A controllable turn-off current source type inverter

Abstract

The application provides a controllable off-current source type converter, each phase of the converter comprising two bridge arms, each bridge arm comprising at least one semiconductor device unit; the semiconductor device unit comprising a first semiconductor device, a resistor R sxi , and an RCD-R circuit, the first semiconductor device being connected in parallel with the resistor R sxi , the RCD-R circuit, a diode device D dxi , and a resistor R dbxi being connected in series and then connected in parallel with the resistor R daxi , and a capacitor C xi being connected in series to form the RCD-R circuit. The technical scheme of the application ensures that the charge and discharge of the semiconductor device unit are in different loops, and avoids high overvoltage caused by LC undamped resonance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of converters, and particularly relates to a controllable turn-off current source type converter. BACKGROUND

[0002] The controllable turn-off current source type converter is based on a three-phase six-bridge-arm topology, adopts inverse resistance type fully-controlled devices, and has a voltage reduction characteristic at the DC side. The maximum voltage borne by each bridge arm is the line voltage peak value, which is less than 2 times the phase voltage peak value in the voltage source type device, so that the number of series devices can be reduced. During each commutation process, the bridge arm voltage changes are low, so that the loss of the voltage sharing loop is reduced. The controllable turn-off current source type converter can be used for high-voltage direct current transmission to solve the commutation failure problem, and can also be used for medium and low voltage occasions, such as AC grid closing, DC power distribution, grid ice melting, etc.

[0003] Due to the stray inductance of the commutation loop, an absorption loop needs to be connected in parallel to the semiconductor device, which is usually composed of RC series, and this loop also plays a role in turn-off voltage sharing. The resistance R plays a damping role, suppresses the resonance overvoltage of the capacitor C and the stray inductance L of the loop, and limits the discharge current of the capacitor C when the semiconductor device is turned on, so the resistance value cannot be too small. When the rated current of the converter is very large, the current is transferred to the RC loop at the moment of turn-off of the semiconductor device, a very large voltage is generated on R, which exceeds the maximum withstand voltage of the device, and the device is damaged. SUMMARY

[0004] In order to solve the above problems, the application provides a controllable turn-off current source type converter.

[0005] Each phase of the converter comprises two bridge arms, and each bridge arm comprises at least one semiconductor device unit;

[0006] The semiconductor device unit comprises a first semiconductor device, a resistance R sxi and an RCD-R circuit, and the semiconductor device is connected in parallel with the resistance R sxi and the RCD-R circuit.

[0007] The diode device D dxi and the resistance R dbxi are connected in series, and then connected in parallel with the resistance R daxi , and then connected in series with the capacitor C xi to form the RCD-R circuit.

[0008] The first semiconductor device comprises a fully-controlled semiconductor device T xi and a diode device D xi .

[0009] The resistance value of the resistance R daxi is greater than the resistance value of the resistance R dbxi .

[0010] The resistance R dbxi is determined by the formula R dbxi < U m / I m ; wherein U m is the safe working voltage of the series connection of the controllable semiconductor device T xi and the diode device D xi , and I m is the maximum turn-off current for the inverter design.

[0011] The resistance R daxi is determined by the formula ; wherein U Nm is the rated steady-state withstand voltage of the series connection of the controllable semiconductor device T xi and the diode device D xi , and I Tm is the maximum turn-off current of the controllable semiconductor device T xi .

[0012] The rated steady-state withstand voltage U Nm is equal to the AC line voltage peak value U lmax divided by the minimum number of series units n per bridge arm.

[0013] The minimum value C of the capacitance C xi in the RCD-R circuit is determined by the equations and ; wherein L c is the loop stray inductance on the inverter, U m is the limiting voltage of the series connection of the controllable semiconductor device T xi and the diode device D xi , U Nm is the rated steady-state withstand voltage of the series connection of the controllable semiconductor device T xi and the diode device D xi , and n is the minimum number of series units per bridge arm.

[0014] The diode devices D xi and D dxi are connected with opposite conduction directions.

[0015] The controllable semiconductor device T xi is an IGBT device or an IGCT device.

[0016] Compared with the prior art, the technical scheme of the application has the following advantages: the charging and discharging of the technical scheme of the application are different circuits, and different resistance values can be selected for the circuits to adapt to the requirements under different conditions; the technical scheme of the application can effectively provide damping for the charging process of the capacitor, and avoid high overvoltage caused by LC undamped resonance. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical scheme in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0018] Figure 1 The first prior art scheme of the converter involved in the application.

[0019] Figure 2 The second prior art scheme of the converter involved in the application.

[0020] Figure 3 The controllable turn-off current source type converter topology of the embodiment of the application. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical scheme and advantages of the embodiments of the application more clear, the technical scheme in the embodiments of the application will be clearly and completely described below in combination with the drawings in the embodiments of the application. Obviously, the described embodiments are some embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the application.

[0022] As Figure 1 shown is the first prior art scheme of the converter involved in the application. The converter provides electric energy through an AC power supply and a power grid, and then connects a plurality of bridge arms through a series LC filter and a loop stray inductance, Figure 1 The bridge arms shown above are six, and in actual application, the bridge arms can be less than six or more than six. In the figure, V sa , V sb and V sc are an AC power supply or a power grid; L a1 , L b1 , L c1 and C a , C b , C c compose an LC filter; L cLoop stray inductance. Each bridge arm is composed of multiple semiconductor device units, such as Figure 1 as shown above, wherein the multiple semiconductor device units on one bridge arm include U cp1 , U cp2 , … U cpn , each of which is further composed of an absorbing and voltage-sharing circuit, a fully-controlled semiconductor device, and a diode device, wherein the fully-controlled semiconductor device includes an IGBT device or an IGCT device. The semiconductor device unit includes a fully-controlled semiconductor device T xi , a diode device D xi , a resistor R sxi , a resistor R dxi , and a capacitor C xi ; the resistor R dxi and the capacitor C xi form an RC series circuit; the fully-controlled semiconductor device T xi and the diode device D xi are connected in series, and then connected in parallel with the resistor R sxi and the RC circuit. Due to the stray inductance L c on the converter, the RC series circuit on the semiconductor device unit plays a role of voltage-sharing turn-off, and the resistor R dxi plays a role of damping, thereby inhibiting resonance overvoltage of the capacitor C xi and the stray inductance L c , and limiting the discharge current of the capacitor C xi when the semiconductor device is turned on, so that the resistance value cannot be too small. When the rated current of the converter is very large, the current is transferred to the RC loop at the moment of turn-off of the semiconductor device, and a very large voltage is generated on the resistor R dxi , which may exceed the maximum voltage of the device and damage the device, so the resistance value cannot be too large, which also causes the limitation of the converter as shown in Figure 1 .

[0023] As shown in Figure 2 is a second prior art scheme of the converter involved in the present patent. The converter is provided with power by an AC power source and a power grid, and then connected with multiple bridge arms through a series LC filter and loop stray inductance, Figure 2 as shown above, wherein the bridge arms are six, and in actual application, the bridge arms can be less than six or more than six. In the figure, V sa , V sb , and V sc are AC power sources or power grids; L a1 , L b1 , L c1 , C a , C b , and C c form an LC filter; and L cThis is the stray inductance of the loop. Each bridge arm consists of multiple semiconductor device units, such as... Figure 2 As shown above, one of the multiple semiconductor device units on one of the bridge arms includes U cp1 U cp2 ...U cpn Each semiconductor device unit consists of absorption and voltage equalization circuits, a fully controlled semiconductor device, and a diode device. The fully controlled semiconductor device includes either an IGBT device or an IGCT device. The semiconductor device unit includes a fully controlled semiconductor device T. xi Diode device D xi Diode device D dxi Resistance R sxi Resistance R dxi and capacitor C xi The resistor R dxi With diode device D dxi After being connected in parallel, it is connected to capacitor C. xi Series connection to form an RCD circuit; the fully controlled semiconductor device T xi and diode device D xi Connected in series, and then with resistor R sxi It is connected in parallel with the RCD circuit. Compared to Figure 1 The existing technical solution shown is Figure 2 The prior art solution shown has resistance R dxi A diode device D is connected in parallel across both ends. dxi Therefore, capacitor C xi The charging and discharging currents pass through different circuits, and during discharge, the capacitor C... xi After passing through resistor R dxi To fully control semiconductor devices T xi and diode device D xi During discharge, current flows through the diode device D during charging. dxi To capacitor C xi Charging is problematic because this circuit cannot provide damping for the capacitor charging process, thus it cannot avoid high overvoltage caused by undamped LC resonance.

[0024] like Figure 3 The diagram shown is a topology of a controllable turn-off current source converter according to an embodiment of the present invention. The converter receives power from an AC power source and the power grid, and then connects to multiple bridge arms via a series LC filter and a loop stray inductor. Figure 3 The bridge shown above has six arms; in practical applications, there may be fewer or more than six arms. (See diagram V.) sa V sb and V sc AC power source or power grid; L a1 L b1 L c1 With Ca , C b , C c LC filter; L c is the loop stray inductance. Each bridge arm is composed of a plurality of semiconductor device units, as shown in Figure 3 , wherein the plurality of semiconductor device units on one bridge arm comprises U cp1 , U cp2 , … U cpn , each semiconductor device unit is further composed of an absorbing and voltage equalizing circuit, a full-controlled semiconductor device, and a diode device, wherein the full-controlled semiconductor device comprises an IGBT device or an IGCT device. The semiconductor device unit comprises a full-controlled semiconductor device T xi , a diode device D xi , a diode device D dxi , a resistor R sxi , a resistor R daxi , a resistor R dbxi , and a capacitor C xi ; the diode device D dxi and the resistor R dbxi are connected in series and then connected in parallel with the resistor R daxi and then connected in series with the capacitor C xi to form an RCD-R circuit; the full-controlled semiconductor device T xi and the diode device D xi are connected in series and then connected in parallel with the resistor R sxi and the RCD-R circuit. When the capacitor C xi is charging, the current flows through D dxi and R dbxi to charge the capacitor C xi ; when the capacitor C xi is discharging, the current flows through R daxi to discharge the device T xi and D xi . It can be seen that the charging and discharging of the capacitor C xi in the technical solution of the embodiment of the present application is in different loops, and different resistance values can be selected, and the resistor is connected in series with the diode device D dxi , which can effectively provide damping for the charging process of the capacitor C xi and avoid high overvoltage caused by LC undamped resonance.

[0025] Further, the diode devices D xi and D dxi are connected in opposite directions.

[0026] As shown above, the converter of the present invention includes two bridge arms for each phase, and each bridge arm includes at least one semiconductor device unit; the semiconductor device unit includes a first semiconductor device and a resistor R. sxi And an RCD-R circuit, wherein the first semiconductor device is connected to resistor R sxi The RCD-R circuits are connected in parallel; the RCD-R circuit includes a capacitor C connected in series. xi and resistance R daxi The resistor R daxi A resistor R is connected in parallel at both ends and in series. dbxi and diode device D dxi The first semiconductor device includes fully controlled semiconductor devices T connected in series. xi and diode device D xi The resistor R daxi The resistance is greater than the resistance R. dbxi The resistance value. The first semiconductor device can also be a fully controllable semiconductor device with reverse voltage blocking capability (reverse resistance type).

[0027] In device T xi and device D xi When turned off, the current flows through D dxi and R dbxi Flow, for capacitance C xi When charging, the current is completely transferred to capacitor C immediately after the circuit is turned off. xi The loop in R dbxi A voltage is generated on the device to protect it; this voltage should not exceed the device's withstand voltage limit. This applies to R. dbxi The resistance value has certain requirements, and the resistor R dbxi The resistance range is determined by the formula R. dbxi <U m / I m Confirmed; where U m For the fully controlled semiconductor device T connected in series xi and diode device D xi The safe operating voltage is typically the nominal intermediate DC voltage or the repetitive peak voltage. m The maximum shutdown current designed for the converter.

[0028] In device T xi and device D xi When turned on, capacitor C xi Current passes through R daxi To device T xi and D xi Discharge, to protect the device, the discharge current shall not exceed 1 / 3 of the device's maximum turn-off current. The resistor R... daxi The resistance range is determined by the formula. determined; wherein U Nm is the rated steady state withstand voltage of the series connected controllable semiconductor devices T xi and diode devices D xi , which is the highest withstand voltage steady state at the designed rated AC voltage, and I Tm is the maximum turn-off current of the controllable semiconductor devices T xi . The rated steady state withstand voltage U Nm is equal to the AC line voltage peak value U lmax divided by the minimum number of series units n per bridge leg.

[0029] The minimum value C of the capacitance C xi in the RCD-R circuit is determined by the equation and ; wherein L c is the loop stray inductance on the inverter, and U m is the limit withstand voltage of the series connected controllable semiconductor devices T xi and diode devices D xi , and U Nm is the rated steady state withstand voltage of the series connected controllable semiconductor devices T xi and diode devices D xi , and n is the minimum number of series units per bridge leg.

[0030] Further, the embodiments of the present application are illustrated by specific numerical values, the AC power supply or grid of the embodiments of the present application provides an AC voltage rated at 10 kV, 7 semiconductor device units are connected in series on one bridge leg, the maximum withstand voltage of a single device is 3000 V, the stray inductance is 3.5 uH, the maximum turn-off current of the inverter design is 4000 A, the maximum turn-off current of the device T xi is 5000 A, and the inverter is 4000 A. The resistance value of the resistor R dbxi is R dbxi < U m / I m = 3000 V / 4000 A = 0.75 Ω, so the resistance value of the resistor R dbxi may be selected as 0.7 Ω. The resistance value of the resistor R daxi is so the resistance value of the resistor R daxi may be selected as 1.5 Ω. At the same time, according to the solutions of and , C = 0.4107 uF, and the actual selected C = 0.5 uF.

[0031] Although some specific embodiments of the present application have been described in detail by way of examples, one skilled in the art should understand that the above examples are only for the purpose of illustration, but not for the purpose of limiting the scope of the present application. One skilled in the art should understand that the modifications to the technical solutions described in the above embodiments or the equivalent replacements of some technical features therein can be made without departing from the scope and spirit of the present application, and these modifications and replacements are within the protection scope of the present application.

Claims

1. A controllable turn-off current source type inverter, characterized by, The converter comprises two bridge arms per phase, each bridge arm comprising at least one semiconductor device unit; The semiconductor device unit includes a first semiconductor device, a resistor and an RCD-R circuit, the first semiconductor device being connected in parallel with the resistor , the RCD-R circuit The first semiconductor device comprises a series connection of all-controllable semiconductor devices and diode devices ; Diode device and a resistor connected in series with a resistor connected in parallel and a capacitor connected in series to form an RCD-R circuit; Diode device in series and resistance forming a capacitor charging circuit; through resistance forming a capacitor discharging circuit; the capacitance of the capacitor in the RCD-R circuit The minimum value of the capacitance is determined by the equation and where is the loop inductance on the converter, the is the limiting voltage of the series connected semiconductor devices and diode devices the is the rated steady state withstand voltage of the series connected semiconductor devices and diode devices .

2. The converter of claim 1, characterized in that The resistance has a resistance value greater than the resistance value.

3. The converter of claim 1, wherein, the resistance is determined by the formula where is the safe working voltage of the series connected fully controlled semiconductor device and diode device , and is the maximum turn-off current for the inverter design.

4. The converter of claim 1, wherein, The resistance is in the range determined by the formula ; wherein is the rated steady state withstand voltage of the series connected fully controlled semiconductor device and diode device , and is the maximum turn-off current of the fully controlled semiconductor device .

5. The converter of claim 4, wherein, said rated steady state withstand voltage is equal to the ac line voltage peak divided by the minimum number of series cells per bridge leg n.

6. The converter according to any of claims 1-5, characterized by The diode device And The connected conductive directions are opposite.

7. The converter according to any of claims 1-5, characterized by The full-controlled semiconductor device is an IGBT device or an IGCT device.

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