CN115714549A

CN115714549A - Bidirectional DC-AC converter

Info

Publication number: CN115714549A
Application number: CN202310013488.0A
Authority: CN
Inventors: 赵小超; 郑钊; 郑明才; 郑金兵; 肖锋
Original assignee: Hunan First Normal University
Current assignee: Hunan First Normal University
Priority date: 2023-01-05
Filing date: 2023-01-05
Publication date: 2023-02-24
Anticipated expiration: 2043-01-05
Also published as: CN115714549B

Abstract

The invention discloses a bidirectional DC-AC converter, which adopts a DC-pulsating DC bidirectional conversion main circuit, a pulsating DC-AC bidirectional conversion main circuit, a first regulating circuit, a second regulating circuit, a third regulating circuit, a first PWM circuit, a second PWM circuit, a third PWM circuit, a first driving circuit, a second driving circuit, a third driving circuit and a digital control circuit, wherein the DC-pulsating DC bidirectional conversion main circuit and the pulsating DC-AC bidirectional conversion main circuit are connected through a middle port of two-stage cascade. The converter adopts a two-stage protection and two-stage control mode, the basic protection is born by a pure hardware circuit, the reliability and the rapidity are ensured, the comprehensive intelligent protection is born by software in digital control, and the flexibility and the comprehensiveness are ensured; the high-frequency control is completed by a pure hardware circuit, the real-time performance of the control is ensured, and the low-frequency control is born by software in the digital control, so that the flexibility and the high cost performance are ensured.

Description

Bidirectional DC-AC converter

Technical Field

The invention relates to the technical field of current conversion, and particularly discloses a bidirectional DC-AC converter which can be widely applied to the fields of photovoltaic power generation, energy storage power stations, storage battery charging and discharging and the like requiring bidirectional flow of direct current/alternating current electric energy and can realize forward conversion from the direct current electric energy to the alternating current electric energy and reverse conversion from the alternating current electric energy to the direct current electric energy under different working conditions.

Background

The DC-AC converter realizes the inversion conversion from Direct Current (DC) to Alternating Current (AC); the AC-DC converter realizes Alternating Current (AC) to Direct Current (DC) rectification conversion. The unidirectional DC-AC converter and the AC-DC converter which are connected in parallel in the reverse direction can realize bidirectional DC-AC conversion, but the efficiency, the volume, the cost, the control complexity, the control effect and the like of the converters are not ideal, and particularly, the alternating current grid connection performance is limited.

The prior art has the following defects:

(1) The traditional DC-AC converter or AC-DC converter can only realize one-way conversion, when the traditional DC-AC converter and the AC-DC converter are connected in parallel to realize the two-way DC-AC conversion function, two sets of systems work in a time-sharing mode, the number of components used by the systems is large, particularly, the number of power devices is large, and therefore the cost is high, the size is large, and the cost performance is not high.

(2) The traditional DC-AC converter has relatively low working frequency, and the required capacity of an inductive device and a capacitive device is large, so that the equipment volume is large, and the power density of the converter is not high.

(3) The traditional DC-AC converter has relatively low working frequency, larger inductive device parameters, larger energy storage period by period, less fine energy control granularity, difficult improvement of the output precision of the converter, large time constant of a dynamic circuit and complex control algorithm when reaching higher control indexes.

(4) The traditional DC-AC converter has relatively large switching period and great difficulty in accurate realization of soft switching, so that the switching loss of a power switching tube is great, and the improvement of the efficiency of the converter is limited.

(5) When the working frequency of a switching tube of a traditional DC-AC converter is further improved, the switching tube of the same bridge arm is easy to be directly connected to cause damage to components.

Therefore, the existing DC-AC converter or AC-DC converter can only realize unidirectional conversion, which is a technical problem to be solved at present.

Disclosure of Invention

The invention provides a bidirectional DC-AC converter, which aims to solve the technical problem that the existing DC-AC converter or AC-DC converter can only realize unidirectional conversion.

The invention relates to a bidirectional DC-AC converter, which comprises a DC-pulsating DC bidirectional conversion main circuit, a pulsating DC-AC bidirectional conversion main circuit, a first regulating circuit, a second regulating circuit, a third regulating circuit, a first PWM circuit, a second PWM circuit, a third PWM circuit, a first driving circuit, a second driving circuit, a third driving circuit and a digital control circuit, wherein the DC-pulsating DC bidirectional conversion main circuit and the pulsating DC-AC bidirectional conversion main circuit are connected through two-stage cascaded middle ports; the DC-pulsating DC bidirectional conversion main circuit is respectively connected with a first regulating circuit, a first PWM circuit, a first driving circuit, a second regulating circuit, a second PWM circuit and a second driving circuit; the pulsating DC-AC bidirectional conversion main circuit is respectively connected with a third regulating circuit, a third PWM circuit and a third driving circuit; the digital control circuit is respectively connected with the DC-pulsating DC bidirectional conversion main circuit, the pulsating DC-AC bidirectional conversion main circuit, the first regulating circuit, the second regulating circuit, the third regulating circuit, the first PWM circuit, the second PWM circuit, the third PWM circuit, the first driving circuit, the second driving circuit and the third driving circuit; the free end of the DC-pulsating DC bidirectional conversion main circuit is a first port, and the free end of the pulsating DC-AC bidirectional conversion main circuit is a second port; when the forward DC-AC is converted, the first port is used as a direct current input port, the middle port is used as a middle pulsating direct current port, and the second port is used as an alternating current output port; when the reverse DC-AC conversion is carried out, the second port is used as an alternating current input port, the middle port is used as a middle pulse direct current port, and the first port is used as a direct current output port; the DC-pulsating DC bidirectional conversion main circuit is used for completing bidirectional power conversion between direct current and pulsating direct current; the pulsating DC-AC bidirectional conversion main circuit is used for completing bidirectional power conversion between pulsating direct current and alternating current; the first regulating circuit is used for finishing signal conditioning and protection signal formation during DC-pulsating DC forward conversion control; the first PWM circuit is used for completing the formation of PWM control pulses during the forward conversion of the DC-pulsating DC; the first driving circuit is used for completing the driving of a switching tube during the DC-pulsating DC forward conversion; the second regulating circuit is used for finishing signal conditioning and protection signal formation during DC-pulsating DC reverse conversion control; the second PWM circuit is used for finishing the formation of PWM control pulse during the DC-pulsating DC reverse conversion; the second driving circuit is used for completing the driving of a switching tube during the DC-pulsating DC reverse conversion; the third regulating circuit is used for finishing signal conditioning and protection signal formation during the control of the pulsating DC-AC forward conversion; the third PWM circuit is used for completing the formation of PWM control pulse during the forward conversion of the pulsating DC-AC; the third driving circuit is used for completing the driving of the switching tube during the forward conversion of the pulsating DC-AC; the digital control circuit is used as a comprehensive control unit of the bidirectional DC-AC converter.

Further, the DC-pulsating DC bidirectional conversion main circuit comprises a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a first high-frequency rectifying diode, a second high-frequency rectifying diode, a third high-frequency rectifying diode, a fourth high-frequency rectifying diode, a first high-frequency filter inductor, a second high-frequency filter inductor, a third high-frequency filter inductor, a fourth high-frequency filter inductor, a first high-frequency buffer absorption circuit, a second high-frequency buffer absorption circuit, a third high-frequency buffer absorption circuit, a fourth high-frequency buffer absorption circuit and a high-frequency power transformer, wherein the first switch tube, the first high-frequency rectifying diode, the first high-frequency filter inductor and the first high-frequency buffer absorption circuit are connected with 1-2 windings of the high-frequency power transformer after being interconnected; the second switch tube, the second high-frequency rectifier diode, the second high-frequency filter inductor and the second high-frequency buffer absorption circuit are connected with the 2-3 windings of the high-frequency power transformer after being interconnected; the third switching tube, the third high-frequency rectifying diode, the third high-frequency filter inductor and the third high-frequency buffer absorption circuit are connected with 13-14 windings of the high-frequency power transformer after being interconnected; and the fourth switching tube, the fourth high-frequency rectifier diode, the fourth high-frequency filter inductor and the fourth high-frequency buffer absorption circuit are connected with 12-13 windings of the high-frequency power transformer after being interconnected.

Further, the pulsating DC-AC bidirectional conversion main circuit comprises a fifth switch tube, a sixth switch tube, a seventh switch tube, an eighth switch tube, a fifth high-frequency rectifying diode, a sixth high-frequency rectifying diode, a seventh high-frequency rectifying diode, an eighth high-frequency rectifying diode, a fifth high-frequency buffering and absorbing circuit, a sixth high-frequency buffering and absorbing circuit, a seventh high-frequency buffering and absorbing circuit, an eighth high-frequency buffering and absorbing circuit, a power frequency current transformer, a first electrical isolation optocoupler and a second electrical isolation optocoupler, wherein the fifth switch tube, the fifth high-frequency rectifying diode and the fifth high-frequency buffering and absorbing circuit are connected with the positive end of the middle port, the positive input end of the first electrical isolation optocoupler and the negative input end of the second electrical isolation optocoupler respectively after being interconnected; the sixth switching tube, the sixth high-frequency rectifying diode and the sixth high-frequency buffering absorption circuit are connected with the negative end of the middle port, the positive input end of the first electrical isolation optocoupler and the negative input end of the second electrical isolation optocoupler respectively after being interconnected; the seventh switch tube, the seventh high-frequency rectifier diode and the seventh high-frequency buffer absorption circuit are connected with the positive end of the second port, the negative input end of the first electrical isolation optocoupler and the positive input end of the second electrical isolation optocoupler respectively after being interconnected; the eighth switching tube, the eighth high-frequency rectifying diode and the eighth high-frequency buffering absorption circuit are connected with the positive end of the second port, the negative input end of the first electrical isolation optocoupler and the positive input end of the second electrical isolation optocoupler respectively after being interconnected; and the power frequency current transformer is connected with the second port.

Furthermore, the first regulating circuit comprises a first reference voltage circuit, a first current sampling circuit, a first amplifying circuit and a first comparing circuit, wherein the first current sampling circuit is connected with the first comparing circuit through the first amplifying circuit, and the output end of the first reference voltage circuit is connected with the first comparing circuit.

Furthermore, the second regulating circuit comprises a second reference voltage circuit, a second current sampling circuit, a second amplifying circuit and a second comparing circuit, wherein the second current sampling circuit is connected with the second comparing circuit through the second amplifying circuit, and the output end of the second reference voltage circuit is connected with the second comparing circuit.

Furthermore, the third regulating circuit comprises a third reference voltage circuit, a third current sampling circuit, a third amplifying circuit and a third comparing circuit, the third current sampling circuit is connected with the third comparing circuit through the third amplifying circuit, and the output end of the third reference voltage circuit is connected with the third comparing circuit.

Furthermore, the first PWM circuit comprises a first oscillator, a first inverter, a third electrical isolation optocoupler, a first follower and a first comparator, wherein the first oscillator is connected with the first inverter; the third electric isolation optocoupler is connected with the first comparator through the first follower.

Further, the second PWM circuit includes a second oscillator, a second inverter, a fourth electrically isolated optocoupler, a second follower, and a second comparator, the second oscillator is connected to the second inverter; the fourth electric isolation optocoupler is connected with the second comparator through the second follower; the third PWM circuit comprises a first voltage reference module, a second voltage reference module, a third comparator and a fourth comparator, wherein the first voltage reference module is connected with the third comparator; the second voltage reference module is connected with the fourth comparator.

Furthermore, the first driving circuit comprises a first driving chip and a second driving chip, the first driving chip is connected with the first switch tube, and the second driving chip is connected with the second switch tube; the second driving circuit comprises a third driving chip and a fourth driving chip, the third driving chip is connected with a third switching tube, and the fourth driving chip is connected with a fourth switching tube; the third driving circuit comprises a fifth driving chip, a sixth driving chip, a seventh driving chip and an eighth driving chip, the fifth driving chip is connected with the fifth switching tube, the sixth driving chip is connected with the sixth switching tube, the seventh driving chip is connected with the seventh switching tube, and the eighth driving chip is connected with the eighth switching tube.

Furthermore, the digital control circuit comprises a CPU board, and the CPU board is respectively connected with the first switching tube, the second switching tube, the third switching tube, the fourth switching tube, the fifth switching tube, the sixth switching tube, the seventh switching tube and the eighth switching tube.

The beneficial effects obtained by the invention are as follows:

the invention provides a bidirectional DC-AC converter, which adopts a DC-pulsating DC bidirectional conversion main circuit, a pulsating DC-AC bidirectional conversion main circuit, a first regulating circuit, a second regulating circuit, a third regulating circuit, a first PWM circuit, a second PWM circuit, a third PWM circuit, a first driving circuit, a second driving circuit, a third driving circuit and a digital control circuit, wherein the DC-pulsating DC bidirectional conversion main circuit is used for completing bidirectional power conversion between direct current and pulsating direct current; the pulsating DC-AC bidirectional conversion main circuit is used for completing bidirectional power conversion between pulsating direct current and alternating current; the first regulating circuit is used for finishing signal conditioning and protection signal formation during DC-pulsating DC forward conversion control; the first PWM circuit is used for completing the formation of PWM control pulses during the forward conversion of DC-pulsating DC; the first driving circuit is used for completing the driving of a switching tube during the forward conversion of the DC-pulsating DC; the second regulating circuit is used for finishing signal conditioning and protection signal formation during DC-pulsating DC reverse conversion control; the second PWM circuit is used for completing the formation of PWM control pulse when DC-pulsating DC reverse conversion is completed; the second driving circuit is used for completing the driving of a switching tube during the DC-pulsating DC reverse conversion; the third regulating circuit is used for finishing signal conditioning and protection signal formation during the control of the pulsating DC-AC forward conversion; the third PWM circuit is used for finishing the formation of PWM control pulse during the forward conversion of the pulsating DC-AC; the third driving circuit is used for completing the driving of the switching tube during the forward conversion of the pulsating DC-AC; the digital control circuit is used as a comprehensive control unit of the bidirectional DC-AC converter. The bidirectional DC-AC converter provided by the invention is formed by cascading DC-pulsating DC bidirectional conversion and pulsating DC-AC bidirectional conversion, wherein the DC-pulsating DC bidirectional conversion part adopts high-frequency (500KHz to 10MHz) PWM control, the pulsating DC-AC bidirectional conversion part adopts power-frequency (50 Hz) pulse control, the performance index is improved by utilizing the high-frequency control, and the direct connection and the switching loss are avoided by utilizing the low-frequency control; the converter adopts a two-stage protection and two-stage control mode, the basic protection is born by a pure hardware circuit, the reliability and the rapidity are ensured, the comprehensive intelligent protection is born by software in digital control, and the flexibility and the comprehensiveness are ensured; the high-frequency control is completed by a pure hardware circuit, so that the real-time performance of the control is ensured, and the low-frequency control is borne by software in the digital control, so that the flexibility and the high cost performance are ensured; the DC part and the AC part of the converter are electrically isolated by adopting a high-frequency transformer, a two-way push-pull topological structure is adopted, and the homonymous ends of multiple windings of the transformer are optimally distributed, so that the load balance is ensured, the direct-current component in the transformer is reduced, and the safety and reliability of high-power transmission of the transformer are ensured; the DC-pulsating DC bidirectional conversion part works in a high-frequency (500KHz to 10MHz) state, and parameters of required inductive devices and capacitive devices are small, so that the whole converter is small in size and high in power density; the inductive device has small parameters, small energy storage energy in a single period and fine control granularity, so the system has high control precision; the parameters of the inductive and capacitive devices are small, the dynamic time constant of the system is small, the control algorithm is simplified, the real-time performance is good, and the system implementation cost can be reduced; the converter can realize bidirectional DC-AC conversion, and the application field and the application range of the DC-AC converter are enlarged; the buffer circuit and related device parameters are optimized, when the switching tube is switched from a conducting state to a switching-off state, due to the effect of the parallel capacitor in the buffer circuit, the instantaneous voltage at two ends of the switching tube is low during state switching, and the switching loss is small; when the switching tube is switched from the off state to the on state, the instantaneous current flowing through the switching tube is small due to the effect of the series inductor, and the switching loss is small. Therefore, the total switching loss is small, and the converter efficiency is high; the high-frequency PWM control pulse is generated by adopting an oscillator and is adjustable, and when the switching speed level of a switching tube is increased, seamless upgrade of a product is facilitated; the converter adopts a hierarchical control mode of basic control and comprehensive control, which is convenient for realizing individualized requirements in a digital controller through software aiming at different application scenes, improving the intelligence and the comprehensiveness of the converter and further increasing the applicability and the application range of the converter; when the converter is in forward conversion or reverse conversion, the high-frequency transformer is provided with two main windings with opposite current directions to work in an interlaced mode, 4 windings of the auxiliary power supply also work in an interlaced mode in two groups, compared with a single-ended forward or flyback converter, the high-frequency transformer is extremely low in direct current component and large in transmittable power, and compared with a bridge circuit, the direct connection of a switching tube is avoided; the bridge type inversion part adopts power frequency pulse control, the switching period is long, enough dead time is allowed, and the direct connection risk of the switching tubes on the same bridge arm is reduced.

Drawings

FIG. 1 is a functional block diagram of one embodiment of a bi-directional DC-AC converter provided by the present invention;

fig. 2 is a schematic circuit diagram of an embodiment of the DC-ripple DC bidirectional converter main circuit shown in fig. 1;

FIG. 3 is a schematic circuit diagram of an embodiment of the pulsating DC-AC bidirectional converter main circuit shown in FIG. 1;

FIG. 4 is a schematic circuit diagram of an embodiment of the auxiliary power circuit shown in FIG. 1;

FIG. 5 is a schematic circuit diagram of an embodiment of the first regulating circuit shown in FIG. 1;

FIG. 6 is a schematic circuit diagram of an embodiment of the second regulating circuit shown in FIG. 1;

FIG. 7 is a schematic circuit diagram of an embodiment of the third regulating circuit shown in FIG. 1;

FIG. 8 is a schematic circuit diagram of an embodiment of the first PWM circuit shown in FIG. 1;

FIG. 9 is a schematic circuit diagram of an embodiment of the second PWM circuit shown in FIG. 1;

FIG. 10 is a schematic circuit diagram of an embodiment of the third PWM circuit shown in FIG. 1;

FIG. 11 (a) is a schematic circuit diagram of an embodiment of a first driver chip in the first driver circuit shown in FIG. 1;

FIG. 11 (b) is a schematic diagram illustrating a circuit of an embodiment of a second driver chip in the first driver circuit shown in FIG. 1;

FIG. 12 (a) is a schematic circuit diagram of an embodiment of a third driver chip in the second driver circuit shown in FIG. 1;

FIG. 12 (b) is a schematic circuit diagram of an embodiment of a fourth driver chip in the second driver circuit shown in FIG. 1;

FIG. 13 (a) is a schematic circuit diagram of an embodiment of a fifth driver chip in the third driver circuit shown in FIG. 1;

FIG. 13 (b) is a schematic circuit diagram of an embodiment of a sixth driver chip in the third driver circuit shown in FIG. 1;

FIG. 13 (c) is a schematic circuit diagram of an embodiment of a seventh driver chip in the third driver circuit shown in FIG. 1;

FIG. 13 (d) is a schematic diagram illustrating a circuit of an embodiment of an eighth driver chip in the third driver circuit shown in FIG. 1;

FIG. 14 is a schematic circuit diagram of an embodiment of the digital control circuit shown in FIG. 1;

fig. 15 (a) is a diagram showing a given pulse form of an alternating current and a given effect of a smoothed alternating current after smoothing and filtering in a bidirectional DC-AC converter provided by the present invention;

fig. 15 (b) is a diagram of the pulse form of the AC output and the effect of the smooth filtered pulsating DC output during the DC-pulsating DC forward conversion in the bidirectional DC-AC converter provided by the present invention;

fig. 16 (a) is a diagram of the DC output effect when the bidirectional DC-AC converter provided by the present invention performs reverse conversion;

fig. 16 (b) is a diagram showing the effect of power frequency AC output when the bidirectional DC-AC converter provided by the present invention is used for forward conversion.

The reference numbers illustrate:

10. a DC-pulsating DC bidirectional conversion main circuit; 20. the pulsating DC-AC bidirectional conversion main circuit; 31. a first regulating circuit; 32. a second regulating circuit; 33. a third regulating circuit; 41. a first PWM circuit; 42. a second PWM circuit; 43. a third PWM circuit; 51. a first drive circuit; 52. a second drive circuit; 53. a third drive circuit; 60. a digital control circuit; 70. an auxiliary power supply circuit.

Detailed Description

In order to better understand the technical solution, the technical solution will be described in detail with reference to the drawings and the specific embodiments.

As shown in fig. 1, a first embodiment of the present invention provides a bidirectional DC-AC converter, which includes a DC-ripple DC bidirectional conversion main circuit 10, a ripple DC-AC bidirectional conversion main circuit 20, a first adjusting circuit 31, a second adjusting circuit 32, a third adjusting circuit 33, a first PWM circuit 41, a second PWM circuit 42, a third PWM circuit 43, a first driving circuit 51, a second driving circuit 52, a third driving circuit 53, and a digital control circuit 60, wherein the DC-ripple DC bidirectional conversion main circuit 10 and the ripple DC-AC bidirectional conversion main circuit 20 are connected through two cascaded intermediate ports; the DC-pulsating DC bidirectional conversion main circuit 10 is respectively connected with a first regulating circuit 31, a first PWM circuit 41, a first driving circuit 51, a second regulating circuit 32, a second PWM circuit 42 and a second driving circuit 52; the pulsating DC-AC bidirectional conversion main circuit 20 is respectively connected with the third regulating circuit 33, the third PWM circuit 43 and the third driving circuit 53; the digital control circuit 60 is respectively connected with the DC-pulsating DC bidirectional conversion main circuit 10, the pulsating DC-AC bidirectional conversion main circuit 20, the first regulating circuit 31, the second regulating circuit 32, the third regulating circuit 33, the first PWM circuit 41, the second PWM circuit 42, the third PWM circuit 43, the first drive circuit 51, the second drive circuit 52 and the third drive circuit 53; the free end of the DC-pulsating DC bidirectional conversion main circuit 10 is a first port, and the free end of the pulsating DC-AC bidirectional conversion main circuit 20 is a second port; when the forward DC-AC conversion is carried out, the first port is used as a direct current input port, the middle port is used as a middle pulse direct current port, and the second port is used as an alternating current output port; when the reverse DC-AC conversion is carried out, the second port is used as an alternating current input port, the middle port is used as a middle pulsating direct current port, and the first port is used as a direct current output port; the DC-pulsating DC bidirectional conversion main circuit 10 is used for completing bidirectional power conversion between direct current and pulsating direct current; the pulsating DC-AC bidirectional conversion main circuit 20 is used for completing bidirectional power conversion between pulsating direct current and alternating current; the first regulating circuit 31 is used for completing signal conditioning and protection signal formation during DC-pulsating DC forward conversion control; the first PWM circuit 41 is used to complete the formation of PWM control pulses at the time of DC-pulsating DC forward conversion; the first driving circuit 51 is used for completing the driving of a switching tube during the forward conversion of DC-pulsating DC; the second regulating circuit 32 is used for signal conditioning and protection signal formation when finishing the control of the DC-pulsating DC reverse conversion; the second PWM circuit 42 is used to complete the formation of PWM control pulses during DC-to-pulsating DC reverse conversion; the second driving circuit 52 is used for completing the driving of the switching tube during the reverse conversion of the DC-pulsating DC; the third regulating circuit 33 is used for signal conditioning and protection signal formation when the pulsating DC-AC forward conversion control is completed; the third PWM circuit 43 is used to complete the formation of PWM control pulses during the pulsating DC-AC forward transform; the third driving circuit 53 is used for completing the driving of the switching tube during the forward conversion of the pulsating DC-AC; the digital control circuit 60 is used as an integrated control unit for the bidirectional DC-AC converter.

In the above structure, please refer to fig. 2, fig. 2 is a schematic circuit schematic diagram of an embodiment of the DC-DC bidirectional conversion main circuit shown in fig. 1, in this embodiment, the DC-DC bidirectional conversion main circuit 10 includes a first switch tube Q1, a second switch tube Q2, a third switch tube Q3, a fourth switch tube Q4, a first high-frequency rectifying diode D1, a second high-frequency rectifying diode D2, a third high-frequency rectifying diode D3, a fourth high-frequency rectifying diode D4, a first high-frequency filtering inductor L1, a second high-frequency filtering inductor L2, a third high-frequency filtering inductor L3, a fourth high-frequency filtering inductor L4, a first high-frequency buffering and absorbing circuit, a second high-frequency buffering and absorbing circuit, a third high-frequency buffering and absorbing circuit, a fourth high-frequency buffering and absorbing circuit, and a high-frequency power transformer T1, and the first switch tube Q1, the first high-frequency rectifying diode D1, the first high-frequency filtering inductor L1 and the first high-frequency buffering and absorbing circuit are connected to a 1-2 of the high-frequency power transformer T1; the second switch tube Q2, the second high-frequency rectifier diode D2, the second high-frequency filter inductor L2 and the second high-frequency buffer absorption circuit are connected with a 2-3 winding of the high-frequency power transformer T1 after being interconnected; the third switching tube Q3, the third high-frequency rectifying diode D3, the third high-frequency filter inductor L3 and the third high-frequency buffer absorption circuit are connected with 13-14 windings of the high-frequency power transformer T1 after being interconnected; and a fourth switching tube Q4, a fourth high-frequency rectifying diode D4, a fourth high-frequency filter inductor L4 and a fourth high-frequency buffer absorption circuit are interconnected and then connected with 12-13 windings of a high-frequency power transformer T1. The bidirectional DC-AC converter provided in this embodiment adopts the DC-pulsating DC bidirectional conversion main circuit to complete bidirectional power conversion between direct current and pulsating direct current.

Further, referring to fig. 3, fig. 3 is a schematic circuit schematic diagram of an embodiment of the pulsating DC-AC bidirectional conversion main circuit shown in fig. 1, in this embodiment, the pulsating DC-AC bidirectional conversion main circuit 20 includes a fifth switching tube Q5, a sixth switching tube Q6, a seventh switching tube Q7, an eighth switching tube Q8, a fifth high-frequency rectifying diode D12, a sixth high-frequency rectifying diode D13, a seventh high-frequency rectifying diode D14, an eighth high-frequency rectifying diode D15, a fifth high-frequency buffer absorption circuit, a sixth high-frequency buffer absorption circuit, a seventh high-frequency buffer absorption circuit, an eighth high-frequency buffer absorption circuit, a power frequency current transformer HG1, a first electrical isolation optocoupler O1 and a second electrical isolation optocoupler O2, and the fifth switching tube Q5, the fifth high-frequency rectifying diode D12 and the fifth high-frequency buffer absorption circuit are connected to a positive terminal of the intermediate port, a positive input terminal of the first electrical isolation optocoupler O1, and a negative optical isolation input terminal of the second electrical isolation optocoupler O2, respectively; the sixth switching tube Q6, the sixth high-frequency rectifying diode D13 and the sixth high-frequency buffer absorption circuit are connected with the negative end of the middle port, the positive input end of the first electrical isolation optocoupler O1 and the negative input end of the second electrical isolation optocoupler O2 respectively after being interconnected; the seventh switching tube Q7, the seventh high-frequency rectifying diode D14 and the seventh high-frequency buffer absorption circuit are connected with the positive end of the second port, the negative input end of the first electrical isolation optocoupler O1 and the positive input end of the second electrical isolation optocoupler O2 respectively after being interconnected; an eighth switching tube Q8, an eighth high-frequency rectifier diode D15 and an eighth high-frequency buffer absorption circuit are connected with the positive end of the second port, the negative input end of the first electrical isolation optocoupler O1 and the positive input end of the second electrical isolation optocoupler O2 respectively after being interconnected; and the power frequency current transformer HG1 is connected with the second port. The bidirectional DC-AC converter provided in this embodiment adopts the pulsating DC-AC bidirectional conversion main circuit 20 to complete bidirectional power conversion between pulsating direct current and alternating current.

Further, referring to fig. 5 to 7, fig. 5 is a schematic circuit diagram of an embodiment of the first adjusting circuit shown in fig. 1, in which the first adjusting circuit 31 includes a first reference voltage circuit, a first current sampling circuit, a first amplifying circuit and a first comparing circuit, the first current sampling circuit is connected to the first comparing circuit through the first amplifying circuit, and an output end of the first reference voltage circuit is connected to the first comparing circuit. Referring to fig. 6, the second adjusting circuit 32 includes a second reference voltage circuit, a second current sampling circuit, a second amplifying circuit and a second comparing circuit, the second current sampling circuit is connected to the second comparing circuit through the second amplifying circuit, and an output terminal of the second reference voltage circuit is connected to the second comparing circuit. Referring to fig. 7, the third adjusting circuit 33 includes a third reference voltage circuit, a third current sampling circuit, a third amplifying circuit and a third comparing circuit, the third current sampling circuit is connected to the third comparing circuit through the third amplifying circuit, and an output terminal of the third reference voltage circuit is connected to the third comparing circuit. In the bidirectional DC-AC converter provided in this embodiment, the first regulating circuit 31 is adopted to complete signal conditioning and protection signal formation during DC-pulsating DC forward conversion control; a second regulating circuit 32 is adopted to complete signal conditioning and protection signal formation during DC-pulsating DC reverse conversion control; and a third regulating circuit 33 is adopted to complete signal conditioning and protection signal formation during the pulsating DC-AC forward conversion control.

Preferably, referring to fig. 8 to 10, fig. 8 is a schematic circuit diagram of an embodiment of the first PWM circuit shown in fig. 1, in this embodiment, the first PWM circuit 41 includes a first oscillator U14, a first inverter U15A, a third electrical isolation optocoupler O3, a first follower U16A and a first comparator U17A, and the first oscillator U14 is connected to the first inverter U15A; the third electrical isolation optocoupler O3 is connected with the first comparator U17A through the first follower U16A. Referring to fig. 9, the second PWM circuit 42 includes a second oscillator U19, a second inverter U20A, a fourth electrically isolated optocoupler O9, a second follower U21A, and a second comparator U22A, where the second oscillator U19 is connected to the second inverter U20A; the fourth electrically isolating optocoupler O9 is connected to the second comparator U22A via a second follower U21A. In fig. 10, the third PWM circuit 43 includes a first voltage reference module, a second voltage reference module, a third comparator U24A and a fourth comparator U25A, the first voltage reference module is connected with the third comparator U24A; the second voltage reference module is connected to a fourth comparator U25A. In the bidirectional DC-AC converter provided in this embodiment, the first PWM circuit 41 is adopted to alternately provide effective pulses to the first switching tube Q1 and the second switching tube Q2 of the DC-pulsating DC forward conversion; a second PWM circuit 42 is adopted to alternately provide effective pulses for a third switching tube Q3 and a fourth switching tube Q4 of the DC-pulsating DC reverse conversion; and the third PWM circuit 43 is adopted to alternately provide effective pulses for the switching tubes of the inverter bridge during the forward conversion of the pulsating DC-AC, namely the fifth switching tube Q5-the eighth switching tube Q8 and the sixth switching tube Q6-the seventh switching tube Q7.

Preferably, referring to fig. 11 (a) to 13 (d), in the bidirectional DC-AC converter provided in the present embodiment, the first driving circuit 51 includes a first driving chip U26 and a second driving chip U27, the first driving chip U26 is connected to the first switching tube Q1, and the second driving chip U27 is connected to the second switching tube Q2; the second driving circuit 52 comprises a third driving chip U28 and a fourth driving chip U29, the third driving chip U28 is connected with the third switching tube Q3, and the fourth driving chip U29 is connected with the fourth switching tube Q4; the third driving circuit 53 includes a fifth driving chip U30, a sixth driving chip U31, a seventh driving chip U32, and an eighth driving chip U33, the fifth driving chip U30 is connected to the fifth switching tube Q5, the sixth driving chip U31 is connected to the sixth switching tube Q6, the seventh driving chip U32 is connected to the seventh switching tube Q7, and the eighth driving chip U33 is connected to the eighth switching tube Q8. The bidirectional DC-AC converter provided by the present embodiment is driven by a switching tube during DC-pulsating DC forward conversion of the first driving circuit 51; the second driving circuit is adopted to complete the driving of the switching tube during the DC-pulsating DC reverse conversion; and a third driving circuit is adopted to complete the driving of the switching tube when the pulsating DC-AC forward conversion is completed.

Further, referring to fig. 14, fig. 14 is a schematic circuit schematic diagram of an embodiment of the digital control circuit shown in fig. 1, in the embodiment, the digital control circuit 60 includes a CPU board, and the CPU board is respectively connected to the first switching tube Q1, the second switching tube Q2, the third switching tube Q3, the fourth switching tube Q4, the fifth switching tube Q5, the sixth switching tube Q6, the seventh switching tube Q7, and the eighth switching tube Q8. The bidirectional DC-AC converter provided in this embodiment uses the digital control circuit 60 as an integrated control unit of the bidirectional DC-AC converter.

As shown in fig. 1 to fig. 16 (b), the bidirectional DC-AC converter provided in this embodiment operates according to the following principle:

(I) bidirectional DC-AC converter assembly

The bidirectional DC-AC converter consists of a DC-pulsating DC bidirectional conversion main circuit 10, a pulsating DC-AC bidirectional conversion main circuit 20, a first regulating circuit 31, a second regulating circuit 32, a third regulating circuit 33, a first PWM circuit 41, a second PWM circuit 42, a third PWM circuit 43, a first driving circuit 51, a second driving circuit 52, a third driving circuit 53, a digital control circuit 60 and an auxiliary power supply circuit 70. There are two input/output ports to the outside: U1-GND1 port and UA1-UA2 port, and another intermediate port U2-GND23 for two-stage cascade connection. During forward DC-AC conversion, U1-GND1 is a direct current input port, U2-GND23 is a middle pulsating direct current port, and UA1-UA2 is an alternating current output port; during reverse DC-AC conversion, UA1-UA2 are AC input ports, U2-GND23 are intermediate pulsating DC ports, and U1-GND1 are DC output ports. The DC-pulsating DC bidirectional conversion main circuit completes bidirectional power conversion between direct current and pulsating direct current, and the pulsating DC-AC bidirectional conversion main circuit completes bidirectional power conversion between pulsating direct current and alternating current. The first regulating circuit 31 completes signal conditioning and protection signal formation during DC-pulsating DC forward conversion control, the first PWM circuit 41 completes PWM (Pulse Width Modulation) control Pulse formation during DC-pulsating DC forward conversion, and the first driving circuit 51 completes switching tube driving during DC-pulsating DC forward conversion. The second regulating circuit 32 completes signal conditioning and protection signal formation during DC-pulsating DC reverse conversion control, the second PWM circuit 42 completes PWM control pulse formation during DC-pulsating DC reverse conversion, and the second driving circuit 52 completes switching tube driving during DC-pulsating DC reverse conversion. The third regulating circuit 33 completes signal conditioning and protection signal formation when the pulsating DC-AC forward conversion control is completed, the third PWM circuit 43 completes PWM control pulse formation when the pulsating DC-AC forward conversion is completed, and the third driving circuit 53 completes switching tube driving when the pulsating DC-AC forward conversion is completed. The pulsating DC-AC reverse conversion is realized by natural rectification of a diode bridge circuit in the pulsating DC-AC bidirectional conversion main circuit; the digital control circuit is used as a comprehensive control unit of the bidirectional DC-AC converter; the auxiliary power supply circuit generates working power supply required by the operation of each component module circuit of the bidirectional DC-AC converter.

In the block diagram of the bidirectional DC-AC converter shown in fig. 1, the signals between the constituent blocks are illustrated as follows:

u1: the positive end of the direct current input during the forward DC-AC conversion and the negative end of the direct current output during the reverse DC-AC conversion.

GND1: the terminal is a direct current input "-" terminal during forward DC-AC conversion, and a direct current output "-" terminal during reverse DC-AC conversion, and is also a voltage reference terminal of a circuit associated with the ports of the bidirectional DC-AC converters U1-GND 1.

U2: the "+" terminal of the pulsating dc voltage.

GND23: is the "-" end of the pulsating direct current voltage and is also the voltage reference end of the DC-pulsating DC inverse conversion and pulsating DC-AC conversion part.

A UA1: the alternating current output end 1 during bidirectional DC-AC forward conversion is also the alternating current input end 1 during bidirectional DC-AC reverse conversion.

And 2, UA2: the alternating current output end 2 is used during bidirectional DC-AC forward conversion, and the alternating current input end 2 is also used during bidirectional DC-AC reverse conversion.

VCC1: the auxiliary power supply circuit is supplied with the working power supply of the first regulating circuit 31, the first PWM circuit 41 and the first drive circuit 51, and the corresponding voltage reference terminal is GND1.

VCC2: the auxiliary power supply circuit is supplied with the working power supply of the second regulating circuit 32, the second PWM circuit 42 and the second drive circuit 52, and the corresponding voltage reference terminal is GND23.

VCC3: the auxiliary power supply circuit is supplied with the operating power supply of the third regulating circuit 33, the third PWM circuit 43, and the third drive circuit 53, and the corresponding voltage reference terminal is GND23.

VCC: and supplying the auxiliary power supply circuit with the working power supply of the digital control circuit.

GND: is the voltage reference terminal of the digital control circuit.

U1F: the voltage sampling signal of the port of the DC-AC converter U1-GND1 is transmitted to the first regulating circuit 31, the second regulating circuit 32 and the digital control circuit by the main circuit.

I1F: the current sampling signal of the port of the DC-AC converter U1-GND1 is transmitted to the first regulating circuit 31, the second regulating circuit 32 and the digital control circuit by the main circuit.

T1F: the temperature sampling signal, which is a DC-pulsating DC forward conversion part, is supplied from the main circuit to the first regulating circuit 31 and the digital control circuit 60.

U2F: the pulsating direct current voltage sampling signal of the U2-GND23 port is transmitted to the second regulating circuit 32, the first regulating circuit 31, the third regulating circuit 33 and the digital control circuit 60 by the main circuit.

I2F: the current sampling signal of the port U2-GND23 is transmitted to the second regulating circuit 32, the first regulating circuit 31, the third regulating circuit 33 and the digital control circuit 60 by the main circuit.

T2F: the temperature sampling signal, which is the DC-pulsating DC-inversion section, is supplied from the main circuit to the second regulating circuit 32 and the digital control circuit 60.

UAF: the AC voltage sampling signals for the ports of the DC-AC converters UA1 to UA2 are supplied by the main circuit to the third regulating circuit 33 and the digital control circuit 60.

I3F: the AC output current sampling signals for the ports of the DC-AC converters UA1 to UA2 are fed from the main circuit to the third regulating circuit 33 and the digital control circuit 60.

T3F: the temperature sampling signal for the pulsating DC-AC conversion section is supplied from the main circuit to the third regulation circuit 33 and the digital control circuit 60.

PZX1: the first DC-ripple DC forward conversion control signal is supplied from the digital control circuit 60 to the first PWM circuit 41.

PZX2: the second DC-ripple DC forward conversion control signal is supplied to the first PWM circuit 41 by the digital control circuit 60.

SINP: a given signal is supplied to the first PWM circuit 41 by the digital control circuit 60 for an alternating current output at the time of forward conversion of the DC-AC converter.

PFX3: the first DC-to-pulsating DC inverse conversion control signal is supplied from the digital control circuit to the second PWM circuit 42.

PFX4: the second DC-to-pulsating DC inverse conversion control signal is supplied from the digital control circuit to the second PWM circuit 42.

DCP: a given signal is supplied to the second PWM circuit 42 from the digital control circuit for the DC output at the time of the reverse conversion of the DC-AC converter.

PN58: and a digital control circuit transmits a third PWM circuit 43 for outputting a positive half-wave control signal for alternating current during the forward conversion of the pulsating DC-AC, and the third PWM circuit is finally used for driving a switching tube pair of a fifth switching tube Q5-an eighth switching tube Q8 in the main circuit of the bidirectional conversion of the pulsating DC-AC.

PN67: and a third PWM circuit 43 is transmitted by a digital control circuit for outputting a negative half-wave control signal for alternating current during the forward conversion of the pulsating DC-AC, and is finally used for driving a switching tube pair of a sixth switching tube Q6-a seventh switching tube Q7 in the main circuit of the bidirectional conversion of the pulsating DC-AC.

U1P: the overvoltage protection signal, which is the dc voltage U1, is transmitted from the first regulating circuit 31 to the first PWM circuit 41, and is forwarded from the second regulating circuit 32 to the second PWM circuit 42.

I1P: the overcurrent protection signal, which is a dc current I1, is transmitted from the first regulating circuit 31 to the first PWM circuit 41, and is forwarded from the second regulating circuit 32 to the second PWM circuit 42.

T1P: the over-temperature protection signal, which is a part of the DC-to-pulsating DC forward conversion, is supplied to the first PWM circuit 41 by the first regulating circuit 31.

U2P: the second PWM circuit 42 is supplied from the second regulator circuit 32, and the first PWM circuit 41 and the third PWM circuit 33 are transferred from the first regulator circuit 31 to the third PWM circuit 43 as an overvoltage protection signal for the pulsating dc voltage U2.

I2P: the overcurrent protection signal, which is a pulsating dc current I2, is transmitted from the second regulating circuit 32 to the second PWM circuit 42, and is transmitted from the first regulating circuit 31 to the first PWM circuit 41, and is transmitted from the third regulating circuit 33 to the third PWM circuit 43.

T2P: the over-temperature protection signal, which is part of the DC-to-pulsating DC reverse conversion, is supplied by the second regulating circuit 32 to the second PWM circuit 42.

U3P: an overvoltage protection signal for the ac voltage UA is supplied from the third control circuit 33 to the third PWM circuit 43.

I3P: the overcurrent protection signal, which is an ac current I3, is supplied from the third regulating circuit 33 to the third PWM circuit 43.

T3P: the over-temperature protection signal for the pulsating DC-AC conversion part is supplied from the third regulator circuit 33 to the third PWM circuit 43.

P1: the first pulse control signal is sent from the first PWM circuit 41 to the DC-pulsating DC forward conversion part via the first driving circuit 51, and controls the first switch Q1.

P2: the second pulse control signal is sent from the first PWM circuit 41 to the DC-pulsating DC forward conversion part via the first driving circuit 51, and controls the second switching tube Q2.

P3: the third pulse control signal is sent from the second PWM circuit 42 to the DC-to-pulsating DC inverse conversion part via the second driving circuit 52, and controls the third switching transistor Q3.

P4: the fourth pulse control signal is sent from the second PWM circuit 42 to the DC-to-pulsating DC inverse transformation section via the second driving circuit 52, and controls the fourth switching tube Q4.

P5: the fifth pulse control signal is sent from the third PWM circuit 43 to the pulsating DC-AC conversion circuit via the third driving circuit 53, and controls the fifth switching transistor Q5.

P6: the sixth pulse control signal is sent from the third PWM circuit 43 to the pulsating DC-AC conversion circuit via the third driving circuit 53, and controls the sixth switching tube Q6.

P7: the seventh pulse control signal is sent from the third PWM circuit 43 to the pulsating DC-AC conversion circuit via the third driving circuit 53, and controls the seventh switching tube Q7.

P8: the eighth pulse control signal is sent from the third PWM circuit 43 to the pulsating DC-AC conversion circuit via the third driving circuit 53, and controls the eighth switching tube Q8.

(II) bidirectional DC-AC converter power conversion scheme

The power conversion of the bidirectional DC-AC converter is divided into main power conversion and auxiliary power conversion.

The main power conversion of the bidirectional DC-AC converter is formed by cascading a DC-pulsating DC bidirectional conversion main circuit and a pulsating DC-AC bidirectional conversion main circuit. The bidirectional DC-AC converter converts DC into AC when converting in forward direction, wherein the DC-pulsating DC conversion part converts the input DC voltage into absolute value

A varying pulsating DC voltage, the pulsating DC-AC conversion part inputting the pulsating DC voltage

Conversion to ac output voltage

. When the bidirectional DC-AC converter is reversely converted, the alternating current is converted into the direct current, wherein the pulsating DC-AC conversion part converts the alternating current voltage

Naturally rectified into pulsating DC voltage by a diode bridge rectifier circuit

The DC-pulsating DC conversion section pulsates the DC voltage

Converted to a dc voltage.

The auxiliary power supply power conversion part is provided with starting voltage by forward input direct current U1 when the bidirectional DC-AC converter is in forward conversion, and is provided with starting voltage by pulsating direct current U2 when the bidirectional DC-AC converter is in reverse conversion. After the auxiliary power supply is started to work, 4 groups of power supplies such as VCC1, VCC2, VCC3 and VCC are generated by electromagnetic induction of the auxiliary winding of the transformer and respectively provide working power supplies for a DC-pulsating DC forward conversion part, a DC-pulsating DC reverse conversion part, a pulsating DC-AC conversion part, a digital control circuit and the like.

Working principle of main power conversion circuit of (III) bidirectional DC-AC converter

The main power conversion circuit of the bidirectional DC-AC converter is formed by cascading a DC-pulsating DC bidirectional conversion main circuit and a pulsating DC-AC bidirectional conversion main circuit.

(1) Working principle of DC-pulsating DC bidirectional conversion main circuit

The DC-pulsating DC bidirectional conversion main circuit is as shown in figure 2, and completes bidirectional conversion from DC to pulsating DC in a high-frequency (500KHz to 10MHz) PWM control mode, and mainly comprises MOS (Metal-Oxide-Semiconductor) switching tubes Q1-Q4, high-frequency rectifier diodes D1-D4, high-frequency filter inductors L1-L4, high-frequency filter capacitors C3 and C17, a low-frequency filter and energy storage capacitor E3, high-frequency buffer absorption circuits C1-D5, C2-D6, C3-D7, C4-D8, current sampling resistors R5 and R6, a high-frequency power transformer T1 and the like. The direct current voltage U1 is a direct current input voltage during DC-pulsating DC forward conversion or a direct current output voltage during reverse conversion, GND1 is a reference ground of a direct current U1 associated circuit, U1F is a voltage sampling signal of a U1-GND1 port, I1F is a current sampling signal of the U1-GND1 port, and P1 and P2 are control pulses of working switch tubes Q1 and Q2 during forward conversion respectively. The pulsating direct current voltage U2 is a pulsating output voltage during DC-pulsating DC forward conversion or a pulsating input voltage during reverse conversion, GND23 is a reference ground of a U2 related circuit, U2F is a voltage sampling signal of a U2-GND23 port, I2F is a current sampling signal of the U2-GND23 port, and P3 and P4 are control pulses of working switch tubes Q3 and Q4 during reverse conversion respectively.

When the DC-pulsating DC bidirectional conversion circuit works in the forward direction, under the control of control pulses P1, P2, P3 and P4, the switching tubes Q1 and Q2 work, Q3 and Q4 are switched off, the port of U1-GND1 is a direct current input port, the port of U2-GND23 is a pulsating direct current output port, and the switching tubes Q1 and Q2 are alternately switched on or switched off during the forward direction work. When the switch tube Q1 is switched on and the switch tube Q2 is switched off, current flows through a winding 1-2 of the transformer T1, a winding 13-14 generates induced electromotive force and enables a rectifier tube D3 to be switched on in the forward direction, the induced electromotive force of the winding 13-14 is rectified by a diode D3, and after LC is slightly filtered, pulsating direct current is output to a port U2-GND 23; when the switch tube Q2 is switched on and the switch tube Q1 is switched off, current flows through windings 2-3 of the transformer T1, the windings 12-13 generate induced electromotive force and enable the rectifier tube D4 to be switched on in the forward direction, the induced electromotive force of the windings 12-13 is rectified by the diode D4, and after filtering by the LC, pulsating direct current is output to the port U2-GND23. The pulse width of the high-frequency PWM control pulse P1 and P2 is modulated according to 50Hz sinusoidal alternating current, so that the pulsating direct-current voltage output by the U2-GND23 port is forced to be 50Hz sinusoidal alternating current absolute value waveform, and the pulsating direct-current voltage is converted into sinusoidal alternating current output by the post-stage pulsating DC-AC bidirectional conversion main circuit.

When the DC-pulsating DC bidirectional conversion circuit works reversely, under the control of control pulses P1, P2, P3 and P4, the switching tubes Q3 and Q4 work, Q1 and Q2 are switched off, the port of U2-GND23 is a pulsating direct current input port, the port of U1-GND1 is a direct current output port, and the switching tubes Q3 and Q4 are alternately switched on or switched off during reverse work. When the switch tube Q3 is switched on and the switch tube Q4 is switched off, current flows through windings 13 to 14 of the transformer T1, the windings 1 to 2 generate induced electromotive force and enable the rectifier tube D1 to be switched on in the forward direction, and the induced electromotive force of the windings 1 to 2 is rectified by the diode D1 and filtered by the LC and then outputs direct current to a port U1 to GND 1; when the switch tube Q4 is switched on and the switch tube Q3 is switched off, current flows through windings 12-13 of the transformer T1, the windings 2-3 generate induced electromotive force and enable the rectifier tube D2 to be switched on in the forward direction, and the induced electromotive force of the windings 2-3 is rectified by the diode D2 and filtered by the LC and then outputs direct current to the port U1-GND 1. The pulse widths of the high-frequency PWM control pulses P3 and P4 are modulated according to the constant direct-current voltage, and the direct-current voltage output by the port U1-GND1 is forced to be the constant direct-current voltage waveform.

(2) Working principle of main circuit of pulsating DC-AC bidirectional converter

The pulsating DC-AC bidirectional conversion main circuit is shown in figure 3, completes bidirectional conversion between pulsating DC and power frequency alternating current, and mainly comprises MOS (metal oxide semiconductor) switching tubes Q5-Q8, power frequency rectifier tubes D12-D15, buffer circuits D16-C9, buffer circuits D17-C10, buffer circuits D18-C11, buffer circuits D19-C12, a power frequency current transformer HG1, voltage sampling resistors R17-R22, electric isolation optocouplers O1-O2 and the like. The U2-GND23 port is a pulsating direct current port, the UA1-UA2 port is a power frequency alternating current port, the UAF is a voltage sampling signal of the UA1-UA2 alternating current port, and the I3F is a current sampling signal of the UA1-UA2 alternating current port.

When the pulsating DC-AC bidirectional conversion main circuit is subjected to forward conversion, power frequency pulses P5-P8 control switching tubes Q5-Q8 to be switched on or off, and when Q5 and Q8 are switched on and Q6 and Q7 are switched off, pulsating direct current input from a U2-GND23 port is converted into positive half waves of alternating sine, and the positive half waves are output from a UA1-UA2 alternating current port; when Q6 and Q7 are switched on and Q5 and Q8 are switched off, converting pulsating direct current input from the port U2-GND23 into negative half waves of alternating sine and outputting the negative half waves from the AC port UA1-UA 2; the switching tube pairs Q5-Q8 and Q6-Q7 are switched on or off in turn according to the power frequency, and the alternating current ports UA1-UA2 output sine wave voltages with alternating positive and negative polarities.

When the pulsating DC-AC bidirectional conversion main circuit performs reverse conversion, the switching tubes Q5-Q8 are turned off, sine alternating currents of the alternating current ports UA1-UA2 are converted into pulsating direct currents through the pulsating direct current ports U2-GND23 and sent to the DC-pulsating DC conversion main circuit through the power frequency rectifier bridge formed by the rectifier diodes D12-D15.

Working principle of auxiliary power supply of (four) bidirectional DC-AC converter

The auxiliary power supply circuit of the bidirectional DC-AC converter is shown in fig. 4. When the bidirectional DC-AC converter works in the forward direction, the direct-current voltage U1 of the port U1-GND1 provides starting voltage for the auxiliary power supply circuit, the capacitor E1 is charged through D20-R1// R2, then VCC1 is established through voltage stabilization of the voltage stabilizer Z1, power is supplied to the first adjusting circuit 31, the first PWM circuit 41 and the first driving circuit 51, the switching tubes Q1 and Q2 start to work, when the switching tube Q1 is conducted and the switching tube Q2 is turned off, the auxiliary power supply windings 4-5 and 10-11 of the transformer T1 generate induction current, and when the switching tube Q2 is conducted and the switching tube Q1 is turned on, the auxiliary power supply windings 6-7 and 8-9 of the transformer T1 generate induction current. When the bidirectional DC-AC converter works reversely, the pulsating direct current voltage U2 at the port U2-GND23 provides starting voltage for the auxiliary power supply circuit, the capacitor E2 is charged through D21-R3// R4, VCC2 is established through voltage stabilization of the voltage stabilizer Z2, power is supplied to the second regulating circuit 32, the second PWM circuit 42 and the second driving circuit 52, the switching tubes Q3 and Q4 start to work, when the switching tube Q3 is conducted and the switching tube Q4 is turned off, the auxiliary power supply windings 4-5 and 10-11 of the transformer T1 generate induction current, and when the switching tube Q4 is conducted and the switching tube Q3 is turned off, the auxiliary power supply windings 6-7 and 8-9 of the transformer T1 generate induction current. Q1-Q2 or Q3-Q4 high frequency turns on or off alternately, the induced current of every auxiliary power supply winding charges for the electrolytic capacitor after the rectification of the correspondent rectifier diode separately, set up stable output power VCC1, VCC2, VCC3, VCC after the voltage regulation of the voltage stabilizer, offer the working power for the corresponding associated circuit separately, VCC is the high performance linear power after two voltage stabilizations through voltage stabilizer Z3 and linear voltage stabilizer U1, the digital control circuit comprising CPU supplies power specializedly.

Working principle of regulating circuit of (V) bidirectional DC-AC converter

The regulating circuit of the bidirectional DC-AC converter mainly completes the conditioning of detection signals and the formation of protection signals such as overvoltage, overcurrent and overtemperature. The bidirectional DC-AC converter comprises three types of control such as DC-pulsating DC forward control, DC-pulsating DC reverse control and pulsating DC-AC forward control, and the corresponding regulating circuits are a first regulating circuit 31, a second regulating circuit 32, a third regulating circuit 33 and the like.

(1) Operating principle of the first control circuit 31

The first adjusting circuit 31 is shown in fig. 5. The first regulating circuit 31 is powered by VCC1, and VCC1 is regulated by R31-Z5, and then potentiometers RW1, RW2, RW3 generate 3 reference voltages I1REF, T1REF and U1REF, respectively. The current sampling signal I1F of the U1-GND1 port is amplified by U2B after passing through a follower U2A, the amplified current signal I1FD is compared with I1REF to form an over-current protection signal I1P, when the I1FD is larger than the I1REF, the I1P is at a high level, otherwise, the I1P is at a low level. And comparing the voltage sampling signal U1F at the port of U1-GND1 with U1REF to form an overvoltage protection signal U1P, wherein when the U1F is greater than the U1REF, the U1P is at a high level, otherwise, the U1P is at a low level. And comparing the temperature sampling signal T1F of the DC-ripple DC forward conversion part with the temperature sampling signal T1REF to form an over-temperature protection signal T1P, wherein when the T1F is greater than the T1REF, the T1P is at a high level, otherwise, the T1P is at a low level.

(2) Second control circuit 32 operating principle

The second regulating circuit 32 is shown in fig. 6. The second regulating circuit 32 is powered by VCC2, and VCC2 is regulated by R47-Z6 and then generates 3 reference voltages I2REF, T2REF and U2REF by potentiometers RW4, RW5 and RW6, respectively. The current sampling signal I2F of the U2-GND23 port is amplified by U6B after passing through the follower U6A, the amplified current signal I2FD is compared with I2REF to form an over-current protection signal I2P, when the I2FD is larger than the I2REF, the I2P is high level, otherwise, the I2P is low level. And comparing the voltage sampling signal U2F at the port U2-GND23 with the voltage sampling signal U2REF to form an overvoltage protection signal U2P, wherein when the U2F is greater than the U2REF, the U2P is at a high level, and otherwise, the U2P is at a low level. And comparing the temperature sampling signal T2F of the DC-ripple DC inverse conversion part with the temperature sampling signal T2REF to form an over-temperature protection signal T2P, wherein when the T2F is greater than the T2REF, the T2P is at a high level, otherwise, the T2P is at a low level.

(3) Operating principle of the third regulating circuit 33

The third regulating circuit 33 is shown in fig. 7. The third regulating circuit 33 is powered by VCC3, and VCC3 is regulated by R63-Z7 and then generates 3 reference voltages I3REF, T3REF and U3REF by potentiometers RW7, RW8 and RW9, respectively. The current sampling signal I3F of the UA1-UA2 port is amplified by U10B after passing through a follower U10A, the amplified current signal I3FD is compared with I3REF to form an over-current protection signal I3P, when the I3FD is larger than the I3REF, the I3P is at a high level, otherwise, the I3P is at a low level. And comparing the voltage sampling signals U3F of the UA1-UA2 ports with U3REF to form an overvoltage protection signal U3P, wherein when the U3F is greater than the U3REF, the U3P is at a high level, and otherwise, the U3P is at a low level. And comparing the temperature sampling signal T3F of the pulsating DC-AC conversion part with the temperature sampling signal T3REF to form an over-temperature protection signal T3P, wherein when the T3F is more than the T3REF, the T3P is high level, otherwise, the T3P is low level.

Work principle of PWM circuit of (six) bidirectional DC-AC converter

The PWM circuit of the bidirectional DC-AC converter mainly completes the formation of effective control pulses P1-P8 corresponding to the switching tubes Q1-Q8. The bidirectional DC-AC converter comprises three types of control such as DC-pulsating DC forward control, DC-pulsating DC reverse control, pulsating DC-AC forward control and the like, and the corresponding PWM circuits are three, namely a first PWM circuit 41, a second PWM circuit 42, a third PWM circuit 43 and the like.

(1) First PWM circuit 41 operating principle

The first PWM circuit 41 is shown in fig. 8. The first PWM circuit 41 is powered by VCC1 to alternately provide effective pulses to the working switching tubes Q1, Q2 of the DC-to-pulsating DC forward conversion. An oscillator formed by a device U14 generates a high-frequency (500KHz to 10MHz) clock with the frequency adjustable by RW10 and the duty ratio of 50%, wherein the high-level time period of the clock is used as a working signal ZX1 of Q1 during DC-pulsating DC forward conversion, and the low-level time period of the clock is reversed by U15A and then is used as a working signal ZX2 of Q2 during DC-pulsating DC forward conversion. Alternating current given signal SINP from a digital control circuit forms a smooth alternating current given signal SING after being isolated by an optical coupler O3, filtered by C29 and followed by U16A, and is compared with a voltage sampling signal U2F at a port of U2-GND23 to generate an initial control pulse signal PZX when DC-pulsating DC forward conversion is carried out, wherein PZX is high level when U2F is higher than SING, and otherwise, PZX is low level. In the circuit, an initial given voltage at the time of starting the converter is provided by R83-R84-D32. The effective control pulse P10 provided to the switching tube Q1 is formed by comparing the initial pulse PZX and the Q2 working signal ZX2, the protection signal U1P, the protection signal I1P, the protection signal T1P, the protection signal U2P, the protection signal I2P, the digital control signal PZX1, and the like with HLREF1 through U17A, and when all input signals at the U17A reverse input end are low, P10 is high, otherwise, it is low. The effective control pulse P20 provided to the switching tube Q2 is formed by comparing the initial pulse PZX and the Q1 working signal ZX1, the protection signal U1P, the protection signal I1P, the protection signal T1P, the protection signal U2P, the protection signal I2P, the digital control signal PZX2, and the like with HLREF1 via U18A, and when all signals at the reverse input end of U18A are low level, P20 is high level, otherwise, it is low level.

(2) Second PWM circuit 42 operating principle

The second PWM circuit 42 is shown in fig. 9. The second PWM circuit 42 is powered by VCC2 to alternately provide active pulses to the DC-pulsed DC-reverse converted working switching transistors Q3, Q4. An oscillator formed by a device U19 generates a high-frequency (500KHz to 10MHz) clock with the frequency adjustable by RW14 and the duty ratio of 50%, the high-level period of the clock is used as a working signal FX1 of a Q3 in the DC-pulsating DC reverse conversion, and the low-level period of the clock is reversed by U20A and then used as a working signal FX2 of a Q4 in the DC-pulsating DC reverse conversion. A direct current given signal DCP from a digital control circuit forms a constant direct current given voltage DCG after being isolated by an optical coupler O9, filtered by C34 and followed by U21A, and is compared with a voltage sampling signal U1F of a port of U1-GND1 to generate an initial control pulse signal PFX when the DC-pulsating DC is reversely converted, wherein the PFX is at a high level when the U1F is higher than the DCG, and the PFX is at a low level otherwise. In the circuit, an initial given voltage at the time of starting the converter is provided by R110-R111-D49. The effective control pulse P30 provided to the switching tube Q3 is formed by comparing the initial pulse PFX and the Q4 working signal FX2, the protection signal U2P, the protection signal I2P, the protection signal T2P, the protection signal U1P, the protection signal I1P, the digital control signal PFX3, and the like with HLREF2 through U22A, and when all signals at the reverse input end of U22A are low level, P30 is high level, otherwise, it is low level. The effective control pulse P40 provided to the switching tube Q4 is formed by comparing the initial pulse PFX with the Q3 working signal FX1, the protection signal U2P, the protection signal I2P, the protection signal T2P, the protection signal U1P, the protection signal I1P, the digital control signal PFX4, and the like with HLREF2 via U23A, and when all signals at the reverse input end of U23A are low, P40 is high, otherwise, it is low.

(3) Third PWM circuit 43 operating principle

The third PWM circuit 43 is shown in fig. 10. The third PWM circuit 43 is powered by VCC3, and alternately provides effective pulses for Q5-Q8 and Q6-Q7 of a switching tube pair of an inverter bridge during the forward conversion of the pulsating DC-AC, the initial pulses come from a digital control circuit, and the pulse frequency is power frequency (50 Hz). R132-Z10-RW18 forms a voltage reference signal HLREFNB. The active control pulse P580 provided to the pair of switching tubes Q5-Q8 is formed by comparing the initial pulse NP58 from the digital control circuit with the protection signal U3P, the protection signal I3P, the protection signal T3P, the protection signal U2P, the protection signal I2P, etc. in common with HLREFNB via U24A, and P580 is high when all signals at the reverse input terminal of U24A are low, otherwise, it is low. The effective control pulse P670 provided for the pair Q6-Q7 of switching tubes is formed by comparing the initial pulse NP67 from the digital control circuit with the protection signal U3P, the protection signal I3P, the protection signal T3P, the protection signal U2P, the protection signal I2P and the like with HLREFNB through U25A, and when all signals at the reverse input end of U25A are low, P670 is high, otherwise, the P is low.

(VII) operating principle of drive circuit

The drive circuit of the bidirectional DC-AC converter mainly enhances the drive capability of the switch tubes Q1-Q8 corresponding to the control pulses P1-P8. The bidirectional DC-AC converter includes three types of control such as DC-pulsating DC forward control, DC-pulsating DC reverse control, pulsating DC-AC forward control, etc., and the corresponding drive circuits are three of a first drive circuit 51, a second drive circuit 52, a third drive circuit 53, etc.

The drive circuit of the bidirectional DC-AC converter is shown in fig. 11 (a) to 13 (d). The first driving circuit 51 is powered by VCC1, and the pulse P10 is boosted by the first driving chip U26 to form P1 to drive the switching tube Q1, and the pulse P20 is boosted by the second driving chip U27 to form P2 to drive the switching tube Q2. The second driving circuit 52 is powered by VCC2, and the pulse P30 is driven by the driving chip U28 to form P3 to drive the switching tube Q3, and the pulse P40 is driven by the driving chip U29 to form P4 to drive the switching tube Q4. The third driving circuit 53 is powered by VCC3, and the pulse P580 is driven by the driving chip U30 to form a P5 to drive the switching tube Q5, the pulse P580 is driven by the driving chip U33 to form a P8 to drive the switching tube Q8, the pulse P670 is driven by the driving chip U31 to form a P6 to drive the switching tube Q6, and the pulse P670 is driven by the driving chip U32 to form a P7 to drive the switching tube Q7.

Working principle of digital control circuit

As shown in fig. 14, the digital control circuit of the bidirectional DC-AC converter mainly performs state detection of the bidirectional DC-AC converter and intelligent control or auxiliary control of the switching tubes Q1 to Q8, and is supplied with power by VCC. Signals of an auxiliary working power supply VCC1, VCC2, VCC3, a voltage sample U1F and a current sample I1F of a U1-GND1 port, a temperature sample T1F of a DC-pulsating DC forward conversion part, a voltage sample U2F and a current sample I2F of a U2-GND23 port, a temperature sample T2F of a DC-pulsating DC reverse conversion part, a voltage sample U3F and a current sample I3F of a UA1-UA2 port, a temperature sample T3F of a pulsating DC-AC conversion part and the like are transmitted to an A/D interface of a CPU board after optical coupling isolation. The CPU board detects, calculates and judges the state of the bidirectional DC-AC converter, and respectively outputs a DC-pulsating DC forward conversion control signal PZX1, a DC-pulsating DC forward conversion control signal PZX2, a DC-pulsating DC reverse conversion control signal PFX3, a DC-pulsating DC reverse conversion control signal PFX4, an alternating current output positive half-wave control signal NP58 during pulsating DC-AC forward conversion, an alternating current output negative half-wave control signal NP67 during pulsating DC-AC forward conversion and the like to control each switching tube of the DC-pulsating DC forward conversion part, the DC-pulsating DC reverse conversion part and the pulsating DC-AC forward conversion part after optical coupling isolation.

(ninth) Explanation of Effect

The alternating current given during forward conversion and the direct current given during reverse conversion of the bidirectional DC-AC converter are given in a pulse form by a digital control circuit, and a smooth alternating current given signal during forward conversion or a constant direct current given signal during reverse conversion is formed after filtering. The converter performs output control at a given signal, wherein the pulsating DC control effect of the DC-pulsating DC forward conversion is shown in fig. 15 (a) and 15 (b), and the forward and reverse output effects of the bidirectional DC-AC converter are shown in fig. 16 (a) and 16 (b). Fig. 15 (a) shows the pulse shape of the ac current and the smooth ac current effect after smooth filtering, and fig. 15 (b) shows the pulse shape of the ac output and the smooth DC current effect after smooth filtering at the time of DC/pulsating DC forward conversion. Fig. 16 (a) shows the DC output effect when the bidirectional DC-AC converter performs reverse conversion, and fig. 16 (b) shows the AC output effect at the power frequency when the bidirectional DC-AC converter performs forward conversion. Wherein, U _G (t) is a pulse form given by AC, U _GP And (t) smoothing the smoothed alternating current after smoothing filtering. U shape _DC (t) is direct current in the case of reverse conversion, U _AC And (t) is power frequency alternating current during forward conversion.

Compared with the traditional DC-AC converter, the bidirectional DC-AC converter has the following advantages:

(1) The converter is formed by cascading DC-pulsating DC bidirectional conversion and pulsating DC-AC bidirectional conversion, wherein the DC-pulsating DC bidirectional conversion part adopts high-frequency (500KHz to 10MHz) PWM control, the pulsating DC-AC bidirectional conversion part adopts power-frequency (50 Hz) pulse control, the performance index is improved by utilizing the high-frequency control, and the direct connection and the switching loss are avoided by utilizing the low-frequency control.

(2) The converter adopts a two-stage protection and two-stage control mode, the basic protection is born by a pure hardware circuit, the reliability and the rapidity are ensured, the comprehensive intelligent protection is born by software in digital control, and the flexibility and the comprehensiveness are ensured; the high-frequency control is completed by a pure hardware circuit, the real-time performance of the control is guaranteed, and the low-frequency control is borne by software in the digital control, so that the flexibility and the high cost performance are guaranteed.

(3) A high-frequency transformer is adopted between the DC part and the AC part of the converter for electrical isolation, a two-way push-pull topological structure is adopted, and the homonymous ends of multiple windings of the transformer are optimally distributed, so that load balance is guaranteed, direct-current components in the transformer are reduced, and the safety and reliability of high-power transmission of the transformer are guaranteed.

(4) The DC-pulsating DC bidirectional conversion part works in a high-frequency (500KHz to 10MHz) state, and parameters of required inductive devices and capacitive devices are small, so that the whole converter is small in size and high in power density; the inductive device has small parameters, small energy storage energy in a single period and fine control granularity, so the system has high control precision; the parameters of inductive and capacitive devices are small, the dynamic time constant of the system is small, the control algorithm is simplified, the real-time performance is good, and the system implementation cost can be reduced.

(5) The converter can realize bidirectional DC-AC conversion, and the application field and the application range of the DC-AC converter are expanded.

(6) The buffer circuit and related device parameters are optimized, when the switching tube is switched from a conducting state to a disconnecting state, due to the effect of the parallel capacitor in the buffer circuit, the instantaneous voltage at two ends of the switching tube is low during state switching, and the switching loss is small; when the switching tube is switched from the off state to the on state, the instantaneous current flowing through the switching tube is small due to the effect of the series inductor, and the switching loss is small. Therefore, the total switching loss is small, and the converter efficiency is high.

(7) The high-frequency PWM control pulse is generated by adopting an oscillator and is adjustable, and when the switching speed level of the switching tube is increased, seamless upgrade of products is facilitated.

(8) The converter adopts a hierarchical control mode of basic control and comprehensive control, which is convenient for realizing individual requirements in a digital controller through software aiming at different application scenes, improves the intelligence and the comprehensiveness of the converter and is convenient for further increasing the applicability and the application range of the converter.

(9) When the converter is in forward conversion or reverse conversion, the high-frequency transformer is provided with two main windings with opposite current directions to work in an interlaced mode, 4 windings of the auxiliary power supply also work in an interlaced mode in two groups, compared with a single-ended forward or flyback converter, the high-frequency transformer is extremely low in direct current component and large in transmittable power, and compared with a bridge circuit, the direct connection of a switching tube is avoided; the bridge type inversion part adopts power frequency pulse control, has long switching period, allows enough dead time, and reduces the direct connection risk of the switching tubes on the same bridge arm.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention. It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims

1. A bidirectional DC-AC converter is characterized by comprising a DC-pulsating DC bidirectional conversion main circuit (10), a pulsating DC-AC bidirectional conversion main circuit (20), a first regulating circuit (31), a second regulating circuit (32), a third regulating circuit (33), a first PWM circuit (41), a second PWM circuit (42), a third PWM circuit (43), a first driving circuit (51), a second driving circuit (52), a third driving circuit (53) and a digital control circuit (60), wherein the DC-pulsating DC bidirectional conversion main circuit (10) and the pulsating DC-AC bidirectional conversion main circuit (20) are connected through two-stage cascaded middle ports; the DC-pulsating DC bidirectional conversion main circuit (10) is respectively connected with the first regulating circuit (31), the first PWM circuit (41), the first driving circuit (51), the second regulating circuit (32), the second PWM circuit (42) and the second driving circuit (52); the pulsating DC-AC bidirectional conversion main circuit (20) is respectively connected with the third regulating circuit (33), the third PWM circuit (43) and the third driving circuit (53); the digital control circuit (60) is respectively connected with the DC-pulsating DC bidirectional conversion main circuit (10), the pulsating DC-AC bidirectional conversion main circuit (20), the first regulating circuit (31), the second regulating circuit (32), the third regulating circuit (33), the first PWM circuit (41), the second PWM circuit (42), the third PWM circuit (43), the first drive circuit (51), the second drive circuit (52) and the third drive circuit (53); the free end of the DC-pulsating DC bidirectional conversion main circuit (10) is a first port, and the free end of the pulsating DC-AC bidirectional conversion main circuit (20) is a second port; when the forward DC-AC conversion is carried out, the first port is used as a direct current input port, the middle port is used as a middle pulsating direct current port, and the second port is used as an alternating current output port; when the reverse DC-AC conversion is carried out, the second port is used as an alternating current input port, the middle port is used as a middle pulse direct current port, and the first port is used as a direct current output port; the DC-pulsating DC bidirectional conversion main circuit (10) is used for completing bidirectional power conversion between direct current and pulsating direct current; the pulsating DC-AC bidirectional conversion main circuit (20) is used for completing bidirectional power conversion between pulsating direct current and alternating current; the first regulating circuit (31) is used for finishing signal conditioning and protection signal formation during DC-pulsating DC forward conversion control; the first PWM circuit (41) is used for completing the formation of PWM control pulses during the DC-pulsating DC forward conversion; the first driving circuit (51) is used for completing the driving of a switching tube during DC-pulsating DC forward conversion; the second regulating circuit (32) is used for finishing signal conditioning and protection signal formation during DC-pulsating DC reverse conversion control; the second PWM circuit (42) is used for completing the formation of PWM control pulses during the DC-pulsating DC reverse conversion; the second driving circuit (52) is used for completing the driving of a switching tube during the reverse conversion of DC-pulsating DC; the third regulating circuit (33) is used for signal conditioning and protection signal formation when the pulsating DC-AC forward conversion control is finished; the third PWM circuit (43) is used for completing the formation of PWM control pulses during the pulsating DC-AC forward conversion; the third driving circuit (53) is used for completing the driving of a switching tube during the forward conversion of the pulsating DC-AC; the digital control circuit (60) is used as a comprehensive control unit of the bidirectional DC-AC converter.

2. The bidirectional DC-AC converter according to claim 1, wherein the DC-ripple DC bidirectional converter main circuit (10) comprises a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a first high-frequency rectifier diode, a second high-frequency rectifier diode, a third high-frequency rectifier diode, a fourth high-frequency rectifier diode, a first high-frequency filter inductor, a second high-frequency filter inductor, a third high-frequency filter inductor, a fourth high-frequency filter inductor, a first high-frequency buffer absorption circuit, a second high-frequency buffer absorption circuit, a third high-frequency buffer absorption circuit, a fourth high-frequency buffer absorption circuit, and a high-frequency power transformer, wherein the first switch tube, the first high-frequency rectifier diode, the first high-frequency filter inductor, and the first high-frequency buffer absorption circuit are interconnected and connected to 1-2 windings of the high-frequency power transformer; the second switch tube, the second high-frequency rectifier diode, the second high-frequency filter inductor and the second high-frequency buffer absorption circuit are connected with the 2-3 winding of the high-frequency power transformer after being interconnected; the third switching tube, the third high-frequency rectifier diode, the third high-frequency filter inductor and the third high-frequency buffer absorption circuit are connected with 13-14 windings of the high-frequency power transformer after being interconnected; the fourth switch tube, the fourth high-frequency rectifier diode, the fourth high-frequency filter inductor and the fourth high-frequency buffer absorption circuit are connected with 12-13 windings of the high-frequency power transformer after being interconnected.

3. The bidirectional DC-AC converter according to claim 2, wherein the pulsating DC-AC bidirectional converter main circuit (20) comprises a fifth switching tube, a sixth switching tube, a seventh switching tube, an eighth switching tube, a fifth high-frequency rectifying diode, a sixth high-frequency rectifying diode, a seventh high-frequency rectifying diode, an eighth high-frequency rectifying diode, a fifth high-frequency buffer absorption circuit, a sixth high-frequency buffer absorption circuit, a seventh high-frequency buffer absorption circuit, an eighth high-frequency buffer absorption circuit, a power frequency current transformer, a first electrically isolating optocoupler and a second electrically isolating optocoupler, and the fifth switching tube, the fifth high-frequency rectifying diode and the fifth high-frequency buffer absorption circuit are interconnected to be connected to the positive terminal of the intermediate port, the positive input terminal of the first electrically isolating optocoupler, and the negative input terminal of the second electrically isolating optocoupler, respectively; the sixth switching tube, the sixth high-frequency rectifying diode and the sixth high-frequency buffer absorption circuit are connected with each other and then are respectively connected with the negative end of the middle port, the positive input end of the first electrical isolation optocoupler and the negative input end of the second electrical isolation optocoupler; the seventh switch tube, the seventh high-frequency rectifier diode and the seventh high-frequency buffer absorption circuit are connected with one another and then are respectively connected with the positive end of the second port, the negative input end of the first electrical isolation optocoupler and the positive input end of the second electrical isolation optocoupler; the eighth switching tube, the eighth high-frequency rectifying diode and the eighth high-frequency buffer absorption circuit are connected with the positive end of the second port, the negative input end of the first electrical isolation optocoupler and the positive input end of the second electrical isolation optocoupler respectively after being interconnected; and the power frequency current transformer is connected with the second port.

4. A bidirectional DC-AC converter as claimed in claim 3, characterized in that the first regulating circuit (31) comprises a first reference voltage circuit, a first current sampling circuit, a first amplifying circuit and a first comparing circuit, the first current sampling circuit being connected to the first comparing circuit via the first amplifying circuit, the output of the first reference voltage circuit being connected to the first comparing circuit.

5. A bi-directional DC-AC converter as claimed in claim 3, characterized in that the second regulating circuit (32) comprises a second reference voltage circuit, a second current sampling circuit, a second amplifying circuit and a second comparing circuit, the second current sampling circuit being connected to the second comparing circuit via the second amplifying circuit, the output of the second reference voltage circuit being connected to the second comparing circuit.

6. A bidirectional DC-AC converter as claimed in claim 3, characterized in that the third regulating circuit (33) comprises a third reference voltage circuit, a third current sampling circuit, a third amplifying circuit and a third comparing circuit, the third current sampling circuit being connected to the third comparing circuit via the third amplifying circuit, the output of the third reference voltage circuit being connected to the third comparing circuit.

7. A bidirectional DC-AC converter as claimed in claim 3, characterized in that said first PWM circuit (41) comprises a first oscillator, a first inverter, a third electrically isolated optocoupler, a first follower and a first comparator, said first oscillator being connected to said first inverter; the third electrical isolation optocoupler is connected with the first comparator through the first follower.

8. A bi-directional DC-AC converter according to claim 3, characterized in that the second PWM circuit (42) comprises a second oscillator, a second inverter, a fourth electrically isolated optocoupler, a second follower and a second comparator, the second oscillator being connected to the second inverter; the fourth electrical isolation optocoupler is connected with the second comparator through the second follower; the third PWM circuit (43) comprises a first voltage reference module, a second voltage reference module, a third comparator and a fourth comparator, and the first voltage reference module is connected with the third comparator; the second voltage reference module is connected with the fourth comparator.

9. A bi-directional DC-AC converter according to claim 3, characterized in that the first driver circuit (51) comprises a first driver chip and a second driver chip, the first driver chip being connected to the first switching tube and the second driver chip being connected to the second switching tube; the second driving circuit (52) comprises a third driving chip and a fourth driving chip, the third driving chip is connected with the third switching tube, and the fourth driving chip is connected with the fourth switching tube; the third driving circuit (53) comprises a fifth driving chip, a sixth driving chip, a seventh driving chip and an eighth driving chip, the fifth driving chip is connected with the fifth switching tube, the sixth driving chip is connected with the sixth switching tube, the seventh driving chip is connected with the seventh switching tube, and the eighth driving chip is connected with the eighth switching tube.

10. The bi-directional DC-AC converter according to claim 3, wherein said digital control circuit (60) includes a CPU board connected to said first switch tube, said second switch tube, said third switch tube, said fourth switch tube, said fifth switch tube, said sixth switch tube, said seventh switch tube and said eighth switch tube, respectively.