An isolation transformer

Abstract

The invention discloses an isolation transformer device, which includes an AC power input and an input end connected in series with an inductor, multiple input capacitor groups, multiple high-voltage inverter modules, one or more transformers, and a low-voltage rectifier module. The isolation transformer device of the invention can be directly connected to high-voltage AC power, can realize the bidirectional flow of electric energy, and can arbitrarily convert electric energy between high-voltage AC power and low-voltage AC power or low-voltage DC power. The circuit structure is simple, the number of transformation stages is small, and a multi-winding high-frequency transformer can be used. It has low cost, high reliability, small size, and high efficiency.

Description

Technical Field

[0001] The invention relates to an isolation transformer device used in a power grid power supply system, belonging to the field of power electronics. Background Art

[0002] With the improvement of people's living standards and the popularization of household appliances, the electricity consumption of residential users, in particular, has increased significantly year by year. However, the speed of updating and transforming the distribution lines of factories, mines, residential areas, shops, etc. is relatively lagging, resulting in the voltage at the end of the line being far below the allowable range. At the same time, the voltage fluctuates greatly, and the power grid is frequently overloaded. Non-lighting loads such as washing machines, air conditioners, and televisions are difficult to work normally, and cause great harm to electrical equipment. At the same time, the traditional power supply system uses a huge amount of power frequency transformers, which consumes a large amount of copper, iron and other metals, and uses a large amount of insulating oil and other materials, causing serious environmental pollution.

[0003] With the continuous development of power electronics technology, it has become feasible to replace traditional transformers with isolation transformer technology based on power electronics technology, also known as power electronic transformers, and improve traditional power supply methods. After replacing traditional transformers with power electronics technology, the consumption of metal material resources can be greatly reduced, the transformer's self-consumption can be reduced, the power supply voltage can be stabilized locally, high-voltage household power supply can be realized, the use of low-voltage cables can be greatly reduced, the distribution network construction cost can be reduced, and the line network loss can be reduced.

[0004] Chinese patent CN105932883A discloses a power electronic transformer based on energy injection direct AC-AC converter, which can realize single-stage conversion and bidirectional transmission of energy, has simple topology, high conversion efficiency, small size and low cost. However, since its semiconductor devices need to withstand input voltage, it can only be used in occasions with low grid voltage. At present, the main lines of power supply and distribution network systems at home and abroad generally use 6kv, 10kv, and 35kv. With the current level of semiconductor devices, it is difficult to meet the requirements.

[0005] Chinese patent CN105897004A discloses a multi-level DC bus self-balancing power electronic transformer topology, which uses multi-level midpoint clamping technology to achieve high voltage input, does not require voltage feedback of DC bus capacitors for capacitor voltage balancing, and greatly simplifies the control algorithm on the rectifier side. However, the circuit structure is complex, with 4-level conversion, high cost, and large self-loss, making it difficult to promote and apply widely.

[0006] Chinese patent CN105680488A discloses an MMC type multi-port power electronic transformer for AC / DC hybrid distribution network, which adopts MMC cascade mode and can directly input high voltage. However, the circuit is also complex in structure, with 4-level conversion, high cost, large self-loss, and difficult to be widely promoted and applied. Summary of the invention

[0007] The purpose of the present invention is to design an isolation transformer device, which can be directly connected to high-voltage alternating current, can realize bidirectional flow of electric energy, and arbitrarily convert electric energy between high-voltage alternating current and low-voltage alternating current or low-voltage direct current. It has a simple circuit structure, a small number of transformation stages, can use a multi-winding high-frequency transformer, has low cost, high reliability, small size, and high efficiency.

[0008] An isolating transformer device of the present invention comprises:

[0009] An input terminal (Vin1, Vin2) connected to a power grid, wherein one of the input terminals is connected in series with an inductor (1), wherein the inductor (1) is used to filter out high-frequency pulsating components of the input current of the power grid;

[0010] A plurality of input capacitor groups (2), each input capacitor group (2) being formed by two capacitors connected in series, and the plurality of input capacitor groups (2) being connected in series to form a capacitor group string, one end of the capacitor group string being connected to the inductor (1), and the other end being connected to another input end (Vin2) of the power grid, the input capacitor group (2) cooperating with the inductor (1) to filter out pulsating components of the current, and at the same time, the plurality of input capacitor groups (2) connected in series also play a role in input voltage equalization;

[0011] A plurality of high-voltage modules, wherein the three input terminals of each high-voltage module are respectively connected to the two terminals and the midpoint of the input capacitor group (2), and the high-voltage module chops and modulates the low-frequency voltage into a high-frequency voltage to reduce the volume and weight of the transformer, while realizing bidirectional energy transfer;

[0012] A plurality of series capacitors (7), one end of each of which is connected in series with an output (Uo1) of the high-voltage module, coupling the high-frequency voltage output by the high-voltage module to a subsequent transformer and blocking low-frequency voltage components;

[0013] One or more transformers (3), wherein both ends of multiple primary windings of the one or more transformers (3) are respectively connected to one end of the series capacitor (7) and an output end (Uo2) of the high-voltage module, so that the transformer (3) realizes electrical isolation, transfers energy between the primary and secondary sides, and realizes bidirectional energy transfer; the primary winding of the transformer (3) may also be connected in series with an inductor, and when the leakage inductance of the transformer (3) is small, the inductance value may be increased by the inductor to reduce the high-frequency current pulsation component of the winding of the transformer (3).

[0014] A low-voltage module (5) has an input end respectively connected to one or more secondary windings of the transformer (3), and an output end forming an output end of the current conversion device. The low-voltage module (5) completes the rectification, filtering and inversion output functions of the high-frequency voltage outputted by the secondary side of the transformer, and can transmit electric energy in both directions.

[0015] An isolation transformer device of the present invention, wherein the high-voltage module is composed of four semiconductor switch devices (6) divided into two groups, each group being connected in series in the same direction; the two groups of semiconductor switch devices (6) are further connected in reverse series, and their two ends (Ui1, Ui2) are respectively connected to the two ends of the input capacitor group (2) as input ends, and their midpoint (Ui0) is connected to the midpoint of the input capacitor group (2); in the two groups of semiconductor switch devices (6) connected in series in the same direction, the midpoints (Uo1, Uo2) of the two groups serve as two output ends of the high-voltage module; the semiconductor switch device (6) may be a power semiconductor such as a reverse-conducting IGBT, MOSFET, IGCT, etc.

[0016] An isolation transformer device of the present invention, wherein the one or more transformers (3) include:

[0017] A plurality of primary windings, one end of each primary winding being connected to the output end of the high voltage module, and the other end being connected to one end of the series capacitor (7);

[0018] One or more secondary windings, each of the secondary windings being connected to a low-voltage module (5); further, two ends of the plurality of secondary windings may be connected in parallel and then connected to the low-voltage module (5);

[0019] One or more iron cores, each iron core is wound with at least one primary winding and one secondary winding, and multiple primary and secondary windings can share one iron core.

[0020] An isolation transformer device according to the present invention, the low-voltage module (5) comprises:

[0021] One or more rectifier modules, whose input ends are respectively connected to the secondary winding of the transformer (3);

[0022] One or more output modules, the input end of the output module is connected in parallel with the output end of the rectifier module, and the output end of the output module serves as the output end (Vo1, Vo2) of the device.

[0023] The rectifier module described in the low-voltage module (5) of the present invention comprises:

[0024] Two semiconductor switching devices connected in series form a bridge arm, whose two endpoints form the output terminals (+, -) of the rectifier module, and the midpoint of the bridge arm serves as an input terminal of the rectifier module. The semiconductor switching device may be a power semiconductor such as a reverse-conducting IGBT, MOSFET, or IGCT;

[0025] Two capacitors (4) are connected in series, both ends of which are connected in parallel to the two output ends of the bridge arm, and the midpoint thereof serves as another input end of the rectifier module.

[0026] The rectifier module described in the low-voltage module (5) of the present invention comprises:

[0027] A single-phase inverter bridge circuit composed of four semiconductor switching devices, whose two positive and negative terminals form the output terminals (+, -) of the rectifier module, and the midpoints of the two bridge arms serve as the two input terminals of the rectifier module. The semiconductor switching device can be a power semiconductor such as a reverse-conducting IGBT, MOSFET, or IGCT;

[0028] A capacitor has two ends connected in parallel with the positive and negative output ends of the inverter bridge circuit.

[0029] The midpoint of the bridge arm of the rectifier module of the low-voltage module (5) of the present invention is connected to the input end via an inductor. When the leakage inductance of the transformer (3) is small, the inductance value can be increased by the inductor to reduce the high-frequency current pulsation component.

[0030] The output module of the low-voltage module (5) of the present invention is composed of two semiconductor switch devices connected in series to form a bridge arm, whose two end points form the input ends (+, -) of the output module, and the midpoint of the bridge arm is connected to an inductor, and the other end of the inductor serves as the output end of the output module; the midpoint of the output capacitor group (4) is led out as another output end; the semiconductor switch device can be a reverse-conducting power semiconductor such as IGBT, MOSFET, IGCT, etc.

[0031] The output module of the low-voltage module (5) of the present invention is a single-phase inverter bridge circuit composed of four semiconductor switch devices, whose two positive and negative terminals form the input terminals (+, -) of the output module, and the midpoint of one bridge arm is connected to an inductor and then led out, and the midpoint of the other bridge arm serves as the output terminal of the output module; the semiconductor switch device can be a power semiconductor such as a reverse-conducting IGBT, MOSFET, IGCT, etc.

[0032] The present invention adopts the above technical solution to produce the following beneficial technical effects:

[0033] The present invention can realize the basic functions of the traditional power frequency transformer, such as voltage transformation, isolation, and bidirectional energy transfer. The primary side current conversion part adopts a single-stage low-frequency AC to high-frequency AC conversion scheme. Compared with the existing technology, it significantly reduces the complexity of the circuit and the cost of the device, and has higher working efficiency. The current conversion circuit of the present invention works in a low voltage state, with low electromagnetic interference and radiation such as dv / dt, and high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The invention discloses an electrical structure block diagram of an isolation transformer device.

[0035] Figure 2It is a circuit schematic diagram of the high voltage module of the present invention.

[0036] Figure 3 This is a schematic diagram of the rectifier module circuit of the low-voltage module (5) of the present invention.

[0037] Figure 4 This is another circuit principle diagram of the rectifier module of the low-voltage module (5) of the present invention.

[0038] Figure 5 This is a circuit structure diagram of an output module of a low voltage module (5) of the present invention.

[0039] Figure 6 This is another circuit structure diagram of the output module of the low voltage module (5) of the present invention. DETAILED DESCRIPTION

[0040] In order to describe the present invention in more detail, the implementation and working process of an isolation transformer device of the present invention are described in detail below in conjunction with the accompanying drawings.

[0041] like Figure 1 The figure shows an electrical structure diagram of an isolation transformer device of the present invention. A high-voltage AC power source is connected via ports Vin1 and Vin2, one of the input terminals is connected in series with an inductor (1), and the inductor (1) is used to filter out the high-frequency pulsating component of the input current of the power grid; the inductor (1) is connected in parallel to the capacitor string of the power grid, and in cooperation with the inductor (1), the pulsating component of the current can be filtered out. At the same time, the multiple capacitor strings connected in series also play a role in equalizing the input voltage, thereby realizing the conversion of the input high-voltage AC power into multiple-stage series-connected low-voltage AC power. The number of input capacitor groups (2) is determined by the voltage level of the input power grid. The more capacitors are connected in series, the lower the voltage borne by each capacitor group.

[0042] The present invention discloses an isolation transformer device comprising a plurality of high-voltage modules, wherein two input terminals and a midpoint of each high-voltage module are respectively connected to two terminals and a midpoint of the input capacitor group (2), and the number of high-voltage modules is consistent with the input capacitor group (2), so that the input voltage of each high-voltage module is low-voltage voltage after voltage division by a capacitor string, and thus the internal circuit of each high-voltage module only needs to withstand a corresponding low-level voltage. The high-voltage module operates in a PWM pulse width modulation state, and chops and modulates a low-frequency voltage into a high-frequency voltage, thereby reducing the volume and weight of the transformer.

[0043] The present invention comprises a plurality of series capacitors (7), wherein the series capacitors (7) are connected in series with an output (Uo1) of the high-voltage module, and the other end of the series capacitors (7) is connected with the primary winding of the transformer. The series capacitors (7) couple the high-frequency voltage output by the high-voltage module to the subsequent transformer and block the low-frequency voltage component.

[0044] The present invention discloses an isolation transformer device comprising one or more transformers (3), wherein the two ends of the primary windings of the transformers (3) are respectively connected to the output end of the high-voltage module and the series capacitor (7), and the high-frequency voltage after PWM pulse width modulation output by the high-voltage module is connected to the primary winding through the input capacitor group (2) to form a loop, and the electric energy is transmitted to the secondary winding after isolation by the transformer. According to different application occasions, each primary winding of the one or more transformers (3) may correspond to an iron core, and multiple primary windings may also share an iron core; each primary winding may correspond to a secondary winding, or multiple primary windings may correspond to one or more secondary windings; the primary winding of the transformer (3) may also be connected in series with an inductor, and when the leakage inductance of the transformer (3) is small, the inductance value may be increased by the inductor to reduce the high-frequency current pulsation component of the transformer winding.

[0045] The secondary winding of the transformer is connected to a low-voltage module (5), and the low-voltage module (5) completes the high-frequency rectification, filtering and inverter output functions of the secondary output of the transformer.

[0046] Figure 2 The circuit diagram of the high-voltage module of the present invention comprises four semiconductor switch devices (6) connected in series, wherein the upper and lower ends and the midpoint are input ends (Ui1, Ui2, Ui0), connected to the two ends and the midpoint of the input capacitor group (2), and the midpoints (Uo1, Uo2) of the two groups of semiconductor switch devices (6) connected in series in the same direction serve as the two output ends of the high-voltage module, one of which is connected to the series capacitor (7) and then connected to the primary winding of the transformer, and the other output end of the high-voltage module is connected to the other end of the primary winding of the transformer; when the input voltage is positive or negative, the four semiconductor switch devices (6) work together in a certain order to perform PWM pulse width modulation, thereby realizing the conversion of the input voltage into a high-frequency voltage.

[0047] Figure 3 The circuit schematic diagram of the rectifier module of the low-voltage module (5) of the present invention is shown. The rectifier module includes two semiconductor switch devices connected in series to form a bridge arm, whose two endpoints form the output end (+, -) of the rectifier module, and the midpoint of the bridge arm serves as an input end of the rectifier module. The semiconductor switch device can be a power semiconductor such as a reverse-conducting IGBT, MOSFET, IGCT, etc. The rectifier module also includes two capacitors (4) connected in series, whose two ends are connected in parallel with the two output ends of the bridge arm, and the midpoint serves as another input end of the rectifier module. The input end of the rectifier module is connected to the secondary winding of the transformer (3), and the high-frequency voltage entering from the secondary winding of the transformer (3) is converted into a DC voltage or a pulsating DC voltage through the rectifier module and the capacitor (4), thereby realizing the rectification function. At the same time, the rectifier module can also work in a reversible state, thereby realizing the reverse transmission of electric energy.

[0048] Figure 4 This is another circuit schematic diagram of the rectifier module of the low voltage module (5) of the present invention. Figure 3 The difference between the embodiments is that a single-phase inverter bridge circuit composed of four semiconductor switch devices is used, the midpoint of the two bridge arms is used as the input end of the rectifier module, and the capacitor does not need to be connected in series. Figure 3 The embodiments are the same and will not be described again.

[0049] The bridge arm midpoint of the rectifier module may also be connected in series with an inductor as an input terminal. When the leakage inductance of the transformer (3) is small, the inductance value may be increased by the inductor to reduce the high-frequency current pulsation component.

[0050] Figure 5 The circuit structure diagram of the output module of the low-voltage module (5) of the present invention is shown. The output module is composed of two semiconductor switching devices connected in series to form a bridge arm, whose two endpoints form the input end (+, -) of the output module, which is connected in parallel with the output end (+, -) of the rectifier module. The midpoint of the bridge arm is connected to an inductor, and the other end of the inductor serves as the output end of the output module; and the midpoint of the output capacitor group (4) is led out as another output end; the semiconductor switching device can be a power semiconductor such as a reverse-conducting IGBT, MOSFET, IGCT, etc. The output module converts the rectified DC voltage or pulsating DC voltage into a voltage-controllable low-frequency AC through the semiconductor switching device. At the same time, the output module can also work in a reversible state, thereby realizing the reverse transmission of electric energy.

[0051] Figure 6 is another circuit structure diagram of the output module of the low voltage module (5) of the present invention. Figure 5 The difference between the embodiment is that a single-phase inverter bridge circuit composed of four semiconductor switch devices is used, and the midpoints of the two bridge arms are used as the input and output ends of the output module. Figure 3 The embodiments are the same and will not be described again.

[0052] The above are only preferred embodiments of the present invention. It should be pointed out that the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the field without departing from the purpose of the present invention. The above preferred embodiments should not be regarded as limitations on the present invention. The protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. An isolation transformer, characterized in that: It includes: An input terminal (Vin1, Vin2) connected to a power grid, wherein one of the input terminals is connected in series with an inductor (1), wherein the inductor (1) is used to filter out high-frequency pulsating components of the input current of the power grid; A plurality of input capacitor groups (2), each input capacitor group (2) being formed by two capacitors connected in series, and the plurality of input capacitor groups (2) being connected in series to form a capacitor group string, one end of the capacitor group string being connected to the inductor (1), and the other end being connected to another input end (Vin2) of the power grid, the input capacitor group (2) cooperating with the inductor (1) to filter out pulsating components of the current, and at the same time, the plurality of input capacitor groups (2) connected in series also play a role in balancing the input voltage; A plurality of high-voltage modules, wherein the three input terminals (Ui1, Ui2, Ui0) of each high-voltage module are respectively connected to the two terminals and the midpoint of the input capacitor group (2); the high-voltage module chops and modulates the low-frequency voltage into a high-frequency voltage to reduce the volume and weight of the transformer and realizes bidirectional energy transfer at the same time; the high-voltage module is composed of four semiconductor switch devices (6) divided into two groups, each group being connected in series in the same direction; the two groups of semiconductor switch devices (6) are connected in series in reverse direction, and the two terminals (Ui1, Ui2) thereof are respectively connected to the two terminals of the input capacitor group (2) as input terminals, and the midpoint (Ui0) thereof is connected to the midpoint of the input capacitor group (2); in the two groups of semiconductor switch devices (6) connected in series in the same direction, the midpoints of the two groups serve as the two output terminals of the high-voltage module; the semiconductor switch device (6) is a reverse-conducting IGBT, MOSFET or IGCT; A plurality of series capacitors (7), one end of each of which is connected in series with an output (Uo1) of the high-voltage module, coupling the high-frequency voltage output by the high-voltage module to a subsequent transformer and blocking low-frequency voltage components; One or more transformers (3), wherein both ends of multiple primary windings of the one or more transformers (3) are respectively connected to one end of the series capacitor (7) and an output end (Uo2) of a high-voltage module, the transformer (3) realizes electrical isolation, and simultaneously transfers energy between the primary and secondary sides, and realizes bidirectional energy transfer; the primary winding of the transformer (3) is also connected in series with an inductor, and the inductor is used to increase the inductance value so as to reduce the high-frequency current pulsation component of the winding of the transformer (3); the one or more transformers (3) comprise: multiple primary windings, one end of each primary winding is connected to the output end of the high-voltage module, and the other end is connected to one end of the series capacitor (7); one or more secondary windings, the two ends of the multiple secondary windings are connected in parallel and then connected to a low-voltage module (5); one or more iron cores, each iron core is wound with at least one primary winding and one secondary winding, and multiple primary and secondary windings share one iron core; A low-voltage module (5) whose input end is respectively connected to one or more secondary windings of the transformer (3), and whose output end forms the output end of the isolation transformer device. The low-voltage module (5) completes the rectification, filtering and inversion output functions of the high-frequency voltage output by the secondary side of the transformer, and can transmit electric energy in both directions.

2. The isolating transformer device according to claim 1, characterized in that: The low-voltage module (5) comprises: One or more rectifier modules, whose input ends are respectively connected to the secondary winding of the transformer (3); One or more output modules, the input end of the output module is connected in parallel with the output end of the rectifier module, and the output end of the output module serves as the output end (Vo1, Vo2) of the device.

3. The isolating transformer device according to claim 2, characterized in that: The rectifier module comprises: Two semiconductor switching devices connected in series form a bridge arm, whose two ends form the output ends of the rectifier module, and the midpoint of the bridge arm serves as an input end of the rectifier module, wherein the semiconductor switching device is a reverse-conducting IGBT, MOSFET or IGCT; Two capacitors (4) are connected in series, both ends of which are connected in parallel to the two output ends of the bridge arm, and the midpoint thereof serves as another input end of the rectifier module.

4. The isolation transformer device according to claim 2, characterized in that: The rectifier module comprises: A single-phase inverter bridge circuit composed of four semiconductor switching devices, whose two positive and negative ends form the output ends of the rectifier module, and the midpoints of the two bridge arms serve as the two input ends of the rectifier module, and the semiconductor switching devices are reverse-conducting IGBTs, MOSFETs or IGCTs; A capacitor has two ends connected in parallel with the positive and negative output ends of the inverter bridge circuit.

5. The isolating transformer device according to claim 2, characterized in that: The output module is a single-phase inverter bridge circuit composed of four semiconductor switching devices, whose two positive and negative terminals form the input end of the output module, and the midpoint of one bridge arm is connected to an inductor and then led out, and the midpoint of the other bridge arm serves as the output end of the output module; the semiconductor switching device is a reverse-conducting IGBT, MOSFET or IGCT.

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