Fault ride-through method based on hybrid synchronous control voltage / current source mode switching

Abstract

This invention, based on a hybrid synchronous control voltage / current source mode switching fault ride-through method, addresses the challenges of fault ride-through (FRT) in emerging power systems by overcoming the limitations of existing solutions from three key dimensions: overcurrent limiting, fault synchronization, and reactive power support. Based on a hybrid synchronous control strategy, this invention significantly improves system damping characteristics, effectively ensuring the synchronous stability of the inverter during faults. Simultaneously, by utilizing the simplified detection of the current limiter's saturation signal, combined with a hybrid voltage / current source control architecture, it achieves intelligent control that enables smooth mode switching without complex switching logic or grid information. Furthermore, this invention exhibits excellent short-circuit ratio (SCR) adaptability, maintaining stable operation under varying grid strength conditions, providing an innovative solution for improving the grid-friendliness of renewable energy integration and optimizing the transient performance of power systems.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of fault ride-through, and in particular to a fault ride-through method based on mixed synchronous control voltage / current source mode switching. BACKGROUND

[0002] Grid-forming (GFM) inverters have current-following and voltage-forming characteristics, similar to traditional synchronous generators (SGs). The mainstream grid-forming control includes droop control, virtual synchronous generator (VSG) control and hybrid synchronous control (HSC). Unlike synchronous machines, which can withstand 5-7pu short-circuit current, due to the limitations of semiconductor devices, the short-circuit current of inverters can only be limited to 1.2-2pu. Overcurrent limitation is crucial for GFM inverters. At the same time, maintaining synchronization with the grid under fault conditions and providing voltage support according to grid specifications are also basic requirements for the application of GFM inverters.

[0003] Current research efforts to enhance the fault ride-through (FRT) capability of GFM inverters mainly focus on three key levels: 1) overcurrent limitation; 2) synchronization stability; 3) active fault ride-through service. Overcurrent limitation is the primary requirement to ensure the survival of inverters under fault conditions. On the basis of current limitation, the second requirement is to maintain synchronization stability, especially during faults. The third requirement is active fault ride-through service, which requires supporting frequency / voltage under fault conditions and achieving flexible fault recovery from fault operation to normal operation. This layer enables the inverter to inject fault current to contribute to grid recovery capability, in line with grid specification requirements.

[0004] The above FRT requirements divided into three control objectives are crucial for the large-scale deployment of GFM inverters. Although some methods have been proposed, a unified solution that can address all three issues simultaneously is still needed. Figure 4

[0005] Compared with the prior art, the differences are as follows:

[0006] I. Comparison with patent CN202411676429.2 "Inverter control method and system based on power value regulation";

[0007] ​Patent CN202411676429.2 provides an inverter control method and system based on power value setting. The method has clear control technology principle and small difficulty. The power instruction switching is carried out on the traditional VSG control, sufficient reactive power can be output under the premise of providing inertia support to the power grid system, and the current limiting link is added in the control link for the overcurrent problem of the inverter during the fault, so as to maintain the safe and stable operation of the inverter. However, this method only considers the problems of synchronous stability and support during fault occurrence and fault maintenance, and does not consider how the inverter switches back to the grid mode after fault recovery, which may exist the risk of not being able to exit the current limiting mode.

[0008] In the "a fault ride-through method of voltage and current source mode switching based on hybrid synchronization control" provided by the present application, only simple fusion of parameter change and control delay can realize smooth mode switching, and there is no risk of not being able to exit the current saturation.

[0009] II. Comparison with patent CN202410787854.2 "a droop control inverter current limiting control method and system";

[0010] In patent CN202410787854.2, a droop control inverter current limiting control method and system are disclosed. The virtual impedance size and active reference value constraint condition when the fault current is equal to the current limiting value are accurately obtained through phasor analysis. The virtual impedance-current difference proportional coefficient and active reference value-current difference proportional coefficient are designed considering the most serious current limiting condition. The adaptive current change during fault is proportional to increase the virtual impedance and reduce the active reference value, which can meet the current limiting requirement under different depth of power grid voltage drop. The fault current is indirectly limited through the adjustment of virtual impedance and active reference value, the voltage source characteristics of the droop control inverter are retained, and the system fault ride-through capability is significantly enhanced. However, this method cannot provide reactive power support to the power grid during fault.

[0011] In the "a fault ride-through method of voltage and current source mode switching based on hybrid synchronization control" provided by the present application, according to the grid connection criterion, sufficient reactive power is provided to support the power grid voltage during fault. SUMMARY

[0012] To address the aforementioned technical challenges, this invention proposes a fault ride-through method based on hybrid synchronous control voltage / current source mode switching. Addressing the challenges of fault ride-through (FRT) in novel power systems, this invention overcomes the limitations of existing solutions from three key dimensions: overcurrent limiting, fault synchronization, and reactive power support. Based on a hybrid synchronous control strategy, this invention significantly improves system damping characteristics, effectively ensuring the synchronous stability of the inverter during faults. Simultaneously, by utilizing the simplified detection of the current limiter's saturation signal, combined with a hybrid voltage / current source control architecture, it achieves intelligent control that enables smooth mode switching without complex switching logic or grid information. Furthermore, this invention possesses excellent short-circuit ratio (SCR) adaptability, maintaining stable operation under varying grid strength conditions, providing an innovative solution for improving the grid-friendliness of renewable energy integration and optimizing the transient performance of power systems.

[0013] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0014] The fault ride-through method based on hybrid synchronous control voltage / current source mode switching includes the following steps:

[0015] Step 1) Measure the output current and voltage of the inverter and calculate the corresponding output power P and Q;

[0016] Step 2) Determine the internal potential phase angle by measuring the inverter's output voltage and calculating the inverter's output power;

[0017] Step 3) Calculate the reference current value i output by the controlled voltage control module by measuring the output voltage of the inverter. ref1 ;

[0018] Step 4) Calculate the current reference value i output by the controlled current control module by measuring the output voltage and current of the inverter. ref2 ;

[0019] Step 5) by i ref1 and i ref2 Calculated current reference value i ref ;

[0020] Step 6) Current reference value i ref After processing by the current limiter, a limited current reference value i is generated. lim ;

[0021] Step 7) Obtain the restricted current reference value i from the previous step lim The inverter is controlled by a pulse width modulation (PWM) unit using a modulated signal.

[0022] As a further improvement to the present invention, the calculation of output power P and Q in step 1) is as follows:

[0023]

[0024]

[0025] In the formula, This refers to the active power output of the inverter. This refers to the reactive power output of the inverter. Let be the d-axis component of the inverter's output voltage in the dq coordinate system. Let q be the output voltage of the inverter in the dq coordinate system. Let d be the d-axis component of the inverter's output current in the dq coordinate system. Let q be the q-axis component of the inverter's output current in the dq coordinate system.

[0026] As a further improvement of the present invention, the internal potential phase angle in step 2) is the internal potential phase angle based on hybrid synchronous control;

[0027] The internal potential phase angle generation calculation based on hybrid synchronous control is as follows:

[0028]

[0029] Where θ represents the reference angle generated by hybrid synchronous control, used for the dq / abc variation in inverter control, ɷ n and ɷ v P represents the reference angular frequency and the output angular frequency, respectively. ref P and V are the inverter's active power reference value and output active power, respectively. pcc_q This represents the q-axis component of the output voltage at the PCC, where m is the droop active power factor and k is the input voltage. pcc_q coefficient.

[0030] As a further improvement of the present invention, in step 3), the controlled voltage source control module uses PI voltage control to obtain the current reference value i output by the controlled voltage control module. ref1 :

[0031]

[0032] Among them, i dref1 and i qref1 The current reference value i output by the controlled voltage control module ref1 The components on the d-axis and q-axis, k vp and k vi These are the proportional and integral parameters of the controlled voltage source loop, E ref This represents the reference value for voltage amplitude, v. pcc_d V represents the d-axis component of the output voltage at point PCC. pcc_qThe q-axis component of the output voltage at point PCC is represented, where s is the Laplace operator, and i dref1 and i qref1 The current reference value is calculated by the controlled voltage source control module.

[0033] As a further improvement of the present invention, in step 4), the controlled current control module adopts decoupled PQ control to obtain the current reference value i output by the controlled current control module. ref2 :

[0034]

[0035] Among them, i dref2 and i qref2 The current reference value i calculated by the controlled current source control module ref2 Components on the d-axis and q-axis, P * lim and Q * lim These represent the reference values ​​for active and reactive power, respectively, v pcc_d V represents the d-axis component of the output voltage at point PCC. pcc_q This represents the q-axis component of the output voltage at point PCC.

[0036] To meet power grid specifications, P * lim and Q * lim The design is as follows:

[0037]

[0038] Among them, S rated V represents the rated apparent output power, and λ represents the voltage sag ratio when reactive power is injected into the grid, as typically defined in grid specifications. g P is the grid voltage. ref This is the active power reference value of the inverter, E is the internal potential voltage, and ɷ n and ɷ v These represent the reference angular frequency and the output angular frequency, respectively, and m is the active droop coefficient.

[0039] As a further improvement of the present invention, the current reference value i in step 5) ref ;

[0040]

[0041] Where D represents the ratio between the controlled voltage source and the controlled current source loop;

[0042] When a fault occurs, the current limiter triggers current limiting and generates a mode switching signal, adjusting D from 0.5 to 1, thereby switching the inverter from hybrid voltage / current source mode to current source mode. After the fault is cleared, when P returns to P... ref Afterwards, the switching is delayed for a period of time to avoid transient oscillations. The inverter activation mode is switched, and D changes from 1 to 0.5.

[0043] As a further improvement of the present invention, the restricted current reference value i in step 6) lim ;

[0044] .

[0045] Among them, I max The maximum current amplitude set for the inverter, i dref and i qref These are the current reference values ​​i ref Components on the d-axis and q-axis.

[0046] Beneficial effects:

[0047] This invention proposes a fault ride-through method based on hybrid synchronous control for voltage / current source mode switching. This method significantly enhances system damping, effectively solves the synchronous stability problem of inverters during faults, and achieves intelligent and smooth mode switching without complex switching logic or additional grid information. It robustly suppresses overcurrent and provides effective reactive power support to maintain voltage. At the same time, its excellent short-circuit ratio (SCR) adaptability ensures stable operation under different grid strength conditions, significantly improves the friendliness of new energy grid integration, and optimizes the transient performance of the power system. Attached Figure Description

[0048] Figure 1 This is a flowchart of the present invention;

[0049] Figure 2 This is a schematic diagram of the control scheme of the present invention;

[0050] Figure 3 This is a diagram of mode switching signals;

[0051] Figure 4 The hierarchical structure required for the FRT of the GFM inverter;

[0052] Figure 5 Diagram of the experimental platform;

[0053] Figure 6 The voltage and current waveforms are shown during the fault occurrence phase.

[0054] Figure 7 The output power and frequency response diagrams during the fault period are shown.

[0055] Figure 8 The voltage and current waveforms are shown after the fault has been cleared.

[0056] Figure 9 The output power and frequency response diagrams are shown after the fault is cleared. Detailed Implementation

[0057] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0058] This invention proposes a fault ride-through method based on voltage / current source mode switching using hybrid synchronous control, as shown in the flowchart below. Figure 1 As shown. Figure 1 In the diagram, the purple box represents the synchronization control module, which generates the inverter phase angle through hybrid synchronization control; the yellow box represents the controlled voltage source control module, which generates current reference value 1; the green box represents the controlled current source control module, which generates current reference value 2; and then, through weighted mixing, the final current reference value is generated; the white box represents the mode switching control module.

[0059] First, construct the hybrid synchronous control loop for the grid-connected (GFM) inverter; second, design the hybrid voltage / current source control architecture; third, refine the mode switching loop and current limiter. The specific steps are as follows:

[0060] 1. Based on hybrid synchronous control, generate the phase angle for inverter dq / abc conversion:

[0061] The synchronization loop used to generate the phase angle θ of the abc / dq transformation is based on v pcc_q The hybrid synchronous control formula is as follows:

[0062]

[0063] Where θ represents the reference angle generated by hybrid synchronous control, used for the dq / abc variation in inverter control. ref and ɷ represent the angular frequency reference value and the output angular frequency, respectively. P ref P and V represent the inverter's active power reference value and output active power, respectively. pcc_q This represents the q-axis component of the output voltage at the PCC. m is the droop active power factor, and k is the input voltage. pcc_q coefficient.

[0064] 2. Design a hybrid voltage / current source control architecture:

[0065] Hybrid voltage / current source loop is used to generate current reference value i ref It consists of two parts: generating i ref1 Controlled voltage source control and generation of i ref2 Controlled current source control.

[0066] The controlled voltage source control uses conventional PI voltage control:

[0067]

[0068] Where, k vp and k vi These are the proportional and integral parameters of the controlled voltage source loop, respectively. E ref This indicates the reference value for voltage amplitude. pcc_d This represents the d-axis component of the output voltage at point PCC.

[0069] Controlled current source control uses decoupled PQ control to obtain the current reference value i. ref2 :

[0070]

[0071] Among them, P * lim and Q * lim These represent the reference values ​​for active and reactive power, respectively. To meet power grid specifications, and because P... * lim and Q * lim The design is as follows:

[0072]

[0073]

[0074] Among them, S rated V represents the rated apparent output power, and λ represents the voltage sag ratio when reactive power is injected into the grid, as typically defined in grid specifications. g This is the grid voltage.

[0075] 3. Mode switching control:

[0076] Current reference value i ref is i ref1 and i ref2 The weighted average is shown below:

[0077]

[0078] Where D represents the ratio between the controlled voltage source and the controlled current source loop.

[0079] Changes in D Figure 3As shown. When a fault occurs, the current limiter triggers current limiting and generates a mode switching signal, adjusting D from 0.5 to 1, thereby switching the inverter from hybrid voltage / current source mode to current source mode. After the fault is cleared, when P returns to P... ref Afterwards, the switching is delayed for a period of time to avoid transient oscillations. The inverter activation mode is switched, and D changes from 1 to 0.5.

[0080] 4. Circular limiter:

[0081] Current reference value i ref After processing by the current limiter, a limited current reference value i is generated. lim :

[0082] .

[0083] The inverter is controlled by a pulse width modulation (PWM) unit using a modulated signal.

[0084] A schematic diagram of a fault ride-through scheme based on voltage / current source mode switching using hybrid synchronous control is shown below. Figure 2 As shown.

[0085] 5. Experimental verification

[0086] Experiments were conducted using an RTU-BOX and an RTI-INV8020IR inverter to verify the feasibility of the proposed method. The experimental platform configuration is as follows: Figure 5 As shown. The inverter's switching frequency is 10kHz. A three-phase grid voltage drop to 0.25 pu is selected as the fault condition.

[0087] Figure 6 and Figure 7 Experimental results under the proposed control scheme are presented. The proposed control scheme effectively limits the output current within a threshold range under fault conditions. During a fault, the inverter's active power drops to near zero, while the reactive power reaches 206 Var, meeting the core requirements of the power grid. Furthermore, after a small fluctuation, the inverter's frequency remains consistent with the grid frequency, and the inverter maintains synchronization with the grid system.

[0088] Figure 8 and Figure 9 The experimental waveforms of the proposed control scheme after fault clearance are shown. After fault clearance, the inverter's output power recovers rapidly. Subsequently, the inverter activates mode switching, recovers quickly, and the mode switching is smooth with minimal oscillation.

[0089] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any modifications or equivalent changes made based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A fault ride-through method based on hybrid synchronous control voltage / current source mode switching, characterized in that, Includes the following steps: Step 1) Measure the output current and voltage of the inverter and calculate the corresponding output power P and Q; Step 2) Determine the internal potential phase angle by measuring the inverter's output voltage and calculating the inverter's output power; Step 3) Calculate the reference current value i output by the controlled voltage control module by measuring the output voltage of the inverter. ref1 ; In step 3), the controlled voltage source control module uses PI voltage control to obtain the current reference value i output by the controlled voltage control module. ref1 : ； Among them, i dref1 and i qref1 The current reference value i output by the controlled voltage control module ref1 The components on the d-axis and q-axis, k vp and k vi These are the proportional and integral parameters of the controlled voltage source loop, E ref This represents the reference value for voltage amplitude, v. pcc_d V represents the d-axis component of the output voltage at point PCC. pcc_q The q-axis component of the output voltage at point PCC is represented, where s is the Laplace operator, and i dref1 and i qref1 The current reference value is calculated by the controlled voltage source control module; Step 4) Calculate the current reference value i output by the controlled current control module by measuring the output voltage and current of the inverter. ref2 ; In step 4), the controlled current control module uses decoupled PQ control to obtain the current reference value i output by the controlled current control module. ref2 : ； Among them, i dref2 and i qref2 The current reference value i calculated by the controlled current source control module ref2 Components on the d-axis and q-axis, P * lim and Q * lim These represent the reference values ​​for active and reactive power, respectively, v pcc_d V represents the d-axis component of the output voltage at point PCC. pcc_q This represents the q-axis component of the output voltage at point PCC. To meet power grid specifications, P... * lim and Q * lim The design is as follows: ； ； Among them, S rated V represents the rated apparent output power, and λ represents the voltage sag ratio when reactive power is injected into the grid, as typically defined in grid specifications. g P is the grid voltage. ref This is the active power reference value of the inverter, E is the internal potential voltage, and ɷ n and ɷ v These represent the reference angular frequency and the output angular frequency, respectively, where m is the active power droop coefficient; Step 5) by i ref1 and i ref2 Calculated current reference value i ref ; Step 6) Current reference value i ref After processing by the current limiter, a limited current reference value i is generated. lim ; Step 7) Obtain the restricted current reference value i from the previous step lim The inverter is controlled by a pulse width modulation (PWM) unit using a modulated signal.

2. The fault ride-through method based on hybrid synchronous control voltage / current source mode switching according to claim 1, characterized in that, The output power P and Q in step 1) are calculated as follows: ； ； In the formula, This refers to the active power output of the inverter. This refers to the reactive power output of the inverter. Let be the d-axis component of the inverter's output voltage in the dq coordinate system. Let q be the output voltage of the inverter in the dq coordinate system. Let d be the d-axis component of the inverter's output current in the dq coordinate system. Let q be the q-axis component of the inverter's output current in the dq coordinate system.

3. The fault ride-through method based on hybrid synchronous control voltage / current source mode switching according to claim 1, characterized in that, In step 2), the internal potential phase angle is the internal potential phase angle based on hybrid synchronous control; The internal potential phase angle generation calculation based on hybrid synchronous control is as follows: ； Where θ represents the reference angle generated by hybrid synchronous control, used for the dq / abc variation in inverter control, ɷ n and ɷ v P represents the reference angular frequency and the output angular frequency, respectively. ref P and V are the inverter's active power reference value and output active power, respectively. pcc_q This represents the q-axis component of the output voltage at the PCC, where m is the droop active power factor and k is the input voltage. pcc_q coefficient.

4. The fault ride-through method based on hybrid synchronous control voltage / current source mode switching according to claim 1, characterized in that, In step 5), the current reference value i ref ; ； ； Where D represents the ratio between the controlled voltage source and the controlled current source loop; When a fault occurs, the current limiter triggers current limiting and generates a mode switching signal, adjusting D from 0.5 to 1, thereby switching the inverter from hybrid voltage / current source mode to current source mode. After the fault is cleared, when P returns to P... ref Afterwards, the switching is delayed for a period of time to avoid transient oscillations. The inverter activation mode is switched, and D changes from 1 to 0.

5.

5. The fault ride-through method based on hybrid synchronous control voltage / current source mode switching according to claim 1, characterized in that, In step 6), the reference value of the restricted current i lim ; ； Among them, I max The maximum current amplitude set for the inverter, i dref and i qref These are the current reference values ​​i ref Components on the d-axis and q-axis.

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