A method and device for intelligent switching of power grid phase without impact

Abstract

The application discloses a kind of power grid phase different no impact intelligent switching method and device, device includes H bridge circuit, and the midpoint of left, right half bridge is connected corresponding phase line and neutral line by LC filter circuit, and left, right half bridge both ends are connected load after supporting capacitor in parallel, method includes: calculating three-phase voltage unbalance degree;Unbalance degree exceeds the moment of threshold value is decision moment, according to load current, voltage time series data calculation load equivalent impedance, according to load equivalent impedance and decision moment phase voltage and load voltage calculation each phase impact cost, with impact cost minimum phase as target phase;Double-loop control is carried out to target phase H bridge circuit, so that its output voltage tracks decision moment load voltage, if the difference of both is less than the time that safety threshold value meets requirement, after closing the static switch of target phase, control target phase H bridge circuit output voltage transition to target phase real voltage, and shut off the static switch of original phase.The application realizes the truly no impact switching of sensitive load.

Description

Technical Field

[0001] This invention relates to the field of power distribution network control, and specifically to a method and device for phase-to-phase intelligent switching of a power grid without impact. Background Technology

[0002] With the rapid development of the economy and society, the proportion of single-phase loads (such as residential electricity and commercial office electricity) in low-voltage distribution networks has increased dramatically, and their electricity consumption behavior has significant randomness and spatiotemporal unevenness, leading to increasingly prominent three-phase load imbalance problems. Three-phase imbalance can cause a series of power quality problems, such as excessive neutral current, increased transformer losses, three-phase voltage deviation, and even threats to the safe operation of power distribution equipment, seriously restricting the power supply efficiency, power quality, and safety reliability of the distribution network.

[0003] To address three-phase imbalance, existing technical solutions can be mainly categorized as follows:

[0004] 1. Traditional passive compensation devices: These devices (such as three-phase unbalanced automatic adjusting capacitor compensation devices) compensate for the reactive component of the load and partially correct the imbalance by switching capacitor banks connected between the phase line and the neutral line. However, this method has a slow response time (on the order of seconds) and cannot solve the fundamental problem caused by uneven distribution of active load, thus its improvement effect is limited.

[0005] 2. Phase switching technology based on mechanical switches: This technology switches the load from the heavily loaded phase to the lightly loaded phase using mechanical switches such as contactors or circuit breakers. Although this method can directly transfer active load, the operating time of its core component, the mechanical switch, is as long as hundreds of milliseconds or even seconds, which cannot meet the needs of sensitive loads with high requirements for power supply continuity. More seriously, the mechanical switch generates electric arcs during opening and closing, leading to easy contact erosion, short service life, and high maintenance costs.

[0006] 3. Solid-State Transfer Switches (SSTS) Based on Power Electronic Devices: SSTS utilizes fully controllable devices such as thyristors (SCRs) or insulated-gate bipolar transistors (IGBTs) to achieve millisecond-level fast switching, representing a current advanced research direction. However, its mainstream control strategy suffers from fundamental bottlenecks, severely limiting its performance in complex power distribution network environments:

[0007] Heavy dependence on voltage / current zero-crossing points: To reduce switching losses and inrush current impacts, most SSTS control strategies must switch precisely at the moment a current or voltage zero-crossing is detected. However, in actual distribution networks, load currents (especially nonlinear loads) exhibit severe waveform distortion and may not have stable zero-crossing points, leading to delayed or failed switching and the loss of their speed advantage. In the worst case, the system may have to wait for nearly one power frequency cycle (20ms) before performing a switch.

[0008] The potential impact risks of "blind switching": Existing strategies only focus on "when to switch", but cannot predict and control the transient effects brought about by the switching action itself. When there is a large phase difference between the target phase voltage and the load current, even if the switching is at the zero crossing point, a huge active power surge current (inrush current) will be generated instantaneously after the switching, which poses a threat to sensitive loads and the switching devices themselves.

[0009] Lack of adaptability to load characteristics: Existing methods typically only consider the voltage or load factor of the source side (grid) when selecting the target phase, without taking into account the instantaneous characteristics (such as impedance characteristics and current phase) of the load side (the load to be switched). This "one-size-fits-all" strategy makes it difficult to achieve optimal shock-free switching under complex load conditions.

[0010] In summary, existing three-phase imbalance mitigation technologies, especially the advanced SSTS scheme, suffer from a core deficiency: they are limited by the traditional "zero-crossing detection" approach, making it impossible to achieve truly fast, smooth, and intelligent phase switching under non-ideal grid conditions (such as waveform distortion). Therefore, there is an urgent need for a completely new control paradigm that can break free from dependence on physical zero-crossing points and proactively create safe switching conditions, thereby achieving a qualitative leap in the performance of distribution network imbalance mitigation. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a method and device for phase-to-phase intelligent switching of the power grid, which is based on load characteristic prediction and virtual vector synchronization, completely eliminates the dependence on the zero-crossing point of the power grid voltage / current, fundamentally eliminates the inrush current during switching, realizes truly shock-free switching of sensitive loads, and significantly improves the intelligence level and adaptability of the system.

[0012] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0013] A method for seamless intelligent phase switching in a power grid is disclosed. The method is applied to a seamless intelligent phase switching device, which includes an H-bridge circuit corresponding to each phase. The midpoints of the left and right halves of the H-bridge circuit are connected to the corresponding phase line and neutral line via LC filter circuits, respectively. The left and right halves of the H-bridge circuit are connected in parallel with corresponding phase support capacitors, which are then connected to the load via corresponding phase static switches. The method includes:

[0014] Real-time acquisition of three-phase voltage, load current, and load voltage; calculation of three-phase voltage imbalance based on three-phase voltage.

[0015] If the three-phase voltage imbalance exceeds the set threshold, the corresponding time is taken as the decision time. The equivalent load impedance is calculated based on the time series data of the load current and load voltage. The impact cost of each phase is calculated based on the equivalent load impedance and the voltage of each phase and the load voltage at the decision time. The phase with the minimum impact cost is selected as the target phase.

[0016] Based on the load voltage at the decision time, a voltage command is generated to perform dual closed-loop control on the H-bridge circuit of the target phase, so that the output voltage of the H-bridge circuit of the target phase tracks the load voltage at the decision time. If the time requirement is met when the difference between the output voltage and the load voltage at the decision time is less than the safety threshold, the static switch of the target phase is closed to switch the phase from the original phase to the target phase. Then, the voltage command is changed to make the output voltage of the H-bridge circuit of the target phase transition to the actual voltage of the target phase.

[0017] When the primary phase current drops to the specified current value, the static switch of the primary phase is turned off.

[0018] Furthermore, when calculating the three-phase voltage imbalance based on the three-phase voltage, the symmetrical component method is specifically used. The positive-sequence voltage component and the negative-sequence voltage component are calculated based on the three-phase voltage. Then, the negative-sequence voltage component is divided by the positive-sequence voltage component as a percentage to obtain the three-phase voltage imbalance.

[0019] Furthermore, when calculating the equivalent load impedance based on the time-series data of the load current and load voltage, the recursive least squares method is specifically used to calculate the equivalent load impedance based on the time-series data of the load current and load voltage.

[0020] Furthermore, when calculating the impact cost of each phase based on the load equivalent impedance and the voltage of each phase at the decision time and the load voltage, the absolute value of the difference between the voltage of each phase at the decision time and the load voltage at the decision time is calculated separately. Then, the absolute value of each phase is divided by the absolute value of the load equivalent impedance and multiplied by an empirical coefficient to obtain the impact cost of each phase.

[0021] Furthermore, the requirement that the time difference between the output voltage and the load voltage at the decision time is less than the safety threshold specifically means that the time difference between the output voltage and the load voltage at the decision time is less than the safety threshold reaches a specified duration.

[0022] Furthermore, when the voltage command is changed to transition the output voltage of the H-bridge circuit of the target phase to the actual voltage of the target phase, the voltage command changes over time as follows:

[0023]

[0024] in, After the static switch of the target phase is closed Voltage command at any moment From 0 to , For the transition period, Indicates the moment of decision The value of the load voltage, This represents the actual voltage value of the target phase.

[0025] Furthermore, the specified current value is a specified proportion of the rated current.

[0026] Furthermore, when calculating the three-phase voltage imbalance based on the three-phase voltage, specifically, the three-phase voltage imbalance is calculated based on the three-phase voltage in each preset cycle. When the three-phase voltage imbalance exceeds a set threshold, if the number of consecutive times the three-phase voltage imbalance exceeds the set threshold is greater than a specified value, then the step of taking the corresponding time as the decision time is executed. If the number of consecutive times the three-phase voltage imbalance exceeds the set threshold is less than a specified value, then wait until the next cycle arrives and calculate the three-phase voltage imbalance again based on the three-phase voltage.

[0027] Furthermore, the H-bridge circuit is an H-bridge power converter composed of IGBTs. Before generating a voltage command based on the load voltage at the decision moment to perform dual closed-loop control on the H-bridge circuit of the target phase, the method further includes: setting the voltage outer loop PI parameters and the current inner loop PI parameters; driving all four IGBTs of the target phase H-bridge power converter to be in a high-frequency switching state based on the voltage outer loop PI parameters and the current inner loop PI parameters, thereby controlling the control mode of the target phase H-bridge power converter to PWM rectification mode; after turning off the static switch of the original phase, the method further includes: setting the drive signals of the two IGBTs in the upper arm of the target phase H-bridge power converter to a constant off level, and setting the drive signals of the two IGBTs in the lower arm to a constant on level, thereby switching the control mode of the target phase H-bridge power converter from PWM rectification back to standby mode to reduce losses.

[0028] This invention also proposes a power grid phase-separation shockless intelligent switching device, including a main power circuit, a sampling circuit, and a controller. The main power circuit includes an H-bridge circuit corresponding to each phase. The H-bridge circuit is an H-bridge power converter composed of IGBTs. The midpoints of the left and right halves of the H-bridge power converter are connected to the corresponding phase line and neutral line after passing through LC filter circuits, respectively. The left and right halves of the H-bridge power converter are connected in parallel with corresponding phase support capacitors and then connected to the load through corresponding phase static switches. The sampling circuit is connected to each phase and the load. The input terminal of the controller is connected to the sampling circuit to obtain current and voltage sampling signals. The output terminal of the controller is connected to the H-bridge power converter and the static switch, respectively. The controller is programmed or configured to implement the power grid phase-separation shockless intelligent switching method.

[0029] Compared with the prior art, the advantages of the present invention are as follows:

[0030] This invention employs a "synchronization first, connection second, and transfer third" strategy. First, it generates a voltage command based on the load voltage at the decision-making moment to perform dual closed-loop control on the H-bridge circuit of the target phase, ensuring the output voltage of the target phase's H-bridge circuit tracks the load voltage at the decision-making moment. Then, if the time required for the difference between the output voltage and the load voltage at the decision-making moment to be less than a safety threshold is met, the static switch of the target phase is closed. Finally, it changes the voltage command to transition the output voltage of the target phase's H-bridge circuit to the actual voltage of the target phase. This strategy fundamentally avoids inrush current caused by voltage and phase differences, achieving "seamless" switching of sensitive loads.

[0031] This invention generates a voltage command based on the load voltage at the decision moment to perform dual closed-loop control on the H-bridge circuit of the target phase, so that the output voltage of the H-bridge circuit of the target phase tracks the load voltage at the decision moment. Through "virtual synchronization" technology, the switching decision and execution are freed from the constraints of the power frequency cycle, and the maximum switching delay is reduced from the order of 20ms to 3-5ms, achieving a qualitative leap.

[0032] This invention introduces an impact prediction model based on the instantaneous characteristics of the load. The equivalent impedance of the load is calculated based on the time-series data of the load current and load voltage. The impact cost of each phase is calculated based on the equivalent impedance of the load and the voltage of each phase at the decision time and the load voltage. The phase with the minimum impact cost is selected as the target phase, which upgrades the switching decision from a simple "choose the lighter" to a globally optimal "choose the stable", significantly improving the adaptability and reliability of the system.

[0033] This invention calculates the equivalent load impedance based on the timing data of load current and load voltage, and performs dual closed-loop control on the H-bridge circuit of the target phase. It is insensitive to non-ideal operating conditions such as power grid waveform distortion and harmonics, and solves the problem of failure of traditional SSTS in zero-crossing detection under nonlinear loads, thus having a wider range of applications. Attached Figure Description

[0034] Figure 1 This is a circuit diagram of the main power circuit in the power grid phase-separated impact-free intelligent switching device according to an embodiment of the present invention.

[0035] Figure 2 This is a flowchart of a power grid phase-to-phase intelligent switching method according to an embodiment of the present invention. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0037] To overcome the shortcomings of existing technologies, rapid and shock-free phase switching can be achieved based on load characteristic prediction and virtual vector synchronization. The core objective is:

[0038] Completely eliminates the dependence on the zero-crossing point of the grid voltage / current, enabling rapid switching that can be initiated at any point on the current waveform, minimizing switching delay.

[0039] Achieving truly "impact-free" smooth switching fundamentally eliminates inrush current caused by phase and voltage differences, ensuring the safe operation of sensitive loads.

[0040] By introducing instantaneous load characteristics as the core decision-making basis, the switching decision is upgraded from a simple "choose the lightest option" to a globally optimal "choose the most stable option", thereby improving the system's intelligence and adaptability.

[0041] Based on the above ideas, this embodiment proposes a power grid phase-to-phase intelligent switching method without impact. Its core idea is to predict the load characteristics in real time and control the target phase to generate a "virtual voltage" that is synchronized with the current voltage of the load. After achieving voltage synchronization, the electrical connection is completed first, and then the power is seamlessly transferred through a smooth transition of the modulation wave.

[0042] The method of this embodiment is applied to a specific power grid phase-separate shockless intelligent switching device, which includes at least:

[0043] Main power circuit: Consists of three identical single-phase intelligent phase selection switch units, corresponding to phases A, B, and C respectively. For example... Figure 1 As shown, each unit includes an H-bridge circuit, which can be an H-bridge power converter composed of IGBTs. The midpoints of the left and right halves of the bridge, as the two ends of the AC side, are connected to the corresponding phase line and neutral line after passing through an LC filter circuit, respectively. The two ends of the left and right halves of the bridge, as the two ends of the DC side, are connected in parallel with the corresponding phase support capacitors and then through the corresponding phase static switches (such as...). Connect the load. The static switch is used to carry current in steady state, reducing the conduction loss of the H-bridge.

[0044] In this embodiment, each H-bridge uses an FF75R12RT4 type IGBT module and a DC support capacitor. The AC side filter inductor is 470μF. The filter capacitor is 2mH. 10μF. Static switch. It is implemented using the same type of IGBT.

[0045] Sampling circuit: includes voltage sensors (for detecting three-phase voltage) and load voltage ) and current sensor (for detecting load current) (and the current of each phase), the signal is conditioned and then sent to the controller. In this embodiment, the voltage sensor is type LV25-P and the current sensor is type HNC-50A.

[0046] Controller: Employs a high-performance digital signal processor (DSP, such as TMS320F28379D) or FPGA to execute all monitoring, calculation, and control algorithms. In this embodiment, the controller uses a TI TMS320F28379D DSP with a clock frequency of 200MHz, providing sufficient computing power.

[0047] Drive and protection circuit: Used to drive the IGBT and provide real-time protection against overcurrent, overvoltage, and overtemperature. In this embodiment, the drive circuit uses the 2ED020I12-F2 driver chip and includes an overcurrent protection circuit based on a Hall sensor.

[0048] The controllers in the aforementioned functional modules are programmed or configured to execute the methods of this embodiment, such as... Figure 2 As shown, the method includes:

[0049] S1) Real-time monitoring of system status and assessment of imbalance:

[0050] The system collects three-phase voltage, load current, and load voltage in real time. It calculates the three-phase voltage imbalance based on the three-phase voltage. If the three-phase voltage imbalance exceeds a set threshold, the corresponding moment is used as the decision moment, triggering a phase switching decision. Specifically, this includes:

[0051] S101) acquires the three-phase grid voltage in real time at a sampling frequency higher than 20kHz. and load voltage and load current ;

[0052] S102) Calculate the current three-phase voltage imbalance ε and compare it with the threshold. In comparison, in this embodiment, when calculating the three-phase voltage imbalance based on the three-phase voltage, the three-phase voltage imbalance is specifically calculated every preset period (e.g., 1ms). Specifically, the symmetrical component method is used to calculate the positive sequence voltage component based on the three-phase voltage. and negative sequence voltage components Then, the negative sequence voltage component is divided by the positive sequence voltage component as a percentage to obtain the three-phase voltage imbalance:

[0053]

[0054] threshold The typical value is 2%. In this embodiment, a threshold is set. When the three-phase voltage imbalance exceeds a set threshold, if the number of consecutive times the three-phase voltage imbalance exceeds the set threshold is greater than a specified value, then the step of using the corresponding time as the decision time is executed. If the number of consecutive times the three-phase voltage imbalance exceeds the set threshold is less than a specified value, then the process waits for the next cycle and calculates the three-phase voltage imbalance again based on the three-phase voltage. In this embodiment, the specified value is set to 3, so that when three consecutive calculation cycles meet the requirement... At that time, a phase switching decision is triggered.

[0055] S2: Intelligent target phase selection based on load characteristic prediction:

[0056] The equivalent load impedance is calculated based on the time-series data of load current and load voltage. The impact cost of each phase is then calculated based on the equivalent load impedance and the voltage of each phase at the decision point relative to the load voltage. The phase with the lowest impact cost is selected as the target phase. This step is crucial to the intelligence of the method in this embodiment. It does not simply select the phase with the lightest load, but rather predicts the potential impact cost of switching to each phase, thereby selecting the optimal target phase. Specifically, this includes:

[0057] S103) Establish an equivalent load model. At the instant of the switching decision (on the order of microseconds), the load characteristics are assumed to remain unchanged. The load is equivalent to a resistor. With inductance A series circuit. Its equivalent impedance and power factor angle The voltage and current waveform data from the most recent cycle can be used for online identification using the recursive least squares (RLS) method. In this embodiment, specifically, the most recent 20ms data is extracted. and The time-series data is used to identify the equivalent resistance in real time using the RLS algorithm. and equivalent inductance Based on the identification results, the equivalent impedance amplitude of the load at the current power frequency is... and power factor angle Calculated by the following formula:

[0058]

[0059]

[0060] in, This is the angular frequency of the power grid.

[0061] S104) Calculate the switching impact cost function. For each candidate phase (x∈{a,b,c}), calculate the maximum instantaneous current surge that may occur if the load is switched to this phase. The calculation formula is as follows:

[0062]

[0063] in, The candidate phase voltage at the decision time The instantaneous value, It is an empirical coefficient that takes into account the transient process (usually taken as 1.5~2.5), and in this embodiment, the empirical coefficient k is taken as 2.0.

[0064] Impact cost function That is, take it as:

[0065]

[0066] Therefore, in this embodiment, when calculating the impact cost of each phase based on the load equivalent impedance and the voltage of each phase and the load voltage at the decision time, the absolute value of the difference between the voltage of each phase and the load voltage at the decision time is calculated separately. Then, the absolute value of each phase is divided by the absolute value of the load equivalent impedance and multiplied by an empirical coefficient to obtain the impact cost of each phase.

[0067] S105) Select the optimal target phase. Select the phase that maximizes the impact cost function. The smallest phase is taken as the target phase, that is:

[0068]

[0069] For example, if the original phase is phase A, then the current time... Based on the instantaneous value, the switching to phase B and phase C is calculated through the above steps. .Compare and The phase corresponding to the smaller value is selected as the target phase.

[0070] S3: Virtual Vector Synchronization and Impact-Free Access

[0071] Based on the load voltage at the decision-making moment, a voltage command is generated to perform dual closed-loop control on the H-bridge circuit of the target phase, ensuring that the output voltage of the H-bridge circuit of the target phase tracks the load voltage at the decision-making moment. If the time required for the difference between the output voltage and the load voltage at the decision-making moment to be less than a safety threshold is met, the static switch of the target phase is closed, switching the phase from the original phase to the target phase. Then, the voltage command is changed to transition the output voltage of the H-bridge circuit of the target phase to the actual voltage of the target phase. This is the core execution step for achieving shockless switching, specifically including:

[0072] S106) Target Phase H-Bridge Circuit Parameter Configuration: Controls the target phase H-bridge circuit to enter PWM rectification mode. The voltage outer loop PI parameter is set to... The current inner loop PI parameter is set to... .

[0073] S107) Virtual Synchronization Voltage Command Generation: Setting Voltage Command The initial value is the voltage across the current load. The instantaneous value, At the decision moment, high-bandwidth voltage and current dual closed-loop control (such as a PI controller) is used to adjust the voltage at the bridge arm output. Fast Tracking ,Right now At this point, the target phase bridge arm acts as a controllable voltage source, its output voltage is synchronized with the load voltage, and the voltage difference between the two is... It is controlled within a very small range (e.g., less than 5V).

[0074] S108) Pre-connection: When the time requirement is met that the difference between the output voltage and the load voltage at the decision moment is less than the safety threshold, the static switch of the target phase is closed.

[0075] In this embodiment, the requirement that the time difference between the output voltage and the load voltage at the decision time is less than the safety threshold specifically means that the time difference between the output voltage and the load voltage at the decision time is less than the safety threshold reaches a specified duration (e.g., 10 μs). For example, when phase B is the target phase, when the voltage error... After maintaining this position for 10 μs, a command is issued to close the target phase static switch. Because the voltage difference is extremely small, only a negligible circulating current is generated at the moment of closing.

[0076] S109) Power Smoothing Transfer: After the target phase static switch is closed, the voltage command is changed to transition the output voltage of the H-bridge power converter of the target phase to the actual voltage of the target phase. Specifically, the voltage command is changed smoothly with a preset slope. to make it from The true voltage transitioning to the target phase This ensures that after the target phase static switch is closed, during the transition time, it will... from Linear ramp transition to target phase voltage During this process, the load current will smoothly and continuously transfer from the original phase to the target phase. The transient process can be described by the following function of voltage command changing with time:

[0077]

[0078] in, After the static switch of the target phase is closed Voltage command at any moment From 0 to , This is the transition time (typically 1-2ms). Indicates the moment of decision The value of the load voltage, This represents the actual voltage value of the target phase.

[0079] S4: Original phase cutoff and switching completed:

[0080] Monitoring the original phase current .when When the current drops to a specified value close to zero (e.g., below 5% of the rated current), the static switch of the original phase is turned off. Subsequently, the control mode of the target phase H-bridge can be switched from PWM rectification back to standby mode to reduce losses. This completes the entire shockless switching process.

[0081] Assuming the rated current is 50A, then the primary phase current... When the absolute value is less than 2.5A (assuming the rated current is 5% of 50A), the original phase static switch is turned off. Switch the target phase H-bridge control mode back to standby. The switching process is complete.

[0082] In this embodiment, the specific operation of switching the control mode of the target phase H-bridge from PWM rectification back to standby mode is executed by the software logic of the controller (DSP). Essentially, this involves controlling the four IGBTs of the H-bridge (such as...) Figure 1 The drive signals (PWM1H, PWM1L, PWM2H, PWM2L) of T1, T2, T3, and T4 in the code are reconfigured. The specific steps are as follows:

[0083] Signal status in PWM rectification mode: In this mode, the controller runs a dual-loop (outer voltage loop, inner current loop) PWM modulation algorithm. The PWM signal is dynamically generated, enabling the H-bridge to operate as a controllable rectifier, absorbing or supplying specific power from the grid side to precisely control its output voltage V_out. At this time, all four IGBTs are in a high-frequency switching state.

[0084] Triggering and Operation for Switching to Standby Mode: When the primary phase static switch is turned off and the switching process is complete, the controller performs the following operations to achieve low-loss standby: a. Stop the PWM modulation algorithm: Exit the voltage and current dual closed-loop control program. b. Output fixed drive logic: The controller configures the output pins that generate the PWM signal to output a fixed combination of levels. A typical low-loss standby configuration is: set the drive signals of the two IGBTs (T1, T3) of the upper bridge arm to a constant off level (low level), and set the drive signals of the two IGBTs (T2, T4) of the lower bridge arm to a constant on level (high level). c. State maintenance and monitoring: Under this fixed drive signal, the lower bridge arm of the H-bridge is on, and the upper bridge arm is off. At this time, the two ends of the AC side of the H-bridge (i.e., the input of the LC filter circuit) are short-circuited to the DC side negative bus (or neutral potential) through the on-state lower bridge arm IGBTs (T2, T4). This state prevents the H-bridge from generating active voltage output, and since all IGBTs are in a stable on or off state (no switching action), switching losses are reduced to near zero, achieving the goal of "standby to reduce losses." Simultaneously, the controller maintains monitoring of the grid voltage and load status, preparing for the next possible switching request.

[0085] Reactivation from standby mode: When the system determines again that phase switching is required and the H-bridge is selected as the target phase, the controller first restores its PWM signal output function, re-runs the dual closed-loop control algorithm, and smoothly transitions the drive signal from the fixed standby logic to the dynamic PWM waveform, thereby quickly entering the PWM rectification mode and performing a new round of "virtual synchronization" and access operations.

[0086] Through the clearly defined software control process described above, the H-bridge circuit achieves reliable and rapid switching between the two operating modes of "high-performance PWM rectification" and "low-loss standby".

[0087] In summary, this invention proposes a method and device for shock-free intelligent phase switching in a power grid, addressing the problems of existing solid-state transfer switch (SSTS) technology, such as heavy reliance on the grid's zero-crossing point, current surges during switching, and insufficient intelligence in decision-making. The core of the method lies in: first, real-time monitoring of the three-phase imbalance of the power grid; after exceeding a threshold, intelligent selection of the optimal target phase by identifying the instantaneous characteristics of the load and predicting the impact cost of switching to each candidate phase; then, controlling the IGBT power converter of the target phase to generate a "virtual voltage" precisely synchronized with the current load voltage; after achieving deadbeat pre-connection, seamless transfer of load power to the target phase is achieved through a modulated wave smooth transition algorithm. The corresponding device includes a main power circuit composed of an H-bridge of IGBTs, a high-precision sampling circuit, a digital controller based on a high-speed DSP / FPGA, and a drive and protection circuit. The beneficial effects of this invention are as follows: it completely eliminates the dependence on the zero-crossing point of the grid voltage / current, reducing the maximum switching delay from 20ms to 3-5ms; through the strategy of "synchronization first, connection then transfer", it fundamentally eliminates the switching inrush current and realizes a truly shock-free switching of sensitive loads; and it introduces a predictive decision-making mechanism based on the instantaneous characteristics of the load, which significantly improves the intelligence level and adaptability of the system.

[0088] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-readable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create a machine for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to operate in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1The functions specified in one or more boxes. These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable apparatus for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0089] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for seamless intelligent phase switching in a power grid, characterized in that, The method is applied to a phase-separated, shock-free intelligent switching device for power grids. The device includes an H-bridge circuit corresponding to each phase. The midpoints of the left and right halves of the H-bridge circuit are connected to the corresponding phase line and neutral line via LC filter circuits, respectively. The left and right halves of the H-bridge circuit are connected in parallel with corresponding phase support capacitors, which are then connected to the load via corresponding phase static switches. The method includes: Real-time acquisition of three-phase voltage, load current, and load voltage; calculation of three-phase voltage imbalance based on three-phase voltage. If the three-phase voltage imbalance exceeds the set threshold, the corresponding time is taken as the decision time. The load equivalent impedance is calculated based on the time-series data of the load current and load voltage. The impact cost of each phase is calculated based on the load equivalent impedance and the voltage of each phase and the load voltage at the decision time. The phase with the smallest impact cost is selected as the target phase. Specifically, when calculating the impact cost of each phase based on the load equivalent impedance and the voltage of each phase and the load voltage at the decision time, the absolute value of the difference between the voltage of each phase and the load voltage at the decision time is calculated. Then, the absolute value of each phase is divided by the absolute value of the load equivalent impedance and multiplied by an empirical coefficient to obtain the impact cost of each phase. Based on the load voltage at the decision time, a voltage command is generated to perform dual closed-loop control on the H-bridge circuit of the target phase, so that the output voltage of the H-bridge circuit of the target phase tracks the load voltage at the decision time. If the time required for the difference between the output voltage and the load voltage at the decision time to be less than the safety threshold is met, the static switch of the target phase is closed to switch the phase from the original phase to the target phase. Then, the voltage command is changed to make the output voltage of the H-bridge circuit of the target phase transition to the actual voltage of the target phase. Specifically, the time required for the difference between the output voltage and the load voltage at the decision time to be less than the safety threshold is when the time required for the difference between the output voltage and the load voltage at the decision time to be less than the safety threshold reaches a specified duration. When the primary phase current drops to the specified current value, the static switch of the primary phase is turned off.

2. The power grid phase-separation intelligent switching method according to claim 1, characterized in that, When calculating the three-phase voltage imbalance based on the three-phase voltage, the symmetrical component method is used. The positive-sequence voltage component and the negative-sequence voltage component are calculated based on the three-phase voltage. Then, the negative-sequence voltage component is divided by the positive-sequence voltage component as a percentage to obtain the three-phase voltage imbalance.

3. The power grid phase-separation intelligent switching method according to claim 1, characterized in that, When calculating the equivalent load impedance based on the time-series data of load current and load voltage, the recursive least squares method is specifically used to calculate the equivalent load impedance based on the time-series data of load current and load voltage.

4. The power grid phase-separation intelligent switching method without impact according to claim 1, characterized in that, When the voltage command is changed to transition the output voltage of the H-bridge circuit of the target phase to the actual voltage of the target phase, the voltage command changes over time as follows: in, After the static switch of the target phase is closed Voltage command at any moment From 0 to , For the transition period, Indicates the moment of decision The value of the load voltage, This represents the actual voltage value of the target phase.

5. The power grid phase-separation intelligent switching method without impact according to claim 1, characterized in that, The specified current value is a specified percentage of the rated current.

6. The power grid phase-separation intelligent switching method according to claim 1, characterized in that, When calculating the three-phase voltage imbalance based on the three-phase voltage, specifically, the three-phase voltage imbalance is calculated based on the three-phase voltage in each preset cycle. When the three-phase voltage imbalance exceeds a set threshold, if the number of consecutive times the three-phase voltage imbalance exceeds the set threshold is greater than a specified value, then the step of taking the corresponding time as the decision time is executed. If the number of consecutive times the three-phase voltage imbalance exceeds the set threshold is less than a specified value, then wait until the next cycle arrives and calculate the three-phase voltage imbalance again based on the three-phase voltage.

7. The power grid phase-separation intelligent switching method without impact according to claim 1, characterized in that, The H-bridge circuit is an H-bridge power converter composed of IGBTs. Before generating a voltage command based on the load voltage at the decision moment to perform dual closed-loop control on the H-bridge circuit of the target phase, the following steps are included: setting the voltage outer loop PI parameters and the current inner loop PI parameters; driving all four IGBTs of the target phase H-bridge power converter to be in a high-frequency switching state according to the voltage outer loop PI parameters and the current inner loop PI parameters, thereby controlling the control mode of the target phase H-bridge power converter to PWM rectification mode; after turning off the static switch of the original phase, the following steps are included: setting the drive signals of the two IGBTs in the upper arm of the target phase H-bridge power converter to a constant off level, and setting the drive signals of the two IGBTs in the lower arm to a constant on level, thereby switching the control mode of the target phase H-bridge power converter from PWM rectification back to standby mode to reduce losses.

8. A power grid phase-separation shockless intelligent switching device, characterized in that, The system includes a main power circuit, a sampling circuit, and a controller. The main power circuit includes an H-bridge circuit corresponding to each phase. The H-bridge circuit is an H-bridge power converter composed of IGBTs. The midpoints of the left and right halves of the H-bridge power converter are connected to the corresponding phase line and neutral line after passing through LC filter circuits, respectively. The left and right halves of the H-bridge power converter are connected in parallel with corresponding phase support capacitors and then connected to the load through corresponding phase static switches. The sampling circuit is connected to each phase and the load, respectively. The input terminal of the controller is connected to the sampling circuit to obtain current and voltage sampling signals. The output terminal of the controller is connected to the H-bridge power converter and the static switch, respectively. The controller is programmed or configured to implement the grid phase-to-phase intelligent switching method according to any one of claims 1 to 7.

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