Method for suppressing overvoltage of inner tube of ANPC three-level converter

Abstract

According to the method for suppressing the overvoltage of the inner tubes of the ANPC three-level converter, an RCD buffer absorption circuit is additionally arranged on the inner tube of each phase of the ANPC three-level converter and is used for suppressing the overvoltage generated during current conversion of the inner tubes. Taking a phase as an example, the RCD buffer absorption circuit comprises a diode DS1, a capacitor CS1 and a resistor RS1, and the anode of an inner tube S2 is connected with the anode of the diode DS1 and one end of the resistor RS1; the cathode of the inner tube S2 is connected with the anode of the inner tube S3; the cathode of the diode DS1 and the other end of the resistor RS1 are connected with one end of the capacitor CS1, and the other end of the capacitor CS1 is connected with the cathode of the inner tube S3. According to the method for adding the RCD buffer absorption circuit, the amplitude of inner tube overvoltage generated in dead time during voltage vector switching can be remarkably reduced, an ANPC three-level converter device is protected against overvoltage damage, and the reliability of the ANPC three-level converter is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converters, and particularly to a method for suppressing overvoltage of inner tubes in an ANPC three-level converter. Background Art

[0002] The topology of the Active Neutral Point Clamped three-level converter (ANPC) is widely used in the power conversion units of frequency converters for large-capacity pumped storage units and wind turbine converters. The ANPC three-level topology is as Figure 1 shown. The Active Neutral Point Clamped (ANPC) converter can select IGCT / IGBT as the fully controlled power device and is equipped with an antiparallel freewheeling diode. The converter can output three levels: positive (E), negative (-E), and zero (O). Due to the bidirectional flow of the neutral point clamping current, the ANPC converter has multiple zero-level current conduction modes. There are 4 common operating switching states of the ANPC three-level converter, as shown in Table 1.

[0003] Table 1 PWM Modulation Switching State Table of ANPC Three-Level Converter

[0004] S1 S2 S3 S4 S5 S6 Transmission voltage V Voltage vector 1 1 0 0 0 1 E V1 0 1 0 1 1 0 0 V2 1 0 1 0 0 1 0 V3 0 0 1 1 1 0 -E V4

[0005] The voltage vectors of the four operating states are respectively denoted as V1, V2, V3, and V4. By controlling the turn-on and turn-off of the fully controlled IGCT device, the ANPC three-level converter can achieve bidirectional AC-DC power conversion by outputting positive, negative, and zero levels.

[0006] When applying the four voltage vectors, according to the different directions of the AC current of the ANPC three-level converter, there are a total of eight current conduction paths as Figure 2 shown. When the power electronic switch device is working, in order to prevent faults such as short circuits between the positive and negative poles of the DC capacitor, a dead time needs to be set, that is, after sending a turn-off signal to the power device that is conducting, a certain time is delayed, and then the next power device is turned on. The delayed time is the dead time. When the ANPC three-level converter is running, considering the dead time, an overvoltage problem of the inner tubes will occur during the dead time of vector switching, causing the inner tubes S2 and S3 to withstand the entire DC bus voltage and resulting in overvoltage failure. Taking the vector switching from V3+ to V4+ as an example, as Figure 3As shown. When the V3+ vector is applied, S1, S3, and S6 give turn-on signals. At this time, the voltage of S1 is zero, and S2 is connected in parallel with Cd1 and bears 1 / 2 times the DC bus voltage E. When switching from the V3+ vector to the V4+ vector, there is a dead time of 40 us in the middle. During the dead time, D3 and D4 conduct. Since the voltage of S1 was zero at the previous moment, when turning off S1, a negative current is injected into the gate, and the voltage of S1 remains zero. Therefore, the inner tube S2 bears the entire DC bus voltage 2E during the entire dead time. The experimental waveform is as Figure 4 shown.

[0007] The existing method to solve the overvoltage problem of the inner tube is to reduce the dead time and add a neutral point balance resistor to the clamping diode to improve the leakage current distribution of the power device and enhance the blocking voltage ability of the device. Adding a neutral point balance resistor can improve the leakage current distribution and enhance the blocking voltage ability of the device, but it still cannot solve the problem of the inner tube bearing an overvoltage of 2E during the dead time. The 2E voltage usually exceeds the blocking voltage ability of the power device, bringing potential hazards to the normal operation of the ANPC three-level converter. Summary of the Invention

[0008] To solve the above technical problems, the present invention provides a method for suppressing the overvoltage of the inner tube of an ANPC three-level converter. An RCD buffer absorption circuit is configured on the inner tube of the ANPC three-level converter to suppress the overvoltage problem that may occur in the inner tube during the commutation dead time.

[0009] The technical solution adopted by the present invention is:

[0010] A method for suppressing the overvoltage of the inner tube of an ANPC three-level converter, adding an RCD buffer absorption circuit to the inner tube of each phase of the ANPC three-level converter to suppress the overvoltage that occurs during commutation of the inner tube.

[0011] The RCD buffer absorption circuit includes: diode D S1 , capacitor C S1 , resistor R S1 . The anode of the inner tube S2 is respectively connected to the anode of diode D S1 , one end of resistor R S1 ; the cathode of the inner tube S2 is connected to the anode of the inner tube S3; the cathode of diode D S1 , the other end of resistor R S1 are both connected to one end of capacitor C S1 , and the other end of capacitor C S1 is connected to the cathode of the inner tube S3.

[0012] The inner tube S2 and the inner tube S3 are full-controlled power devices IGCT or IGBT.

[0013] When the ANPC three-level converter commutates normally, diode D S1is in the off state; when the ANPC three-level converter enters the vector switching dead time, the sudden appearance of the overvoltage across the inner tube S2 causes the diode D S1 to conduct, and the capacitor C S1 is connected in parallel across the inner tube S2 to charge, reducing the amplitude of the overvoltage borne by the inner tube S2.

[0014] A method for suppressing the overvoltage of the inner tube of an ANPC three-level converter according to the present invention has the following technical effects:

[0015] Compared with the technical solution using a neutral point balancing resistor, the method of adding an RCD buffer absorption circuit proposed by the present invention can significantly reduce the amplitude of the overvoltage of the inner tube generated during the dead time when the voltage vector is switched, protect the ANPC three-level converter device from overvoltage damage, and improve the reliability of the ANPC three-level converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below in conjunction with the drawings and embodiments:

[0017] Figure 1 is the topological structure diagram of an ANPC three-level converter.

[0018] Figure 2 is the schematic diagram of eight current conduction paths of an ANPC three-level converter.

[0019] Figure 3 is the schematic diagram of the vector switching current path from V3+ to V4+.

[0020] Figure 4 is the vector switching waveform diagram from V3+ to V4+ (inner tube S2 in the dead time).

[0021] Figure 5 is the ANPC inner tube RCD buffer absorption circuit diagram (taking phase a as an example).

[0022] Figure 6 is the vector switching waveform diagram from V3+ to V4+ (after the RCD buffer circuit is introduced for the inner tube). DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] Example 1:

[0024] The present invention provides a method for suppressing the overvoltage of the inner tube of an ANPC three-level converter. An RCD buffer absorption circuit is added to the inner tube, and the overvoltage that may occur in the inner tube during the commutation dead time is suppressed by the function of the RCD buffer absorption circuit to suppress voltage fluctuations.

[0025] The present invention adds an RCD buffer absorption circuit to the inner tube of each phase of the ANPC three-level converter to suppress the overvoltage that occurs during commutation of the inner tube. As Figure 5As shown, taking phase a as an example, the RCD buffer absorption circuit includes: diode D S1 , capacitor C S1 , resistor R S1 . The anode of the inner tube S2 is respectively connected to the anode of diode D S1 , one end of resistor R S1 ; the cathode of the inner tube S2 is connected to the anode of the inner tube S3; the cathode of diode D S1 , the other end of resistor R S1 are both connected to one end of capacitor C S1 , and the other end of capacitor C S1 is connected to the cathode of the inner tube S3.

[0026] The inner tube S2 and the inner tube S3 are full-controlled power devices IGCT or IGBT.

[0027] Embodiment 2:

[0028] The present invention also provides a buffer absorption circuit for suppressing overvoltage of the inner tube in an NPC three-level converter. Taking phase a as an example, the circuit includes:

[0029] diode D S1 , capacitor C S1 , resistor R S1 ; the anode of the inner tube S2 in any one phase of the ANPC three-level converter is respectively connected to the anode of diode D S1 , one end of resistor R S1 ; the cathode of the inner tube S2 is connected to the anode of the inner tube S3 in this phase; the cathode of diode D S1 , the other end of resistor R S1 are both connected to one end of capacitor C S1 , and the other end of capacitor C S1 is connected to the cathode of the inner tube S3.

[0030] In the a, b, and c phases of the ANPC three-level converter, the other two phases also respectively include inner tubes composed of two full-controlled power devices IGCT or IGBT. Any one of the other two phases also includes an added RCD buffer absorption circuit.

[0031] Embodiment 3:

[0032] The present invention also provides an ANPC three-level converter including an inner tube overvoltage buffer absorption circuit. As shown in Figure 1 , Figure 5 , the specific structure is as follows:

[0033] Taking phase a as an example, it includes switch tube S1, inner tube S2, inner tube S3, switch tube S4, switch tube S5, switch tube S6, diode D S1 , capacitor C S1 , resistor R S1RCD snubber circuit formed by connection;

[0034] Diodes D1, D2, D3, D4, D5, D6 are reversely connected in parallel across the two ends of switch tubes S1, inner tube S2, inner tube S3, switch tube S4, switch tube S5, and switch tube S6 respectively.

[0035] Capacitor C d1 The positive electrode is connected to the anode of switch tube S1, and capacitor C d1 The negative electrode is respectively connected to capacitor C d2 positive electrode, the cathode of switch tube S5, and the anode of switch tube S6;

[0036] The cathode of switch tube S1 is respectively connected to the anode of inner tube S2, one end of resistor R S1 one end, and the anode of diode D S1 and the anode of switch tube S5;

[0037] The cathode of inner tube S2 is connected to the anode of inner tube S3; the other end of resistor R S1 the other end, and diode D S1 The cathodes are all connected to one end of capacitor C S1 one end;

[0038] The cathode of inner tube S3 is respectively connected to the anode of switch tube S4, the other end of capacitor C S1 and the cathode of switch tube S6;

[0039] The cathode of switch tube S4 is connected to the negative electrode of capacitor C d2 negative electrode;

[0040] The cathode of inner tube S2 and the anode of inner tube S3 are connected to form the a-phase output terminal;

[0041] Similarly, in the b-phase, it includes switch tubes S1', inner tube S2', inner tube S3', switch tube S4', switch tube S5', switch tube S6', diode D S1 ', capacitor C S1 ', and resistor R S1 ' to form an RCD snubber circuit;

[0042] Diodes D1', D2', D3', D4', D5', D6' are reversely connected in parallel across the two ends of switch tubes S1', inner tube S2', inner tube S3', switch tube S4', switch tube S5', and switch tube S6' respectively.

[0043] Capacitor C d1 ' The positive electrode is connected to the anode of switch tube S1', and capacitor C d1 ' The negative electrode is respectively connected to capacitor C d2 ' positive electrode, the cathode of switch tube S5', and the anode of switch tube S6';

[0044] The cathode of switch tube S1' is respectively connected to the anode of inner tube S2', one end of resistor RS1 'One end, diode D S1 'Anode, anode of switch tube S5;

[0045] The cathode of inner tube S2 is connected to the anode of inner tube S3; resistor R S1 'The other end, diode D S1 'The cathodes are all connected to capacitor C S1 'One end;

[0046] The cathode of inner tube S3 is respectively connected to the anode of switch tube S4, capacitor C S1 'The other end, cathode of switch tube S6;

[0047] The cathode of switch tube S4 is connected to capacitor C d2 'Negative pole;

[0048] The cathode of inner tube S2 and the anode of inner tube S3 are connected to form the b-phase output terminal;

[0049] Similarly, in the c-phase, it includes switch tube S1”, inner tube S2”, inner tube S3”, switch tube S4”, switch tube S5”, switch tube S6”, diode D S1 ”, capacitor C S1 ”, resistor R S1 ” connected to form an RCD snubber circuit;

[0050] Diodes D1”, D2”, D3”, D4”, D5”, D6” are respectively reversely connected in parallel at both ends of switch tube S1”, inner tube S2”, inner tube S3”, switch tube S4”, switch tube S5”, switch tube S6”,

[0051] Capacitor C d1 ”The positive pole is connected to the anode of switch tube S1”, capacitor C d1 ”The negative pole is respectively connected to the positive pole of capacitor C d2 ”The cathode of switch tube S5, the anode of switch tube S6;

[0052] The cathode of switch tube S1 is respectively connected to the anode of inner tube S2, resistor R S1 ”One end, diode D S1 ”Anode, anode of switch tube S5;

[0053] The cathode of inner tube S2 is connected to the anode of inner tube S3; resistor R S1 ”The other end, diode D S1 ”The cathodes are all connected to capacitor C S1 ”One end;

[0054] The cathode of inner tube S3 is respectively connected to the anode of switch tube S4, capacitor C S1 ”The other end, cathode of switch tube S6;

[0055] The cathode of switch tube S4 is connected to capacitor C d2 negative electrode;

[0056] The cathode of inner tube S2 and the anode of inner tube S3 are connected to form the c-phase output terminal.

[0057] The RCD snubber circuit can suppress voltage fluctuations in the circuit to protect circuit components from damage. When the ANPC three-level converter is commutating normally, that is, during the non-vector switching time, taking the a-phase as an example, diode D S1 is in the off state; when the ANPC three-level converter enters the vector switching dead time, the sudden overvoltage across inner tube S2 causes diode D S1 to conduct, and capacitor C S1 is charged in parallel across inner tube S2, reducing the amplitude of the overvoltage borne by inner tube S2.

[0058] After the RCD snubber circuit is introduced into the inner tube of the ANPC three-level converter, the overvoltage problem of the inner tube during the vector switching from V3+ to V4+ is effectively suppressed, and the waveform diagram is as shown in Figure 6 shown. By comparing with Figure 4 , the amplitude of the voltage overshoot on inner tube S2 decreases significantly compared with the case without the RCD snubber circuit. The inner tube S2 no longer bears twice the bus voltage, reducing the overvoltage across inner tube S2 and significantly improving the safety of the device.

Claims

1. A method for suppressing overvoltage of the inner tubes of an ANPC three-level converter, characterized in that: An RCD buffer absorption circuit is added to the inner tubes of each phase of the ANPC three-level converter to suppress the overvoltage that occurs in the inner tubes during commutation.

2. The method for suppressing overvoltage of the inner tube of an ANPC three-level converter according to claim 1, characterized in that: The RCD buffer absorption circuit includes: diode D S1 , capacitor C S1 , resistor R S1 . The anode of the inner tube S2 is respectively connected to the anode of the diode D S1 and one end of the resistor R S1 ; the cathode of the inner tube S2 is connected to the anode of the inner tube S3; the cathode of the diode D S1 and the other end of the resistor R S1 are both connected to one end of the capacitor C S1 ; the other end of the capacitor C S1 is connected to the cathode of the inner tube S3.

3. The method for suppressing overvoltage of the inner tube of an ANPC three-level converter according to claim 1, characterized in that: The inner tubes S2 and S3 are full-controlled power devices, namely IGCT or IGBT.

4. The suppression method for overvoltage of the inner tube of an ANPC three-level converter according to claim 1, characterized in that: When the ANPC three-level converter conducts normal commutation, diode D S1 is in the off state; when the ANPC three-level converter enters the vector switching dead time, the sudden appearance of an overvoltage across the inner switch S2 causes diode D S1 to conduct, and capacitor C S1 is connected in parallel across the inner switch S2 to charge, reducing the amplitude of the overvoltage borne by the inner switch S2.

5. A buffer absorption circuit for suppressing overvoltage of the inner tube in an NPC three-level converter, characterized in that: The circuit includes: diode D S1 , capacitor C S1 , resistor R S1 ; The anode of the inner tube S2 in any one phase of the ANPC three-level converter is respectively connected to the anode of the diode D S1 and one end of the resistor R S1 ; the cathode of the inner tube S2 is connected to the anode of the inner tube S3 in this phase; the cathode of the diode D S1 and the other end of the resistor R S1 are both connected to one end of the capacitor C S1 ; the other end of the capacitor C S1 is connected to the cathode of the inner tube S3.

6. An ANPC three-level converter comprising an inner tube overvoltage buffer absorption circuit, characterized in that: In phase a, it includes a switching tube S1, an inner tube S2, an inner tube S3, a switching tube S4, a switching tube S5, a switching tube S6, and a diode D S1 , a capacitor C S1 , a resistor R S1 connected to form an RCD snubber circuit; Diodes D1, D2, D3, D4, D5, and D6 are reversely connected in parallel across the two ends of switch tubes S1, inner tubes S2, inner tubes S3, switch tubes S4, switch tubes S5, and switch tubes S6 respectively. Capacitor C d1 The positive electrode is connected to the anode of the switching transistor S1, and the capacitor C d1 The negative electrode is respectively connected to the capacitor C d2 positive electrode, the cathode of the switching transistor S5, and the anode of the switching transistor S6; The cathode of the switching transistor S1 is respectively connected to the anode of the inner tube S2, one end of the resistor R, the anode of the diode D, and the anode of the switching transistor S5; S1 one end, diode D S1 anode, anode of switching transistor S5; The cathode of the inner tube S2 is connected to the anode of the inner tube S3; resistor R S1 The other end, diode D S1 The cathodes are all connected to one end of capacitor C S1 One end; The cathode of the inner tube S3 is respectively connected to the anode of the switching tube S4 and the capacitor C S1 The other end and the cathode of the switching tube S6; The cathode of the switching transistor S4 is connected to the capacitor C d2 negative electrode; The cathode of inner tube S2 and the anode of inner tube S3 are connected to form the a-phase output terminal. In phase b, it includes a switching tube S1', an inner tube S2', an inner tube S3', a switching tube S4', a switching tube S5', a switching tube S6', and a diode D S1 ', a capacitor C S1 ', a resistor R S1 ' connected to form an RCD snubber circuit; Diodes D1', D2', D3', D4', D5', and D6' are reversely connected in parallel across the two ends of switch tubes S1', inner tubes S2', inner tubes S3', switch tubes S4', switch tubes S5', and switch tubes S6' respectively. Capacitor C d1 'The positive electrode is connected to the anode of the switching transistor S1', capacitor C d1 'The negative electrode is respectively connected to capacitor C d2 'The positive electrode, the cathode of the switching transistor S5, and the anode of the switching transistor S6; The cathode of the switching transistor S1' is respectively connected to the anode of the inner transistor S2', one end of the resistor R S1 ', one end of the diode D S1 ' anode, the anode of the switching transistor S5'; The cathode of the inner tube S2' is connected to the anode of the inner tube S3'; resistor R S1 The other end of ', diode D S1 The cathodes of'are all connected to one end of capacitor C S1 One end; The cathode of the inner tube S3' is respectively connected to the anode of the switching tube S4', one end of the capacitor C S1 's other end, and the cathode of the switching tube S6'; The cathode of the switching transistor S4' is connected to the capacitor C d2 negative electrode; The cathode of inner tube S2' and the anode of inner tube S3' are connected to form the b-phase output terminal. In phase c, it includes a switching tube S1", an inner tube S2", an inner tube S3", a switching tube S4", a switching tube S5", a switching tube S6", and a diode D S1 ", a capacitor C S1 ", a resistor R S1 " to form an RCD snubber circuit Diodes D1", D2", D3", D4", D5", and D6" are reversely connected in parallel across the two ends of switch tubes S1", inner tubes S2", inner tubes S3", switch tubes S4", switch tubes S5", and switch tubes S6" respectively. Capacitor C d1 The anode of the "positive electrode connected to the switching transistor S1" is the capacitor C d1 The negative electrode is respectively connected to the capacitor C d2 "the positive electrode, the cathode of the switching transistor S5, and the anode of the switching transistor S6; The cathode of the switching transistor S1 is respectively connected to the anode of the inner tube S2, one end of the resistor R, the anode of the diode D, and the anode of the switching transistor S5; S1 and one end of the resistor R, the anode of the diode D; S1 and the anode of the switching transistor S5; The cathode of the inner tube S2” is connected to the anode of the inner tube S3”; resistor R S1 The other end, diode D S1 The cathodes of both are connected to capacitor C S1 One end; The cathode of the inner tube S3” is respectively connected to the anode of the switching tube S4”, the other end of the capacitor C S1 and the cathode of the switching tube S6” The cathode of switch tube S4 is connected to capacitor C d2 negative electrode; The cathode of inner tube S2" and the anode of inner tube S3" are connected to form the c-phase output terminal.

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