CN115765007A

CN115765007A - Electromechanical transient modeling method and system for distributed photovoltaic inverter

Info

Publication number: CN115765007A
Application number: CN202211484665.5A
Authority: CN
Inventors: 葛路明; 曲立楠; 吴福保; 朱凌志; 陈宁
Original assignee: China Electric Power Research Institute Co Ltd CEPRI
Current assignee: China Electric Power Research Institute Co Ltd CEPRI
Priority date: 2022-11-24
Filing date: 2022-11-24
Publication date: 2023-03-07

Abstract

The invention provides an electromechanical transient modeling method and an electromechanical transient modeling system for a distributed photovoltaic inverter, which comprise the following steps: determining the running state of the inverter and the switching relation among the running states based on the transient characteristic of the distributed photovoltaic inverter without the low-voltage ride through function when executing the control logic; determining a switching criterion required by switching among the operation states based on the switching relation among the operation states; determining each electric quantity and numerical value of the inverter based on the switching relation among the operation states and the switching criterion required by switching among the operation states; performing electromechanical transient modeling of the inverter by taking each electrical quantity value as input, and outputting active current and reactive current of the inverter in the simulation process; by utilizing the electromechanical transient model of the distributed photovoltaic inverter constructed by the invention, the transient characteristic of the distributed photovoltaic inverter without a low voltage ride through function during overcurrent wave sealing or overvoltage load shedding can be accurately simulated, and the accuracy and the precision of the analysis and calculation of active power and reactive power during overcurrent wave sealing or overvoltage load shedding can be improved.

Description

Electromechanical transient modeling method and system for distributed photovoltaic inverter

Technical Field

The invention belongs to the field of new energy power generation technology and power systems, and particularly relates to an electromechanical transient modeling method and system for a distributed photovoltaic inverter.

Background

Distributed photovoltaic is developed rapidly, and influences on safety and stability of a power system are increased. Unlike centralized photovoltaic inverters, distributed photovoltaic inverters generally do not include a low/high voltage ride through mode. In order to protect the safety of equipment, control logics such as overcurrent sealing waves, overvoltage load shedding and the like are arranged in distributed photovoltaic inverters of various models, the transient characteristics are complex, and difficulties are brought to power grid stability analysis. When the power grid has a short-circuit fault, the inverter may have instantaneous overcurrent at the moment of the voltage drop of the power grid. The inverter has a weak overcurrent capacity due to the limitation of the capacity of a switching tube of the inverter, and the typical value of the maximum overcurrent capacity is 1.1-1.2 times of rated current. In order to avoid permanent damage to equipment caused by overcurrent, many equipment manufacturers can carry out wave-sealing control by setting hardware and software modes, the output current can be rapidly reduced to 0, and the response time of the process is generally hundreds of microseconds. From the perspective of a large power grid, the distributed photovoltaic system is equivalent to no longer outputting any active power and reactive power, and a huge impact is generated on the power grid. The distributed photovoltaic is connected to a low-voltage distribution network, and the low-voltage distribution line has a high resistance/reactance ratio. Under the distributed photovoltaic high-power working condition, a large amount of active power is sent to a power grid in a reverse mode, and the tail end voltage is possibly increased. Therefore, relevant standards in the field require that the inverter can reduce active power output in case of overvoltage, for example australia and new zealand standard AS/NZS 4777.2. This illustrates that many distributed inverters are provided with overvoltage load shedding control logic.

In regional power grids with high permeability distributed photovoltaics, the distributed photovoltaics have become one of the important power sources in the system, and the transient characteristics of the distributed photovoltaics have important influence on the grid failure and recovery process. In order to analyze the transient stability of the grid, this transient characteristic of the distributed photovoltaic has to be accurately simulated. The existing electromechanical transient modeling technology is generally based on a voltage outer ring-current inner ring double-ring control strategy, and simulates the transient characteristics of an inverter by identifying main circuit parameters and controller parameters of the inverter. The double-loop control strategy of the voltage outer loop-current inner loop is a control strategy in a normal steady-state operation state. When a power grid fails, voltage fluctuates in a large range, the inverter can be switched to an overcurrent wave-sealing or overvoltage load-shedding strategy, and the transient characteristic presented by the inverter to the outside is greatly different from the characteristic in normal steady-state operation. When the inverter enters an overcurrent closed-wave state, the output current of the inverter is rapidly reduced to 0, and active power and reactive power are not output to the outside; when the inverter enters an overvoltage load shedding state, the inverter can gradually reduce active power according to the terminal voltage. And the double-loop control strategy only tries to maintain the active state and the reactive state of the inverter in the state before the fault. Therefore, the transient characteristics of over-current wave sealing or over-voltage load shedding are difficult to accurately simulate by adopting a double-loop control strategy in the prior art.

Disclosure of Invention

In order to overcome the defect that the prior art is difficult to accurately simulate the transient characteristics of over-current wave sealing or over-voltage load shedding of the distributed photovoltaic inverter, the invention provides an electromechanical transient modeling method of the distributed photovoltaic inverter, which comprises the following steps:

determining the operation state of the inverter and the switching relation among the operation states based on the transient characteristic of the distributed photovoltaic inverter without the low voltage ride through function when executing control logic;

determining a switching criterion required by switching among the operating states based on the switching relation among the operating states;

determining each electrical quantity and each electrical quantity value of the inverter based on the switching relation among the operation states and the switching criterion required by switching among the operation states;

performing electromechanical transient modeling on the inverter by taking the electrical quantity values as input, and outputting active current and reactive current of the inverter in a transient process;

and the active current and the reactive current are respectively output through an active power controller and a reactive power controller.

Preferably, the operating state includes: normal operation state, overvoltage unloading state, overcurrent wave sealing state and wave sealing recovery state.

Preferably, the switching relationship between the operation states includes: the normal operation state is switched to an overvoltage load shedding state;

determining a switching criterion required for switching between the operating states based on the switching relationship between the operating states, including: the voltage of the inverter is higher than an overvoltage load shedding threshold value and is used as a switching criterion when the normal operation state is switched to an overvoltage load shedding state;

wherein the overvoltage load shedding threshold is determined based on a typical value of the overvoltage load shedding threshold in combination with a model of the inverter.

Preferably, determining the electrical quantities and the electrical quantity values of the inverter based on the switching relationship between the operating states and the switching criterion required for switching between the operating states includes:

determining the electrical quantity of the inverter to be voltage based on a switching criterion that the voltage of the inverter is higher than an overvoltage load shedding threshold;

and switching to an overvoltage load shedding state based on the normal operation state, determining the electrical quantity of the inverter to be active power and active current in the overvoltage load shedding state, and determining the values of the active power and the active current in the overvoltage load shedding state.

Preferably, the performing the electromechanical transient modeling on the inverter by using the electrical quantity values as inputs includes:

inputting values of active power and active current in the overvoltage and load shedding state;

maintaining the active power from the value of the active power in an overvoltage load shedding state according to a time constant of the initial active power of high-voltage load shedding;

based on the reduction rate of the high-voltage load shedding active current, reducing the active current from the value of the active current in an overvoltage load shedding state;

wherein the high voltage load shedding initial active power holding time constant is determined based on a typical value of the high voltage load shedding initial active power holding time constant in combination with a model of the inverter; the high voltage load shedding active current reduction rate is determined based on a typical value of the high voltage load shedding active current reduction rate in combination with the model of the inverter.

Preferably, the switching relationship between the operation states includes: switching the overvoltage load shedding state into a normal operation state;

determining a switching criterion required for switching between the operating states based on the switching relationship between the operating states, including: and taking the voltage of the inverter lower than the overvoltage and load shedding threshold value as a switching criterion when the overvoltage and load shedding state is switched to a normal running state.

determining the electrical quantity of the inverter to be voltage based on a switching criterion that the voltage of the inverter is lower than an overvoltage load shedding threshold;

and switching to a normal operation state based on the overvoltage load shedding state, determining the active power and the active current when the electrical quantity of the inverter is in the overvoltage load shedding state, and determining the numerical values of the active power and the active current in the overvoltage load shedding state.

comparing the active power value in the overvoltage load shedding state with an active power threshold value; if the active power value in the overvoltage load shedding state is smaller than or equal to the active power threshold value, based on a first active delay recovery time, maintaining the active power according to the active power value in the overvoltage load shedding state; otherwise, based on a second active delay recovery time, maintaining the active power according to the active power value in the overvoltage load shedding state;

recovering the active current from the value of the active current in the overvoltage and load shedding state to the value of the active current in the normal operation state based on the active current recovery rate;

wherein the active power threshold is determined based on a typical value of the active power threshold in combination with a model of the inverter; the first active delay recovery time is determined based on a typical value of the first active delay recovery time in combination with a model of the inverter; the second active delay recovery time is determined based on a typical value of the second active delay recovery time in combination with a model of the inverter; the active current recovery rate is determined based on a typical value of the active current recovery rate in combination with the model of the inverter; the first active delay recovery time is greater than the second active delay recovery time.

Preferably, the switching relationship between the operating states includes: the normal operation state is switched to an overcurrent wave-sealing state;

determining a switching criterion required for switching between the operating states based on the switching relationship between the operating states, including: taking the voltage of the inverter lower than a low-voltage wave-sealing threshold value and the voltage of the inverter meeting an over-current wave-sealing condition as a switching criterion when a normal operation state is switched to an over-current wave-sealing state;

wherein the low voltage blocking threshold is determined based on a typical value of the low voltage blocking threshold in combination with a model of the inverter.

Preferably, the switching relationship between the operating states includes: the overvoltage load shedding state is switched to an overcurrent wave sealing state;

determining a switching criterion required for switching between the operating states based on the switching relationship between the operating states, including: and taking the voltage of the inverter higher than the overvoltage load shedding threshold value and the voltage of the inverter meeting the overcurrent wave-sealing condition as a switching criterion when the overvoltage load shedding state is switched to the overcurrent wave-sealing state.

Preferably, the switching relationship between the operating states includes: the wave-sealing recovery state is switched to an over-current wave-sealing state;

determining a switching criterion required for switching between the operating states based on the switching relationship between the operating states, including: and taking the voltage of the inverter to meet the overcurrent wave sealing condition as a switching criterion when the wave sealing recovery state is switched to the overcurrent wave sealing state.

Preferably, the determining electrical quantities and electrical quantity values of the inverter based on the switching relationship between the operating states and the switching criterion required for switching between the operating states includes:

determining the electric quantity of the inverter to be voltage based on the fact that the voltage of the inverter is lower than a low-voltage wave-sealing threshold value and meets the switching criterion of an over-current wave-sealing condition, the voltage of the inverter is higher than an over-voltage load-shedding threshold value and meets the switching criterion of the over-current wave-sealing condition, and the voltage of the inverter meets the over-current wave-sealing condition;

and based on the switching of the normal operation state into an overcurrent wave sealing state, the switching of the overvoltage load shedding state into an overcurrent wave sealing state and the switching of the wave sealing recovery state into an overcurrent wave sealing state, determining the electrical quantity of the inverter as active power and active current in the overcurrent wave sealing state, and determining the numerical values of the active power and the active current in the overcurrent wave sealing state.

inputting values of active power and active current in the overcurrent sealing wave state;

carrying out overcurrent wave sealing according to the values of active power and active current in the overcurrent wave sealing state on the basis of a wave sealing duration threshold;

wherein the envelope duration threshold is determined based on a typical value of the envelope duration threshold in combination with a model of the inverter; and the values of the active power and the active current in the overcurrent sealing wave state are 0.

Preferably, the over-current wave-blocking condition includes: the product of the current value of the inverter in the normal operation state and the voltage fluctuation of the inverter is larger than a wave-blocking threshold value;

wherein the blocking threshold is determined based on a typical value of the blocking threshold in combination with the model of the inverter.

Preferably, the over-current wave-blocking condition is represented by the following formula:

in the formula I ₀ Is the current value of the inverter in the normal operation state, Δ V is the fluctuation of the inverter at the moment of voltage recovery or drop, V (t-t) _a ) T before voltage fluctuation _a Voltage value of time, V (t) is the voltage value at the moment of voltage fluctuation, K _block Is the envelope threshold.

Preferably, the switching relationship between the operating states includes: the over-current wave-sealing state is switched to a wave-sealing recovery state;

determining a switching criterion required for switching between the operating states based on the switching relationship between the operating states, including: and taking the sealing wave duration time of the inverter exceeding a sealing wave duration time threshold value as a switching criterion when the overcurrent sealing wave state is switched to the sealing wave recovery state.

and based on the switching of the over-current wave-sealing state into a wave-sealing recovery state and the fact that the wave-sealing duration time of the inverter exceeds a wave-sealing duration time threshold value, determining the electric quantity of the inverter as the active current and the reactive current in the over-current wave-sealing state, and determining the numerical values of the active current and the reactive current in the over-current wave-sealing state.

inputting the numerical values of active current and reactive current in the overcurrent closed-wave state;

restoring the active current from the active current value in the overcurrent closed-wave state to the active current value in the normal operation state based on the closed-wave end active current restoration rate;

based on the wave-sealing finishing reactive current recovery rate, recovering the reactive current from the reactive current value in the overcurrent wave-sealing state to the reactive current value in the normal operation state;

wherein the envelope end active current recovery rate is determined based on a typical value of the envelope end active current recovery rate in combination with a model of the inverter; the rate of end of capping reactive current recovery is determined based on typical values of the rate of end of capping reactive current recovery in combination with the model of the inverter.

Preferably, the switching relationship between the operating states includes: switching the wave-sealing recovery state into a normal operation state;

determining a switching criterion required for switching between the operating states based on the switching relationship between the operating states, including: and taking the numerical value of the active current and the reactive current in the transient process of the inverter, which are both recovered to the normal running state, as a switching criterion when the wave-blocking recovery state is switched to the normal running state.

determining the electric quantity of the inverter as the active current and the reactive current in the transient process of the inverter based on a switching criterion of the numerical value of the active current and the reactive current in the transient process of the inverter, wherein the numerical value of the active current and the reactive current are recovered to a normal operation state;

and switching to a normal operation state based on the wave-blocking recovery state, determining the active power and the reactive power when the electric quantity of the inverter is in the normal operation state, and determining an active power value, a reactive power value, an active power reference value and a reactive power reference value in the normal operation state.

inputting an active power value, a reactive power value, an active power reference value and a reactive power reference value in the normal operation state;

determining an active deviation based on the active power reference value and the active power value, and outputting an active current by inputting the active deviation into an active power controller;

determining a reactive deviation based on the reactive power reference value and the reactive power value, and outputting a reactive current by inputting the reactive deviation into a reactive power controller;

wherein the active power controller and the reactive power controller are proportional-integral regulators.

Based on the same inventive concept, the invention also provides a distributed photovoltaic inverter electromechanical transient modeling system, which comprises: the device comprises an operation state module, a switching criterion module, an electrical quantity module and a simulation module;

the operation state module is used for determining the operation state of the inverter and the switching relation among the operation states based on the transient state characteristic of the distributed photovoltaic inverter without the low voltage ride through function when executing the control logic;

the switching criterion module is used for determining a switching criterion required by switching among the operating states based on the switching relation among the operating states;

the electrical quantity module is configured to determine each electrical quantity and each electrical quantity value of the inverter based on the switching relationship between the operation states and a switching criterion required for switching between the operation states;

the simulation module is used for performing electromechanical transient modeling on the inverter by taking each electrical quantity value as input, and taking active current and reactive current of the inverter in a transient process as output;

Preferably, the switching relationship between the operating states includes: the normal operation state is switched to an overvoltage load shedding state;

when the normal operation state is switched to the overvoltage load shedding state, the switching criterion module is specifically configured to: the voltage of the inverter is higher than an overvoltage load shedding threshold value and is used as a switching criterion when the normal operation state is switched to an overvoltage load shedding state;

Preferably, when the voltage of the inverter is higher than the overvoltage/load reduction threshold as the switching criterion, the electrical quantity module is specifically configured to:

determining the electrical quantity of the inverter to be voltage based on a switching criterion that the voltage of the inverter is higher than an overvoltage load shedding threshold value;

and switching to an overvoltage load shedding state based on the normal operation state, determining the electric quantity of the inverter to be active power and active current in the overvoltage load shedding state, and determining the numerical values of the active power and the active current in the overvoltage load shedding state.

Preferably, when the values of the active power and the active current in the overvoltage and load shedding state are the values of the electrical quantity, the simulation module is specifically configured to:

maintaining a time constant according to the initial active power of high-voltage load shedding, and maintaining the active power from the active power value in an overvoltage load shedding state;

the high-voltage load shedding initial active power keeping time constant is determined based on a typical value of the high-voltage load shedding initial active power keeping time constant and in combination with the model of the inverter; the high voltage load shedding active current droop rate is determined based on a typical value of the high voltage load shedding active current droop rate in combination with the model of the inverter.

Preferably, the switching relationship between the operating states includes: switching the overvoltage load shedding state into a normal operation state;

when the overvoltage load shedding state is switched to the normal operation state, the switching criterion module is specifically configured to: and taking the voltage of the inverter lower than the overvoltage load shedding threshold as a switching criterion when the normal operation state is switched to the overvoltage load shedding state.

Preferably, when the voltage of the inverter is lower than the overvoltage load shedding threshold as the switching criterion, the electrical quantity module is specifically configured to:

and switching to a normal operation state based on an overvoltage load shedding state, determining active power and active current when the electrical quantity of the inverter is in the overvoltage load shedding state, and determining the numerical values of the active power and the active current in the overvoltage load shedding state.

comparing the active power value in the overvoltage load shedding state with an active power threshold value; if the active power value in the overvoltage load shedding state is smaller than or equal to the active power threshold value, based on first active delay recovery time, maintaining the active power according to the active power value in the overvoltage load shedding state; otherwise, based on a second active delay recovery time, maintaining the active power according to the active power value in the overvoltage load shedding state;

Preferably, the switching relationship between the operation states includes: the normal operation state is switched to an overcurrent wave-sealing state;

when the normal operation state is switched to the over-current wave sealing state, the switching criterion module is specifically configured to: taking the voltage of the inverter lower than a low-voltage wave-sealing threshold value and the voltage of the inverter meeting an over-current wave-sealing condition as a switching criterion when a normal operation state is switched to an over-current wave-sealing state;

when the overvoltage load shedding state is switched to the overcurrent wave sealing state, the switching criterion module is specifically used for: and taking the voltage of the inverter higher than the overvoltage load shedding threshold value and the voltage of the inverter meeting the overcurrent wave sealing condition as a switching criterion when the overvoltage load shedding state is switched to the overcurrent wave sealing state.

Preferably, the switching relationship between the operation states includes: the wave-sealing recovery state is switched to an over-current wave-sealing state;

when the wave blocking recovery state is switched to the over-current wave blocking state, the switching criterion module is specifically configured to: and taking the voltage of the inverter to meet the overcurrent wave sealing condition as a switching criterion when the wave sealing recovery state is switched to the overcurrent wave sealing state.

Preferably, when the switching criterion that the voltage of the inverter is lower than the low-voltage blocking threshold and the voltage of the inverter satisfies the over-current blocking condition, the switching criterion that the voltage of the inverter is higher than the over-voltage load shedding threshold and the voltage of the inverter satisfies the over-current blocking condition, and the switching criterion that the voltage of the inverter satisfies the over-current blocking condition are taken as the switching criterion, the electrical quantity module is specifically configured to:

determining the electric quantity of the inverter to be voltage based on a switching criterion that the voltage of the inverter is lower than a low-voltage wave-sealing threshold value and meets an overcurrent wave-sealing condition, a switching criterion that the voltage of the inverter is higher than an overvoltage load-shedding threshold value and meets an overcurrent wave-sealing condition, and a switching criterion that the voltage of the inverter meets an overcurrent wave-sealing condition;

and based on the switching of the normal operation state into an overcurrent wave sealing state, the switching of the overvoltage load shedding state into an overcurrent wave sealing state and the switching of the wave sealing recovery state into an overcurrent wave sealing state, determining the electrical quantity of the inverter as active power and active current in the overcurrent wave sealing state, and determining the numerical value of the active power and the active current in the overcurrent wave sealing state.

Preferably, when the values of the active power and the active current in the over-current sealed wave state are electrical quantity values, the simulation module is specifically configured to:

carrying out overcurrent wave sealing according to the numerical values of active power and active current in the overcurrent wave sealing state on the basis of a wave sealing duration threshold;

wherein the envelope duration threshold is determined based on a typical value of the envelope duration threshold in combination with a model of the inverter; and the values of the active power and the active current in the overcurrent closed-wave state are 0.

when the over-current wave-sealing state is switched to the wave-sealing recovery state, the switching criterion module is specifically configured to: and taking the sealing wave duration time of the inverter exceeding a sealing wave duration time threshold value as a switching criterion when the overcurrent sealing wave state is switched to the sealing wave recovery state.

Preferably, when the blocking duration of the inverter exceeds the blocking duration threshold as a switching criterion, the electrical quantity module is specifically configured to:

Preferably, when the values of the active current and the reactive current in the over-current sealed wave state are the values of the electrical quantity, the simulation module is specifically configured to:

inputting values of active current and reactive current in the overcurrent sealing wave state;

Preferably, the switching relationship between the operation states includes: switching the wave-sealing recovery state into a normal operation state;

when the wave-sealing recovery state is switched to the normal operation state, the switching criterion module is specifically configured to: and taking the numerical value of restoring the active current and the reactive current in the transient process of the inverter to the normal operation state as a switching criterion when the wave-sealing restoration state is switched to the normal operation state.

Preferably, when a numerical value that both an active current and a reactive current in the transient process of the inverter are restored to a normal operation state is taken as a switching criterion, the electrical quantity module is specifically configured to:

and switching to a normal operation state based on the blocking wave recovery state, and determining an active power value, a reactive power value, an active power reference value and a reactive power reference value when the electric quantity value of the inverter is in the normal operation state.

Preferably, when the active power value, the reactive power value, the active power reference value, and the reactive power reference value in the normal operation state are electric quantity values, the simulation module is specifically configured to:

Based on the same inventive concept, the invention also provides a computer device, comprising:

one or more processors;

a memory for storing one or more programs;

the one or more programs, when executed by the one or more processors, implement the distributed photovoltaic inverter electromechanical transient modeling method.

Based on the same inventive concept, the invention further provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed, the distributed photovoltaic inverter electromechanical transient modeling method is realized.

Compared with the closest prior art, the invention has the following beneficial effects:

1. the invention provides an electromechanical transient modeling method and system for a distributed photovoltaic inverter, which comprises the following steps: determining the operation state of the inverter and the switching relation among the operation states based on the transient characteristic of the distributed photovoltaic inverter without the low voltage ride through function when executing the control logic; determining a switching criterion required by switching among the operating states based on the switching relation among the operating states; determining each electrical quantity and each electrical quantity value of the inverter based on the switching relation among the operation states and the switching criterion required by switching among the operation states; performing electromechanical transient modeling on the inverter by taking the electrical quantity values as input, and outputting active current and reactive current of the inverter in a transient process; the active current and the reactive current are respectively output through an active power controller and a reactive power controller; in the modeling process, the operation states of the distributed photovoltaic inverter, the switching relation among the operation states and the switching criterion are fully considered, and the transient characteristics of the distributed photovoltaic inverter without a low-voltage ride-through function during overcurrent sealing or overvoltage load shedding can be accurately simulated;

2. the method provided by the invention is used for constructing the electromechanical transient model of the distributed photovoltaic inverter, so that the accuracy and precision of active and reactive analysis and calculation of the distributed photovoltaic inverter during overcurrent wave sealing or overvoltage load shedding can be improved, guidance can be provided for regional power grid operation control containing high-permeability distributed photovoltaic, and the method has a wide application prospect.

Drawings

Fig. 1 is a schematic diagram of a control strategy of a conventional distributed photovoltaic inverter modeling method provided by the present invention;

fig. 2 is a schematic diagram of a control strategy of an actual distributed photovoltaic inverter provided by the present invention;

fig. 3 is a schematic flow chart of an electromechanical transient modeling method of a distributed photovoltaic inverter provided by the invention;

fig. 4 is a schematic diagram of the operating states of the distributed photovoltaic inverter and a switching relationship between the operating states according to the electromechanical transient modeling method for the distributed photovoltaic inverter provided by the present invention;

fig. 5 is a control block diagram of a distributed photovoltaic inverter in a normal operating state according to the electromechanical transient modeling method for the distributed photovoltaic inverter provided by the present invention;

fig. 6 is a schematic diagram of a basic structure of an electromechanical transient modeling system of a distributed photovoltaic inverter provided by the present invention.

Detailed Description

The prior art is generally based on a voltage outer loop-current inner loop double-loop control strategy to simulate the transient characteristics of an inverter. The control strategy diagram is shown in fig. 1, namely, only a double-loop control strategy is adopted, and even if the inverter fails, a current reference command i of a d axis is sent out only through a double-loop controller _dref Since the inverter is normally operated in the unity power factor mode, the q-axis current reference command i _qref And then a dq-axis current reference command is input to a current inner loop controller to maintain the active power and the reactive power of the inverter as far as possible as the state before the fault and finally control the inverter body, but the overvoltage load shedding or overcurrent envelope control strategy of the inverter cannot be considered. In fact, the control strategy of the distributed pv inverter without the low voltage ride through function is shown in fig. 2, that is, when the distributed pv inverter without the low voltage ride through function fails (i.e., switches from the normal operation state to the over-voltage load shedding state or the over-current wave blocking state), the inverter may also switch states in addition to the dual-loop control strategy. When the state is switched to an overvoltage load shedding state, the active power can be gradually reduced; and when the state is switched to an overcurrent sealing wave state, controlling the inverter to completely output no current. Therefore, the transient characteristics of the distributed photovoltaic inverter without the low voltage ride through function cannot be simulated by adopting the double-loop control strategy. In view of the above, the present invention provides a distributed photovoltaic inverter electromechanical transient modeling method and system.

The following detailed description of embodiments of the invention is provided in connection with the accompanying drawings.

Example 1:

the invention provides an electromechanical transient modeling method of a distributed photovoltaic inverter, a flow schematic diagram of which is shown in fig. 3, and the electromechanical transient modeling method comprises the following steps:

step 1: determining the operation state of the inverter and the switching relation among the operation states based on the transient characteristic of the distributed photovoltaic inverter without the low voltage ride through function when executing control logic;

step 2: determining a switching criterion required by switching among the operating states based on the switching relation among the operating states;

and step 3: determining each electrical quantity and each electrical quantity value of the inverter based on the switching relation among the operation states and the switching criterion required by switching among the operation states;

and 4, step 4: performing electromechanical transient modeling on the inverter by taking the electrical quantity values as input, and outputting active current and reactive current of the inverter in a transient process;

Fig. 4 is a schematic diagram illustrating an operation state of a distributed photovoltaic inverter and a switching relationship between the operation states, where the operation states include: 4 normal running states (state 0), overvoltage load shedding states (state 1), overcurrent wave sealing states (state 2) and wave sealing recovery states (state 3); the switching relationship among the operating states comprises: the normal operation state is switched to an overvoltage load shedding state, the overvoltage load shedding state is switched to a normal operation state, the normal operation state is switched to an overcurrent wave sealing state, the overvoltage load shedding state is switched to an overcurrent wave sealing state, the wave sealing recovery state is switched to an overcurrent wave sealing state, the overcurrent wave sealing state is switched to a wave sealing recovery state, and the wave sealing recovery state is switched to a normal operation state.

The following description of steps 2-4 is made in terms of the switching relationship between the operating states:

A. when the normal operation state is switched to an overvoltage load shedding state:

the step 2 specifically comprises the following steps:

the voltage of the inverter is higher than an overvoltage load shedding threshold value and is used as a switching criterion when a normal operation state is switched to an overvoltage load shedding state;

The step 3 specifically comprises the following steps:

The step 4 specifically comprises the following steps:

B. When the overvoltage load shedding state is switched to a normal operation state:

the step 2 specifically comprises the following steps:

and taking the voltage of the inverter lower than the overvoltage load shedding threshold value as a switching criterion when the overvoltage load shedding state is switched to a normal operation state.

The step 3 specifically comprises the following steps:

The step 4 specifically comprises the following steps:

C. When the normal operation state is switched to an overcurrent wave sealing state:

the step 2 specifically comprises the following steps:

taking the voltage of the inverter lower than a low-voltage wave-sealing threshold value and the voltage of the inverter meeting an over-current wave-sealing condition as a switching criterion when a normal operation state is switched to an over-current wave-sealing state;

D. When the overvoltage unloading state is switched to the overcurrent wave sealing state:

the step 2 specifically comprises the following steps:

and taking the voltage of the inverter higher than the overvoltage load shedding threshold value and the voltage of the inverter meeting the overcurrent wave sealing condition as a switching criterion when the overvoltage load shedding state is switched to the overcurrent wave sealing state.

E. When the wave-sealing recovery state is switched to the over-current wave-sealing state:

the step 2 specifically comprises the following steps:

and taking the voltage of the inverter to meet the overcurrent wave sealing condition as a switching criterion when the wave sealing recovery state is switched to the overcurrent wave sealing state.

Wherein, the over-current wave-sealing condition is expressed by the following formula:

in the formula I ₀ Is the current value of the inverter in normal operation state, Δ V is the fluctuation of the inverter at the moment of voltage recovery or drop, V (t-0.01) is the voltage value 10 milliseconds before the voltage fluctuation, V (t) is the voltage value at the moment of voltage fluctuation, K _block Is the envelope threshold.

When the normal operation state is switched to an overcurrent wave sealing state, an overvoltage load shedding state is switched to an overcurrent wave sealing state, and a wave sealing recovery state is switched to an overcurrent wave sealing state, the determined electrical quantities and the electrical quantities of the inverter are the same, and the simulated transient characteristics are also the same, so that the step 3 is as follows:

And step 4 is that:

F. When the over-current wave-sealing state is switched to the wave-sealing recovery state:

the step 2 specifically comprises the following steps:

and taking the wave-blocking duration of the inverter exceeding a wave-blocking duration threshold as a switching criterion when the over-current wave-blocking state is switched to the wave-blocking recovery state.

The step 3 specifically comprises:

and determining the electric quantity of the inverter as the active current and the reactive current in the overcurrent wave-sealing state and determining the numerical values of the active current and the reactive current in the overcurrent wave-sealing state based on the switching of the overcurrent wave-sealing state into the wave-sealing recovery state and the condition that the wave-sealing duration time of the inverter exceeds the wave-sealing duration time threshold value.

The step 4 specifically comprises the following steps:

based on the wave-sealing finishing reactive current recovery rate, recovering the reactive current from the reactive current value in the overcurrent wave-sealing state to the reactive current value in the normal running state;

G. When the wave-sealing recovery state is switched to the normal operation state:

the step 2 specifically comprises the following steps:

and taking the numerical value of restoring the active current and the reactive current in the transient process of the inverter to the normal operation state as a switching criterion when the wave-sealing restoration state is switched to the normal operation state.

The step 3 specifically comprises the following steps:

switching to a normal operation state based on the wave-blocking recovery state, determining active power and reactive power when the electric quantity of the inverter is in the normal operation state, and determining an active power value, a reactive power value, an active power reference value and a reactive power reference value in the normal operation state; wherein the active power reference value and the reactive power reference value are determined based on the model of the inverter itself.

The step 4 specifically comprises the following steps:

FIG. 5 is a control block diagram of a distributed photovoltaic inverter in a normal operation state, in which PI is a proportional-integral regulator, two proportional-integral regulators are respectively used as an active power controller and a reactive power controller, P is an active power value, and P is a power value _ref Is an active power reference value, i _d Is the active current, Q is the reactive power value, Q _ref Is a reference value of reactive power, i _q Is a reactive current.

The method comprises the steps of constructing an electromechanical transient model of the distributed photovoltaic inverter. Wherein, the overvoltage load shedding threshold, the high-voltage load shedding initial active power holding time constant, the high-voltage load shedding active current decreasing rate, the active power threshold, the first active delay recovery time, the second active delay recovery time, the active current recovery rate, the low-voltage blocking threshold, the blocking duration threshold, the blocking ending active current recovery rate, and the blocking ending reactive current recovery rate are shown in table 1.

TABLE 1 parameter table

Parameter name	Meaning of parameters	Unit of	Typical value
				V _highin	Overvoltage load shedding threshold	pu	1.17
T _highin	High voltage load shedding initial active power holding time constant	s	0.4
				K _down1	High voltage load shedding active current reduction rate	pu/s	1.8
P _highout	Active power threshold	pu	0.05
				T _highout1	First active delay recovery time	s	1.5
T _highout2	Second active delay recovery time	s	0
				R _up1	Active current recovery rate	pu/s	0.2
V _lowin	Low voltage blocking threshold	pu	0.8
				K _block	Envelope threshold	pu	0.21
T _block	Envelope duration threshold	s	0.5
				R _up2	Active current recovery rate at end of wave sealing	pu/s	0.2
R _up3	Rate of reactive current recovery at end of envelope	pu/s	0.05

Typical values of the parameters in the table are obtained through multiple tests based on the model and the parameters of the distributed photovoltaic inverter.

The method constructs the electromechanical transient model of the distributed photovoltaic inverter by determining the switching relation among the running states of the distributed photovoltaic inverter, switching criteria and input electrical quantity, and can accurately simulate the transient characteristic of the distributed photovoltaic inverter without low-voltage ride-through function during overcurrent sealing wave or overvoltage load shedding; the method provided by the invention is used for constructing the electromechanical transient model of the distributed photovoltaic inverter, so that the accuracy and precision of active and reactive analysis and calculation during overcurrent wave sealing or overvoltage load shedding of the distributed photovoltaic inverter can be improved, guidance can be provided for regional power grid operation control containing high-permeability distributed photovoltaic, and the method has a wide application prospect.

Example 2:

by utilizing the electromechanical transient modeling method of the distributed photovoltaic inverter, provided by the invention, an electromechanical transient model of the distributed photovoltaic inverter can be constructed.

The electric quantity input by the model is voltage, current and power, the output variable of the model is active current and reactive current of the inverter in the transient process, the input electric quantity is compared with an operating state switching criterion to determine the operating state at the next moment, the transient characteristic is simulated according to the control logic of different operating states of the inverter, and the active current and the reactive current are finally output. The present embodiment introduces an application of the distributed photovoltaic inverter electromechanical transient model, including:

the method comprises the following steps of (1) obtaining a current electric quantity value and a current running state of the distributed photovoltaic inverter without a low-voltage ride-through function;

step (2), inputting the current electrical quantity and the current operation state into a distributed photovoltaic inverter electromechanical transient model;

step (3), in the current running state, determining a switching relation between running states according to a switching criterion based on the current electrical quantity;

and (4) simulating the transient characteristic of the distributed photovoltaic inverter during the switching of the operating states based on the electrical quantity, the switching relation among the operating states and the control logic of the inverter.

The following description of the electromechanical transient modeling of the inverter is carried out based on the method described in the steps (1) - (4) according to the switching relationship among 7 operation states:

A. when the inverter is in a normal operation state, inputting the current voltage of the inverter, and judging whether the current voltage of the inverter is greater than an overvoltage load shedding threshold value or not; if the current voltage of the inverter is greater than the overvoltage load shedding threshold value, determining that the running state of the inverter is switched to an overvoltage load shedding state; otherwise, maintaining the normal operation state;

when the inverter is determined to be switched from a normal operation state to an overvoltage load shedding state, maintaining the current active power of the inverter according to a high-voltage load shedding initial active power holding time constant; the present active current is then reduced based on the high voltage load shedding active current reduction rate until the voltage is below the overvoltage load shedding threshold or the active current drops to 0.

B. When the inverter is in an overvoltage load shedding state, inputting the current voltage of the inverter, and judging whether the current voltage of the inverter is smaller than an overvoltage load shedding threshold value or not; if the current voltage of the inverter is smaller than the overvoltage load shedding threshold value, determining that the running state of the inverter is switched to a normal running state; otherwise, the state is still an overvoltage load shedding state;

when the inverter is determined to be switched from an overvoltage load shedding state to a normal operation state, judging whether the current active power of the inverter is smaller than an active power threshold value; if the current active power of the inverter is less than or equal to the active power threshold value, maintaining the current active power of the inverter according to first active delay recovery time; otherwise, maintaining the current active power of the inverter according to a second active delay recovery time; and after the active power of the inverter is maintained according to the first active delay recovery time or the second active delay recovery time, increasing the current active current of the inverter to a value in a normal operation state according to the active current recovery rate.

C. When the inverter is in a normal operation state, inputting the current voltage of the inverter, judging whether the current voltage of the inverter is smaller than a low-voltage wave-sealing threshold value or not, and judging whether the current voltage of the inverter meets an overcurrent wave-sealing condition or not; if the current voltage of the inverter is smaller than a low-voltage wave-sealing threshold value and meets an overcurrent wave-sealing condition, determining that the running state of the inverter is switched to an overcurrent wave-sealing state; otherwise, the operation state is normal;

and when the inverter is determined to be switched from the normal operation state to the overcurrent wave sealing state, the overcurrent wave sealing state of the inverter is maintained according to the wave sealing duration time threshold, and the active current and the reactive current are both 0 during the overcurrent wave sealing period.

D. When the inverter is in an overvoltage load shedding state, inputting the current voltage of the inverter, judging whether the current voltage of the inverter is greater than an overvoltage load shedding threshold value or not, and judging whether the current voltage of the inverter meets an overcurrent wave sealing condition or not; if the current voltage of the inverter is greater than the overvoltage and load shedding threshold value and meets the overcurrent wave sealing condition, determining that the running state of the inverter is switched to an overcurrent wave sealing state; otherwise, the state is an overvoltage load shedding state;

and when the inverter is determined to be switched from the overvoltage load shedding state to the overcurrent wave sealing state, the overcurrent wave sealing state of the inverter is kept according to a wave sealing duration time threshold, and active current and reactive current are both 0 during the overcurrent wave sealing period.

E. When the inverter is in a wave-blocking recovery state, inputting the current voltage of the inverter, and judging whether the current voltage of the inverter meets an overcurrent wave-blocking condition or not; if the current voltage of the inverter meets the overcurrent wave sealing condition, determining that the running state of the inverter is switched to an overcurrent wave sealing state; otherwise, the wave-sealing recovery state is adopted;

and when the inverter is determined to be switched from the wave blocking recovery state to the overcurrent wave blocking state, the overcurrent wave blocking state of the inverter is kept according to a wave blocking duration threshold, and active current and reactive current are both 0 during the overcurrent wave blocking period.

The wave sealing conditions in the switching relations C, D and E among the operation states are as follows:

F. When the inverter is in the overcurrent wave-sealing state, judging whether the continuous time after the inverter is switched to the overcurrent wave-sealing state exceeds a wave-sealing continuous time threshold value or not; if the continuous time after the inverter is switched to the overcurrent wave-sealing state exceeds the wave-sealing continuous time threshold, determining that the running state of the inverter is switched to the wave-sealing recovery state; otherwise, the state is an overcurrent wave sealing state;

and when the inverter is determined to be switched from the overcurrent wave-blocking state to the wave-blocking recovery state, respectively recovering the current active current and the current reactive current of the inverter to the values in the normal operation state according to the wave-blocking finishing active current recovery rate and the wave-blocking finishing reactive current recovery rate.

G. When the inverter is in a wave-sealing recovery state, judging whether the current active current and the current reactive current of the inverter are both recovered to the values in a normal operation state; if the current active current and the current reactive current of the inverter are both restored to the values in the normal running state, determining that the running state of the inverter is switched to the normal running state; otherwise, the wave-sealing recovery state is adopted;

when the inverter is determined to be switched from a wave-sealing recovery state to a normal operation state, inputting an active power value, a reactive power value, an active power reference value and a reactive power reference value in the normal operation state; determining an active deviation based on the active power reference value and the active power value, and outputting an active current by inputting the active deviation into an active power controller; and determining a reactive deviation based on the reactive power reference value and the reactive power value, and outputting a reactive current by inputting the reactive deviation into a reactive power controller.

A description of the electromechanical transient modeling described above is shown in table 2.

TABLE 2 State switching criterion and transient behavior thereof

The invention sets the running state of the inverter to be a normal running state, an overcurrent wave sealing state, a wave sealing recovery state and an overvoltage load shedding state respectively. The method has the advantages that switching among different control states is realized through state switching criteria, the transient characteristics of the distributed photovoltaic inverter when a power grid fails are simulated according to the control logic of the distributed photovoltaic inverter, the key transient characteristics in the switching process among the states including the overcurrent wave-sealing state, the overvoltage load-shedding state and the like can be accurately simulated, the active and reactive analysis and calculation precision and accuracy of the distributed photovoltaic inverter during overcurrent wave-sealing state or overvoltage load-shedding state can be improved, guidance can be provided for regional power grid operation control of high-permeability distributed photovoltaic, and the method has wide application prospects.

Example 3:

based on the same inventive concept, the invention further provides an electromechanical transient modeling system of a distributed photovoltaic inverter, a basic structural schematic diagram of which is shown in fig. 6, and the electromechanical transient modeling system comprises: the device comprises an operating state module, a switching criterion module, an electric quantity module and a simulation module;

the switching criterion module is used for determining switching criteria required by switching among the operating states based on the switching relation among the operating states;

the simulation module is used for performing electromechanical transient modeling on the inverter by taking the electric quantity values as input, and outputting active current and reactive current of the inverter in a transient process;

Preferably, when the voltage of the inverter is higher than the overvoltage/underload threshold as the switching criterion, the electrical quantity module is specifically configured to:

Preferably, when the values of the active power and the active current in the overvoltage and load shedding state are electrical quantity values, the simulation module is specifically configured to:

wherein the high voltage load shedding initial active power holding time constant is determined based on a typical value of the high voltage load shedding initial active power holding time constant in combination with a model of the inverter; the high voltage load shedding active current droop rate is determined based on a typical value of the high voltage load shedding active current droop rate in combination with the model of the inverter.

when the overvoltage load shedding state is switched to the normal operation state, the switching criterion module is specifically configured to: and taking the voltage of the inverter lower than the overvoltage load shedding threshold value as a switching criterion when the normal operation state is switched to the overvoltage load shedding state.

Preferably, when the voltage of the inverter is lower than the overvoltage/underload threshold as the switching criterion, the electrical quantity module is specifically configured to:

wherein the active power threshold is determined based on a typical value of the active power threshold in combination with a model of the inverter; the first active delay recovery time is determined based on a typical value of the first active delay recovery time in combination with a model of the inverter; the second active delay recovery time is determined based on a typical value of the second active delay recovery time in combination with the model of the inverter; the active current recovery rate is determined based on a typical value of the active current recovery rate in combination with the model of the inverter; the first active delay recovery time is greater than the second active delay recovery time.

Preferably, the switching relationship between the operating states includes: switching the normal operation state into an overcurrent wave sealing state;

when the overvoltage load shedding state is switched to the overcurrent wave sealing state, the switching criterion module is specifically configured to: and taking the voltage of the inverter higher than the overvoltage load shedding threshold value and the voltage of the inverter meeting the overcurrent wave-sealing condition as a switching criterion when the overvoltage load shedding state is switched to the overcurrent wave-sealing state.

Preferably, when the values of the active power and the active current in the over-current sealing wave state are the values of the electrical quantity, the simulation module is specifically configured to:

Preferably, the over-current wave-blocking condition includes: the product of the current value of the inverter in the normal running state and the voltage fluctuation of the inverter is larger than a wave-blocking threshold value;

in the formula I ₀ Is the current value of the inverter in the normal operation state, Δ V is the fluctuation of the inverter at the moment of voltage recovery or drop, V (t-0.01) is the voltage value 10 milliseconds before the voltage fluctuation, and V (t) isVoltage value at the moment of voltage fluctuation, K _block Is the envelope threshold.

Preferably, the switching relationship between the operation states includes: the over-current wave-sealing state is switched to a wave-sealing recovery state;

Preferably, when the values of the active current and the reactive current in the over-current sealing wave state are the values of the electrical quantity, the simulation module is specifically configured to:

wherein the envelope end active current recovery rate is determined based on a typical value of the envelope end active current recovery rate in combination with a model of the inverter; the end-of-envelope reactive current recovery rate is determined based on a typical value of the end-of-envelope reactive current recovery rate in combination with the model of the inverter.

when the wave-sealing recovery state is switched to the normal operation state, the switching criterion module is specifically configured to: and taking the numerical value of the active current and the reactive current in the transient process of the inverter, which are both recovered to the normal running state, as a switching criterion when the wave-blocking recovery state is switched to the normal running state.

Preferably, when a value that both the active current and the reactive current in the transient process of the inverter are restored to the normal operation state is taken as a switching criterion, the electrical quantity module is specifically configured to:

determining the electric quantity of the inverter to be the active current and the reactive current in the transient process of the inverter based on the switching criterion of the numerical value that the active current and the reactive current in the transient process of the inverter are both recovered to the normal running state;

The method constructs the electromechanical transient model of the distributed photovoltaic inverter by determining the switching relation among the running states of the distributed photovoltaic inverter, switching criteria and input electrical quantity, and can accurately simulate the transient characteristic of the distributed photovoltaic inverter without low-voltage ride-through function during overcurrent sealing wave or overvoltage load shedding; the system provided by the invention is used for constructing the electromechanical transient model of the distributed photovoltaic inverter, so that the accuracy and precision of active and reactive analysis and calculation of the distributed photovoltaic inverter during overcurrent wave sealing or overvoltage load shedding can be improved, guidance can be provided for regional power grid operation control containing high-permeability distributed photovoltaic, and the system has a wide application prospect.

Example 4:

based on the same inventive concept, the present invention also provides a computer apparatus comprising a processor and a memory, the memory being configured to store a computer program comprising program instructions, the processor being configured to execute the program instructions stored by the computer storage medium. The Processor may be a Central Processing Unit (CPU), and may also be other general purpose processors, digital Signal Processors (DSPs), application Specific Integrated Circuits (ASICs), field-Programmable gate arrays (FPGAs) or other Programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc., which are a computing core and a control core of the terminal, and are specifically adapted to load and execute one or more instructions in a computer storage medium so as to implement a corresponding method flow or a corresponding function, so as to implement the steps of the distributed photovoltaic inverter electromechanical transient modeling method in the foregoing embodiments.

By means of the computer equipment provided by the embodiment, an electromechanical transient modeling method of the distributed photovoltaic inverter is achieved, an electromechanical transient model of the distributed photovoltaic inverter is built by determining a switching relation and a switching criterion among running states of the distributed photovoltaic inverter and an input electric quantity, transient characteristics of the distributed photovoltaic inverter without a low-voltage ride-through function during overcurrent sealing or overvoltage load shedding can be accurately simulated, the accuracy and the precision of active and reactive analysis and calculation of the distributed photovoltaic inverter during overcurrent sealing or overvoltage load shedding can be improved, guidance can be provided for running control of a regional power grid containing high-permeability distributed photovoltaic, and the distributed photovoltaic inverter electromechanical transient modeling method has a wide application prospect.

Example 5:

based on the same inventive concept, the present invention further provides a storage medium, in particular a computer readable storage medium (Memory), which is a Memory device in a computer device and is used for storing programs and data. It is understood that the computer readable storage medium herein can include both built-in storage media in the computer device and, of course, extended storage media supported by the computer device. The computer-readable storage medium provides a storage space storing an operating system of the terminal. Also, one or more instructions, which may be one or more computer programs (including program code), are stored in the memory space and are adapted to be loaded and executed by the processor. It should be noted that the computer readable storage medium may be a high-speed RAM memory, or a non-volatile memory (non-volatile memory), such as at least one disk memory. One or more instructions stored in the computer-readable storage medium may be loaded and executed by the processor to implement the steps of the distributed photovoltaic inverter electromechanical transient modeling method in the above embodiments.

By means of the storage medium provided by the embodiment, an electromechanical transient modeling method of the distributed photovoltaic inverter is achieved, an electromechanical transient model of the distributed photovoltaic inverter is built by determining the switching relation and the switching criterion among the running states of the distributed photovoltaic inverter and the input electric quantity, the transient characteristic of the distributed photovoltaic inverter without a low-voltage ride-through function during overcurrent sealing wave or overvoltage load shedding can be accurately simulated, the accuracy and the precision of active and reactive analysis and calculation during overcurrent sealing wave or overvoltage load shedding of the distributed photovoltaic inverter can be improved, guidance can be provided for running control of a regional power grid containing high-permeability distributed photovoltaic, and the electromechanical transient modeling method has a wide application prospect.

As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.

The present invention has been described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may 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 means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

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 such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the scope of protection thereof, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: after reading this disclosure, those skilled in the art will be able to make various changes, modifications and equivalents to the embodiments of the invention, which fall within the scope of the appended claims.

Claims

1. A distributed photovoltaic inverter electromechanical transient modeling method is characterized by comprising the following steps:

determining the operation state of the inverter and the switching relation among the operation states based on the transient characteristic of the distributed photovoltaic inverter without the low voltage ride through function when executing the control logic;

2. The method of claim 1, wherein the operational state comprises: normal operation state, overvoltage unloading state, overcurrent wave sealing state and wave sealing recovery state.

3. The method of claim 2, wherein the switching relationship between the operating states comprises: the normal operation state is switched to an overvoltage load shedding state;

4. The method of claim 3, wherein determining the electrical quantities and the electrical quantity values of the inverter based on the switching relationships between the operating states and the switching criteria required for switching between the operating states comprises:

5. The method of claim 4, wherein said electromechanical transient modeling of said inverter with said respective electrical quantity values as inputs comprises:

6. The method of claim 2, wherein the switching relationship between the operating states comprises: switching the overvoltage load shedding state into a normal operation state;

determining a switching criterion required for switching between the operating states based on the switching relationship between the operating states, including: and taking the voltage of the inverter lower than the overvoltage load shedding threshold value as a switching criterion when the overvoltage load shedding state is switched to a normal operation state.

7. The method of claim 6, wherein determining the electrical quantities and the electrical quantity values of the inverter based on the switching relationships between the operating states and the switching criteria required for switching between the operating states comprises:

8. The method of claim 7, wherein said electromechanically modeling the inverter with the respective electrical quantity values as inputs comprises:

9. The method of claim 2, wherein the switching relationship between the operating states comprises: switching the normal operation state into an overcurrent wave sealing state;

10. The method of claim 2, wherein the switching relationship between the operating states comprises: the overvoltage load shedding state is switched to an overcurrent wave sealing state;

determining a switching criterion required for switching between the operating states based on the switching relationship between the operating states, including: and taking the voltage of the inverter higher than the overvoltage load shedding threshold value and the voltage of the inverter meeting the overcurrent wave sealing condition as a switching criterion when the overvoltage load shedding state is switched to the overcurrent wave sealing state.

11. The method of claim 2, wherein the switching relationship between the operating states comprises: the wave-sealing recovery state is switched to an over-current wave-sealing state;

determining a switching criterion required for switching between the operating states based on the switching relationship between the operating states, including: and taking the voltage of the inverter to meet the overcurrent wave-sealing condition as a switching criterion when the wave-sealing recovery state is switched to the overcurrent wave-sealing state.

12. The method according to claim 9, 10 or 11, wherein the determining electrical quantities and electrical quantity values of the inverter based on the switching relationship between the operating states and the switching criterion required for switching between the operating states comprises:

13. The method of claim 12, wherein said electromechanically modeling the inverter with the respective electrical quantity values as inputs comprises:

14. The method of claim 9, 10, or 11, wherein the over-current sealing condition comprises: the product of the current value of the inverter in the normal operation state and the voltage fluctuation of the inverter is larger than a wave-blocking threshold value;

15. The method of claim 14, wherein the over-current blocking condition is expressed by:

in the formula I ₀ Is the current value of the inverter in the normal operation state, and is the fluctuation of the inverter at the moment of voltage recovery or drop, V (t-t) _a ) T before voltage fluctuation _a Voltage value of time, V (t) is the voltage value at the moment of voltage fluctuation, K _block Is the envelope threshold.

16. The method of claim 2, wherein the switching relationship between the operating states comprises: switching the over-current wave-sealing state into a wave-sealing recovery state;

determining a switching criterion required for switching between the operating states based on the switching relationship between the operating states, including: and taking the wave-blocking duration of the inverter exceeding a wave-blocking duration threshold as a switching criterion when the over-current wave-blocking state is switched to the wave-blocking recovery state.

17. The method of claim 16, wherein determining the electrical quantities and the electrical quantity values of the inverter based on the switching relationships between the operating states and the switching criteria required to switch between the operating states comprises:

18. The method of claim 17, wherein said electromechanically modeling the inverter with the respective electrical quantity values as inputs comprises:

restoring the active current from the active current value in the overcurrent blocking wave state to the active current value in the normal operation state based on the blocking wave finishing active current restoring rate;

19. The method of claim 2, wherein the switching relationship between the operating states comprises: switching the wave-sealing recovery state into a normal operation state;

20. The method as claimed in claim 19, wherein determining the electrical quantities and the electrical quantity values of the inverter based on the switching relationships between the operating states and the switching criteria required for switching between the operating states comprises:

and switching to a normal operation state based on the blocking wave recovery state, determining the active power and the reactive power of the inverter when the electric quantity of the inverter is in the normal operation state, and determining an active power value, a reactive power value, an active power reference value and a reactive power reference value in the normal operation state.

21. The method of claim 20, wherein said electromechanically modeling said inverter with said respective electrical quantity values as inputs comprises:

22. A distributed photovoltaic inverter electromechanical transient modeling system, comprising: the device comprises an operation state module, a switching criterion module, an electrical quantity module and a simulation module;

23. The system of claim 22, wherein the operational state comprises: normal operation state, overvoltage unloading state, overcurrent wave sealing state and wave sealing recovery state.

24. A computer device, comprising:

one or more processors;

a memory for storing one or more programs;

the one or more programs, when executed by the one or more processors, implement a distributed photovoltaic inverter electromechanical transient modeling method of any of claims 1 to 21.

25. A computer-readable storage medium, characterized in that there is stored thereon a computer program which, when executed, implements a distributed photovoltaic inverter electromechanical transient modeling method according to any one of claims 1 to 21.