Virtual three-phase network control method for four-leg single-phase modular multilevel converter

Abstract

The present application discloses to the railway traction power supply system technical field, especially relates to four bridge arm single-phase modular multilevel converter virtual three-phase network construction control method, including: using virtual three-phase construction method constructs virtual C phase, obtains the output current and output voltage after virtualization by combining virtual C phase with alternating current measurement synchronization control link;The output current and output voltage after virtualization are carried out dq coordinate transformation, and reference voltage is obtained;The reference voltage is sent into voltage current double closed loop control as input, and difference mode voltage is obtained;The difference mode voltage is used to calculate two-phase 4 bridge arm voltage reference value, and the pulse signal output trigger signal is output through the modulation link to trigger each sub-module of MMC.The problem that the single-phase side PR control calculation complexity is high and the dynamic response ability is poor is solved;The control architecture of three-phase, single-phase side of three-phase-single-phase MMC converter is unified, and the design complexity of related control system is simplified.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of railway traction power supply system, and particularly relates to a virtual three-phase network control method for a four-bridge-arm single-phase modular multilevel converter. BACKGROUND

[0002] The traction power supply system is an important component of high-speed railway. The in-phase power supply scheme based on power electronic conversion technology has become a new trend in the development of railway traction power supply system because it can solve the problem of overpassing. With the development and wide application of modular multilevel converter technology, the modular multilevel converter type through in-phase scheme (MMC-TC-TTPS) based on three-phase-single-phase MMC conversion has the advantages of low switching frequency, low loss and low harmonic content, and is considered as an important scheme to realize the in-phase power supply of traction power supply system.

[0003] The control strategies of MMC in the prior art mainly include active power-reactive power (P-Q) control, direct current voltage-reactive power (Udc-Q) control and voltage-frequency (V-f) control. Among them, the control strategy of the three-phase side of MMC-TC-TTPS is mainly based on PI controller according to the specific needs. The PI controller is suitable for direct current system or dq rotating coordinate system, so in the three control strategies, the relevant variables need to be rotated and transformed (dq coordinate system) to control the relevant variables. The control strategy of the single-phase side based on PR controller is based on the static abc coordinate system, but it needs to design a high-order resonance link, and also needs to consider harmonic compensation and higher computational complexity of digital implementation.

[0004] Some studies in the prior art use P-Q control or Udc-Q control to ensure the controllability of the amplitude and phase of the output voltage of the alternating current side in view of the high-quality demand of the voltage of the single-phase side. Some studies use direct voltage control strategy to ensure the stability of the output voltage amplitude and the constancy of the frequency. However, these strategies have different degrees of difficulty and different control benefits, and are not universal.

[0005] The single-phase MMC control method based on PR control in the prior art is mainly based on the control of alternating current signals, and needs to additionally set the resonance bandwidth (ωc) and the resonance gain (Kr), which are complex to optimize and difficult to adjust. In addition, the PR controller cannot compensate multiple harmonics at the same time, and needs to design additional direct current compensation. In terms of digital complexity, the PR controller needs to use a more complex discretization method, such as Tustin transformation. Therefore, the PR controller has certain shortcomings in terms of computational complexity, dynamic response ability and other indicators.

[0006] The four-leg single-phase modular multilevel converter (MMC) is an important component of a three-phase-single-phase MMC converter and a face-to-face high-medium voltage MMC DC transformer. The four-leg single-phase MMC in the prior art usually adopts a control architecture based on a PR controller. The PR control has the disadvantages of being greatly affected by frequency factors, complicated control process, and complicated parameter design. Especially for the three-phase-single-phase MMC converter, since the three-phase side mainly adopts a PI-based control architecture, if the single-phase side adopts a PR-based control architecture, the control architectures of the three-phase side and the single-phase side are different, which greatly increases the complexity of the design of the converter control system.

[0007] Therefore, there is an urgent need for a four-leg single-phase modular multilevel converter virtual three-phase network control method, which improves the control method of the four-leg single-phase MMC, solves the problems of high PR control calculation complexity and poor dynamic response capability of the single-phase side, and unifies the control architectures of the three-phase side and the single-phase side of the three-phase-single-phase MMC converter, and simplifies the design complexity of the related control system. SUMMARY

[0008] The purpose of the present application is to provide a four-leg single-phase modular multilevel converter virtual three-phase network control method, comprising the following steps:

[0009] A virtual C phase is constructed using a virtual three-phase construction method, and the virtual C phase is combined with an AC measurement synchronization control link to obtain a virtual output current i abc and an output voltage u abc ;

[0010] The virtual output current i abc and the output voltage u abc are subjected to dq coordinate transformation to obtain reference voltages u d_ref and u q_ref ;

[0011] The reference voltages u d_ref and u q_ref are input into a voltage and current double-loop control as inputs to obtain difference mode voltages u diff_d and u diff_q ;

[0012] The difference mode voltages u diff_d and u diff_q are used to calculate two-phase four-leg voltage reference values u ap , u an , u bp , and u bn , and pulse signals are output through a modulation link to trigger each sub-module of the MMC.

[0013] The virtual three-phase construction method for constructing the virtual C phase comprises:

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

[0015] By measurement, we obtain known quantities, i.e. original A, B phase voltage and current u a , u b , i a , i b ;

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

[0017]

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

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

[0020] The specific steps for obtaining reference voltages u d_ref and u q_ref are as follows:

[0021] The virtual output voltage u abc and the virtual output current i abc are subjected to dq coordinate transformation to obtain u d , u q and i d , i q ;

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

[0023] The phase angle θ generated in the dq coordinate transformation is calculated, and the phase angle θ is generated by the frequency control of the controller;

[0024] θ = 2πft

[0025] In the formula, f is the frequency in the V-f network control, f = 50 Hz;

[0026] The MMC submodule capacitor voltage is calculated as The amplitude u peak is

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

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

[0029] The reference voltage u d_ref and u q_ref are input into the voltage and current double closed loop control link;

[0030] In the voltage outer loop, u d_ref and u q_ref respectively generate difference values Δu d , Δu q with u d , u q , to obtain the current reference values i d_ref , i q_ref in the dq coordinate axis;

[0031] In the inner current inner loop, i d_ref , i q_ref generate difference values Δi d , Δi q with i d , i q , and after the PI controller, the differential mode voltage u diff_d and u diff_q in the dq coordinate are further obtained.

[0032] The two-phase 4-bridge arm voltage reference values u diff_d , u diff_q are calculated using the differential mode voltage u ap , u an, u bp , u bn The specific steps include:

[0033] Input differential mode voltage u diff_d And u diff_q , the park inverse transformation is used for coordinate transformation, and the reference voltages of the upper and lower bridge arms of phases A and B are calculated:

[0034]

[0035] In the formula, The unit values of the output voltages of the upper and lower bridge arms of phase j are respectively u dcN Indicate the rated value of the direct current voltage.

[0036] The output pulse signal through the modulation link triggers the MMC sub-modules, and finally the pulse signal generated by the NLC is transmitted to the MMC sub-modules.

[0037] Another object of the application 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 four-bridge-arm single-phase modular multilevel converter virtual three-phase network construction control method.

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

[0039] The application has the following beneficial effects:

[0040] The four-bridge-arm single-phase modular multilevel converter virtual three-phase network construction control method disclosed by the application has the following beneficial effects:

[0041] 1. The construction method is simple and suitable for most single-phase-three-phase MMC through-phase systems, and has universality.

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

[0043] 3. The four-bridge-arm single-phase modular multilevel converter conventional control is affected by frequency factors, has a complex control process, and has complex parameter design. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The figure is a flowchart of the four-bridge-arm single-phase modular multilevel converter virtual three-phase network construction control method.

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

[0047] Figure 4 This is a schematic diagram of the single-phase virtual three-phase construction method according to an embodiment of the present invention;

[0048] Figure 5 This is a schematic diagram of the Matlab / Simulink simulation results of an embodiment of the present invention. Detailed Implementation

[0049] This invention provides a virtual three-phase grid control method for a four-arm single-phase modular multilevel converter. The invention will be further described in detail below with reference to the accompanying drawings.

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

[0051] A virtual C-phase is constructed using a virtual three-phase construction method. This virtual C-phase is then integrated with an AC synchronization control loop to obtain the virtual output current i. abc and output voltage u abc ;

[0052] For the virtualized output current i abc and output voltage u abc Perform a dq coordinate transformation to obtain the reference voltage u. d_ref and u q_ref ;

[0053] Reference voltage u d_ref and u q_ref The voltage and current are fed into a dual closed-loop control system to obtain the differential voltage u. diff_d and u diff_q ;

[0054] Using differential mode voltage u diff_d and u diff_q Calculate the reference voltage values ​​u for the four bridge arms of the two phases. ap u an u bp u bn The modulation stage outputs pulse signals to trigger each sub-module of the MMC.

[0055] In the embodiment, a virtual three-phase construction method is provided, and a virtual three-phase MMC control method based on V-f network control is realized. In the design of the control strategy of the three-phase side, the V-f network control utilizes park transformation to perform coordinate conversion. 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, and therefore the three-phase currents are linearly related (i.e., the sum of the three-phase currents is 0). According to this principle, in the coordinate transformation of the single-phase system, a virtual C phase is established by using the assumption of three-phase symmetry (i.e., the sum of the three-phase currents is 0), which is combined with the actual A and B phases to obtain virtual V abc and I abc , which further participates in the subsequent control link.

[0056] The following will be specifically explained for each step.

[0057] First, the virtual C phase is constructed by using the virtual three-phase construction method, and the virtual C phase is combined with the AC measurement synchronization control link to obtain the virtual output current i abc and the virtual output voltage u abc .

[0058] The virtual C phase constructed by using the virtual three-phase construction method includes:

[0059] Based on the assumption of ABC three-phase symmetry, it is obtained that u a + u b + u c = 0, i a + i b + i c = 0.

[0060] The known quantities are obtained by measurement, and the known quantities are the voltage and current of the original A and B phases u a , u b , i a , i b .

[0061] The virtual C phase is constructed by the known quantities:

[0062]

[0063] The virtual output voltage u abc and the virtual output current i abc are obtained by combining the virtual C phase with the measured A and B phases.

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

[0065] In the embodiment, the virtual phase C is constructed based on the three-phase symmetry assumption (u a +u b +u c =0, i a +i b +i c =0, ) and the calculation results u c , i c are combined with the output currents and output voltages of phases A and B obtained by the AC measurement synchronization control link to obtain the virtual u abc , i abc .

[0066] The vector forms of the virtual output voltage u abc and the virtual output current i abc are as follows:

[0067]

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

[0069] The original A, B phase voltages and currents u a , u b , i a , i b are measured. Based on the three-phase symmetry assumption, it is known 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] The virtual C phase is combined with the measured A and B phases to obtain the newly generated u abc , i abc .

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

[0073] The specific steps for obtaining reference voltage u d_ref and u q_ref are as follows:

[0074] The virtual output voltage u abc and the virtual output current i abc are subjected to dq coordinate transformation to obtain u d , u q and i d , i q ;

[0075] u d = U m cos ωt, u q = U m sin ωt; i d = I m cos ωt, i q = I m sin ωt

[0076] The phase angle θ generated in the dq coordinate transformation is calculated, and the phase angle θ is generated by the frequency control of the controller;

[0077] θ = 2πft

[0078] In the formula, f is the frequency in the V-f network control, f = 50 Hz;

[0079] The MMC sub-module capacitor voltage is calculated as amplitude u peak is

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

[0081] In this embodiment, when generating the ABC phase voltage reference value u abc_ref , the amplitude u peak is calculated as a peak value; meanwhile, the reference value used in the per-unit calculation when the dq coordinate transformation is performed on u abc , u abc_ref is u peak。

[0082] In this embodiment, u abc , i abc is subjected to dq coordinate transformation to obtain 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 from θ = 2πω; at the same time, u abc u is obtained after dq coordinate transformation d u q Thus, 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] Calculating the reference voltage along the dq axis first requires calculating the reference voltage in the abc coordinate system based on the system's rated capacity. After per-unit scaling, the voltage is then calculated based on this angle θ. 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] In the formula, 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 The output voltage and output current of phases A and B of the synchronous control loop are respectively used to realize the method of constructing a virtual three-phase system 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 from θ = 2πω, and then the phase-locked angle can be obtained through integration. The MMC submodule capacitor voltage is... Amplitude u peak for The reference voltage u is obtained after dq coordinate transformation. d_ref u q_ref .

[0090] Next, the reference voltage u d_ref and uq_ref The voltage and current are fed into a dual closed-loop control system to obtain the differential voltage u. diff_d and u diff_q ;

[0091] The reference voltage u d_ref and u q_ref The voltage and current are fed into a dual closed-loop control system to obtain the differential voltage u. diff_d and u diff_q The specific steps include:

[0092] Reference voltage u d_ref and u q_ref The voltage and current dual closed-loop control circuit is fed in;

[0093] u in the voltage outer loop d_ref and u q_ref respectively with u d u q Generate the difference Δu d , Δu q The reference current value i under the dq coordinate axis is obtained. d_ref i q_ref ;

[0094] In the inner loop of the internal flow, i d_ref i q_ref with i d i q Generate the difference Δi d , Δi q After passing through a PI controller, the differential voltage u in the dq coordinate system is further obtained. diff_d and u diff_q .

[0095] In this embodiment, the differential-mode voltage u in the dq coordinate system is obtained using the existing voltage-current dual closed-loop method. diff_d and u diff_q。

[0096] In this embodiment, u d_ref u q_ref The voltage and current are fed into a dual closed-loop control system to obtain the differential voltage u. diff_d u diff_q The reference voltage u d_ref u q_ref Input is fed into a voltage and current dual closed-loop control loop; in the voltage outer loop, u d_ref u q_ref respectively with u d u q Generate the difference Δu d , Δu q The reference current value i under the dq coordinate axis is obtained. d_ref iq_ref ; in the inner flow ring, i d_ref , i q_ref and i d , i q produce difference Δi d , Δi q , after PI controller, further get the differential mode voltage in dq coordinate.

[0097] Finally, using differential mode voltage u diff_d and u diff_q , four bridge arm voltage reference values u ap , u an , u bp , u bn are calculated, and pulse signals are output through the modulation link to trigger each MMC sub-module.

[0098] The specific steps of calculating the four bridge arm voltage reference values u diff_d , u diff_q , u ap , u an , u bp , u bn using differential mode voltage u diff_d and u diff_q include:

[0099] Input differential mode voltage u diff_d and u diff_q , and perform coordinate transformation using park inverse transformation to calculate the upper and lower bridge arm reference voltages of phase A and phase B:

[0100]

[0101] In the formula, are the per-unit values of the upper and lower bridge arm output voltages of phase j, respectively; u dcN represents the rated value of the DC voltage.

[0102] The pulse signals generated by the modulation link to trigger each MMC sub-module specifically include: finally, the pulse signals generated by NLC are transmitted to the MMC sub-modules.

[0103] In this embodiment, four bridge arm voltage reference values u diff_d , u diff_q , u ap , u an , u bp , u bn are calculated using differential mode voltage u diff_d , u diff_q , and pulse signals are output through the modulation link to trigger each MMC sub-module. After obtaining the differential mode voltage, coordinate transformation is performed using park inverse transformation, and the upper and lower bridge arm reference voltages of phase A and phase B are obtained according to the following formula.

[0104]

[0105] wherein are the normalized values of the upper and lower bridge arm output voltages of phase j, respectively; u dcN represents the DC voltage rated value.Finally, the pulse signal generated by NLC is transmitted to the MMC sub-module.

[0106] Another embodiment of the present application discloses a computer readable storage medium, which stores computer programs / instructions, and the computer programs / instructions are executed by a processor to realize the steps of the virtual three-phase network construction control method of the four-bridge-arm single-phase modular multilevel converter.

[0107] Another embodiment of the present application discloses a computer program product, which comprises computer programs / instructions, and the computer programs / instructions are executed by a processor to realize the steps of the virtual three-phase network construction control method of the four-bridge-arm single-phase modular multilevel converter.

[0108] To verify the effectiveness of the virtual three-phase network construction control method of the four-bridge-arm single-phase modular multilevel converter, the following simulation test is performed.

[0109] The present application is verified by Matlab / Simulink simulation, and the specific simulation parameters are shown in Table 1.

[0110] Table 1 Simulation parameter table

[0111]

[0112] The simulation results of the present application based on Matlab / Simulink are shown in Table 1. Figure 5

[0113] The virtual three-phase network construction control method of the four-bridge-arm single-phase modular multilevel converter disclosed in the present application enables the PI controller which is not applicable to single-phase to be used through virtual three-phase, and the results Figure 5 show that the simulation system can reach steady state in a short time, proving the availability of the method.

[0114] It can be proved by the simulation results that the control method of the four-bridge-arm single-phase MMC is improved, a network construction control method based on virtual three-phase is proposed, and the problems of high PR control calculation complexity and poor dynamic response ability of the single-phase side can be solved. At the same time, the network construction method can unify the control architecture of the three-phase and single-phase sides of the three-phase-single-phase MMC converter, and simplify the design complexity of the related control system.

[0115] ​The four-bridge-arm single-phase modular multilevel converter virtual three-phase network control method disclosed by the application can uniformly control two sides of single-phase and three-phase, does not need to separately design control strategies of two sides, and does not need to simplify the control strategy of single-phase, thereby improving the control precision and efficiency of the system while reducing the complexity of system design. Meanwhile, the method has strong universality, does not affect the selection of the system control strategy under different design targets, and can solve the problems of the conventional control of the four-bridge-arm single-phase modular multilevel converter, such as great influence of frequency factors, high digital complexity, and complex parameter design.

Claims

1. A virtual three-phase grid connection control method for a four-leg single-phase modular multilevel converter, characterized in that, The method comprises the following steps: The virtual C phase is constructed by using a virtual three-phase construction method, and the virtual C phase is combined with an AC measurement synchronization control link to obtain a virtual output current i abc and an output voltage u abc ; The output current i abc and the output voltage u abc after virtualization are subjected to a dq coordinate transformation to obtain a reference voltage u d_ref and u q_ref ; The reference voltage u d_ref and u q_ref are fed as input to the voltage current double closed loop control, obtaining the differential mode voltage u diff_d and u diff_q ; The differential mode voltage u diff_d and u diff_q The four bridge arm voltage reference values u ap , u an , u bp , u bn of two phases are calculated, and pulse signals are output through a modulation link to trigger each sub-module of the MMC. The step of constructing the virtual C phase by the virtual three-phase construction method comprises: 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; By measuring a known quantity, said known quantity being the voltage current u of the original A, B phase a , b , a , b ; The virtual C phase is constructed by a known amount: ， The virtual C phase is combined with the measured A and B phases to obtain a virtual output voltage u abc and a virtual output current i 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 virtual phase C; 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 d-axis output current; i q is the q-axis output current; The reference voltage u is obtained by the following steps: d_ref and u q_ref The specific steps are as follows: The output voltage u abc and the output current i abc after the virtualization are obtained by dq coordinate transformation as u d , u q and i d , i q ; = = = = ， Generating a phase angle in a dq coordinate transformation , the phase angle being generated by the controller controlling the frequency ; ， In the formula, f is the frequency in V-f network construction control, f=50 Hz; The MMC sub-module capacitance voltage is calculated as , the amplitude u peak is ; After the dq coordinate transformation, the reference voltage u d_ref , u q_ref ; denotes the DC voltage rating.

2. The virtual three-phase network control method for four-leg single-phase modular multilevel converter according to claim 1, characterized in that, The reference voltage u d_ref and u q_ref are input into the voltage and current double closed-loop control to obtain 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 is sent to the voltage and current double closed-loop control link. In the voltage outer loop u d_ref and u q_ref produce a difference d u q u d u q , to obtain the current reference value i d_ref , i q_ref in the dq coordinate axis;​ In the inner flow inner ring, i d_ref 、 q_ref With i d 、 q Generate difference i d i q , after PI controller further get difference mode voltage u diff_d And u diff_q In dq coordinates.

3. The virtual three-phase network control method for four-leg single-phase modular multilevel converter according to claim 1, characterized in that, The use of differential mode voltage u diff_d and u diff_q The specific steps for calculating the four bridge arm voltage reference values u ap , u an , u bp , u bn include: Input differential mode voltage u diff_d and u diff_q A, B phase upper and lower bridge arm reference voltage is calculated by Park inverse transformation. , j = a, b wherein , are the normalized values of the upper and lower bridge arm output voltages of phase j, respectively.

4. The virtual three-phase network control method for four-leg single-phase modular multilevel converter according to claim 1, characterized in that, The step of outputting the pulse signal through the modulation link to trigger each sub-module of the MMC comprises: finally, the pulse signal generated by the NLC is transmitted to the MMC sub-module.

5. A computer readable storage medium having stored thereon computer programs / instructions, characterized in that, The computer program / instruction is executed by the processor to implement the steps of the virtual three-phase network construction control method of the four-bridge-arm single-phase modular multilevel converter according to any one of claims 1-4.

6. A computer program product comprising computer programs / instructions, characterized in that, The computer program / instruction is executed by the processor to implement the steps of the virtual three-phase network construction control method of the four-bridge-arm single-phase modular multilevel converter according to any one of claims 1-4.

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