A DC-MMC control method, system, device and storage medium

Abstract

The application discloses a DC-MMC control method, system and device and a storage medium, relates to the control field, and the scheme is combined with the decoupling control and the inversion control of the energy ring and the current ring, obtains the mth phase upper bridge arm modulation signal and the mth phase lower bridge arm modulation signal, and thus controls the DC-MMC. Thus, the scheme constructs the current ring and the energy ring through the double closed-loop control and the inversion control, thereby realizing the global control of system state variables, minimizing the bridge arm current alternating component, and avoiding the instability of the DC-MMC caused by the inaccurate control of the current component when the disturbance occurs.

Description

TECHNICAL FIELD

[0001] The present application relates to the control field, in particular to a DC-MMC control method, system, device and storage medium. BACKGROUND

[0002] In recent years, in order to alleviate the shortage crisis of traditional fossil energy, more and more renewable distributed power is put into the power grid, and the input of a large number of DC / DC converters (Direct current / Direct current converter, DC / DC converter) has become an effective way to solve the problem of voltage level of renewable energy access and sending, which enables interconnection between various distributed power sources and realizes power transmission between power sources. The DC-MMC is a kind of modular multilevel DC converter. Since the DC-MMC is a multivariable and strongly coupled system, if the control of the current component of the DC-MMC is not accurate when the disturbance occurs, the DC-MMC will be unstable, which makes the design of the double closed-loop controller for controlling the DC-MMC a challenging task. SUMMARY

[0003] The purpose of the present application is to provide a DC-MMC control method, system, device and storage medium, which constructs a current loop and an energy loop through double closed-loop control and backstepping control, thereby realizing global control of system state variables and minimizing the AC component of the bridge arm current, avoiding the instability of the DC-MMC due to inaccurate control of the current component when the disturbance occurs.

[0004] To solve the above technical problems, the present application provides a DC-MMC control method, the DC-MMC includes M-phase upper bridge arms and M-phase lower bridge arms, M≥2, 1≤m≤M, m and M are integers;

[0005] The method comprises:

[0006] The actual value of the capacitor voltage of the upper bridge arm of the mth phase and the actual value of the capacitor voltage of the lower bridge arm of the mth phase are used to generate the decoupling current reference value of the mth phase through the energy loop;

[0007] The decoupling current reference value of the mth phase and the actual value of the decoupling current of the mth phase are used to generate the decoupling voltage reference value of the mth phase through the current loop;

[0008] The first ratio between the voltage reference value of the upper bridge arm of the mth phase generated by backstepping transformation of the decoupling voltage reference value of the mth phase and the capacitor voltage reference value of the upper bridge arm of the mth phase is used to determine the modulation signal of the upper bridge arm of the mth phase;

[0009] determining a modulation signal of the lower bridge arm of the mth phase based on a second ratio between the lower bridge arm voltage reference value of the mth phase generated by the mth phase decoupling voltage reference value after the inverse transformation and the capacitor voltage reference value of the lower upper bridge arm of the mth phase;

[0010] controlling the upper bridge arm of the mth phase and the lower bridge arm of the mth phase respectively based on the modulation signal of the upper bridge arm of the mth phase and the modulation signal of the lower bridge arm of the mth phase.

[0011] Preferably, the mth phase decoupling current reference value is generated by an energy loop based on the capacitor voltage actual value of the upper bridge arm of the mth phase and the capacitor voltage actual value of the lower bridge arm of the mth phase, comprising:

[0012] calculating a first stored energy of the upper bridge arm of the mth phase based on the capacitor voltage actual value of the upper bridge arm of the mth phase and the capacitance value of the upper bridge arm of the mth phase, and calculating a second stored energy of the lower bridge arm of the mth phase based on the capacitor voltage actual value of the lower bridge arm of the mth phase and the capacitance value of the lower bridge arm of the mth phase;

[0013] calculating the average power and the power difference of the upper bridge arm of the mth phase and the lower bridge arm of the mth phase based on the first stored energy and the second stored energy;

[0014] calculating the mth phase decoupling voltage reference value based on the average power and the power difference.

[0015] Preferably, the mth phase decoupling voltage reference value is generated by a current loop based on the decoupling current reference value of the mth phase and the decoupling current actual value of the mth phase, comprising:

[0016] performing PR tracking regulation on the difference between the decoupling current actual value of the mth phase and the decoupling current reference value of the mth phase, and calculating the decoupling voltage reference value of the mth phase based on the high-voltage side voltage value of the mth phase and the low-voltage side voltage value of the mth phase.

[0017] Preferably, the decoupling current reference value of the mth phase comprises a direct current differential current reference value of the mth phase, an alternating current differential current reference value of the mth phase, a direct current phase current reference value of the mth phase and an alternating current phase current reference value of the mth phase.

[0018] Preferably, the decoupling voltage reference value of the mth phase comprises a differential voltage reference value of the mth phase and a phase voltage reference value of the mth phase.

[0019] Preferably, the DC-MMC further comprises an M-phase output filter inductor, the upper bridge arm of the mth phase is connected with the lower bridge arm of the mth phase and the output filter inductor of the mth phase in series, the upper bridge arm of the mth phase and the lower bridge arm of the mth phase constitute a high-voltage side of the mth phase of the DC-MMC in series, the high-voltage sides of the M phases are connected in parallel to constitute a total high-voltage side, the lower bridge arm of the mth phase and the output filter inductor of the mth phase constitute a low-voltage side of the mth phase of the DC-MMC in series, and the low-voltage sides of the M phases are connected in parallel to constitute a total low-voltage side; the upper bridge arm and the lower bridge arm comprise a bridge arm inductor.

[0020] The ratio of the output filter inductor of the mth phase to the bridge arm inductor of the mth phase is greater than a preset value.

[0021] Preferably, the modulation signal of the upper bridge arm of the mth phase is determined based on a first ratio between the upper bridge arm voltage reference value of the mth phase generated by the decoupling voltage reference value of the mth phase after inversion transformation and the capacitor voltage reference value of the upper bridge arm of the mth phase, comprising:

[0022] The decoupling voltage reference value of the mth phase is calculated by inversion to generate the upper bridge arm voltage reference value of the mth phase;

[0023] The first ratio of the upper bridge arm voltage reference value of the mth phase and the capacitor voltage reference value of the upper bridge arm of the mth phase is calculated to determine the modulation signal of the upper bridge arm of the mth phase.

[0024] The modulation signal of the lower bridge arm of the mth phase is determined based on a second ratio between the lower bridge arm voltage reference value of the mth phase generated by the decoupling voltage reference value of the mth phase after inversion transformation and the capacitor voltage reference value of the lower bridge arm of the mth phase, comprising:

[0025] The decoupling voltage reference value of the mth phase is calculated by inversion to generate the lower bridge arm voltage reference value of the mth phase;

[0026] The second ratio of the lower bridge arm voltage reference value of the mth phase and the capacitor voltage reference value of the lower bridge arm of the mth phase is calculated to determine the modulation signal of the lower bridge arm of the mth phase.

[0027] To solve the above technical problems, the present application provides a DC-MMC control system, the DC-MMC comprising M-phase upper bridge arms and M-phase lower bridge arms, M≥2, 1≤m≤M, m and M are both integers;

[0028] The system comprises:

[0029] A first generation unit is configured to generate an mth-phase decoupling current reference value by an energy ring based on an actual capacitor voltage value of the upper bridge arm of the mth phase and an actual capacitor voltage value of the lower bridge arm of the mth phase;

[0030] The second generation unit is used to generate a decoupling voltage reference value for the m-th phase based on the decoupling current reference value and the actual decoupling current value of the m-th phase through a current loop.

[0031] The first determining unit is used to determine the modulation signal of the upper bridge arm of the m-th phase based on a first ratio between the upper bridge arm voltage reference value of the m-th phase generated by the inversion transformation of the decoupling voltage reference value of the m-th phase and the capacitor voltage reference value of the upper bridge arm of the m-th phase.

[0032] The second determining unit is used to determine the modulation signal of the lower bridge arm in the m-th phase based on a second ratio between the lower bridge arm voltage reference value in the m-th phase generated by the inversion transformation of the decoupling voltage reference value in the m-th phase and the capacitor voltage reference value of the upper lower bridge arm in the m-th phase.

[0033] The control unit is used to control the upper arm and the lower arm of the m-th phase respectively based on the modulation signal of the upper arm of the m-th phase and the modulation signal of the lower arm of the m-th phase.

[0034] To solve the above-mentioned technical problems, the present invention provides a DC-MMC control device, comprising:

[0035] Memory, used to store computer programs;

[0036] A processor is used to implement the steps of the DC-MMC control method as described above when executing the computer program.

[0037] To address the aforementioned technical problems, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the DC-MMC control method described above.

[0038] This application provides a DC-MMC control method, system, device, and storage medium, relating to the field of control. In this scheme, decoupled control of the energy loop and current loop is combined with inversion control to obtain the modulation signals of the m-th phase upper arm and m-th phase lower arm, thereby controlling the DC-MMC. Therefore, this scheme constructs current and energy loops through dual closed-loop control and inversion control, achieving global control of the system state variables. This minimizes the AC component of the arm current and avoids DC-MMC instability caused by inaccurate control of the current component during disturbances. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the prior art and embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 A flowchart illustrating a DC-MMC control method provided by the present invention;

[0041] Figure 2 This is a schematic diagram of the voltage divider DC-MMC structure provided by the present invention;

[0042] Figure 3 A schematic diagram of the AC voltage components in two reference frames provided in this application;

[0043] Figure 4 A schematic diagram of the bridge arm energy model provided in this application;

[0044] Figure 5 A schematic diagram of the mathematical model of the voltage divider DC-MMC current loop provided in this application;

[0045] Figure 6 A schematic diagram illustrating the design concept of the voltage divider DC-MMC dual closed-loop controller provided in this application;

[0046] Figure 7 A schematic diagram of the energy loop control structure provided in this application;

[0047] Figure 8 A schematic diagram of the current loop controller provided in this application;

[0048] Figure 9 A schematic diagram of the AC components of voltage and current in a voltage divider DC-MMC provided in this application;

[0049] Figure 10 This is a schematic diagram of differential current control provided in this application;

[0050] Figure 11 This is a schematic diagram of the low-voltage side phase current control provided in this application;

[0051] Figure 12 This is a schematic diagram of the structure of a DC-MMC control system provided by the present invention;

[0052] Figure 13 This is a schematic diagram of the structure of a DC-MMC control device provided by the present invention. Detailed Implementation

[0053] The core of this invention is to provide a DC-MMC control method, system, device, and storage medium. Through dual closed-loop control and inversion control, a current loop and an energy loop are constructed, thereby achieving global control of the system state variables. This can minimize the AC component of the bridge arm current and avoid DC-MMC instability caused by inaccurate control of the current component during disturbances.

[0054] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] Please refer to Figure 1 , Figure 1 The present invention provides a schematic flowchart of a DC-MMC control method, wherein the DC-MMC includes an M-phase upper bridge arm and an M-phase lower bridge arm, where M≥2, 1≤m≤M, and m and M are both integers;

[0056] The method includes:

[0057] S11: Based on the actual value of the capacitor voltage of the upper arm of the m-th phase and the actual value of the capacitor voltage of the lower arm of the m-th phase, a reference value of the decoupling current of the m-th phase is generated through the energy loop.

[0058] S12: Based on the decoupling current reference value of phase m and the actual decoupling current value of phase m, a decoupling voltage reference value of phase m is generated through a current loop;

[0059] S13: Determine the modulation signal of the upper bridge arm in the m-th phase based on the first ratio between the upper bridge arm voltage reference value in the m-th phase generated by the inversion transformation of the decoupling voltage reference value in the m-th phase and the capacitor voltage reference value of the upper bridge arm in the m-th phase.

[0060] S14: Determine the modulation signal of the lower bridge arm in the m-th phase based on the second ratio between the lower bridge arm voltage reference value in the m-th phase generated by the inversion transformation of the decoupling voltage reference value in the m-th phase and the capacitor voltage reference value of the upper lower bridge arm in the m-th phase.

[0061] S15: Control the upper arm and the lower arm of phase m respectively based on the modulation signal of the upper arm of phase m and the modulation signal of the lower arm of phase m.

[0062] In recent years, to alleviate the shortage crisis of traditional fossil fuels, an increasing number of renewable distributed power sources have been put into the grid. The large-scale deployment of DC / DC converters has become an effective way to solve the problem of connecting and transmitting renewable energy sources with diverse voltage levels. This enables interconnection between distributed power sources, achieving power transfer between them. Since DC-MMC is a multivariable, strongly coupled system, the design of a dual-loop controller is a challenging task. The design concept of decoupling control is to decouple the control loops or controlled variables of the system, making the controller and the controlled variables independent control systems corresponding to each other. Domestic and foreign scholars have conducted in-depth research on nonlinear control methods such as feedback linearization control, sliding mode control, predictive control, and inverse control. Among them, inverse control is an effective control method for handling uncertain nonlinear systems. Inverse control is applied to DC-MMC systems, using the idea of ​​model inversion to design the energy outer loop controller and the current inner loop controller. The main function of the current inner loop is to increase the system bandwidth, improve the system's dynamic response, enhance its adaptability to disturbances, and reduce harmonic content. The main function of the energy outer loop is to stabilize the capacitor voltage of the submodules and extract the current component from it. This dual closed-loop control can control the modulation voltage while minimizing the AC component of the bridge arm current, thus avoiding instability of the converter caused by inaccurate control of the current component during disturbances.

[0063] Please refer to Figure 2 , Figure 2 This is a schematic diagram of the voltage divider DC-MMC structure provided by the present invention. Figure 2 Taking M=3 as an example, it includes M-phase upper bridge arm 1, M-phase lower bridge arm 2, M-phase output filter inductor 3 and M-phase controller. The m-th phase upper bridge arm 1 is connected to the m-th phase lower bridge arm 2 and the m-th phase output filter inductor 3 respectively. The m-th phase upper bridge arm 1 and the m-th phase lower bridge arm 2 are connected in series to form the m-th phase high voltage side of the voltage divider DC-MMC. The M-phase high voltage side is connected in parallel to form the total high voltage side. The m-th phase lower bridge arm 2 and the m-th phase output filter inductor 3 are connected in series to form the m-th phase low voltage side of the voltage divider DC-MMC. The M-phase low voltage side is connected in parallel to form the total low voltage side. M≥2, 1≤m≤M.

[0064] Please refer to Figure 3 , Figure 3 This is a schematic diagram of the AC voltage components in two reference frames provided in this application. Specifically, it shows the AC differential voltage v. diffAC and AC phase voltage v sAC The included angle θ V The AC modulation voltage v of the upper arm of the m-th phase muAC and the AC modulation voltage v of the lower bridge arm of phase m mlAC The angle between

[0065] The voltage divider DC-MMC bridge arm voltages are decoupled. One decoupling method is to use the average value of the sum of the voltages of the upper bridge arm 1 and the lower bridge arm 2 of the m-th phase. The other method is to use the average value of the difference between the voltages of the upper bridge arm 1 and the lower bridge arm 2 of the m-th phase.

[0066] In addition, such as Figure 4 As shown, Figure 4 The schematic diagram of the bridge arm energy model provided in this application shows that one decoupling process is to add the capacitor voltage of the upper bridge arm 1 submodule of phase m and the capacitor voltage of the lower bridge arm 2 submodule of phase m, and the other process is to subtract the capacitor voltage of the upper bridge arm 1 submodule of phase m and the capacitor voltage of the lower bridge arm 2 submodule of phase m.

[0067] As a preferred embodiment, a decoupling current reference value for phase m is generated through an energy loop based on the actual values ​​of the capacitor voltage of the upper arm of phase m and the capacitor voltage of the lower arm of phase m, including:

[0068] The first stored energy of the upper bridge arm in phase m is calculated based on the actual value of the capacitor voltage of the upper bridge arm in phase m and the capacitance value of the upper bridge arm in phase m, and the second stored energy of the lower bridge arm in phase m is calculated based on the actual value of the capacitor voltage of the lower bridge arm in phase m and the capacitance value of the lower bridge arm in phase m.

[0069] Calculate the average power and power difference between the upper arm and the lower arm of phase m based on the first stored energy and the second stored energy;

[0070] The reference value of the decoupling current of the m-th phase is calculated based on the average power and the power difference.

[0071] The specific principle is as follows: The relationship between energy and the decoupled current is explained from the perspective of voltage divider DC-MMC energy. Based on this idea, a dual closed-loop controller for both the converter's energy and current is designed. This strategy enables the bridge arms to maintain energy balance while ensuring good transient characteristics of the system.

[0072] W is stipulated u and W l Let be the first stored energy of the upper bridge arm 1 of phase m and the second stored energy of the lower bridge arm 2 of phase m in a voltage divider DC-MMC, respectively; that is, the capacitor voltage of the submodule of the upper bridge arm 1 of phase m and the capacitor voltage of the submodule of the lower bridge arm 2 of phase m. Then, the relationship between the converter bridge arm voltage, current and energy can be expressed as:

[0073]

[0074]

[0075] Among them, the equivalent capacitance C of the series connection of the upper bridge arm 1 of the m-th phase is specified. tu The equivalent capacitance C in series with the lower bridge arm 2 of phase m tl The values ​​are completely equal, so we use C for all of them. arm It means, v uCt V is the capacitor voltage of the upper bridge arm submodule of phase m. mu Let i be the modulation voltage of the upper arm of phase m. u Let v be the current in the upper arm of phase m. diff For differential voltage, i diff For differential current, v s For phase voltage, i s V is the phase current. lCt V is the capacitor voltage of the lower bridge arm submodule of phase m. ml Let i be the modulation voltage of the lower arm of phase m. l For the lower bridge arm current, the dynamic expression for the converter bridge arm submodule capacitor is:

[0076]

[0077] Where C SM U represents the dynamic capacitance value of the bridge arm, that is, the actual capacitance voltage of the upper bridge arm in phase m and the actual capacitance voltage of the lower bridge arm in phase m. muCt Let u be the capacitor voltage of the upper bridge arm submodule of phase m. mlCt Let u be the capacitor voltage of the lower bridge arm submodule of phase m. mpCt u represents the voltage value of the p-th capacitor in the m-th phase (p = 1, 2, ..., N). mqCt This represents the voltage value of the q-th capacitor in the m-th phase (q = N+1, N+2, ..., 2N), i mu Let i be the current in the upper arm of phase m. ml Let be the current of the lower arm of phase m.

[0078] When the voltage ratio of the voltage divider DC-MMC is not 0.5, the number of submodules connected to the upper arm 1 and lower arm 2 of phase m are different. Therefore, the energy stored in the upper arm 1 and lower arm 2 of phase m are also unequal. As shown in the above formula, the energy stored in the upper arm 1 and lower arm 2 of phase m of the voltage divider DC-MMC is coupled. Therefore, the arm energy needs to be decoupled, and a new variable W is defined. c Σ and W c Δ Let the sum and difference operations represent the energies of the bridge arms, then we have:

[0079] W c Σ =W u +W l ;

[0080] W c Δ =W u +W l ;

[0081] From the above formula, the energy equation of the bridge arm after decoupling can be obtained as follows:

[0082]

[0083]

[0084] The average power of the upper arm and lower arm of phase m can be obtained from the above formula. Since both voltage and current are expressed as a sum of DC and AC components, the average power can also be expressed using DC and AC components:

[0085]

[0086] Among them, P c Σ v is the average power of the upper arm of phase m and the lower arm of phase m. diffDC V is the DC differential voltage of the m-th phase. diffAC Let i be the AC differential voltage of the m-th phase. diffDC Let i be the DC differential current of the m-th phase. diffAC Let v be the differential AC current of the m-th phase. sDC Let v be the DC phase voltage of the m-th phase. sAC Let i be the AC phase voltage of the m-th phase. sDC Let i be the DC phase current of the m-th phase. sAC Let be the AC phase current of the m-th phase, and T be the period.

[0087] If the average power generated by sinusoidal voltage and current at different frequencies is zero, then the above formula can be simplified to:

[0088] P c Σ =2v diffDC i diffAC +v sDC i sDC +v muAC i muAC +v mlAC i mlAC ;

[0089] Among them, v muAC Let i be the AC modulation voltage of the upper arm of phase m. muAC V is the AC modulation current of the upper arm of phase m. mlAC Let i be the AC modulation voltage of the lower arm of phase m. mlAC This is the AC modulation current of the lower arm of phase m.

[0090] Based on the working principle of the voltage divider DC-MMC, the AC power components of the upper bridge arm 1 and lower bridge arm 2 of the converter have equal amplitudes but opposite signs. Therefore, the AC components in the above formula cancel each other out, and the above formula can be rewritten as follows:

[0091]

[0092] Among them, v dc1 This represents the high-voltage side voltage value, v. dc2 This refers to the low-voltage side voltage value; please refer to [reference needed]. Figure 4 , Figure 4 This is a schematic diagram illustrating the calculation of average power and power difference provided by the present invention.

[0093] As can be seen from the formula, Provides the DC component of the system current i diffDC and i sDC .

[0094] The total power of the submodule capacitors can be considered as the power reserve of the entire converter branch, which can be expressed as the difference between the input power and the output power:

[0095] P c Δ =P1-P2;

[0096] Where P1 is the output power of the DC-MMC, P2 is the input power of the DC-MMC, and P... c Δ This represents the total power of the capacitors in all the upper and lower bridge arm submodules.

[0097] Therefore, in order to balance the total capacitor energy of the converter, P1 should be equal to P2.

[0098] Similarly, when the converter voltage and current are decomposed into DC and AC components, the average expression for the converter arm energy difference, i.e., the total power of the capacitors in all upper and lower arm submodules, can be written as:

[0099]

[0100] Based on the properties of average power, the above equation can be rearranged as:

[0101]

[0102] In addition, such as Figure 4 As shown above, based on the assumption that the converter arm current contains only DC and fundamental frequency AC components, the reference value for the differential current is defined. and the reference value of the output phase current for:

[0103]

[0104]

[0105] in, This is the reference value for the DC differential voltage of the m-th phase. This is the reference value for the AC differential voltage of the m-th phase. This is the reference value for the DC phase current of phase m. This is the reference value for the AC phase current of the m-th phase.

[0106] Please refer to Figure 5 , Figure 5 This is a schematic diagram illustrating the calculation relationship between the modulation signal and the decoupling voltage provided by the present invention.

[0107] from Figure 4 and Figure 5 The calculation process can be reversed to calculate the modulation signal of the upper arm of phase m and the modulation signal of the lower arm of phase m, so as to control the upper arm of phase m and the lower arm of phase m.

[0108] The above analysis decouples the voltage divider DC-MMC model and builds a decoupled voltage divider DC-MMC mathematical model, laying the foundation for the design of the dual closed-loop controller of the converter below.

[0109] As a preferred embodiment, the modulation signal of the upper arm of the m-th phase is determined based on a first ratio between the upper arm voltage reference value of the m-th phase generated by inversion transformation of the decoupling voltage reference value of the m-th phase and the capacitor voltage reference value of the upper arm of the m-th phase, including:

[0110] The decoupling voltage reference value of phase m is inverted to generate the upper arm voltage reference value of phase m.

[0111] Calculate the first ratio between the reference voltage value of the upper arm of phase m and the reference capacitor voltage value of the upper arm of phase m to determine the modulation signal of the upper arm of phase m.

[0112] The modulation signal of the lower bridge arm of phase m is determined based on a second ratio between the lower bridge arm voltage reference value of phase m (generated by inversion transformation of the decoupling voltage reference value of phase m) and the capacitor voltage reference value of the upper lower bridge arm of phase m, including:

[0113] The decoupling voltage reference value of phase m is inverted to generate the lower arm voltage reference value of phase m.

[0114] Calculate the second ratio between the reference voltage value of the lower arm of phase m and the reference capacitor voltage value of the lower arm of phase m to determine the modulation signal of the lower arm of phase m.

[0115] Specifically, please refer toFigure 6 , Figure 6 This application provides a schematic diagram of a voltage divider DC-MMC dual closed-loop controller design. The energy loop maintains the energy balance between the upper bridge arm 1 and the lower bridge arm 2 of a single phase and provides a reference value for the current loop. The current loop provides a modulation signal to the converter and achieves zero steady-state error current tracking. This application also improves the converter's transmission power by optimizing converter parameters.

[0116] Reference Figure 6 This is a closed-loop control strategy under the new reference frame, in which... and These represent the reference values ​​of the capacitor voltage of the upper arm 1 of phase m and the capacitor voltage of the lower arm 2 of phase m, respectively. ctotu and v ctotl These are the actual values ​​of the capacitor voltage of the upper arm 1 of phase m and the lower arm 2 of phase m, measured after filtering. After decoupling, the system can be divided into two independent subsystems, where... This is the reference value for the first subsystem. This is the reference value for the second subsystem. Specifically, the decoupling current reference value for the m-th phase includes the DC differential current reference value for the m-th phase. Reference value of AC differential current for phase m Reference value of DC phase current of phase m and the reference value of the AC phase current of the m-th phase

[0117] The above content analyzes the energy decoupling mathematical model of voltage divider DC-MMC, and based on the idea of ​​inverse control, it... Figure 4 Inverse control is performed, and the decoupling current component is extracted from the sum and difference of the bridge arm energies, as shown in the schematic diagram. Figure 7 As shown, Figure 7 The schematic diagram of the energy loop control structure provided in this application shows that, That is, P c Σ The reference value. The energy ring control area, also known as the outer ring, aims to achieve energy balance between the upper bridge arm 1 and the lower bridge arm 2.

[0118] In this embodiment, for the voltage divider DC-MMC current inner loop design, Figure 5 The mathematical model of the current loop has been identified. Based on the principle of model inversion, that is, the control command is obtained by using the generalized inverse matrix based on the estimated state deviation, and the system is then reverse-engineered to achieve the desired goal. Please refer to [link / reference]. Figure 8 , Figure 8 This is a schematic diagram of the current loop controller provided in this application. This controller enables the current i... diff i s Track their reference values ​​separately Provide v diff v s The reference value, that is, the decoupling voltage reference value of the m-th phase, includes the differential voltage reference value of the m-th phase. and the reference value of the m-th phase voltage Finally, the modulation signal of the upper arm of the m-th phase is generated. and the modulation signal of the lower arm of the m-th phase It can also adjust the current i of the upper arm 1 of the m-th phase. u The current i in the lower arm 2 of phase m l In a preferred embodiment, when generating the decoupling voltage reference value of phase m based on the decoupling current reference value and the actual decoupling current value of phase m through a current loop, specifically, but not limited to, performing PR tracking adjustment on the difference between the actual decoupling current value and the decoupling current reference value of phase m, and calculating the decoupling voltage reference value of phase m based on the high-voltage side voltage value and the low-voltage side voltage value of phase m. Here, current AC component tracking can effectively eliminate harmonic components in the converter, and using a PR regulator can achieve better results in eliminating static errors.

[0119] As a preferred embodiment, the proportional resonant controller used in the voltage divider DC-MMC current loop can achieve zero steady-state error tracking of AC quantities, with good tracking performance and high output voltage and current quality. Its transfer function expression can be written as:

[0120]

[0121] Where, k p k represents the proportional gain of the controller. r Let ω be the second-order resonant gain of the controller. c ω0 is its cutoff frequency, used to reduce the sensitivity of the controller during frequency shift, and ω0 is the fundamental angular frequency.

[0122] In a voltage divider DC-MMC system, a PR controller is used to track and adjust the system. As long as the PR parameters are properly tuned, the entire converter control system can achieve satisfactory results.

[0123] In this embodiment, neglecting the losses in the voltage divider DC-MMC system, the AC component of the system voltage in steady state can be expressed in phasor form as follows:

[0124]

[0125]

[0126] in, Let m be the reference value vector of the AC differential voltage of phase m. Let m be the reference vector of the AC differential current of phase m. Let m be the reference value vector of the AC phase voltage of phase m. This is the reference vector for the AC phase current of the m-th phase.

[0127] In a voltage divider DC-MMC balanced three-phase system, the AC differential voltage reference value AC phase voltage reference value The AC modulation voltage reference value of the upper bridge arm of phase m can be used. and the reference value of AC modulation voltage of the lower arm of phase m Represented as:

[0128]

[0129] As a preferred embodiment, the voltages of the upper arm 1 and lower arm 2 of the voltage divider DC-MMC can be written as:

[0130]

[0131] In this embodiment, to improve the overall operating performance of the voltage divider DC-MMC converter, it is necessary to improve the performance of each phase branch. Since the AC components of the voltages in the upper arm 1 and lower arm 2 of the converter introduce AC current, which increases the electrical losses of the converter, the selection of the amplitude of the AC components of the voltages in the upper arm 1 and lower arm 2 has a significant impact on the converter's efficiency and size. In high-voltage, high-power converters, the number of arm submodules is related to the DC voltage level at both ends of the converter and the rated capacitor voltage of the submodules, and multiple phase branches are needed to balance the DC power in the converter. Due to different selections of the converter's AC parameters, there is a maximum limit to the DC power transmitted by a single phase branch. Increasing the number of branches or submodules of the converter can improve the power transmission limit of the converter, but it will also increase the size and cost of the converter. To minimize the number of phases in the converter branches, high power transmission can be achieved by optimizing the converter parameters.

[0132] Where, θ vmu Let θ be the phase of the modulation voltage of the upper arm of phase m. vml Let m be the phase of the modulation voltage of the lower bridge arm. V is the AC modulation voltage of the upper arm of phase m. muAC and the AC modulation voltage V of the lower bridge arm of phase m mlAC The angle between Reference values.

[0133] And according to the above formula, we can let To maximize the value, take π / 2. Even if To increase the converter's transmission power by setting it to 1. According to... Figure 2At this point, for the AC component of the voltage divided by DC-MMC modulation, we have:

[0134]

[0135] Based on the principle of minimizing the AC component of the system

[0136] For a voltage divider DC-MMC to function properly, the following conditions must be met:

[0137] (1) When the converter is working normally, this submodule is similar to the half-bridge submodule, so the instantaneous bridge arm voltage must be greater than zero.

[0138] (2) The maximum instantaneous bridge arm voltage must be less than the high voltage side voltage.

[0139] Based on this, the maximum value of the AC component amplitude of the voltage in the upper arm 1 and lower arm 2 of the voltage divider DC-MMC can be expressed as:

[0140] |v juAC | max =min[v juDC ,(v dc1 -v juDC )];

[0141] |v jlAC | max =min[v jlDC ,(v dc1 -v jlDC )];

[0142] In this embodiment, The phase angle difference between the voltages of the upper arm and the lower arm of the m-th phase is given by the following formula: regardless of... What is the value, voltage? and The phasor angle difference is a constant value of π / 2. Please refer to [reference needed]. Figure 9 , Figure 9 A schematic diagram of the AC components of voltage and current in the voltage divider DC-MMC provided in this application.

[0143] In this embodiment, it can be and V s * The relationship between them is represented as follows:

[0144]

[0145] As a preferred embodiment, the following may be included:

[0146]

[0147] Based on the above analysis, the existing technology can be described as follows:

[0148]

[0149] And we can obtain:

[0150]

[0151] In this embodiment, the voltage V of the upper bridge arm 1 and the lower bridge arm 2 can be used as a reference. muAC and V mlAC Determine v sAC and v diffAC Reference values:

[0152]

[0153]

[0154] As a preferred embodiment, the voltage divider DC-MMC impedance can be simplified to obtain the current. and The reference value is:

[0155]

[0156]

[0157] In existing technologies, it is known that the voltage divider type DC-MMC decoupling voltage can independently control the magnitude of the corresponding decoupling current, and the relationship between the reference values ​​of the AC components of the decoupling current can be obtained, i.e.:

[0158]

[0159] In this embodiment, it is known that the current in the voltage divider DC-MMC bridge arm contains both DC and AC components. Figure 10 A schematic diagram of differential current control provided in this application.

[0160] Figure 11 This is a schematic diagram of the low-voltage side phase current control provided in this application.

[0161] Based on the above embodiments:

[0162] In a preferred embodiment, the upper and lower arms of the DC-MMC include multiple sub-modules based on RB-IGBT construction.

[0163] The submodule enables the converter to interrupt short-circuit faults and solves the problems of the half-bridge submodule only being able to output non-negative voltages and the full-bridge submodule having large conduction losses.

[0164] In a preferred embodiment, the DC-MMC further includes an M-phase output filter inductor. The upper bridge arm of the m-th phase is connected to the lower bridge arm of the m-th phase and the output filter inductor of the m-th phase. The upper bridge arm and the lower bridge arm of the m-th phase are connected in series to form the high-voltage side of the m-th phase of the DC-MMC. The high-voltage sides of the M-phases are connected in parallel to form the total high-voltage side. The lower bridge arm of the m-th phase and the output filter inductor of the m-th phase are connected in series to form the low-voltage side of the m-th phase of the DC-MMC. The low-voltage sides of the M-phases are connected in parallel to form the total low-voltage side. The upper and lower bridge arms include bridge arm inductors.

[0165] The ratio of the output filter inductance Ls of phase m to the bridge arm inductance L of phase m is greater than the preset value.

[0166] In this application, high power transmission can be achieved by increasing the Ls / L ratio. When the Ls value in the converter is much larger than the L value, the inductance in the above formula can be taken as an extreme value of 1 / L. When 1 / L is larger, the amplitude of the AC voltage component used to balance the energy of the upper bridge arm 1 and the lower bridge arm 2 is smaller. Therefore, the AC voltage component can be reduced by selecting the Ls / L ratio.

[0167] Please refer to Figure 12 , Figure 12 This is a schematic diagram of a DC-MMC control system provided by the present invention. The DC-MMC includes an M-phase upper bridge arm, an M-phase lower bridge arm, and an M-phase output filter inductor. The m-th phase upper bridge arm is connected to the m-th phase lower bridge arm and the m-th phase output filter inductor. The m-th phase upper bridge arm and the m-th phase lower bridge arm are connected in series to form the m-th phase high-voltage side of the DC-MMC. The M-phase high-voltage sides are connected in parallel to form the total high-voltage side. The m-th phase lower bridge arm and the m-th phase output filter inductor are connected in series to form the m-th phase low-voltage side of the DC-MMC. The M-phase low-voltage sides are connected in parallel to form the total low-voltage side. M≥2, 1≤m≤M, and m and M are both integers.

[0168] The system includes:

[0169] The first comparison unit 121 is used to compare the capacitor voltage of the upper and lower bridge arms of the m-th phase with the capacitor voltage reference value to obtain the decoupling current reference value of the m-th phase generated by the energy loop.

[0170] The second comparison unit 122 is used to compare the reference value of the decoupling current of the m-th phase with the actual value of the decoupling current of the m-th phase to obtain the reference value of the decoupling voltage of the m-th phase generated by the current loop.

[0171] The determining unit 123 is used to determine the ratio of the voltage reference values ​​of the upper and lower bridge arms of the m-th phase after the inversion transformation of the decoupling voltage reference value to the capacitor voltage reference values ​​of the upper and lower bridge arms of the m-th phase, so as to obtain the modulation signals of the upper and lower bridge arms of the m-th phase.

[0172] Control unit 124 is used to control the upper arm and lower arm of phase m based on the modulation signals of the upper arm and lower arm of phase m.

[0173] For an introduction to the DC-MMC control system provided by this invention, please refer to the above method embodiments; the invention itself will not be described in detail here.

[0174] Please refer to Figure 13 , Figure 13 This is a schematic diagram of a DC-MMC control device provided by the present invention. The device includes:

[0175] Memory 131 is used to store computer programs;

[0176] The processor 132 is used to implement the steps of the DC-MMC control method described above when executing a computer program.

[0177] For a description of the DC-MMC control device provided by the present invention, please refer to the above method embodiments; the present invention will not be described in detail here.

[0178] The computer-readable storage medium of the present invention stores a computer program, which, when executed by a processor, implements the steps of the DC-MMC control method described above.

[0179] For a description of the computer-readable storage medium provided by the present invention, please refer to the above method embodiments; the present invention will not be described again here.

[0180] It should also be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0181] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A DC-MMC control method, characterized by, The DC-MMC comprises M upper bridge arms and M lower bridge arms, M≥2, 1≤m≤M, m and M are integers; The method comprises: generating an mth phase decoupling current reference value based on the actual capacitor voltage value of the mth phase upper bridge arm and the actual capacitor voltage value of the mth phase lower bridge arm through an energy loop; generating an mth phase decoupling voltage reference value based on the mth phase decoupling current reference value and the actual mth phase decoupling current value through a current loop; determining the modulation signal of the mth phase upper bridge arm based on a first ratio between the mth phase upper bridge arm voltage reference value generated by the mth phase decoupling voltage reference value after inverse transformation and the capacitor voltage reference value of the mth phase upper bridge arm; determining the modulation signal of the mth phase lower bridge arm based on a second ratio between the mth phase lower bridge arm voltage reference value generated by the mth phase decoupling voltage reference value after inverse transformation and the capacitor voltage reference value of the mth phase lower bridge arm; controlling the mth phase upper bridge arm and the mth phase lower bridge arm based on the modulation signals of the mth phase upper bridge arm and the mth phase lower bridge arm.

2. The DC-MMC control method of claim 1, wherein, The method for generating an mth phase decoupling current reference value based on the actual capacitor voltage value of the mth phase upper bridge arm and the actual capacitor voltage value of the mth phase lower bridge arm through an energy loop comprises: calculating a first stored energy of the mth phase upper bridge arm based on the actual capacitor voltage value of the mth phase upper bridge arm and the capacitance value of the mth phase upper bridge arm, and calculating a second stored energy of the mth phase lower bridge arm based on the actual capacitor voltage value of the mth phase lower bridge arm and the capacitance value of the mth phase lower bridge arm; calculating the average power and the power difference of the mth phase upper bridge arm and the mth phase lower bridge arm based on the first stored energy and the second stored energy; calculating the mth phase decoupling current reference value based on the average power and the power difference.

3. The DC-MMC control method of claim 1, wherein, The method for generating an mth phase decoupling voltage reference value based on the mth phase decoupling current reference value and the actual mth phase decoupling current value through a current loop comprises: performing PR tracking adjustment on the difference between the actual mth phase decoupling current value and the mth phase decoupling current reference value, and calculating the mth phase decoupling voltage reference value based on the high-voltage side voltage value of the mth phase and the low-voltage side voltage value of the mth phase.

4. The DC-MMC control method of claim 1, wherein, The mth phase decoupling current reference value comprises an mth phase DC differential current reference value, an mth phase AC differential current reference value, an mth phase DC phase current reference value and an mth phase AC phase current reference value.

5. The DC-MMC control method of claim 1, wherein, The mth phase decoupling voltage reference value comprises an mth phase differential voltage reference value and an mth phase phase voltage reference value.

6. The DC-MMC control method of claim 1, wherein, The DC-MMC further comprises M output filter inductors, the mth phase upper bridge arm is connected with the mth phase lower bridge arm and the mth phase output filter inductor, the mth phase upper bridge arm and the mth phase lower bridge arm are connected in series to form a high-voltage side of the mth phase of the DC-MMC, M high-voltage sides are connected in parallel to form a total high-voltage side, the mth phase lower bridge arm and the mth phase output filter inductor are connected in series to form a low-voltage side of the mth phase of the DC-MMC, and M low-voltage sides are connected in parallel to form a total low-voltage side; the upper bridge arm and the lower bridge arm comprise a bridge arm inductor. A ratio of the output filter inductance of the mth phase to the bridge arm inductance of the mth phase is greater than a preset value.

7. The DC-MMC control method according to any one of claims 1-6, characterized by, The first ratio between the upper bridge arm voltage reference value of the mth phase generated by the decoupling voltage reference value of the mth phase after inversion transformation and the capacitor voltage reference value of the upper bridge arm of the mth phase is used to determine the modulation signal of the upper bridge arm of the mth phase, including: The decoupling voltage reference value of the mth phase is calculated by inversion to generate the upper bridge arm voltage reference value of the mth phase; The first ratio between the upper bridge arm voltage reference value of the mth phase and the capacitor voltage reference value of the upper bridge arm of the mth phase is calculated to determine the modulation signal of the upper bridge arm of the mth phase; The second ratio between the lower bridge arm voltage reference value of the mth phase generated by the decoupling voltage reference value of the mth phase after inversion transformation and the capacitor voltage reference value of the lower bridge arm of the mth phase is used to determine the modulation signal of the lower bridge arm of the mth phase, including: The decoupling voltage reference value of the mth phase is calculated by inversion to generate the lower bridge arm voltage reference value of the mth phase; The second ratio between the lower bridge arm voltage reference value of the mth phase and the capacitor voltage reference value of the lower bridge arm of the mth phase is calculated to determine the modulation signal of the lower bridge arm of the mth phase.

8. A DC-MMC control system, characterized by, The DC-MMC includes M upper bridge arms and M lower bridge arms, M≥2, 1≤m≤M, m and M are integers; The system includes: The first generation unit is configured to generate the decoupling current reference value of the mth phase by energy loop based on the capacitor voltage actual value of the upper bridge arm of the mth phase and the capacitor voltage actual value of the lower bridge arm of the mth phase; The second generation unit is configured to generate the decoupling voltage reference value of the mth phase by current loop based on the decoupling current reference value of the mth phase and the decoupling current actual value of the mth phase; The first determination unit is configured to determine the modulation signal of the upper bridge arm of the mth phase based on the first ratio between the upper bridge arm voltage reference value of the mth phase generated by the decoupling voltage reference value of the mth phase after inversion transformation and the capacitor voltage reference value of the upper bridge arm of the mth phase; The second determination unit is configured to determine the modulation signal of the lower bridge arm of the mth phase based on the second ratio between the lower bridge arm voltage reference value of the mth phase generated by the decoupling voltage reference value of the mth phase after inversion transformation and the capacitor voltage reference value of the lower bridge arm of the mth phase; The control unit is configured to control the upper bridge arm of the mth phase and the lower bridge arm of the mth phase respectively based on the modulation signal of the upper bridge arm of the mth phase and the modulation signal of the lower bridge arm of the mth phase.

9. A DC-MMC control device characterized by comprising: It includes: The memory is configured to store a computer program; The processor is configured to execute the computer program to implement the steps of the DC-MMC control method according to any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer program is stored on the computer readable storage medium and is executed by the processor to implement the steps of the DC-MMC control method according to any one of claims 1 to 7.

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