AC voltage regulating device and control method

Abstract

The present invention discloses an AC voltage regulating device and a control method, comprising input terminals (Ui1, Ui2) connected to a power grid, an input capacitor (3), an upper bridge arm (1), a lower bridge arm (2), an absorption module (4), and a discharge module (14). By adjusting the PWM duty cycle of the switch devices in the upper bridge arm (1) and the lower bridge arm (2), the total output voltage of Uo1 and Uo2 can be controlled to achieve a preset voltage value. The AC voltage regulating device and the control method of the present invention can realize direct voltage stabilization of AC power supply, significantly reduce the circuit complexity and device cost compared with the existing technology, and can effectively stabilize the power supply voltage of the power grid. The device has the advantages of fast response speed, low cost, simple control method, high reliability, convenient maintenance, and high efficiency.

Description

Technical Field

[0001] The present invention relates to an AC voltage regulating device and a control method for a power grid power supply system, and belongs to the field of power electronics. Background Art

[0002] With the improvement of people's living standards and the popularization of household appliances, electricity consumption, especially in residential users, has increased significantly year by year. However, the pace of upgrading and upgrading power distribution lines in factories, mines, residential communities, and shops has lagged behind. As a result, the voltage at the end of the line is far below the allowable range, and the voltage fluctuates greatly. The power grid is frequently overloaded, making it difficult for non-lighting loads such as washing machines, air conditioners, and televisions to operate normally, and causing significant damage to electrical equipment. At the same time, the large number of rotating equipment such as motors and compressors and power electronic devices used in these new electrical loads have a high demand for reactive power and generate a large amount of high-order harmonic currents. This has led to a significant increase in low-voltage line losses, a low power factor for the entire power grid, and large fluctuations in the supply voltage.

[0003] The best solution to the aforementioned low voltage and large voltage fluctuations is to install a voltage stabilizer directly on the distribution network. Adding an automatic voltage regulator to the low-voltage grid automatically adjusts the supply voltage in real time, stabilizing it at a standard value. This device can directly provide reactive power to power users, increasing the actual transmission capacity of the distribution network, improving the operational safety of power transformers, and significantly reducing voltage fluctuations caused by lightning strikes, momentary short circuits, and overloads on high-voltage lines, thereby protecting power users.

[0004] Chinese patent CN204360256U discloses a contactless AC voltage stabilizer that uses a multi-winding transformer and a multi-way thyristor switching switch to achieve voltage stabilization. This technology is a step-by-step voltage regulator. To achieve a small step difference, many thyristor switching switches are required, which makes the circuit complex and expensive. At the same time, due to the slow switching speed of the thyristor switch, the fastest is only 10ms, which is unable to cope with the rapid voltage fluctuations of the power grid. In particular, when the output voltage is adjusted to a high level, if the power grid voltage rises rapidly, the output voltage will generate overvoltage due to the slow response speed, endangering the safety of electrical equipment. Summary of the Invention

[0005] The purpose of the present invention is to design an AC voltage regulating device and control method, which can effectively stabilize the power supply voltage of the power grid and realize two-way transmission of electric energy. It has the advantages of fast response speed, low cost, high reliability, simple control, easy maintenance and high efficiency.

[0006] An AC voltage regulating device according to the present invention comprises:

[0007] Connect to the input terminals of the power grid (Ui1, Ui2) and access the AC power grid voltage;

[0008] An input capacitor (3), wherein two ends of the input capacitor (3) are respectively connected to the input terminals (Ui1, Ui2), and are used to filter out high-frequency components of the grid voltage and current and stabilize the input voltage;

[0009] An upper bridge arm (1), one end of which is connected to the input end (Ui1) and the other end of which is connected to the output end (Uo1), is used for voltage and current conversion between input and output, and can realize bidirectional flow of electric energy;

[0010] The lower bridge arm (2) has one end connected to the output end (Uo1) and the other end connected to the input end (Ui2), and is used for voltage and current conversion between input and output, and can realize bidirectional flow of electric energy;

[0011] an absorption module (4), which is respectively connected to the midpoint of the upper bridge arm (1), the midpoint of the lower bridge arm (2), and the input terminal (Ui2), and is used to absorb overvoltage generated during the operation of the circuit of the device;

[0012] A discharge module (14) is connected to the absorption module (4) and is used to discharge the electricity stored in the absorption module (4).

[0013] An AC voltage regulating device of the present invention further includes an input inductor (5) connected in series to the input end of the power grid for filtering out high-frequency components of the power grid current; and an output inductor (6) connected in series to the output end of the device for filtering out high-frequency components of the output voltage and current.

[0014] The present invention relates to an AC voltage regulating device, wherein the upper bridge arm (1) and the lower bridge arm (2) respectively comprise two semiconductor switching devices, an upper tube (7) and a lower tube (8), and an upper tube (10) and a lower tube (9), which are connected in reverse series, forming two bridge arms composed of semiconductor switching devices, and the midpoints of the two bridge arms are connected to an output inductor (6) or serve as an output end (Uo1) of the device; the semiconductor switching device is a power semiconductor such as a reverse-conducting IGBT, MOSFET, or IGCT.

[0015] The present invention relates to an AC voltage regulating device, wherein the upper bridge arm (1) and the lower bridge arm (2) respectively comprise two reversely connected semiconductor switching devices, an upper tube (7) and a lower tube (8), and an upper tube (10) and a lower tube (9), forming two bridge arms composed of semiconductor switching devices; wherein the upper tube (7) and the lower tube (8) are connected in series with a common drain, and the upper tube (10) and the lower tube (9) are connected in series with a common source, or the upper tube (7) and the lower tube (8) are connected in series with a common source, and the upper tube (10) and the lower tube (9) are connected in series with a common drain; and the semiconductor switching device is a power semiconductor such as a reverse conducting IGBT, a MOSFET, or an IGCT.

[0016] The AC voltage regulating device of the present invention, wherein the absorption module (4) comprises: two diodes (11) connected to a common cathode, and a diode (12), wherein the anode of the diode (11) is connected to the midpoint of the upper bridge arm (1), and the anode of the diode (12) is connected to the input terminal (Ui2);

[0017] A capacitor (13) has one end connected to the common end of the diode (11) and the diode (12), and the other end connected to the midpoint of the lower bridge arm (2); when the circuit of the device generates an overvoltage, current will pass through the diode (11) or the diode (12) to charge the capacitor (13), thereby achieving the purpose of absorbing the overvoltage.

[0018] The present invention relates to an AC voltage regulating device, wherein the discharge module (14) comprises a circuit in which a semiconductor switch device and a discharge resistor are connected in series, and the two ends of the series circuit are respectively connected to the two ends of the capacitor (13) in the absorption module (4). When the voltage across the capacitor exceeds a preset value, the semiconductor switch device is turned on, so that the electric energy stored in the capacitor (13) is discharged through the discharge resistor, thereby maintaining the capacitor voltage within a set range.

[0019] The present invention provides an AC voltage regulating device and a control method, wherein the device comprises input terminals (Ui1, Ui2), an input capacitor (3), an upper bridge arm (1), a lower bridge arm (2), an absorption module (4), and a discharge module (14); the control method comprises:

[0020] When the voltage at the input terminal (Ui1, Ui2) is positive, the lower tube (8) and the lower tube (9) of the semiconductor switch device operate in a PWM modulation complementary state, and the upper tube (7) and the upper tube (10) operate in a conduction state, thereby generating a PWM modulated positive voltage between the two output terminals (Uo1, Uo2) with the terminal voltage of the input capacitor (3) as the fundamental wave;

[0021] When the voltage at the input terminal (Ui1, Ui2) is negative, the upper tube (7) and the upper tube (10) of the semiconductor switch device operate in a PWM modulation complementary state, and the lower tube (8) and the lower tube (9) operate in a conduction state, thereby generating a PWM modulated negative voltage between the two output terminals (Uo1, Uo2) with the terminal voltage of the input capacitor (3) as the fundamental wave;

[0022] By adjusting the PWM duty cycle of the switching devices in the upper bridge arm (1) and the lower bridge arm (2), the output voltages of Uo1 and Uo2 can be controlled to reach a preset voltage value; if Uo1 and Uo2 are used as inputs and Ui1 and Ui2 are used as outputs, a boost function can be achieved and electric energy can be transmitted bidirectionally.

[0023] A control method for an AC voltage regulating device of the present invention further includes:

[0024] When the output current is positive (current flows out of Uo1 and flows into Uo2), at least one of the lower tube (8) and the upper tube (10) is kept in an open state, which ensures that the output current has a freewheeling path, thereby avoiding overvoltage caused by rapid current cut-off;

[0025] When the output current is negative (current flows in from Uo1 and flows out from Uo2), at least one of the upper tube (7) and the lower tube (9) is kept in an open state, which ensures that the output current has a freewheeling path, thereby avoiding overvoltage caused by rapid current cut-off.

[0026] A control method for an AC voltage regulating device of the present invention further includes:

[0027] The upper tube (7) and the upper tube (10) are provided with an opening dead zone time, that is, after the upper tube (7) is turned off, the upper tube (10) can be opened after a preset time delay, and after the upper tube (10) is turned off, the upper tube (7) can be opened after a preset time delay;

[0028] Similarly, the lower tube (8) and the lower tube (9) are provided with an opening dead time;

[0029] By setting the dead time, the short circuit caused by the direct conduction of two complementary switching devices can be avoided.

[0030] A control method for an AC voltage regulating device of the present invention further includes:

[0031] When the voltage across the capacitor (13) inside the absorption module (4) exceeds a preset value, the semiconductor switch device in the discharge module (14) is turned on, so that the electric energy stored in the capacitor (13) is discharged through the discharge resistor;

[0032] When the voltage across the capacitor (13) inside the absorption module (4) is lower than a preset value, the semiconductor switch device in the discharge module (14) is turned off, and the release of the electric energy stored in the capacitor (13) stops;

[0033] Through the above method and steps, the voltage across the capacitor (13) can always be maintained within a preset range.

[0034] The present invention adopts the above technical solution, which can produce the following beneficial technical effects:

[0035] The present invention can realize direct voltage stabilization and bidirectional transmission of AC power supply. Compared with existing technologies, it significantly reduces the complexity of lines and device costs, and can effectively stabilize the power supply voltage of the power grid. It has the advantages of fast response speed, low cost, simple control, high reliability, easy maintenance and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is an electrical structure block diagram of an AC voltage regulating device of the present invention.

[0037] Figure 2 This is another electrical structure block diagram of an AC voltage regulating device of the present invention.

[0038] Figure 3 This is an electrical schematic diagram of the absorption module (4) of the present invention. DETAILED DESCRIPTION

[0039] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions of this application will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0040] The terms "including," "having," and any variations thereof, as used in the embodiments of this application, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or units is not limited to the listed steps or units but may optionally include other steps or units not listed, or may optionally include other steps or units inherent to the process, method, product, or apparatus.

[0041] Figure 1 This is a block diagram of the electrical structure of an AC voltage regulator of the present invention. As shown in the figure, the grid voltage is connected to the device through the input terminals (Ui1, Ui2). The two terminals of the input capacitor (3) in Figure (1) are connected to the input terminals (Ui1, Ui2) respectively to filter out the high-frequency components of the grid voltage and current and stabilize the input voltage.

[0042] The upper bridge arm (1) of the device of the present invention has one end connected to the input end (Ui1) and the other end connected to the output end (Uo1), while the lower bridge arm (2) has one end connected to the output end (Uo1) and the other end connected to the input end (Ui2). This connection mode forms a bipolar step-down circuit and can realize the bidirectional flow of electric energy;

[0043] The absorption module (4) of the device of the present invention is respectively connected to the midpoint of the upper bridge arm (1), the midpoint of the lower bridge arm (2), and the input terminal (Ui2), and is used to absorb the overvoltage generated during the operation of the circuit of the device;

[0044] The discharge module (14) of the device of the present invention is connected to the absorption module (4) and is used to discharge the electricity stored in the absorption module (4).

[0045] The upper bridge arm (1) and the lower bridge arm (2) of the device of the present invention respectively include two semiconductor switching devices, an upper tube (7) and a lower tube (8), and an upper tube (10) and a lower tube (9), which are connected in reverse series, forming two bridge arms composed of semiconductor switching devices. The midpoint of the two bridge arms serves as the output end (Uo1) of the device and can also be connected to an output inductor (6). The semiconductor switching device is a power semiconductor such as a reverse-conducting IGBT, MOSFET, or IGCT. By coordinating PWM modulation between the upper tube and the lower tube of the present invention, the functions of AC voltage regulation and bidirectional energy transfer can be achieved.

[0046] Furthermore, the upper bridge arm (1) and the lower bridge arm (2) of the device of the present invention respectively include two reverse-connected semiconductor switching devices, an upper tube (7) and a lower tube (8), and an upper tube (10) and a lower tube (9), to form two bridge arms composed of semiconductor switching devices; wherein the upper tube (7) and the lower tube (8) are connected in series with a common drain, and the upper tube (10) and the lower tube (9) are connected in series with a common source, or the upper tube (7) and the lower tube (8) are connected in series with a common source, and the upper tube (10) and the lower tube (9) are connected in series with a common drain; the semiconductor switching device is a power semiconductor such as a reverse-conducting IGBT, MOSFET, or IGCT.

[0047] Figure 2 This is another electrical structure block diagram of an AC voltage regulating device of the present invention. It includes an input inductor (5) connected in series to the input end of the power grid, and an output inductor (6) connected in series to the output end of the device. These two inductors are used to filter out high-frequency components of the input and output voltages and currents, respectively, and eliminate electromagnetic interference.

[0048] Figure 3 The absorption module (4) of the device of the present invention comprises two diodes (11) and a diode (12) connected to a common cathode, wherein the anode of the diode (11) is connected to the midpoint of the upper bridge arm (1), and the anode of the diode (12) is connected to the input terminal (Ui2); and further comprises a capacitor (13), one end of which is connected to the common end of the diode (11) and the diode (12), and the other end is connected to the midpoint of the lower bridge arm (2); when the circuit of the device generates an overvoltage, current will pass through the diode (11) or the diode (12) to charge the capacitor (13), thereby achieving the purpose of absorbing the overvoltage.

[0049] The discharge module (14) of the device of the present invention includes a circuit in which a semiconductor switch device and a discharge resistor are connected in series. The two ends of the series circuit are respectively connected to the two ends of the capacitor (13) in the absorption module (4). When the voltage across the capacitor exceeds a preset value, the semiconductor switch device is turned on, so that the electric energy stored in the capacitor (13) is discharged through the discharge resistor, thereby maintaining the capacitor voltage within a set range. The switch device in the discharge module (14) can be a power semiconductor such as an IGBT, a MOSFET, or an IGCT. The resistance value and power of the discharge resistor are calculated and set according to the voltage and power of the specific device.

[0050] based on Figure 1 Figure 2 and Figure 3 The control method of the AC voltage regulating device of the present invention has the following working steps:

[0051] When the voltage at the input terminal (Ui1, Ui2) is positive, the lower tube (8) and the lower tube (9) of the semiconductor switch device work in the PWM modulation complementary state, and the upper tube (7) and the upper tube (10) work in the conduction state, thereby generating a PWM modulated voltage between its two output terminals (Uo1, Uo2) with the terminal voltage of the input capacitor (3) as the fundamental wave;

[0052] When the voltage at the input terminal (Ui1, Ui2) is negative, the upper tube (7) and the upper tube (10) of the semiconductor switch device operate in a PWM modulation complementary state, and the lower tube (8) and the lower tube (9) operate in a conducting state, thereby generating a PWM modulated voltage between the two output terminals (Uo1, Uo2) with the terminal voltage of the input capacitor (3) as the fundamental wave;

[0053] By adjusting the PWM duty cycle of the switching devices in the upper bridge arm (1) and the lower bridge arm (2), the output voltages of Uo1 and Uo2 can be controlled to reach a preset voltage value; if Uo1 and Uo2 are used as inputs and Ui1 and Ui2 are used as outputs, a boost function can be achieved and electric energy can be transmitted bidirectionally.

[0054] The control method of the AC voltage regulating device of the present invention further comprises the following steps during its working process:

[0055] When the output current is positive (current flows out from Uo1 and flows into Uo2), at least one of the lower tube (8) and the upper tube (10) is kept in an open state, so that the output current can be ensured to have a freewheeling path, thereby avoiding the overvoltage caused by rapid current cut-off. The freewheeling path is that the output current passes through the lower tube (9) and the upper tube (10) or the output current passes through the lower tube (8) and the upper tube (7);

[0056] When the output current is negative (current flows in from Uo1 and flows out from Uo2), at least one of the upper tube (7) and the lower tube (9) is kept in an open state, thereby ensuring that the output current has a freewheeling path, thereby avoiding overvoltage caused by rapid current cut-off. The freewheeling path is that the output current passes through the lower tube (9) and the upper tube (10) or the output current passes through the lower tube (8) and the upper tube (7).

[0057] The control method of the AC voltage regulating device of the present invention further comprises the following steps during its working process:

[0058] The upper tube (7) and the upper tube (10) are provided with an opening dead zone time, that is, after the upper tube (7) is turned off, the upper tube (10) can be opened after a preset time delay, and after the upper tube (10) is turned off, the upper tube (7) can be opened after a preset time delay;

[0059] Similarly, the lower tube (8) and the lower tube (9) are provided with an opening dead time;

[0060] By setting the dead time, short circuits caused by direct conduction of two complementary switching devices can be avoided. The length of the dead time is determined by the switching characteristics of the selected semiconductor switching devices and is generally a few microseconds.

[0061] The control method of the AC voltage regulating device of the present invention further comprises the following steps during its working process:

[0062] When the voltage across the capacitor (13) inside the absorption module (4) exceeds a preset value, the semiconductor switch device in the discharge module (14) is turned on, so that the electric energy stored in the capacitor (13) is discharged through the discharge resistor;

[0063] When the voltage across the capacitor (13) inside the absorption module (4) is lower than a preset value, the semiconductor switch device in the discharge module (14) is turned off, and the release of the electric energy stored in the capacitor (13) stops;

[0064] Through the above method and steps, the voltage across the capacitor (13) can always be maintained within a preset range.

[0065] When the output current direction is incorrectly judged or the PWM timing is incorrect due to various abnormal reasons, an overvoltage may be generated in the circuit. The absorption module (4) can absorb the overvoltage and charge the capacitor (13). This step can ensure that the capacitor voltage in the absorption circuit is maintained at a safe value, and it is easy to further increase the capacitor voltage detection function, thereby realizing the overvoltage alarm function and improving the safety of the circuit.

[0066] The above are merely preferred embodiments of the present invention. It should be noted that the present invention is not limited to the above embodiments. Various modifications can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. The above preferred embodiments should not be considered as limitations on the present invention. The scope of protection of the present invention should be based on the scope defined by the claims. Those skilled in the art can make various improvements and modifications without departing from the spirit and scope of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An AC voltage regulating device, characterized in that: It includes: Connect the first input terminal (Ui1) and the second input terminal (Ui2) of the power grid to the AC power grid voltage; An input capacitor (3), wherein two endpoints of the input capacitor (3) are respectively connected to the first input terminal (Ui1) and the second input terminal (Ui2), and are used to filter out high-frequency components of the grid voltage and current and stabilize the input voltage; An upper bridge arm (1), one end of which is connected to the first input end (Ui1) and the other end of which is connected to the first output end (Uo1), is used for voltage and current conversion between input and output, and can realize bidirectional flow of electric energy; A lower bridge arm (2), one end of which is connected to the first output end (Uo1) and the other end of which is connected to the second input end (Ui2), is used for voltage and current conversion between input and output, and can realize bidirectional flow of electric energy; An absorption module (4) is connected to the midpoint of the upper bridge arm (1), the midpoint of the lower bridge arm (2), and the second input terminal (Ui2) respectively, and is used to absorb overvoltage generated during the operation of the circuit of the device; the absorption module (4) includes: a first diode (11), a second diode (12), and a capacitor (13); when the circuit of the device generates an overvoltage, current will pass through the first diode (11) or the second diode (12) to charge the capacitor (13), thereby achieving the purpose of absorbing the overvoltage; a discharge module (14), connected to the absorption module (4) and used to discharge the electricity stored in the absorption module (4); The upper bridge arm (1) and the lower bridge arm (2) respectively include two semiconductor switching devices, a first upper tube (7) and a first lower tube (8), and a second upper tube (10) and a second lower tube (9), which are connected in reverse series, forming two bridge arms composed of semiconductor switching devices; wherein the first upper tube (7) is connected to the first input terminal (Ui1), the second upper tube (10) is connected to the second input terminal (Ui2), and the common terminal of the first lower tube (8) and the second lower tube (9) is connected to the first output terminal (Uo1); the first upper tube (7) and the first lower tube (8) are connected in series with a common drain, and the second upper tube (10) and the second lower tube (9) are connected in series with a common source, or the first upper tube (7) and the first lower tube (8) are connected in series with a common source, and the second upper tube (10) and the second lower tube (9) are connected in series with a common drain; the semiconductor switching device is one of a reverse conducting IGBT, a MOSFET, and an IGCT; When the voltages at the first input terminal (Ui1) and the second input terminal (Ui2) are positive, the first lower tube (8) and the second lower tube (9) of the semiconductor switch device operate in a PWM modulation complementary state, and the first upper tube (7) and the second upper tube (10) operate in a conducting state, thereby generating a PWM modulated positive voltage between the first output terminal (Uo1) and the second output terminal (Uo2) with the terminal voltage of the input capacitor (3) as the fundamental wave; When the voltages at the first input terminal (Ui1) and the second input terminal (Ui2) are negative, the first upper tube (7) and the second upper tube (10) of the semiconductor switch device operate in a PWM modulation complementary state, and the first lower tube (8) and the second lower tube (9) operate in a conducting state, thereby generating a PWM modulated negative voltage between the first output terminal (Uo1) and the second output terminal (Uo2) with the terminal voltage of the input capacitor (3) as the fundamental wave; By adjusting the PWM duty cycle of the switching devices in the upper bridge arm (1) and the lower bridge arm (2), the output voltage of the first output terminal (Uo1) and the second output terminal (Uo2) can be controlled to achieve a preset voltage value; if the first output terminal (Uo1) and the second output terminal (Uo2) are used as inputs, and the first input terminal (Ui1) and the second input terminal (Ui2) are used as outputs, a boost function can be achieved, and electric energy can be bidirectionally transmitted.

2. The AC voltage regulating device according to claim 1, characterized in that: It also includes: An input inductor (5) connected in series to the grid input terminal for filtering out high-frequency components of the grid current; An output inductor (6) is connected in series to the output end of the device and is used to filter out high-frequency components of the output voltage and current.

3. The AC voltage regulating device according to claim 1, characterized in that: The midpoint of the two bridge arms is connected to the output inductor (6), or serves as the first output terminal (Uo1) of the device.

4. An AC voltage regulating device according to claim 1 or 2, characterized in that: in, The first diode (11) and the second diode (12) are connected to a common cathode; the anode of the first diode (11) is connected to the midpoint of the upper bridge arm (1), and the anode of the second diode (12) is connected to the second input terminal (Ui2); One end of the capacitor (13) is connected to the common end of the first diode (11) and the second diode (12), and the other end is connected to the midpoint of the lower bridge arm (2).

5. An AC voltage regulating device according to claim 1 or 2, characterized in that: The discharge module (14) includes a circuit in which a semiconductor switch device and a discharge resistor are connected in series, and the two ends of the series circuit are respectively connected to the two ends of the capacitor (13) in the absorption module (4). When the voltage across the capacitor exceeds a preset value, the semiconductor switch device in the discharge module (14) is turned on, so that the electric energy stored in the capacitor (13) is discharged through the discharge resistor, thereby maintaining the capacitor voltage within a set range.

6. A control method for an AC voltage regulator according to claim 1, characterized in that: The device comprises a first input terminal (Ui1), a second input terminal (Ui2), an input capacitor (3), an upper bridge arm (1), a lower bridge arm (2), an absorption module (4) and a discharge module (14); the control method comprises: When the voltages at the first input terminal (Ui1) and the second input terminal (Ui2) are positive, the first lower tube (8) and the second lower tube (9) of the semiconductor switch device operate in a PWM modulation complementary state, and the first upper tube (7) and the second upper tube (10) operate in a conducting state, thereby generating a PWM modulated positive voltage between the first output terminal (Uo1) and the second output terminal (Uo2) with the terminal voltage of the input capacitor (3) as the fundamental wave; When the voltages at the first input terminal (Ui1) and the second input terminal (Ui2) are negative, the first upper tube (7) and the second upper tube (10) of the semiconductor switch device operate in a PWM modulation complementary state, and the first lower tube (8) and the second lower tube (9) operate in a conducting state, thereby generating a PWM modulated negative voltage between the first output terminal (Uo1) and the second output terminal (Uo2) with the terminal voltage of the input capacitor (3) as the fundamental wave; By adjusting the PWM duty cycle of the switching devices in the upper bridge arm (1) and the lower bridge arm (2), the output voltage of the first output terminal (Uo1) and the second output terminal (Uo2) can be controlled to achieve a preset voltage value; if the first output terminal (Uo1) and the second output terminal (Uo2) are used as inputs, and the first input terminal (Ui1) and the second input terminal (Ui2) are used as outputs, a boost function can be achieved, and electric energy can be bidirectionally transmitted.

7. The control method according to claim 6, characterized in that: It also includes: When the output current is positive and the current flows out of the first output terminal (Uo1) and flows into the second output terminal (Uo2), at least one of the first lower tube (8) and the second upper tube (10) is kept in an open state, thereby ensuring that the output current has a freewheeling path, thereby avoiding overvoltage caused by rapid current cut-off; When the output current is negative and the current flows into the first output terminal (Uo1) and flows out of the second output terminal (Uo2), at least one of the first upper tube (7) and the second lower tube (9) is kept in an open state, thereby ensuring that the output current has a freewheeling path, thereby avoiding overvoltage caused by rapid current cut-off.

8. The control method according to claim 6, characterized in that: It also includes: The first upper tube (7) and the second upper tube (10) are provided with an opening dead zone time, that is, after the first upper tube (7) is turned off, a preset time is required before the second upper tube (10) can be opened, and after the second upper tube (10) is turned off, a preset time is required before the first upper tube (7) can be opened; Similarly, the first lower tube (8) and the second lower tube (9) are provided with an opening dead time; By setting the dead time, a short circuit caused by direct conduction of two complementary switching devices can be avoided.

9. The control method according to claim 6, characterized in that: It also includes: When the voltage across the capacitor (13) inside the absorption module (4) exceeds a preset value, the semiconductor switch device in the discharge module (14) is turned on, so that the electric energy stored in the capacitor (13) is discharged through the discharge resistor in the discharge module; When the voltage across the capacitor (13) inside the absorption module (4) is lower than a preset value, the semiconductor switch device in the discharge module (14) is turned off, and the release of the electric energy stored in the capacitor (13) stops; Through the above method and steps, the voltage across the capacitor (13) can always be maintained within a preset range.

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