CN115714549B

CN115714549B - Bidirectional DC-AC converter

Info

Publication number: CN115714549B
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: 2023-04-28
Anticipated expiration: 2043-01-05
Also published as: CN115714549A

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 is connected with the pulsating DC-AC bidirectional conversion main circuit through a two-stage cascade intermediate port. The converter adopts a two-stage protection and two-stage control mode, the basic protection is carried by a pure hardware circuit, the reliability and the rapidity are ensured, the comprehensive intelligent protection is carried 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, the low-frequency control is borne by software in the digital control, and 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, in particular to 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 direct current/alternating current electric energy bidirectional flow and can realize the forward conversion from direct current electric energy to alternating current electric energy and the reverse conversion from alternating current electric energy to direct current electric energy under different working conditions.

Background

The DC-AC converter realizes inversion conversion from Direct Current (DC) to alternating Current (Alternating Current, AC); the AC-DC converter performs a rectified conversion of alternating Current (Alternating Current, AC) to Direct Current (DC). The unidirectional DC-AC converter and the unidirectional AC-DC converter which are connected in parallel in an anti-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 converter are not ideal, and especially the AC grid connection performance is limited.

The prior art has the following defects:

(1) When the traditional DC-AC converter and the AC-DC converter are connected in parallel to realize the bidirectional DC-AC conversion function, the two sets of systems work in a time-sharing way, and the number of components used by the systems is large, particularly the number of power devices is large, so that the cost is high, the volume is large and the cost performance is low.

(2) The traditional DC-AC converter has relatively low working frequency, and the required inductive devices and capacitive devices have large capacity, so that the equipment has large volume 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 energy per cycle, insufficient 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 large switching loss of a power switch tube due to relatively large switching period and large difficulty in accurate implementation of a soft switch, and the improvement of the efficiency of the converter is limited.

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

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

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 is connected with the pulsating DC-AC bidirectional conversion main circuit through a two-stage cascade intermediate port; the DC-pulsating DC bidirectional conversion main circuit is respectively connected with the first regulating circuit, the first PWM circuit, the first driving circuit, the second regulating circuit, the second PWM circuit and the second driving circuit; the pulsating DC-AC bidirectional conversion main circuit is respectively connected with the third regulating circuit, the third PWM circuit and the 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 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 performed, 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 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 completing 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 DC-pulsating DC forward conversion; the first driving circuit is used for driving a switching tube when DC-pulsating DC forward conversion is completed; the second regulating circuit is used for completing 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 pulses during DC-pulsating DC reverse conversion; the second driving circuit is used for driving the switching tube when the DC-pulsating DC reverse conversion is completed; the third regulating circuit is used for completing signal conditioning and protection signal formation during pulsating DC-AC forward conversion control; the third PWM circuit is used for completing the formation of PWM control pulses during the pulsating DC-AC forward conversion; the third driving circuit is used for driving a switching tube when the pulsating DC-AC forward conversion is completed; the digital control circuit is used as an integrated 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 filtering inductor, a second high-frequency filtering inductor, a third high-frequency filtering inductor, a fourth high-frequency filtering 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 filtering 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 rectifying diode, the second high-frequency filtering inductor and the second high-frequency buffer absorption circuit are connected with 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; the fourth switching tube, the fourth high-frequency rectifying diode, the fourth high-frequency filtering 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 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 electric isolation optocoupler and a second electric isolation optocoupler, wherein the fifth switching tube, the fifth high-frequency rectifying diode and the fifth high-frequency buffer absorption circuit are respectively connected with the positive electrode end of the middle port, the positive electrode input end of the first electric isolation optocoupler and the negative electrode input end of the second electric isolation optocoupler after being connected with each other; the sixth switching tube, the sixth high-frequency rectifying diode and the sixth high-frequency buffer absorption circuit are connected with the negative electrode end of the intermediate port, the positive electrode input end of the first electric isolation optocoupler and the negative electrode input end of the second electric isolation optocoupler after being interconnected; the seventh switching tube, the seventh high-frequency rectifying diode and the seventh high-frequency buffer absorption circuit are connected with the positive electrode end of the second port, the negative electrode input end of the first electric isolation optocoupler and the positive electrode input end of the second electric isolation optocoupler after being interconnected; the eighth switching tube, the eighth high-frequency rectifying diode and the eighth high-frequency buffer absorption circuit are connected with the positive electrode end of the second port, the negative electrode input end of the first electric isolation optocoupler and the positive electrode input end of the second electric isolation optocoupler after being interconnected; the power frequency current transformer is connected with the second port.

Further, 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.

Further, 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.

Further, the third regulating circuit comprises a third reference voltage circuit, a third current sampling circuit, a third amplifying circuit and a third comparing circuit, wherein 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.

Further, the first PWM circuit comprises a first oscillator, a first inverter, a third electrically isolated optocoupler, a first follower and a first comparator, wherein the first oscillator is connected with the first inverter; the third electrically isolated optocoupler is connected to the first comparator through the first follower.

Further, the second PWM circuit comprises a second oscillator, a second inverter, a fourth electrically isolated optocoupler, a second follower and a second comparator, and the second oscillator is connected with 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.

Further, the first driving circuit comprises a first driving chip and a second driving chip, the first driving chip is connected with the first switching tube, and the second driving chip is connected with the second switching tube; the second driving circuit 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 comprises a fifth driving chip, a sixth driving chip, a seventh driving chip and an eighth driving chip, wherein 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.

Further, the digital control circuit comprises a CPU board, and the CPU board is respectively connected with the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch 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 completing 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 DC-pulsating DC forward conversion; the first driving circuit is used for driving a switching tube when DC-pulsating DC forward conversion is completed; the second regulating circuit is used for completing 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 pulses during DC-pulsating DC reverse conversion; the second driving circuit is used for driving the switching tube when the DC-pulsating DC reverse conversion is completed; the third regulating circuit is used for completing signal conditioning and protection signal formation during pulsating DC-AC forward conversion control; the third PWM circuit is used for completing the formation of PWM control pulses during the pulsating DC-AC forward conversion; the third driving circuit is used for driving a switching tube when the pulsating DC-AC forward conversion is completed; the digital control circuit is used as an integrated control unit of the bidirectional DC-AC converter. The bidirectional DC-AC converter provided by the invention is formed by two-stage conversion cascade connection of DC-pulse DC bidirectional conversion and pulse DC-AC bidirectional conversion, wherein a DC-pulse DC bidirectional conversion part adopts high-frequency (500 KHz-10 MHz) PWM control, a pulse control of power frequency (50 Hz) is adopted by the pulse DC-AC bidirectional conversion part, the performance index is improved by utilizing the high-frequency control, the direct connection is avoided by utilizing the low-frequency control, and the switching loss is reduced; the converter adopts a two-stage protection and two-stage control mode, the basic protection is carried by a pure hardware circuit, the reliability and the rapidity are ensured, the comprehensive intelligent protection is carried 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 bidirectional 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 (500 KHz-10 MHz) state, and the required inductive device and the required capacitive device have small parameters and small volume, so that the whole converter has small volume and high power density; the inductive device has small parameters, small single-period energy storage energy and fine control granularity, so the system control precision is high; the inductive and capacitive device parameters are small, the dynamic time constant of the system is small, the control algorithm is simplified, the instantaneity is good, and the system realization 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 the on state to the off state, the instantaneous voltage at two ends of the switching tube is low during state switching due to the action of the parallel capacitor in the buffer circuit, and the switching loss is small; when the switching tube is switched from an off state to an on state, the instant current flowing through the switching tube is small due to the effect of the series inductor, and the switching loss is small. The total switching loss is small, and the converter efficiency is high; the high-frequency PWM control pulse is generated by an oscillator and is adjustable, and after the switching speed level of the switching tube is improved, seamless upgrading of products is facilitated; the converter adopts a hierarchical control mode of basic control and comprehensive control, so that personalized requirements can be conveniently realized in the digital controller through software according to different application scenes, the intelligence and the comprehensiveness of the converter are improved, and the applicability and the application range of the converter are further conveniently increased; the converter has two main windings with opposite current directions to stagger when in forward conversion or reverse conversion, 4 windings of the auxiliary power supply also stagger in two groups, compared with a single-end forward or reverse conversion converter, the direct current component in the converter is extremely low, the transmissible power is high, 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 switching tubes on the same bridge arm.

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 one embodiment of the DC-pulsed DC bi-directional conversion main circuit shown in FIG. 1;

FIG. 3 is a schematic circuit diagram of one embodiment of the pulsating DC-AC bi-directional conversion 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 adjusting circuit shown in FIG. 1;

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

FIG. 7 is a schematic circuit diagram of an embodiment of the third adjusting 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 driving chip in the first driving circuit shown in FIG. 1;

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

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

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

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

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

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

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

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

FIG. 15 (a) is a graph of a given pulse form of an alternating current and a smoothed alternating current in a bi-directional DC-AC converter according to the present invention;

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

Fig. 16 (a) is a graph of DC output effects of the bidirectional DC-AC converter according to the present invention during reverse conversion;

fig. 16 (b) is a graph of the effect of power frequency AC output during forward conversion of the bidirectional DC-AC converter provided by the present invention.

Reference numerals illustrate:

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

Detailed Description

In order to better understand the above technical solutions, the following detailed description will be given with reference to the accompanying drawings and specific embodiments.

As shown in fig. 1, a first embodiment of the present invention proposes 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-stage cascade intermediate ports; the DC-ripple DC bidirectional conversion main circuit 10 is connected to the first regulator circuit 31, the first PWM circuit 41, the first drive circuit 51, the second regulator circuit 32, the second PWM circuit 42, and the second drive circuit 52, respectively; the ripple DC-AC bidirectional conversion main circuit 20 is connected to the third regulator circuit 33, the third PWM circuit 43, and the third drive circuit 53, respectively; the digital control circuit 60 is connected to the DC-ripple DC bi-directional conversion main circuit 10, the ripple DC-AC bi-directional conversion main circuit 20, the first adjusting circuit 31, the second adjusting circuit 32, the third adjusting circuit 33, the first PWM circuit 41, the second PWM circuit 42, the third PWM circuit 43, the first driving circuit 51, the second driving circuit 52, and the third driving circuit 53, respectively; the free end of the DC-pulsating DC bi-directional conversion main circuit 10 is a first port, and the free end of the pulsating DC-AC bi-directional 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 performed, 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 bi-directional conversion main circuit 20 is used for performing bi-directional power conversion between pulsating DC and AC; 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 for completing 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 switching tube driving during the DC-pulsating DC forward conversion; the second regulating circuit 32 is used for signal conditioning and protection signal formation when the DC-pulsating DC reverse conversion control is completed; the second PWM circuit 42 is used for completing the formation of PWM control pulses during DC-ripple DC reverse conversion; the second driving circuit 52 is used for completing the switching tube driving during the DC-pulsating DC reverse conversion; the third adjusting 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 at the time of the pulsating DC-AC forward conversion; the third driving circuit 53 is used for completing the switching tube driving during the pulsating DC-AC forward conversion; the digital control circuit 60 is used as an integrated control unit for the bi-directional DC-AC converter.

In the above-mentioned structure, please refer to fig. 2, fig. 2 is a schematic circuit diagram of an embodiment of the DC-pulsating DC bi-directional conversion main circuit shown in fig. 1, in this embodiment, the DC-pulsating DC bi-directional conversion main circuit 10 includes a first switching tube Q1, a second switching tube Q2, a third switching tube Q3, a fourth switching 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 inductance L1, a second high-frequency filtering inductance L2, a third high-frequency filtering inductance L3, a fourth high-frequency filtering inductance L4, a first high-frequency buffer absorption circuit, a second high-frequency buffer absorption circuit, a third high-frequency buffer absorption circuit, and a high-frequency power transformer T1, and the first switching tube Q1, the first high-frequency rectifying diode D1, the first high-frequency filtering inductance L1 and the first high-frequency buffer absorption circuit are connected to the high-frequency winding 1-2 after interconnection; the second switching tube Q2, the second high-frequency rectifying diode D2, the second high-frequency filtering inductor L2 and the second high-frequency buffer absorption circuit are connected with the windings 2-3 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 filtering 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; the fourth switching tube Q4, the fourth high-frequency rectifying diode D4, the fourth high-frequency filtering inductor L4 and the fourth high-frequency buffer absorption circuit are connected with 12-13 windings of the high-frequency power transformer T1 after being interconnected. The bidirectional DC-AC converter provided by the embodiment adopts a 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 diagram of an embodiment of the pulsating DC-AC bidirectional conversion main circuit shown in fig. 1, in which 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 electrically isolated optocoupler O1 and a second electrically isolated optocoupler O2, and after being interconnected, the fifth switching tube Q5, the fifth high-frequency rectifying diode D12 and the fifth high-frequency buffer absorption circuit are respectively connected to an anode terminal of the intermediate port, an anode input terminal of the first electrically isolated optocoupler O1 and a cathode terminal of the second electrically isolated optocoupler O2; 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 electrode end of the intermediate port, the positive electrode input end of the first electric isolation optocoupler O1 and the negative electrode input end of the second electric isolation optocoupler O2 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 electrode end of the second port, the negative electrode input end of the first electric isolation optocoupler O1 and the positive electrode input end of the second electric isolation optocoupler O2 after being interconnected; the eighth switching tube Q8, the eighth high-frequency rectifying diode D15 and the eighth high-frequency buffer absorption circuit are connected with the positive electrode end of the second port, the negative electrode input end of the first electric isolation optocoupler O1 and the positive electrode input end of the second electric isolation optocoupler O2 respectively after being interconnected; 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 perform bidirectional power conversion between pulsating DC and AC.

Further, please refer 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 this embodiment, 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 with the first comparing circuit through the first amplifying circuit, and an output end of the first reference voltage circuit is connected with 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 end of the second reference voltage circuit is connected to the second comparing circuit. Please refer 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, wherein the third current sampling circuit is connected with the third comparing circuit through the third amplifying circuit, and an output end of the third reference voltage circuit is connected with the third comparing circuit. The bidirectional DC-AC converter provided in this embodiment employs the first adjusting circuit 31 to complete signal conditioning and protection signal formation during DC-pulsating DC forward conversion control; the second regulating circuit 32 is adopted to complete signal conditioning and protection signal formation during DC-pulsating DC reverse conversion control; the third regulating circuit 33 is used for signal conditioning and protection signal formation during 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 electrically isolated 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 electrically isolated optocoupler O3 is connected to the first comparator U17A via a 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 isolated 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 being connected to the third comparator U24A; the second voltage reference module is connected to the fourth comparator U25A. The bidirectional DC-AC converter provided by the embodiment adopts the first PWM circuit 41 to alternately provide effective pulses for the first switching tube Q1 and the second switching tube Q2 of DC-pulsating DC forward conversion; the second PWM circuit 42 is adopted to alternately provide effective pulses for the third switching tube Q3 and the fourth switching tube Q4 of the DC-pulsating DC reverse conversion; the third PWM circuit 43 is used to alternately supply effective pulses to the switching tubes of the inverter bridge for the fifth switching tube Q5-eighth switching tube Q8 and the sixth switching tube Q6-seventh switching tube Q7 during the forward conversion of the pulsating DC-AC.

Preferably, referring to fig. 11 (a) to 13 (d), 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 embodiment adopts a switching tube for driving when the first driving circuit 51 DC-pulsating DC is in forward conversion; the switching tube driving during the DC-pulsating DC reverse conversion is completed by adopting a second driving circuit; 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, please refer to fig. 14, fig. 14 is a schematic circuit diagram of an embodiment of the digital control circuit shown in fig. 1, in which the digital control circuit 60 includes a CPU board 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, respectively. The bidirectional DC-AC converter provided in this embodiment adopts the digital control circuit 60 as the integrated control unit of the bidirectional DC-AC converter.

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

bi-directional DC-AC converter assembly

The bi-directional DC-AC converter is composed of a DC-ripple DC bi-directional conversion main circuit 10, a ripple DC-AC bi-directional conversion main circuit 20, a first regulation circuit 31, a second regulation circuit 32, a third regulation circuit 33, a first PWM circuit 41, a second PWM circuit 42, a third PWM circuit 43, a first drive circuit 51, a second drive circuit 52, a third drive circuit 53, a digital control circuit 60, and an auxiliary power supply circuit 70. There are two input/output ports to the outside: the U1-GND1 port and the UA1-UA2 ports are provided with an 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 an intermediate pulsating direct current port, and UA1-UA2 are alternating current output ports; 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 is used for completing bidirectional power conversion between direct current and pulsating direct current, and 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 31 completes signal conditioning and protection signal formation during DC-pulsating DC forward conversion control, the first PWM circuit 41 completes formation of PWM (Pulse Width Modulation) control pulse 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 at the time of DC-pulsating DC reverse conversion control, the second PWM circuit 42 completes formation of PWM control pulses at the time of DC-pulsating DC reverse conversion, and the second driving circuit 52 completes switching tube driving at the time of DC-pulsating DC reverse conversion. The third regulating circuit 33 completes signal conditioning and protection signal formation at the time of pulsating DC-AC forward conversion control, the third PWM circuit 43 completes formation of PWM control pulses at the time of pulsating DC-AC forward conversion, and the third driving circuit 53 completes switching tube driving at the time of pulsating DC-AC forward conversion. The pulsating DC-AC reverse conversion is realized by natural rectification of a diode bridge circuit in a 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 circuit generates working power required by the working of each component module circuit of the bidirectional DC-AC converter.

In the block diagram of the bi-directional DC-AC converter shown in fig. 1, signals between the respective constituent blocks are described as follows:

u1: the positive DC-AC conversion circuit is used for inputting a direct current (plus) terminal during positive DC-AC conversion and outputting a direct current (plus) terminal during reverse DC-AC conversion.

GND1: the direct current input "-" end when the direct current is converted by the forward DC-AC, and the direct current output "-" end when the direct current is converted by the reverse DC-AC are also voltage reference ends of circuits associated with the ports of the bidirectional DC-AC converter U1-GND 1.

U2: is the "+" end of the pulsating direct voltage.

GND23: the "-" terminal of the pulsating direct voltage is also the voltage reference terminal of the DC-pulsating DC reverse conversion and pulsating DC-AC conversion section.

UA1: the AC output 1 end in the bidirectional DC-AC forward conversion is also the AC input 1 end in the bidirectional DC-AC reverse conversion.

UA2: the AC output 2 end in the bidirectional DC-AC forward conversion is also the AC input 2 end in the bidirectional DC-AC reverse conversion.

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

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

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

VCC: the auxiliary power supply circuit is supplied 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 for the port of the DC-AC converter U1-GND1 is supplied from the main circuit to the first regulation circuit 31, the second regulation circuit 32 and the digital control circuit.

I1F: the current sampling signal, which is the port of the DC-AC converter U1-GND1, is supplied from the main circuit to the first regulation circuit 31, the second regulation circuit 32, and the digital control circuit.

T1F: the temperature sampling signal, which is the DC-pulsating DC forward converting portion, is supplied from the main circuit to the first regulation 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 sample signal for the U2-GND23 port is supplied by the main circuit to the second regulating circuit 32, the first regulating circuit 31, the third regulating circuit 33 and the digital control circuit 60.

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

UAF: the AC voltage sample signal at the ports of the DC-AC converters UA1-UA2 is supplied by the main circuit to the third regulating circuit 33 and the digital control circuit 60.

I3F: the AC output current sample signal, which is the port of the DC-AC converter UA1-UA2, is supplied by 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 control signal, which is the first DC-ripple DC forward conversion control signal, is supplied to the first PWM circuit 41 by the digital control circuit 60.

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 output for the alternating current at the time of forward conversion of the DC-AC converter, and is supplied to the first PWM circuit 41 by the digital control circuit 60.

PFX3: the control signal is supplied by the digital control circuit to the second PWM circuit 42 as a first DC-pulsating DC reverse conversion control signal.

PFX4: the control signal is supplied by the digital control circuit to the second PWM circuit 42 as a second DC-pulsating DC reverse conversion control signal.

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

PN58: the third PWM circuit 43 is fed by a digital control circuit for outputting a positive half-wave control signal for AC during the pulsating DC-AC forward conversion, and is finally used for driving the pair of switching tubes Q5 to Q8 in the pulsating DC-AC bidirectional conversion main circuit.

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

U1P: the overvoltage protection signal, which is the dc voltage U1, is supplied by the first regulator circuit 31 to the first PWM circuit 41 and is transferred by the second regulator circuit 32 to the second PWM circuit 42.

I1P: the overcurrent protection signal, which is the dc current I1, is supplied from the first regulator circuit 31 to the first PWM circuit 41 and is transferred from the second regulator circuit 32 to the second PWM circuit 42.

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

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

I2P: the overcurrent protection signal for pulsating the dc current I2 is supplied from the second regulator circuit 32 to the second PWM circuit 42, and is transferred from the first regulator circuit 31 to the first PWM circuit 41 and from the third regulator circuit 33 to the third PWM circuit 43.

T2P: the over-temperature protection signal, which is a DC-pulsating DC reverse conversion section, is supplied from the second regulator circuit 32 to the second PWM circuit 42.

U3P: the overvoltage protection signal, which is an ac voltage UA, is supplied by the third regulating circuit 33 to the third PWM circuit 43.

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

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

P1: the first PWM circuit 41 supplies the first pulse control signal to the DC-pulsating DC forward converting section via the first driving circuit 51 to control the first switching tube Q1.

P2: the second pulse control signal is sent from the first PWM circuit 41 to the DC-pulsating DC forward converting section via the first driving circuit 51 to control the second switching tube Q2.

P3: the third pulse control signal is sent to the DC-pulsating DC reverse conversion section from the second PWM circuit 42 via the second driving circuit 52 to control the third switching tube Q3.

P4: the fourth pulse control signal is sent to the DC-pulsating DC reverse conversion section by the second PWM circuit 42 via the second driving circuit 52 to control the fourth switching tube Q4.

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

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

P7: the seventh pulse control signal is sent from the third PWM circuit 43 to the ripple 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 ripple DC-AC conversion circuit via the third driving circuit 53 to control the eighth switching tube Q8.

Two-way DC-AC converter power conversion scheme

The power conversion of the bi-directional DC-AC converter is divided into a main power conversion and an auxiliary power supply power conversion.

The main power conversion of the bidirectional DC-AC converter is formed by cascade connection of a DC-pulsating DC bidirectional conversion main circuit and a pulsating DC-AC bidirectional conversion main circuit. The DC-AC converter converts DC into AC during forward conversion, wherein the DC-pulsating DC conversion section converts the input DC voltage into a voltage of absolute value

Varying pulsating direct current voltage, the pulsating DC-AC conversion section converting the pulsating direct current input voltage +.>

Conversion to AC output voltage

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

Naturally rectifying the power supply voltage into pulsating direct current voltage through a diode bridge rectifying circuit

The DC-pulsating DC converting section pulses the DC voltage +.>

Is converted into a direct current voltage.

The auxiliary power supply power conversion section supplies a start-up voltage from the forward input direct current U1 at the time of forward conversion of the bidirectional DC-AC converter, and supplies a start-up voltage from the pulsating direct current U2 at the time of reverse conversion. After the auxiliary power supply starts to work, 4 groups of power supplies such as VCC1, VCC2, VCC3, VCC and the like are generated by electromagnetic induction of the auxiliary winding of the transformer, and working power supplies are respectively provided for the DC-pulsating DC forward conversion part, the DC-pulsating DC reverse conversion part, the pulsating DC-AC conversion part, the digital control circuit and the like.

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

The bi-directional DC-AC converter main power conversion circuit is composed of a DC-ripple DC bi-directional conversion main circuit and a ripple DC-AC bi-directional conversion main circuit cascade.

(1) DC-pulsating DC bidirectional conversion main circuit working principle

The DC-pulsating DC bidirectional conversion main circuit is shown in fig. 2, and the bidirectional conversion from DC to pulsating DC is completed by a high-frequency (500 KHz-10 MHz) PWM control mode, and mainly comprises MOS (Metal-Oxide-Semiconductor) switching tubes Q1-Q4, high-frequency rectifying 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 direct current input voltage during direct current-pulsating DC forward conversion or direct current output voltage during reverse conversion, GND1 is reference ground of a direct current U1 related circuit, U1F is a voltage sampling signal of a U1-GND1 port, I1F is a current sampling signal of a U1-GND1 port, and P1 and P2 are control pulses of working switching 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 the 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 a U2-GND23 port, and P3 and P4 are control pulses of working switching 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, the Q3 and Q4 are turned off, the U1-GND1 port is a direct current input port, the U2-GND23 port is a pulsating direct current output port, and the switching tubes Q1 and Q2 are alternately turned on or turned off during the forward direction. When the switching tube Q1 is switched on and the switching tube Q2 is switched off, current flows in windings 1-2 of the transformer T1, the windings 13-14 generate induced electromotive force and enable the rectifying tube D3 to be switched on in the forward direction, and the induced electromotive force of the windings 13-14 is rectified by the diode D3 and filtered slightly by the LC and then outputs pulsating direct current to a U2-GND23 port; when the switching tube Q2 is switched on and the switching tube Q1 is switched off, current flows in the windings 2-3 of the transformer T1, induced electromotive force is generated by the windings 12-13, the rectifying tube D4 is switched on in the forward direction, and the induced electromotive force of the windings 12-13 is rectified by the diode D4 and filtered slightly by the LC and then pulsating direct current is output to the port U2-GND 23. The pulse width of the high-frequency PWM control pulses 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 absolute value waveform is converted into sinusoidal alternating current output by a 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, switching tubes Q3 and Q4 work, Q1 and Q2 are turned off, a U2-GND23 port is a pulsating direct current input port, a U1-GND1 port is a direct current output port, and switching tubes Q3 and Q4 are alternately turned on or turned off during the reverse work. When the switching tube Q3 is switched on and the switching tube Q4 is switched off, current flows in windings 13-14 of the transformer T1, the windings 1-2 generate induced electromotive force and enable the rectifying tube D1 to be switched on in the forward direction, and the induced electromotive force of the windings 1-2 outputs direct current to a U1-GND1 port after being rectified by the diode D1 and filtered by LC; when the switching tube Q4 is switched on and the switching 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 rectifying 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 LC and then outputs direct current to the U1-GND1 port. The pulse width of the high-frequency PWM control pulses P3 and P4 is modulated according to constant direct current voltage, so that the direct current voltage output by the U1-GND1 port is forced to be a constant direct current voltage waveform.

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

The main circuit of the pulse DC-AC bidirectional conversion is shown in FIG. 3, and is mainly composed of MOS switching tubes Q5-Q8, power frequency rectifying 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, UA1-UA2 is a power frequency alternating current port, UAF is a voltage sampling signal of the UA1-UA2 alternating current port, and I3F is a current sampling signal of the UA1-UA2 alternating current port.

When the pulsating DC-AC bidirectional conversion main circuit is in 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 by a U2-GND23 port is converted into alternating sinusoidal positive half waves which are output from a UA1-UA2 alternating port; when Q6 and Q7 are on, Q5 and Q8 are off, the pulsating direct current input by the U2-GND23 port is converted into the negative half wave of alternating current sine, and the negative half wave is output from the UA1-UA2 alternating current port; the switch tube pairs Q5-Q8 and Q6-Q7 are alternately turned on or off according to power frequency, and alternating current ports UA1-UA2 output sine wave voltages with positive and negative alternation.

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

(IV) principle of operation of auxiliary power supply of bidirectional DC-AC converter

The auxiliary power circuit of the bi-directional DC-AC converter is shown in fig. 4. When the bidirectional DC-AC converter works in the forward direction, a direct current voltage U1 of a U1-GND1 port provides a starting voltage for an auxiliary power supply circuit, a capacitor E1 is charged through D20-R1// R2, then VCC1 is built through voltage stabilization of a voltage stabilizer Z1, a first regulating circuit 31, a first PWM circuit 41 and a first driving circuit 51 are powered, switching tubes Q1 and Q2 start to work, when the switching tubes Q1 are conducted and Q2 are turned off, auxiliary power supply windings 4-5 and 10-11 of a transformer T1 generate induction currents, and when the switching tubes Q2 are conducted and Q1 is turned off, auxiliary power supply windings 6-7 and 8-9 of the transformer T1 generate induction currents. When the bidirectional DC-AC converter works reversely, a pulsating direct current voltage U2 of a U2-GND23 port provides a starting voltage for an auxiliary power supply circuit, a capacitor E2 is charged through D21-R3// R4, VCC2 is built through voltage stabilization of a voltage stabilizer Z2, a second regulating circuit 32, a second PWM circuit 42 and a second driving circuit 52 are powered, switching tubes Q3 and Q4 start to work, when the switching tubes Q3 are conducted and Q4 are turned off, auxiliary power supply windings 4-5 and 10-11 of a transformer T1 generate induction currents, and when the switching tubes Q4 are conducted and Q3 is turned off, auxiliary power supply windings 6-7 and 8-9 of the transformer T1 generate induction currents. Q1-Q2 or Q3-Q4 are alternately switched on or off at high frequency, the induction current of each auxiliary power winding is rectified by a corresponding rectifying diode to charge an electrolytic capacitor, stable output power sources VCC1, VCC2, VCC3 and VCC are established after the voltage is stabilized by a voltage stabilizer, working power sources are respectively provided for corresponding related circuits, wherein VCC is a high-performance linear power source after the voltage is stabilized twice by the voltage stabilizer Z3 and the linear voltage stabilizer U1, and the power sources are specially used for supplying power to a digital control circuit containing a CPU.

Working principle of regulating circuit of 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, namely DC-pulsating DC forward control, DC-pulsating DC reverse control and pulsating DC-AC forward control, and the corresponding regulating circuits comprise a first regulating circuit 31, a second regulating circuit 32 and a third regulating circuit 33.

(1) Principle of operation of the first regulating circuit 31

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

(2) Second regulating circuit 32 principle of operation

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

(3) Third regulating circuit 33 principle of operation

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

Working principle of PWM circuit of 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 transistors Q1-Q8. The bidirectional DC-AC converter comprises three types of control, namely DC-pulsating DC forward control, DC-pulsating DC reverse control and pulsating DC-AC forward control, and the corresponding PWM circuits comprise three types of first PWM circuits 41, second PWM circuits 42 and third PWM circuits 43.

(1) First PWM circuit 41 principle of operation

The first PWM circuit 41 is shown in fig. 8. The first PWM circuit 41 is powered by VCC1 to alternately provide active pulses to the operating switching tubes Q1, Q2 of the DC-to-ripple DC forward converter. The oscillator formed by the device U14 generates a high-frequency (500 KHz-10 MHz) clock with the frequency being adjustable through RW10 and the duty ratio being 50%, the high-level period of the clock is used as a working signal ZX1 of Q1 during DC-pulsating DC forward conversion, and the low-level period of the clock is used as a working signal ZX2 of Q2 during DC-pulsating DC forward conversion after being inverted through U15A. The alternating current given signal SINP from the digital control circuit is isolated by an optocoupler O3, filtered by C29 and followed by U16A to form a smooth alternating current given signal SING, and compared with a U2-GND23 port voltage sampling signal U2F to generate an initial control pulse signal PZX when DC-pulsating DC forward conversion is carried out, wherein the initial control pulse signal is PZX high level when U2F is higher than the SING, and otherwise the initial control pulse signal is low level. In the circuit, an initial given voltage at the start-up of 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 with 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 the U17A, wherein when all input signals at the inverting input end of the U17A are at low level, P10 is at high level, otherwise, is at low level. The effective control pulse P20 provided to the switching tube Q2 is formed by comparing the initial pulse PZX with 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 through the U18A, where when all signals at the inverting input terminal of the U18A are low, P20 is high, otherwise, is low.

(2) Second PWM circuit 42 principle of operation

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 operating switching transistors Q3, Q4. The oscillator formed by the device U19 generates a high-frequency (500 KHz-10 MHz) clock with the frequency being adjustable through RW14 and the duty ratio being 50%, the high level period of the clock is used as the working signal FX1 of the Q3 during DC-pulsating DC reverse conversion, and the low level period of the clock is used as the working signal FX2 of the Q4 during DC-pulsating DC reverse conversion after being reversed through U20A. The DC given signal DCP from the digital control circuit is isolated by an optocoupler O9, filtered by C34 and followed by U21A to form constant DC given voltage DCG, and compared with a U1-GND1 port voltage sampling signal U1F, an initial control pulse signal PFX is generated when DC-pulse DC is reversely converted, and PFX is high level when U1F is higher than DCG, otherwise, the initial control pulse signal PFX is low level. In the circuit, an initial given voltage at the start-up of 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 the HLREF2 through the U22A, where when all signals at the inverting input terminal of the U22A are low, P30 is high, otherwise is low. The effective control pulse P40 provided to the switching tube Q4 is formed by comparing the initial pulse PFX and 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 through the U23A, and when all signals at the inverting input terminal of the U23A are at low level, P40 is at high level, otherwise is at low level.

(3) Third PWM circuit 43 principle of operation

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

(seventh) principle of operation of drive Circuit

The driving circuit of the bidirectional DC-AC converter mainly completes the enhancement of the driving capability of the switching tubes Q1-Q8 corresponding to the control pulses P1-P8. The bidirectional DC-AC converter comprises three types of control, namely DC-pulsating DC forward control, DC-pulsating DC reverse control and pulsating DC-AC forward control, and the corresponding driving circuits comprise three types of first driving circuit 51, second driving circuit 52 and third driving circuit 53.

The driving 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 forms a pulse P1 to drive the switching tube Q1 after the driving capability of the pulse P10 is increased by the first driving chip U26, and forms a pulse P2 to drive the switching tube Q2 after the driving capability of the pulse P20 is increased by the second driving chip U27. The second driving circuit 52 is powered by VCC2, and drives the switching transistor Q3 by forming P3 after the driving capability of the pulse P30 is increased by the driving chip U28, and drives the switching transistor Q4 by forming P4 after the driving capability of the pulse P40 is increased by the driving chip U29. The third driving circuit 53 is powered by VCC3, and forms a P5 driving switch Q5 after the driving capability of the pulse P580 is increased by the driving chip U30, forms a P8 driving switch Q8 after the driving capability of the pulse P580 is increased by the driving chip U33, forms a P6 driving switch Q6 after the driving capability of the pulse P670 is increased by the driving chip U31, and forms a P7 driving switch Q7 after the driving capability of the pulse P670 is increased by the driving chip U32.

(eight) digital control circuit working principle

The digital control circuit of the bidirectional DC-AC converter is shown in fig. 14, and mainly completes the state detection of the bidirectional DC-AC converter and the intelligent control or auxiliary control of the switching tubes Q1-Q8, and is powered by VCC. The signals of the voltage sampling U1F of the ports of the auxiliary working power supplies VCC1, VCC2, VCC3 and U1-GND1, the voltage sampling U2F of the ports of the temperature sampling T1F, U2-GND23 of the current sampling I1F, DC-pulsating DC forward conversion part, the voltage sampling U3F of the ports of the temperature sampling T2F, UA1-UA2 of the current sampling I2F, DC-pulsating DC reverse conversion part, the current sampling I3F, the temperature sampling T3F of the pulsating DC-AC conversion part and the like are isolated by optical coupling and then sent to the A/D interface of the CPU board. The CPU board detects, calculates and judges the state of the bidirectional DC-AC converter, and outputs control signals such as 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 AC output positive half-wave control signal NP58 during the pulsating DC-AC forward conversion, and an AC output negative half-wave control signal NP67 during the pulsating DC-AC forward conversion, respectively, and the like, and the control signals are isolated by an optocoupler to control the switching tubes of the DC-pulsating DC forward conversion section, the DC-pulsating DC reverse conversion section, and the pulsating DC-AC forward conversion section.

(ninth) Effect description

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

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

(1) The converter is formed by cascade connection of DC-pulse DC bidirectional conversion and pulse DC-AC bidirectional conversion, the DC-pulse DC bidirectional conversion part adopts high-frequency (500 KHz-10 MHz) PWM control, the pulse DC-AC bidirectional conversion part adopts power frequency (50 Hz) pulse control, the high-frequency control is utilized to improve the performance index, the low-frequency control is utilized to avoid direct connection and reduce the switching loss.

(2) The converter adopts a two-stage protection and two-stage control mode, the basic protection is carried by a pure hardware circuit, the reliability and the rapidity are ensured, the comprehensive intelligent protection is carried 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, the low-frequency control is borne by software in the digital control, and the flexibility and the high cost performance are ensured.

(3) The DC part and the AC part of the converter are electrically isolated by adopting a high-frequency transformer, a bidirectional 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.

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

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

(6) The buffer circuit and related device parameters are optimized, when the switching tube is switched from the on state to the off state, the instantaneous voltage at two ends of the switching tube is low during state switching due to the action of the parallel capacitor in the buffer circuit, and the switching loss is small; when the switching tube is switched from an off state to an on state, the instant 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 an oscillator and is adjustable, and after the switching speed level of the switching tube is improved, seamless upgrading of products is facilitated.

(8) The converter adopts a hierarchical control mode of basic control and comprehensive control, so that individuation requirements can be conveniently realized in the digital controller through software according to different application scenes, the intelligence and the comprehensiveness of the converter are improved, and the applicability and the application range of the converter are further increased.

(9) The converter has two main windings with opposite current directions to stagger when in forward conversion or reverse conversion, 4 windings of the auxiliary power supply also stagger in two groups, compared with a single-end forward or reverse conversion converter, the direct current component in the converter is extremely low, the transmissible power is high, 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 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. It is therefore intended that the following claims be interpreted as including the 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 modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

1. The 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 a two-stage cascade intermediate port; 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-ripple DC bidirectional conversion main circuit (10), the ripple 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 driving circuit (51), the second driving circuit (52) and the third driving 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 DC-AC conversion is performed in the reverse direction, 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 for completing the formation of PWM control pulses during DC-pulsating DC forward conversion; the first driving circuit (51) is used for completing the switching tube driving during the DC-pulsating DC forward conversion; the second regulating circuit (32) is used for completing 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 DC-pulsating DC reverse conversion; the second driving circuit (52) is used for completing the switching tube driving during the DC-pulsating DC reverse conversion; the third regulating circuit (33) is used for completing signal conditioning and protection signal formation during pulsating DC-AC forward conversion control; 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 driving a switching tube when the pulsating DC-AC forward conversion is completed; the digital control circuit (60) is used as an integrated control unit of the bidirectional DC-AC converter;

The DC-pulsating DC bidirectional conversion main circuit (10) 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 filtering inductor, a second high-frequency filtering inductor, a third high-frequency filtering inductor, a fourth high-frequency filtering 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 filtering inductor and the first high-frequency buffer absorption circuit are connected with each other and then are connected with P of the high-frequency power transformer _1-2 The windings are connected; the second switch tube, the second high-frequency rectifying diode, the second high-frequency filtering inductor and the second high-frequency buffer absorption circuit are interconnected and then connected with the P of the high-frequency power transformer _2-3 The windings are connected; the third switch tube, the third high-frequency rectifying diode, the third high-frequency filter inductor and the third high-frequency buffer absorption circuit are interconnected and then connected with S of the high-frequency power transformer _13-14 The windings are connected; the fourth switch tube, the fourth high-frequency rectifying diode, the fourth high-frequency filter inductor and the fourth high-frequency buffer absorption circuit are interconnected and then connected with the S of the high-frequency power transformer _12-13 The windings are connected;

the pulse DC-AC bidirectional conversion 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 electric isolation optocoupler and a second electric isolation optocoupler, wherein the fifth switching tube, the fifth high-frequency rectifying diode and the fifth high-frequency buffer absorption circuit are connected with the positive electrode end of the middle port, the positive electrode input end of the first electric isolation optocoupler and the negative electrode input end of the second electric isolation optocoupler respectively after being interconnected; the sixth switching tube, the sixth high-frequency rectifying diode and the sixth high-frequency buffer absorption circuit are connected with the negative electrode end of the intermediate port, the positive electrode input end of the first electric isolation optocoupler and the negative electrode input end of the second electric isolation optocoupler after being interconnected; the seventh switching tube, the seventh high-frequency rectifying diode and the seventh high-frequency buffer absorption circuit are connected with the positive electrode end of the second port, the negative electrode input end of the first electric isolation optocoupler and the positive electrode input end of the second electric isolation optocoupler after being interconnected; the eighth switching tube, the eighth high-frequency rectifying diode and the eighth high-frequency buffer absorption circuit are connected with the positive electrode end of the second port, the negative electrode input end of the first electric isolation optocoupler and the positive electrode input end of the second electric isolation optocoupler after being interconnected; the power frequency current transformer is connected with the second port.

2. The bi-directional DC-AC converter according to claim 1, wherein the first regulation 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 is connected to the first comparing circuit through the first amplifying circuit, and an output terminal of the first reference voltage circuit is connected to the first comparing circuit.

3. The bi-directional DC-AC converter of claim 1 wherein said second regulation circuit (32) comprises a second reference voltage circuit, a second current sampling circuit, a second amplifying circuit and a second comparing circuit, said second current sampling circuit being connected to said second comparing circuit through said second amplifying circuit, an output of said second reference voltage circuit being connected to said second comparing circuit.

4. The bi-directional DC-AC converter according to claim 1, wherein the third regulation 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 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.

5. The bi-directional DC-AC converter according to claim 1, characterized in that the first PWM circuit (41) comprises a first oscillator, a first inverter, a third electrically isolated optocoupler, a first follower and a first comparator, the first oscillator being connected to the first inverter; the third electrically isolated optocoupler is connected with the first comparator through the first follower.

6. The bi-directional DC-AC converter of claim 1 wherein 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, wherein the first voltage reference module is connected with the third comparator; the second voltage reference module is connected with the fourth comparator.

7. The bi-directional DC-AC converter according to claim 1, wherein the first driving circuit (51) comprises a first driving chip and a second driving chip, the first driving chip being connected to the first switching tube, the second driving 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, wherein 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.

8. The bi-directional DC-AC converter of claim 1 wherein said digital control circuit (60) comprises a CPU board connected to said first switching tube, said second switching tube, said third switching tube, said fourth switching tube, said fifth switching tube, said sixth switching tube, said seventh switching tube, and said eighth switching tube, respectively.