Low-voltage spare power automatic switching control method and device compatible with photovoltaic and energy storage

Abstract

The invention discloses a photovoltaic and energy storage compatible low-voltage spare power automatic switching control method and device, which is applied to a group of main and standby power supply switching systems, and comprises the following steps: utilizing an integrated hybrid inverter module at the moment of a mains supply fault, and performing dynamic buffering through an energy storage battery before an ATS physically disconnects a main power supply; compensating the difference between the power required by the load and the current photovoltaic actual output power so as to maintain the stability of the voltage and frequency of the load side; under the condition that the electric energy quality of the load side is not sensed, seamless switching from the mains supply to the photovoltaic energy storage combined power supply mode is carried out; and after the switching is completed, dynamically adjusting the discharge depth and rate of the energy storage according to the real-time illumination intensity and load change through a self-adaptive impedance matching algorithm. According to the invention, the hybrid inverter integrated with the high-speed DSP controller and the voltage source type inversion topology is arranged, so that smooth, efficient and seamless switching and cooperative power supply among the power grid, photovoltaic power, energy storage and load can be realized in the automatic switching execution process of the power grid.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system automation control, in particular to a low-voltage standby automatic switching control method and device suitable for low-voltage distribution networks and capable of integrating distributed photovoltaic (PV) power generation systems and energy storage systems (ESS). BACKGROUND

[0002] In modern low-voltage distribution systems, the automatic transfer switch (ATS) is the core equipment to ensure the continuity of power supply for critical loads. Its basic function is to automatically switch the load to the backup power source (such as a diesel generator) when the main power source (mains) fails. With the advancement of technology and the popularity of distributed energy, photovoltaic power generation systems and energy storage systems are increasingly used as backup power sources or connected in parallel with the main power source.

[0003] However, there are still the following technical problems when directly applying traditional ATS to low-voltage systems containing photovoltaics and energy storage: (1) Switching interruption problem: Traditional ATSs mostly use a "break-before-make" mechanical switching method, which has a millisecond-level power interruption time. For sensitive loads in fields such as hospitals, data centers, and precision manufacturing, this interruption is unacceptable and can lead to equipment downtime, data loss, and other serious consequences.

[0004] (2) Photovoltaic volatility impact: Photovoltaic power generation has significant intermittency and volatility. When the mains fail, if the light conditions change dramatically (such as cloud cover), the photovoltaic output power will drop sharply. At this time, if the load is directly switched to the photovoltaic system, it may fail due to insufficient power, causing the system voltage to collapse.

[0005] (3) Low system efficiency: Existing compatibility solutions usually involve simple stacking of components without integrated collaborative control strategies. For example, before and after switching, the maximum power point of photovoltaics, the charge and discharge state of energy storage, and the output impedance of inverters are not optimized and matched, resulting in significant energy loss during conversion and transmission, and low overall system operation efficiency.

[0006] (4) Control logic incompatibility: Some existing technologies attempt to combine energy storage and photovoltaics, such as through isolated inverters or multifunctional switching switches, but their designs are not optimized for the specific challenges of low-voltage (<1000V) systems. These solutions are often complex and costly, and do not propose an integrated design that uses energy storage as a "dynamic buffer bridge" to achieve zero-interruption switching and adaptively adjusts energy flow based on real-time operating conditions to maximize efficiency.

[0007] Therefore, the market urgently needs a backup power automatic switching control technology specially designed for low-voltage systems, which can deeply integrate photovoltaic and energy storage and realize truly seamless, efficient and intelligent switching.

[0008] To this end, the application provides a low-voltage backup power automatic switching control method and device compatible with photovoltaic and energy storage, which is specially designed for low-voltage systems, can deeply integrate photovoltaic and energy storage, and realizes truly seamless, efficient and intelligent switching, so as to solve the above technical problems. SUMMARY

[0009] The main purpose of the application is to provide a low-voltage backup power automatic switching control method and device compatible with photovoltaic and energy storage, which aims to solve the technical problems of power interruption, voltage impact, low system efficiency and damage to sensitive loads in the switching process caused by the intermittency and volatility of photovoltaic power generation when the traditional backup power automatic switching device accesses new energy, and realizes smooth, efficient and seamless switching and collaborative power supply between the power grid, photovoltaic, energy storage and load, so as to solve the technical problems proposed in the background technology.

[0010] The application solves the above technical problems by adopting the following technical solutions: A low-voltage backup power automatic switching control method compatible with photovoltaic and energy storage, applied to a group of main and backup power switching systems, comprising: In the instant of power failure, instead of performing the traditional "first disconnect and then connect" hard switching, a group of integrated hybrid inverter modules are used to dynamically buffer through energy storage batteries before the ATS physically disconnects the main power, to accurately compensate for the difference between the power required by the load and the actual output power of photovoltaic at that time, so as to maintain the stability of the voltage and frequency on the load side; In the case of no perception of load side power quality, seamlessly switch from power supply to photovoltaic energy storage combined power supply mode; After switching is completed, through an adaptive impedance matching algorithm, the depth and rate of discharging of the energy storage are dynamically adjusted according to real-time light intensity and load changes.

[0011] Preferably, the power failure is continuously collected by a monitoring module at a high frequency (such as kHz level) to confirm the electrical parameters of the designated key nodes of the system, wherein the electrical parameters include: voltage, frequency and phase of the main power grid; output voltage, current and environmental light intensity of the photovoltaic array; state of charge (SOC), terminal voltage and current of the energy storage battery; and real-time power demand on the load side; Among them, the voltage of the main power grid is collected and detected at the moment The instantaneous voltage is collected and detected, and its effective value and frequency are calculated, and the calculation formula is: , is the voltage of the main power grid at The instantaneous voltage value at time t. One cycle of the grid voltage, The root mean square (RMS) value of the main grid voltage; Photovoltaic output power is measured in real time by the output voltage of the photovoltaic array. and current The calculation is as follows: , For photovoltaic arrays in Instantaneous output power at a given moment For photovoltaic arrays in The instantaneous output voltage at a given moment. For photovoltaic arrays in Instantaneous output current at any given moment; Among these methods, the ampere-hour integral method is used to dynamically estimate the state of charge (SOC) of energy storage, and the calculation formula is as follows: , for The state of charge of the energy storage at any given time. Initial time The state of charge, This refers to the rated capacity (Ah) of the energy storage battery. This is the instantaneous current of the energy storage battery (negative for charging, positive for discharging). The charge / discharge coulombic efficiency of the battery; When the voltage amplitude and frequency of the main grid exceed the preset safety threshold and remain so for a specified period of time, it is determined that there is a mains power fault in the main grid. The determination formula is as follows:

[0012]

[0013] in, and These represent the voltage fault flag and the frequency fault flag, respectively. If the result of the judgment formula is 1, then there is a mains power fault in the mains power grid; otherwise, there is a mains power fault in the mains power grid. and These represent the preset lower and upper voltage thresholds, respectively. The rated frequency of the power grid (e.g., 50Hz or 60Hz). The maximum allowable frequency deviation threshold, The effective value of the main grid voltage. This refers to the real-time frequency of the main power grid. Preferably, the specific operation process of the hybrid inverter module for dynamic buffering via energy storage battery includes: L1. Measurement load side at Instantaneous voltage at time t and instantaneous current Calculate the active power of the real-time load. The calculation formula is as follows: ,in One cycle of the grid voltage; L2. The hybrid inverter uses real-time monitored load power... and photovoltaic output power Calculate the power gap (The power that energy storage needs to compensate for) can be calculated using the following formula: ,in This is expressed as the reference output power of the energy storage system; L3. Controls the energy storage system's precise output with a microsecond-level response speed. Power of size; At this point, the reference current is calculated based on the energy storage power and the battery terminal voltage, using the following formula:

[0014] in, This is the reference discharge current for the energy storage system. This represents the real-time terminal voltage of the energy storage battery. From the load side's perspective, the required total power is now... Depend on Together with energy storage, the current on the grid side rapidly approaches zero.

[0015] Preferably, the hybrid inverter module employs a dual closed-loop PID control strategy, including current-loop PID control and voltage-loop PID control, to achieve high-precision and rapid tracking of the energy storage current, wherein: (1) The inner current loop PID controller is based on the reference current of the energy storage system. With actual energy storage current The error is used to control the voltage of the output inverter bridge arm. The mathematical expression for the voltage control output of the PID (proportional-integral) controller is as follows:

[0016] in, and These are the proportional and integral gain coefficients of the inner current loop, respectively, used to represent the PID controller transfer function operation to express the controller's sensitivity to current errors, i.e., the voltage regulation corresponding to a unit current error. This voltage control signal... Used to generate PWM to drive the inverter bridge arm; (2) The voltage outer loop PID controller is based on the effective value of the target voltage on the load side. Compared with the actual load-side voltage RMS value The error is used to output the current reference signal of the energy storage system. The mathematical expression for the voltage control output of the PID (proportional-integral) controller is as follows:

[0017] in, and These are the proportional and integral gain coefficients of the outer voltage loop, respectively, used to represent the operation of the PID controller's transfer function, expressing the controller's sensitivity to voltage errors, i.e., the current regulation corresponding to a unit voltage error.

[0018] Furthermore, the current inner loop controller here is used to generate a voltage control signal based on the current error in order to achieve rapid current tracking.

[0019] Furthermore, taking the formula of the current inner-loop PID controller as an example, the principle is explained. Here, the controller has a conversion function: The essence of the PID controller is a transfer function, and its function is to map the input signal (current error, unit: A) into the output control signal (voltage command, unit: V).

[0020] In this formula, the physical unit of the coefficient is the proportional gain coefficient. It is not a dimensionless constant; its physical unit is V / A (volts per ampere). Physically, it is equivalent to "virtual impedance," representing the controller's sensitivity to current errors, i.e., the voltage regulation corresponding to a unit current error. Similarly, the integral gain coefficient... The physical unit is V / (A·s).

[0021] Therefore, through coefficients and Dimensional conversion: the calculation result on the right side of the formula is in physical units the same as the voltage control signal on the left side. Keeping the values ​​consistent (both in volts V), this formula accurately expresses the physical mechanism of controlling the output current by adjusting the inverter port voltage.

[0022] The technical principle of voltage loop PID control output is the same.

[0023] Preferably, the adaptive impedance matching algorithm is used to predict the maximum output power of the photovoltaic system at the next moment (e.g., on the order of seconds) based on the real-time monitored irradiance, and dynamically adjusts the equivalent output impedance of the hybrid inverter and the discharge strategy of the energy storage system in conjunction with load changes, specifically including: ST1. Based on Light intensity at any time and solar panel temperature The mathematical formula for constructing a prediction model for the maximum power point of photovoltaic power at this time is as follows:

[0024] wherein, is the predicted maximum output power of the photovoltaic at time is the peak power of the photovoltaic under standard test conditions at time and are the real-time solar irradiance and the standard solar irradiance (1000 W / m 2 ) at time is the power temperature coefficient at time and are the real-time panel temperature and the standard test temperature (25°C), respectively; ST2. Based on the photovoltaic maximum power point prediction model, define the system efficiency that needs to be maximized at time is:

[0025] wherein, is the instantaneous total efficiency of the system, is the actual discharge power of the energy storage system, and are the load power and the photovoltaic output power monitored in real time by the hybrid inverter, respectively; ST3. Calculate the impedance matching adjustment factor for dynamically adjusting the energy storage discharge depth, and the associated formula is:

[0026] wherein, the value range of is [0, 1], when tends to 1, it means that the load is prioritized, and when tends to 0, it means that the photovoltaic is prioritized, is the maximum output power of the photovoltaic array calculated according to the real-time solar irradiance and environmental temperature through the photovoltaic maximum power point prediction model at ST4. Based on the adjustment factor , the gradient ascent method is used to iteratively update to find the optimal to maximize the system efficiency , and the calculation formula is:

[0027] wherein, is the impedance matching adjustment factor of the next control period, an impedance matching adjustment factor before updating, a learning rate or an iteration step size, indicates the system efficiency a gradient of the adjustment factor.

[0028] Preferably, after the main power grid is restored to normal and stable operation for a specified time, a synchronous grid connection program is started, the output voltage frequency, amplitude and phase are accurately synchronized to be completely consistent with the main power grid by using a phase-locked loop (PLL) technology of the hybrid inverter, and then the ATS is controlled to be closed at the synchronization point to achieve undisturbed re-switching of the load, and the main and backup power switching system is restored to the grid-connected operation state thereafter.

[0029] Preferably, the hybrid inverter uses a phase-locked loop technology to obtain a phase error through dq transformation to achieve synchronization of the output voltage frequency, amplitude and phase to be completely consistent with the main power grid, and the transformation formula is:

[0030] wherein, is a phase difference between the inverter output voltage and the grid voltage, and are components of the grid voltage in the dq synchronous rotating coordinate system, respectively, is an output phase of the inverter internal phase-locked loop.

[0031] A low-voltage backup automatic switching control device compatible with photovoltaic and energy storage is applied to a group of main and backup power switching systems, and is connected with a group of energy storage devices and an automatic transfer switch (ATS) of the system for control, and is used to execute any of the low-voltage backup automatic switching control methods compatible with photovoltaic and energy storage, and comprises: a monitoring module for continuously collecting electrical parameters of a specified node of the system at a high frequency, and provided with a specified safety threshold value, and when the main grid voltage amplitude and frequency in the collected parameters exceed the specified safety threshold value, a "dynamic buffer bridge" function activation instruction is issued; a hybrid inverter module for receiving the function activation instruction and using a built-in high-speed DSP controller and a voltage source type inverter topology to realize seamless energy flow between photovoltaic DC, energy storage DC and load AC side, so that the current flowing through the ATS city power side contact is substantially zero, and then a switching processing signal is issued; a switching processing module for controlling the automatic transfer switch (ATS) to be mechanically disconnected after receiving the switching processing signal; after the automatic transfer switch (ATS) is switched, a self-adaptive impedance matching algorithm is used to control dynamic adjustment of energy storage charging and discharging.

[0032] In yet another aspect, the present application also discloses a computer readable storage medium, which stores a computer program, and the computer program, when executed by a processor, causes the processor to perform the steps of the above method.

[0033] In yet another aspect, the present application also discloses a computer device, which comprises a memory and a processor, and the memory stores a computer program, and the computer program, when executed by the processor, causes the processor to perform the steps of the above method.

[0034] From the above technical solution, the present application provides a low-voltage spare power automatic switching control method and device compatible with photovoltaic and energy storage. Compared with the prior art, the present application has the following advantages: 1. The present application constructs a set of specially designed hybrid inverters, which integrates a high-speed DSP controller and an advanced voltage source inverter (VSI) topology inside, and can use a set of energy storage devices to take over the load in advance before the automatic switching of the power grid, so as to realize the seamless flow of energy between photovoltaic DC, energy storage DC and load AC side in a low-voltage environment, and eliminate all power gaps caused by switching interruption in the process of switching from mains power supply to off-grid power supply.

[0035] 2. The present application sets an adaptive impedance matching algorithm, which can adjust the discharge current of the energy storage and the PWM (pulse width modulation) control strategy of the inverter in real time, so that the equivalent output impedance of the "photovoltaic + energy storage" power supply system and the load impedance are optimally matched, thereby maximizing the system efficiency and avoiding the blind discharge of the energy storage system or the waste of photovoltaic power in the traditional scheme.

[0036] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present application, nor is it used to limit the scope of the present application. Other features of the present application will become apparent from the following description. Of course, any product implementing the present application does not necessarily need to achieve all the advantages described above. BRIEF DESCRIPTION OF DRAWINGS

[0037] The accompanying drawings, which form a part of the present application, are intended to provide further understanding of the present application, and the illustrative embodiments of the present application and their descriptions serve to explain the present application, and do not constitute improper limitations on the present application. In the drawings: Figure 1 It is a schematic diagram of the overall process of the present application. DETAILED DESCRIPTION

[0038] 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 a part of the embodiments of the present invention, and not all of them. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. 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.

[0039] For details in the embodiments, please refer to Figure 1 .

[0040] like Figure 1 As shown in the embodiments of this invention, the low-voltage standby automatic transfer control method compatible with photovoltaics and energy storage can, at the moment of a mains power failure, no longer perform the traditional "disconnect first, connect later" hard switching. Instead, it utilizes an integrated hybrid inverter module with energy storage batteries as a "dynamic buffer bridge." Before the ATS physically disconnects the mains power, the energy storage system intervenes in advance to accurately compensate for the difference between the power required by the load and the actual output power of the photovoltaic at that time, thereby maintaining the stability of the load-side voltage and frequency. This achieves a seamless switch from mains power to a "photovoltaic + energy storage" joint power supply mode without affecting the power quality on the load side. After the switch is completed, the system activates an adaptive impedance matching algorithm to dynamically adjust the discharge depth and rate of the energy storage based on real-time light intensity and load changes, maximizing the utilization rate of photovoltaic energy and improving the overall system efficiency by approximately 20%. It can mainly solve the technical problems of power interruption, voltage surge, low system efficiency and damage to sensitive loads during the switching process caused by the intermittency and volatility of photovoltaic power generation when traditional backup automatic transfer devices are connected to new energy sources. It can achieve smooth, efficient and seamless switching and coordinated power supply between the grid, photovoltaic, energy storage and load.

[0041] The specific implementation process includes the following steps: Step 1: Real-time monitoring of the entire system under all operating conditions Mains power failures are confirmed by continuously collecting electrical parameters of designated key nodes of the system at high frequencies (such as kHz) through the monitoring module. These electrical parameters include: voltage, frequency, and phase of the main grid; output voltage, current, and ambient light intensity of the photovoltaic array; state of charge (SOC), terminal voltage, and current of the energy storage battery; and real-time power demand on the load side. These data form the basis for all subsequent decisions and controls.

[0042] Among them, the main grid voltage passes through Instantaneous voltage at time t Collect and detect data, and calculate its effective value. and frequency The calculation formula is as follows: , the instantaneous voltage value of the main grid at the moment, a period of the grid voltage, the root mean square value (effective value) of the main grid voltage; The photovoltaic output power is calculated by real-time measurement of the output voltage and current of the photovoltaic array and current , and the calculation formula is: , the instantaneous output power of the photovoltaic array at the moment, the instantaneous output voltage of the photovoltaic array at the moment, the instantaneous output current of the photovoltaic array at the moment; wherein, the state of charge (SOC) of the energy storage is dynamically estimated by ampere-hour integration method, and the calculation formula is: , the state of charge at the moment, the state of charge at the initial moment, the rated capacity (Ah) of the energy storage battery, the instantaneous current of the energy storage battery (negative for charging and positive for discharging), the charge-discharge coulomb efficiency of the battery; Step 2: Accurate diagnosis and prediction of main grid failure When the amplitude and frequency of the main grid voltage exceed the preset safety threshold (for example, voltage drop exceeds 15%, frequency deviation exceeds 0.5 Hz) and continue for a certain time (such as 20 ms), the control system determines that the main grid fails. The purpose of this step is to quickly and accurately identify the working condition that needs to start the backup power supply. Specifically, when the amplitude and frequency of the main grid voltage exceed the preset safety threshold and continue for a specified time, it is determined that the main grid has a power failure, and the determination formula is:

[0043]

[0044]

[0045] wherein, and respectively represent the voltage fault flag and the frequency fault flag, and the determination formula result is 1, which means that the main grid has a power failure, otherwise the main grid has a power failure, and respectively represent the preset lower and upper voltage thresholds, ​​​​​​The rated frequency of the power grid (e.g., 50Hz or 60Hz). The maximum allowable frequency deviation threshold, The effective value of the main grid voltage. This refers to the real-time frequency of the main power grid.

[0046] Step 3: Activation of the dynamic buffer bridge and power pre-compensation When a main grid fault is detected, the ATS is not immediately commanded to operate. Instead, a command is immediately sent to the hybrid inverter module to activate the "dynamic buffer bridge" function.

[0047] The specific operation process of the hybrid inverter module using energy storage batteries for dynamic buffering (activating the "dynamic buffer bridge" function) includes: L1. Measurement load side at Instantaneous voltage at time t and instantaneous current Calculate the active power of the real-time load. The calculation formula is as follows: ,in One cycle of the grid voltage; L2. Based on the real-time monitored load power and photovoltaic output power Calculate the power gap (The power that energy storage needs to compensate for) can be calculated using the following formula: ,exist This is expressed as the reference output power of the energy storage system; L3. Controls the energy storage system's precise output with a microsecond-level response speed. Power of size; At this point, the reference current is calculated based on the energy storage power command and the battery terminal voltage, using the following formula:

[0048] in, This is the reference discharge current for the energy storage system. This represents the real-time terminal voltage of the energy storage battery. From the load side's perspective, the required total power is now... Depend on Together with energy storage, the current on the grid side rapidly approaches zero.

[0049] It also needs to be further supplemented here that the conventional backup power supply adopted by the prior art switches only after the power grid "dies", while the present application uses energy storage to take over the load in advance at the moment when the power grid is "dying" but has not been completely disconnected. This process is realized through a specially designed hybrid inverter, which integrates a high-speed DSP controller and an advanced voltage source inverter (VSI) topology. It can realize seamless energy flow between photovoltaic DC, energy storage DC and load AC side in a low-voltage environment. The energy storage battery is not only a backup power supply, but also a dynamic and active power buffer, which fills all power gaps in the process of switching from grid power supply to off-grid power supply, thereby fundamentally eliminating switching interruption.

[0050] In addition, it can be further disclosed that the hybrid inverter module adopts a double closed-loop PID control strategy including current loop PID control and voltage loop PID control to realize high-precision and rapid tracking of energy storage current, wherein: (1) The current inner loop PID controller outputs the voltage control signal of the inverter bridge arm according to the error between the reference current of the energy storage system and the actual energy storage current The mathematical expression of the voltage control output of the PID (proportional-integral) controller is:

[0051] Among them, and are the proportional and integral gain coefficients of the current inner loop, which are used to represent the transfer function operation of the PID controller to express the sensitivity of the controller to the current error, i.e. the voltage adjustment amount corresponding to a unit current error. The voltage control signal is used to generate the PWM drive inverter bridge arm; (2) The voltage outer loop PID controller outputs the reference current signal of the energy storage system according to the error between the target voltage effective value of the load side and the actual voltage effective value of the load side The mathematical expression of the voltage control output of the PID (proportional-integral) controller is:

[0052] Among them, and are the proportional and integral gain coefficients of the voltage outer loop, which are used to represent the transfer function operation of the PID controller to express the sensitivity of the controller to the voltage error, i.e. the current adjustment amount corresponding to a unit voltage error.

[0053] ​​Further, the formula of the current inner loop PID controller is taken as an example to illustrate the principle, where the conversion of the controller exists: the essence of the PID controller is a transfer function, which maps the input signal (current error, unit: A) to the output control signal (voltage command, unit: V).

[0054] In this formula, the physical units of the coefficients are: the proportional gain coefficient is not a dimensionless constant, and its physical unit is V / A (volt / ampere), which is equivalent to "virtual impedance" in physical meaning, representing the sensitivity of the controller to the current error, i.e., the voltage adjustment corresponding to a unit current error. Similarly, the integral gain coefficient has a physical unit of V / (A·s).

[0055] Therefore, through the dimensional conversion of the coefficients and , the calculation result on the right side of the formula is consistent with the voltage control signal on the left side in physical units (both are volts V), and the formula accurately represents the physical mechanism of controlling the output current by adjusting the inverter port voltage.

[0056] The technical principle of the voltage loop PID control output is the same.

[0057] Further, the current inner loop controller is used to generate a voltage control signal based on the current error to achieve fast tracking of the current, which is the voltage control signal (output) of the inverter bridge arm, used to directly generate a PWM (pulse width modulation) waveform to drive the power switch tube of the inverter to act, which is the reference current (target value) of the energy storage system, calculated by the voltage outer loop, used to represent the ideal current value required by the system at the current time, which is the actual detected energy storage current (feedback value), which is the actual current data collected in real time by the sensor, represents the current error signal, i.e., the difference between the target current and the actual current, represents the proportional gain coefficient of the current inner loop, used to determine the response strength of the controller to the current error, and the larger the gain, the faster the response, represents the integral gain coefficient of the current inner loop, used to eliminate the steady-state error of the system, which adjusts the output by accumulating past errors to ensure that the actual current can eventually track the reference current without error.

[0058] Further, the voltage outer loop controller is also used to calculate the current command required by the system based on the deviation of the load voltage.

[0059] At this time Reference current (output) of the energy storage system, used as the input target value of the current inner loop, indicating how much current the system needs to output or absorb to maintain voltage stability, Target voltage RMS (set value) of the load side, usually the rated voltage of the system (e.g. 220V or 380V), Actual detected voltage RMS (feedback value) of the load side, Voltage error signal, Proportional gain coefficient of the voltage outer loop, used for rapid adjustment of voltage fluctuations, Integral gain coefficient of the voltage outer loop, used to eliminate the steady-state deviation of the voltage and ensure that the output voltage is long-term stable at the set value.

[0060] Further, the entire system adopts a cascade control (double closed loop) structure: Outer loop (voltage loop): responsible for maintaining the stability of the load voltage. When the voltage deviates from the target value, the outer loop PID controller calculates the size of the current adjustment ; Inner loop (current loop): responsible for quickly executing the current command. It receives the current reference value from the outer loop and adjusts the inverter output voltage to force the actual current to quickly and accurately follow the reference value; This structure not only ensures the stability of the voltage, but also takes advantage of the high bandwidth characteristics of the current loop to achieve rapid suppression of disturbances.

[0061] Fourth step: safe switching under zero current / zero voltage Since the power pre-compensation in the previous step has made the current flowing through the ATS mains side contact almost zero, the control system then sends a disconnection command to the ATS. Mechanical disconnection under near-zero current can greatly reduce the generation of electric arc, protect the contact, prolong the service life of the ATS device, and improve the safety of switching.

[0062] Fifth step: adaptive impedance matching in off-grid mode After switching, the system enters the off-grid mode powered by photovoltaic and energy storage combined, and then starts the adaptive impedance matching algorithm. The adaptive impedance matching algorithm can predict the maximum output power of the photovoltaic in the next time slice (such as seconds) according to the real-time monitored light intensity, and dynamically adjust the equivalent output impedance of the hybrid inverter and the discharge strategy of the energy storage system combined with the load change.

[0063] Specifically includes: ST1. Based on the light intensity and the panel temperature The photovoltaic maximum power point prediction model at this time is constructed, and the model mathematical formula is:

[0064] Among them, is the predicted photovoltaic maximum output power at the moment, is the photovoltaic peak power under standard test conditions at the moment, is the real-time light intensity at the moment, and is the standard light intensity (1000 W / m 2 ), and are the real-time panel temperature and the standard test temperature (25°C) respectively; is the power temperature coefficient at the moment, ST2. Based on the photovoltaic maximum power point prediction model, the system efficiency that needs to be maximized at the moment is defined as is:

[0065] Among them, is the instantaneous total efficiency of the system, is the actual discharge power of the energy storage system, and are the load power and photovoltaic output power monitored in real time by the hybrid inverter respectively; ST3. Calculate the impedance matching adjustment factor for dynamically adjusting the energy storage discharge depth, and the associated formula is:

[0066] Among them, the value range of is [0, 1], when tends to 1, it means to prefer to meet the load, and when tends to 0, it means to prefer to use photovoltaic, is the maximum output power of the photovoltaic array calculated according to the real-time light intensity and environmental temperature through the photovoltaic maximum power point prediction model at the moment; ST4. Based on the adjustment factor , the gradient ascent method is used to iteratively update and find the optimal to maximize the system efficiency , and the calculation formula is:

[0067] Among them,​​​​ impedance matching adjustment factor for the next control period, impedance matching adjustment factor before update, learning rate or iteration step size, system efficiency gradient of the adjustment factor.

[0068] It should also be further pointed out here that the adaptive impedance matching algorithm at this time aims to maximize the system efficiency, which adjusts the discharge current of the energy storage and the PWM (pulse width modulation) control strategy of the inverter in real time, so that the equivalent output impedance of the "photovoltaic + energy storage" power supply system and the load impedance are optimally matched. In the specific implementation process, when the light is sufficient, the algorithm will preferentially increase the output weight of the photovoltaic, reduce the discharge of the energy storage, and even charge the energy storage in the case of small load. When the light is weak (such as cloud passing), the algorithm will instantaneously increase the discharge depth of the energy storage to ensure the stability of the load voltage. This fine dynamic adjustment avoids the blind discharge of the energy storage system or the waste of photovoltaic power in the traditional scheme, and can increase the efficiency by 20%.

[0069] Step 6: Synchronous grid connection after the main grid is restored When the monitoring system detects that the main grid is restored to normal and stable operation for a period of time, the control system will start the synchronous grid connection program. At this time, the hybrid inverter accurately synchronizes the frequency, amplitude and phase of its output voltage to the main grid through the phase-locked loop (PLL) technology, and then controls the ATS to close at the synchronization point to realize the "undisturbed" back-to-load. After that, the system returns to the grid-connected operation state.

[0070] The hybrid inverter uses a phase-locked loop technology to obtain a phase error through dq transformation to synchronize the frequency, amplitude and phase of the output voltage to the main grid. The transformation formula is:

[0071] wherein, is the phase difference between the inverter output voltage and the grid voltage, and are the components of the grid voltage in the dq synchronous rotating coordinate system, respectively, is the output phase of the inverter internal phase-locked loop.

[0072] On the other hand, the application also discloses a low-voltage backup automatic switching control device compatible with photovoltaic and energy storage, which is applied to a group of main and backup power supply switching systems and connected with a group of energy storage devices and an automatic transfer switch (ATS) of the system for control, used for executing the low-voltage backup automatic switching control method compatible with photovoltaic and energy storage of the above-mentioned embodiment, comprising: ​A monitoring module is configured to continuously collect electrical parameters of the designated nodes of the system at high frequency, and is provided with a designated safety threshold, and when the voltage amplitude and frequency of the main power grid exceed the designated safety threshold, an activation instruction of the dynamic buffer bridge function is sent out; A hybrid inverter module is configured to utilize the built-in high-speed DSP controller and voltage source type inverter topology to achieve seamless energy flow between the photovoltaic DC, energy storage DC and load AC side after receiving the activation instruction, so that the current flowing through the ATS power side contact is substantially zero, and then a switching processing signal is sent out; A switching processing module is configured to control the mechanical disconnection of the automatic transfer switch ATS after receiving the switching processing signal; The automatic transfer switch ATS is switched, and the dynamic adjustment of the energy storage charging and discharging is realized through the adaptive impedance matching algorithm.

[0073] The method and device proposed in the above embodiment are further compared and verified by the following test method, specifically including: A small commercial building low-voltage power distribution system is simulated, which is installed with the device of the present application to perform the method of the present application, wherein: the main power supply is 220V / 50Hz power supply, and is matched with a set of distributed power supply (50kWp photovoltaic array and 100kWh / 50kW energy storage system), at this time, there are key loads with a total power of 40kW, including servers, UPS, lighting and office equipment and other sensitive loads.

[0074] The comparison object is a small commercial building low-voltage power distribution system which adopts the same capacity of photovoltaic and energy storage, but is equipped with a switching control scheme of a traditional mechanical ATS.

[0075] At this time, the switching result test is carried out under the condition that the power failure (voltage drop to 70% of the normal value) of the power supply occurs suddenly at 14:00 (good light condition but intermittent cloud cover) in the afternoon, and the test process and results are as follows: (I) Test process of the traditional ATS scheme (a) The power failure occurs, and the controller detects the voltage anomaly; (b) After about 50ms of delay confirmation, the ATS sends out a disconnection instruction of the main power grid; (c) The ATS mechanical structure acts, and the time consumption is about 100ms, during which the load is completely powered off; (d) The ATS is closed to the standby power supply side, and the inverter starts to send photovoltaic and energy storage power to the load; (e) At this time, there is about 150ms of power supply interruption on the load side, resulting in server restart and lighting device flicker, and due to the cloud cover, the photovoltaic power drops suddenly, the load side voltage drops by more than 25% in the switching moment, and the system recovery time is long.

[0076] (II) Test process of the scheme of the present application (a) Power failure occurs, and the controller diagnoses the failure within 20 ms; (b) The dynamic buffer bridge is immediately activated, and the hybrid inverter responds within 5 ms, and the energy storage system supplements the power difference between the photovoltaic and the load. At this time, the current flowing through the ATS contact of the power supply side is close to zero; (c) After the energy storage system completely "takes over" the load, the controller issues a disconnection instruction to the ATS; (d) The ATS is safely disconnected under zero current conditions, and no arc is generated; (e) The system seamlessly transitions to an off-grid mode, and the adaptive impedance matching algorithm is started, which optimizes the energy storage discharge rate in real time according to the changes in light caused by cloud drift; (f) At this time, the voltage on the load side fluctuates by less than 2%, and there is no perception of power interruption, and the server and all devices are running normally. The overall energy utilization rate of the system is high, and the operation is stable (III) The final test results are shown in the following table:

[0077] Through the comparison of the above test scenarios, it can be seen that the low-voltage automatic switching control method and device compatible with photovoltaic and energy storage proposed by the present application has overwhelming advantages in power supply continuity, power quality, system operation efficiency and device safety compared with the prior art.

[0078] In another aspect, the present application also discloses a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to make the processor execute the steps of the above method.

[0079] In another aspect, the present application also discloses a computer device, which comprises a memory and a processor, and the memory stores a computer program, and the computer program is executed by the processor to make the processor execute the steps of the above method.

[0080] In another embodiment provided by the present application, a computer program product containing instructions is also provided, which makes a computer execute the low-voltage automatic switching control method compatible with photovoltaic and energy storage in any of the above embodiments when the computer program product is run on the computer.

[0081] It can be understood that the system provided by the embodiments of the present application corresponds to the method provided by the embodiments of the present application, and the explanation, examples and beneficial effects of the related content can be referred to the corresponding part in the above method.

[0082] The embodiment of the present application further provides an electronic device, comprising a processor, a communication interface, a memory and a communication bus, wherein the processor, the communication interface and the memory complete mutual communication through the communication bus, The memory is used for storing a computer program. The processor is used for executing the program stored on the memory, and realizes the compatible photovoltaic and energy storage low-voltage backup automatic switching control method.

[0083] The communication bus mentioned in the above electronic device can be a peripheral component interconnect bus or an extended industry standard architecture bus.

[0084] The communication interface is used for communication between the above electronic device and other devices.

[0085] The memory can include a random access memory and can also include a non-volatile memory, for example, at least one disk memory. Optionally, the memory can also be at least one storage device located away from the aforementioned processor.

[0086] The processor mentioned above can be a general-purpose processor, including a central processing unit, a network processing unit and the like; can also be a digital signal processor, an application specific integrated circuit, a field programmable gate array or other programmable logic device, a discrete gate or transistor logic device, a discrete hardware component.

[0087] It should be further explained that the electronic device further comprises a terminal device, and the terminal device can also be referred to as a terminal, a user equipment, a mobile station, a mobile terminal and the like. The terminal device can be a mobile phone, a smart television, a wearable device, a tablet computer, a computer with wireless transceiver function, a virtual reality terminal device, an augmented reality terminal device, a wireless terminal in industrial control, a wireless terminal in unmanned driving, a wireless terminal in remote surgery, a wireless terminal in smart power grid, a wireless terminal in transportation safety, a wireless terminal in smart city, a wireless terminal in smart home and the like. The embodiment of the present application does not limit the specific technology and specific device form of the terminal device.

[0088] In the above embodiments, all or part can be implemented by software, hardware, firmware or any combination thereof. When implemented by software, all or part can be implemented in the form of a computer program product. The computer program product includes one or more computer instructions. When loaded and executed by a computer, the computer instructions generate all or part of the processes or functions described in the embodiments of the present application. The computer can be a general purpose computer, a special purpose computer, a computer network or other programmable device. The computer instructions can be stored in a computer readable storage medium or transferred from one computer readable storage medium to another computer readable storage medium, for example, the computer instructions can be transferred from one website, computer, server or data center to another website, computer, server or data center through wired or wireless manner. The computer readable storage medium can be any available medium accessible by a computer or a data storage device such as a server, data center and the like integrated with one or more available media sets. The available medium can be magnetic medium, optical medium or semiconductor medium, etc.

[0089] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0090] In addition, it should be noted that if the embodiments of the present application involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement condition, etc. between components in a certain posture, and if the certain posture changes, the directional indications also change accordingly.

[0091] In addition, if the embodiments of the present application involve descriptions of "first", "second", etc., the descriptions of "first", "second", etc. are only for description purposes and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing throughout the text includes three parallel solutions. Taking "A and / or B" as an example, it includes A solution, or B solution, or A and B solutions. In addition, in the embodiments of the present application, "multiple" means more than two. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the realization of a person skilled in the art, and when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist and is not within the protection scope required by the present application.

Claims

1. A low-voltage standby automatic transfer control method compatible with photovoltaic and energy storage, applied to a set of main and standby power supply switching systems, characterized in that, include: In the event of a mains power failure, an integrated set of hybrid inverter modules is used to dynamically buffer the load through energy storage batteries before the ATS physically disconnects the main power supply, compensating for the difference between the power required by the load and the actual output power of the photovoltaic system at that time, so as to maintain the stability of the load-side voltage and frequency. Seamless switching from mains power to photovoltaic energy storage combined power supply mode is achieved without any noticeable power quality issues on the load side. After the switch is completed, the discharge depth and rate of the energy storage are dynamically adjusted according to the real-time light intensity and load changes through an adaptive impedance matching algorithm.

2. The low-voltage backup automatic transfer control method compatible with photovoltaics and energy storage as described in claim 1, characterized in that, The mains power failure is confirmed by continuously collecting electrical parameters from designated nodes of the system through the monitoring module. These electrical parameters include: the voltage, frequency, and phase of the main grid; the output voltage, current, and ambient light intensity of the photovoltaic array; the state of charge, terminal voltage, and current of the energy storage battery; and the real-time power demand on the load side. When the voltage amplitude and frequency of the main grid exceed the preset safety threshold and remain so for a specified period of time, it is determined that there is a mains power fault in the main grid. The determination formula is as follows: in, and These represent the voltage fault flag and the frequency fault flag, respectively. If the result of the judgment formula is 1, then there is a mains power fault in the mains power grid; otherwise, there is a mains power fault in the mains power grid. and These represent the preset lower and upper voltage thresholds, respectively. The rated frequency of the power grid. The maximum allowable frequency deviation threshold, The effective value of the main grid voltage. This refers to the real-time frequency of the main power grid.

3. The low-voltage backup automatic transfer control method compatible with photovoltaics and energy storage as described in claim 2, characterized in that, The specific operation process of the hybrid inverter module using energy storage batteries for dynamic buffering includes: L1. Measurement load side at Instantaneous voltage at time t and instantaneous current Calculate the real-time active power of the load. The calculation formula is as follows: in One cycle of the grid voltage; L2. The hybrid inverter monitors the real-time active power of the load. and photovoltaic output power Calculate the power gap The calculation formula is as follows: exist This is the reference output power of the energy storage system; L3. Controls the energy storage system's precise output with a microsecond-level response speed. Power of size; At this point, the reference current is calculated based on the energy storage power and the battery terminal voltage, using the following formula: in, This is the reference discharge current for the energy storage system. This represents the real-time terminal voltage of the energy storage battery.

4. The low-voltage backup automatic transfer control method compatible with photovoltaics and energy storage as described in claim 3, characterized in that, The hybrid inverter module employs a dual closed-loop PID control strategy, including current-loop PID control and voltage-loop PID control, to achieve high-precision and rapid tracking of the energy storage current. (1) The inner current loop PID controller is based on the reference current of the energy storage system. With actual energy storage current The error is used to control the voltage of the output inverter bridge arm. The mathematical expression for the voltage control output of the PID controller is as follows: in, and These are the proportional and integral gain coefficients of the inner current loop, respectively, used to represent the PID controller transfer function operation to express the controller's sensitivity to current errors, i.e., the voltage regulation corresponding to a unit current error. This voltage control signal... Used to generate PWM drive inverter bridge arms; (2) The voltage outer loop PID controller is based on the effective value of the target voltage on the load side. Compared with the actual load-side voltage RMS value The error is used to output the current reference signal of the energy storage system. The mathematical expression for the voltage control output of the PID controller is as follows: in, and These are the proportional and integral gain coefficients of the outer voltage loop, respectively, used to represent the operation of the PID controller's transfer function, expressing the controller's sensitivity to voltage errors, i.e., the current regulation corresponding to a unit voltage error.

5. The low-voltage backup automatic transfer control method compatible with photovoltaics and energy storage as described in claim 1, characterized in that, The adaptive impedance matching algorithm is used to predict the maximum output power of the photovoltaic system at the next moment based on the real-time monitored irradiance, and dynamically adjusts the equivalent output impedance of the hybrid inverter and the discharge strategy of the energy storage system in conjunction with load changes. Specifically, it includes: ST1. Based on Light intensity at any time and solar panel temperature The mathematical formula for constructing a prediction model for the maximum power point of photovoltaic power at this time is as follows: in, for The maximum output power of photovoltaic power is predicted at any time. for Peak photovoltaic power under standard test conditions at any given time and They are respectively Real-time light intensity and standard light intensity at all times. for Temperature coefficient of power at any time and These are the real-time solar panel temperature and the standard test temperature, respectively. ST2. Based on the photovoltaic maximum power point prediction model, define The system efficiency that needs to be maximized at all times for: in, The system's instantaneous total efficiency. This represents the actual discharge power of the energy storage system. and These are the hybrid inverter's real-time monitored load power and photovoltaic output power, respectively. ST3. Calculate the impedance matching adjustment factor for dynamically adjusting the depth of energy storage discharge. The relevant formula is: in, The value range of is [0, 1]. A value close to 1 indicates that the load should be prioritized. A value close to 0 indicates that photovoltaic power is being prioritized. To determine the photovoltaic maximum power point based on real-time light intensity and ambient temperature. The time-based prediction model is used to represent the calculated maximum output power of the photovoltaic array; ST4. Based on adjustment factors The optimal value is found through iterative updates using the gradient ascent method. To maximize system efficiency The calculation formula is as follows: in, This is the impedance matching adjustment factor for the next control cycle. This is the impedance matching adjustment factor before the update. For learning rate, Indicates system efficiency The gradient of the adjustment factor.

6. The low-voltage backup automatic transfer control method compatible with photovoltaics and energy storage as described in claim 1, characterized in that, After the main grid returns to normal and operates stably for a specified time, the synchronous grid connection procedure is initiated. The frequency, amplitude and phase of the output voltage are synchronized with the main grid by using phase-locked loop technology through the hybrid inverter. Then, the ATS is closed at the synchronization point to achieve a disturbance-free back-switch of the load, and the main and backup power switching system is then restored to the grid-connected operation state.

7. The low-voltage backup automatic transfer control method compatible with photovoltaics and energy storage as described in claim 6, characterized in that, The hybrid inverter employs phase-locked loop (PLL) technology to obtain the phase error through dq transformation, thereby synchronizing the frequency, amplitude, and phase of the output voltage to be completely consistent with the main power grid. The transformation formula is as follows: in, The phase difference between the inverter output voltage and the grid voltage. and These are the components of the grid voltage in the dq synchronous rotating coordinate system. This refers to the output phase of the phase-locked loop inside the inverter.

8. A low-voltage standby automatic transfer control device compatible with photovoltaic and energy storage, applied to a set of main and standby power switching systems, and connected to a set of energy storage devices and the automatic transfer switch (ATS) of the system for control, used to execute the low-voltage standby automatic transfer control method compatible with photovoltaic and energy storage as described in any one of claims 1-7, characterized in that, include: The monitoring module is used to continuously collect electrical parameters of designated nodes of the system at high frequency, and is set with a specified safety threshold. When the main grid voltage amplitude and frequency in the collected parameters exceed the specified safety threshold, a "dynamic buffer bridge" function activation command is issued. The hybrid inverter module, upon receiving a function activation command, utilizes a built-in high-speed DSP controller and voltage source inverter topology to achieve seamless energy flow between the photovoltaic DC, energy storage DC, and the load AC side, ensuring that the current flowing through the ATS mains side contacts is essentially zero, and then sends a switching processing signal. The switching processing module is used to control the automatic transfer switch (ATS) to mechanically disconnect after receiving the switching processing signal. After the automatic transfer switch (ATS) completes its switching, the energy storage charging and discharging are dynamically adjusted through an adaptive impedance matching algorithm.

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