Secondary side circuit, single-phase and three-phase AC / DC converter and control method

Abstract

The invention discloses a secondary circuit, a single-phase and three-phase AC / DC converter and a control method, in the secondary circuit, one end of a first secondary winding is connected with the positive electrode of a first diode, the negative electrode of the first diode, one end of a second capacitor and the current input end of a second switch are connected together, and the other end of the second switch is connected with the negative electrode of a second secondary winding. One end of the second secondary winding is connected with 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, and 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 with a secondary side ground wire; the DC converter comprises the secondary circuit. The secondary circuit and the AC / DC converter are simple in circuit, high in efficiency, low in cost, small in size and high in universality.

Description

Technical Field

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

[0002] In existing single-phase AC-DC converters, usually two methods are adopted to achieve high-frequency isolation and grid connection. The first is to use a flyback conversion topology to achieve high-frequency isolation, and then add power-frequency commutation to follow the grid frequency to achieve the grid connection function; the second is to use a full-bridge or half-bridge topology to achieve high-frequency isolation, and then add a stage of high-frequency inversion to achieve the grid connection function. However, due to having two-stage power conversion, both of them have problems such as low system efficiency and high cost. Summary of the Invention

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

[0004] First of all, the present invention provides a secondary circuit. 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, and 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, and 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. 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 wire; alternatively, 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 current output end of the seventh switch and the eighth switch respectively correspond to the positive electrode and negative electrode of the first diode and the second diode.

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

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

[0007] Further, 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 multilevel circuit.

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

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

[0010] Further, 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.

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

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

[0013] Further, when the primary circuit is a two-level half-bridge circuit, the chopper circuit includes a half-bridge arm. Both 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 both ends of the primary side of the transformer.

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

[0015] Further, the fully controlled switch is any one of a MOSFET, a BJT, an IGBT, a JFET, a transistor, and a Relay.

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

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

[0018] In addition, the present invention also provides an AC-DC converter control method, which is applied to the AC-DC converter, and stores and transfers energy through the transformer, so as to achieve energy transfer under the positive and negative cycles of the AC power frequency.

[0019] Furthermore, when the primary circuit is a flyback circuit, the AC-DC converter control method is as follows: in the first process of the positive half-cycle AC power frequency period, 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 period, the primary switch is turned off, and the switch in the secondary circuit is controlled so that the first secondary winding of the transformer secondary releases energy; in the first process of the negative half-cycle AC power frequency period, 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 period, the primary switch is turned off, and the switch in the secondary circuit is controlled so that the second secondary winding of the transformer secondary releases energy; when the primary circuit is a full-bridge circuit or a two-level half-bridge circuit, the AC-DC converter control method is as follows: in the first process of the positive half-cycle AC power frequency period, control 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 period, demagnetize through the primary side of the transformer, and in the secondary circuit, the second capacitor provides a DC support function for the output end of the secondary circuit; in the first process of the negative half-cycle AC power frequency period, control 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 period, demagnetize through the primary side of the transformer, and in the secondary circuit, the third capacitor provides a DC support function for the output end of the secondary circuit. Description of the Drawings

[0020] Figure 1 Schematic diagram of the secondary circuit according to an embodiment of the present invention; Figure 2 Circuit diagram of the single-phase AC-DC converter according to the first embodiment of the present invention; Figure 3 Circuit diagram of the single-phase AC-DC converter according to the second embodiment of the present invention; Figure 4 For Figure 3 Circuit corresponding working timing diagram; Figure 5 ForFigure 3 Current flow path diagram of the circuit when the transformer is magnetized during the positive half-cycle of the AC voltage; Figure 6 For Figure 3 Current flow path diagram of the circuit when the transformer is demagnetized during the positive half-cycle of the AC voltage; Figure 7 For Figure 3 Current flow path diagram of the circuit when the transformer is magnetized during the negative half-cycle of the AC voltage; Figure 8 For Figure 3 Current flow path diagram of the circuit when the transformer is demagnetized during the negative half-cycle of the AC voltage; Figure 9 Single-phase AC-DC converter circuit diagram of the third embodiment of the present invention; Figure 10 For Figure 9 Corresponding working timing diagram of the circuit; Figure 11 For Figure 9 Current flow path diagram of the circuit when the transformer is magnetized during the positive half-cycle of the AC voltage; Figure 12 For Figure 9 Current flow path diagram of the circuit when the transformer is demagnetized during the positive half-cycle of the AC voltage; Figure 13 For Figure 9 Current flow path diagram of the circuit when the transformer is magnetized during the negative half-cycle of the AC voltage; Figure 14 For Figure 9 Current flow path diagram of the circuit when the transformer is demagnetized during the negative half-cycle of the AC voltage; Figure 15 Single-phase AC-DC converter circuit diagram of the fourth embodiment of the present invention; Figure 16 For Figure 15 Corresponding working timing diagram of the circuit; Figure 17 For Figure 15 Current flow path diagram of the circuit when the transformer is magnetized during the positive half-cycle of the AC voltage; Figure 18 For Figure 15 Current flow path diagram of the circuit when the transformer is demagnetized during the positive half-cycle of the AC voltage; Figure 19 For Figure 15 Current flow path diagram of the circuit when the transformer is magnetized during the negative half-cycle of the AC voltage; Figure 20 For Figure 15 Current flow path diagram of the circuit when the transformer is demagnetized during the negative half-cycle of the AC voltage; Figure 21 Three-phase AC-DC converter circuit diagram of the fifth embodiment of the present invention; Figure 22 This is the circuit diagram of a three-phase AC-DC converter according to the sixth embodiment of the present invention.

[0021] Description of main component symbols: 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 wire; Grid, AC power 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 wire.

[0022] The following specific embodiments will further illustrate the present invention in conjunction with the above-mentioned drawings. Specific embodiments

[0023] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0024] Please refer to Figure 1 , which is a schematic diagram of the secondary circuit according to an embodiment of the present invention. Among them, 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), the first diode D1, the second capacitor C2, the third capacitor C3, the second diode D2, the secondary ground wire GNDS, the second switch Q2, and the third switch Q3. One end of the first secondary winding W21 is connected to the positive electrode of the first diode D1, and the negative electrode of the first diode D1, one end of the second capacitor C2, and the current input end of the second switch Q2 are connected together. One end of the second secondary winding W22 is connected to the cathode of the second diode D2, and 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 wire GNDS. Among them, the first common end and the secondary ground wire GNDS form the output end of the secondary circuit, that is, the output end of the entire single-phase AC-DC converter.

[0025] In other embodiments, the first diode D1 is replaced by a seventh switch. Understandably, the current input end and the current output end of the seventh switch respectively correspond to the positive electrode and the negative electrode of the first diode D1.

[0026] In other embodiments, the second diode D2 can be replaced by an eighth switch. Understandably, the current input terminal and the current output terminal of the eighth switch respectively correspond to the positive electrode and the negative electrode of the second diode D2.

[0027] In other embodiments, the first diode D1 and the second diode D2 can be replaced by a seventh switch and an eighth switch respectively. Understandably, the current input terminal and the current output terminal of the seventh switch respectively correspond to the positive electrode and the negative electrode of the first diode D1; the current input terminal and the current output terminal of the eighth switch respectively correspond to the positive electrode and the negative electrode of the second diode D2. Embodiment

[0028] Please refer to Figure 2 , which is a schematic circuit diagram of the first embodiment of the single-phase AC-DC converter of the present invention. In this embodiment, the single-phase AC-DC converter includes a primary circuit and the aforementioned secondary circuit.

[0029] Among them, 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.

[0030] Understandably, the primary circuit converts the DC voltage into a chopped pulse voltage waveform through the chopper circuit for transformer coupling. By controlling the duty cycle and / or the switching frequency of the chopper circuit in the primary circuit, the output voltage / current of the secondary circuit is adjusted. More specifically, the primary circuit converts the DC voltage into a chopped pulse voltage waveform through the on and off of the switching device in the chopper circuit for transformer coupling. By controlling the duty cycle and / or the switching frequency of the switching device in the chopper circuit in the primary circuit, the output voltage / current of the secondary circuit is adjusted.

[0031] Among them, 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 rectified filtering and at the same time provide a DC support function for the output end of the secondary circuit. Second, when the secondary side of the transformer Tr is not working, they provide a DC support function for the output end of the secondary circuit.

[0032] In one embodiment, a fourth capacitor C4 is connected between the aforementioned first common end of the single-phase AC-DC converter of the present invention and the secondary ground wire GNDS.

[0033] In one embodiment, an AC power grid Grid is connected between the aforementioned first common end of the single-phase AC-DC converter of the present invention and the secondary ground wire GNDS.

[0034] In one embodiment, a fourth capacitor C4 and an AC grid Grid are connected between the aforementioned first common terminal of the single-phase AC-DC converter of the present invention and the secondary ground wire GNDS, and the AC grid Grid is connected in parallel with the fourth capacitor C4.

[0035] It can be understood that, in one embodiment, the DC power supply C1 can be a capacitor or other types of DC power supplies.

[0036] As can be seen from the above, in the single-phase AC-DC converter of the present invention, since only two diodes are used on the secondary side, the power conversion circuit is simplified, the system loss is reduced, and thus a single-stage conversion effect can be achieved on the basis of improving efficiency. Embodiment

[0037] Please refer to Figure 3 , which is a circuit schematic diagram of the second embodiment of the single-phase AC-DC converter of the present invention. In this embodiment, the single-phase AC-DC converter includes a primary circuit and a secondary circuit. 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. Among them, the chopper circuit includes a primary switch Q1. The DC power supply C1, the primary side of the transformer Tr, and the primary switch Q1 are connected in series in sequence to form a primary circuit. 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.

[0038] In the second embodiment, the secondary circuit is the same as that in the first embodiment and will not be described in detail here.

[0039] Figure 4 For Figure 3 the corresponding working timing diagram of the circuit; in combination with Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8The working principle of the single-phase AC-DC converter in the first embodiment of the present invention will be described. The primary winding W1 of the transformer Tr is respectively connected to the DC power supply C1 and the primary switch Q1 to store energy under switching chopping. The first secondary winding W21 and the second secondary winding W22 of the transformer Tr are respectively connected to the first diode D1, the second diode D2 and the secondary ground wire GNDS. Energy is transferred from the primary side to the secondary side through the transformer. At the same time, the phase sequence and phase angle of the current will follow and be consistent with the voltage of the AC power grid Grid. According to the power frequency period of the AC power grid Grid, the second switch Q2 and the third switch Q3 are controlled to conduct in their positive and negative half-cycles respectively. Specifically, in the positive half-cycle of the AC power frequency period, the second switch Q2 conducts, and the third switch Q3 is off. The excitation and demagnetization of the transformer are carried out through the primary winding W1 and the secondary winding (the first secondary winding W21) respectively. In the negative half-cycle of the AC power frequency period, the second switch Q2 is off, and the third switch Q3 conducts. The excitation and demagnetization of the transformer are carried out through the primary winding W1 and the secondary winding (the second secondary winding W22) respectively.

[0040] Specifically, Figure 3 The control method / working principle of the single-phase AC-DC converter shown is as follows: In the first process of the positive half-cycle of the AC power frequency period (see Figure 4 and Figure 5 ), corresponding to the stage where the drive of Q1 is high level, the drive of Q2 is high level, and the drive of Q3 is low level in Figure 4 ), the primary switch Q1 conducts, the second switch Q2 conducts, and the third switch Q3 is off. The flowing path of the primary current ip is: DC power supply C1, primary winding W1, primary switch Q1, DC power supply C1. The flowing path of the secondary current is: secondary ground wire GNDS, second capacitor C2, second switch Q2, fourth capacitor C4 or / and AC power grid Grid, secondary ground wire GNDS. It can be understood that this first process of the positive half-cycle of the AC power frequency period is the first energy storage process. In the secondary circuit, the second capacitor C2 provides a DC support function for the output end of the secondary circuit.

[0041] In the second process of the positive half-cycle of the AC power frequency period (see Figure 4 and Figure 6 ), corresponding to Figure 4In the stage where Q1 is driven to a low level, Q2 is driven to a high level, and Q3 is driven to a low level, the primary switch Q1 is turned off, the second switch Q2 is turned on, and the third switch Q3 is turned off. The primary circuit is in a disconnected state, so there is no current on the primary side. The secondary current is has two flow paths, one is the first secondary winding W21, the first diode D1, the second switch Q2, the fourth capacitor C4 or / and the AC power grid Grid, the secondary ground wire GNDS, the first secondary winding W21, and the other is the first secondary winding W21, the first diode D1, the second capacitor C2, the secondary ground wire GNDS, and the first secondary winding W21. It can be understood that the second process of the positive half-cycle AC power frequency cycle is the first energy release process, and the first secondary winding W21 of the secondary side of the transformer releases energy for use by the secondary circuit.

[0042] During the first negative half-cycle of the AC power frequency cycle (see Figure 4 and Figure 7 ),correspond Figure 4 In the stage where Q1 is driven to a high level, Q2 is driven to a low level, and Q3 is driven to a high level, the primary switch Q1 is turned on, the second switch Q2 is turned off, and the third switch Q3 is turned on. The flow path of the primary current ip is the DC power supply C1, the primary winding W1, the primary switch Q1, and the DC power supply C1, and the flow path of the secondary current is is the secondary ground GNDS, the fourth capacitor C4 or / and 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 a DC support function for the output end of the secondary circuit.

[0043] During the second negative half-cycle of the AC power frequency cycle (see Figure 4 and Figure 8 ),correspond Figure 4 In the stage where Q1 is driven to a low level, Q2 is driven to a low level, and Q3 is driven to a high level, the primary switch Q1 is turned off, the second switch Q2 is turned off, and the third switch Q3 is turned on. The primary circuit is in a disconnected state, so there is no current in the primary side. The secondary current is has two flow paths, one is the second secondary winding W22, the secondary ground line GNDS, the fourth capacitor C4 or / and the AC grid Grid, the third switch Q3, the second diode D2, and the second secondary winding W22, and the other is the second secondary winding W22, the secondary ground line GNDS, the third capacitor C3, the second diode D2, and the second secondary winding W22. The second process of the negative half-cycle AC power frequency cycle is the second energy release process, and the second secondary winding W22 of the transformer secondary side releases energy for use by the secondary circuit.

[0044] It can be understood that in the second embodiment, the primary circuit of the single-phase AC-DC converter is a flyback circuit / topology. Example

[0045] Figure 9 This is the circuit diagram of a single-phase AC-DC converter according to the third embodiment of the present invention. In this embodiment, the single-phase AC-DC converter also includes a primary circuit and a secondary circuit. The primary circuit includes the primary side of the transformer Tr and a chopper circuit. Compared with Figure 3 the single-phase AC-DC converter in the embodiment, the difference is that the primary circuit in the third embodiment is a full-bridge circuit / topology, and the chopper circuit therein includes a full-bridge arm. The two outer ends of the full-bridge arm are connected to both ends of the DC power supply C1, and the two midpoint ends of the full-bridge arm are connected to both ends of the primary winding W1.

[0046] In one embodiment, the full-bridge arm includes four primary switches, namely the first primary switch Q1a, the second primary switch Q1b, the third primary switch Q1c, and the 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 the first outer 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 the second outer 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 the first midpoint end of the full-bridge arm. The current output end of the third primary switch Q1c and the current input end of the fourth primary switch Q1d are connected together to form the second midpoint end of the full-bridge arm. The first outer end of the full-bridge arm is connected to one end of the DC power supply C1, and the second outer end of the full-bridge arm is connected to the other end of the DC power supply C1. The first midpoint end of the full-bridge arm is connected to one end of the primary winding W1 of the transformer Tr, and the other end of the primary winding W1 of the transformer Tr is connected to the second midpoint end of the full-bridge arm. The current output end of the primary switch Q1 is connected to the other end of the DC power supply C1.

[0047] Specifically, Figure 9 the control method / working principle of the shown single-phase AC-DC converter is as follows: In the first process of the positive half-cycle AC power frequency period (see Figure 10 and Figure 11 ), corresponding to Figure 10During the stage where the Q1a drive and Q1d drive are at high level, the Q1b drive and Q1c drive are at low level, the Q2 drive is at high level, and the Q3 drive is at 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 flow path of the primary current ip is: DC power supply C1, first primary switch Q1a, primary winding W1, fourth primary switch Q1d, DC power supply C1. The secondary current is has two flow paths. One is: first secondary winding W21, first diode D1, second switch Q2, fourth capacitor C4 or / and AC grid Grid, secondary ground wire GNDS, first secondary winding W21. The other is: first secondary winding W21, first diode D1, second capacitor C2, first secondary winding W21. It can be understood that during the first process of this positive half-cycle AC power frequency period, 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.

[0048] During the second process of the positive half-cycle AC power frequency period (see Figure 10 and Figure 12 ), corresponding to Figure 10 the stage where the Q1a drive and Q1d drive are at low level, the Q1b drive and Q1c drive are at high level, the Q2 drive is at high level, and the Q3 drive is at low level, the first primary switch Q1a and the fourth primary switch Q1d are turned off, the second primary switch Q1b and the third primary switch Q1c are turned on, the second switch Q2 is turned on, and the third switch Q3 is turned off. The flow path of the primary current ip is: DC power supply C1, third primary switch Q1c, primary winding W1, second primary switch Q1b, DC power supply C1. The flow path of the secondary current is is: secondary ground wire GNDS, second capacitor C2, second switch Q2, fourth capacitor C4 or / and AC grid Grid, secondary ground wire GNDS. It can be understood that during the second process of this positive half-cycle AC power frequency period, demagnetization is carried out through the primary side of the transformer Tr. In the secondary circuit, the second capacitor C2 provides a DC support function for the output end of the secondary circuit.

[0049] During the first process of the negative half-cycle AC power frequency period (see Figure 10 and Figure 13 ), corresponding to Figure 10When the Q1a drive and Q1d drive are at high level, the Q1b drive and Q1c drive are at low level, the Q2 drive is at low level, and the Q3 drive is at 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 flow path of the primary current ip is: DC power supply C1, first primary switch Q1a, primary winding W1, fourth primary switch Q1d, DC power supply C1. There are two flow paths for the secondary current is. One is: secondary winding W22, secondary ground wire GNDS, fourth capacitor C4 or / and AC grid Grid, third switch Q3, second diode D2, secondary winding W22. The other is: secondary winding W22, third capacitor C3, second diode D2, secondary winding W22. It can be understood that during the first process of the negative half-cycle AC power frequency period, energy is transferred from the primary side of the transformer Tr to the secondary winding W22 of the transformer secondary side for use by the secondary circuit.

[0050] During the second process of the negative half-cycle AC power frequency period (see Figure 10 and Figure 14 ), corresponding to Figure 10 the stage where the Q1a drive and Q1d drive are at low level, the Q1b drive and Q1c drive are at high level, the Q2 drive is at low level, and the Q3 drive is at high level, the first primary switch Q1a and the fourth primary switch Q1d are turned off, the second primary switch Q1b and the third primary switch Q1c are turned on, the second switch Q2 is turned off, and the third switch Q3 is turned on. The flow path of the primary current ip is: DC power supply C1, third primary switch Q1c, primary winding W1, second primary switch Q1b, DC power supply C1. The flow path of the secondary current is is: secondary ground wire GNDS, fourth capacitor C4 or / and AC grid Grid, third switch Q3, third capacitor C3, secondary ground wire GNDS. It can be understood that during the second process of the negative half-cycle AC power frequency period, demagnetization is carried out through the primary side of the transformer Tr. In the secondary circuit, the third capacitor C3 provides a DC support function for the output end of the secondary circuit. Embodiment

[0051] Figure 15 is the circuit diagram of a single-phase AC-DC converter according to the fourth embodiment of the present invention. In this embodiment, the single-phase AC-DC converter also includes a primary circuit and a secondary circuit. The primary circuit includes the primary side of the transformer Tr and a chopper circuit. Compared with the single-phase AC-DC converter in Figure 3 the embodiment, the difference is that the primary circuit in the fourth embodiment is a two-level half-bridge circuit / topology. Among them, 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.

[0052] In one embodiment, the DC power supply C1 includes a first DC power supply C11 and a second DC power supply C12 connected in series. The common terminal 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 terminal of the two, or the midpoint terminal of the DC power supply.

[0053] 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 terminal of the first primary switch Q1a (i.e., the first outer end of the half-bridge arm). The current output terminal of the first primary switch Q1a is connected to the current input terminal of the second primary switch Q1b and the cathode of the first primary diode Dp1. The current output terminal of the second primary switch Q1b is connected to the current output terminal of the third primary switch Q1c to form the first midpoint terminal of the half-bridge arm, which is 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 to form the second midpoint terminal of the half-bridge arm, which is connected to the other end of the primary winding W1, the midpoint terminal of the DC power supply, and the primary ground wire 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 terminal of the fourth primary switch Q1d (i.e., the second outer end of the half-bridge arm). The current output terminal of the fourth primary switch Q1d is connected to the current input terminal of the third primary switch Q1c and the anode of the second primary diode Dp2.

[0054] Specifically, Figure 15 The control method / working principle of the single-phase AC-DC converter shown is as follows: During the first process of the positive half-cycle AC power frequency period (see Figure 16 and Figure 17 ), corresponding to Figure 16During the stage where the Q1a drive and the Q1b drive are at high level, the Q1c drive and the Q1d drive are at low level, the Q2 drive is at high level, and the Q3 drive is at 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 flowing path of the primary current ip is: primary ground wire GNDP, first DC power supply C11, first primary switch Q1a, second primary switch Q1b, primary winding W1, primary ground wire GNDP. The secondary current is has two flowing paths. One is the first secondary winding W21, first diode D1, second switch Q2, fourth capacitor C4 or / and AC grid Grid, secondary ground wire GNDS, first secondary winding W21. The other is the first secondary winding W21, first diode D1, second capacitor C2, first secondary winding W21. It can be understood that during the first process of this positive half-cycle AC power frequency period, 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.

[0055] During the second process of the positive half-cycle AC power frequency period (see Figure 16 and Figure 18 ), corresponding to Figure 16 the stage where the Q1a drive is at low level, the Q1b drive is at high level, the Q1c drive and the Q1d drive are at low level, the Q2 drive is at high level, and the Q3 drive is at low level, the first primary switch Q1a is turned off, the second primary switch Q1b is 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 flowing path of the primary current ip is: primary ground wire GNDP, first primary diode Dp1, second primary switch Q1b, primary winding W1, primary ground wire GNDP. The flowing path of the secondary current is is: secondary ground wire GNDS, second capacitor C2, second switch Q2, fourth capacitor C4 or / and AC grid Grid, secondary ground wire GNDS. It can be understood that during the second process of this positive half-cycle AC power frequency period, demagnetization is carried out through the primary side of the transformer Tr. In the secondary circuit, the second capacitor C2 provides a DC support function for the output end of the secondary circuit.

[0056] During the first process of the negative half-cycle AC power frequency period (see Figure 16 and Figure 19 ), corresponding to Figure 16When the Q1a drive and Q1b drive are at low level, the Q1c drive and Q1d drive are at high level, the Q2 drive is at low level, and the Q3 drive is at 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 flow path of the primary current ip is: primary ground wire GNDP, primary winding W1, third primary switch Q1c, fourth primary switch Q1d, second DC power supply C12, primary ground wire GNDP. There are two flow paths for the secondary current is. One is the second secondary winding W22, secondary ground wire GNDS, fourth capacitor C4 or / and AC grid Grid, third switch Q3, second diode D2, second secondary winding W22. The other is the second secondary winding W22, third capacitor C3, second diode D2, second secondary winding W22. It can be understood that during the first process of the negative half-cycle AC power frequency period, energy is transferred from the primary side of the transformer Tr to the second secondary winding W22 of the transformer secondary side for use by the secondary circuit.

[0057] During the second process of the negative half-cycle AC power frequency period (see Figure 16 and Figure 20 ), corresponding to Figure 16 the stage where the Q1a drive and Q1b drive are at low level, the Q1c drive is at high level, the Q1d drive is at low level, the Q2 drive is at low level, and the Q3 drive is at high level, the primary switch Q1 is turned off, the second switch Q2 is turned off, and the third switch Q3 is turned on. The flow path of the primary current ip is: primary ground wire GNDP, primary winding W1, third primary switch Q1c, primary side diode Dp2, primary ground wire GNDP. The flow path of the secondary current is is: secondary ground wire GNDS, fourth capacitor C4 or / and AC grid Grid, third switch Q3, third capacitor C3, secondary ground wire GNDS. It can be understood that during the second process of the negative half-cycle AC power frequency period, demagnetization is carried out through the primary side of the transformer Tr. In the secondary circuit, the third capacitor C3 provides a DC support function for the output end of the secondary circuit.

[0058] It can be understood that in other embodiments, the primary circuit of the single-phase AC-DC converter of the present invention can be an NPC circuit / topology, T-type circuit / topology, H-bridge circuit / topology, MMC (modular multilevel) circuit / topology, Cascade multilevel circuit / topology, etc., which will not be elaborated here.

[0059] It can be understood that in some embodiments, the switches involved in the single-phase AC-DC converter of the present invention can be fully controlled switches or semi-controlled switches such as MOSFET, BJT, IGBT, JFET, transistor, Relay, etc.

[0060] 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 AC-DC 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 it to be disconnected at other times (when the corresponding secondary side of the transformer is not working).

[0061] Specifically, in the case where the seventh switch replaces the first diode D1 in the second embodiment, the seventh switch is controlled to be turned on in the second process of the positive half-cycle AC power frequency cycle, and the seventh switch is controlled to be turned off in the other three processes; in the case where 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 in the second process of the negative half-cycle AC power frequency cycle, and the eighth switch is controlled to be turned off in the other three processes. In the case where the seventh switch replaces the first diode D1 in the third / fourth embodiment, the seventh switch is controlled to be turned on in the first process of the positive half-cycle AC power frequency cycle, and the seventh switch is controlled to be turned off in the other three processes; in the case where the eighth switch replaces the second diode D2 in the third / fourth embodiment, the eighth switch is controlled to be turned on in the first process of the negative half-cycle AC power frequency cycle, and the eighth switch is controlled to be turned off in the other three processes.

[0062] Specifically, in the case where 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 in the second process of the positive half-cycle AC power frequency cycle, and the seventh switch is controlled to be turned off in the other three processes; the eighth switch is controlled to be turned on in the second process of the negative half-cycle AC power frequency cycle, and the eighth switch is controlled to be turned off in the other three processes. And in the case where the seventh switch and the eighth switch replace the first diode D1 and the second diode D2 in the third / fourth embodiment respectively, the seventh switch is controlled to be turned on in the first process of the positive half-cycle AC power frequency cycle, and the seventh switch is controlled to be turned off in the other three processes; the eighth switch is controlled to be turned on in the first process of the negative half-cycle AC power frequency cycle, and the eighth switch is controlled to be turned off in the other three processes. Example

[0063] like Figure 21 As shown, the present invention also provides a three-phase AC / DC converter, including three of the above-mentioned single-phase AC / DC converters, wherein the DC power supplies at the input end of each single-phase AC / DC converter are connected in parallel, and the three output L-line terminals of the three-phase AC / DC converter are L1, L2, and L3 (i.e., the first common terminal of each single-phase AC / DC converter). In one embodiment, L1, L2, and L3 are respectively connected to the three phases of the power grid, i.e., the U phase, the V phase, and the W phase, and the three output N-line terminals GNDS of the three-phase AC / DC converter are connected together with the ground wire of the power grid. Example

[0064] like Figure 22As shown in the figure, the present invention also provides a three-phase AC-DC converter, which includes three aforementioned single-phase AC-DC converters. Among them, the input ends of each single-phase AC-DC converter share the same DC power supply. The three output L-line terminals of the three-phase AC-DC converter are L1, L2, and L3 (i.e., the first common terminal of each single-phase AC-DC 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. The three output N-line terminals GNDS of the three-phase AC-DC converter are connected together with the power grid ground wire.

[0065] The AC-DC converter of the present invention uses a more concise circuit to achieve single-stage conversion. It can not only improve the system conversion efficiency but also reduce the cost of semiconductor devices, thus making the entire energy conversion system have high efficiency, low cost, small volume, and wide universality.

[0066] Moreover, the control method of the AC-DC converter of the present invention is applied to the single-phase AC-DC converter and the three-phase AC-DC converter of the present invention. It stores and transfers energy through a transformer, thereby realizing the transfer of energy under the positive and negative cycles of the AC power frequency.

[0067] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation to the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A secondary side circuit, characterized in that, It includes the first secondary winding of the transformer, the second secondary winding of the transformer, the first diode, the second capacitor, the third capacitor, the second diode, the secondary ground wire, the second switch, the third switch and the fourth capacitor. One end of the first secondary winding is connected to the positive electrode of the first diode, and 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, and 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 terminal. 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 wire; alternatively, 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.

2. A single-phase AC-DC converter, characterized in that, It includes the secondary circuit described in Claim 1, and further includes a primary circuit. The primary circuit includes a transformer primary and a chopper circuit. The input end of the chopper circuit is connected to a DC power supply, and the output end of the chopper circuit is connected to the transformer primary. The chopper circuit is used to control the on-off of the current of the transformer primary.

3. The single-phase AC-DC converter according to claim 2, wherein 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 multilevel circuit.

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

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

6. The single-phase AC-DC converter according to any one of claims 2 to 5, characterized in that, 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.

7. The single-phase AC-DC converter according to any one of claims 2 to 5, characterized in that, When the primary circuit is a full-bridge circuit, the chopper circuit includes a full-bridge arm. The two outer ends of the full-bridge arm are connected to both ends of the DC power supply, and the two midpoint ends of the full-bridge arm are connected to both ends of the transformer primary.

8. The single-phase AC-DC converter according to claim 7, wherein The full-bridge arm includes first, second, third, and fourth primary switches; the current input ends of the first primary switch and the third primary switch are connected together, and the current output ends of the second primary switch and the fourth primary switch are connected together to respectively form 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 form the first and second midpoint ends of the full-bridge arm.

9. The single-phase AC-DC converter according to any one of claims 2 to 5, characterized in that, When the primary circuit is a two-level half-bridge circuit, the chopper circuit includes a half-bridge arm. Both 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 both ends of the transformer primary.

10. The single-phase AC-DC converter according to any one of claims 2 to 5, characterized in that, The switch of the single-phase AC-DC converter is a fully controlled switch or a semi-controlled switch.

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

12. A three-phase AC-DC converter, characterized in that, It includes three single-phase AC-DC converters as described in any one of claims 2-11.

13. The three-phase AC-DC converter according to claim 12, wherein The first common ends of the three single-phase AC-DC converters are respectively the three output L-line ends of the three-phase AC-DC converter; the DC power supplies at the input ends of each single-phase AC-DC converter are connected in parallel with each other, or the input ends of each single-phase AC-DC converter share the same DC power supply.

14. A control method for an AC-DC converter, applied to the AC-DC converter according to any one of claims 2-11, characterized in that, Energy is stored and transferred through the transformer, so as to achieve energy transfer under positive and negative cycles of AC power frequency.

15. The AC-DC converter control method according to claim 14, wherein, When the primary circuit is a flyback circuit, the control method of the AC-DC converter is as follows: in the first process of the positive half-cycle AC power frequency period, 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 period, the primary switch is turned off, and the switch in the secondary circuit is controlled so that the first secondary winding of the transformer secondary releases energy; in the first process of the negative half-cycle AC power frequency period, 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 period, the primary switch is turned off, and the switch in the secondary circuit is controlled so that the second secondary winding of the transformer secondary releases energy; when the primary circuit is a full-bridge circuit or a two-level half-bridge circuit, the control method of the AC-DC converter is as follows: in the first process of the positive half-cycle AC power frequency period, control 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 period, demagnetize through the primary side of the transformer, and in the secondary circuit, the second capacitor provides a DC support function for the output end of the secondary circuit; in the first process of the negative half-cycle AC power frequency period, control 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 period, demagnetize through the primary side of the transformer, and in the secondary circuit, the third capacitor provides a DC support function for the output end of the secondary circuit.

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