Switching Control Method of Grid-Forming Inverters with Phase Support Capability under Fault Conditions

Abstract

The invention discloses a switching control method for a network-forming inverter with phase support ability under faults. The network-forming inverter normally operates in the voltage source control mode. When the current exceeds the limit under the detected fault, an angular velocity compensation control link based on the change of the power grid phase is put into operation to reduce the phase difference between the internal potential phase of the inverter output and the actual power grid phase, and at the same time provide phase support ability. A PI control link is introduced into the current limiting control module to improve the situation that the amplitude of the internal potential changes violently due to current limiting under faults. Through the control of the internal potential phase and amplitude under faults, the smooth switching between the voltage source control mode and the current source control mode is realized, overcoming the problems of insufficient synchronous support ability during the fault of the network-forming grid-connected inverter and large impact and easy transient instability during the resynchronization process after the fault, improving the stability of the network-forming new energy power generation equipment, and having good application value.

Description

Technical Field

[0001] The present invention relates to a switching control method for a network-forming inverter with phase support ability under faults, belonging to the technical field of new energy power generation. Background Art

[0002] In recent years, with the wide access of large-scale new energy, traditional synchronous machines have been increasingly replaced by new energy converters, and network-forming inverters have also been widely mentioned and studied. The network-forming inverter can provide stable voltage and phase support, playing a function and effect similar to that of a conventional synchronous generator. Without considering current over-limit, direct voltage control is considered to be able to provide strong voltage and phase support capabilities.

[0003] However, due to the poor voltage and current withstand capabilities of power electronic devices, the grid-connected inverter undertaking the network-forming task will face more serious over-current problems during faults under the direct voltage control structure. The prior art proposes a direct voltage control method based on current limit control, but the current limit control causes the amplitude of the internal electromotive force to change violently, weakening the stability of the grid-connected equipment.

[0004] In addition, the voltage-current double closed-loop structure can effectively limit the output current of the inverter during faults, but the response of the double closed-loop structure is slower than that of the direct voltage control. And when switching to the current source mode based on phase-locked control during the current limiting period, it cannot provide stable synchronous phase support capabilities, and also faces the problem of excessive impact during the resynchronization process caused by the continuous increase of the grid phase and the inverter output phase during faults and is prone to transient instability.

[0005] Therefore, those skilled in the art are urgently required to solve the problems of insufficient phase support ability of the inverter during faults and the smooth switching between the voltage source mode and the current source mode after faults. Summary of the Invention

[0006] Objective: In order to overcome the problems of insufficient support ability of the network-forming inverter during faults and large current impact and easy transient instability during the resynchronization process after faults in the prior art, the present invention provides a switching control method for a network-forming inverter with phase support ability under faults, improving the transient stability of new energy grid-connected equipment.

[0007] Technical Solution: To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, a switching control method for a network-forming inverter with phase support ability under faults includes the following steps:

[0009] Step 1: Obtain the AC voltage and AC current at the grid connection point of the three-phase inverter, and perform Park transformation on the AC voltage and AC current at the grid connection point to obtain the AC voltage value and AC current value at the grid connection point of the corresponding physical quantities in the dq coordinate system.

[0010] Step 2: Calculate the active power P on the AC side of the three-phase inverter according to the AC voltage value and AC current value of the grid connection point in the dq coordinate system e and reactive power Q e .

[0011] Step 3: Calculate the phase θ of the grid voltage according to the three-phase grid voltage g , and the amplitude V of the grid voltage g .

[0012] Step 4: According to the given active power command value P of the three-phase inverter ref , the rated angular frequency ω of the grid ref , the obtained phase θ of the grid voltage g , the output signal T of the current over-limit link calculated in step 6 at the previous moment LIM , and the active power P output by the three-phase inverter e , calculate the phase θ of the internal electromotive force of the three-phase inverter VSG .

[0013] Step 5: According to the given reactive power command value Q of the three-phase inverter ref , the reference value E0 of the grid voltage amplitude, and the reactive power Q output by the three-phase inverter e , calculate the amplitude E of the internal electromotive force of the three-phase inverter.

[0014] Step 6: According to the amplitude E of the internal electromotive force of the three-phase inverter, the filter inductor L, and the current limit value I of the three-phase inverter max , the grid voltage amplitude V g , the AC current I at the grid connection point g , the virtual rotor angular velocity ω VSG , and the AC voltage value and AC current value at the grid connection point in the dq coordinate system, calculate the amplitude E' of the internal electromotive force of the three-phase inverter after amplitude limiting, and the output signal T of the current over-limit link at the current moment LIM .

[0015] Step 7: According to the amplitude E' of the internal electromotive force of the three-phase inverter after amplitude limiting and the phase θ of the internal electromotive force of the three-phase inverter VSG , use θ VSG as the rotation angle for Park inverse transformation to obtain the modulation wave of the three-phase inverter, and modulate the modulation wave of the three-phase inverter with the carrier signal V m to generate the switching control signal D for controlling the three-phase inverter.

[0016] As a preferred solution, the specific steps of step 4 are as follows:

[0017] Step 4.1: Subtract the active power P output by the three-phase inverter e from the given active power command value P of the three-phase inverterref , the rated angular frequency ω of the power grid ref Input the rotor motion equation to obtain the virtual rotor angular velocity ω V .

[0018] Step 4.2: According to the output signal T of the current over-limit link calculated in Step 6 at the previous moment LIM , obtain the angular velocity compensation command ω com , and add the virtual rotor angular velocity ω V to the angular velocity compensation command ω com . After addition, the compensated virtual rotor angular velocity ω at the current moment is obtained VSG .

[0019] Step 4.3: Pass the compensated virtual rotor angular velocity ω at the current moment VSG through the integral link to obtain the internal potential phase θ of the three-phase inverter VSG .

[0020] As an optimal solution, the method for obtaining the angular velocity compensation command ω is as follows: com The obtaining method is as follows:

[0021] Step 4.2.1: Substitute the known active power P output by the three-phase inverter e , the compensated angular velocity ω at the previous moment VSG , the AC voltage V at the grid connection point g , the AC current I at the grid connection point g , and the filter inductor L into Formula 1 to calculate the control phase θ at the grid connection point of the three-phase inverter gc .

[0022] The Formula 1 is calculated as follows:

[0023]

[0024] Step 4.2.2: After subtracting the grid voltage phase θ g from θ gc , pass it through PI control to obtain the angular velocity compensation command ω com .

[0025] Step 4.2.3: When the output signal T of the current over-limit link calculated in Step 6 at the previous moment LIM = 1, output the angular velocity compensation command ω com , otherwise, output the angular velocity compensation command ω com as 0.

[0026] As an optimal solution, the calculation formula for the internal potential amplitude E of the three-phase inverter is as follows:

[0027]

[0028] Among them, K q is the reactive power integration coefficient, and s is the Laplace operator.

[0029] As an optimal solution, the specific steps of step 6 are as follows:

[0030] 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 at the current moment VSG , 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 d-axis and q-axis components of the reference value of the output current of the three-phase inverter and

[0031] The formula 3 is calculated as follows:

[0032]

[0033] Among them, i sd and i sq are the d-axis component and the q-axis component of the AC current at the grid connection point respectively, u sd and u sq are the d-axis component and the q-axis component of the grid connection point AC voltage, and α is the closed-loop desired bandwidth of current control, which can be set manually.

[0034] Step 6.2: Limit the d-axis and q-axis components and of the reference value of the output current of the three-phase inverter to obtain the limited d-axis and q-axis components of the current and

[0035] The d-axis and q-axis components of the current and are calculated as follows:

[0036]

[0037] Among them, is the current phase angle, and the value range is 0° to 90°, which can be set manually. I max is the current limit value of the three-phase inverter. It represents the maximum short-time overcurrent level that the three-phase inverter can withstand, usually 1.3 pu.

[0038] Step 6.3: Calculate the d-axis and q-axis components of the internal potential amplitude according to the limited d-axis and q-axis components and of the current.

[0039] The d-axis and q-axis components u cd and u cq of the internal potential amplitude are calculated as follows:

[0040]

[0041] Among them, H d (s) is the d-axis PI control link, and H q (s) is the q-axis PI control link, where s is the Laplace operator. α is the closed-loop desired bandwidth of current control and can be set manually.

[0042] Step 6.4: Synthesize the d-axis and q-axis components u cd and u cq of the internal electromotive force amplitude to obtain the limited three-phase inverter internal electromotive force amplitude E'.

[0043] Step 6.5: Judge and I max in magnitude. When , the output signal T LIM of the current over-limit link at the current moment is 1; otherwise, the output signal T LIM of the current over-limit link at the current moment is 0.

[0044] As a preferred solution,

[0045] Among them, the PI control d-axis and q-axis proportionality coefficients are: k pd =1, k pq =1; the PI control d-axis and q-axis integral coefficient value ranges 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.

[0046] In the second aspect, a grid-forming inverter switching control device with phase support ability under faults includes the following modules:

[0047] Voltage and current measurement module: used to obtain the AC voltage and AC current at the connection point of the three-phase inverter, and perform Park transformation on the AC voltage and AC current at the connection point to obtain the AC voltage value and AC current value at the connection point in the dq coordinate system.

[0048] Power calculation module: used to calculate the three-phase inverter AC side active power P e and reactive power Q e according to the AC voltage value and AC current value at the connection point in the dq coordinate system.

[0049] PLL phase-locked module: used to calculate the grid voltage phase θ g , grid voltage amplitude V g according to the three-phase grid voltage.

[0050] Internal potential phase generation module: used to calculate the internal potential phase θ of the three-phase inverter according to the active power command value P given by the three-phase inverter ref , the rated angular frequency ω of the power grid ref , the obtained power grid voltage phase θ g , the output signal T of the current over-limit link calculated by the internal potential amplitude limiting module at the previous moment LIM , the active power P output by the three-phase inverter e , and calculate the internal potential phase θ of the three-phase inverter VSG .

[0051] 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 given by the three-phase inverter ref , the reference value E0 of the power grid voltage amplitude, and the reactive power Q output by the three-phase inverter e , and calculate the internal potential amplitude E of the three-phase inverter.

[0052] Internal potential amplitude limiting module: used to calculate the limited internal potential amplitude E' of the three-phase inverter according to the internal potential amplitude E of the three-phase inverter, the filter inductor L, and the current limit value I of the three-phase inverter max , the power grid voltage amplitude V g , the AC current I at the grid connection point g , the virtual rotor angular velocity ω VSG , the AC voltage value and AC current value at the grid connection point in the dq coordinate system, and calculate the output signal T of the current over-limit link at the current moment LIM .

[0053] Modulation module: used to perform Park inverse transformation with θ as the rotation angle to obtain the modulation wave of the three-phase inverter according to the limited internal potential amplitude E' of the three-phase inverter and the internal potential phase θ of the three-phase inverter, and modulate the modulation wave of the three-phase inverter with the carrier signal V VSG , and generate the switching control signal D for controlling the three-phase inverter. VSG as the rotation angle for Park inverse transformation to obtain the modulation wave of the three-phase inverter, and modulate the modulation wave of the three-phase inverter with the carrier signal V m to generate the switching control signal D for controlling the three-phase inverter.

[0054] As a preferred solution, the specific functions of the internal potential phase generation module are as follows:

[0055] Step 4.1: Input the active power P output by the three-phase inverter e , the active power command value P given by the three-phase inverter ref , and the rated angular frequency ω of the power grid ref into the rotor motion equation to obtain the virtual rotor angular velocity ω V .

[0056] Step 4.2: Obtain the angular velocity compensation command ω LIM according to the output signal T of the current over-limit link calculated by the internal potential amplitude limiting module at the previous moment com , and add the angular velocity compensation command ω to the virtual rotor angular velocity ωV After adding to the angular velocity compensation command ω com the compensated virtual rotor angular velocity ω at the current moment is obtained VSG .

[0057] Step 4.3: Pass the compensated virtual rotor angular velocity ω at the current moment VSG through an integration link to obtain the internal potential phase θ of the three-phase inverter VSG .

[0058] As an optimal solution, the method for obtaining the angular velocity compensation command ω com is as follows:

[0059] Step 4.2.1: Substitute the known active power P output by the three-phase inverter e , the angular velocity ω compensated at the previous moment VSG , the AC voltage V at the grid connection point g , and the AC current I at the grid connection point g , and the filter inductor L into Formula 1 to calculate the control phase θ at the grid connection point of the three-phase inverter gc .

[0060] The said Formula 1 has the following calculation formula:

[0061]

[0062] Step 4.2.2: After subtracting the grid voltage phase θ g from θ gc , obtain the angular velocity compensation command ω through PI control com .

[0063] Step 4.2.3: When the output signal T of the current overlimit link calculated by the internal potential amplitude limiting module at the previous moment LIM = 1, output the angular velocity compensation command ω com , otherwise, output the angular velocity compensation command ω com as 0.

[0064] As an optimal solution, the calculation formula for the internal potential amplitude E of the three-phase inverter is as follows:

[0065]

[0066] where K q is the reactive power integration coefficient and s is the Laplace operator.

[0067] As an optimal solution, the specific functions of the internal potential amplitude limiting module are as follows:

[0068] Step 6.1: Substitute the known internal potential amplitude E of the three-phase inverter, the filter inductor L, and the compensated virtual rotor angular velocity ω at the current momentVSG Substitute the AC voltage value and AC current value of the grid connection point in the dq coordinate system into Formula 3 to calculate the d-axis and q-axis components \(i_{d}^{*}\) and \(i_{q}^{*}\) of the output current reference value of the three-phase inverter. s * d and \(i_{q}^{*}\) s * q .

[0069] For the above-mentioned Formula 3, the calculation formula is as follows:

[0070]

[0071] Where \(i_{d}\) sd and \(i_{q}\) sq are the d-axis component and q-axis component of the AC current at the grid connection point respectively, \(u_{d}\) sd and \(u_{q}\) sq are the d-axis component and q-axis component of the AC voltage at the grid connection point, and \(\alpha\) is the closed-loop desired bandwidth of current control, which can be set manually.

[0072] Step 6.2: Limit the d-axis and q-axis components \(i_{d}^{*}\) and \(i_{q}^{*}\) of the output current reference value of the three-phase inverter to obtain the limited d-axis and q-axis components \(i_{d}^{lim}\) and \(i_{q}^{lim}\)

[0073] The calculation formulas for the d-axis and q-axis components \(i_{d}^{lim}\) and \(i_{q}^{lim}\) are as follows:

[0074]

[0075] Where \(\theta\) is the current phase angle, and its value range is 0° to 90°, which can be set manually. \(I_{lim}\) max is the current limit value of the three-phase inverter, representing the maximum short-time overcurrent level that the three-phase inverter can withstand, usually 1.3 pu.

[0076] Step 6.3: Calculate the d-axis and q-axis components of the internal potential amplitude according to the limited d-axis and q-axis components \(i_{d}^{lim}\) and \(i_{q}^{lim}\) .

[0077] The d-axis and q-axis components \(u_{d}^{e}\) cd and \(u_{q}^{e}\) cq of the internal potential amplitude are calculated as follows:

[0078]

[0079] Where \(H_{d}\) d (s) is the d-axis PI control link, \(H_{q}\) q(s) is the PI control link on the q-axis, where s is the Laplace operator. α is the closed-loop desired bandwidth of the current control and can be set manually.

[0080] Step 6.4: Synthesize the inner potential amplitude d and the q-axis components u cd and u cq to obtain the limited three-phase inverter inner potential amplitude E'.

[0081] Step 6.5: Judge and I max in magnitude. When , the output signal T LIM of the current over-limit link at the current moment is 1; otherwise, the output signal T LIM of the current over-limit link at the current moment is 0.

[0082] As a preferred solution,

[0083] wherein, the PI control d and q-axis proportionality coefficients are: k pd = 1, k pq = 1; the PI control d and q-axis integral coefficient value ranges 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.

[0084] Beneficial effects: The grid-forming inverter switching control method with phase support ability under faults provided by the present invention enables the grid-forming inverter to operate normally in the voltage source control mode. When current over-limit is detected under faults, an angular velocity compensation control link based on the grid phase change is put into operation to reduce the phase difference between the inner potential phase of the inverter output and the actual grid phase, and at the same time provide phase support ability. A PI control link is introduced into the current limiting control module to improve the situation where the inner potential amplitude changes violently due to current limiting under faults. Through the control of the inner potential phase and amplitude under faults, smooth switching between the voltage source control mode and the current source control mode is achieved, overcoming the problems of insufficient synchronous support ability of the grid-forming grid-connected inverter during faults and large impact and easy transient instability during the post-fault resynchronization process, improving the stability of the grid-forming new energy power generation equipment, and having good application value.

[0085] Compared with the prior art, the present invention has the following beneficial effects for the new energy power generation system:

[0086] 1. The grid-forming inverter controlled by the method of the present invention can limit its own fault current and the impact current during the resynchronization process of the grid-forming inverter during the grid fault period and the fault recovery process, and at the same time track the grid phase change to improve the transient stability of the grid-forming inverter.

[0087] 2. The grid-forming inverter controlled by the method of the present invention can provide phase support during grid faults, providing stable phase support for other types of inverters in the grid, such as the grid-following inverters widely used currently, under normal and fault conditions, and improving the control performance and transient stability of the grid-following inverters. Compared with the existing grid-forming inverters that can only provide phase support under normal conditions, the improvement of the phase support ability under faults is more needed by the grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 It is a schematic structural diagram of the switching control system of the grid-forming inverter with phase support ability under faults according to the present invention.

[0089] Figure 2 It is a schematic structural diagram of the switching control device of the grid-forming inverter with phase support ability under faults according to the present invention.

[0090] Figure 3 It is a control block diagram of the internal potential phase generation method of the grid-forming inverter with phase support ability under faults according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0091] The present invention will be further described in detail below with reference to specific embodiments.

[0092] As Figure 1 shown, in the first embodiment, a switching control system of a grid-forming inverter with phase support ability under faults includes 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 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.

[0093] The voltage and current measurement module is used to measure and sample the AC voltage and AC current at the connection point of the three-phase inverter.

[0094] The PLL phase-locked module is used to calculate the grid voltage phase based on the three-phase voltage on the grid side.

[0095] The controller executes the switching control method of the grid-forming inverter with phase support ability under faults, and is used to generate the switching control signal for controlling the grid-forming inverter.

[0096] The internal potential refers to the potential at the connection node between the three-phase inverter and the filter inductor, including the amplitude and phase of the potential.

[0097] In the second embodiment, a switching control method of a grid-forming inverter with phase support ability under faults includes the following steps:

[0098] Step 1: Obtain the AC voltage and AC current at the grid connection point of the three-phase inverter, and perform Park transformation on the AC voltage and AC current at the grid connection point to obtain the AC voltage value and AC current value at the grid connection point of the corresponding physical quantities in the dq coordinate system.

[0099] Step 2: Calculate the active power P on the AC side of the three-phase inverter according to the AC voltage value and AC current value at the grid connection point in the dq coordinate system e and the reactive power Q e .

[0100] Step 3: Calculate the phase θ of the grid voltage and the amplitude V of the grid voltage according to the three-phase voltage on the grid side g , the grid voltage amplitude V g .

[0101] Step 4: According to the given active power command value P of the three-phase inverter ref , the rated angular frequency ω of the grid ref , the obtained phase θ of the grid voltage g , the output signal T of the current over-limit link calculated in step 6 at the previous moment LIM , the active power P output by the three-phase inverter e , calculate the phase θ of the internal electromotive force of the three-phase inverter VSG .

[0102] Step 5: According to the given reactive power command value Q of the three-phase inverter ref , the reference value E0 of the grid voltage amplitude, the reactive power Q output by the three-phase inverter e , calculate the amplitude E of the internal electromotive force of the three-phase inverter.

[0103] Step 6: According to the amplitude E of the internal electromotive force of the three-phase inverter, the filter inductor L and the current limit value I of the three-phase inverter max , the grid voltage amplitude V g , the AC current I at the grid connection point g , the virtual rotor angular velocity ω VSG , the AC voltage value and AC current value at the grid connection point in the dq coordinate system, calculate the amplitude E' of the internal electromotive force of the three-phase inverter after limiting, and the output signal T of the current over-limit link at the current moment LIM .

[0104] Step 7: According to the amplitude E' of the internal electromotive force of the three-phase inverter after limiting and the phase θ of the internal electromotive force of the three-phase inverter VSG , use θ VSG as the rotation angle for Park inverse transformation to obtain the modulation wave of the three-phase inverter, and modulate the modulation wave of the three-phase inverter with the carrier signal V m to generate the switching control signal D for controlling the three-phase inverter.

[0105] Furthermore, for step 4, the specific steps are as follows:

[0106] Step 4.1: The three-phase inverter outputs active power P e , the active power command value P given by the three-phase inverter ref , grid rated angular frequency ω ref Input the rotor motion equation to obtain the virtual rotor angular velocity ω V .

[0107] Step 4.2: According to the current over-limit link output signal T calculated in step 6 at the previous moment LIM , get the angular velocity compensation instruction ω com , the virtual rotor angular velocity ω V and angular velocity compensation command ω com After adding, the virtual rotor angular velocity ω after compensation at the current moment is obtained VSG .

[0108] Step 4.3: The virtual rotor angular velocity ω after compensation at the current moment VSG After the integration link, the potential phase θ in the three-phase inverter is obtained VSG .

[0109] Furthermore, the angular velocity compensation instruction ω com The acquisition method is as follows:

[0110] Step 4.2.1: The known three-phase inverter output active power P e , the angular velocity ω after compensation at the last moment VSG , the AC voltage V at the grid point g , AC current I at the grid connection point g , substitute the filter inductor L into formula 1, and calculate the control phase θ of the three-phase inverter grid connection point gc .

[0111] The calculation formula of formula 1 is as follows:

[0112]

[0113] Step 4.2.2: Set the grid voltage phase θ g With θ gc After making the difference, the angular velocity compensation command ω is obtained through PI control com .

[0114] Step 4.2.3: When the current over-limit link output signal T calculated in step 6 at the previous moment LIM =1, the output angular velocity compensation command ω com , otherwise, output angular velocity compensation command ω com is 0.

[0115] When the current exceeds the limit, the angular velocity compensation control link is put into operation, which can track the phase change of the power grid while retaining the rotor motion equation link. The benefits are as follows:

[0116] 1) Since the rotor motion equation is retained, a certain phase support ability is provided when the current exceeds the limit (i.e., during the power grid fault), which can prevent the transient instability of other grid-connected inverters.

[0117] 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 phase during fault recovery and resynchronization is reduced, and the impact current during the resynchronization process is reduced.

[0118] Furthermore, the calculation formula for the internal electromotive force amplitude E of the three-phase inverter is as follows:

[0119]

[0120] Among them, K q is the reactive power integration coefficient, and s is the Laplace operator.

[0121] Furthermore, the specific steps of step 6 are as follows:

[0122] Step 6.1: Substitute the known internal electromotive force amplitude E of the three-phase inverter, the filter inductor L, the compensated virtual rotor angular velocity ω at the current moment VSG , the AC voltage value and AC current value of the grid connection point in the dq coordinate system into formula 3 to calculate the d-axis and q-axis components of the reference value of the three-phase inverter output current and

[0123] The formula 3 is calculated as follows:

[0124]

[0125] Among them, i sd and i sq are the d-axis component and q-axis component of the AC current at the grid connection point respectively, u sd and u sq are the d-axis component and q-axis component of the grid connection point AC voltage, and α is the closed-loop expected bandwidth of the current control, which can be set manually.

[0126] Step 6.2: Limit the d-axis and q-axis components and of the reference value of the three-phase inverter output current to obtain the limited d-axis and q-axis components of the current and

[0127] The d-axis and q-axis components of the current and are calculated as follows:

[0128]

[0129] Among them, is the current phase angle, and its value range is 0° to 90°, which 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 1.3 pu.

[0130] Step 6.3: Calculate the d-axis and q-axis components of the internal potential amplitude according to the current d-axis and q-axis components after amplitude limiting and

[0131] The d-axis and q-axis components u of the internal potential amplitude cd and u cq , and the calculation formula is as follows:

[0132]

[0133] Among them, H d (s) is the d-axis PI control link, H q (s) is the q-axis PI control link, and s is the Laplace operator. α is the closed-loop expected bandwidth of current control, which can be set manually.

[0134] Step 6.4: Synthesize the d-axis and q-axis components u of the internal potential amplitude cd and u cq to obtain the internal potential amplitude E' of the three-phase inverter after amplitude limiting.

[0135] Step 6.5: Judge the magnitude of and I max . When , the output signal T of the current over-limit link at the current moment LIM is 1, otherwise, the output signal T of the current over-limit link at the current moment LIM is 0.

[0136] Furthermore,

[0137] Among them, the proportional coefficients of the PI control d-axis and q-axis are: k pd =1, k pq =1; the integral coefficients of the PI control d-axis and q-axis have a value range of: 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.

[0138] For example, Figure 2As shown in the figure, the third embodiment is a grid-forming inverter switching control device with phase support ability under faults, including the following modules:

[0139] Voltage and current measurement module: It is used to obtain the AC voltage and AC current at the connection point of the three-phase inverter, and perform Park transformation on the AC voltage and AC current at the connection point to obtain the AC voltage value and AC current value at the connection point in the dq coordinate system corresponding to the physical quantities.

[0140] Power calculation module: It is used to calculate the active power P on the AC side of the three-phase inverter according to the AC voltage value and AC current value at the connection point in the dq coordinate system e and reactive power Q e .

[0141] PLL phase-locked module: It is used to calculate the grid voltage phase θ according to the three-phase voltage on the grid side g , grid voltage amplitude V g .

[0142] Internal potential phase generation module: It is used to calculate the internal potential phase θ of the three-phase inverter according to the given active power command value P of the three-phase inverter ref , grid rated angular frequency ω ref , the obtained grid voltage phase θ g , the output signal T of the current over-limit link calculated by the internal potential amplitude limiting module at the previous moment LIM , the active power P output by the three-phase inverter e , and calculate the internal potential phase θ of the three-phase inverter VSG .

[0143] Internal potential amplitude generation module: It is used to calculate the internal potential amplitude E of the three-phase inverter according to the given reactive power command value Q of the three-phase inverter ref , the reference value E0 of the grid voltage amplitude, the reactive power Q output by the three-phase inverter e , and calculate the internal potential amplitude E of the three-phase inverter.

[0144] Internal potential amplitude limiting module: It is used to calculate the limited internal potential amplitude E' of the three-phase inverter according to the internal potential amplitude E of the three-phase inverter, filter inductance L, and current limit value I of the three-phase inverter max , grid voltage amplitude V g , AC current I at the connection point g , virtual rotor angular velocity ω VSG , AC voltage value and AC current value at the connection point in the dq coordinate system, and calculate the output signal T of the current over-limit link at the current moment LIM .

[0145] Modulation module: It is used to use the limited internal potential amplitude E' of the three-phase inverter and the internal potential phase θ of the three-phase inverter VSG , with θ VSGAs the Park inverse transformation is performed with the rotation angle to obtain the modulation wave of the three-phase inverter, the modulation wave of the three-phase inverter is used to modulate the carrier signal V m to generate the switching control signal D for controlling the three-phase inverter.

[0146] Furthermore, the internal potential phase generation module consists of an analog rotor motion equation link and an angular velocity compensation control link based on the grid phase change. The specific functions are as follows:

[0147] Step 4.1: Input the active power P e output by the three-phase inverter, the active power command value P ref given by the three-phase inverter, and the grid rated angular frequency ω ref into the rotor motion equation to obtain the virtual rotor angular velocity ω V .

[0148] Step 4.2: According to the output signal T LIM of the current over-limit link calculated by the internal potential amplitude limit module at the previous moment, obtain the angular velocity compensation command ω com , add the virtual rotor angular velocity ω V to the angular velocity compensation command ω com to obtain the compensated virtual rotor angular velocity ω VSG at the current moment.

[0149] Step 4.3: Integrate the compensated virtual rotor angular velocity ω VSG at the current moment through an integration link to obtain the internal potential phase θ VSG of the three-phase inverter.

[0150] As Figure 3 shown, furthermore, the method for obtaining the angular velocity compensation command ω com is as follows:

[0151] Step 4.2.1: Input the known active power P e output by the three-phase inverter, the compensated angular velocity ω VSG at the previous moment, the AC voltage V g at the grid connection point, the AC current I g at the grid connection point, and the filter inductor L into Formula 1 to calculate the control phase θ gc at the grid connection point of the three-phase inverter.

[0152] The Formula 1 is calculated as follows:

[0153]

[0154] Step 4.2.2: Subtract the grid voltage phase θ g from θ gcAfter taking the difference, the angular velocity compensation command ω is obtained through PI control com .

[0155] Step 4.2.3: When the output signal T of the current over-limit link calculated by the potential amplitude limit module in the previous moment LIM = 1, the angular velocity compensation command ω is output com , otherwise, the angular velocity compensation command ω com is 0.

[0156] When the current is over-limit, the angular velocity compensation control link is put into operation, which can track the grid phase change while retaining the rotor motion equation link. The benefits are as follows:

[0157] 1) Since the rotor motion equation is retained, a certain phase support ability is provided during current over-limit (i.e., during grid faults), which can prevent the transient instability of other grid-connected inverters.

[0158] 2) Since the three-phase inverter tracks the grid phase change, the phase difference between the output phase of the three-phase inverter and the grid phase during fault recovery and resynchronization is reduced, and the impact current during the resynchronization process is decreased.

[0159] Furthermore, the calculation formula of the internal potential amplitude E of the three-phase inverter is as follows:

[0160]

[0161] where K q is the reactive power integration coefficient, and s is the Laplace operator.

[0162] Furthermore, the internal potential amplitude limit module adds a PI control link H(s) on the basis of the traditional current limit control strategy to improve the situation that the internal potential amplitude changes violently due to current limit during faults. Due to the inherent regulation performance of the PI control link, the transient stability of the direct voltage control type grid-forming inverter can be improved through reasonable parameter setting. The specific functions are as follows:

[0163] Step 6.1: Substitute the known internal potential amplitude E of the three-phase inverter, filter inductor L, the compensated virtual rotor angular velocity ω VSG at the current moment, the AC voltage value and AC current value of the grid connection point in the dq coordinate system into Formula 3 to calculate the d-axis and q-axis components of the output current reference value of the three-phase inverter and

[0164] Formula 3 has the following calculation formula:

[0165]

[0166] where i sd and isq are the d-axis component and q-axis component of the AC current at the point of common coupling, respectively, u sd and u sq are the d-axis component and q-axis component of the AC voltage at the point of common coupling, and α is the closed-loop desired bandwidth of the current control, which can be set manually.

[0167] Step 6.2: Limit the d-axis and q-axis components and of the reference values of the output current of the three-phase inverter to obtain the limited d-axis and q-axis components of the current and

[0168] The d-axis and q-axis components of the current and are calculated as follows:

[0169]

[0170] where is the current phase angle, with a value range of 0° to 90°, which can be set manually. I max is the current limit value of the three-phase inverter. It represents the maximum short-time overcurrent level that the three-phase inverter can withstand, usually 1.3 pu.

[0171] Step 6.3: Calculate the d-axis and q-axis components of the internal potential amplitude according to the limited d-axis and q-axis components and of the current.

[0172] The d-axis and q-axis components u cd and u cq of the internal potential amplitude are calculated as follows:

[0173]

[0174] where H d (s) is the d-axis PI control link, H q (s) is the q-axis PI control link, and s is the Laplace operator. α is the closed-loop desired bandwidth of the current control, which can be set manually.

[0175] Step 6.4: Synthesize the d-axis and q-axis components u cd and u cq of the internal potential amplitude to obtain the limited internal potential amplitude E' of the three-phase inverter.

[0176] Step 6.5: Judge and I max in size. When , the output signal T LIM of the current over-limit link at the current moment is 1; otherwise, the output signal TLIM is 0.

[0177] Furthermore,

[0178] wherein, the values of the proportional coefficients of the PI control for the d - axis and q - axis are: k pd = 1, k pq = 1; the value ranges of the integral coefficients of the PI control for the d - axis and q - axis are: 0 < k id ≤ 5, 0 < k iq ≤ 0.1, and the specific values are determined according to the results of simulation experiments. s is the Laplace operator.

[0179] Those skilled in the art should understand that the embodiments of the present invention can be provided as a method, a system, or a computer program product. Therefore, the present invention can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present invention can take the form of a computer program product implemented on one or more computer - usable storage media (including but not limited to disk memories, CD - ROMs, optical memories, etc.) containing computer - usable program code.

[0180] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general - purpose computer, a special - purpose computer, an embedded processor, or other programmable data - processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data - processing devices generate a device for realizing the functions specified in Figure 1 one or more of the flows Figure 1 one or more of the blocks.

[0181] These computer program instructions can also be stored in a computer - readable memory that can direct a computer or other programmable data - processing devices to work in a specific manner, such that the instructions stored in the computer - readable memory generate a manufactured article including an instruction device, and the instruction device realizes the functions specified in Figure 1 one or more of the flows Figure 1 one or more of the blocks.

[0182] These computer program instructions can also be loaded onto a computer or other programmable data - processing devices, such that a series of operation steps are executed on the computer or other programmable devices to generate a computer - implemented process, so that the instructions executed on the computer or other programmable devices provide for realizing the functions in Figure 1One process or multiple processes and / or boxes Figure 1 Steps of functions specified in one box or multiple boxes.

[0183] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A switching control method for a network-forming inverter with phase support ability under faults, characterized in that: It includes the following steps: Step 1: Obtain the AC voltage and AC current at the grid connection point of the three-phase inverter, and perform Park transformation on the AC voltage and AC current at the grid connection point to obtain the AC voltage value and AC current value at the grid connection point of the corresponding physical quantities in the dq coordinate system; Step 2: Calculate the active power P and reactive power Q on the AC side of the three-phase inverter according to the AC voltage value and AC current value of the grid connection point in the dq coordinate system e and the reactive power Q e ; Step 3: Calculate the grid voltage phase θ based on the three-phase grid-side voltage g , and the grid voltage amplitude V g ; Step 4: According to the active power command value P given by the three-phase inverter ref , the rated angular frequency ω of the power grid ref , the obtained phase θ of the grid voltage g , the output signal T of the current over-limit link calculated in step 6 at the previous moment LIM , the active power P output by the three-phase inverter e , calculate the phase θ of the internal electromotive force of the three-phase inverter VSG ; Step 5: According to the reactive power command value Q given by the three-phase inverter ref , the reference value E0 of the grid voltage amplitude, and the active power Q output by the three-phase inverter e , calculate the amplitude E of the internal electromotive force of the three-phase inverter; Step 6: According to the internal electromotive force amplitude E of the three-phase inverter, the filter inductance L, and the current limit amplitude I of the three-phase inverter max , the grid voltage amplitude V g , the AC current I at the grid connection point g , the virtual rotor angular velocity ω VSG , the AC voltage value and AC current value at the grid connection point in the dq coordinate system, calculate the limited internal electromotive force amplitude E' of the three-phase inverter, and the output signal T of the current over-limit link at the current moment LIM ; Step 7: Based on the amplitude E' of the internal electromotive force in the three-phase inverter after amplitude limiting and the phase θ of the internal electromotive force in the three-phase inverter VSG , using θ VSG as the rotation angle for Park inverse transformation to obtain the modulation wave of the three-phase inverter, and modulating the modulation wave of the three-phase inverter with the carrier signal V m to generate the switching control signal D for controlling the three-phase inverter.

2. The switching control method of the network-forming inverter with phase support ability under faults according to claim 1, characterized in that: For step 4, the specific steps are as follows: Step 4.1: Input the active power P output by the three-phase inverter, e the active power command value P ref given by the three-phase inverter, and the rated angular frequency ω ref of the power grid into the rotor motion equation to obtain the virtual rotor angular velocity ω V ; Step 4.2: Obtain the angular velocity compensation command ω LIM according to the output signal T of the current - limit - exceeding link of the current calculated in step 6 at the previous moment com . Add the virtual rotor angular velocity ω V and the angular velocity compensation command ω com . After addition, obtain the compensated virtual rotor angular velocity ω VSG at the current moment; Step 4.3: Integrate the compensated virtual rotor angular velocity ω at the current moment VSG to obtain the phase θ of the internal electromotive force in the three-phase inverter VSG .

3. The switching control method of the network-forming inverter with phase support ability under faults according to claim 2, characterized in that: The angular velocity compensation command ω com The acquisition method is as follows: Step 4.2.1: Substitute the known active power P output by the three-phase inverter e , the compensated angular velocity ω at the previous moment VSG , the AC voltage V at the grid connection point g , and the AC current I at the grid connection point g , and the filter inductor L into Equation 1 to calculate the control phase θ at the grid connection point of the three-phase inverter gc ; For formula 1, the calculation formula is as follows: Step 4.2.2: After taking the difference between the grid voltage phase θ g and θ gc and passing it through PI control, the angular velocity compensation command ω com is obtained; Step 4.2.3: When the output signal T of the current over-limit link calculated in step 6 at the previous moment LIM = 1, output the angular velocity compensation command ω com , otherwise, output the angular velocity compensation command ω com is 0.

4. The switching control method of the network-forming inverter with phase support ability under faults according to claim 1, characterized in that: The calculation formula for the amplitude E of the internal electromotive force in the three-phase inverter is as follows: Among them, K q is the reactive power integration coefficient, and s is the Laplace operator.

5. The switching control method of the network-forming inverter with phase support ability under faults according to claim 1, characterized in that: For step 6, the specific steps are as follows: Step 6.1: Substitute the known internal potential amplitude E of the three-phase inverter, the filter inductor L, the virtual rotor angular velocity ω compensated at the current moment, VSG the AC voltage value and AC current value of the grid connection point in the dq coordinate system into Formula 3 to calculate the d-axis and q-axis components of the reference value of the output current of the three-phase inverter and For formula 3, the calculation formula is as follows: wherein, i sd and i sq are respectively the d-axis component and the q-axis component of the alternating current at the grid connection point, u sd and u sq are the d-axis component and the q-axis component of the alternating current voltage at the grid connection point, and α is the closed-loop desired bandwidth of the current control; Step 6.2: Limit the d-axis and q-axis components of the three-phase inverter output current reference value and to obtain the limited d-axis and q-axis components of the current and d-axis and q-axis components of current and The calculation formulas are as follows: Among them, is the current phase angle; I max is the current limit value of the three-phase inverter; Step 6.3: Calculate the d-axis and q-axis components of the internal potential amplitude according to the limited current d-axis and q-axis components and ​ d-axis and q-axis components u of the internal potential amplitude cd and u cq The calculation formulas are as follows: Among them, H d (s) is the d-axis PI control link, and H q (s) is the q-axis PI control link, s is the Laplace operator; α is the closed-loop desired bandwidth of current control; Step 6.4: Synthesize the amplitude d and q-axis components u cd and u cq to obtain the amplitude E' of the internal potential of the three-phase inverter after amplitude limiting; Step 6.5: Determine the size of I max When the output signal T of the current moment current over-limit link is 1, otherwise, the output signal T of the current moment current over-limit link LIM is 0. LIM ​ 6. The switching control method of the network-forming inverter with phase support ability under faults according to claim 5, characterized in that: Among them, the values of the proportional coefficients of the PI control for the d-axis and q-axis are: k pd = 1, k pq = 1; the value range of the integral coefficients of the PI control for the d-axis and q-axis is: 0 < k id ≤ 5, 0 < k iq ≤ 0.1, where s is the Laplace operator.

7. A grid-forming inverter switching control device with phase support ability under faults, characterized in that: It includes the following modules: Voltage and current measurement module: used to obtain the AC voltage and AC current at the grid connection point of the three-phase inverter, and perform Park transformation on the AC voltage and AC current at the grid connection point to obtain the AC voltage value and AC current value at the grid connection point of the corresponding physical quantities in the dq coordinate system; Power calculation module: used to calculate the three-phase inverter's AC-side active power P based on the AC voltage value and AC current value at the grid connection point in the dq coordinate system e and reactive power Q e ; PLL phase-locked module: used to calculate the grid voltage phase θ based on the three-phase voltage on the grid side g , grid voltage amplitude V g ; Internal potential phase generation module: used to calculate the internal potential phase θ of the three-phase inverter according to the given active power command value P of the three-phase inverter ref , the rated angular frequency ω of the power grid ref , the obtained grid voltage phase θ g , the output signal T of the current over-limit link calculated by the internal potential amplitude limiting module at the previous moment LIM , the active power P output by the three-phase inverter e , calculate the internal potential phase θ of the three-phase inverter VSG ; 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 given by the three-phase inverter ref , the reference value E0 of the grid voltage amplitude, and the active power Q output by the three-phase inverter e , and calculate the internal potential amplitude E of the three-phase inverter; Internal potential amplitude limiting module: used to calculate the amplitude E' of the internal potential of the three-phase inverter after limiting according to the amplitude E of the internal potential of the three-phase inverter, the filter inductor L, the current limit amplitude I of the three-phase inverter max , the amplitude V of the grid voltage g , the AC current I at the grid connection point g , the virtual rotor angular velocity ω VSG , the AC voltage value and AC current value at the grid connection point in the dq coordinate system, and calculate the output signal T of the current over-limit link at the current moment LIM ; Modulation module: used to, according to the amplitude E' of the internal electromotive force in the three-phase inverter after amplitude limiting and the phase θ of the internal electromotive force in the three-phase inverter VSG , with θ VSG as the rotation angle for Park inverse transformation to obtain the modulation wave of the three-phase inverter, and modulate the modulation wave of the three-phase inverter with the carrier signal V m to generate the switching control signal D for controlling the three-phase inverter.

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