Short-circuit detection method and circuit for t-type three-level inverter bridge arm

Abstract

The application discloses a short-circuit detection method and circuit for a T-type three-level inverter bridge arm, and the method comprises the following steps: disabling inverter wave generation of an inverter; disconnecting a grid-connected switch between an output end of a bridge arm of the inverter and a power grid, and then reconnecting a switch between the output end of the bridge arm of the inverter and the power grid; judging whether an inverter phase voltage effective value is greater than a preset voltage threshold value within a preset time; disconnecting the switch between the output end of the bridge arm of the inverter and the power grid again, and then reconnecting the grid-connected switch between the output end of the bridge arm of the inverter and the power grid; and judging whether an inductance current effective value is greater than a current threshold value. Therefore, before the T-type three-level inverter is connected to the power grid, whether the switch tube of the bridge arm is short-circuited can be detected by judging whether the inverter phase voltage effective value or the inductance current effective value is greater than the set threshold value, so that effective detection of the short circuit of the T-type three-level inverter bridge arm is realized.

Description

Technical Field

[0001] This invention relates to the field of inverter circuit technology, and in particular to a short-circuit detection method and circuit for a T-type three-level inverter bridge arm. Background Technology

[0002] In the field of new energy power generation, the main circuit of the T-type three-level inverter is a common circuit. In this circuit, the first and third switches of each phase bridge arm are complementary, the second and fourth switches are complementary, and a dead time is usually set to prevent shoot-through.

[0003] In a three-phase grid-connected inverter, before the inverter is connected to the grid, a voltage waveform with the same frequency, amplitude, and phase as the grid is generated by controlling the on and off of the power switching transistors. This is called inverter waveform generation. Then, the output-side relay is energized to reduce the inrush current caused by the voltage difference between the inverter and the grid side. After the relay is energized, the inverter is connected to the grid, realizing the transfer of energy.

[0004] However, during long-term inverter operation, short circuits or open circuits in the power switching transistors are inevitable due to issues such as drive interference or poor heat dissipation. In the event of a short circuit in the power switching transistor, inverter operation is generally not permitted, as this would cause a shoot-through in the bridge arm, leading to transistor damage. Currently, existing technologies lack effective detection methods for short circuits in power switching transistors. Summary of the Invention

[0005] The technical problem to be solved by this invention is how to achieve effective detection of short circuits in the bridge arms of a T-type three-level inverter.

[0006] To address the aforementioned technical problems, the first aspect of this invention discloses a short-circuit detection method for a bridge arm of a T-type three-level inverter, the method comprising:

[0007] Prevent the inverter from generating inverter waves;

[0008] Disconnect the grid connection switch between the output terminal of the inverter's bridge arm and the power grid;

[0009] Determine whether the effective value of the inverter voltage is greater than a preset voltage threshold within a preset time period;

[0010] If the effective value of the inverter voltage is greater than the voltage threshold, then it is determined that the first or fourth switch of the bridge arm is short-circuited.

[0011] In an optional embodiment, the method further includes:

[0012] Close the grid-connected switch;

[0013] Determine whether the effective value of the inductor current corresponding to the bridge arm is greater than a preset current threshold within a preset time period;

[0014] If the effective value of the inductor current is greater than the current threshold, then it is determined that the second or third switch of the bridge arm is short-circuited.

[0015] In an optional embodiment, the method further includes:

[0016] A switch and a resistor are also connected between the output terminal and the grid-connected switch, and the switch and the resistor are connected in parallel.

[0017] After disconnecting the grid-connected switch between the output terminal of the inverter's bridge arm and the power grid, and before determining whether the effective value of the inverter phase voltage is greater than a preset voltage threshold within a preset time period, the method further includes:

[0018] Close the switch;

[0019] After determining whether the effective value of the inverter voltage is greater than a preset voltage threshold within a preset time period, and before closing the grid-connected switch, the method further includes:

[0020] Disconnect the switch.

[0021] In an optional embodiment, the method further includes:

[0022] If it is determined that any one of the switches in the bridge arm is short-circuited, then the grid-connected switch is disconnected and the switch is closed, so that the inverter returns to its initial state.

[0023] In an optional embodiment, the method further includes:

[0024] If it is determined that all the switches in the bridge arm are not short-circuited, then the grid-connected switch is disconnected and the switch is closed to allow the inverter to perform open-loop waveform generation.

[0025] Determine whether the effective value of the instantaneous difference between the inverter phase voltage and the grid phase voltage is greater than the preset instantaneous difference threshold within a preset time period;

[0026] If the effective value of the instantaneous voltage difference is greater than the instantaneous voltage difference threshold, then the grid-connected switch is disconnected and the switch is closed to return the inverter to its initial state.

[0027] If the effective value of the instantaneous voltage difference is not greater than the instantaneous difference threshold, then the grid-connected switch is closed, allowing the inverter to enter the grid-connected state.

[0028] In an optional embodiment, determining that the first or fourth switch of the bridge arm is short-circuited includes:

[0029] If the reverse phase voltage is equal to the positive bus voltage, then the first switch of the bridge arm is determined to be short-circuited;

[0030] If the reverse phase voltage is equal to the negative bus voltage, then the fourth switch of the bridge arm is determined to be short-circuited.

[0031] The second aspect of the present invention discloses a short-circuit detection circuit for a T-type three-level inverter bridge arm. The circuit includes at least: an inverter bridge arm, a switch, and a resistor; the first terminal of the switch, the first terminal of the resistor, and the output terminal of the bridge arm are connected, and the second terminal of the switch and the second terminal of the resistor are used for connection to the power grid.

[0032] In this embodiment of the invention, before the T-type three-level inverter is connected to the grid, the inverter's inverter power generation is prohibited. The grid connection switch between the output terminal of the inverter's bridge arm and the grid is disconnected, and the switch between the output terminal of the inverter's bridge arm and the grid is closed. It is determined whether the effective value of the inverter phase voltage is greater than a preset voltage threshold within a preset time. If the effective value of the inverter phase voltage is greater than the voltage threshold, it is determined that the first or fourth switch of the bridge arm is short-circuited. If the effective value of the inverter phase voltage is not greater than the voltage threshold, the switch between the output terminal of the inverter's bridge arm and the grid is disconnected, and then the grid connection switch between the output terminal of the inverter's bridge arm and the grid is closed. It is determined whether the effective value of the inductor current is greater than the current threshold. If the effective value of the inductor current is greater than the current threshold, it is determined that the second or third switch of the bridge arm is short-circuited. This allows for the detection of short circuits in the bridge arm's switching transistors before the T-type three-level inverter is connected to the grid. This is achieved by detecting whether the effective value of the inverter phase voltage or the effective value of the inductor current of the bridge arm is greater than a set threshold. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a flowchart illustrating a short-circuit detection method for a T-type three-level inverter bridge arm disclosed in an embodiment of the present invention.

[0035] Figure 2 This is a simplified flowchart of a short-circuit detection method for a T-type three-level inverter bridge arm disclosed in an embodiment of the present invention;

[0036] Figure 3This shows the main circuit of a commonly used T-type three-level inverter;

[0037] Figure 4 This shows the circuit formed by the main circuit of a T-type three-level inverter that still generates inverter waves when the switching transistor VA1 is short-circuited;

[0038] Figure 5 It shows the relationship with Figure 1 The short-circuit detection method in this paper is used in conjunction with the short-circuit detection circuit of the T-type three-level inverter bridge arm;

[0039] Figure 6 This shows the circuit formed in the main circuit of a T-type three-level inverter when the first switch of the first phase is short-circuited;

[0040] Figure 7 This shows the circuit formed in the main circuit of a T-type three-level inverter when the fourth switch of the first phase is short-circuited;

[0041] Figure 8 This illustrates the circuit formed in the main circuit of a T-type three-level inverter when the second or third switch of the first phase is short-circuited. Detailed Implementation

[0042] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, apparatus, product, or end that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or ends.

[0044] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0045] This invention discloses a short-circuit detection method and circuit for a bridge arm of a T-type three-level inverter. Before the T-type three-level inverter is connected to the grid, the inverter's inverter power generation is prohibited. The grid connection switch between the output terminal of the inverter's bridge arm and the grid is disconnected, and the switch between the output terminal of the inverter's bridge arm and the grid is closed. It is determined whether the effective value of the inverter phase voltage is greater than a preset voltage threshold within a preset time. If the effective value of the inverter phase voltage is greater than the voltage threshold, the first or fourth switch of the bridge arm is determined to be short-circuited. If the effective value of the inverter phase voltage is not greater than the voltage threshold, the switch between the output terminal of the inverter's bridge arm and the grid is disconnected, and the grid connection switch between the output terminal of the inverter's bridge arm and the grid is closed. It is determined whether the effective value of the inductor current is greater than the current threshold. If the effective value of the inductor current is greater than the current threshold, the second or third switch of the bridge arm is determined to be short-circuited. This allows for the detection of short circuits in the bridge arm switches by checking whether the effective value of the inverter phase voltage or the effective value of the inductor current of the bridge arm exceeds a set threshold before the T-type three-level inverter is connected to the grid. This enables effective detection of short circuits in the bridge arms of the T-type three-level inverter. Detailed explanations follow.

[0046] Example 1

[0047] Please see Figure 1 , Figure 1 This is a schematic flowchart of a short-circuit detection method for a T-type three-level inverter bridge arm disclosed in an embodiment of the present invention. Figure 1 As shown, the short-circuit detection method for the bridge arm of this T-type three-level inverter may include the following operations:

[0048] 101. Inverter wave generation is prohibited.

[0049] 102. Disconnect the grid connection switch between the output terminal of the inverter's bridge arm and the power grid.

[0050] 103. Close the switch.

[0051] 104. Determine whether the effective value of the inverter voltage is greater than the preset voltage threshold within a preset time.

[0052] 105. If the effective value of the inverter voltage is greater than the voltage threshold, then it is determined that the first or fourth switch of the bridge arm is short-circuited.

[0053] 106. If the effective value of the inverter voltage is not greater than the voltage threshold, then disconnect the switch.

[0054] 107. Close the grid-connected switch.

[0055] 108. Determine whether the effective value of the inductor current corresponding to the bridge arm is greater than a preset current threshold within a preset time.

[0056] 109. If the effective value of the inductor current is greater than the current threshold, then it is determined that the second or third switch of the bridge arm is short-circuited.

[0057] 110. If the effective value of the inductor current is not greater than the current threshold, then disconnect the grid-connected switch and close the switch to enable the inverter to perform open-loop waveform generation.

[0058] 111. Determine whether the effective value of the instantaneous difference between the inverter phase voltage and the grid phase voltage is greater than the preset instantaneous difference threshold within a preset time period.

[0059] 112. If the effective value of the instantaneous voltage difference is greater than the instantaneous difference threshold or if any switch of the bridge arm is determined to be short-circuited, then the grid-connected switch is disconnected and the switch is closed to return the inverter to the initial state.

[0060] 113. If the effective value of the instantaneous voltage difference is not greater than the instantaneous difference threshold, then close the grid connection switch to allow the inverter to enter the grid connection state.

[0061] To better understand the overall process of the short-circuit detection method for the bridge arm of the T-type three-level inverter in this embodiment of the invention, please refer to... Figure 2 A simplified flowchart of the short-circuit detection method for the bridge arm of a T-type three-level inverter.

[0062] Figure 3 This shows the main circuit of a commonly used T-type three-level inverter.

[0063] like Figure 3 As shown in the diagram, switches VA1, VA2, VA3, and VA4 are, in order, the first, second, third, and fourth switches of the first phase; switches VB1, VB2, VB3, and VB4 are, in order, the first, second, third, and fourth switches of the second phase; and switches VC1, VC2, VC3, and VC4 are, in order, the first, second, third, and fourth switches of the third phase. Each phase's bridge arm output is connected to the grid via an inductor L, a capacitor C, and a grid-connected switch RELAY (which can be a grid-side relay).

[0064] Figure 4 This shows the circuit formed by the main circuit of a T-type three-level inverter when the switching transistor VA1 is short-circuited, and it still generates an inverter wave.

[0065] like Figure 4As shown, if inverter wave generation continues when switch VA1 is short-circuited, a loop will be formed between switch VA1, switch VA2 and switch VA3. Therefore, inverter wave generation is usually not allowed, otherwise it will cause a bridge arm shoot-through and damage the switch.

[0066] Figure 5 It shows the relationship with Figure 1 The short-circuit detection method in this paper is used in conjunction with the short-circuit detection circuit of the bridge arm of the T-type three-level inverter.

[0067] like Figure 5 As shown, a resistor R and a switch K are added to the grid loop in each phase arm. The switch K controls the connection or disconnection of the resistor R. The switch K is normally closed and only opens when a short circuit is detected in the second or third switch of each phase.

[0068] When the inverter is normally connected to the grid, the grid-connection switch RELAY on the grid side is closed, and the voltage of the filter capacitor C is typically sampled as the inverter phase voltage. When the inverter transitions from normal grid-connection to grid-off state, this filter capacitor voltage discharges, and within a sufficiently long time, it drops to approximately zero. When the inverter is disconnected from the grid, it is defined as being in its initial state, inverter waveform generation is disabled, the grid-connection switch RELAY is opened, and switch K is closed.

[0069] When the switching transistors of the bridge arm are short-circuited, it can be divided into the first / fourth switching transistor of the bridge arm being short-circuited, or the second / third switching transistor of the bridge arm being short-circuited.

[0070] Figure 6 This shows the circuit formed in the main circuit of a T-type three-level inverter when the first switch of the first phase is short-circuited.

[0071] like Figure 6 As shown, when the first switch of the first phase is short-circuited, then through Figure 6 The circuit shown generates a voltage across the filter capacitor C. The voltage across the filter capacitor is equal to the voltage at point O, which is the positive half-bus voltage. In other words, the inverter voltage of the first phase is equal to the positive bus voltage.

[0072] Figure 7 This shows the circuit formed in the main circuit of a T-type three-level inverter when the fourth switch of the first phase is short-circuited.

[0073] like Figure 7 As shown, when the fourth switch of the first phase is short-circuited, then through... Figure 7 The circuit shown generates a voltage across the filter capacitor C. The voltage across the filter capacitor is the negative half-bus voltage relative to the voltage at point O, which means that the inverter voltage of the first phase is equal to the negative bus voltage.

[0074] Therefore, combining Figure 6 and Figure 7 The principle illustrated above can be used to explain steps 101, 102, 103, 104, and 105. During the inverter's grid-connected self-test, before the inverter generates a waveform, the grid-connected switch RELAY is first disconnected, and switch K is closed. Then, the effective value of the inverter phase voltage is checked to see if it exceeds a certain voltage threshold. If it does not decrease within a given time, it is considered that a short circuit has occurred in the first or fourth switch. At this point, the inverter can be returned to its initial state, and inverter waveform generation can be disabled. If the effective value of the inverter phase voltage is detected to decrease within a given time and not exceed a certain voltage threshold, it can be determined that the first and fourth switches are not short-circuited. At this point, the next step of short-circuit detection for the second and third switches can be performed.

[0075] Figure 8 This illustrates the circuit formed in the main circuit of a T-type three-level inverter when the second or third switch of the first phase is short-circuited.

[0076] Combination Figure 8 The principle illustrated above can be used to explain steps 106, 107, 108, and 109. First, disconnect switch K to connect resistor R, then close the grid-connected switch RELAY. Specifically, assuming the second switch transistor of the first phase is short-circuited, there will be a voltage drop across resistor R and inductor L, which will flow through... Figure 8 The circuit shown carries current. The resistor R prevents damage to the transistors from excessive inrush current when the grid-connected switch RELAY is closed. If the effective value of the inductor current in the first phase is detected to be greater than a certain current threshold, it is determined that the second or third switch of the first phase is short-circuited. If the effective value of the inductor current in the first phase is not greater than the certain current threshold, it is determined that the second and third switches of the first phase are not short-circuited. After determining that the second or third switch of the first phase is short-circuited, the inverter can be returned to its initial state, and inverter waveform generation can be disabled. After determining that the second and third switches of the first phase are not short-circuited, the grid-connected switch RELAY can be opened first, and then switch K can be closed to start inverter waveform generation and prepare for grid connection.

[0077] It should be noted that the above short-circuit detection method is not limited to short-circuit detection of the first, second, third, and fourth switching transistors; it is also applicable to short circuits of multiple transistors or anti-parallel diodes.

[0078] It should be noted that since the function of resistor R is to prevent excessive inrush current from damaging the transistor when the grid-connected switch RELAY is closed, the above-mentioned short-circuit detection method can still be used to some extent to detect short circuits in the switching transistors even when resistor R and switch K are not introduced into the circuit. This is especially true for the short-circuit detection of the first and fourth switching transistors, where the short-circuit detection process does not detect the current, so it is still applicable even when resistor R and switch K are not introduced into the circuit.

[0079] For steps 110, 111, 112, and 113 above, after disconnecting the grid-connection switch RELAY, closing switch K, and generating inverter waveforms in preparation for grid connection, it is possible to further check whether the frequency, amplitude, and phase of the inverter voltage and the grid voltage are consistent. If they are consistent, the grid-connection switch RELAY can be closed to put the inverter into grid-connection mode and perform grid connection. If they are inconsistent, the grid-connection switch RELAY can be disconnected, and switch K can be closed to return the inverter to its initial state and stop grid connection. This makes the grid connection process safer and more reliable. Specifically, checking whether the frequency, amplitude, and phase of the inverter voltage and the grid voltage are consistent can be achieved by detecting whether the effective value of the instantaneous difference between the inverter phase voltage and the grid phase voltage within a preset time is greater than a preset instantaneous difference threshold.

[0080] The short-circuit detection method and circuit described in this invention require only the addition of a set of resistors R and switches K to the grid loop for each phase bridge arm compared to traditional circuits. The increase in hardware cost is small. It can detect short-circuit faults in the switches of each phase bridge arm before the inverter is connected to the grid, and there is no detection blind spot. It avoids the inverter generating waves when the power switch tube is short-circuited, which can cause the bridge arm to shoot through and damage the tube. The detection method is safe and effective. Before the T-type three-level inverter is connected to the grid, inverter power generation is prohibited. The grid connection switch between the output terminal of the inverter's bridge arm and the grid is disconnected, and the switch between the output terminal of the inverter's bridge arm and the grid is closed. It is determined whether the effective value of the inverter phase voltage is greater than a preset voltage threshold within a preset time. If the effective value of the inverter phase voltage is greater than the voltage threshold, it is determined that the first or fourth switch of the bridge arm is short-circuited. If the effective value of the inverter phase voltage is not greater than the voltage threshold, the switch between the output terminal of the inverter's bridge arm and the grid is disconnected, and then the grid connection switch between the output terminal of the inverter's bridge arm and the grid is closed. It is then determined whether the effective value of the inductor current is greater than the current threshold. If the effective value of the inductor current is greater than the current threshold, it is determined that the second or third switch of the bridge arm is short-circuited. This allows for the detection of short circuits in the bridge arm switches by checking whether the effective value of the inverter phase voltage or the effective value of the inductor current exceeds a set threshold before the T-type three-level inverter is connected to the grid. Furthermore, if no short circuit is detected, the system can further check whether the inverter voltage and grid voltage frequency, amplitude, and phase are consistent, further ensuring the safety and stability of the grid connection process.

[0081] Finally, it should be noted that the short-circuit detection method and circuit for a T-type three-level inverter bridge arm disclosed in the embodiments of the present invention are merely preferred embodiments of the present invention and are only used to illustrate the technical solutions of the present invention, not to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A short-circuit detection method for a bridge arm of a T-type three-level inverter, characterized in that, The short-circuit detection circuit of the T-type three-level inverter bridge arm includes at least: the inverter bridge arm, a grid-connected switch, a switch, and a resistor; the first terminal of the switch, the first terminal of the resistor, and the output terminal of the bridge arm are connected; the second terminal of the switch and the second terminal of the resistor are connected to the first terminal of the grid-connected switch; the second terminal of the grid-connected switch is used for connection to the power grid; the method includes: Prevent the inverter from generating inverter waves; Disconnect the grid connection switch between the output terminal of the inverter's bridge arm and the power grid; Close the switch; Determine whether the effective value of the inverter voltage is greater than a preset voltage threshold within a preset time period; If the effective value of the inverter voltage is greater than the voltage threshold, then it is determined that the first or fourth switch of the bridge arm is short-circuited; Disconnect the switch; Close the grid-connected switch; Determine whether the effective value of the inductor current corresponding to the bridge arm is greater than a preset current threshold within a preset time period; If the effective value of the inductor current is greater than the current threshold, then it is determined that the second or third switch of the bridge arm is short-circuited. If it is determined that all the switches in the bridge arm are not short-circuited, then the grid-connected switch is disconnected and the switch is closed to allow the inverter to perform open-loop waveform generation. Determine whether the effective value of the instantaneous difference between the inverter phase voltage and the grid phase voltage is greater than the preset instantaneous difference threshold within a preset time period; If the effective value of the instantaneous voltage difference is greater than the instantaneous voltage difference threshold, then the grid-connected switch is disconnected and the switch is closed to return the inverter to its initial state. If the effective value of the instantaneous voltage difference is not greater than the instantaneous difference threshold, then the grid-connected switch is closed, allowing the inverter to enter the grid-connected state.

2. The short-circuit detection method for a T-type three-level inverter bridge arm according to claim 1, characterized in that, The method further includes: If it is determined that any one of the switches in the bridge arm is short-circuited, then the grid-connected switch is disconnected and the switch is closed, so that the inverter returns to its initial state.

3. The short-circuit detection method for a T-type three-level inverter bridge arm according to any one of claims 1-2, characterized in that, The determination that the first or fourth switch of the bridge arm is short-circuited includes: If the reverse phase voltage is equal to the positive bus voltage, then the first switch of the bridge arm is determined to be short-circuited; If the reverse phase voltage is equal to the negative bus voltage, then the fourth switch of the bridge arm is determined to be short-circuited.

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