CN113922687A - Cascaded multi-level conversion device, control method and controller thereof - Google Patents
Cascaded multi-level conversion device, control method and controller thereof Download PDFInfo
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Abstract
A cascade multi-level conversion device, a control method and a controller thereof are provided, wherein the conversion device comprises a three-phase inverter, and the three-phase inverter comprises two power modules and four capacitors; a capacitor is connected between the neutral point of each power module and the positive bus and the negative bus; the output end of each power module is respectively connected with a three-phase stator of the motor; the control method of the cascade multi-level conversion device comprises the step of cooperatively suppressing the common-mode voltage of the cascade multi-level conversion device by controlling the common-mode voltage output by the two power modules, so that the purpose of suppressing the common-mode voltage output by the cascade multi-level conversion device is achieved. The invention realizes the improvement of the voltage and the power of the whole cascade type multi-level conversion system through the two power modules, and the control method is simple, strong in practicability and easy to popularize and use.
Description
Technical Field
The invention relates to a multi-level converter and a control method thereof, belonging to the technical field of multi-level converter control.
Background
The motor system in China occupies a large area in energy utilization, and the improvement of the efficiency of the motor system is of great importance for improving the energy utilization rate in China. Compared with a low-voltage motor system, the high-voltage motor has the natural advantage of high efficiency, so that the high-voltage motor and a control system thereof can be more widely applied in the future. The high-voltage motor is generally driven by a high-voltage inverter, the high-voltage inverter is generally limited by the withstand voltage of a semiconductor device by adopting a topology structure of a multilevel converter, and research work for the multilevel converter is continued in order to enable the multilevel converter to output more excellent electric energy quality and improve the reliability of the multilevel converter.
The traditional multilevel converter topology has respective defects, for example, a diode clamping type multilevel converter has the problems of complex midpoint potential control and large number of diodes, a flying capacitor type multilevel converter has the problems of large number of capacitors and large volume and low reliability of equipment, an H-cascade type high-voltage converter can drag a high-voltage motor, but the four-quadrant operation is difficult to realize, so that feedback energy cannot return to a power grid, and the system efficiency is greatly reduced, so that a practical multilevel converter device capable of operating in four quadrants is lacked in the high-voltage field of 6kV and above.
Disclosure of Invention
The invention aims to provide a cascade multilevel converter and a control method which are simple in structure and control and can operate in four quadrants, so as to solve the problems in the background technology.
In order to achieve the purpose, the invention provides the following technical scheme: a cascaded multilevel conversion device, comprising: the cascaded multi-level conversion device comprises a three-phase inverter, wherein the three-phase inverter comprises two power modules M1, M2 and four capacitors; a capacitor is connected between the neutral point of each power module and the positive bus and the negative bus; the output end of each power module is respectively connected with a three-phase stator of the motor; the control method of the cascade multilevel converter comprises the following steps:
setting a reference voltage given vector output by the cascade multi-level conversion device as the sum of reference voltage given vectors of the two power modules;
calculating respective zero sequence voltage components according to the given vectors of the reference voltages of the power modules;
the control of the midpoint voltage of each power module is realized by a method of superposing a zero sequence voltage component on a given vector of a reference voltage;
controlling bridge arm capacitance voltages of the power modules based on the voltage closed loop, and acquiring the bridge arm capacitance voltages of each power module;
calculating the common-mode voltage output by each power module according to the reference voltage vector of the superposed zero-sequence voltage component and the bridge arm capacitance voltage;
the common-mode voltage output by the two power modules is controlled to cooperatively suppress the common-mode voltage of the cascaded multi-level conversion device, so that the purpose of suppressing the common-mode voltage output by the cascaded multi-level conversion device is achieved.
Preferably, the setting of the reference voltage given vector output by the cascaded multilevel conversion device to be the sum of the reference voltage given vectors of the two power modules includes:
acquiring a reference voltage vector set required to be output by the cascade multi-level conversion device;
the reference voltage vector which needs to be output by the cascade type multi-level conversion device is given and generated by the cooperation of each power module M1 and M2; namely, it is
Uref＝Uref_M1+Uref_M2 (1)
In the formula of UrefGiven reference voltage vector, U, to be output by a cascade-type multilevel converterref_M1Given the reference voltage vector generated by the power module M1, Uref_M2Given by the reference voltage vector generated by power module M2.
Preferably, the respective zero-sequence voltage components are calculated according to the reference voltage given vector of each power module, and the zero-sequence voltage components are:
in the formula:
for the zero-sequence voltage component, m, n and k0Calculating coefficients for the zero sequence voltage component, K being the number of levels output by the power module, UdcIs the power module bus voltage;
the maximum value of the three-phase reference voltage vector in the power module;
is the minimum value of the three-phase reference voltage vector in the power module.
Preferably, the controlling of the bridge arm capacitance voltage of each power module based on the voltage closed loop includes,
collecting the voltage of the bridge arm capacitor controlled in each power module and the current direction of the bridge arm capacitor;
selecting a proper redundant switch state according to the voltage closed loop;
controlling the charging and discharging process of the controlled bridge arm capacitor through the state of the redundant switch, realizing the control of the bridge arm capacitor voltage, and acquiring the bridge arm capacitor voltage at the current moment;
the wave equation of the bridge arm capacitance voltage at the current moment is as follows:
wherein Δ T is a current ioAction time of (C)fIs the capacitance value of the bridge arm capacitance, Δ ufxIs the fluctuation amplitude of the bridge arm capacitance voltage u'fxThe bridge arm capacitance voltage at the last moment.
Preferably, the calculating the common-mode voltage output by each power module according to the reference voltage vector of the superimposed zero-sequence voltage component and the bridge arm capacitance voltage specifically includes:
in the formula: e is the magnitude of one level of the power module, and is equal to U in valuedc/(K-1)，UdcIs the bus voltage of the power module, K is the number of levels output by the power module, ufa、ufb、ufcRespectively representing the capacitance voltage in the three-phase bridge arm corresponding to the power module; wherein v isa、vb、vcOn-off state, v, of three-phase corresponding output of power modulea、vb、vcThe relationship to the reference voltage vector is as follows,
taking phase A of power module M1 as an example, vaAnd
the relational equation of (A) is as follows:
in the formula (I), the compound is shown in the specification,
the reference voltage vector of the zero sequence voltage component is superimposed for power module M1.
Preferably, the cooperative suppression of the common-mode voltage of the cascaded multilevel converter by controlling the common-mode voltage output by the two power modules specifically includes,
the common-mode voltage output by the cascaded multilevel conversion device is generated by two power modules together, i.e.
Ucom＝(Ucom_M1+Ucom_M2)/2
In the formula of UcomIs a common mode voltage, Ucom_M1、Ucom_M2Is a common mode voltage generated by two power modules;
the method for controlling the common-mode voltage output by the two power modules and cooperatively suppressing the common-mode voltage of the cascaded multi-level conversion device comprises 2 steps:
(1) enabling the common mode voltage generated by the two power modules to be 0;
(2) under the condition that the common mode voltage is not zero, the common mode voltage generated by the two power modules is enabled to be largeSmall exactly opposite, i.e. Ucom_M1＝-Ucom_M2。
In another aspect, the present invention further includes a controller of a cascaded multi-level converter, the controller being connected to two power modules M1 and M2 of the cascaded multi-level converter and being configured to perform the above-mentioned cascaded multi-level converter control method.
In another aspect, the present invention further includes a cascaded multilevel converter including a three-phase inverter, the three-phase inverter including two power modules and four capacitors;
a capacitor is connected between the neutral point of the power module and the positive bus and between the neutral point of the power module and the negative bus;
the output ends of the power modules are respectively connected with a three-phase stator of the motor;
and the control input end of the power module is connected with the controller.
Preferably, the power modules M1 and M2 have the same structure.
Preferably, the power modules M1 and M2 are both composed of a set of three-phase multilevel converters.
The invention has the beneficial effects that:
compared with the traditional diode clamping type multi-level conversion device and the capacitance flying type multi-level conversion device, the invention has the characteristic of simple structure, does not need a plurality of independent direct current sources and does not have direct series connection of switching tubes in the circuit. The voltage and power of the whole cascade system are improved through the two power units, the whole device can easily realize four-quadrant operation, and compared with the traditional multi-level conversion device, the multi-level conversion device has the characteristics of simpler control, higher practicability, and easier popularization and use.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.
Fig. 1 is a topology structure diagram of a cascade multilevel converter according to an embodiment of the present invention;
fig. 2 is a flowchart of a control method of a cascade multilevel converter according to an embodiment of the present invention;
fig. 3 is a flowchart illustrating control of the bridge arm capacitor voltage inside the power module according to an embodiment of the present invention;
FIG. 4 is a topology diagram of a power module according to an embodiment of the present invention, which illustrates a diode-clamped three-level converter;
FIG. 5 is a waveform of a load phase voltage outputted from a switching device when a diode-clamped three-level converter is used as an example of a power module according to an embodiment of the present invention;
fig. 6 is an FFT analysis diagram of the phase-a current waveform and the phase-a current corresponding to the output of the switching device in the power module according to the embodiment of the present invention, which uses the diode clamp type three-level converter as an example;
FIG. 7 is a diagram illustrating waveforms of midpoint voltages of two power units when the power module is a diode-clamped three-level converter according to an embodiment of the present invention;
fig. 8 is a diagram illustrating a common mode voltage waveform output by the switching device in the power module according to the embodiment of the present invention, which is illustrated by a diode-clamped three-level converter.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, the disclosed embodiment provides a cascaded multilevel conversion device, which is a three-phase inverter including two power modules M1, M2 and four capacitors; a capacitor is connected between the neutral point of each power module and the positive bus and the negative bus; and the output end of each power module is respectively connected with a three-phase stator of the motor.
Specifically, the cascade multi-level conversion device comprises a three-phase inverter consisting of two power modules and four capacitors, wherein the power modules are divided into a power module M1 and a power module M2, each power module is provided with six electrical connection points, and the capacitors are divided into a capacitor C1, a capacitor C2, a capacitor C3 and a capacitor C4. The first electrical connection point and the second electrical connection point of the power module M1 are connected with the capacitor C1, the second electrical connection point and the third electrical connection point of the power module M1 are connected with the capacitor C2, the fourth electrical connection point, the fifth electrical connection point and the sixth electrical connection point of the power module M1 are respectively connected with A, B, C of the three-phase stator of the motor, the first electrical connection point and the second electrical connection point of the power module M2 are connected with the capacitor C3, the second electrical connection point and the third electrical connection point of the power module M2 are connected with the capacitor C4, and the fourth electrical connection point, the fifth electrical connection point and the sixth electrical connection point of the power module M2 are respectively connected with a, b and C of the three-phase stator of the motor. The positive bus of the three-phase multi-level inverter is the first electrical connection point of the power module, the negative bus of the three-phase multi-level inverter is the third electrical connection point of the power module, the neutral point of the three-phase multi-level inverter is the second electrical connection point of the power module, and the three output ends of the three-phase multi-level inverter are the fourth, fifth and sixth electrical connection points of the power module respectively.
Further, it is preferable that the three-phase multilevel converters in the power modules M1 and M2 have the same configuration. Of course, the appropriate three-phase multi-level converter structure can be flexibly selected according to the actual system requirement.
Further, the power modules M1 and M2 are both composed of a set of three-phase multilevel converters. The three-phase multi-level converter can be a three-phase two-level converter, a three-phase three-level converter or a three-phase five-level or even more level converter.
Based on the above device, an embodiment of the present invention provides a method for controlling a cascaded multilevel conversion device, where the method for controlling the cascaded multilevel conversion device includes the following steps:
s100: and setting a reference voltage given vector output by the cascade type multi-level conversion device to be the sum of the reference voltage given vectors of the two power modules.
Specifically, the method comprises the following steps:
acquiring a reference voltage vector set required to be output by the cascade multi-level conversion device;
the reference voltage vector which needs to be output by the cascade type multi-level conversion device is given and generated by the cooperation of each power module M1 and M2; namely, it is
Uref＝Uref_M1+Uref_M2 (1)
In the formula of UrefGiven reference voltage vector, U, to be output by a cascade-type multilevel converterref_M1Given the reference voltage vector generated by the power module M1, Uref_M2Given by the reference voltage vector generated by power module M2.
It can be seen from the formula (1) that the voltage output by the cascaded multilevel converter is cooperatively generated by the power modules M1 and M2, so that the maximum voltage that the whole converter can output is the sum of the maximum voltages that the two power modules can output, and the maximum power that the whole converter can output is also the sum of the maximum powers that the two power modules can output.
The cascade multilevel converter after cooperative control is adopted to output three-phase current without third harmonic, the sine degree is very high, and distortion is avoided; meanwhile, the equivalent switching frequency output by the conversion device can be equal to the sum of the switching frequencies of the two power units through the cooperative control, so that the aim of waiting to the higher equivalent switching frequency by actually adopting the low switching frequency is fulfilled, the switching loss of the two power units is reduced, and the conversion efficiency of the whole cascade type multi-level conversion device is improved.
S200: and calculating respective zero sequence voltage components according to the reference voltage given vectors of the power modules.
Specifically, this step is exemplified by a power module M1, in which zero sequence voltage is present
The calculation formula of (2) is as follows:
in the formula: m, n and k0Calculating coefficients for the zero sequence component, K being the number of levels output by the power module, UdcIs the power module bus voltage;
is the maximum value of the three-phase reference voltage vector in the power module M1;
is the minimum value of the three-phase reference voltage vector in the power module M1.
S300: and realizing the control of the midpoint voltage of each power module by a method of superposing the zero-sequence voltage components by the given vector of the reference voltage.
Specifically, the midpoint voltage control of the power modules in this step specifically adopts a power module independent control method, that is, the power modules M1 and M2 are controlled as two independent converters when the midpoint potentials inside the power modules M1 and M2 are controlled; the method of overlapping zero sequence components can be specifically adopted for the point voltage control of each power module, and at this time, it needs to be noted that when the zero sequence components are overlapped, the power modules need to overlap the same zero sequence components at the same time by three phases so as to ensure that the line voltage output by the power modules is unchanged. Adding the three-phase reference voltage vector magnitude and the calculated zero sequence component to obtain a reference voltage given vector after the zero sequence component is superposed:
in the formula: u shaperef_M1_a、Uref_M1_bAnd Uref_M1_cIs the magnitude of the original reference voltage vector in power module M1;
and
the three-phase reference voltage vector is obtained by superposing the zero-sequence component in the power module M1.
S400: and controlling bridge arm capacitance voltages of the power modules based on the voltage closed loop, and acquiring the bridge arm capacitance voltages of each power module.
Specifically, the method comprises the following steps:
collecting the voltage of the bridge arm capacitor controlled in each power module and the current direction of the bridge arm capacitor;
selecting a proper redundant switch state according to the voltage closed loop;
controlling the charging and discharging process of the controlled bridge arm capacitor through the state of the redundant switch, realizing the control of the bridge arm capacitor voltage, and acquiring the bridge arm capacitor voltage at the current moment;
the wave equation of the bridge arm capacitance voltage at the current moment is as follows:
wherein Δ T is a current ioAction time of (C)fIs the capacitance value of the bridge arm capacitance, Δ ufxIs the fluctuation amplitude of the bridge arm capacitance voltage u'fxThe bridge arm capacitance voltage at the last moment.
The specific flow chart is shown in FIG. 3, in which
Representing the magnitude of the reference voltage vector u after superposition of zero-sequence voltage components of one of the phases of the power moduleoRepresenting the voltage output of the phase, E representing the magnitude of a level of the power module, ufIs the magnitude of the capacitor voltage in the phase leg, ioS is a storage variable of a switch state to be output for the magnitude of the phase arm current.
S500: and calculating the common-mode voltage output by each power module according to the reference voltage vector of the superposed zero-sequence voltage component and the bridge arm capacitance voltage.
The common-mode voltage output by the power module has a direct relationship with the switching state output by the power module, and the output common-mode voltages corresponding to different switching states may be different, so that the magnitude of the output common-mode voltage corresponding to each switching state needs to be accurately known, and the switching state of the three-phase output of the power module is set as (v)a,vb,vc)。
Taking phase A of power module M1 as an example, vaAnd
the relationship of (a) to (b) is as follows:
in the formula: e is the magnitude of one level of the power module, and is equal to U in valuedc/(K-1)，UdcThe voltage is the bus voltage of the power module, and K is the level number output by the power module.
Its corresponding common mode voltage UcomIs composed of
In the formula: u. offa、ufb、ufcRespectively representing the capacitance voltage in the three-phase bridge arm corresponding to the power module.
U can be adjusted without considering the voltage of the bridge arm capacitorfa、ufb、ufcThe three bridge arm voltages are idealized to say that the three bridge arm voltages are always equal to E, and then ufa＝ufb＝ufcIn this case, the calculation of the common mode voltage is simplified, but the calculated common mode voltage does not reflect the actual magnitude of the common mode voltage. Therefore, if the accurate control of the common-mode voltage output by the cascaded multi-level conversion device is to be realized, calculation must be performed according to the reference voltage vector of each power module and the accurate bridge arm capacitance voltage, so that the magnitude of the common-mode voltage of the whole conversion device is suppressed as much as possible.
S600: the common-mode voltage output by the two power modules is controlled to cooperatively suppress the common-mode voltage of the cascaded multi-level conversion device, so that the purpose of suppressing the common-mode voltage output by the cascaded multi-level conversion device is achieved. The specific implementation mode is as follows:
the common mode voltage output by the cascade multi-level conversion device is UcomThe common mode voltage is generated by the power modules M1 and M2 together, i.e.
Ucom＝(Ucom_M1+Ucom_M2)/2 (3)
In the formula of Ucom_M1For common mode voltage, U, generated by power module M1com_M2Is the common mode voltage generated by power module M2.
As can be seen from equation (3), there are two methods for completely eliminating the common mode voltage output by the cascaded multilevel converter: firstly, the common-mode voltages generated by the two power modules are both 0, that is, the common-mode voltage generated by the power module M1 and the common-mode voltage generated by the power module M2 are both 0; secondly, under the condition that the common mode voltage is not zero, the common mode voltages generated by the two power modules are completely opposite in magnitude, namely Ucom_M1＝-Ucom_M2。
An embodiment of the present invention further provides a controller of a cascaded multi-level converter, a topological structure of the cascaded multi-level converter is shown in fig. 1, the controller is connected to two power modules M1 and M2 of the cascaded multi-level converter, the controller acquires voltage and current of the cascaded multi-level converter as feedback signals and sends the feedback signals to the controller, and through operation calculation of a control algorithm provided by the present invention, switching state signals output by each power module in the cascaded multi-level converter are finally obtained, and the obtained switching states are sent to a driving system to control on and off of each power device in the cascaded multi-level converter.
The controller is used for setting a reference voltage given vector output by the cascade multi-level conversion device to be equal to the sum of reference voltage given vectors of the two power modules; calculating respective zero sequence voltage components according to the given vectors of the reference voltages of the power modules; the control of the midpoint voltage of each power module is realized by a method of superposing a zero sequence voltage component on a given vector of a reference voltage; controlling bridge arm capacitance voltages of the power modules based on the voltage closed loop, and acquiring the bridge arm capacitance voltages of each power module; calculating the common-mode voltage output by each power module according to the reference voltage vector of the superposed zero-sequence voltage component and the bridge arm capacitance voltage; the common-mode voltage output by the two power modules is controlled to cooperatively suppress the common-mode voltage of the cascaded multi-level conversion device, so that the purpose of suppressing the common-mode voltage output by the cascaded multi-level conversion device is achieved. Namely, the control method of the cascade multi-level converter provided in the above embodiment is performed.
Fig. 4 shows that the power modules M1 and M2 in the embodiment of the present invention both use three-phase diode-clamped three-level inverters as power module topologies. At the moment, the formed cascade type multi-level conversion device is a cascade type five-level conversion device, and the device can be applied to the field of high-voltage high-power frequency conversion.
The control method of the invention is adopted to explain the control of the cascade multilevel converter under the simulation condition that the power module takes a three-phase diode clamping type three-level inverter as an example, the output voltage of the converter is 6kV, and the power output is 4 MW.
As can be seen from fig. 5, when the cooperative control is adopted, the a-phase output voltage U of the power module M1 M13000V, phase a output voltage U of power module M2M2＝-UM1at-3000V, the A-phase output voltage U of the cascade multi-level conversion deviceao＝UM1-UM26000V. The level number of the phase voltage levels of the power modules M1 and M2 is only 3, while the level number of the phase voltage levels of the multi-level conversion device is up to 17, and the level number is greatly improved, so that the voltage and power of the whole conversion device are improved, current harmonics output by the converter can be effectively reduced, and the output performance of the conversion device is greatly improved. As can be seen from FIG. 6, the three-phase current output by the conversion device has very high sine degree and no distortion, and the FFT analysis of the three-phase current further verifies the inversionThe output of the converter has the advantages of no third harmonic and equivalent switching frequency superposition. As can be seen from fig. 7, the midpoint voltages of the two power modules are well controlled, and the fluctuation of the midpoint voltages of the two power modules is within ± 25V at a high power output of 4MW, which illustrates the effectiveness of the midpoint potential control method in the present invention.
As can be seen from fig. 8, by using the common mode voltage suppression method of the present invention, the common mode voltage of the cascaded multilevel converter is always zero, which verifies the effectiveness of the common mode voltage suppression method of the present invention.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (10)
1. A control method of a cascade multilevel conversion device is characterized in that: the cascaded multi-level conversion device comprises a three-phase inverter, wherein the three-phase inverter comprises two power modules M1 and M2 and four capacitors; a capacitor is connected between the neutral point of each power module and the positive bus and the negative bus; the output end of each power module is respectively connected with a three-phase stator of the motor; the control method of the cascade multilevel converter comprises the following steps:
setting a reference voltage given vector output by the cascade multi-level conversion device as the sum of reference voltage given vectors of the two power modules;
calculating respective zero sequence voltage components according to the given vectors of the reference voltages of the power modules;
the control of the midpoint voltage of each power module is realized by a method of superposing a zero sequence voltage component on a given vector of a reference voltage;
controlling bridge arm capacitance voltages of the power modules based on the voltage closed loop, and acquiring the bridge arm capacitance voltages of each power module;
calculating the common-mode voltage output by each power module according to the reference voltage vector of the superposed zero-sequence voltage component and the bridge arm capacitance voltage;
the common-mode voltage output by the two power modules is controlled to cooperatively suppress the common-mode voltage of the cascaded multi-level conversion device, so that the purpose of suppressing the common-mode voltage output by the cascaded multi-level conversion device is achieved.
2. The control method of the cascade multilevel converter according to claim 1, characterized in that: the setting of the reference voltage given vector output by the cascaded multilevel conversion device as the sum of the reference voltage given vectors of the two power modules comprises the following steps:
acquiring a reference voltage vector set required to be output by the cascade multi-level conversion device;
the reference voltage vector which needs to be output by the cascade type multi-level conversion device is given and generated by the cooperation of each power module M1 and M2; namely, it is
Uref＝Uref_M1+Uref_M2 (1)
In the formula of UrefGiven reference voltage vector, U, to be output by a cascade-type multilevel converterref_M1Given the reference voltage vector generated by the power module M1, Uref_M2Given by the reference voltage vector generated by power module M2.
3. The control method of the cascade multilevel converter according to claim 1, characterized in that: calculating respective zero-sequence voltage components according to the given vector of the reference voltage of each power module, wherein the zero-sequence voltage components are as follows:
in the formula:
for the zero-sequence voltage component, m, n and k0The coefficients are calculated for the zero sequence voltage components,k is the number of levels output by the power module, UdcIn order to provide the bus voltage for the power module,
the maximum value of the three-phase reference voltage vector in the power module,
is the minimum value of the three-phase reference voltage vector in the power module.
4. The control method of the cascade multilevel converter according to claim 1, characterized in that: the voltage-based closed loop controls the bridge arm capacitance voltage of each power module, including,
collecting the voltage of the bridge arm capacitor controlled in each power module and the current direction of the bridge arm capacitor;
selecting a redundant switch state according to the voltage closed loop;
controlling the charging and discharging process of the controlled bridge arm capacitor through the state of the redundant switch, realizing the control of the bridge arm capacitor voltage, and acquiring the bridge arm capacitor voltage at the current moment;
the wave equation of the bridge arm capacitance voltage at the current moment is as follows:
wherein Δ T is a current ioAction time of (C)fIs the capacitance value of the bridge arm capacitance, Δ ufxIs the fluctuation amplitude of the bridge arm capacitance voltage u'fxThe bridge arm capacitance voltage at the last moment.
5. The control method of the cascaded multilevel converter according to claim 4, wherein: the calculating the common-mode voltage output by each power module according to the reference voltage vector of the superposed zero-sequence voltage component and the bridge arm capacitance voltage specifically comprises the following steps:
in the formula: e is the magnitude of one level of the power module, and is equal to U in valuedc/(K-1)，UdcIs the bus voltage of the power module, K is the number of levels output by the power module, ufa、ufb、ufcRespectively representing the capacitance voltage in the three-phase bridge arm corresponding to the power module; wherein v isa、vb、vcOn-off state, v, of three-phase corresponding output of power modulea、vb、vcThe relationship to the reference voltage vector is as follows,
taking phase A of power module M1 as an example, vaAnd
the relational equation of (A) is as follows:
in the formula (I), the compound is shown in the specification,
the reference voltage vector of the zero sequence voltage component is superimposed for power module M1.
6. The control method of the cascaded multilevel converter according to claim 5, wherein: the cooperative suppression of the common-mode voltage of the cascaded multilevel conversion device by controlling the common-mode voltage output by the two power modules specifically comprises,
the common-mode voltage output by the cascaded multilevel conversion device is generated by two power modules together, i.e.
Ucom＝(Ucom_M1+Ucom_M2)/2
In the formula of UcomIs a common mode voltage, Ucom_M1、Ucom_M2Is composed of two power modulesThe generated common mode voltage;
the method for controlling the common-mode voltage output by the two power modules and cooperatively suppressing the common-mode voltage of the cascaded multi-level conversion device comprises 2 steps:
(1) enabling the common mode voltage generated by the two power modules to be 0;
(2) under the condition that the common mode voltage is not zero, the common mode voltages generated by the two power modules are completely opposite in magnitude, namely Ucom_M1＝-Ucom_M2。
7. A controller of a cascaded multi-level converter, wherein the controller is connected with two power modules M1 and M2 of the cascaded multi-level converter and is used for executing a control method of the cascaded multi-level converter according to any one of claims 1 to 6.
8. A cascaded multi-level conversion device is characterized by comprising a three-phase inverter, wherein the three-phase inverter comprises two power modules M1 and M2 and four capacitors; a capacitor is connected between the neutral point of the power module and the positive bus and between the neutral point of the power module and the negative bus;
the output ends of the power modules are respectively connected with a three-phase stator of the motor;
the control input of the power module is connected to the controller of claim 7.
9. The cascaded multilevel converter according to claim 8, wherein the power modules M1 and M2 are identical in structure.
10. The cascaded multilevel converter according to claim 9, wherein the power modules M1 and M2 are each composed of a set of three-phase multilevel converters.
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