阅读说明：本技术 一种dc/ac电力变换装置 (DC/AC power conversion device ) 是由 王文波 王宏 鲁锦锋 周洪伟 张燕 于 2020-07-17 设计创作，主要内容包括：本发明公开了一种DC/AC电力变换装置,由上母线电容、下母线电容、第一开关模块、第二开关模块、第三开关模块、第四开关模块、第一单向导通器件、第二单向导通器件、第三单向导通器件、第四单向导通器件、第五单向导通器件、第六单向导通器件和飞跨电容C<Sub>fly</Sub>组成；本发明中第五单向导通器件和第六单向导通器件组成启动单元,确保在飞跨电容的电压建立过程中不会导致开关模块过压击穿；飞跨电容C<Sub>fly</Sub>存在可使电流起到倍频的作用,减小电感的体积和损耗；同时,对比普通的NPC拓扑,由于飞跨电容的存在可使四个开关模块的损耗更加均匀,进而将模块应用到更大功率的场景。(The invention discloses a DC/AC power conversion device which comprises an upper bus capacitor, a lower bus capacitor, a first switch module, a second switch module, a third switch module, a fourth switch module, a first one-way conduction device, a second one-way conduction device, a third one-way conduction device, a fourth one-way conduction device, a fifth one-way conduction device, a sixth one-way conduction device and a flying capacitor C fly Composition is carried out; according to the invention, the fifth one-way conduction device and the sixth one-way conduction device form a starting unit, so that overvoltage breakdown of a switch module cannot be caused in the voltage establishment process of the flying capacitor; flying capacitor C fly The inductor can enable the current to play a role in frequency doubling, and the size and the loss of the inductor are reduced; meanwhile, compared with the common NPC topology, the loss of the four switch modules can be more uniform due to the flying capacitor, and the modules are applied to the NPC topologyHigh power scenes.)

1. A DC/AC power conversion device comprises an upper bus capacitor (C)_bus+) Lower bus capacitor (C)_bus-) The switch comprises a first switch module (T1), a second switch module (T2), a third switch module (T3), a fourth switch module (T4), a first one-way conduction device (D1), a second one-way conduction device (D2), a third one-way conduction device (D3) and a fourth one-way conduction device (D4); lower bus capacitor (C)_bus-) Upper bus capacitor (C)_bus+) The first switch module (T1), the second switch module (T2), the third switch module (T3) and the fourth switch module (T4) are sequentially connected in series to form a loop; the lower bus capacitor (C)_bus-) Is electrically connected with the upper bus capacitor (C)_bus+) A negative terminal of (a); upper bus capacitor (C)_bus+) Is electrically connected to the positive terminal of the first switch module (T1); the negative terminal of the first switch module (T1) is electrically connected to the positive terminal of the second switch module (T2); the negative terminal (T2) of the second switch module is electrically connected to the positive terminal of the third switch module (T3); the negative terminal of the third switching module (T3) is electrically connected to the positive terminal of the fourth switching module (T4); the negative terminal of the fourth switch module (T4) is electrically connected to the lower bus capacitor (C)_bus-) A negative terminal of (a);

the positive terminal of the first switch module (T1) is electrically connected with the reverse cut-off terminal of the first unidirectional conducting device (D1); the negative end of the first switch module (T1) is electrically connected with the positive conducting end of the first one-way conducting device (D1);

the positive terminal of the second switch module (T2) is electrically connected with the reverse cut-off terminal of a second unidirectional conducting device (D2); the negative end of the second switch module (T2) is electrically connected with the positive conducting end of the second one-way conducting device (D2);

the positive terminal of the third switching module (T3) is electrically connected with the reverse cut-to-end terminal of a third unidirectional conducting device (D3); the negative end of the third switching module (T3) is electrically connected with the positive conducting end of the third one-way conducting device (D3);

the positive terminal of the fourth switching module (T4) is electrically connected with the reverse cut-off terminal of a fourth unidirectional conducting device (D4); the negative end of the fourth switch module (T4) is electrically connected with the positive conducting end of the fourth unidirectional conducting device (D4);

the electrical connection point of the second switch module (T2) and the third switch module (T3) is led out as an AC output point; the method is characterized in that: further comprising a flying capacitor (C)_fly)；

Said flying capacitor (C)_fly) Is electrically connected at a common point of the first switch module (T1) and the second switch module (T2); flying capacitor (C)_fly) Is electrically connected at a common point of the third switch module (T3) and the fourth switch module (T4).

2. The DC/AC power conversion device according to claim 1, characterized in that: said flying capacitor (C)_fly) Flying capacitor (C) in an uncharged state prior to normal operation of said DC/AC power conversion device_fly) The voltage at the two ends is 0; said flying capacitor (C)_fly) A flying capacitor (C) in a charged state when the DC/AC power conversion device is in normal operation_fly) The voltage at both ends is close to the upper bus capacitance (C)_bus+) And lower bus capacitor (C)_bus-) Half of the sum;

said flying capacitor (C)_fly) The number of modes of the switch module can be increased, namely, a 0-state switch mode is added;

under the condition that the frequencies of the first switch module (T1), the second switch module (T2), the third switch module (T3) and the fourth switch module (T4) are not changed, the current frequency can be multiplied, and the effect of reducing current harmonics is achieved.

3. The DC/AC power conversion device according to claim 1, characterized in that: when the DC/AC power conversion device works normally, the opening time and the current of the four switch modules are the same, and the loss distribution is more uniform; when the DC/AC power conversion device works normally, the conduction time and the current of the four unidirectional conduction devices are the same, and the loss distribution is more uniform; since there are no local hot spots, the current can be pushed to a higher power level with the same current.

4. The DC/AC power conversion device of claim 1, whichIs characterized in that: the DC/AC power conversion apparatus further includes a start-up circuit including a fifth unidirectional conductive device (D5) and a sixth unidirectional conductive device (D6), wherein a reverse cut-off end of the fifth unidirectional conductive device (D5) is electrically connected to the flying capacitor (C)_fly) A positive terminal of; the forward conducting terminal of the fifth unidirectional conducting device (D5) is electrically connected to the reverse cut-off terminal of the sixth unidirectional conducting device (D6); the common end of the fifth one-way conduction device (D5) and the sixth one-way conduction device (D6) is electrically connected with the upper bus capacitor (C)_bus+) And lower bus capacitor (C)_bus-) A common terminal of (a); the positive conducting end of the sixth unidirectional conducting device (D6) is electrically connected with the flying capacitor (C)_fly) The negative terminal of (a).

5. The DC/AC power conversion device according to claim 4, characterized in that: the DC/AC power conversion device flying capacitor (C) before normal operation_fly) The voltage at two ends is 0 when the battery is not charged; imparting flying capacitance (C) by separately turning on a first switch module (T1) and a fourth switch module (T4)_fly) When the first switch module (T1) is charged and turned on, the positive end of the fourth unidirectional conducting device (D4) is clamped to the lower bus capacitor (C) due to the clamping effect of the sixth unidirectional conducting device (D6)_bus-) Ensuring that the voltage stress of the fourth switching module (T4) is equal to the lower bus capacitance (C)_bus-) Is not broken down by voltage; in the same way, the flying capacitor (C) is provided with the fourth one-way conduction device (D4)_fly) During charging, the negative terminal of the first switch module (T1) can be clamped to the upper bus capacitor (C) due to the clamping effect of the fifth unidirectional conductive device (D5)_bus+) Ensuring that the voltage stress of the first switching module (T1) is equal to the upper bus capacitance (C)_bus+) Is not broken down by voltage.

6. The DC/AC power conversion device according to claim 1, characterized in that: the DC/AC power conversion device further includes a start-up circuit including a first switch (S1) and a second switch (S2), wherein a positive terminal of the first switch (S1) is electrically connected to the flying capacitor (C)_fly) A positive terminal of; the negative terminal of the first switch (S1) is electrically connected to the upper bus capacitor(C_bus+) And lower bus capacitor (C)_bus-) A common terminal of (a); the negative terminal of the second switch (S2) is electrically connected to the flying capacitor (C)_fly) And the positive terminal of the second switch (S2) is electrically connected to the upper bus capacitor (C)_bus+) And lower bus capacitor (C)_bus-) To the public terminal.

7. The DC/AC power conversion device according to claim 6, characterized in that: the second switch (S2) is in an open state when not started normally and working normally, is closed only when started, and is opened before the wave emission of the second switch module T2 after the start is finished (S2); due to the addition of the second switch (S2), the flying capacitor (C)_fly) When no voltage is built up, the flying capacitor (C) is supplied by opening the first switch module (T1)_fly) Charging to ensure that the voltage at two ends of the fourth switch module (T4) does not exceed the voltage of the lower bus capacitor, and effectively protecting the fourth switch module (T4); the first switch (S1) is in an open state when not started normally and working normally, is closed only when started, and is opened before the wave emission of the second switch module T2 after the start is finished (S1); due to the addition of the first switch (S1), the flying capacitor (C)_fly) When no voltage is built up, the flying capacitor (C) is supplied by opening the fourth switch module (T4)_fly) And charging to ensure that the voltage at two ends of the first switch module (T1) does not exceed the voltage of the upper bus capacitor, thereby effectively protecting the first switch module (T1).

8. The DC/AC power conversion device according to claim 1, characterized in that: the DC/AC power conversion device also comprises a starting circuit which is an isolation charging circuit, and one end of the isolation charging circuit is electrically connected with the flying capacitor (C)_fly) A positive terminal of; the other end is electrically connected to the flying capacitor (C)_fly) The isolation charging circuit is used for supplying flying capacitor (C)_fly) Charging, when the DC/AC power conversion device is ready to operate, the flying capacitor (C)_fly) The flying capacitor (C) is supplied by an isolated charging circuit without building up a voltage_fly) Charging, the capacitor is charged to half of the sum of the voltages of the upper bus capacitor and the lower bus capacitor, and the flying capacitor(C_fly) And after the charging is finished, the isolation charging circuit is cut off.

9. The DC/AC power conversion device according to claim 1, characterized in that: the upper bus capacitor (C)_bus+) Comprising two first upper bus capacitors (C) connected in series_bus1+) Negative terminal and second upper bus capacitance (C)_bus2+) Said lower bus capacitor (C)_bus-) Comprising two first lower bus capacitors (C) connected in series_bus1-) And a second lower bus capacitor (C)_bus2-) Simultaneously adding a first switch (S1) and a second switch (S2), wherein one end of the first switch (S1) is electrically connected with the first upper bus capacitor (C)_bus1+) Negative terminal and second upper bus capacitance (C)_bus2+) The common point of the positive terminals, the other terminal of the first switch (S1) being connected to the flying capacitor (C)_fly) On the positive terminal of the switch; one end of the second switch (S2) is electrically connected to the first lower bus capacitor (C)_bus1-) Negative terminal and second lower bus capacitance (C)_bus2-) The common point of the positive terminals, the other terminal of the second switch (S2) being connected to the flying capacitor (C)_fly) On the negative end of (c).

10. The DC/AC power conversion device according to claim 9, characterized in that: when the DC/AC power conversion device is not started or normally works, the first switch (S1) and the second switch (S2) are in an open state, and when the DC/AC power conversion device is started, the flying capacitor is charged by manually or controlling the first switch, the second switch (S1) and the second switch (S2) to be closed, and the flying capacitor is charged to the second upper bus capacitor (C2)_bus2+) And a first lower bus capacitor (C)_bus1-) The first switch (S1) and the second switch (S2) are turned off after the sum of the voltages.

Technical Field

The present invention relates to the field of DC/AC power conversion devices, and more particularly, to a high power density, grid-connected friendly power conversion circuit.

Background

The DC/AC conversion circuit is generally referred to as an inverter power conversion circuit or a DC/AC or AC/DC bidirectional conversion circuit, i.e., a multi-level DC/AC conversion circuit that inputs a DC voltage and outputs an AC voltage to perform power conversion is generally referred to as a multi-level DC/AC conversion circuit that can output three levels or more. Currently common in the industry are three-level power conversion circuits, such as NPCs, including T-type NPCs and INPC topologies, as shown in fig. 1 a.

For the INPC circuit shown in fig. 1a and 1b, under the operating condition of power factor 1, the operating condition widely exists in the new energy grid-connected system, for example: wind power, photovoltaic and the like, the T1 tube has conduction loss and larger switching loss, the T2 tube only has conduction loss, and in practical industrial application, the loss of the T1 tube is far greater than that of the T2 tube, so that the T1 tube cannot be applied to scenes with higher power levels due to thermal limitation. In addition, in the application of fig. 1, the current frequency is equal to the switching frequency of the T1 tube, and to increase the current frequency and reduce the current ripple, the switching frequency of the T1 tube must be increased. Since the frequency of the T1 tube is in positive correlation with heat generation, the increase in frequency causes a rapid rise in heat generation, and the use of the circuit is greatly limited.

Disclosure of Invention

In order to overcome the problems of the prior art, the present invention provides a DC/AC power conversion apparatus, which can solve the problems of the prior art that the local overheating and the current frequency are strictly limited by the frequency of the switch module due to the uneven heat generation of each switch module.

In order to achieve the purpose, the invention adopts the following technical scheme:

a DC/AC power conversion device comprises an upper bus capacitor C_bus+Lower busCapacitor C_bus-The switch comprises a first switch module T1, a second switch module T2, a third switch module T3, a fourth switch module T4, a first unidirectional conducting device D1, a second unidirectional conducting device D2, a third unidirectional conducting device D3 and a fourth unidirectional conducting device D4; lower bus capacitor C_bus-Upper bus capacitor C_bus+The first switch module T1, the second switch module T2, the third switch module T3 and the fourth switch module T4 are sequentially connected in series to form a loop; the lower bus capacitor C_bus-Is electrically connected with the upper bus capacitor C_bus+A negative terminal of (a); upper bus capacitor C_bus+Is electrically connected to the positive terminal of the first switch module T1; the negative terminal of the first switch module T1 is electrically connected to the positive terminal of the second switch module T2; the negative terminal T2 of the second switch module is electrically connected to the positive terminal of the third switch module T3; the negative terminal of the third switching module T3 is electrically connected to the positive terminal of the fourth switching module T4; the negative terminal of the fourth switch module T4 is electrically connected to the lower bus capacitor C_bus-A negative terminal of (a); the positive terminal of the first switch module T1 is electrically connected with the inverted terminal of the first unidirectional conducting device D1; the negative end of the first switch module T1 is electrically connected with the positive conducting end of the first unidirectional conducting device D1; the positive terminal of the second switch module T2 is electrically connected with the inverted terminal of the second unidirectional conducting device D2; the negative end of the second switch module T2 is electrically connected to the positive conducting end of the second unidirectional conducting device D2; the positive terminal of the third switching module T3 is electrically connected with the inverted terminal of the third unidirectional conducting device D3; the negative end of the third switching module T3 is electrically connected to the forward conducting end of the third unidirectional conducting device D3; the positive end of the fourth switching module T4 is electrically connected with the reverse cut-off end of the fourth unidirectional conducting device D4; the negative end of the fourth switching module T4 is electrically connected with the positive conducting end of the fourth unidirectional conducting device D4; the electrical connection point of the second switch module T2 and the third switch module T3 is led out as an AC output point; further comprising a flying capacitor C_fly(ii) a The flying capacitor C_flyIs electrically connected at a common point of the first and second switch modules T1 and T2; flying capacitor C_flyIs electrically connected at a common point of the third and fourth switching modules T3 and T4.

The flying capacitor C_flyBefore the DC/AC power conversion device works normally, the flying capacitor C is in an uncharged state_flyThe voltage at the two ends is 0; the flying capacitor C_flyThe flying capacitor C is charged when the DC/AC power conversion device works normally_flyThe voltage at two ends is close to the upper bus capacitor C_bus+And a lower bus capacitor C_bus-Half of the sum; the flying capacitor C_flyThe number of modes of the switch module can be increased, namely, a 0-state switch mode is added; under the condition that the frequencies of the first switch module T1, the second switch module T2, the third switch module T3 and the fourth switch module T4 are not changed, the current frequency can be multiplied, and the effect of reducing current harmonics is achieved.

When the DC/AC power conversion device works normally, the opening time and the current of the four switch modules are the same, and the loss distribution is more uniform; when the DC/AC power conversion device works normally, the conduction time and the current of the four unidirectional conduction devices are the same, and the loss distribution is more uniform; since there are no local hot spots, the current can be pushed to a higher power level with the same current.

The DC/AC power conversion apparatus further includes a start-up circuit including a fifth unidirectional conductive device D5 and a sixth unidirectional conductive device D6, wherein an inverted terminating end of the fifth unidirectional conductive device D5 is electrically connected to the flying capacitor C_flyA positive terminal of; the forward conducting terminal of the fifth unidirectional conducting device D5 is electrically connected to the reverse cut-off terminal of the sixth unidirectional conducting device D6; the common end of the fifth one-way conduction device D5 and the sixth one-way conduction device D6 is electrically connected with the upper bus capacitor C_bus+And a lower bus capacitor C_bus-A common terminal of (a); the positive conducting end of the sixth unidirectional conducting device D6 is electrically connected to the flying capacitor C_flyThe negative terminal of (a).

The flying capacitor C of the DC/AC power conversion device before normal operation_flyThe voltage at two ends is 0 when the battery is not charged; flying capacitor C is given by turning on first and fourth switch modules T1 and T4, respectively_flyWhen the first switch module T1 is turned on during charging, the clamping effect of the sixth unidirectional conducting device D6 clamps the positive terminal of the fourth unidirectional conducting device D4Position-to-lower bus capacitor C_bus-To ensure that the voltage stress of the fourth switch module T4 is equal to the lower bus capacitance C_bus-Is not broken down by voltage; similarly, the flying capacitor C is provided with a fourth one-way conduction device D4_flyDuring charging, due to the clamping effect of the fifth unidirectional device D5, the negative terminal of the first switch module T1 can be clamped to the upper bus capacitor C_bus+Ensures that the voltage stress of the first switch module T1 is equal to the upper bus capacitance C_bus+Is not broken down by voltage.

The DC/AC power conversion device further includes a start-up circuit including a first switch S1 and a second switch S2, wherein the reverse cutoff end of the first switch S1 is electrically connected to the flying capacitor C_flyA positive terminal of; the forward conducting end of the first switch S1 is electrically connected to the reverse cut-off end of the sixth unidirectional conducting device D6; the common end of the first switch S1 and the second switch S2 is electrically connected with the upper bus capacitor C_bus+And a lower bus capacitor C_bus-A common terminal of (a); the forward conducting end of the second switch S2 is electrically connected to the flying capacitor C_flyThe negative terminal of (a).

The second switch S2 is in an open state when not started normally and working normally, is closed only when started, and is opened before the wave of the second switch module T2 after the start is finished S2; due to the addition of the second switch S2, the flying capacitor C_flyWhen no voltage is built up, the flying capacitor C is supplied by opening the first switch module T1_flyCharging to ensure that the voltage at two ends of the fourth switch module T4 does not exceed the voltage of the lower bus capacitor, and effectively protecting the fourth switch module T4; the first switch S1 is in an open state when the first switch is not started normally and works normally, is closed only when the first switch is started, and is opened S1 before the second switch module T2 waves after the start is finished; due to the addition of the first switch S1, the flying capacitor C_flyWhen no voltage is built up, the flying capacitor C is supplied by opening the fourth switch module T4_flyAnd charging is carried out, so that the voltage at two ends of the first switch module T1 cannot exceed the voltage of the upper bus capacitor, and the first switch module T1 is effectively protected.

The DC/AC power conversion device further includes a start-up circuit, the start-up circuitThe circuit is an isolation charging circuit, and one end of the isolation charging circuit is electrically connected with the flying capacitor C_flyA positive terminal of; the other end is electrically connected to the flying capacitor C_flyThe isolation charging circuit is used for supplying flying capacitor C_flyCharging, when the DC/AC power conversion device is ready to operate, the flying capacitor C_flyThe flying capacitor C is supplied by an isolated charging circuit without building up voltage_flyCharging, the capacitor is charged to half of the sum of the voltages of the upper bus capacitor and the lower bus capacitor, and the flying capacitor C_flyAnd after the charging is finished, the isolation charging circuit is cut off.

The upper bus capacitor C_bus+Comprises two first upper bus capacitors C connected in series_bus1+Negative terminal and second upper bus capacitor C_bus2+The lower bus capacitor C_bus-Comprises two first lower bus capacitors C connected in series_bus1-And a second lower bus capacitor C_bus2-Simultaneously adding a first switch S1 and a second switch S2, wherein one end of the first switch S1 is electrically connected with the first upper bus capacitor C_bus1+Negative terminal and second upper bus capacitor C_bus2+The common point of the positive terminals, the other terminal of the first switch S1 being connected to the flying capacitor C_flyOn the positive terminal of the switch; one end of the second switch S2 is electrically connected to the first lower bus capacitor C_bus1-Negative terminal and second lower bus capacitor C_bus2-The common point of the positive terminals, the other terminal of the second switch S2 being connected to the flying capacitor C_flyOn the negative end of (c).

When the DC/AC power conversion device is not started or normally works, the first switch S1 and the second switch S2 are in an open state, and when the DC/AC power conversion device is started, the flying capacitor is charged by manually or controlling the first switch S1 and the second switch S2 to be closed, and the flying capacitor is charged to the second upper bus capacitor C_bus2+And a first lower bus capacitor C_bus1-The sum of the voltages turns off the first switch S1 and the second switch S2.

Compared with the prior art, the invention has the following advantages:

due to the existence of the flying capacitor, an O-state switching mode is added, so that a frequency doubling effect is formed, namely the current frequency is equal to twice the frequency of the switching module; meanwhile, when the four switch modules work normally, the on-time and the current of the four switch modules are the same, and the loss distribution is more uniform.

Due to the existence of the special starting circuit, when the flying capacitor does not build voltage, the flying capacitor can be safely charged through the starting circuit and the switch module, and the starting circuit can effectively protect the switch module in the charging process and prevent overvoltage breakdown.

Drawings

In order to more clearly illustrate the technical solutions in the implementation of the present application or the prior art, a brief description will be given below of the drawings used in the description of the embodiments of the present application or the prior art. It is clear that the following figures are some embodiments of the present application, from which other figures can be derived by a person skilled in the art without inventive effort.

Fig. 1a is a schematic diagram of an I-shaped clamp midpoint three-level inversion structure.

Fig. 1b shows the relationship between the output voltage and the switching state of an I-clamp midpoint three-level inverter.

FIG. 2 is a schematic diagram of a flying capacitor type DC/AC power conversion device according to the present invention.

Fig. 3a1, 3a2, and 3a3 show a switching mode P and a switching mode 0, respectively, of the first half cycle of the flying capacitor DC/AC power conversion device at a power factor of 1₁And switching mode 0₂。

Fig. 3b shows a relationship between the output voltage and the switching state in the first half cycle of the flying capacitor DC/AC power converter with a power factor of 1.

Fig. 4 shows the relationship between the output voltage and the switching state in one switching cycle.

FIG. 5 is a first schematic diagram of a DC/AC power conversion device according to the present invention.

Fig. 6 is a first schematic diagram of a starting circuit of the DC/AC power conversion device according to the present invention.

Fig. 7 is a second schematic diagram of a starting circuit of the DC/AC power converter according to the present invention.

Fig. 8 is a third schematic diagram of a starting circuit of the DC/AC power conversion device according to the present invention.

Fig. 9 is a fourth schematic diagram of a starting circuit of the DC/AC power conversion device according to the present invention.

Detailed Description

In order to make the technical solution better understood by those skilled in the art, the DC/AC power conversion device of the present invention will be described in further detail with reference to the accompanying drawings and the detailed description.

The DC/AC power conversion device circuit in the embodiment of the present application mainly includes:

as shown in FIG. 2, the DC/AC power converter of the present invention is composed of an upper bus capacitor C_bus+Lower bus capacitor C_bus-The switch comprises a first switch module T1, a second switch module T2, a third switch module T3, a fourth switch module T4, a first unidirectional conducting device D1, a second unidirectional conducting device D2, a third unidirectional conducting device D3 and a fourth unidirectional conducting device D4; lower bus capacitor C_bus-Upper bus capacitor C_bus+The first switch module T1, the second switch module T2, the third switch module T3 and the fourth switch module T4 are sequentially connected in series to form a loop; the lower bus capacitor C_bus-Is electrically connected with the upper bus capacitor C_bus+A negative terminal of (a); upper bus capacitor C_bus+Is electrically connected to the positive terminal of the first switch module T1; the negative terminal of the first switch module T1 is electrically connected to the positive terminal of the second switch module T2; the negative terminal T2 of the second switch module is electrically connected to the positive terminal of the third switch module T3; the negative terminal of the third switching module T3 is electrically connected to the positive terminal of the fourth switching module T4; the negative terminal of the fourth switch module T4 is electrically connected to the lower bus capacitor C_bus-A negative terminal of (a); the positive terminal of the first switch module T1 is electrically connected with the inverted terminal of the first unidirectional conducting device D1; the negative end of the first switch module T1 is electrically connected with the positive conducting end of the first unidirectional conducting device D1; the positive terminal of the second switch module T2 is electrically connected with the inverted terminal of the second unidirectional conducting device D2; the negative end of the second switch module T2 is electrically connected to the positive conducting end of the second unidirectional conducting device D2; the positive terminal of the third switching module T3 is electrically connected with the inverted terminal of the third unidirectional conducting device D3; the negative terminal of the third switching module T3 and the forward direction of the third unidirectional conducting device D3The through ends are electrically connected; the positive end of the fourth switching module T4 is electrically connected with the reverse cut-off end of the fourth unidirectional conducting device D4; the negative end of the fourth switching module T4 is electrically connected with the positive conducting end of the fourth unidirectional conducting device D4; the electrical connection point of the second switch module T2 and the third switch module T3 is led out as an AC output point; further comprising a flying capacitor C_fly(ii) a The flying capacitor C_flyIs electrically connected at a common point of the first and second switch modules T1 and T2; flying capacitor C_flyIs electrically connected at a common point of the third and fourth switching modules T3 and T4.

The flying capacitor C_flyBefore the DC/AC power conversion device works normally, the flying capacitor C is in an uncharged state_flyThe voltage at the two ends is 0; the flying capacitor C_flyThe flying capacitor C is charged when the DC/AC power conversion device works normally_flyThe voltage at two ends is close to the upper bus capacitor C_bus+And a lower bus capacitor C_bus-Half of the sum; the flying capacitor C_flyThe number of modes of the switch module can be increased, namely, a 0-state switch mode is added; under the condition that the frequencies of the first switch module T1, the second switch module T2, the third switch module T3 and the fourth switch module T4 are not changed, the current frequency can be multiplied, and the effect of reducing current harmonics is achieved.

Fig. 3a1, 3a2, and 3a3 are three switching modes of the flying capacitor DC/AC power conversion device in the first half cycle at a power factor of 1, respectively. Defining P state as AC output potential equal to bus +; defining O state as AC output potential equal to bus_NIn the O state, two switching modes are included, respectively O₁State and O₂State; define the N state as the AC output potential being equal to bus-. Meanwhile, definition 1 in fig. 3b represents the corresponding switch module conducting state; 0 represents the corresponding switch module off state. Fig. 3a1, 3a2 and 3a3 show three modes of wave generation and current flow in the positive half cycle under the condition of power factor 1, and fig. 3b shows the operating states of the switch modules corresponding to the three modes in fig. 3 a. In the switching mode P, the first and second switch modules T1 and T2 are turned on, and the current passes through the first switch moduleA switch module T1 and a second switch module T2 output, AC output and bus + same potential; in switching mode O₁At this time, the first switch module T1 and the third switch module T3 are turned on, and the flying capacitor C is turned on_flyThe positive electrode has the same potential as the bus +, and the voltage at the two ends of the flying capacitor is always equal to the upper bus capacitor C_bus+And a lower bus capacitor C_bus-Half of the sum of, and thus the flying capacitor C_flyNegative electrode and bus_NAt the same potential, the current passes through the first switch module T1 and the flying capacitor C_flyAnd a third one-way conduction device D3, the AC output and the negative pole of the flying capacitor are at the same potential as bus_N(ii) a In switching mode O₂At this time, the second switch module T2 and the fourth switch module T4 are turned on, and the flying capacitor C is connected_flyNegative pole is at the same potential as bus, due to flying capacitor C_flyThe voltage at both ends is always equal to the upper bus capacitor C_bus+And a lower bus capacitor C_bus-Half of the sum of, and thus the flying capacitor C_flyPositive electrode and bus_NSame potential, current slave flying capacitor C_flyThe positive pole is output through a second switch module T2, and the same potential of the AC output and the positive pole of the flying capacitor is bus_N. In particular, in normal operation, the flying capacitor C_flyThe voltage at the two ends is half of the sum of the upper bus capacitor voltage and the lower bus capacitor voltage. From the three modes of the positive half period, the mode of the negative half period is easily known, and at the same time, the switching mode when the power factor is not 1 is also easily known.

Fig. 4 shows the relationship between the output voltage and the switching state in one switching cycle. As shown in fig. 4, two switching modes P and one switching mode O occur in one switching cycle of the switching module respectively₁And switching mode O₂. As can be seen from fig. 4, the switching mode is converted twice in one switching period of the switching module, that is, the output current is also converted twice, so as to form a frequency doubling effect. Similarly, as can be seen from fig. 4, the voltage and current and the on-time of the first switch module T1 and the second switch module T2 are the same in one switching cycle, so the heat loss generated by the first switch module T1 and the second switch module T2 is the same, and the heat generation is uniform.

In fig. 4, the wave of the first switch module T1 and the wave of the second switch module T2 have a phase shift of 180 °, and the values are not fixed in different wave-transmitting and control logics, and may be any phase-shift angle between greater than 0 ° and equal to or less than 180 °, which may be specifically designed in combination with the practice of the control strategy. In the phase shift range, 180 ° is selected to be most advantageous for the filter of the output in the DC/AC power conversion device.

Fig. 5 is another schematic diagram of the DC/AC power conversion device according to the present invention. When the device is not working normally, the flying capacitor C_flyThe voltage is not established at the two ends, the voltage at the two ends is 0V, the first switch module T1 is enabled to be in a conducting state at the moment, and the upper bus capacitor C_bus+And a lower bus capacitor C_bus-Will be applied all across the fourth switch module T4. The voltage class of the switch module of fig. 5 is selected to be half the bus voltage, which would cause the fourth switch module T4 to break down over voltage if the upper bus voltage and the lower bus voltage were applied simultaneously across the fourth switch module T4. Similar to the principle of fig. 5, it is known that when the voltage of the flying capacitor is not built up, turning on the fourth switch module T4 may cause the first switch module T1 to break down by overvoltage, resulting in irreversible damage.

Fig. 6 is a diagram illustrating an embodiment of a starting circuit of the DC/AC power conversion device according to the present invention. As can be seen from fig. 5, under the operating condition that no starting circuit is provided and the flying capacitor voltage is not built up, no matter the first switch module T1 or the fourth switch module T4 is turned on first, the circuit is damaged, and an embodiment of the starting circuit is proposed herein, as shown in fig. 6. The sixth one-way conduction device D6 is added, and due to the existence of the sixth one-way conduction device D6, the voltage at two ends of the fourth switch module can be ensured not to exceed the voltage of the lower bus capacitor, and at the moment, the first switch module T1 is switched on to supply the flying capacitor C with the flying capacitor when the voltage of the flying capacitor is not established_flyCharging can ensure that the fourth switch module T4 cannot be broken down and the flying capacitor C can be ensured_flyThe charging is stabilized to the upper bus voltage. Similarly, the fifth one-way conduction device D5 is added, and due to the existence of the fifth one-way conduction device D5, it can be ensured that the voltage at the two ends of the first switch module T1 does not exceed the voltage of the upper bus capacitor, and at this time, the fourth switch is turned on when the flying capacitor voltage is not establishedThe off-module T4 charges the flying capacitor, so as to ensure that the first switch module T1 is not broken down and ensure that the flying capacitor C is also ensured_flyThe charging is stabilized to the upper bus voltage. In a DC/AC power converter, upper and lower bus voltages are equal, and a flying capacitor C_flyThe voltage at the two ends is equal to the upper bus voltage, namely half of the sum of the upper bus capacitor voltage and the lower bus capacitor voltage.

Fig. 7 is a diagram illustrating an embodiment of a starting circuit of the DC/AC power conversion device according to the present invention. Analyzing fig. 5, it can be seen that under the operating condition that there is no starting circuit and the flying capacitor voltage is not established, no matter the first switch module T1 or the fourth switch module T4 is turned on first, the circuit is damaged, and another embodiment of the starting circuit is proposed herein, the corresponding bits of the fifth single-phase conducting device D5 and the sixth single-phase conducting device D6 in fig. 6 are replaced by the first switch S1 and the second switch S2, as shown in fig. 7. One end of the second switch S2 is connected to the upper bus capacitor C_bus+And a lower bus capacitor C_bus-And the other end of the common connection point is connected to the negative terminal of the flying capacitor. The switches in the present embodiment include relays, contactors, circuit breakers, power semiconductor switches (e.g., reverse conducting IGBTs, MOSFETs, etc.). The second switch S2 is in an open state when not normally activated and operating normally, and is closed only when activated, and the second switch S2 is opened after the activation before the second switch module T2 emits a wave. Similar to the sixth single-phase-turn-on device D6 in FIG. 6, due to the addition of the second switch S2, the flying capacitor C_flyWhen no voltage is built up, the flying capacitor C is supplied by opening the first switch module T1_flyAnd (6) charging. The voltage at the two ends of the fourth switch module T4 can not exceed the voltage of the lower bus capacitor, and the fourth switch module T4 is effectively protected. Similarly, the first switch S1 is in an open state when not normally activated and operating normally, and is closed only when activated, and the first switch S1 is opened before the second switch module T2 emits a wave after the activation is completed. Similar to the fifth single-phase-turn-on device D5 in FIG. 6, due to the addition of the first switch S1, the flying capacitor C_flyWhen no voltage is built up, the flying capacitor C is supplied by opening the fourth switch module T4_flyAnd (6) charging. It can be ensured that the voltage across the first switch module T1 does not exceed the upper busThe capacitor voltage, effectively protecting the first switch module T1.

FIG. 8 is a diagram of an embodiment of a DC/AC power conversion device start-up circuit for charging flying capacitors in an isolated charging circuit according to the present invention. One end of the isolation charging circuit is electrically connected to the flying capacitor C_flyA positive terminal of; the other end is electrically connected to the flying capacitor C_flyThe isolation charging circuit is specially used for supplying flying capacitor C_flyAnd (6) charging. When the DC/AC power conversion device is ready to operate, the flying capacitor C is used_flyThe flying capacitor C is supplied by an isolated charging circuit without building up voltage_flyCharging, the capacitor is charged to half of the sum of the voltages of the upper bus capacitor and the lower bus capacitor, and the flying capacitor C_flyCharging to the upper bus voltage or the lower bus voltage, completing the charging, and then disconnecting the isolation charging circuit from the flying capacitor. The power supply of the isolated charging circuit can be from a direct current bus or an Alternating Current (AC) side, or a special power supply.

Fig. 9 shows an embodiment of a starting circuit of the DC/AC power converter according to the present invention. In some practical industrial application environments, the upper bus and the lower bus have higher voltage, and the requirement cannot be met by only one capacitor, so that 2 capacitors are connected in series for replacement. The present embodiment is characterized in that when the upper and lower bus capacitors are replaced by 2 capacitors in series, a first switch S1 and a second switch S2 are added. One end of the first switch S1 is electrically connected to the first upper bus capacitor C_bus1+Negative terminal and second upper bus capacitor C_bus2+The common point of the positive terminals, the other terminal of the first switch S1 being connected to the flying capacitor C_flyOn the positive end of (c). One end of the second switch S2 is electrically connected to the first lower bus capacitor C_bus1-Negative terminal and second lower bus capacitor C_bus2-The common point of the positive terminals, the other terminal of the second switch S2 being connected to the flying capacitor C_flyOn the negative end of (c). When the flying capacitor is not started or normally works, the first switch S1 and the second switch S2 are in an open state, and when the flying capacitor is started, the flying capacitor is charged by manually or controlling the first switch S1 and the second switch S2 to be closed, and the flying capacitor is charged to the second upper bus capacitor C_bus2+And a first lower bus capacitor C_bus1-The sum of the voltages turns off the first switch S1 and the second switchAnd (S2).