CN116054233A - Switching control method of grid-structured inverter with phase supporting capability under fault - Google Patents

Abstract

The invention discloses a switching control method for a grid-type inverter with phase support capability under fault conditions. The grid-type inverter normally works in the voltage source control mode. The angular velocity compensation control link reduces the difference between the potential phase of the inverter output and the actual phase of the power grid, and at the same time provides phase support capabilities. The PI control link is introduced in the current limiting control module to improve the situation that the internal potential amplitude changes drastically due to current limiting under fault conditions. The smooth switching between the voltage source control mode and the current source control mode is realized through the control of the internal potential phase and amplitude under fault conditions, which overcomes the insufficient synchronization support capability during the fault period of the grid-connected grid-connected inverter and the large impact and easy transient of the resynchronization process after the fault. It solves the problem of state instability, improves the stability of grid-type new energy power generation equipment, and has good application value.

Description

Switching control method of grid-connected inverter with phase support capability under fault conditions

Technical Field

The invention relates to a switching control method for a grid-connected inverter with phase support capability under fault conditions, and belongs to the technical field of new energy power generation.

Background Art

In recent years, with the widespread access to large-scale renewable energy, traditional synchronous machines are increasingly being replaced by renewable energy converters, and grid-connected inverters have also been widely mentioned and studied. Grid-connected inverters can provide stable voltage and phase support, and have functions and effects similar to conventional synchronous generators. Without considering current over-limit, direct voltage control is considered to be able to provide strong voltage and phase support capabilities.

However, due to the poor voltage and current resistance of power electronic devices, the grid-connected inverter responsible for grid construction will face more serious overcurrent problems during faults under the direct voltage control structure. The prior art proposes a direct voltage control method based on current limiting control, but the current limiting control causes the internal potential amplitude to change dramatically, weakening the stability of the grid-connected equipment.

In addition, the voltage-current dual closed-loop structure can effectively limit the inverter output current during a fault, but the dual closed-loop structure responds more slowly than direct voltage control, and switches to the current source mode based on phase-locked control during the current limiting period, which cannot provide stable synchronous phase support capabilities. It also faces the problem of excessive impact and easy transient instability during the resynchronization process caused by the continuous widening of the grid phase and the inverter output phase during the fault.

Therefore, those skilled in the art urgently need to solve the problem of insufficient phase support capability of the inverter during a fault and smooth switching between the voltage source mode and the current source mode after a fault.

Summary of the invention

Purpose: In order to overcome the problems in the prior art of insufficient support capacity of grid-connected inverters during faults, large current shock during resynchronization after faults, and easy transient instability, the present invention provides a switching control method for grid-connected inverters with phase support capability under faults, thereby improving the transient stability of new energy grid-connected equipment.

Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is:

In a first aspect, a switching control method of a grid-connected inverter with phase support capability under fault conditions is provided, comprising the following steps:

Step 1: Obtain the AC voltage and AC current of the grid-connected point of the three-phase inverter, and perform Park transformation on the AC voltage and AC current of the grid-connected point to obtain the AC voltage value and AC current value of the grid-connected point of the corresponding physical quantity in the dq coordinate system.

Step 2: Calculate the AC side active power _Pe and reactive power _Qe of the three-phase inverter according to the AC voltage and AC current values of the grid connection point in the dq coordinate system.

Step 3: Calculate the grid voltage phase θ _g and grid voltage amplitude V _g according to the three-phase voltage on the grid side.

Step 4: Calculate the potential phase θ VSG in the three-phase inverter according to the active power command value _Pref given by the three-phase inverter, the rated angular frequency _ωref of the grid, the obtained grid voltage phase _θg , the current over-limit link output signal _TLIM calculated in step ₆ at the previous moment, and the three-phase inverter output active power _Pe .

Step 5: Calculate the potential amplitude E in the three-phase inverter according to the reactive power command value Q _ref given by the three-phase inverter, the reference value E ₀ of the grid voltage amplitude, and the three-phase inverter output active power Q _e .

Step 6: According to the potential amplitude E in the three-phase inverter, the filter inductor L and the current limit value I _max of the three-phase inverter, the grid voltage amplitude V _g , the AC current I _g of the grid connection point, the virtual rotor angular velocity ω _VSG , the AC voltage value and AC current value of the grid connection point in the dq coordinate system, calculate the potential amplitude E' in the three-phase inverter after limiting and the current over-limit link output signal T _LIM at the current moment.

Step 7: Based on the potential amplitude E' and the potential phase θ _VSG of the three-phase inverter after limiting, Park inverse transformation is performed with θ _VSG as the commutation angle to obtain the three-phase inverter modulation wave, and the three-phase inverter modulation wave is modulated on the carrier signal V _m to generate a switch control signal D for controlling the three-phase inverter.

As a preferred solution, the specific steps of step 4 are as follows:

Step 4.1: Input the three-phase inverter output active power _Pe , the three-phase inverter given active power command value _Pref , and the grid rated angular frequency _ωref into the rotor motion equation to obtain the virtual rotor angular velocity _ωV .

Step 4.2: According to the current over-limit link output signal T _LIM calculated in step 6 at the previous moment, the angular velocity compensation command ω _com is obtained, and the virtual rotor angular velocity ω _V is added to the angular velocity compensation command ω _com to obtain the compensated virtual rotor angular velocity ω _VSG at the current moment.

Step 4.3: The virtual rotor angular velocity ω _VSG after compensation at the current moment is passed through an integration link to obtain the potential phase θ _VSG inside the three-phase inverter.

As a preferred solution, the method for obtaining the angular velocity compensation instruction ω _com is as follows:

Step 4.2.1: Substitute the known three-phase inverter output active power _Pe , the compensated angular velocity ω _VSG at the previous moment, the AC voltage _Vg at the grid connection point, the AC current _Ig at the grid connection point, and the filter inductor L into Formula 1 to calculate the three-phase inverter grid connection point control phase _θgc .

The calculation formula of formula 1 is as follows:

Step 4.2.2: After subtracting the grid voltage phase _θg from _θgc , the angular velocity compensation command _ωcom is obtained through PI control.

Step 4.2.3: When the current over-limit link output signal T _LIM calculated in step 6 at the previous moment is 1, the angular velocity compensation command ω _com is output; otherwise, the angular velocity compensation command ω _com is 0.

As a preferred solution, the calculation formula of the potential amplitude E in the three-phase inverter is as follows:

Among them, K _q is the reactive integration coefficient and s is the Laplace operator.

As a preferred solution, the specific steps of step 6 are as follows:

和

Step 6.1: Substitute the known three-phase inverter internal potential amplitude E, filter inductance L, virtual rotor angular velocity ω _VSG after compensation at the current moment, and the AC voltage and AC current values of the grid connection point in the dq coordinate system into Formula 3 to calculate the d-axis and q-axis components of the three-phase inverter output current reference value.

and

The calculation formula of formula 3 is as follows:

Among them, _isd and _isq are the d-axis component and q-axis component of the AC current at the grid connection point, u _sd and u _sq are the d-axis component and q-axis component of the AC voltage at the grid connection point, and α is the closed-loop expected bandwidth of the current control, which can be set manually.

和

进行限幅，得到限幅后的电流d、q轴分量

和

Step 6.2: Calculate the d-axis and q-axis components of the three-phase inverter output current reference value

and

Perform amplitude limiting to obtain the current d and q axis components after amplitude limiting

and

和

计算公式如下：Current d and q axis components

and

The calculation formula is as follows:

为电流相角，取值范围为0°～90°，可人工设置。I_max为三相逆变器电流限幅值。代表三相逆变器最大可以承受的短时过流水平，通常为1.3pu。in,

It is the current phase angle, ranging from 0° to 90°, and can be set manually. _{I max} is the current limit value of the three-phase inverter. It represents the maximum short-term overcurrent level that the three-phase inverter can withstand, usually 1.3pu.

和

计算内电势幅值d轴、q轴分量。Step 6.3: According to the current d and q axis components after limiting

and

Calculate the d-axis and q-axis components of the internal potential amplitude.

The internal potential amplitude d-axis, q-axis components u _cd and u _cq are calculated as follows:

Wherein, _Hd (s) is the d-axis PI control link, _Hq (s) is the q-axis PI control link, s is the Laplace operator, and α is the closed-loop expected bandwidth of the current control, which can be set manually.

Step 6.4: Synthesize the internal potential amplitude d, q-axis components u _cd and _ucq to obtain the internal potential amplitude E' of the three-phase inverter after limiting.

与I_max大小，当

时，当前时刻电流越限环节输出信号T_LIM为1，否则，当前时刻电流越限环节输出信号T_LIM为0。Step 6.5: Judgement

With I _max size, when

When the current over-limit link output signal T _LIM at the current moment is 1, otherwise, the current over-limit link output signal T _LIM at the current moment is 0.

As a preferred option,

Among them, the values of PI control d and q axis proportional coefficients are: k _pd =1, k _pq =1; the value ranges of PI control d and q axis integral coefficients are: 0＜k _id ≤5, 0＜k _iq ≤0.1, and the specific values are determined according to the simulation experiment results. s is the Laplace operator.

In a second aspect, a grid-type inverter switching control device with phase support capability under fault conditions includes the following modules:

Voltage and current measurement module: used to obtain the AC voltage and AC current of the three-phase inverter grid-connected point, and perform Park transformation on the AC voltage and AC current of the grid-connected point to obtain the AC voltage and AC current values of the grid-connected point in the dq coordinate system of the corresponding physical quantity.

Power calculation module: used to calculate the active power _Pe and reactive power _Qe on the AC side of the three-phase inverter according to the AC voltage and AC current values of the grid connection point in the dq coordinate system.

PLL phase-locked module: used to calculate the grid voltage phase θ _g and grid voltage amplitude V _g according to the three-phase voltage on the grid side.

Internal potential phase generation module: used to calculate the internal potential phase θ _VSG of the three-phase inverter according to the active power command value _Pref given by the three-phase inverter, the rated angular frequency _ωref of the power grid, the obtained power grid voltage phase _θg , the current over-limit link output signal _TLIM calculated by the internal potential amplitude limiting module at the previous _moment , and the three-phase inverter output active power Pe.

Internal potential amplitude generation module: used to calculate the internal potential amplitude E of the three-phase inverter according to the reactive power command value Q _ref given by the three-phase inverter, the reference value E ₀ of the grid voltage amplitude, and the three-phase inverter output active power Q _e .

Internal potential amplitude limiting module: used to calculate the internal potential amplitude E' of the three-phase inverter after limiting according to the internal potential amplitude E of the three-phase inverter, the filter inductance L and the current limit value I _max of the three-phase inverter, the grid voltage amplitude V _g , the AC current I _g of the grid connection point, the virtual rotor angular velocity ω _VSG , the AC voltage value and AC current value of the grid connection point in the dq coordinate system, and the current over-limit link output signal T _LIM at the current moment.

Modulation module: used to obtain the three-phase inverter modulation wave by Park inverse transformation according to the potential amplitude E' and the potential phase θ _VSG of the three-phase _inverter after limiting, and to modulate the carrier signal V _m with the three-phase inverter modulation wave to generate the switch control signal D for controlling the three-phase inverter.

As a preferred solution, the internal potential phase generation module has the following specific functions:

Step 4.1: Input the three-phase inverter output active power _Pe , the three-phase inverter given active power command value _Pref , and the grid rated angular frequency _ωref into the rotor motion equation to obtain the virtual rotor angular velocity _ωV .

Step 4.2: According to the current over-limit link output signal T _LIM calculated by the potential amplitude limiting module in the previous moment, the angular velocity compensation instruction ω _com is obtained, and the virtual rotor angular velocity ω _VSG after compensation at the current moment is obtained by adding the virtual rotor angular velocity ω _V to the angular velocity compensation instruction ω _com .

Step 4.3: The virtual rotor angular velocity ω _VSG after compensation at the current moment is passed through an integration link to obtain the potential phase θ _VSG inside the three-phase inverter.

As a preferred solution, the method for obtaining the angular velocity compensation instruction ω _com is as follows:

Step 4.2.1: Substitute the known three-phase inverter output active power _Pe , the compensated angular velocity ω _VSG at the previous moment, the AC voltage _Vg at the grid connection point, the AC current _Ig at the grid connection point, and the filter inductor L into Formula 1 to calculate the three-phase inverter grid connection point control phase _θgc .

The calculation formula of formula 1 is as follows:

Step 4.2.2: After subtracting the grid voltage phase _θg from _θgc , the angular velocity compensation command _ωcom is obtained through PI control.

Step 4.2.3: When the current over-limit link output signal T _LIM =1 calculated by the potential amplitude limiting module in the previous moment, the angular velocity compensation command ω _com is output; otherwise, the angular velocity compensation command ω _com is output as 0.

As a preferred solution, the calculation formula of the potential amplitude E in the three-phase inverter is as follows:

Among them, K _q is the reactive integration coefficient and s is the Laplace operator.

As a preferred solution, the internal potential amplitude limiting module has the following specific functions:

Step 6.1: Substitute the known internal potential amplitude E of the three-phase inverter, the filter inductance L, the compensated virtual rotor angular velocity ω _VSG at the current moment, the AC voltage value and the AC current value of the grid connection point in the dq coordinate system into Formula 3 to calculate the output current reference value d, q-axis components i _s * _d and i _s * _q of the three-phase inverter.

The calculation formula of formula 3 is as follows:

Among them, _isd and _isq are the d-axis component and q-axis component of the AC current at the grid connection point, u _sd and u _sq are the d-axis component and q-axis component of the AC voltage at the grid connection point, and α is the closed-loop expected bandwidth of the current control, which can be set manually.

和

进行限幅，得到限幅后的电流d、q轴分量

和

Step 6.2: Calculate the d-axis and q-axis components of the three-phase inverter output current reference value

and

Perform amplitude limiting to obtain the current d and q axis components after amplitude limiting

and

和

计算公式如下：Current d and q axis components

and

The calculation formula is as follows:

为电流相角，取值范围为0°～90°，可人工设置。I_max为三相逆变器电流限幅值。代表三相逆变器最大可以承受的短时过流水平，通常为1.3pu。in,

It is the current phase angle, ranging from 0° to 90°, and can be set manually. _{I max} is the current limit value of the three-phase inverter. It represents the maximum short-term overcurrent level that the three-phase inverter can withstand, usually 1.3pu.

和

计算内电势幅值d轴、q轴分量。Step 6.3: According to the current d and q axis components after limiting

and

Calculate the d-axis and q-axis components of the internal potential amplitude.

The internal potential amplitude d-axis, q-axis components u _cd and u _cq are calculated as follows:

Wherein, _Hd (s) is the d-axis PI control link, _Hq (s) is the q-axis PI control link, s is the Laplace operator, and α is the closed-loop expected bandwidth of the current control, which can be set manually.

Step 6.4: Synthesize the internal potential amplitude d, q-axis components u _cd and _ucq to obtain the internal potential amplitude E' of the three-phase inverter after limiting.

与I_max大小，当

时，当前时刻电流越限环节输出信号T_LIM为1，否则，当前时刻电流越限环节输出信号T_LIM为0。Step 6.5: Judgement

With I _max size, when

When the current over-limit link output signal T _LIM at the current moment is 1, otherwise, the current over-limit link output signal T _LIM at the current moment is 0.

As a preferred option,

Among them, the values of PI control d and q axis proportional coefficients are: k _pd =1, k _pq =1; the value ranges of PI control d and q axis integral coefficients are: 0＜k _id ≤5, 0＜k _iq ≤0.1, and the specific values are determined according to the simulation experiment results. s is the Laplace operator.

Beneficial effects: The present invention provides a switching control method for a grid-connected inverter with phase support capability under faults. The grid-connected inverter works normally in the voltage source control mode. When it is detected that the current exceeds the limit under fault, the angular velocity compensation control link based on the phase change of the power grid is put into use to reduce the difference between the internal potential phase of the inverter output and the actual phase of the power grid, while providing phase support capability. The PI control link is introduced into the current limiting control module to improve the situation where the internal potential amplitude changes drastically due to the current limiting under fault. The smooth switching between the voltage source control mode and the current source control mode is achieved by controlling the internal potential phase and amplitude under fault, overcoming the problems of insufficient synchronization support capability of the grid-connected inverter during faults and large impact and easy transient instability during the resynchronization process after the fault, thereby improving the stability of the grid-connected new energy power generation equipment and having good application value.

Compared with the prior art, the present invention has the following beneficial effects on the new energy power generation system:

1. The grid-connected inverter controlled by the method of the present invention can limit the fault current of the grid-connected inverter itself and the impact current of the resynchronization process during the grid fault and fault recovery process, and at the same time track the grid phase change to improve the transient stability of the grid-connected inverter.

2. The grid-type inverter controlled by the method of the present invention can provide phase support capability during grid faults, and provide stable phase support under normal and fault conditions for other types of inverters in the grid, such as the widely used grid-type inverters, to improve the control performance and transient stability of the grid-type inverters. Compared with the existing grid-type inverters that can only provide phase support capability under normal conditions, the improvement of phase support capability under faults is more needed by the grid.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic structural diagram of a grid-connected inverter switching control system with phase support capability under fault conditions according to the present invention.

FIG. 2 is a schematic structural diagram of a grid-type inverter switching control device with phase support capability under fault conditions according to the present invention.

FIG3 is a control block diagram of a method for generating potential phase in a grid-connected inverter with phase support capability under fault conditions according to the present invention.

DETAILED DESCRIPTION

The present invention will be further described below in conjunction with specific embodiments.

As shown in Figure 1, the first embodiment is a grid-type inverter switching control system with phase support capability under faults, including a DC power supply, which is connected to the grid after passing through a three-phase inverter main circuit and a filter inductor. It also includes a voltage and current measurement module connected to the grid connection point between the filter inductor and the grid, a PLL phase-locked module connected to the voltage and current measurement module, and a controller connected to the three-phase inverter main circuit.

The voltage and current measurement module is used to measure and sample the AC voltage and AC current at the grid connection point of the three-phase inverter.

The PLL phase-locked module is used to calculate the grid voltage phase according to the three-phase voltage on the grid side.

The controller executes a switching control method for a grid-type inverter with a phase support capability under fault conditions, and is used to generate a switch control signal for controlling the grid-type inverter.

The internal potential refers to the potential of the connection node between the three-phase inverter and the filter inductor, including the amplitude and phase of the potential.

A second embodiment of a switching control method for a grid-connected inverter with phase support capability under fault conditions includes the following steps:

Step 1: Obtain the AC voltage and AC current of the grid-connected point of the three-phase inverter, and perform Park transformation on the AC voltage and AC current of the grid-connected point to obtain the AC voltage value and AC current value of the grid-connected point of the corresponding physical quantity in the dq coordinate system.

Step 2: Calculate the AC side active power _Pe and reactive power _Qe of the three-phase inverter according to the AC voltage and AC current values of the grid connection point in the dq coordinate system.

Step 3: Calculate the grid voltage phase θ _g and grid voltage amplitude V _g according to the three-phase voltage on the grid side.

Step 4: Calculate the potential phase θ VSG in the three-phase inverter according to the active power command value _Pref given by the three-phase inverter, the rated angular frequency _ωref of the grid, the obtained grid voltage phase _θg , the current over-limit link output signal _TLIM calculated in step ₆ at the previous moment, and the three-phase inverter output active power _Pe .

Step 5: Calculate the potential amplitude E in the three-phase inverter according to the reactive power command value Q _ref given by the three-phase inverter, the reference value E ₀ of the grid voltage amplitude, and the three-phase inverter output active power Q _e .

Step 6: According to the potential amplitude E in the three-phase inverter, the filter inductor L and the current limit value I _max of the three-phase inverter, the grid voltage amplitude V _g , the AC current I _g of the grid connection point, the virtual rotor angular velocity ω _VSG , the AC voltage value and AC current value of the grid connection point in the dq coordinate system, calculate the potential amplitude E' in the three-phase inverter after limiting and the current over-limit link output signal T _LIM at the current moment.

Step 7: Based on the potential amplitude E' and the potential phase θ _VSG of the three-phase inverter after limiting, Park inverse transformation is performed with θ _VSG as the commutation angle to obtain the three-phase inverter modulation wave, and the three-phase inverter modulation wave is modulated on the carrier signal V _m to generate a switch control signal D for controlling the three-phase inverter.

Furthermore, the specific steps of step 4 are as follows:

Step 4.1: Input the three-phase inverter output active power _Pe , the three-phase inverter given active power command value _Pref , and the grid rated angular frequency _ωref into the rotor motion equation to obtain the virtual rotor angular velocity _ωV .

Step 4.2: According to the current over-limit link output signal T _LIM calculated in step 6 at the previous moment, the angular velocity compensation command ω _com is obtained, and the virtual rotor angular velocity ω _V is added to the angular velocity compensation command ω _com to obtain the compensated virtual rotor angular velocity ω _VSG at the current moment.

Step 4.3: The virtual rotor angular velocity ω _VSG after compensation at the current moment is passed through an integration link to obtain the potential phase θ _VSG inside the three-phase inverter.

Furthermore, the method for obtaining the angular velocity compensation instruction ω _com is as follows:

Step 4.2.1: Substitute the known three-phase inverter output active power _Pe , the compensated angular velocity ω _VSG at the previous moment, the AC voltage _Vg at the grid connection point, the AC current _Ig at the grid connection point, and the filter inductor L into Formula 1 to calculate the three-phase inverter grid connection point control phase _θgc .

The calculation formula of formula 1 is as follows:

Step 4.2.2: After subtracting the grid voltage phase _θg from _θgc , the angular velocity compensation command _ωcom is obtained through PI control.

Step 4.2.3: When the current over-limit link output signal T _LIM calculated in step 6 at the previous moment is 1, the angular velocity compensation command ω _com is output; otherwise, the angular velocity compensation command ω _com is 0.

When the current exceeds the limit, the angular velocity compensation control link is put into use, which can track the phase change of the power grid while retaining the rotor motion equation link. The benefits are:

1) Since the rotor motion equation is retained, a certain phase support capability is provided when the current exceeds the limit (i.e. during grid faults), which can prevent transient instability of other grid-following inverters.

2) Since the three-phase inverter tracks the phase change of the power grid, the phase difference between the output phase of the three-phase inverter and the power grid is reduced during fault recovery and resynchronization, and the impact current of the resynchronization process is reduced.

Furthermore, the calculation formula of the potential amplitude E in the three-phase inverter is as follows:

Among them, K _q is the reactive integration coefficient and s is the Laplace operator.

Furthermore, the specific steps of step 6 are as follows:

和

Step 6.1: Substitute the known three-phase inverter internal potential amplitude E, filter inductance L, virtual rotor angular velocity ω _VSG after compensation at the current moment, and the AC voltage and AC current values of the grid connection point in the dq coordinate system into Formula 3 to calculate the d-axis and q-axis components of the three-phase inverter output current reference value.

and

The calculation formula of formula 3 is as follows:

Among them, _isd and _isq are the d-axis component and q-axis component of the AC current at the grid connection point, u _sd and u _sq are the d-axis component and q-axis component of the AC voltage at the grid connection point, and α is the closed-loop expected bandwidth of the current control, which can be set manually.

和

进行限幅，得到限幅后的电流d、q轴分量

和

Step 6.2: Calculate the d-axis and q-axis components of the three-phase inverter output current reference value

and

Perform amplitude limiting to obtain the current d and q axis components after amplitude limiting

and

和

计算公式如下：Current d and q axis components

and

The calculation formula is as follows:

为电流相角，取值范围为0°～90°，可人工设置。I_max为三相逆变器电流限幅值。代表三相逆变器最大可以承受的短时过流水平，通常为1.3pu。in,

It is the current phase angle, ranging from 0° to 90°, and can be set manually. _{I max} is the current limit value of the three-phase inverter. It represents the maximum short-term overcurrent level that the three-phase inverter can withstand, usually 1.3pu.

和

计算内电势幅值d轴、q轴分量。Step 6.3: According to the current d and q axis components after limiting

and

Calculate the d-axis and q-axis components of the internal potential amplitude.

The internal potential amplitude d-axis, q-axis components u _cd and u _cq are calculated as follows:

Wherein, _Hd (s) is the d-axis PI control link, _Hq (s) is the q-axis PI control link, s is the Laplace operator, and α is the closed-loop expected bandwidth of the current control, which can be set manually.

Step 6.4: Synthesize the internal potential amplitude d, q-axis components u _cd and _ucq to obtain the internal potential amplitude E' of the three-phase inverter after limiting.

与I_max大小，当

时，当前时刻电流越限环节输出信号T_LIM为1，否则，当前时刻电流越限环节输出信号T_LIM为0。Step 6.5: Judgement

With I _max size, when

When the current over-limit link output signal T _LIM at the current moment is 1, otherwise, the current over-limit link output signal T _LIM at the current moment is 0.

Further,

Among them, the values of PI control d and q axis proportional coefficients are: k _pd =1, k _pq =1; the value ranges of PI control d and q axis integral coefficients are: 0＜k _id ≤5, 0＜k _iq ≤0.1, and the specific values are determined according to the simulation experiment results. s is the Laplace operator.

As shown in FIG. 2 , a third embodiment of a grid-connected inverter switching control device with phase support capability under fault conditions includes the following modules:

Voltage and current measurement module: used to obtain the AC voltage and AC current of the three-phase inverter grid-connected point, and perform Park transformation on the AC voltage and AC current of the grid-connected point to obtain the AC voltage and AC current values of the grid-connected point in the dq coordinate system of the corresponding physical quantity.

Power calculation module: used to calculate the active power _Pe and reactive power _Qe on the AC side of the three-phase inverter according to the AC voltage and AC current values of the grid connection point in the dq coordinate system.

PLL phase-locked module: used to calculate the grid voltage phase θ _g and grid voltage amplitude V _g according to the three-phase voltage on the grid side.

Internal potential phase generation module: used to calculate the internal potential phase θ _VSG of the three-phase inverter according to the active power command value _Pref given by the three-phase inverter, the rated angular frequency _ωref of the power grid, the obtained power grid voltage phase _θg , the current over-limit link output signal _TLIM calculated by the internal potential amplitude limiting module at the previous _moment , and the three-phase inverter output active power Pe.

Internal potential amplitude generation module: used to calculate the internal potential amplitude E of the three-phase inverter according to the reactive power command value Q _ref given by the three-phase inverter, the reference value E ₀ of the grid voltage amplitude, and the three-phase inverter output active power Q _e .

Internal potential amplitude limiting module: used to calculate the internal potential amplitude E' of the three-phase inverter after limiting according to the internal potential amplitude E of the three-phase inverter, the filter inductance L and the current limit value I _max of the three-phase inverter, the grid voltage amplitude V _g , the AC current I _g of the grid connection point, the virtual rotor angular velocity ω _VSG , the AC voltage value and AC current value of the grid connection point in the dq coordinate system, and the current over-limit link output signal T _LIM at the current moment.

Modulation module: used to obtain the three-phase inverter modulation wave by Park inverse transformation according to the potential amplitude E' and the potential phase θ _VSG of the three-phase _inverter after limiting, and to modulate the carrier signal V _m with the three-phase inverter modulation wave to generate the switch control signal D for controlling the three-phase inverter.

Furthermore, the internal potential phase generation module is composed of a rotor motion equation simulation link and an angular velocity compensation control link based on grid phase changes. The specific functions are as follows:

Step 4.1: Input the three-phase inverter output active power _Pe , the three-phase inverter given active power command value _Pref , and the grid rated angular frequency _ωref into the rotor motion equation to obtain the virtual rotor angular velocity _ωV .

Step 4.2: According to the current over-limit link output signal T _LIM calculated by the potential amplitude limiting module in the previous moment, the angular velocity compensation instruction ω _com is obtained, and the virtual rotor angular velocity ω _VSG after compensation at the current moment is obtained by adding the virtual rotor angular velocity ω _V to the angular velocity compensation instruction ω _com .

Step 4.3: The virtual rotor angular velocity ω _VSG after compensation at the current moment is passed through an integration link to obtain the potential phase θ _VSG inside the three-phase inverter.

As shown in FIG3 , further, the method for obtaining the angular velocity compensation instruction ω _com is as follows:

Step 4.2.1: Substitute the known three-phase inverter output active power _Pe , the compensated angular velocity ω _VSG at the previous moment, the AC voltage _Vg at the grid connection point, the AC current _Ig at the grid connection point, and the filter inductor L into Formula 1 to calculate the three-phase inverter grid connection point control phase _θgc .

The calculation formula of formula 1 is as follows:

Step 4.2.2: After subtracting the grid voltage phase _θg from _θgc , the angular velocity compensation command _ωcom is obtained through PI control.

Step 4.2.3: When the current over-limit link output signal T _LIM =1 calculated by the potential amplitude limiting module in the previous moment, the angular velocity compensation command ω _com is output; otherwise, the angular velocity compensation command ω _com is output as 0.

When the current exceeds the limit, the angular velocity compensation control link is put into use, which can track the phase change of the power grid while retaining the rotor motion equation link. The benefits are:

1) Since the rotor motion equation is retained, a certain phase support capability is provided when the current exceeds the limit (i.e. during grid faults), which can prevent transient instability of other grid-following inverters.

2) Since the three-phase inverter tracks the phase change of the power grid, the phase difference between the output phase of the three-phase inverter and the power grid is reduced during fault recovery and resynchronization, and the impact current of the resynchronization process is reduced.

Furthermore, the calculation formula of the potential amplitude E in the three-phase inverter is as follows:

Among them, K _q is the reactive integration coefficient and s is the Laplace operator.

Furthermore, the internal potential amplitude limiting module adds a PI control link H(s) on the basis of the traditional current limiting control strategy to improve the situation where the internal potential amplitude changes dramatically due to current limiting under fault conditions. Due to the inherent regulation performance of the PI control link, the transient stability of the direct voltage control type grid-connected inverter can be improved through reasonable parameter settings. The specific functions are as follows:

和

Step 6.1: Substitute the known three-phase inverter internal potential amplitude E, filter inductance L, virtual rotor angular velocity ω _VSG after compensation at the current moment, and the AC voltage and AC current values of the grid connection point in the dq coordinate system into Formula 3 to calculate the d-axis and q-axis components of the three-phase inverter output current reference value.

and

The calculation formula of formula 3 is as follows:

Among them, _isd and _isq are the d-axis component and q-axis component of the AC current at the grid connection point, u _sd and u _sq are the d-axis component and q-axis component of the AC voltage at the grid connection point, and α is the closed-loop expected bandwidth of the current control, which can be set manually.

和

进行限幅，得到限幅后的电流d、q轴分量

和

Step 6.2: Calculate the d-axis and q-axis components of the three-phase inverter output current reference value

and

Perform amplitude limiting to obtain the current d and q axis components after amplitude limiting

and

和

计算公式如下：Current d and q axis components

and

The calculation formula is as follows:

为电流相角，取值范围为0°～90°，可人工设置。I_max为三相逆变器电流限幅值。代表三相逆变器最大可以承受的短时过流水平，通常为1.3pu。in,

It is the current phase angle, ranging from 0° to 90°, and can be set manually. _{I max} is the current limit value of the three-phase inverter. It represents the maximum short-term overcurrent level that the three-phase inverter can withstand, usually 1.3pu.

和

计算内电势幅值d轴、q轴分量。Step 6.3: According to the current d and q axis components after limiting

and

Calculate the d-axis and q-axis components of the internal potential amplitude.

The internal potential amplitude d-axis, q-axis components u _cd and u _cq are calculated as follows:

Wherein, _Hd (s) is the d-axis PI control link, _Hq (s) is the q-axis PI control link, s is the Laplace operator, and α is the closed-loop expected bandwidth of the current control, which can be set manually.

Step 6.4: Synthesize the internal potential amplitude d, q-axis components u _cd and _ucq to obtain the internal potential amplitude E' of the three-phase inverter after limiting.

与I_max大小，当

时，当前时刻电流越限环节输出信号T_LIM为1，否则，当前时刻电流越限环节输出信号T_LIM为0。Step 6.5: Judgement

With I _max size, when

When the current over-limit link output signal T _LIM at the current moment is 1, otherwise, the current over-limit link output signal T _LIM at the current moment is 0.

Further,

Among them, the values of PI control d and q axis proportional coefficients are: k _pd =1, k _pq =1; the value ranges of PI control d and q axis integral coefficients are: 0＜k _id ≤5, 0＜k _iq ≤0.1, and the specific values are determined according to the simulation experiment results. s is the Laplace operator.

Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

The present invention is described with reference to the flowchart and/or block diagram of the method, device (system), and computer program product according to the embodiment of the present invention. It should be understood that each process and/or box in the flowchart and/or block diagram, as well as the combination of the process and/or box in the flowchart and/or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device produce a device for implementing the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory produce a manufactured product including an instruction device that implements the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.

These computer program instructions may also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, whereby the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more processes in the flowchart and/or one or more boxes in the block diagram.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (7)

1. The method for switching control of the grid-structured inverter with the phase supporting capability under the fault is characterized by comprising the following steps of: the method comprises the following steps:

step 1: acquiring alternating voltage and alternating current of a grid-connected point of a three-phase inverter, and performing Park conversion on the alternating voltage and the alternating current of the grid-connected point to obtain alternating voltage values and alternating current values of the grid-connected point of the corresponding physical quantity under a dq coordinate system;

step 2: calculating the active power P of the alternating current side of the three-phase inverter according to the alternating current voltage value and the alternating current value of the grid-connected point under the dq coordinate system _e And reactive power Q _e ；

Step 3: calculating the phase theta of the power grid voltage according to the three-phase voltage of the power grid side _g Grid voltage amplitude V _g ；

Step 4: according to the given active power command value P of the three-phase inverter _ref Rated angular frequency omega of power grid _ref The obtained grid voltage phase theta _g Outputting a signal T in the current out-of-limit link calculated in the step 6 at the previous moment _LIM The three-phase inverter outputs active power P _e Calculating the potential phase θ in a three-phase inverter _VSG ；

Step 5: according to the reactive power command value Q given by the three-phase inverter _ref Reference value E of the grid voltage amplitude ₀ The three-phase inverter outputs active power Q _e Calculating the potential amplitude E in the three-phase inverter;

step 6: according to the internal potential amplitude E, the filter inductance L and the three-phase inversion of the three-phase inverterCurrent limiting value I _max Grid voltage amplitude V _g AC current I of the parallel network _g Virtual rotor angular velocity omega _VSG AC voltage value and AC current value of the grid-connected point under dq coordinate system, calculating amplitude limiting three-phase inverter internal potential amplitude E' and outputting signal T in current out-of-limit link _LIM ；

Step 7: according to amplitude E' of electric potential in three-phase inverter after amplitude limitation, phase theta of electric potential in three-phase inverter _VSG At θ _VSG Performing Park inverse transformation as a rotation angle to obtain a three-phase inverter modulation wave, and comparing the three-phase inverter modulation wave with a carrier signal V _m Modulation is performed to generate a switching control signal D for controlling the three-phase inverter.

2. The method for switching control of a grid-tied inverter with phase support under fault capability according to claim 1, wherein: the specific steps of the step 4 are as follows:

step 4.1: outputting active power P from three-phase inverter _e Active power command value P given by three-phase inverter _ref Rated angular frequency omega of power grid _ref Inputting the rotor motion equation to obtain the virtual rotor angular velocity omega _V ；

Step 4.2: outputting a signal T according to the current out-of-limit link calculated in the previous time step 6 _LIM Acquiring an angular velocity compensation command omega _com Virtual rotor angular velocity ω _V With angular velocity compensation command omega _com After addition, the virtual rotor angular velocity omega compensated at the current moment is obtained _VSG ；

Step 4.3: compensating the current moment to obtain the virtual rotor angular velocity omega _VSG Obtaining the potential phase theta in the three-phase inverter through an integration link _VSG 。

3. The method for switching control of a grid-tied inverter with phase support under fault capability according to claim 2, wherein: the angular velocity compensation command omega _com The acquisition method comprises the following steps:

step 4.2.1: will be knownThree-phase inverter outputs active power P _e Angular velocity omega after compensation at last moment _VSG Ac voltage V of grid-connected point _g AC current I of the parallel network _g Substituting the filter inductance L into the formula 1, and calculating to obtain the control phase theta of the grid-connected point of the three-phase inverter _gc ；

The formula 1 is calculated as follows:

step 4.2.2: phase θ of the grid voltage _g And theta _gc After the difference is made, the angular velocity compensation instruction omega is obtained through PI control _com ；

Step 4.2.3: outputting a signal T in the current out-of-limit link calculated in the step 6 at the previous moment _LIM When=1, an angular velocity compensation command ω is output _com Otherwise, outputting an angular velocity compensation command omega _com Is 0.

4. The method for switching control of a grid-tied inverter with phase support under fault capability according to claim 1, wherein: the calculation formula of the potential amplitude E in the three-phase inverter is as follows:

wherein ,K_q And s is a Laplacian operator and is a reactive integration coefficient.

5. The method for switching control of a grid-tied inverter with phase support under fault capability according to claim 1, wherein: the specific steps of the step 6 are as follows:

step 6.1: the known potential amplitude E, the filter inductance L and the virtual rotor angular velocity omega after the current time compensation in the three-phase inverter _VSG Substituting the alternating current voltage value and the alternating current value of the grid-connected point under the dq coordinate system into the formula 3, and calculatingCalculating to obtain d-axis and q-axis components of the output current reference value of the three-phase inverter

and

The formula 3 is calculated as follows:

wherein ,i_sd and i_sq D-axis component and q-axis component of alternating current of grid-connected point respectively, u _sd and u_sq D-axis component and q-axis component of the grid-connected point alternating current voltage, and alpha is the closed loop expected bandwidth of current control;

step 6.2: outputting d-axis and q-axis components of current reference values to a three-phase inverter

and

Clipping is performed to obtain the d and q axis components of the current after clipping>

and

Current d, q-axis component

and

The calculation formula is as follows:

wherein ,

is the phase angle of the current; i _max The current limiting value of the three-phase inverter is;

step 6.3: based on the d-and q-axis components of the limited current

and

Calculating the d-axis and q-axis components of the internal potential amplitude;

internal potential amplitude d-axis, q-axis component u _cd and u_cq The calculation formula is as follows:

wherein ,H_d (s) is d-axis PI control link, H _q (s) is a q-axis PI control link, s is a Laplacian; α is the closed loop desired bandwidth of the current control;

step 6.4: the internal potential amplitude d, q-axis component u _cd and u_cq Synthesizing to obtain amplitude-limited potential amplitude E' in the three-phase inverter;

step 6.5: judging

And I _max Size, when->

When the current is over the limit, a signal T is output _LIM 1, otherwise, outputting a signal T in the current out-of-limit link at the current moment _LIM Is 0.

6. The method for switching control of a grid-tied inverter with phase support under fault capability according to claim 5, wherein:

the ratio coefficient values of the d and q axes of the PI control are as follows: k (k) _pd ＝1，k _pq =1; the PI control d and q axis integral coefficient value ranges are as follows: k is 0 < k _id ≤5，0＜k _iq Less than or equal to 0.1.s is the Laplace operator.

7. A network-structured inverter switching control device with a phase supporting capability under faults is characterized in that: the device comprises the following modules:

the voltage and current measuring module is used for: the method comprises the steps of obtaining alternating voltage and alternating current of a grid-connected point of a three-phase inverter, performing Park conversion on the alternating voltage and the alternating current of the grid-connected point, and obtaining alternating voltage values and alternating current values of the grid-connected point of the corresponding physical quantity under a dq coordinate system;

and a power calculation module: calculating the active power P of the alternating current side of the three-phase inverter according to the alternating current voltage value and the alternating current value of the grid-connected point under the dq coordinate system _e And reactive power Q _e ；

PLL phase lock module: for calculating the phase theta of the grid voltage from the three-phase voltage of the grid side _g Grid voltage amplitude V _g ；

An internal potential phase generation module: for setting the active power command value P according to a three-phase inverter _ref Rated angular frequency omega of power grid _ref The obtained grid voltage phase theta _g The current out-of-limit link output signal T calculated by the potential amplitude limiting module in the last moment _LIM The three-phase inverter outputs active power P _e Calculating the potential phase θ in a three-phase inverter _VSG ；

An internal potential amplitude generation module: for setting reactive power command value Q according to three-phase inverter _ref Reference value E of the grid voltage amplitude ₀ The three-phase inverter outputs active power Q _e Calculating the potential amplitude E in the three-phase inverter;

an internal potential amplitude limiting module: for determining the amplitude E of the internal potential of the three-phase inverter, the filter inductance L and the current limiting value I of the three-phase inverter _max Grid voltage amplitude V _g AC current I of the parallel network _g Virtual rotor angular velocity omega _VSG AC voltage value and AC current value of the grid-connected point under dq coordinate system, calculating amplitude limiting three-phase inverter internal potential amplitude E' and outputting signal T in current out-of-limit link _LIM ；

And a modulation module: for determining the phase θ of the electric potential in the three-phase inverter according to the amplitude E' of the electric potential in the three-phase inverter after amplitude limiting _VSG At θ _VSG Performing Park inverse transformation as a rotation angle to obtain a three-phase inverter modulation wave, and comparing the three-phase inverter modulation wave with a carrier signal V _m Modulation is performed to generate a switching control signal D for controlling the three-phase inverter.

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