light and no-load losses in the existing photovoltaic and energy storage microgrid system in off-grid mode, thereby improving the operating economy and off-grid power supply reliability of the photovoltaic and energy storage system.

Description

Technical Field

[0001] The present invention relates to the technical field of microgrids, and in particular to an off-grid load adaptive control system and control method for a photovoltaic storage microgrid. Background Art

[0002] Due to complex terrain, high grid construction costs, and ecological red line protection, remote mountainous areas have a relatively weak grid structure and low power supply reliability. Building off-grid photovoltaic and storage microgrids in remote mountainous areas can solve the problem of power supply reliability, reduce grid operation and maintenance costs, and improve the ability to absorb distributed new energy.

[0003] In the microgrid system, the energy routing system composed of various converters is responsible for realizing the power conversion between various ports, and its performance optimization and efficiency improvement have always been a hot topic of research. In off-grid mode, the inverter in the microgrid must work in voltage source mode to maintain a stable AC voltage output. At this time, the switching action of the internal devices of the energy router will generate switching losses on the one hand; on the other hand, it will introduce filter inductor current ripple and generate inductor losses. Affected by the above losses, even under light and no-load conditions, the converter in the microgrid system will still generate certain losses. It is worth noting that in application scenarios such as ordinary residential users and remote mountainous areas, there are a lot of light and no-load time in the microgrid in a day. Continuous and high light and no-load losses will seriously consume the energy storage power and reduce the overall efficiency and power supply reliability of the photovoltaic storage system.

[0004] In summary, there is an urgent need for an off-grid load adaptive control system and control method for a photovoltaic energy storage microgrid to reduce the light-load and no-load losses of the microgrid system in the off-grid operation mode. Summary of the invention

[0005] The purpose of the present invention is to provide an off-grid load adaptive control system for a photovoltaic storage microgrid, aiming to solve the problem of how to reduce the light-load and no-load losses of the microgrid system in an off-grid operation mode. The specific technical solution is as follows:

[0006] A photovoltaic storage microgrid off-grid load adaptive control system, comprising a photovoltaic storage microgrid energy routing system and an adaptive controller;

[0007] The photovoltaic microgrid energy routing system includes photovoltaic cells, energy storage batteries, photovoltaic access converters, energy storage converters, inverters and DC busbars; multiple photovoltaic cells are connected to the DC busbar through photovoltaic access converters, and the photovoltaic access converters control the unidirectional transmission of power from the photovoltaic cells to the DC busbar; multiple energy storage batteries are connected to the DC busbar through energy storage converters, and the energy storage converters control the bidirectional transmission of power between the energy storage batteries and the DC busbar; multiple inverters are arranged between the DC busbar and the AC busbar;

[0008] The adaptive controller includes a detection module, a microprocessor and a communication module; the detection module is used to sample the voltage and current signals of the inverter connected to the AC bus; the communication module is used to enable the adaptive controller to communicate with the photovoltaic access converter, each energy storage converter and each inverter; the microprocessor is used to process signals from the photovoltaic access converter, the detection module, each energy storage converter and each inverter, and issue control instructions to the photovoltaic access converter, each energy storage converter and each inverter.

[0009] The present invention also provides a control method for the off-grid load adaptive control system of the photovoltaic storage microgrid:

[0010] Calculate the total AC load based on the voltage and current signals sampled by the detection module , control the number of inverters put into operation and the total AC load The changes in are positively correlated;

[0011] Get its input power from the photovoltaic access converter , obtain the SOC signal of the energy storage battery connected to the energy storage converter from the energy storage converter, and obtain the AC active load through the detection module ;

[0012] When there is sunlight and the photovoltaic is connected to the input power of the inverter Not less than AC active load When the SOC value is lower than SOC max If there is an energy storage battery, all energy storage converters are controlled to be put into operation, and the photovoltaic access converter performs maximum power tracking control. The photovoltaic access converter supplies the remaining power outside the load for the SOC value lower than the SOC max The energy storage battery is charged and the SOC value reaches SOC max The energy storage converter does not transmit power; if the SOC value of all energy storage batteries reaches SOC max When the PV access converter is controlled to exit operation, all energy storage converters are controlled to start operation. Each energy storage converter operates according to the AC active load. The transmission power is distributed according to the ratio of the rated power of each energy storage converter. During operation, when the SOC value of the energy storage battery put into operation is lower than the threshold SOC max_low When the PV access converter is controlled to resume operation, SOC min <SOC max_low <SOC max , SOC min is the lower limit of SOC of the energy storage battery, SOC max Energy storage battery SOC upper limit value;

[0013] When there is sunlight and the photovoltaic is connected to the input power of the inverter Lower than AC active load When the holding time is less than or equal to the time threshold T, the SOC value is controlled to be higher than SOC min The energy storage converters corresponding to the energy storage batteries are put into operation. and The transmission power is distributed according to the difference between and the ratio of the rated powers of each energy storage converter;

[0014] When there is sunlight and the photovoltaic is connected to the input power of the inverter Lower than AC active load When the holding time is greater than the time threshold T, the control system enters the orderly switching mode of the energy storage converter: the SOC value is controlled to be lower than SOC min The energy storage converter corresponding to the energy storage battery is shut down, and the SOC value is higher than SOC min The energy storage converter corresponding to the energy storage battery is used as an alternative energy storage converter. With AC active load A corresponding number of energy storage converters are selected from the candidate energy storage converters according to the difference between the two and put into operation;

[0015] When there is no sunlight, control the photovoltaic access converter and the SOC value is lower than SOC min The energy storage converter corresponding to the energy storage battery exits operation, and the system enters the orderly switching mode of the energy storage converter: the SOC value is higher than SOC min The energy storage converter corresponding to the energy storage battery is used as an alternative energy storage converter, according to the AC active load A corresponding number of energy storage converters are selected from the candidate energy storage converters and put into operation.

[0016] The preferred technical solution is the number of inverters put into operation and the total AC load. The changes are positively correlated, specifically:

[0017] Arrange the inverters from high to low according to their operating efficiency and number them. The rated power of each inverter in the order of arrangement is: , ,……, , the output power corresponding to the peak efficiency of each inverter is , ,……, ,in is the total number of inverters;

[0018] According to the total AC load And formula (1) to calculate The value of controls the 1st to the The inverter No. was put into operation;

[0019] (1)

[0020] in, , Indicates The output power corresponding to the peak efficiency of the inverter is is the upper power threshold, is the lower power threshold.

[0021] The preferred technical solution above is based on the input power With AC active load The difference between the two is used to select a corresponding number of energy storage converters from the candidate energy storage converters for operation, specifically:

[0022] Set all SOC values ​​above SOC min The energy storage converters corresponding to the energy storage batteries are sorted and numbered from large to small according to the capacity of the energy storage batteries to obtain a candidate energy storage converter sequence 1; the rated power of each energy storage converter in the candidate energy storage converter sequence 1 is , ,……, , the output power corresponding to the peak efficiency of each energy storage converter is , ,……, ,in represents the number of candidate energy storage converters in the candidate energy storage converter sequence 1;

[0023] According to input power With AC active load The difference between the two and the formula (2) is used to calculate The value of controls the first to the second energy storage converters in the sequence of the candidate energy storage converters. The energy storage converter No. was put into operation;

[0024] (2)

[0025] in, , Indicates The output power corresponding to the peak efficiency of the alternative energy storage converter is: Indicates the upper power threshold. Indicates the lower power threshold.

[0026] The preferred technical solution is as follows: when the input power With AC active load The difference between is less than or equal to When the output power is only controlled to The energy storage converter is put into operation. When the input power With AC active load The difference between them is further less than the threshold When the control output power is The energy storage converter works intermittently according to the voltage fluctuation of the DC bus.

[0027] The preferred technical solution is based on the AC active load. Select a corresponding number of energy storage converters from the candidate energy storage converters and put them into operation, specifically:

[0028] Set all SOC values ​​above SOC min The energy storage converters corresponding to the energy storage batteries are sorted and numbered from large to small according to the capacity of the energy storage batteries to obtain a second candidate energy storage converter sequence; the rated power of each energy storage converter in the second candidate energy storage converter sequence is , ,……, , the output power corresponding to the peak efficiency of each energy storage converter is , ,……, ,in represents the number of candidate energy storage converters in the second candidate energy storage converter sequence;

[0029] According to AC active load And formula (4) to calculate The value of controls the first to the second candidate energy storage converter sequence. The energy storage converter No. was put into operation;

[0030] (4)

[0031] in, , Indicates The output power corresponding to the peak efficiency of the alternative energy storage converter is: Indicates the upper power threshold. Indicates the lower power threshold.

[0032] The preferred technical solution above is when the AC active load Less than or equal to When the output power is only controlled to The energy storage converter is put into operation. When the AC active load Further below the threshold When the control output power is The energy storage converter works intermittently according to the voltage fluctuation of the DC bus.

[0033] The preferred technical solution is to control the energy storage converter to work intermittently, specifically: setting the upper limit of the DC bus voltage fluctuation and lower limit , when the DC bus voltage reaches When the energy storage converter blocks the drive signal, the DC bus voltage drops; when the DC bus voltage drops to When the energy storage converter sends out a driving signal, the DC bus voltage rises; this cycle is repeated to achieve intermittent operation.

[0034] In the above technical solution, the threshold value is preferably The calculation formula is:

[0035] (3)

[0036] in, is the DC bus capacitor value, is the switching action cycle of the energy storage converter.

[0037] Preferably in the above technical solution, the control method is executed by the microprocessor.

[0038] The application of the technical solution of the present invention has the following beneficial effects:

[0039] The present invention provides a load adaptive control system and a control method that can improve the comprehensive efficiency of off-grid operation of a photovoltaic and energy storage microgrid. The control method detects the operating parameters of the AC load, photovoltaic cells and energy storage batteries, optimizes the switching state, working order and working mode of the photovoltaic access converter, energy storage converter and inverter in the photovoltaic and energy storage microgrid system, removes unnecessary converter losses, and enables the system to operate in a range with higher comprehensive efficiency. The problem of excessive light and no-load losses in the existing photovoltaic and energy storage microgrid system in off-grid mode is solved, thereby improving the operating economy and off-grid power supply reliability of the photovoltaic and energy storage system.

[0040] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0042] Figure 1 It is the structural block diagram of the off-grid load adaptive control system of the photovoltaic storage microgrid;

[0043] Figure 2 is the input power Greater than AC active load The control logic diagram of photovoltaic access converter;

[0044] Figure 3 It is a schematic diagram of intermittent control of energy storage converter;

[0045] Figure 4 It is the waveform diagram of the inverter output voltage and current in the simulation verification;

[0046] Figure 5 It is the inverter output power waveform in the simulation verification;

[0047] Figure 6 It is the output voltage and current waveform of the energy storage converter in the simulation verification;

[0048] Figure 7 It is the output power waveform of the energy storage converter in the simulation verification;

[0049] Figure 8 It is a waveform diagram of the resonant converter excitation current, primary upper tube drive signal, primary lower tube drive signal and DC bus voltage in the intermittent working mode of the energy storage converter in the simulation verification; DETAILED DESCRIPTION

[0050] In order to facilitate the understanding of the present invention, the present invention will be described more fully below, and preferred embodiments of the present invention are provided. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0052] Example:

[0053] See also Figure 1 , This embodiment provides a photovoltaic storage microgrid off-grid load adaptive control system, which includes a photovoltaic storage microgrid energy routing system and an adaptive controller;

[0054] The photovoltaic microgrid energy routing system includes photovoltaic cells, energy storage batteries, photovoltaic access converters, energy storage converters, inverters and DC busbars; multiple photovoltaic cells are connected to the DC busbar via photovoltaic access converters, and the photovoltaic access converters control the unidirectional transmission of power from the photovoltaic cells to the DC busbar; multiple energy storage batteries are connected to the DC busbar via energy storage converters (that is, the energy storage batteries and energy storage converters are arranged in a one-to-one correspondence), and the energy storage converters control the bidirectional transmission of power between the energy storage batteries and the DC busbar; multiple inverters are arranged between the DC busbar and the AC busbar.

[0055] The adaptive controller includes a detection module, a microprocessor and a communication module; the detection module is used to sample the voltage and current signals of the inverter connected to the AC bus; the communication module is used to enable the adaptive controller to communicate with the photovoltaic access converter, each energy storage converter and each inverter; the microprocessor is used to process signals from the photovoltaic access converter, the detection module, each energy storage converter and each inverter, and issue control instructions to the photovoltaic access converter, each energy storage converter and each inverter.

[0056] Preferably, in the photovoltaic storage microgrid energy routing system of this embodiment, multiple photovoltaic cells are first connected in series and then connected to the photovoltaic access converter. In some embodiments, multiple photovoltaic cells and the photovoltaic access converter may be connected in parallel, and then the photovoltaic access converter is connected to the DC bus; those skilled in the art can select and adjust the connection method between the photovoltaic cells and the photovoltaic access converter according to common sense in the art.

[0057] This embodiment further provides a control method for the off-grid load adaptive control system of the photovoltaic storage microgrid:

[0058] Control method of the inverter part:

[0059] Calculate the total AC load based on the voltage and current signals sampled by the detection module The number of inverters put into operation in the off-grid load adaptive control system of the photovoltaic storage microgrid and the total AC load The change of is positively correlated, so that the photovoltaic storage microgrid off-grid load adaptive control system always operates in a higher efficiency range.

[0060] Furthermore, the number of inverters put into operation and the total AC load The changes are positively correlated, specifically:

[0061] First, the inverters are arranged and numbered from high to low according to their operating efficiency, and the rated power of each inverter in the arrangement order is , ,……, , the output power corresponding to the peak efficiency of each inverter is , ,……, ,in is the total number of inverters;

[0062] Then, according to the total AC load And formula (1) to calculate The value of controls the 1st to the The inverter No. is put into operation, and the remaining inverters (i.e. +1 to The inverter will exit operation to remove excess inverter losses and make the entire system operate in a higher efficiency range.

[0063] (1)

[0064] in, , Indicates The output power corresponding to the peak efficiency of the inverter is and They are the upper and lower power thresholds, respectively.

[0065] Preferably, in this embodiment, the switching on and off of the inverter is based on the total AC load. The total AC load changes dynamically with the change of When the load decreases, the total number of inverters put into operation decreases accordingly, and the total AC load As the efficiency increases, the total number of inverters put into operation increases accordingly, so that the entire system can always operate in a higher efficiency range.

[0066] Preferably, to ensure the stability of the control system, the inverter should be switched on and off according to the upper power threshold. , lower power threshold Setting a certain hysteresis interval is common knowledge in the art and will not be described in detail in this embodiment.

[0067] Control methods of photovoltaic access converter and energy storage converter:

[0068] First, the adaptive controller obtains the input power from the photovoltaic inverter. , obtain the SOC signal (State Of Charge) of the energy storage battery connected to the energy storage converter from the energy storage converter, and obtain the AC active load through the detection module ;

[0069] Photovoltaic cells can be in working state when there is sunlight. In actual engineering applications, it is generally necessary to consider the input power of the photovoltaic inverter. Greater than or equal to AC active load The situation and input power Less than AC active load Therefore, in this embodiment, corresponding control methods are given for these two situations, as follows:

[0070] When there is sunlight and the photovoltaic is connected to the input power of the inverter Not less than (i.e. greater than or equal to) AC active load When the SOC value is lower than SOC max If there is an energy storage battery, all energy storage converters are controlled to be put into operation (i.e., the energy storage converter does not block the drive pulse and keeps the energy storage converter running), and the photovoltaic access converter performs maximum power point tracking control (MPPT). The photovoltaic access converter supplies the remaining power outside the load for the SOC value lower than the SOC max The energy storage battery is charged and the SOC value reaches SOC max The energy storage converter does not transmit power, but only provides DC bus voltage support; if the SOC value of all energy storage batteries reaches SOC max When the PV access converter is controlled to exit operation, all energy storage converters are controlled to start operation. Each energy storage converter operates according to the AC active load. The transmission power is distributed according to the ratio of the rated power of each energy storage converter. During operation, when the SOC value of the energy storage battery put into operation is lower than the threshold SOC max_low When the PV access converter is controlled to resume operation, the control logic of the PV access converter in this process is as follows: Figure 2 As shown;

[0071] Furthermore, after the photovoltaic access converter is put back into operation, according to the input power With AC active load The relationship between the input power Greater than or equal to AC active load , or, the input power Less than AC active load ) Select the corresponding control method; among them, SOC min <SOC max_low <SOC max , SOC min is the lower limit of SOC of the energy storage battery, SOC max Energy storage battery SOC upper limit value;

[0072] When there is sunlight and the photovoltaic is connected to the input power of the inverter Lower than AC active load When the holding time is less than or equal to the time threshold T, the SOC value is controlled to be higher than SOC minThe energy storage converters corresponding to the energy storage batteries are put into operation. and The transmission power is distributed according to the difference between and the ratio of the rated powers of each energy storage converter;

[0073] When there is sunlight and the photovoltaic is connected to the input power of the inverter Lower than AC active load When the holding time is greater than the time threshold T, the control system enters the orderly switching mode of the energy storage converter: the SOC value is controlled to be lower than SOC min The energy storage converter corresponding to the energy storage battery is shut down, and the SOC value is higher than SOC min The energy storage converter corresponding to the energy storage battery is used as an alternative energy storage converter. With AC active load A corresponding number of energy storage converters are selected from the candidate energy storage converters according to the difference between the two and put into operation;

[0074] Preferably, the time threshold T is determined based on experience. The time threshold T is set to prevent and When jitter occurs in a very close area, the system control logic switches repeatedly.

[0075] Furthermore, according to the input power With AC active load The difference between the two is used to select a corresponding number of energy storage converters from the candidate energy storage converters for operation, specifically:

[0076] First, all SOC values ​​above SOC min The energy storage converters corresponding to the energy storage batteries are sorted and numbered from large to small according to the capacity of the energy storage batteries to obtain a candidate energy storage converter sequence 1; the rated power of each energy storage converter in the candidate energy storage converter sequence 1 is , ,……, , the output power corresponding to the peak efficiency of each energy storage converter is , ,……, ,in Indicates the number of alternative energy storage converters in the first alternative energy storage converter sequence.

[0077] Then, according to the input power With AC active load The difference between the two and the formula (2) is used to calculate The value of controls the first to the second energy storage converters in the sequence of the candidate energy storage converters. The energy storage converter No. is put into operation, and the remaining (i.e. +1 to The energy storage converter (signal) will exit operation to remove the excess energy storage converter loss and make the entire system operate in a higher efficiency range.

[0078] (2)

[0079] in, , Indicates The output power corresponding to the peak efficiency of the alternative energy storage converter is: and Represents the upper and lower power thresholds respectively.

[0080] Furthermore, in the energy storage converter put into operation, when the SOC value of a certain energy storage battery is lower than SOC min When the adaptive controller controls the energy storage converter corresponding to the energy storage battery to exit operation, and removes the energy storage converter from the candidate energy storage converter sequence one, and at the same time moves the candidate energy storage converter behind the energy storage converter in sequence one forward one position in sequence one, that is, updates the candidate energy storage converter sequence one.

[0081] Preferably, in this embodiment, the energy storage converter is switched on and off according to the input power With AC active load The difference between the input power varies dynamically with the change of With AC active load When the difference between the two decreases, the total number of energy storage converters put into operation decreases accordingly, and the input power With AC active load When the difference between them increases, the total number of energy storage converters put into operation increases accordingly, so that the entire system can always operate in a higher efficiency range.

[0082] Furthermore, when the input power With AC active load The difference between is less than or equal to When the output power is only controlled to The energy storage converter is put into operation. When the input power With AC active load The difference between them is further less than the threshold When (i.e. Less than ), the control output power is The energy storage converter works intermittently according to the voltage fluctuation of the DC bus;

[0083] Furthermore, the output power is controlled to The energy storage converter works intermittently, specifically: setting the upper limit of DC bus voltage fluctuation and lower limit , when the DC bus voltage reaches When the output power is The energy storage converter locks the drive signal (i.e. exits operation), and the DC bus voltage drops; when the DC bus voltage drops to When the output power is The energy storage converter sends a driving signal (i.e., is put into operation), causing the DC bus voltage to rise, and this cycle is repeated to achieve intermittent operation.

[0084] in, It should be selected according to the withstand voltage of the internal components of the energy storage converter. It must not be lower than the lower limit of the DC bus voltage required for the output AC bus voltage.

[0085] Furthermore, since the loss of the energy storage converter during startup is slightly greater than the loss during stable operation, the DC bus voltage Down to The longer the time is, the better the loss reduction effect is, so this time is taken as Energy storage converter switching cycle When The calculation formula is:

[0086] (3)

[0087] in, is the DC bus capacitor value.

[0088] For ease of understanding, this embodiment provides a schematic diagram of intermittent control of the energy storage converter in a series resonant converter, such as Figure 3 As shown, Figure 3 middle v gs1 , v gs2 , v gs3 , v gs4 , v gs5 , v gs6 , v gs7 , v gs8 Both represent the switch tube drive signal. i r is the resonant cavity current, i m is the resonant converter excitation current, P is the transmission power, U dc is the DC bus voltage,T b-on is the start-up time of the energy storage converter in intermittent control, T b-off is the rest time of the energy storage converter in intermittent control, is the upper limit of DC bus voltage fluctuation, is the lower limit of DC bus voltage fluctuation, for and The difference between .

[0089] Preferably, to ensure the stability of the control system, the energy storage converter should be switched on and off and the start and stop of the intermittent working mode should be based on the upper power threshold. , lower power threshold and threshold Setting a certain hysteresis interval is common knowledge in the art and will not be described in detail in this embodiment.

[0090] When there is no sunlight, the adaptive controller controls the photovoltaic access converter and the SOC value is lower than SOC min The energy storage converter corresponding to the energy storage battery exits operation, and the system enters the orderly switching mode of the energy storage converter: the SOC value is higher than SOC min The energy storage converter corresponding to the energy storage battery is used as an alternative energy storage converter, according to the AC active load Select a corresponding number of energy storage converters from the candidate energy storage converters and put them into operation. The number of energy storage converters selected from the candidate energy storage converters is proportional to the AC active load. There is a positive correlation between them;

[0091] Furthermore, according to the AC active load Select a corresponding number of energy storage converters from the candidate energy storage converters and put them into operation, specifically:

[0092] Set all SOC values ​​above SOC min The energy storage converters corresponding to the energy storage batteries are sorted and numbered from large to small according to the capacity of the energy storage batteries to obtain a second candidate energy storage converter sequence; the rated power of each energy storage converter in the second candidate energy storage converter sequence is , ,……, , the output power corresponding to the peak efficiency of each energy storage converter is , ,……, ,in represents the number of candidate energy storage converters in the second candidate energy storage converter sequence;

[0093] According to AC active load And formula (4) to calculate The value of controls the first to the second candidate energy storage converter sequence. The energy storage converter No. is put into operation, and the remaining (i.e. +1 to The energy storage converter (signal) will exit operation to remove the excess energy storage converter loss and make the entire system operate in a higher efficiency range.

[0094] (4)

[0095] in, , Indicates The output power corresponding to the peak efficiency of the alternative energy storage converter is: and Represents the upper and lower power thresholds respectively.

[0096] Similarly, in a storage converter that is put into operation, when the SOC value of a storage battery is lower than SOC min When the adaptive controller controls the energy storage converter corresponding to the energy storage battery to exit operation, removes the energy storage converter from the second candidate energy storage converter sequence, and moves the second candidate energy storage converter behind the energy storage converter in sequence one position forward in sequence two, that is, updates the second candidate energy storage converter sequence.

[0097] Similarly, when the AC active load Less than or equal to When the output power is only controlled to The energy storage converter is put into operation. When the AC active load Further below the threshold When (i.e. Less than ), the control output power is The energy storage converter works intermittently according to the voltage fluctuation of the DC bus.

[0098] Furthermore, the output power is controlled to The energy storage converter works intermittently according to the voltage fluctuation of the DC bus and controls the output power to be The energy storage converter performs intermittent operation in the same way; similarly, to ensure the stability of the control system, the energy storage converter's switching on and off and the start and stop of the intermittent operation mode should be based on the upper power threshold , lower power threshold and threshold Setting a certain hysteresis interval is common knowledge in the art and will not be described in detail in this embodiment.

[0099] Preferably, in this embodiment, each energy storage converter and each inverter adopts droop control, and the energy storage converter and inverter put into operation distribute output power according to their respective rated power sizes or rated power ratios.

[0100] So far, the control method in this embodiment has been described in detail. In some embodiments, the multiple inverters and multiple energy storage converters in the off-grid load adaptive control system of the photovoltaic storage microgrid may all be of the same specification. In this case, the control method of this embodiment can also be used. When sorting the inverters, each inverter is regarded as parallel and numbered in sequence. The same applies to the sorting of the alternative energy storage converters.

[0101] Simulation verification:

[0102] The microgrid system in this simulation case consists of: three single-phase inverters of the same specifications, using virtual synchronous motor control, with a rated power of 5kW and a peak efficiency corresponding to a power of 3kW, numbered inv1, inv2, and inv3, respectively, and a circuit topology of single-phase full-bridge. Three energy storage converters of the same specifications, with a rated power of 5kW and a peak efficiency corresponding to a power of 3kW, numbered bat1, bat2, and bat3, respectively, and a circuit topology of LLC resonant converter plus bidirectional Buck / Boost, where the LLC converter has a resonant frequency of 114kHz, a switching frequency of 110kHz, and operates in DCX mode with secondary synchronous rectification. Photovoltaic cells and photovoltaic access converters are not considered in this simulation case, that is, the working conditions of the microgrid system when there is no light are simulated and verified.

[0103] During the simulation, the AC load of the microgrid dropped from 12kW to 5kW and then to 2.8kW in off-grid operation. The simulation results are as follows: Figure 4-Figure 7 As shown:

[0104] Figure 4 The inverter output voltage and current waveforms when the control method of this embodiment is adopted are shown in FIG. U ac Indicates the voltage of the AC bus, I inv1 represents the output current of inverter inv1, I inv2 represents the output current of inverter inv2, I inv3 Represents the output current of inverter inv3; Figure 5 The inverter output power waveform when the control method of this embodiment is adopted is shown in FIG. represents the output power of inverter inv1, represents the output power of inverter inv2, Indicates the output power of inverter inv3.

[0105] from Figure 4 and Figure 5 It can be seen that: before 5s, the load was 12kW, and the three inverters each output 4kW. At 5s, the load dropped to 5kW, inverter inv3 exited operation, and inverters inv1 and inv2 each output 2.5kW. When the control method of this embodiment is not adopted, the three inverters each output 1.67kW; in contrast, when the control method of this embodiment is adopted, the inverter operating point is closer to the maximum efficiency point, and the system efficiency is higher. At 7s, the load dropped to 2.8kW, inverter inv2 exited operation, and inverter inv1 independently output 2.8kW; when the control method of this embodiment is not adopted, the three inverters each output 0.93KW; in contrast, when the control method of this embodiment is adopted, the inverter operating point is closer to the maximum efficiency point, and the system efficiency is higher.

[0106] Figure 6 The output voltage and current waveforms of the energy storage converter when the control method of this embodiment is adopted are shown in FIG. U dc represents the voltage of the DC bus, Represents the output current of the energy storage converter bat1, Represents the output current of the energy storage converter bat2, Represents the output current of the energy storage converter bat3; Figure 7 The output power waveform of the energy storage converter when the control method of this embodiment is adopted is shown in FIG. Represents the output power of the energy storage converter bat1, Represents the output power of the energy storage converter bat2, Represents the output power of the energy storage converter bat3.

[0107] from Figure 6 and Figure 7 It can be seen that: before 2s, the load was 12kW, and the three energy storage inverters each output 4kW. At 2s, the load dropped to 5kW, the energy storage inverter bat3 stopped running, and the energy storage inverters bat1 and bat2 each output 2.5kW. When the control method of this embodiment is not adopted, the three energy storage inverters each output 1.67kW; in comparison, when the control method of this embodiment is adopted, the operating point of the energy storage inverter is closer to the maximum efficiency point, and the system efficiency is higher. At 2.5s, the energy storage battery of the energy storage inverter bat2 is discharged to SOC min, the energy storage converter bat2 stops running, and the energy storage converter bat3 resumes running. At 3s, the load drops to 2.8kW, the energy storage converter bat3 stops running, and the energy storage converter bat1 outputs 2.8kW independently; when the control method of this embodiment is not adopted, the two energy storage converters each output 1.4kW; in comparison, the working point of the energy storage converter when the control method of this embodiment is adopted is closer to the maximum efficiency point, and the system efficiency is higher.

[0108] Figure 8 The resonant converter excitation current is shown when the energy storage output power drops from 2.5kW to 250W. i m , primary side upper tube drive signal v dh , primary side lower tube drive signal v dl , DC bus voltage U dc At the beginning, the output power of the energy storage converter is 2.5kW, and the DC bus voltage is stable at 400V; at 0.25s, the output power of the energy storage converter drops from 2.5kW to 250W, the system is almost unloaded, and the energy storage converter starts intermittent working mode control. Figure 8 As shown, the energy storage converter starts and stops cyclically. U dc At the preset 399V ( U max ) and 390V ( U min ). As we all know, the main loss of the resonant converter is the high-frequency transformer core loss. When the energy storage converter stops working, v dh and v dl atresia, i m is 0, removing the core loss in this period of time. Although the RMS of the resonant current under intermittent control is higher than that in the continuous working mode, the increase in conduction loss and winding loss introduced by it is much smaller than the reduction in the core loss of the high-frequency transformer. Therefore, intermittent control can reduce the overall loss of the converter.

[0109] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A control method for an off-grid load adaptive control system of a photovoltaic microgrid, wherein the off-grid load adaptive control system of a photovoltaic microgrid comprises a photovoltaic microgrid energy routing system and an adaptive controller; the photovoltaic microgrid energy routing system comprises a photovoltaic cell, an energy storage battery, a photovoltaic access converter, an energy storage converter, an inverter and a DC bus; a plurality of photovoltaic cells are connected to the DC bus via a photovoltaic access converter, and the photovoltaic access converter controls the unidirectional transmission of power from the photovoltaic cell to the DC bus; a plurality of energy storage batteries are respectively connected to the DC bus via energy storage converters, and the energy storage converter controls the power between the energy storage battery and the DC bus bidirectional transmission between the DC busbars; multiple inverters are arranged between the DC busbars and the AC busbars; the adaptive controller comprises a detection module, a microprocessor and a communication module; the detection module is used to sample the voltage and current signals of the inverter connected to the AC busbar; the communication module is used to realize the communication between the adaptive controller and the photovoltaic access converter, each energy storage converter and each inverter; the microprocessor is used to process the signals from the photovoltaic access converter, the detection module, each energy storage converter and each inverter, and send control instructions to the photovoltaic access converter, each energy storage converter and each inverter; it is characterized in that: Calculate the total AC load based on the voltage and current signals sampled by the detection module , control the number of inverters put into operation and the total AC load The changes in are positively correlated; Get its input power from the photovoltaic access converter , obtain the SOC signal of the energy storage battery connected to the energy storage converter from the energy storage converter, and obtain the AC active load through the detection module ; When there is sunlight and the photovoltaic is connected to the input power of the inverter Not less than AC active load When the SOC value is lower than SOC max If there is an energy storage battery, all energy storage converters are controlled to be put into operation, and the photovoltaic access converter performs maximum power tracking control. The photovoltaic access converter supplies the remaining power outside the load for the SOC value lower than the SOC max The energy storage battery is charged and the SOC value reaches SOC max The energy storage converter does not transmit power; if the SOC value of all energy storage batteries reaches SOC max When the PV access converter is controlled to exit operation, all energy storage converters are controlled to start operation. Each energy storage converter operates according to the AC active load. The transmission power is distributed according to the ratio of the rated power of each energy storage converter. During operation, when the SOC value of the energy storage battery put into operation is lower than the threshold SOC max_low When the PV access converter is controlled to resume operation, SOC min < SOC max_low <SOC max , SOC min is the lower limit of SOC of the energy storage battery, SOC max Energy storage battery SOC upper limit value; When there is sunlight and the photovoltaic is connected to the input power of the inverter Lower than AC active load When the holding time is less than or equal to the time threshold T, the SOC value is controlled to be higher than SOC min The energy storage converters corresponding to the energy storage batteries are put into operation. and The transmission power is distributed according to the difference between and the ratio of the rated powers of each energy storage converter; When there is sunlight and the photovoltaic is connected to the input power of the inverter Lower than AC active load When the holding time is greater than the time threshold T, the control system enters the orderly switching mode of the energy storage converter: the SOC value is controlled to be lower than SOC min The energy storage converter corresponding to the energy storage battery is shut down, and the SOC value is higher than SOC min The energy storage converter corresponding to the energy storage battery is used as an alternative energy storage converter. With AC active load A corresponding number of energy storage converters are selected from the candidate energy storage converters according to the difference between the two and put into operation; When there is no sunlight, control the photovoltaic access converter and the SOC value is lower than SOC min The energy storage converter corresponding to the energy storage battery exits operation, and the system enters the orderly switching mode of the energy storage converter: the SOC value is higher than SOC min The energy storage converter corresponding to the energy storage battery is used as an alternative energy storage converter, according to the AC active load A corresponding number of energy storage converters are selected from the candidate energy storage converters and put into operation.

2. The control method according to claim 1, characterized in that: Number of inverters put into operation and total AC load The changes are positively correlated, specifically: Arrange and number the inverters according to their operating efficiency from high to low, and obtain the rated power of each inverter in the order of arrangement: , ,……, , the output power corresponding to the peak efficiency of each inverter is , ,……, ,in is the total number of inverters; According to the total AC load And formula (1) to calculate The value of controls the 1st to the The inverter No. was put into operation; （1） in, , Indicates The output power corresponding to the peak efficiency of the inverter is For No. 1 to The upper power threshold of the inverter is formed by For No. 1 to -The lower power threshold formed by inverter No.

1.

3. The control method according to claim 1, characterized in that: According to input power With AC active load The difference between the two is used to select a corresponding number of energy storage converters from the candidate energy storage converters for operation, specifically: Set all SOC values ​​above SOC min The energy storage converters corresponding to the energy storage batteries are sorted and numbered from large to small according to the capacity of the energy storage batteries to obtain a candidate energy storage converter sequence 1; the rated power of each energy storage converter in the candidate energy storage converter sequence 1 is , ,……, , the output power corresponding to the peak efficiency of each energy storage converter is , ,……, ,in represents the number of candidate energy storage converters in the candidate energy storage converter sequence 1; According to input power With AC active load The difference between the two and the formula (2) is used to calculate The value of controls the first to the second energy storage converters in the sequence of the candidate energy storage converters. The energy storage converter No. was put into operation; （2） in, , Indicates The output power corresponding to the peak efficiency of the alternative energy storage converter is: Indicates the number 1 to 2 in the candidate energy storage converter sequence 1. The upper power threshold of the energy storage converter is Indicates the number 1 to 2 in the candidate energy storage converter sequence 1. -The lower power threshold formed by the No. 1 energy storage converter.

4. The control method according to claim 3, characterized in that: When the input power With AC active load The difference between is less than or equal to When the output power is only controlled to The energy storage converter is put into operation. When the input power With AC active load The difference between them is further less than the threshold When the control output power is The energy storage converter works intermittently according to the voltage fluctuation of the DC bus.

5. The control method according to claim 4, characterized in that: According to AC active load Select a corresponding number of energy storage converters from the candidate energy storage converters and put them into operation, specifically: Set all SOC values ​​above SOC min The energy storage converters corresponding to the energy storage batteries are sorted and numbered from large to small according to the capacity of the energy storage batteries to obtain a second candidate energy storage converter sequence; the rated power of each energy storage converter in the second candidate energy storage converter sequence is , ,……, , the output power corresponding to the peak efficiency of each energy storage converter is , ,……, ,in represents the number of candidate energy storage converters in the candidate energy storage converter sequence 2; According to AC active load And formula (4) to calculate The value of controls the first to the second candidate energy storage converter sequence. The energy storage converter No. was put into operation; （4） in, , Indicates The output power corresponding to the peak efficiency of the alternative energy storage converter is: Indicates the number 1 to 2 in the second sequence of the candidate energy storage converters. The upper power threshold of the energy storage converter is Indicates the number 1 to 2 in the second sequence of the candidate energy storage converters. -The lower power threshold formed by the No. 1 energy storage converter.

6. The control method according to claim 5, characterized in that: When the AC active load Less than or equal to When the output power is only controlled to The energy storage converter is put into operation. When the AC active load Further below the threshold When the control output power is The energy storage converter works intermittently according to the voltage fluctuation of the DC bus.

7. The control method according to claim 6, characterized in that: Control the energy storage converter to work intermittently, specifically: set the upper limit of DC bus voltage fluctuation and lower limit , when the DC bus voltage reaches When the energy storage converter blocks the drive signal, the DC bus voltage drops; when the DC bus voltage drops to When the energy storage converter sends out a driving signal, the DC bus voltage rises; this cycle is repeated to achieve intermittent operation.

8. The control method according to claim 7, characterized in that: Threshold The calculation formula is: （3） in, is the DC bus capacitor value, is the switching action cycle of the energy storage converter, Indicates the switching cycle of the energy storage converter The number of .

9. The control method according to any one of claims 1 to 8, characterized in that: The control method is executed by the microprocessor.

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