Auxiliary side circuit, single-phase and three-phase dc-ac converter and control method

Abstract

The application discloses a secondary side circuit, a single-phase and three-phase DC-AC converter and a control method. In the secondary side circuit, one end of a first secondary winding is connected to the anode of a first diode, the cathode of the first diode and one end of a second capacitor are connected to the current input end of a second switch, one end of a second secondary winding is connected to the cathode of a second diode, the anode of the second diode, one end of a third capacitor and the current output end of a third switch are connected together, the current output end of the second switch and the current input end of the third switch are connected together to form a first common end, the other end of the first secondary winding, the other end of the second secondary winding, the other end of the second capacitor and the other end of the third capacitor are all connected to a secondary side ground wire. The DC converter comprises the secondary side circuit. The above-mentioned secondary side circuit and DC-AC converter are simple in circuit, high in efficiency, low in cost, small in size and strong in universality.

Description

Technical Field

[0001] The present invention relates to the field of new energy, and in particular to a secondary circuit, a single-phase and three-phase DC-AC converter, and a control method. Background Art

[0002] Existing single-phase DC-AC converters typically achieve high-frequency isolation and grid connection using two approaches. The first uses a flyback topology for high-frequency isolation, coupled with power-frequency commutation to follow the grid frequency for grid connection. The second employs a full-bridge or half-bridge topology for high-frequency isolation, followed by a single-stage high-frequency inverter for grid connection. However, both approaches, due to their two-stage power conversion, suffer from low system efficiency and high costs. Summary of the Invention

[0003] The purpose of the present invention is first to provide a secondary circuit, a single-phase DC-AC converter, a three-phase DC-AC converter, and a single-phase DC-AC converter control method to solve the problems of low system efficiency and high cost in the prior art.

[0004] First, the present invention provides a secondary circuit, comprising a first secondary winding of a transformer, a second secondary winding of the transformer, a first diode, a second capacitor, a third capacitor, a second diode, a secondary ground, a second switch, a third switch, and a fourth capacitor. One end of the first secondary winding is connected to the anode of the first diode, the cathode of the first diode, one end of the second capacitor, and a current input end of the second switch are connected together, one end of the second secondary winding is connected to the cathode of the second diode, the anode of the second diode, one end of the third capacitor, and a current output end of the third switch are connected together, the current output end of the second switch and the current input end of the third switch are connected together to form a first common end, and the other end of the first secondary winding, the other end of the second secondary winding, the other end of the second capacitor, and the other end of the third capacitor are all connected to the secondary ground; alternatively, the first diode is replaced by a seventh switch; alternatively, / or, the second diode is replaced by an eighth switch; wherein the current input end and current output end of the seventh switch and the eighth switch correspond to the anode and cathode of the first diode and the second diode, respectively.

[0005] Secondly, the present invention also provides a single-phase DC-AC converter, including the secondary circuit and the primary circuit, the primary circuit including the primary side of the transformer and a chopper circuit, the input end of the chopper circuit is connected to a DC power supply, the output end of the chopper circuit is connected to the primary side of the transformer, and the chopper circuit is used to control the on and off of the primary side current of the transformer.

[0006] The above-mentioned single-phase DC-AC converter has the advantages of high efficiency, low cost, small size, and strong universality through simple circuit design.

[0007] Furthermore, the primary circuit is any one of a flyback circuit, a full-bridge circuit, a two-level half-bridge circuit, an NPC circuit, a T-type circuit, an H-bridge circuit, an MMC circuit, and a Cascade multi-level circuit.

[0008] Furthermore, a fourth capacitor is connected between the first common terminal and the secondary ground line.

[0009] Furthermore, a power grid is connected between the first common terminal and the secondary ground line.

[0010] Furthermore, when the primary circuit is a flyback circuit, the chopper circuit includes a primary switch, and the DC power supply, the transformer primary, and the primary switch are connected in series to form a primary loop.

[0011] Furthermore, when the primary circuit is a full-bridge circuit, the chopper circuit includes a full-bridge arm, two outer ends of the full-bridge arm are connected to two ends of the DC power supply, and two midpoints of the full-bridge arm are connected to two ends of the primary side of the transformer.

[0012] Furthermore, the full-bridge arm includes a first, second, third, and fourth primary switches; the current input end of the first primary switch and the current input end of the third primary switch are connected together, and the current output end of the second primary switch and the current output end of the fourth primary switch are connected together to respectively constitute the first and second outer ends of the full-bridge arm; the current output end of the first primary switch and the current input end of the second primary switch are connected together, and the current output end of the third primary switch and the current input end of the fourth primary switch are connected together to respectively constitute the first and second midpoint ends of the full-bridge arm.

[0013] Furthermore, when the primary circuit is a two-level half-bridge circuit, the chopper circuit includes a half-bridge arm, the two ends of the DC power supply are connected to the two outer ends of the half-bridge arm, and the two midpoint ends of the half-bridge arm are respectively connected to the two ends of the primary side of the transformer.

[0014] Furthermore, the switch of the single-phase DC-AC converter is a fully controlled switch or a half-controlled switch.

[0015] Furthermore, the fully controlled switch is any one of MOSFET, BJT, IGBT, JFET, transistor, and relay.

[0016] Furthermore, the present invention also provides a three-phase DC-AC converter, comprising three of the above-mentioned single-phase DC-AC converters.

[0017] Furthermore, the first common terminals of the three single-phase DC-AC converters are respectively the three output L-line terminals of the three-phase DC-AC converter; the DC power supplies at the input terminals of each single-phase DC-AC converter are connected in parallel, or the input terminals of each single-phase DC-AC converter share the same DC power supply.

[0018] Furthermore, the present invention provides a DC-AC converter control method, which is applied to the DC-AC converter, and stores and transfers energy through the transformer, thereby realizing energy transfer under positive and negative cycles of the AC power frequency.

[0019] Furthermore, when the primary circuit is a flyback circuit, the DC-AC converter control method is as follows: in the first process of the positive half-cycle AC power frequency cycle, the primary switch in the primary circuit is turned on, and the switch in the secondary circuit is controlled so that the second capacitor provides a DC support function for the output end of the secondary circuit; in the second process of the positive half-cycle AC power frequency cycle, the primary switch is turned off, and the switch in the secondary circuit is controlled so that the first secondary winding of the secondary side of the transformer releases energy; in the first process of the negative half-cycle AC power frequency cycle, the primary switch is turned on, and the switch in the secondary circuit is controlled so that the third capacitor provides a DC support function for the output end of the secondary circuit; in the second process of the negative half-cycle AC power frequency cycle, the primary switch is turned off, and the switch in the secondary circuit is controlled. , so that the second secondary winding on the secondary side of the transformer releases energy; when the primary circuit is a full-bridge circuit or a two-level half-bridge circuit, the DC-AC converter control method is: in the first process of the positive half-cycle AC power frequency cycle, controlling the energy to be transferred from the primary side of the transformer to the first secondary winding; in the second process of the positive half-cycle AC power frequency cycle, demagnetization is performed through the primary side of the transformer, and in the secondary circuit, a DC support effect is provided for the output end of the secondary circuit through the second capacitor; in the first process of the negative half-cycle AC power frequency cycle, controlling the energy to be transferred from the primary side of the transformer to the second secondary winding; in the second process of the negative half-cycle AC power frequency cycle, demagnetization is performed through the primary side of the transformer, and in the secondary circuit, a DC support effect is provided for the output end of the secondary circuit through the third capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 1 is a schematic diagram of a secondary circuit according to an embodiment of the present invention;

[0021] Figure 2 A circuit diagram of a single-phase DC-AC converter according to a first embodiment of the present invention;

[0022] Figure 3 A circuit diagram of a single-phase DC-AC converter according to a second embodiment of the present invention;

[0023] Figure 4 for Figure 3 The corresponding working timing diagram of the circuit;

[0024] Figure 5 for Figure 3 The current flow path diagram of the circuit when the transformer is excited in the positive half cycle of the AC voltage;

[0025] Figure 6 for Figure 3 The current flow path diagram of the circuit when the transformer is demagnetized during the positive half cycle of the AC voltage;

[0026] Figure 7 for Figure 3 Circuit diagram of transformer excitation current flow path in the negative half cycle of AC voltage;

[0027] Figure 8 for Figure 3 The current flow path diagram when the transformer is demagnetized during the negative half cycle of the AC voltage;

[0028] Figure 9 A circuit diagram of a single-phase DC-AC converter according to a third embodiment of the present invention;

[0029] Figure 10 for Figure 9 The corresponding working timing diagram of the circuit;

[0030] Figure 11 for Figure 9 The current flow path diagram of the circuit when the transformer is excited in the positive half cycle of the AC voltage;

[0031] Figure 12 for Figure 9 The current flow path diagram of the circuit when the transformer is demagnetized during the positive half cycle of the AC voltage;

[0032] Figure 13 for Figure 9 Circuit diagram of transformer excitation current flow path in the negative half cycle of AC voltage;

[0033] Figure 14 for Figure 9 The current flow path diagram when the transformer is demagnetized during the negative half cycle of the AC voltage;

[0034] Figure 15 A circuit diagram of a single-phase DC-AC converter according to a fourth embodiment of the present invention;

[0035] Figure 16 for Figure 15 The corresponding working timing diagram of the circuit;

[0036] Figure 17 for Figure 15 The current flow path diagram of the circuit when the transformer is excited in the positive half cycle of the AC voltage;

[0037] Figure 18 for Figure 15 The current flow path diagram of the circuit when the transformer is demagnetized during the positive half cycle of the AC voltage;

[0038] Figure 19 for Figure 15 Circuit diagram of transformer excitation current flow path in the negative half cycle of AC voltage;

[0039] Figure 20 for Figure 15 The current flow path diagram when the transformer is demagnetized during the negative half cycle of the AC voltage;

[0040] Figure 21 A circuit diagram of a three-phase DC-AC converter according to a fifth embodiment of the present invention;

[0041] Figure 22 FIG. 4 is a circuit diagram of a three-phase DC-AC converter according to a sixth embodiment of the present invention.

[0042] Description of main component symbols:

[0043] C1, DC power supply; Tr, transformer; Q1 primary switch; W21, first secondary winding; W22, second secondary winding; D1, first diode; C2, second capacitor; C3, third capacitor; D2, second diode; Q3, third switch; C4, fourth capacitor; GNDS, secondary ground; Grid, AC grid; Q1a, first primary switch; Q1b, second primary switch; Q1c, third primary switch; Q1d, fourth primary switch; Dp1, first primary diode; Dp2, second primary diode; GNDP, primary ground.

[0044] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0045] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The drawings illustrate several embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present invention.

[0046] See also Figure 1, is a schematic diagram of a secondary circuit according to an embodiment of the present invention. The secondary circuit includes the secondary side of the transformer (i.e., the first secondary winding W21 and the second secondary winding W22 of the transformer Tr), a first diode D1, a second capacitor C2, a third capacitor C3, a second diode D2, a secondary ground line GNDS, a second switch Q2, and a third switch Q3. One end of the first secondary winding W21 is connected to the anode of the first diode D1, the cathode of the first diode D1, one end of the second capacitor C2, and the current input terminal of the second switch Q2 are connected together, and one end of the second secondary winding W22 is connected to the cathode of the second diode D2. The anode of the second diode D2, one end of the third capacitor C3, and the current output end of the third switch Q3 are connected together. The current output end of the second switch Q2 and the current input end of the third switch Q3 are connected together to form a first common end. The other end of the first secondary winding W21, the other end of the second secondary winding W22, the other end of the second capacitor C2, and the other end of the third capacitor C3 are all connected to the secondary ground line GNDS. The first common end and the secondary ground line GNDS constitute the output end of the secondary circuit, that is, the output end of the entire single-phase DC-AC converter.

[0047] In other embodiments, the first diode D1 is replaced by a seventh switch. It is understandable that the current input terminal and the current output terminal of the seventh switch correspond to the anode and the cathode of the first diode D1, respectively.

[0048] In other embodiments, the second diode D2 may be replaced by an eighth switch. It is understandable that the current input terminal and the current output terminal of the eighth switch correspond to the anode and the cathode of the second diode D2, respectively.

[0049] In other embodiments, the first diode D1 and the second diode D2 can be replaced by a seventh switch and an eighth switch, respectively. It can be understood that the current input end and the current output end of the seventh switch correspond to the positive electrode and the negative electrode of the first diode D1, respectively; the current input end and the current output end of the eighth switch correspond to the positive electrode and the negative electrode of the second diode D2, respectively. Example

[0050] See also Figure 2 , is a circuit diagram of a first embodiment of a single-phase DC-AC converter according to the present invention. In this embodiment, the single-phase DC-AC converter includes a primary circuit and the aforementioned secondary circuit.

[0051] The primary circuit includes the primary side of the transformer Tr (i.e., the primary winding W1 of the transformer Tr) and a chopper circuit. The input end of the chopper circuit is connected to the DC power supply C1, and the output end of the chopper circuit is connected to the primary side of the transformer Tr. The chopper circuit is used to control the on and off of the primary current of the transformer.

[0052] As can be understood, the primary circuit converts the DC voltage into a chopped pulse voltage waveform through the chopper circuit for transformer coupling. The output voltage / current of the secondary circuit is adjusted by controlling the duty cycle and / or switching frequency of the chopper circuit in the primary circuit. More specifically, the primary circuit converts the DC voltage into a chopped pulse voltage waveform through the on-off switching of the switching devices in the chopper circuit for transformer coupling. The output voltage / current of the secondary circuit is adjusted by controlling the duty cycle and / or switching frequency of the switching devices in the chopper circuit in the primary circuit.

[0053] The second capacitor C2 and the third capacitor C3 have two functions: first, when the secondary side of the transformer Tr is working (releasing energy), they perform filtering after rectification and provide DC support for the output end of the secondary circuit; second, when the secondary side of the transformer Tr is not working, they provide DC support for the output end of the secondary circuit.

[0054] In one embodiment, a fourth capacitor C4 is connected between the first common terminal and the secondary ground line GNDS of the single-phase DC-AC converter of the present invention.

[0055] In one embodiment, the AC grid Grid is connected between the first common terminal and the secondary ground line GNDS of the single-phase DC-AC converter of the present invention.

[0056] In one embodiment, a fourth capacitor C4 and an AC grid Grid are connected between the first common terminal and the secondary ground GNDS of the single-phase DC-AC converter of the present invention. The AC grid Grid and the fourth capacitor C4 are connected in parallel.

[0057] It can be understood that, in one embodiment, the DC power source C1 can be a capacitor or other types of DC power sources.

[0058] As can be seen from the above, the single-phase DC-AC converter of the present invention uses only two diodes on the secondary side, so the power conversion circuit is simplified and the system loss is reduced, thereby achieving a single-stage conversion effect while improving efficiency. Example

[0059] See also Figure 3, is a circuit diagram of a second embodiment of a single-phase DC-AC converter according to the present invention. In this embodiment, the single-phase DC-AC converter includes a primary circuit and a secondary circuit. The primary circuit comprises the primary side of a transformer Tr (i.e., the primary winding W1 of the transformer Tr) and a chopper circuit. The chopper circuit includes a primary switch Q1. A DC power supply C1, the primary side of the transformer Tr, and the primary switch Q1 are connected in series to form a primary loop. More specifically, one end of the DC power supply C1 is connected to one end of the primary winding W1 of the transformer Tr, the other end of the primary winding W1 of the transformer Tr is connected to the current input end of the primary switch Q1, and the current output end of the primary switch Q1 is connected to the other end of the DC power supply C1.

[0060] In the second embodiment, the secondary circuit is the same as that in the first embodiment and will not be described again here.

[0061] Figure 4 for Figure 3 The corresponding working timing diagram of the circuit; combined with Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 、 Figure 7 、 Figure 8 The working principle of the single-phase DC-AC converter according to the first embodiment of the present invention is described. The primary winding W1 of the transformer Tr is connected to a DC power source C1 and a primary switch Q1, respectively, to store energy during switching chopping. The first and second secondary windings W21 and W22 of the transformer Tr are connected to a first diode D1, a second diode D2, and the secondary ground line GNDS, respectively. Energy is converted from the primary side to the secondary side through the transformer, and the current phase sequence and phase angle follow and remain consistent with the voltage of the AC grid Grid. Based on the power frequency cycle of the AC grid Grid, the second switch Q2 and the third switch Q3 are controlled to conduct during the positive and negative half-cycles, respectively. Specifically, during the positive half-cycle of the AC power frequency cycle, the second switch Q2 is turned on and the third switch Q3 is turned off. The transformer is excited and demagnetized through the primary winding W1 and the secondary winding (the first secondary winding W21), respectively. During the negative half-cycle of the AC power frequency cycle, the second switch Q2 is turned off and the third switch Q3 is turned on. The transformer is excited and demagnetized through the primary winding W1 and the secondary winding (the second secondary winding W22), respectively.

[0062] Specifically, Figure 3 The control method / working principle of the single-phase DC-AC converter shown is:

[0063] During the first half of the AC power frequency cycle (see Figure 4 and Figure 5 ),correspond Figure 4During the phases where Q1 is driven high, Q2 is driven high, and Q3 is driven low, the primary switch Q1 is on, the second switch Q2 is on, and the third switch Q3 is off. The primary current ip flows through the DC power supply C1, the primary winding W1, the primary switch Q1, and the DC power supply C1. The secondary current is flows through the secondary ground GNDS, the second capacitor C2, the second switch Q2, the fourth capacitor C4 and / or the AC grid Grid, and the secondary ground GNDS. It can be understood that the first process of the positive half-cycle of the AC power frequency cycle is the first energy storage process. In the secondary circuit, the second capacitor C2 provides DC support for the output terminal of the secondary circuit.

[0064] During the second half of the AC power frequency cycle (see Figure 4 and Figure 6 ),correspond Figure 4 During the phase where Q1 is driven low, Q2 is driven high, and Q3 is driven low, the primary switch Q1 is off, the second switch Q2 is on, and the third switch Q3 is off. The primary circuit is disconnected, resulting in no current flowing through the primary. The secondary current is has two flow paths: one through the first secondary winding W21, the first diode D1, the second switch Q2, the fourth capacitor C4 and / or the AC grid Grid, the secondary ground GNDS, and the first secondary winding W21; the other through the first secondary winding W21, the first diode D1, the second capacitor C2, the secondary ground GNDS, and the first secondary winding W21. It can be understood that the second process of the positive half-cycle of the AC power frequency cycle is the first energy release process, in which the first secondary winding W21 on the secondary side of the transformer releases energy for use in the secondary circuit.

[0065] During the first negative half-cycle of the AC power frequency cycle (see Figure 4 and Figure 7 ),correspond Figure 4 During the phase where Q1 is driven high, Q2 is driven low, and Q3 is driven high, the primary switch Q1 is on, the second switch Q2 is off, and the third switch Q3 is on. The primary current ip flows through the DC power supply C1, the primary winding W1, the primary switch Q1, and the DC power supply C1. The secondary current is flows through the secondary ground GNDS, the fourth capacitor C4 and / or the AC grid Grid, the third switch Q3, the third capacitor C3, and the secondary ground GNDS. It can be understood that the first process of the negative half-cycle AC power frequency cycle is the second energy storage process. In the secondary circuit, the third capacitor C3 provides DC support for the output terminal of the secondary circuit.

[0066] During the second negative half-cycle of the AC power frequency cycle (see Figure 4 and Figure 8 ),correspond Figure 4During the phase where Q1 is driven low, Q2 is driven low, and Q3 is driven high, the primary switch Q1 is off, the second switch Q2 is off, and the third switch Q3 is on. The primary circuit is disconnected, resulting in no current flowing on the primary side. The secondary current is has two flow paths: one through the second secondary winding W22, the secondary ground GNDS, the fourth capacitor C4 and / or the AC grid Grid, the third switch Q3, the second diode D2, and the second secondary winding W22; the other through the second secondary winding W22, the secondary ground GNDS, the third capacitor C3, the second diode D2, and the second secondary winding W22. The second process of the negative half-cycle of the AC power frequency cycle is the second energy release process, in which the second secondary winding W22 on the secondary side of the transformer releases energy for use in the secondary circuit.

[0067] It can be understood that in the second embodiment, the primary circuit of the single-phase DC-AC converter is a flyback circuit / topology. Example

[0068] Figure 9 The single-phase DC-AC converter circuit diagram of the third embodiment of the present invention is shown in FIG. In this embodiment, the single-phase DC-AC converter also includes a primary circuit and a secondary circuit. The primary circuit includes the primary side of the transformer Tr and the chopper circuit. Figure 3 Compared with the single-phase DC-AC converter in the embodiment, the difference is that the primary circuit in the third embodiment is a full-bridge circuit / topology, in which the chopper circuit includes a full-bridge arm, the two outer ends of the full-bridge arm are connected to the two ends of the DC power supply C1, and the two midpoints of the full-bridge arm are connected to the two ends of the primary winding W1.

[0069] In one embodiment, the full-bridge arm includes four primary switches, namely, a first primary switch Q1a, a second primary switch Q1b, a third primary switch Q1c, and a fourth primary switch Q1d. The current input end of the first primary switch Q1a and the current input end of the third primary switch Q1c are connected together to form a first external end of the full-bridge arm. The current output end of the second primary switch Q1b and the current output end of the fourth primary switch Q1d are connected together to form a second external end of the full-bridge arm. The current output end of the first primary switch Q1a and the current input end of the second primary switch Q1b are connected together to form a second external end of the full-bridge arm. The input terminals of the third primary switch Q1c and the current input terminal of the fourth primary switch Q1d are connected together to form the first midpoint terminal of the full-bridge arm, the current output terminal of the third primary switch Q1c and the current input terminal of the fourth primary switch Q1d are connected together to form the second midpoint terminal of the full-bridge arm, the first external terminal of the full-bridge arm is connected to one end of the DC power supply C1, and the second external terminal of the full-bridge arm is connected to the other end of the DC power supply C1; the first midpoint terminal of the full-bridge arm is connected to one end of the primary winding W1 of the transformer Tr, the other end of the primary winding W1 of the transformer Tr is connected to the second midpoint terminal of the full-bridge arm, and the current output terminal of the primary switch Q1 is connected to the other end of the DC power supply C1.

[0070] Specifically, Figure 9The control method / working principle of the single-phase DC-AC converter shown is:

[0071] During the first half of the AC power frequency cycle (see Figure 10 and Figure 11 ),correspond Figure 10 In the stage where Q1a and Q1d are driven at a high level, Q1b and Q1c are driven at a low level, Q2 is driven at a high level, and Q3 is driven at a low level, the first primary switch Q1a and the fourth primary switch Q1d are turned on, the second primary switch Q1b and the third primary switch Q1c are turned off, the second switch Q2 is turned on, and the third switch Q3 is turned off. The primary current ip flows through the DC power supply C1, the first primary switch Q1a, the primary winding W1, the fourth primary switch Q1d, and the DC power supply C1. The secondary current is has two flow paths: one is through the first secondary winding W21, the first diode D1, the second switch Q2, the fourth capacitor C4 and / or the AC grid Grid, the secondary ground GNDS, and the first secondary winding W21; the other is through the first secondary winding W21, the first diode D1, the second capacitor C2, and the first secondary winding W21. It can be understood that during the first process of the positive half-cycle AC power frequency cycle, energy is transferred from the primary side of the transformer Tr to the first secondary winding W21 of the secondary side of the transformer for use by the secondary circuit.

[0072] During the second half of the AC power frequency cycle (see Figure 10 and Figure 12 ),correspond Figure 10 During the phase where Q1a and Q1d are driven low, Q1b and Q1c are driven high, Q2 is driven high, and Q3 is driven low, the first primary switch Q1a and the fourth primary switch Q1d are off, the second primary switch Q1b and the third primary switch Q1c are on, the second switch Q2 is on, and the third switch Q3 is off. The primary current ip flows through the DC power supply C1, the third primary switch Q1c, the primary winding W1, the second primary switch Q1b, and the DC power supply C1. The secondary current is flows through the secondary ground GNDS, the second capacitor C2, the second switch Q2, the fourth capacitor C4 and / or the AC grid Grid, and the secondary ground GNDS. It can be understood that during the second positive half-cycle of the AC power frequency cycle, demagnetization is performed through the primary side of the transformer Tr. In the secondary circuit, the second capacitor C2 provides DC support for the output terminal of the secondary circuit.

[0073] During the first negative half-cycle of the AC power frequency cycle (see Figure 10 and Figure 13 ),correspond Figure 10In the stage where Q1a and Q1d are driven at a high level, Q1b and Q1c are driven at a low level, Q2 is driven at a low level, and Q3 is driven at a high level, the first primary switch Q1a and the fourth primary switch Q1d are turned on, the second primary switch Q1b and the third primary switch Q1c are turned off, the second switch Q2 is turned off, and the third switch Q3 is turned on. The primary current ip flows through the DC power supply C1, the first primary switch Q1a, the primary winding W1, the fourth primary switch Q1d, and the DC power supply C1. The secondary current is has two flows: one through the second secondary winding W22, the secondary ground GNDS, the fourth capacitor C4 and / or the AC grid Grid, the third switch Q3, the second diode D2, and the second secondary winding W22; and the other through the second secondary winding W22, the third capacitor C3, the second diode D2, and the second secondary winding W22. It can be understood that during the first process of the negative half-cycle AC power frequency cycle, energy is transferred from the primary side of the transformer Tr to the second secondary winding W22 of the secondary side of the transformer for use by the secondary circuit.

[0074] During the second negative half-cycle of the AC power frequency cycle (see Figure 10 and Figure 14 ),correspond Figure 10 During the phase where Q1a and Q1d are driven low, Q1b and Q1c are driven high, Q2 is driven low, and Q3 is driven high, the first and fourth primary switches Q1a and Q1d are off, the second and third primary switches Q1b and Q1c are on, the second switch Q2 is off, and the third switch Q3 is on. The primary current ip flows through the DC power supply C1, the third primary switch Q1c, the primary winding W1, the second primary switch Q1b, and the DC power supply C1. The secondary current is flows through the secondary ground GNDS, the fourth capacitor C4 and / or the AC grid Grid, the third switch Q3, the third capacitor C3, and the secondary ground GNDS. It can be understood that during the second negative half-cycle of the AC power frequency cycle, demagnetization is performed via the primary side of the transformer Tr. In the secondary circuit, the third capacitor C3 provides DC support for the output terminal of the secondary circuit. Example

[0075] Figure 15 This is a circuit diagram of a single-phase DC-AC converter according to a fourth embodiment of the present invention. In this embodiment, the single-phase DC-AC converter also includes a primary circuit and a secondary circuit. The primary circuit includes the primary side of the transformer Tr and the chopper circuit. Figure 3 Compared with the single-phase DC-AC converter in the embodiment, the difference is that the primary circuit in the fourth embodiment is a two-level half-bridge circuit / topology, wherein the chopper circuit includes a half-bridge arm, the two ends of the DC power supply are connected to the two outer ends of the half-bridge arm, and the two midpoint ends of the half-bridge arm are respectively connected to the two ends of the primary winding W1.

[0076] In one embodiment, the DC power supply C1 includes two first DC power supplies C11 and second DC power supplies C12 connected in series, and the common end of the two (i.e., the other end of the first DC power supply C11 and the other end of the second DC power supply C12) is the midpoint of the two, or the midpoint of the DC power supply.

[0077] In one embodiment, the half-bridge arm includes four primary switches and two primary diodes. The four primary switches include a first primary switch Q1a, a second primary switch Q1b, a third primary switch Q1c, and a fourth primary switch Q1d. The two primary diodes include a first primary diode Dp1 and a second primary diode Dp2. One end of the first DC power supply C11 (i.e., the first end of the DC power supply) is connected to the current input end of the first primary switch Q1a (i.e., the first outer end of the half-bridge leg). The current output end of the first primary switch Q1a is connected to the current input end of the second primary switch Q1b and the cathode of the first primary diode Dp1. The current output end of the second primary switch Q1b is connected to the current output end of the third primary switch Q1c, forming the first midpoint of the half-bridge leg and connected to one end of the primary winding W1. The anode of the first primary diode Dp1 is connected to the cathode of the second primary diode Dp2, forming the second midpoint of the half-bridge leg and connected to the other end of the primary winding W1, the midpoint of the DC power supply, and the primary ground GNDP. One end of the second DC power supply C12 (i.e., the second end of the DC power supply) is connected to the current input end of the fourth primary switch Q1d (i.e., the second outer end of the half-bridge leg). The current output end of the fourth primary switch Q1d is connected to the current input end of the third primary switch Q1c and the anode of the second primary diode Dp2.

[0078] Specifically, Figure 15 The control method / working principle of the single-phase DC-AC converter shown is:

[0079] During the first half of the AC power frequency cycle (see Figure 16 and Figure 17 ),correspond Figure 16In the stage where Q1a and Q1b are driven at a high level, Q1c and Q1d are driven at a low level, Q2 is driven at a high level, and Q3 is driven at a low level, the first primary switch Q1a and the second primary switch Q1b are turned on, the third primary switch Q1c and the fourth primary switch Q1d are turned off, the second switch Q2 is turned on, and the third switch Q3 is turned off. The primary current ip flows through the primary ground GNDP, the first DC power supply C11, the first primary switch Q1a, the second primary switch Q1b, the primary winding W1, and the primary ground GNDP. The secondary current is has two flows: one through the first secondary winding W21, the first diode D1, the second switch Q2, the fourth capacitor C4 and / or the AC grid Grid, the secondary ground GNDS, and the first secondary winding W21; and the other through the first secondary winding W21, the first diode D1, the second capacitor C2, and the first secondary winding W21. It can be understood that during the first process of the positive half-cycle AC power frequency cycle, energy is transferred from the primary side of the transformer Tr to the first secondary winding W21 of the secondary side of the transformer for use by the secondary circuit.

[0080] During the second half of the AC power frequency cycle (see Figure 16 and Figure 18 ),correspond Figure 16 During the phase where Q1a is driven low, Q1b is driven high, Q1c and Q1d are driven low, Q2 is driven high, and Q3 is driven low, the first primary switch Q1a is off, the second primary switch Q1b is on, the third primary switch Q1c and the fourth primary switch Q1d are off, the second switch Q2 is on, and the third switch Q3 is off. The primary current ip flows through the primary ground GNDP, the first primary diode Dp1, the second primary switch Q1b, the primary winding W1, and the primary ground GNDP. The secondary current is flows through the secondary ground GNDS, the second capacitor C2, the second switch Q2, the fourth capacitor C4 and / or the AC grid Grid, and the secondary ground GNDS. It can be understood that during the second positive half-cycle of the AC power frequency cycle, demagnetization is performed through the primary side of the transformer Tr. In the secondary circuit, the second capacitor C2 provides DC support for the output terminal of the secondary circuit.

[0081] During the first negative half-cycle of the AC power frequency cycle (see Figure 16 and Figure 19 ),correspond Figure 16In the stage where Q1a and Q1b are driven at a low level, Q1c and Q1d are driven at a high level, Q2 is driven at a low level, and Q3 is driven at a high level, the first primary switch Q1a and the second primary switch Q1b are turned on, the third primary switch Q1c and the fourth primary switch Q1d are turned off, the second switch Q2 is turned off, and the third switch Q3 is turned on. The primary current ip flows through the primary ground GNDP, the primary winding W1, the third primary switch Q1c, the fourth primary switch Q1d, the second DC power supply C12, and the primary ground GNDP. The secondary current is has two flows: one through the second secondary winding W22, the secondary ground GNDS, the fourth capacitor C4 and / or the AC grid Grid, the third switch Q3, the second diode D2, and the second secondary winding W22; and the other through the second secondary winding W22, the third capacitor C3, the second diode D2, and the second secondary winding W22. It can be understood that during the first process of the negative half-cycle AC power frequency cycle, energy is transferred from the primary side of the transformer Tr to the second secondary winding W22 of the secondary side of the transformer for use by the secondary circuit.

[0082] During the second negative half-cycle of the AC power frequency cycle (see Figure 16 and Figure 20 ),correspond Figure 16 During the phases where Q1a and Q1b are driven low, Q1c is driven high, Q1d is driven low, Q2 is driven low, and Q3 is driven high, the primary switch Q1 is off, the second switch Q2 is off, and the third switch Q3 is on. The primary current ip flows through the primary ground GNDP, the primary winding W1, the third primary switch Q1c, the second primary diode Dp2, and the primary ground GNDP. The secondary current is flows through the secondary ground GNDS, the fourth capacitor C4 and / or the AC grid Grid, the third switch Q3, the third capacitor C3, and the secondary ground GNDS. It can be understood that during the second phase of the negative half-cycle AC power frequency cycle, demagnetization occurs through the primary side of the transformer Tr. In the secondary circuit, the third capacitor C3 provides DC support for the output terminal of the secondary circuit.

[0083] It can be understood that in other embodiments, the primary circuit of the single-phase DC-AC converter of the present invention may be an NPC circuit / topology, a T-type circuit / topology, an H-bridge circuit / topology, an MMC (modular multilevel) circuit / topology, a Cascade multilevel circuit / topology, etc., which will not be repeated here.

[0084] It can be understood that in some embodiments, the switches involved in the single-phase DC-AC converter of the present invention may be fully controlled switches or half-controlled switches such as MOSFET, BJT, IGBT, JFET, transistor, relay, etc.

[0085] It can be understood that in other embodiments, when the first diode D1 and the second diode D2 are replaced by the seventh switch and the eighth switch, the control method of the corresponding single-phase DC-AC converter is similar to the above-mentioned method. It is only necessary to control the corresponding seventh switch or the eighth switch to be turned on when the corresponding secondary side of the transformer is working, and to control the corresponding seventh switch or the eighth switch to be turned off at other times (when the corresponding secondary side of the transformer is not working).

[0086] Specifically, when the seventh switch replaces the first diode D1 in the second embodiment, the seventh switch is controlled to be turned on during the second period of the positive half-cycle AC power frequency cycle, and is controlled to be turned off during the other three periods. When the eighth switch replaces the first diode D1 and the second diode D2 in the second embodiment, the eighth switch is controlled to be turned on during the second period of the negative half-cycle AC power frequency cycle, and is controlled to be turned off during the other three periods. When the seventh switch replaces the first diode D1 in the third / fourth embodiment, the seventh switch is controlled to be turned on during the first period of the positive half-cycle AC power frequency cycle, and is controlled to be turned off during the other three periods. When the eighth switch replaces the second diode D2 in the third / fourth embodiment, the eighth switch is controlled to be turned on during the first period of the negative half-cycle AC power frequency cycle, and is controlled to be turned off during the other three periods.

[0087] Specifically, when the seventh switch and the eighth switch replace the first diode D1 and the second diode D2 in the second embodiment, respectively, the seventh switch is controlled to be turned on during the second period of the positive half-cycle AC power frequency cycle and to be turned off during the other three periods; the eighth switch is controlled to be turned on during the second period of the negative half-cycle AC power frequency cycle and to be turned off during the other three periods. Furthermore, when the seventh switch and the eighth switch replace the first diode D1 and the second diode D2 in the third / fourth embodiments, respectively, the seventh switch is controlled to be turned on during the first period of the positive half-cycle AC power frequency cycle and to be turned off during the other three periods; the eighth switch is controlled to be turned on during the first period of the negative half-cycle AC power frequency cycle and to be turned off during the other three periods. Example

[0088] like Figure 21 As shown, the present invention further provides a three-phase DC-AC converter, comprising three of the aforementioned single-phase DC-AC converters, wherein the DC power supplies at the input ends of each single-phase DC-AC converter are connected in parallel, and the three output L-line terminals of the three-phase DC-AC converter are L1, L2, and L3 (i.e., the first common terminal of each single-phase DC-AC converter). In one embodiment, L1, L2, and L3 are respectively connected to the three phases of the power grid, namely, the U phase, the V phase, and the W phase, and the three output N-line terminals GNDS of the three-phase DC-AC converter are connected to the power grid ground. Example

[0089] like Figure 22As shown, the present invention further provides a three-phase DC-AC converter, comprising three of the aforementioned single-phase DC-AC converters, wherein the input terminals of each single-phase DC-AC converter share a common DC power supply, and the three output L-line terminals of the three-phase DC-AC converter are L1, L2, and L3 (i.e., the first common terminal of each single-phase DC-AC converter). In one embodiment, L1, L2, and L3 are respectively connected to the three phases of the power grid, namely, the U phase, the V phase, and the W phase, and the three output N-line terminals GNDS of the three-phase DC-AC converter are connected to the power grid ground.

[0090] The DC-AC converter of the present invention uses a simpler circuit to achieve single-stage conversion, which not only improves the system conversion efficiency but also reduces the cost of semiconductor devices, thereby making the entire energy conversion system high in efficiency, low in cost, small in size, and widely applicable.

[0091] Furthermore, the DC-AC converter control method of the present invention is applied to the single-phase DC-AC converter and the three-phase DC-AC converter of the present invention, and stores and transfers energy through the transformer, thereby realizing energy transfer under the positive and negative cycles of the AC industrial frequency.

[0092] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A single-phase DC-AC converter, characterized in that: The secondary circuit includes a first secondary winding of a transformer, a second secondary winding of the transformer, a first diode, a second capacitor, a third capacitor, a second diode, a secondary ground wire, a second switch, a third switch, and a fourth capacitor. One end of the first secondary winding is connected to the positive electrode of the first diode, the negative electrode of the first diode, one end of the second capacitor, and the current input end of the second switch are connected together, one end of the second secondary winding is connected to the cathode of the second diode, the anode of the second diode, one end of the third capacitor, and the current output end of the third switch are connected together, the current output end of the second switch and the current input end of the third switch are connected together to form a first common end, and the first secondary winding is connected to the positive electrode of the first diode, the negative electrode of the first diode, one end of the second capacitor, and the current input end of the third switch are connected together. The other end of the primary winding, the other end of the second secondary winding, the other end of the second capacitor and the other end of the third capacitor are all connected to the secondary ground; or, the first diode is replaced by a seventh switch; or / and, the second diode is replaced by an eighth switch; wherein, the current input end and the current output end of the seventh switch and the eighth switch respectively correspond to the positive electrode and the negative electrode of the first diode and the second diode respectively; further comprising a primary circuit, the primary circuit comprising a transformer primary and a chopper circuit, the input end of the chopper circuit being connected to a DC power supply, the output end of the chopper circuit being connected to the transformer primary, the chopper circuit being used to control the on and off of the transformer primary current; storing and Transfer energy, thereby realizing energy transfer under the positive and negative cycles of the AC power frequency; when the primary circuit is a flyback circuit, the DC-AC converter control method is as follows: in the first process of the positive half-cycle AC power frequency cycle, the primary switch in the primary circuit is turned on, and the switch in the secondary circuit is controlled so that the second capacitor provides a DC support function for the output end of the secondary circuit; in the second process of the positive half-cycle AC power frequency cycle, the primary switch is turned off, and the switch in the secondary circuit is controlled so that the first secondary winding of the secondary side of the transformer releases energy; in the first process of the negative half-cycle AC power frequency cycle, the primary switch is turned on, and the switch in the secondary circuit is controlled so that the third capacitor provides a DC support function for the output end of the secondary circuit Supporting role; in the second process of the negative half-cycle AC power frequency cycle, the primary switch is disconnected, and the switch in the secondary circuit is controlled to release energy from the second secondary winding of the secondary side of the transformer; when the primary circuit is a full-bridge circuit or a two-level half-bridge circuit, the DC-AC converter control method is as follows: in the first process of the positive half-cycle AC power frequency cycle, energy is controlled to be transferred from the primary side of the transformer to the first secondary winding; in the second process of the positive half-cycle AC power frequency cycle, demagnetization is performed through the primary side of the transformer, and in the secondary circuit, a DC support effect is provided for the output end of the secondary circuit through the second capacitor; in the first process of the negative half-cycle AC power frequency cycle, energy is controlled to be transferred from the primary side of the transformer to the second secondary winding;During the second process of the negative half-cycle AC power frequency cycle, demagnetization is performed through the primary side of the transformer, and in the secondary circuit, a DC support function is provided for the output end of the secondary circuit through the third capacitor.

2. The single-phase DC-AC converter according to claim 1, characterized in that: The primary circuit is any one of a flyback circuit, a full-bridge circuit, a two-level half-bridge circuit, an NPC circuit, a T-type circuit, an H-bridge circuit, an MMC circuit, and a Cascade multi-level circuit.

3. The single-phase DC-AC converter according to claim 2, characterized in that: A fourth capacitor is connected between the first common terminal and the secondary ground line.

4. The single-phase DC-AC converter according to claim 3, characterized in that: A power grid is connected between the first common terminal and the secondary ground line.

5. The single-phase DC-AC converter according to any one of claims 2 to 4, characterized in that: When the primary circuit is a flyback circuit, the chopper circuit includes a primary switch, and the DC power supply, the primary side of the transformer and the primary switch are connected in series to form a primary loop.

6. The single-phase DC-AC converter according to any one of claims 2 to 4, characterized in that: When the primary circuit is a full-bridge circuit, the chopper circuit includes a full-bridge arm, two outer ends of the full-bridge arm are connected to the two ends of the DC power supply, and two midpoints of the full-bridge arm are connected to the two ends of the primary side of the transformer.

7. The single-phase DC-AC converter according to claim 6, characterized in that: The full-bridge arm includes first, second, third, and fourth primary switches; the current input end of the first primary switch is connected to the current input end of the third primary switch, and the current output end of the second primary switch is connected to the current output end of the fourth primary switch, respectively forming the first and second outer ends of the full-bridge arm; the current output end of the first primary switch is connected to the current input end of the second primary switch, and the current output end of the third primary switch is connected to the current input end of the fourth primary switch, respectively forming the first and second midpoint ends of the full-bridge arm.

8. The single-phase DC-AC converter according to any one of claims 2 to 4, characterized in that: When the primary circuit is a two-level half-bridge circuit, the chopper circuit includes a half-bridge arm, the two ends of the DC power supply are connected to the two outer ends of the half-bridge arm, and the two midpoint ends of the half-bridge arm are respectively connected to the two ends of the primary side of the transformer.

9. The single-phase DC-AC converter according to any one of claims 2 to 4, characterized in that: The switch of the single-phase DC-AC converter is a fully controlled switch or a half-controlled switch.

10. The single-phase DC-AC converter according to claim 9, characterized in that: The fully controlled switch is any one of MOSFET, BJT, IGBT, JFET, transistor, and relay.

11. A three-phase DC-AC converter, characterized in that: The device comprises three single-phase DC-AC converters according to any one of claims 2 to 10.

12. The three-phase DC-AC converter according to claim 11, characterized in that: The first common terminals of the three single-phase DC-AC converters are respectively the three output L-line terminals of the three-phase DC-AC converters; the DC power supplies at the input terminals of each single-phase DC-AC converter are connected in parallel, or the input terminals of each single-phase DC-AC converter share the same DC power supply.

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