CN107634659A - A Control Method of Expanding the Operating Area of Hybrid MMC - Google Patents

Abstract

The invention discloses a kind of control method of expansion mixed type MMC operation areas, including the capacitance voltage of half-bridge submodule and the capacitance voltage of full-bridge submodule in detection in real time and more each mutually each bridge arm, if the difference between the two is more than voltage threshold Δ v_c, by controlling full-bridge submodule and half-bridge submodule to turn on quantity, meet bridge arm output voltage in j phasesMeet bridge arm output voltage under j phasesThe charge and discharge area of increase half-bridge submodule is realized by changing upper and lower bridge arm current amplitude and phase, and then expands mixed type MMC operation areas；2 frequencys multiplication and 3 multiplied frequency harmonics are suppressed respectively to improve the performance of the two in AC and DC side simultaneously.It is the operation area that need not sacrifice transverter compared to traditional technical scheme, the characteristics of this programme, it is not necessary to increase the ratio of full-bridge submodule in mixed type MMC, while transverter also retains good fault ride-through capacity and AC pressure-raising service ability.

Description

A Control Method of Expanding the Operating Area of Hybrid MMC

technical field

The invention belongs to the technical field of multi-level power electronic converters, and more specifically relates to a control method for expanding the operation area of a hybrid MMC.

Background technique

Compared with traditional two-level and three-level converters, modular multilevel converters can easily achieve higher voltage and higher power levels, and it has become the preferred topology for HVDC converters. The ability to handle DC short-circuit faults is a problem that must be faced in the field of HVDC transmission. Among the many converter topologies with DC short-circuit fault handling capability, the hybrid modular multilevel converter whose number of half-bridge and full-bridge sub-modules in the bridge arm meets 1:1 has lower operating cost and High operating efficiency. At present, this topology has been favored by domestic manufacturers of HVDC converter valve products. In order to further increase the utilization rate of power devices, the hybrid MMC can also operate in high AC voltage operation occasions by increasing the number of full-bridge sub-modules in the bridge arm. In addition, the hybrid MMC should have a certain low DC voltage operation capability to avoid DC voltage flashover in extreme weather.

When the hybrid MMC operates in a high modulation ratio situation, the full-bridge sub-module in the bridge arm needs to output a negative level. In a fundamental frequency period, the half-bridge sub-module of the same bridge arm will continue to charge (discharge), while the full The bridge sub-module will continue to discharge (charge), the capacitor voltage in the half-bridge sub-module will continue to rise and the full-bridge sub-module will continue to drop, or the capacitor voltage in the half-bridge sub-module will continue to rise and the full-bridge sub-module will continue to drop, resulting in the failure of the hybrid MMC Operation, which in turn leads to the technical problem of the small operating area of the hybrid MMC.

Contents of the invention

For the above defects, the present invention provides a control method for expanding the operating area of hybrid MMC, aiming to solve the problems caused by the continuous charging (discharging) of the half-bridge sub-module and the continuous discharging (charging) of the full-bridge sub-module in the hybrid MMC. The MMC does not function properly, which in turn leads to technical problems with the small operating area of the hybrid MMC.

In order to achieve the above object, the invention provides a kind of control method that expands hybrid MMC operation area, and each bridge arm of hybrid MMC all comprises a plurality of full-bridge submodules and a plurality of half-bridge submodules, comprising the following steps:

(1) Real-time detection of the capacitance voltage of the half-bridge sub-module and the capacitance voltage of the full-bridge sub-module in each bridge arm of each phase;

(2) Judging whether the difference between the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in each bridge arm of each phase is greater than the voltage threshold, if so, then enter step (3); otherwise continue to perform step (1);

(3) Obtain the first additional voltage v _j1 of the j-th phase by controlling the j-th phase sine wave current command, the j-th phase circulating current detected in real time by the hybrid MMC AC side, and the hybrid-type MMC DC side current through proportional resonance control;

The second additional voltage v _j2 of the jth phase is obtained by controlling the jth phase double frequency circulating current instruction, the jth phase circulating current detected in real time by the hybrid MMC AC side, and the hybrid MMC DC side current through proportional resonance control;

The third additional voltage v _j3 of the j-th phase is obtained by resonantly controlling the triple-frequency circulating current command of the j-th phase and the hybrid MMC DC side current;

The fourth additional voltage v _j4 of the j-th phase is obtained by controlling the double-frequency harmonic command of the j-th phase and the hybrid MMC AC side current through proportional resonance control;

The fifth additional voltage v _j5 of the j-th phase is obtained by proportionally controlling the j-th phase upper bridge arm capacitor voltage and the j-th phase lower bridge arm capacitor voltage;

By controlling the conduction quantity of the full-bridge sub-module and the half-bridge sub-module of the j-phase bridge arm, the output voltage of the j-phase upper bridge arm satisfies The output voltage of the lower bridge arm of phase j satisfies And let j traverse its value; by increasing the first additional voltage to the fifth additional voltage on the upper and lower bridge arms, changing the current amplitude and phase of the upper and lower bridge arms of each phase, to increase the charging and discharging area of the half-bridge sub-module , and then expand the hybrid MMC operating area;

Among them, v _dc is the DC side port voltage of the hybrid MMC, e _j is the internal potential of the jth phase output from the AC side of the hybrid MMC, and j=a, b, c, a, b, and c represent the three phases of A, B, and C respectively phase; v _j1 is the first additional voltage of the j-th phase; v _j2 is the second additional voltage of the j-th phase; v _j3 is the third additional voltage of the j-th phase; v _j4 is the fourth additional voltage of the j-th phase; v _j5 is the fifth additional voltage of the jth phase.

Preferably, in the step (3), the phase of the jth phase sine wave current command of each phase is 90 degrees from the phase of the jth internal potential output of the hybrid MMC AC side of each phase, and the jth phase sine wave current of each phase is The command frequency is 50Hz;

If the hybrid MMC runs on the rectifier, the amplitude of the sine wave current command of the jth phase of each phase satisfies that the maximum value of the bridge arm current after adding the first additional voltage and the second additional voltage is greater than 0.15 times the current amplitude of the AC side, if When the hybrid MMC runs on the inverter, the amplitude of the sine wave current command of the jth phase of each phase meets the requirement that the minimum value of the bridge arm current after adding the first additional voltage and the second additional voltage is less than minus 0.15 times the current amplitude of the AC side .

Preferably, in the step (3), the first additional voltage of the jth phase is obtained according to the following steps:

The difference between the j-th phase circulating current detected in real time on the AC side of the hybrid MMC and 1/3 of the current value on the DC side of the hybrid MMC is used as a high-order component in the circulating current;

The first additional voltage of the j-th phase is obtained by performing proportional resonance control on the difference between the j-th phase sine wave current command and the high-order component in the circulating current.

Preferably, in the step (3), the second additional voltage of the jth phase is obtained according to the following steps:

The difference between the j-th phase circulating current detected in real time on the AC side of the hybrid MMC and 1/3 of the current value on the DC side of the hybrid MMC is used as a high-order component in the circulating current;

Proportional resonance control is performed on the difference between the double-frequency circulating current command of the j-th phase and the high-order component in the circulating current to obtain the second additional voltage of the j-phase, where the double-frequency circulating current command value of the j-th phase is zero, and the hybrid MMC The circulating current of the jth phase on the AC side is obtained by averaging the detected upper bridge arm current and the lower bridge arm current.

Preferably, in the step (3), the third additional voltage of the jth phase is obtained according to the following steps:

Perform resonant control on the difference between the triple frequency circulating current command of the jth phase and the DC side current of the hybrid MMC to obtain the third additional voltage of the j phase, wherein the jth phase triple frequency circulating current command value is zero, and the hybrid MMC AC The circulating current of the jth phase on the side is obtained by taking the average value of the detected upper bridge arm current and the lower bridge arm current.

Preferably, in the step (3), the fourth additional voltage of the jth phase is obtained according to the following steps:

The fourth additional voltage of the j-phase is obtained by controlling the difference between the j-th phase double-frequency harmonic command and the hybrid MMC AC side current through proportional resonance control, wherein the j-th phase double-frequency harmonic command value is zero.

Preferably, in the step (3), the number ΔN of submodule switching is determined according to the bridge arm voltage, and the submodules are switched in the following order:

When the output voltage of the bridge arm is positive and the current of the bridge arm is positive, choose to invest in the ΔN submodules with the lowest voltage ranking among all the submodules or choose to cut off the ΔN submodules with the highest voltage ranking among all the submodules;

When the output voltage of the bridge arm is positive and the current of the bridge arm is negative, choose to invest in the ΔN submodules with the highest voltage ranking among all the submodules or choose to cut off the ΔN submodules with the lowest voltage ranking among all the submodules;

When the output voltage of the bridge arm is negative and the current of the bridge arm is positive, choose to invest in the ΔN submodules with the highest voltage ranking among all the full-bridge submodules or choose to cut off the ΔN submodules with the lowest voltage ranking among all the full-bridge submodules;

When the output voltage of the bridge arm is negative and the current of the bridge arm is negative, choose to invest in the ΔN submodules with the lowest voltage ranking among all the full-bridge submodules or choose to cut off the ΔN submodules with the highest voltage ranking among all the full-bridge submodules.

Further, the proportion of the number of full-bridge sub-modules and half-bridge sub-modules in the hybrid MMC can be any positive value.

Compared with the prior art, the above technical solution conceived by the present invention has the following technical effects:

1. By adding the first additional voltage to the fifth additional voltage on the upper and lower bridge arms, the current amplitude and phase of the upper and lower bridge arms are changed, thereby increasing the charging and discharging area of the half-bridge sub-module, and realizing the charging of the half-bridge sub-module The discharge area is close to the charge and discharge area of the full-bridge sub-module, so as to avoid the continuous rise of the capacitor voltage in the half-bridge sub-module and the continuous drop of the full-bridge sub-module, or the continuous rise of the capacitor voltage in the half-bridge sub-module and the continuous drop of the full-bridge sub-module, ensuring AC Under the condition that the operating point of the DC side remains unchanged, the reliable operation of the converter can be realized, and the operating area of the hybrid MMC can be expanded.

2. Compared with the scheme of increasing the proportion of full-bridge sub-modules in the bridge arm, this scheme can save costs and improve the operating efficiency under normal operation conditions.

3. The solution conceived by the present invention does not need to change the symmetrical topology of the upper and lower bridge arms of the converter, and thus has good DC fault ride-through capability and AC boosting operation capability.

4. In this solution, by adding a third additional voltage and a fourth additional voltage on the upper and lower bridge arms, the harmonics of the double frequency and triple frequency are respectively suppressed on the AC side and the DC side to improve the performance of both.

Description of drawings

Fig. 1 is the topological structure of hybrid MMC in a kind of control method that expands hybrid MMC operation area provided by the present invention;

Fig. 2 is the flow chart of a kind of control method of enlarging hybrid MMC operation area provided by the present invention;

Fig. 3 is the performance diagram of the first embodiment of the control method first embodiment and the first comparative embodiment of a kind of expansion hybrid MMC operation area provided by the present invention, wherein, the performance diagram of the first comparative embodiment of Fig. 3 (A) , Fig. 3 (A) (a) is the A-phase AC output current waveform in the first comparative embodiment, Fig. 3 (A) (b) is the A-phase circulating current waveform in the first comparative embodiment, Fig. 3 (A) (c ) is the submodule capacitor voltage waveform in the A-phase lower bridge arm in the first comparative embodiment; Fig. 3 (B) (a) is the A-phase AC output current waveform in the first embodiment, and Fig. 3 (B) (b) It is the A-phase circulating current waveform in the first embodiment, and Fig. 3 (B) (c) is the sub-module capacitor voltage waveform in the lower bridge arm of the A-phase in the first embodiment;

Fig. 4 is the performance diagram of the second embodiment of the control method of a kind of expansion hybrid MMC operation area provided by the present invention and the performance diagram of the second comparative embodiment, wherein, the performance diagram of the second comparative embodiment of Fig. 4 (A) , Fig. 4 (A) (a) is the A-phase AC output current waveform in the second comparative embodiment, Fig. 4 (A) (b) is the A-phase circulating current waveform in the second comparative embodiment, Fig. 4 (A) (c ) is the submodule capacitor voltage waveform in the A-phase lower bridge arm in the second comparative embodiment; Fig. 4 (B) (a) is the A-phase AC output current waveform in the second embodiment, and Fig. 4 (B) (b) It is the A-phase circulating current waveform in the second embodiment, and FIG. 4(B)(c) is the sub-module capacitor voltage waveform in the lower bridge arm of the A-phase in the second embodiment.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Fig. 1 is the topological structure of the hybrid MMC in the control method for expanding the hybrid MMC operating area provided by the present invention, the upper bridge arm connected to the alternating current j phase includes a plurality of full-bridge submodules and a plurality of half-bridge submodules, connected to the alternating current j The lower bridge arm of the phase includes a plurality of full-bridge sub-modules and a plurality of half-bridge sub-modules, wherein, j=a, b, c, and a, b, c represent AC phases A, B, and C respectively, and the half-bridge sub-module It can output positive level and zero level, and the full bridge sub-module can output positive level, negative level and zero level.

Fig. 2 is the flow chart of the control method of expanding hybrid MMC operating area provided by the present invention; The method comprises:

(1) Real-time detection of the capacitance voltage of the half-bridge sub-module and the capacitance voltage of the full-bridge sub-module in each bridge arm of each phase;

(2) Determine whether the difference between the capacitance voltage of the half-bridge sub-module in each bridge arm of each phase and the capacitance voltage of the full-bridge sub-module is greater than the voltage threshold, if the capacitance voltage of the half-bridge sub-module in a certain bridge arm of a certain phase and the full-bridge sub-module If the difference between the capacitor voltages of the modules is greater than the voltage threshold, go to step (3), otherwise go to step (1); the voltage threshold is determined according to the operating requirements, and the voltage threshold is generally 0.1V _c , where V _c is the rated voltage of the sub-module.

(3) The first additional voltage v _j1 of the jth phase obtained by proportional resonance control of the jth phase sine wave current command, the jth phase circulating current on the AC side of the hybrid MMC, and the hybrid MMC DC side current; specifically, according to The difference between the jth phase circulating current on the AC side of the hybrid MMC and 1/3 of the DC side current of the hybrid MMC obtains the high-order component in the circulating current, whose harmonic order is greater than or equal to 1, and the jth phase sine wave current command Proportional resonance control is performed after making a difference with the high-order component in the circulating current to obtain the first additional voltage v _j1 of the jth phase.

Among them, the resonant frequency of the proportional resonance control is 50Hz, and the circulating current of the jth phase on the AC side of the hybrid MMC is obtained by taking the average value of the detected upper bridge arm current and the lower bridge arm current, and the phase of the jth phase sine wave current command is mixed with The phase difference of the electric potential in the jth phase of the type MMC AC side output is 90 degrees, and the frequency of the sine wave current command of the jth phase is the fundamental frequency; so that the phase difference of the sine wave current command among the three phases is 120 degrees in sequence, and the positive sequence is satisfied. relation;

If the hybrid MMC operates on the rectifier, the amplitude of the sine wave current command of the jth phase should meet the requirement that the maximum value of the bridge arm current after adding the first additional voltage and the second additional voltage should be greater than 0.15 times the current amplitude of the AC side. If the hybrid type When the MMC runs on the inverter, the amplitude of the sine wave current command of the jth phase should meet the minimum value of the bridge arm current after adding the first additional voltage and the second additional voltage and should be less than negative 0.15 times of the current amplitude of the AC side.

The second additional voltage v _j2 of the j-th phase is obtained by proportional resonance control of the j-th phase double-frequency circulating current command, the j-th phase circulating current on the AC side of the hybrid MMC, and the hybrid-type MMC DC side current; specifically, according to the hybrid The difference between the jth phase circulating current on the MMC AC side and 1/3 of the hybrid MMC DC side current obtains the high-order component in the circulating current, whose harmonic order is greater than or equal to 1, and the jth phase double frequency harmonic command After making a difference with the high-order component in the circulating current, proportional resonance control is performed to obtain the second additional voltage v _j2 of the j-th phase; wherein, the j-th phase double-frequency circulating current command is zero, and the resonance frequency of the proportional resonance control is 100Hz, so as to realize Suppresses the double frequency component of the AC output current.

The third additional voltage v _j3 of the j phase is obtained by resonantly controlling the jth phase triple frequency circulating current command and the hybrid MMC DC side current; specifically, the jth phase triple frequency circulating current command and the hybrid MMC DC side Resonance control is performed on the current difference to obtain the third additional voltage v _j3 of the jth phase; wherein, the jth phase triple frequency circulating current command is zero, and the resonant frequency of the resonance control is 150Hz, so as to realize the triple frequency in the DC current The weight is assisted with suppression.

The fourth additional voltage v _j4 of the j-phase is obtained by proportionally resonantly controlling the double-frequency harmonic command of the j-th phase and the hybrid MMC AC side current; specifically, the j-phase double-frequency harmonic command and the hybrid MMC The fourth additional voltage v _j4 of the j-th phase obtained by the difference of the MMC AC side current through the proportional resonance control, wherein the j-th phase double-frequency harmonic command is zero, and the resonance frequency of the proportional resonance control is 100Hz, so as to realize the The double frequency component of the AC output current is suppressed.

The fifth additional voltage v _j5 of the j-th phase is obtained by proportionally controlling the j-th phase upper bridge arm capacitor voltage and the j-th phase lower bridge arm capacitor voltage.

By controlling the number of full-bridge sub-modules and half-bridge sub-modules in the j-phase bridge arm, the output voltage of the j-phase upper bridge arm meets The output voltage of the lower bridge arm of phase j satisfies And let j traverse a, b, c.

Among them, v _dc is the port voltage of the DC side of the hybrid MMC, and e _j is the internal potential of the jth phase output by the AC side of the hybrid MMC.

By adding the first additional voltage to the fifth additional voltage in the upper and lower bridge arms, changing the current amplitude and phase of the upper and lower bridge arms of the j-phase, the charging and discharging area of the half-bridge sub-module of the j-phase is close to the charging and discharging area of the full-bridge sub-module, and then Avoid continuous rise of the capacitor voltage in the half-bridge sub-module while the continuous drop of the full-bridge sub-module or continuous rise of the capacitor voltage in the half-bridge sub-module while the continuous drop of the full-bridge sub-module, to ensure that the operating point of the AC and DC sides remains unchanged, and then realize Reliable operation of the converter, and then realize the expansion of the operation area of the hybrid MMC.

In the control method provided by the present invention, the upper and lower bridge arms of each phase adopt the following switching sub-module sequence rules. According to the voltage of the bridge arm, determine the number ΔN of sub-module switching, and switch the sub-modules in the following order, so that the output voltage of the upper bridge arm of phase j satisfies The output voltage of the lower bridge arm of phase j satisfies

When the output voltage of the bridge arm is positive and the current of the bridge arm is positive, choose to invest in the ΔN submodules with the lowest voltage ranking among all submodules or choose to cut off the ΔN submodules with the highest voltage ranking among all submodules, and the submodules include the full bridge submodule and half-bridge submodules;

When the output voltage of the bridge arm is positive and the current of the bridge arm is negative, choose to invest in the ΔN submodules with the highest voltage ranking among all the submodules or choose to cut off the ΔN submodules with the lowest voltage ranking among all the submodules;

When the output voltage of the bridge arm is negative and the current of the bridge arm is positive, choose to invest in the ΔN submodules with the highest voltage ranking among all the full-bridge submodules or choose to cut off the ΔN submodules with the lowest voltage ranking among all the full-bridge submodules;

When the output voltage of the bridge arm is negative and the current of the bridge arm is negative, choose to invest in the ΔN submodules with the lowest voltage ranking among all the full-bridge submodules or choose to cut off the ΔN submodules with the highest voltage ranking among all the full-bridge submodules.

The control method of expanding the hybrid MMC operation area provided by the present invention is based on the physical experiment platform of the three-phase hybrid MMC, and the number ratio of the full bridge sub-module and the half bridge sub-module of each phase upper bridge arm is 2:1, and the full bridge sub-module The number of modules is 2, the capacitor rated voltage ratio is 1:1, both are 100V, the ratio of the number of full-bridge sub-modules and half-bridge sub-modules in the lower bridge arm of each phase is 2:1, and the number of full-bridge sub-modules is 2 The rated voltage ratio of the capacitor is 1:1, both are 100V; the rated voltage of the DC side during normal operation is V _dc = 200V.

The first embodiment and the first comparative example:

When the MMC converter has a constant resistance load and the modulation coefficient of the AC side is increased from 1.8 to 1.9, that is, when the transmission power increases from 3.6kW to 4.0kW, the existing control method is used to change the conduction of the upper bridge arm and the lower bridge arm. The number of full-bridge sub-modules and the number of half-bridge sub-modules of , so that the output voltage of the upper bridge arm of phase j satisfies Make the output voltage of the lower bridge arm of phase j equal to As a first comparative example. FIG. 3(A) shows the A-phase current, the A-phase circulating current and the sub-module capacitor voltage waveform of the lower bridge arm of the A-phase in the first comparative example sequentially from top to bottom. As shown in Figure 3A(c), it can be found that after the modulation factor increases, the capacitor voltage of the full-bridge sub-module keeps dropping, while the capacitor voltage of the half-bridge sub-module keeps rising. When the capacitor voltage of the half-bridge sub-module rises to about 120V, the system shuts down.

Using the control method provided by the present invention, when the difference between the capacitance voltage of the half-bridge sub-module and the capacitance voltage of the full-bridge sub-module in each bridge arm of each phase is greater than the voltage threshold of 1.5V, by controlling the full-bridge sub-module and the half-bridge sub-module The number of conductions, so that the output voltage of the upper bridge arm of phase j satisfies The output voltage of the lower bridge arm of phase j satisfies Wherein, the magnitude of the sine wave current command of the jth phase is 6A. FIG. 3B shows the A-phase current, the A-phase circulating current and the sub-module capacitor voltage waveform of the lower bridge arm of the A-phase in the first embodiment sequentially from top to bottom. As shown in Figure 3B(c), it can be found that the capacitor voltage of the sub-module remains stable, and does not continuously rise or fall within a fundamental frequency cycle, and the hybrid MMC can run for a long time.

The second embodiment and the second comparative example:

When the rated voltage on the DC side drops from 200V to 160V and the grid side power factor is below 1, the converter transmits 2.4kW of active power to the grid. Using the existing control method, by changing the number of full-bridge sub-modules and the number of half-bridge sub-modules in which the upper bridge arm and the lower bridge arm are turned on, the output voltage of the j-phase upper bridge arm satisfies Make the output voltage of the lower bridge arm of phase j equal to As a second comparative example. Figure 4A shows the voltage waveform of the DC side, the circulating current of phase A, and the capacitor voltage waveform of the sub-module of the lower bridge arm of phase A from top to bottom. As shown in Figure 4A(c), it can be found that after the DC voltage drops, the capacitor voltage of the full-bridge sub-module keeps dropping, while the capacitor voltage of the half-bridge sub-module keeps rising. When the capacitor voltage of the half-bridge sub-module rises to about 120V, the system shuts down.

Using the control method provided by the present invention, when the difference between the capacitance voltage of the half-bridge sub-module and the capacitance voltage of the full-bridge sub-module in each bridge arm of each phase is greater than the voltage threshold of 1.5V, by controlling the full-bridge sub-module and the half-bridge sub-module The number of conductions, so that the output voltage of the upper bridge arm of phase j satisfies The output voltage of the lower bridge arm of phase j satisfies Wherein, the magnitude of the sine wave current command of the jth phase is 4.2A. Figure 4B shows the voltage waveform of the DC side, the circulating current of phase A, and the capacitor voltage waveform of the sub-module of the lower bridge arm of phase A from top to bottom. As shown in Figure 4B(c), it can be found that the capacitor voltage of the sub-module remains stable, and does not continuously rise or fall within a fundamental frequency cycle, and the hybrid MMC can run for a long time.

Those skilled in the art can easily understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (8)

1. a kind of control method that expands hybrid type MMC operating area, each bridge arm of described hybrid type MMC all comprises a plurality of full bridge submodules and a plurality of half bridge submodules, it is characterized in that, comprises the following steps: (1) Real-time detection of the capacitance voltage of the half-bridge sub-module and the capacitance voltage of the full-bridge sub-module in each bridge arm of each phase; (2) Judging whether the difference between the capacitance voltage of the half-bridge submodule and the capacitance voltage of the full-bridge submodule in each bridge arm of each phase is greater than the voltage threshold, if so, then enter step (3); otherwise perform step (1); (3) Obtain the first additional voltage _vj1 of the j-phase by controlling the j-phase sine wave current command, the j-phase circulating current of the hybrid MMC, and the hybrid MMC DC side current through proportional resonance control; The second additional voltage v _j2 of the j-th phase is obtained by proportional resonance control of the j-th phase double-frequency circulating current command, the j-th phase circulating current on the AC side of the hybrid MMC, and the hybrid-type MMC DC side current; The third additional voltage v _j3 of the j-th phase is obtained by resonantly controlling the triple-frequency circulating current command of the j-th phase and the hybrid MMC DC side current; The fourth additional voltage v _j4 of the j-th phase is obtained by controlling the double-frequency harmonic command of the j-th phase and the hybrid MMC AC side current through proportional resonance control; The fifth additional voltage v _j5 of the j-th phase is obtained by proportionally controlling the j-th phase upper bridge arm capacitor voltage and the j-th phase lower bridge arm capacitor voltage; By controlling the conduction quantity of the full-bridge sub-module and the half-bridge sub-module of the j-phase bridge arm, the output voltage of the j-phase upper bridge arm satisfies The output voltage of the lower bridge arm of phase j satisfies And let j traverse its value; by increasing the first additional voltage to the fifth additional voltage on the upper and lower bridge arms, changing the current amplitude and phase of the upper and lower bridge arms of each phase, to increase the charging and discharging area of the half-bridge sub-module , and then expand the hybrid MMC operating area; Among them, v _dc is the DC side port voltage of the hybrid MMC, e _j is the internal potential of the jth phase output from the AC side of the hybrid MMC, and j=a, b, c, a, b, and c represent the three phases of A, B, and C respectively phase; v _j1 is the first additional voltage of the j-th phase; v _j2 is the second additional voltage of the j-th phase; v _j3 is the third additional voltage of the j-th phase; v _j4 is the fourth additional voltage of the j-th phase; v _j5 is the fifth additional voltage of the jth phase. 2. control method according to claim 1, is characterized in that, the phase of described j phase sine wave current instruction in described step (3) and the phase phase of described hybrid MMC AC side output j phase internal potential The difference is 90 degrees, and the frequency of the jth phase sine wave current command is 50 Hz; If the hybrid MMC operates on the rectifier, the amplitude of the j-th phase sine wave current command satisfies that the maximum value of the bridge arm current after adding the first additional voltage and the second additional voltage is greater than 0.15 times of the current amplitude of the AC side, if If the hybrid MMC runs on the inverter, then the amplitude of the j-th phase sine wave current command satisfies that the minimum value of the bridge arm current after adding the first additional voltage and the second additional voltage is less than negative 0.15 times of the current amplitude of the AC side . 3. The control method according to claim 1 or 2, characterized in that, in the step (3), the first additional voltage of the j phase is obtained according to the following steps: The difference between the j-th phase circulating current on the AC side of the hybrid MMC and 1/3 of the current value on the DC side of the hybrid MMC is used as a high-order component in the circulating current; Proportional resonance control is performed on the difference between the jth phase sine wave current command and the high-order component in the circulating current to obtain the first additional voltage of the jth phase. 4. The control method according to any one of claims 1 to 3, characterized in that, in the step (3), the second additional voltage of the jth phase is obtained according to the following steps: The difference between the j-th phase circulating current on the AC side of the hybrid MMC and 1/3 of the current value on the DC side of the hybrid MMC is used as a high-order component in the circulating current; Proportional resonance control is performed on the difference between the j-th phase double-frequency circulating current command and the high-order component in the circulating current to obtain the second additional voltage of the j-th phase, wherein the value of the j-th phase double-frequency circulating current command value is zero , the circulating current of the jth phase on the AC side of the hybrid MMC is obtained by taking the average value of the detected upper bridge arm current and the lower bridge arm current. 5. The control method according to any one of claims 1 to 4, characterized in that, in the step (3), the third additional voltage of the jth phase is obtained according to the following steps: performing resonance control on the difference between the jth phase triple frequency circulating current command and the hybrid MMC DC side current to obtain the third additional voltage of the j phase, wherein the jth phase triple frequency circulating current command value is zero, The circulating current of the jth phase on the AC side of the hybrid MMC is obtained by taking the average value of the detected upper bridge arm current and the lower bridge arm current. 6. The control method according to any one of claims 1 to 5, characterized in that, in the step (3), the fourth additional voltage of the jth phase is obtained according to the following steps: The difference between the jth phase double frequency harmonic command and the hybrid MMC AC side current is controlled by proportional resonance to obtain the fourth additional voltage of the j phase, wherein the jth phase double frequency harmonic command value is zero . 7. The control method according to any one of claims 1 to 6, characterized in that, in the step (3), the number ΔN of sub-module switching is determined according to the bridge arm voltage, and the sub-modules are switched in the following order : When the output voltage of the bridge arm is positive and the current of the bridge arm is positive, choose to invest in the ΔN submodules with the lowest voltage ranking among all the submodules or choose to cut off the ΔN submodules with the highest voltage ranking among all the submodules; When the output voltage of the bridge arm is positive and the current of the bridge arm is negative, choose to invest in the ΔN submodules with the highest voltage ranking among all the submodules or choose to cut off the ΔN submodules with the lowest voltage ranking among all the submodules; When the output voltage of the bridge arm is negative and the current of the bridge arm is positive, choose to invest in the ΔN submodules with the highest voltage ranking among all the full-bridge submodules or choose to cut off the ΔN submodules with the lowest voltage ranking among all the full-bridge submodules; When the output voltage of the bridge arm is negative and the current of the bridge arm is negative, choose to invest in the ΔN submodules with the lowest voltage ranking among all the full-bridge submodules or choose to cut off the ΔN submodules with the highest voltage ranking among all the full-bridge submodules. 8. The control method according to any one of claims 1 to 7, characterized in that the ratio of the number of full-bridge sub-modules and half-bridge sub-modules in the hybrid MMC can be any positive value.