Three-phase single-stage AC-DC converter for high-frequency isolated power factor correction

Abstract

The present invention provides a three-phase single-stage AC / DC converter for realizing high-frequency isolated power factor correction, and relates to the technical field of converters. The three-phase single-stage AC / DC converter of the present invention comprises three AC modules with transformers, three DC modules, a fifth switch and two switch groups that satisfy a bidirectional current path. The three AC modules with transformers all comprise a first inductor, an intermediate capacitor, a second inductor and a transformer. When the three-phase single-stage AC / DC converter is working, the current direction in the three DC modules is that the third port flows to the second port, and the second port flows to the first port. The two switch groups that satisfy the bidirectional current path are complementary to the fifth switch. The circuit structure of the three-phase single-stage AC / DC converter proposed by the present invention is simple, and a one-level architecture is adopted. When realizing power factor correction and step-up and step-down conversion, the number of components of the circuit is saved, and the cost is greatly reduced while improving system efficiency and reducing system volume.

Description

Technical Field

[0001] The invention relates to the technical field of converters, and in particular to a three-phase single-stage AC / DC converter for realizing high-frequency isolation power factor correction. Background Art

[0002] In applications with high power demand, such as electric vehicle charging, data center and communication base station power supply, the converter is required to have power factor correction (PFC) function, and is generally an isolated PFC converter. An isolated PFC converter usually consists of two stages. The front stage is an AC / DC converter, which mainly improves the power factor of the circuit, reduces the harmonic content of the converter input current, and thus reduces the converter's interference with the power grid; the back stage is a DC / DC converter, which contains a high-frequency transformer to achieve safe and reliable power supply.

[0003] However, the electric energy of the isolated PFC converter is converted twice, and its efficiency is low. 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 single-stage AC-DC converter for realizing high-frequency isolated power factor correction, which solves the technical problem of low efficiency of the existing isolated PFC converter.

[0006] (II) Technical solution

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

[0008] The present invention provides a three-phase single-stage AC / DC converter for realizing high-frequency isolated power factor correction, comprising three AC modules with transformers, three DC modules, a fifth switch and two switch groups satisfying a bidirectional current path;

[0009] Each AC module with a transformer includes two input terminals and two output terminals; each DC module includes three ports, wherein the first ports of the three DC modules are connected together, the third ports of the three DC modules are connected together, and the second port is located between the first port and the third port and is an external connection terminal;

[0010] The three AC modules with transformers all include a first inductor, an intermediate capacitor, a second inductor and a transformer; wherein the first end of the first inductor is the first input end of the AC module, the second end of the first inductor is connected to the first end of the primary coil of the transformer via the intermediate capacitor, the second end of the primary coil is the second input end of the AC module, and the second inductor is connected in parallel with the primary coil; the first end of the secondary coil of the transformer is the first output end of the AC module, and the second end of the secondary coil is the second output end of the AC module;

[0011] The first input end of each AC module with a transformer is respectively connected to the A, B, and C phases of the three-phase power grid, and the second input ends of the three AC modules with transformers are connected together;

[0012] The first output ends of the three AC modules with transformers are respectively connected to the second ports of the three DC modules, and the second output ends of the three AC modules with transformers are connected together;

[0013] The common end of the first ports of the three DC modules is connected to the first end of the load, and the common end of the third ports of the three DC modules is connected to the second end of the load via the fifth switch;

[0014] A switch connection terminal is provided between the first inductor and the intermediate capacitor of each AC module with a transformer, and a switch group satisfying a bidirectional current path is connected between the switch connection terminals of the AC module connected to the B phase and the other two AC modules respectively;

[0015] When the three-phase single-stage AC / DC converter is working, the current direction in the three DC modules is that the third port flows to the second port, and the second port flows to the first port; the two switch groups that meet the bidirectional current path are complementarily turned on with the fifth switch.

[0016] Preferably, the switch group satisfying the bidirectional current path includes one single-pole switch or two single-pole switches.

[0017] Preferably, the switch group satisfying the bidirectional current path includes two switch tubes with freewheeling diodes.

[0018] Preferably, in the DC module, a switch tube or a single-pole switch is connected between the first port and the second port, and between the second port and the third port.

[0019] Preferably, in the DC module, diodes are connected between the first port and the second port and between the second port and the third port; wherein the cathode of the first diode is connected to the first port, and the anode is connected to the second port; wherein the cathode of the second diode is connected to the second port, and the anode is connected to the third port.

[0020] Preferably, the fifth switch is a switch tube or a single-pole switch.

[0021] Preferably, the output voltage step-up and step-down control is achieved by changing the duty ratio of two switch groups satisfying the bidirectional current path.

[0022] Preferably, the output voltage step-up and step-down control is achieved by changing the transformer turns ratio.

[0023] Preferably, a filter capacitor is connected in parallel across the load.

[0024] Preferably, the two switch groups satisfying the bidirectional current path share a switch control signal.

[0025] (III) Beneficial effects

[0026] The present invention provides a three-phase single-stage AC / DC converter for realizing high-frequency isolated power factor correction. Compared with the prior art, it has the following beneficial effects:

[0027] The three-phase single-stage AC-DC converter for realizing high-frequency isolated power factor correction proposed in the present invention has a simple circuit structure and is easy to control. It adopts a one-level architecture and saves the number of circuit components while realizing power factor correction and step-up and step-down conversion, thereby greatly reducing costs while improving system efficiency and reducing system size. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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.

[0029] Figure 1 It is a circuit structure diagram of an existing isolated PFC converter;

[0030] Figure 2 for Figure 1 A specific circuit diagram of a front-stage PFC circuit of an isolated PFC converter shown;

[0031] Figure 3 for Figure 1 The specific circuit diagram of the post-stage LLC circuit of the isolated PFC converter shown;

[0032] Figure 4 The circuit diagram of the existing common isolated PFC converter is shown below;

[0033] Figure 5 A circuit structure diagram of a three-phase single-stage AC-DC converter for realizing high-frequency isolated power factor correction according to an embodiment of the present invention;

[0034] Figure 6 for Figure 5 The first specific circuit diagram of the circuit structure diagram shown, in which the switches in the AC module and the DC module are both single-pole switches;

[0035] Figure 7 for Figure 5 The second specific circuit diagram of the circuit structure diagram shown in the figure; in this circuit, the switch in the AC module uses a switch tube, and the DC module realizes unidirectional conduction through a diode;

[0036] Figure 8 for Figure 7 The circuit diagram shown is in working mode one;

[0037] Fig. 9 for Figure 7 The circuit diagram shown is in working mode 2;

[0038] Fig.10 for Figure 7 The circuit diagram shown is in working mode three;

[0039] Fig.11 for Figure 7 The circuit diagram shown is in working mode four;

[0040] Fig.12 for Figure 7 The circuit diagram shown is in working mode five;

[0041] Fig.13 for Figure 7 The circuit diagram shown is in working mode six;

[0042] Fig.14 for Figure 7 The circuit diagram shown is in working mode seven;

[0043] Fig.15 for Figure 7 The circuit diagram shown achieves the output voltage and input current tracking the input voltage phase waveform during boosting;

[0044] Fig.16 for Fig.15 The A phase in the middle outputs a local amplified waveform;

[0045] Fig.17 for Figure 7 The circuit diagram shown realizes the output voltage and input current tracking the input voltage phase waveform during voltage reduction;

[0046] Fig.18 for Fig.17 The A phase outputs a local amplified waveform. DETAILED DESCRIPTION

[0047] 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.

[0048] 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 refers to 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.

[0049] The embodiment of the present application solves the technical problem of low efficiency of existing isolated PFC converters by providing a three-phase single-stage AC / DC converter that realizes high-frequency isolated power factor correction. It adopts a one-stage energy conversion to realize AC / DC conversion, replacing the mainstream AC / DC+DC / DC two-stage architecture, using fewer devices, achieving high efficiency and low cost.

[0050] The technical solution in the embodiment of the present application is to solve the above technical problems, and the overall idea is as follows:

[0051] like Figure 1 As shown in FIG. 1 , the existing isolated PFC converter mainly uses a front-stage PFC circuit and a rear-stage LLC converter. The front-stage PFC circuit is generally a three-phase bridge uncontrolled rectifier circuit, such as Figure 2 As shown in Figure 3, the input is AC voltage, and the rectifier circuit is composed of 6 diodes. The output is connected to the BOOST converter to achieve AC / DC conversion and power factor correction. The post-stage LLC converter realizes DC / DC conversion and controls the output voltage within the required voltage range. The specific circuit is shown in Figure 3. Common isolated PFC converters also include Figure 4The circuit shown adopts a three-phase six-switch PFC in the front stage and an isolated DC / DC converter in the back stage. The front stage of the circuit obtains the grid voltage phase through a phase-locked loop, and then realizes power factor correction through modulation technology. The back stage realizes isolation function and DC / DC conversion.

[0052] However, the two-stage PFC converter not only has low energy conversion efficiency, but also uses more components, is large in size and has high cost. Moreover, the circuit structure of this type of converter is relatively complex, which leads to a relatively complex control algorithm.

[0053] In order to solve the above problems, an embodiment of the present invention proposes a three-phase single-stage AC / DC converter that realizes the power supply function only through one-stage energy conversion. The three-phase single-stage AC / DC converter uses one-stage energy conversion to realize AC / DC conversion, replacing the existing mainstream AC / DC+DC / DC two-stage architecture, using fewer devices, achieving high efficiency and low cost. At the same time, the three-phase single-stage AC / DC converter is composed of three modular SEPIC (single ended primary inductor converter) circuits. There is no phase-to-phase coupling between the three-phase currents, and each phase can be independently controlled and driven. The required control circuit is simpler and the control algorithm is simpler. In addition, the three-phase single-stage AC / DC converter has both power factor correction and buck-boost functions.

[0054] 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.

[0055] Embodiment 1:

[0056] The embodiment of the present invention provides a three-phase single-stage AC-DC converter for realizing high-frequency isolation power factor correction, such as Figure 5 As shown, it includes three AC modules with transformers, three DC modules, a fifth switch and a switch group that satisfies a bidirectional current path, wherein each AC module with a transformer includes two input terminals and two output terminals; each DC module includes three ports, wherein the first ports of the three DC modules are connected together, the third ports of the three DC modules are connected together, and the second ports of the three DC modules are located between the first port and the third port and are external connection terminals;

[0057] The three AC modules with transformers all include a first inductor, an intermediate capacitor, a second inductor and a transformer; wherein the first end of the first inductor is the first input end of the AC module, the second end of the first inductor is connected to the first end of the primary coil of the transformer via the intermediate capacitor, the second end of the primary coil is the second input end of the AC module, and the second inductor is connected in parallel with the primary coil; the first end of the secondary coil of the transformer is the first output end of the AC module, and the second end of the secondary coil is the second output end of the AC module;

[0058] The first input end of each AC module with a transformer is respectively connected to the A, B, and C phases of the three-phase power grid, and the second input ends of the three AC modules with transformers are connected together;

[0059] The first output ends of the three AC modules with transformers are respectively connected to the second ports of the three DC modules, and the second output ends of the three AC modules with transformers are connected together;

[0060] The common end of the first ports of the three DC modules is connected to the first end of the load, and the common end of the third ports of the three DC modules is connected to the second end of the load via the fifth switch;

[0061] A switch connection terminal is provided between the first inductor and the intermediate capacitor of each AC module with a transformer, and a switch group satisfying a bidirectional current path is connected between the switch connection terminals of the AC module connected to the B phase and the other two AC modules respectively;

[0062] When the three-phase single-stage AC-DC converter is working, the current direction in the three DC modules is that the third port flows to the second port, and the second port flows to the first port;

[0063] The two switch groups satisfying the bidirectional current path and the fifth switch are complementarily turned on.

[0064] It should be noted that, in a specific implementation process, the connection position of the second inductor in each AC module can be changed to be connected in parallel with the secondary coil.

[0065] It should be noted that, in the specific implementation process, the switch group that satisfies the bidirectional current path can be a single-pole switch, or a switch group consisting of two switch tubes, of course, it can also be a thyristor, etc., and a switch or a diode can be connected between the first port and the second port, and between the second port and the third port in the DC module to realize the current direction from the third port to the second port, and from the second port to the first port. Among them, Figure 6 and Figure 7 The circuit diagrams shown are two different implementations. It should be noted that: Figure 6 The switch group that satisfies the bidirectional current path can also be a single-pole switch.

[0066] Below Figure 7 Taking the circuit diagram shown in FIG. 1 as an example, a modal analysis is performed on the three-phase single-stage AC-DC converter for realizing high-frequency isolated power factor correction according to an embodiment of the present invention.

[0067] Figure 7 The three-phase single-stage AC-DC converter for realizing high-frequency isolated power factor correction shown in FIG. 1 includes 5 switch tubes, 6 diodes, 3 transformers, 6 inductors and 3 capacitors. The switches S1-S4 share a switch control signal and the switches S 1- S 4 and switch S 5 complementary conduction. The AC / DC conversion can be realized by one-stage energy conversion without the need for traditional AC / DC-DC / DC conversion. The circuit composed of each AC module with a transformer and the corresponding DC module can be regarded as a SEPIC circuit with a transformer, which can achieve voltage boost or voltage reduction.

[0068] by Figure 7 Take the circuit of 30° as an example to analyze the working mode of the circuit. V A >0> V C > V B , and the switch S 1- S 4 signal and S 5 complementary, switch S 1- S 4 Use the same drive signal.

[0069] Working mode 1: Figure 8 As shown, the switch tube S 1- S 4 is turned on, the power supply directly charges the 6 inductors. At this time, the inductors L a , L b , L c As the current increases, the inductance L ma , L mb , L mc The current decreases due to the switch S 5 is cut off and the transformer stops working.

[0070] Working mode 2: Fig. 9 As shown, the inductor L ma , L mb , Lmc The current starts to charge in reverse, and the charging current comes from the respective capacitors, and the power supply to the inductor L a , L b , L c During charging, the currents of the six inductors increase linearly.

[0071] Working mode three: Fig.10 As shown, the switch S 1- S 4 Shutdown, switch S 5 is turned on, and the 6 inductors all continue to flow to the load end through the transformer. The inductor current decreases linearly. According to the direction of the current flow, in this mode, the diode D 1. D 6. D 2 conduction, and the inductor L ma The voltage is 2 / 3 of the load voltage, the inductor L mb ,inductance L mc The voltage is 1 / 3 of the load voltage.

[0072] Working mode 4: Fig.11 As shown, since the phase voltage of phase C is the smallest, the initial phase current of phase C is the smallest, so the inductance of phase C is L mc The current of the transformer T c The current gradually decreases.

[0073] Working mode 5: Fig.12 As shown, when the C phase inductor L mc When the current of phase C gradually increases in the reverse direction and becomes equal to the input current of phase C, the transformer of phase C stops working and the corresponding diode D 2 is turned off. At this time, the inductor L ma and inductance L mb The voltage is 1 / 2 of the load voltage.

[0074] Working mode six: Fig.13 As shown, the inductance of phase A L ma The current at the other positions begins to reverse and gradually increases linearly. The current flow direction and state at other positions are still consistent with the last described flow direction and state of the current at that position in the above modes 1 to 5 (other states remain unchanged).

[0075] Working mode seven: Fig.14 As shown, the inductance of phase BL mb The current in the reverse direction also begins to increase gradually, and finally the AB phase inductance L ma , L mb When the current is equal to the input phase current of each phase at the same time, the AB phase transformer stops working and enters the discontinuous current mode. At this time, the mode of the circuit will be the same as mode 1. Next, wait for the switch control signal to enter the next mode.

[0076] In other sectors of a power grid cycle, the analysis method of the circuit's working mode is consistent. The circuit realizes power factor correction while also realizing the functions of boosting and bucking.

[0077] The voltage gain of the circuit is related to the duty cycle of the switch, the transformer ratio, and the circuit parameters. By adjusting the above parameters, the output voltage can be changed.

[0078] Taking phase A as an example, the voltage gain corresponding to each switching cycle in the circuit is M The calculation formula is as follows:

[0079] =

[0080] The ratio of the primary side of the transformer to the secondary side is n, D is the duty cycle of the front switch group, and 1-D is the duty cycle of the fifth switch. Compared with previous solutions, this topology can realize boost and buck rectification modes in one-stage conversion. With appropriate control, it also has power factor correction function.

[0081] It should be noted that when designing the AC-DC converter, the voltage can be increased or decreased by the turns ratio of the transformer and the circuit parameters. In general, the voltage can be increased or decreased by changing the duty cycle and the turns ratio of the transformer.

[0082] Compared with the general one-stage energy conversion equipment, when the AC-DC converter of the embodiment of the present invention is in the step-up and step-down state, the subsequent diode will not have a surge current. The simulation waveform of the AC-DC converter of the embodiment of the present invention to achieve the step-up process is as follows: Fig.15 and Fig.16 As shown, the input voltage is 311V and the output voltage is 350V.

[0083] The simulation waveform of the voltage reduction process of the AC / DC converter according to the embodiment of the present invention is as follows: Fig.17 and Fig.18 As shown. Its input voltage is 311V and the output voltage is 70V.

[0084] In summary, compared with the prior art, the present invention has the following beneficial effects:

[0085] 1. The AC / DC conversion is realized by adopting one-stage energy conversion, replacing the mainstream AC / DC+DC / DC two-stage architecture. It uses fewer devices and has a simpler control circuit, achieving high efficiency and low cost.

[0086] 2. The switch tube on the load side is turned on in a complementary manner with the switch tube on the output side. Each phase is actually a SEPIC converter with a transformer. Therefore, while realizing power factor correction, it also has the functions of input and output isolation, voltage boost and voltage reduction.

[0087] 3. The transformer and the load-side switch make the three-phase circuits uncoupled, and the control method of each phase is the same as that of the single-phase circuit, making the circuit easy to control.

[0088] 4. The circuit is essentially a SEPIC circuit with a transformer, so you only need to change the duty cycle of the input side switch, the transformer ratio, and the circuit parameters to achieve output voltage step-up and step-down control. For the designed object, you can still change the duty cycle of the input side switch to achieve step-up and step-down control.

[0089] 5. Compared with the existing two-stage converter, the embodiment of the present invention does not require a bus capacitor, which can effectively solve the problem of shortening the converter life due to the easy aging of the bus capacitor, thereby increasing the service life of the converter.

[0090] 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.

[0091] 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 single-stage AC / DC converter for realizing high-frequency isolated power factor correction, characterized in that: It includes three AC modules with transformers, three DC modules, a fifth switch and two switch groups that meet bidirectional current paths; Each AC module with a transformer includes two input terminals and two output terminals; each DC module includes three ports, wherein the first ports of the three DC modules are connected together, the third ports of the three DC modules are connected together, and the second port is located between the first port and the third port and is an external connection terminal; The three AC modules with transformers all include a first inductor, an intermediate capacitor, a second inductor and a transformer; wherein the first end of the first inductor is the first input end of the AC module, the second end of the first inductor is connected to the first end of the primary coil of the transformer via the intermediate capacitor, the second end of the primary coil is the second input end of the AC module, and the second inductor is connected in parallel with the primary coil; the first end of the secondary coil of the transformer is the first output end of the AC module, and the second end of the secondary coil is the second output end of the AC module; The first input end of each AC module with a transformer is respectively connected to the A, B, and C phases of the three-phase power grid, and the second input ends of the three AC modules with transformers are connected together; The first output ends of the three AC modules with transformers are respectively connected to the second ports of the three DC modules, and the second output ends of the three AC modules with transformers are connected together; The common end of the first ports of the three DC modules is connected to the first end of the load, and the common end of the third ports of the three DC modules is connected to the second end of the load via the fifth switch; A switch connection terminal is provided between the first inductor and the intermediate capacitor of each AC module with a transformer, and a switch group satisfying a bidirectional current path is connected between the switch connection terminals of the AC module connected to the B phase and the other two AC modules respectively; When the three-phase single-stage AC / DC converter is working, the current direction in the three DC modules is that the third port flows to the second port, and the second port flows to the first port; the two switch groups that meet the bidirectional current path are complementarily turned on with the fifth switch.

2. The three-phase single-stage AC-DC converter for realizing high-frequency isolated power factor correction as claimed in claim 1, characterized in that: The switch group satisfying the bidirectional current path includes one single-pole switch or two single-pole switches.

3. The three-phase single-stage AC-DC converter for realizing high-frequency isolated power factor correction as claimed in claim 1, characterized in that: The switch group satisfying the bidirectional current path includes two switch tubes with freewheeling diodes.

4. The three-phase single-stage AC-DC converter for realizing high-frequency isolated power factor correction as claimed in claim 1, characterized in that: In the DC module, a switch tube or a single-pole switch is connected between the first port and the second port, and between the second port and the third port.

5. The three-phase single-stage AC-DC converter for realizing high-frequency isolated power factor correction as claimed in claim 1, characterized in that: In the DC module, diodes are connected between the first port and the second port, and between the second port and the third port; wherein the cathode of the first diode is connected to the first port, and the anode is connected to the second port; and the cathode of the second diode is connected to the second port, and the anode is connected to the third port.

6. The three-phase single-stage AC-DC converter for realizing high-frequency isolated power factor correction as claimed in claim 1, characterized in that: The fifth switch is a switch tube or a single-pole switch.

7. The three-phase single-stage AC-DC converter for realizing high-frequency isolated power factor correction according to any one of claims 1 to 6, characterized in that: The output voltage step-up and step-down control is achieved by changing the duty ratio of two switch groups that satisfy the bidirectional current path.

8. The three-phase single-stage AC-DC converter for realizing high-frequency isolated power factor correction according to any one of claims 1 to 6, characterized in that: The output voltage step-up and step-down can be controlled by changing the transformer turns ratio.

9. The three-phase single-stage AC-DC converter for realizing high-frequency isolated power factor correction according to any one of claims 1 to 6, characterized in that: A filter capacitor is connected in parallel at both ends of the load.

10. The three-phase single-stage AC-DC converter for realizing high-frequency isolated power factor correction according to any one of claims 1 to 6, characterized in that: The two switch groups satisfying the bidirectional current path share a switch control signal.

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