Control method and device for three-level circuit

Abstract

The present invention discloses a control method and device for a three-level circuit, the control method comprising the following steps: when it is detected that the three-level circuit is in an overcurrent protection mode, the first switch tube and the fourth switch tube are controlled to be turned off; when the next switching cycle comes, the protection of the first switch tube is released or the protection of the fourth switch tube is released; when the current of the three-level circuit continues to rise or is greater than a preset current value, the second switch tube and the third switch tube are both turned off. The control method can solve the problem of turning off the voltage spike of the first and fourth switch tubes and reducing the turn-off loss, and control the increase of the operating frequency of the switch tube under OCP.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and in particular to a control method and a device for a three-level circuit. Background Art

[0002] The three-level circuit is a commonly used circuit, and its types usually include: neutral point clamped type, flying capacitor type and cascade type. The neutral point clamped three-level circuit (i.e. NPC-1 type circuit) is as follows Figure 1 As shown, T1, T2, T3 and T4 are all switching tubes, and D1, D2, D3 and D4 are respectively anti-parallel diodes of T1, T2, T3 and T4, or body diodes of the switching tubes.

[0003] like Figure 1 As shown, the normal working conditions include: (1) T1 and T2 are turned on, and the current path is BUS+→T1→T2→L→C1→connection point N; (2) T1 is turned off, T2 is turned on, and the current path is connection point N→D5→T2→L→C1→connection point N; (3) T3 and T4 are turned on, and the current path is BUS-→T4→T3→L→C1→connection point N.

[0004] like Figure 1 As shown in the figure, the working conditions in OCP (OverCurrent Protection) mode include:

[0005] Scenario 1: T1 and T2 are turned off at the same time, and the current path is BUS+→C2→C3→BUS-D4→D3→L→C1→connection point N. It is understandable that in this mode, T1 and T2 are turned off at the same time, the freewheeling loop is long, and the voltage of BUS+ and BUS- is borne, which will cause the turn-off spike and loss to increase. In addition, T1 and T2 usually have uneven voltage division, which will cause the turn-off instant spike to increase.

[0006] Case 2: T1 is turned off, T2 is turned on, and the current path is BUS+→C2→D5→C2→T2→D3→L→C1→connection point N. In this mode, if T1 is turned off first, the current follows the normal freewheeling loop, and the voltage of T1 is clamped to BUS+, and there is no increase in the turn-off spike caused by uneven voltage division. When T2 is turned off after a dead time, the turning off of T2 will cause switching loss.

[0007] In addition, in case 1 or case 2, if the normal current drops after T1 is turned off, the OCP protection point is released and T1 is turned on again. If the release point is set improperly, T1 will cause multiple off / on cycles in the same switching period, causing the switching frequency of T1 to increase.

[0008] It is understandable that the flying capacitor type and cascade type three-level circuits also have the above problems.

[0009] Therefore, in the three-level circuit, how to solve the problem of turning off the voltage spike of the first and fourth switches and reduce the turn-off loss, and control the increase of the operating frequency of the switches under OCP, becomes an urgent problem to be solved. Summary of the invention

[0010] In view of this, the main object of the present invention is to provide a control method and device for a three-level circuit.

[0011] To achieve the above-mentioned purpose, the technical solution of the present invention is implemented as follows: a control method for a three-level circuit, the three-level circuit includes at least one diode-clamped three-level bridge arm, the diode-clamped three-level bridge arm includes two clamping diodes and four switch tubes connected in series in sequence: a first switch tube, a second switch tube, a third switch tube and a fourth switch tube; comprising the following steps: when it is detected that the three-level circuit is in an overcurrent protection mode, the first switch tube and the fourth switch tube are controlled to be turned off; when the next switching cycle comes, the protection of the first switch tube is released or the protection of the fourth switch tube is released; when the current of the three-level circuit continues to rise or is greater than a preset current value, the second switch tube and the third switch tube are both turned off.

[0012] As an improvement of an embodiment of the present invention, the “detecting that the three-level circuit is in the overcurrent protection mode” specifically includes: when the first switch tube and the second switch tube are turned off at the same time, it is detected that the three-level circuit is in the overcurrent protection mode.

[0013] As an improvement of an embodiment of the present invention, the “detecting that the three-level circuit is in the overcurrent protection mode” specifically includes: when the first switch tube is turned off and the second switch tube is turned on, it is detected that the three-level circuit is in the overcurrent protection mode.

[0014] As an improvement of the embodiment of the present invention, the following steps are also included: when the current of the three-level circuit is less than or equal to a preset current value and does not continue to rise, the states of the second switch tube and the third switch tube are kept unchanged.

[0015] As an improvement of an embodiment of the present invention, the "releasing the protection of the first switch tube or releasing the protection of the fourth switch tube when the next switching cycle comes" specifically includes: when the next switching cycle comes, releasing the protection of the first switch tube or releasing the protection of the fourth switch tube, and then controlling the three-level circuit to be in normal working state.

[0016] An embodiment of the present invention further provides a control device for a three-level circuit, wherein the three-level circuit includes at least one diode-clamped three-level bridge arm, wherein the diode-clamped three-level bridge arm includes two clamping diodes and four switch tubes connected in series in sequence: a first switch tube, a second switch tube, a third switch tube and a fourth switch tube; and includes the following modules: a state detection module, which is used to control the first switch tube and the fourth switch tube to be turned off when it is detected that the three-level circuit is in an overcurrent protection mode; a first processing module, which is used to release the protection of the first switch tube or the protection of the fourth switch tube when the next switching cycle comes; and a second processing module, which is used to turn off both the second switch tube and the third switch tube when the current of the three-level circuit continues to rise or is greater than a preset current value.

[0017] As an improvement of the embodiment of the present invention, the state detection module is further used for: when the first switch tube and the second switch tube are turned off at the same time, detecting that the three-level circuit is in the overcurrent protection mode.

[0018] As an improvement of the embodiment of the present invention, the state detection module is further used for: when the first switch tube is turned off and the second switch tube is turned on, detecting that the three-level circuit is in the overcurrent protection mode.

[0019] As an improvement of the embodiment of the present invention, the following modules are also included: a third processing module, which is used to keep the states of the second switch tube and the third switch tube unchanged when the current of the three-level circuit is less than or equal to a preset current value and does not continue to rise.

[0020] As an improvement of the embodiment of the present invention, the first processing module is further used to: release the protection of the first switch tube or release the protection of the fourth switch tube when the next switching cycle comes, and then control the three-level circuit to be in a normal working state.

[0021] The control method and device for a three-level circuit provided by the embodiment of the present invention have the following advantages: The embodiment of the present invention discloses a control method and device for a three-level circuit, and the control method includes the following steps: when it is detected that the three-level circuit is in an overcurrent protection mode, the first switch tube and the fourth switch tube are controlled to be turned off; when the next switching cycle comes, the protection of the first switch tube is released or the protection of the fourth switch tube is released; when the current of the three-level circuit continues to rise or is greater than the preset current value, the second switch tube and the third switch tube are both turned off. The control method can solve the problem of turning off the voltage spike of the first and fourth switch tubes and reducing the turn-off loss, and control the increase of the operating frequency of the switch tube under OCP. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A structural diagram of a three-level circuit provided by an embodiment of the present invention;

[0023] Figure 2 A schematic flow chart of a control method for a three-level circuit provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be described in detail below in conjunction with the embodiments shown in the accompanying drawings. However, the embodiments do not limit the present invention, and any structural, methodological, or functional changes made by a person skilled in the art based on the embodiments are all within the protection scope of the present invention.

[0025] The following description and accompanying drawings fully illustrate the specific embodiments of this article so that those skilled in the art can practice them. Parts and features of some embodiments may be included in or replace parts and features of other embodiments. The scope of the embodiments of this article includes the entire scope of the claims, as well as all available equivalents of the claims. Herein, the terms "first", "second", etc. are only used to distinguish one element from another, without requiring or implying any actual relationship or order between these elements. In fact, the first element can also be called the second element, and vice versa. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that the structure, device or equipment including a series of elements includes not only those elements, but also other elements that are not explicitly listed, or also include elements inherent to such structure, device or equipment. In the absence of more restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the structure, device or equipment including the elements. Each embodiment is described in a progressive manner herein, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the embodiments can be referred to each other.

[0026] The terms "longitudinal", "lateral", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. in this document indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing this document and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In the description of this document, unless otherwise specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a mechanical connection or an electrical connection, it can also be the internal communication of two elements, it can be a direct connection, or it can be an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0027] Embodiment 1 of the present invention provides a control method for a three-level circuit. Figure 1 As shown, the three-level circuit includes at least one diode-clamped three-level bridge arm, and the diode-clamped three-level bridge arm includes two clamping diodes and four switch tubes connected in series in sequence: a first switch tube T1, a second switch tube T2, a third switch tube T3 and a fourth switch tube T4; Figure 2 As shown, the following steps are included:

[0028] Step 201: when it is detected that the three-level circuit is in the overcurrent protection mode, the first switch tube T1 and the fourth switch tube T4 are controlled to be turned off;

[0029] Step 202: when the next switching cycle comes, release the protection of the first switch tube T1 or release the protection of the fourth switch tube T4; that is, when the outflow current of the three-level circuit appears the next rising edge or the next falling edge, it indicates that the next switching cycle has arrived.

[0030] Step 203: When the current of the three-level circuit continues to rise or is greater than a preset current value, the second switch tube T2 and the third switch tube T3 are both turned off.

[0031] Here, when overcurrent protection occurs, the first and fourth switch tubes need to be closed in time. In order to prevent the switch tube from being repeatedly opened and closed due to differences in inductance and hysteresis points of overcurrent protection release in the overcurrent protection mode, resulting in frequency doubling and damage to the switch tube. Improper hysteresis point setting causes multiple switch cycles to be closed continuously, resulting in insufficient starting energy for the output load, and slow startup under nonlinear loads. The second and third switch tubes are closed at the same time without distinguishing between current states and after a fixed dead zone delay time, which may cause an increase in switch tube losses in the overcurrent protection mode.

[0032] This control method has the following advantages: 1. There is no need to accurately set the current protection hysteresis. When overcurrent protection occurs, the first and fourth switch tubes are turned off and frequency-locked control is performed to achieve the purpose of cycle-by-cycle. 2. The current of the second and third switch tubes is monitored to determine whether the current is externally abnormal or internally in a normal closed state. The second and third switch tubes are turned off only when there is an abnormality, otherwise no processing is performed.

[0033] In this embodiment, “detecting that the three-level circuit is in the overcurrent protection mode” specifically includes: when the first switch tube T1 and the second switch tube T2 are turned off at the same time, it is detected that the three-level circuit is in the overcurrent protection mode.

[0034] In this embodiment, “detecting that the three-level circuit is in the overcurrent protection mode” specifically includes: when the first switch tube T1 is turned off and the second switch tube T2 is turned on, it is detected that the three-level circuit is in the overcurrent protection mode.

[0035] In this embodiment, the following steps are also included: when the current of the three-level circuit is less than or equal to the preset current value and does not continue to rise, the states of the second switch tube T2 and the third switch tube T3 are kept unchanged. When it is determined whether the current is an external abnormality or an internal normal closed state, the second and third switch tubes are closed only when there is an abnormality, otherwise no processing is performed.

[0036] In this embodiment, “when the next switching cycle comes, the protection of the first switch tube T1 is released or the protection of the fourth switch tube T4 is released” specifically includes: when the next switching cycle comes, the protection of the first switch tube T1 is released or the protection of the fourth switch tube T4 is released, and then the three-level circuit is controlled to be in a normal working state.

[0037] Embodiment 2 of the present invention provides a control device for a three-level circuit, wherein the three-level circuit includes at least one diode-clamped three-level bridge arm, wherein the diode-clamped three-level bridge arm includes two clamping diodes and four switch tubes connected in series in sequence: a first switch tube T1, a second switch tube T2, a third switch tube T3 and a fourth switch tube T4; and includes the following modules:

[0038] A state detection module, used to control the first switch tube T1 and the fourth switch tube T4 to turn off when detecting that the three-level circuit is in an overcurrent protection mode;

[0039] A first processing module is used to release the protection of the first switch tube T1 or the protection of the fourth switch tube T4 when the next switching cycle comes;

[0040] The second processing module is used to turn off both the second switch tube T2 and the third switch tube T3 when the current of the three-level circuit continues to rise or is greater than a preset current value.

[0041] In this embodiment, the state detection module is further used for: when the first switch tube T1 and the second switch tube T2 are turned off at the same time, detecting that the three-level circuit is in the overcurrent protection mode.

[0042] In this embodiment, the state detection module is further used for: when the first switch tube T1 is turned off and the second switch tube T2 is turned on, detecting that the three-level circuit is in the overcurrent protection mode.

[0043] In this embodiment, the following modules are also included: a third processing module, which is used to keep the states of the second switch tube T2 and the third switch tube T3 unchanged when the current of the three-level circuit is less than or equal to a preset current value and does not continue to rise.

[0044] In this embodiment, the first processing module is further used to: release the protection of the first switch tube T1 or release the protection of the fourth switch tube T4 when the next switching cycle comes, and then control the three-level circuit to be in a normal working state.

[0045] It should be understood that although this specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each implementation mode may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

[0046] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent implementation methods or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A control method for a three-level circuit, wherein the three-level circuit comprises at least one diode-clamped three-level bridge arm, wherein the diode-clamped three-level bridge arm comprises two clamping diodes and four switch tubes connected in series in sequence: a first switch tube (T1), a second switch tube (T2), a third switch tube (T3) and a fourth switch tube (T4); characterized in that: The following steps are involved: When it is detected that the three-level circuit is in an overcurrent protection mode, the first switch tube (T1) and the fourth switch tube (T4) are controlled to be turned off; When the next switching cycle comes, the protection of the first switch tube (T1) is released or the protection of the fourth switch tube (T4) is released; When the current of the three-level circuit is greater than a preset current value, the second switch tube (T2) and the third switch tube (T3) are both turned off; When the current of the three-level circuit is less than or equal to a preset current value and does not continue to rise, the states of the second switch tube (T2) and the third switch tube (T3) are kept unchanged.

2. The control method according to claim 1, characterized in that: The “detecting that the three-level circuit is in the overcurrent protection mode” specifically includes: When the first switch tube (T1) and the second switch tube (T2) are turned off at the same time, it is detected that the three-level circuit is in an overcurrent protection mode.

3. The control method according to claim 1, characterized in that: The “detecting that the three-level circuit is in the overcurrent protection mode” specifically includes: When the first switch tube (T1) is turned off and the second switch tube (T2) is turned on, it is detected that the three-level circuit is in an overcurrent protection mode.

4. The control method according to claim 1, characterized in that: The “releasing the protection of the first switch tube (T1) or releasing the protection of the fourth switch tube (T4) when the next switch cycle comes” specifically includes: When the next switching cycle comes, the protection of the first switch tube (T1) is released or the protection of the fourth switch tube (T4) is released, and then the three-level circuit is controlled to be in a normal working state.

5. A control device for a three-level circuit, the three-level circuit comprising at least one diode-clamped three-level bridge arm, the diode-clamped three-level bridge arm comprising two clamping diodes and four switch tubes connected in series in sequence: a first switch tube (T1), a second switch tube (T2), a third switch tube (T3) and a fourth switch tube (T4); characterized in that: Includes the following modules: A state detection module, used for controlling the first switch tube (T1) and the fourth switch tube (T4) to turn off when detecting that the three-level circuit is in an overcurrent protection mode; A first processing module, used for releasing the protection of the first switch tube (T1) or releasing the protection of the fourth switch tube (T4) when the next switch cycle comes; A second processing module, used for turning off both the second switch tube (T2) and the third switch tube (T3) when the current of the three-level circuit is greater than a preset current value; The third processing module is used to keep the states of the second switch tube (T2) and the third switch tube (T3) unchanged when the current of the three-level circuit is less than or equal to a preset current value and does not continue to rise.

6. The control device according to claim 5, characterized in that: The state detection module is also used for: When the first switch tube (T1) and the second switch tube (T2) are turned off at the same time, it is detected that the three-level circuit is in an overcurrent protection mode.

7. The control device according to claim 5, characterized in that: The state detection module is also used for: When the first switch tube (T1) is turned off and the second switch tube (T2) is turned on, it is detected that the three-level circuit is in an overcurrent protection mode.

8. The control device according to claim 5, characterized in that: The first processing module is also used for: When the next switching cycle comes, the protection of the first switch tube (T1) is released or the protection of the fourth switch tube (T4) is released, and then the three-level circuit is controlled to be in a normal working state.

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