Small-loop commutation modulation method of three-level converter

Abstract

The invention provides a small-loop commutation modulation method for a three-level converter, and the method specifically comprises the steps: in a positive half period of modulation voltage, when a modulation wave is smaller than an upper carrier wave, a bridge arm outputs a first zero level state, a switching tube T2 and a switching tube T5 of the three-level converter are switched on at the same time, and other switching tubes of the three-level converter are switched off; in the negative half period of the modulation voltage, when the modulation wave is larger than the lower carrier wave, the bridge arm outputs a second zero level state, the switching tube T3 and the switching tube T6 of the three-level converter are switched on at the same time, and the other switching tubes of the three-level converter are switched off. According to the invention, the turn-off overvoltage of the switch tube is reduced, and the switch tube is prevented from losing efficacy due to di / dt intolerance during small current conduction.

Description

Technical Field

[0001] The invention belongs to the technical field of medium and low voltage direct current distribution networks, and in particular relates to a small loop commutation modulation method for a three-level converter. Background Art

[0002] Flexible converters, represented by three-level converters, are the core equipment of flexible distribution networks. They can realize AC / DC power conversion, and thus achieve power mutual assistance, reliability improvement, and new energy carrying capacity improvement of distribution networks.

[0003] With the increase of power level of flexible power distribution system, the power level of flexible converter is required to be further improved. One feasible method is to use high-power IGCT devices to build three-level converter, so as to improve the power capacity of converter. The power module of converter using IGCT devices usually adopts crimping structure, which leads to the long commutation loop and large stray inductance of the loop, resulting in the risk of overvoltage failure of IGCT devices. Usually, small capacitors are connected in parallel at both ends of the power device to absorb the transient high-frequency voltage oscillation of the power device switch, which will increase the system cost and loss.

[0004] Compared with the NPC (Neutral Point Clamped) three-level topology, the active neutral point clamped ANPC (Active Neutral Point Clamped) three-level topology can be unaffected by the direction of the load current flow, and actively control the current to commutate through a short loop to reduce the IGCT device shutdown overvoltage, thereby reducing the capacitance of the parallel absorption capacitor and reducing the system cost. However, the charging and discharging current of the parallel capacitors at both ends of the device will be superimposed on the IGCT device that has been turned on. When the IGCT is in the case of low current, the charging and discharging current of the parallel capacitor may cause the IGCT current to decrease to zero on the one hand, and on the other hand, it may cause the IGCT to withstand di / dt damage.

[0005] Therefore, it is necessary to design a small-loop commutation modulation method for a three-level converter to solve the above technical problems. Summary of the invention

[0006] In view of the above technical problems, the present invention provides a small loop commutation modulation method for a three-level converter, wherein the method comprises:

[0007] In the positive half cycle of the modulation voltage:

[0008] When the modulated wave is smaller than the upper carrier wave, the bridge arm outputs the first zero-level state, the switch tubes T2 and T5 of the three-level converter are turned on at the same time, and the other switch tubes of the three-level converter are turned off;

[0009] In the negative half cycle of the modulation voltage:

[0010] When the modulation wave is greater than the download wave, the bridge arm outputs a second zero-level state, the switch tubes T3 and T6 of the three-level converter are turned on at the same time, and the remaining switch tubes of the three-level converter are turned off.

[0011] Furthermore, the method further comprises, in a positive half cycle of the modulation voltage:

[0012] When the modulated wave is greater than the upper carrier wave, the bridge arm outputs a non-zero level state, and the switch tubes T1, T2, and T6 of the three-level converter are turned on at the same time, and the remaining switch tubes are turned off.

[0013] Furthermore, the method further comprises, in a positive half cycle of the modulation voltage:

[0014] The internal re-triggering function of the switch tube is enabled at the driving level, and when the load current reaches a first preset value, T1 is turned on and T2 is externally re-triggered at the same time.

[0015] Furthermore, the method further comprises, in a negative half cycle of the modulation voltage:

[0016] When the modulation wave is smaller than the download wave, the bridge arm outputs a non-zero level state, and the switch tubes T3, T4, and T5 of the three-level converter are turned on at the same time, and the other switch tubes are turned off.

[0017] Furthermore, the method further comprises, in a negative half cycle of the modulation voltage:

[0018] The internal re-triggering function of the switch tube is enabled at the driving level, and when the load current reaches the second preset value, T4 is turned on and T3 is externally re-triggered at the same time.

[0019] Further, the single-phase bridge arm of the three-level converter includes a switch tube T1, the switch tube T2, the switch tube T3, the switch tube T4, the switch tube T5, the switch tube T6, a capacitor C1 and a capacitor C2, wherein the switch tube T1, the switch tube T2, the switch tube T3, the switch tube T4 are sequentially connected in series, and the capacitor C1 and the capacitor C2 are sequentially connected in series, and are all connected between the DC upper bus and the DC lower bus, the switch tube T5 and the switch tube T6 are connected in series in parallel with the branch in which the switch tube T2 and the switch tube T3 are connected in series, the midpoint between the capacitor C1 and the capacitor C2 is connected to the midpoint between the switch tube T5 and the switch tube T6, and the midpoint between the switch tube T2 and the switch tube T3 is connected to the AC port.

[0020] Furthermore, the single-phase bridge arm of the three-level converter further includes a diode D1, a diode D2, a diode D3, a diode D4, a diode D5 and a diode D6, wherein:

[0021] The diode D1 , the diode D2 , the diode D3 , the diode D4 , the diode D5 and the diode D6 are respectively connected in anti-parallel with the switch tubes T1 , T2 , T3 , T4 , T5 and T6 .

[0022] On the other hand, the present invention also provides a small loop commutation modulation system for a three-level converter, wherein the system comprises:

[0023] The first modulation module is configured to control the bridge arm to output a second zero-level state during a positive half cycle of the modulation voltage and when the modulation wave is smaller than the upper carrier, that is, to control the switch tubes T2 and T5 of the three-level converter to be turned on at the same time, and the remaining switch tubes of the three-level converter to be turned off;

[0024] The second modulation module is configured to control the bridge arm to output a second zero-level state during the negative half cycle of the modulation voltage and when the modulation wave is greater than the load wave, that is, to control the switch tubes T3 and T6 of the three-level converter to be turned on at the same time, and the remaining switch tubes of the three-level converter to be turned off.

[0025] Further, the single-phase bridge arm of the three-level converter includes a switch tube T1, the switch tube T2, the switch tube T3, the switch tube T4, the switch tube T5, the switch tube T6, a capacitor C1 and a capacitor C2, wherein the switch tube T1, the switch tube T2, the switch tube T3, the switch tube T4 are sequentially connected in series, and the capacitor C1 and the capacitor C2 are sequentially connected in series, and are all connected between the DC upper bus and the DC lower bus, the switch tube T5 and the switch tube T6 are connected in series in parallel with the branch in which the switch tube T2 and the switch tube T3 are connected in series, the midpoint between the capacitor C1 and the capacitor C2 is connected to the midpoint between the switch tube T5 and the switch tube T6, and the midpoint between the switch tube T2 and the switch tube T3 is connected to the AC port.

[0026] Furthermore, the single-phase bridge arm of the three-level converter further includes a diode D1, a diode D2, a diode D3, a diode D4, a diode D5 and a diode D6, wherein:

[0027] The diode D1 , the diode D2 , the diode D3 , the diode D4 , the diode D5 and the diode D6 are respectively connected in anti-parallel with the switch tubes T1 , T2 , T3 , T4 , T5 and T6 .

[0028] The present invention provides a small loop commutation modulation method for a three-level converter, which reduces the switch-off overvoltage of a switch tube (such as an IGCT) and prevents the switch tube from failing due to di / dt intolerance when conducting a small current.

[0029] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 A flowchart of a small-loop commutation modulation method for a three-level converter according to an embodiment of the present invention is shown;

[0032] Figure 2 A topology diagram of a three-level converter according to an embodiment of the present invention is shown;

[0033] Figure 3 A state switching diagram corresponding to six level states according to an embodiment of the present invention is shown;

[0034] Figure 4 A schematic diagram of a full small loop modulation method with a retriggering operation according to an embodiment of the present invention is shown;

[0035] Figure 5 A structural diagram of a small-loop commutation modulation system of a three-level converter according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] like Figure 1 As shown, the present invention provides a small loop commutation modulation method for a three-level converter, wherein the three-level converter in the present invention is exemplarily an ANPC three-level converter, such as Figure 2 As shown, the single-phase bridge arm of the three-level converter includes a switch tube T1, a switch tube T2, a switch tube T3, a switch tube T4, a switch tube T5, a switch tube T6, a capacitor C1 and a capacitor C2.

[0038] Among them, C1 and C2 are the capacitors of the upper and lower DC busbars respectively, T1 to T6 are high-power IGCT (Integrated Gate-Commutated Thyristor) devices. T5 and T6 are called clamping switches, T1 and T4 are external switches, and T2 and T3 are internal switches.

[0039] After T1, T2, T3, and T4 are connected in series in sequence, and after C1 and C2 are connected in series in sequence, they are all connected between the DC upper bus and the DC lower bus. After T5 and T6 are connected in series, they are connected in parallel with the branch in which T2 and T3 are connected in series. The midpoint O between C1 and C2 is connected to the midpoint between T5 and T6, and the midpoint between T2 and T3 is connected to the AC port.

[0040] The single-phase bridge arm of the three-level converter further includes a diode D1, a diode D2, a diode D3, a diode D4, a diode D5 and a diode D6, wherein D1, D2, D3, D4, D5 and D6 are anti-parallel connected with T1, T2, T3, T4, T5 and T6 respectively.

[0041] There are 6 types of switch action logic and output level states for the ANPC three-level converter, as shown in Table 1:

[0042] Table 1 ANPC three-level converter switch status

[0043] Serial Number Level status <![CDATA[T1]]> <![CDATA[T2]]> <![CDATA[T3]]> <![CDATA[T4]]> <![CDATA[T5]]> <![CDATA[T6]]> AC port output voltage 1 P 1 1 0 0 0 1 +Udc / 2 2 <![CDATA[OU1]]> 0 1 0 0 1 0 0 3 <![CDATA[OU2]]> 0 1 0 1 1 0 0 4 <![CDATA[OL1]]> 0 0 1 0 0 1 0 5 <![CDATA[OL2]]> 1 0 1 0 0 1 0 6 N 0 0 1 1 1 0 -Udc / 2

[0044] There are 12 kinds of state switching corresponding to the 6 level states, such as Figure 3 As shown, P switches to OL2, P switches to OU1, OL2 switches to OU2, OL2 switches to P, OU2 switches to OL2, OU2 switches to N, N switches to OU2, N switches to OL1, OL1 switches to N, OL1 switches to OU1, OU1 switches to OL1, OU1 switches to P, and the commutation between N and OU2 is a long loop commutation. The converter power module using IGCT devices usually adopts a crimping structure, and the stray inductance of the loop is large under long loop commutation. This will cause the IGCT device to have the risk of overvoltage failure during shutdown. Usually, a small capacitor is connected in parallel at both ends of the device to absorb the transient high-frequency voltage oscillation of the device switch, but this will increase the system cost and loss. In addition, the charging and discharging current of the parallel capacitors at both ends of the device will be superimposed on the IGCT device that has been turned on. In the case of small current of IGCT, the charging and discharging current of the parallel capacitors may cause the IGCT device to withstand di / dt damage.

[0045] The small-loop commutation modulation method with re-triggering operation proposed in the present invention can, on the one hand, shorten the commutation path and reduce the IGCT device shutdown overvoltage, and on the other hand, improve the working reliability of the IGCT device through the re-triggering operation, thereby solving the above-mentioned problems. The small-loop commutation modulation method is introduced in detail below.

[0046] Table 1 above contains two non-zero level states (i.e., P and N) and four zero level states (i.e., OU1, OU2, OL2 and OL1). The small loop commutation modulation strategy only uses the two zero level states OU1 and OL1. The generation principle of the proposed small loop commutation modulation strategy with re-triggering operation is as follows: Figure 4 As shown, where Uout is Figure 2 The bridge arm output voltage in .

[0047] In some embodiments of the present invention, the small loop commutation modulation method includes:

[0048] In the positive half cycle of the modulation voltage:

[0049] When the modulated wave is smaller than the upper carrier wave, the bridge arm outputs the OU1 state, i.e., the first zero-level state, and the switch tubes T2 and T5 of the three-level converter are turned on at the same time, and the other switch tubes are turned off;

[0050] In the negative half cycle of the modulation voltage:

[0051] When the modulation wave is greater than the download wave, the bridge arm outputs the OL1 state, that is, the second zero-level state, and the switch tubes T3 and T6 of the three-level converter are turned on at the same time, and the other switch tubes are turned off.

[0052] In addition, in some embodiments of the present invention, the small loop commutation modulation method with retriggering operation includes:

[0053] In the positive half cycle of the modulation voltage: when the modulation wave is greater than the upper carrier, the bridge arm outputs a non-zero level state P, and the switch tubes T1, T2, and T6 of the three-level converter are turned on at the same time, and the remaining switch tubes are turned off. The IGCT internal re-trigger function is enabled at the drive level, and when the load current reaches a first preset value that is smaller, T1 is turned on and T2 is externally re-triggered.

[0054] In the negative half cycle of the modulation voltage: when the modulation wave is less than the load wave, the bridge arm outputs the non-zero level state N, and the switch tubes T3, T4, and T5 of the three-level converter are turned on at the same time, and the other switch tubes are turned off. The internal re-triggering function of the switch tube IGCT is enabled at the drive level, and when the second preset value of the load current is small, T4 is turned on and T3 is externally re-triggered.

[0055] On the other hand, the present invention also provides a small loop commutation modulation system for a three-level converter, the system is based on Figure 2 The single-phase bridge arm of the three-level converter shown in the figure is realized, that is, the single-phase bridge arm of the three-level converter includes a switch tube T1, the switch tube T2, the switch tube T3, the switch tube T4, the switch tube T5, the switch tube T6, a capacitor C1 and a capacitor C2. Among them, C1 and C2 are capacitors of the DC upper bus and the lower bus respectively, and T1 to T6 are high-power IGCT devices. T5 and T6 are called clamping switch tubes, T1 and T4 are switch tubes outside the bridge arm, and T2 and T3 are switch tubes inside the bridge arm. After T1, T2, T3, T4 are connected in series in sequence, and after C1 and C2 are connected in series in sequence, they are all connected between the DC upper bus and the DC lower bus. After T5 and T6 are connected in series, they are connected in parallel with the branch connected in series with T2 and T3. The midpoint O between C1 and C2 is connected to the midpoint between T5 and T6, and the midpoint between T2 and T3 is connected to the AC port. The single-phase bridge arm of the three-level converter further includes a diode D1, a diode D2, a diode D3, a diode D4, a diode D5 and a diode D6, wherein D1, D2, D3, D4, D5 and D6 are anti-parallel connected with T1, T2, T3, T4, T5 and T6 respectively.

[0056] Wherein, the system comprises:

[0057] The first modulation module is configured to control the bridge arm to output a zero-level OU1 state during the positive half cycle of the modulation voltage and when the modulation wave is smaller than the upper carrier, that is, to control the switch tubes T2 and T5 of the three-level converter to be turned on at the same time, and the other switch tubes to be turned off;

[0058] The second modulation module is configured to control the bridge arm to output the zero-level OL1 state during the negative half cycle of the modulation voltage and when the modulation wave is greater than the download wave, that is, to control the switch tubes T3 and T6 of the three-level converter to be turned on at the same time, and the other switch tubes to be turned off.

[0059] In summary, the small-loop commutation modulation method of a three-level converter provided by the present invention reduces the IGCT turn-off overvoltage and prevents the IGCT from failing due to di / dt intolerance when conducting a small current.

[0060] Among them, the functions and methods implemented by other modules of the small-loop commutation modulation system of a three-level converter of the present invention correspond to the functions and methods implemented in the small-loop commutation modulation method of a three-level converter of the present invention and other steps, and therefore, they are not repeated here.

[0061] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A small loop commutation modulation method for a three-level converter, wherein: The method comprises: In the positive half cycle of the modulation voltage: When the modulated wave is smaller than the upper carrier wave, the bridge arm outputs the first zero-level state, the switch tubes T2 and T5 of the three-level converter are turned on at the same time, and the other switch tubes of the three-level converter are turned off; In the negative half cycle of the modulation voltage: When the modulation wave is greater than the download wave, the bridge arm outputs a second zero-level state, the switch tubes T3 and T6 of the three-level converter are turned on at the same time, and the remaining switch tubes of the three-level converter are turned off.

2. A small loop commutation modulation method for a three-level converter according to claim 1, wherein: The method further comprises, in a positive half cycle of the modulation voltage: When the modulated wave is greater than the upper carrier wave, the bridge arm outputs a non-zero level state, and the switch tubes T1, T2, and T6 of the three-level converter are turned on at the same time, and the remaining switch tubes are turned off.

3. A small loop commutation modulation method for a three-level converter according to claim 2, wherein: The method further comprises, during a positive half cycle of the modulation voltage: The internal re-triggering function of the switch tube is enabled at the driving level, and when the load current reaches a first preset value, T1 is turned on and T2 is externally re-triggered at the same time.

4. A small loop commutation modulation method for a three-level converter according to any one of claims 1 to 3, wherein: The method further comprises, during a negative half cycle of the modulation voltage: When the modulation wave is smaller than the download wave, the bridge arm outputs a non-zero level state, and the switch tubes T3, T4, and T5 of the three-level converter are turned on at the same time, and the other switch tubes are turned off.

5. A small loop commutation modulation method for a three-level converter according to claim 4, wherein: The method further comprises, during a negative half cycle of the modulation voltage: The internal re-triggering function of the switch tube is enabled at the driving level, and when the load current reaches the second preset value, T4 is turned on and T3 is externally re-triggered at the same time.

6. A small loop commutation modulation method for a three-level converter according to claim 1, wherein: The single-phase bridge arm of the three-level converter includes a switch tube T1, the switch tube T2, the switch tube T3, the switch tube T4, the switch tube T5, the switch tube T6, a capacitor C1 and a capacitor C2, wherein the switch tube T1, the switch tube T2, the switch tube T3 and the switch tube T4 are sequentially connected in series, and the capacitor C1 and the capacitor C2 are sequentially connected in series, and are all connected between the DC upper bus and the DC lower bus, the switch tube T5 and the switch tube T6 are connected in series in parallel with the branch in which the switch tube T2 and the switch tube T3 are connected in series, the midpoint between the capacitor C1 and the capacitor C2 is connected to the midpoint between the switch tube T5 and the switch tube T6, and the midpoint between the switch tube T2 and the switch tube T3 is connected to the AC port.

7. A small loop commutation modulation method for a three-level converter according to claim 5, wherein: The single-phase bridge arm of the three-level converter further includes a diode D1, a diode D2, a diode D3, a diode D4, a diode D5 and a diode D6, wherein: The diode D1 , the diode D2 , the diode D3 , the diode D4 , the diode D5 and the diode D6 are respectively connected in anti-parallel with the switch tubes T1 , T2 , T3 , T4 , T5 and T6 .

8. A small loop commutation modulation system for a three-level converter, wherein: The system comprises: The first modulation module is configured to control the bridge arm to output a second zero-level state during a positive half cycle of the modulation voltage and when the modulation wave is smaller than the upper carrier, that is, to control the switch tubes T2 and T5 of the three-level converter to be turned on at the same time, and the remaining switch tubes of the three-level converter to be turned off; The second modulation module is configured to control the bridge arm to output a second zero-level state during the negative half cycle of the modulation voltage and when the modulation wave is greater than the load wave, that is, to control the switch tubes T3 and T6 of the three-level converter to be turned on at the same time, and the remaining switch tubes of the three-level converter to be turned off.

9. A small loop commutation modulation system for a three-level converter according to claim 8, wherein: The single-phase bridge arm of the three-level converter includes a switch tube T1, the switch tube T2, the switch tube T3, the switch tube T4, the switch tube T5, the switch tube T6, a capacitor C1 and a capacitor C2, wherein the switch tube T1, the switch tube T2, the switch tube T3 and the switch tube T4 are sequentially connected in series, and the capacitor C1 and the capacitor C2 are sequentially connected in series, and are all connected between the DC upper bus and the DC lower bus, the switch tube T5 and the switch tube T6 are connected in series in parallel with the branch in which the switch tube T2 and the switch tube T3 are connected in series, the midpoint between the capacitor C1 and the capacitor C2 is connected to the midpoint between the switch tube T5 and the switch tube T6, and the midpoint between the switch tube T2 and the switch tube T3 is connected to the AC port.

10. A small loop commutation modulation system for a three-level converter according to claim 9, wherein: The single-phase bridge arm of the three-level converter further includes a diode D1, a diode D2, a diode D3, a diode D4, a diode D5 and a diode D6, wherein: The diode D1 , the diode D2 , the diode D3 , the diode D4 , the diode D5 and the diode D6 are respectively connected in anti-parallel with the switch tubes T1 , T2 , T3 , T4 , T5 and T6 .

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