Five-level bidirectional inverter

Abstract

Disclosed in the present invention is a five-level bidirectional inverter, comprising a controller and a bidirectional inverter circuit. The bidirectional inverter circuit comprises a direct current (DC), an alternating current (AC) filter capacitor Cf, an AC, a high-frequency vertical bridge arm, a power-frequency vertical bridge arm, a high-frequency horizontal bridge arm, and two DC filter capacitors. The high-frequency vertical bridge arm and the power-frequency vertical bridge arm are both formed by connecting two power switching transistors in series; the high-frequency horizontal bridge arm is formed by connecting two power switching transistors back-to-back in series; two ends of the high-frequency vertical bridge arm and two ends of the power-frequency vertical bridge arm are respectively connected to positive and negative electrodes of the DC; and the controller controls the bidirectional inverter circuit to work in an off-grid inverter mode, a grid-connected inverter mode or a rectification mode. In the present invention, the output voltage is at five levels, and the output equivalent frequency is four times the switching frequency, thereby improving the conversion efficiency of the inverter, reducing the output voltage or current harmonics, and reducing the volume of filter inductors; and the modulation method in the present invention is simple, so that the design of the controller can be simplified.

Description

Five-level bidirectional inverter Technical Field

[0001] This invention relates to the field of new energy power technology, and in particular to a five-level bidirectional inverter. Background Technology

[0002] DC-AC inverter topologies typically use a full-bridge circuit (i.e., a bidirectional H4 topology), as shown in Figure 1. This includes a DC filter capacitor Cdc, four power switches Q1~Q4 and their body diodes, AC filter inductors L1 and L2, and an AC filter capacitor Cf. The bidirectional H4 topology has significant advantages such as simple structure and mature control methods, and is widely used in industrial and residential inverters.

[0003] When the bidirectional H4 topology employs bipolar high-frequency sinusoidal pulse width modulation (SPWM), all four power switches operate in high-frequency switching mode, resulting in significant switching power consumption, particularly from the body diode's reverse recovery power consumption. This leads to low conversion efficiency and makes it difficult to increase the switching frequency. While unipolar or hybrid modulation methods can be used to improve efficiency, the output voltage becomes three-level, with the output equivalent frequency only twice the switching frequency. This results in a larger output filter inductance and further hinders efficiency improvements. Multilevel bidirectional inverter circuits have become a key research area in new energy power electronics, aiming to reduce switching power consumption and achieve smaller size. Summary of the Invention

[0004] The technical problem to be solved by the embodiments of the present invention is to provide a five-level bidirectional inverter to improve inverter conversion efficiency, reduce output voltage or current harmonics, and reduce the size of filter inductor.

[0005] To address the aforementioned technical problems, this invention proposes a five-level bidirectional inverter, comprising a controller and a bidirectional inverter circuit. The bidirectional inverter circuit includes a DC converter, an AC filter capacitor Cf, an AC converter, a high-frequency vertical bridge arm, a power frequency vertical bridge arm, a high-frequency horizontal bridge arm, and two DC filter capacitors.

[0006] Two DC filter capacitors are connected in series and then in parallel with the DC capacitor; the AC filter capacitor Cf is connected in parallel with the AC capacitor; both the high-frequency vertical bridge arm and the power frequency vertical bridge arm are composed of two power switching transistors connected in series, and the high-frequency horizontal bridge arm is composed of two power switching transistors connected in series back to back; the two ends of the high-frequency vertical bridge arm and the power frequency vertical bridge arm are respectively connected to the positive and negative terminals of the DC capacitor; one end of the high-frequency horizontal bridge arm is connected to the middle of the two DC filter capacitors, and the other end is connected to the midpoint of the high-frequency vertical bridge arm or the midpoint of the power frequency vertical bridge arm; the two ends of the AC capacitor are respectively connected to the midpoint of the high-frequency vertical bridge arm and the midpoint of the power frequency vertical bridge arm.

[0007] The controller controls the high-frequency vertical bridge arm, the power frequency vertical bridge arm, and the high-frequency horizontal bridge arm, enabling the bidirectional inverter circuit to operate in off-grid inverter mode, grid-connected inverter mode, or rectification mode.

[0008] Furthermore, the bidirectional inverter circuit also includes:

[0009] One AC filter inductor is used to connect the high-frequency vertical bridge arm midpoint or the power frequency vertical bridge arm midpoint to the AC circuit; or

[0010] Two AC filter inductors are connected to the AC circuit through one at the midpoint of the high-frequency vertical bridge arm and one at the midpoint of the power frequency vertical bridge arm.

[0011] Furthermore, when the sinusoidal alternating current is in the positive or negative half-cycle, one power switch of the high-frequency vertical bridge arm and the high-frequency horizontal bridge arm operates at high frequency, and the body diode of the other power switch of the high-frequency vertical bridge arm and the high-frequency horizontal bridge arm conducts freewheeling; the power switch of the power frequency vertical bridge arm operates at power frequency and conducts continuously.

[0012] Furthermore, the controller includes a drive unit, a control and waveform generation unit, a gating unit, and an AC / DC side voltage and inductor current sampling feedback circuit. The AC / DC side voltage and inductor current sampling feedback circuit is used to sample the AC side voltage, DC side voltage, and inductor current. The input terminal of the gating unit is connected to the output terminal of the AC / DC side voltage and inductor current sampling feedback circuit. The output terminal of the gating unit is connected to the input terminal of the control and waveform generation unit. The output terminal of the control and waveform generation unit is connected to the input terminal of the drive unit. The drive unit is connected to the high-frequency vertical bridge arm, the power frequency vertical bridge arm, and the high-frequency horizontal bridge arm. The control and waveform generation unit generates a PWM pulse width modulation drive signal, which controls the power switching transistors of the high-frequency vertical bridge arm, the power frequency vertical bridge arm, and the high-frequency horizontal bridge arm through the drive unit.

[0013] Furthermore, the AC / DC side voltage and inductor current sampling feedback circuit includes a voltage error amplifier U1, a current error amplifier U2, a voltage error amplifier U3, an amplifier U4, a multiplier U5, and resistors R1, R2, R3, and R4. Resistors R1 and R2 sample the AC side voltage and are connected to the negative input terminal of the voltage error amplifier U1. The positive input terminal of U1 is connected to an AC sinusoidal voltage reference signal. The output terminal of U1 is connected to the positive input terminal of the current error amplifier U2, and the inductor current sampling signal is connected to the negative input terminal of U2. The output of U2 is connected to one input of the gating unit; resistors R3 and R4 sample the DC side voltage and connect it to the negative input of voltage error amplifier U3; the positive input of U3 is connected to the DC voltage reference signal; the output of U3 is connected to one input of multiplier U5; the AC side voltage sampled by resistors R1 and R2 is connected to the other input of multiplier U5; the output of U5 is connected to the positive input of current error amplifier U4; the inductor current sampling signal is connected to the negative input of U4; and the output of U4 is connected to the other input of the gating unit.

[0014] Furthermore, the bidirectional inverter circuit has multiple sets, and the multiple sets of bidirectional inverter circuits operate in a two-phase or multi-phase interleaved parallel or series manner.

[0015] Furthermore, the AC is an AC power supply or an inverter load AC, and the DC is a DC power supply or a rectifier load DC.

[0016] The beneficial effects of the present invention are: (1) The output voltage of the present invention is five-level, realizing bidirectional power conversion, and the power factor is adjustable; (2) The output equivalent frequency of the present invention is four times the switching frequency, thereby improving the inverter conversion efficiency, reducing output voltage or current harmonics, and reducing the volume of the filter inductor; (3) The modulation method of the present invention is simple and can simplify the controller design. Attached Figure Description

[0017] Figure 1 is a circuit diagram of a traditional bidirectional full-bridge inverter circuit.

[0018] Figure 2 is a circuit diagram of a five-level bidirectional inverter according to an embodiment of the present invention.

[0019] Figure 3 is a circuit diagram of the five-level bidirectional inverter of Embodiment 1 of the present invention.

[0020] Figure 4 is a schematic diagram of the main operating waveforms of the five-level bidirectional inverter of Embodiment 1 of the present invention.

[0021] Figure 5 is a circuit diagram of the five-level bidirectional inverter circuit with a single filter inductor according to Embodiment 2 of the present invention. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] In this embodiment of the invention, directional indicators (such as up, down, left, right, front, back, etc.) are only used to explain the relative positional relationship and movement of each component in a specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0024] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features.

[0025] Referring to Figures 2-5, the five-level bidirectional inverter of this embodiment mainly consists of a bidirectional inverter circuit and its controller. The bidirectional inverter circuit includes a DC power supply or rectified load (DC), DC filter capacitors Cd1 and Cd2, AC filter inductors L1 and L2, AC filter capacitor Cf, an AC power supply or inverter load (AC), and three bridge arms: a high-frequency vertical bridge arm, a power frequency vertical bridge arm, and a high-frequency horizontal bridge arm. The vertical bridge arm consists of two power switches connected in series, and the horizontal bridge arm consists of two power switches connected back-to-back in series. The high-frequency and power frequency vertical bridge arms are connected to the positive and negative terminals of DC, respectively. The high-frequency horizontal bridge arm is connected to the midpoint "0" of Cd1 and Cd2 and the midpoint "1" of the high-frequency vertical bridge arm, respectively. The midpoint of the power frequency vertical bridge arm is "2". During the positive or negative half-cycle of the sinusoidal alternating current, one power switch of the high-frequency vertical bridge arm and the high-frequency horizontal bridge arm operates at high frequency, while the body diode of the other power switch conducts freewheeling; the power switch of the power frequency vertical bridge arm operates at power frequency and remains continuously conducting.

[0026] Bidirectional inverters are used for bidirectional DC-AC power conversion. They can flexibly operate in off-grid inverter (also known as passive inverter) mode, grid-connected inverter (also known as active inverter) mode, and rectification mode as needed. In inverter mode, power flows from the DC side (DC) to the AC side (AC). After internal logic processing and control, the controller outputs drive signals to the power switching transistors, enabling high-frequency switching using pulse width modulation (PWM). The DC voltage is filtered by Cd1 and Cd2 to form the DC midpoint voltage. This voltage is then switched at high frequency and power frequency by the three bridge arm power switching transistors, and further filtered by L1, L2, and Cf to finally generate a stable AC sinusoidal voltage or current. Because the bidirectional inverter circuit outputs a five-level voltage, its output equivalent frequency is four times the switching frequency, thereby improving the inverter's conversion efficiency, reducing output voltage or current harmonics, and decreasing the size of the filter inductor. Conversely, the flow of electrical energy from the AC side to the DC side is called rectification mode. Its power flow path is dual to that of the inverter mode, and its working principle is similar to that of the inverter mode, so it will not be elaborated here. Therefore, the inverter of this invention can achieve bidirectional power conversion.

[0027] The controller employs appropriate modulation methods to control the high-frequency vertical bridge arm, the power frequency vertical bridge arm, and the high-frequency horizontal bridge arm, enabling the bidirectional inverter circuit to operate in off-grid inverter mode, grid-connected inverter mode, or rectification mode, achieving a five-level output voltage for the bidirectional inverter circuit. The controller detects the AC output voltage or current to determine the input conditions and load status. After processing and calculation, it generates a PWM drive signal to control the high-frequency and power frequency switches of the power transistors, controlling the bidirectional inverter circuit to operate in inverter or rectification mode. Simultaneously, it achieves adjustable power factor and stabilizes the output voltage or current through closed-loop feedback.

[0028] Power switching transistors can be insulated gate bipolar transistors (IGBTs), metal oxide field-effect transistors (MOSFETs), or third-generation wide bandgap (WBG) power devices such as silicon carbide (SiC) and gallium nitride (GaN) MOSFETs. These fully controlled power switching transistors can also be used in combination.

[0029] The controller can be built using discrete electronic components or designed using application-specific integrated circuits (ASICs), such as analog control chips, software-programmable microcontrollers (MCUs), digital signal processors (DSPs), or programmable logic devices (FPGAs / CPLDs). The bidirectional inverter circuit can be implemented using discrete components or integrated circuits, or it can be integrated into the controller to form a large-scale hybrid integrated circuit. This highly integrated controller design can further reduce the size of the bidirectional inverter.

[0030] The output voltage of this invention is five-level, and the output equivalent frequency is four times the switching frequency, thereby improving the inverter conversion efficiency, reducing output voltage or current harmonics, and reducing the size of the filter inductor. Therefore, it has high industrial application value. This invention can be widely used in various bidirectional or unidirectional DC-AC inverter circuits, such as solar photovoltaic power generation, grid-connected and off-grid residential and industrial energy storage systems, portable mobile energy storage power supplies, uninterruptible power supplies, battery formation power supplies, regenerative aging power supplies, and electric vehicle motor drivers, as well as industrial power supplies and switching power supplies.

[0031] Example 1, as shown in Figure 3, mainly includes a DC power supply DC, DC filter capacitors Cd1 and Cd2, a high-frequency vertical bridge arm composed of power switches Q1 and Q2 and their internal or external body diodes DQ1 and DQ2 connected in series, a power frequency vertical bridge arm composed of power switches Q3 and Q4 and their internal or external body diodes DQ3 and DQ4 connected in series, a high-frequency horizontal bridge arm composed of power switches Q5 and Q6 and their internal or external body diodes DQ5 and DQ6 connected in series, AC double filter inductors L1 and L2, AC filter capacitor Cf, AC power supply AC, and a controller. The DC voltage Vdc is connected to one end of Cd1 and Cd2 respectively, and the other ends of Cd1 and Cd2 are connected to form the DC midpoint. The outlet of Q1 and the positive terminal of DQ1 are connected to the inlet of Q2 and the negative terminal of DQ2, also known as the midpoint of the high-frequency vertical bridge arm. This connection is then connected to one end of L1, the inlet of Q6, and the negative terminal of DQ6. The outlet of Q6 and the positive terminal of DQ6 are connected to the outlet of Q5 and the positive terminal of DQ5. The inlet of Q5 and the negative terminal of DQ5 are connected to the DC midpoint. The outlet of Q3 and the positive terminal of DQ3 are connected to the inlet of Q4 and the negative terminal of DQ4, also known as the midpoint of the power frequency vertical bridge arm, and this connection is then connected to one end of L2. Depending on the direction of current flow in or out of the fully controlled power switch, the inlet is the drain (D) of the MOSFET or the collector (C) of the IGBT, and the outlet is the source (S) of the MOSFET or the emitter (E) of the IGBT. The driving signal is the gate (G) of the MOSFET or IGBT. This principle applies to WBG devices such as SiC and GaN. The other ends of L1 and L2 are connected to Cf and the AC voltage Vac. The high-frequency vertical bridge arm and the high-frequency horizontal bridge arm operate with PWM high-frequency switching, while the power frequency vertical bridge arm operates with power frequency, or low frequency switching.

[0032] The controller consists of multiple functional units, including AC / DC side voltage and inductor current sampling feedback circuits. These circuits include voltage and current error amplifiers U1-U4, a multiplier U5, a gating unit U6, a control and waveform generation unit U7, a drive unit U8, an inductor current sampling device, and peripheral circuits. Resistors R1 and R2 sample the AC side voltage and connect it to the negative input of voltage error amplifier U1. The positive input of U1 is connected to the AC sinusoidal voltage reference signal Vra. The output of U1 is connected to the positive input of current error amplifier U2. The inductor current sampling signal Iac from the inductor current sampling device is connected to the negative input of U2, and the output of U2 is connected to the first input of gating unit U6. The inductor current sampling device can optionally be a current sensor, a current transformer, or a resistor. Resistors R3 and R4 sample the DC side voltage and connect it to the negative input of voltage error amplifier U3. The positive input of U3 is connected to the DC voltage reference signal Vrd. The output of U3 is connected to the first input of multiplier U5. The AC side voltages sampled by R1 and R2 are simultaneously connected to the second input of U5. The output of U5 is connected to the positive input of current error amplifier U4. The inductor current sampling signal Iac is connected to the negative input of U4. The output of U4 is connected to the second input of gating unit U6. The output of U6 is connected to the input of control and waveform generation unit U7. U6 receives commands to determine the AC / DC power flow direction and detects the AC / DC voltage amplitude to determine the operating mode. The output of control and waveform generation unit U7 is connected to the input of drive unit U8, thereby generating a PWM pulse width modulation drive signal, which then drives the power switching transistors Q1~Q6 of the switching bridge arm through the output of U8.

[0033] In inverter mode, the power flow path is as follows: DC power is filtered by capacitors Cd1 and Cd2 and then supplied to the three bridge arms. The controller outputs a PWM signal, which is then amplified by the drive circuit and supplied to the power switches Q1~Q6, corresponding to the positive and negative half-cycles of the sinusoidal AC power supply, respectively. This generates a sinusoidal pulse width modulation (SPWM) high-frequency square wave and a power frequency square wave, which are then filtered by L1 and L2 and further filtered by Cf to generate an AC sine wave. This allows for operation in both off-grid and grid-connected inverter modes. In off-grid inverter mode, the generated AC voltage is supplied to the inverter load; in grid-connected inverter mode, the generated AC current is supplied to the grid, thus forming AC. U1 samples the AC output voltage Vac and adjusts the inverter output voltage to achieve voltage regulation through a corresponding voltage outer-loop proportional-integral (PI) compensation design. U2 samples the current Iac of the filter inductor L2 and, through a corresponding current inner-loop proportional-integral (PI) compensation design, can be controlled in average current mode or peak current mode, thereby improving its dynamic response performance. It should be noted that the voltage error amplifier and current error amplifier in the controller can employ second-order or multi-order PI compensation, proportional-integral-derivative (PID) control, or other intelligent control methods. Optionally, the controller can also employ other control methods, such as quasi-resonant control, single-cycle control, continuous current conduction mode (CCM), discontinuous current conduction mode (DCM), critical current conduction mode (CRM), etc., without affecting its electrical performance and effect. The power flow path in rectification mode is dual to that in inverter mode, and the working principle is similar, so it will not be elaborated further here.

[0034] In inverter mode, with the sinusoidal AC current in its positive half-cycle, Q1 operates as a high-frequency switch, Q5 is continuously on or operating as a high-frequency switch. When Q1 and Q5 are operating, their duty cycles, as well as DQ2 and DQ6, change according to a two-stage SPWM pattern. Q4 is continuously on, and Q3 is continuously off. Optionally, Q2 and Q6 can operate in synchronous rectification mode, and in each switching cycle, DQ2 and DQ6 are turned on slightly after being turned on, thus achieving zero-voltage switching (ZVS) for Q2 and Q6. The main operating waveforms are shown in Figure 4, from top to bottom: the drive signals for power switches Q1~Q6, the voltage difference V12 between the midpoint of the high-frequency and mains frequency vertical bridge arms, the AC output voltage VAC, and the currents iL1 and iL2 of the filter inductors L1 and L2.

[0035] When |VAC|>1 / 2*Vdc, Q3 remains off, Q4 and Q5 operate in power frequency mode and remain on, and Q1 operates in the first high-frequency SPWM mode with a duty cycle of D∙sin(ωt+θ), where ω is the angular frequency of the sinusoidal AC current and θ is the phase angle of the sinusoidal AC current. It should be noted that Q1~Q6 can utilize their body diodes DQ1~DQ6 or be connected in parallel with external diodes. When Q1 is on, Vdc provides power to the AC through Q4 and stores energy in L1 and L2. When Q1 is off, the energy stored in L1 and L2 discharges into the AC through Q4, Q5, and DQ6, resulting in two voltage levels: "+Vdc" and "+1 / 2Vdc". When |VAC| < 1 / 2 * Vdc, Q1 is off, Q3 remains off, Q4 continues to conduct in power frequency mode, and Q5 and DQ6 operate in the second high-frequency SPWM mode, with a duty cycle still D∙sin(ωt+θ). When Q5 is on, the voltage Vc2 of the filter capacitor Cd2 continues to supply power to the AC through Q4, and also continues to store power for L1 and L2. When Q5 is off, the stored power in L1 and L2 discharges into the AC through Q4 and DQ2, thus V12 has two levels: "+1 / 2Vdc" and "0". Therefore, during the positive half-cycle of the sinusoidal AC current, V12 has three levels: "+Vdc", "+1 / 2Vdc", and "0".

[0036] During the negative half-cycle of the sinusoidal AC current, high-frequency switch Q2 operates, and either Q6 remains continuously on or operates at its high-frequency level. When Q2 and Q6 are operating, their duty cycles, as well as DQ1 and DQ5, change according to a two-stage SPWM pattern. Q3 remains continuously on, and Q4 remains continuously off. Optionally, Q1 and Q5 can operate in synchronous rectification mode (ZVS). Similarly, when |VAC|>1 / 2*Vdc, V12 has two voltage levels: "-Vdc" and "-1 / 2Vdc"; when |VAC|<1 / 2*Vdc, V12 has two voltage levels: "-1 / 2Vdc" and "0". Therefore, during the negative half-cycle of the sinusoidal AC current, V12 has three voltage levels: "-Vdc", "-1 / 2Vdc", and "0".

[0037] In summary, in inverter mode and throughout the entire cycle of a sinusoidal AC current, V12 in the bidirectional inverter circuit has five voltage levels: "+Vdc", "+1 / 2Vdc", "0", "-1 / 2Vdc", and "-Vdc". Based on the inductor volt-second balance principle, the instantaneous AC value can be derived. .

[0038] The rectification mode and inverter mode are dual, and their working principles are similar. In rectification mode, when the sinusoidal AC current is in its positive half-cycle, the high-frequency switch Q2 operates, and Q6 is continuously conducting or operating. When the high-frequency switches Q2 and Q6 are operating, their duty cycles and DQ1 and DQ5 change according to the two-stage SPWM rule. Q4 is continuously conducting, and Q3 is continuously off. Optionally, Q1 and Q5 can operate in synchronous rectification mode to achieve ZVS. Similarly, when |VAC|>1 / 2*Vdc, V12 has two levels: "+Vdc" and "+1 / 2Vdc". When |VAC|<1 / 2*Vdc, V12 has two levels: "+1 / 2Vdc" and "0". Therefore, during the positive half-cycle of the sinusoidal AC current, V12 has three levels: "+Vdc", "+1 / 2Vdc", and "0". During the negative half-cycle of the sinusoidal AC current, high-frequency switch Q1 operates, and either Q5 remains continuously on or operates at its own high-frequency level. When Q1 and Q5 are operating, their duty cycles, as well as DQ2 and DQ6, change according to a two-stage SPWM pattern. Q3 remains continuously on, and Q4 remains continuously off. Optionally, Q2 and Q6 can operate in synchronous rectification mode to achieve ZVS. Similarly, when |VAC|>1 / 2*Vdc, V12 has two voltage levels: "-Vdc" and "-1 / 2Vdc"; when |VAC|<1 / 2*Vdc, V12 has two voltage levels: "-1 / 2Vdc" and "0". Therefore, during the positive half-cycle of the sinusoidal AC current, V12 has three voltage levels: "-Vdc", "-1 / 2Vdc", and "0". In summary, in rectification mode and throughout the entire cycle of a sinusoidal AC current, V12 in the bidirectional inverter circuit has five voltage levels: "+Vdc", "+1 / 2Vdc", "0", "-1 / 2Vdc", and "-Vdc". Based on the inductor volt-second balance principle, the DC voltage can be calculated. .

[0039] In Example 2, optionally, L2 is removed from Figure 3, thus forming a single-filter inductor five-level bidirectional inverter circuit, as shown in Figure 5. The electromagnetic compatibility (EMC) performance of the single-filter inductor bidirectional inverter circuit is slightly worse than that of the double-filter inductor circuit, but the component cost is lower, and relatively improved interference suppression measures are required. For simplicity, internal or external diodes are not shown on any of the power switches; their operating principle and modulation method are basically similar to those in Figures 2-4, and will not be described again here.

[0040] In Example 3, optionally, L1 is removed from Figure 3, thus forming another single-filter inductor five-level bidirectional inverter circuit. Its working principle and modulation method are basically similar to those in Figures 2-4, and will not be described again here.

[0041] In Example 4, optionally, the high-frequency horizontal bridge arm in Figure 3 can also be reconnected between the midpoint "2" of the power frequency vertical bridge arm and the DC midpoint "0". The high-frequency and power frequency of the vertical bridge arm are interchanged, that is, Q1 and Q2 constitute the power frequency vertical bridge arm, and Q3 and Q4 constitute the high-frequency vertical bridge arm. Therefore, a new bidirectional inverter circuit with dual-filter inductors and single-filter inductors can also be formed. Its working principle and modulation method are basically similar to those in Figures 2 to 4, and will not be described again here.

[0042] It should be noted that the above embodiments are all for a single bidirectional inverter circuit. In reality, these inverter circuits can operate in a two-phase or multi-phase interleaved parallel or series configuration to achieve higher power or higher voltage levels. Their working principle and modulation method are basically similar to those in Figures 2 and 3, and will not be described again here.

[0043] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A five-level bidirectional inverter, characterized in that, The system includes a controller and a bidirectional inverter circuit. The bidirectional inverter circuit includes DC and AC filter capacitors Cf, AC, a high-frequency vertical bridge arm, a power frequency vertical bridge arm, a high-frequency horizontal bridge arm, and two DC filter capacitors. Two DC filter capacitors are connected in series and then in parallel with the DC capacitor; the AC filter capacitor Cf is connected in parallel with the AC capacitor; both the high-frequency vertical bridge arm and the power frequency vertical bridge arm are composed of two power switching transistors connected in series, and the high-frequency horizontal bridge arm is composed of two power switching transistors connected in series back to back; the two ends of the high-frequency vertical bridge arm and the power frequency vertical bridge arm are respectively connected to the positive and negative terminals of the DC capacitor; one end of the high-frequency horizontal bridge arm is connected to the middle of the two DC filter capacitors, and the other end is connected to the midpoint of the high-frequency vertical bridge arm or the midpoint of the power frequency vertical bridge arm; the two ends of the AC capacitor are respectively connected to the midpoint of the high-frequency vertical bridge arm and the midpoint of the power frequency vertical bridge arm. The controller controls the high-frequency vertical bridge arm, the power frequency vertical bridge arm, and the high-frequency horizontal bridge arm, enabling the bidirectional inverter circuit to operate in off-grid inverter mode, grid-connected inverter mode, or rectification mode.

2. The five-level bidirectional inverter as described in claim 1, characterized in that, The bidirectional inverter circuit also includes: One AC filter inductor is used to connect the high-frequency vertical bridge arm midpoint or the power frequency vertical bridge arm midpoint to the AC circuit; or Two AC filter inductors are connected to the AC circuit through one at the midpoint of the high-frequency vertical bridge arm and one at the midpoint of the power frequency vertical bridge arm.

3. The five-level bidirectional inverter as described in claim 1, characterized in that, When the sinusoidal alternating current is in the positive or negative half-cycle, one power switch of the high-frequency vertical bridge arm and the high-frequency horizontal bridge arm operates at high frequency, and the body diode of the other power switch of the high-frequency vertical bridge arm and the high-frequency horizontal bridge arm conducts freewheeling current; the power switch of the power frequency vertical bridge arm operates at power frequency and conducts continuously.

4. The five-level bidirectional inverter as described in claim 1, characterized in that, The controller includes a drive unit, a control and waveform generation unit, a gating unit, and an AC / DC side voltage and inductor current sampling feedback circuit. The AC / DC side voltage and inductor current sampling feedback circuit is used to sample the AC side voltage, DC side voltage, and inductor current. The input terminal of the gating unit is connected to the output terminal of the AC / DC side voltage and inductor current sampling feedback circuit. The output terminal of the gating unit is connected to the input terminal of the control and waveform generation unit. The output terminal of the control and waveform generation unit is connected to the input terminal of the drive unit. The drive unit is connected to the high-frequency vertical bridge arm, the power frequency vertical bridge arm, and the high-frequency horizontal bridge arm. The control and waveform generation unit generates a PWM pulse width modulation drive signal, which controls the power switching transistors of the high-frequency vertical bridge arm, the power frequency vertical bridge arm, and the high-frequency horizontal bridge arm through the drive unit.

5. The five-level bidirectional inverter as described in claim 4, characterized in that, The AC / DC side voltage and inductor current sampling feedback circuit includes a voltage error amplifier U1, a current error amplifier U2, a voltage error amplifier U3, an amplifier U4, a multiplier U5, and resistors R1, R2, R3, and R4. Resistors R1 and R2 sample the AC side voltage and connect to the negative input of voltage error amplifier U1. The positive input of U1 is connected to an AC sinusoidal voltage reference signal. The output of U1 is connected to the positive input of current error amplifier U2. The inductor current sampling signal is connected to the negative input of U2, and the output of U2 is connected to one input of the gating unit. Resistors R3 and R4 sample the DC side voltage and connect to the negative input of voltage error amplifier U3. The positive input of U3 is connected to a DC voltage reference signal, and the output of U3 is connected to one input of multiplier U5. The AC side voltage sampled by resistors R1 and R2 is simultaneously connected to the other input of multiplier U5. The output of U5 is connected to the positive input of current error amplifier U4. The inductor current sampling signal is connected to the negative input of U4, and the output of U4 is connected to the other input of the gating unit.

6. The five-level bidirectional inverter as described in claim 1, characterized in that, The bidirectional inverter circuit has multiple sets, and the multiple sets of bidirectional inverter circuits work in a two-phase or multi-phase interleaved parallel or series manner.

7. The five-level bidirectional inverter as described in claim 1, characterized in that, The AC is an AC power supply or an inverter load AC, and the DC is a DC power supply or a rectifier load DC.

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