Two-stage multi-mode bidirectional inverter circuit

Abstract

The invention discloses a two-stage multi-mode bidirectional inverter circuit, which comprises a direct-current power supply DC, an alternating-current power supply AC, a DC / DC circuit, a direct-current voltage-dividing capacitor Cb1, a direct-current voltage-dividing capacitor Cb2, a DC / AC circuit and a controller, and is characterized in that a negative electrode of a second port of the DC / DC circuit is connected with a negative electrode of the direct-current voltage-dividing capacitor Cb1 and a negative electrode of a direct-current port of the DC / AC circuit; a middle point of a second port of the DC / DC circuit is connected with a negative electrode of a direct-current voltage-dividing capacitor Cb1 and a positive electrode of a direct-current voltage-dividing capacitor Cb2, and is connected to an alternating-current neutral line N; the AC port of the DC / AC circuit is connected with an AC live wire L1 and an AC live wire L2. The controller stably outputs voltage or current by controlling the DC / DC circuit and the DC / AC circuit, and bidirectional electric energy conversion is achieved. According to the invention, direct-current capacitance and additional circuits do not need to be increased, the size of the device is reduced, the system cost is reduced, the conversion efficiency is improved, and the device can be widely applied to new energy power generation and energy storage and other industrial and civil bidirectional power conversion systems so as to meet the global power supply and consumption requirements.

Description

Technical Field

[0001] The present invention relates to the field of new energy power electronics technology, and in particular to a two-stage multi-mode bidirectional inverter circuit. Background Art

[0002] Most countries in the world use single-phase and three-phase power systems. However, in the power supply systems of North America and some other countries, two-wire (L1-L2), i.e., single-phase power systems, single-wire (L1-N and / or L2-N), or two-wire parallel (L1 / L2-N) power supply modes are used. In order to adapt to the global market, new energy power generation systems need to flexibly switch between these power supply modes and be able to achieve bidirectional power conversion.

[0003] Two-stage multi-mode power supply systems usually use symmetrical double half-bridge inverter circuits, such as Figure 1 As shown, it includes two DC filter capacitors Cd1, Cd2, four power switch tubes Q1~Q4 and their body diodes, AC filter inductors L1, L2, and AC filter capacitors Cf1, Cf2. The power conversion from DC to AC is called inversion (DC / AC), the power conversion from AC to DC is called rectification (AC / DC), and the power conversion from DC to DC is called buck-boost (DC / DC). In the inversion mode: when the two-wire power supply mode, i.e., the single-phase power system, Cd1, Cd2 and Cf1, Cf2 are connected in series for filtering, Q1~Q4 form a traditional bidirectional full-bridge circuit, L1, L2 are connected in series for filtering, and supply electrical energy to the series-connected AC power supplies Va, Vc. At the same time, the load RL1 and RL2 are connected in series to obtain electrical energy from the two live wires without passing through the N wire. In the single-wire power supply mode, Cd1, Q1, Q2, L1, Cf1 form the first bidirectional half-bridge circuit, and Cd2, Q3, Q4, L2, Cf2 form the second bidirectional half-bridge circuit, thus forming a bidirectional inverter circuit. The two supply electrical energy to Va, RL1 and Vc, RL2 respectively through the N wire.

[0004] The two-wire parallel power supply mode is similar to the single-wire mode and still shares the N wire. The difference is only that the two live wires are directly connected in parallel. Therefore, the amplitudes, frequencies and phases of the two groups of single-phase AC voltages must be exactly the same. Conversely, the rectification mode is similar to it and will not be elaborated here. The traditional bidirectional inverter circuit can achieve bidirectional power conversion and has the main advantages of simple circuit structure and mature modulation method.

[0005] If the two loads RL1 and RL2 are of different sizes, or in the case of non-linear loads, especially half-wave rectifier loads, when operating in the single-line inverter mode or the rectifier mode with different amplitudes of two AC power supplies, there is a large voltage difference across Cd1 and Cd2. Therefore, the problem of uneven voltage sharing in the intermediate DC bus voltage-dividing capacitors is inevitable. To achieve voltage sharing of the DC voltage-dividing capacitors, filtering capacitors with a relatively large capacitance are preferably selected, which leads to an excessive volume of the device; or an additional voltage-sharing circuit is added, generally in the form of a buck-boost circuit, to achieve energy exchange of the voltage-dividing capacitors. However, the control method is relatively complex, the conversion efficiency decreases, and at the same time, the volume increases and the cost rises. Therefore, simply and effectively solving the problem of capacitor voltage sharing in a multi-mode power supply bidirectional inverter circuit has become one of the research focuses in the field of new energy power electronics. Summary of the Invention

[0006] The technical problem to be solved by the embodiments of the present invention is to provide a two-stage multi-mode bidirectional inverter circuit to reduce the volume, lower the cost, and improve the conversion efficiency.

[0007] To solve the above technical problem, the embodiments of the present invention propose a two-stage multi-mode bidirectional inverter circuit, including a DC power supply DC, an AC power supply AC, a DC / DC circuit, a DC voltage-dividing capacitor Cb1, a DC voltage-dividing capacitor Cb2, a DC / AC circuit, and a controller. Among them, the AC power supply AC includes an AC live wire L1, an AC live wire L2, and an AC neutral wire N; The positive electrode of the first port of the DC / DC circuit is connected to the positive and negative electrodes of the DC power supply DC. The positive electrode of the second port of the DC / DC circuit is connected to the positive electrode of the DC voltage-dividing capacitor Cb1 and the positive electrode of the DC port of the DC / AC circuit. The negative electrode of the second port of the DC / DC circuit is connected to the negative electrode of the DC voltage-dividing capacitor Cb1 and the negative electrode of the DC port of the DC / AC circuit. The midpoint of the second port of the DC / DC circuit is connected to the negative electrode of the DC voltage-dividing capacitor Cb1 and the positive electrode of the DC voltage-dividing capacitor Cb2, and is connected to the AC neutral wire N. The AC ports of the DC / AC circuit are respectively connected to the AC live wire L1 and the AC live wire L2. The controller controls the DC / DC circuit and the DC / AC circuit to stabilize the output voltage or current by sampling the AC and DC side voltage and current signals, identifying the input and output power flow directions, and realizing bidirectional power conversion.

[0008] Further, the DC / DC circuit uses an isolated topology or a non-isolated topology with DC voltage division.

[0009] Further, the DC / DC circuit includes a high-frequency isolation transformer, and the transformer includes a primary winding and two secondary windings. The number of turns of the two secondary windings is the same, so that the two DC capacitors are naturally voltage-shared in the single-line or double-line parallel power supply mode.

[0010] Furthermore, the DC / DC circuit and / or the DC / AC circuit adopt interleaved parallel connection or cascade connection, or adopt a multilevel circuit.

[0011] Furthermore, the DC / DC circuit and / or the DC / AC circuit adopt voltage mode control, average current mode control, peak current mode control, quasi-resonant control, single-cycle control, continuous conduction mode control, discontinuous conduction mode control or critical conduction mode control.

[0012] Furthermore, the controller dynamically obtains the voltage and current values of the DC power supply or the AC power supply, compares the obtained current actual output value with the target value; dynamically confirms the duty cycle of the switching tube and the adjustment instruction of working or not working in the DC / DC circuit and the DC / AC circuit according to the comparison result; the controller controls the switching tubes in the DC / DC circuit and the DC / AC circuit to execute the instruction, and dynamically controls the energy storage / discharge time, so that the current actual output value approaches the target value.

[0013] Furthermore, the controller includes a sampling, conditioning and feedback circuit and a switching tube driving circuit.

[0014] Furthermore, the DC / DC circuit operates in high-frequency pulse width modulation, and the DC / AC circuit operates in high-frequency sine wave pulse width modulation.

[0015] Furthermore, the controller is built with discrete electronic components or an integrated circuit.

[0016] Furthermore, the inverter circuit operates in double-phase wire, single-phase wire, single-phase wire series and double-phase wire parallel power supply modes, and can flexibly switch between the 4 power supply modes.

[0017] The beneficial effects of the present invention are as follows: (1) The present invention can realize natural voltage sharing of two DC voltage-dividing capacitors; (2) The present invention does not need to additionally add a voltage-sharing circuit, but reuses the power components in the DC / DC circuit, thereby reducing the volume of the device, lowering the system cost, and improving the conversion efficiency; (3) The present invention operates in a double-phase wire, i.e., a single-phase power system, single-phase wire, single-phase wire series and double-phase wire parallel power supply modes, and can flexibly switch between these power supply modes to meet the global power supply and consumption requirements; (4) The present invention realizes bidirectional power conversion between AC and DC power supplies or power grids: rectifying and charging or inverting and discharging, without the need to separately configure a charger or an inverter; (5) The control method of the present invention can simplify the design of the controller and meet the diverse requirements of electrical loads and grid scheduling. Description of the Drawings

[0018] Figure 1It is the circuit diagram of a traditional bidirectional inverter circuit.

[0019] Figure 2 It is the schematic diagram of the structure of a two - stage multi - mode bidirectional inverter circuit according to an embodiment of the present invention.

[0020] Figure 3 It is the output control flow chart of a two - stage multi - mode bidirectional inverter circuit according to an embodiment of the present invention.

[0021] Figure 4 It is the capacitor voltage equalization control flow chart of a two - stage multi - mode bidirectional inverter circuit according to an embodiment of the present invention.

[0022] Figure 5 It is the circuit diagram of a two - stage multi - mode bidirectional inverter circuit according to an embodiment of the present invention.

[0023] Figure 6 It is the main working waveform diagram of a two - stage multi - mode bidirectional inverter circuit according to an embodiment of the present invention.

[0024] Figure 7 It is the circuit diagram of the primary circuit of an isolated DC / DC circuit in Embodiment 1 of the present invention, which adopts a half - bridge form.

[0025] Figure 8 It is the circuit diagram of the primary circuit of an isolated DC / DC circuit in Embodiment 2 of the present invention, which adopts a full - bridge form.

[0026] Figure 9 It is the circuit diagram of the primary circuit of an isolated DC / DC circuit in Embodiment 3 of the present invention, which adopts a soft - switching resonant push - pull form.

[0027] Figure 10 It is the circuit diagram of the primary circuit of an isolated DC / DC circuit in Embodiment 4 of the present invention, which adopts another type of resonant push - pull form.

[0028] Figure 11 It is the circuit diagram of the secondary circuit of an isolated DC / DC circuit in Embodiment 5 of the present invention, which adopts a type of resonant push - pull form.

[0029] Figure 12 It is the circuit diagram of a non - isolated DC / DC circuit in Embodiment 6 of the present invention, which adopts a bidirectional Buck / Boost circuit.

[0030] Figure 13 It is the circuit diagram of a DC / AC circuit in Embodiment 7 of the present invention.

[0031] Figure 14 It is the circuit diagram of the intermediate DC bus accessing other Boost DC power supplies in Embodiment 8 of the present invention. Detailed implementation manners

[0032] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0033] In the embodiments of the present invention, if there are directional indications (such as up, down, left, right, front, back...), they are only used to explain the relative positional relationship and movement conditions between components in a specific posture (as shown in the drawings). If the specific posture changes, the directional indications will also change accordingly.

[0034] In addition, in the present invention, the descriptions involving "first", "second", etc. are only for descriptive purposes, and cannot be understood as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature.

[0035] Please refer to Figure 2 , the two-stage multi-mode bidirectional inverter circuit in the embodiments of the present invention includes a DC power supply DC, an AC power supply AC, a DC / DC circuit, DC voltage dividing capacitors Cb1, Cb2, a DC / AC circuit, and a controller. The present invention can be widely applied to various bidirectional or unidirectional charging or inverter circuits, such as new energy systems like solar photovoltaic power generation, off-grid and grid-connected household and industrial and commercial energy storage, portable mobile energy storage power supplies, uninterruptible power supplies, battery formation power supplies, feedback aging power supplies, frequency converters, and active filters, as well as industrial power supplies, switching power supplies, etc.

[0036] The DC voltage dividing capacitors are Cb1 and Cb2, the AC loads are RLa and RLc, the AC power supplies are Va and Vc, and AC. Among them, the voltage across Cb1 is +BUS, the voltage across Cb2 is -BUS, and the two are connected in series to form the intermediate DC bus BUS. The positive and negative poles of the DC power supply DC are respectively connected to the positive and negative poles of the first port of the DC / DC circuit, and the positive and negative poles of its second port are respectively connected to the positive pole of the DC voltage dividing capacitor Cb1 and the negative pole of Cb2, and then connected to the positive and negative poles of the DC port of the DC / AC circuit. Its AC ports are respectively connected to the first and second AC live wires L1 and L2. The midpoint of the second port of the DC / DC circuit is respectively connected to the negative pole of Cb1 and the positive pole of Cb2, and then connected to the AC neutral line N. The voltage difference between L1 and N is the AC power supply Va, the voltage difference between N and L2 is the AC power supply Vc, and Va and Vc are connected in series and equivalent to the AC power supply AC. The controller includes a sampling, conditioning and feedback circuit, and a switching tube driving circuit, etc. The DC / DC circuit operates in high-frequency pulse width modulation (PWM), and the DC / AC circuit operates in high-frequency sine wave pulse width modulation (SPWM) to achieve bidirectional power conversion, that is, the rectification mode or the inversion mode.

[0037] According to actual application requirements, the present invention can flexibly operate in off-grid inversion, grid-connected inversion, and rectification modes. The power flow path (inversion) from a DC power source to an AC power source is as follows: In the double-phase or single-phase series power supply mode, that is, when the grid voltage or AC output of a single-phase power system is 220V / 230V / 240V, the DC / DC circuit, the DC / AC circuit, and Cb1 and Cb2 are equivalently connected in series to form the same inverter circuit. An intermediate DC bus is formed across Cb1 and Cb2, generating an AC sine wave voltage to supply power to the series-connected AC power sources Va and Vc, i.e., Vac, or the grid. At the same time, the loads RLa and RLc are connected in series to obtain power from the two live wires L1 and L2 without passing through the N wire. Therefore, the double-phase power supply mode is essentially a single-phase power system. In the single-phase series power supply mode, when the grid voltage or AC output is 100V / 110V / 120V, the DC / DC circuit and the DC / AC circuit respectively form two inverter circuits with Cb1 and Cb2, forming +BUS and -BUS across Cb1 and Cb2 respectively. The two generate two AC sine wave voltages respectively, and then supply power to Va, RLa, Vc, RLc, or the grid through the N wire from the two live wires L1 and L2 respectively. In the single-phase series power supply mode, the two AC output powers can be different, thus adapting to different types of electrical loads. In the double-phase parallel power supply mode, when the grid voltage or AC output is 100V / 110V / 120V, similar to the single-phase series power supply mode, two inverter circuits are still formed. The difference is only that the two live wires L1 and L2 are directly connected in parallel, and through appropriate control, the amplitudes, frequencies, and phases of the two AC voltages Va and Vc are exactly the same, so they can operate in parallel. Conversely, the power flow path (rectification) from an AC power source to a battery is as follows: The AC power source provides a sine wave voltage, which is rectified by the DC / AC circuit to form an intermediate DC bus, and then after being converted by the DC / DC circuit, each battery is charged in a constant current or constant voltage manner. Its working principle is similar to the inversion mode and will not be elaborated here. It should be noted that in these modes, both the DC / DC and DC / AC are bidirectional inverter circuits.

[0038] In the double-phase or single-phase series power supply mode, that is, in a single-phase power system, there is only the same inverter circuit in the system. The DC capacitors Cb1 and Cb2 are equivalently connected in series to work, and there is no problem of voltage equalization in the intermediate DC bus. In the single-phase and double-phase parallel power supply modes, although the DC capacitors Cb1 and Cb2 work independently, both are connected to the midpoint of the DC / DC circuit through the N wire. In the inversion / rectification mode, in fact, the two DC voltage dividers in the DC / DC circuit can respectively and independently supply / absorb electrical energy to / from Cb1 and Cb2 in real time. By designing the number of turns of the two secondary windings or the DC voltage dividers to be the same, the internal natural voltage equalization can be achieved across Cb1 and Cb2. The flow chart of the output control method is as Figure 3 shown, and the flow chart of the capacitor voltage equalization control method is as Figure 4As shown. By sampling the AC and DC side voltage and current signals, the controller identifies the input and output power flow directions, determines and controls the operation of the power switching transistors in the DC / DC circuit and the DC / AC circuit according to the actual operating conditions, and stabilizes the output voltage or current by providing real-time closed-loop feedback of the working state, adaptively controls the operation in the inverter or rectifier mode, and realizes bidirectional power conversion. The control method of the present invention simplifies the controller design and meets the requirements of diverse electrical loads and power supplies. Optionally, a battery is used on the DC side, thus further expanding the application scope, such as new energy energy storage systems, etc.

[0039] The DC / DC circuit can use either an isolated topology, including but not limited to half-bridge, full-bridge, push-pull, flyback, forward, forward-flyback, etc., which includes a high-frequency isolation transformer. The transformer has a primary winding and two secondary windings, or the secondary winding is in the form of a center tap, or combines switching resonance technologies such as LLC, LCC, LCLC, CLCL, basic series-parallel, etc. resonance circuits. It can also use non-isolated topologies with DC voltage division such as Buck, Boost, Buck-Boost, Cuk, SEPIC, ZETA, etc. The DC / AC circuit adopts a full-bridge or half-bridge or other improved forms. The DC / DC circuit and / or the DC / AC circuit can use interleaved parallel or cascaded technologies, and can also use various multilevel circuits to achieve higher power levels or higher voltage levels. It should be noted that the DC / DC circuit and / or the DC / AC circuit can adopt voltage mode control, or can also adopt average current mode, peak current mode control, quasi-resonant control, single-cycle control, etc., and can also adopt different working modes such as continuous conduction mode (CCM), discontinuous conduction mode (DCM), or critical conduction mode (CRM), etc.

[0040] The power switching transistors in the DC / DC circuit and the DC / AC circuit use fully controlled devices such as metal oxide field effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), etc., and can also use third-generation wide bandgap (WBG) power devices such as silicon carbide (SiC), gallium nitride (GaN) MOSFETs, etc., and these fully controlled power switching transistors can also be used in combination.

[0041] The controller can be built using discrete electronic components, or can be designed and used with application-specific integrated circuits such as analog control chips, microcontrollers (MCUs) programmed by software, digital signal processors (DSPs), or programmable logic devices (FPGA / CPLDs), etc. It can adopt either a discrete device method or an integrated method, or can be integrated into the controller uniformly to form a large-scale hybrid integrated circuit. This high-integration controller design can further reduce the volume of the present invention.

[0042] The present invention does not require increasing the DC capacitance or adding additional circuits. From the aspects of reducing the device volume, lowering the system cost, and improving the conversion efficiency, it can be widely applied to new energy power generation, energy storage, and other industrial and civil bidirectional power conversion systems to meet the global power supply and demand requirements.

[0043] As shown in the embodiment Figure 5 , DC is the DC power supply. In the isolated DC / DC circuit, the primary circuit adopts a push-pull form, including the DC filter capacitor Cd, the high-frequency isolation transformer TX, and the MOSFET switches Q1 and Q2. Its secondary circuit adopts a double half-bridge form, including the MOSFET switches Q3 to Q6, as well as the resonance inductors Ls1, Ls2 and the resonance capacitors Cs1, Cs2 of the two resonance circuits. The DC voltage dividing capacitors are Cb1 and Cb2. The DC / AC circuit adopts a full-bridge form, including the IGBT switches Q7 to Q8, as well as the AC filter inductors Lf1, Lf2 and the filter capacitors Cf1, Cf2 of the filter circuit. For the convenience of explaining the basic principle, Figure 5 the internal or external diodes of the power switch tubes are not drawn in the figure, but it does not affect their actual functions and performances. The DC power supply DC is connected to Q1, Q2 and the transformer TX in the primary push-pull circuit. After its output passes through the two resonance circuits composed of Ls1, Cs1 and Ls2, Cs2, it is synchronously rectified by the secondary double half-bridge circuit Q3 to Q6 and then connected to the intermediate DC bus voltage dividing capacitors Cb1, Cb2. Then, it passes through the AC full-bridge circuit Q7 to Q10 and is filtered by Lf1, Cf1 and Lf2, Cf2 and then connected to the first and second AC live wires L1 and L2. The common connection point or the center tap of the two secondary windings of the transformer TX is the midpoint of the second port of the DC / DC circuit and is respectively connected to the negative pole of Cb1 and the positive pole of Cb2 and then connected to the AC neutral line N. The voltage difference between L1 and N is the AC power supply Va, and the voltage difference between N and L2 is the AC power supply Vc. Va and Vc are connected in series and equivalent to the AC power supply AC.

[0044] When the double live wire or single live wire series power supply mode, i.e., the single-phase power system, the Q1~Q6, TX in the DC / DC circuit and Ls1, Ls2, Cs1, Cs2, the Q7~Q10 in the DC / AC circuit and Lf1, Lf2, Cf1, Cf2, and Cb1, Cb2 form the same inverter circuit. Among them, Ls1 and Ls2, Cs1 and Cs2, Lf1 and Lf2, Cf1 and Cf2, and Cb1 and Cb2 are respectively equivalent in series. Thus, an intermediate DC bus is formed at both ends of Cb1 and Cb2, providing or obtaining electrical energy from the series AC power supplies Va and Vc, i.e., Vac, or the power grid. At the same time, the load RLa and RLc are in series to obtain electrical energy from the two live wires L1 and L2 without passing through the N wire. In the single live wire power supply mode, due to the presence of the N wire, the Q1~Q6, TX in the DC / DC circuit and Ls1, Ls2, Cs1, Cs2, the Q7~Q10 in the DC / AC circuit and Lf1, Lf2, Cf1, Cf2, and Cb1, Cb2 form two inverter circuits. Among them, Ls1 and Ls2, Cs1 and Cs2, Lf1 and Lf2, Cf1, and Cf2, and Cb1 and Cb2 work independently. Thus, +BUS and -BUS are respectively formed at both ends of Cb1 and Cb2, and they respectively provide or obtain electrical energy from the two live wires L1 and L2 through the N wire to Va, RLa and Vc, RLc or the power grid. The double live wire parallel power supply mode is similar to the single live wire power supply mode, and the difference is only that the two live wires L1 and L2 are directly parallel, and through appropriate control, the amplitudes, frequencies and phases of the two AC voltages Va and Vc are exactly the same, so they can work in parallel.

[0045] In the inverter mode, energy is provided by the DC power supply DC. The DC / DC push-pull circuit works in the DC boost (Boost) mode. At this time, the MOSFET switching tubes Q1 and Q2 are the main tubes, working in high-frequency PWM modulation. The MOSFET switching tubes Q3~Q6 are synchronous rectifier tubes, boosting the DC voltage to the DC bus voltage BUS and applying it to both ends of Cb1 and Cb2, respectively forming +BUS and -BUS. In each high-frequency switching cycle, the synchronous rectifier tube turns on slightly later after the internal or externally added diode conducts, so that zero voltage switching (ZVS) can be achieved. The DC / AC full-bridge circuit works in the inverter mode. At the same time, the IGBT switching tubes Q7~Q10 are the main tubes, working in high-frequency SPWM modulation, converting the BUS voltage into a sine wave voltage output to provide energy to the single-phase AC power Vac or Va, Vc. In the single live wire power supply mode of Va and Vc, the main working waveforms are as Figure 6As shown, from top to bottom are the Q1 and Q2 drive signals, the BUS, +BUS, and -BUS voltages, the Q7~Q9 drive signals, Vac and Va, Vc, and the Va load current Io. Assume that Vc is under light load, and the Va load suddenly increases, that is, when Io has a step change from low to high, the corresponding +BUS has a transient undershoot, but can quickly return to the steady-state value. From the transient state to the recovery of the steady state, although the controller also participates in the regulation, in fact, the two secondary windings of the transformer TX in the DC / DC circuit can independently supply electrical energy to Cb1 and Cb2 through Q3~Q6. By designing the same number of turns of the two secondary windings, intrinsic natural voltage equalization can be achieved at both ends of Cb1 and Cb2. In the rectification mode, energy is provided by the AC power supply or the single-phase power Vac or Va, Vc of the power grid. The DC / AC full-bridge circuit operates in the rectification mode. Vac or Va, Vc passes through the filter capacitors Cf1 and Cf2 in the DC / AC circuit. The IGBT switching tubes Q7~Q10 are the main tubes and operate in high-frequency SPWM modulation for power factor correction (PFC) rectification to form the DC bus voltage BUS, which is applied to both ends of Cb1 and Cb2 to form +BUS and -BUS respectively. PFC has various control methods such as totem pole, bipolar, and unipolar, which will not be elaborated here. The DC / DC push-pull circuit operates in the DC buck (Buck) mode. At the same time, the MOSFET switching tubes Q3~Q6 are the main tubes and operate in high-frequency PWM modulation. The MOSFET switching tubes Q1 and Q2 are synchronous rectifier tubes. The BUS voltage provides energy to the DC power supply DC through the two resonant circuits composed of Ls1 and Cs1, Ls2 and Cs2 and TX. The rectification and charging can be carried out in a constant current or constant voltage manner. PWM modulation of DC / DC and SPWM modulation of DC / AC are traditional modulation measures, which will not be elaborated here. In fact, Ls1 and Cs1, Ls2 and Cs2 form two series resonant circuits. Optionally, further combining the excitation inductance of the high-frequency isolation transformer TX or an external inductor can also form a series-parallel resonant circuit.

[0046] As an implementation manner, the isolated DC / DC primary circuit uses a half-bridge form (HB), as shown in Embodiment 1 Figure 7 shown. Other circuits and controllers adopt Figures 2 - 6 a similar manner, and the working principle is basically the same as it, which will not be elaborated here.

[0047] As an implementation manner, the isolated DC / DC primary circuit uses a full-bridge form (FB), as shown in Embodiment 2 Figure 8 shown. Other circuits and controllers adopt Figures 2 - 6 a similar manner, and the working principle is basically the same as it, which will not be elaborated here.

[0048] As an implementation, the isolated DC / DC primary circuit uses a soft-switching resonant push-pull form (RPP). Example 3 is as shown in Figure 9 . Optionally, the DC / DC primary circuit adopts the Figures 7 - 8 circuit form, and its working principle is the same, which will not be elaborated here. Other circuits and controllers adopt the Figures 2 - 6 similar method, and their working principles are basically the same, which will not be elaborated here.

[0049] As an implementation, the isolated DC / DC primary circuit uses another type of resonant push-pull form (RPP). Example 4 is as shown in Figure 10 . Optionally, the DC / DC primary circuit adopts the Figures 7 - 8 circuit form, and its working principle is the same, which will not be elaborated here. Other circuits and controllers adopt the Figures 2 - 6 similar method, and their working principles are basically the same, which will not be elaborated here.

[0050] As an implementation, the isolated DC / DC secondary circuit uses another type of resonant technology, that is, compared with Figure 6 , Cs1 and Cs2 are removed. Example 5 is as shown in Figure 11 . Optionally, the DC / DC primary circuit adopts the Figures 7 - 10 circuit form, and its working principle is the same, which will not be elaborated here. Other circuits and controllers adopt the Figures 2 - 6 similar method, and their working principles are basically the same, which will not be elaborated here.

[0051] Actually, the isolated DC / DC circuit can also use other various isolated topologies. Optionally, the DC / DC circuit uses a half-bridge, full-bridge, flyback, forward, forward-flyback, etc., or combines resonant technologies such as LLC, LCC, LCLC, CLCL, basic series-parallel, etc. resonant circuits. Other circuits and controllers adopt the Figures 2 - 6 similar method, and their working principles are basically the same, which will not be elaborated here. It should be noted that the DC / DC circuit can also not adopt the resonant technology, but use the hard-switching push-pull, half-bridge and full-bridge of traditional PWM modulation, which does not affect the normal operation.

[0052] The above DC / DC circuits all use isolation type. Actually, Buck, Boost, Buck-Boost, Cuk, SEPIC, ZETA, etc. with DC voltage division non-isolation topologies can also be used. In Example 6, the non-isolated DC / DC circuit uses a bidirectional Buck / Boost circuit as shown in Figure 12 . When the power is transmitted for charging and discharging in both directions, this circuit can both step up and step down the voltage. Other circuits and controllers adopt the Figures 2 - 6 similar method, and their working principles are basically the same, which will not be elaborated here.

[0053] As an implementation manner, the DC / AC circuit uses another form. Embodiment 7 is as follows Figure 13 shown. Optionally, the DC / DC circuit adopts Figure 5 , Figures 7 - 12 circuit forms, and their working principles are the same, so they will not be elaborated here. Other circuits and controllers adopt Figures 2 - 6 similar manners, and their working principles are basically similar, so they will not be elaborated here. Optionally, the DC / AC circuit uses a half-bridge form. It should be noted that the DC / AC circuit can also adopt soft-switching resonance technology, which does not affect its normal operation.

[0054] As an implementation manner, other DC power supplies DC2 are connected to both the positive and negative terminals of the intermediate DC bus, namely Cb1 and Cb2, in Figure 2 , Figure 5 . Embodiment 8 is as follows Figure 14 shown. The other DC power supply DC2 is connected to the DC bus BUS through the corresponding Boost step-up DC / DC circuit. Optionally, the DC / DC circuit and the DC / AC circuit adopt Figure 5 , Figures 7 - 13 circuit forms, and their working principles are the same, so they will not be elaborated here. Other circuits and controllers adopt Figures 2 - 6 similar manners, and their working principles are basically similar, so they will not be elaborated here. Optionally, the corresponding DC / DC circuit for connecting other DC power supplies uses non-isolated or isolated topologies, including but not limited to non-isolated topologies such as Buck, Boost, Buck-Boost, Cuk, SEPIC, ZETA, etc., and isolated topologies such as half-bridge, full-bridge, push-pull, flyback, forward, forward-flyback, etc., and various resonance technologies can also be combined.

[0055] The specific experimental data and test results of each embodiment of the present invention are shown in Table 1 in detail. The test conditions are as follows: single-phase live wire power supply mode, the DC power supply DC uses a 48Vdc lithium battery, the AC voltages Va and Vc correspond to 120Va respectively, the SPWM switching frequency is 20kHz, and the PWM frequency is 50kHz. Electrical parameters of electronic components: MOSFET 6mΩ / 150V, 33mΩ / 650V, IGBT 50A / 650V, resonance inductor 10uH, resonance capacitor 47nF, AC filter inductor 1mH, AC filter capacitor 6.6uF.

[0056]

[0057] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirits of the present invention. The scope of the present invention is defined by the appended claims and their equivalent scopes.

Claims

1. A two-stage multi-mode bidirectional inverter circuit, characterized in that It includes a DC power supply DC, an AC power supply AC, a DC / DC circuit, a DC voltage-dividing capacitor Cb1, a DC voltage-dividing capacitor Cb2, a DC / AC circuit and a controller. Among them, the AC power supply AC includes an AC live wire L1, an AC live wire L2 and an AC neutral wire N; The positive pole of the first port of the DC / DC circuit is connected to the positive and negative poles of the DC power supply DC. The positive pole of the second port of the DC / DC circuit is connected to the positive pole of the DC voltage-dividing capacitor Cb1 and the positive pole of the DC port of the DC / AC circuit. The negative pole of the second port of the DC / DC circuit is connected to the negative pole of the DC voltage-dividing capacitor Cb1 and the negative pole of the DC port of the DC / AC circuit. The midpoint of the second port of the DC / DC circuit is connected to the negative pole of the DC voltage-dividing capacitor Cb1 and the positive pole of the DC voltage-dividing capacitor Cb2, and is connected to the AC neutral wire N. The AC ports of the DC / AC circuit are respectively connected to the AC live wire L1 and the AC live wire L2. The controller identifies the input and output power flow directions by sampling the AC and DC side voltage and current signals, and controls the DC / DC circuit and the DC / AC circuit to stabilize the output voltage or current, realizing bidirectional power conversion.

2. The two-stage multi-mode bidirectional inverter circuit according to claim 1, wherein The DC / DC circuit uses an isolated topology or a non-isolated topology with DC voltage division.

3. The two-stage multi-mode bidirectional inverter circuit according to claim 2, wherein The DC / DC circuit includes a high-frequency isolation transformer, and the transformer includes a primary winding and two secondary windings. The number of turns of the two secondary windings is the same, and in the single live wire or double live wire parallel power supply mode, the two DC capacitors are naturally voltage-equalized.

4. The two-stage multi-mode bidirectional inverter circuit according to claim 1, characterized in that, The DC / DC circuit and / or the DC / AC circuit adopt interleaved parallel connection or cascade connection, or adopt a multilevel circuit.

5. The two-stage multi-mode bidirectional inverter circuit according to claim 1, characterized in that, The DC / DC circuit and / or the DC / AC circuit adopt voltage mode control, average current mode control, peak current mode control, quasi-resonant control, single-cycle control, continuous conduction mode control of current, discontinuous conduction mode control of current or critical conduction mode control of current.

6. The two-stage multi-mode bidirectional inverter circuit according to claim 1, wherein, The controller dynamically obtains the voltage and current values of the DC power supply DC or the AC power supply AC, and compares the obtained current actual output value with the target value; according to the comparison result, dynamically confirms the adjustment instructions of the duty cycle and working state of the switching tubes in the DC / DC circuit and the DC / AC circuit; the controller controls the switching tubes in the DC / DC circuit and the DC / AC circuit to execute the instructions, dynamically controls the energy storage / discharge time, so that the current actual output value approaches the target value.

7. The two-stage multi-mode bidirectional inverter circuit according to claim 1, characterized in that The controller includes a sampling, conditioning and feedback circuit and a switching tube driving circuit.

8. The two-stage multi-mode bidirectional inverter circuit according to claim 7, wherein The DC / DC circuit operates in high-frequency pulse width modulation, and the DC / AC circuit operates in high-frequency sine wave pulse width modulation.

9. The two-stage multi-mode bidirectional inverter circuit according to claim 7, characterized in that, The controller is built with discrete electronic components or uses an integrated circuit.

10. The two-stage multi-mode bidirectional inverter circuit according to claim 1, wherein, The inverter circuit operates in the double live wire, single live wire, single live wire series and double live wire parallel power supply modes, and can flexibly switch between the 4 power supply modes.

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