Control method of photovoltaic energy storage system

Abstract

The invention discloses a control method for a photovoltaic energy storage system, and the method comprises the steps: selecting an operation mode, the operation mode comprises a first mode, and in the first mode, step 1, judging whether the power generation amount of a photovoltaic system is sufficient or not; 2, if the phase change material is sufficient, the photovoltaic system supplies power to the inverter compressor, the operation frequency of the inverter compressor is controlled, the inverter compressor is shut down until the phase change material in the photovoltaic energy storage system reaches the set temperature, and in the process, the battery is charged with surplus electricity; 3, if not, the operation frequency of the inverter compressor is controlled according to the photovoltaic generating capacity at the current moment and the preset temperature condition, and the inverter compressor is shut down until the phase-change material reaches the set temperature; 4, judging whether the photovoltaic generating capacity at the current moment meets the requirement that the inverter compressor operates at the lowest frequency of the standard working condition or not; and 5, if not, power is supplied to the inverter compressor through the battery and the photovoltaic system at the same time, and the inverter compressor is made to operate at the lowest frequency of the standard working condition and shut down until the phase change material reaches the set temperature or the voltage of the battery is lower than the set voltage value. The technical effect that the endurance of the energy storage system can be greatly prolonged while enough energy storage efficiency is guaranteed is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of cold chain equipment, and in particular to a control method for a photovoltaic energy storage system. Background Art

[0002] With the continuous development of my country's fruit and vegetable cold chain transportation industry in recent years, the market demand for cold chain logistics vehicles has continued to increase. The potential of China's cold chain logistics market is enormous. Therefore, combined with national policies promoting energy conservation and environmental protection, the rapid development of new energy cold chain transport vehicles has become inevitable. To reduce energy consumption, new energy cold chain transport vehicles are generally equipped with photovoltaic systems. In sufficient sunlight, these systems can generate electricity to power the energy storage systems in the cold chain vehicles. However, the energy storage systems with photovoltaic systems in related technologies are not flexible enough and have a low battery life. Summary of the Invention

[0003] The main purpose of the present invention is to provide a control method for a photovoltaic energy storage system to solve the problem of low photovoltaic endurance of an energy storage system with a photovoltaic system in the related art.

[0004] To achieve the above objectives, the present invention provides a control method for a photovoltaic energy storage system, comprising:

[0005] An operating mode is selected, where the operating mode includes a first mode. In the first mode:

[0006] Step 1: Determine whether the power generation of the photovoltaic system is sufficient;

[0007] Step 2: If sufficient, the photovoltaic system supplies power to the variable frequency compressor and adjusts the operating frequency of the variable frequency compressor according to the preset temperature conditions until the phase change material in the photovoltaic energy storage system reaches the set temperature and stops. During this process, the excess power is charged to the battery;

[0008] Step 3: If it is insufficient, the operating frequency of the variable frequency compressor is controlled according to the current photovoltaic power generation and the preset temperature conditions until the phase change material reaches the set temperature and stops;

[0009] Step 4: Determine whether the photovoltaic power generation at the current moment satisfies the minimum frequency of the variable frequency compressor under standard operating conditions;

[0010] Step 5: If not, the variable frequency compressor is powered by both the battery and the photovoltaic system, and the variable frequency compressor is operated at the lowest frequency of the standard operating condition until the phase change material reaches the set temperature or the battery voltage is lower than the set voltage value and stops.

[0011] Furthermore, the operating mode includes a second mode, in which:

[0012] Step 1: Determine whether the power generation of the photovoltaic system is sufficient;

[0013] Step 2: If sufficient, the photovoltaic system supplies power to the variable frequency compressor and adjusts the operating frequency of the variable frequency compressor according to the preset temperature conditions until the phase change material in the photovoltaic energy storage system reaches the set temperature and stops. During this process, the excess power is charged to the battery;

[0014] Step 3: If it is insufficient, the operating frequency of the variable frequency compressor is controlled according to the current photovoltaic power generation and the preset temperature conditions until the phase change material reaches the set temperature and stops;

[0015] Step 4: Determine whether the photovoltaic power generation at the current moment satisfies the minimum frequency of the variable frequency compressor under standard operating conditions;

[0016] Step 5: If the conditions are not met, the variable frequency compressor is powered by both the battery and the photovoltaic system, and the variable frequency compressor is operated at the lowest frequency under standard operating conditions until the phase change material reaches a set temperature and stops.

[0017] Step 6: If the battery voltage is lower than the set voltage value before the phase change material reaches the set temperature, the AC power is used to supply power to the variable frequency compressor and charge the battery, so that the operating frequency of the variable frequency compressor reaches the maximum set value until the phase change material reaches the set temperature and stops;

[0018] Step 7: When the battery voltage reaches the conversion voltage, execute steps 1 to 6.

[0019] Furthermore, in the second mode, after turning on the energy-saving switch, steps 1 to 7 in the second mode are executed;

[0020] After turning off the energy-saving switch, perform the following steps:

[0021] The inverter compressor is powered by mains electricity and its operating frequency is controlled according to preset temperature conditions until the phase change material reaches the set stop temperature and stops.

[0022] Furthermore, the operating mode includes a third mode, in which:

[0023] The inverter compressor is powered by mains electricity and its operating frequency is controlled according to preset temperature conditions until the phase change material reaches the set stop temperature and stops.

[0024] Furthermore, in step 2 and step 3, controlling the operating frequency of the variable frequency compressor according to the preset temperature condition includes:

[0025] When the phase change material is cooled and stored cold by the variable frequency compressor,

[0026] obtaining a temperature of the phase change material;

[0027] When the temperature of the phase change material is within a safe temperature range, controlling the variable frequency compressor to operate at a maximum frequency allowed under the current environment;

[0028] When the temperature of the phase change material is lower than the safe temperature range, obtaining the current air temperature in the box;

[0029] The temperature of the phase change material is compared with the air temperature, and the operating frequency of the variable frequency compressor is controlled according to the compared temperature difference.

[0030] Furthermore, the temperature of the phase change material is compared with the air temperature, and the operating frequency of the variable frequency compressor is controlled according to the compared temperature difference, including:

[0031] Comparing the temperature of the phase change material with the air temperature, and when the temperature difference is greater than a set threshold, controlling the variable frequency compressor to operate at a maximum frequency allowed under the current environment;

[0032] When the temperature difference is less than or equal to a set threshold, the variable frequency compressor is controlled to reduce the operating frequency.

[0033] Furthermore, when the temperature difference is less than or equal to a set threshold, controlling the variable frequency compressor to reduce the operating frequency includes:

[0034] When the temperature difference is equal to the threshold, controlling the variable frequency compressor to reduce the current operating frequency by 30%-60%;

[0035] When the temperature difference is less than a set threshold, the temperature of the phase change material and the current air temperature in the box are obtained in stages, and the temperature of the phase change material and the current air temperature in the box are compared in each stage;

[0036] According to the compared temperature difference, the operating frequency of the variable frequency compressor is reduced according to the set frequency value in each stage until the temperature difference is equal to the preset difference.

[0037] Furthermore, in step 2, the maximum frequency allowed under the current environment is the maximum rated frequency of the variable frequency compressor;

[0038] In step 3, the maximum frequency allowed under the current environment is: the maximum frequency allowed for the variable frequency compressor under the photovoltaic power generation at the current moment.

[0039] Furthermore, the safe temperature range is greater than 0°C, and the threshold is set to 1°C-4°C.

[0040] Furthermore, the operation mode also includes a defrost mode, in which the photovoltaic energy storage system is controlled to operate under a refrigeration condition;

[0041] When the condenser temperature of the photovoltaic energy storage system is higher than the set temperature or the defrost time is greater than the maximum defrost time, the defrost ends.

[0042] In the embodiment of the present invention, in the first mode, it is first determined whether the power generation of the photovoltaic system is sufficient. If sufficient, the photovoltaic system supplies power to the variable frequency compressor, and controls the operating frequency of the variable frequency compressor according to the preset temperature condition until the phase change material in the photovoltaic energy storage system reaches the set temperature and stops. In this process, the surplus power is charged to the battery; if insufficient, the operating frequency of the variable frequency compressor is controlled according to the photovoltaic power generation at the current moment and the preset temperature condition until the phase change material reaches the set temperature and stops; it is determined whether the photovoltaic power generation at the current moment meets the minimum frequency of the variable frequency compressor under the standard working condition; if not, the battery and the photovoltaic system are used to supply power to the variable frequency compressor at the same time. The inverter compressor is powered by a power supply and operates at the lowest frequency under standard working conditions until the phase change material reaches a set temperature or the battery voltage is lower than a set voltage value and stops. This achieves the goal of both quickly storing energy and charging the battery to increase the power when the photovoltaic system has sufficient power generation. When the photovoltaic system is insufficient, the operating frequency of the inverter compressor is adjusted according to the current photovoltaic power generation, and the inverter compressor can operate for a longer time by utilizing the photovoltaic power generation. When the power generation is very low, the battery is used for power supply. This achieves the technical effect of greatly increasing the endurance of the energy storage system while ensuring sufficient energy storage efficiency, thereby solving the problem of low photovoltaic endurance of the energy storage system with a photovoltaic system in the related art. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a schematic diagram of a first mode of a control method according to an embodiment of the present invention;

[0044] Figure 2 is a schematic diagram of the second mode of the control method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0046] It should be noted that the terms "first," "second," and the like in the specification and claims of the present invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that the terms used in this manner are interchangeable where appropriate to facilitate the description of the embodiments of the present invention.

[0047] In the present invention, the terms "upper," "lower," "inner," and the like indicate positions or locations based on those shown in the accompanying drawings. These terms are primarily intended to better describe the present invention and its embodiments and are not intended to limit the devices, elements, or components indicated to having a specific orientation, or to being constructed or operated in a specific orientation.

[0048] Furthermore, some of the above terms may be used to express other meanings besides indicating a position or location. For example, the term "on" may also be used to indicate a dependency or connection in certain circumstances. Those skilled in the art will understand the specific meanings of these terms in the present invention based on the specific circumstances.

[0049] Furthermore, the terms "disposed," "provided with," "connected," and "fixed" should be interpreted broadly. For example, "connected" can mean a fixed connection, a removable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection, an indirect connection through an intermediary, or an internal communication between two devices, elements, or components. Those skilled in the art will understand the specific meanings of these terms in the present invention based on the specific circumstances.

[0050] Additionally, the term "plurality" shall mean two or more.

[0051] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0052] Taking the cold chain box as an example, the photovoltaic energy storage system may include a photovoltaic panel arranged on the top of the cold chain box, an energy storage module arranged inside the cold chain box, including phase change materials, etc., a compressor unit arranged outside the cold chain box, and a charger, inverter, battery, etc. connected to the photovoltaic panel, as well as pipelines arranged inside and outside the cold chain box, etc. The compressor unit can be used to input the gas-liquid mixed heat exchange medium into the energy storage module in a positive direction or to input the gaseous heat exchange medium into the energy storage module in a reverse direction, so that the energy storage module absorbs cold and stores cold or absorbs heat and stores heat. For the specific structure, please refer to the content disclosed in Chinese patent CN115009143A.

[0053] An embodiment of the present invention provides a control method for a photovoltaic energy storage system, comprising:

[0054] An operating mode is selected, where the operating mode includes a first mode. In the first mode:

[0055] Step 1: Determine whether the power generation of the photovoltaic system is sufficient;

[0056] The power generation of a photovoltaic system can be obtained by reading the inverter's current and voltage through the inverter, that is, the power generation is directly related to the power generation power. Therefore, the power generation power of the photovoltaic system can be determined by judging the magnitude of the current and voltage, and thus the power generation. When the current power generation power is greater than the set power generation power, the current power generation is considered sufficient; when it is less than the power generation power, the current power generation is considered insufficient. The set power generation power can be a fixed value or a variable value. When a fixed value is selected, it can be determined based on the rated power of the variable frequency compressor. When a variable value is selected, the required power of the variable frequency compressor can be determined based on the energy release power of the current energy storage module and the energy loss power of the cold chain box.

[0057] In some embodiments, the required power P of the variable frequency compressor is determined according to the following formula: need :

[0058] P need =max(0,P loss -η pcm )

[0059] P loss =U·A·(T env -T set )

[0060] Among them, P loss is the energy damage power, η pcm is the energy release power of the energy storage module, which is obtained according to the characteristics of the phase change material in the energy storage module, η pcm is a constant; U is the heat transfer coefficient of the cold chain box, which is a calibrated constant in W / m 2 K, A is the surface area of ​​the cold chain box, which is a constant, T env is the air temperature in the box, obtained through the temperature sensor, T set is the set shutdown air temperature, which is a constant.

[0061] Based on the above formula, the current required power P of the variable frequency compressor can be determined need Therefore, the current power demand of the variable frequency compressor can be compared with the current power generation of the photovoltaic system. If the power generation of the photovoltaic system is greater than or equal to the current power demand of the variable frequency compressor, it is judged that the photovoltaic power generation is sufficient. After this setting, the power demand P of the variable frequency compressor need It is a variable value. Compared with the set fixed demand power, more electricity can be used to charge the battery, further improving the energy utilization rate of photovoltaics.

[0062] Step 2: If sufficient, the photovoltaic system supplies power to the variable frequency compressor and controls the operating frequency of the variable frequency compressor according to the preset temperature conditions until the phase change material in the photovoltaic energy storage system reaches the set temperature and stops. During this process, the excess power is charged to the battery;

[0063] When sufficient power is generated, the PV system fully supplies power to the inverter compressor, increasing its operating frequency. When the inverter compressor's operating frequency reaches the set value, the PV system continues to maintain the set frequency and activates the battery charging circuit. Excess power is then used to charge the battery, increasing its capacity. When the phase-change material within the PV energy storage module reaches the set temperature, the inverter compressor shuts down. The PV system's power generation now fully charges the battery, maximizing solar energy utilization and minimizing solar energy waste.

[0064] Step 3: If it is insufficient, the operating frequency of the variable frequency compressor is controlled according to the current photovoltaic power generation and the preset temperature conditions until the phase change material reaches the set temperature and stops;

[0065] If the photovoltaic system's power generation is insufficient, meaning the generated power falls below a set value, the inverter compressor's operating frequency needs to be reduced. This frequency is determined based on the current photovoltaic power generation (i.e., generated current and voltage) and preset temperature conditions. At this point, the photovoltaic system's power generation can fully supply the inverter compressor. If the generated current and voltage continue to decrease, the inverter compressor's operating frequency will also continue to decrease.

[0066] Step 4: Determine whether the photovoltaic power generation at the current moment satisfies the minimum frequency of the variable frequency compressor under standard operating conditions;

[0067] During the execution of step 3, it is determined in real time or in stages whether the current generating current and generating voltage meet the minimum frequency required for the variable frequency compressor to operate under standard operating conditions.

[0068] Step 5: If not, the variable frequency compressor is powered by both the battery and the photovoltaic system, and the variable frequency compressor is operated at the lowest frequency of the standard operating condition until the phase change material reaches the set temperature or the battery voltage is lower than the set voltage value and stops.

[0069] If it is determined that the current power generation is insufficient to support the inverter compressor at the minimum frequency required for standard operating conditions, the battery and photovoltaic system will simultaneously supply power to the inverter compressor, allowing it to operate at the minimum frequency required for standard operating conditions and slowly accumulate energy. The inverter compressor will be shut down when the phase change material in the energy storage module reaches the set temperature, or when the battery voltage is too low. It should be noted that if the photovoltaic system is unable to power the inverter compressor due to low photovoltaic power generation, the battery alone will be used to power the compressor.

[0070] Furthermore, while the battery is supplying power to the inverter compressor, the PV system's power generation is still being assessed. When the PV system's power generation is sufficient to keep the inverter compressor running at its lowest frequency under standard operating conditions, the PV system alone powers the compressor, eliminating any additional battery consumption. If the PV system's power generation is sufficient due to weather conditions, the excess power is used to charge the battery, fully utilizing the PV power generation and further improving battery life.

[0071] In this embodiment, a variable-frequency compressor passes a medium into the energy storage module, causing the phase-change material to undergo a phase change to achieve energy storage. Depending on the operating conditions, the phase-change material can be used to store either cold or heat. During cold or heat storage, the variable-frequency compressor is activated by a temperature sensor that detects the temperature of the phase-change material. When the phase-change material temperature exceeds a set value, the variable-frequency compressor is activated to store cold. When the phase-change material temperature falls below a set value, the variable-frequency compressor is activated to store heat. The entire system can be integrated and controlled via a PLC controller.

[0072] This embodiment achieves the purpose of being able to quickly store energy and charge the battery to increase the power when the photovoltaic system's power generation is sufficient, reducing the energy storage efficiency when it is insufficient, and using the power generation of the photovoltaic system to operate for a longer time, and being powered by the battery when the power generation is very low. This ensures that while ensuring sufficient energy storage efficiency, the endurance of the energy storage system can be greatly increased, thereby solving the problem of low photovoltaic endurance of the energy storage system with a photovoltaic system in related technologies.

[0073] The above embodiment describes the first operating mode. To improve the flexibility of use, the photovoltaic energy storage system in this embodiment also includes a second operating mode. In the second mode:

[0074] Step 1: Determine whether the power generation of the photovoltaic system is sufficient;

[0075] The power generation of a photovoltaic system can be obtained by reading the inverter's current and voltage through the inverter, that is, the power generation is directly related to the power generation power. Therefore, the power generation power of the photovoltaic system can be determined by judging the magnitude of the current and voltage, and thus the power generation. When the current power generation power is greater than the set power generation power, the current power generation is considered sufficient; when it is less than the power generation power, the current power generation is considered insufficient. The set power generation power can be a fixed value or a variable value. When a fixed value is selected, it can be determined based on the rated power of the variable frequency compressor. When a variable value is selected, the required power of the variable frequency compressor can be determined based on the energy release power of the current energy storage module and the energy loss power of the cold chain box.

[0076] Step 2: If sufficient, the photovoltaic system supplies power to the variable frequency compressor and controls the operating frequency of the variable frequency compressor according to the preset temperature conditions until the phase change material in the photovoltaic energy storage system reaches the set temperature and stops. During this process, the excess power is charged to the battery;

[0077] When sufficient power is generated, the PV system fully supplies power to the inverter compressor, increasing its operating frequency. When the inverter compressor's operating frequency reaches the set value, the PV system continues to power the compressor at the set frequency. Excess power is used to charge the battery, increasing its capacity. When the phase change material within the PV energy storage module reaches the set temperature, the inverter compressor is shut down, and the PV system's power generation fully charges the battery.

[0078] Step 3: If it is insufficient, the operating frequency of the variable frequency compressor is controlled according to the current photovoltaic power generation and the preset temperature conditions until the phase change material reaches the set temperature and stops;

[0079] If the photovoltaic system's power generation is insufficient, meaning the generated power falls below a set value, the inverter compressor's operating frequency needs to be reduced. This frequency is determined based on the current photovoltaic power generation (i.e., generated current and voltage) and preset temperature conditions. At this point, the photovoltaic system's power generation can fully supply the inverter compressor. If the generated current and voltage continue to decrease, the inverter compressor's operating frequency will also continue to decrease.

[0080] Step 4: Determine whether the photovoltaic power generation at the current moment satisfies the minimum frequency of the variable frequency compressor under standard operating conditions;

[0081] During the execution of step 3, it is determined in real time or in stages whether the current generating current and generating voltage meet the minimum frequency required for the variable frequency compressor to operate under standard operating conditions.

[0082] Step 5: If the conditions are not met, the variable frequency compressor is powered by both the battery and the photovoltaic system, and the variable frequency compressor is operated at the lowest frequency under standard operating conditions until the phase change material reaches a set temperature and stops.

[0083] If the current generated power is insufficient to maintain the inverter compressor at its minimum frequency under standard operating conditions, the battery and photovoltaic system will simultaneously supply power to the inverter compressor, allowing it to operate at its minimum frequency under standard operating conditions and slowly accumulate energy. When the phase change material in the energy storage module reaches the set temperature, the inverter compressor will be shut down.

[0084] Step 6: If the battery voltage is lower than the set voltage value before the phase change material reaches the set temperature, the AC power is used to power the variable frequency compressor and charge the battery, and the operating frequency of the variable frequency compressor is controlled according to the preset temperature conditions until the phase change material reaches the set temperature and stops.

[0085] Because the battery's charge level fluctuates, the battery voltage may fall below the set voltage before the phase-change material reaches the set temperature. In this case, the battery cannot maintain normal operation of the inverter compressor. Therefore, the inverter compressor is powered by the mains, and its operating frequency is controlled according to the preset temperature conditions, allowing the phase-change material to rapidly accumulate energy. Simultaneously, the mains charges the battery, increasing its charge level. This complementary combination of mains power and photovoltaics ensures the normal operation of the inverter compressor.

[0086] During the mains power supply process, there are at least two situations. If the temperature of the phase-change material reaches the set value before the battery has charged to the set voltage, the inverter compressor shuts down and the mains continues to charge the battery until the battery voltage reaches the set voltage. If the temperature of the phase-change material has not reached the set value after the battery has charged to the set voltage, the inverter compressor is switched to the battery, operating at the lowest frequency under standard operating conditions. Steps 1 to 6 are performed simultaneously, meaning that after switching to battery power, the PV system's current power generation continues to be determined. This effectively reduces mains power usage, further reducing operating costs and maximizing solar energy utilization.

[0087] In this embodiment, the first mode and the second mode are two modes in which the photovoltaic energy storage system can operate, and the user can choose to operate in the first mode or the second mode.

[0088] Since the inverter compressor can be powered by mains electricity in the second mode, in order to further improve the flexibility of use, in the second mode, after turning on the energy-saving switch, steps 1 to 7 in the second mode are executed;

[0089] After turning off the energy-saving switch, perform the following steps:

[0090] The inverter compressor is powered by mains electricity and its operating frequency is controlled according to preset temperature conditions until the phase change material reaches the set stop temperature and stops.

[0091] Specifically, in the second mode, the energy-saving switch can be turned on. At this time, the system needs to determine whether the photovoltaic power generation is sufficient and execute steps 2 to 7 accordingly. In the second mode, the energy-saving switch can also be turned off. At this time, the system no longer determines whether the photovoltaic power generation is sufficient, and the inverter compressor is directly powered by the mains.

[0092] In the second mode, the phase change material can store cold or heat, also depending on the operating conditions. During this mode, the inverter compressor is activated by a temperature sensor that detects the temperature of the phase change material. When the temperature of the phase change material exceeds the set value, the inverter compressor activates to store cold. When the temperature of the phase change material falls below the set value, the inverter compressor activates to store heat.

[0093] In one embodiment, the operating mode includes a third mode, in which:

[0094] The inverter compressor is powered by mains electricity and its operating frequency is controlled according to preset temperature conditions until the phase change material reaches the set stop temperature and stops.

[0095] In this embodiment, the third mode is one of the modes in which the photovoltaic energy storage system can operate independently. In this mode, the variable frequency compressor is completely powered by the mains electricity. Compared with the first mode and the second mode, this mode can enable the variable frequency compressor to quickly store energy and improve the energy storage efficiency.

[0096] During the phase-change material energy storage process, energy is transferred from the refrigerant to the phase-change material (PCM) and then to the air inside the cold chain box. The temperature of the PCM closer to the refrigerant is lower. The inverter compressor's shutdown temperature is generally the air temperature—that is, the air temperature inside the cold chain box—and this temperature serves as a reference for controlling whether the inverter compressor will shut down. If the air temperature has not yet reached the set value, or if there is sufficient battery power or mains power, the inverter compressor will operate at a higher frequency to achieve rapid energy storage. The transfer of the PCM's temperature to the air inside the box takes time, and the inverter compressor changes the PCM's temperature through the refrigerant. This transfer also takes time. Therefore, when the air temperature reaches the shutdown temperature, the PCM's temperature is often lower than the air temperature, especially in the PCM's portion near the refrigerant pipes. Even if the inverter compressor shuts down at this point, the cooler PCM will further lower the air temperature inside the box, especially near the inner wall. For refrigerated fruits and vegetables, excessively low temperatures can easily cause frostbite.

[0097] In addition, when the temperature of the phase change material is low, the energy storage efficiency of the variable frequency compressor at a high operating frequency is reduced, and the energy utilization rate is not high.

[0098] To this end, in this embodiment, whether in the first mode, the second mode or the third mode, controlling the operating frequency of the variable frequency compressor according to the preset temperature condition includes:

[0099] When the phase change material is cooled and stored cold by the variable frequency compressor,

[0100] Acquiring the temperature of the phase change material, specifically by reading the temperature of the phase change material through a preset temperature sensor, the process can be real-time or staged;

[0101] When the temperature of the phase change material is within a safe temperature range, controlling the variable frequency compressor to operate at a maximum frequency allowed under the current environment;

[0102] A safe temperature range for the phase change material is preset. The specific value can be set based on the characteristics of the phase change material and the performance of the variable frequency compressor, and is not limited in this embodiment. Within this safe temperature range, the variable frequency compressor has high energy storage efficiency while preventing the air temperature inside the chamber from falling too low. Therefore, when the phase change material temperature exceeds the safe temperature range, the variable frequency compressor operates at the maximum frequency allowed by the current environment, rapidly storing energy.

[0103] It should be noted that the maximum allowable frequency of the inverter compressor varies in different modes and under different conditions. In the first and second modes, when the PV system's power generation is sufficient, and in the third mode, the maximum allowable frequency is the maximum rated frequency of the inverter compressor. In the first and second modes, when the PV system's power generation is insufficient, the maximum allowable frequency is determined based on the PV power generation. Specifically, in these environments, the operating frequency of the inverter compressor is aligned with the PV power generation; the greater the PV power generation, the higher the operating frequency of the inverter compressor.

[0104] When the temperature of the phase change material is lower than the safe temperature range, obtaining the current air temperature in the box;

[0105] When the variable frequency compressor is operating at the maximum frequency allowed in the current environment, and the temperature sensor detects that the temperature of the phase change material is below the temperature range, another temperature sensor is used to detect the air temperature in the box, especially the air temperature near the phase change material area. In some embodiments, multiple temperature detections can be performed, and the weighted value or the highest value is taken as the current air temperature. In this embodiment, multiple temperature detections are performed on the phase change material and the air temperature.

[0106] The temperature of the phase change material is compared with the air temperature, and the operating frequency of the variable frequency compressor is controlled according to the compared temperature difference.

[0107] Generally, the air temperature is higher than the temperature of the phase change material, and the operating frequency of the variable frequency compressor is controlled according to the temperature difference. Specifically, the process includes:

[0108] Comparing the temperature of the phase change material with the air temperature, and when the temperature difference is greater than a set threshold, controlling the variable frequency compressor to operate at a maximum frequency allowed under the current environment;

[0109] The air temperature inside the box is affected by the environment and the fruits and vegetables stored, and varies in different situations. When the temperature of the phase change material falls below the safe temperature range, there may be a significant temperature difference between the phase change material and the air. Therefore, the variable frequency compressor can still be controlled to operate at the maximum frequency allowed in the current environment, rapidly reducing the temperature of the phase change material and, therefore, the air temperature inside the box.

[0110] When the temperature difference is less than or equal to a set threshold, the variable frequency compressor is controlled to reduce the operating frequency.

[0111] When the temperature of the phase change material is lower than the safe temperature range and the temperature difference between the phase change material and the air temperature is less than the set threshold, the operating frequency of the variable frequency compressor is controlled to decrease, so that the cooling rate of the phase change material is reduced, and the temperature of the phase change material can have enough time to be transferred to the air in the box to reduce the air temperature in the box, so that the temperature of the phase change material gradually approaches the air temperature, avoiding the problem that the phase change material temperature is too low after the air temperature reaches the set value and the machine is shut down, causing the air temperature to further decrease.

[0112] Furthermore, due to the lower temperature of the phase change material, the reduced operating frequency of the inverter compressor can match the phase change material's cooling rate, improving energy utilization. In both the first and second modes with the energy-saving switch on, if the inverter compressor's operating frequency is reduced according to preset temperature conditions and the photovoltaic power generation exceeds the power required by the current inverter compressor operating frequency, the excess power can still be used to charge the battery, further improving solar energy utilization.

[0113] In one embodiment, when the temperature difference is less than or equal to a set threshold, controlling the variable frequency compressor to reduce the operating frequency includes:

[0114] When the temperature difference is equal to the threshold, controlling the variable frequency compressor to reduce the current operating frequency by 30%-60%;

[0115] When the temperature difference is less than a set threshold, the temperature of the phase change material and the current air temperature in the box are obtained in stages, and the temperature of the phase change material and the current air temperature in the box are compared in each stage;

[0116] According to the compared temperature difference, the operating frequency of the variable frequency compressor is reduced according to the set frequency value in each stage until the temperature difference is equal to the preset difference.

[0117] In this embodiment, the temperature of the phase change material and the air temperature inside the chamber are measured at regular intervals. As the variable frequency compressor continues to operate, the air temperature continues to decrease. As the cooling rate of the phase change material slows, the temperature difference between the phase change material and the air gradually decreases. During this process, a decreasing temperature gradient can be set. When the temperature gradient decreases by one level, the variable frequency compressor reduces its operating frequency by one level accordingly until the temperature difference reaches the preset value.

[0118] In some embodiments, the time interval can be 10 seconds, 30 seconds, etc. When the temperature difference is first detected to be equal to the set threshold, the frequency of the variable frequency compressor is controlled to be reduced by 50% (based on the current frequency), and then the frequency of the variable frequency compressor is gradually reduced based on the temperature difference values ​​obtained in stages. A correspondence between the frequency of the variable frequency compressor and the temperature difference can be pre-established and introduced into the system. During the cold storage process, the variable frequency compressor automatically reduces its frequency according to this correspondence.

[0119] Specifically, a corresponding relationship between the operating frequency of the variable frequency compressor and the temperature difference is established in advance;

[0120] According to the compared temperature difference, the operating frequency of the variable frequency compressor is reduced according to the set frequency value in each stage until the temperature difference is equal to the preset difference, specifically:

[0121] According to the compared temperature difference and the pre-established corresponding relationship, the operating frequency of the variable frequency compressor is reduced until the temperature difference is equal to the preset difference.

[0122] The closer the temperature difference is to the preset difference, the greater the frequency reduction of the variable frequency compressor. In a very close time period, the variable frequency compressor can use pulses to finely adjust the temperature, that is, the variable frequency compressor starts and shuts down at a certain frequency, thereby strictly controlling the temperature drop rate of the phase change material.

[0123] In some embodiments, the safe temperature range is greater than 0°C, and may be 1°C, 2°C, etc., and the threshold is set at 1°C-4°C.

[0124] It should be noted that the safe temperature range and threshold are not fixed. They can be set according to the characteristics of fruits and vegetables. The system can be built-in or allow users to input the optimal storage temperature range for specific fruits and vegetables and the maximum safe temperature difference tolerance for the fruits and vegetables.

[0125] Furthermore, the operating mode also includes a defrost mode. In the heating mode, the condenser of the external cooler becomes an evaporator because the four-way valve is open. When the evaporation temperature is low, the evaporator will frost. In the heating mode, the control system will automatically defrost according to the running time of the heating compressor. When encountering special weather or working conditions, manual defrosting can be performed. When manual defrosting is turned on, the compressor unit starts, the four-way valve does not start, and it operates in cooling mode. The defrost ends when the condenser temperature is higher than the set temperature or the defrost time is greater than the maximum defrost time.

[0126] In one embodiment, the photovoltaic energy storage system applied to the present invention includes: a plc (programmable logic controller), a temperature module, a temperature sensor, a solenoid valve, a four-way valve, a variable frequency compressor, a driver, a condensing fan, an electronic expansion valve controller, a pressure sensor, a bms lithium battery with communication function, a photovoltaic energy storage inverter, etc.

[0127] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A control method for a photovoltaic energy storage system, characterized in that: include: An operating mode is selected, where the operating mode includes a first mode. In the first mode: Step 1: Determine whether the power generation of the photovoltaic system is sufficient; Step 2: If sufficient, the photovoltaic system supplies power to the variable frequency compressor and controls the operating frequency of the variable frequency compressor according to the preset temperature conditions until the phase change material in the photovoltaic energy storage system reaches the set temperature and stops. During this process, the excess power is charged to the battery; Step 3: If it is insufficient, the operating frequency of the variable frequency compressor is controlled according to the current photovoltaic power generation and the preset temperature conditions until the phase change material reaches the set temperature and stops; Step 4: Determine whether the photovoltaic power generation at the current moment satisfies the minimum frequency of the variable frequency compressor under standard operating conditions; Step 5: If the conditions are not met, the variable frequency compressor is powered by both the battery and the photovoltaic system, and the variable frequency compressor is operated at the lowest frequency under standard operating conditions until the phase change material reaches a set temperature or the battery voltage is lower than a set voltage value and stops.

2. The control method according to claim 1, characterized in that: The operating mode includes a second mode, in which: Step 1: Determine whether the power generation of the photovoltaic system is sufficient; Step 2: If sufficient, the photovoltaic system supplies power to the variable frequency compressor and controls the operating frequency of the variable frequency compressor according to the preset temperature conditions until the phase change material in the photovoltaic energy storage system reaches the set temperature and stops. During this process, the excess power is charged to the battery; Step 3: If it is insufficient, the operating frequency of the variable frequency compressor is controlled according to the current photovoltaic power generation and the preset temperature conditions until the phase change material reaches the set temperature and stops; Step 4: Determine whether the photovoltaic power generation at the current moment satisfies the minimum frequency of the variable frequency compressor under standard operating conditions; Step 5: If the conditions are not met, the variable frequency compressor is powered by both the battery and the photovoltaic system, and the variable frequency compressor is operated at the lowest frequency under standard operating conditions until the phase change material reaches a set temperature and stops. Step 6: If the battery voltage is lower than the set voltage value before the phase change material reaches the set temperature, the AC power is used to power the variable frequency compressor and charge the battery, and the operating frequency of the variable frequency compressor is controlled according to the preset temperature conditions until the phase change material reaches the set temperature and stops. Step 7: When the battery voltage reaches the conversion voltage, execute steps 1 to 6.

3. The control method according to claim 1, wherein: In the second mode, after turning on the energy-saving switch, execute steps 1 to 7 in the second mode; After turning off the energy-saving switch, perform the following steps: The inverter compressor is powered by mains electricity and its operating frequency is controlled according to preset temperature conditions until the phase change material reaches the set stop temperature and stops.

4. The control method according to claim 1, wherein: The operating mode includes a third mode, in which: The inverter compressor is powered by mains electricity and its operating frequency is controlled according to preset temperature conditions until the phase change material reaches the set stop temperature and stops.

5. The control method according to any one of claims 1 to 4, characterized in that: The step of controlling the operating frequency of the variable frequency compressor according to the preset temperature condition includes: When the phase change material is cooled and stored cold by the variable frequency compressor, obtaining a temperature of the phase change material; When the temperature of the phase change material is within a safe temperature range, controlling the variable frequency compressor to operate at a maximum frequency allowed under the current environment; When the temperature of the phase change material is lower than the safe temperature range, obtaining the current air temperature in the box; The temperature of the phase change material is compared with the air temperature, and the operating frequency of the variable frequency compressor is controlled according to the compared temperature difference.

6. The control method according to claim 5, characterized in that: Comparing the temperature of the phase change material with the air temperature, and controlling the operating frequency of the variable frequency compressor according to the compared temperature difference, comprising: Comparing the temperature of the phase change material with the air temperature, and when the temperature difference is greater than a set threshold, controlling the variable frequency compressor to operate at a maximum frequency allowed under the current environment; When the temperature difference is less than or equal to a set threshold, the variable frequency compressor is controlled to reduce the operating frequency.

7. The control method according to claim 6, characterized in that: When the temperature difference is less than or equal to a set threshold, controlling the variable frequency compressor to reduce the operating frequency includes: When the temperature difference is equal to the threshold, controlling the variable frequency compressor to reduce the current operating frequency by 30%-60%; When the temperature difference is less than a set threshold, the temperature of the phase change material and the current air temperature in the box are obtained in stages, and the temperature of the phase change material and the current air temperature in the box are compared in each stage; According to the compared temperature difference, the operating frequency of the variable frequency compressor is reduced according to the set frequency value in each stage until the temperature difference is equal to the preset difference.

8. The control method according to claim 6, characterized in that: In step 2, the maximum frequency allowed under the current environment is the maximum rated frequency of the variable frequency compressor; In step 3, the maximum frequency allowed under the current environment is: the maximum frequency allowed for the variable frequency compressor under the photovoltaic power generation at the current moment.

9. The control method according to claim 7, characterized in that: The safety temperature range is greater than 0°C, and the threshold is set to 1°C-4°C.

10. The control method according to claim 1, characterized in that: The operating mode also includes a defrost mode, in which the photovoltaic energy storage system is controlled to operate under a refrigeration condition; When the condenser temperature of the photovoltaic energy storage system is higher than the set temperature or the defrost time is greater than the maximum defrost time, the defrost ends.

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