Bidirectional AC / AC converter for three-phase primary energy conversion and control method thereof

Abstract

The present invention provides a three-phase one-stage energy conversion bidirectional AC / AC converter and a control method thereof, and relates to the technical field of converters. The bidirectional AC / AC converter of the present invention uses one-stage energy conversion to realize AC / AC conversion, replacing the mainstream, AC / DC+DC / AC two-stage architecture, using fewer devices, achieving high efficiency and low cost, not using bus capacitors, and not being affected by the service life of the bus. At the same time, four groups of switch groups are used to construct a bidirectional energy path, and the proposed AC / AC converter can realize bidirectional operation.

Description

Technical Field

[0001] The present invention relates to the technical field of converters, and in particular to a three-phase primary energy conversion bidirectional AC / AC converter and a control method thereof. Background Art

[0002] In the process of power transmission, the stability of voltage determines the quality of power. To ensure the stability and diversity of AC / AC conversion, a common solution is to use back-to-back AC / AC converters, such as Figure 1 As shown, the front stage is a rectifier circuit, which first performs AC / DC conversion, and the back stage adopts an inverter circuit to achieve DC / AC conversion.

[0003] However, the two-stage back-to-back AC / AC converter needs to undergo two-stage energy conversion, AC / DC-DC / AC, and the two-stage energy conversion results in relatively low efficiency. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the deficiencies of the prior art, the present invention provides a three-phase one-stage energy conversion bidirectional AC / AC converter and a control method thereof, which solves the technical problem of low efficiency of the existing two-stage AC / AC converter.

[0006] (II) Technical solution

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] In a first aspect, the present invention provides a three-phase primary energy conversion bidirectional AC / AC converter, comprising a first switch group, a second switch group, a first intermediate inductor, a second intermediate inductor, a first voltage stabilizing filter capacitor, a second voltage stabilizing filter capacitor, a third voltage stabilizing filter capacitor, an A phase circuit, a B phase circuit and a C phase circuit;

[0009] The A-phase circuit includes a first inductor, a first intermediate capacitor, and a third switch group, wherein the first end of the first inductor is the first connection port of the A-phase circuit, the second end of the first inductor is connected to the first end of the third switch group via the first intermediate capacitor, and the second end of the third switch group is connected to the second connection port of the A-phase circuit;

[0010] The B-phase circuit includes a second inductor and a second intermediate capacitor, wherein the first end of the second inductor is the first connection port of the B-phase circuit, the second end of the first inductor is connected to the first end of the second intermediate capacitor, and the second end of the second intermediate capacitor is connected to the second connection port of the B-phase circuit;

[0011] The C phase circuit includes a third inductor, a third intermediate capacitor, and a fourth switch group, wherein a first end of the third inductor is a first connection port of the C phase circuit, a second end of the third inductor is connected to a first end of the fourth switch group via the third intermediate capacitor, and a second end of the fourth switch group is connected to a second connection port of the B phase circuit;

[0012] A first end of the first switch group is connected to a common end of the first inductor and the first intermediate capacitor, and a second end of the first switch group is connected to a common end of the second inductor and the second intermediate capacitor; a first end of the second switch group is connected to a second end of the first switch group, and a second end of the second switch group is connected to a common end of the third inductor and the third intermediate capacitor;

[0013] The first end of the first intermediate inductor is connected to the common end of the first intermediate capacitor and the third switch group, and the second end of the first intermediate inductor is connected to the second end of the second intermediate capacitor; the first end of the second intermediate inductor is connected to the second end of the first intermediate inductor, and the second end of the second intermediate inductor is connected to the common end of the third intermediate capacitor and the fourth switch group;

[0014] The first end of the first voltage stabilizing filter capacitor is connected to the second end of the third switch group, and the second end of the first voltage stabilizing filter capacitor is connected to the second end of the fourth switch group; the first end of the second voltage stabilizing filter capacitor is connected to the second connection port of the A phase circuit, and the second end of the second voltage stabilizing filter capacitor is connected to the second connection port of the B phase circuit; the first end of the third voltage stabilizing filter capacitor is connected to the first end of the second voltage stabilizing filter capacitor, and the second end of the third voltage stabilizing filter capacitor is connected to the second connection port of the A phase circuit;

[0015] Among them, the first switch group, the second switch group, the third switch group, and the fourth switch group all satisfy a bidirectional current path, and bidirectional energy flow is achieved by turning on or off the switches in the four switch groups.

[0016] Preferably, the first switch group, the second switch group, the third switch group and the fourth switch group each include two IGBTs with emitters connected to each other, and a freewheeling diode is connected in reverse parallel to each IGBT.

[0017] Preferably, the IGBT with two connected emitters includes three working states, namely:

[0018] In the first working state, the first switch tube is turned on, and the freewheeling diode connected in reverse parallel to the second switch tube is turned on;

[0019] In the second working state, the freewheeling diode connected in reverse parallel to the first switch tube is turned on, and the second switch tube is turned on;

[0020] In the third working state, both the first switch tube and the second switch tube are turned off.

[0021] Preferably, the bidirectional AC / AC converter includes two operating modes;

[0022] Among them, working mode 1: the first switch group and the second switch group are in the first working state or the second working state; the third switch group and the fourth switch group are in the third working state;

[0023] Working mode two: the first switch group and the second switch group are in the third working state, and the third switch group and the fourth switch group are in the first working state or the second working state.

[0024] Preferably, the voltage of the input AC power supply is increased or decreased by controlling the duty ratio of the first switch group, the second switch group, the third switch group, and the fourth switch group.

[0025] Preferably, the first connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to an AC voltage, and the second connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to an AC voltage;

[0026] Alternatively, the first connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to an AC voltage, and the second connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to a load;

[0027] Alternatively, the first connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to a load, and the second connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to an AC voltage.

[0028] In a second aspect, the present invention provides a control method for a three-phase primary energy conversion bidirectional AC / AC converter, which is used to control the three-phase primary energy conversion bidirectional AC / AC converter as described above, and the control method includes:

[0029] The on-duty ratio of the first switch group and the second switch group is controlled to be D, and the on-duty ratio of the third switch group and the fourth switch group is controlled to be 1-D.

[0030] The voltage at the first connection port of each phase is Vx , x = a , b , c ; The voltage of the second connection port of each phase V1x ; The relationship between the two voltages is: V1x =D / (1-D)* Vx

[0031] Control the size of the on-duty cycle D to achieve voltage boost or voltage reduction.

[0032] Preferably, when the first connection port of each phase is connected to the input voltage, that is Vx is the input voltage, V1x For the output voltage, when D is set to a fixed value greater than 0.5, boost is achieved, and when D is set to a fixed value less than 0.5, buck is achieved.

[0033] Preferably, when the second connection port of each phase is connected to the input voltage, that is V1x is the input voltage, Vx For the output voltage, when D is set to a fixed value less than 0.5, boost is achieved, and when D is set to a fixed value greater than 0.5, buck is achieved.

[0034] Preferably, the first switch group and the second switch group share a driving signal, and the third switch group and the fourth switch group share a driving signal. The driving signal and the voltage direction of the switch group determine whether the switch device and the freewheeling diode in each switch group are turned on or off, and the duty cycle of the target output voltage is fixed to achieve AC / AC conversion.

[0035] (III) Beneficial effects

[0036] The present invention provides a three-phase primary energy conversion bidirectional AC / AC converter and a control method thereof. Compared with the prior art, it has the following beneficial effects:

[0037] The present invention proposes a three-phase one-stage energy conversion bidirectional AC / AC converter and a control method thereof. The converter adopts one-stage energy conversion to realize AC / AC conversion, replacing the mainstream, AC / DC+DC / AC two-stage architecture, using fewer devices, achieving high efficiency and low cost, not using bus capacitors, and not being affected by the service life of the bus. At the same time, four groups of switch groups are used to construct a bidirectional energy path. The proposed AC / AC converter can realize bidirectional operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 A circuit diagram of an existing back-to-back AC / AC converter;

[0040] Figure 2 is a circuit diagram of an existing cascade Buck-Boost converter;

[0041] Figure 3The circuit diagram of the existing phase-controllable three-phase Buck type AC / AC converter;

[0042] Figure 4 This is a schematic diagram of a bidirectional AC / AC converter for three-phase primary energy conversion in Example 1;

[0043] Figure 5 for Figure 4 Circuit diagram when power is connected to both sides of the frame diagram shown;

[0044] Figure 6 for Figure 4 A circuit diagram in which the first side of the frame diagram is connected to a power source and the second side is connected to a load;

[0045] Figure 7 for Figure 4 A circuit diagram in which the first side of the frame diagram is connected to a load and the second side is connected to a power supply;

[0046] Figure 8 for Figure 6 A schematic diagram of working mode 1 of the circuit diagram shown;

[0047] Fig. 9 for Figure 6 A schematic diagram of working mode 2 of the circuit diagram shown;

[0048] Fig.10 for Figure 6 A schematic diagram of the working mode 1 of the circuit diagram shown;

[0049] Fig.11 for Figure 6 A schematic diagram of the working mode 2 of the circuit diagram shown;

[0050] Fig.12 for Figure 6 A schematic diagram of the working mode 3 of the circuit diagram shown;

[0051] Fig.13 for Figure 6 A schematic diagram of the working mode 4 of the circuit diagram shown;

[0052] Fig.14 for Figure 6 The circuit diagram shown is a simulation waveform diagram when the duty cycle is 0.4;

[0053] Fig.15 for Figure 6 The circuit diagram shown is a simulated waveform diagram when the duty cycle is 0.6. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] It should be noted that, for the convenience of description, the switch IGBT is used to represent the controllable (on and off) switch tube in the embodiment of the present invention, but the switch tube in the present invention is not limited to IGBT. Take IGBT as an example for explanation. The first end of the IGBT refers to the collector, the second end is the emitter, and the control end refers to the gate. A driving control signal is applied to the control end of each switch tube in the embodiment of the present invention. For the sake of brevity, it will not be repeated later. The power switch tube in the embodiment of the present invention can also be implemented by other controllable switch tube devices other than IGBT, such as MOSFET. At the same time, in order to ensure the normal operation of each switch device in the embodiment of the present invention, a freewheeling diode needs to be connected in parallel to each switch device. The parallel connection direction of the freewheeling diode is related to the type of the switch device. The technician can set it according to the type of the switch device, which is not limited here. If not specified, the switch device defaults to including a freewheeling diode, which will be pointed out in this embodiment in special cases.

[0056] The embodiment of the present application solves the technical problem of low efficiency of the existing two-stage AC / AC converter by providing a three-phase one-stage energy conversion bidirectional AC / AC converter and a control method thereof, and adopts one-stage energy conversion to realize AC / AC conversion and improve efficiency.

[0057] The technical solution in the embodiment of the present application is to solve the above technical problems, and the overall idea is as follows:

[0058] The existing AC / AC converters mainly include back-to-back AC / AC converters, cascaded Buck-Boost converters and phase-controlled three-phase Buck AC / AC converters. Figure 1 As shown, the front stage is a rectifier circuit, and the back stage uses an inverter circuit to achieve DC / AC conversion.

[0059] The cascade Buck-Boost converter takes a single-phase two-level cascade converter as an example. Figure 2As shown in the figure, the circuit is composed of two cascaded converters, Buck type and Boost type. According to the comparison of the input voltage and output voltage amplitude, it has the functions of boosting, filtering and bucking at the same time. When the front-stage Buck circuit works and the rear-stage Boost circuit does not work, the circuit works in Buck mode; when the front-stage Buck circuit does not work and the rear-stage Boost circuit works, the circuit works in Boost mode; when the switch tubes S1 and S4 are turned on, S2 and S3 are turned off, and the input voltage fluctuates slightly, the circuit works in filtering mode.

[0060] Phase controllable three-phase Buck type AC / AC converter such as Figure 3 As shown in the figure, it is mainly composed of 3 single-phase Buck AC conversion units and a three-phase output filter, in which the filter capacitors are connected in a triangle connection. The single-phase analysis includes: four switch tubes, and the three-phase circuit is 12 switch tubes, and each circuit requires 2 capacitors and 2 inductors. The circuit is composed of 3 single-phase Buck AC units and a three-phase output filter. The filter capacitors are connected in a triangle connection, so that the 3rd harmonic voltages in the 3 single-phase Buck AC units cancel each other, and then ensure that the 3rd harmonic current does not flow through the output filter inductor, and a phase-controllable sinusoidal output line voltage is obtained at the output end.

[0061] However, if Figure 1 The two-stage back-to-back ACAC converter shown in the figure needs to undergo two-stage energy conversion, which has low efficiency, and at the same time, it uses many components, is costly, and has a problem with the life of the busbar capacitor. Figure 2 The cascaded Buck-Boost converter shown in FIG. 1 has many components and high cost when used in three-phase applications. Figure 3 The phase-controllable three-phase Buck-type AC / AC converter topology shown can only achieve voltage reduction, and uses many devices and is costly.

[0062] In order to overcome the above problems, the embodiment of the present invention proposes a three-phase one-stage energy conversion bidirectional AC / AC converter and a control method thereof. The converter uses one-stage energy conversion to realize AC / AC conversion, replacing the mainstream, AC / DC+DC / AC two-stage architecture, using fewer devices, achieving high efficiency and low cost. At the same time, the converter can be operated at a boost voltage or a step-down voltage. In addition, the converter uses a top switch to construct a bidirectional energy path, which can realize bidirectional operation.

[0063] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0064] Embodiment 1:

[0065] This embodiment provides a three-phase primary energy conversion bidirectional AC / AC converter, such as Figure 4 As shown, the converter includes a first switch group, a second switch group, a first intermediate inductor, a second intermediate inductor, a first voltage stabilizing filter capacitor, a second voltage stabilizing filter capacitor, a third voltage stabilizing filter capacitor, an A phase circuit, a B phase circuit and a C phase circuit (it should be noted that in the embodiment of the present invention, ABC only represents the sequence number of the three-phase circuit, and does not correspond to the phase sequence of the three-phase circuit of the power grid one by one);

[0066] The A-phase circuit includes a first inductor, a first intermediate capacitor, and a third switch group, wherein the first end of the first inductor is the first connection port of the A-phase circuit, the second end of the first inductor is connected to the first end of the third switch group via the first intermediate capacitor, and the second end of the third switch group is connected to the second connection port of the A-phase circuit;

[0067] The B-phase circuit includes a second inductor and a second intermediate capacitor, wherein the first end of the second inductor is the first connection port of the B-phase circuit, the second end of the first inductor is connected to the first end of the second intermediate capacitor, and the second end of the second intermediate capacitor is connected to the second connection port of the B-phase circuit;

[0068] The C phase circuit includes a third inductor, a third intermediate capacitor, and a fourth switch group, wherein a first end of the third inductor is a first connection port of the C phase circuit, a second end of the third inductor is connected to a first end of the fourth switch group via the third intermediate capacitor, and a second end of the fourth switch group is connected to a second connection port of the B phase circuit;

[0069] A first end of the first switch group is connected to a common end of the first inductor and the first intermediate capacitor, and a second end of the first switch group is connected to a common end of the second inductor and the second intermediate capacitor; a first end of the second switch group is connected to a second end of the first switch group, and a second end of the second switch group is connected to a common end of the third inductor and the third intermediate capacitor;

[0070] The first end of the first intermediate inductor is connected to the common end of the first intermediate capacitor and the third switch group, and the second end of the first intermediate inductor is connected to the second end of the second intermediate capacitor; the first end of the second intermediate inductor is connected to the second end of the first intermediate inductor, and the second end of the second intermediate inductor is connected to the common end of the third intermediate capacitor and the fourth switch group;

[0071] The first end of the first voltage stabilizing filter capacitor is connected to the second end of the third switch group, and the second end of the first voltage stabilizing filter capacitor is connected to the second end of the fourth switch group; the first end of the second voltage stabilizing filter capacitor is connected to the second connection port of the A phase circuit, and the second end of the second voltage stabilizing filter capacitor is connected to the second connection port of the B phase circuit; the first end of the third voltage stabilizing filter capacitor is connected to the first end of the second voltage stabilizing filter capacitor, and the second end of the third voltage stabilizing filter capacitor is connected to the second connection port of the A phase circuit;

[0072] Among them, the first switch group, the second switch group, the third switch group, and the fourth switch group all satisfy a bidirectional current path, and bidirectional energy flow is achieved by turning on or off the switches in the four switch groups.

[0073] It should be noted that in Figure 4 In the A, B, C three-phase circuit, the first, second, and third inductors are La, Lb, and Lc, respectively, and the first, second, and third intermediate capacitors are Ca, Cb, and Cc, respectively. The first intermediate inductor is Lab, and the second intermediate inductor is Lbc. The first, second, and third voltage stabilizing filter capacitors are C1, C2, and C3, respectively. Of course, in the specific implementation process, the intermediate inductor, the intermediate capacitor, etc. can be an inductor group, a capacitor group, etc. composed of multiple devices. Figure 4 In the example, a capacitor, inductor, etc. is taken as an example. A1 represents the first connection port of the A phase circuit, A2 represents the second connection port of the A phase circuit, and similarly, B1, B2, C1, and C2 represent the two connection ports of the corresponding phases.

[0074] It should be noted that if Figure 5 In the figure, the four switch groups in the embodiment of the present invention all use two IGBTs facing each other. In fact, other forms of switch tubes, such as MOSFET, or other switch structures that can satisfy the bidirectional current path can also be used. Figure 5 In the embodiment, the first connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to the AC voltage, and the second connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to the AC voltage, which is a bidirectional AC / AC converter with power supply on both sides.

[0075] In a specific implementation process, the first connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to the AC voltage, and the second connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to the load, such as Figure 6 The connection method of the three-phase primary energy conversion bidirectional AC / AC converter may also include: the first connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to the load, and the second connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to the AC voltage, such as Figure 7 shown.

[0076] Figure 5~Figure 7 The operating modes of the converters shown are similar, so only one of them is analyzed. Figure 6 The circuit shown performs modal analysis on the converter:

[0077] The converter contains four switch groups, switches T1-T4 form the first and second switch groups; switches T5-T8 form the third and fourth switch groups. Each switch group has three working modes, as shown in Table 1, taking the first switch group as an example:

[0078] Table 1 Three switching modes of the first switch group

[0079]

[0080] Each switch group will have three modes, such as the first switch group. Mode 1 and Mode 2 are conduction modes with different current flow directions, and Mode 3 is a completely shutoff mode. If Mode 1 and Mode 2 are used as conduction modes, and Mode 3 is used as a shutoff mode, then the converter will have the following two main operating modes. The switch group in each operating mode will have different switch combinations of switch group modes 1, 2, and 3, so the two main operating modes are introduced first, and then examples are given to illustrate the different operating modes of the circuit.

[0081] Working mode is the same as Figure 8 As shown, at this time, the two groups of top switches composed of switches T1-T4 work in the conduction mode, and the two groups of top switches composed of switches T5-T8 work in the off mode. At this time, the input AC voltages Va, Vb, Vc and the three input inductors La, Lb, Lc are all star-connected, and the three input inductors La, Lb, Lc are equal in size, so the three input AC voltages will charge the three input inductors La, Lb, Lc through the two groups of top switches, and the voltages of the three input inductors La, Lb, Lc are equal to the instantaneous value of the AC input voltage of the corresponding phase; the three intermediate capacitor voltages Ca, Cb, Cc will charge the two output inductors Lab, Lbc through the two groups of top switches, and the average value of the three intermediate capacitor voltages is equal to the AC input voltage of the corresponding phase; the three voltage stabilizing filter capacitors C1, C2, C3 continue to flow to the load; since the two groups of top switches composed of switches T5-T8 work in the off mode, there is no energy flow between the load and the AC input power supply.

[0082] Working mode 2 Fig. 9 As shown, at this time, the two groups of top switches composed of switches T1-T4 work in the off mode, and the two groups of top switches composed of switches T5-T8 work in the on mode. At this time, the input AC voltages Va, Vb, Vc and the three input inductors La, Lb, Lc, the three intermediate capacitors Ca, Cb, Cc, and the load form a star connection, so the three input AC voltages and the three input inductors La, Lb, Lc will charge the three intermediate capacitors Ca, Cb, Cc and the load through the two groups of top switches; the two output inductors Lab and Lbc will also charge the load through the two groups of top switches.

[0083] The converter has the above two main working modes. The switch groups in each working mode will have different switch combinations of switch group mode one, two, and three. The following examples illustrate the different working modes of the circuit.

[0084] Working mode is the same as Fig.10 As shown, at this time, the two groups of top switches composed of switches T5-T8 work in the off mode, switches T1 and T3 are turned on, and the anti-parallel diodes of switches T2 and T4 are turned on. At this time, the three input AC voltages will charge the three input inductors La, Lb, and Lc through the two groups of top switches, the input inductors La and Lb are charged forward, and the input inductor Lc is charged reversely; the three intermediate capacitor voltages Ca, Cb, and Cc will charge the two output inductors Lab and Lbc through the two groups of top switches; the three voltage stabilizing filter capacitors C1, C2, and C3 will continue to flow to the load; since the two groups of top switches composed of switches T5-T8 work in the off mode, there is no energy flow between the load and the AC input power supply.

[0085] Working mode 2 Fig.11 As shown, at this time, the two groups of top switches composed of switches T1-T4 work in the off mode, switches T5 and T8 are turned on, and the anti-parallel diodes of switches T6 and T7 are turned on. At this time, the input AC voltages Va, Vb, Vc and the three input inductors La, Lb, Lc, the three intermediate capacitors Ca, Cb, Cc, and the load form a star connection, so the three input AC voltages and the three input inductors La, Lb, Lc will charge the three intermediate capacitors Ca, Cb, Cc and the load through the two groups of top switches; the two output inductors Lab and Lbc will also charge the load through the two groups of top switches.

[0086] Working mode three Fig.12 As shown, at this time, the two groups of top switches composed of switches T5-T8 work in the off mode, switches T2 and T4 are turned on, and the anti-parallel diodes of switches T1 and T3 are turned on. At this time, the three input AC voltages will charge the three input inductors La, Lb, and Lc through the two groups of top switches, the input inductors La and Lb are reversely charged, and the input inductor Lc is forwardly charged; the three intermediate capacitor voltages Ca, Cb, and Cc will charge the two output inductors Lab and Lbc through the two groups of top switches; the three voltage stabilizing filter capacitors C1, C2, and C3 continue to flow to the load; since the two groups of top switches composed of switches T5-T8 work in the off mode, there is no energy flow between the load and the AC input power supply.

[0087] Working mode four Fig.13 As shown, at this time, the two groups of top switches composed of switches T1-T4 work in the off mode, switches T6 and T7 are turned on, and the anti-parallel diodes of switches T5 and T8 are turned on. At this time, the input AC voltages Va, Vb, Vc and the three input inductors La, Lb, Lc, the three intermediate capacitors Ca, Cb, Cc, and the load form a star connection, so the three input AC voltages and the three input inductors La, Lb, Lc will charge the three intermediate capacitors Ca, Cb, Cc and the load through the two groups of top switches; the two output inductors Lab and Lbc will also charge the load through the two groups of top switches.

[0088] Embodiment 2:

[0089] An embodiment of the present invention provides a control method for a three-phase primary energy conversion bidirectional AC / AC converter, the method comprising:

[0090] Combination Figure 8 and Fig. 9 The mathematical relationship between input and output voltage is given below:

[0091] If the switch tubes T1, T2, T3 and T4 form the first and second groups of switches with a duty cycle of D, the switch tubes T5, T6, T7, T8 form the third and fourth groups of switches with a duty cycle of 1-D (Note: According to the two modes given by the circuit, when each switch group is working, one switch is always forward-conducting and the other switch is anti-parallel diode-conducting, which is determined by the drive signal and the voltage of the switch group. Therefore, the duty cycle in the control method refers to the duty cycle of the switch group). The first connection port of each phase is connected to the input voltage Vx For example, the output voltage of each phase is V1x =D / (1-D)* Vx ( x = a , b , c ), it can be concluded that the output voltage of each phase is only related to the input voltage of the corresponding phase and the conduction duty cycle of the switch group. When the switch tubes T1, T2, T3 and T4 form the first and second groups of switches with a conduction duty cycle D>0.5, a voltage increase can be achieved; when the switch tubes T1, T2, T3 and T4 form the first and second groups of switches with a conduction duty cycle D<0.5, a voltage decrease can be achieved.

[0092] The input voltage is AC voltage, according to the output voltage V1x =D / (1-D)* Vx ( x = a , b , c ), in order to achieve AC / AC conversion, only the duty cycle needs to be fixed. When the voltage is required to be increased, the duty cycle D>0.5 takes a fixed value; when the voltage is required to be reduced, the duty cycle D<0.5 takes a fixed value;

[0093] Due to the on-off characteristics of the fully controllable device, the first and second switch groups share a drive signal, and the third and fourth switch groups share a drive signal. The drive signal and the voltage direction of the switch group determine whether the devices and diodes in each switch group are turned on or off. By fixing the duty cycle of the target output voltage, AC / AC conversion can be achieved (since the drives of the first switch group and the second switch group are complementary, a switching dead zone needs to be added in actual application).

[0094] The simulation results are as follows when the duty cycle is 0.4 and 0.6 respectively. Fig.14 and Fig.15 As shown:

[0095] When the input voltage is a three-phase symmetrical AC voltage with a peak value of 300V, when the first and second switch groups D=0.4, the output voltage peak is about 205V, and the output voltage of each phase is in phase with the corresponding phase input voltage; when the input voltage is a three-phase symmetrical AC voltage with a peak value of 320V, when the first and second switch groups D=0.6, the output voltage peak is about 500V, and the output voltage of each phase is in phase with the corresponding phase input voltage, which is consistent with the theoretical value.

[0096] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0097] 1. The embodiment of the present invention proposes a three-phase one-stage energy conversion bidirectional AC / AC converter and a control method thereof. The converter adopts one-stage energy conversion to realize AC / AC conversion, replacing the mainstream, AC / DC+DC / AC two-stage architecture, using fewer devices, achieving high efficiency and low cost. At the same time, a bidirectional energy path is constructed using top switches, and the proposed AC / AC converter can realize bidirectional operation.

[0098] 2. The bidirectional AC / AC converter for three-phase primary energy conversion in the embodiment of the present invention is coupled in circuit form. After mathematical analysis, the output voltage of each phase is only related to the input voltage of the corresponding phase. Therefore, the three-phase circuit is decoupled in mathematical relationship, and therefore relatively easy to control.

[0099] 3. The embodiment of the present invention can control the bidirectional AC / AC converter to achieve voltage reduction or voltage increase by controlling the duty cycle of the switch group.

[0100] 4. There is no need to set bus capacitors in the converter, which not only reduces the cost but also avoids the problem of bus capacitor service life.

[0101] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0102] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A three-phase primary energy conversion bidirectional AC / AC converter, characterized in that: It includes a first switch group, a second switch group, a first intermediate inductor, a second intermediate inductor, a first voltage stabilizing filter capacitor, a second voltage stabilizing filter capacitor, a third voltage stabilizing filter capacitor, an A phase circuit, a B phase circuit and a C phase circuit; The A-phase circuit includes a first inductor, a first intermediate capacitor, and a third switch group, wherein the first end of the first inductor is the first connection port of the A-phase circuit, the second end of the first inductor is connected to the first end of the third switch group via the first intermediate capacitor, and the second end of the third switch group is connected to the second connection port of the A-phase circuit; The B-phase circuit includes a second inductor and a second intermediate capacitor, wherein the first end of the second inductor is the first connection port of the B-phase circuit, the second end of the first inductor is connected to the first end of the second intermediate capacitor, and the second end of the second intermediate capacitor is connected to the second connection port of the B-phase circuit; The C phase circuit includes a third inductor, a third intermediate capacitor, and a fourth switch group, wherein a first end of the third inductor is a first connection port of the C phase circuit, a second end of the third inductor is connected to a first end of the fourth switch group via the third intermediate capacitor, and a second end of the fourth switch group is connected to a second connection port of the B phase circuit; A first end of the first switch group is connected to a common end of the first inductor and the first intermediate capacitor, and a second end of the first switch group is connected to a common end of the second inductor and the second intermediate capacitor; a first end of the second switch group is connected to a second end of the first switch group, and a second end of the second switch group is connected to a common end of the third inductor and the third intermediate capacitor; The first end of the first intermediate inductor is connected to the common end of the first intermediate capacitor and the third switch group, and the second end of the first intermediate inductor is connected to the second end of the second intermediate capacitor; the first end of the second intermediate inductor is connected to the second end of the first intermediate inductor, and the second end of the second intermediate inductor is connected to the common end of the third intermediate capacitor and the fourth switch group; The first end of the first voltage stabilizing filter capacitor is connected to the second end of the third switch group, and the second end of the first voltage stabilizing filter capacitor is connected to the second end of the fourth switch group; the first end of the second voltage stabilizing filter capacitor is connected to the second connection port of the A phase circuit, and the second end of the second voltage stabilizing filter capacitor is connected to the second connection port of the B phase circuit; the first end of the third voltage stabilizing filter capacitor is connected to the first end of the second voltage stabilizing filter capacitor, and the second end of the third voltage stabilizing filter capacitor is connected to the second connection port of the A phase circuit; Among them, the first switch group, the second switch group, the third switch group, and the fourth switch group all satisfy a bidirectional current path, and bidirectional energy flow is achieved by turning on or off the switches in the four switch groups.

2. The three-phase primary energy conversion bidirectional AC / AC converter according to claim 1, characterized in that: The first switch group, the second switch group, the third switch group and the fourth switch group each include two IGBTs with emitters connected to each other, and a freewheeling diode is connected in reverse parallel to each IGBT.

3. The three-phase primary energy conversion bidirectional AC / AC converter according to claim 2, characterized in that: The IGBT with two connected emitters includes three working states, namely: In the first working state, the first switch tube is turned on, and the freewheeling diode connected in reverse parallel to the second switch tube is turned on; In the second working state, the freewheeling diode connected in reverse parallel to the first switch tube is turned on, and the second switch tube is turned on; In the third working state, both the first switch tube and the second switch tube are turned off.

4. The three-phase primary energy conversion bidirectional AC / AC converter according to claim 3, characterized in that: The bidirectional AC / AC converter includes two working modes; Among them, working mode 1: the first switch group and the second switch group are in the first working state or the second working state; the third switch group and the fourth switch group are in the third working state; Working mode two: the first switch group and the second switch group are in the third working state, and the third switch group and the fourth switch group are in the first working state or the second working state.

5. The three-phase primary energy conversion bidirectional AC / AC converter according to claim 1, characterized in that: By controlling the duty ratios of the first switch group, the second switch group, the third switch group, and the fourth switch group, the voltage of the input AC power source can be increased or decreased.

6. The bidirectional AC / AC converter for three-phase primary energy conversion according to any one of claims 1 to 5, characterized in that: The first connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to an AC voltage, and the second connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to an AC voltage; Alternatively, the first connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to an AC voltage, and the second connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to a load; Alternatively, the first connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to a load, and the second connection ports of the A-phase circuit, the B-phase circuit and the C-phase circuit are connected to an AC voltage.

7. A control method for a three-phase primary energy conversion bidirectional AC / AC converter, characterized in that: Used to control the bidirectional AC / AC converter for three-phase primary energy conversion as claimed in any one of claims 1 to 6, the control method comprising: The on-duty ratio of the first switch group and the second switch group is controlled to be D, and the on-duty ratio of the third switch group and the fourth switch group is controlled to be 1-D. The voltage at the first connection port of each phase is Vx , x = a , b , c ; The voltage of the second connection port of each phase V1x ; The relationship between the two voltages is: V1x =D / (1-D)* Vx Control the size of the on-duty cycle D to achieve voltage boost or voltage reduction.

8. The control method of the three-phase primary energy conversion bidirectional AC / AC converter according to claim 7, characterized in that: When the first connection port of each phase is connected to the input voltage, that is Vx is the input voltage, V1x For the output voltage, when D is set to a fixed value greater than 0.5, boost is achieved, and when D is set to a fixed value less than 0.5, buck is achieved.

9. The control method of the three-phase primary energy conversion bidirectional AC / AC converter according to claim 7, characterized in that: When the second connection port of each phase is connected to the input voltage, that is V1x is the input voltage, Vx For the output voltage, when D is set to a fixed value less than 0.5, boost is achieved, and when D is set to a fixed value greater than 0.5, buck is achieved.

10. The control method of the bidirectional AC / AC converter for three-phase primary energy conversion according to any one of claims 7 to 9, characterized in that: The first switch group and the second switch group share a driving signal, and the third switch group and the fourth switch group share a driving signal. The driving signal and the voltage direction of the switch group determine whether the switch device and the freewheeling diode in each switch group are turned on or off, and the duty cycle of the target output voltage is fixed to achieve AC / AC conversion.

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