Interphase circulating current control method suitable for connecting three phases output by UPS (Uninterrupted Power Supply) into single phase in parallel

Abstract

The invention provides an interphase circulation control method suitable for connecting three phases output by a UPS (Uninterrupted Power Supply) into a single phase in parallel, and relates to the technical field of power electronic loop control. According to the technical scheme, the hardware current sharing mode is adopted by default to be matched with the three-phase synchronous wave sending mode, when the interphase circulation value exceeds the preset circulation threshold value, the scheme is automatically switched to the software current sharing mode to start the PI controller for intervention, and intelligent control strategy selection according to the actual circulation state is achieved. Compared with a mode of carrying out high-frequency sampling calculation in each PWM switching period in the prior art, by determining a control framework of the reference phase and the adjustment phase, only PI operation and duty ratio adjustment are carried out on the adjustment phase, and the calculation amount of single calculation is further reduced. According to the scheme, on the premise that it is guaranteed that the PI controller can control the interphase circulation value within the preset circulation threshold range and the interphase circulation balance precision is achieved, the operation burden of the CPU of the UPS control system is remarkably reduced.

Description

Technical Field

[0001] This application relates to the field of power electronic loop control technology, specifically to a phase-to-phase circulating current control method applicable to three-phase parallel connection of UPS output into a single phase. Background Technology

[0002] An uninterruptible power supply (UPS) is a device that uses an inverter to convert the DC power from an energy storage device into AC power for continuous supply when the mains power is abnormal. In UPS system applications, to meet the demands of single-phase loads, the outputs of three-phase inverters are often connected in parallel to form a single-phase output. Because the output voltage amplitudes of each phase of the three-phase inverter differ, circulating currents will be generated between the phases after parallel connection. These circulating currents can cause uneven current stress distribution in power devices, leading to overheating and failure; they can also introduce interference signals into the inverter control loop, causing system oscillations; and they can consume part of the load capacity, causing the UPS to overload prematurely. Therefore, effective control of interphase circulating currents is necessary.

[0003] The most common interphase circulating current equalization method in existing technologies is pure software high-frequency control. This method achieves precise current equalization by sampling three-phase current, calculating the circulating current difference, and adjusting the inverter duty cycle in real time during each PWM switching cycle. However, this method has significant drawbacks in UPS control systems. The interrupt service routine of the UPS system mainly handles core functions such as rectifier loop control and dual closed-loop control of inverter voltage and current. The high-frequency interphase circulating current control loop also needs to be added to the interrupt service routine for execution. It completes intensive computational tasks such as multi-phase current sampling, difference calculation, PI adjustment, and duty cycle update in each switching cycle, which leads to a significant increase in interrupt time, a significant increase in CPU utilization and computational burden, and affects the normal execution of other UPS control logic. Summary of the Invention

[0004] This application provides a phase-to-phase circulating current control method applicable to three-phase parallel connection of UPS output into a single phase, which can reduce the CPU's computational burden while ensuring the accuracy of phase-to-phase circulating current balance.

[0005] Firstly, this application provides a phase-to-phase circulating current control method applicable to three-phase parallel connection of UPS output into a single phase, the method comprising: Collect the effective value of the inverter current of each phase of the three-phase UPS power supply according to the preset power frequency cycle; Identify one reference phase and the other two remaining adjustment phases in the three-phase UPS power supply, and determine the difference between the effective value of the inverter current between each adjustment phase and the reference phase as the corresponding interphase circulating current value. When the circulating current value between each phase does not exceed the preset circulating current threshold, and the three-phase UPS power supply is in the default hardware current sharing mode, the waveform generation mode of each adjustment phase and the reference phase is determined to be the three-phase synchronous waveform generation mode. When the interphase circulating current value exceeds the preset circulating current threshold, the three-phase UPS power supply is controlled to switch from the default hardware current sharing mode to the software current sharing mode, and the waveform generation mode of the adjustment phase and the reference phase is determined to be the three-phase independent waveform generation mode. The inverter duty cycle of the adjustment phase is adjusted by the PI controller until the corresponding interphase circulating current value does not exceed the circulating current threshold.

[0006] By adopting the above technical solution, a hardware current sharing mode combined with three-phase synchronous waveform generation is used by default. When hardware consistency requirements are met, no software intervention for calculation and adjustment is needed; the natural balance of inter-phase circulating current is achieved directly through the inherent characteristics of the circuit, avoiding unnecessary CPU computational overhead. When the inter-phase circulating current value exceeds the preset circulating current threshold, the solution automatically switches to software current sharing mode and activates the PI controller for intervention, realizing intelligent selection of control strategy based on the actual circulating current state. Compared with the existing technology that performs high-frequency sampling calculations in each PWM switching cycle, by determining the control architecture of the reference phase and the adjustment phase, only PI calculations and duty cycle adjustments are performed on the adjustment phase, further reducing the computational load of a single calculation. This solution significantly reduces the computational burden on the UPS control system CPU while ensuring that the PI controller can control the inter-phase circulating current value within the preset circulating current threshold range and achieve accurate inter-phase circulating current balancing.

[0007] Secondly, this application provides a phase-to-phase circulating current control system suitable for three-phase parallel connection of UPS output into a single phase, the system comprising: The data acquisition module is used to acquire the effective value of the inverter current of each phase of the three-phase UPS power supply according to a preset power frequency cycle. The interphase circulating current calculation module is used to determine one reference phase and the other two remaining adjustment phases in a three-phase UPS power supply, and to determine the difference between the effective value of the inverter current between each adjustment phase and the reference phase as the corresponding interphase circulating current value. The hardware current sharing mode maintenance module is used to determine the waveform generation mode of each adjustment phase and the reference phase as the three-phase synchronous waveform generation mode when the circulating current value between each phase does not exceed the preset circulating current threshold and the three-phase UPS power supply is in the default hardware current sharing mode. The software current sharing mode control module is used to control the three-phase UPS power supply to switch from the default hardware current sharing mode to the software current sharing mode when the inter-phase circulating current value exceeds the preset circulating current threshold. It also determines the waveform generation mode of the adjustment phase and the reference phase as the three-phase independent waveform generation mode, and adjusts the inverter duty cycle of the adjustment phase through the PI controller until the corresponding inter-phase circulating current value does not exceed the circulating current threshold.

[0008] Thirdly, this application provides a computer storage medium that stores multiple instructions adapted for loading by a processor and executing any of the methods described above.

[0009] Fourthly, this application provides an electronic device including a processor, a memory, and a transceiver. The memory is used to store instructions, the transceiver is used to communicate with other devices, and the processor is used to execute the instructions stored in the memory to cause the electronic device to perform any of the methods described above.

[0010] In summary, the beneficial effects of the technical solution of this application include: By default employing hardware current sharing mode in conjunction with three-phase synchronous waveform generation, and provided hardware consistency requirements are met, no software intervention for calculation and adjustment is needed. The system directly relies on the inherent characteristics of the circuit to achieve natural phase-to-phase circulating current balance, avoiding unnecessary CPU computational overhead. When the phase-to-phase circulating current value exceeds the preset circulating current threshold, the solution automatically switches to software current sharing mode and activates the PI controller for intervention, achieving intelligent selection of control strategy based on the actual circulating current state. Compared to existing technologies that perform high-frequency sampling calculations in each PWM switching cycle, this solution, by defining the control architecture of the reference phase and the adjustment phase, only performs PI calculations and duty cycle adjustments on the adjustment phase, further reducing the computational load per calculation. This solution significantly reduces the computational burden on the UPS control system's CPU while ensuring that the PI controller can control the phase-to-phase circulating current value within the preset circulating current threshold range and achieve phase-to-phase circulating current balancing accuracy. Attached Figure Description

[0011] Figure 1 This is a schematic flowchart of a phase-to-phase circulating current control method for a UPS output three-phase parallel connection into a single phase, provided in an embodiment of this application. Figure 2 This is an exemplary system block diagram provided in this application embodiment for interphase circulating current control of three-phase output of a UPS connected in parallel to form a single phase; Figure 3 This is a flowchart illustrating an exemplary method for controlling interphase circulating current in a UPS output where three phases are connected in parallel to form a single phase, as provided in this application embodiment. Figure 4 This is a schematic diagram of a phase-to-phase circulating current control system for a UPS output three-phase parallel connection into a single phase, provided in an embodiment of this application. Figure 5 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application.

[0012] Explanation of reference numerals in the attached figures: 500, electronic device; 501, processor; 502, communication bus; 503, user interface; 504, network interface; 505, memory. Detailed Implementation

[0013] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0014] In the description of the embodiments of this application, words such as "illustrative," "for example," or "for example" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as "illustrative," "for example," or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design solutions. Rather, the use of words such as "illustrative," "for example," or "for example" is intended to present the relevant concepts in a specific manner.

[0015] In the description of the embodiments of this application, the term "multiple" means two or more. For example, multiple systems means two or more systems, and multiple screen terminals means two or more screen terminals. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. The terms "comprising," "including," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0016] Please see Figure 1 This document presents a flowchart illustrating a phase-to-phase circulating current control method for a UPS output where three phases are connected in parallel to form a single phase, as provided in this embodiment. This method can be implemented using a computer program, a microcontroller, or run on a von Neumann-based phase-to-phase circulating current control system for a UPS output where three phases are connected in parallel to form a single phase. The computer program can be integrated into the application or run as a standalone utility application. The specific steps of the phase-to-phase circulating current control method for a UPS output where three phases are connected in parallel to form a single phase are described in detail below.

[0017] S101: Collect the effective value of the inverter current of each phase of the three-phase UPS power supply according to the preset power frequency cycle; Among them, the preset power frequency cycle refers to the sampling period determined according to the basic frequency of the power grid, which is usually the mains power cycle, such as 20ms in a 50Hz power grid. This period is used to determine the time interval for collecting the effective value of the inverter current; a three-phase UPS power supply refers to an uninterruptible power supply system with three independent inverter bridge arms: R phase, S phase, and T phase. These three phases can output independently or in parallel; the effective value of the inverter current represents the root mean square value of the inverter output current of each phase within a complete power frequency cycle. This value can truly reflect the effective power transmission capacity of the current.

[0018] Specifically, the system first determines the sampling period based on the current operating frequency, triggering the sampling calculation process at the end of each operating frequency cycle. The controller acquires the instantaneous inverter current values ​​of phases R, S, and T through high-speed AD sampling. These instantaneous values ​​are continuously acquired throughout the entire operating frequency cycle. The sampling frequency is typically the PWM switching frequency or an integer multiple thereof to ensure sampling accuracy. After a complete operating frequency cycle, the system calculates the effective value for each phase. The calculation method involves first squaring the current values ​​at all sampling points within the cycle, then calculating the average of these squared values, and finally taking the square root of the average value to obtain the effective inverter current value for that phase. Because the sampling period covers the complete sine wave cycle, interference caused by instantaneous fluctuations can be eliminated, making the calculation results more stable and reliable.

[0019] In some embodiments, the acquisition and calculation of the RMS value of the inverter current can be achieved in several ways: Optionally, a hardware RMS calculation chip can be used. First, a dedicated RMS measurement chip (such as AD637, LTC1966, etc.) is connected to the current sampling circuit of each phase. Then, the RMS value of the current is calculated in real time through an analog signal processing circuit. Finally, at the end of each power frequency cycle, the microcontroller reads the RMS voltage signal output by the chip through an AD converter and converts it into a digital quantity. The advantage of this method is that it reduces the computational burden on the CPU, but it increases the hardware cost. Optionally, a software discrete sampling calculation method can be used. First, the three-phase current is synchronously sampled at fixed moments in each PWM cycle. The sampling frequency is set to an integer multiple of the PWM frequency to ensure sampling synchronization. Then, the sampled instantaneous current values ​​are stored in a circular buffer. When the number of sampling points in one power frequency cycle reaches a preset value (e.g., 400 samplings at 50Hz, resulting in 400 sampling points per cycle), the 400 sampled values ​​are squared and summed. The sum is then divided by the number of sampling points to obtain the average value. Finally, the square root of this average value is taken to obtain the effective value. This purely software approach is highly flexible but consumes certain CPU resources and storage space. It is understandable that a DMA-based fast sampling method or a hardware-accelerated calculation method using a digital signal processor can also be used to acquire the effective value of the inverter current; this is not limited here.

[0020] S102: Determine one reference phase and the other two remaining adjustment phases of the three-phase UPS power supply, and determine the difference between the effective value of the inverter current between each adjustment phase and the reference phase as the corresponding interphase circulating current value. In this context, the reference phase refers to a phase selected as the reference standard during interphase circulating current control. The control parameters of this phase remain unchanged, and other phases are adjusted based on this phase. Typically, phase S is selected as the reference phase. The adjustment phase indicates the phase that needs to be controlled and adjusted to eliminate interphase circulating current. In a three-phase system, when phase S is selected as the reference phase, phases R and T are the adjustment phases. The inverter parameters of these two phases will be dynamically adjusted according to the current difference with the reference phase. The interphase circulating current value refers to the difference in the effective value of the inverter current between the adjustment phase and the reference phase. This difference reflects the degree of imbalance in the interphase current distribution.

[0021] Specifically, this step is executed immediately after obtaining the effective values ​​of the three-phase inverter current to quantify the degree of current imbalance between phases. The system first determines the reference phase based on a preset control strategy, typically setting phase S as the reference phase because it is in the middle of the three phases, making control more symmetrical and stable. After determining the reference phase, the system identifies phases R and T as the adjustment phases that need adjustment. Then, the interphase circulating current value is calculated. For phase R, the interphase circulating current value of RS is obtained using the formula e(t)_RS=RInvCurRms-SInvCurRms, where RInvCurRms represents the effective value of the inverter current in phase R, and SInvCurRms represents the effective value of the inverter current in phase S. For phase T, the interphase circulating current value of ST is obtained using the formula e(t)_ST=TInvCurRms-SInvCurRms, where TInvCurRms represents the effective value of the inverter current in phase T.

[0022] Optionally, for determining the reference phase, current characteristic indicators can be extracted from the effective value of the inverter current, and interphase circulating current indicators can be extracted from the interphase circulating current values; the reference phase is then determined based on the current characteristic indicators and the interphase circulating current indicators. The interphase circulating current indicators represent the degree of imbalance between the output currents of each phase.

[0023] In some embodiments, to improve the scientific rigor and adaptability of the reference phase selection, an intelligent reference phase determination method based on multi-dimensional index evaluation can be adopted. This method no longer simply fixes the S phase as the reference phase, but comprehensively considers the actual operating state of each phase, and dynamically selects the optimal reference phase by analyzing the RMS characteristics of the inverter current and the inter-phase circulating current distribution, thereby making subsequent circulating current control more efficient and stable.

[0024] In practical implementation, the system first extracts current characteristic indicators from the effective values ​​of the three-phase inverter current RInvCurRms, SInvCurRms, and TInvCurRms. These indicators include three dimensions: the magnitude of the current in each phase, current stability, and current variation trend. The magnitude of the current directly reflects the load currently borne by that phase. Current stability is assessed by calculating the standard deviation of the effective current values ​​over multiple consecutive power frequency cycles; a smaller standard deviation indicates a more stable current in that phase. The current variation trend is determined by comparing the difference between the current value in the current cycle and the current value in the previous cycle to determine whether the phase is in a dynamic adjustment state. The system calculates the standard deviation of the current in each phase using the formula StdDev=sqrt(∑(I_current-I_avg)² / N), where I_current is the current value in the current cycle, and I_avg is the average current value over the most recent N cycles, with N typically being 5 to 10 power frequency cycles. Simultaneously, the system extracts the interphase circulation index from the calculated interphase circulation values. This index mainly assesses the degree of circulation deviation between the other two phases when a certain phase is used as a reference. It is calculated by assuming the total circulation deviation when phase R is used as a reference, Sum_R = |SInvCurRms-RInvCurRms| + |TInvCurRms-RInvCurRms|, assuming the total circulation deviation when phase S is used as a reference, Sum_S = |RInvCurRms-SInvCurRms| + |TInvCurRms-SInvCurRms|, and assuming the total circulation deviation when phase T is used as a reference, Sum_T = |RInvCurRms-TInvCurRms| + |SInvCurRms-TInvCurRms|. The smaller the total deviation, the smaller the circulation adjustment amount of the adjusting phase when phase T is used as a reference.

[0025] S103: When the circulating current value between each phase does not exceed the preset circulating current threshold, if the three-phase UPS power supply is in the default hardware current sharing mode, the waveform generation mode of each adjustment phase and the reference phase will be determined as the three-phase synchronous waveform generation mode. Among them, the preset circulating current threshold refers to the upper limit of the allowable range of inter-phase circulating current set in advance by the system, denoted as InvCirLimit. This threshold is determined by the software developers based on the system's power level, device characteristics, and heat dissipation capacity, and is usually set between 3% and 10% of the rated current. The hardware current sharing mode refers to the working mode that relies on the consistency of hardware circuits to achieve natural current balance between phases. In this mode, no active circulating current control is performed by the software. Each phase achieves current balance by driving the same power devices and filter circuits through synchronous PWM signals. The three-phase synchronous waveform generation mode refers to the control mode in which the R phase, S phase, and T phase use the exact same PWM duty cycle and phase for driving. That is, the S phase PWM is equal to the T phase PWM, which is equal to the R phase PWM. The switching time of the three phases is strictly synchronized. Only the PWM parameters of one phase need to be calculated and then synchronously applied to the other two phases. The waveform generation mode refers to the generation and output strategy of the PWM signal, including synchronous waveform generation and independent waveform generation modes. Synchronous waveform generation means that multiple phases use the same PWM parameters, while independent waveform generation means that each phase calculates and outputs different PWM parameters.

[0026] Specifically, the system first takes the absolute values ​​of the two phase-to-phase circulating currents, ΔI_CIR_RS and ΔI_CIR_ST, and then compares them with the preset circulating current threshold InvCirLimit. The judgment condition is whether both |ΔI_CIR_RS|≤InvCirLimit and |ΔI_CIR_ST|≤InvCirLimit are simultaneously true. When both circulating current values ​​are within the threshold range, it indicates that the current hardware consistency is good, the current difference between the three phases is within an acceptable range, and no software intervention is required. However, before executing three-phase synchronous waveform generation, the system needs to further determine whether the corresponding PI controllers for each adjustment have been started. This is because if the PI controllers have already been started and are working, then the circulating current value within the threshold may be the result of the PI controller adjustment. In this case, the PI controllers should not be shut down immediately, but the software current sharing mode should continue to be maintained. Only when the circulating current value is within the threshold and the PI controllers of each adjustment phase have not been started can it be confirmed that the current is a good current sharing state achieved by hardware consistency, and only then will the system set the waveform generation mode to three-phase synchronous waveform generation mode. In the three-phase synchronous waveform mode, the system only calculates the PWM duty cycle of the S phase (reference phase) and then directly copies the duty cycle value to the R phase and T phase, thereby reducing the PWM calculation workload by two-thirds and significantly reducing the CPU interrupt utilization rate.

[0027] S104: When the interphase circulating current value exceeds the preset circulating current threshold, the three-phase UPS power supply is controlled to switch from the default hardware current sharing mode to the software current sharing mode, and the waveform generation mode of the adjustment phase and the reference phase is determined to be the three-phase independent waveform generation mode. The inverter duty cycle of the adjustment phase is adjusted by the PI controller until the corresponding interphase circulating current value does not exceed the circulating current threshold.

[0028] Among them, the software current sharing mode refers to the working mode in which the PWM parameters of each phase are actively calculated and adjusted by software algorithm to achieve current balance. In this mode, the control parameters of each phase are dynamically calculated by software according to the real-time current difference, no longer relying on the inherent consistency of the hardware circuit; the three-phase independent waveform generation mode refers to the control mode in which the R phase, S phase and T phase independently calculate the PWM duty cycle and output timing according to their own control requirements. The PWM parameters of each phase can be different, allowing the hardware differences to be compensated by differentiated duty cycles; the PI controller stands for proportional-integral controller, which is a classic closed-loop control algorithm. It includes a proportional element and an integral element. The proportional element Kp responds quickly according to the current error, and the integral element Ki eliminates steady-state deviation by accumulating historical errors. Its output formula is u(t)=Kp×e(t)+Ki×∫e(t)dt; the inverter duty cycle refers to the proportion of the high level time of the inverter bridge arm PWM signal to the entire PWM cycle. This proportion directly determines the effective value of the inverter output voltage. Adjusting the duty cycle can change the output voltage and thus affect the output current.

[0029] Specifically, this step is triggered immediately upon detecting that any interphase circulating current value exceeds the threshold, initiating active software circulating current control. The system detects excessive circulating current by logically judging whether the absolute value of the RS interphase circulating current value or the absolute value of the ST interphase circulating current value exceeds the preset circulating current threshold. If either condition is true, it indicates that hardware current sharing is insufficient, and software current sharing must be initiated. First, the system switches its operating mode from hardware current sharing mode to software current sharing mode. This switch is achieved by setting a global mode flag and triggering the corresponding mode switching interrupt handler. Then, the system changes the waveform generation method from three-phase synchronous waveform generation to three-phase independent waveform generation. This means that the PWM calculations for the R and T phases will be independent of the S phase, no longer simply copying the S phase PWM parameters. Next, the system starts its respective PI controllers for the R and T phases. The input to the R phase PI controller is the RS interphase circulating current value, and the input to the T phase PI controller is the ST interphase circulating current value. The PI controller calculates proportional and integral regulation based on the interphase circulating current value. The integral regulation is obtained by adding the historical error integral value to the product of the current interphase circulating current value and the integral gain. The PI controller output is then fed into the inverter voltage RMS loop for processing. The sign of the circulating current value determines whether to increase or decrease the output voltage of the adjusted phase: when the interphase circulating current value is greater than zero, it indicates that the adjusted phase current is too large, and its output voltage needs to be reduced; the output of the inverter voltage RMS loop is subtracted from the PI controller output. When the interphase circulating current value is less than zero, it indicates that the adjusted phase current is too small, and its output voltage needs to be increased; the output of the inverter voltage RMS loop is added to the PI controller output. The adjusted voltage RMS output is further converted into a PWM duty cycle, and the inverter output voltage is actually adjusted by changing the duty cycle. This closed-loop regulation process continues in each power frequency cycle until both the RS and ST interphase circulating current values ​​converge to the threshold range. At this point, the interphase circulating current is effectively suppressed, but the system remains in software current sharing mode, continuing to monitor circulating current changes to prevent further exceedances.

[0030] For the specific flow sharing control process in this application, please refer to [link / reference]. Figure 2 , Figure 2 This application provides an exemplary system block diagram for interphase circulating current control of a UPS output where three phases are connected in parallel to form a single phase. Figure 2 The example uses phase S as the reference phase. From... Figure 2 As can be seen, the entire control system receives the effective values ​​of the R-phase inverter current, the S-phase inverter current, and the T-phase inverter current as input signals. These three input signals represent the actual current values ​​output by the three-phase inverters, respectively. The system contains two parallel control paths, corresponding to RS-phase interphase circulating current control and ST-phase interphase circulating current control, respectively.

[0031] In the RS phase-to-phase circulating current control path, the effective values ​​of the R-phase inverter current and the S-phase inverter current are first input to the RS phase-to-phase circulating current calculation module. This module calculates the difference between the two-phase currents to obtain the RS phase-to-phase circulating current. Then, the RS phase-to-phase circulating current enters the RS phase-to-phase circulating current threshold determination module. This module determines whether the absolute value of the RS phase-to-phase circulating current is within a preset threshold range. If it exceeds the threshold range, the subsequent PI control loop is activated; if it is within the threshold range, no adjustment is made. Next, the RS phase-to-phase circulating current is sent to the RS phase-to-phase circulating current PI controller. This PI controller performs proportional-integral calculations based on the RS phase-to-phase circulating current error integral, outputting a current adjustment amount. This current adjustment amount is input to the R-phase inverter voltage effective value loop. In this loop, the current adjustment amount is superimposed on the conventional voltage control output of the R-phase, obtaining the R-phase voltage command value after circulating current compensation.

[0032] In the ST phase-to-phase circulating current control path, the effective values ​​of the S-phase inverter current and the T-phase inverter current are first input to the ST phase-to-phase circulating current calculation module. This module calculates the difference between the two phase currents to obtain the ST phase-to-phase circulating current. Then, the ST phase-to-phase circulating current enters the ST phase-to-phase circulating current threshold determination module. This module also determines whether the absolute value of the ST phase-to-phase circulating current exceeds a preset threshold range, and decides whether to initiate regulation based on the determination result. Next, the ST phase-to-phase circulating current is sent to the ST phase-to-phase circulating current PI controller. This PI controller performs proportional-integral calculations based on the ST phase-to-phase circulating current error integral, outputting the current adjustment amount for the T phase. This current adjustment amount is input to the T-phase inverter voltage effective value loop. In this loop, the current adjustment amount is superimposed on the T-phase conventional voltage control output to obtain the T-phase voltage command value after circulating current compensation.

[0033] Since phase S is set as the reference phase, the S-phase inverter voltage RMS loop does not receive adjustment input from the circulating current PI controller and operates only according to conventional voltage control output. The outputs of the R-phase and T-phase inverter voltage RMS loops are modulated by PWM to generate R / S / T three-phase synchronous and independent three-phase waveform signals, respectively. The three-phase synchronous waveform signal ensures that the switching actions of the three-phase inverter remain phase-synchronized, while the three-phase independent waveform signal independently adjusts the PWM duty cycle of each phase according to the needs of circulating current control. Through this dual-path parallel control architecture, the system can simultaneously and precisely adjust the output voltages of phases R and T, aligning the R-phase current with the S-phase current and the T-phase current with the S-phase current, ultimately achieving balanced output of the three-phase current and effectively suppressing interphase circulating current.

[0034] Based on the above embodiments, as an optional implementation method, the method of adjusting the inverter duty cycle of the adjustment phase by means of the PI controller in S104 can be specifically implemented through the following steps S201-S203.

[0035] S201: Obtain the integral of the interphase circulating current error of the adjusted phase, and input the integral of the interphase circulating current error of the adjusted phase and the interphase circulating current value into the PI controller to obtain the current loop adjustment output value; Among them, the phase-to-phase circulating current error integral refers to the value obtained by accumulating the phase-to-phase circulating current values ​​detected in each sampling period according to the integral algorithm during the software current sharing control process. This integral reflects the cumulative effect of the circulating current deviation and is used to eliminate the steady-state error of the system. The current loop adjustment output value represents the control quantity calculated by the PI controller based on the current phase-to-phase circulating current value and the historical integral. This output value will be applied to the inverter voltage regulation stage to guide the voltage adjustment direction and amplitude of the adjusted phase.

[0036] Specifically, this step is executed at the end of each power frequency cycle after the software current sharing mode is started, and is used to calculate the adjustment output of the PI controller. The system first reads the integral value of the interphase circulating current error corresponding to the adjustment from the memory. This integral value has been calculated and saved in the previous control cycle. For the R-phase adjustment phase, the RS-phase interphase circulating current error integral value is read; for the T-phase adjustment phase, the ST-phase interphase circulating current error integral value is read. After reading, the system simultaneously sends the interphase circulating current error integral value and the interphase circulating current value newly acquired and calculated in the current power frequency cycle to the PI controller of the corresponding adjustment phase. The PI controller internally has two parallel processing paths: a proportional calculation channel and an integral calculation channel. In the proportional calculation channel, the interphase circulating current value is multiplied by the preset proportional gain parameter to obtain the proportional adjustment component, which can quickly respond to the current circulating current deviation. In the integral calculation channel, the interphase circulating current error integral value is first multiplied by the integral gain parameter to obtain the integral adjustment component, which can eliminate long-term steady-state deviations. Then, the proportional adjustment component and the integral adjustment component are summed to obtain the total output of the PI controller, i.e., the current loop adjustment output value. The sign and magnitude of the current loop adjustment output value directly reflect the amount of output voltage that needs to be increased or decreased in the adjusted phase.

[0037] Optionally, the integral of the interphase circulating current error and the interphase circulating current value of the adjusted phase are substituted into the interphase circulating current control formula in the PI controller to obtain the current loop adjustment output value. The interphase circulation control formula is: U(t) = Kp*e(t) + SumError; Where U(t) represents the current loop adjustment output value, Kp represents the proportional gain of the PI controller, e(t) represents the corresponding interphase circulating current value, and SumError represents the integral amount of the interphase circulating current error.

[0038] The meanings of each part in the formula are as follows: The current loop adjustment output value on the left side of the equal sign represents the final control quantity output by the PI controller. This value will act on the voltage regulation stage of the adjusted phase to guide the direction and magnitude of the increase or decrease of the phase output voltage. The right side of the equal sign contains two summed terms: the first is the proportional control component, and the second is the integral control component. The proportional control component is obtained by multiplying the proportional gain by the interphase circulating current value. The proportional gain is the proportional coefficient parameter of the PI controller, which determines the controller's response speed and response strength to the current circulating current deviation. The larger the value, the more sensitive the response to the circulating current deviation. The interphase circulating current value represents the current difference between the adjusted phase and the reference phase within the current power frequency cycle. The sign of this difference reflects whether the current of the adjusted phase is larger or smaller than the current of the reference phase, and the absolute value reflects the degree of deviation. The integral control component is the integral of the interphase circulating current error. This quantity is the cumulative value of the circulating current deviation in each historical sampling cycle, reflecting the time accumulation effect of the circulating current deviation.

[0039] The calculation principle of this formula is based on the classical PI control theory. When the interphase circulating current value is not zero, it indicates that there is a current deviation between the adjusting phase and the reference phase. The proportional control term multiplies the interphase circulating current value by a proportional gain, enabling the controller to react immediately to the current circulating current deviation and generate an adjustment amount proportional to the magnitude of the deviation. The characteristic of proportional control is rapid response and the ability to quickly suppress sudden changes in circulating current, but proportional control alone cannot completely eliminate steady-state deviation. The integral control term accumulates historical circulating current errors to form an integral quantity of interphase circulating current error. This integral quantity will continue to grow as the deviation persists until it stops changing when the deviation is completely eliminated. The role of integral control is to eliminate the steady-state error of the system. Even if the circulating current deviation is small, as long as it persists, the integral term will continue to accumulate and generate sufficient control output to completely eliminate the deviation. The current loop adjustment output value obtained by adding the proportional and integral terms has the advantages of both fast response and zero steady-state error. It can react promptly to rapid changes in circulating current and accurately control the circulating current to zero in steady state.

[0040] The PI control formula is used in this application to achieve precise interphase circulating current suppression in a three-phase UPS system connected in parallel to form a single phase. When three-phase inverters supply power to a single-phase load in parallel, differences in output characteristics and parameters between the inverters, as well as uneven load distribution, can lead to interphase circulating currents. These circulating currents not only increase the system's circulating current losses but may also trigger inverter overload protection, affecting system reliability. By employing this PI control formula, the system can quickly calculate the required voltage adjustment based on the real-time detected interphase circulating current value. The proportional term enables rapid suppression of sudden circulating current changes, while the integral term completely eliminates minute circulating currents. S202: Output the current loop adjustment output value to the inverter voltage RMS value loop, and calculate and adjust the corresponding inverter voltage RMS value output value; The inverter voltage RMS loop refers to the closed-loop control loop in the UPS system responsible for adjusting the RMS value of the inverter output voltage. This loop receives the voltage setpoint and the actual voltage feedback value, and calculates the required inverter voltage output based on the deviation. In this invention, the loop also needs to be superimposed with the adjustment amount of the circulating current control. The inverter voltage RMS output value represents the voltage command value calculated by the voltage control loop and superimposed with the circulating current adjustment. This value will be converted into the PWM duty cycle in subsequent steps to drive the switching devices of the inverter bridge arm.

[0041] Specifically, this step is executed immediately after the current loop adjustment output value is calculated, and is used to integrate the circulating current control quantity into the voltage regulation process. The system first reads the normal output of the inverter voltage RMS loop, which is the reference voltage regulation quantity calculated by the voltage outer loop PI controller based on the difference between the voltage setpoint and the voltage feedback value. For the reference phase, its inverter voltage RMS output value is directly equal to the normal output of the inverter voltage RMS loop, and no circulating current adjustment is required. For the adjustment phase, the current loop adjustment output value needs to be added to or subtracted from the normal output of the inverter voltage RMS loop. The specific addition direction depends on the sign of the current loop adjustment output value, which is determined by the positive or negative sign of the inter-phase circulating current value. When the current loop adjustment output value is positive, it indicates that the output current of the adjustment phase is greater than that of the reference phase, and the output voltage of the adjustment phase needs to be reduced to reduce its output current. At this time, the absolute value of the current loop adjustment output value is subtracted from the normal output of the inverter voltage RMS loop to obtain the inverter voltage RMS output value of the adjustment phase. When the current loop adjustment output value is negative, it indicates that the output current of the adjusted phase is less than that of the reference phase. Therefore, the output voltage of the adjusted phase needs to be increased to enhance its output current. In this case, the absolute value of the current loop adjustment output value is added to the normal output of the inverter voltage RMS loop to obtain the RMS output value of the adjusted phase. Through this addition and subtraction, the voltage adjustment amount by the circulating current control is precisely integrated into the output of the voltage control loop, achieving coordinated control of circulating current suppression and voltage regulation.

[0042] Based on the above embodiments, as an optional implementation method, the method of outputting the current loop adjustment output value to the inverter voltage effective value loop in S202 and calculating and adjusting the corresponding inverter voltage effective value output value can be specifically implemented through the following steps S2021-S2024.

[0043] S2021: Obtain the original output value of the adjustment phase in the inverter voltage RMS loop; The original output value refers to the reference voltage control quantity calculated by the voltage outer loop PI controller when the inverter voltage effective value loop does not consider the circulating current adjustment. This value is generated by the deviation between the voltage setpoint and the voltage feedback value after PI calculation, and represents the standard modulation signal amplitude required to maintain the stability of the output voltage.

[0044] Specifically, this step is executed immediately after the current loop adjustment output value is calculated, serving as a preparatory step for integrating the circulating current control quantity into voltage regulation. The system first locates the inverter voltage RMS controller module corresponding to the adjustment phase. This module performs routine voltage closed-loop control calculations in each control cycle. The voltage controller receives two input signals: one is the voltage setpoint, which is set by the host system or user to determine the desired output voltage amplitude; the other is the voltage feedback value, which comes from the voltage sampling circuit at the output end and is used to calculate the actual output voltage RMS value. The voltage controller calculates the difference between the voltage setpoint and the voltage feedback value to obtain the voltage error, and then sends the voltage error to the voltage loop PI regulator for proportional-integral calculation. The voltage loop PI regulator internally maintains the integral accumulation of the voltage error. Multiplying the current voltage error by the proportional gain yields the proportional regulation, and multiplying the integral accumulation of the voltage error by the integral gain yields the integral regulation. The sum of these two values ​​is output to the voltage controller's output register, where the value stored is the original output value.

[0045] S2022: Determine whether the corresponding phase-to-phase circulating current value is greater than zero; S2023: If the interphase circulating current value is greater than zero, the original output value is subtracted from the current loop adjustment output value to obtain the effective value of the inverter voltage output value, so as to reduce the output voltage of the adjustment phase; Specifically, this step is executed after the condition that the interphase circulating current value is greater than zero is met, achieving the control objective of reducing the output current of the regulating phase by lowering its output voltage. When the interphase circulating current value is greater than zero, it means that the actual output current of the regulating phase exceeds the output current of the reference phase, the regulating phase inverter is outputting excessive power to the load side, and at the same time, some current forms a circulating current flowing back to the reference phase. In this state, it is necessary to reduce the output voltage amplitude of the regulating phase to effectively increase its output impedance, thereby reducing the current supplied by the regulating phase to the load, and finally reducing the regulating phase current to the same level as the reference phase current. The system first reads the previously saved original output value from the temporary variable, which represents the standard control quantity for maintaining stable output voltage. Then it reads the current loop adjustment output value, which is calculated by the PI controller based on the interphase circulating current value and the integral of the circulating current error, and its magnitude reflects the voltage amplitude required to suppress the circulating current. Then, a subtraction operation is performed, subtracting the current loop adjustment output value from the original output value to obtain the effective value of the inverter voltage output after circulating current compensation. The subtraction operation makes the effective value of the inverter voltage output less than the original output value. When this output value is applied to the subsequent PWM modulation stage, it will reduce the duty cycle, shorten the conduction time of the inverter bridge arm, and reduce the effective value of the output voltage.

[0046] S2024: If the phase-to-phase circulating current value is less than zero, the original output value is added to the current loop adjustment output value to obtain the effective value of the inverter voltage output value, thereby increasing the output voltage of the adjusted phase.

[0047] Specifically, this step is executed after determining that the interphase circulating current value is less than zero, achieving the control objective of increasing the output current of the regulating phase by increasing its output voltage. When the interphase circulating current value is less than zero, it means that the actual output current of the regulating phase is lower than the output current of the reference phase. The power output from the regulating phase inverter to the load side is insufficient, and the reference phase bears more load current. Simultaneously, some current forms a circulating current flowing from the reference phase to the regulating phase. In this state, it is necessary to increase the output voltage amplitude of the regulating phase to effectively reduce its output impedance, thereby increasing the current supplied by the regulating phase to the load, ultimately increasing the regulating phase current to the level equal to the reference phase current. The system first reads the previously saved original output value from temporary variables. This value is the reference control quantity used by the voltage loop PI controller to maintain stable voltage output. Then, it reads the current loop regulating output value. Since the interphase circulating current value is less than zero, the current loop regulating output value output by the PI controller usually carries a negative sign or is marked as a boost direction in the control logic. Next, an addition operation is performed, adding the absolute value of the current loop regulating output value to the original output value to obtain the effective value of the inverter voltage after circulating current compensation. The addition operation makes the effective value of the inverter voltage output greater than the original output value. When this output value is transmitted to the PWM modulation stage, it will increase the duty cycle, prolong the conduction time of the inverter bridge arm, and increase the effective value of the output voltage.

[0048] S203: Determine the target duty cycle of the adjustment phase based on the effective value of the inverter voltage output, and adjust the inverter duty cycle of the adjustment phase according to the target duty cycle.

[0049] The target duty cycle refers to the expected value of the PWM signal duty cycle calculated based on the effective value of the inverter voltage output. This duty cycle determines the proportion of the on-time of the inverter bridge arm to the entire switching cycle. The inverter duty cycle refers to the actual PWM duty cycle value currently applied to the inverter bridge arm drive circuit. This value is achieved through the configuration of the timer compare register and determines the actual on-time of the power switch.

[0050] Specifically, this step is executed immediately after the effective value of the inverter voltage is calculated, and it is used to convert the voltage command into the actual PWM drive signal. The system first calls the duty cycle conversion function, which establishes the correspondence between the effective value of the inverter voltage and the PWM duty cycle based on the inverter's output characteristics. The input of the conversion function is the effective value of the inverter voltage, and the output is the corresponding target duty cycle value. The conversion process considers the influence of factors such as DC bus voltage, modulation method, and filter parameters. For systems using sinusoidal pulse width modulation, the conversion function divides the effective value of the inverter voltage output by the DC bus voltage to obtain the modulation ratio, and then calculates the duty cycle variation pattern in each switching cycle based on the modulation ratio. For systems using space vector modulation, the conversion function calculates the corresponding voltage vector based on the effective value of the inverter voltage output, and then obtains the duty cycle sequence of the three-phase bridge arms according to the vector synthesis principle. After obtaining the target duty cycle, the system compares this value with the current actual inverter duty cycle. If there is a difference between the target duty cycle and the current duty cycle, the configuration of the PWM generator needs to be updated. The system writes the target duty cycle value into the PWM timer compare register of the corresponding adjustment phase. The value of this register determines the moment when the level toggles when the timer count value equals the compare value, thus changing the duty cycle of the PWM signal. The write operation is typically performed at a specific update moment in the PWM cycle to avoid waveform distortion caused by updates in the middle of half a cycle. After the update is complete, the new duty cycle takes effect at the start of the next PWM cycle. The inverter bridge arms switch according to the new duty cycle, outputting the corresponding voltage waveform, thereby achieving precise control of the output voltage of the adjustment phase.

[0051] Based on the above embodiments, as an optional implementation method, in step S103, when the circulating current value between each phase does not exceed the preset circulating current threshold and the three-phase UPS power supply is in the default hardware current sharing mode, the wave generation mode of each adjustment phase and the reference phase is determined as the calculation method of the three-phase synchronous wave generation mode, specifically including steps S301-S302.

[0052] S301: When the circulating current value between each phase does not exceed the preset circulating current threshold, determine whether the corresponding PI controller for each adjustment is started. Specifically, the program first reads all interphase circulating current values ​​stored in the memory sequentially. Since the system uses one phase as the reference phase and the others as adjustment phases, the number of interphase circulating current values ​​to be read is equal to the number of adjustment phases. For a three-phase UPS system, typically one phase is selected as the reference phase and the other two as adjustment phases, so two interphase circulating current values ​​need to be read for judgment. After reading, the program compares the absolute value of each interphase circulating current value with a preset circulating current threshold one by one. The comparison operation is implemented through numerical magnitude judgment instructions. If the absolute value of a certain interphase circulating current value exceeds the preset circulating current threshold, it indicates that there is a large current imbalance between the adjustment phase and the reference phase. The comparison result is an over-threshold state. At this time, the precondition of this step is not met, and the program does not execute the subsequent PI controller start-up status judgment, but directly jumps to the circulating current active control flow to start the PI controller of the corresponding adjustment phase for circulating current suppression. If the absolute values ​​of all inter-phase circulating currents do not exceed the preset circulating current threshold, it indicates that the current difference between each adjusted phase and the reference phase is within the normal range, and the comparison result is within the threshold state. At this time, the precondition of this step is met, and the program continues to execute the PI controller startup status judgment operation. The program sequentially accesses the PI controller instance corresponding to each adjustment and reads the startup status flag bit inside each PI controller. This flag bit records whether the PI controller is currently in working state. If the startup status flag bit of a certain PI controller is true, it means that the PI controller is performing circulating current control calculation, and the system is in software active current sharing mode. If the startup status flag bits of all PI controllers are false, it means that all PI controllers are not working, and the system is in hardware current sharing mode.

[0053] S302: If none of the corresponding PI controllers for each adjustment are started, then confirm that the three-phase UPS power supply is in the default hardware current sharing mode, and determine the waveform generation mode of each adjustment phase and the reference phase as the three-phase synchronous waveform generation mode.

[0054] Specifically, when none of the corresponding PI controllers are activated, it indicates that the system is not currently executing any software-level active current sharing control algorithm, and the inverters rely entirely on the inherent characteristics of the hardware circuitry to achieve current distribution. First, the system operating mode flag is set to hardware current sharing mode. This flag is stored in the system status register for use by the monitoring program and the host computer. Confirmation of hardware current sharing mode means that the system recognizes the current circulating current level as being within the range that the hardware circuitry can handle. The consistency of hardware parameters such as the output impedance characteristics of each inverter, transformer leakage inductance parameters, and filter inductance values ​​is sufficient to ensure balanced current distribution, eliminating the need for manual intervention by adjusting the output voltage of each phase. In hardware current sharing mode, the system uses a three-phase synchronous waveform generation method to generate PWM drive signals. The implementation process is as follows: the PWM generation module first generates a unified modulation reference signal, which is a sine wave template with a frequency equal to the power frequency and an initial phase angle set to zero degrees. Then, this modulation reference signal is simultaneously distributed to the respective PWM modulators of the three-phase inverters, ensuring that all three PWM modulators receive the exact same modulation reference signal. Next, each PWM modulator multiplies the received modulation reference signal with the amplitude control value of its own phase to obtain the actual modulated wave signal of its own phase. Since the modulation reference signals of the three phases are in phase, even if the amplitude control values ​​of each phase are slightly different, the zero-crossing times of the modulated waves of each phase remain consistent, and the phase relationship remains synchronized.

[0055] Please see details. Figure 3 , Figure 3 This application provides an exemplary flowchart of a phase-to-phase circulating current control method applicable to a UPS output where three phases are connected in parallel to form a single phase. Figure 3 The complete control flow from system startup to the completion of circulating current control is demonstrated. This flow covers key aspects such as circulating current detection, threshold judgment, control mode selection, and waveform configuration. The adaptive switching between hardware current sharing mode and software active current sharing mode is achieved through multi-level judgment branches.

[0056] After the process starts at the initiation node, it first enters the RS / ST interphase circulating current calculation module. This module is responsible for collecting the effective values ​​of the output current of each of the R, S, and T phases, and using one of these phases as the reference phase, calculating the current difference between the other adjustment phases and the reference phase to obtain the RS and ST interphase circulating current values. After the circulating current calculation is completed, the process enters the first judgment node. This judgment node determines whether the RS / ST interphase circulating current is greater than a threshold. Specifically, it compares the absolute value of the RS interphase circulating current with a preset circulating current threshold, and simultaneously compares the absolute value of the ST interphase circulating current with the preset circulating current threshold. Only when the absolute values ​​of both interphase circulating currents do not exceed the preset circulating current threshold is the judgment result negative; otherwise, the judgment result is positive.

[0057] When the judgment result is yes, it indicates that at least one phase's circulating current value exceeds the threshold range, and the system needs to activate active circulating current control measures. At this time, the process directly jumps to the right branch to enter the RS / ST phase-to-phase circulating current PI controller module. This module activates the PI controller for the corresponding phase, reads the phase-to-phase circulating current value and the integral of the circulating current error, and calculates the current loop adjustment output value through the PI control algorithm for subsequent voltage adjustment operations. After the PI controller module completes its execution, the process enters the R / T phase inverter voltage RMS loop module. This module is responsible for obtaining the original output value of each phase in the inverter voltage RMS loop, and determining whether to increase or decrease the output voltage of the phase based on the positive or negative sign of the phase-to-phase circulating current value. The final inverter voltage RMS output value is obtained by adding or subtracting the original output value from the current loop adjustment output value. After the voltage adjustment is completed, the process enters the R / S / T three-phase asynchronous waveform generation module. This module configures the effective output value of the inverter voltage of each adjusted phase into its own independent PWM modulator, so that each phase is PWM modulated according to different voltage amplitudes. The active suppression of circulating current is achieved through the differentiated control of the output voltage of each phase. Finally, the process reaches the end node to complete one control cycle.

[0058] When the result of the first judgment node is negative, it indicates that all phase-to-phase circulating current values ​​have not exceeded the preset threshold, and the system is operating well. At this time, the process enters the left branch and reaches the second judgment node. This judgment node determines whether the RS / ST phase-to-phase circulating current PI control has been started. Specifically, it checks the start status flag bit inside each PI controller corresponding to the adjustment in turn. Only when the start status flag bit of all PI controllers is false, that is, all PI controllers are not working, is the judgment result negative; otherwise, the judgment result is positive. When the result of the second judgment node is positive, it indicates that although the current circulating current value has not exceeded the threshold, the PI controller is still in the start state and is performing the circulating current control task. This situation usually occurs in the transition stage when the circulating current has just been suppressed below the threshold but the controller has not yet exited. At this time, the process merges from the positive branch of the second judgment node into the right main process and enters the RS / ST phase-to-phase circulating current PI controller module to continue performing the circulating current control calculation. The subsequent process is exactly the same as the aforementioned circulating current exceeding the threshold branch, passing through the R / T phase inverter voltage effective value loop module and the R / S / T three-phase asynchronous wave generation module in turn, and finally reaching the end node. When the result of the second judgment node is negative, it means that the circulating current value has not exceeded the threshold and the PI controllers have not been started. The system is in a fully hardware current sharing working state. At this time, the process enters the RS / ST three-phase synchronous waveform generation module. This module confirms the system operation mode as hardware current sharing mode and configures the PWM generation module to use the three-phase synchronous waveform generation method to keep the modulation reference signal of the three-phase inverter in the same phase and frequency. The output voltage waveforms of each phase are completely synchronized on the time axis. The natural balanced distribution of current is achieved by relying on the inherent characteristics of the hardware circuit. Finally, the process directly reaches the end node to complete this control cycle.

[0059] The entire process structure achieves flexible switching between three operating modes through a two-level decision branch. The first-level decision, based on the circulating current threshold, divides the process into an active control branch and a further decision branch. The second-level decision, based on the PI controller's startup status, further subdivides the further decision branch into a continuation control branch and a hardware current sharing branch, ensuring that the system can select the most suitable control strategy under different operating conditions. The main process on the right corresponds to the software active current sharing mode, which calculates the voltage adjustment through the PI controller and uses asynchronous waveform generation to achieve precise circulating current suppression, suitable for operating conditions with large circulating current or deviations in hardware parameters. The branch process on the left corresponds to the hardware current sharing mode, which relies on the symmetry of circuit parameters and the synchronous waveform generation strategy to achieve passive current sharing, suitable for normal operating conditions with small circulating current and good hardware characteristics. The switching between the two modes is entirely driven by the real-time detection results of the circulating current value, requiring no manual intervention. This achieves intelligent and adaptive circulating current control, reducing the system's control complexity and computational burden while ensuring the effectiveness of circulating current suppression.

[0060] Optionally, if the corresponding PI controller has been activated, the current sharing state of the three-phase UPS power supply will be maintained in software current sharing mode.

[0061] Specifically, after comparing the inter-phase circulating current values ​​with the preset circulating current thresholds, the program proceeds to check the PI controller's startup status. This involves sequentially reading the startup status flags from the corresponding PI controller instances for each adjustment phase. These startup status flags are Boolean variables stored in the PI controller's data structure. When the PI controller is activated and begins circulating current control operations, this flag is set to true; when the PI controller is stopped and exits the control task, this flag is cleared to false. The program iterates through all the PI controller instances for each adjustment phase, checking the startup status flag values ​​of each instance. If any flag is found to be true, it indicates that the PI controller has been activated.

[0062] Based on the above embodiments, as an optional implementation method, the method of collecting the effective value of the inverter current of each phase of the three-phase UPS power supply according to the preset power frequency cycle in step S101 can be specifically implemented through the following steps S401-S402.

[0063] S401: Obtain the operating frequency of the three-phase UPS power supply in the actual application scenario, and determine the power frequency cycle based on the operating frequency; The operating frequency refers to the frequency parameter of the AC voltage output by the three-phase UPS power supply. This frequency determines the time required for the output voltage waveform to complete a full sine cycle. Common operating frequencies include two standard values: 50 Hz and 60 Hz. The specific value is determined by the power grid standard of the area where the UPS power supply is located or the user's equipment requirements.

[0064] Specifically, this step is executed first when the circulating current control process starts, serving as the time reference for subsequent circulating current sampling calculations. First, the operating frequency parameter stored in the UPS power system configuration register is read. This parameter is written to the configuration storage area during system initialization based on local power grid standards or user-defined values ​​and remains unchanged during normal operation. After reading the operating frequency value, the program performs a reciprocal operation to obtain the duration of the power frequency cycle. The reciprocal operation is achieved by dividing the value by 1 by the Hertz value of the operating frequency, and the result is in seconds.

[0065] S402: At the end of each power frequency cycle, collect the effective value of the inverter current of each phase of the three-phase UPS power supply during the power frequency cycle.

[0066] Specifically, this step is triggered when the power frequency cycle timer generates a cycle end signal, enabling synchronous acquisition and RMS value calculation of the three-phase inverter output current. High-frequency current sampling is continuously performed within each power frequency cycle, with the sampling frequency typically set to hundreds to thousands of times the operating frequency to ensure sufficient sampling points within a single cycle to guarantee the accuracy of the RMS value calculation. Current sampling is achieved through Hall effect sensors or current transformers. The sensors convert the current signals at the output terminals of each phase inverter into voltage signals, which are then amplified and filtered by an analog signal conditioning circuit before being sent to an analog-to-digital converter (ADC) for digital processing. The ADC periodically converts the analog voltage signals into digital quantities according to a preset sampling frequency. Each converted digital quantity represents the instantaneous current value at the corresponding sampling moment. During the operation of the power frequency cycle, the instantaneous current value data output by the ADC is read in real time through an interrupt service routine or direct memory access, and the data is stored according to phase identifiers in the R-phase current sampling buffer, S-phase current sampling buffer, and T-phase current sampling buffer, respectively. When the power frequency cycle timer count reaches the end of the cycle, the timer generates a cycle end interrupt or sets the cycle end flag, triggering the start of the valid value calculation program.

[0067] The following are system embodiments of this application, which can be used to execute the method embodiments of this application. For details not disclosed in the system embodiments of this application, please refer to the method embodiments of the application.

[0068] Please see Figure 4 This illustration shows a schematic diagram of a phase-to-phase circulating current control system for a UPS output three-phase parallel connection into a single phase, provided by an exemplary embodiment of this application. This system can be implemented entirely or partially through software, hardware, or a combination of both. The phase-to-phase circulating current control system for a UPS output three-phase parallel connection into a single phase includes: The data acquisition module is used to acquire the effective value of the inverter current of each phase of the three-phase UPS power supply according to a preset power frequency cycle. The interphase circulating current calculation module is used to determine one reference phase and the other two remaining adjustment phases in a three-phase UPS power supply, and to determine the difference between the effective value of the inverter current between each adjustment phase and the reference phase as the corresponding interphase circulating current value. The hardware current sharing mode maintenance module is used to determine the waveform generation mode of each adjustment phase and the reference phase as the three-phase synchronous waveform generation mode when the circulating current value between each phase does not exceed the preset circulating current threshold and the three-phase UPS power supply is in the default hardware current sharing mode. The software current sharing mode control module is used to control the three-phase UPS power supply to switch from the default hardware current sharing mode to the software current sharing mode when the inter-phase circulating current value exceeds the preset circulating current threshold. It also determines the waveform generation mode of the adjustment phase and the reference phase as the three-phase independent waveform generation mode, and adjusts the inverter duty cycle of the adjustment phase through the PI controller until the corresponding inter-phase circulating current value does not exceed the circulating current threshold.

[0069] This application also provides a computer storage medium that can store multiple instructions. The instructions are adapted to be loaded and executed by a processor, such as the phase-to-phase circulating current control method applicable to the three-phase parallel connection of UPS output into a single phase as described in the above embodiments. For the specific execution process, please refer to the detailed description of the embodiments, which will not be repeated here.

[0070] Please see Figure 5 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. Figure 5 As shown, the electronic device 500 may include: at least one processor 501, at least one network interface 504, user interface 503, memory 505, and at least one communication bus 502.

[0071] The communication bus 502 is used to enable communication between these components.

[0072] The user interface 503 may include a display screen and a camera.

[0073] The network interface 504 may optionally include a standard wired interface or a wireless interface (such as a Wi-Fi interface).

[0074] The processor 501 may include one or more processing cores. The processor 501 connects to various parts of the server using various interfaces and lines, and performs various server functions and processes data by running or executing instructions, programs, code sets, or instruction sets stored in memory 505, and by calling data stored in memory 505. Optionally, the processor 501 may be implemented using at least one hardware form of digital signal processing, field-programmable gate array, or programmable logic array. The processor 501 may integrate one or more of the following: a central processing unit (CPU), a graphics processing unit (GPU), and a modem. The CPU primarily handles the operating system, user interface, and applications; the GPU is responsible for rendering and drawing the content required for display; and the modem handles wireless communication. It is understood that the modem may also be implemented as a separate chip, without being integrated into the processor 501.

[0075] The memory 505 may include random access memory (RAM) or read-only memory (ROM). Optionally, the memory 505 may include a non-transitory computer-readable medium. The memory 505 may be used to store instructions, programs, code, code sets, or instruction sets. The memory 505 may include a program storage area and a data storage area. The program storage area may store instructions for implementing an operating system, instructions for at least one function (such as touch functionality, sound playback functionality, image playback functionality, etc.), instructions for implementing the various method embodiments described above, etc.; the data storage area may store data involved in the various method embodiments described above, etc. Optionally, the memory 505 may also be at least one storage device located remotely from the aforementioned processor 501. Figure 5 As shown, the memory 505, which serves as a computer storage medium, may include an operating system, a network communication module, a user interface module, and an application program for a phase-to-phase circulating current control method suitable for three-phase parallel connection of UPS output into a single phase.

[0076] exist Figure 5 In the electronic device 500 shown, the user interface 503 is mainly used to provide an input interface for the user and to obtain the user input data; while the processor 501 can be used to call an application program stored in the memory 505 that is suitable for a phase-to-phase circulating current control method for three-phase parallel connection of UPS output into a single phase. When executed by one or more processors, the electronic device executes one or more methods as described in the above embodiments.

[0077] An electronic device readable storage medium stores instructions that, when executed by one or more processors, cause the electronic device to perform one or more methods as described in the above embodiments.

[0078] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to this application.

[0079] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0080] In the several embodiments provided in this application, it should be understood that the disclosed apparatus can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the shown or discussed mutual couplings or direct couplings or communication connections may be through some service interfaces; indirect couplings or communication connections between apparatuses or units may be electrical or other forms.

[0081] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0082] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0083] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage device (CMD). Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a memory and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this application. The aforementioned memory includes various media capable of storing program code, such as USB flash drives, portable hard drives, magnetic disks, or optical disks.

[0084] The above are merely exemplary embodiments of this disclosure and should not be construed as limiting the scope of this disclosure. Any equivalent changes and modifications made in accordance with the teachings of this disclosure shall still fall within the scope of this disclosure. Those skilled in the art will readily conceive of other embodiments of this disclosure upon considering the specification and practical application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not described in this disclosure.

Claims

1. A phase-to-phase circulating current control method applicable to three-phase parallel connection of UPS output into a single phase, characterized in that, The method includes: Collect the effective value of the inverter current of each phase of the three-phase UPS power supply according to the preset power frequency cycle; Identify one reference phase and the other two remaining adjustment phases of the three-phase UPS power supply, and determine the difference between the effective value of the inverter current between each adjustment phase and the reference phase as the interphase circulating current value corresponding to the adjustment. When the interphase circulating current value does not exceed the preset circulating current threshold and the three-phase UPS power supply is in the default hardware current sharing mode, the waveform generation mode of each adjustment phase and the reference phase is determined to be the three-phase synchronous waveform generation mode. When any of the phase-to-phase circulating current values ​​exceeds the preset circulating current threshold, the three-phase UPS power supply is controlled to switch from the default hardware current sharing mode to the software current sharing mode, and the waveform generation mode of the adjustment phase and the reference phase is determined to be the three-phase independent waveform generation mode. The inverter duty cycle of the adjustment phase is adjusted by the PI controller until the corresponding phase-to-phase circulating current value does not exceed the circulating current threshold.

2. The method according to claim 1, characterized in that, The adjustment of the inverter duty cycle of the adjustment phase via a PI controller includes: The integral of the interphase circulating current error of the adjusted phase is obtained, and the integral of the interphase circulating current error of the adjusted phase and the interphase circulating current value are input into the PI controller to obtain the current loop adjustment output value. The dimension of the current loop adjustment output value is voltage value. The current loop is adjusted and output to the inverter voltage RMS value loop, and the corresponding inverter voltage RMS value is calculated. The target duty cycle of the adjustment phase is determined based on the effective value output of the inverter voltage, and the inverter duty cycle of the adjustment phase is adjusted according to the target duty cycle.

3. The method according to claim 2, characterized in that, The step of inputting the phase-to-phase circulating current error integral and the phase-to-phase circulating current value into the PI controller to obtain the current loop adjustment output value includes: Substituting the integral of the interphase circulating current error and the interphase circulating current value of the adjusted phase into the interphase circulating current control formula in the PI controller, the current loop adjustment output value is obtained. The interphase circulation control formula is as follows: U(t) = Kp*e(t) + SumError; Wherein, U(t) represents the current loop adjustment output value, Kp represents the proportional gain of the PI controller, e(t) represents the phase-to-phase circulating current value corresponding to the adjustment, and SumError represents the phase-to-phase circulating current error integral.

4. The method according to claim 2, characterized in that, The step of adjusting the current loop output value and outputting it to the inverter voltage RMS loop, and calculating the corresponding inverter voltage RMS output value, includes: Obtain the original output value of the adjusted phase in the inverter voltage RMS loop; Determine whether the corresponding phase-to-phase circulating current value is greater than zero; If the interphase circulating current value is greater than zero, the original output value is subtracted from the current loop adjustment output value to obtain the effective value of the inverter voltage output, thereby reducing the output voltage of the adjustment phase; If the interphase circulating current value is less than zero, the original output value is added to the current loop adjustment output value to obtain the effective value of the inverter voltage output value, thereby increasing the output voltage of the adjusted phase.

5. The method according to claim 1, characterized in that, When the circulating current values ​​between each phase do not exceed the preset circulating current threshold, and the three-phase UPS power supply is in the default hardware current sharing mode, the waveform generation mode of each adjustment phase and the reference phase is determined to be the three-phase synchronous waveform generation mode, including: When none of the phase-to-phase circulating current values ​​exceed the preset circulating current threshold, determine whether the corresponding PI controller for each adjustment is activated. If none of the PI controllers corresponding to each adjustment are started, then the three-phase UPS power supply is confirmed to be in the default hardware current sharing mode, and the wave generation mode of each adjustment phase and the reference phase is determined to be the three-phase synchronous wave generation mode.

6. The method according to claim 5, characterized in that, The method further includes: If the corresponding PI controller for the adjustment has been activated, the current sharing state of the three-phase UPS power supply will be maintained in software current sharing mode.

7. The method according to claim 1, characterized in that, The step of collecting the effective values ​​of the inverter current of each phase of the three-phase UPS power supply according to a preset power frequency cycle includes: Obtain the operating frequency of the three-phase UPS power supply in the actual application scenario, and determine the power frequency cycle based on the operating frequency; At the end of each power frequency cycle, the effective value of the inverter current of each phase of the three-phase UPS power supply during the power frequency cycle is collected.

8. A phase-to-phase circulating current control system suitable for three-phase parallel connection of UPS output into a single phase, characterized in that, The system includes: The data acquisition module is used to acquire the effective value of the inverter current of each phase of the three-phase UPS power supply according to a preset power frequency cycle. The interphase circulating current calculation module is used to determine one reference phase and the other two remaining adjustment phases of the three-phase UPS power supply, and to determine the difference between the effective value of the inverter current between each adjustment phase and the reference phase as the interphase circulating current value corresponding to the adjustment phase. The hardware current sharing mode maintenance module is used to determine the waveform generation mode of each adjustment phase and the reference phase as the three-phase synchronous waveform generation mode when the circulating current value between each phase does not exceed the preset circulating current threshold and the three-phase UPS power supply is in the default hardware current sharing mode. The software current sharing mode control module is used to control the three-phase UPS power supply to switch from the default hardware current sharing mode to the software current sharing mode when any of the inter-phase circulating current values ​​exceeds the preset circulating current threshold. The module also determines the waveform generation mode of the adjustment phase and the reference phase as the three-phase independent waveform generation mode and adjusts the inverter duty cycle of the adjustment phase through the PI controller until the corresponding inter-phase circulating current value does not exceed the circulating current threshold.

9. A computer storage medium, characterized in that, The computer storage medium stores a plurality of instructions, which are adapted to be loaded by a processor and executed as described in any one of claims 1 to 7.

10. An electronic device, characterized in that, The device includes a processor, a memory, and a transceiver, wherein the memory is used to store instructions, the transceiver is used to communicate with other devices, and the processor is used to execute the instructions stored in the memory to cause the electronic device to perform the method as described in any one of claims 1 to 7.

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