Frequency-limited sliding mode control system of plateau low-temperature heat pump in large temperature and humidity difference environment

Abstract

The application discloses a frequency limiting amplitude sliding mode control system of a plateau low-temperature heat pump under a large temperature and humidity difference environment, relates to the technical field of heat pump frequency conversion control, and comprises a heat occupation module, a frequency limiting amplitude module, a sliding mode construction module and a frequency control module. The heat occupation module calculates an external cold and internal heat occupation amount based on environmental air pressure, device temperature and off-grid electric energy coupling; the frequency limiting amplitude module generates a total frequency limiting amplitude boundary in combination with a refrigeration cycle safety margin and the external cold and internal heat occupation amount; the sliding mode construction module introduces an upper cycle non-execution residual amount compensation and constructs an external cold and internal heat absorption type sliding mode surface; and the frequency control module outputs a final frequency instruction under the constraint of the total frequency limiting amplitude boundary and closes loop transmission of the residual amount. The application overcomes the adjustment conflict between electric control heat reduction and external heating demand under plateau extreme working conditions, eliminates high-frequency buffeting near a dynamic limiting amplitude boundary, and guarantees smooth and safe operation of the unit.

Description

Technical Field

[0001] This invention relates to the field of heat pump frequency conversion control technology, specifically to a frequency limiting sliding mode control system for a low-temperature heat pump operating at high altitudes under conditions of large temperature and humidity differences. Background Technology

[0002] In high-altitude and frigid regions, off-grid multi-energy complementary integrated energy supply systems, comprising distributed wind power, photovoltaic power generation, and energy storage systems, are a key approach to addressing clean heating needs in areas without grid coverage. As the core energy-consuming and heat-generating equipment of this system, the high-altitude low-temperature heat pump typically uses a vapor compression cycle driven by a variable frequency compressor to regulate heating output. Due to the highly unique characteristics of off-grid combined operating conditions at high altitudes, system operation is severely affected by the interplay of environmental boundaries, the refrigeration cycle, and fluctuations on the power supply side. The low air pressure at high altitudes leads to a significant decrease in air density, resulting in a degradation of the convective heat transfer capacity of the outdoor heat exchanger. Simultaneously, the variable frequency drive module and power devices within the outdoor enclosed enclosure, heavily reliant on natural convection or forced air cooling, experience a severe reduction in their heat dissipation efficiency. During winter operation, although the external environment is extremely cold, the intense solar radiation heat input during the day, the high electrical losses of the variable frequency drive itself, and the unstable power fluctuations of the off-grid power supply causing changes in current load can lead to extremely severe heat accumulation inside the electrical control cabin or power devices, making the temperature rise of internal core components easily approach safe limits.

[0003] Conventional low-temperature heat pump controllers typically set the compressor operating frequency boundary to a fixed value, or are entirely dominated by thermodynamic parameters within the refrigeration cycle, such as exhaust temperature, operating current, and suction-discharge pressure ratio. They fail to establish dynamic thermal constraints on the electronic control side caused by factors such as reduced external low-pressure heat dissipation, solar-assisted heat generation, and fluctuations in off-grid power supply. In extreme conditions of extreme cold and severe heat buildup in internal components, the low outlet water temperature caused by the low external temperature strongly encourages conventional control mechanisms to increase the compressor operating frequency to compensate for the heat load shortfall. However, the electronically controlled variable frequency drive side, due to weakened convection and excessive temperature rise, has already reached its permissible operating threshold, urgently requiring a reduction or suppression of the compressor frequency. At this point, a directional conflict arises between the controller's adjustment intent and the actual load-bearing limit of the underlying actuators. Traditional controllers cannot reconcile these constraints, blindly calculating and outputting theoretically excessive frequency commands that are impractical in engineering applications. This results in a long-term input saturation deviation between the theoretical target and the actual operating frequency. Due to the lack of dynamic quantitative measurement of this special constraint state and the absorption and correction mechanism for the limited residual amount across cycles, the switching link of the control system is prone to disordered and frequent control mode jumps near the variable and constrained dynamic amplitude limiting frequency boundary, thereby inducing high-frequency jitter of control commands over a wide range, causing frequent passive intervention of inverter overheating derating, mismatch of the entire unit's heating output, serious lag in the recovery performance of outlet water temperature, and a significant decrease in overall operating energy efficiency, directly threatening the safe operation of the heating system in high-altitude and cold off-grid environments. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a frequency-limiting sliding mode control system for low-temperature heat pumps operating in high-altitude environments with large temperature and humidity differences. This system solves the problems of long-term mismatch between control commands and execution frequencies caused by the variable frequency drive reaching the thermal derating boundary prematurely in high-altitude environments with large temperature and humidity differences and off-grid power supply, the tendency of sliding mode control to generate high-frequency chattering near the dynamic limiting boundary, and the resulting severe degradation of the unit's heating efficiency.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a frequency limiting sliding mode control system for a high-altitude low-temperature heat pump operating under conditions of large temperature and humidity differences, comprising: The thermal occupancy module is used to obtain the current atmospheric pressure, outdoor ambient temperature, electronic control cavity temperature, frequency converter drive temperature, power device temperature, current input power of heat pump and off-grid available margin power. Combined with the internally calibrated start-up occupancy reference power and power supply occupancy amplification factor, it calculates the high altitude low pressure correction term, total electronic control heat synthesis amount and electric power load occupancy rate, and multiplies the three to generate the external cold and internal heat occupancy amount. The frequency limiting module is used to obtain the compressor discharge temperature, compressor operating current, compressor discharge pressure and compressor suction pressure, and calculate the safety margin of discharge temperature, operating current and pressure ratio in combination with the preset rated maximum operating frequency. Based on the minimum value of each safety margin and the rated maximum operating frequency, the upper limit of the cycle side frequency is calculated, and the minimum value of the rated maximum operating frequency attenuated by the external cooling and internal heating occupancy and the upper limit of the cycle side frequency are taken to generate the total frequency limiting boundary. The sliding form construction module is used to calculate the basic sliding form surface based on the target and actual outlet water temperature. It subtracts the product compensation term of the external cooling and internal heating occupancy and the unexecuted residual from the previous cycle from the basic sliding form surface to construct an external cooling and internal heating absorption type sliding form surface. The frequency control module is used to generate an unlimited desired frequency based on an externally cold and internally hot absorbing sliding surface. It outputs a final frequency command constrained by the total frequency limiting boundary. The unexecuted residual in the current cycle is calculated from the difference between the unlimited desired frequency and the final frequency command and passed to the next cycle.

[0006] Preferably, the process of calculating the total heat synthesis amount of the electronic control module by the heat occupancy module includes: The temperature differences between the electronic control cavity, the frequency converter drive, and the power device and the outdoor ambient temperature are calculated as the accumulated waste heat. The differences between the preset upper limit of cavity temperature, upper limit of drive temperature, and upper limit of device temperature and the outdoor ambient temperature are calculated as the available heat dissipation temperature difference. The ratio of accumulated residual heat to available heat dissipation temperature difference is calculated, and the ratio result is limited to the range of zero to one through saturation limiting operation, thereby obtaining the relative heat occupation of the cavity, the relative heat occupation of the drive, and the relative heat occupation of the device. The relative thermal occupancy of the cavity, the relative thermal occupancy of the drive, and the relative thermal occupancy of the device are multiplied by preset thermal occupancy weights, preset thermal occupancy weights, and preset thermal occupancy weights, respectively, and the sum of the multiplication results is used to obtain the total thermal synthesis amount of the electronic control.

[0007] Preferably, the process of the hot-slot module calculating the high-altitude low-voltage correction term and the power load occupancy rate includes: The quotient of standard atmospheric pressure and current atmospheric pressure is used to obtain the high-altitude low-pressure correction term; The sum of the current input power of the heat pump and the starting standby reference power is calculated as the current load occupancy; The total available power capacity of the microgrid is obtained by adding the current load occupancy to the off-grid available surplus power. The power load occupancy rate is obtained by calculating the quotient of the current load occupancy and the total available power capacity of the microgrid.

[0008] Preferably, the process of generating the external cold and internal hot space occupancy amount by the heat occupancy module includes: Multiply the power occupancy amplification factor by the power load occupancy rate, and add one to the product to obtain the sum term; The external cold and internal heat occupancy is generated by multiplying the high altitude and low pressure correction term, the total heat synthesis quantity of the electronic control, and the sum term.

[0009] Preferably, the process by which the frequency limiting module calculates the exhaust temperature safety margin, operating current safety margin, and pressure ratio safety margin includes: The current pressure ratio is obtained by calculating the quotient of the compressor discharge pressure and the compressor suction pressure; The difference between the preset exhaust temperature protection limit and the compressor exhaust temperature is calculated as the numerator, and the difference between the exhaust temperature protection limit and the nominal exhaust temperature is calculated as the denominator. The quotient of the numerator and denominator is calculated, and the quotient is limited to the range of zero to one through saturation limiting operation to obtain the exhaust temperature safety margin. The difference between the preset upper limit of the operating current protection and the compressor operating current is calculated as the numerator, and the difference between the upper limit of the operating current protection and the nominal current of the compressor is calculated as the denominator. The quotient of the numerator and denominator is calculated, and the quotient is limited to the range of zero to one through saturation limiting operation to obtain the operating current safety margin. The difference between the preset pressure ratio protection limit and the current pressure ratio is calculated as the numerator, and the difference between the pressure ratio protection limit and the nominal safe pressure ratio is calculated as the denominator. The quotient of the numerator and denominator is calculated, and the quotient is limited to the range of zero to one through saturation limiting operation to obtain the pressure ratio safety margin.

[0010] Preferably, the process of the frequency limiting module generating the total frequency limiting boundary includes: The minimum value among the exhaust temperature safety margin, operating current safety margin, and pressure ratio safety margin is taken as the product attenuation coefficient. The upper limit of the cycle side frequency is calculated by multiplying the product attenuation coefficient by the rated maximum operating frequency. Add one to the external cooling and internal heating space occupancy to obtain the denominator term, and calculate the quotient of the rated maximum operating frequency and the denominator term to obtain the frequency boundary of the electronic control side. The total frequency limiting boundary is generated by taking the minimum value between the frequency boundary on the electronic control side and the upper limit of the frequency on the cyclic side.

[0011] Preferably, the process of calculating the basic sliding surface using the sliding mode construction module includes: Obtain the target outlet water temperature and the actual outlet water temperature, and calculate the difference between the target outlet water temperature and the actual outlet water temperature to obtain the outlet water temperature error; The normalized temperature error for the current period is obtained by calculating the quotient of the water temperature error and the preset error normalization benchmark. The change in normalized error is obtained by calculating the difference between the normalized temperature error of the current period and the normalized temperature error of the previous period. The normalized error change is multiplied by the preset error change weight, and the product is added to the normalized temperature error of the current cycle to construct the basic sliding surface.

[0012] Preferably, the process of constructing an externally cold and internally heat-absorbing sliding surface using a sliding mold construction module includes: Extract residual data from the previous cycle that was not executed in internal storage; The product compensation term is constructed by multiplying the external cold and internal heat occupancy amount, the unexecuted residual amount from the previous cycle, and the preset external cold and internal heat absorption coefficient. A sliding surface with external cooling and internal heat absorption is constructed by subtracting the product compensation term from the basic sliding surface.

[0013] Preferably, the process by which the frequency control module generates the unlimited desired frequency includes: The sum of the absolute value of the externally cold and internally hot absorbing sliding surface and the preset sliding surface smoothing factor is used as the denominator, and the externally cold and internally hot absorbing sliding surface is used as the numerator. The smoothing ratio is calculated by quotienting the numerator and denominator. The sliding mode frequency adjustment is obtained by multiplying the smoothing ratio by the preset single-cycle sliding mode gain. The unlimited desired frequency is generated by adding the final frequency command of the previous cycle stored internally to the sliding mode frequency adjustment.

[0014] Preferably, the process of the frequency control module outputting the final frequency command and calculating the unexecuted residual in this cycle includes: When the total frequency limiting boundary is lower than the preset minimum stable operating frequency, the final frequency command will be set to zero to execute a shutdown. When the total frequency limiting boundary is not lower than the minimum stable operating frequency, the unlimited expected frequency is limited between the minimum stable operating frequency and the total frequency limiting boundary to obtain the final frequency command; Calculate the difference between the unlimited expected frequency and the final frequency command, calculate the quotient of the difference and the rated maximum operating frequency, and limit the quotient to the range of zero to one through saturation limiting operation to obtain the unexecuted residual for this cycle; The final frequency command and any unexecuted residuals from the current cycle are overwritten into internal memory and passed to the next control cycle.

[0015] Compared with existing technologies, it has the following advantages: This proposed frequency-limiting sliding mode control system for high-altitude low-temperature heat pumps operating under large temperature and humidity differences possesses the ability to address complex composite constraints. Conventional heat pump frequency conversion control typically relies solely on safety parameters within the refrigeration cycle to establish rigid limits, failing to cope with the deterioration of heat dissipation due to low altitude and air pressure, strong radiative heat input, and the multi-dimensional interplay of off-grid power supply fluctuations leading to heat accumulation in power devices. This solution comprehensively collects air pressure, multi-point temperature rise, and available microgrid capacity through a thermal occupancy module, converting these into low-pressure correction, total electrical control heat synthesis, and electrical power load occupancy, and implementing nonlinear coupling to obtain a unified external cooling and internal heat occupancy. Based on the frequency boundary of the electrical control side demodulated from the external cooling and internal heat occupancy, a dual-track decision is made between the lower limit of the conventional refrigeration cycle side, enabling the compressor's frequency upper limit to proactively respond to the thermal limitation state of the internal inverter devices. This solution fundamentally resolves the directional conflict between the strong frequency increase trend caused by extreme external cold and the frequency reduction demand caused by internal electrical control thermal saturation. It ensures that the underlying power components are not triggered by overheating protection shutdown due to blind frequency increase when encountering extreme internal thermal pressure, and significantly improves the hardware operation safety of the unit under harsh off-grid conditions at high altitudes.

[0016] This invention effectively eliminates input saturation and high-frequency switching chattering in sliding mode control near the dynamic limiting boundary by constructing a cross-cycle non-executable frequency residual absorption mechanism. In actual operation, once the actuator is constrained by the aforementioned dynamic frequency boundary, a mismatched residual deviation will occur between the theoretical target and the actual command. Conventional sliding mode laws often blindly follow the outlet water temperature error for integration or gain accumulation when the actuator experiences limiting saturation, leading to disordered jumps in the control mode on the limiting line. This solution captures the difference between the unlimited expected frequency and the final frequency command in real time, converts it into a dimensionless control residual, and transmits it to subsequent cycles. In the sliding surface construction, it actively subtracts the product compensation term generated by the unexecuted residual of the current cycle and the external cooling and internal heating occupancy. The externally cooled and internally heated absorbing sliding surface gives the control surface the adaptive ability to actively relieve pressure and resist saturation correction according to the degree of execution constraints. It cuts off the error accumulation link in the saturation state, thereby eliminating high-frequency switching disturbances near the boundary at the source, ensuring the smoothness of the control output, avoiding frequent passive intervention of the variable frequency drive protection, and improving the overall operating efficiency of the heat pump unit while significantly accelerating the response speed of the outlet water temperature recovery. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the system framework of the present invention.

[0018] Figure 2 This is a schematic diagram of the system execution flow of the present invention. 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figures 1 to 2 This application provides a frequency limiting sliding mode control system for a high-altitude low-temperature heat pump under large temperature and humidity difference conditions, including a thermal occupancy module, a frequency limiting module, a sliding mode structure module, and a frequency control module. The thermal occupancy module acquires outdoor ambient temperature, current atmospheric pressure, electronic control cavity temperature, inverter drive temperature, power device temperature, and current heat pump input power via underlying communication buses such as RS485 or CAN bus and sensor interfaces, and reads off-grid available reserve power from the microgrid energy management system. Simultaneously, based on pre-written upper limits for cavity temperature, drive temperature, and device temperature in the controller, it performs overflow prevention and limiting processing on the underlying data.

[0021] Specifically, the overflow prevention and limiting process uses a preset non-zero constant, such as 0.1 degrees Celsius, as the minimum calculated temperature difference denominator. When the temperature difference between the upper limit of the allowable temperature of the electronic control cavity, the upper limit of the allowable temperature of the drive, or the upper limit of the allowable temperature of the device and the outdoor ambient temperature is less than this minimum calculated temperature difference denominator, the controller forcibly replaces the denominator variable with the minimum calculated temperature difference denominator. Similarly, for the overall power data, a minimum calculated power denominator, such as 1 watt, is set. When the sum of the current input power of the heat pump, the starting standby reference power, and the off-grid available margin power is less than this threshold, a forced replacement is performed. For air pressure data, a minimum calculated air pressure denominator, such as 50 kPa, is set. When the collected current atmospheric pressure is less than this air pressure denominator, it is forcibly replaced with this air pressure denominator. The above technical operations give the control system the ability to prevent numerical crashes when sensor disconnections, short circuits, or communication distortions cause abnormal readings, avoiding overflow in subsequent division operations and ensuring the operational stability of the control algorithm.

[0022] The thermal occupancy module calculates the relative thermal occupancy of the electronic control cavity, frequency converter drive, and power devices respectively.

[0023] Specifically, taking a variable frequency drive (VFD) as an example, the controller calculates the difference between the VFD drive temperature and the outdoor ambient temperature as the residual heat accumulated inside the VFD drive relative to the environment. Simultaneously, it calculates the difference between the drive's maximum allowable temperature and the outdoor ambient temperature as the theoretically available heat dissipation temperature difference in the current environment. The accumulated residual heat and the available heat dissipation temperature difference are then quotiented, and a saturation limiting operation strictly restricts the ratio to the range of zero to one, yielding the dimensionless relative heat occupancy of the drive. Using the same quotient and saturation limiting operation, the module simultaneously calculates the dimensionless relative heat occupancy of the cavity and the relative heat occupancy of the components. This operation transforms multi-point discrete absolute temperature data into a dynamic thermal pressure index relative to the ambient cooling capacity, enabling the system to quantify the degree to which internal components approach thermal overload.

[0024] The thermal occupancy module multiplies the obtained relative thermal occupancy of the cavity, relative thermal occupancy of the drive, and relative thermal occupancy of the device by the corresponding proportion weight parameters, and sums the product results of the three to obtain the total thermal synthesis amount of the electronic control.

[0025] Specifically, the controller retrieves the internally calibrated cavity heat ratio weight, drive heat ratio weight, and device heat ratio weight, and the sum of these three weighting coefficients is limited to one. This weighted summation technique balances the differences in thermal inertia caused by the packaging characteristics and heat conduction paths of different electrical components, so that the final output total thermal synthesis of the electronic control system can comprehensively reflect the thermal limiting critical state of the entire outdoor-side frequency converter electronic control system.

[0026] It should be noted that those skilled in the art can obtain specific weight values ​​by performing conventional temperature rise test calibration based on the differences in heat dissipation power density of different components inside the frequency converter. Generally, power devices, as the core heat source and with the smallest heat capacity, are assigned a higher weight than the frequency converter drive module, while the weight of the frequency converter drive module is higher than that of the electronic control cavity, which has a larger ambient heat capacity.

[0027] The hot occupancy module calculates the high-altitude low-pressure correction term based on the current atmospheric pressure and calculates the power load occupancy rate based on the power acquisition data.

[0028] Specifically, the controller calculates the quotient of the built-in standard atmospheric pressure (101.325 kPa) and the current atmospheric pressure to obtain a high-altitude low-pressure correction term. Simultaneously, it calculates the sum of the heat pump's current input power and the start-up baseline power as the current load occupancy; this current load occupancy is then added to the off-grid available reserve power to obtain the total available electrical capacity of the microgrid. Finally, the quotient of the current load occupancy and the total available electrical capacity of the microgrid is calculated to obtain the power load occupancy rate. The aforementioned high-altitude low-pressure correction term objectively quantifies the impact of low atmospheric pressure at high altitudes on the degradation of convective heat dissipation capacity. Introducing the start-up baseline power into the load calculation is to overcome the control blind spot where the calculated power occupancy is zero during compressor shutdown or low-frequency, low-power consumption phases, thus bidirectionally coupling the heat dissipation degradation caused by air pressure with the heat generation constraints caused by microgrid power shortages.

[0029] It should be noted that the starting standby power can be extracted from the nominal power value corresponding to the lowest stable operating frequency given in the variable frequency compressor specification sheet.

[0030] The thermal occupancy module generates the external cold and internal heat occupancy amount through nonlinear coupling based on the above-mentioned high-altitude low-pressure correction term, total electrical control heat synthesis amount, and electrical power load occupancy rate. Its calculation logic is as follows: In the formula, The external cold and internal heat occupancy is the core output value representing the integration of environmental, electronic control, and power constraint strength. This is a high-altitude, low-pressure correction term, representing a quantification of the degree to which thin air reduces heat dissipation; is the total heat synthesis of the electronic control system, representing the overall internal heat occupancy of the electronic control system after comprehensive weighting; q is the energy supply occupancy amplification factor, representing a constant indicating the degree of amplification of the impact of off-grid power shortage on heat accumulation; Electricity load occupancy rate represents the proportion of electricity consumed by the heat pump unit relative to the total available capacity of the microgrid.

[0031] Specifically, this nonlinear calculation logic adds a factor representing the hardware thermal load state to the factor representing the impact of power fluctuations on the power supply side, resulting in a sum term, and then performs a product synthesis. The generated external cooling and internal heating occupancy is directly sent to subsequent modular calculations as a core feedforward parameter for cross-cycle transmission. The larger this parameter value, the stronger the limiting constraint on internal heating and external cooling. This analytical solution replaces the multivariate nested lookup table judgment rule, reducing the computational power of the frequency converter.

[0032] It should be noted that the power occupancy amplification factor is calibrated based on the power fluctuation immunity level of the matched wind-solar-storage microgrid inverter. In typical off-grid wind-solar-storage power supply scenarios, this power occupancy amplification factor is set between 0.5 and 2.5. The smaller the microgrid capacity or the higher the load fluctuation rate, the higher the value of this amplification factor should be.

[0033] Among them, the frequency limiting module obtains the compressor discharge temperature, compressor operating current, compressor discharge pressure and compressor suction pressure through the underlying data acquisition interface, and extracts the external cooling and internal heat occupancy amount issued by the front-end heat occupancy module, and performs data validity judgment and anti-overflow processing in combination with the compressor's own protection specifications.

[0034] Specifically, to address potential disconnections or communication failures in the underlying sensors, the controller continuously assesses the validity of the aforementioned exhaust temperature, current, and pressure data. When any critical protection data point is invalid, the controller abandons using the estimated value for frequency upscaling and instead forcibly sets the corresponding safety margin to zero. Simultaneously, a minimum intake pressure threshold is set for the current pressure ratio calculation. When the compressor intake pressure falls below this threshold, the pressure ratio safety margin is directly set to zero to avoid division by zero errors. These operations provide the controller with fault protection capabilities in the face of missing sensor data. Resetting the safety margin to zero is equivalent to locking the upper frequency limit to zero in subsequent calculations, thereby ensuring the system can safely shut down under abnormal operating conditions. The aforementioned minimum inhalation pressure threshold is determined by the lower limit of the range of the low-pressure sensor or the maximum allowable low-pressure alarm value of the system, which can be directly obtained from the sensor's specifications by those skilled in the art.

[0035] The frequency limiting module calculates the safety margins for exhaust temperature, operating current, and pressure ratio based on the pre-processed valid data.

[0036] Specifically, the controller calculates the quotient of the compressor discharge pressure and the compressor suction pressure to obtain the current pressure ratio. Then, it calculates the difference between the upper limit of the discharge temperature protection and the compressor discharge temperature as the numerator, and the difference between the upper limit of the discharge temperature protection and the nominal discharge temperature as the denominator. The quotient of these two values ​​is then calculated, and a saturation limiting operation strictly confines the result to the range of zero to one, yielding a dimensionless discharge temperature safety margin. Using the same difference quotient calculation and saturation limiting operation, the controller simultaneously calculates the operating current safety margin and the pressure ratio safety margin. These operations unify operating parameters, which originally had different physical dimensions and alarm thresholds, into a safety attenuation coefficient between zero and one. The smaller the value, the closer the refrigeration cycle is to the protection limit.

[0037] It should be noted that the nominal values ​​of exhaust temperature, compressor nominal current, and nominal safe pressure ratio are parameters determined by those skilled in the art by consulting the pressure-enthalpy diagram operating envelope provided by the variable frequency compressor manufacturer and extracting the recommended rated operating condition design point.

[0038] Based on the above three safety margins and the external cooling and internal heating space occupancy, the frequency limiting module comprehensively generates the total frequency limiting boundary that determines the compressor's highest executable frequency. The calculation process is as follows: In the formula, This is the upper limit of the cycle-side frequency, representing the highest permissible frequency that is only constrained by the refrigeration cycle margin; Rated maximum operating frequency, representing the maximum permissible mechanical operating frequency specified on the compressor's nameplate; This is to ensure a safety margin for exhaust temperature. For operating current safety margin; This is the pressure ratio safety margin; This represents the total frequency limiting boundary, indicating the upper limit of the compressor frequency being dynamically limited. This represents the external cold and internal heat occupancy amount, which is the multi-dimensional comprehensive thermal occupancy constraint value generated by Module 1.

[0039] Specifically, the first step of the formula uses the minimum value among the three refrigeration cycle safety margins as the product attenuation coefficient, and multiplies this product attenuation coefficient by the rated maximum operating frequency to calculate the upper limit of the cycle-side frequency. The second step divides the rated maximum operating frequency by the denominator after adding one to the external cooling and internal heat occupancy, yielding the electronic control-side frequency boundary. This electronic control-side frequency boundary is the rated maximum operating frequency attenuated by the external cooling and internal heat occupancy, and is then compared with the cycle-side upper limit, taking the smaller value. This logic ensures that the compressor's frequency upper limit is no longer solely determined by the overheating or overload state of the refrigeration cycle itself, but rather dynamically transforms the internal heat accumulation limit of the electronic control system into a limiting boundary, preventing the controller from outputting unexecutable frequency ramp commands.

[0040] It should be noted that the rated maximum operating frequency is an inherent hardware specification constant of the compressor. The introduction of this constant ensures that the limiting calculation results are always anchored within the safe hardware-permissible envelope range of the compressor, ensuring the stable operation of the control algorithm.

[0041] The sliding formwork construction module obtains the target outlet water temperature and the actual outlet water temperature, and calculates the normalized temperature error and the basic sliding formwork surface by combining the pre-calibrated error normalization benchmark.

[0042] Specifically, the controller calculates the difference between the target outlet water temperature and the actual outlet water temperature to obtain the outlet water temperature error. To eliminate the interference of the dimensional temperature deviation on the control gain, the controller calculates the quotient of this outlet water temperature error and the error normalization benchmark to obtain the normalized temperature error. Subsequently, the difference between the normalized temperature error of the current control cycle and the previous cycle is calculated to obtain the normalized error change. This normalized error change is multiplied by the internally calibrated error change weight and added to the normalized temperature error of the current cycle to obtain the dimensionless basic sliding surface. The above technical operation transforms the external temperature difference into a control tracking parameter, providing a basic state surface for subsequent sliding mode control.

[0043] It should be noted that the error normalization reference is a built-in calibration constant of the controller with temperature units. To prevent division by zero overflow, the controller automatically verifies this error normalization reference before performing quotient calculations. If its value is abnormally lower than the minimum resolution of the temperature sensor, such as 0.1 degrees Celsius, it is forcibly replaced with the value of that resolution. The specific value of this reference can be calibrated through routine experiments based on the normal temperature fluctuation range allowed for heat pump terminal heating.

[0044] The sliding mode construction module extracts the unexecuted residuals from the previous cycle that are passed across cycles in the internal memory.

[0045] Specifically, the controller directly calls up the unexecuted residual indicators written to memory in the previous control cycle. This operation enables the controller to remember the actuator's constrained state in the previous cycle, transforming the execution constraint phenomenon into a quantifiable indicator that can be directly invoked across cycles.

[0046] It should be noted that when the heat pump system is in the first control cycle of initial startup or recovery from protection shutdown, the unexecuted residual amount and normalized error change amount of the previous cycle stored internally are forcibly reset to zero during the controller initialization phase to avoid abnormal interference from the historical shutdown state on the sliding mode calculation in the early stage of startup.

[0047] Based on the aforementioned basic sliding surface, the unexecuted residual from the previous cycle, and the external cooling and internal heating occupancy amounts issued by the pre-heating occupancy module, the sliding surface construction module constructs an external cooling and internal heating absorption type sliding surface. Its core calculation logic is as follows: In the formula, It is an externally cold and internally hot absorbing sliding surface, representing the anti-vibration control surface after absorbing the limited residual amount; The basic sliding surface represents the standard sliding amount that only considers temperature error and the rate of change of error; The external cooling and internal heating absorption coefficient represents a constant that determines the residual absorption intensity of the sliding mode surface at unexecutable frequencies; The external cold and internal heat occupancy amount represents the multi-dimensional electronically controlled thermal constraint strength value generated by the front-end module; This represents the unexecuted residual from the previous cycle, indicating the proportion of frequency deviation that was theoretically expected to be output in the previous cycle but was intercepted by the boundary.

[0048] Specifically, this nonlinear calculation logic multiplies the external cooling and internal heating occupancy amount with the unexecuted residual from the previous cycle, and adds an adjustment to the external cooling and internal heating absorption coefficient to construct a product compensation term. Subtracting this product compensation term from the basic sliding surface ensures that when the electronic control system is in a state of limited external cooling and internal heating and the frequency increase command was intercepted in the previous cycle, the sliding surface value in the current cycle will actively decrease to weaken the frequency increase trend. This operation prevents the sliding mode controller from continuing to accumulate tracking errors when it is in an input saturation state, and eliminates the high-frequency chattering phenomenon of control commands near the amplitude limit boundary.

[0049] It should be noted that the external cooling and internal heating absorption coefficient is an internally calibrated dimensionless parameter. The larger the value of this coefficient, the stronger the absorption and weakening effect of the external cooling and internal heating state on the residual frequencies that cannot be executed, and the more significant the anti-jitter smoothing effect near the frequency boundary. Those skilled in the art can weigh the smoothness of the amplitude limiting boundary with the temperature tracking response speed and determine the range of values ​​for this coefficient through conventional prototype temperature control tests.

[0050] Among them, the frequency control module, based on the externally cooled and internally heated absorbing sliding surface issued by the pre-mounted sliding mode construction module, combined with the internally calibrated control gain and smoothing parameters, generates the sliding mode frequency adjustment amount and the unlimited expected frequency for this cycle.

[0051] Specifically, the controller calculates the sum of the absolute value of the externally cooled and internally heated absorbing sliding surface and the smoothing factor of the sliding surface as the denominator, and uses the externally cooled and internally heated absorbing sliding surface as the numerator to calculate the quotient and obtain the smoothing ratio. This smoothing ratio is multiplied by the single-cycle sliding gain to obtain the sliding frequency adjustment amount with frequency units. Subsequently, the controller adds the final frequency command of the previous cycle stored internally to the above sliding frequency adjustment amount to generate the unlimited expected frequency for the current cycle. This operation replaces the discontinuous symbol switching logic with a continuous smoothing function, and uses the actual output and executed historical commands as a reference during superposition, avoiding integral saturation and ineffective accumulation of the adjustment amount by the controller.

[0052] It should be noted that both the single-cycle sliding mode gain and the sliding surface smoothing factor are constants tuned internally by the controller. The single-cycle sliding mode gain limits the maximum allowable frequency adjustment step size within a single control cycle, for example, 2 Hz. The sliding surface smoothing factor is used to eliminate high-frequency switching disturbances at zero crossings. Those skilled in the art can determine the values ​​of these constants through conventional closed-loop step response tests.

[0053] The frequency control module compares and decides the unlimited expected frequency with the total frequency limiting boundary issued by the pre-frequency limiting module, and outputs the final frequency command to the compressor inverter drive side.

[0054] Specifically, the controller determines the relationship between the total frequency limiting boundary and the minimum stable operating frequency. When the total frequency limiting boundary is lower than the minimum stable operating frequency, the system is deemed to lack safe operating conditions, and the controller directly sets the final frequency command to zero to execute a shutdown while maintaining protection monitoring. When the total frequency limiting boundary is not lower than the minimum stable operating frequency, the controller limits the unlimited desired frequency between the minimum stable operating frequency and the total frequency limiting boundary to obtain the final frequency command. This operation ensures that the compressor neither exceeds the safety limits of the electronic control and refrigeration cycle, nor enters the low-frequency operating range lacking lubrication, and forcibly cuts off power output to protect the hardware when the system lacks operating conditions. The minimum stable operating frequency refers to the underlying frequency reference, such as 15 Hz, that can maintain normal oil return circulation inside the compressor. This parameter can be extracted from the inverter compressor's specifications and directly written into the controller.

[0055] After outputting the final frequency command, the frequency control module synchronously calculates the unexecuted residual value for the current cycle based on the actual limiting deviation, thus completing the closed-loop update of the control state. Its calculation logic is as follows: In the formula, The unexecuted residual amount for this period represents the proportion of frequency deviations that were intercepted by the amplitude limiting boundary during this period. The unlimited expected frequency represents the theoretical target frequency for this cycle that is not limited. The final frequency instruction represents the control instruction executed at the final output of this cycle. The rated maximum operating frequency represents the highest operating frequency allowed by the compressor hardware. Operator This means that the valid values ​​of the calculation results are limited to the range of zero to one.

[0056] Specifically, the above calculation process obtains the frequency difference between the theoretically expected output and the actual implemented command, divides it by the rated maximum operating frequency to convert it into a dimensionless frequency deviation ratio. The unexecuted residual value from this cycle will be directly passed to the next control cycle as a historical memory state, triggering the residual absorption mechanism of the sliding surface in the next cycle. This closed-loop algorithm enables the control system to have cross-cycle feedback regulation capability, cutting off the error accumulation link when the actuator is in a limited-amplitude saturation state.

[0057] It should be noted that after completing the calculation of unexecuted residual values ​​for the current cycle, the controller synchronously overwrites the final frequency command and unexecuted residual values ​​for the current cycle into the internal memory as historical parameters for the next cycle. If the current cycle is shut down due to protection trigger, the above status record value is forcibly reset to zero to prevent interference from abnormal residual data when the system resumes operation after protection is lifted.

[0058] The above embodiments are only used to illustrate the technical methods of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical methods of the present invention without departing from the spirit and scope of the technical methods of the present invention.

Claims

1. A frequency-limiting sliding mode control system for a low-temperature heat pump operating at high altitudes under conditions of large temperature and humidity differences, characterized in that: include: The thermal occupancy module is used to obtain the current atmospheric pressure, outdoor ambient temperature, electronic control cavity temperature, frequency converter drive temperature, power device temperature, current input power of heat pump and off-grid available margin power. Combined with the internally calibrated start-up occupancy reference power and power supply occupancy amplification factor, it calculates the high altitude low pressure correction term, total electronic control heat synthesis amount and electric power load occupancy rate, and multiplies the three to generate the external cold and internal heat occupancy amount. The frequency limiting module is used to obtain the compressor discharge temperature, compressor operating current, compressor discharge pressure and compressor suction pressure, and calculate the safety margin of discharge temperature, operating current and pressure ratio in combination with the preset rated maximum operating frequency. Based on the minimum value of each safety margin and the rated maximum operating frequency, the upper limit of the cycle side frequency is calculated, and the minimum value of the rated maximum operating frequency attenuated by the external cooling and internal heating occupancy and the upper limit of the cycle side frequency are taken to generate the total frequency limiting boundary. The sliding form construction module is used to calculate the basic sliding form surface based on the target and actual outlet water temperature. It subtracts the product compensation term of the external cooling and internal heating occupancy and the unexecuted residual from the previous cycle from the basic sliding form surface to construct an external cooling and internal heating absorption type sliding form surface. The frequency control module is used to generate an unlimited desired frequency based on an externally cold and internally hot absorbing sliding surface. It outputs a final frequency command constrained by the total frequency limiting boundary. The unexecuted residual in the current cycle is calculated from the difference between the unlimited desired frequency and the final frequency command and passed to the next cycle.

2. The frequency limiting sliding mode control system for a high-altitude low-temperature heat pump under large temperature and humidity differences as described in claim 1, characterized in that, The process of calculating the total heat synthesis amount of the electronic control system by the heat occupancy module includes: The temperature differences between the electronic control cavity, the frequency converter drive, and the power device and the outdoor ambient temperature are calculated as the accumulated waste heat. The differences between the preset upper limit of cavity temperature, upper limit of drive temperature, and upper limit of device temperature and the outdoor ambient temperature are calculated as the available heat dissipation temperature difference. The ratio of accumulated residual heat to available heat dissipation temperature difference is calculated, and the ratio result is limited to the range of zero to one through saturation limiting operation, thereby obtaining the relative heat occupation of the cavity, the relative heat occupation of the drive, and the relative heat occupation of the device. The relative thermal occupancy of the cavity, the relative thermal occupancy of the drive, and the relative thermal occupancy of the device are multiplied by preset thermal occupancy weights, preset thermal occupancy weights, and preset thermal occupancy weights, respectively, and the sum of the multiplication results is used to obtain the total thermal synthesis amount of the electronic control.

3. The frequency limiting sliding mode control system for a high-altitude low-temperature heat pump under large temperature and humidity differences as described in claim 1, characterized in that, The process of calculating the high-altitude low-voltage correction term and power load occupancy rate by the hot-slot module includes: The quotient of standard atmospheric pressure and current atmospheric pressure is used to obtain the high-altitude low-pressure correction term; The sum of the current input power of the heat pump and the starting standby reference power is calculated as the current load occupancy; The total available power capacity of the microgrid is obtained by adding the current load occupancy to the off-grid available surplus power. The power load occupancy rate is obtained by calculating the quotient of the current load occupancy and the total available power capacity of the microgrid.

4. The frequency limiting sliding mode control system for a high-altitude low-temperature heat pump under large temperature and humidity differences as described in claim 3, characterized in that, The process of generating external cold and internal hot space occupancy by the hot space occupancy module includes: Multiply the power occupancy amplification factor by the power load occupancy rate, and add one to the product to obtain the sum term; The external cold and internal heat occupancy is generated by multiplying the high altitude and low pressure correction term, the total heat synthesis quantity of the electronic control, and the sum term.

5. The frequency limiting sliding mode control system for a high-altitude low-temperature heat pump under large temperature and humidity differences according to claim 1, characterized in that, The process by which the frequency limiting module calculates the safety margins for exhaust temperature, operating current, and pressure ratio includes: The current pressure ratio is obtained by calculating the quotient of the compressor discharge pressure and the compressor suction pressure; The difference between the preset exhaust temperature protection limit and the compressor exhaust temperature is calculated as the numerator, and the difference between the exhaust temperature protection limit and the nominal exhaust temperature is calculated as the denominator. The quotient of the numerator and denominator is calculated, and the quotient is limited to the range of zero to one through saturation limiting operation to obtain the exhaust temperature safety margin. The difference between the preset upper limit of the operating current protection and the compressor operating current is calculated as the numerator, and the difference between the upper limit of the operating current protection and the nominal current of the compressor is calculated as the denominator. The quotient of the numerator and denominator is calculated, and the quotient is limited to the range of zero to one through saturation limiting operation to obtain the operating current safety margin. The difference between the preset pressure ratio protection limit and the current pressure ratio is calculated as the numerator, and the difference between the pressure ratio protection limit and the nominal safe pressure ratio is calculated as the denominator. The quotient of the numerator and denominator is calculated, and the quotient is limited to the range of zero to one through saturation limiting operation to obtain the pressure ratio safety margin.

6. The frequency limiting sliding mode control system for a high-altitude low-temperature heat pump under large temperature and humidity differences as described in claim 5, is characterized in that, The process by which the frequency limiting module generates the total frequency limiting boundary includes: The minimum value among the exhaust temperature safety margin, operating current safety margin, and pressure ratio safety margin is taken as the product attenuation coefficient. The upper limit of the cycle side frequency is calculated by multiplying the product attenuation coefficient by the rated maximum operating frequency. Add one to the external cooling and internal heating space occupancy to obtain the denominator term, and calculate the quotient of the rated maximum operating frequency and the denominator term to obtain the frequency boundary of the electronic control side. The total frequency limiting boundary is generated by taking the minimum value between the frequency boundary on the electronic control side and the upper limit of the frequency on the cyclic side.

7. The frequency limiting sliding mode control system for a high-altitude low-temperature heat pump under large temperature and humidity differences as described in claim 1, characterized in that, The process of calculating the basic sliding surface using the sliding mode construction module includes: Obtain the target outlet water temperature and the actual outlet water temperature, and calculate the difference between the target outlet water temperature and the actual outlet water temperature to obtain the outlet water temperature error; The normalized temperature error for the current period is obtained by calculating the quotient of the water temperature error and the preset error normalization benchmark. The change in normalized error is obtained by calculating the difference between the normalized temperature error of the current period and the normalized temperature error of the previous period. The normalized error change is multiplied by the preset error change weight, and the product is added to the normalized temperature error of the current cycle to construct the basic sliding surface.

8. The frequency limiting sliding mode control system for a high-altitude low-temperature heat pump under large temperature and humidity differences as described in claim 7, characterized in that, The process of constructing an externally cooling and internally heating absorbing sliding surface using a sliding mode construction module includes: Extract residual data from the previous cycle that was not executed in internal storage; The product compensation term is constructed by multiplying the external cold and internal heat occupancy amount, the unexecuted residual amount from the previous cycle, and the preset external cold and internal heat absorption coefficient. A sliding surface with external cooling and internal heat absorption is constructed by subtracting the product compensation term from the basic sliding surface.

9. The frequency limiting sliding mode control system for a high-altitude low-temperature heat pump under large temperature and humidity differences according to claim 1, characterized in that, The process by which the frequency control module generates the unlimited desired frequency includes: The sum of the absolute value of the externally cold and internally hot absorbing sliding surface and the preset sliding surface smoothing factor is used as the denominator, and the externally cold and internally hot absorbing sliding surface is used as the numerator. The smoothing ratio is calculated by quotienting the numerator and denominator. The sliding mode frequency adjustment is obtained by multiplying the smoothing ratio by the preset single-cycle sliding mode gain. The unlimited desired frequency is generated by adding the final frequency command of the previous cycle stored internally to the sliding mode frequency adjustment.

10. The frequency limiting sliding mode control system for a high-altitude low-temperature heat pump under large temperature and humidity differences according to claim 1, characterized in that, The frequency control module outputs the final frequency command and calculates the unused residual capacity for this cycle, including: When the total frequency limiting boundary is lower than the preset minimum stable operating frequency, the final frequency command will be set to zero to execute a shutdown. When the total frequency limiting boundary is not lower than the minimum stable operating frequency, the unlimited expected frequency is limited between the minimum stable operating frequency and the total frequency limiting boundary to obtain the final frequency command; Calculate the difference between the unlimited expected frequency and the final frequency command, calculate the quotient of the difference and the rated maximum operating frequency, and limit the quotient to the range of zero to one through saturation limiting operation to obtain the unexecuted residual for this cycle; The final frequency command and any unexecuted residuals from the current cycle are overwritten into internal memory and passed to the next control cycle.

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