Hybrid multilevel bidirectional split-phase inverter

Abstract

Disclosed in embodiments of the present invention is a hybrid multilevel bidirectional split-phase inverter, comprising a bidirectional inverter circuit and a controller, wherein the bidirectional inverter circuit comprises a direct current (DC), two alternating currents (ACs), two DC filter capacitors, two AC filter inductors, two AC filter capacitors, two vertical bridge arms and two horizontal bridge arms; each vertical bridge arm consists of two power switch transistors connected back-to-back in series, and each horizontal bridge arm consists of two power switch transistors connected back-to-back in series; and the controller collects AC and DC side voltage and current signals, flexibly switches between several modes, and stabilizes the output voltage or current. In the present invention, the output voltage is five-level in a dual-live-wire mode or in a single-phase power system, and the output voltage is three-level in a single-live-wire or parallel dual-live-wire mode. In the present invention, the output equivalent frequency is several times higher than the switching frequency, thereby improving the conversion efficiency of the inverter, reducing the output voltage or current harmonics, and decreasing the size of the filter inductors. Therefore, the present invention has high industrial application value.

Description

Hybrid multilevel bidirectional split-phase inverter Technical Field

[0001] This invention relates to the field of new energy power electronics technology, and in particular to a hybrid multilevel bidirectional split-phase inverter. Background Technology

[0002] In North American renewable energy power supply systems, dual live wire (L1-L2), single live wire (L1-N and / or L2-N), or dual live wire parallel (L1 / L2-N) modes are used. These modes can be flexibly switched and bidirectional power conversion can be achieved. Therefore, the design of bidirectional split-phase inverters is relatively complex.

[0003] Bidirectional split-phase inverters typically use symmetrical inverter circuits, as shown in Figure 1. This circuit includes two DC filter capacitors Cd1 and Cd2, four power switching transistors Q1~Q4 and their body diodes, AC filter inductors L1 and L2, and AC filter capacitors Cf1 and Cf2. The conversion of DC to AC power is called inversion, and the conversion of AC to DC power is called rectification. In inverter operating mode: in dual-wire mode or single-phase power system, Cd1, Cd2, and Cf1, Cf2 are connected in series for filtering. Q1~Q4 form a traditional bidirectional full-bridge inverter circuit. L1 and L2 are connected in series for filtering, providing power to the series-connected AC power supplies Va and Vc. Simultaneously, the loads RL1 and RL2 are connected in series and obtain power from the two live wires without going through the neutral (N) wire. In single-wire mode, Cd1, Q1, Q2, L1, and Cf1 form the first bidirectional half-bridge inverter circuit, and Cd2, Q3, Q4, L2, and Cf2 form the second bidirectional half-bridge inverter circuit, thus forming a bidirectional split-phase inverter circuit. Both circuits supply power to Va, RL1 and Vc, RL2 respectively through the N line.

[0004] The dual-wire parallel mode is similar to the single-wire mode, still forming a bidirectional split-phase inverter circuit. The only difference is that the two wires are directly connected in parallel, therefore the amplitude, frequency, and phase of the two sets of single-phase AC voltages must be exactly the same. Conversely, the rectification mode is similar, and will not be elaborated here. Traditional split-phase inverter circuits can achieve bidirectional power conversion and have the main advantages of simple circuit structure and mature modulation methods.

[0005] Traditional bidirectional split-phase inverter circuits are simple to control, but regardless of whether they operate in dual-wire or single-wire mode, they must employ bipolar high-frequency sinusoidal pulse width modulation (SPWM). All four power switches operate in high-frequency switching mode, resulting in significant switching power consumption, especially in the body diode's reverse recovery mode, leading to low conversion efficiency. Furthermore, the output voltage is limited to only two levels—"+Vdc" and "-Vdc" or "+1 / 2Vdc" and "-1 / 2Vdc"—in different modes. The output frequency is equivalent to the switching frequency, resulting in a large output filter inductor and making it difficult to further improve conversion efficiency. Multilevel bidirectional split-phase inverter circuits have become a key research focus in the field of new energy power electronics, aiming to reduce switching power consumption, achieve smaller size, and flexibly switch between multiple modes. Summary of the Invention

[0006] The technical problem to be solved by the embodiments of the present invention is to provide a hybrid multilevel bidirectional split-phase inverter to improve inverter conversion efficiency and reduce output voltage or current harmonics.

[0007] To address the aforementioned technical problems, this invention proposes a hybrid multilevel bidirectional split-phase inverter, comprising a bidirectional inverter circuit and a controller. The bidirectional inverter circuit includes a DC converter, two sets of AC converters, two DC filter capacitors, two AC filter inductors, two sets of AC filter capacitors, two vertical bridge arms, and two horizontal bridge arms. The two DC filter capacitors are connected in series and then in parallel with the DC converter. The two sets of AC filter capacitors are connected in parallel with the two sets of AC converters, respectively. Each vertical bridge arm is composed of two power switching transistors connected in series, and each horizontal bridge arm is composed of two power switching transistors connected back-to-back in series. The two ends of the two vertical bridge arms are respectively connected to the positive and negative terminals of the DC converter. One end of each of the two horizontal bridge arms is connected to the midpoint of the two vertical bridge arms, and the other end of each horizontal bridge arm is connected to the middle of the two DC filter capacitors. Each midpoint of the two vertical bridge arms is connected to the live wire of the two sets of AC converters through an AC filter inductor.

[0008] The controller collects AC and DC side voltage and current signals, controls the two vertical bridge arms and the two horizontal bridge arms, so that the bidirectional inverter circuit can operate in off-grid inverter mode, grid-connected inverter mode or rectification mode, and stabilize the output voltage or current.

[0009] Furthermore, the DC is a DC-side power supply or a rectifier load DC, and the AC is an AC-side power supply or an inverter load AC; the two sets of AC form a single-live-wire or dual-live-wire parallel mode, or a dual-live-wire mode or a single-phase power system.

[0010] Furthermore, the controller controls the bidirectional inverter circuit to output a five-level voltage in dual-wire mode or single-phase power system, and a three-level voltage in single-wire or dual-wire parallel mode.

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

[0012] Furthermore, the controller includes a gating unit, a drive unit, an inverter control circuit, and a rectifier control circuit. The inverter control circuit consists of a control and waveform generation unit U5 and two symmetrical AC output voltage and current sampling and feedback circuits. The rectifier control circuit consists of a control and waveform generation unit U11, a DC output voltage sampling and feedback circuit, and two symmetrical AC input current sampling and feedback circuits. The two input terminals of the gating unit are respectively connected to the output terminals of the control and waveform generation unit U5 and the control and waveform generation unit U11. The gating unit is connected to the drive unit, the inverter control circuit, and the rectifier control circuit. The drive unit drives the power switching transistors of the two vertical bridge arms and the two horizontal bridge arms.

[0013] Furthermore, the AC output voltage and current sampling and feedback circuit includes a voltage error amplifier U1, a current error amplifier U3, resistors R5 and R6, a voltage compensator PI1, and a current compensator PI3. Resistors R5 and R6 are connected in series to sample the AC output voltage. The negative input terminal of the voltage error amplifier U1 is connected between resistors R5 and R6. The positive input terminal of the voltage error amplifier U1 is connected to an AC sinusoidal voltage reference signal. The output terminal of the voltage error amplifier U1 is connected to the positive input terminal of the current error amplifier U3. The negative input terminal of the current error amplifier U3 samples the current signal of one of the AC filter inductors. The output terminal of the current error amplifier U3 is connected to one of the input terminals of the control and waveform generation unit U5. The two ends of the voltage compensator PI1 are respectively connected to the negative input terminal and the output terminal of the voltage error amplifier U1, and the two ends of the current compensator PI3 are respectively connected to the negative input terminal and the output terminal of the current error amplifier U3.

[0014] Furthermore, the DC output voltage sampling and feedback circuit includes resistors R3 and R4, a voltage error amplifier U6, and a voltage compensator PI5. Resistors R3 and R4 are used to sample the DC output voltage. The negative input terminal of the voltage error amplifier U6 is connected between resistors R3 and R4, the positive input terminal of the voltage error amplifier U6 is connected to the DC voltage reference signal, and the output terminal of the voltage error amplifier U6 is connected to the input terminals of the two AC input current sampling and feedback circuits. The two ends of the voltage compensator PI5 are connected to the negative input terminal and the output terminal of the voltage error amplifier U6, respectively.

[0015] Furthermore, the AC input current sampling and feedback circuit includes a multiplier U7, a current error amplifier U9, and a current compensator PI6. One input terminal of the multiplier U7 is connected to the output terminal of the voltage error amplifier U6. Resistors R5 and R6 sample the AC input voltage and are connected to the other input terminal of the multiplier U7. The output terminal of the multiplier U7 is connected to the positive input terminal of the current error amplifier U9. The negative input terminal of the current error amplifier U9 samples the current signal of one of the AC filter inductors. The output terminal of the current error amplifier U9 is connected to one input terminal of the control and waveform generation unit U11. The two ends of the current compensator PI6 are connected to the output terminal and the negative input terminal of the current error amplifier U9, respectively.

[0016] Furthermore, the bidirectional inverter circuit includes four or more even-numbered AC filter inductors, vertical bridge arms, and horizontal bridge arms. The multiple sets of vertical bridge arms and horizontal bridge arms are interleaved and connected in parallel to form a multi-phase interleaved parallel bidirectional split-phase inverter circuit.

[0017] The beneficial effects of this invention are as follows: the output voltage of this invention is five-level or three-level, realizing bidirectional power conversion, and the power factor is adjustable; the output equivalent frequency of this invention is several times the switching frequency, thereby improving the inverter conversion efficiency, reducing output voltage or current harmonics, and reducing the size of the filter inductor; this invention contains an active clamping function, further reducing common-mode leakage current and improving the safety of inverter operation and personal operation; this invention operates in dual-live-wire, single-live-wire, dual-live-wire parallel mode, or single-phase power system, and can flexibly switch between several modes; the modulation method of this invention is simple and can simplify controller design. Attached Figure Description

[0018] Figure 1 is a circuit diagram of a traditional bidirectional split-phase inverter circuit.

[0019] Figure 2 is a circuit diagram of the hybrid multilevel bidirectional split-phase inverter according to an embodiment of the present invention.

[0020] Figure 3 is a circuit diagram of the hybrid multilevel bidirectional split-phase inverter of Embodiment 1 of the present invention.

[0021] Figure 4 is a diagram of the main operating waveforms of Embodiment 1 of the present invention in dual-wire mode or single-phase power system.

[0022] Figure 5 is a diagram of the main operating waveforms of Embodiment 1 of the present invention in single-wire or dual-wire parallel mode.

[0023] Figure 6 is a circuit diagram of the hybrid multilevel bidirectional split-phase inverter of Embodiment 2 of the present invention. Detailed Implementation

[0024] 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.

[0025] 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.

[0026] 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.

[0027] Please refer to Figures 2 to 6. The hybrid multilevel bidirectional split-phase inverter of this invention includes a bidirectional inverter circuit and a controller.

[0028] 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 capacitors Cf1 and Cf2, an AC power supply or inverter load (AC), and four bridge arms: two vertical bridge arms and two horizontal bridge arms. Each vertical bridge arm consists of two power transistors connected in series, and each horizontal bridge arm consists of two power transistors connected back-to-back in series. The two vertical bridge arms are connected to the positive and negative terminals of the DC power supply, respectively. The two horizontal bridge arms are connected to the midpoints of Cd1 and Cd2, and the midpoint of each vertical bridge arm, respectively. Vertical bridge arms 1 and 2 are connected to the live wire via L1 and L2, respectively, and are called the live wire bridge arms. Horizontal bridge arms 1 and 2 are connected to the midpoints of Cd1 and Cd2, respectively. During the positive or negative half-cycle of the sinusoidal alternating current, the high-frequency switch of the power switch tube in the vertical bridge arm is working or continuously conducting for part of the time, while one power switch tube in the horizontal bridge arm is working at the power frequency, and the body diode of the other power switch tube is conducting with freewheeling current.

[0029] The inverter of this invention is used for bidirectional DC-AC power conversion and can flexibly operate in off-grid inverter (also known as passive inverter) and grid-connected inverter (also known as active inverter) modes as needed, as well as rectification mode. The power flow path (inverting) of electrical energy from DC power supply to AC power supply is as follows: In dual-wire mode or single-phase power system, Cf1 and Cf2 are filtered in series, and the vertical bridge arms 1 and 2 and the horizontal bridge arms 1 and 2 constitute an inverter circuit. After passing through two series-connected filter inductors L1 and L2, electrical energy is provided to the series-connected AC power supply Va and Vc. At the same time, the loads RL1 and RL2 are connected in series and obtain electrical energy from the two live wires without passing through the neutral wire. In single-wire mode, vertical bridge arm 1 and horizontal bridge arm 1, along with filter inductor L1 and AC filter capacitor Cf1, constitute the first inverter circuit; vertical bridge arm 2 and horizontal bridge arm 2, along with filter inductor L2 and AC filter capacitor Cf2, constitute the second inverter circuit, thus forming a split-phase inverter circuit. Both circuits supply power to Va, RL1 and Vc, RL2 respectively via the neutral (N) line. To accommodate different load types, the amplitude, frequency, and phase of the two single-phase AC voltages in single-wire mode can be different. The dual-wire parallel mode is similar to the single-wire mode, still forming a split-phase inverter circuit. The difference is that the two wires are directly connected in parallel; therefore, the amplitude, frequency, and phase of the two single-phase AC voltages must be exactly the same.

[0030] The controller of this invention employs a corresponding modulation method. The bidirectional inverter circuit outputs a five-level voltage in dual-wire mode or a single-phase system, and a three-level voltage in single-wire or dual-wire parallel mode, hence the term "hybrid multi-level." The controller detects the AC output voltage or current to determine the input conditions and load status. After processing and calculation, it generates a drive signal for the four bridge arm power switches, enabling high-frequency switching using sinusoidal pulse width modulation (SPWM). 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 power switches, and further filtered by L1, L2, and Cf1 and Cf2, ultimately providing a stable voltage or current to the AC power supply Va, Vc or the AC load RL1, RL2. Because the bidirectional inverter circuit outputs a hybrid multi-level voltage, its output equivalent frequency is several 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. Since the AC neutral (N) line is directly connected to the DC neutral point, it effectively incorporates an active clamping function, thereby further reducing common-mode leakage current and improving inverter operation and operator safety. Conversely, the power flow path (rectification) of electrical energy from AC to DC power sources and its working principle are similar, and will not be elaborated upon here.

[0031] Therefore, this invention can achieve bidirectional power conversion. By sampling the AC and DC side voltage and current signals, the controller identifies the input and output power flow direction, automatically operates in inverter or rectification mode, and determines the conditions to control the high-frequency and power frequency switching of the power switching transistors. At the same time, it achieves adjustable power factor and stabilizes the output voltage or current through closed-loop feedback.

[0032] The power switching transistors of the present invention can be insulated gate bipolar transistors (IGBTs), metal oxide field-effect transistors (MOSFETs), and can be replaced with third-generation wide bandgap (WBG) power devices, such as silicon carbide (SiC) MOSFETs, gallium nitride (GaN) MOSFETs, etc., or these fully controllable power switching transistors can be used in combination.

[0033] The controller of this invention can be built using discrete electronic components or designed using application-specific integrated circuits, such as analog control chips, software-programmable microcontrollers (MCUs), digital signal processors (DSPs), or programmable logic devices (FPGAs / CPLDs). The bidirectional inverter circuit of this invention 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.

[0034] This invention can be widely applied to various bidirectional or unidirectional DC-AC inverter circuits, such as new energy systems like solar photovoltaic power generation, grid-connected and off-grid residential and industrial energy storage, portable mobile energy storage power supplies, uninterruptible power supplies, battery formation power supplies, regenerative aging power supplies, electric vehicle motor drives, as well as industrial power supplies, switching power supplies, etc.

[0035] Example 1: As shown in Figure 3, the hybrid multilevel bidirectional split-phase inverter of this embodiment mainly includes a DC power supply DC, DC filter capacitors Cd1 and Cd2, vertical bridge arms 1 and 2 and horizontal bridge arms 1 and 2, AC filter inductors L1 and L2, AC filter capacitors Cf1 and Cf2, AC power supplies Va and Vc for grid-connected power generation of new energy sources, AC loads RL1 and RL2 for off-grid or other applications, and a controller. Power switches Q1 and Q2, along with their internal or external diodes DQ1 and DQ2, are connected in series to form vertical bridge arm 1. Power switches Q3 and Q4, along with their internal or external diodes DQ3 and DQ4, are connected in series to form vertical bridge arm 2. Power switches Q5 and Q6, along with their internal or external diodes DQ5 and DQ6, are connected back-to-back in series to form horizontal bridge arm 1. Power switches Q7 and Q8, along with their internal or external diodes DQ7 and DQ8, are connected back-to-back in series to form horizontal bridge arm 2. The DC voltage Vdc is connected to one end of Cd1 and Cd2 respectively. The other ends of Cd1 and Cd2 are connected to form the DC midpoint or AC neutral line "N". The outlet of Q1 and the positive terminal of DQ1 are connected to the inlet of Q2 and the negative terminal of DQ2, which is also called the midpoint of vertical bridge arm 1. It is connected to one end of L1 and 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 "N". The outlet of Q3 and the positive terminal of DQ3 are connected to the inlet of Q4 and the negative terminal of DQ4, which is also called the midpoint of vertical bridge arm 2. It is connected to one end of L2 and the inlet of Q8 and the negative terminal of DQ8. The outlet of Q8 and the positive terminal of DQ8 are connected to the outlet of Q7 and the positive terminal of DQ7. The inlet of Q7 and the negative terminal of DQ7 are connected to "N". Based on the direction of current inflow or outflow in a fully controlled power switch, the inflow terminal is the drain (D) of the MOSFET or the collector (C) of the IGBT, and the outflow terminal is the source (S) of the MOSFET or the emitter (E) of the IGBT. The drive signal is the gate (G) of the MOSFET or IGBT. The same principle applies to WBG devices such as SiC and GaN. The other end of L1 and L2 is connected to one end of Cf1 and Cf2 and the two live wires of the AC voltage Vac. The other end of Cf1 and Cf2 is connected to "N".

[0036] In dual-wire mode or single-phase power system, Cf1 and Cf2 are filtered in series. The vertical bridge arms 1 and 2 and the horizontal bridge arms 1 and 2 form an inverter circuit. Through two series-filtered inductors L1 and L2, power is supplied to the series-connected AC power supply Va and Vc. At the same time, the loads RL1 and RL2 are connected in series and obtain power from the two live wires without going through the neutral wire.

[0037] In single-wire mode, vertical bridge arm 1 and horizontal bridge arm 1, filter inductor L1 and AC filter capacitor Cf1 constitute the first inverter circuit; vertical bridge arm 2 and horizontal bridge arm 2, filter inductor L2 and AC filter capacitor Cf2 constitute the second inverter circuit, thus forming a split-phase inverter circuit. The two circuits supply power to Va, RL1 and Vc, RL2 respectively through the N line.

[0038] The dual-live-wire parallel mode is similar to the single-live-wire mode, still forming a split-phase inverter circuit. The only difference is that the two live wires are directly connected in parallel, so the amplitude, frequency and phase of the two sets of single-phase AC voltages must be exactly the same.

[0039] The controller is divided into inverter control and rectifier control sections, including gating unit U12, drive unit U13, inverter control circuit and rectifier control circuit.

[0040] The inverter control circuit consists of a control and waveform generation unit U5 and two symmetrical AC output voltage and current sampling and feedback circuits. These include voltage error amplifiers U1 and U2, current error amplifiers U3 and U4, voltage and current compensators PI1-4, control and waveform generation unit U5, and peripheral circuits. In the first AC output voltage and current sampling and feedback circuit, resistors R5 and R6 sample the AC output voltage Va and connect it to the negative input terminal of U1. The positive input terminal of U1 is connected to the AC sinusoidal voltage reference signal Vr1. The output terminal of U1 is connected to the positive input terminal of U3. The current signal Ia from L1 is connected to the negative input terminal of U3, and the output terminal of U3 is connected to the input terminal of U5. The current sampling device can optionally be a current sensor, current transformer, or resistor. This is a dual closed-loop inverter control system with an outer voltage loop and an inner current loop. The voltage compensator PI1 achieves stable operation of Va through the outer voltage loop composed of U1 and peripheral components, while the current compensator PI3 achieves stable operation of Ia through the inner current loop composed of U3 and peripheral components. The second AC output voltage and current sampling and feedback circuit is completely symmetrical to the first AC output voltage and current sampling and feedback circuit. It mainly consists of U2, U4, PI2, and PI4, and the connection method is basically similar to it, so it will not be described again here. One input terminal of the gating unit U12 is connected to the output terminal of U5.

[0041] The rectifier control circuit consists of a control and waveform generation unit U11, a DC output voltage sampling and feedback circuit, and two symmetrical AC input current sampling and feedback circuits. Specifically, it includes a voltage error amplifier U6, multipliers U7 and U8, current error amplifiers U9 and U10, voltage and current compensators PI5-7, the control and waveform generation unit U11, and peripheral circuits. In the DC output voltage sampling and feedback circuit, resistors R3 and R4 sample the DC output voltage and connect it to the negative input terminal of U6. The positive input terminal of U6 is connected to the DC voltage reference signal Vr. The output terminal of U6 is connected to one input terminal of U7 and U8. Resistors R5 and R6 sample the AC input voltage Va and connect it to the other input terminal of U7. The output terminal of U7 is connected to the positive input terminal of U9 in the first AC input current sampling and feedback circuit. The current signal Ia of L1 is connected to the negative input terminal of U9, and the output terminal of U9 is connected to one input terminal of U11. The current sampling device can optionally be a current sensor, a current transformer, or a resistor. This is a dual closed-loop rectifier control system with an outer voltage loop and an inner current loop. Voltage compensator PI5 achieves a stable DC output voltage through the outer voltage loop composed of U6 and external components. Current compensator PI6 achieves Ia and Va with the same frequency and phase through the inner current loop composed of U9 and external components, thus achieving power factor correction and low current harmonics. The power factor is also adjustable. The second AC input current sampling and feedback circuit is completely symmetrical to the first AC input current sampling and feedback circuit, mainly composed of U8, U10, and PI7. Its connection method is basically similar and will not be described further here.

[0042] The other input terminal of the gating unit U12 is connected to the output terminal of U11. The input terminal of the driving unit U13 is connected to the output terminal of U12, thereby generating a pulse driving signal to drive the power switching transistors Q1~Q8.

[0043] 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, generating a sinusoidal pulse width modulation (SPWM) high-frequency square wave and a power frequency square wave. After passing through the inverter bridge arms to generate a high-frequency square wave, it is filtered by L1, L2 and Cf1, Cf2 to provide the output voltage to Va, Vc and / or RL1, RL2. It can operate in off-grid or grid-connected inverter modes. In off-grid inverter mode, it generates AC voltage to supply the inverter load; in grid-connected inverter mode, it generates AC current to supply the grid, thus forming AC. In dual-wire mode, U1 and U2 sample the AC output voltages Va and Vc respectively, and obtain the voltage between the two wires after relevant calculations. In single-wire or dual-wire parallel mode, U1 and U2 directly sample the AC output voltages Va and Vc respectively, and adjust the output voltage and achieve voltage regulation through the corresponding compensators PI1 and PI2. In dual-wire mode, U3 or U4 samples the current Ia of filter inductor L1 or the current Ic of filter inductor L2 respectively, and selects one of them as the current sampling signal. In single-wire or dual-wire parallel mode, U3 and U4 directly sample the currents Ia and Ic of filter inductors L1 and L2 respectively, and control them using average current mode or peak current mode through the corresponding compensators PI3 and PI4, thereby improving its dynamic response performance.

[0044] 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), or other intelligent control methods. Optionally, the controller can also employ other types of 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.

[0045] In dual-wire mode or single-phase power system inverter operation mode, when the sinusoidal AC current is in the positive half-cycle, high-frequency switch Q1 is working, high-frequency switch Q4 is working and continuously conducting for part of the time, Q5 and Q8 are continuously conducting, and Q2 and Q3 are continuously turning off. When high-frequency switches Q1 and Q4 are working, their duty cycles change according to the two-stage SPWM law.

[0046] Optionally, Q6 and Q7 can operate in synchronous rectification mode, and each switching cycle will turn on slightly after DQ6 and DQ7 have been turned on, thus enabling Q6 and Q7 to achieve zero-voltage switching (ZVS). The main operating waveforms are shown in Figure 4. The midpoint of vertical bridge arm 1 is "1", and the midpoint of vertical bridge arm 2 is "2". From top to bottom, they represent the drive signals of power switches Q1~Q8, the voltage difference V12 between the midpoints of vertical bridge arms 1 and 2, the AC output voltage VAC, and the currents iL1 and iL2 of the filter inductors L1 and L2. When |VAC|>1 / 2*Vdc, Q2 and Q3 are continuously off, Q4, Q5, and Q8 operate in power frequency mode and are continuously 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~Q8 can utilize their body diodes DQ1~DQ8 or be connected in parallel with external diodes. When Q1 is on, Vdc provides power to AC through Q4 and stores energy in L1 and L2. When Q1 is off, the energy stored in L1 and L2 is discharged to AC via Q4, Q5, and DQ6, resulting in two voltage levels: "+Vdc" and "+1 / 2Vdc". When |VAC| < 1 / 2 * Vdc, Q1 is off, Q2 and Q3 remain off, while Q5, Q8, DQ6, and DQ7 remain on. Q4 operates in the second high-frequency SPWM mode, with its duty cycle still being D∙sin(ωt+θ). When Q4 is on, the voltage Vc2 of the filter capacitor Cd2 continues to supply power to the AC through Q4, and also continues to store energy in L1 and L2. When Q4 is off, the energy stored in L1 and L2 discharges into the AC through Q5, Q8, DQ6, and DQ7, thus 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".

[0047] During the negative half-cycle of the sinusoidal AC current, high-frequency switch Q2 operates, high-frequency switch Q3 operates and conducts continuously for part of the time, Q6 and Q7 conduct continuously, and Q1 and Q4 are continuously off. The duty cycle of high-frequency switches Q2 and Q3 changes according to a two-stage SPWM pattern. Optionally, Q5 and Q8 can operate in synchronous rectification mode, and each switching cycle, Q5 and Q8 turn on slightly after being turned on, thus achieving ZVS for Q5 and Q8. 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 negative half-cycle of the sinusoidal AC current, V12 has three levels: "-Vdc", "-1 / 2Vdc", and "0".

[0048] In summary, in the dual-wire mode or single-phase power system inverter operation mode, and within the entire cycle of sinusoidal AC power, 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. .

[0049] In single-wire or dual-wire parallel inverter operation mode, with the sinusoidal AC current in the positive half-cycle, Q5 and Q8 are continuously on, Q2 and Q3 are continuously off, and Q1 and Q4 operate as high-frequency switches with their duty cycles varying according to the SPWM pattern. Optionally, Q6 and Q7 can operate in synchronous rectification mode, and in each switching cycle, Q6 and Q7 are turned on slightly after being turned on, thus achieving ZVS for Q6 and Q7. The main operating waveforms are shown in Figure 5, from top to bottom: the drive signals for power switches Q1~Q8, the voltage difference V12 between the midpoints 1 and 2 of the vertical bridge arm, the two AC output voltages Va and Vc, and the currents iL1 and iL2 of the filter inductors L1 and L2. Q5 and Q8 operate in power frequency mode and are continuously on, while Q1 and Q4 operate in 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. When Q1 and Q4 are on, the voltages Vd1 and Vd2 of the filter capacitors Cd1 and Cd2 respectively provide energy to Va and Vc, and store energy in L1 and L2 respectively; when Q1 and Q4 are off, the energy stored in L1 and L2 is discharged to Va and Vc through Q5 and DQ6, Q8 and DQ7 respectively, so V12 has two levels: "+1 / 2Vdc" and "+0".

[0050] When the sinusoidal AC current is in its negative half-cycle, Q6 and Q7 are continuously conducting, while Q1 and Q4 are continuously off. Q2 and Q3 operate as high-frequency switches, their duty cycles varying according to the SPWM pattern. Optionally, Q5 and Q8 can operate in synchronous rectification mode, turning on slightly after DQ5 and DQ8 have turned on in each switching cycle, thus achieving ZVS for Q5 and Q8. Similarly, V12 will have two voltage levels: "-1 / 2Vdc" and "0".

[0051] In summary, in single-wire or dual-wire parallel inverter operation mode with a sinusoidal AC current throughout the entire cycle, V12 in the bidirectional inverter circuit has three voltage levels: "+1 / 2Vdc", "0", and "-1 / 2Vdc". Based on the inductor volt-second balance principle, the instantaneous AC value can be derived. .

[0052] The rectification and inversion modes are dual in operation and have similar working principles. In rectification mode, the power flow path is as follows: the controller outputs a drive signal, which is then amplified by the gate-level drive circuit and supplied to Q1~Q8. The AC voltages Va and Vc generate a high-frequency square wave through the four bridge arms, and after filtering by L1, L2, Cf1, and Cf2, the output voltage is supplied to the DC load RL. In dual-wire mode, the AC input voltages Va and Vc are sampled and fed to multipliers U7 and U8, and the voltage between the two wires is obtained after relevant calculations. In single-wire or dual-wire parallel mode, the AC input voltages Va and Vc are directly sampled and fed to multipliers U7 and U8. In dual-wire mode, U9 or U10 samples the current Ia of filter inductor L1 or the current Ic of filter inductor L2, respectively, selecting one of them as the current sampling signal. In single-wire or dual-wire parallel mode, U9 and U10 directly sample the currents Ia and Ic of filter inductors L1 and L2, respectively, and adjust the input current magnitude and phase through corresponding compensators PI6 and PI7 to achieve PFC function. Average current mode or peak current mode control can be used to improve its dynamic response performance. In all these modes, U6 samples the DC output voltage to achieve stable operation.

[0053] In dual-wire mode or single-phase power system rectification mode, with the sinusoidal AC current in its positive half-cycle, high-frequency switch Q2 operates, high-frequency switch Q4 operates and conducts continuously for part of the time, Q3 remains off, and high-frequency switches Q6 and Q7 operate. The duty cycle of high-frequency switches Q2 and Q4 changes according to a two-stage SPWM pattern. Optionally, Q5 and Q8 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".

[0054] During the negative half-cycle of the sinusoidal AC current, high-frequency switch Q1 operates, high-frequency switch Q3 operates and conducts continuously for part of the time, Q4 remains off, and high-frequency switches Q5 and Q8 operate. The duty cycles of high-frequency switches Q1 and Q3 change according to a two-stage SPWM pattern. Optionally, Q6 and Q7 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 negative half-cycle of the sinusoidal AC current, Vm has three levels: "-Vdc", "-1 / 2Vdc", and "0".

[0055] In summary, in a dual-wire or single-phase power system operating under rectifier mode and with a sinusoidal AC current throughout its entire cycle, V12 in the bidirectional inverter circuit exhibits 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. .

[0056] Similarly, in single-wire or dual-wire parallel rectifier operation mode with a sinusoidal AC current throughout the entire cycle, V12 in the bidirectional inverter circuit has three voltage levels: "+1 / 2Vdc", "0", and "-1 / 2Vdc". Based on the inductor volt-second balance principle, the DC voltage can be calculated. .

[0057] Optionally, an interleaved parallel circuit can be added to Figure 3, as shown in Figure 6 for Embodiment 2: Q11, Q12, Q15, Q16, and L11 correspond to Q13, Q14, Q17, Q18, and L12; Q21, Q22, Q25, Q26, and L21 correspond to Q23, Q24, Q27, Q28, and L22, respectively forming two-phase interleaved parallel connections, thereby further improving the output power of the bidirectional split-phase inverter. For simplicity, internal or external diodes are not shown on any of the power switches; their operating principles and modulation methods are basically similar to those in Figures 2-5, and will not be repeated here. It should be noted that the interleaved parallel connection is not limited to two phases and can also be extended to a multi-phase interleaved parallel bidirectional split-phase inverter circuit.

[0058] This invention provides a five-level output voltage in dual-wire mode or single-phase power systems, with an active clamping function to reduce common-mode leakage current. In single-wire or dual-wire parallel mode, the output voltage is three-level, and it can flexibly switch between these modes. The output equivalent frequency is several times the switching frequency, thereby improving inverter conversion efficiency, reducing output voltage or current harmonics, and decreasing the size of the filter inductor, thus possessing high industrial application value.

[0059] 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 hybrid multi-level bidirectional split-phase inverter, characterized by, The bidirectional inverter circuit comprises a DC, two groups of AC, two DC filter capacitors, two AC filter inductors, two groups of AC filter capacitors, two vertical bridge arms and two horizontal bridge arms, the two DC filter capacitors are connected in series, and the series connection is connected in parallel with the DC; the two groups of AC filter capacitors are connected in parallel with the two groups of AC respectively; the vertical bridge arm is composed of two power switch tubes connected in series, and the horizontal bridge arm is composed of two power switch tubes connected in back-to-back series, and the two vertical bridge arms are respectively connected to the positive and negative poles of the DC; one end of the two horizontal bridge arms is respectively connected to the midpoint of the two vertical bridge arms, and the other end of the two horizontal bridge arms is connected to the middle of the two DC filter capacitors; the midpoint of the two vertical bridge arms is respectively connected to the live wire of the two groups of AC through an AC filter inductor; The controller collects AC and DC side voltage and current signals, controls the two vertical bridge arms and the two horizontal bridge arms, so that the bidirectional inverter circuit works in off-grid inverter mode, grid-connected inverter mode or rectifier mode, and stabilizes the output voltage or current.

2. The hybrid multi-level bidirectional split-phase inverter of claim 1, wherein, The DC is a DC side power supply or a rectifier load DC, and the AC is an AC side power supply or an inverter load AC; the two groups of AC constitute a single live line or double live line parallel mode, or a double live line mode or a single-phase power system.

3. The hybrid multi-level bidirectional split-phase inverter of claim 2, wherein, The controller controls the bidirectional inverter circuit to output a five-level voltage in a double live line mode or a single-phase power system, and to output a three-level voltage in a single live line or double live line parallel mode.

4. The hybrid multi-level bidirectional split-phase inverter of claim 1, wherein, During the positive half cycle or the negative half cycle of the sinusoidal alternating current, the power switch tube of the vertical bridge arm works in high-frequency switching or is continuously turned on in part of the period; one power switch tube of the horizontal bridge arm works in power-frequency switching, and the other power switch tube works in body diode freewheeling conduction.

5. The hybrid multi-level bidirectional split-phase inverter of claim 1, wherein, The controller comprises a gating unit, a driving unit, an inverter control circuit and a rectifier control circuit, the inverter control circuit is composed of a control and emission unit U5 and two symmetrical AC output voltage and current sampling and feedback circuits, the rectifier control circuit is composed of a control and emission unit U11, one DC output voltage sampling and feedback circuit and two symmetrical AC input current sampling and feedback circuits; the two input ends of the gating unit are respectively connected to the output ends of the control and emission unit U5 and the control and emission unit U11; The gating unit is connected to the driving unit, the inverter control circuit and the rectifier control circuit, and the driving unit drives the power switch tubes of the two vertical bridge arms and the two horizontal bridge arms.

6. The hybrid multi-level bidirectional split-phase inverter of claim 5, wherein, The AC output voltage and current sampling and feedback circuit comprises a voltage error amplifier U1, a current error amplifier U3, a resistor R5, a resistor R6, a voltage compensator PI1 and a current compensator PI3. The resistor R5 and the resistor R6 are connected in series to sample an AC output voltage. The negative input terminal of the voltage error amplifier U1 is connected between the resistor R5 and the resistor R6. The positive input terminal of the voltage error amplifier U1 is connected to an AC sinusoidal wave voltage reference signal. The output terminal of the voltage error amplifier U1 is connected to the positive input terminal of the current error amplifier U3. The negative input terminal of the current error amplifier U3 samples a current signal of one of the AC filter inductors. The output terminal of the current error amplifier U3 is connected to one of the input terminals of the control and generating unit U5. The voltage compensator PI1 is connected to the negative input terminal and the output terminal of the voltage error amplifier U1 respectively. The current compensator PI3 is connected to the negative input terminal and the output terminal of the current error amplifier U3 respectively.

7. The hybrid multi-level bidirectional split-phase inverter of claim 6, wherein, The DC output voltage sampling and feedback circuit comprises a resistor R3, a resistor R4, a voltage error amplifier U6 and a voltage compensator PI5. The resistor R3 and the resistor R4 are used to sample a DC output voltage. The negative input terminal of the voltage error amplifier U6 is connected between the resistor R3 and the resistor R4. The positive input terminal of the voltage error amplifier U6 is connected to a DC voltage reference signal. The output terminal of the voltage error amplifier U6 is connected to the input terminals of the two AC input current sampling and feedback circuits. The two terminals of the voltage compensator PI5 are connected to the negative input terminal and the output terminal of the voltage error amplifier U6 respectively.

8. The hybrid multi-level bidirectional split-phase inverter of claim 7, wherein, The AC input current sampling and feedback circuit comprises a multiplier U7, a current error amplifier U9 and a current compensator PI6. One input terminal of the multiplier U7 is connected to the output terminal of the voltage error amplifier U6. The resistor R5 and the resistor R6 are connected to the other input terminal of the multiplier U7 to sample an AC input voltage. The output terminal of the multiplier U7 is connected to the positive input terminal of the current error amplifier U9. The negative input terminal of the current error amplifier U9 samples a current signal of one of the AC filter inductors. The output terminal of the current error amplifier U9 is connected to one of the input terminals of the control and generating unit U11. The two terminals of the current compensator PI6 are connected to the output terminal and the negative input terminal of the current error amplifier U9 respectively.

9. The hybrid multi-level bidirectional split-phase inverter of claim 1, wherein, The bidirectional inverter circuit comprises four or more groups of even-numbered AC filter inductors, vertical bridge arms and horizontal bridge arms. The groups of vertical bridge arms and horizontal bridge arms are connected in staggered parallel connection to form a multi-phase staggered parallel bidirectional split-phase inverter circuit.

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