A photovoltaic energy storage collaborative cold supplement control method and system suitable for a variable frequency compressor unit

Abstract

The application relates to a photovoltaic energy storage collaborative cold supplement control method and system suitable for a variable frequency compressor unit. PLC acquires real-time photovoltaic power, energy storage battery SOC, refrigeration space temperature, phase change cold storage unit temperature and compressor state, calls a pre-calibrated compressor power-frequency relationship, calculates battery allowed power supplement and compressor available power; determines the cold storage state according to the phase change temperature platform, temperature change rate and accumulated effective refrigeration capacity, generates a main refrigeration request or a photovoltaic cold supplement request, and selects a target operating frequency allowed by the available power. When the photovoltaic power decreases, the battery power limit supplement, the frequency reduction after the continuous insufficient confirmation and the shutdown at the minimum frequency are sequentially executed; the safety protection shutdown is prior to the minimum operating time, and the normal restart is limited by the minimum shutdown interval. The application matches the compressor operating power with the photovoltaic power, energy storage and cold storage demand, reduces the frequent start-stop caused by photovoltaic fluctuation, and improves the photovoltaic on-site utilization rate and the cold storage control reliability.

Description

Technical Field

[0001] This invention relates to the fields of photovoltaic energy storage cold chain refrigeration and industrial automation control technology, and in particular to a photovoltaic energy storage collaborative cooling control method and system suitable for variable frequency compressor units. Background Technology

[0002] Photovoltaic-powered cold storage containers, mobile cold chain equipment, and off-grid cold storage typically employ compressor refrigeration and are equipped with energy storage batteries or phase change cold storage materials to meet cooling needs during periods of fluctuating solar irradiance and no sunlight. Current control methods often use a fixed threshold temperature as the condition for compressor start / stop, or directly start the compressor when the photovoltaic power reaches a certain threshold.

[0003] The above method has at least the following problems: First, the single photovoltaic power threshold does not take into account the actual input power of the variable frequency compressor at different operating frequencies, which can easily lead to power mismatch where the compressor is allowed to start based on the lowest frequency power but is actually running at a higher frequency. Secondly, short-term fluctuations in photovoltaic power can cause the compressor to start and stop repeatedly. Simply extending the operating time may lead to over-discharge of the energy storage battery. Third, relying solely on the temperature of a single point on the phase change heat storage plate to determine the completion of heat storage makes it difficult to identify the degree of latent heat storage within the phase change platform. Fourth, the priority relationship between normal process shutdown, safety protection shutdown, minimum operation, and minimum shutdown interval is unclear.

[0004] Therefore, a method is needed to unify photovoltaic power supply capacity, energy storage battery safety boundary, compressor power-frequency characteristics, and phase change cold storage state into the same closed-loop control process. Summary of the Invention

[0005] To address the shortcomings of existing production technologies, this applicant provides a photovoltaic energy storage-assisted cooling control method and system suitable for variable frequency compressor units. This effectively solves the problems in existing photovoltaic cold chain control, such as the mismatch between compressor operating frequency and available power, frequent start-stop caused by photovoltaic fluctuations, inaccurate judgment of phase change cold storage completion status, and conflicting protection logic. It ensures that the compressor operating power matches the needs of photovoltaic, energy storage, and cold storage, reduces frequent start-stop caused by photovoltaic fluctuations, and improves the local utilization rate of photovoltaics and the reliability of cold storage control.

[0006] The technical solution adopted in this invention is as follows: A photovoltaic energy storage-assisted cooling control method for variable frequency compressor units is provided, applicable to a cold chain refrigeration system including a photovoltaic power generation unit, a photovoltaic energy storage converter, an energy storage battery, a programmable logic controller, a variable frequency compressor unit, and a phase change cold storage unit; the control method includes the following steps: S1. Obtain real-time photovoltaic power Ppv, energy storage battery state of charge SOC, cold storage space temperature Tbox, phase change cold storage unit temperature Tpcm, and the operating and fault status of the variable frequency compressor unit. S2. Call the pre-calibrated compressor power-frequency correspondence Pc(f), determine the battery allowable compensation power Pbat_allow based on the SOC and the allowable discharge power given by the battery management system, and calculate the compressor available power Pavail based on Ppv, Pbat_allow, cooling auxiliary load power Paux and reserved power margin Pres. S3. Based on Tbox and the cold storage state Scold determined by Tpcm, the temperature change rate of Tpcm and the cumulative cooling input of the variable frequency compressor unit, generate a main cooling request or a photovoltaic supplementary cooling request. S4. When the request is valid, select the target operating frequency ftar from Pc(f) that satisfies Pc(f) less than or equal to Pavail, and control the operation of the variable frequency compressor unit according to the limited frequency change rate. S5. When Ppv is insufficient relative to the power required for current operation, the power difference is first made up by the energy storage battery within the range of Pbat_allow. After the power deficiency continues for a preset confirmation time, the operating frequency is reduced. If the operating power is still not met after the operating frequency is reduced to the lowest continuous operating frequency, the variable frequency compressor unit is controlled to stop. S6. Execute control priorities in the order of safety protection, main cooling, photovoltaic supplementary cooling, and standby, and ensure that safety protection shutdown is not subject to minimum operating time restrictions, and that restart after normal shutdown is subject to minimum shutdown interval restrictions.

[0007] As a further improvement to the above technical solution: Pc(f) is obtained by making the variable frequency compressor unit run stably at multiple discrete frequency points and recording the corresponding input power; the corresponding input power between adjacent discrete frequency points is determined by piecewise linear interpolation, and the minimum continuous operating frequency fmin, the maximum allowable operating frequency fmax and the power value corresponding to each frequency point are stored in the programmable logic controller.

[0008] When SOC is less than or equal to the discharge stop threshold SOCoff, Pbat_allow is zero; when SOC is greater than or equal to the start-up threshold SOCon, Pbat_allow takes the smaller value between the battery management system's allowed discharge power and the preset compensation power limit; when SOC is between SOCoff and SOCon, Pbat_allow continuously decreases according to the position of SOC relative to SOCoff and SOCon to form a battery discharge hysteresis zone.

[0009] Determining the cold storage state Scold includes: judging whether Tpcm has entered the phase change platform based on the phase change temperature range of the phase change material; when Tpcm is in the phase change temperature range and its temperature change rate is not greater than a preset change rate threshold, accumulating the effective cooling capacity determined by Pc(f), the cooling performance coefficient corresponding to the operating frequency, and the sampling period; determining Scold by the ratio of the effective cooling capacity to the rated cold storage capacity of the phase change cold storage unit, and correcting Scold using the temperature events when the phase change cold storage unit reaches the complete release or complete cold storage state.

[0010] The main cooling request is generated when Tbox reaches the main cooling start threshold; the photovoltaic cooling request is generated when the main cooling request is invalid, the current period is allowed for supplemental cooling, Scold is not greater than the supplemental cooling start threshold, SOC is not less than SOCon and Pavail can maintain the minimum continuous operating frequency fmin; the photovoltaic cooling request is revoked when Scold reaches the supplemental cooling completion threshold and Tpcm remains below the cold storage completion temperature for a preset duration.

[0011] The Ppv is low-pass filtered and the photovoltaic power change rate is calculated. When the filtered Ppv decreases but the power deficiency duration is less than the preset confirmation duration, the energy storage battery provides transient compensation. When the power deficiency duration reaches the preset confirmation duration, the target operating frequency is reduced by a preset frequency step size. When the filtered Ppv recovers and continues to reach the recovery confirmation duration, the target operating frequency is increased at a rate not greater than the preset frequency ramp.

[0012] The minimum running time is the greater of the time required for the compressor to establish a stable lubrication state and the photovoltaic transient fluctuation filtering time. The minimum shutdown interval is the greater of the time required for the high and low pressure balance of the refrigeration system and the time required for motor cooling. The minimum shutdown interval is achieved by the power-on delay timing process triggered by the shutdown event of the variable frequency compressor unit, and the first start is allowed by the first start permission flag when the system is first powered on.

[0013] When a compressor failure, abnormal refrigeration system pressure, SOC reaching the safety lower limit, or inverter protection signal is detected, a safety protection shutdown is immediately executed. When the communication with the photovoltaic energy storage converter or battery management system is abnormal for a set number of consecutive times, the generation of photovoltaic supplementary cooling requests is prohibited, and the system switches to a degraded control mode that only performs main cooling based on the Tbox and limits the maximum operating frequency.

[0014] A photovoltaic energy storage coordinated cooling control system for variable frequency compressor units includes a photovoltaic power generation unit, a photovoltaic energy storage converter, an energy storage battery, a battery management system, a programmable logic controller (PLC), a frequency converter, a variable frequency compressor unit, a cold storage space temperature sensor, and a phase change cold storage unit temperature sensor. The PLC is communicatively or electrically connected to the photovoltaic energy storage converter, the battery management system, the frequency converter, and each temperature sensor, and is configured to execute a photovoltaic energy storage coordinated cooling control method.

[0015] As a further improvement to the above technical solution: The phase change cold storage unit includes at least one phase change cold storage plate disposed in the cold storage space. The temperature sensor of the phase change cold storage unit is disposed in the phase change material region of the phase change cold storage plate or at a position thermally coupled to the phase change material region. The phase change temperature range of the phase change material matches the target temperature range of the cold storage space.

[0016] The beneficial effects of this invention are as follows: Compared with the control method of starting and stopping based on a fixed power threshold, this invention determines the target frequency based on the actual power-frequency relationship of the compressor, so as to keep the start permission, operating frequency and available energy supply capacity consistent; it handles photovoltaic fluctuations in sequence by limiting battery power, confirming continuous insufficient power, reducing frequency and shutting down, thereby protecting the energy storage battery and reducing unnecessary start-stops; it improves the reliability of cold storage completion determination by identifying the phase change platform and accumulating effective cooling capacity; and it avoids conflicts between minimum operating protection and safety protection by clearly defining the priority of safe shutdown and normal shutdown.

[0017] In addition, the present invention also has the following advantages: (1) This invention establishes an RS485-based communication connection between the PLC and the PCS, and enables the PLC to acquire photovoltaic power generation data in real time through a periodic acquisition process, thereby realizing dynamic response to solar energy resources and significantly improving photovoltaic utilization. Traditional methods rely solely on temperature threshold triggering and cannot detect changes in photovoltaic power, resulting in a large amount of photovoltaic power being wasted.

[0018] (2) This invention constructs a triple joint judgment logic of daytime period flag bit + photovoltaic power threshold + battery SOC threshold to ensure that the cooling operation is only performed under the condition of sufficient energy, avoiding the non-optimal operation state of having light but no electricity available or forcibly consuming power under low irradiance. Such a systematic multi-condition joint judgment mechanism has not been seen in the prior art.

[0019] (3) This invention effectively prevents the variable frequency compressor unit from frequently starting and stopping due to light fluctuations by setting a minimum running timer T1 (30 minutes) and a minimum interval timer T2 (30 minutes). T1=30 minutes is determined based on statistical data of the duration distribution of cloud cover events (82% of the events are <30 minutes), and T2=30 minutes is determined based on the minimum shutdown interval recommended by the scroll compressor manufacturer. These parameters have sufficient engineering basis and are not arbitrarily selected.

[0020] (4) The present invention achieves seamless connection between photovoltaic power generation and battery energy storage by automatically supplementing the difference when the photovoltaic power is insufficient through the battery power compensation step, ensuring that the compressor input power is always not lower than the minimum safe operating power, and improving the reliability and continuity of system operation.

[0021] (5) The present invention achieves a complete intelligent control closed loop by coordinating the dual-mode operation of the main cooling mode and the photovoltaic supplementary cooling mode, and by prioritizing the main cooling request over the photovoltaic supplementary cooling request. This balances the reliability of cold preservation and the utilization rate of photovoltaics.

[0022] (6) Through standardized operating procedures and parameter matching, this invention can be widely applied to remote areas, mobile cold chain equipment and off-grid refrigeration facilities and other scenarios with high energy self-sufficiency requirements, and has good practicality and promotion value. Attached Figure Description

[0023] Figure 1 This is a block diagram of the photovoltaic energy storage collaborative cooling control system of the present invention.

[0024] Figure 2 This is a block diagram of the control data processing and closed-loop regulation of the present invention.

[0025] Figure 3 This is a flowchart of the photovoltaic energy storage coordinated cooling control method of the present invention.

[0026] Figure 4 This is a schematic diagram illustrating the mode priority and power insufficiency response of the present invention.

[0027] Among them: 100, photovoltaic power generation units; 200. Photovoltaic energy storage converter; 300. Energy storage batteries and battery management systems; 400. PLC controller; 500. Variable frequency compressor unit; 510. Frequency converter; 600. Refrigerated space; 610. Temperature sensor for refrigerated space; 620. Phase change cold storage unit; 621. Temperature sensor for phase change cold storage unit. Detailed Implementation

[0028] The specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0029] like Figures 1-4 As shown in this embodiment, the photovoltaic energy storage coordinated cooling control method for variable frequency compressor units is applied to a cold chain refrigeration system including a photovoltaic power generation unit, a photovoltaic energy storage converter, an energy storage battery, a programmable logic controller, a variable frequency compressor unit, and a phase change cold storage unit; the control method includes the following steps: S1. Obtain real-time photovoltaic power Ppv, energy storage battery state of charge SOC, cold storage space temperature Tbox, phase change cold storage unit temperature Tpcm, and the operating and fault status of the variable frequency compressor unit. S2. Call the pre-calibrated compressor power-frequency correspondence Pc(f), determine the battery allowable compensation power Pbat_allow based on the SOC and the allowable discharge power given by the battery management system, and calculate the compressor available power Pavail based on Ppv, Pbat_allow, cooling auxiliary load power Paux and reserved power margin Pres. S3. Based on Tbox and the cold storage state Scold determined by Tpcm, the temperature change rate of Tpcm and the cumulative cooling input of the variable frequency compressor unit, generate a main cooling request or a photovoltaic supplementary cooling request. S4. When the request is valid, select the target operating frequency ftar from Pc(f) that satisfies Pc(f) less than or equal to Pavail, and control the operation of the variable frequency compressor unit according to the limited frequency change rate. S5. When Ppv is insufficient relative to the power required for current operation, the power difference is first made up by the energy storage battery within the range of Pbat_allow. After the power deficiency continues for a preset confirmation time, the operating frequency is reduced. If the operating power is still not met after the operating frequency is reduced to the lowest continuous operating frequency, the variable frequency compressor unit is controlled to stop. S6. Execute control priorities in the order of safety protection, main cooling, photovoltaic supplementary cooling, and standby, and ensure that safety protection shutdown is not subject to minimum operating time restrictions, and that restart after normal shutdown is subject to minimum shutdown interval restrictions.

[0030] Pc(f) is obtained by making the variable frequency compressor unit run stably at multiple discrete frequency points and recording the corresponding input power; the corresponding input power between adjacent discrete frequency points is determined by piecewise linear interpolation, and the minimum continuous operating frequency fmin, the maximum allowable operating frequency fmax and the power value corresponding to each frequency point are stored in the programmable logic controller.

[0031] When SOC is less than or equal to the discharge stop threshold SOCoff, Pbat_allow is zero; when SOC is greater than or equal to the start-up threshold SOCon, Pbat_allow takes the smaller value between the battery management system's allowed discharge power and the preset compensation power limit; when SOC is between SOCoff and SOCon, Pbat_allow continuously decreases according to the position of SOC relative to SOCoff and SOCon to form a battery discharge hysteresis zone.

[0032] Determining the cold storage state (Scold) includes: judging whether Tpcm has entered the phase change platform based on the phase change temperature range of the phase change material; when Tpcm is in the phase change temperature range and its temperature change rate is not greater than a preset change rate threshold, accumulating the effective cooling capacity determined by Pc(f), the cooling performance coefficient corresponding to the operating frequency, and the sampling period; determining Scold by the ratio of the effective cooling capacity to the rated cold storage capacity of the phase change cold storage unit, and correcting Scold using temperature events when the phase change cold storage unit reaches the complete release or complete cold storage state.

[0033] A main cooling request is generated when the Tbox reaches the main cooling start threshold; a photovoltaic cooling request is generated when the main cooling request is invalid, the current period is within the allowed supplemental cooling period, the Scold is not greater than the supplemental cooling start threshold, the SOC is not less than SOCon, and the Pavail can maintain the minimum continuous operating frequency fmin; the photovoltaic cooling request is cancelled when the Scold reaches the supplemental cooling completion threshold and the Tpcm remains below the cold storage completion temperature for a preset duration.

[0034] The Ppv is low-pass filtered and the photovoltaic power change rate is calculated. When the filtered Ppv decreases but the power deficiency duration is less than the preset confirmation time, the energy storage battery provides transient compensation. When the power deficiency duration reaches the preset confirmation time, the target operating frequency is reduced by a preset frequency step size. When the filtered Ppv recovers and continues to reach the recovery confirmation time, the target operating frequency is increased at a rate not greater than the preset frequency ramp.

[0035] The minimum running time is the greater of the time required for the compressor to establish a stable lubrication state and the photovoltaic transient fluctuation filtering time. The minimum shutdown interval is the greater of the time required for the high and low pressure balance of the refrigeration system and the time required for the motor to cool down. The minimum shutdown interval is achieved by the power-on delay timing process triggered by the shutdown event of the variable frequency compressor unit, and the first start is allowed by the first start permission flag when the system is first powered on.

[0036] When a compressor failure, abnormal refrigeration system pressure, SOC reaching the safety lower limit, or inverter protection signal is detected, a safety protection shutdown is immediately executed. When the communication with the photovoltaic energy storage converter or battery management system is abnormal for a set number of consecutive times, the generation of photovoltaic supplementary cooling requests is prohibited, and the system switches to a degraded control mode that only performs main cooling based on the Tbox and limits the maximum operating frequency.

[0037] The photovoltaic energy storage coordinated cooling control system applicable to variable frequency compressor units in this embodiment includes a photovoltaic power generation unit, a photovoltaic energy storage converter, an energy storage battery, a battery management system, a programmable logic controller, a frequency converter, a variable frequency compressor unit, a cold storage space temperature sensor, and a phase change cold storage unit temperature sensor. The programmable logic controller is communicatively or electrically connected to the photovoltaic energy storage converter, the battery management system, the frequency converter, and each temperature sensor, and is configured to execute the photovoltaic energy storage coordinated cooling control method.

[0038] The phase change cold storage unit includes at least one phase change cold storage plate disposed in the cold storage space. The phase change cold storage unit temperature sensor is disposed in the phase change material region of the phase change cold storage plate or at a position thermally coupled to the phase change material region. The phase change temperature range of the phase change material matches the target temperature range of the cold storage space.

[0039] The system composition and calibration of the photovoltaic energy storage-assisted cooling control system in this embodiment are as follows: like Figure 1 As shown, the photovoltaic power generation unit 100 is connected to the photovoltaic energy storage converter 200, which is connected to the energy storage battery and battery management system 300 and the frequency converter 510. The frequency converter 510 drives the variable frequency compressor unit 500. The PLC controller 400 reads the real-time photovoltaic power of the photovoltaic energy storage converter 200 through the RS485 communication interface, and reads the SOC, allowable discharge power and battery fault status provided by the battery management system; the PLC controller 400 reads the temperature sensors 610 and 621 through the analog or digital communication interface, reads the compressor operation and fault status through the digital input interface, sends the operation permission through the digital output interface, and sends the frequency command to the frequency converter 510 through the analog output or fieldbus.

[0040] The phase change cold storage unit 620 is installed within the cold storage space 600, and its phase change temperature range should match the target temperature range of the cold storage space. For example, when used in a freezing environment of approximately -18°C, a phase change material with a phase change temperature range of -23°C to -18°C can be selected; when used in a cold storage environment, a material with a correspondingly higher phase change temperature should be selected. The temperature sensor 621 is installed in the phase change material region or at a location where it is stably thermally coupled to it, avoiding the use of temperature parameters that do not match the operating temperature range of the phase change material.

[0041] During the equipment commissioning phase, the compressor was run stably at fmin, several intermediate frequencies, and fmax, and the input power and coefficient of performance (COP) were recorded to form calibration tables for Pc(f) and COP(f). Taking a variable frequency compressor with a rated input power of 8.5kW and a minimum continuous operating frequency of 30Hz as an example, the input power corresponding to 30Hz can be determined by actual measurement to be approximately 3.2kW, while the power corresponding to 50Hz is calibrated according to the actual rated operating conditions; the controller cannot use the power corresponding to 30Hz as the starting basis for 50Hz operation.

[0042] The cold storage state identification process in this embodiment is as follows: The PLC records Tpcm according to a fixed sampling period and calculates the temperature change rate based on m consecutive sampling points. When Tpcm is within the phase change temperature range and the absolute value of the temperature change rate is not greater than r0, the current stage is identified as a phase change platform. After entering the phase change platform, the effective cooling capacity provided by the compressor is accumulated; when Scold reaches the cooling compensation completion threshold and Tpcm is below the solid phase completion temperature τend, the current cooling storage is confirmed to be complete.

[0043] When the system has been shut down for an extended period and the Tpcm is higher than the liquid phase completion temperature, while the temperature in the cold storage space continues to rise, it is confirmed that the phase change cold storage unit has fully released cold, and the Scold is corrected to 0; when the cold storage completion condition is met, the Scold is corrected to 1. This avoids the problem of not being able to distinguish the degree of cold storage using only a single point temperature within the phase change platform.

[0044] The mode determination and power matching in this embodiment are as follows: The PLC first checks for faults, pressure protection, inverter protection, SOC safety lower limit, and communication status. If no safety event occurs, and the Tbox reaches the main cooling start threshold, it enters the main cooling state; if the main cooling request is invalid, and the allowed supplemental cooling period, insufficient Scold, SOC not lower than SOCon, and Pavail sufficient to maintain fmin are simultaneously met, it enters the photovoltaic supplemental cooling state.

[0045] After entering cooling mode, the PLC selects the maximum frequency not exceeding Pavail from the Pc(f) calibration table as ftar, and generates fcmd by limiting the slope. The battery compensation instruction is determined according to the following formula: Pbat_cmd=limit[Pc(fcmd)+Paux+Pres-Ppv_f,0,Pbat_allow] When a decrease in Ppv_f causes a shortfall, Pbat_cmd first smoothly compensates for the shortfall. If the duration of the shortfall is less than the confirmation period, the compressor frequency remains unchanged; if it continues until the confirmation period, the PLC reduces ftar by frequency steps and correspondingly reduces Pbat_cmd; if it has already decreased to fmin and still cannot satisfy Pc(fmin) + Paux + Pres, then the shutdown condition due to insufficient energy is executed. This process avoids short-term cloud cover directly causing shutdown and also avoids the energy storage battery bearing a short-term supplementary power exceeding the allowable range.

[0046] The start / stop protection and abnormal degradation conditions in this embodiment are as follows: After a normal start-up, the continuous running time will be calculated. When the main cooling or supplementary cooling reaches the normal shutdown condition, if the minimum running time has not yet been reached, the current minimum sustainable frequency will be maintained until the minimum running time is met; however, compressor failure, abnormal pressure, inverter protection, or battery safety lower limit are considered safety events and will result in immediate shutdown, regardless of the minimum running time constraint.

[0047] Both normal and safe shutdowns record the shutdown time and start the minimum shutdown interval timer. A restart permission is granted only if the difference between the current time and the shutdown time reaches Toff. Upon initial power-up, if the system has no valid shutdown record, FIRST_START_ALLOW is set to allow the first startup; this flag is reset after the first startup is completed.

[0048] When PCS or BMS communication fails consecutively a set number of times, the PLC freezes the most recent valid energy data but does not continue to generate photovoltaic cooling requests, switching to degraded control mode. In degraded control mode, only necessary main cooling is performed according to the Tbox, and the highest frequency is limited to a preset safe frequency; the photovoltaic cooling mode can only be resumed after communication is restored and valid data is obtained consecutively a specified number of times.

[0049] The PLC cyclic control process in this embodiment is as follows: The control program executes in a cyclic scanning manner: first, it collects and verifies data; second, it updates Scold, Pbat_allow, and Pavail; third, it updates the state machine according to priority; then, it calculates and outputs ftar, fcmd, and Pbat_cmd; finally, it records the operating status of this cycle, the cumulative effective cooling capacity, and the anomaly count. The sampling period can be determined based on the PCS communication speed, the temperature change rate, and the inverter response time.

[0050] The threshold, confirmation time, slope, rated cold storage capacity, and power calibration values ​​in the above embodiments should all be calibrated according to the specific compressor, phase change material, enclosure heat load, and energy storage battery performance. Any use of the available power calculation, phase change cold storage state identification, frequency matching, and graded protection logic described in this invention falls within the technical concept of this invention.

[0051] Because this invention establishes an RS485-based communication connection between the PCS and PLC, and enables the PLC to acquire photovoltaic power generation data in real time through periodic acquisition steps, it achieves dynamic response to solar energy resources and significantly improves photovoltaic utilization. By configuring energy storage batteries and forming a load-priority power supply circuit with the PCS, a complete cold storage process can still be completed under conditions of insufficient sunlight but sufficient battery power, thus improving the reliability of system operation.

[0052] The multi-condition joint judgment mechanism—combining the temperature of the cold storage plate, photovoltaic power, and battery SOC—is implemented through the PLC's internal logic program, improving control safety and energy efficiency. Simultaneously, by setting minimum operating time and start-stop interval limits in the PLC, frequent start-stop cycles of the variable frequency compressor unit are effectively avoided, extending equipment lifespan.

[0053] Overall, this method, through standardized operating procedures and parameter matching, solves the defects of existing technologies such as insufficient energy utilization and inappropriate timing of supplemental cooling, and has good practicality and promotion value.

[0054] The above description is an explanation of the present invention and not a limitation thereof. The scope of the present invention is defined by the claims. Within the scope of protection of the present invention, any form of modification may be made.

Claims

1. A photovoltaic energy storage-assisted cooling control method suitable for variable frequency compressor units, characterized in that: This method is applied to cold chain refrigeration systems that include photovoltaic power generation units, photovoltaic energy storage converters, energy storage batteries, programmable logic controllers, variable frequency compressor units, and phase change cold storage units; the control method includes the following steps: S1. Obtain real-time photovoltaic power Ppv, energy storage battery state of charge SOC, cold storage space temperature Tbox, phase change cold storage unit temperature Tpcm, and the operating and fault status of the variable frequency compressor unit. S2. Call the pre-calibrated compressor power-frequency correspondence Pc(f), determine the battery allowable compensation power Pbat_allow based on the SOC and the allowable discharge power given by the battery management system, and calculate the compressor available power Pavail based on Ppv, Pbat_allow, cooling auxiliary load power Paux and reserved power margin Pres. S3. Based on Tbox and the cold storage state Scold determined by Tpcm, the temperature change rate of Tpcm and the cumulative cooling input of the variable frequency compressor unit, generate a main cooling request or a photovoltaic supplementary cooling request. S4. When the request is valid, select the target operating frequency ftar from Pc(f) that satisfies Pc(f) less than or equal to Pavail, and control the operation of the variable frequency compressor unit according to the limited frequency change rate. S5. When Ppv is insufficient relative to the power required for current operation, the power difference is first made up by the energy storage battery within the range of Pbat_allow. After the power deficiency continues for a preset confirmation time, the operating frequency is reduced. If the operating power is still not met after the operating frequency is reduced to the lowest continuous operating frequency, the variable frequency compressor unit is controlled to stop. S6. Execute control priorities in the order of safety protection, main cooling, photovoltaic supplementary cooling, and standby, and ensure that safety protection shutdown is not subject to minimum operating time restrictions, and that restart after normal shutdown is subject to minimum shutdown interval restrictions.

2. The photovoltaic energy storage-assisted cooling control method for variable frequency compressor units as described in claim 1, characterized in that: Pc(f) is obtained by making the variable frequency compressor unit run stably at multiple discrete frequency points and recording the corresponding input power; the corresponding input power between adjacent discrete frequency points is determined by piecewise linear interpolation, and the minimum continuous operating frequency fmin, the maximum allowable operating frequency fmax and the power value corresponding to each frequency point are stored in the programmable logic controller.

3. The photovoltaic energy storage-assisted cooling control method for variable frequency compressor units as described in claim 1, characterized in that: When SOC is less than or equal to the discharge stop threshold SOCoff, Pbat_allow is zero; when SOC is greater than or equal to the start-up threshold SOCon, Pbat_allow takes the smaller value between the battery management system's allowed discharge power and the preset compensation power limit; when SOC is between SOCoff and SOCon, Pbat_allow continuously decreases according to the position of SOC relative to SOCoff and SOCon to form a battery discharge hysteresis zone.

4. The photovoltaic energy storage-assisted cooling control method for variable frequency compressor units as described in claim 1, characterized in that: Determining the cold storage state Scold includes: judging whether Tpcm has entered the phase change platform based on the phase change temperature range of the phase change material; when Tpcm is in the phase change temperature range and its temperature change rate is not greater than a preset change rate threshold, accumulating the effective cooling capacity determined by Pc(f), the cooling performance coefficient corresponding to the operating frequency, and the sampling period; determining Scold by the ratio of the effective cooling capacity to the rated cold storage capacity of the phase change cold storage unit, and correcting Scold using the temperature events when the phase change cold storage unit reaches the complete release or complete cold storage state.

5. The photovoltaic energy storage-assisted cooling control method for variable frequency compressor units as described in claim 1, characterized in that: The main cooling request is generated when Tbox reaches the main cooling start threshold; the photovoltaic cooling request is generated when the main cooling request is invalid, the current period is allowed for supplemental cooling, Scold is not greater than the supplemental cooling start threshold, SOC is not less than SOCon and Pavail can maintain the minimum continuous operating frequency fmin; the photovoltaic cooling request is revoked when Scold reaches the supplemental cooling completion threshold and Tpcm remains below the cold storage completion temperature for a preset duration.

6. The photovoltaic energy storage-assisted cooling control method for variable frequency compressor units as described in claim 1, characterized in that: The Ppv is low-pass filtered and the photovoltaic power change rate is calculated; when the filtered Ppv decreases but the power deficiency duration is less than the preset confirmation duration, the energy storage battery provides transient compensation; when the power deficiency duration reaches the preset confirmation duration, the target operating frequency is reduced by a preset frequency step size. When the filtered Ppv recovers and continues to recover for the confirmation time, the target operating frequency is increased at a rate not greater than the preset frequency ramp.

7. The photovoltaic energy storage-assisted cooling control method for variable frequency compressor units as described in claim 1, characterized in that: The minimum running time is the greater of the time required for the compressor to establish a stable lubrication state and the photovoltaic transient fluctuation filtering time. The minimum shutdown interval is the greater of the time required for the high and low pressure balance of the refrigeration system and the time required for motor cooling. The minimum shutdown interval is achieved by the power-on delay timing process triggered by the shutdown event of the variable frequency compressor unit, and the first start is allowed by the first start permission flag when the system is first powered on.

8. The photovoltaic energy storage-assisted cooling control method for variable frequency compressor units as described in claim 1, characterized in that: When a compressor failure, abnormal refrigeration system pressure, SOC reaching the safety lower limit, or inverter protection signal is detected, a safety protection shutdown is immediately executed. When the communication with the photovoltaic energy storage converter or battery management system is abnormal for a set number of consecutive times, the generation of photovoltaic supplementary cooling requests is prohibited, and the system switches to a degraded control mode that only performs main cooling based on the Tbox and limits the maximum operating frequency.

9. A photovoltaic energy storage-assisted cooling control system for variable frequency compressor units as described in claim 1, characterized in that: The system includes a photovoltaic power generation unit, a photovoltaic energy storage converter, an energy storage battery, a battery management system, a programmable logic controller (PLC), a frequency converter, a variable frequency compressor unit, a cold storage space temperature sensor, and a phase change cold storage unit temperature sensor. The PLC is communicatively or electrically connected to the photovoltaic energy storage converter, the battery management system, the frequency converter, and each temperature sensor, and is configured to execute the photovoltaic energy storage collaborative cooling control method as described in any one of claims 1 to 8.

10. The control system as described in claim 9, characterized in that: The phase change cold storage unit includes at least one phase change cold storage plate disposed in the cold storage space. The temperature sensor of the phase change cold storage unit is disposed in the phase change material region of the phase change cold storage plate or at a position thermally coupled to the phase change material region. The phase change temperature range of the phase change material matches the target temperature range of the cold storage space.

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