Virtual three-phase networking control method for four-bridge-arm single-phase modular multilevel converter

Abstract

The invention belongs to the technical field of railway traction power supply systems, and particularly relates to a virtual three-phase networking control method for a four-bridge-arm single-phase modular multilevel converter, which comprises the following steps of: constructing a virtual C phase by using a virtual three-phase construction method, and combining the virtual C phase with an alternating current side synchronous control link to obtain virtualized output current and output voltage; performing dq coordinate transformation on the virtualized output current and output voltage to obtain reference voltage; the reference voltage serves as input and is fed into voltage and current double-closed-loop control, and differential mode voltage is obtained; two-phase four bridge arm voltage reference values are calculated by using the differential mode voltage, and pulse signals are output through a modulation link to trigger each sub-module of the MMC. The problems of high calculation complexity and poor dynamic response capability of single-phase side PR control are solved; the control architecture of the three-phase side and the single-phase side of the three-phase-single-phase MMC converter is unified, and the design complexity of a related control system is simplified.

Description

Technical Field

[0001] The present invention belongs to the technical field of railway traction power supply systems, and in particular relates to a virtual three-phase network control method for a four-bridge-arm single-phase modular multi-level converter. Background Art

[0002] Traction power supply systems are a crucial component of high-speed railways. Co-phase power supply solutions based on power electronic conversion technology have become a new trend in the development of railway traction power supply systems, as they can address the issue of excessive phase separation. With the development and widespread application of modular multilevel converter technology, the modular multilevel converter-through-phase solution (MMC-TC-TTPS) based on three-phase to single-phase MMC conversion offers significant advantages, such as low switching frequency, low losses, and low harmonic content. It is considered a key solution for achieving co-phase power supply in traction power supply systems.

[0003] The existing MMC control strategies mainly include active-reactive (PQ) control, DC voltage-reactive (Udc-Q) control, and voltage-frequency (Vf) control. The control strategy for the three-phase side of the MMC-TC-TTPS will adopt a control strategy based on the PI controller according to specific needs. The PI controller is suitable for DC systems or dq rotating coordinate systems. Therefore, in the three control methods, the relevant variables need to be transformed into a rotating coordinate system (dq coordinate system) to control the relevant variables. The control strategy based on the PR controller on the single-phase side is based on the stationary abc coordinate system, but it requires the design of a high-order resonant link, while considering harmonic compensation and digital implementation with higher computational complexity.

[0004] Some existing research addresses the high voltage quality requirements on the single-phase side by using PQ control or Udc-Q control to ensure controllable amplitude and phase of the AC output voltage. Others employ direct voltage control strategies to ensure stable output voltage amplitude and constant frequency. However, these strategies vary in difficulty and control effectiveness, making them inapplicable to all.

[0005] Existing single-phase MMC control methods based on PR control primarily rely on the control of AC signals. This requires additional settings for the resonant bandwidth (ωc) and resonant gain (Kr), making parameter optimization complex and debugging challenging. Furthermore, PR controllers cannot simultaneously compensate for multiple harmonics and require additional DC compensation. Furthermore, in terms of digital complexity, PR controllers require the use of more complex discretization methods, such as the Tustin transform. Consequently, PR controllers have drawbacks in terms of computational complexity and dynamic response.

[0006] The four-leg single-phase modular multilevel converter (MMC) is a key component of three-phase-to-single-phase MMC converters and face-to-face high- and medium-voltage modular multilevel DC transformers. Existing four-leg single-phase MMCs typically employ a control architecture based on a PR controller. PR control suffers from significant frequency influences, complex control processes, and complex parameter design. This is particularly true for three-phase-to-single-phase MMC converters. Since the three-phase side primarily utilizes a PI-based control architecture, if the single-phase side adopts a PR-based control architecture, the control architectures for the three-phase and single-phase sides differ, significantly increasing the complexity of the converter control system design.

[0007] Therefore, a virtual three-phase network control method for four-leg single-phase modular multilevel converters is urgently needed. The control method of four-leg single-phase MMC should be improved to solve the problems of high computational complexity and poor dynamic response capability of single-phase PR control; the control architecture of the three-phase and single-phase sides of the three-phase-single-phase MMC converter should be unified to simplify the design complexity of the related control systems. Summary of the Invention

[0008] The present invention aims to provide a virtual three-phase network control method for a four-arm single-phase modular multilevel converter, comprising the following steps:

[0009] Use the virtual three-phase construction method to construct the virtual C phase, combine the virtual C phase with the AC synchronous control link, and obtain the virtual output current i abc and output voltage u abc ;

[0010] The output current i after virtualization abc and output voltage u abc Perform dq coordinate transformation to obtain reference voltage u d_ref and u q_ref ;

[0011] The reference voltage u d_ref and u q_ref As input to the voltage and current double closed loop control, the differential mode voltage u diff_d and u diff_q ;

[0012] Using the differential mode voltage u diff_d and u diff_q Calculate the voltage reference value u of the four bridge arms of the two phases ap 、u an 、u bp 、u bn , the pulse signal output by the modulation link triggers each sub-module of the MMC.

[0013] The method of constructing a virtual C phase using a virtual three-phase construction method includes:

[0014] Based on the assumption of ABC three-phase symmetry, we get: a +u b +u c =0,i a +i b +i c =0;

[0015] The known quantity is obtained by measurement, which is the original voltage and current u of phase A and B. a 、u b 、i a 、i b ;

[0016] Construct a virtual C phase from known quantities:

[0017]

[0018] Combine the virtual phase C with the measured phases A and B to get the virtual output voltage u abc And the output current i after virtual abc ;

[0019] Where u a is the output voltage of phase A; u b is the output voltage of phase B; u c is the output voltage of the virtual C phase; i a is the output current of phase A; i b is the output current of phase B; i c is the output current of virtual phase C; u d is the d-axis output voltage; u q is the q-axis output voltage; i d is the output current of d axis; i q is the output current of the q axis.

[0020] The reference voltage u is obtained d_ref and u q_ref The specific steps are:

[0021] The virtual output voltage u abc And the output current i after virtual abc After dq coordinate transformation, we get u d 、u q and i d 、i q ;

[0022] u d =U m cosωt,u q =U m sinωt;i d =Im cosωt,i q =I m sinωt

[0023] Calculate the phase angle θ generated in the dq coordinate transformation, and generate the phase angle θ by controlling the frequency through the controller;

[0024] θ=2πft

[0025] Where, f is the frequency of Vf network control, f = 50Hz;

[0026] Calculate the MMC submodule capacitor voltage as Amplitude u peak for

[0027] After dq coordinate transformation, the reference voltage u is obtained d_ref 、u q_ref .

[0028] The reference voltage u d_ref and u q_ref As input to the voltage and current double closed loop control, the differential mode voltage u diff_d and u diff_q The specific steps include:

[0029] The reference voltage u d_ref and u q_ref Send it into the voltage and current double closed-loop control link;

[0030] In the voltage outer loop u d_ref and u q_ref Respectively with u d 、u q Producing a difference Δu d , Δu q , get the current reference value i under the dq coordinate axis d_ref 、i q_ref ;

[0031] In the inner ring of the inner flow, i d_ref 、i q_ref with i d 、i q Producing a difference Δi d , Δi q After the PI controller, the differential mode voltage u in dq coordinates is further obtained diff_d and u diff_q .

[0032] The differential mode voltage u diff_d and u diff_q Calculate the voltage reference value u of the four bridge arms of the two phases ap 、u an、u bp 、u bn The specific steps include:

[0033] Input differential mode voltage u diff_d and u diff_q , use the Park inverse transformation to perform coordinate transformation and calculate the reference voltage of the upper and lower bridge arms of phases A and B:

[0034]

[0035] Where, are the per-unit values ​​of the output voltages of the upper and lower bridge arms of phase j respectively; u dcN Indicates the DC voltage rating.

[0036] The method of outputting a pulse signal through a modulation link to trigger each sub-module of the MMC specifically includes: finally using the NLC to generate a pulse signal and transmitting it to the MMC sub-module.

[0037] Another object of the present invention is to disclose a computer-readable storage medium having a computer program / instruction stored thereon, which, when executed by a processor, implements the steps of the virtual three-phase network control method of the four-arm single-phase modular multilevel converter described in the present invention.

[0038] Another object of the present invention is to disclose a computer program product, comprising a computer program / instruction, which, when executed by a processor, implements the steps of the virtual three-phase network control method of the four-arm single-phase modular multilevel converter of the present invention.

[0039] The beneficial effects of the present invention are:

[0040] The application of the virtual three-phase network control method of the four-bridge-arm single-phase modular multi-level converter disclosed in the present invention has the following beneficial effects:

[0041] 1. The construction method is simple and applicable to most single-phase to three-phase MMC through-phase systems, with universal applicability;

[0042] 2. After constructing the virtual three-phase, the single-phase side control strategy can directly adopt the three-phase side control strategy, which simplifies the design steps and improves the control accuracy and control efficiency of the system.

[0043] 3. Solve the shortcomings of conventional control of four-arm single-phase modular multilevel converters, such as being greatly affected by frequency factors, complex control process, and complex parameter design. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Schematic diagram of the flow of a virtual three-phase network control method for a four-arm single-phase modular multilevel converter according to the present invention;

[0045] Figure 2 This is a topology diagram of the single-phase side of the MMC-TC-TTPS according to an embodiment of the present invention;

[0046] Figure 3 This is a schematic diagram of the single-phase side control logic of the MMC-TC-TTPS according to an embodiment of the present invention;

[0047] Figure 4 A schematic flow chart of a method for constructing a single-phase side virtual three-phase structure according to an embodiment of the present invention;

[0048] Figure 5 Schematic diagram of Matlab / Simulink simulation results of an embodiment of the present invention. DETAILED DESCRIPTION

[0049] The present invention provides a virtual three-phase network control method for a four-arm single-phase modular multilevel converter, which is further described in detail below with reference to the accompanying drawings.

[0050] like Figure 1 The embodiment of the present invention disclosed herein discloses a virtual three-phase network control method for a four-leg single-phase modular multilevel converter, comprising the following steps:

[0051] Use the virtual three-phase construction method to construct the virtual C phase, combine the virtual C phase with the AC synchronous control link, and obtain the virtual output current i abc and output voltage u abc ;

[0052] The output current i after virtualization abc and output voltage u abc Perform dq coordinate transformation to obtain reference voltage u d_ref and u q_ref ;

[0053] The reference voltage u d_ref and u q_ref As input to the voltage and current double closed loop control, the differential mode voltage u diff_d and u diff_q ;

[0054] Using the differential mode voltage u diff_d and u diff_q Calculate the voltage reference value u of the four bridge arms of the two phases ap 、u an 、u bp 、u bn , the pulse signal output by the modulation link triggers each sub-module of the MMC.

[0055] In this embodiment, a virtual three-phase construction method is provided to implement a virtual three-phase MMC control method based on Vf network control. When designing the control strategy on the three-phase side, Vf network control uses park transformation to transform the coordinates. At this time, only the currents of the d and q axes are considered, and the 0 axis is not considered. This indicates that the system does not allow zero-sequence current to flow, so the three-phase currents are linearly related (that is, the sum of the three-phase currents is 0). Based on this principle, when transforming the coordinates of a single-phase system, a virtual C phase is established using the assumption of three-phase symmetry (that is, the sum of the three-phase currents is 0), which is combined with the actual A and B phases to obtain a virtual V abc and I abc , and then participate in the subsequent control links.

[0056] The following is a detailed explanation of each step.

[0057] First, the virtual three-phase construction method is used to construct the virtual C phase, and the virtual C phase is combined with the AC synchronous control link to obtain the virtual output current i abc and output voltage u abc ;

[0058] The method of constructing a virtual C phase using a virtual three-phase construction method includes:

[0059] Based on the assumption of ABC three-phase symmetry, we get: a +u b +u c =0,i a +i b +i c =0;

[0060] The known quantity is obtained by measurement, which is the original voltage and current u of phase A and B. a 、u b 、i a 、i b ;

[0061] Construct a virtual C phase from known quantities:

[0062]

[0063] Combine the virtual phase C with the measured phases A and B to get the virtual output voltage u abc And the output current i after virtual abc ;

[0064] Where u a is the output voltage of phase A; u b is the output voltage of phase B; u c is the output voltage of the virtual C phase; i a is the output current of phase A; i bis the output current of phase B; i c is the output current of virtual phase C; u d is the d-axis output voltage; u q is the q-axis output voltage; i d is the output current of d axis; i q is the output current of the q axis.

[0065] In this embodiment, based on the three-phase symmetry assumption (u a +u b +u c =0,i a +i b +i c = 0,) construct a virtual C phase and calculate u c 、i c , combined with the A and B phase output currents and output voltages obtained from the AC synchronous control link, the constructed virtual u abc 、i abc .

[0066] The virtual output voltage u abc And the output current i after virtual abc The vector form of is:

[0067]

[0068] In this embodiment, the specific principles are as follows: The topology of the single-phase side of MMC-TC-TTPS is as follows: Figure 2 The control logic of the single-phase side of MMC-TC-TTPS is as shown. Figure 3 shown.

[0069] The original voltage and current u of phase A and B are obtained by measuring a 、u b 、i a 、i b Based on the assumption of ABC three-phase symmetry, we know that: u a +u b +u c =0,i a +i b +i c = 0, so the virtual C phase can be constructed by the known quantities:

[0070]

[0071] Combine the virtual phase C with the measured phases A and B to obtain the newly generated u abc 、i abc .

[0072] Secondly, the output current i abcand output voltage u abc Perform dq coordinate transformation to obtain reference voltage u d_ref and u q_ref ;

[0073] The reference voltage u is obtained d_ref and u q_ref The specific steps are:

[0074] The virtual output voltage u abc And the output current i after virtual abc After dq coordinate transformation, we get u d 、u q and i d 、i q ;

[0075] u d =U m cosωt,u q =U m sinωt;i d =I m cosωt,i q =I m sinωt

[0076] Calculate the phase angle θ generated in the dq coordinate transformation, and generate the phase angle θ by controlling the frequency through the controller;

[0077] θ=2πft

[0078] Where, f is the frequency of Vf network control, f = 50Hz;

[0079] Calculate the MMC submodule capacitor voltage as Amplitude u peak for

[0080] After dq coordinate transformation, the reference voltage u is obtained d_ref 、u q_ref .

[0081] In this embodiment, when generating the ABC phase voltage reference value u abc_ref When the amplitude u peak Calculated as peak value; at the same time u abc 、u abc_ref The reference value used in the per-unit calculation when performing dq coordinate transformation is u peak。

[0082] In this embodiment, u abc 、i abc After dq coordinate transformation, we get u d 、u q and id 、i q ; Since the frequency ω is a constant value in the Vf network control, the phase angle can be directly obtained by θ=2πω; at the same time u abc After dq coordinate transformation, we get u d 、u q , thus obtaining u d_ref 、u q_ref .

[0083] In this embodiment, the reference voltage u is obtained d_ref 、u q_ref The steps include:

[0084] u d =U m cosωt,u q =U m sinωt;

[0085] To calculate the reference voltage of the dq axis, we first need to calculate the reference voltage in the abc coordinate system according to the rated capacity of the system, and then perform per-unit processing and convert u abc_ref Convert to u d_ref 、u q_ref。

[0086] ud _re f=u pea kcosωt,u q_re f=u pea ksinωt

[0087] Where ω is the angular frequency 2πf.

[0088] The control block diagram of the specific control principle of the single-phase side is as follows Figure 4 As shown, Figure 4 in u a 、u b 、i a 、i b They are the output voltage and output current of phase A and B of the synchronous control link, realizing the virtual three-phase construction method on the single-phase side.

[0089] In this embodiment, since the target frequency ω in the Vf network control is a constant value of 50Hz, the phase angle generated in the dq coordinate transformation can be directly obtained by θ=2πω, and then the phase-locked angle can be obtained by integration. The capacitor voltage of the MMC submodule is Amplitude u peak for After dq coordinate transformation, the reference voltage u is obtained d_ref 、u q_ref .

[0090] Again, the reference voltage u d_ref and uq_ref As input to the voltage and current double closed loop control, the differential mode voltage u diff_d and u diff_q ;

[0091] The reference voltage u d_ref and u q_ref As input to the voltage and current double closed loop control, the differential mode voltage u diff_d and u diff_q The specific steps include:

[0092] The reference voltage u d_ref and u q_ref Send it into the voltage and current double closed-loop control link;

[0093] In the voltage outer loop u d_ref and u q_ref Respectively with u d 、u q Producing a difference Δu d , Δu q , get the current reference value i under the dq coordinate axis d_ref 、i q_ref ;

[0094] In the inner ring of the inner flow, i d_ref 、i q_ref with i d 、i q Producing a difference Δi d , Δi q After the PI controller, the differential mode voltage u in dq coordinates is further obtained diff_d and u diff_q .

[0095] In this embodiment, the voltage and current double closed loop method in the prior art is used to obtain the differential mode voltage u under the dq coordinates. diff_d and u diff_q。

[0096] In this embodiment, u d_ref 、u q_ref As input to the voltage and current double closed loop control, the differential mode voltage u diff_d 、u diff_q . Set the reference voltage u d_ref 、u q_ref In the voltage outer loop, u d_ref 、u q_ref Respectively with u d 、u q Producing a difference Δu d , Δu q , get the current reference value i under the dq coordinate axis d_ref 、iq_ref ; In the inner loop of the inner flow, i d_ref 、i q_ref with i d 、i q Producing a difference Δi d , Δi q , after passing through the PI controller, the differential mode voltage in the dq coordinates is further obtained.

[0097] Finally, using the differential mode voltage u diff_d and u diff_q Calculate the voltage reference value u of the four bridge arms of the two phases ap 、u an 、u bp 、u bn , the pulse signal output by the modulation link triggers each sub-module of the MMC.

[0098] The differential mode voltage u diff_d and u diff_q Calculate the voltage reference value u of the four bridge arms of the two phases ap 、u an 、u bp 、u bn The specific steps include:

[0099] Input differential mode voltage u diff_d and u diff_q , use the Park inverse transformation to perform coordinate transformation and calculate the reference voltage of the upper and lower bridge arms of phases A and B:

[0100]

[0101] Where, are the per-unit values ​​of the output voltages of the upper and lower bridge arms of phase j respectively; u dcN Indicates the DC voltage rating.

[0102] The method of outputting a pulse signal through a modulation link to trigger each sub-module of the MMC specifically includes: finally using the NLC to generate a pulse signal and transmitting it to the MMC sub-module.

[0103] In this embodiment, the differential mode voltage u diff_d 、u diff_q Calculate the voltage reference value u of the four bridge arms of the two phases ap 、u an 、u bp 、u bn The modulation link outputs a pulse signal to trigger each MMC submodule. After obtaining the differential mode voltage, the inverse Park transform is used to transform the coordinates and obtain the reference voltages of the upper and lower bridge arms of phases A and B according to the following formula.

[0104]

[0105] in are the per-unit values ​​of the output voltages of the upper and lower bridge arms of phase j respectively; u dcN Finally, the NLC generates a pulse signal and transmits it to the MMC submodule.

[0106] Another embodiment of the present invention discloses a computer-readable storage medium having a computer program / instruction stored thereon. When the computer program / instruction is executed by a processor, the steps of the four-arm single-phase modular multilevel converter virtual three-phase network control method of the present invention are implemented.

[0107] Another aspect of the present invention discloses a computer program product, comprising a computer program / instruction, which, when executed by a processor, implements the steps of the four-arm single-phase modular multilevel converter virtual three-phase network control method of the present invention.

[0108] To verify the effectiveness of the virtual three-phase network control method for a four-arm single-phase modular multilevel converter disclosed in the present invention, the following simulation test was conducted. The specific process of the simulation test is as follows:

[0109] The present invention is experimentally verified based on Matlab / Simulink simulation, and the specific simulation parameters are shown in Table 1.

[0110] Table 1 Simulation parameters

[0111]

[0112] The present invention is based on the simulation results of Matlab / Simulink. Figure 5 shown.

[0113] It is proved that the virtual three-phase network control method of the four-arm single-phase modular multilevel converter disclosed in the present invention enables the PI controller which is not applicable to single-phase to be used by virtual three-phase. Figure 5 It is shown that the simulation system can reach steady state in a relatively short time, which proves the feasibility of the method.

[0114] Simulation results demonstrate that this invention improves the control method for a four-leg single-phase MMC converter and proposes a virtual three-phase-based network control method. This method addresses the high computational complexity and poor dynamic response of single-phase PR control. Furthermore, the proposed network control method unifies the control architectures for both the three-phase and single-phase sides of a three-phase-to-single-phase MMC converter, simplifying the design complexity of the associated control systems.

[0115] The disclosed method for virtual three-phase network control of a four-arm single-phase modular multilevel converter can unify the control of both single-phase and three-phase systems, eliminating the need to design separate control strategies for both sides or simplify the single-phase control strategy. This improves the control accuracy and efficiency of the system while reducing the complexity of system design. This method also possesses strong universality and does not affect the choice of system control strategy under different design objectives. It can address the shortcomings of conventional control of four-arm single-phase modular multilevel converters, such as their significant frequency influence, high digital complexity, and complex parameter design.

Claims

1. A virtual three-phase network control method for a four-arm single-phase modular multilevel converter, characterized in that: The steps include: Use the virtual three-phase construction method to construct the virtual C phase, combine the virtual C phase with the AC synchronous control link, and obtain the virtual output current i abc and output voltage u abc ; The output current i after virtualization abc and output voltage u abc Perform dq coordinate transformation to obtain reference voltage u d_ref and u q_ref ; The reference voltage u d_ref and u q_ref As input to the voltage and current double closed loop control, the differential mode voltage u diff_d and u diff_q ; Using differential mode voltage u diff_d and u diff_q Calculate the voltage reference value u of the four bridge arms of the two phases ap 、u an 、u bp 、u bn , the pulse signal output by the modulation link triggers each sub-module of the MMC.

2. The virtual three-phase network control method of a four-arm single-phase modular multilevel converter according to claim 1 is characterized in that: The method of constructing a virtual C phase using a virtual three-phase construction method includes: Based on the assumption of ABC three-phase symmetry, we get: u a +u b +u c =0,i a +i b +i c =0; The known quantity is obtained by measurement, which is the original voltage and current u of phase A and B. a 、u b 、i a 、i b ; Construct a virtual C phase from known quantities: Combine the virtual phase C with the measured phases A and B to get the virtual output voltage u abc And the output current i after virtual abc ; Where u a is the output voltage of phase A; u b is the output voltage of phase B; u c is the output voltage of the virtual C phase; i a is the output current of phase A; i b is the output current of phase B; i c is the output current of virtual phase C; u d is the d-axis output voltage; u q is the q-axis output voltage; i d is the output current of d axis; i q is the output current of the q axis.

3. The virtual three-phase network control method of a four-arm single-phase modular multilevel converter according to claim 1, characterized in that: The reference voltage u is obtained d_ref and u q_ref The specific steps are: The virtual output voltage u abc And the output current i after virtual abc After dq coordinate transformation, we get u d 、u q and i d 、i q ; u d =U m cosωt,u q =U m sinωt;i d =I m cosωt,i q =I m sinωt Calculate the phase angle θ generated in the dq coordinate transformation, and generate the phase angle θ by controlling the frequency through the controller; θ=2πft Where, f is the frequency of Vf network control, f = 50Hz; Calculate the MMC submodule capacitor voltage as Amplitude u peak for After dq coordinate transformation, the reference voltage u is obtained d_ref 、u q_ref .

4. The virtual three-phase network control method of a four-arm single-phase modular multilevel converter according to claim 1, characterized in that: The reference voltage u d_ref and u q_ref As input to the voltage and current double closed loop control, the differential mode voltage u diff_d and u diff_q The specific steps include: The reference voltage u d_ref and u q_ref Send it into the voltage and current double closed-loop control link; In the voltage outer loop u d_ref and u q_ref Respectively with u d 、u q Producing a difference Δu d , Δu q , get the current reference value i under the dq coordinate axis d_ref 、i q_ref ; In the inner ring of the inner flow, i d_ref 、i q_ref with i d 、i q Producing a difference Δi d , Δi q After the PI controller, the differential mode voltage u in dq coordinates is further obtained diff_d and u diff_q .

5. The virtual three-phase network control method of a four-arm single-phase modular multilevel converter according to claim 1, characterized in that: The differential mode voltage u diff_d and u diff_q Calculate the voltage reference value u of the four bridge arms of the two phases ap 、u an 、u bp 、u bn The specific steps include: Input differential mode voltage u diff_d and u diff_q , use the Park inverse transformation to perform coordinate transformation and calculate the reference voltage of the upper and lower bridge arms of phases A and B: Where, are the per-unit values ​​of the output voltages of the upper and lower bridge arms of phase j respectively; u dcN Indicates the DC voltage rating.

6. The virtual three-phase network control method of a four-arm single-phase modular multilevel converter according to claim 1, characterized in that: The method of outputting a pulse signal through a modulation link to trigger each sub-module of the MMC specifically includes: finally using the NLC to generate a pulse signal and transmitting it to the MMC sub-module.

7. A computer-readable storage medium having a computer program / instruction stored thereon, characterized in that: When the computer program / instruction is executed by a processor, the steps of the four-leg single-phase modular multilevel converter virtual three-phase network control method according to any one of claims 1 to 6 are implemented.

8. A computer program product comprising a computer program / instructions, characterized in that When the computer program / instruction is executed by a processor, the steps of the four-leg single-phase modular multilevel converter virtual three-phase network control method according to any one of claims 1 to 6 are implemented.

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