CN111835247A - Electronic on-load voltage regulator and tap unit thereof - Google Patents
Electronic on-load voltage regulator and tap unit thereof Download PDFInfo
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- CN111835247A CN111835247A CN202010773266.5A CN202010773266A CN111835247A CN 111835247 A CN111835247 A CN 111835247A CN 202010773266 A CN202010773266 A CN 202010773266A CN 111835247 A CN111835247 A CN 111835247A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P13/00—Arrangements for controlling transformers, reactors or choke coils, for the purpose of obtaining a desired output
- H02P13/06—Arrangements for controlling transformers, reactors or choke coils, for the purpose of obtaining a desired output by tap-changing; by rearranging interconnections of windings
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
Abstract
The invention discloses a tap unit of an electronic on-load voltage regulator, which comprises two IGBTs and two freewheeling diodes, wherein the two IGBTs are reversely connected in series, the two freewheeling diodes are respectively connected in parallel with the IGBTs, and the conduction directions of the freewheeling diodes and the IGBTs are opposite. The invention also discloses an electronic on-load voltage regulator which comprises a plurality of tap joint units and a driving loop. Each tap unit is a tap unit as described above, and a plurality of tap units are connected in parallel between the winding side and the load side, wherein the first IGBT is close to the winding side and the second IGBT is close to the load side. The drive circuit takes power from the main circuit and applies a drive voltage to the IGBTs in the tap unit so that the IGBTs are turned on or off. The electronic on-load voltage regulator further comprises a self-starting loop, the self-starting loop is connected with one tap unit in parallel, the self-starting loop comprises a normally closed switch, the normally closed switch is connected to a control relay, and the control relay is driven by a driving loop.
Description
Technical Field
The invention relates to the field of power equipment, in particular to a load voltage regulator.
Background
The transformer is one of the core devices in the power transmission and distribution system. Due to the impedance of the transformer itself, a voltage drop will occur during power transmission and will vary with the load on the user side. The voltage fluctuation of the power grid system and the change of the load at the user side cause larger voltage fluctuation, and the larger voltage fluctuation has accident potential. Therefore, an on-load tap changer (hereinafter, referred to as an on-load tap changer) is disposed in the grid system. On the premise of realizing the local balance of reactive power, when the voltage variation exceeds a fixed value, the on-load voltage regulator can act after a certain time delay to regulate the voltage and keep the voltage stable.
The on-load voltage regulator is provided with a plurality of tap-changing taps corresponding to different levels of voltage, and the on-load voltage regulation is realized by switching among different tap-changing taps through one tap-changing switch under the condition of no power failure. The tap changer of the conventional on-load voltage regulator is mostly in a mechanical type, and the tap changer is immersed in an insulating medium (such as insulating oil), and the insulating medium provides insulation and cooling for the tap changer during the working process. When the mechanical tap changer is switched under load, electric sparks are generated certainly, and the electric sparks cause high temperature of contact parts, so that an insulating medium is oxidized to reduce the insulating performance. The mechanical tap changer requires regular maintenance and repair after a certain number of uses. Generally, mechanical tap changers have a limited service life and require frequent maintenance.
The power electronic element has the advantages of high response speed, no spark in the switching process, long service life, no need of using an insulating medium and the like, and more electronic voltage regulators begin to use the power electronic element to replace a mechanical element. Among power electronic components, an insulated Gate Bipolar transistor (igbt) has both the advantages of high input impedance and low on-state voltage drop, and thus is a very suitable power electronic component for an electronic on-load voltage regulator.
Disclosure of Invention
The invention provides an electronic on-load voltage regulator taking an IGBT (insulated gate bipolar transistor) as a main power electronic element.
According to an embodiment of the invention, a tap unit of an electronic on-load voltage regulator is provided, which includes two IGBTs and two freewheeling diodes, the two IGBTs are connected in series in an inverse direction, the two freewheeling diodes are respectively connected in parallel with the IGBTs, and the conduction directions of the freewheeling diodes and the IGBTs are opposite. Specifically, the method comprises the following steps:
the first IGBT is in forward conduction;
the first freewheeling diode is connected with the first IGBT in parallel, and the first freewheeling diode is in reverse conduction;
the second IGBT is connected with the first IGBT in series and is conducted in the reverse direction;
the second freewheeling diode is connected with the second IGBT in parallel, and the second freewheeling diode is in forward conduction;
the first IGBT and the second freewheeling diode form a forward current path, and the second IGBT and the first freewheeling diode form a reverse current path.
In one embodiment, the tap unit of the electronic load voltage regulator further comprises an auxiliary loop, the first IGBT and the second IGBT connected in series forming a main loop, the auxiliary loop being connected in parallel with the main loop, the auxiliary loop comprising:
an auxiliary loop switch;
the third IGBT is in forward conduction;
the third freewheeling diode is connected with the third IGBT in parallel, and the third freewheeling diode is in reverse conduction;
the fourth IGBT is connected with the third IGBT in series and is conducted in the reverse direction;
the fourth freewheeling diode is connected with the fourth IGBT in parallel, and the fourth freewheeling diode is in forward conduction;
wherein the third IGBT and the fourth freewheel diode form a forward current path, and the fourth IGBT and the third freewheel diode form a reverse current path.
According to an embodiment of the present invention, an electronic on-load voltage regulator is provided, including: several tap units and a drive circuit. Each tap unit is a tap unit as described above, and a plurality of tap units are connected in parallel between the winding side and the load side, wherein the first IGBT is close to the winding side and the second IGBT is close to the load side. The drive circuit takes power from the main circuit and applies a drive voltage to the IGBTs in the tap unit so that the IGBTs are turned on or off.
In one embodiment, the electronic on-load voltage regulator further comprises a self-starting loop. The self-starting circuit is connected with one tap unit in parallel, and comprises a normally closed switch connected to a control relay, and the control relay is driven by a driving circuit. The main circuit is started, the self-starting circuit drives the IGBT in the tap unit which is connected with the self-starting circuit in parallel, the IGBT is started to enable the main circuit to be conducted, the driving circuit obtains power supply from the conducted main circuit and drives the control relay, the control relay enables the normally-closed switch to be disconnected, and the IGBT in the tap unit is controlled by the driving circuit.
In one embodiment, the electronic load voltage regulator switches from the first tap unit to the second tap unit at a forward voltage difference, comprising the process of:
the driving circuit turns off the second IGBT (S1b) of the first tapping unit, and the current continues to pass through the first IGBT (S1a) of the first tapping unit and the second freewheeling diode (D1 b);
the driving loop opens the first IGBT (S2a) of the second tapping unit, and current continues to pass through the first IGBT (S1a) of the first tapping unit and the second freewheeling diode (D1b), and no current passes through the second tapping unit;
the current simultaneously passes through the first IGBT (S1a) and the second freewheeling diode (D1b) of the first tapping unit and the first IGBT (S2a) and the second freewheeling diode (D2b) of the second tapping unit, and the driving loop turns off the first IGBT (S1a) of the first tapping unit;
the drive circuit opens the second IGBT (S2b) of the second tap unit, current passes through the second tap unit and no current passes in the first tap unit, current is switched from the first tap unit to the second tap unit.
In one embodiment, the electronic load voltage regulator switches from the first tap unit to the second tap unit at a negative voltage difference, comprising the process of:
the driving circuit turns off the second IGBT (S1b) of the first tapping unit, and the current continues to pass through the first IGBT (S1a) of the first tapping unit and the second freewheeling diode (D1 b);
the driving circuit opens the first IGBT (S2a) of the second tap unit, and current simultaneously passes through the first IGBT (S1a) and the second freewheel diode (D1b) of the first tap unit and the first IGBT (S2a) and the second freewheel diode (D2b) of the second tap unit;
the driving circuit turns off the first IGBT (S1a) of the first tapping unit, and the current passes through the first IGBT (S2a) of the second tapping unit and the second freewheeling diode (D2 b);
the drive circuit opens the second IGBT (S2b) of the second tap unit, current passes through the second tap unit and no current passes in the first tap unit, current is switched from the first tap unit to the second tap unit.
In one embodiment, the plurality of tap units correspond to different stage voltages, including a neutral tap unit corresponding to a neutral stage, a plurality of positively biased positive tap units corresponding to a positive bias, and a plurality of negatively biased negative tap units corresponding to a negative bias. Several corresponding forward biased forward tap units are located on the forward side of the neutral tap unit and the forward bias of the forward tap unit further from the neutral tap unit is larger. A number of corresponding negatively biased positive tap units are located on the negative side of the neutral tap unit and the more distant negative tap units from the neutral tap unit have a greater negative bias. Adjacent tap units have equal level voltage differences between them.
In one embodiment, a self-start loop is connected in parallel with the neutral tap unit, the main loop is started, and the self-start loop drives the IGBTs in the neutral tap unit.
In one embodiment, the electronic load regulator has 7 tap units, including a neutral tap unit, 3 positive tap units, and 3 negative tap units. Wherein the neutral tap unit corresponds to a neutral level voltage of 10kV, and the level voltage difference between adjacent tap units is
The positive bias of the 3 positive tap units increases in sequence and the negative bias of the 3 negative tap units increases in sequence.
The electronic on-load voltage regulator and the tap unit thereof solve the problem of weak reverse voltage-resisting capability of the IGBT by adopting a mode that two IGBTs are connected in series in a reverse direction and are respectively connected with the freewheeling diodes in the opposite directions of the IGBTs in parallel, so that the two IGBTs are alternately in a blocking state under alternating voltage through the assistance of the freewheeling diodes. The electronic on-load voltage regulator also realizes the self-starting function through the relay loop and the normally closed switch.
Drawings
Fig. 1 discloses a circuit schematic of a tap unit of an electronic on-load voltage regulator according to an embodiment of the present invention.
Fig. 2 discloses a circuit schematic of a tap unit of an electronic on-load voltage regulator according to another embodiment of the present invention.
Fig. 3 illustrates a schematic circuit diagram of an electronic on-load voltage regulator according to an embodiment of the present invention.
Fig. 4a, 4b, 4c, 4d and 4e disclose the switching process of the electronic on-load voltage regulator according to an embodiment of the present invention under the forward voltage difference.
Fig. 5a, 5b, 5c, 5d and 5e disclose the switching process of the electronic on-load voltage regulator under the negative voltage difference according to an embodiment of the present invention.
Detailed Description
An Insulated Gate Bipolar Transistor (IGBT) is a composite fully-controlled voltage-driven power semiconductor device consisting of a BJT (Bipolar junction transistor) and an MOS (insulated Gate field effect transistor), and has the advantages of both high input impedance of the MOSFET and low conduction voltage drop of the GTR. The GTR saturation voltage is reduced, the current carrying density is high, but the driving current is large; the MOSFET has small driving power, high switching speed, large conduction voltage drop and small current carrying density. The IGBT integrates the advantages of the two devices, and has small driving power and reduced saturation voltage. However, when the IGBT is applied to a tap changer of an electronic on-load voltage regulator, a problem also needs to be faced, where the on-load voltage regulator works in an alternating current environment, the voltage borne by the on-load voltage regulator is an alternating voltage alternating in forward and reverse directions, and the directional voltage-withstanding capability of the IGBT is weak. In order to adapt to the problem of bearing alternating voltage under an alternating current environment, the electronic load voltage regulator provided by the invention carries out the following design on a circuit where the IGBT is positioned.
Each tap unit of the electronic on-load voltage regulator comprises two IGBTs and two freewheeling diodes, wherein the two IGBTs are connected in series in a reverse direction, the two freewheeling diodes are respectively connected in parallel with the IGBTs, and the conduction directions of the freewheeling diodes and the IGBTs are opposite. Fig. 1 discloses a circuit schematic of a tap unit of an electronic on-load voltage regulator according to an embodiment of the present invention. Referring to fig. 1, the tap unit of the electronic on-load voltage regulator includes: a first IGBT S1a, a first freewheel diode D1a, a second IGBT S1b, and a second freewheel diode D1 b. The first IGBT S1a is forward-conducting. The first freewheeling diode D1a is connected in parallel with the first IGBT S1a, the first freewheeling diode D1a is reverse conducting, and the first freewheeling diode D1a is opposite in conducting direction to the first IGBT S1 a. The second IGBT S1b is connected in series with the first IGBT S1a, and the second IGBT S1b is reverse conducting. The second IGBT S1b conducts in the opposite direction to the first IGBT S1a, but the second IGBT S1b conducts in the same direction as the first freewheeling diode D1 a. The second freewheeling diode D1b is connected in parallel with the second IGBT S1b and the second freewheeling diode D1b is forward conducting. The second freewheeling diode D1b is opposite in conduction direction to the second IGBT S1b, but in the same conduction direction as the first IGBT S1 a. Thus, the first IGBT S1a and the second freewheel diode D1b form a forward current path, and a current flows through the first IGBT S1a and the second freewheel diode D1b during a forward voltage period of the alternating voltage. The second IGBT S1b and the first freewheel diode D1a form a reverse current path, and during a negative voltage period of the alternating voltage, a current flows through the second IGBT S1b and the first freewheel diode D1 a. In this way, on the current path, each IGBT is connected with a freewheeling diode in series, and the freewheeling diode is used for sharing reverse voltage, so that the problem that the reverse voltage resistance of the IGBT is poor is solved.
Although the IGBT has high breakdown voltage and low on-state loss, it is sometimes difficult to satisfy both of the above-described characteristics of the IGBT at the same time, and the present invention proposes a modified design in order to sufficiently exert both of the above-described characteristics of the IGBT. Fig. 2 discloses a circuit schematic of a tap unit of an electronic on-load voltage regulator according to another embodiment of the present invention. In this variant design, the tap unit of the electronic on-load voltage regulator also includes an auxiliary circuit, the first IGBT S1a, the first freewheeling diode D1a, the second IGBT S1b and the second freewheeling diode D1b shown in fig. 1 forming the main circuit. An auxiliary circuit is connected in parallel with the main circuit, the auxiliary circuit comprising: an auxiliary loop switch Kx, a third IGBT Sxa, a third freewheeling diode Dxa, a fourth IGBTSxb, and a fourth freewheeling diode Dxb. The third IGBT Sxa, the third freewheeling diode Dxa, the fourth IGBTSxb, and the fourth freewheeling diode Dxb in the auxiliary circuit are connected in the same manner and operate on the same principle as the first IGBT S1a, the first freewheeling diode D1a, the second IGBT S1b, and the second freewheeling diode D1b in the main circuit. The third IGBT Sxa is equivalent to the first IGBT S1a, the third freewheel diode Dxa is equivalent to the first freewheel diode D1a, the fourth IGBT Sxb is equivalent to the second IGBT S1b, and the fourth freewheel diode Dxb is equivalent to the second freewheel diode D1 b. When the auxiliary loop switch is switched on, the main loop and the auxiliary loop are connected in parallel, and current flows through the main loop and the auxiliary loop simultaneously, so that better low-on-state loss performance is obtained. When the auxiliary loop is not needed, the auxiliary loop switch is turned off, and only the main loop works, and the circuit is equivalent to the circuit shown in fig. 1.
Fig. 1 and 2 show a schematic circuit diagram of a tap unit of an electronic on-load regulator, and fig. 3 shows a schematic circuit diagram of an electronic on-load regulator according to an embodiment of the present invention, in which each tap unit of the on-load regulator adopts the structure of the tap unit. Referring to fig. 3, the electronic on-load voltage regulator includes: several tap units and a drive circuit. Each of the plurality of tap units is a tap unit as described above, and the plurality of tap units are connected in parallel between the winding side and the load side, wherein the first IGBT is close to the winding side and the second IGBT is close to the load side. The driving circuit a takes power supply from the main circuit and applies a driving voltage to the IGBTs in the tap unit so that the IGBTs are turned on or off. In the embodiment shown in fig. 3, the tap units correspond to different step voltages, and the tap units include a neutral tap unit corresponding to a neutral step, a plurality of positive tap units corresponding to a positive bias, and a plurality of negative tap units corresponding to a negative bias. Number ofThe forward tap units of the respective forward biases are located on the forward side of the neutral tap unit (upper side as viewed in fig. 3) and the forward bias of the forward tap unit farther from the neutral tap unit is larger. Several corresponding negatively biased positive tap units are located on the negative side of the neutral tap unit (lower in the view of fig. 3) and the more distant negative tap units from the neutral tap unit have the greater the reverse bias. Adjacent tap units have equal level voltage differences between them. In the embodiment shown in fig. 3, the input voltage of the electronic on-load voltage regulator is 220kV and the output voltage is 10 kV. The neutral voltage is therefore 10 kV. In the illustrated embodiment, the electronic load regulator has 7 tap units, including a neutral tap unit S4, 3 positive tap units S1, S2 and S3, and 3 negative tap units S5, S6, S7. The neutral tap unit S4 was located in the middle of the 7 tap units, corresponding to a neutral voltage of 10 kV. The voltage difference between adjacent tap units is
The forward bias of the 3 forward tap units increases in sequence, with the forward bias of the forward tap unit S3 nearest the neutral tap unit S4 being
The farther forward tap unit S2 is forward biased to
The farthest forward tap unit S1 is forward biased to
Similarly, the negative tap cell S5 nearest the neutral tap cell S4 is negatively biased as
The further negative tap unit S6 is negatively biased to
The farthest negative tap unit S7 is negatively biased as
The drive circuit a also has a winding, and when there is current in the main circuit, the drive circuit a takes power from the main circuit through the winding and applies a drive voltage to the IGBTs in the tap unit to turn the IGBTs on or off.
When the main loop continuously works, the driving circuit A can continuously obtain power supply from the main loop through the winding to drive each IGBT to be switched on and switched off, but when cold start is needed after the main loop is powered off, because the main loop is not conducted at the moment, the driving circuit A cannot obtain power supply, and an additional starting device is needed to carry out initial start on the IGBT. With continued reference to fig. 3, in this embodiment, the electronic on-load voltage regulator further includes a self-starting circuit connected in parallel with one of the tap units, the self-starting circuit including a normally closed switch K1, the normally closed switch K1 connected to the control relay X1, the control relay X1 driven by the drive circuit a 1. The main circuit is started, the self-starting circuit drives the IGBT in the tap unit which is connected with the self-starting circuit in parallel, the IGBT is started to enable the main circuit to be conducted, the driving circuit obtains power supply from the conducted main circuit and drives the control relay, the control relay enables the normally-closed switch to be disconnected, and the IGBT in the tap unit is controlled by the driving circuit. In the illustrated embodiment, the self-starting circuit is connected in parallel with neutral tap unit S4. The main circuit starts and the self-starting circuit drives the IGBT in the neutral tap unit S4 so that the output of the load voltage regulator is first the reference neutral level voltage of 10 kV. When the main loop is conducted along with the starting of the IGBT, current is generated in the main loop, and at the moment, the driving loop A1 obtains power supply from the conducted main loop and drives the control relay X1. The control relay X1 is actuated to open the normally closed switch K1, the self-starting circuit is withdrawn from the working state, and the IGBT in the tap unit is controlled by the driving circuit A1. After the next main circuit is powered off, the driving circuit A1 is also powered off, the control relay X1 does not work any more, and the normally closed switch K1 returns to the normally closed state to be ready for the next start.
The process of switching the current between different tap units of the electronic load regulator is described below.
Fig. 4a, 4b, 4c, 4d and 4e disclose the switching process of the electronic on-load voltage regulator according to an embodiment of the present invention under the forward voltage difference. Fig. 4a, 4b, 4c, 4d and 4e show equivalent circuit diagrams of a two-stage tap unit. L in fig. 4a, 4b, 4c, 4d and 4e represents a load and the equivalent supply V12 represents the voltage difference between the first stage tap unit and the second stage tap unit. The forward voltage difference, i.e., V12>0, indicates that the switching direction is from the high voltage to the low voltage direction, i.e., from S1 to S7 in fig. 3. In the following description, the first tap unit refers to a tap unit through which a current flows before switching, and the second tap unit refers to a tap unit through which a current flows after switching. The switching in the forward voltage difference, i.e. the voltage of the first tap unit is higher than the voltage of the second tap unit. The handover procedure is as follows:
referring to fig. 4a, before switching begins, the drive loop applies a forward gate voltage to set both the first IGBTS1a and the second IGBT S1b of the first tap unit ON, applies a reverse gate voltage to set both the first IGBT S2a and the second IGBT S2b of the second tap unit OFF, and current passes through the first tap unit while no current passes through the second tap unit. In fig. 4a, the flow of current is indicated by thick lines, which are also indicated in subsequent figures. For convenience of illustration, only the forward current of the forward cycle is shown in fig. 4a, and the current switching process described below is also described by taking the example of current switching during the forward current, so that only the forward current of the forward cycle is shown in the subsequent figures. Although the negative current of the negative going cycle is not illustrated, this does not affect the understanding of those skilled in the art of the tap changing process of the electronic load regulator of the present invention. If the current switching is to be performed at a negative current in a negative cycle, reference may be made to a switching pattern of positive current.
Referring to fig. 4b, the first step of the handover is started. The driving circuit applies negative gate voltage to the second IGBT S1b of the first tap unit so that the IGBT S1b is turned off, and the on-off states of the remaining IGBTs remain unchanged from the state shown in fig. 4 a. Since the second IGBT S1b of the first tap unit is a reverse IGBT, the current path still exists for forward currents: the current continues to be normally conducted through the first IGBT S1a and the second freewheeling diode D1b of the first tap unit.
Referring to fig. 4c, the second step of the handover. The driving circuit applies a forward gate voltage to the first IGBT S2a of the second tap unit so that the IGBT S2a is opened, and the open-closed state of the remaining IGBTs remains the same as the state shown in fig. 4 b. The current now continues through the first IGBT S1a and the second freewheeling diode D1b of the first tap unit. In contrast, in the second tap unit, although the IGBT S2a is already open, no current yet flows, and no current flows in the second tap unit. It should be noted that, although the current switching process is shown in stages in fig. 4a, 4b, 4c, 4d and 4e, in which there is a situation where the switch is turned on but no current flows yet, this is only for illustrative purposes, and in the actual switching process, the current switching is completed in a continuous process within a very short time.
Referring to fig. 4d, a third step of handover. In the phase of the third step, the current passes through the first IGBT S1a and the second freewheel diode D1b of the first tap unit and the first IGBT S2a and the second freewheel diode D2b of the second tap unit at the same time. That is, at the stage of the third step, current flows in both the first tap unit and the second tap unit. At this time, the driving circuit applies a negative gate voltage to the first IGBT S1a of the first tap unit to turn off the IGBT S1a, and the on/off states of the remaining IGBTs remain the same as those shown in fig. 4 c. After the IGBT S1a is turned off, both IGBTs S1a and S1b in the first tap unit are turned off, the positive and negative current paths in the first tap unit are both cut off, and no current flows in the first tap unit.
Referring to fig. 4e, the fourth step of switching, the driving loop applies a forward gate voltage to the second IGBT S2b of the second tap unit to turn on the IGBT S2b, so that the reverse current path of the second tap unit is also conductive. In the state shown in fig. 4e, the drive circuit applies a negative gate voltage to set both the first IGBT S1a and the second IGBT S1b of the first tap unit OFF, and applies a positive gate voltage to set both the first IGBT S2a and the second IGBT S2b of the second tap unit ON, with current passing through the second tap unit and no current passing through the first tap unit. The current is switched from the first tap unit to the second tap unit.
Fig. 5a, 5b, 5c, 5d and 5e disclose the switching process of the electronic on-load voltage regulator under the negative voltage difference according to an embodiment of the present invention. Fig. 5a, 5b, 5c, 5d and 5e show equivalent circuit diagrams of a two-stage tap unit. L in fig. 5a, 5b, 5c, 5d and 5e represents a load and the equivalent supply V12 represents the voltage difference between the first stage tap unit and the second stage tap unit. A negative voltage difference, i.e., V12<0, indicates that the direction of switching is from low voltage to high voltage, i.e., from S7 to S1 in fig. 3. In the following description, the first tap unit refers to a tap unit through which a current flows before switching, and the second tap unit refers to a tap unit through which a current flows after switching. The switching at a negative voltage difference is that the voltage of the first tap unit is higher than the voltage of the second tap unit. The handover procedure is as follows:
referring to fig. 5a, before switching begins, the drive loop applies a forward gate voltage to set both the first IGBTS1a and the second IGBT S1b of the first tap unit ON, applies a reverse gate voltage to set both the first IGBT S2a and the second IGBT S2b of the second tap unit OFF, and current passes through the first tap unit while no current passes through the second tap unit. In fig. 5a, the flow of current is indicated by thick lines, which are also indicated in subsequent figures. For convenience of illustration, only the forward current of the forward cycle is shown in fig. 5a, and the current switching process described below is also described by taking as an example the current switching during the forward current, so that only the forward current of the forward cycle is shown in the subsequent figures. Although the negative current of the negative going cycle is not illustrated, this does not affect the understanding of those skilled in the art of the tap changing process of the electronic load regulator of the present invention. If the current switching is to be performed at a negative current in a negative cycle, reference may be made to a switching pattern of positive current.
Referring to fig. 5b, the first step of the handover is started. The driving circuit applies negative gate voltage to the second IGBT S1b of the first tap unit so that the IGBT S1b is turned off, and the open-closed states of the remaining IGBTs remain unchanged from the state shown in fig. 5 a. Since the second IGBT S1b of the first tap unit is a reverse IGBT, the current path still exists for forward currents: the current continues to be normally conducted through the first IGBT S1a and the second freewheeling diode D1b of the first tap unit.
Referring to fig. 5c, the second step of the handover. The driving circuit applies a forward gate voltage to the first IGBT S2a of the second tap unit so that the IGBT S2a is opened, and the open-closed state of the remaining IGBTs remains the same as the state shown in fig. 5 b. Current simultaneously passes through the first IGBT S1a and the second freewheeling diode D1b of the first tap unit and the first IGBTs2a and the second freewheeling diode D2b of the second tap unit. During switching at a negative voltage difference, current flows in both the first tap unit and the second tap unit in the second step of switching. During the switching process under the forward voltage difference, the current flows through the first tap unit and the second tap unit in the third step of the switching.
Referring to fig. 5d, a third step of handover. The driving circuit applies negative gate voltage to the first IGBT S1a of the first tap unit to turn off the IGBT S1a, and the on-off states of the remaining IGBTs remain unchanged from the state shown in fig. 5 c. After the IGBT S1a is turned off, both IGBTs S1a and S1b in the first tap unit are turned off, the positive and negative current paths in the first tap unit are both cut off, and no current flows in the first tap unit.
Referring to fig. 5e, the fourth step of switching, the driving loop applies a forward gate voltage to the second IGBT S2b of the second tap unit to turn on the IGBT S2b, so that the reverse current path of the second tap unit is also conductive. In the state shown in fig. 5e, the drive circuit applies a negative gate voltage to set both the first IGBT S1a and the second IGBT S1b of the first tap unit OFF, and applies a positive gate voltage to set both the first IGBT S2a and the second IGBT S2b of the second tap unit ON, with current passing through the second tap unit and no current passing through the first tap unit. The current is switched from the first tap unit to the second tap unit.
The electronic on-load voltage regulator and the tap unit thereof solve the problem of weak reverse voltage-resisting capability of the IGBT by adopting a mode that two IGBTs are connected in series in a reverse direction and are respectively connected with the freewheeling diodes in the opposite directions of the IGBTs in parallel, so that the two IGBTs are alternately in a blocking state under alternating voltage through the assistance of the freewheeling diodes. The electronic on-load voltage regulator also realizes the self-starting function through the relay loop and the normally closed switch.
It should also be noted that the above-mentioned embodiments are only specific embodiments of the present invention. It is apparent that the present invention is not limited to the above embodiments and similar changes or modifications can be easily made by those skilled in the art from the disclosure of the present invention and shall fall within the scope of the present invention. The embodiments described above are provided to enable persons skilled in the art to make or use the invention and that modifications or variations can be made to the embodiments described above by persons skilled in the art without departing from the inventive concept of the present invention, so that the scope of protection of the present invention is not limited by the embodiments described above but should be accorded the widest scope consistent with the innovative features set forth in the claims.
Claims (9)
1. A tap unit for an electronic on-load voltage regulator, comprising:
the first IGBT is in forward conduction;
the first freewheeling diode is connected with the first IGBT in parallel, and the first freewheeling diode is in reverse conduction;
the second IGBT is connected with the first IGBT in series and is conducted in the reverse direction;
the second freewheeling diode is connected with the second IGBT in parallel, and the second freewheeling diode is in forward conduction;
the first IGBT and the second freewheeling diode form a forward current path, and the second IGBT and the first freewheeling diode form a reverse current path.
2. The tap unit of an electronic on-load voltage regulator according to claim 1 further comprising an auxiliary loop, the first IGBT and the second IGBT in series forming the auxiliary loop in parallel with the main loop, the auxiliary loop comprising:
an auxiliary loop switch;
the third IGBT is in forward conduction;
the third freewheeling diode is connected with the third IGBT in parallel, and the third freewheeling diode is in reverse conduction;
the fourth IGBT is connected with the third IGBT in series and is conducted in the reverse direction;
the fourth freewheeling diode is connected with the fourth IGBT in parallel, and the fourth freewheeling diode is in forward conduction;
wherein the third IGBT and the fourth freewheel diode form a forward current path, and the fourth IGBT and the third freewheel diode form a reverse current path.
3. An electronic on-load voltage regulator, comprising:
a plurality of tap units, each tap unit being a tap unit as claimed in claim 1 or 2, the plurality of tap units being connected in parallel between the winding side and the load side, wherein the first IGBT is located adjacent the winding side and the second IGBT is located adjacent the load side;
and a driving loop which obtains power supply from the main loop and applies driving voltage to the IGBT in the tap unit so that the IGBT is turned on or off.
4. The electronic on-load voltage regulator of claim 3, further comprising:
the self-starting circuit is connected with one tap unit in parallel and comprises a normally closed switch, the normally closed switch is connected to the control relay, and the control relay is driven by the driving circuit;
the main circuit is started, the self-starting circuit drives the IGBT in the tap unit which is connected with the self-starting circuit in parallel, the IGBT is started to enable the main circuit to be conducted, the driving circuit obtains power supply from the conducted main circuit and drives and controls the relay to enable the normally-closed switch to be disconnected, and the IGBT in the tap unit is controlled by the driving circuit.
5. The electronic on-load voltage regulator of claim 3, wherein switching from the first tap unit to the second tap unit at a forward voltage differential comprises:
the driving circuit turns off the second IGBT (S1b) of the first tapping unit, and the current continues to pass through the first IGBT (S1a) of the first tapping unit and the second freewheeling diode (D1 b);
the driving loop opens the first IGBT (S2a) of the second tapping unit, and current continues to pass through the first IGBT (S1a) of the first tapping unit and the second freewheeling diode (D1b), and no current passes through the second tapping unit;
the current simultaneously passes through the first IGBT (S1a) and the second freewheeling diode (D1b) of the first tapping unit and the first IGBT (S2a) and the second freewheeling diode (D2b) of the second tapping unit, and the driving loop turns off the first IGBT (S1a) of the first tapping unit;
the drive circuit opens the second IGBT (S2b) of the second tap unit, current passes through the second tap unit and no current passes in the first tap unit, current is switched from the first tap unit to the second tap unit.
6. The electronic on-load voltage regulator of claim 3, wherein switching from the first tap unit to the second tap unit at a negative voltage differential comprises:
the driving circuit turns off the second IGBT (S1b) of the first tapping unit, and the current continues to pass through the first IGBT (S1a) of the first tapping unit and the second freewheeling diode (D1 b);
the driving circuit opens the first IGBT (S2a) of the second tap unit, and current simultaneously passes through the first IGBT (S1a) and the second freewheel diode (D1b) of the first tap unit and the first IGBT (S2a) and the second freewheel diode (D2b) of the second tap unit;
the driving circuit turns off the first IGBT (S1a) of the first tapping unit, and the current passes through the first IGBT (S2a) of the second tapping unit and the second freewheeling diode (D2 b);
the drive circuit opens the second IGBT (S2b) of the second tap unit, current passes through the second tap unit and no current passes in the first tap unit, current is switched from the first tap unit to the second tap unit.
7. The electronic on-load voltage regulator of claim 4, wherein the plurality of tap units correspond to different step voltages, including a neutral tap unit corresponding to a neutral step, a plurality of positive tap units corresponding to a positive bias voltage, and a plurality of negative tap units corresponding to a negative bias voltage;
a number of corresponding forward biased forward tap units are located on the forward side of the neutral tap unit and the forward bias of the forward tap units further away from the neutral tap unit is greater;
a number of corresponding negatively biased positive tap units are located on the negative side of the neutral tap unit and the more distant the negative tap units are from the neutral tap unit the greater the reverse bias of the negative tap unit;
adjacent tap units have equal level voltage differences between them.
8. The electronic on-load voltage regulator of claim 7, wherein the self-start loop is connected in parallel with the neutral tap unit, the main loop being started, the self-start loop driving the IGBTs in the neutral tap unit.
9. The electronic on-load regulator of claim 7, wherein the electronic on-load regulator has 7 tap units, including a neutral tap unit, 3 positive tap units, and 3 negative tap units;
wherein neutral tap unit corresponds 10 kV's neutral level voltage, and the level voltage difference between the adjacent tap unit is 10kV i 1.5%, and the forward bias of 3 positive direction tap units increases in proper order, and the reverse bias of 3 negative direction tap units increases in proper order.
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