An off-grid type reverse control all-in-one machine energy scheduling method based on cold storage thermal inertia

Abstract

The application discloses an off-grid type reverse control integrated energy scheduling method based on cold storage thermal inertia, defines a thermal state of charge SOT through a first-order thermal resistance and thermal capacity model, and quantifies the cold storage thermal inertia as virtual energy storage; based on a SOT and SOC cooperative criterion, redundant power is over-cooled and absorbed as cold storage when photovoltaic power is abundant, and cold is released by using thermal inertia when photovoltaic power is insufficient; the second-order change rate of photovoltaic power is used to predict cloud shadow sudden drop and reduce load in advance; and residual error analysis is used to diagnose refrigeration energy efficiency abnormalities in real time. The application breaks through the limitation of electric-thermal scheduling separation, suppresses battery impact and avoids photovoltaic power abandonment through virtual energy storage scheduling by replacing electricity with heat, and improves the service life of the energy storage system and the comprehensive energy utilization rate.

Description

Technical Field

[0001] This invention relates to the field of off-grid photovoltaic / energy storage power supply systems and refrigeration control technology, specifically an energy dispatching method for an off-grid integrated inverter control unit based on the thermal inertia of cold storage. Background Technology

[0002] As a high-power inductive load, the compressor's frequent start-stop cycles and the resulting surge currents and deep charge-discharge cycles severely shorten the lifespan of energy storage batteries, becoming a major bottleneck for system reliability. Simultaneously, the intermittent nature of photovoltaic output and the random fluctuations in cooling load lead to significant problems such as severe power curtailment, susceptibility of busbars to power outages due to cloud cover, and the inability to detect cooling efficiency degradation in real time. To alleviate these contradictions, existing technologies attempt to improve the system through energy storage substitution and energy management. For example, the invention patent with patent application number 201910082332.1, entitled "A Distributed Photovoltaic Cold Storage System for Cold Storage Body," uses phase change material energy storage instead of battery energy storage. It utilizes the solid-liquid phase change process of phase change materials to store daytime solar radiation or off-peak electricity as cooling energy, releasing it at night and during peak electricity consumption periods to achieve peak shaving and continuous cooling. Another example is the invention patent with patent application number 202411402197.1, entitled "An Off-Grid Distributed Solar Photovoltaic Power Generation Energy Storage Cold Storage". This patent uses an MPPT controller to realize a control strategy to match the photovoltaic power generation, the power supply and demand of the energy storage system and the power consumption of the cold storage, aiming to ensure the safety of cooling supply and improve energy utilization efficiency.

[0003] However, the above-mentioned technical solutions still have obvious limitations in actual complex working conditions: Compared with the patent with patent application number 201910082332.1, although it uses phase change material cold storage to replace part of the battery energy storage, the phase change material is encapsulated inside the cold storage wall panel, and the cold storage and release process relies on natural conduction, resulting in a slow response speed and difficulty in coping with minute-level power fluctuations such as cloud shading effects. More importantly, this solution treats the cold storage as a rigid cold storage container and fails to establish a dynamic energy model of the cold storage's own thermal inertia, making it impossible to achieve flexible scheduling based on real-time thermal charge state; Compared with the patent with patent application number 202411402197.1, although it introduces an MPPT controller for energy distribution, it still treats the cold storage as a passive load, with the compressor starting and stopping directly impacting the battery, and lacks an active absorption mechanism for photovoltaic redundant power - the problem of power abandonment still exists when the battery is fully charged. At the same time, this solution does not utilize the thermal inertia of the cold storage as "virtual energy storage" and cannot achieve coordinated scheduling of "heat replacing electricity". In addition, existing solutions generally fail to address the real-time sensing of cold storage refrigeration efficiency degradation, and also lack millisecond-level dynamic support methods for bus voltage under cloud cover effects. Summary of the Invention

[0004] To address the problems of existing technologies, this invention provides an energy scheduling method for an off-grid integrated inverter control unit based on the thermal inertia of cold storage. This invention offers advantages such as online estimation of the cold storage's thermal state of charge, active absorption of redundant electrical energy during overcooling, predictive load reduction and disturbance rejection under cloud cover effects, effective suppression of battery impact during compressor start-up and shutdown, and real-time self-diagnosis of abnormal refrigeration efficiency.

[0005] To solve the above problems, the present invention adopts the following technical solution: An energy scheduling method for an off-grid integrated inverter control unit based on the thermal inertia of cold storage includes the following steps: S1: Obtain the internal temperature of the cold storage, the external ambient temperature, and the power of the compressor; calculate the equivalent energy index of the thermal storage and the state of charge (SOT) of the cold storage using a first-order thermal resistance-capacity model; wherein, the equivalent energy index of the thermal storage includes the equivalent heat capacity of the cold storage. Respectively with the upper limit of temperature and the lower limit of supercooled temperature Determined release of cold energy With rechargeable cold energy The thermal charge state SOT is determined by , The current internal temperature of the cold storage is normalized and determined, and the equivalent thermal resistance and equivalent heat capacity are updated online based on the compressor start-up and shutdown temperature response data; S2: Based on the stated thermal state of charge (SOT), battery state of charge (SOC), and photovoltaic power, perform power allocation in either a charging-cooling mode or a releasing-cooling mode; the SOT and SOC work together for power allocation. When there is excess photovoltaic power, the redundant power is integrated and mapped to a temperature pull-down amount to determine the subcooling target temperature. When there is insufficient photovoltaic power, the thermal inertia of the cold storage is used to release the cold first. S3: Calculate the normalized residual based on the theoretical power reference of the refrigeration system and the filtered actual power, and output an energy efficiency abnormality alarm when the residual is abnormal. S4: Calculate the rate of change of photovoltaic power in real time, issue load reduction command before the photovoltaic power drops significantly, and perform disturbance rejection control based on bus voltage; among them, the second-order rate of change of photovoltaic power is used to predict the photovoltaic power drop and reduce the load in advance.

[0006] S5: Switch the operating mode according to the current photovoltaic power, battery SOC, state of heat charge SOT and bus voltage. The operating modes include subcooling absorption mode, cooling energy saving mode and forced bottom protection mode. In step S1, the equivalent energy index of thermal storage and the state of thermal charge (SOT) of the cold storage are calculated as follows: Calculation of internal temperature changes in the cold storage using a first-order thermal resistance-heat capacity model: ; in, The internal temperature of the cold storage. External ambient temperature, For the equivalent thermal resistance of the cold storage, For the equivalent heat capacity of the cold storage, This refers to the cooling capacity power. The cooling capacity power Through the compressor's electrical power Conversion: ; in, The cooling capacity at time t is expressed in kW. is the overall efficiency coefficient of the refrigeration system, and is a dimensionless parameter; Let be the coefficient of performance for cooling under the current operating conditions at time t, which is a dimensionless parameter. The actual electrical power of the compressor at time t is expressed in kW; t represents time.

[0007] Calculate the releaseable and chargeable cold storage energy using the following formula: ; ; in, Cold storage can release cold energy. Cold storage facilities can be filled with cold energy. The upper limit of the allowable temperature for cold storage. This is the lower limit of the permissible subcooling temperature for cold storage. When the rechargeable cooling energy When the unit is kJ, the equivalent electrical energy in kWh is calculated using the following formula: ; This represents the equivalent electrical energy of rechargeable cold energy, expressed in kWh. The overall efficiency coefficient of the refrigeration system; The coefficient of performance (COP) is the coefficient of performance (COP) under the current operating conditions; 3600 is the conversion factor between kJ and kWh.

[0008] Calculate the state of thermal charge (SOT) using the following formula: ; in, The thermal charge state of the cold storage is represented by a value ranging from 0 to 1, which indicates the thermal saturation of the cold storage. Based on the temperature response data caused by compressor start-up and shutdown, the equivalent thermal resistance is updated online using the recursive least squares method. With equivalent heat capacity .

[0009] The power allocation command in step S2 is executed in the following manner: The net power available for subcooled cold storage can be calculated in real time using the following formula: ; in, This is the net power available for subcooled cold storage. To provide real-time output power for the photovoltaic array Based on base load power, Battery charging power, The reference electrical power required for the compressor to maintain the current internal temperature of the cold storage.

[0010] ; ; in, The reference electrical power of the compressor required to maintain the current internal temperature of the cold storage at time t, in kW; Estimating power for heat leakage in cold storage, in kW; This refers to the external ambient temperature, expressed in °C. This refers to the internal temperature of the cold storage, in °C. The equivalent thermal resistance of the cold storage is expressed in °C / kW. The overall efficiency coefficient of the refrigeration system; t represents the theoretical coefficient of performance (COP); t represents time.

[0011] when >0. When the battery SOC reaches the preset high threshold or charging is limited, and the current internal temperature of the cold storage is higher than the lower limit of the supercooling temperature, the supercooling cold storage logic is triggered. The redundant energy integral is mapped to the temperature pull-down amount using the following formula: ; ; in, This is the integral of redundant electrical energy. This refers to the temperature pull-down of the cold storage caused by the aforementioned redundant electrical energy; Calculate the target temperature using the following formula: ; in, The target control temperature for the cold storage; and for Set upper limit constraints to prevent excessive cooling; When solar power is insufficient, reduce the compressor frequency or shut it down to maintain the cold storage temperature by releasing cold air using thermal inertia; when the SOT (State of Temperature) is below the preset low threshold or the temperature approaches... At that time, the compressor is forced to start to maintain a minimum cooling level; By adjusting the compressor frequency, the photovoltaic power is approximately matched to the sum of the base load power and the compressor power, and the minimum operating and shutdown time protection of the compressor and the instantaneous discharge rate limit of the battery are implemented.

[0012] The energy efficiency anomaly diagnosis in step S3 specifically includes: A theoretical electric power benchmark is established based on the first-order thermal resistance and thermal capacity model. ; ; in, Estimating power for heat leakage in cold storage facilities. This serves as the theoretical electrical power reference for the compressor. This is the theoretical coefficient of performance (COP) of the compressor; Calculate normalized residuals ; in, To normalize the residuals, This represents the actual electrical power of the compressor after filtering. The theoretical electrical power of the compressor is used as the reference, and ε is a small constant to prevent the denominator from being zero; Within the sliding window, if the normalized residual continuously exceeds a preset threshold, an energy efficiency outlier is determined and an alarm is output. The normalized residual is only accumulated during the compressor's steady-state operation phase.

[0013] The disturbance rejection control in step S4 specifically includes: Real-time calculation of the first and second rates of change of photovoltaic power: ; ; in, Let be the first-order rate of change of photovoltaic power. Let be the second-order rate of change of photovoltaic power. Real-time output power for the photovoltaic array; When detected When the value is less than 0 and the amplitude exceeds the preset threshold, the compressor power is reduced in advance to achieve predictive active unloading; If the bus voltage drops below the preset lower limit or the rate of decrease exceeds the preset threshold, a forced load limiting or degradation strategy will be triggered.

[0014] The operating modes also include standby / heat preservation mode and fault / degradation mode.

[0015] In step S5, when the sensor fails or communication fails, the system enters the fault / degradation mode, and the compressor runs at a preset fixed frequency.

[0016] The beneficial effects of this invention are as follows: By quantifying the thermal inertia of cold storage into a state of thermal charge (SOT) using a first-order thermal resistance and thermal capacity model, and identifying the model parameters online, the cold storage has been transformed from a passive load to an active virtual energy storage role, providing quantifiable thermal reserve indicators for energy dispatch. By utilizing a power allocation strategy that combines SOT and SOC, excess power is converted into cold energy storage through supercooling when photovoltaic power is in surplus, and thermal inertia is used to replace battery discharge when photovoltaic power is insufficient. This effectively suppresses the impact of compressor start-up and shutdown on the battery and significantly improves the photovoltaic absorption rate. By using the normalized residual analysis of the theoretical power benchmark and the filtered actual power, online self-diagnosis of cooling energy efficiency is realized, which can issue early warning in the early stage of COP deterioration, making up for the shortcomings of the traditional hardware protection response lag. By predicting the power drop caused by cloud cover through the second-order rate of change of photovoltaic power and reducing the load in advance, combined with the bus voltage backup protection, the risk of power outage caused by photovoltaic power drop is effectively reduced, and the system's adaptability to fluctuating operating conditions is enhanced. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 System control architecture and energy flow topology diagram; Figure 2 Overall flowchart of the method; Figure 3 A comparison chart of photovoltaic power changes and cold storage temperature response, in which... Figure 3 In the diagram, (a) represents the change in photovoltaic power over time. Figure 3 (b) in the figure represents the response relationship between the internal temperature of the cold storage and the traditional solution over time; Figure 4 : Predictive load shedding response characteristic curve based on the second-order rate of change of photovoltaic power a(t); Figure 5 Normalized residual diagnosis and alarm flowchart. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] The system control architecture and energy flow direction adopted in this invention are as follows: Figure 1 As shown, the overall execution flow of the energy scheduling method is as follows: Figure 2 As shown. Figure 1 middle, Let be the charging and discharging power of the energy storage battery at time t, expressed in kW; when only the charging power of the battery is represented, it is denoted as . ; The DC bus voltage at time t is expressed in V. An energy dispatching method for an off-grid integrated inverter control unit based on the thermal inertia of cold storage includes the following steps: S1: Data Acquisition and Thermal Energy Storage Calculation The internal temperature of the cold storage, the external ambient temperature, and the power of the compressor are obtained. The equivalent energy index of the cold storage's thermal energy storage and the state of charge (SOT) are calculated using a first-order thermal resistance-heat capacity model of the cold storage. Calculation of internal temperature changes in the cold storage using a first-order thermal resistance-heat capacity model: ; in, The internal temperature of the cold storage. External ambient temperature, For the equivalent thermal resistance of the cold storage, For the equivalent heat capacity of the cold storage, This refers to the cooling capacity power. Cooling capacity power Through the compressor's electrical power Conversion: ; in, The cooling capacity at time t is expressed in kW. is the overall efficiency coefficient of the refrigeration system, and is a dimensionless parameter; Let be the coefficient of performance for cooling under the current operating conditions at time t, which is a dimensionless parameter. The actual electrical power of the compressor at time t is expressed in kW; t represents time.

[0021] Calculate the releaseable and chargeable cold storage energy using the following formula: ; ; in, Cold storage can release cold energy. Cold storage facilities can be filled with cold energy. The upper limit of the allowable temperature for cold storage. This is the lower limit of the permissible subcooling temperature for cold storage. When the rechargeable cooling energy When the unit is kJ, the equivalent electrical energy in kWh is calculated using the following formula: ; This represents the equivalent electrical energy of rechargeable cold energy, expressed in kWh. The overall efficiency coefficient of the refrigeration system; The coefficient of performance (COP) is the coefficient of performance (COP) under the current operating conditions; 3600 is the conversion factor between kJ and kWh.

[0022] Calculate the state of thermal charge (SOT) using the following formula: ; in, The thermal charge state of the cold storage is represented by a value ranging from 0 to 1, which indicates the thermal saturation of the cold storage. Based on the temperature response data caused by compressor start-up and shutdown, the equivalent thermal resistance is updated online using the recursive least squares method. With equivalent heat capacity .

[0023] S2: Cooling / Release Power Allocation Based on the State of Thermal Charge (SOT), the State of Charge (SOC) of the battery, and the photovoltaic power, power allocation is performed in either a charging-cooling mode or a releasing-cooling mode. SOT and SOC work together for power allocation. When photovoltaic power is abundant, redundant power is integrated and mapped to a temperature pull-down amount to determine the subcooling target temperature. When photovoltaic power is insufficient, the thermal inertia of the cold storage is used for releasing coolness first. Power allocation commands are executed as follows: The net power available for subcooled cold storage can be calculated in real time using the following formula: ; in, This is the net power available for subcooled cold storage. To provide real-time output power for the photovoltaic array Based on base load power, Battery charging power, The reference electrical power required for the compressor to maintain the current internal temperature of the cold storage.

[0024] ; ; in, The reference electrical power of the compressor required to maintain the current internal temperature of the cold storage at time t, in kW; Estimating power for heat leakage in cold storage, in kW; This refers to the external ambient temperature, expressed in °C. This refers to the internal temperature of the cold storage, in °C. The equivalent thermal resistance of the cold storage is expressed in °C / kW. The overall efficiency coefficient of the refrigeration system; t represents the theoretical coefficient of performance (COP); t represents time.

[0025] when >0. When the battery SOC reaches the preset high threshold or charging is limited, and the current internal temperature of the cold storage is higher than the lower limit of the supercooling temperature, the supercooling cold storage logic is triggered. The redundant energy integral is mapped to the temperature pull-down amount using the following formula: ; ; in, This is the integral of redundant electrical energy. This refers to the temperature pull-down of the cold storage caused by the aforementioned redundant electrical energy; Calculate the target temperature using the following formula: ; in, The target control temperature for the cold storage; and for Set upper limit constraints to prevent excessive cooling; When solar power is insufficient, reduce the compressor frequency or shut it down to maintain the cold storage temperature by releasing cold air using thermal inertia; when the SOT (State of Temperature) is below the preset low threshold or the temperature approaches... At that time, the compressor is forced to start to maintain a minimum cooling level; By adjusting the compressor frequency, the photovoltaic power is approximately matched to the sum of the base load power and the compressor power. Minimum compressor operation and shutdown time protection and instantaneous battery discharge rate limitation are implemented. A comparison of the cold storage temperature response under varying photovoltaic power conditions using the method of this invention and conventional control methods is provided. Figure 3 As shown. Figure 3 (a) and Figure 3 (b) uses the same time base, where, Figure 3 In the diagram, (a) represents the change in photovoltaic power over time. Figure 3 (b) in the figure represents the temperature response of the cold storage interior over time under the present invention and the conventional scheme. At time t1, the photovoltaic power is in surplus, battery charging is limited, and the cold storage has rechargeable space. The system starts to perform subcooling storage, causing the temperature inside the cold storage to rise from the set temperature. Gradually decrease to the lower limit of the supercooled temperature Nearby; at time t2, a cloud cover event occurs, causing a rapid decrease in photovoltaic power, and the system performs predictive load shedding; at time t3, the system enters a cold release and power saving mode, utilizing the previously stored cold energy to maintain the cold storage temperature, making the cold storage temperature recovery rate under the present invention lower than that of the traditional scheme, thus forming a thermal inertia-driven cold release advantage range.

[0026] S3: Online Energy Efficiency Diagnosis Based on the theoretical power reference of the refrigeration system and the filtered actual power, the normalized residual is calculated, and an energy efficiency anomaly alarm is output when the residual is abnormal; the energy efficiency anomaly diagnosis specifically includes: A theoretical electric power benchmark is established using a first-order thermal resistance and thermal capacity model: ; ; in, Estimating power for heat leakage in cold storage facilities. This serves as the theoretical electrical power reference for the compressor. This is the theoretical coefficient of performance (COP) of the compressor; Calculate normalized residuals ; in, To normalize the residuals, This represents the actual electrical power of the compressor after filtering. The theoretical electrical power of the compressor is used as the reference, and ε is a small constant to prevent the denominator from being zero; Within the sliding window, if the normalized residual continuously exceeds a preset threshold, an energy efficiency outlier is identified and an alarm is output. The normalized residual is only accumulated during the compressor's steady-state operation. The performance diagnosis and alarm process based on theoretical power, filtered actual power, and normalized residual is as follows: Figure 5 As shown.

[0027] S4: Disturbance Rejection Control Real-time calculation of the rate of change of photovoltaic power, including calculation of the first-order and second-order rates of change of photovoltaic power: ; ; in, Let be the first-order rate of change of photovoltaic power. Let be the second-order rate of change of photovoltaic power. To provide real-time output power for the photovoltaic array A preset second-order rate of change threshold is used. Predictive load shedding response characteristics based on the first-order and second-order rates of change of photovoltaic power are as follows: Figure 4 As shown.

[0028] When it is detected that a(t) < 0 and its absolute value |a(t)| exceeds the preset second-order rate of change threshold, the compressor power command is reduced in advance to achieve predictive active unloading.

[0029] If the bus voltage drops below the preset lower limit or the rate of decrease exceeds the preset threshold, a forced load limiting or degradation strategy will be triggered.

[0030] S5: Operating Mode Switching Based on the current photovoltaic power, battery SOC, state of thermal charge SOT and bus voltage, the operating mode is switched. The operating modes include subcooling absorption mode, cooling release power saving mode and forced bottom protection mode. Supercooling absorption mode: When there is surplus photovoltaic power and limited battery charging, redundant power is used to supercool the cold storage, converting electrical energy into cold energy for storage.

[0031] Cooling and energy-saving mode: When photovoltaic power is insufficient, the cold storage thermal inertia is used first to release cold, reducing the operating frequency of the compressor or stopping it to reduce battery discharge.

[0032] Forced minimum protection mode: When SOT falls below a preset low threshold or the temperature approaches... At that time, the compressor is forced to start to maintain cooling and prevent the cold storage temperature from exceeding the standard.

[0033] Example This embodiment uses a 6.2kW inverter-controlled integrated machine driving a 20-cubic-meter variable frequency cold storage unit as an example to illustrate the execution process of the present invention in detail. The following values ​​are exemplary operating parameters based on 16 300W photovoltaic panels (8 series and 2 parallel), a 15kWh lithium battery pack, and a 20-cubic-meter variable frequency cold storage unit, used to explain the specific execution process of the method of the present invention.

[0034] S1: Data Acquisition and Thermal Energy Storage Calculation Set the cold storage reference temperature Set the upper limit of allowed fluctuations. Set the lower limit of the supercooled temperature. .

[0035] The initial value of the equivalent thermal resistance of the cold storage is set as follows: =5.26℃ / kW, the initial value of the equivalent heat capacity is set to During system operation, based on the cold storage temperature response data caused by compressor start-up and shutdown, the equivalent thermal resistance is calculated using the recursive least squares method. and equivalent heat capacity Perform online corrections.

[0036] Let the real-time monitored environmental data be: ambient temperature Photovoltaic input power .

[0037] At this point, the lithium battery pack has a SOC of 95% and has entered the constant voltage and current limiting charging stage. The battery charging power... Limited to approximately 0.5kW. Base load power. .

[0038] Current storage temperature =-15℃. Compressor efficiency coefficient. =0.9, under current operating conditions, the coefficient of performance (COP) is 2.5, and the compressor power is... =3.8kW. Substitute into the formula to calculate the cooling capacity power: =0.9×2.5×3.8=8.55kW; The rate of temperature change inside the cold storage is calculated using a first-order thermal resistance-heat capacity model. Current storage temperature. The system remains stable at -15°C, indicating that it is in thermal equilibrium, and the cooling capacity equals the heat leakage. =8.55kW, reverse calculation of current equivalent thermal resistance: ; After online correction using the recursive least squares method, the current equivalent thermal resistance is... =5.26°C / kW, substitute into: =0℃ / s; The calculation result is approximately 0, indicating that the cooling capacity power and the heat leakage power of the cold storage are approximately balanced, and the internal temperature of the cold storage is in a stable state.

[0039] Calculate the releasable cold energy of the cold storage: =4600×(0-(-15))=4600×15=69000kJ; Calculate the available cooling energy: =4600×(-15-(-22))=4600×7=32200kJ; Converted to equivalent electrical energy: ≈3.98kWh; This means that the cold storage facility can currently absorb approximately 4.0 kWh of electrical energy and convert it into cold energy for storage.

[0040] The algorithm calculates the State of Heat Charge (SOT) in real time. Current storage temperature. Substitute into the formula to calculate: ≈0.68; Current available rechargeable cold energy space = The cold storage facility was determined to have sufficient potential to accommodate redundant energy.

[0041] S2: Cooling / Release Power Allocation In another scheduling cycle following the stable operating condition described in S1, photovoltaic irradiance is further enhanced, and the output power of the photovoltaic array reaches [a certain value]. =4.8kW. At this point, the battery state of charge reaches a preset high threshold, and the battery management system limits further charging, therefore the battery charging power... =0kW; Base load power =0.3kW. Based on the thermal equilibrium state described in S1, the base power of the compressor required to maintain the current internal temperature of the cold storage is: =3.8 kW; Therefore, the net power available for subcooled cold storage is: = =4.8 - 0.3 - 0 - 3.8 = 0.7kW The target power of the compressor at this time is: = + =4.5kW in, This refers to the target electrical power supplied to the compressor in subcooled cold storage mode, measured in kW.

[0042] The compressor's target power of 4.5kW is lower than the integrated inverter's rated power of 6.2kW, thus meeting the operating power constraint. Because... >0, the battery is in a limited charging state, and the current internal temperature of the cold storage is higher than the lower limit of the supercooling temperature, so the system triggers the supercooling absorption mode.

[0043] Assuming the net subcooling power duration is 60 seconds, the net subcooling energy is: ; Algorithm calculates temperature pull-down amount: ; Based on the current internal temperature of the cold storage =-15℃ and the calculated pulling amount at the temperature =0.021℃, the target control temperature is:

[0044]

[0045] While redundant power persists, the controller continues to reduce the target temperature, but the target temperature must not fall below [a certain level]. =-22℃.

[0046] Based on the above calculations, the controller sets the target control temperature for the current scheduling cycle to [value]. =-15.021℃, and update the target control temperature on a rolling basis according to the redundant energy integration results in subsequent scheduling cycles; at the same time set ≥ A lower limit constraint of -22℃ is set to prevent excessive overcooling. The controller increases the compressor's target power from 3.8kW, required to maintain the current storage temperature, to approximately 4.5kW, utilizing 0.7kW of the net overcooling power for cold storage. When the photovoltaic surplus persists, the controller continuously updates the net overcooling energy, temperature pull-down, and target control temperature in subsequent scheduling cycles, while ensuring that the target control temperature does not fall below the lower limit of the overcooling temperature. =-22℃.

[0047] When solar power is insufficient, reduce the compressor frequency or shut it down to maintain the cold storage temperature by releasing cold air using thermal inertia; when the SOT (State of Temperature) is below the preset low threshold or the temperature approaches... When necessary, the compressor is forced to start to ensure basic cooling; the compressor frequency is adjusted to make the photovoltaic power approximately match the sum of the base load power and the compressor power.

[0048] S3: Online Energy Efficiency Diagnosis After the system returns to steady-state operation, the algorithm performs closed-loop performance analysis.

[0049] Theoretical power benchmark calculation: Based on the current working conditions ( =30℃, =-15℃, =5.26℃ / kW, =2.5), calculate the theoretical heat leakage:

[0050] Theoretical power reference:

[0051] Residual determination: Actual measured compressor power after low-pass filtering .

[0052] Calculate the normalized residual:

[0053] The actual electrical power of the compressor after filtering during normal system operation Compressor theoretical electrical power benchmark Approximation, normalized residual Approaching zero. When the energy efficiency of a refrigeration system deteriorates, for example, dust accumulation on the condenser causes the coefficient of performance (COP) to drop from 2.5 to approximately 1.8, the product of the overall efficiency coefficient and the COP decreases from 2.25 to approximately 1.62. To maintain the same cooling capacity, the power... kW, the actual electrical power of the compressor increases to: =8.55 / (0.9) 1.8) ≈ 5.28kW; = ≈0.39; If the residual exceeds the preset residual threshold of 0.3 for 10 consecutive frames (1 second per frame), it is determined to be an energy efficiency outlier.

[0054] Abnormal Output: Upon triggering, the inverter control unit panel displays an "E03" alarm code, prompting the user to perform preventative maintenance (such as cleaning dust from the condenser and checking the refrigerant charge). In this embodiment, when the COP drops from 2.5 to 1.8, a decrease of approximately 28%, the normalized residual exceeds the preset threshold of 0.3, allowing the system to output an energy efficiency anomaly alarm before further deterioration of cooling performance.

[0055] S4: Disturbance Rejection Control During operation, the system monitored rapid cloud accumulation (simulating typical cloud cover conditions, with photovoltaic power dropping sharply from 4.6kW to 0.8kW within 30 seconds). The first-order rate of change of photovoltaic power was calculated in real time. With second-order rate of change : ; ; Let the sampling period T be s =0.5s, in the steady-state phase before cloud cover occurs, photovoltaic power =4.6kW remains stable, first rate of change ≈0, second rate of change ≈0. Within the first 2 seconds of cloud cover occurrence, photovoltaic power data were continuously collected from 5 photovoltaic power sampling points: 4.55kW, 4.48kW, 4.37kW, 4.22kW, and 4.03kW. The first-order rate of change (difference approximation) was calculated: =(4.48-4.55) / 0.5=-0.14kW / s; =(4.37-4.48) / 0.5=-0.22kW / s; =(4.22-4.37) / 0.5=-0.30kW / s; =(4.03-4.22) / 0.5=-0.38kW / s; Further calculate the second-order rate of change, and denot the second-order rate of change corresponding to the three consecutive sampling intervals as follows: , and : =( - ) / 0.5=(-0.22+0.14) / 0.5=-0.16kW / s 2 ; =( - ) / 0.5=(-0.30+0.22) / 0.5=-0.16kW / s 2 ; =( - ) / 0.5=(-0.38+0.30) / 0.5=-0.16kW / s 2 ; The second-order rates of change for three consecutive sampling periods were calculated as follows: , and All three conditions are met. <0, and | |=0.16 kW / s 2 The second-order rate of change exceeded the preset threshold of 0.10 kW / s for three consecutive sampling periods. 2 Where i = 1, 2, 3. Therefore, the system determines that the photovoltaic power has entered a phase of accelerated decline. Before the bus voltage drops significantly, the system proactively issues a frequency reduction command to the integrated inverter control unit, gradually reducing the compressor operating frequency from 60Hz to 35Hz and the compressor power from 3.8kW to approximately 1.5kW, thereby reducing the instantaneous battery discharge power and the bus voltage drop during the rapid decline in photovoltaic power. If the bus voltage drops below the preset lower limit or the rate of decline exceeds the preset threshold, a forced load limiting or degradation strategy is triggered.

[0056] S5: Operating Mode Switching During the period of persistent cloud cover, the photovoltaic power output further dropped to 0.5kW.

[0057] DC bus voltage was monitored If the voltage drops rapidly from the nominal 48V to 44V and the rate of drop exceeds a preset threshold, the algorithm immediately enters a cooling and power-saving mode, utilizing the supercooled energy (temperature) stored in the cold storage in S2. rebounded to (thermal inertia buffer time), forcing the compressor to enter hibernation.

[0058] During this stage, the lithium battery only needs to support the standby power consumption of the integrated unit (approximately 30W), and the discharge rate is maintained below 0.05C. Approximately 1.5kWh of electrical energy output is replaced by "cooling" due to the thermal inertia of the cold storage. If the traditional solution were used, with the battery supporting the compressor operation throughout, approximately 2.8kWh of electrical energy would be consumed, resulting in higher instantaneous discharge power and greater bus voltage fluctuations.

[0059] To verify the independent contribution of each module of the present invention, an ablation experiment was conducted under the same hardware conditions, with the traditional photovoltaic cold storage control scheme as the baseline. The results are shown in Table 1.

[0060] Table 1 Comparison of Ablation Experiments

[0061] As shown in Table 1, after introducing the thermal model and SOT index (Exp1), the photovoltaic absorption rate increased from 62.3% to 65.1%, and the daily cycle count of the battery decreased slightly. After adding thermal inertia coordinated scheduling (Exp2), the photovoltaic absorption rate increased significantly to 78.4%, and the daily cycle count of the battery plummeted from 18.5 times to 8.7 times, a reduction of 53%. After introducing energy efficiency diagnosis (Exp3), automatic detection of COP degradation was achieved. Finally, after introducing second-order predictive load shedding (Exp4 / this invention), the daily cycle count of the battery further decreased to 5.2 times, and the bus voltage descent depth decreased from the baseline of 12.8V to 5.6V, a reduction of 56%.

[0062] The method of the present invention was compared with existing typical control schemes under the same hardware conditions, and the results are shown in Table 2.

[0063] Table 2 Performance comparison between the method of the present invention and existing solutions

[0064] As shown in Table 2, the method of this invention achieves a photovoltaic absorption rate of 81.2%, which is 18.9 percentage points higher than the traditional start-stop control, 9.7 percentage points higher than the phase change cold storage scheme, and 12.4 percentage points higher than the MPPT scheduling scheme. Regarding the equivalent cycle life of the battery, this invention achieves only 5.2 cycles / day, a reduction of 71.9% compared to the traditional scheme. In terms of bus disturbance immunity, this invention is the only scheme that simultaneously possesses a dual protection mechanism of active predictive load shedding and bus voltage linkage. Regarding energy efficiency self-diagnosis, existing schemes all rely on manual inspection or delayed hardware protection; this invention is the first to achieve online self-diagnosis of cooling energy efficiency based on a thermal resistance and thermal capacity model.

[0065] Based on the comprehensive ablation experiment and overall performance comparison results, the method of this invention realizes the transformation of cold storage from a passive load to an active energy storage role by quantifying the thermal inertia of cold storage into the SOT index. It is significantly superior to the existing scheme in four dimensions: photovoltaic absorption rate, battery cycle life protection, bus disturbance immunity and energy efficiency self-diagnosis. It provides an energy dispatching method that takes into account both economy and reliability for off-grid photovoltaic cold storage systems.

Claims

1. An energy scheduling method for an off-grid integrated inverter control unit based on the thermal inertia of cold storage, characterized in that, Includes the following steps: S1: Obtain the internal temperature of the cold storage, the external ambient temperature, and the power of the compressor. Use the first-order thermal resistance and thermal capacity model of the cold storage to calculate the equivalent energy index of the thermal energy storage and the state of thermal charge (SOT) of the cold storage. S2: Based on the stated thermal state of charge (SOT), battery state of charge (SOC), and photovoltaic power, perform power allocation in either charging-cooling mode or releasing-cooling mode. S3: Calculate the normalized residual based on the theoretical power reference of the refrigeration system and the filtered actual power, and output an energy efficiency abnormality alarm when the residual is abnormal. S4: Calculate the rate of change of photovoltaic power in real time, issue load reduction command before photovoltaic power drops significantly, and perform disturbance rejection control based on bus voltage; S5: Switch the operating mode according to the current photovoltaic power, battery SOC, state of heat charge SOT and bus voltage. The operating modes include subcooling absorption mode, cooling energy saving mode and forced bottom protection mode. In step S1, the equivalent energy index of thermal energy storage includes the equivalent heat capacity of cold storage. Respectively with the upper limit of temperature and the lower limit of supercooled temperature Determined release of cold energy With rechargeable cold energy The thermal charge state SOT is determined by , The current internal temperature of the cold storage is normalized and determined, and the equivalent thermal resistance and equivalent heat capacity are updated online based on the compressor start-stop temperature response data; in step S2, SOT and SOC are used together for power allocation. When there is excess photovoltaic power, the redundant power is mapped to the temperature pull-down amount to determine the subcooling target temperature. When there is insufficient photovoltaic power, the thermal inertia of the cold storage is used to release the cold first; in step S4, the photovoltaic power drop is predicted by the second-order rate of change of photovoltaic power and the load is reduced in advance.

2. The energy scheduling method for an off-grid integrated inverter control unit based on the thermal inertia of cold storage as described in claim 1, characterized in that, The equivalent energy index and state of thermal charge (SOT) of the cold storage in step S1 are calculated as follows: Calculation of internal temperature changes in the cold storage using a first-order thermal resistance-heat capacity model: ； in, The internal temperature of the cold storage. External ambient temperature, For the equivalent thermal resistance of the cold storage, For the equivalent heat capacity of the cold storage, This refers to the cooling capacity power. The cooling capacity power Through the compressor's electrical power Conversion: ； in, The cooling capacity at time t is expressed in kW. is the overall efficiency coefficient of the refrigeration system, and is a dimensionless parameter; Let be the coefficient of performance for cooling under the current operating conditions at time t, which is a dimensionless parameter. The actual electrical power of the compressor at time t is expressed in kW; t represents time. Calculate the releaseable and chargeable cold storage energy using the following formula: ； ； in, Cold storage can release cold energy. Cold storage facilities can be filled with cold energy. The upper limit of the allowable temperature for cold storage. This is the lower limit of the permissible subcooling temperature for cold storage; When the rechargeable cooling energy When the unit is kJ, the equivalent electrical energy in kWh is calculated using the following formula: ； in, This represents the equivalent electrical energy of rechargeable cold energy, expressed in kWh. The overall efficiency coefficient of the refrigeration system; This represents the coefficient of performance (COP) under the current operating conditions; 3600 is the conversion factor between kJ and kWh. Calculate the state of thermal charge (SOT) using the following formula: ； in, The thermal charge state of the cold storage is represented by a value ranging from 0 to 1, which indicates the thermal saturation of the cold storage. Based on the temperature response data caused by compressor start-up and shutdown, the equivalent thermal resistance is updated online using the recursive least squares method. With equivalent heat capacity .

3. The energy scheduling method for an off-grid integrated inverter control unit based on the thermal inertia of cold storage as described in claim 1, characterized in that, The power allocation in the charging or releasing mode described in step S2 is performed as follows: The net power available for subcooled cold storage can be calculated in real time using the following formula: ； in, This is the net power available for subcooled cold storage. To provide real-time output power for the photovoltaic array Based on the base load power, Battery charging power, The required reference electrical power for the compressor to maintain the current internal temperature of the cold storage. ； ； in, The reference electrical power of the compressor required to maintain the current internal temperature of the cold storage at time t, in kW; Estimating power for heat leakage in cold storage, in kW; This refers to the external ambient temperature, expressed in °C. This refers to the internal temperature of the cold storage, in °C. The equivalent thermal resistance of the cold storage is expressed in °C / kW. The overall efficiency coefficient of the refrigeration system; The theoretical coefficient of performance (COP) is given; t represents time. when >

0. When the battery SOC reaches the preset high threshold or charging is limited, and the current internal temperature of the cold storage is higher than the lower limit of the supercooling temperature, the supercooling cold storage logic is triggered. The redundant energy integral is mapped to the temperature pull-down amount using the following formula: ； ； in, This is the integral of redundant electrical energy. This refers to the temperature pull-down of the cold storage caused by the aforementioned redundant electrical energy; And calculate the target temperature using the following formula: ； in, The target control temperature for the cold storage; and for Set an upper limit constraint to prevent excessive cooling; When solar power is insufficient, reduce the compressor frequency or shut it down to maintain the cold storage temperature by releasing cold air using thermal inertia; when the SOT (State of Temperature) is below the preset low threshold or the temperature approaches... At that time, the compressor is forced to start to maintain a minimum cooling level; By adjusting the compressor frequency, the photovoltaic power is approximately matched to the sum of the base load power and the compressor power, and the minimum operating and shutdown time protection of the compressor and the instantaneous discharge rate limit of the battery are implemented.

4. The energy scheduling method for an off-grid integrated inverter control unit based on the thermal inertia of cold storage as described in claim 1, characterized in that, Step S3, which involves calculating the normalized residual based on the theoretical power reference of the refrigeration system and the filtered actual power, and outputting an energy efficiency anomaly alarm when the residual is abnormal, specifically includes: A theoretical electric power benchmark is established based on the first-order thermal resistance and thermal capacity model. ； ； in, Estimating power for heat leakage in cold storage facilities. This serves as the theoretical electrical power reference for the compressor. The overall efficiency coefficient of the refrigeration system is a dimensionless parameter. This is the theoretical coefficient of performance (COP) of the compressor; Calculate normalized residuals ； in, To normalize the residuals, This represents the actual electrical power of the compressor after filtering. The theoretical electrical power of the compressor is used as the reference, and ε is a small constant to prevent the denominator from being zero; Within the sliding window, if the normalized residual continuously exceeds a preset threshold, an energy efficiency outlier is determined and an alarm is output. The normalized residual is only accumulated during the compressor's steady-state operation phase.

5. The energy scheduling method for an off-grid integrated inverter control unit based on the thermal inertia of cold storage according to claim 1, characterized in that, The disturbance rejection control described in step S4 specifically includes: Real-time calculation of the first and second rates of change of photovoltaic power: ； ； in, Let be the first-order rate of change of photovoltaic power. Let be the second-order rate of change of photovoltaic power. Real-time output power for the photovoltaic array; When detected When the value is less than 0 and the amplitude exceeds the preset threshold, the compressor power is reduced in advance to achieve predictive active unloading; If the bus voltage drops below the preset lower limit or the rate of decrease exceeds the preset threshold, a forced load limiting or degradation strategy will be triggered.

6. The energy scheduling method for an off-grid integrated inverter control unit based on the thermal inertia of cold storage according to claim 1, characterized in that, In step S5, a hysteresis comparator is set for switching between different operating modes. The operating modes also include standby / heat preservation mode and fault / degradation mode.

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