CN115395810A

CN115395810A - Multilevel soft switch inverter circuit and balancing method of intermediate level terminal voltage thereof

Info

Publication number: CN115395810A
Application number: CN202211180928.3A
Authority: CN
Inventors: 周衍
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-12-08
Filing date: 2022-09-27
Publication date: 2022-11-25
Also published as: CN114362574A; WO2023103811A1

Abstract

The invention discloses a multilevel soft switching inverter circuit, which comprises inverter driving circuits which are mutually independent in multiple phases and have the same structure; each phase of inverse driving circuit comprises four direct current input ends, an alternating current output end, a switching module, a soft switch inverse module and a control module; the switching module is provided with four input ends and two output ends, and the four input ends are respectively connected with the four direct current input ends; the soft switch inversion module is provided with two input ends and an output end, the two input ends of the soft switch inversion module are respectively connected with the two output ends of the switching module, and the output end of the soft switch inversion module is used as an alternating current output end; the control module is used for controlling the work of each module; the switching module is used for outputting a proper direct-current voltage window to the soft switch inversion module under the control of the control module; the soft switch inversion module is used for converting direct current into alternating current and outputting the alternating current.

Description

Multilevel soft switching inverter circuit and balancing method of intermediate level terminal voltage thereof

Technical Field

The invention relates to the field of inverter driving circuits, in particular to a multilevel soft switching inverter circuit and a method for balancing voltage of a middle level terminal of the multilevel soft switching inverter circuit.

Background

In the existing multi-level soft switching inverter circuit, an intermediate voltage direct current power supply port in a direct current bus in the application of using single direct current power supply or double direct current power supply input is generally obtained by serially dividing a plurality of groups of capacitors, and the charge-discharge state of the capacitors of the existing four-level input inverter driving circuit structure is changed along with the working state and cannot be balanced in an active mode, so that the intermediate voltage end of the direct current bus cannot obtain stable voltage.

Disclosure of Invention

In view of the problems in the background art, an object of the present invention is to provide a multilevel soft switching inverter circuit and a method for balancing intermediate level terminal voltages thereof.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a multi-level soft switching inverter circuit comprises inverter driving circuits which are mutually independent and have the same structure;

each phase of the inversion driving circuit comprises four direct current input ends, an alternating current output end, a switching module, a soft switch inversion module and a control module;

the four direct current input ends are direct current buses with four different levels formed by a plurality of direct current power supplies through a capacitance voltage division structure, and the four direct current input ends are a first direct current end, a second direct current end, a third direct current end and a fourth direct current end in sequence according to the sequence of the potentials from high to low;

the switching module is provided with four input ends and two output ends, and the four input ends are respectively connected with the first direct current end, the second direct current end, the third direct current end and the fourth direct current end;

the soft switch inversion module is provided with two input ends and an output end, the two input ends of the soft switch inversion module are respectively connected with the two output ends of the switching module, and the output end of the soft switch inversion module is used as the alternating current output end;

the control module is used for acquiring relevant working information of the multi-level soft switching inverter circuit and controlling the work of each module according to an acquisition result;

the switching module is used for connecting a proper direct-current voltage window to the soft-switch inversion module under the control of the control module;

the soft switch inversion module is used for converting the direct current provided by the switching module into alternating current to be output.

In some embodiments, the switching module comprises a balanced switching module and a voltage window switching module;

the balanced switching module is provided with two input ends and n output ends, n =1 or 2, and the two input ends of the balanced switching module are respectively connected with a second direct current end and a third direct current end;

the voltage window switching module is provided with two outer input ends, n inner input ends and two output ends, the two outer input ends of the voltage window switching module are respectively connected with the first direct current end and the fourth direct current end, and the n inner input ends are respectively connected with the n output ends of the balance switching module;

two input ends of the soft switch inversion module are respectively connected with two output ends of the voltage window switching module;

the balance switching module is used for compensating charges flowing through the second direct current end and the third direct current end under the control of the control module;

the voltage window switching module is used for connecting a proper direct-current voltage window to the soft switch inversion module under the control of the control module;

the balance switching module and the voltage window switching module respectively comprise a plurality of switching devices, and the control end of each switching device is connected with the control module, so that the switching state of each switching device can be switched under the control of the control module.

In some embodiments, n =2, the balanced switching module comprises a first switching device T _B1 A second switching device T _B2 A third switching device T _B3 And a fourth switching device T _B4 (ii) a The voltage window switching module comprises a fifth switching device T _L1 And a sixth switching device T _L2 Seventh switching device T _L3 And an eighth switching device T _L4 ；

The first switching device T _B1 And a third switching device T _B3 Are all connected with a second direct current terminal, the second switching device T _B2 And a fourth switching device T _B4 Is connected to a third dc terminal, and the first switching device T _B1 And the other end of the first switching device T _B2 Is connected to the other end of the first switching element and serves as a first output end of the balanced switching module, and the third switching element T _B3 And the other end of the fourth switching device T _B4 The other end of the first switching module is connected with the other end of the second switching module and is used as a second output end of the balanced switching module;

the fifth switching device T _L1 And a sixth switching device T _L2 The seventh switching device T is connected in series between the first direct current terminal and the first output terminal of the balanced switching module _L3 And an eighth switching device T _L4 The second output end of the balanced switching module is connected in series with the fourth direct current end;

the soft switch inverter module comprises a half-bridge circuit or a flying capacitor inverter circuit with a positive input end and a negative input end, an inductor L and a plurality of alternating-current end capacitors, wherein the positive input end of the half-bridge circuit or the flying capacitor inverter circuit is connected with a fifth switching device T _L1 And a sixth switching device T _L2 The negative input end of the common end is connected with the seventh switching device T _L3 And an eighth switching device T _L4 The output end of the half-bridge circuit or the flying capacitor inverter circuit is connected with the alternating current output end through the inductor L, one end of the alternating current end capacitor is connected with one direct current input end or the neutral potential, and the other end of the alternating current end capacitor is connected with the alternating current output end.

In some embodiments, n =1, the balanced switching module comprises a first switching device T _B1 And a second switching device T _B2 (ii) a The voltage window switching module comprises a third switchDevice T _L1 And a fourth switching device T _L2 A fifth switching device T _L3 And a sixth switching device T _L4 ；

The first switching device T _B1 Is connected to a second dc terminal, said second switching device T _B2 Is connected to the third dc terminal, and the first switching device T _B1 And the other end of the first switching device T _B2 The other end of the switching module is connected with the other end of the switching module and is used as the output end of the balanced switching module;

the third switching device T _L1 And a fourth switching device T _L2 The fifth switching device T is connected between the first direct current end and the output end of the balanced switching module in series _L3 And a sixth switching device T _L4 The fourth direct current end is connected in series with the output end of the balanced switching module;

the soft switch inverter module comprises a half-bridge circuit or a flying capacitor inverter circuit with a positive input end and a negative input end, an inductor L and a plurality of alternating-current end capacitors, wherein the positive input end of the half-bridge circuit or the flying capacitor inverter circuit is connected with a third switching device T _L1 And a fourth switching device T _L2 The negative input end of the common end is connected with the fifth switching device T _L3 And a sixth switching device T _L4 The output end of the half-bridge circuit or the flying capacitor inverter circuit is connected with the alternating current output end through the inductor L, one end of the alternating current end capacitor is connected with one direct current input end or the neutral potential, and the other end of the alternating current end capacitor is connected with the alternating current output end.

In some embodiments, the power supply further comprises a bidirectional direct current power supply additionally established by using a level node where the second direct current terminal and the third direct current terminal are located.

The invention also provides a method for balancing the intermediate level terminal voltage of the multilevel soft switching inverter circuit, which comprises the following steps:

the multi-level soft switching inverter circuit with n =2 is adopted;

under the control of the control module, the balance switching module automatically switches between a normal mode and a compensation mode to realize the voltage balance of each middle level end in the direct current bus;

in a normal mode, the first switching device T _B1 And a fourth switching device T _B4 Conducting, second switching device T _B2 And a third switching device T _B3 Turning off;

the compensation mode is divided into a compensation mode for the second direct current terminal and a compensation mode for the third direct current terminal;

in a compensation mode for the second direct current terminal, the third switching device T _B3 Conducting, fourth switching device T _B4 Off, first switching device T _B1 And a second switching device T _B2 Not conducting at the same time;

in a compensation mode for the third direct current terminal, the second switching device T _B2 Conducting, first switching device T _B1 Off, third switching device T _B3 And a fourth switching device T _B4 Not simultaneously conducting.

the multi-level soft switching inverter circuit with n =1 is adopted;

under the control of the control module, the balance switching module and the voltage window switching module are automatically switched between a normal mode and a compensation mode so as to realize the voltage balance of each middle level end in the direct current bus;

in the normal mode, the states of the respective switching devices are classified into two cases:

in the first case, the first switching device T _B1 And a fourth switching device T _L2 And a sixth switching device T _L4 Off, second switching device T _B2 A third switching device T _L1 And a fifth switching device T _L3 Conducting;

in the second case, the first switching device T _B1 And a fourth switching device T _L2 And a sixth switching device T _L4 Conducting, second switching device T _B2 A third switching device T _L1 And a fifth switching device T _L3 Turning off;

in a compensation mode for the second direct current terminal, the first switching device T _B1 A third switching device T _L1 And a fifth switching device T _L3 Conducting, second switching device T _B2 And a fourth switching device T _L2 And a sixth switching device T _L4 Turning off;

in a compensation mode for the third direct current terminal, the first switching device T _B1 A third switching device T _L1 And a fifth switching device T _L3 Off, second switching device T _B2 And a fourth switching device T _L2 And a sixth switching device T _L4 And conducting.

In some embodiments, the circuit uses the potential of the middle point between the first direct current terminal and the fourth direct current terminal as a neutral potential reference point, and the absolute values of the voltages of the first direct current terminal, the second direct current terminal, the third direct current terminal and the fourth direct current terminal are respectively expressed as U by taking the potential as a reference point ₁ 、u ₂ 、u ₃ And U ₄ Instantaneous value of voltage at AC output terminal is u _AC ；

Setting a voltage u in a control module ₂ And u ₃ Set value of U _2,set And U _3,set The control module is used for measuring u ₂ And u ₃ And a set value U _2,set And U _3,set Calculating the working interval of each compensation mode required for compensation operation in each half period of the alternating current output;

according to the calculation result, the control module switches the on-off states of the switching devices in the balance switching module and the voltage window switching module to enable the bus current i where the second direct current end and the third direct current end are located ₂ And i ₃ Average value I in period of AC output ₂ And I ₃ Compensating to the target value so as to make the corresponding voltage u ₂ And u ₃ In a steady state, and finally outputting the alternating current in a period u ₂ And u ₃ Average value of U ₂ And U ₃ Is stabilized at a set value U _2,set And U _3,set The above.

In some embodiments, the instantaneous current through the inductor L is represented by i _L Indicating that the average value of the inductor current in a switching period of the soft-switching inverter module is i _L,avg Indicating and setting an inductance reserve voltage U in the control module _res ；

The balance switching module normally works in a normal mode;

when the control module detects that the output end voltage is in the range u _AC ≥u ₂ +U _res Then the control module automatically controls the current i _L,avg The direction control balance switching module is switched to a compensation mode for compensating the second direct current end, and after the compensation operation required by the compensation mode is finished, the control module automatically switches the balance switching module back to a normal mode;

when the control module detects that the output end voltage is in the range u _AC ≤-u ₃ -U _res Then the control module automatically controls the current i _L,avg The direction control balance switching module is switched to a compensation mode for compensating the third direct current end, and when the compensation operation required by the compensation mode is finished, the control module automatically switches the balance switching module back to a normal mode;

when u is _AC <u ₂ And u _AC >-u ₃ When the switching module is in the normal mode, the balance switching module is kept in the normal mode;

the control module is used for controlling the AC output according to the working state of the AC output and the measured u ₂ And u ₃ Calculating a balance phase or a working interval required by voltage balance;

the control module switches the switching state of the switching device in the voltage window switching module according to the calculation result so as to switch the voltage window provided for the soft switching inversion module, so that the voltages of the second direct current end and the third direct current end are balanced in the period of alternating current output.

In some embodiments, if the multilevel soft switching inverter circuit includes a bidirectional dc power source established by a level node where the second dc terminal and the third dc terminal are located, the control module switches the switches in the balanced switching module and the voltage window switching moduleThe switching state of the device is that the bus current i of the second direct current end and the third direct current end is ₂ And i ₃ Average value I in period of AC output ₂ And I ₃ Compensating to a target value, wherein the target value corresponds to an output value required by the bidirectional direct current power supply;

if the multi-level soft switching inverter circuit does not comprise the bidirectional direct-current power supply, the control module switches the switching states of the switching devices in the balance switching module and the voltage window switching module to enable the bus current i where the second direct-current end and the third direct-current end are located ₂ And i ₃ Average value I in period of AC output ₂ And I ₃ Compensating to a target value, wherein the target value is 0.

Compared with the prior art, the multi-level soft switch inverter circuit and the balancing method for the voltage of the intermediate level terminal thereof provided by the invention have the advantages that the switching module is added on the basis of the multi-level soft switch inverter circuit, and the characteristic that the voltage and the current in the alternating current output periodically change is combined, so that the current flowing through each intermediate level terminal is compensated on the premise of realizing the soft switching of a switching device, and the voltage of each intermediate level terminal is actively balanced.

Drawings

Other objects and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings, and may assist in a comprehensive understanding of the invention.

Fig. 1a and 1b are schematic diagrams of multilevel soft switching inverter circuits provided by the present invention in two embodiments;

fig. 2a, 2b, 2c and 2d are schematic diagrams of a multi-level soft-switching inverter circuit based on a single dc power input and a dual dc power input, respectively;

fig. 3a, 3b, 3c and 3d are schematic diagrams of four configurations of a soft-switching inverter module, respectively;

FIGS. 4a, 4b and 4c are schematic diagrams of a multilevel soft switching inverter circuit including a bi-directional DC power source;

FIGS. 5a and 5b are waveform diagrams of voltage and current variations with time during an AC output period according to a first embodiment;

FIGS. 6a and 6b are waveform diagrams of voltage and current variations with time during an AC output period according to a second embodiment;

FIGS. 7a and 7b are waveform diagrams of voltage and current changes with time in an AC output period according to a third embodiment;

FIGS. 8a and 8b are waveform diagrams of voltage and current variations with time in an AC output period according to a fourth embodiment;

FIGS. 9a and 9b are waveform diagrams of voltage and current variations with time in an AC output period according to a fifth embodiment;

FIGS. 10a and 10b are waveform diagrams of voltage and current changes with time in an AC output period according to a sixth embodiment;

fig. 11a and 11b are waveform diagrams of voltage and current changes with time in an ac output period according to a seventh embodiment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the described embodiments of the invention without inventive step, are within the scope of protection of the invention.

Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs.

Referring to fig. 1a and 1b, the present invention provides a multilevel soft switching inverter circuit, which includes an inverter driving circuit 1 having a plurality of phases that are independent from each other and have the same structure; each phase inverter driving circuit 1 comprises four dc input terminals, an ac output terminal, a switching module, a soft switch inverter module 2 and a control module (not shown in the figure); the four direct current input ends are direct current buses with four different levels formed by a plurality of direct current power supplies through a capacitance voltage division structure, and the four direct current input ends are a first direct current end, a second direct current end, a third direct current end and a fourth direct current end in sequence according to the sequence of the potentials from high to low; the switching module is provided with four input ends and two output ends, and the four input ends are respectively connected with the first direct current end, the second direct current end, the third direct current end and the fourth direct current end; the soft switch inversion module 2 has two input ends and an output end, the two input ends of the soft switch inversion module 2 are respectively connected with the two output ends of the voltage window switching module 4, and the output end of the soft switch inversion module 2 is used as an alternating current output end.

The control module is used for acquiring relevant working information of the multilevel soft switching inverter circuit and controlling the work of each module according to an acquisition result; the balance switching module 3 is used for compensating the charges flowing through the second direct current terminal and the third direct current terminal under the control of the control module; the voltage window switching module 4 is used for outputting a proper direct-current voltage window to the soft switch inversion module 2 under the control of the control module; the soft switch inversion module 2 is used for converting the direct current provided by the voltage window switching module 4 into alternating current to be output.

Preferably, the switching module comprises a balanced switching module 3 and a voltage window switching module 4; the balanced switching module 3 has two input ends and n output ends, n =1 or 2, and the two input ends of the balanced switching module 3 are respectively connected with the second direct current end and the third direct current end; the voltage window switching module 4 is provided with two external input ends, n internal input ends and two output ends, the two external input ends of the voltage window switching module 4 are respectively connected with the first direct current end and the fourth direct current end, and the n internal input ends are respectively connected with the n output ends of the balance switching module 3; two input ends of the soft switch inversion module 2 are respectively connected with two output ends of the voltage window switching module 4; the balance switching module 3 is used for compensating the charges flowing through the second direct current terminal and the third direct current terminal under the control of the control module; the voltage window switching module 4 is used for outputting a proper direct-current voltage window to the soft switch inversion module 2 under the control of the control module; the balance switching module 3 and the voltage window switching module 4 both include a plurality of switching devices, and a control end of each switching device is connected to the control module, so that the on-off state of each switching device can be switched under the control of the control module.

In the first exemplary embodiment shown in fig. 1a, n =2; the balanced switching module 3 comprises a first switching device T _B1 A second switching device T _B2 A third switching device T _B3 And a fourth switching device T _B4 (ii) a The voltage window switching module 4 comprises a fifth switching device T _L1 And a sixth switching device T _L2 Seventh switching device T _L3 And an eighth switching device T _L4 (ii) a First switching device T _B1 And a third switching device T _B3 Is connected with a second DC terminal, a second switching device T _B2 And a fourth switching device T _B4 Is connected with the third DC terminal, and the first switching device T _B1 And the other end of the first switching device T _B2 Is connected to the other end of the first switching element and serves as a first output end of the balanced switching module 3, and a third switching element T _B3 And the other end of the fourth switching device T _B4 Is connected with the other end of the switching module to serve as a second output end of the balanced switching module 3; fifth switching device T _L1 And a sixth switching device T _L2 A seventh switching device T connected in series between the first DC terminal and the first output terminal of the balanced switching module 3 _L3 And an eighth switching device T _L4 Is connected in series between the fourth dc terminal and the second output terminal of the balanced switching module 3.

With further reference to fig. 3a, 3b, 3c and 3d, the soft-switched inverter module 2 includes a half-bridge circuit (as shown in fig. 3a and 3 b) or a flying capacitor inverter circuit (as shown in fig. 3c and 3 d) having a positive input terminal and a negative input terminal, and an inductor L and a plurality of ac capacitors, wherein the positive input terminal of the half-bridge circuit or the flying capacitor inverter circuit is connected to the fifth switching device T _L1 And a sixth switching device T _L2 The negative input end of the common end is connected with the seventh switching device T _L3 And an eighth switching device T _L4 A common terminal of (a); the output end of the half-bridge circuit or the flying capacitor inverter circuit is connected with the alternating current output end through an inductor L, one end of an alternating current end capacitor is connected with one direct current input end or neutral potential, and the other end of the alternating current end capacitor is connected with the alternating current output end.

In the second exemplary embodiment shown in fig. 1b, n =1; the balanced switching module 3 comprises a first switching device T _B1 And a second switching device T _B2 (ii) a The voltage window switching module 4 comprises a third switching device T _L1 And a fourth switching device T _L2 A fifth switching device T _L3 And a sixth switching device T _L4 (ii) a First switching device T _B1 Is connected to a second DC terminal, a second switching device T _B2 Is connected to the third dc terminal, and the first switching device T _B1 And the other end of the first switching device T _B2 The other end of the switching module is connected with the other end of the switching module as the output end of the balanced switching module 3; third switching device T _L1 And a fourth switching device T _L2 A fifth switching device T connected in series between the first DC terminal and the output terminal of the balanced switching module 3 _L3 And a sixth switching device T _L4 Is connected in series between the fourth dc terminal and the output terminal of the balanced switching module 3.

The soft switching inverter module 2 comprises a half-bridge circuit or a flying capacitor inverter circuit with a positive input end and a negative input end, an inductor L and a plurality of alternating-current end capacitors, wherein the positive input end of the half-bridge circuit or the flying capacitor inverter circuit is connected with a third switching device T _L1 And a fourth switching device T _L2 The negative input terminal of the first switching device T is connected with the first switch _L3 And a sixth switching device T _L4 The output end of the half-bridge circuit or the flying capacitor inverter circuit is connected with the alternating current output end through an inductor L, one end of an alternating current end capacitor is connected with a direct current input end or a neutral potential, and the other end of the alternating current end capacitor is connected with the alternating current output end.

In the above two embodiments, the switching device in the soft-switching inverter module 2 can pass the inductive current i alternating in direction in each switching cycle _L Zero voltage switching (ZVS, zerovoltagetwitching) is implemented.

It will be appreciated that in comparison with the above two embodiments, the second embodiment shown in fig. 1b employs a smaller number of switching devices, thereby reducing the cost; fig. 1a shows a first embodiment, which is relatively costly, but which enables more modes of operation. Thus, the above two embodiments each have advantages.

It is understood that in both embodiments shown in fig. 1a and 1b, corresponding to the soft-switching inverter module 2 in fig. 3a, a half-bridge circuit is adopted, and the soft-switching inverter module includes two ac-side capacitors C ₁ And C ₂ ，C ₁ Are respectively connected with a first DC end and an AC output end, C ₂ Both ends of the first switch are respectively connected with the fourth direct current end and the alternating current output end. In other embodiments, the soft-switching inverter module 2 may be replaced with other structures. If the structure in FIG. 3b is adopted, a half-bridge circuit is adopted, and only one AC terminal capacitor C is included ₁ ，C ₁ One end is connected with the neutral potential, and the other end is connected with the alternating current output end; or the configuration in fig. 3c is adopted, which is different from the configuration in fig. 3a in that the half-bridge circuit is replaced by a flying capacitor inverter circuit; or the configuration in fig. 3d is used, the difference from the configuration in fig. 3b is that the half-bridge circuit is replaced with a flying capacitor inverter circuit.

Preferably, the multilevel soft switching inverter circuit comprises inverter driving circuits with three phases which are independent from each other and have the same structure.

With further reference to fig. 2a, a multi-level soft switching inverter circuit based on single DC power input is shown, and it can be seen that the first DC terminal and the fourth DC terminal are positive and negative terminals of the DC power DC and are connected through three capacitors C _DC1 、C _DC2 And C _DC3 The input direct current voltage is divided into two intermediate voltages, namely a second direct current terminal and a third direct current terminal, so that a direct current bus with four different levels is formed. It will be appreciated that other configurations may be used to obtain a dc bus with four different levels, for example, as shown in fig. 2b, two dc power supplies may be connected in series based on two dc power inputs, and two intermediate voltages may be obtained through a plurality of capacitors. The specific manner of obtaining the multi-level dc bus through the capacitive voltage dividing structure is known in the art, and the present invention is not limited in detail herein. In addition, it is understood that fig. 2a and 2b each correspond to the circuit configuration shown in fig. 1 a; accordingly, fig. 2c and 2d show cases based on a single dc power input and a double dc power input, respectively, and both correspond to the circuit configuration shown in fig. 1 b.

In another aspect of the present invention, a method for balancing voltages at intermediate levels of a multilevel soft-switching inverter circuit is provided, in which a control module controls a below-described balance switching module 3 to automatically switch between a normal mode and a compensation mode by using the multilevel soft-switching inverter circuit shown in fig. 1a or fig. 1b, so as to achieve voltage balancing of each intermediate level in a dc bus.

When the multilevel soft switching inverter circuit shown in fig. 1a, i.e., n =2, is employed, in the normal mode, the first switching device T _B1 And a fourth switching device T _B4 Conducting, second switching device T _B2 And a third switching device T _B3 Turning off; the compensation mode is divided into a compensation mode for the second direct current terminal and a compensation mode for the third direct current terminal; in a compensation mode for the second direct current terminal, the third switching device T _B3 Conducting, fourth switching device T _B4 Off, first switching device T _B1 And a second switching device T _B2 Not conducting at the same time; in a compensation mode for the third direct current terminal, the second switching device T _B2 Conducting, first switching device T _B1 Turn-off, third switching device T _B3 And a fourth switching device T _B4 Not conducting at the same time.

When the multilevel soft switching inverter circuit shown in fig. 1b, i.e., n =1, is employed, the states of the respective switching devices are divided into two cases in the normal mode: in the first case, the first switching device T _B1 And a fourth switching device T _L2 And a sixth switching device T _L4 Off, second switching device T _B2 A third switching device T _L1 And a fifth switching device T _L3 Conducting; in the second case, the first switching device T _B1 And a fourth switching device T _L2 And a sixth switching device T _L4 Conducting, second switching device T _B2 A third switching device T _L1 And a fifth switching device T _L3 And (6) turning off.

The compensation mode is divided into a compensation mode for the second direct current terminal and a compensation mode for the third direct current terminal; in a compensation mode for the second direct current terminal, the first switching device T _B1 And the third openingOff device T _L1 And a fifth switching device T _L3 Conducting, second switching device T _B2 And a fourth switching device T _L2 And a sixth switching device T _L4 Turning off; in a compensation mode for the third direct current terminal, the first switching device T _B1 A third switching device T _L1 And a fifth switching device T _L3 Off, second switching device T _B2 And a fourth switching device T _L2 And a sixth switching device T _L4 And conducting.

Furthermore, the circuit takes the potential of the middle point between the first direct current terminal and the fourth direct current terminal as a neutral potential reference point, and the absolute values of the voltages of the first direct current terminal, the second direct current terminal, the third direct current terminal and the fourth direct current terminal are respectively expressed as U by taking the potential as reference ₁ 、u ₂ 、u ₃ And U ₄ It can be understood that the potentials of the first dc terminal and the second dc terminal are positive values, and the potentials of the third dc terminal and the fourth dc terminal are negative values; u for instantaneous value of AC output terminal voltage _AC Representing; setting a voltage u in a control module ₂ And u ₃ Set value of U _2,set And U _3,set The control module is used for measuring u ₂ And u ₃ And a set value U _2,set And U _3,set Calculating the working interval of each compensation mode required for compensation operation in each half period of the alternating current output; according to the calculation result, the control module switches the on-off states of the switching devices in the balance switching module 3 and the voltage window switching module 4 to enable the bus current i where the second direct current end and the third direct current end are located ₂ And i ₃ Average value I in period of AC output ₂ And I ₃ Compensating to the target value (in the embodiments corresponding to fig. 2a, 2b, 2c and 2d, the target value is 0) so that the corresponding voltage u ₂ And u ₃ In a steady state, and finally outputting the alternating current in a period u ₂ And u ₃ Average value of U ₂ And U ₃ Is stabilized at a set value U _2,set And U _3,set The above.

Further, the instantaneous current flowing through the inductor L is represented by i _L To express, electricityThe average value of the inductive current in a switching period of the soft switch inversion module 2 is i _L,avg Indicating and setting an inductor reserve voltage U in the control module _res (ii) a The balanced switching module 3 normally operates in the normal mode; when the control module detects that the output end voltage is in the range u _AC ≥u ₂ +U _res Then the control module automatically controls the current i _L,avg The direction control balance switching module 3 is switched to a compensation mode for compensating the second direct current end, and when the compensation operation required by the compensation mode is finished, the control module automatically switches the balance switching module 3 back to a normal mode; when the control module detects that the output end voltage is in the range u _AC ≤-u ₃ -U _res Then the control module automatically controls the current i _L,avg The direction control balance switching module 3 is switched to a compensation mode for compensating the third direct current end, and after the compensation operation required by the compensation mode is finished, the control module automatically switches the balance switching module 3 back to the normal mode. It can be understood that the soft switch inversion module has a high working switching frequency, and the difference between the soft switch inversion module and the AC output is several orders of magnitude compared with the output frequency of the AC output _L,avg The average value of the inductive current in the switching period of the soft switching inversion module 2 is shown, and the current i is approximately ignored because the reactive power generated by the alternating-current end capacitor on the alternating-current output frequency in practical application _L,avg Can be equal to the current i of the alternating current output end in engineering _AC In the subsequent analysis, the average value of each current in the direct current bus in the whole alternating current output period is represented by I.

In addition, when u _AC <u ₂ And u _AC >-u ₃ When the switching module 3 is in the normal mode, the switching module is maintained in the normal mode; the control module is used for controlling the AC output according to the working state of the AC output and the measured u ₂ And u ₃ Calculating a balance phase or a working interval required by voltage balance; the control module switches the switching state of the switching device in the voltage window switching module 4 according to the calculation result to switch the voltage window provided for the soft switching inversion module 2, so that the voltages of the second direct current end and the third direct current end are in the cycle of alternating current outputEquilibrium is achieved in the course of time.

The invention provides a multilevel soft switching inverter circuit and a method for balancing the voltage of an intermediate level terminal thereof, wherein the balancing working principle is as follows:

taking the case of n =2 as an example, referring to fig. 1a, in order to realize continuous zero-voltage switching (ZVS) in the soft-switching inverter module 2, the potential of the dc power supply terminal of the soft-switching inverter module 2 is set to be lower than the potential of the dc power supply terminal of the soft-switching inverter module 2

And

must satisfy the condition

In the invention, the control module obtains the instantaneous voltage u of the output end through real-time measurement _AC Average value i of inductive current in switching period of each soft switch inversion module 2 _L,avg An intermediate voltage u ₂ And u ₃ (ii) a The control module controls the switch combination of the balance switching module 3 and the voltage window switching module 4 by judging the voltage condition required by the soft switch inversion module 2 to work and the current condition required by the balance intermediate voltage, and the voltage condition of a Zero Voltage Switch (ZVS) is met

On the premise of switching the path of the soft switch inversion module 2 connected with the direct current bus, the current is respectively led into different intermediate level nodes in the direct current bus from the soft switch inversion module 2, and the characteristics of periodic variation of the voltage and the current of alternating current output are utilized to balance the intermediate level end.

Balanced switching module 3 in normal mode, T _B1 And T _B4 Conduction, T _B2 And T _B3 According to the circuit structure, the voltage window switching module 4 can obtain two voltage windows [ -u ] overlapped with each other from the DC bus ₃ ,U ₁ ]And [ -U ] ₄ ,u ₂ ]Overlap portion [ -u ] with ₃ ,u ₂ ](ii) a ControlThe system module is based on the instantaneous voltage u at the output end _AC The range control voltage window switching module 4 connects a proper voltage window or an overlapped part thereof with the soft switch inversion module 2; specifically, when T is _L2 And T _L4 Off and T _L1 And T _L3 When conducting

And

when T is _L1 And T _L3 Is turned off and T _L2 And T _L4 When conducting

And

when T is _L1 And T _L4 Off and T _L2 And T _L3 When conducting

And

in the compensation mode for the second DC terminal, T _B3 On, T _B4 Off, T _B1 And T _B2 Not conducting at the same time; in the compensation mode for the third DC terminal, T _B2 Conduction, T _B1 Off, T _B3 And T _B4 Not simultaneously conducting. It will be appreciated that in the compensation mode for the second dc terminal, only T needs to be specified _B3 And T _B4 Of the switch state of _B1 And T _B2 Since the rear-end line is blocked by the voltage window switching module 4, and there is no current therein, as long as the two are not conducted at the same time, the second dc terminal and the third dc terminal are short-circuited, and other switching states have no influence on the circuit function; the same principle applies to the compensation mode of the third DC terminal, as long as T _B3 And T _B4 And conducting the circuit at different times. In compensation modeThe voltage window obtained by the voltage window switching module 4 is changed, so as to further change the potential of the DC power supply end of the soft switch inversion module 2

And

for controlling the intermediate voltage u at the end of the intermediate level ₂ And u ₃ Setting a middle voltage u in the control module according to the balanced voltage ₂ And u ₃ Set value of U _2,set And U _3,set . The control module is used for measuring the intermediate voltage u ₂ And u ₃ And a set value U _2,set And U _3,set Deviation of (3) and voltage of AC output U _AC Current I _AC Calculating the working interval of each compensation mode required for compensation operation in each half period of the alternating current output; and the balance switching module 3 is controlled to switch between a normal mode and a compensation mode according to specific required voltage conditions and current conditions, and the voltage window switching module 4 is controlled to be matched to form a corresponding switch combination. In order to realize Zero Voltage Switching (ZVS) in the soft switch inverter module 2, an inductance reserved voltage U is arranged in the control module according to the design requirement of the inverter circuit _res In the compensation mode, the voltage is used to provide a voltage with alternating direction to the inductor L to establish the alternating inductor current i required for a Zero Voltage Switching (ZVS) in each switching cycle of the soft-switching inverter module 2 _L 。

The control module measures the instantaneous voltage u of the output end in real time _AC Intermediate voltage u ₂ And u ₃ The balance switching module 3 and the voltage window switching module 4 are controlled; when the instantaneous voltage u at the voltage output end _AC Or current i _L,avg When the condition required by the compensation mode is not met, the balance switching module 3 is kept in a normal mode; at the moment, the control module is used for controlling the output end to output the instantaneous voltage u _AC The range controls the switch state of the voltage window switching module 4, so that the input end of the soft switch inversion module 2 starts to be at the initial voltageFinal compliance with voltage conditions

To ensure that the switching devices therein can operate in a Zero Voltage Switching (ZVS) state.

For the case of a higher output voltage, if u _AC ≥u ₂ +U _res Or u _AC ≤-u ₃ -U _res 。

During the balancing process for the second DC terminal, the intermediate voltage u ₂ When the rising trend is presented in the normal mode, the control module judges the required voltage condition u according to the result of real-time measurement _AC ≥u ₂ +U _res And current condition i _L,avg >If 0 is satisfied, the control module switches the balance switching module 3 from the normal mode to the intermediate voltage u according to the working interval of the compensation operation when the two are satisfied simultaneously ₂ The compensation mode of (2); when the intermediate voltage u ₂ When the voltage shows a descending trend in a normal mode, the control module judges the required voltage condition u according to the real-time measurement result _AC ≥u ₂ +U _res And current condition i _L,avg <If 0 is satisfied, the control module switches the balance switching module 3 from the normal mode to the intermediate voltage u according to the working interval of the compensation operation when the two are satisfied simultaneously ₂ The compensation mode of (1); the potential of the DC power supply terminal of the soft-switching inverter module 2 in this compensation operation

And

are respectively equal to U ₁ And u ₂ The control module switches the balance switching module 3 back to the normal mode after the required compensation operation is finished.

Similarly, during balancing for the third dc terminal, the intermediate voltage u ₃ When the rising trend is presented in the normal mode, the control module judges the required voltage condition u according to the result of real-time measurement _AC ≤-u ₃ -U _res And current condition i _L,avg <If 0 is satisfied, the control module switches the balance switching module 3 from the normal mode to the intermediate voltage u according to the working interval of the compensation operation ₃ The compensation mode of (1); when the intermediate voltage u is ₃ When the voltage shows a descending trend in a normal mode, the control module judges the required voltage condition u according to the real-time measurement result _AC ≤-u ₃ -U _res And current condition i _L,avg >If 0 is satisfied, the control module switches the balance switching module 3 from the normal mode to the intermediate voltage u according to the working interval of the compensation operation ₃ The compensation mode of (1); the DC power supply terminal of the soft-switching inverter module 2 is supplied with a voltage during the compensation operation

And

are respectively equal to-u ₃ and-U ₄ The control module switches the balance switching module 3 back to the normal mode after the required compensation operation is finished.

In addition, for the case of a lower output voltage, if u _AC <u ₂ And u _AC >-u ₃ In this case, the treatment can be carried out according to the following two schemes.

In the first scheme, the balanced switching module 3 is kept in the normal mode; the control module outputs working state and intermediate voltage u according to alternating current ₂ And u ₃ Calculating a balance phase required by voltage balance; when the current i _L,avg When a half cycle begins to enter, the control module keeps the current switching state of the voltage window switching module 4 unchanged to a required balance phase, and at the moment, the voltage window connected to the soft switch inversion module 2 keeps unchanged; when the required balance phase is reached, the control module switches the switching state of the voltage window switching module 4, and the other corresponding voltage window in the direct current bus is connected to the soft switch inversion module 2. When each voltage window is connected to the soft switch inversion module 2 by using the periodicity of the alternating currentCurrent i generated in ₂ And i ₃ Equilibrium is achieved in its corresponding half-cycle i ₂ And i ₃ Respectively represent and intermediate voltage u ₂ And u ₃ And the direct current bus current corresponds to the level node.

In the second scheme, the balanced switching module 3 is kept in the normal mode; the control module outputs working state and intermediate voltage u according to alternating current ₂ And u ₃ Calculates the intermediate voltage u ₂ And an intermediate voltage u ₃ Balancing the required working interval of the operation; in this balancing method, the control module controls the switching device T in the voltage window switching module 4 _L1 And T _L4 Off, T _L2 And T _L3 On, overlap of voltage windows [ -u [ ] ₃ ,u ₂ ]Is connected to the soft switch inversion module 2; when the intermediate voltage u is reached ₂ Control module controls switching device T in voltage window switching module 4 during balanced operating interval _L1 And T _L3 Off, T _L2 And T _L4 Conducting to connect the voltage window [ -U [) ₄ ,u ₂ ]A soft switch inversion module 2 is connected; when the intermediate voltage u is reached ₃ Control module controls switching device T in voltage window switching module 4 during balanced operating interval _L2 And T _L4 Off, T _L1 And T _L3 Conducting to connect the voltage window [ -u [) ₃ ,U ₁ ]A soft switch inversion module 2 is connected; after the working interval of the balance operation is finished, the control module switches the voltage connected into the soft switch inversion module 2 back to the overlapped part [ -u ] of the voltage window ₃ ,u ₂ ]The method utilizes the characteristic that the current distribution in the soft switch inversion module 2 changes along with the accessed direct current input voltage to ensure that the current i in the direct current bus ₂ And i ₃ Balancing is achieved in different switch combinations.

Further, the intermediate bus current i ₂ And i ₃ The average values in the switching period during which one soft-switching inverter module 2 operates are respectively represented as i _2,avg And i _3,avg . Referring to FIG. 1a, the current i is known from the circuit structure _2,avg And i _3,avg Direction of and current i _L,avg In the same direction, when the need is reducedVoltage u ₂ When a current i is required _L,avg In the positive direction, when the voltage u needs to be increased ₂ When a current i is required _L,avg Is in the negative direction; when the voltage u needs to be reduced ₃ When a current i is required _L,avg In the negative direction when the voltage u needs to be raised ₃ When a current i is required _L,avg In the positive direction. Average value U of intermediate voltage when positive active power is output from AC output terminal ₂ And U ₃ The voltage rises when the balanced switching module 3 is in the normal mode; when the AC output terminal outputs negative active power, the average value U of the intermediate voltage ₂ And U ₃ The voltage drops when the balanced switching module 3 is in the normal mode; when the AC output end outputs pure reactive power, the average value U of the intermediate voltage ₂ And U ₃ The voltage remains unchanged for the balanced state when the balanced switching module 3 is in the normal mode.

The switching state and the voltage variation trend of each switching device can be referred to the following table:

in the table, the switch states: 1 is ON, 0 is OFF, X and

indicating a state of not conducting at the same time; voltage change: ↓ is ascending, and ↓ is descending, and N is unchanged.

Wherein the balanced switching module 3 is in the normal mode in the connected states a, C, E and the balanced switching module 3 is at an intermediate voltage u in the connected state B ₂ In the connected state D, the balanced switching module 3 is at the intermediate voltage u ₃ The compensation mode of (2). In the normal mode, the control module is dependent on the voltage u _AC The inverter circuit is switched among connection states A, C and E within the range, so that the direct current output of the soft switch inverter module 2 is enabledThe potential connected to the input terminal satisfies the condition of Zero Voltage Switch (ZVS)

When the intermediate voltage needs to be balanced, the control module controls the balance switching module 3 to be switched to a connection state B or D for respectively balancing the intermediate voltage u ₂ Or u ₃ And (6) balancing.

Specific balancing procedures in various embodiments are described below in conjunction with the figures.

Referring to fig. 5a and 5b, in a first embodiment, the output terminal voltage u _AC And current i _L,avg The phase difference of (1) is 0, and the output is positive active power; intermediate voltage u in this operating state ₂ And u ₃ Rises when the balanced switching module 3 is in the normal mode. At t ₁ The instantaneous voltage of the time output end meets the condition u _AC ≥u ₂ +U _res And current i _L,avg Has been in the positive half cycle, and satisfies the intermediate voltage u ₂ The control module controls the balance switching module (3) to switch from the normal mode to the intermediate voltage u ₂ The connection state is switched from a to B; by means of the current distribution characteristic of the soft-switching inverter module 2 and the periodic characteristic of the alternating current, the interval t ₁ ,t ₂ ]And [ T _AC /2,t ₃ ]、[t ₄ ,T _AC ]Current I formed ₂ Compensated to 0, the mathematical expression of its equilibrium state is as follows:

at t ₃ The instantaneous voltage of the time output end meets the condition u _AC ≤-u ₃ -U _res And current i _L,avg Has been in a negative half cycle, at which time the intermediate voltage u is satisfied ₃ In the condition of performing the balancing operation, the control module controls the balancing switching module 3 to switch from the normal mode to the intermediate voltage u ₃ The connection state is switched from C to D; current distribution characteristic and alternating current by means of soft switching inverter module 2Such that in the interval t ₃ ,t ₄ ]And [0,t ₁ ]、[t ₂ ,T _AC /2]Current I formed ₃ Compensated to 0, the equilibrium state is mathematically expressed as follows:

referring to fig. 6a and 6b, in a second embodiment, the output terminal voltage u _AC And current i _L,avg The phase difference is more than 0 and less than 90 degrees, and the output is positive active power; intermediate voltage u in this operating state ₂ And u ₃ Rises when the balanced switching module 3 is in the normal mode. At t ₁ The instantaneous voltage of the output end at the moment meets the condition u _AC ≥u ₂ +U _res And current i _L,avg In the positive half cycle, the intermediate voltage u is satisfied ₂ In the condition of performing the balancing operation, the control module controls the balancing switching module 3 to switch from the normal mode to the intermediate voltage u ₂ The connection state is switched from a to B; by means of the current distribution characteristic of the soft-switching inverter module 2 and the periodic characteristic of the alternating current, the interval t ₁ ,t ₂ ]And { T } _AC /2,t ₃ ]、[t ₄ ,T _AC ]Current I formed ₂ Is compensated to 0. At t ₃ The instantaneous voltage of the output end at the moment meets the condition u _AC ≤-u ₃ -U _res And current i _L,avg In the negative half cycle, the intermediate voltage u is satisfied ₃ In the condition of performing the balancing operation, the control module controls the balancing switching module 3 to switch from the normal mode to the intermediate voltage u ₃ I.e. the connection state is switched from C to D, by means of the current distribution characteristic of the soft-switching inverter module 2 and the periodic characteristic of the alternating current such that in the interval t ₃ ,t ₄ ]And [0,t ₁ ]、[t ₂ ,T _AC /2]Current I formed ₃ Is compensated to 0.

Referring to fig. 7a and 7b, in a third embodiment, the output terminal voltage u _AC And a current i _L,avg Is more than 90 smallAt 180 degrees, the output is negative active power; intermediate voltage u in this operating state ₂ And u ₃ And falls when the balanced switching module 3 is in the normal mode. At t ₁ The instantaneous voltage of the time output end meets the condition u _AC ≥u ₂ +U _res And current i _L,avg Has been in a negative half cycle, at which time the intermediate voltage u is satisfied ₂ In the condition of performing the balancing operation, the control module controls the balancing switching module 3 to switch from the normal mode to the intermediate voltage u ₂ The connection state is switched from a to B; by means of the current distribution characteristic of the soft-switching inverter module 2 and the periodic characteristic of the alternating current, the interval t ₁ ,t ₂ ]And [ T _AC /2,t ₃ ]、[t ₄ ,T _AC ]Current I formed ₂ Is compensated to 0. At t ₃ The instantaneous voltage of the time output end meets the condition u _AC ≤-u ₃ -U _res And current i _L,avg Has been in a positive half cycle, at which time a medium voltage u is satisfied ₃ The control module controls the balance switching module 3 to switch from the normal mode to the intermediate voltage u ₃ In the compensation mode of (2), i.e. switching from the connection state C to the connection state D, by means of the current distribution characteristic of the soft-switching inverter module 2 and the periodic characteristic of the alternating current in the interval t ₃ ,t ₄ ]And [0, t ₁ ]、[t ₂ ,T _AC /2]Current I formed ₃ Is compensated to 0.

Referring to fig. 8a and 8b, in the fourth embodiment, the difference from the scheme in the previous embodiment is that the instantaneous voltage u is output _AC Voltage window [ -u ] above a set voltage threshold ₃ ,U ₁ ]Is switched to the soft switch inversion module 2; when the instantaneous voltage u at the output terminal _AC Below a set voltage threshold a voltage window [ -U ] ₄ ,u ₂ ]Is switched to the soft switch inversion module 2; wherein for an intermediate voltage u ₂ And u ₃ The balancing method of (3) is the same as that in the first to third embodiments described above.

Referring to fig. 9a and 9b, in the fifth embodiment, the difference from the solution in the previous embodiment is that when the solution is usedInstantaneous voltage u at output terminal _AC In the overlapping part of the voltage window [ -u [ ] ₃ ,u ₂ ]The time-voltage window switching module 4 connects the overlapped part into the soft switch inversion module 2 to wait for the instantaneous voltage u at the output end _AC After the corresponding threshold value is exceeded, the control module controls the voltage window switching module 4 to switch the corresponding voltage window into the soft switch inversion module 2; wherein for an intermediate voltage u ₂ And u ₃ The balancing method of (3) is the same as that in the first to third embodiments described above.

Referring to fig. 10a and 10b, in the sixth embodiment, the difference from the previous embodiments is that the instantaneous voltage u is output _AC In this embodiment, the first scheme is adopted, and the control module switches the voltage window switching module 4 between the connection states a and C, and switches the time point of the voltage window switching and the current i _L,avg Generates phase difference by simulating the working state of pure reactive power to ensure that the intermediate voltage u ₂ And u ₃ The balance is achieved within the period of the ac output. The mathematical expression of the equilibrium state is:

referring to FIGS. 11a and 11b, in the seventh embodiment, the instantaneous voltage u is generated due to the output terminal _AC The difference between the sixth embodiment, in which the second scheme is adopted, and the control module switches the voltage window switching module 4 between the connection states a, C and E, and utilizes the characteristic that the current distribution ratio of the soft switch inverter module 2 is related to the ratio of the dc input voltage to the output end voltageRespectively to the intermediate voltage u ₂ And u ₃ The currents at the level nodes are balanced. The mathematical expression of the equilibrium state is:

in addition, for the multilevel soft switching inverter circuit provided by the invention, the working range of the compensation operation can be changed to break the situation of the intermediate voltage u ₂ And u ₃ A charge balance state is established on the level node, so that the difference of the injected charges can be controlled at the intermediate voltage u ₂ And u ₃ The level nodes at which (i.e. the second dc terminal and the third dc terminal) a bidirectional dc power supply 5 is established to provide power to external devices, as is illustrated with reference to fig. 4 a-4 c.

Fig. 4a shows a multi-level soft switching inverter circuit with single dc power input and multi-phase ac output including a bi-directional dc power supply 5; FIG. 4b is a multi-level soft switching inverter circuit with dual DC power inputs and multi-phase AC outputs comprising a bi-directional DC power supply 5; fig. 4c shows a multilevel soft switching inverter circuit with dual dc power inputs and multi-phase ac outputs comprising two bi-directional dc power supplies 5.

For the multilevel soft switching inverter circuit of the bidirectional direct current power supply 5, the control method is similar to the method, and the balance switching module 3 and the voltage window switching module 4 are switched to be in the connection state according to the requirement under the control of the control module, so as to obtain the stably required intermediate voltage u ₂ And u ₃ It is possible to realize the establishment of the stable bidirectional direct-current power supply 5 thereon while stably balancing the intermediate voltage. It will be appreciated that, unlike the various embodiments described above, it is desirable to have the average current I during a full ac output period ₂ And I ₃ Is compensated to 0; in applications involving a bi-directional DC power supply 5, this is due to the need to provide an output currentTime I ₂ And I ₃ Is not 0, but is controlled by a control module ₂ And I ₃ Compensating to a target value corresponding to the output value of the bidirectional DC power supply 5, and balancing the intermediate voltage u ₂ And u ₃ Meanwhile, the second direct current terminal and the third direct current terminal output current with required direction and magnitude.

The specific principle of the balancing operation is described above for the case of n = 2.

Similarly, in the case of n =1, referring to fig. 1b, in the present embodiment, the switching state and the voltage variation trend of each switching device can refer to the following table:

in the table, the switch states: 1 is on, 0 is off; voltage change: ↓ is ascending, and ↓ is descending, and N is unchanged.

Wherein the connection states A1 and C1 are for the normal mode of the balanced switching module 3 and the connection states B1 and D1 are for the compensation mode. In the circuit structure, when the alternating current output voltage is near the zero-crossing point, the connection state is switched from A1 to C1 or from C1 to A1 according to the variation trend of the alternating current output voltage. The switching process can be completed in one switching cycle to ensure that the soft-switching inverter module 2 can always provide the inductor voltage with alternating directions in each switching cycle. The switching signals of the switching devices in the soft switching inversion module 2 are used for carrying out synchronous switching control on the switching devices in the balance switching module 3 and the voltage window switching module 4, so that the state switching process can be better realized.

In this embodiment, a specific control manner is similar to the case of the multilevel soft switching inverter circuit corresponding to fig. 1a, and the operation modes corresponding to fig. 5a and 5b, fig. 6a and 6b, fig. 7a and 7b, fig. 8a and 8b, and fig. 10a and 10b can be realized as well, but the operation modes corresponding to fig. 9a and 9b, and fig. 11a and 11b cannot be realized because the number of switching devices is reduced. Compared with the case corresponding to fig. 1a, since the number of switching devices is reduced in the structure of fig. 1b, a partial connection state is lost, so that the balancing capability thereof is partially limited. Therefore, the circuit structure in fig. 1b is relatively suitable for the application environment with high and stable ac output voltage, such as: a photovoltaic inverter.

In addition, it is understood that the balanced switching module 3 and the voltage window switching module 4 in fig. 4a, 4b and 4c each correspond to the circuit configuration in fig. 1 a. For the circuit configuration of fig. 1b, the balancing principle is the same as for the configuration of fig. 1a, so that the method described above for providing the bidirectional dc power supply 5 is equally applicable to the circuit configuration of fig. 1 b. I.e. the balanced switching module 3 and the voltage window switching module 4 in fig. 4a, 4b and 4c, may also adopt the circuit configuration shown in fig. 1 b.

In the invention, based on the control signal of the Switching device in the soft Switching inversion module 2, zero Current Switching (ZCS) can be realized in the Switching devices of the balanced Switching module 3 and the voltage window Switching module 4 in a synchronous Switching manner, so as to further reduce the Switching loss of the system and improve the electric energy conversion efficiency.

Through the switch combination of the balance switching module and the voltage window switching module, the invention can balance the capacitor voltage of each direct current bus in the multi-level direct current bus and simultaneously keep supplying the voltage condition required by establishing alternating inductive current (such as TCM control) in each switching period to the inversion module

Therefore, soft switching of the switching device can be continuously realized in the inverter module so as to reduce switching loss and improve the electric energy conversion efficiency of the system.

In summary, the multi-level soft switch inverter circuit and the method for balancing the voltage at the intermediate level thereof provided by the present invention compensate the charge flowing through each intermediate level end on the premise of realizing soft switching by adding the balancing switching module between the voltage window switching module and the multi-level flat current bus and combining the characteristic of the periodic variation of the voltage and the current in the alternating current output on the basis of the existing multi-level soft switch inverter circuit, thereby actively balancing each intermediate level end in the direct current bus to obtain stable voltage.

The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only examples of the present invention, and should not be construed as limiting the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A multi-level soft switching inverter circuit is characterized by comprising inverter driving circuits (1) which are mutually independent and have the same structure;

each phase of the inversion driving circuit (1) comprises four direct current input ends, an alternating current output end, a switching module, a soft switch inversion module (2) and a control module;

the soft switch inversion module (2) is provided with two input ends and an output end, the two input ends of the soft switch inversion module (2) are respectively connected with the two output ends of the switching module, and the output end of the soft switch inversion module (2) is used as the alternating current output end;

the control module is used for acquiring relevant working information of the multilevel soft switching inverter circuit and controlling the work of each module according to an acquisition result;

the switching module is used for connecting a proper direct-current voltage window to the soft-switching inversion module (2) under the control of the control module;

the soft switch inversion module (2) is used for converting the direct current provided by the switching module into alternating current to be output.

2. The multilevel soft switching inverter circuit according to claim 1, wherein the switching module comprises a balanced switching module (3) and a voltage window switching module (4);

the balanced switching module (3) is provided with two input ends and n output ends, n =1 or 2, and the two input ends of the balanced switching module (3) are respectively connected with a second direct current end and a third direct current end;

the voltage window switching module (4) is provided with two external input ends, n internal input ends and two output ends, the two external input ends of the voltage window switching module (4) are respectively connected with the first direct current end and the fourth direct current end, and the n internal input ends are respectively connected with the n output ends of the balance switching module (3);

two input ends of the soft switch inversion module (2) are respectively connected with two output ends of the voltage window switching module (4);

the balance switching module (3) is used for compensating charges flowing through the second direct current end and the third direct current end under the control of the control module;

the voltage window switching module (4) is used for connecting a proper direct-current voltage window to the soft switch inversion module (2) under the control of the control module;

the balance switching module (3) and the voltage window switching module (4) respectively comprise a plurality of switching devices, and the control end of each switching device is connected with the control module, so that the switching state of each switching device can be switched under the control of the control module.

3. Multilevel soft switching inverter circuit according to claim 2, characterized in that n =2, the balanced switching module (3) comprising a first switching device T _B1 A second switching device T _B2 A third switching device T _B3 And a fourthOff device T _B4 (ii) a The voltage window switching module (4) comprises a fifth switching device T _L1 And a sixth switching device T _L2 Seventh switching device T _L3 And an eighth switching device T _L4 ；

The first switching device T _B1 And a third switching device T _B3 Are connected to a second dc terminal, the second switching device T _B2 And a fourth switching device T _B4 Is connected to a third dc terminal, and the first switching device T _B1 And the other end of the first switching device T _B2 Is connected to the other end of the first switching element and is used as a first output end of the balanced switching module (3), and the third switching element T _B3 And the other end of the fourth switching device T _B4 Is connected with the other end of the switching module as a second output end of the balanced switching module (3);

the fifth switching device T _L1 And a sixth switching device T _L2 Connected in series between the first DC terminal and the first output terminal of the balanced switching module (3), and the seventh switching device T _L3 And an eighth switching device T _L4 Is connected in series between the fourth DC terminal and the second output terminal of the balanced switching module (3);

the soft switch inverter module (2) comprises a half-bridge circuit or a flying capacitor inverter circuit with a positive input end and a negative input end, an inductor L and a plurality of alternating-current end capacitors, wherein the positive input end of the half-bridge circuit or the flying capacitor inverter circuit is connected with a fifth switching device T _L1 And a sixth switching device T _L2 The negative input terminal of the first switch device T is connected with the first switch device _L3 And an eighth switching device T _L4 The output end of the half-bridge circuit or the flying capacitor inverter circuit is connected with the alternating current output end through the inductor L, one end of the alternating current end capacitor is connected with one direct current input end or the neutral potential, and the other end of the alternating current end capacitor is connected with the alternating current output end.

4. Multilevel soft-switching inverter circuit according to claim 2, characterized in that n =1, the balanced switching module (3) comprising a first switching device T _B1 And a secondSwitching device T _B2 (ii) a The voltage window switching module (4) comprises a third switching device T _L1 And a fourth switching device T _L2 A fifth switching device T _L3 And a sixth switching device T _L4 ；

The first switching device T _B1 Is connected to a second dc terminal, said second switching device T _B2 Is connected to the third dc terminal, and the first switching device T _B1 And the other end of the first switching device T _B2 Is connected with the other end of the switching module and is used as the output end of the balance switching module (3);

the third switching device T _L1 And a fourth switching device T _L2 Is connected in series between the first direct current end and the output end of the balanced switching module (3), and the fifth switching device T _L3 And a sixth switching device T _L4 Is connected in series between the fourth direct current end and the output end of the balanced switching module (3);

the soft switch inverter module (2) comprises a half-bridge circuit or a flying capacitor inverter circuit with a positive input end and a negative input end, an inductor L and a plurality of alternating-current end capacitors, wherein the positive input end of the half-bridge circuit or the flying capacitor inverter circuit is connected with a third switch device T _L1 And a fourth switching device T _L2 The negative input terminal of the first switching device T is connected with the first switch _L3 And a sixth switching device T _L4 The output end of the half-bridge circuit or the flying capacitor inverter circuit is connected with the alternating current output end through the inductor L, one end of the alternating current end capacitor is connected with one direct current input end or the neutral potential, and the other end of the alternating current end capacitor is connected with the alternating current output end.

5. The multilevel soft switching inverter circuit according to claim 1, further comprising a bi-directional dc power supply (5) additionally established by a level node where the second dc terminal and the third dc terminal are located.

6. A method for balancing the voltage of the middle level terminal of a multilevel soft switching inverter circuit is characterized in that:

the multilevel soft switching inverter circuit of claim 3 is adopted, namely n =2;

under the control of the control module, the balance switching module (3) automatically switches between a normal mode and a compensation mode to realize the voltage balance of each middle level end in the direct current bus;

in the normal mode, the first switching device T _B1 And a fourth switching device T _B4 Conducting, second switching device T _B2 And a third switching device T _B3 Turning off;

in a compensation mode for the third DC terminal, the second switching device T _B2 Conducting, first switching device T _B1 Turn-off, third switching device T _B3 And a fourth switching device T _B4 Not simultaneously conducting.

7. A method for balancing intermediate level terminal voltage of a multilevel soft switching inverter circuit is characterized in that:

using the multilevel soft-switched inverter circuit of claim 4, i.e., n =1;

under the control of the control module, the balance switching module (3) and the voltage window switching module (4) are automatically switched between a normal mode and a compensation mode to realize the voltage balance of each middle level end in the direct current bus;

second kindIn this case, the first switching device T _B1 And a fourth switching device T _L2 And a sixth switching device T _L4 Conducting, second switching device T _B2 A third switching device T _L1 And a fifth switching device T _L3 Turning off;

8. A method according to claim 6 or 7, characterized in that the potential of the middle point between the first DC terminal and the fourth DC terminal is used as a neutral potential reference point in the circuit, and the absolute values of the voltages of the first DC terminal, the second DC terminal, the third DC terminal and the fourth DC terminal are expressed as Uc respectively by using the potential as a reference ₁ 、u ₂ 、u ₃ And U ₄ Instantaneous value of voltage at AC output terminal is u _AC ；

according to the calculation result, the control module switches the switching states of the switching devices in the balance switching module (3) and the voltage window switching module (4) to connect the second direct current end and the third direct current endAt bus current i ₂ And i ₃ Average value I in period of AC output ₂ And I ₃ Compensating to the target value so as to make the corresponding voltage u ₂ And u ₃ In a steady state, and finally outputting the alternating current in a period u ₂ And u ₃ Average value of U ₂ And U ₃ Is stabilized at a set value U _2,set And U _3,set The above.

9. The method of claim 8, wherein the instantaneous current through the inductor L is represented by i _L Indicating that the average value of the inductive current in a switching cycle of the soft-switching inverter module (2) is i _L,avg Indicating and setting an inductance reserve voltage U in the control module _res ；

The balanced switching module (3) normally operates in a normal mode;

when the control module detects that the output end voltage is in the range u _AC ≥u ₂ +U _res Then the control module automatically controls the current i _L,avg The direction control balance switching module (3) is switched to a compensation mode for compensating the second direct current end, and after the compensation operation required by the compensation mode is finished, the control module automatically switches the balance switching module (3) back to a normal mode;

when the control module detects that the output end voltage is in the range u _AC ≤-u ₃ -U _res Then the control module automatically controls the current i _L,avg The direction control balance switching module (3) is switched to a compensation mode for compensating the third direct current end, and when the compensation operation required by the compensation mode is finished, the control module automatically switches the balance switching module (3) back to a normal mode;

when u is _AC <u ₂ And u _AC >-u ₃ When the balance switching module (3) is in the normal mode;

and the control module switches the switching state of a switching device in the voltage window switching module (4) according to the calculation result so as to switch the voltage window provided for the soft switching inversion module (2), so that the voltages of the second direct current end and the third direct current end are balanced in the period of alternating current output.

10. The method according to claim 8, wherein if the multilevel soft switching inverter circuit comprises a bidirectional dc power supply (5) established by using a level node where the second dc terminal and the third dc terminal are located, the control module switches the switching states of the switching devices in the balanced switching module (3) and the voltage window switching module (4) to change the bus current i where the second dc terminal and the third dc terminal are located ₂ And i ₃ Average value I in period of AC output ₂ And I ₃ Compensating to a target value, wherein the target value corresponds to an output value required by the bidirectional direct current power supply (5);

if the multi-level soft switching inverter circuit does not comprise the bidirectional direct-current power supply (5), the control module switches the switching states of the switching devices in the balance switching module (3) and the voltage window switching module (4) to enable the bus current i where the second direct-current end and the third direct-current end are located ₂ And i ₃ Average value I in period of AC output ₂ And I ₃ Compensating to a target value, wherein the target value is 0.