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CN-121508342-B - Multi-machine parallel and off-grid starting control method for grid-connected inverter

CN121508342BCN 121508342 BCN121508342 BCN 121508342BCN-121508342-B

Abstract

The invention discloses a grid-built inverter multi-machine parallel connection and off-grid starting control method which comprises the steps that a starting control loop performs starting mode selection on a first inverter according to received external Cmd instructions, the first inverter runs according to a control strategy of the starting mode after determining the starting mode, the starting control loop of a second inverter selects the starting mode according to the received external Cmd instructions, an enabling PWM (pulse width modulation) module of the second inverter tracks rated voltage established by the first inverter at a public connection point to achieve synchronization, and the first two steps are repeated until the rated voltage of all the inverters achieves synchronization, closing operation is performed, and the like. The invention can realize the control strategies of the inverter cluster in different states are mutually independent through the zone bit switching among multiple stages, realize the modularized decoupling of the starting flow and eliminate the response lag problem of the traditional linear control logic.

Inventors

  • DU WENHAO
  • LIU ZHIBO
  • JIA YANG

Assignees

  • 天津瑞源电气有限公司

Dates

Publication Date
20260508
Application Date
20260114

Claims (9)

  1. 1. A multi-machine parallel and off-grid starting control method for a grid-structured inverter is characterized by comprising the following steps: S1, a starting control loop of a first inverter selects a starting mode according to a received external Cmd instruction; S2, after the first inverter determines a starting mode, the first inverter operates according to a control strategy of the starting mode, and the first inverter raises the output voltage to be rated according to a set voltage raising rate, so that the rated voltage of a common connection point is built; S3, the starting control ring of the second inverter selects a starting mode according to the received external Cmd instruction; s4, enabling a PWM module of the second inverter, tracking rated voltage established by the first inverter at a public connection point, and realizing synchronization; S5, repeating the step S3 and the step S4 until the rated voltages of all the inverters are synchronous, executing a closing operation, completing parallel starting after closing, and synchronously switching a state mark from a starting incomplete state to a starting complete state after the successful parallel starting is determined; The starting control loop is arranged between the power outer loop control and the voltage current inner loop control, and seamless synergy of parallel starting and voltage active support of the off-grid unit are realized through a layered finite state machine; The selection of the starting mode is realized based on an inverter running state transition model of a hierarchical finite state machine, the inverter running state transition model comprises a starting state layer, a normal state layer and a fault state layer, and the state condition of the current inverter running state transition model is indicated through a state mark operatingStatusFlag.
  2. 2. The method for controlling multi-machine parallel and off-grid start of a grid-built inverter of claim 1, wherein the start-up status layer is startupStatus, which is used as a start-up logic execution layer of the inverter, and the start-up status layer comprises gridMode mode and offGridMode mode, and the mode of the start-up status layer is selected by receiving an external Cmd command; the normal state layer is normalStatus and is used for continuously operating the system after the starting state is finished, and when the system detects that the starting state is finished, the system can enter the continuously operating state in the normal state layer; The fault state layer is faultStatus, which is a processing layer of fault event in the starting process of the inverter, and the starting instruction issues error class and the starting process is abnormal, and jumps to the fault state layer for processing.
  3. 3. The method for controlling the parallel and off-grid start of the grid-connected inverter according to claim 1, wherein the specific method for selecting the start mode is as follows: S11, after receiving an external Cmd instruction, the inverter to be started currently enters a starting mode selection mode, and other non-started inverters are initialized by fault state switching marks; S12, after an inverter fault state switching mark is initialized, the inverter to be started at present firstly selects a starting mode to operate in gridMode mode or offGridMode mode of a starting state layer through a mark IV, then judges the state through the current operating state output by a mark V, judges whether the starting process is finished or not, and if the starting process is not finished, reenters the starting state layer through a mark I through system control, and then performs gridMode mode or offGridMode mode selection of the starting state again until the starting is finished; s13, after the inverter is started, a starting state completion sign is output after a starting state layer startupStatus is finished, state judgment is carried out through a sign V, the next beat of operation state is judged, and after the starting state is judged, the inverter jumps to the position below a normal state layer normalStatus through a sign II through system control; S14, if the inverter breaks down during the starting period, outputting the current fault state under the starting state layer startupStatus through different fault marks in the mark V, and jumping to the position under the fault state layer faultStatus through the mark III by the system control after the state judgment.
  4. 4. The method for controlling multi-machine parallel and off-grid start of a grid-connected inverter according to claim 3, wherein the inverter fault state switching sign comprises a sign I, a sign II, a sign III, a sign IV and a sign V; The mark I is a start running state indication mark FINISHFLAG =0; the mark II is a normal operation state indication mark FINISHFLAG =1; The flag III is a fault running state indication flag FINISHFLAG =2; The mark IV is a starting mode instruction mark Power_status_cmd, and operates in gridMode mode when Power_status_cmd=2, operates in offGridMode mode when Power_status_cmd=1, and issues an instruction error when Power_status_cmd is not equal to 1 n 2; the flag V is a status flag operatingStatusFlag, operatingStatusFlag =0 indicating whether the startup is completed or not, operatingStatusFlag =1 indicating that the startup is completed, and operatingStatusFlag =2 indicating that the startup is not completed.
  5. 5. The method for controlling multi-machine parallel and off-grid start of a grid-connected inverter as set forth in claim 2, wherein the control strategy of offGridMode modes of the start-up status layer is as follows: (1) (2) In the formula (1), U droopRef is a reactive ring voltage reference value, the unit is V, U Ramp is a voltage lifting intermediate variable value, the unit is V, K is a voltage lifting slope, the unit is V/s, T s is a system control period, the unit is s, and U N is a rated voltage, and the unit is V; In the formula (2), U deltaPre is a presynchronization voltage compensation value, the unit is V, omega deltaPre is a presynchronization angular frequency compensation value, the unit is rad/s, P transmit_Cmd is a wave-generating control instruction, and P switch_Cmd is a closing control instruction.
  6. 6. The method for controlling multi-machine parallel and off-grid start of a grid-connected inverter as set forth in claim 2, wherein the control strategy of gridMode modes of the start-up status layer is as follows: (3) In the formula (3), U droopRef is a reactive ring voltage reference value, the unit is V, U deltaPre is a presynchronization voltage compensation value, the unit is V, omega deltaPre is a presynchronization angular frequency compensation value, the unit is rad/s, U N is a rated voltage, the unit is V, U delta is a presynchronization voltage compensation calculation value, omega delta is a presynchronization angular frequency compensation calculation value, P transmit_Cmd is a wave-emitting control command, and P switch_Cmd is a closing control command.
  7. 7. The method for controlling the parallel and off-grid start of the grid-connected inverter of claim 2, wherein the control strategy of the normal state layer normalStatus is as follows: (4) In the formula (4), U droopRef is a reactive ring voltage reference value, the unit is V, U deltaPre is a presynchronization voltage compensation value, the unit is V, omega deltaPre is a presynchronization angular frequency compensation value, the unit is rad/s, P transmit_Cmd is a wave-generating control instruction, P switch_Cmd is a closing control instruction, and U N is a rated voltage, and the unit is V.
  8. 8. The method for controlling the parallel and off-grid start of the grid-connected inverter of claim 2, wherein the control strategy of the fault state layer faultStatus is as follows: (5) In the formula (5), U droopRef is a reactive ring voltage reference value, the unit is V, U deltaPre is a presynchronization voltage compensation value, the unit is V, omega deltaPre is a presynchronization angular frequency compensation value, the unit is rad/s, P transmit_Cmd is a wave-generating control instruction, and P switch_Cmd is a closing control instruction.
  9. 9. The method for controlling parallel connection and off-grid start of network-structured inverters of claim 4, wherein the condition of the offGridMode state is that a system receives a control strategy of a start mode instruction Power_status_cmd=1 to select offGridMode mode, firstly, a closing instruction is sent through a closing mark Pre_switch_cmd=1, then whether a closing Feedback mark Pre_switch_feed back meets a formula (6), an off-grid closing timeout offGridSwitchTime timer is met, then the wave control mark Pwm_transmit_cmd is enabled to control wave generation through a formula (7), and U droopRef voltage lifting is controlled according to the formula (1), and if the formula (6) is not met, a closing timeout offGridSwitchTime timer starts timing; (6); (7); The condition for entering gridMode state is that the system receives a control strategy of a starting mode instruction Power_status_cmd=2 to select gridMode mode, firstly, the wave control mark Pwm_Transmit_cmd is controlled to wave through a formula (7) and U droopRef =U N is performed under grid connection operation, then, whether a synchronous switching-on mark Pre_switch_flag meets a formula (8), if the formula (8) is not met and a formula (9) synchronous threshold is not met, the synchronous timeout PRESWITCHTIME timer counts time and clears a presynchronizing delay PRESYNCTIME timer, if the formula (8) is not met, the formula (9) is not met, whether a delay timer PRESYNCTIME meets a formula (10) is judged, switching-on is controlled through a switching-on mark pre_switch_cmd=1, and clears a PRESYNCTIME timer, and then the delay timer PRESYNCTIME is timed when the formula (8) is met, and then, if the formula (6) is not met, the formula (6) is met, the switching-on timeout GRIDSWITCHTIME timer is met, and clears the grid connection timer is started, otherwise, the timer GRIDSWITCHTIME is cleared; (8); (9); (10); wherein U TH is a voltage synchronization threshold, the unit is V, omega TH is an angular frequency synchronization threshold, the unit is rad/s, U deltaPre is a presynchronization voltage compensation value, the unit is V, and omega deltaPre is a presynchronization angular frequency compensation value, the unit is rad/s; The condition for entering faultStatus state is that when the system receives a start mode instruction Power_status_cmd not equal to 1n 2, the instruction is issued incorrectly, the system jumps to faultStatus directly in the current running period, when the off-grid closing timeout offGridSwitchTime timer time satisfies formula (11), the synchronization timeout PRESWITCHTIME timer time satisfies formula (12), the grid-connected closing timeout GRIDSWITCHTIME timer satisfies formula (13), the current beat output running exception flag operatingStatusFlag in offGridMode mode after offGridSwitchTime timer satisfies the condition, and the current beat output running exception flag operatingStatusFlag in gridMode mode after GRIDSWITCHTIME timer and PRESWITCHTIME timer satisfy the condition; when the abnormality mark meets the formula (14), the next beat of the control system jumps to faultStatus after the state judgment; (11); (12); (13); (14); The conditions for entering normalStatus state include offGridMode mode condition and gridMode mode condition, wherein the offGridMode mode condition is that under offGridMode mode, when a closing Feedback mark pre_switch_feed back satisfies formula (6), a control voltage U droopRef satisfies U droopRef ≥U N in formula (1) and an off-grid closing timeout offGridSwitchTime timer does not satisfy formula (11), the gridMode mode condition is that under gridMode mode, a synchronous timeout PRESWITCHTIME timer does not satisfy formula (12), a synchronous closing mark pre_switch_flag satisfies formula (8), when the closing Feedback mark pre_switch_feed back satisfies formula (6), and when offGridMode mode condition or gridMode mode condition is satisfied, a offGridMode mode or gridMode mode currently beats output a running completion mark operatingStatusFlag, when the running completion mark satisfies formula (15), the control system next beats to jump to a normal state layer normalStatus after state judgment; (15)。

Description

Multi-machine parallel and off-grid starting control method for grid-connected inverter Technical Field The invention belongs to the field of power electronic control, and particularly relates to a multi-machine parallel and off-grid starting control method for a grid-built inverter. Background With the improvement of the permeability of renewable energy sources, the function of parallel operation of a plurality of inverters in micro-grid support and auxiliary service is increasingly critical. However, the initial start-up is especially in the off-grid switching and off-grid cold start-up scenes, the off-grid parallel synchronization stage has no voltage reference, the phase/amplitude/frequency deviation caused by the fact that the synchronization before parallel operation is insufficient (namely, the phase of the voltage amplitude is not completely synchronous between an inverter which is connected in parallel and an inverter which is connected in parallel) causes impact current, IGBT safety and system stability are threatened, the off-grid mode switching process is easy to cause voltage frequency fluctuation, power oscillation or short-time power failure due to insufficient dynamic coordination, and power supply quality is reduced and protection is misoperation are avoided, so that a multi-machine coordination off-grid start-up method which is efficient, robust, strong in adaptability and capable of reducing communication dependence as much as possible is needed. Disclosure of Invention The invention provides a method for controlling multi-machine parallel and off-grid starting of a grid-structured inverter, which aims to overcome the defects existing in the prior art. The invention is realized by the following technical scheme: A multi-machine parallel and off-grid start control method of a grid-connected inverter comprises the following steps: S1, a starting control loop of a first inverter selects a starting mode according to a received external Cmd (Command Prompt) instruction; S2, after the first inverter determines a starting mode, the first inverter operates according to a control strategy of the starting mode, and the first inverter raises output voltage to rated voltage according to a set voltage raising rate to construct rated voltage of a common connection point; S3, the starting control ring of the second inverter selects a starting mode according to the received external Cmd instruction; s4, enabling a PWM module of the second inverter, tracking rated voltage established by the first inverter at a public connection point, and realizing synchronization; And S5, repeating the step S3 and the step S4 until the rated voltages of all the inverters are synchronous, executing a closing operation, completing parallel starting after closing, and synchronously switching a state mark (mark V) from a starting incomplete state (operatingStatusFlag =0) to a starting complete state (operatingStatusFlag =1) after the parallel starting is determined to be successful (locking parallel). In the technical scheme, the starting control loop is arranged between the power outer loop control and the voltage current inner loop control, and seamless cooperation of parallel starting and voltage active support of the off-grid unit are realized through the layered finite state machine. In the above technical solution, the selection of the starting mode is implemented based on an inverter running state transition model of a hierarchical finite state machine, where the inverter running state transition model includes a starting state layer, a normal state layer, and a fault state layer, and the state condition of the current inverter running state transition model is indicated by a state flag operatingStatusFlag; the starting state layer is startupStatus which is used as a starting logic execution layer of the inverter, the starting state layer comprises a gridMode mode and a offGridMode mode, and the mode of the starting state layer is selected through an external Cmd instruction; the normal state layer is normalStatus and is used for continuously operating the system after the starting state is finished, and when the system detects that the starting state is finished, the system can enter the continuously operating state in the normal state layer; The fault state layer is faultStatus, which is a processing layer of fault event in the starting process of the inverter, the starting instruction issues error class and the starting process is abnormal, and jumps to the fault state layer for processing, wherein the starting instruction refers to power_status_cmd not equal to 1 n 2. In the above technical solution, the specific method for selecting the starting mode includes: S11, after receiving an external Cmd instruction, the inverter to be started currently enters a starting mode for selection, and fault state switching marks of other non-started inverters are initialized, so that the inverter is started to keep the original