Hybrid multilevel bidirectional split-phase inverter

Abstract

The embodiment of the present invention discloses a hybrid multi-level bidirectional split-phase inverter, including a bidirectional inverter circuit and a controller. The bidirectional inverter circuit includes 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 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 back to back in series. The controller collects AC and DC side voltage and current signals, flexibly switches between several modes, and stabilizes the output voltage or current. The output voltage of the present invention is five-level in dual live wire mode or single-phase power system, and the output voltage is three-level in single live wire or dual live wire parallel mode. The output equivalent frequency of the present invention is several times the switching frequency, thereby improving the inverter conversion efficiency, reducing the output voltage or current harmonics, and reducing the volume of the filter inductor, so it has a high industrial application value.

Description

Technical Field

[0001] The present invention relates to the field of new energy power electronic technology, and in particular to a hybrid multi-level bidirectional split-phase inverter. Background Art

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

[0003] Bidirectional split-phase inverters usually use symmetrical inverter circuits, such as Figure 1 As shown. This circuit includes two DC filter capacitors Cd1 and Cd2, four power switch tubes Q1~Q4 and their body diodes, AC filter inductors L1 and L2, and AC filter capacitors Cf1 and Cf2. The power conversion from DC to AC is called inversion, and the power conversion from AC to DC is called rectification. In the inverter working mode: in dual live 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, and provide power to the series-connected AC power sources Va and Vc. At the same time, the loads RL1 and RL2 are connected in series to obtain power from the two live wires instead of the N wire. In single live 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, thereby forming a bidirectional split-phase inverter circuit, and the two respectively provide power to Va, RL1 and Vc, RL2 through the N line.

[0004] The dual-phase parallel mode is similar to the single-phase mode, and still constitutes a bidirectional 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. Conversely, the rectification working mode is similar to it, and it will not be repeated here. The traditional split-phase inverter circuit can realize bidirectional power conversion, and has the main advantages of simple circuit structure and mature modulation method.

[0005] The traditional bidirectional split-phase inverter circuit is simple to control, but whether it works in dual-fire or single-fire mode, bipolar high-frequency sinusoidal pulse width modulation (SPWM) must be used. The four power switches all work in high-frequency switching state, and the switching power consumption is large, especially the reverse recovery power consumption of the body diode is large, resulting in low conversion efficiency. In addition, the output voltage in different modes is only "+Vdc" and "-Vdc" or "+1 / 2Vdc" and "-1 / 2Vdc". The output frequency is equivalent to the switching frequency, resulting in a large output filter inductance and difficulty in further improving the conversion efficiency. Multi-level bidirectional split-phase inverter circuits have become one of the research focuses in the field of new energy power electronics, which is used 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 multi-level bidirectional split-phase inverter to improve the inverter conversion efficiency and reduce the output voltage or current harmonics.

[0007] In order to solve the above technical problems, an embodiment of the present invention proposes a hybrid multi-level bidirectional split-phase inverter, including a bidirectional inverter circuit and a controller. The bidirectional inverter circuit includes 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 connected in parallel with the DC after being connected in series; 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 series back to back, and the two ends of the two vertical bridge arms are respectively connected to the positive and negative poles of DC; one end of the two horizontal bridge arms is respectively connected to the midpoints 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 midpoints of the two vertical bridge arms are respectively connected to the live wires of the two groups of AC through an AC filter inductor;

[0008] The controller collects the voltage and current signals on the AC and DC sides, controls the two vertical bridge arms and the two horizontal bridge arms, enables the bidirectional inverter circuit to operate in an off-grid inverter mode, a grid-connected inverter mode or a rectifier mode, and stabilizes 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 groups of ACs constitute a single live wire or a dual live wire parallel mode, or constitute 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 a dual-live-wire mode or a single-phase power system, and to output a three-level voltage in a single-live-wire or dual-live-wire parallel mode.

[0011] Furthermore, during the positive half cycle or negative half cycle of the sinusoidal alternating current, the power switch tube of the vertical bridge arm operates as a high-frequency switch or is continuously turned on for part of the period; one power switch tube of the horizontal bridge arm operates as an industrial-frequency switch, and the body diode of the other power switch tube is turned on for freewheeling.

[0012] Furthermore, the controller includes 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 wave generating unit U5 and two symmetrical AC output voltage and current sampling and feedback circuits. The rectifier control circuit is composed of a control and wave generating unit U11, a 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 wave generating unit U5 and the control and wave generating unit U11. The gating unit is connected to the driving unit, the inverter control circuit and the rectifier control circuit. The driving unit correspondingly drives the power switch tubes 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, 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 and are used to sample the 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 the 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 wave generating 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 a resistor R3, a resistor R4, a voltage error amplifier U6, and a voltage compensator PI5. The 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 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 two AC input current sampling and feedback circuits. The two ends of the voltage compensator PI5 are respectively connected to the negative input terminal and the output terminal of the voltage error amplifier U6.

[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 connect it 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 an input terminal of the control and wave generating unit U11. The two ends of the current compensator PI6 are respectively connected to the output terminal and the negative input terminal of the current error amplifier U9.

[0016] Furthermore, the bidirectional inverter circuit includes 4 or more even groups of AC filter inductors, vertical bridge arms and horizontal bridge arms, and multiple groups of vertical bridge arms and horizontal bridge arms are staggered in parallel to form a multi-phase staggered parallel bidirectional split-phase inverter circuit.

[0017] The beneficial effects of the present invention are as follows: the output voltage of the present invention is five-level or three-level, bidirectional electric energy conversion is realized, and the power factor is adjustable; the output equivalent frequency of the present invention is several times the switching frequency, thereby improving the inverter conversion efficiency, reducing the output voltage or current harmonics, and reducing the filter inductor volume; the present invention contains an active clamping function, further reducing the common-mode leakage current, and improving the inverter operation and personal operation safety; the present invention works 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 the present invention is simple and can simplify the controller design. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0019] Figure 2 4 is a circuit diagram of a hybrid multi-level bidirectional split-phase inverter according to an embodiment of the present invention.

[0020] Figure 3 4 is a circuit diagram of a hybrid multi-level bidirectional split-phase inverter according to Embodiment 1 of the present invention.

[0021] Figure 4 This is a main working waveform diagram of Example 1 of the present invention in a dual-live-wire mode or a single-phase electrical system.

[0022] Figure 5 This is a main working waveform diagram of Example 1 of the present invention in a single-live-wire or dual-live-wire parallel mode.

[0023] Figure 6 4 is a circuit diagram of a hybrid multi-level bidirectional split-phase inverter according to Embodiment 2 of the present invention. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The present invention is further described in detail below in conjunction with the drawings and specific embodiments.

[0025] In the embodiments of the present invention, if there are directional indications (such as up, down, left, right, front, back, etc.), they are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0026] In addition, in the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0027] Please refer to Figure 2 to Figure 6 The hybrid multi-level bidirectional split-phase inverter of the embodiment of the present invention includes a bidirectional inverter circuit and a controller.

[0028] The bidirectional inverter circuit includes a DC side power supply or a rectifier load DC, a DC filter capacitor Cd1, a DC filter capacitor Cd2, an AC filter inductor L1, an AC filter inductor L2, an AC filter capacitor Cf1, an AC filter capacitor Cf2, an AC side power supply or an inverter load AC, and four bridge arms: two vertical bridge arms and two horizontal bridge arms. 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 back to back in series. The two ends of the two vertical bridge arms are respectively connected to the positive and negative poles of DC, and the two ends of the two horizontal bridge arms are respectively connected to the midpoints of Cd1 and Cd2 and the midpoint of the vertical bridge arm. Among them, the vertical bridge arm 1 and the vertical bridge arm 2 are respectively connected to the live wire through L1 and L2, which are called the live wire bridge arm, and the horizontal bridge arm 1 and the horizontal bridge arm 2 are respectively connected to the midpoints of Cd1 and Cd2. During the positive or negative half cycle of the sinusoidal alternating current, the power switch tube in the vertical bridge arm operates as a high-frequency switch or is continuously turned on for part of the time period, and one power switch tube in the horizontal bridge arm operates as an industrial-frequency switch, while the body diode of the other power switch tube is turned on for freewheeling.

[0029] The inverter of the present invention is used for bidirectional direct current-alternating current (DC / AC) power conversion, and can flexibly work in off-grid inversion (also called passive inversion) and grid-connected inversion (also called active inversion), as well as rectification mode according to needs. The power flow (inversion) path of electric energy from a DC power source to an AC power source is: in a dual live wire mode or a single-phase power system, Cf1 and Cf2 are connected in series for filtering, and vertical bridge arms 1 and 2 and horizontal bridge arms 1 and 2 form an inverter circuit, which provides electric energy to the AC power sources Va and Vc connected in series through two series filter inductors L1 and L2, and at the same time, loads RL1 and RL2 are connected in series to obtain electric energy from two live wires without passing through the N wire. In single live 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, thereby forming a split-phase inverter circuit, and the two provide power to Va, RL1 and Vc, RL2 respectively through the N line. In order to adapt to different load types, the amplitude, frequency and phase of the two sets of single-phase AC voltages in the single live wire mode can be different. The dual live wire parallel mode is similar to the single live wire, and still constitutes 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.

[0030] The controller of the present invention adopts a corresponding modulation method. The output voltage of the bidirectional inverter circuit is five-level in the dual live wire mode or single-phase power system, and three-level in the single live wire or dual live wire parallel mode, so it is called a hybrid multi-level. The controller detects the AC output voltage or current, determines the input condition and load condition, and after processing and calculation, generates a drive signal to the four bridge arm power switch tubes, and works with a sine wave pulse width modulation (SPWM) high-frequency switch. DC is filtered by Cd1 and Cd2 to form a DC midpoint voltage, and is switched by the power switch tube at high frequency and industrial frequency, and then filtered by L1, L2 and Cf1, Cf2, and finally provides a stable voltage or current to the AC power source Va, Vc or the AC load RL1, RL2. Since the output voltage of the bidirectional inverter circuit is a hybrid multi-level, its output equivalent frequency is several times the switching frequency, thereby improving the inverter conversion efficiency, reducing the output voltage or current harmonics, and reducing the volume of the filter inductor. Since the AC N line is directly connected to the DC midpoint, it is equivalent to having an active clamping function, which further reduces the common-mode leakage current and improves the inverter operation and personal operation safety. Conversely, the power flow (rectification) path and working principle of electric energy from the AC power supply to the DC power supply are similar, so they will not be repeated here.

[0031] Therefore, the present invention can realize bidirectional power conversion. By sampling the voltage and current signals on the AC and DC sides, the controller identifies the input and output power flow directions, automatically operates in the inversion or rectification mode, and determines the conditions to control the high-frequency and industrial frequency switching of the power switch tube, while realizing adjustable power factor and stabilizing the output voltage or current through closed-loop feedback.

[0032] The power switch tube of the present invention can use an insulated gate bipolar transistor (IGBT), a metal oxide field effect transistor (MOSFET), and can be replaced by a third-generation wide bandgap (WBG) power device, such as silicon carbide (SiC), gallium nitride (GaN) MOSFET, etc., and these fully controlled power switch tubes can also be used in combination.

[0033] The controller of the present invention can be constructed using discrete electronic components, or can be designed and used with dedicated integrated circuits, such as analog control chips, single-chip microcomputers (MCUs) programmed by software, digital signal processors (DSPs), or programmable logic devices (FPGA / CPLDs). The bidirectional inverter circuit of the present invention can be constructed using discrete components or integrated components, or can be integrated into a controller to form a large-scale hybrid integrated circuit. This highly integrated controller design can further reduce the size of the bidirectional inverter.

[0034] The present invention can be widely used in various bidirectional or unidirectional direct current-alternating current (DC / AC) inverter circuits, such as solar photovoltaic power generation, off-grid household and industrial and commercial energy storage and other new energy systems, portable mobile energy storage power supplies, uninterruptible power supplies, battery formation power supplies, feedback aging power supplies and electric vehicle motor drivers, as well as industrial power supplies, switching power supplies, etc.

[0035] Example 1: Figure 3As shown, the hybrid multi-level bidirectional split-phase inverter of the embodiment of the present invention 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, AC loads RL1 and RL2 for off-grid or other applications, and a controller. The power switch tube Q1 and the power switch tube Q2 and their internal or external diodes DQ1 and DQ2 are connected in series to form a vertical bridge arm 1, the power switch tube Q3 and the power switch tube Q4 and their internal or external diodes DQ3 and DQ4 are connected in series to form a vertical bridge arm 2, the power switch tube Q5 and the power switch tube Q6 and their internal or external diodes DQ5 and DQ6 are connected in series back to back to form a horizontal bridge arm 1, and the power switch tube Q7 and the power switch tube Q8 and their internal or external diodes DQ7 and DQ8 are connected in series back to back to form a horizontal bridge arm 2. 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 a DC midpoint or AC neutral line "N". The outflow end of Q1 and the positive electrode of DQ1 are connected to the inflow end of Q2 and the negative electrode of DQ2, also known as the midpoint of vertical bridge arm 1, and connected to one end of L1 and the inflow end of Q6 and the negative electrode of DQ6, the outflow end of Q6 and the positive electrode of DQ6 are connected to the outflow end of Q5 and the positive electrode of DQ5, and the inflow end of Q5 and the negative electrode of DQ5 are connected to "N". The outflow end of Q3 and the positive electrode of DQ3 are connected to the inflow end of Q4 and the negative electrode of DQ4, also known as the midpoint of vertical bridge arm 2, and connected to one end of L2 and the inflow end of Q8 and the negative electrode of DQ8, the outflow end of Q8 and the positive electrode of DQ8 are connected to the outflow end of Q7 and the positive electrode of DQ7, and the inflow end of Q7 and the negative electrode of DQ7 are connected to "N". According to the current inflow or outflow direction of the fully controlled power switch tube, the inflow end is the MOSFET drain (D) or IGBT collector (C), the outflow end is the MOSFET source (S) or IGBT emitter (E), the drive signal is the MOSFET or IGBT gate (G), and WBG devices such as SiC, GaN, etc. are similar. The other end of L1 and L2 is connected to one end of Cf1 and Cf2 and the two live wires of AC voltage Vac, and the other end of Cf1 and Cf2 is connected to "N".

[0036] In dual live wire mode or single-phase power system, Cf1 and Cf2 are connected in series for filtering, and the vertical bridge arms 1 and 2 and the horizontal bridge arms 1 and 2 form an inverter circuit, which provides power to the series-connected AC power sources Va and Vc through two series-connected filter inductors L1 and L2. At the same time, the loads RL1 and RL2 are connected in series to obtain power from the two live wires instead of the N wire.

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

[0038] The dual-live-wire parallel mode is similar to the single-live-wire mode and still constitutes 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 an inverter control part and a rectifier control part, including a gating unit U12, a driving unit U13, an inverter control circuit and a rectifier control circuit.

[0040] The inverter control circuit is composed of a control and wave generating unit U5 and two symmetrical AC output voltage and current sampling and feedback circuits. That is, voltage error amplifiers U1, U2 and current error amplifiers U3, U4, voltage and current compensators PI1~4, control and wave generating 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 are connected to the negative input terminal of U1, and the positive input terminal of U1 is connected to the AC sine wave voltage reference signal Vr1. The output terminal of U1 is connected to the positive input terminal of U3. The L1 current signal Ia 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 use a current sensor, a current transformer or a resistor. This is a dual closed-loop inverter control system with a voltage outer loop and a current inner loop. The voltage compensator PI1 realizes the stable operation of Va through the voltage outer loop composed of U1 and peripheral devices, and the current compensator PI3 realizes the stable operation of Ia through the current inner loop composed of U3 and peripheral devices. The second AC output voltage and current sampling and feedback circuit is completely symmetrical with the first AC output voltage and current sampling and feedback circuit, and is mainly composed of U2, U4 and PI2, PI4, and the connection method is basically similar, so it will not be repeated here. One input terminal of the selection unit U12 is connected to the output terminal of U5.

[0041] The rectifier control circuit is composed of a control and wave unit U11, a DC output voltage sampling and feedback circuit and two symmetrical AC input current sampling and feedback circuits. That is, the voltage error amplifier U6, multipliers U7, U8, current error amplifiers U9, U10, voltage and current compensators PI5~7, control and wave unit U11, and peripheral circuits. In the DC output voltage sampling and feedback circuit, resistors R3 and R4 sample the DC output voltage and are connected to the negative input terminal of U6, and 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 are connected to the other input terminal of U7, and 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 L1 current signal Ia 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 use a current sensor, a current transformer or a resistor. This is a dual closed-loop rectifier control system with a voltage outer loop and a current inner loop. The voltage compensator PI5 realizes a stable DC output voltage through a voltage outer loop composed of U6 and peripheral devices. The current compensator PI6 realizes the same frequency and phase of Ia and Va through a current inner loop composed of U9 and peripheral devices, so as to achieve the effect of power factor correction and low current harmonics, and the power factor is adjustable. The second AC input current sampling and feedback circuit is completely symmetrical with the first AC input current sampling and feedback circuit, mainly composed of U8, U10 and PI7, and the connection method is basically similar to it, so it will not be repeated 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 switch tubes Q1~Q8.

[0043] In the inverter working mode, the power flow path is as follows: after DC is filtered by capacitors Cd1 and Cd2, it is provided to the three bridge arms. The controller outputs a PWM signal and provides it to the power switch tubes Q1~Q6 through the drive amplifier circuit, corresponding to the positive and negative half cycles of the sinusoidal AC power supply, respectively, to generate a sinusoidal pulse width modulation (SPWM) high-frequency square wave and an industrial frequency square wave. After the high-frequency square wave is generated by the inverter bridge arm, it is filtered by L1, L2 and Cf1, Cf2 to provide the output voltage to Va, Vc or / and RL1, RL2, and can work in off-grid inverter or grid-connected inverter mode. During off-grid inverter, AC voltage is generated and provided to the inverter load, and during grid-connected inverter, AC current is generated and provided to the grid, thus forming AC. In dual-live mode, U1 and U2 sample the AC output voltage Va and Vc respectively, and obtain the voltage between the two live wires after relevant calculations; in single-live or dual-live parallel mode, U1 and U2 directly sample the AC output voltage Va and Vc respectively, and adjust the output voltage and achieve voltage stabilization through the corresponding compensators PI1 and PI2. In dual-live mode, U3 or U4 samples the current Ia of the filter inductor L1 or the current Ic of the filter inductor L2 respectively, and selects one of the two as the current sampling signal; in single-live or dual-live parallel mode, U3 and U4 directly sample the current Ia and Ic of the filter inductor L1 and L2 respectively, and through the corresponding compensators PI3 and PI4, average current mode or peak current mode control can be adopted to improve its dynamic response performance.

[0044] It should be noted that the voltage error amplifier and current error amplifier in the controller can adopt second-order or multi-order PI compensation, proportional integral differential (PID), or other intelligent control methods. Optionally, the controller can also adopt other types of control methods, such as quasi-resonant control, single-cycle control, current continuous conduction mode (CCM), current discontinuous mode (DCM), current critical conduction mode (CRM), etc., which does not affect its electrical performance and effect.

[0045] In dual-live-wire mode or single-phase power system inverter working mode and the sinusoidal AC power is in the positive half cycle, Q1 high-frequency switch works, Q4 high-frequency switch works and is continuously turned on for part of the time, Q5 and Q8 are continuously turned on, Q2 and Q3 are continuously turned off, and the duty cycle of Q1 and Q4 high-frequency switches changes according to the two-stage SPWM law when they work.

[0046] Optionally, Q6 and Q7 can work in synchronous rectification mode, and in each switching cycle, they are turned on later than DQ6 and DQ7 are turned on, so that Q6 and Q7 can achieve zero voltage switching (ZVS). The main working waveforms are as follows: Figure 4As shown, the middle point of vertical bridge arm 1 is "1", the middle point of vertical bridge arm 2 is "2", and from top to bottom are the drive signals of power switch tubes Q1~Q8, the voltage difference V12 between the middle points of vertical bridge arms 1 and 2, the AC output voltage VAC, and the currents iL1 and iL2 of filter inductors L1 and L2. When |VAC|>1 / 2*Vdc, Q2 and Q3 are continuously turned off, Q4, Q5 and Q8 work in industrial frequency mode and are continuously turned on, and Q1 works in the first high-frequency SPWM mode, and its duty cycle is , where ω is the angular frequency of the sinusoidal AC power, and θ is the phase angle of the sinusoidal AC power. It should be noted that Q1~Q8 can use their body diodes DQ1~DQ8 or connect external diodes. When Q1 is turned on, Vdc provides electrical energy to the AC through Q4 on the one hand, and stores electrical energy to L1 and L2 on the other hand; when Q1 is turned off, the electrical energy stored in L1 and L2 is discharged to the AC through Q4, Q5, and DQ6, so V12 is at two levels of "+Vdc" and "+1 / 2Vdc". When |VAC|<1 / 2*Vdc, Q1 is turned off, Q2 and Q3 continue to be turned off, Q5, Q8 and DQ6, DQ7 continue to be turned on, and Q4 operates in the second high-frequency SPWM mode, and its duty cycle is still When Q4 is turned on, the voltage Vc2 of the filter capacitor Cd2 continues to provide power to the AC through Q4, and continues to store power in L1 and L2; when Q4 is turned off, the power stored in L1 and L2 is discharged to the AC through Q5, Q8, DQ6 and DQ7, so V12 has two levels of "+1 / 2Vdc" and "0". Therefore, V12 has three levels of "+Vdc", "+1 / 2Vdc" and "0" in the positive half cycle of the sinusoidal alternating current.

[0047] When the sinusoidal alternating current is in the negative half cycle, Q2 high-frequency switch works, Q3 high-frequency switch works and is continuously turned on for part of the time period, Q6 and Q7 are continuously turned on, Q1 and Q4 are continuously turned off, and the duty cycle of Q2 and Q3 high-frequency switches changes according to the two-stage SPWM law when they work. Optionally, Q5 and Q8 can work in synchronous rectification mode, and each switching cycle is turned on later after DQ5 and DQ8 are turned on, so that Q5 and Q8 can achieve ZVS. Similarly, when |VAC|>1 / 2*Vdc, V12 has two levels of "-Vdc" and "-1 / 2Vdc", and when |VAC|<1 / 2*Vdc, V12 has two levels of "-1 / 2Vdc" and "0". Therefore, V12 has three levels of "-Vdc", "-1 / 2Vdc" and "0" in the negative half cycle of sinusoidal alternating current.

[0048] In summary, in dual live wire mode or single-phase power system inverter working mode and in the full cycle of sinusoidal AC, V12 in the bidirectional inverter circuit has five levels: "+Vdc", "+1 / 2Vdc", "0", "-1 / 2Vdc", and "-Vdc". According to the inductor volt-second balance principle, the AC instantaneous value can be obtained .

[0049] When the single-live-wire or dual-live-wire parallel mode inverter working mode is in the positive half cycle of the sinusoidal AC, Q5 and Q8 are continuously turned on, Q2 and Q3 are continuously turned off, and Q1 and Q4 work in high-frequency switching mode with a duty cycle that changes according to the SPWM law. Optionally, Q6 and Q7 can work in synchronous rectification mode, and each switching cycle is turned on later than DQ6 and DQ7, so that Q6 and Q7 can achieve ZVS. The main working waveforms are as follows: Figure 5 As shown in the figure, from top to bottom, they are the drive signals of power switch tubes Q1~Q8, the voltage difference V12 between the middle points 1 and 2 of the vertical bridge arms, the two AC output voltages Va, Vc, and the currents iL1, iL2 of the filter inductors L1 and L2. Q5 and Q8 work in the industrial frequency mode and are continuously turned on, while Q1 and Q4 work in the high-frequency SPWM mode, and their duty cycle is , where ω is the angular frequency of the sine wave AC power, and θ is the phase angle of the sine wave AC power. When Q1 and Q4 are turned on, the voltages Vd1 and Vd2 of the filter capacitors Cd1 and Cd2 provide energy to Va and Vc on the one hand, and store energy in L1 and L2 on the other hand; when Q1 and Q4 are turned off, the energy stored in L1 and L2 is discharged to Va and Vc through Q5 and DQ6, Q8 and DQ7, respectively, so V12 is at two levels of "+1 / 2Vdc" and "+0".

[0050] When the sinusoidal alternating current is in the negative half cycle, Q6 and Q7 are continuously turned on, Q1 and Q4 are continuously turned off, and Q2 and Q3 work as high-frequency switches with their duty ratio changing according to the SPWM law. Optionally, Q5 and Q8 can work in synchronous rectification mode, and each switching cycle is turned on later than DQ5 and DQ8, so that Q5 and Q8 can achieve ZVS. Similarly, at this time, V12 is at two levels of "-1 / 2Vdc" and "0".

[0051] In summary, in the inverter working mode of single live wire or dual live wire single parallel mode and in the full cycle of sinusoidal AC, V12 in the bidirectional inverter circuit has three levels of "+1 / 2Vdc", "0", and "-1 / 2Vdc". According to the inductor volt-second balance principle, the AC instantaneous value can be obtained .

[0052] The rectifier and inverter working modes are in a dual relationship, and their working principles are similar. The power flow path in the rectifier working mode is: the controller outputs the drive signal and provides it to Q1~Q8 through the gate drive amplifier circuit. The AC voltage Va and Vc pass through the four bridge arms to generate high-frequency square waves, and then provide the output voltage to the DC load RL after filtering by L1, L2 and Cf1, Cf2. In the dual-live mode, the AC input voltage Va and Vc are sampled and given to the multipliers U7 and U8 respectively, and the voltage between the two live wires is obtained after related operations; in the single-live or dual-live parallel mode, the AC input voltage Va and Vc are directly sampled and given to the multipliers U7 and U8 respectively. In dual live wire mode, U9 or U10 samples the current Ia of the filter inductor L1 or the current Ic of the filter inductor L2, and selects one of the two as the current sampling signal; in single live wire or dual live wire parallel mode, U9 and U10 directly sample the current Ia and Ic of the filter inductors L1 and L2, respectively, and adjust the input current size and phase through the corresponding compensators PI6 and PI7 to achieve the PFC function. The average current mode or peak current mode control can be used to improve its dynamic response performance. In these modes, U6 samples the DC output voltage to achieve its stable operation.

[0053] In dual live wire mode or single-phase power system rectification working mode and when the sinusoidal alternating current is in the positive half cycle, Q2 high frequency switch works, Q4 high frequency switch works and is continuously turned on for part of the time period, Q3 is continuously turned off, Q6 and Q7 high frequency switches work, and the duty cycle of Q2 and Q4 high frequency switches changes according to the two-stage SPWM law when they work. Optionally, Q5 and Q8 can work in synchronous rectification mode to achieve ZVS. Similarly, when |VAC|>1 / 2*Vdc, V12 has two levels of "+Vdc" and "+1 / 2Vdc", and when |VAC|<1 / 2*Vdc, V12 has two levels of "+1 / 2Vdc" and "0". Therefore, V12 has three levels of "+Vdc", "+1 / 2Vdc" and "0" in the positive half cycle of sinusoidal alternating current.

[0054] When the sinusoidal alternating current is in the negative half cycle, Q1 high frequency switch works, Q3 high frequency switch works and is continuously turned on for part of the time period, Q4 is continuously turned off, Q5 and Q8 high frequency switches work, and the duty cycle of Q1 and Q3 high frequency switches when working changes according to the two-stage SPWM law. Optionally, Q6 and Q7 can work in synchronous rectification mode to achieve ZVS. Similarly, when |VAC|>1 / 2*Vdc, V12 has two levels of "-Vdc" and "-1 / 2Vdc", and when |VAC|<1 / 2*Vdc, V12 has two levels of "-1 / 2Vdc" and "0". Therefore, Vm has three levels of "-Vdc", "-1 / 2Vdc" and "0" in the negative half cycle of sinusoidal alternating current.

[0055] In summary, in dual live wire mode or single-phase power system rectification working mode and in the full cycle of sinusoidal AC, V12 in the bidirectional inverter circuit has five levels: "+Vdc", "+1 / 2Vdc", "0", "-1 / 2Vdc", and "-Vdc". According to the inductor volt-second balance principle, the DC voltage can be obtained .

[0056] Similarly, in the single-live or dual-live parallel mode rectification working mode and in the full cycle of sinusoidal AC, V12 in the bidirectional inverter circuit has three levels: "+1 / 2Vdc", "0", and "-1 / 2Vdc". According to the inductor volt-second balance principle, the DC voltage can be obtained .

[0057] Optionally, in Figure 3 A set of interleaved parallel circuits is added, and Example 2 is as follows Figure 6 As shown: Q11, Q12, Q15, Q16 and L11 correspond to Q13, Q14, Q17, Q18 and L12, and Q21, Q22, Q25, Q26 and L21 correspond to Q23, Q24, Q27, Q28 and L22 to form two-phase staggered parallel connection, thereby further improving the output power of the bidirectional split-phase inverter. In order to simplify the diagram, no internal or external diodes are drawn on all power switch tubes. Their working principles and modulation methods are similar to Figure 2~Figure 5 It should be noted that the staggered parallel connection is not limited to two phases, but can also be extended to a multi-phase staggered parallel bidirectional split-phase inverter circuit.

[0058] The output voltage of the present invention is five-level in dual-live mode or single-phase power system, and contains active clamping function to reduce common-mode leakage current; the output voltage is three-level in single-live mode or dual-live parallel mode, and can be flexibly switched between these modes. The output equivalent frequency is several times the switching frequency, thereby improving the inverter conversion efficiency, reducing the output voltage or current harmonics, and reducing the filter inductor volume, so it has high industrial application value.

[0059] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A hybrid multi-level bidirectional split-phase inverter, characterized in that: It includes a bidirectional inverter circuit and a controller. The bidirectional inverter circuit includes 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 connected in parallel with the DC after being connected in series; 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 series back to back, and the two ends of 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 midpoints of the two vertical bridge arms, and the other ends of the two horizontal bridge arms are connected to the middle of the two DC filter capacitors; the midpoints of the two vertical bridge arms are respectively connected to the live wires of the two groups of AC through an AC filter inductor; The controller collects the voltage and current signals of the AC and DC sides, controls the two vertical bridge arms and the two horizontal bridge arms, enables the bidirectional inverter circuit to work in an off-grid inverter mode, a grid-connected inverter mode or a rectifier mode, and stabilizes the output voltage or current; 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 form a single live wire or a double live wire parallel mode, or form a double live wire mode or a single-phase power system; The controller controls the bidirectional inverter circuit to output a five-level voltage in a dual-live-wire mode or a single-phase power system, and to output a three-level voltage in a single-live-wire or dual-live-wire parallel mode; One of the vertical bridge arms is composed of power switch tube Q1 and power switch tube Q2 and their internal or external diodes DQ1 and DQ2 connected in series, the other vertical bridge arm is composed of power switch tube Q3 and power switch tube Q4 and their internal or external diodes DQ3 and DQ4 connected in series, one of the horizontal bridge arms is composed of power switch tube Q5 and power switch tube Q6 and their internal or external diodes DQ5 and DQ6 connected in series back to back, the other horizontal bridge arm is composed of power switch tube Q7 and power switch tube Q8 and their internal or external diodes DQ7 and DQ8 connected in series back to back; the controller outputs SPWM high-frequency square wave and industrial frequency square wave; When the dual-live-wire mode or the single-phase power system inverter working mode is in the positive half cycle of the sinusoidal AC, Q1 high-frequency switch works, Q4 high-frequency switch works and is continuously turned on for part of the time, Q5 and Q8 are continuously turned on, Q2 and Q3 are continuously turned off, and the duty ratio of Q1 and Q4 high-frequency switches when working changes according to the two-stage SPWM law; the two-stage SPWM includes the first stage high-frequency SPWM and the second stage high-frequency SPWM, and the duty ratios of the first stage high-frequency SPWM and the second stage high-frequency SPWM are both , where ω is the angular frequency of the sine wave AC power, θ is the phase angle of the sine wave AC power; In dual-live-wire mode or single-phase power system inverter working mode and when the sinusoidal AC power is in the negative half cycle, Q2 high-frequency switch works, Q3 high-frequency switch works and is continuously turned on for part of the time, Q6 and Q7 are continuously turned on, Q1 and Q4 are continuously turned off, and the duty ratio of Q2 and Q3 high-frequency switches changes according to the two-stage SPWM law when they work; When the single-live-wire or dual-live-wire parallel mode inverter working mode is in the positive half cycle of the sinusoidal AC, Q5 and Q8 are continuously turned on, Q2 and Q3 are continuously turned off, and Q1 and Q4 work as high-frequency switches, and their duty cycle changes according to the SPWM law; when the single-live-wire or dual-live-wire parallel mode inverter working mode is in the negative half cycle of the sinusoidal AC, Q6 and Q7 are continuously turned on, Q1 and Q4 are continuously turned off, and Q2 and Q3 work as high-frequency switches, and their duty cycle changes according to the SPWM law; In dual-live-wire mode or single-phase power system rectification mode and when the sinusoidal AC power is in the positive half cycle, Q2 high-frequency switch works, Q4 high-frequency switch works and is continuously turned on for part of the time, Q3 is continuously turned off, Q6 and Q7 high-frequency switches work, and the duty ratio of Q2 and Q4 high-frequency switches changes according to the two-stage SPWM law when they work; In dual-live-wire mode or single-phase power system rectification working mode and when the sinusoidal AC power is in the negative half cycle, Q1 high-frequency switch works, Q3 high-frequency switch works and is continuously turned on for part of the time, Q4 is continuously turned off, Q5 and Q8 high-frequency switches work, and the duty cycle of Q1 and Q3 high-frequency switches changes according to the two-stage SPWM law when they work.

2. The hybrid multi-level bidirectional split-phase inverter according to claim 1, characterized in that: During the positive half cycle or negative half cycle of the sinusoidal alternating current, the power switch tube of the vertical bridge arm operates as a high-frequency switch or is continuously turned on for part of the time period; one power switch tube of the horizontal bridge arm operates as an industrial frequency switch, and the body diode of the other power switch tube is turned on for freewheeling.

3. The hybrid multi-level bidirectional split-phase inverter according to claim 1, characterized in that: The controller includes 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 wave generating unit U5 and two symmetrical AC output voltage and current sampling and feedback circuits. The rectifier control circuit is composed of a control and wave generating unit U11, a 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 wave generating unit U5 and the control and wave generating unit U11. The gating unit is connected to the driving unit, the inverter control circuit and the rectifier control circuit, and the driving unit corresponds to driving the power switch tubes of the two vertical bridge arms and the two horizontal bridge arms.

4. The hybrid multi-level bidirectional split-phase inverter according to claim 3, characterized in that: The AC output voltage and current sampling and feedback circuit includes 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 and are used to sample the 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 the 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 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 wave generating 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.

5. The hybrid multi-level bidirectional split-phase inverter according to claim 4, characterized in that: The DC output voltage sampling and feedback circuit includes a resistor R3, a resistor R4, a voltage error amplifier U6, and a voltage compensator PI5. The 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 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 two AC input current sampling and feedback circuits. The two ends of the voltage compensator PI5 are respectively connected to the negative input terminal and the output terminal of the voltage error amplifier U6.

6. The hybrid multi-level bidirectional split-phase inverter according to claim 5, characterized in that: 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 connect it 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 an input terminal of the control and wave generating unit U11. The two ends of the current compensator PI6 are respectively connected to the output terminal and the negative input terminal of the current error amplifier U9.

7. The hybrid multi-level bidirectional split-phase inverter according to claim 1, characterized in that: The bidirectional inverter circuit includes 4 or more even-numbered groups of AC filter inductors, vertical bridge arms and horizontal bridge arms. Multiple groups of vertical bridge arms and horizontal bridge arms are staggered in parallel to form a multi-phase staggered parallel bidirectional split-phase inverter circuit.

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