A millisecond-class off-grid seamless switchover system and method

Abstract

The application provides a millisecond-level off-grid seamless switching system and method, relates to the technical field of micro-grid and uninterrupted power supply control, and the system comprises an energy management system, a static transfer switch connected with an external power grid and a networked energy storage converter for supplying power to a load. The networked energy storage converter and the static transfer switch are connected through a CAN2.0 bus direct connection architecture for communication. The energy management system tracks power grid parameters in a grid-connected stage, identifies abnormalities through high-frequency sampling when encountering power grid faults, and triggers the static transfer switch to disconnect the physical connection. After the physical connection is disconnected, the networked energy storage converter is switched to an off-grid mode based on V / f control and virtual synchronous machine technology to take over the load. The application controls the time delay and voltage and frequency fluctuation in the grid-connected and off-grid switching process within a preset threshold range, and meets the power supply switching index of the scene with high power supply continuity requirements.

Description

Technical Field

[0001] This invention relates to the field of microgrid and uninterruptible power supply control technology, and in particular to a millisecond-level on-grid and off-grid seamless switching system and method. Background Technology

[0002] In the current power system operating environment, the requirements for power supply continuity indicators are increasing across various application scenarios, and certain sensitive loads have an objective need for uninterrupted power supply. In planned operation scenarios such as low-voltage uninterrupted maintenance and distribution transformer capacity expansion, as well as in sudden abnormal situations such as a drop in main power supply, external emergency power supply equipment is usually required to maintain the continuous operation of the relevant loads.

[0003] Existing emergency power supply equipment experiences lengthy startup or power mode switching processes after external power grid failures. These mode transitions typically take seconds or even longer. This time delay makes transient power outages or significant fluctuations in bus parameters during power handover susceptible, causing the equipment to fail to meet the operational requirements of microgrids and emergency power supply scenarios demanding high power continuity. To address these specific power consumption environments, it is necessary to further optimize the system communication links and underlying control architecture to reduce the overall time required for on-grid / off-grid switching. Summary of the Invention

[0004] The purpose of this invention is to provide a millisecond-level on- and off-grid seamless switching system and method to solve the problems pointed out in the background art.

[0005] In a first aspect, an embodiment of the present invention provides a millisecond-level seamless on-grid / off-grid handover system, comprising: Energy management system; At least one static transfer switch, the input of which is connected to the external power grid and the output of which is connected to the local microgrid bus; At least one grid-type energy storage converter, wherein the AC side of the grid-type energy storage converter is connected in parallel to the local microgrid bus and is connected to the static transfer switch through the local microgrid bus to provide power to the load connected to the local microgrid bus; The energy management system establishes communication connections with the static transfer switch and the grid-type energy storage converter respectively; the grid-type energy storage converter and the static transfer switch communicate through a CAN2.0 bus direct connection architecture that eliminates communication relay nodes; The energy management system is configured to: continuously track grid parameters during the grid-connected phase; when encountering a grid fault, identify grid anomalies through a set sampling frequency and trigger the static transfer switch to disconnect the physical connection with the faulty grid; after the physical connection is disconnected, control the grid-connected energy storage converter to switch to off-grid mode based on V / f control and virtual synchronous machine technology to take over the load; wherein, at the instant the off-grid condition is determined, the grid-connected energy storage converter freezes the phase angle status register value of the phase-locked loop in the grid-connected control loop and uses it as the initial substitution value for the integral part of the rotor motion equation in the virtual synchronous machine control algorithm to maintain the continuity of the local bus voltage phase at the moment of switching.

[0006] Optionally, the static transfer switch uses a thyristor component; the hardware response time of the static transfer switch itself is less than or equal to 1ms.

[0007] Optionally, the grid-type energy storage converter has a built-in computing chip with a heterogeneous architecture of digital signal processor and field programmable gate array; the instruction execution time of the grid-type energy storage converter is less than or equal to 5ms.

[0008] Optionally, in the CAN2.0 bus direct connection architecture, the highest priority identifier is assigned to the grid fault flag bit and the mode switching command; the single-frame data transmission time between the grid-type energy storage converter and the static transfer switch is less than or equal to 5ms.

[0009] Optionally, the sampling frequency is set to 1000Hz; the fault detection algorithm embedded in the energy management system can identify power grid loss of voltage, undervoltage, or frequency anomalies within less than or equal to 1ms.

[0010] Optionally, upon detecting the anomaly, the energy management system triggers the static transfer switch to disconnect the physical connection within a time of less than or equal to 8ms.

[0011] Optionally, after the physical connection is disconnected, the grid-type energy storage converter completes the power supply mode switching within less than or equal to 10ms; autonomously establishes and maintains a stable 380V AC voltage with a frequency of 50Hz; and controls the entire seamless switching process between grid and off-grid within 20ms, with voltage and frequency fluctuations controlled within ±1%.

[0012] Optionally, a power restoration exit mechanism is also included: when the power grid restores power, the grid-type energy storage converter tracks and collects the restored mains power parameters and performs dynamic phase-locked adjustment; the grid-type energy storage converter calibrates its own output to achieve the same amplitude, frequency, and phase as the external power grid.

[0013] Optionally, after locking the synchronization state, the system instructs the static transfer switch to smoothly close and switch back to the external power grid side within 20ms to eliminate the risk of circulating current impact or secondary power failure at the moment of power restoration.

[0014] Secondly, the present invention provides a millisecond-level seamless on-grid / off-grid handover method, applied to the millisecond-level seamless on-grid / off-grid handover system described in any of the first aspects, the method comprising the following steps: Grid-connected standby steps: The static transfer switch remains in the conducting state; the energy management system continuously collects and tracks external grid parameters; the grid-connected energy storage converter is in grid-supported mode, and its internal phase-locked loop extracts and follows the frequency and phase of the grid voltage in real time, and is in standby state. Fault detection and disconnection steps: The energy management system continuously performs discrete sampling and calculation on the grid-side voltage according to the set high-frequency sampling frequency; when a fault occurs in the external power grid, the energy management system generates a trip signal based on the identified abnormal state, triggering the static transfer switch to disconnect the physical connection between the local microgrid bus and the faulty power grid; Off-grid takeover steps based on phase angle status register value handover: At the instant the physical connection is determined to be disconnected and the off-grid condition is met, the grid-type energy storage converter performs control loop reconstruction; the grid-type energy storage converter freezes the phase angle status register value of the phase-locked loop in the grid-connected control loop and uses it as the initial substitution value for the integral part of the rotor motion equation in the virtual synchronous machine control algorithm for value handover; subsequently, the grid-type energy storage converter switches to off-grid constant voltage and constant frequency mode based on V / f control strategy and virtual synchronous machine technology, and autonomously establishes and maintains a stable AC voltage to take over the load; Synchronous closing procedure after power restoration: When the external power grid resumes normal power supply, the grid-type energy storage converter collects the restored grid voltage signal and activates the dynamic phase-locked loop adjustment algorithm; the grid-type energy storage converter adjusts the frequency and phase of its own output voltage until it reaches a synchronous state with the external power grid voltage in terms of amplitude, frequency, and phase; after locking the synchronous state, the system generates a closing command to trigger the static transfer switch to perform smooth closing and switch back to the external power grid main power supply state.

[0015] The present invention has achieved the following beneficial effects: This invention integrates an energy management system, a static transfer switch, and a grid-connected energy storage converter. Combined with a direct-connect architecture that eliminates communication relays and coordinated control algorithms, it can rapidly disconnect the physical connection and allow the energy storage unit to take over power supply upon detecting a grid fault. This mechanism controls the entire grid-connection / off-grid switching process to the millisecond level, while suppressing the amplitude and frequency fluctuations of the load-side bus voltage within a small range. Furthermore, the system's power restoration and exit mechanism utilizes dynamic phase-locked loop adjustment to achieve smooth closed-loop switching with the same amplitude, frequency, and phase. This design addresses the pain points of slow backup power startup and long switching times, providing continuous and stable power support for microgrids and specific sensitive loads, and reducing the risk of secondary power outages or equipment restarts caused by switching transients.

[0016] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a structural connection topology diagram of a millisecond-level on-grid and off-grid seamless handover system according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating the execution steps of a millisecond-level seamless handover method for on-grid and off-grid communication in an embodiment of the present invention. Detailed Implementation

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

[0020] In the current power system operating environment, there are requirements for assessing power supply continuity indicators and for uninterrupted power supply to specific sensitive loads. Existing emergency power supply equipment has a long startup or mode switching time after a grid failure, typically on the order of seconds or even longer, which cannot meet the power supply switching indicators in specific scenarios. Based on this, this application provides a millisecond-level seamless grid-connected and off-grid switching system and method, mainly applied to microgrids and emergency power supply scenarios with high power supply continuity requirements, aiming to control the time delay and voltage and frequency fluctuations during grid-connected and off-grid switching within a preset threshold range.

[0021] See attached document Figure 1 As shown in the figure, this invention discloses a millisecond-level seamless on-grid / off-grid switching system. The system mainly includes an energy management system, at least one static transfer switch, and at least one grid-type energy storage converter. In terms of system topology, the input terminal of the static transfer switch is connected to the external power grid, and the output terminal is connected to the local microgrid bus. The AC side of the grid-type energy storage converter is connected in parallel to the local microgrid bus and, through this bus, to the static transfer switch, thereby providing power to the loads connected to this bus. In terms of communication topology, a direct connection architecture via a controller area network (CAN) bus is configured between the grid-type energy storage converter and the static transfer switch. The energy management system establishes communication connections with both the static transfer switch and the grid-type energy storage converter to issue control commands and receive device status data.

[0022] It is understood that the system in this embodiment is built on a large-capacity energy storage platform. In a specific implementation scenario, the platform is configured with a 352.08kWh energy storage battery pack to provide energy reserves for the system's grid-connected / off-grid switching and subsequent off-grid operation. In terms of hardware configuration, the system includes a 250kW static transfer switch and a 125kW grid-connected energy storage converter. Furthermore, the configuration ratio of the static transfer switch and the grid-connected energy storage converter is designed as a hierarchical combination, meaning the system includes at least one static transfer switch and at least one grid-connected energy storage converter. This modular configuration scheme allows the system to parallel expand the number of static transfer switches and grid-connected energy storage converters according to the rated capacity of the load and the on-site power supply requirements. Any combination of these components under this configuration logic falls within the protection scope defined by this system.

[0023] Specifically, the energy management system is configured to continuously collect and track the operating parameters of the external power grid during the grid-connected phase. When a grid fault event is detected, the energy management system identifies abnormal grid parameters based on a preset high-frequency sampling algorithm and generates a disconnection command to trigger the static transfer switch to disconnect the physical connection between the local microgrid bus and the faulty external power grid. After the logical condition for disconnection is met, the energy management system issues a mode switching command to the grid-connected energy storage converter, controlling the grid-connected energy storage converter to switch from grid-connected mode to off-grid mode to take over the load and maintain the voltage and frequency stability of the local microgrid bus.

[0024] Furthermore, regarding the control of the system's underlying hardware response time, this embodiment has specifically selected and configured the internal components of the static transfer switch. The static transfer switch uses a high-power thyristor as the core power switching device. Specifically, the static transfer switch is internally configured with an independent high-frequency pulse trigger board and absorption circuit. When a turn-off level signal is received, the trigger board immediately blocks the gate trigger pulse of the thyristor; simultaneously, combined with the instantaneous polarity of the local bus voltage, the main circuit current is rapidly decayed to below the holding current by utilizing the AC zero-crossing natural commutation characteristics of the thyristor or the configured forced commutation capacitor circuit, thereby achieving rapid blocking of the physical path. In particular, to overcome the physical limitation that the AC zero-crossing natural commutation can last up to 10ms, the forced commutation capacitor circuit is configured with a pre-charge capacitor and an auxiliary switching transistor. When the system receives a shutdown signal, the auxiliary switch turns on, and the pre-charge capacitor rapidly applies a reverse transient bias voltage to the high-power thyristor in the main circuit. Within tens of microseconds, this forces the current in the main thyristor to be withdrawn and forces it to turn off at zero crossing, thus ensuring that the overall hardware response time is not limited by the grid phase and is strictly constrained to within 1ms. Specifically, the lower limit of the pre-charge capacitor's capacity in the forced commutation capacitor circuit is determined by multiplying the maximum expected peak load current of the local microgrid bus by the rated turn-off time of the high-power thyristor, and then dividing by the pre-charge voltage. The rated turn-off time parameter of the thyristor is typically selected from 50 to 200 microseconds according to the device datasheet. The pre-charge capacitor maintains a constant reverse bias voltage through an independent DC boost chopper circuit, and the absolute value of the pre-charge voltage is set to 1.2 to 1.5 times the rated peak voltage of the local AC bus. This ensures that when shutdown is triggered at any AC phase point, the transient energy released by the capacitor is sufficient to force the main circuit current to decay rapidly below the holding current. With this hardware configuration, the hardware response time of the static transfer switch is controlled to be less than or equal to 1ms. This 1ms hardware response time refers to the maximum time required from the moment the drive circuit of the static transfer switch receives the turn-off level signal until the high-power thyristor in the main circuit is completely turned off, cutting off the current path between the external power grid and the local bus.

[0025] In conjunction with the static transfer switch, the grid-type energy storage converter also features timely configuration at the controller hardware level. Specifically, the control board of the grid-type energy storage converter incorporates a high-speed computing chip. This high-speed computing chip employs a heterogeneous hardware architecture combining a digital signal processor (DSP) and a field-programmable gate array (FPGA). The DSP is responsible for executing the voltage-current dual-loop control algorithm and mode switching logic. The voltage-current dual-loop control algorithm uses a cascaded architecture of outer-loop voltage proportional-integral control and inner-loop current proportional-resonant control. The outer voltage loop amplifies and integrates the deviation between the AC fundamental voltage command and the actual sampled voltage to output the reference command for the inner current loop. The inner current loop sets the resonant control point for the 50Hz fundamental frequency of the power grid, setting the resonant bandwidth parameter within the range of 3.14 to 15.7 radians per second, thereby ensuring dynamic response speed while achieving zero steady-state error tracking control of the AC fundamental current. The FPGA is responsible for high-speed parallel analog-to-digital conversion of multiple analog signals and the generation and hardware output of the dead time of the pulse width modulation signal. The control interrupt cycle of the digital signal processor is set to no more than several hundred microseconds, thereby converging the time from a single protocol parsing to the output of the updated drive signal to within 5ms. This instruction execution time refers to the time required from receiving the mode switching message from the communication interface of the grid-type energy storage converter, through protocol parsing and control algorithm switching calculations, until the updated pulse width modulation drive signal is output to the inverter bridge power devices.

[0026] At the data interaction architecture level between system components, the grid-type energy storage converter and the static transfer switch adopt a direct CAN 2.0 bus connection architecture. This direct connection architecture eliminates intermediate forwarding nodes such as communication management units, network switches, or protocol conversion gateways that may exist in conventional microgrid system communication networks. The CAN interface of the grid-type energy storage converter is directly connected point-to-point to the CAN interface of the static transfer switch via a physical twisted-pair cable. In this direct connection topology, the communication nodes of the energy management system, the static transfer switch, and the grid-type energy storage converter are configured within the same physical network segment and are not connected to other non-real-time data nodes. By assigning the highest priority identifiers to the grid fault flag and mode switching command at the data link layer, critical action messages gain priority in bus arbitration, thereby avoiding communication collision delays when multiple nodes are concurrent. Specifically, the CAN 2.0 bus baud rate is configured to 1 Mbps and uses a standard frame format. The transmission time of a single frame message at the physical layer is only about 130 microseconds. Combined with the interrupt response cycle of hundreds of microseconds set by the high-speed computing chip, the total time for single-frame data to be framed at the sending end, transmitted at the physical layer, and parsed at the receiving end is ensured to have extremely high redundancy at the underlying time scale, thus enabling stable convergence within a time threshold of less than or equal to 5ms. In this repeaterless communication link, the transmission time of single-frame data between the network-type energy storage converter and the static transfer switch is controlled to less than or equal to 5ms. This transmission time covers the message framing process at the sending end CAN controller, the physical layer bus level transmission, and the parsing process at the receiving end CAN controller, thereby reducing the communication latency of the system under abnormal operating conditions.

[0027] Regarding the fault detection logic of the energy management system, in this embodiment, the data sampling module is configured to set the sampling frequency of the power grid parameters to 1000Hz. At the data acquisition hardware level, the sampling module includes a voltage sensor with a high common-mode rejection ratio and a synchronous sampling analog-to-digital converter. The main frequency clock of the energy management system is equipped with a hardware timer configured to trigger a priority analog-to-digital conversion interrupt every 1 millisecond to ensure the time determinism and equal intervals of the 1000Hz sampling frequency. The energy management system embeds a fault detection algorithm that performs real-time calculations on a continuous sequence of sampling points based on a sliding time window to extract the effective value, phase angle, and frequency parameters of the instantaneous voltage of the power grid. The data length of the sliding time window is set to the total number of sampling points contained within a single power frequency cycle; in this system with a 1000Hz sampling frequency and a 50Hz power frequency configuration, the window length is fixed at 20 sampling points. The discrete calculation steps for the effective value of the instantaneous voltage are: calculate the sum of squares of all discrete voltage sampling points within the window, obtain their arithmetic mean, and then perform a square root operation to obtain the result. Each time the sliding window receives a new analog-to-digital conversion sampling point, it automatically removes the oldest data point on the timeline and triggers an iterative calculation.

[0028] Based on the aforementioned high-frequency sampling rate of 1000Hz, the fault detection algorithm is configured to output anomaly identification results within a time period of less than or equal to 1ms. When the external power grid experiences voltage loss, undervoltage, or frequency anomalies, the algorithm can identify parameter exceeding limits within the first or second sampling period and generate a power grid fault flag. Specifically, the fault detection algorithm employs an orthogonal decoupling transformation based on instantaneous reactive power theory. The energy management system maps the sampled discrete values ​​of instantaneous AC voltage in the three-phase stationary coordinate system to DC components in the dq coordinate system, which rotates synchronously with the fundamental frequency of the power grid, through Clark and Park transformations. By comparing the square root modulus of the sum of squares of the d-axis and q-axis voltage components with a preset reference modulus within a single calculation cycle, transient numerical identification of power grid voltage dips or voltage loss states is achieved. The specific transformation and extraction steps are as follows: First, through the Clarke transform, using specific scaling factors and trigonometric function projection relationships, the discrete voltage in the three-phase stationary coordinate system is mapped to components in the two-phase stationary orthogonal coordinate system; then, combined with the instantaneous phase angle locked by the system, it is further projected onto the synchronously rotating dq coordinate system through the rotation matrix of the Park transform. The modulus of the transient voltage amplitude is obtained by calculating the square root of the sum of the squares of the d-axis and q-axis components. The logical judgment condition of the abnormal state is specifically quantified as follows: when the voltage amplitude modulus extracted within two consecutive sampling periods drops below 85% of the rated voltage reference modulus, or when the instantaneous offset of the grid frequency calculated based on the dq-axis phase angle derivative exceeds ±0.5Hz, the energy management system confirms that the grid has an abnormality and sets the fault flag.

[0029] Upon detecting the aforementioned power grid anomaly flag, the system enters a physical disconnection execution sequence. Specifically, the energy management system sends a disconnection command to the static transfer switch via the communication bus. Considering the static transfer switch's hardware response time of less than or equal to 1ms, and the system's communication and computation delays, the entire physical connection disconnection process is controlled within a specific time window. The system limits the total time for the energy management system to trigger the static transfer switch to disconnect the physical connection to be less than or equal to 8ms. This 8ms time point is defined as the starting point of the objective physical moment of the power grid fault and the ending point of the moment when the static transfer switch completely blocks the electrical connection between the external power grid and the local load. Thus, the physical connection between the local load bus and the faulty power grid is disconnected, and the duration of this physical disconnection process is controlled within 8ms. The 8ms time constraint mechanism is executed by the system-level hardware response timing allocation, specifically including: a data sampling and abnormal state model calculation stage of no more than 1ms, a CAN bus action command message framing, physical layer transmission and receiver parsing stage of no more than 5ms, and a thyristor turn-off circuit physical commutation action stage of no more than 1ms. The system's internal hardware gate circuit transmission delay is used as a redundant time margin.

[0030] Furthermore, after confirming that the static transfer switch has disconnected its physical connection, the system enters the off-grid takeover execution sequence. Upon receiving the off-grid takeover command, the grid-connected energy storage converter must complete the switching of its power supply control mode within a time window of less than or equal to 10ms. During this process, the grid-connected energy storage converter switches its control strategy from current source following control during grid connection to voltage source support control during off-grid operation. To maintain the continuity of the local bus voltage phase at the moment of switching, when the grid-connected energy storage converter performs control algorithm reconstruction, the initial voltage reference phase angle and reference frequency called by its off-grid control loop are directly extracted and inherited from the last effective steady-state data of the power grid locked by the internal phase-locked loop of the energy storage converter before the external power grid fault occurred. Specifically, the controller's built-in state machine freezes the phase angle state register value of the phase-locked loop (PLL) in the grid-connected control loop at the instant the off-grid condition is determined, and directly uses it as the initial input value for the rotor motion equation integral stage in the virtual synchronous machine control algorithm, realizing the direct assignment and handover of the phase angle state variable at the underlying DSP register level. By controlling the numerical handover of state variables between different underlying algorithms, transient overcurrent in the inverter bridge caused by sudden jumps in initial phase difference during mode switching is avoided.

[0031] As a specific implementation, the grid-connected energy storage converter establishes voltage in off-grid mode based on a V / f control algorithm and virtual synchronous machine technology. Under V / f control, the energy storage converter maintains constant output voltage and frequency through internally set voltage amplitude reference commands and frequency reference commands. Simultaneously, virtual synchronous machine technology is introduced to simulate the rotor inertia and damping characteristic equations of a traditional synchronous generator in the control loop. When a power surge occurs at the moment of off-grid connection, the virtual synchronous machine algorithm adjusts the frequency change rate according to a preset virtual inertia coefficient and suppresses power oscillations according to a preset virtual damping coefficient. Specifically, the virtual synchronous machine algorithm constructs a mathematical model in the controller's software logic that includes an active power-frequency droop characteristic equation and a rotor motion equation. The active power-frequency droop equation is used to adjust the output frequency command according to the increment of the load's active power; the rotor motion equation introduces damping and inertia parameters to calculate and output the delayed actual reference frequency and phase angle, thereby mitigating the rate of frequency drop caused by sudden changes in active power. The calculation steps of the rotor motion equation are as follows: obtain the difference between the active power reference command given by the system and the actual output electromagnetic power of the converter; subtract the product of the damping coefficient and the angular frequency deviation from this difference; finally, divide the result by the product of the virtual inertia coefficient and the rated angular frequency to obtain the rate of change of the output angular frequency (i.e., the angular frequency derivative); and obtain the actual reference phase angle by integrating over time. In terms of parameter settings, the virtual inertia coefficient is tuned according to the maximum allowable rate of frequency change of the system, with a value range of 0.5 to 2.5 kg / m²; the virtual damping coefficient is tuned according to the tolerance of the system's steady-state frequency deviation, with a value range of 15 to 80 Nm / s / radian. Through the operational adjustment of the grid-type energy storage converter, the system establishes and maintains a stable 380V AC line voltage after the physical disconnection of the power grid, and stabilizes the output frequency at 50Hz.

[0032] By incorporating the aforementioned fault detection, static transfer switch disconnection, and mode switching takeover of the grid-connected energy storage converter, the system in this embodiment completes the entire seamless grid-connected / off-grid switching process within 20ms. Furthermore, through the coordinated adjustment of the V / f of the grid-connected energy storage converter and the virtual synchronous machine, the amplitude and frequency fluctuations of the load-side bus voltage are suppressed to within ±1% of the rated value during the transient process of grid-connected / off-grid switching and the subsequent off-grid steady-state operation. In addition, during the off-grid operation phase, the energy management system calculates and displays the remaining power supply duration parameters in real time based on the current state of charge of the energy storage battery pack and the real-time power consumption of the load.

[0033] In some embodiments, the system is also configured with a power restoration exit mechanism to address grid restoration scenarios after external grid faults are cleared. Specifically, when the external grid completes emergency repairs or successfully recloses automatically, restoring normal voltage and frequency power supply, the voltage transformer installed on the grid side of the static transfer switch feeds back the collected mains power restoration signal to the energy management system and the grid-type energy storage converter.

[0034] After entering the power restoration exit phase, the grid-type energy storage converter maintains off-grid power supply to the load and simultaneously initiates active tracking logic. The grid-type energy storage converter acquires the restored mains power parameters at high frequency and uses them as a reference target. A dynamic phase-locked loop (PLL) adjustment algorithm is activated in the control loop of the grid-type energy storage converter. This algorithm calculates the phase difference, frequency deviation, and amplitude difference between the local microgrid bus voltage and the restored mains voltage. The algorithm includes a phase detector, a loop filter, and a voltage-controlled oscillator (VCO) software model. During the power restoration tracking phase, the algorithm updates the proportional-integral (PI) parameters of the loop filter through an adaptive adjustment mechanism. Specifically, this adaptive adjustment mechanism establishes a positive correlation mapping function between the proportional gain and the absolute value of the instantaneous phase deviation. In the initial stage of power restoration tracking, when the phase deviation is large, a high proportional gain is output to amplify the feedforward signal, achieving rapid phase angle catching up. When the phase deviation approaches the zero synchronization threshold, the proportional gain automatically and nonlinearly decays to the basic stable value, thereby accelerating the phase convergence speed of the VCO output while avoiding phase angle overshoot and system oscillation during the lock-in moment. Specifically, the positive correlation mapping function is defined as a variable structure proportional adjustment rule with exponential decay characteristics. The proportional gain consists of the sum of the basic stabilization gain and the dynamic compensation gain; the dynamic compensation gain is calculated by multiplying the maximum feedforward amplification gain by a nonlinear decay factor, which is directly driven by the absolute value of the instantaneous phase deviation. When the phase deviation is large, the decay factor approaches 1, resulting in high output gain; when tracking enters the synchronization threshold band, the decay factor rapidly approaches 0. The specific numerical range of the synchronization threshold band is strictly defined as follows: the absolute value of the phase deviation is less than or equal to 0.05 radians, and the absolute value of the frequency deviation is less than or equal to 0.1 Hz. When the dynamic parameters fall within this threshold band for 20 consecutive milliseconds, the system retains only the basic stabilization gain to maintain phase lock. Simultaneously, the fundamental frequency of the grid voltage is introduced as a feedforward compensation amount to reduce the steady-state phase angle error during dynamic tracking.

[0035] Based on the aforementioned deviation values, the grid-type energy storage converter gradually calibrates its output AC voltage by fine-tuning the frequency reference value and voltage amplitude command of its internal virtual synchronous machine algorithm. This calibration process continues until the output voltage of the grid-type energy storage converter and the voltage of the external power grid reach a state of synchronization with the same amplitude, frequency, and phase.

[0036] After the system confirms through synchronization detection logic that the waveform has been locked in a highly synchronized state, the energy management system or grid-connected energy storage converter issues a grid-connection closing command. Before performing the physical closing operation, the system hardware is equipped with a differential voltage detection circuit for real-time measurement of the instantaneous voltage difference between the grid side of the static transfer switch and the local microgrid bus side. The energy management system outputs a gate trigger conduction signal to the static transfer switch only when the absolute value of the instantaneous voltage difference is within a safe threshold band for a consecutive preset number of power frequency cycles, and the voltage waveform crosses zero. The consecutive preset number of power frequency cycles is specifically set to continuously monitor 3 to 5 complete AC fundamental frequency cycles (i.e., a confirmation window lasting 60 to 100 milliseconds); the safe threshold band for the absolute value of the instantaneous voltage difference is specifically defined as follows: the absolute value of the voltage difference across the static transfer switch must not exceed 10 volts, and the rate of change of the transient phase difference must not exceed 0.02 radians per millisecond. The system only allows the smooth closing action to be performed when the waveform parameters strictly meet this judgment boundary condition throughout the aforementioned time window. Because the voltage waveforms on both sides of the static transfer switch are in the same amplitude, frequency, and phase at the moment of closing, the potential difference generated by the closing action approaches zero. The system instructs the static transfer switch to perform a smooth closing action within a 20ms time window, switching the local microgrid back to the external grid side, avoiding the risk of secondary power outages caused by sudden phase changes in the load. After closing, the grid-connected energy storage converter smoothly switches from off-grid constant voltage and frequency mode to grid-connected operation mode. Subsequently, the system controls the energy storage converter to automatically execute power reduction logic until the output power drops to zero. At this time, subsequent operations such as disconnecting the energized equipment cables can be performed. The above-mentioned power restoration detection, dynamic phase locking, synchronous grid connection, and load reduction processes are automatically executed according to the preset logic sequence within the system.

[0037] This application also provides a millisecond-level seamless offline handover method based on the aforementioned system. The operational logic of this method corresponds to that of the aforementioned system embodiment. Specifically, refer to the appendix. Figure 2 As shown, the method includes the following steps performed sequentially: The first step is the grid-connected standby step. After the system completes physical wiring and equipment initialization, it performs live phase detection and grid connection. During this stage, the main control circuit of the static transfer switch receives a closing command, maintaining the thyristor's conduction state; the power consumption of the load connected to the local microgrid bus is mainly provided by the external power grid as the primary power source. During this period, the sampling module of the energy management system continuously collects and tracks grid parameters. The operating mode of the grid-connected energy storage converter is set to grid-supported mode, and its internal phase-locked loop extracts and follows the frequency and phase of the grid voltage in real time, remaining in a hot standby state, neither outputting active power to the grid nor maintaining it at a set standby power level.

[0038] The second step is the fault detection and disconnection step. During equipment operation, the energy management system continuously samples and processes the three-phase voltage on the grid side at a sampling frequency of 1000Hz. When a fault occurs in the external power grid, causing the voltage or frequency to deviate from the normal operating range, the fault detection algorithm embedded in the energy management system identifies the abnormal state within the first calculation cycle after the judgment condition is met, based on a preset fault judgment threshold. After identifying the abnormality, the energy management system immediately generates and sends a trip signal through the communication link, triggering the static transfer switch to operate and controlling the high-power thyristor inside to turn off, thereby disconnecting the physical connection between the local load bus and the faulty power grid.

[0039] The third step is the off-grid takeover step. After detecting that the physical connection of the static transfer switch has been disconnected, the system enters the independent operation state. Within 10ms after the off-grid conditions are determined, the control system of the grid-connected energy storage converter performs a structural reconfiguration of the control loop. Specifically, the grid-connected energy storage converter, based on the V / f control strategy and virtual synchronous machine technology, converts the control mode to an off-grid constant voltage and constant frequency mode. According to the preset virtual inertia and damping parameters, the energy storage converter takes over the power supply control of the local bus and load, and autonomously establishes and maintains a stable AC voltage with an amplitude of 380V and a frequency of 50Hz. The entire grid-connected / off-grid switching process from the occurrence of a grid fault to the complete establishment of the off-grid voltage by the energy storage converter is limited to within 20ms on the time axis, and the voltage and frequency fluctuation parameters of the output power are limited to a fluctuation range of ±1% by the system control loop.

[0040] The fourth step is the power restoration synchronization closing step. During off-grid operation, the system continuously monitors the voltage status of the external power grid. When the external power grid fault is cleared and normal power supply is restored, the mains monitoring module of the grid-type energy storage converter collects the restored grid voltage signal. The dynamic phase-locked loop adjustment algorithm inside the energy storage converter is activated. By calculating and adjusting the frequency and phase of its own output voltage, the device output is calibrated until the local bus voltage and the external power grid voltage parameters reach a synchronized state of the same amplitude, frequency, and phase within the tolerance range. After locking this highly synchronized state, the control system generates a closing command and sends it to the static transfer switch, instructing it to perform a smooth closing within a 20ms action cycle. After the closing action is completed, the system switches back from the off-grid independent power supply state to the external power grid main power supply state.

[0041] In specific application scenarios, the system and method provided in this application can be adapted to power environments with specific restrictions on power outages. For example, in low-voltage uninterrupted maintenance application scenarios, such as planned maintenance operations like transformer capacity expansion and low-voltage line renovation, the load of the maintenance section can be temporarily powered by this system. At the moment of power outage during maintenance and at the moment of power restoration after maintenance, this system maintains the load bus voltage in a continuous state based on the aforementioned rapid disconnection and takeover mechanism and the same-frequency and same-phase power restoration closing mechanism. Under this technical application, computer network terminals, digital monitoring and recording equipment, and medical testing instruments with voltage-sensitive characteristics connected to the bus will receive continuous level signals and will not trigger low-voltage restart logic.

[0042] In another power supply scenario, this system can be directly connected in parallel as a backup for the main power supply. When the main power supply experiences a power outage, the system automatically executes the aforementioned disconnection and off-grid takeover steps to maintain voltage continuity for critical loads within the site. Furthermore, because the system physically disconnects from the faulty grid and establishes a microgrid support internally, during line maintenance work, the lines on the grid side at the fault point are de-energized. In off-grid mode, the system's power will not be reverse-transmitted to the grid side via a static transfer switch, thus mitigating electrical safety incidents at the physical isolation level.

[0043] The various embodiments in this specification are described in a progressive or parallel manner. Each embodiment focuses on its connection or supplement to other embodiments. Similar or identical hardware foundations or logical parts between embodiments can be referred to interchangeably. For the hardware devices or system topologies disclosed in the embodiments, since they correspond to the control logic or method flows disclosed in the embodiments, the relevant method control details in the system structure description can be found in the detailed description of the method section.

[0044] Those skilled in the art will further understand that the control modules, logic judgment units, and algorithm execution steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in the form of electronic hardware logic circuits, computer software program code, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the logical composition and processing steps of each example have been generally described in terms of functional modules in the foregoing description. Whether these functions are executed by pure hardware circuits or by a processor reading software instructions depends on the specific application constraints such as cost control and response time requirements in the implementation of the technical solution in a particular product. Those skilled in the art can use different code architectures or hardware combinations to implement the described functions for each specific application scenario; however, equivalent substitutions of such implementation forms all fall within the scope of protection defined by the claims of this application.

[0045] The methods, algorithms, or logical steps described in conjunction with the embodiments disclosed herein can be directly implemented using integrated circuit hardware, software program modules executed by a microprocessor, or a combination of both. The software program modules can be stored in any other form of data storage medium known in the art, such as random access memory, read-only memory, electrically programmable read-only memory, electrically erasable programmable read-only memory, or hardware registers. Without causing logical conflicts, the execution order of the various steps described in the specification can be adjusted according to the interrupt priority or multi-threading configuration of the controller.

[0046] Finally, it should be noted that in the description herein, relational designations such as "first" and "second" are used merely to distinguish one component, data, or operational step from another component, data, or operational step of the same name, and do not necessarily require or imply any objective primary or secondary relationship or temporal order between these entities or operations. Furthermore, the terms "include," "contain," or any other variations thereof are intended to cover a non-exclusive inclusion relationship, such that a control process, judgment method, physical article, or system apparatus that comprises a series of technical elements includes not only those elements expressly listed in the specification, but also other conventional elements not expressly listed but well-known in the art, or supporting elements inherent to the physical connection and basic operation of such process, method, article, or apparatus. Unless further restrictive, the inclusion of a technical element by a statement that defines "…" does not exclude the presence of other similar elemental structures in the process, method, physical apparatus, or system that includes said particular element.

[0047] The millisecond-level on / off-grid handover system and method provided by the embodiments of the present invention have been described in detail above. Specific implementation scenarios and parameter configuration examples have been used to illustrate the system connection principle and control execution method of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the core logic of the system architecture and its corresponding method steps. Furthermore, for those skilled in the art, based on the technical ideas disclosed in the present invention, there will be changes and equivalent substitutions in the specific underlying code writing, component selection, and extension of specific application scenarios. Therefore, the detailed description in this specification should not be construed as the sole limitation of the present invention.

Claims

1. A millisecond-level seamless on / offline handover system, characterized in that, include: Energy management system; At least one static transfer switch, the input of which is connected to the external power grid and the output of which is connected to the local microgrid bus; At least one grid-type energy storage converter, wherein the AC side of the grid-type energy storage converter is connected in parallel to the local microgrid bus and is connected to the static transfer switch through the local microgrid bus to provide power to the load connected to the local microgrid bus; The energy management system establishes communication connections with the static transfer switch and the grid-type energy storage converter respectively; the grid-type energy storage converter and the static transfer switch communicate through a CAN2.0 bus direct connection architecture that eliminates communication relay nodes; The energy management system is configured to: continuously track grid parameters during the grid-connected phase; when a grid fault occurs, identify the grid anomaly through a set sampling frequency and trigger the static transfer switch to disconnect the physical connection with the faulty grid; after the physical connection is disconnected, control the grid-connected energy storage converter to switch to off-grid mode based on V / f control and virtual synchronous machine technology to take over the load; wherein, at the instant the off-grid condition is determined, the grid-connected energy storage converter freezes the phase angle status register value of the phase-locked loop in the grid-connected control loop and uses it as the initial substitution value for the integral part of the rotor motion equation in the virtual synchronous machine control algorithm for numerical handover, so as to maintain the continuity of the local bus voltage phase at the moment of switching. The static transfer switch uses a thyristor component; the hardware response time of the static transfer switch itself is less than or equal to 1ms. In the CAN2.0 bus direct connection architecture, the highest priority identifier is assigned to the grid fault flag bit and the mode switching command; the single-frame data transmission time between the grid-type energy storage converter and the static transfer switch is less than or equal to 5ms.

2. The millisecond-level seamless on / offline handover system according to claim 1, characterized in that, The grid-type energy storage converter has a built-in computing chip with a heterogeneous architecture of digital signal processor and field programmable gate array; the instruction execution time of the grid-type energy storage converter is less than or equal to 5ms.

3. The millisecond-level seamless on / offline handover system according to claim 1, characterized in that, The sampling frequency is set to 1000Hz; the fault detection algorithm embedded in the energy management system can identify power grid loss of voltage, undervoltage, or frequency abnormality within less than or equal to 1ms.

4. The millisecond-level seamless on / offline handover system according to claim 3, characterized in that, Upon detecting the anomaly, the energy management system triggers the static transfer switch to disconnect the physical connection within a time of less than or equal to 8ms.

5. The millisecond-level seamless on-grid / off-grid handover system according to claim 4, characterized in that, The grid-type energy storage converter completes the power supply mode switching within less than or equal to 10ms after the physical connection is disconnected; autonomously establishes and maintains a stable 380V AC voltage with a frequency of 50Hz; and controls the entire on-grid and off-grid seamless switching process to be completed within 20ms, with voltage and frequency fluctuations controlled within ±1%.

6. The millisecond-level seamless on / offline handover system according to claim 1, characterized in that, It also includes a power restoration exit mechanism: when the power grid restores power, the grid-type energy storage converter tracks and collects the restored mains power parameters and performs dynamic phase-locked adjustment; the grid-type energy storage converter calibrates its own output to achieve the same amplitude, frequency and phase as the external power grid.

7. The millisecond-level seamless on / offline handover system according to claim 6, characterized in that, After locking the synchronization state, the static transfer switch smoothly closes within 20ms and switches back to the external power grid side to eliminate the risk of circulating current impact or secondary power failure at the moment of power restoration.

8. A millisecond-level seamless handover method for parallel and offline operations, applied to the millisecond-level seamless handover system for parallel and offline operations as described in any one of claims 1 to 7, characterized in that, The method includes the following steps: Grid-connected standby steps: The static transfer switch remains in the conducting state; the energy management system continuously collects and tracks external grid parameters; the grid-connected energy storage converter is in grid-supported mode, and its internal phase-locked loop extracts and follows the frequency and phase of the grid voltage in real time, and is in standby state. Fault detection and disconnection steps: The energy management system continuously performs discrete sampling and calculation on the grid-side voltage according to the set high-frequency sampling frequency; when a fault occurs in the external power grid, the energy management system generates a trip signal based on the identified abnormal state, triggering the static transfer switch to disconnect the physical connection between the local microgrid bus and the faulty power grid; Off-grid takeover steps based on phase angle status register value handover: At the instant the physical connection is determined to be disconnected and the off-grid condition is met, the grid-type energy storage converter performs control loop reconstruction; the grid-type energy storage converter freezes the phase angle status register value of the phase-locked loop in the grid-connected control loop and uses it as the initial substitution value for the integral part of the rotor motion equation in the virtual synchronous machine control algorithm for value handover; subsequently, the grid-type energy storage converter switches to off-grid constant voltage and constant frequency mode based on V / f control strategy and virtual synchronous machine technology, and autonomously establishes and maintains a stable AC voltage to take over the load; Synchronous closing procedure after power restoration: When the external power grid resumes normal power supply, the grid-type energy storage converter collects the restored grid voltage signal and activates the dynamic phase-locked loop adjustment algorithm; the grid-type energy storage converter adjusts the frequency and phase of its own output voltage until it reaches a synchronous state with the external power grid voltage in terms of amplitude, frequency, and phase; after locking the synchronous state, the system generates a closing command to trigger the static transfer switch to perform smooth closing and switch back to the external power grid main power supply state.

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