Control method of photovoltaic energy storage system for cold chain equipment

Abstract

The invention discloses a control method of a photovoltaic energy storage system for cold chain equipment. The control method comprises the following steps: judging whether the generating capacity of a photovoltaic system is sufficient or not; 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 power; if not, the operation frequency of the inverter compressor is controlled, and the inverter compressor is shut down until the phase-change material reaches the set temperature; 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 is judged; 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 shut down until the phase-change material reaches the set temperature; if the voltage of the battery is lower than a set voltage value before the phase-change material reaches the set temperature, the mains supply supplies power to the inverter compressor and charges the battery, the operation frequency of the inverter compressor is controlled, and the inverter compressor is stopped until the phase-change material reaches the set temperature; and when the voltage of the battery reaches the conversion voltage, the process is repeated. 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] This invention relates to the field of cold chain equipment technology, and more specifically, to a control method for a photovoltaic energy storage system used in cold chain equipment. Background Technology

[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 been increasing, indicating huge potential in China's cold chain logistics market. Therefore, combined with national policies promoting energy conservation and environmental protection, the rapid development of new energy cold chain transport vehicles is inevitable. To reduce energy consumption, most new energy cold chain transport vehicles are equipped with photovoltaic systems. Under sufficient sunlight, these systems can generate electricity to power the energy storage system within the vehicle. However, energy storage systems with photovoltaic components in related technologies are not very flexible in use, and their range is relatively short. Summary of the Invention

[0003] The main objective of this invention is to provide a control method for a photovoltaic energy storage system for cold chain equipment, so as to solve the problems of insufficient flexibility and low photovoltaic range in the use of energy storage systems with photovoltaic systems in related technologies.

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

[0005] The operating mode is selected, including a first mode, in which:

[0006] Step 1: Determine if the photovoltaic system generates enough power;

[0007] 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 used to charge the battery.

[0008] Step 3: If insufficient, control the operating frequency of the inverter compressor according to the current photovoltaic power generation and the preset temperature conditions until the phase change material reaches the set temperature and then stops.

[0009] Step 4: Determine whether the current photovoltaic power generation meets the minimum frequency requirement for the inverter compressor to operate under standard conditions.

[0010] Step 5: If the conditions are not met, power is supplied to the variable frequency compressor simultaneously through 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 the set temperature and then stops.

[0011] Step 6: If the battery voltage is lower than the set voltage value before the phase change material reaches the set temperature, the mains power will supply power to the inverter compressor and charge the battery. The operating frequency of the inverter compressor will be controlled according to the preset temperature conditions until the phase change material reaches the set temperature and then the compressor will stop.

[0012] Step 7: When the battery voltage reaches the conversion voltage, proceed with steps 1 to 6.

[0013] Furthermore, in the first mode, after turning on the energy-saving switch, steps 1-7 in the first mode are executed;

[0014] After turning off the energy-saving switch, perform the following steps:

[0015] 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 the compressor stops.

[0016] Furthermore, the operating mode includes a second mode, in which:

[0017] 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 the compressor stops.

[0018] Furthermore, in steps 2 and 3, controlling the operating frequency of the variable frequency compressor according to preset temperature conditions includes:

[0019] When the phase change material is cooled and stored by the variable frequency compressor,

[0020] Obtain the temperature of the phase change material;

[0021] When the temperature of the phase change material is within a safe temperature range, the variable frequency compressor is controlled to operate at the maximum frequency allowed under the current environment.

[0022] When the temperature of the phase change material is below the safe temperature range, obtain the current air temperature inside the chamber;

[0023] The temperature of the phase change material is compared with the air temperature, and the operating frequency of the variable frequency compressor is controlled based on the temperature difference.

[0024] 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 based on the temperature difference, including:

[0025] The temperature of the phase change material is compared with the air temperature. When the temperature difference is greater than a set threshold, the variable frequency compressor is controlled to operate at the maximum frequency allowed under the current environment.

[0026] When the temperature difference is less than or equal to the set threshold, the variable frequency compressor is controlled to reduce its operating frequency.

[0027] Furthermore, when the temperature difference is less than or equal to a set threshold, the variable frequency compressor is controlled to reduce its operating frequency, including:

[0028] When the temperature difference is equal to the threshold, the variable frequency compressor is controlled to reduce its operating frequency by 30%-60% based on the current operating frequency;

[0029] When the temperature difference is less than the set threshold, the temperature of the phase change material and the current air temperature in the chamber are obtained in stages, and the temperature of the phase change material and the current air temperature in the chamber are compared in each stage.

[0030] Based on the temperature difference after comparison, the operating frequency of the variable frequency compressor is reduced at each stage according to a set frequency value until the temperature difference equals the preset difference value.

[0031] Furthermore, a correspondence between the operating frequency of the variable frequency compressor and the temperature difference is established in advance;

[0032] Based on the compared temperature difference, the operating frequency of the variable frequency compressor is reduced at each stage according to a set frequency value until the temperature difference equals the preset difference value, specifically:

[0033] Based on the temperature difference after comparison and the pre-established correspondence, the operating frequency of the variable frequency compressor is reduced until the temperature difference equals the preset difference.

[0034] Furthermore, in step 2, the maximum frequency allowed under the current environment is the maximum rated frequency of the variable frequency compressor;

[0035] In step 3, the maximum permissible frequency under the current environment is: the maximum permissible frequency of the variable frequency compressor under the photovoltaic power generation at the current moment.

[0036] Furthermore, the safe temperature range is greater than 0°, and the set threshold is 1°-4°.

[0037] Furthermore, the operating mode also includes a defrosting mode, in which the photovoltaic energy storage system is controlled to operate under cooling conditions;

[0038] Defrosting ends when the condenser temperature of the photovoltaic energy storage system is higher than the set temperature or the defrosting time is longer than the maximum defrosting time.

[0039] In this embodiment of the 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 preset temperature conditions until the phase change material in the photovoltaic energy storage system reaches the set temperature and stops. During this process, excess power is used to charge the battery. If 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. It is then determined whether the current photovoltaic power generation meets the minimum frequency requirement for the variable frequency compressor to operate under standard conditions. If not, the battery and the photovoltaic system simultaneously supply power to the variable frequency compressor, and the variable frequency compressor operates at the minimum frequency requirement under standard conditions until the phase change material reaches the set temperature or the battery voltage reaches the set value. When the voltage drops below the set value, the system shuts down. If the battery voltage is lower than the set value before the phase change material reaches the set temperature, the mains power supplies power to the inverter compressor and charges the battery. The operating frequency of the inverter compressor is controlled according to the preset temperature conditions until the phase change material reaches the set temperature and shuts down. On the one hand, this achieves the goal of quickly storing energy and charging the battery to increase the power when the photovoltaic system generates sufficient power. On the other hand, when the photovoltaic power generation is insufficient, the operating frequency of the inverter compressor is adjusted according to the current photovoltaic power generation to utilize the photovoltaic power generation for longer operation. When the power generation is very low, the battery supplies power. This achieves the technical effect of greatly increasing the battery life of the energy storage system while ensuring sufficient energy storage efficiency, thereby solving the problem of low photovoltaic battery life in related technologies.

[0040] On the other hand, when the battery power is too low, it automatically switches to mains power, which supplies power to the inverter compressor and charges the battery at the same time. After the battery is charged to a certain level, the photovoltaic power generation is assessed, and the system selects between photovoltaic power supply and battery power based on the result. This makes it more flexible in use and can effectively reduce mains power consumption. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the control method according to an embodiment of the present invention. Detailed Implementation

[0042] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0043] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of the invention described herein.

[0044] In this invention, the terms "upper," "lower," "inner," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing the invention and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0045] Furthermore, in addition to indicating direction or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in certain situations to indicate a dependency or connection. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0046] Furthermore, the terms "set up," "equipped with," "connected," and "fixed" should be interpreted broadly. For example, "connected" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0047] In addition, the term "multiple" should mean two or more.

[0048] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0049] Taking a cold chain box as an example, a photovoltaic energy storage system may include a photovoltaic panel installed on the top of the cold chain box, an energy storage module installed inside the cold chain box, including phase change materials, etc., a compressor unit installed outside the cold chain box, and a charger, inverter, battery, etc. connected to the photovoltaic panel, as well as pipelines installed inside and outside the cold chain box, etc. The compressor unit can input the heat exchange medium that mixes gas and liquid in the forward direction into the energy storage module or input the gaseous heat exchange medium in the reverse direction into the energy storage module, 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.

[0050] like Figure 1As shown, this embodiment of the invention provides a control method for a photovoltaic energy storage system for cold chain equipment, including:

[0051] The operating mode is selected, including a first mode, in which:

[0052] Step 1: Determine if the photovoltaic system generates enough power;

[0053] The power generation of a photovoltaic (PV) system can be obtained by reading the inverter's current and voltage, meaning there is a direct correlation between power generation and output power. Therefore, the power output of the PV system can be determined by judging the magnitude of the current and voltage, thus determining the power generation. When the current power output is greater than the set power output, the current power generation is considered sufficient; when it is less than the set power output, the current power generation is considered insufficient. The set power output 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.

[0054] In some implementations, the required power P of the variable frequency compressor is determined according to the following formula. need :

[0055] P need =max(0, P) loss -η pcm )

[0056] P loss =U·A·(T) env -T set )

[0057] Among them, P loss For energy damage power, η pcm The energy release power of the energy storage module is obtained based on 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, a calibrated constant, with units of W / m². 2 K and A are the surface areas of the cold chain box, which are constants, and T is the surface area of ​​the cold chain box. env The temperature of the air inside the chamber is obtained through a temperature sensor, T set The set air temperature is a constant.

[0058] Based on the above formula, the current power demand 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 the current power demand of the variable frequency compressor, it is judged that the photovoltaic power generation is sufficient.

[0059] 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 used to charge the battery.

[0060] When power generation is sufficient, the photovoltaic system can supply power entirely to the variable frequency compressor, increasing its operating frequency. When the variable frequency compressor reaches its set operating frequency, the photovoltaic system continues to power it at that frequency, with any excess power charging the battery to increase its capacity. When the phase change material in the energy storage module reaches its set temperature, the variable frequency compressor shuts down, at which point the photovoltaic system's power generation is entirely used to charge the battery.

[0061] Step 3: If insufficient, control the operating frequency of the inverter compressor according to the current photovoltaic power generation and the preset temperature conditions until the phase change material reaches the set temperature and then stops.

[0062] When it is determined that the photovoltaic power generation system is insufficient, i.e., the power generation current and voltage are lower than the set values, the operating frequency of the inverter compressor needs to be reduced. During this process, the operating frequency of the inverter compressor is determined based on the current photovoltaic power generation (i.e., power generation current and voltage) and preset temperature conditions. At this time, the power generation of the photovoltaic system can fully supply the inverter compressor. If the power generation current and voltage continue to decrease, the operating frequency of the inverter compressor will also continue to decrease.

[0063] Step 4: Determine whether the current photovoltaic power generation meets the minimum frequency requirement for the inverter compressor to operate under standard conditions.

[0064] During step 3, it is determined in real time or in stages whether the current power generation current and voltage meet the requirements for the variable frequency compressor to operate at the lowest frequency under standard operating conditions.

[0065] Step 5: If the conditions are not met, power is supplied to the variable frequency compressor simultaneously through the battery and photovoltaic system, and the variable frequency compressor is operated at the lowest frequency under standard operating conditions until the phase change material reaches the set temperature and then stops.

[0066] When it is determined that the current power generation is insufficient to support the inverter compressor operating at the minimum frequency under standard conditions, the battery and photovoltaic system simultaneously supply power to the inverter compressor, enabling it to operate at the minimum frequency under standard conditions for slow energy storage. The minimum frequency under standard conditions is a preset frequency, and its specific value is not limited here. When the phase change material in the energy storage module reaches the set temperature, the inverter compressor is shut down.

[0067] Furthermore, while the battery is supplying power to the inverter compressor, the power generation of the photovoltaic system is still assessed. If the photovoltaic system's power generation is sufficient to power the inverter compressor at its minimum operating frequency under standard conditions, then only the photovoltaic system supplies power to the inverter compressor, without consuming additional battery power. When the photovoltaic system generates sufficient power due to weather conditions, the excess power is used to charge the battery, thus fully utilizing the photovoltaic power generation and further improving the driving range.

[0068] Step 6: If the battery voltage is lower than the set voltage value before the phase change material reaches the set temperature, the mains power will supply power to the inverter compressor and charge the battery. The operating frequency of the inverter compressor will be controlled according to the preset temperature conditions until the phase change material reaches the set temperature and then the compressor will stop.

[0069] Because the battery's charge level is variable, the battery voltage may drop below the set value before the phase change material reaches its set temperature, preventing the battery from maintaining the inverter compressor's normal operation. Therefore, the inverter compressor is powered by mains electricity, and its operating frequency is controlled according to preset temperature conditions, allowing the phase change material to quickly store energy. Simultaneously, the mains electricity charges the battery, increasing its capacity. This complementary use of mains power and photovoltaic power ensures the inverter compressor's normal operation and improves the flexibility of the photovoltaic energy storage system.

[0070] During mains power supply, at least two scenarios exist: First, if the phase change material reaches its set temperature before the battery is charged to the set voltage, the inverter compressor stops, and the mains continues charging the battery until the battery voltage reaches the set value. Second, if the phase change material's temperature has not yet reached the set value after the battery has been charged to the set voltage, the system switches to battery power for the inverter compressor, allowing it to operate at the lowest frequency under standard conditions. Simultaneously, steps 1 through 6 are executed, meaning that after switching to battery power, the system continues to assess whether the photovoltaic system's power generation is sufficient. This effectively reduces mains power usage, further reducing operating costs and maximizing the utilization of solar energy.

[0071] In this embodiment, a variable frequency compressor introduces a medium into the energy storage module, causing the phase change material (PCM) to undergo a phase change to achieve energy storage. Depending on the operating conditions, the PCM can store cold or heat. During cold or heat storage, the start-up of the variable frequency compressor is controlled by a temperature sensor detecting the temperature of the PCM. When the temperature of the PCM is higher than a set value, the variable frequency compressor is activated for cold storage. When the temperature of the PCM is lower than the set value, the variable frequency compressor is activated for heat storage. The entire system can be integrated and controlled by a PLC controller.

[0072] This embodiment achieves the goal of rapidly storing energy and charging the battery to increase power when the photovoltaic system generates sufficient power, reducing energy storage efficiency when the power generation is insufficient, utilizing the photovoltaic system's power generation to operate for a longer period of time, and then using the battery to power the system when the power generation is very low. This achieves the goal of greatly increasing the battery life of the energy storage system while ensuring sufficient energy storage efficiency, thereby solving the problem of low photovoltaic battery life of energy storage systems with photovoltaic systems in related technologies.

[0073] In one embodiment, the operating mode further includes a second mode, which includes the following steps:

[0074] Step 1: Determine if the photovoltaic system generates enough power;

[0075] The power generation of a photovoltaic (PV) system can be obtained by reading the inverter's current and voltage, meaning there is a direct correlation between power generation and output power. Therefore, the power output of the PV system can be determined by judging the magnitude of the current and voltage, thus determining the power generation. When the current power output is greater than the set power output, the current power generation is considered sufficient; when it is less than the set power output, the current power generation is considered insufficient. The set power output 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 used to charge the battery.

[0077] When power generation is sufficient, the photovoltaic system can supply power entirely to the inverter compressor, increasing its operating frequency. When the inverter compressor reaches its set operating frequency, the photovoltaic system continues to power it at that frequency, with any excess power charging the battery to increase its capacity. When the phase change material in the energy storage module of the photovoltaic system reaches its set temperature, the inverter compressor shuts down. At this point, the photovoltaic system's power generation is entirely used to charge the battery, maximizing solar energy utilization and preventing waste.

[0078] Step 3: If insufficient, control the operating frequency of the inverter compressor according to the current photovoltaic power generation and the preset temperature conditions until the phase change material reaches the set temperature and then stops.

[0079] When it is determined that the photovoltaic power generation system is insufficient, i.e., the power generation current and voltage are lower than the set values, the operating frequency of the inverter compressor needs to be reduced. During this process, the operating frequency of the inverter compressor is determined based on the current photovoltaic power generation (i.e., power generation current and voltage) and preset temperature conditions. At this time, the power generation of the photovoltaic system can fully supply the inverter compressor. If the power generation current and voltage continue to decrease, the operating frequency of the inverter compressor will also continue to decrease.

[0080] Step 4: Determine whether the current photovoltaic power generation meets the minimum frequency requirement for the inverter compressor to operate under standard conditions.

[0081] During step 3, it is determined in real time or in stages whether the current power generation current and voltage meet the requirements for the variable frequency compressor to operate at the lowest frequency under standard operating conditions.

[0082] Step 5: If the conditions are not met, power is supplied to the variable frequency compressor simultaneously through the battery and photovoltaic system, and the variable frequency compressor is operated at the lowest frequency under standard operating conditions until the phase change material reaches the set temperature or the battery voltage is lower than the set voltage value, at which point the compressor stops.

[0083] When it is determined that the current power generation is insufficient to support the inverter compressor operating at the minimum frequency under standard conditions, both the battery and the photovoltaic system simultaneously supply power to the inverter compressor, enabling it to operate at the minimum frequency under standard conditions and slowly store energy. The inverter compressor will stop 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 supply power to the inverter compressor due to insufficient photovoltaic power generation, then only the battery will supply power to the inverter compressor.

[0084] Furthermore, while the battery is supplying power to the inverter compressor, the power generation of the photovoltaic system is still assessed. If the photovoltaic system's power generation is sufficient to power the inverter compressor at its minimum operating frequency under standard conditions, then only the photovoltaic system supplies power to the inverter compressor, without consuming additional battery power. When the photovoltaic system generates sufficient power due to weather conditions, the excess power is used to charge the battery, thus fully utilizing the photovoltaic power generation and further improving the driving range.

[0085] In this embodiment, the first mode and the second mode are two operating modes of the photovoltaic energy storage system, and the user can choose to operate in the first mode or the second mode.

[0086] Since the inverter compressor can be powered by mains power in the first mode, in order to further improve the flexibility of use, in the first mode, after turning on the energy-saving switch, steps 1-7 in the first mode are executed;

[0087] After turning off the energy-saving switch, perform the following steps:

[0088] 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 the compressor stops.

[0089] Specifically, in the first mode, the energy-saving switch can be turned on. In this case, the system needs to determine whether the photovoltaic power generation is sufficient and execute steps 2 to 7 accordingly. In the first mode, the energy-saving switch can also be turned off. In this case, the system no longer determines whether the photovoltaic power generation is sufficient, but directly supplies power to the inverter compressor from the mains power.

[0090] In the first mode, the phase change material (PCM) can be used for both cold and heat storage, depending on the operating conditions. During cold or heat storage, the variable frequency compressor's startup is controlled by a temperature sensor detecting the PCM's temperature. When the PCM's temperature exceeds a set value, the compressor starts for cold storage. When the PCM's temperature falls below the set value, the compressor starts for heat storage.

[0091] In one implementation, the operating mode includes a third mode, in which:

[0092] 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 the compressor stops.

[0093] 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 inverter compressor is powered entirely by the mains power. Compared with the first and second modes, this mode enables the inverter compressor to store energy quickly and improves the energy storage efficiency.

[0094] During the energy storage process of phase change materials (PCMs), the energy transfer occurs via the refrigerant medium—PCM—internal air of the cold chain compartment. The portion of the PCM closer to the refrigerant medium has a lower temperature. The inverter compressor's shutdown temperature is generally the air temperature, i.e., the air temperature inside the cold chain compartment, and this temperature is used as a reference to control whether the inverter compressor stops. When the air temperature has not yet reached the set value, the inverter compressor will operate at a higher frequency to achieve rapid energy storage, provided there is sufficient power or it is powered by mains electricity. Because the transfer of temperature from the PCM to the air inside the compartment requires a certain process and time, and the inverter compressor also changes the temperature of the PCM through the refrigerant medium, the transfer of temperature from the refrigerant medium to the PCM also requires a certain process and time. Therefore, when the air temperature reaches the shutdown temperature, the temperature of the PCM is often lower than the air temperature, especially the portion of the PCM near the refrigerant flow pipes. Therefore, even if the inverter compressor stops at this point, the lower-temperature PCM will further reduce the air temperature inside the compartment, especially the temperature of the area near the inner wall. For fruit and vegetable refrigeration, excessively low temperatures can easily cause frost damage.

[0095] In addition, when the temperature of the phase change material is low, the energy storage efficiency of the variable frequency compressor at high operating frequency decreases, resulting in low energy utilization.

[0096] Therefore, in this embodiment, regardless of whether it is the first mode, the second mode, or the third mode, controlling the operating frequency of the variable frequency compressor according to the preset temperature conditions includes:

[0097] When the phase change material is cooled and stored by the variable frequency compressor,

[0098] The temperature of the phase change material can be obtained, specifically by reading the temperature of the phase change material through a preset temperature sensor. This process can be real-time or in stages.

[0099] When the temperature of the phase change material is within a safe temperature range, the variable frequency compressor is controlled to operate at the maximum frequency allowed under the current environment.

[0100] A preset safe temperature range for the phase change material is defined. The specific value can be set based on the characteristics of the phase change material and the performance of the variable frequency compressor; this embodiment does not impose any restrictions. Within this safe temperature range, the variable frequency compressor has high energy storage efficiency without causing the air temperature inside the chamber to drop too low. Therefore, when the temperature of the phase change material exceeds the safe temperature range, the variable frequency compressor operates at the maximum permissible frequency under the current environment to rapidly store energy.

[0101] It should be noted that the maximum permissible frequency of the variable frequency compressor varies under different modes and conditions. In the first and second modes, when the photovoltaic system generates sufficient power, and in the third mode, the maximum permissible frequency under the current environment is the maximum rated frequency of the variable frequency compressor. In the first and second modes, when the photovoltaic system generates insufficient power, the maximum permissible frequency under the current environment needs to be determined based on the photovoltaic power generation. Specifically, in this environment, the operating frequency of the variable frequency compressor is kept in match with the photovoltaic power generation; the greater the photovoltaic power generation, the higher the operating frequency of the variable frequency compressor.

[0102] When the temperature of the phase change material is below the safe temperature range, obtain the current air temperature inside the chamber;

[0103] When the variable frequency compressor is operating at the maximum permissible frequency under the current environment, and the temperature sensor detects that the temperature of the phase change material is below the temperature range, another temperature sensor detects the air temperature inside the chamber, especially the air temperature near the phase change material. In some embodiments, multi-point temperature detection can be performed, and the weighted value or the highest value can be taken as the current air temperature. This embodiment includes multi-point temperature detection of the phase change material and multi-point temperature detection of the air temperature.

[0104] The temperature of the phase change material is compared with the air temperature, and the operating frequency of the variable frequency compressor is controlled based on the temperature difference.

[0105] 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 based on this temperature difference. Specifically, the process includes:

[0106] The temperature of the phase change material is compared with the air temperature. When the temperature difference is greater than a set threshold, the variable frequency compressor is controlled to operate at the maximum frequency allowed under the current environment.

[0107] The air temperature inside the chamber is affected by the environment and the stored fruits and vegetables, and varies under different conditions. When the temperature of the phase change material is below the safe temperature range, there may be a large temperature difference between the phase change material and the air temperature. Therefore, the variable frequency compressor can still be controlled to operate at the maximum frequency allowed under the current environment, so that the temperature of the phase change material drops rapidly, thereby rapidly reducing the air temperature inside the chamber.

[0108] When the temperature difference is less than or equal to the set threshold, the variable frequency compressor is controlled to reduce its operating frequency.

[0109] When the temperature of the phase change material is below 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 reduced, which slows down the cooling rate of the phase change material. This allows the temperature of the phase change material to be transferred to the air inside the chamber for a sufficient time to lower the air temperature inside the chamber, so that the temperature of the phase change material gradually approaches the air temperature. This avoids the problem of the phase change material temperature being too low and causing the air temperature to drop further after the air temperature reaches the set value and the compressor stops.

[0110] Furthermore, because phase change materials have a low temperature, the reduced operating frequency of the inverter compressor can match the cold storage rate of the phase change material, improving energy utilization. In environments where the energy-saving switch is turned on in both the first and second modes, if the photovoltaic power generation exceeds the electricity required for the current operating frequency of the inverter compressor after reducing its operating frequency according to preset temperature conditions, the excess electricity can still charge the battery, thereby further improving the utilization rate of solar energy.

[0111] In one embodiment, when the temperature difference is less than or equal to a set threshold, controlling the variable frequency compressor to reduce its operating frequency includes:

[0112] When the temperature difference is equal to the threshold, the variable frequency compressor is controlled to reduce its operating frequency by 30%-60% based on the current operating frequency;

[0113] When the temperature difference is less than the set threshold, the temperature of the phase change material and the current air temperature in the chamber are obtained in stages, and the temperature of the phase change material and the current air temperature in the chamber are compared in each stage.

[0114] Based on the temperature difference, the operating frequency of the variable frequency compressor is reduced at each stage according to a set frequency value until the temperature difference equals the preset difference.

[0115] In this embodiment, the temperature of the phase change material and the air temperature inside the chamber can be acquired at certain time intervals. Since the variable frequency compressor runs continuously, the air temperature will continuously decrease, and as the cooling rate of the phase change material slows down, the temperature difference between the phase change material and the air will gradually decrease. During this process, a decreasing temperature gradient can be set. When the temperature gradient decreases by one gradient, the variable frequency compressor correspondingly reduces its operating frequency by one gradient until the temperature difference equals a preset value. In some embodiments, the time interval can be 10 seconds, 30 seconds, etc. When the temperature difference is first detected to equal the set threshold, the frequency of the variable frequency compressor is controlled to decrease by 50% (based on the current frequency), and then the frequency of the variable frequency compressor is gradually reduced according to the temperature difference acquired in stages. A correspondence between the frequency of the variable frequency compressor and the temperature difference can be pre-established and imported into the system. During the cold storage process, the variable frequency compressor automatically reduces its frequency according to this correspondence.

[0116] Specifically, the correspondence between the operating frequency of the variable frequency compressor and the temperature difference can be established in advance;

[0117] Based on the compared temperature difference, the operating frequency of the variable frequency compressor is reduced at each stage according to a set frequency value until the temperature difference equals the preset difference value, specifically:

[0118] Based on the temperature difference after comparison and the pre-established correspondence, the operating frequency of the variable frequency compressor is reduced until the temperature difference equals the preset difference.

[0119] When the temperature difference is closer to the preset difference, the frequency of the variable frequency compressor decreases more. Within 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 stops at a certain frequency, thereby strictly controlling the rate at which the temperature of the phase change material decreases.

[0120] In some implementations, the safe temperature range is greater than 0°, and can be 1°, 2°, etc., with the threshold set to 1°-4°.

[0121] It should be noted that the safe temperature range and threshold are not fixed. The safe temperature range and threshold can be set according to the characteristics of fruits and vegetables. The system can be built-in or users can input the optimal storage temperature range for specific fruits and vegetables as well as the maximum safe temperature difference tolerance for those fruits and vegetables.

[0122] Furthermore, the operating modes also include a defrost mode. In heating mode, the condenser of the external cooling unit becomes an evaporator due to the opening of the four-way valve. When the evaporation temperature is low, the evaporator will frost up. In heating mode, the control system will automatically defrost according to the running time of the heating compressor. In case of special weather or operating conditions, manual defrosting can be performed. When manual defrosting is activated, the compressor unit starts, the four-way valve does not start, and it operates in cooling mode. Defrosting ends when the condenser temperature is higher than the set temperature or the defrosting time is longer than the maximum defrosting time.

[0123] 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 condenser fan, an electronic expansion valve controller, a pressure sensor, a BMS lithium battery with communication function, and a photovoltaic energy storage inverter integrated machine, etc.

[0124] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A control method for a photovoltaic energy storage system used in cold chain equipment, characterized in that, include: The operating mode is selected, including a first mode, which includes the following steps: Step 1: Determine if the photovoltaic system generates enough power; 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 used to charge the battery. Step 3: If insufficient, control the operating frequency of the inverter compressor according to the current photovoltaic power generation and the preset temperature conditions until the phase change material reaches the set temperature and then stops. Step 4: Determine whether the current photovoltaic power generation meets the minimum frequency requirement for the inverter compressor to operate under standard conditions. Step 5: If the conditions are not met, power is supplied to the variable frequency compressor simultaneously through 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 the set temperature and then stops. Step 6: If the battery voltage is lower than the set voltage value before the phase change material reaches the set temperature, the mains power will supply power to the inverter compressor and charge the battery. The operating frequency of the inverter compressor will be controlled according to the preset temperature conditions until the phase change material reaches the set temperature and then the compressor will stop. Step 7: When the battery voltage reaches the conversion voltage, proceed with steps 1 to 6.

2. The control method according to claim 1, characterized in that, In the first mode, after turning on the energy-saving switch, execute steps 1-7 in the first 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 the compressor stops.

3. The control method according to claim 1, characterized in that, The operating mode includes a second 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 the compressor stops.

4. The control method according to any one of claims 1 to 3, characterized in that, The method of controlling the operating frequency of the variable frequency compressor according to preset temperature conditions includes: When the phase change material is cooled and stored by the variable frequency compressor, Obtain the temperature of the phase change material; When the temperature of the phase change material is within a safe temperature range, the variable frequency compressor is controlled to operate at the maximum frequency allowed under the current environment. When the temperature of the phase change material is below the safe temperature range, obtain the current air temperature inside the chamber; The temperature of the phase change material is compared with the air temperature, and the operating frequency of the variable frequency compressor is controlled based on the temperature difference.

5. The control method according to claim 4, characterized in that, The process of comparing the temperature of the phase change material with the air temperature and controlling the operating frequency of the variable frequency compressor based on the temperature difference includes: The temperature of the phase change material is compared with the air temperature. When the temperature difference is greater than a set threshold, the variable frequency compressor is controlled to operate at the maximum frequency allowed under the current environment. When the temperature difference is less than or equal to the set threshold, the variable frequency compressor is controlled to reduce its operating frequency.

6. The control method according to claim 5, characterized in that, When the temperature difference is less than or equal to a set threshold, the variable frequency compressor is controlled to reduce its operating frequency, including: When the temperature difference is equal to the threshold, the variable frequency compressor is controlled to reduce its operating frequency by 30%-60% based on the current operating frequency; When the temperature difference is less than the set threshold, the temperature of the phase change material and the current air temperature in the chamber are obtained in stages, and the temperature of the phase change material and the current air temperature in the chamber are compared in each stage. Based on the temperature difference after comparison, the operating frequency of the variable frequency compressor is reduced at each stage according to a set frequency value until the temperature difference equals the preset difference value.

7. The control method according to claim 6, characterized in that, Also includes: Establish a pre-defined relationship between the operating frequency of the variable frequency compressor and the temperature difference; Based on the compared temperature difference, the operating frequency of the variable frequency compressor is reduced at each stage according to a set frequency value until the temperature difference equals the preset difference value, specifically: Based on the temperature difference after comparison and the pre-established correspondence, the operating frequency of the variable frequency compressor is reduced until the temperature difference equals the preset difference.

8. The control method according to claim 6, characterized in that, In step 2, the maximum permissible frequency under the current environment is the maximum rated frequency of the variable frequency compressor; In step 3, the maximum permissible frequency under the current environment is: the maximum permissible frequency of 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 safe temperature range is greater than 0°, and the set threshold is 1°-4°.

10. The control method according to claim 1, characterized in that, The operating mode also includes a defrosting mode, in which the photovoltaic energy storage system is controlled to operate under cooling conditions. Defrosting ends when the condenser temperature of the photovoltaic energy storage system is higher than the set temperature or the defrosting time is longer than the maximum defrosting time.

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