Neutral line access detection method of three-phase inverter, three-phase inverter and energy storage converter

Abstract

The invention provides a neutral line access detection method of a three-phase inverter, the three-phase inverter and an energy storage converter. The three-phase inverter comprises a three-phase inverter circuit and a fault detection circuit. The fault detection circuit comprises three detection branches with the same impedance. An alternating current port of the three-phase inverter circuit comprises three phase line terminals and a neutral line terminal, and each phase line terminal is connected with the neutral line terminal through a corresponding detection branch. A first detection branch of the three detection branches comprises a first switch unit used for disconnecting the first detection branch. The method comprises the steps that when an alternating current port is connected into a three-phase power distribution system, a first switch unit is closed, and the voltage between a phase line terminal where a first detection branch is located and a neutral line terminal is acquired to serve as first voltage; turning off the first switch unit and acquiring a voltage between the phase line terminal and the neutral line terminal where the first detection branch is located as a second voltage; and determining a neutral line access detection result according to the relationship between the first voltage and the second voltage.

Description

Technical Field

[0001] The present application relates to the technical field of electronic power conversion, and in particular to a neutral line access detection method for a three-phase inverter, a three-phase inverter and an energy storage converter. Background Art

[0002] In the related art, the N-phase missing detection scheme of the power grid is generally based on the voltage difference between the neutral point voltage calculated by the three phase line terminals of the device and the N-phase voltage of the power grid, or the magnitude and phase of the phase voltage measured by the device end, to determine whether the N-phase of the external power supply connected to the device is missing. In this way, the voltage difference between the neutral point voltage and the N-phase voltage of the power grid or the abnormal phase voltage can only be detected when the three phase line terminals of the device are connected to the user load and the three-phase load is unbalanced. However, on the one hand, when the load imbalance of the three phase line terminals of the device is small, the fault cannot be detected. On the other hand, when the abnormality is detected, if the load imbalance of the three phase line terminals of the device is large, the load of the device may have been subjected to 2 to 3 times the rated voltage of the device, and it is very likely that the device will be damaged due to overvoltage, and the effect of protecting the device in advance cannot be achieved. In addition, the calculation process of calculating the voltage difference between the neutral point voltage and the N-phase voltage of the power grid, or the phase of the phase voltage measured by the device, is complicated and the calculation amount is relatively large, the risk of false alarm is large, and the reliability is not high. Summary of the invention

[0003] In view of this, the present application provides a neutral line access detection method for a three-phase inverter, a three-phase inverter and an energy storage converter, which can quickly detect whether the neutral line terminal is connected to the neutral line of the three-phase power distribution system without relying on load access.

[0004] In a first aspect, the present application provides a method for detecting neutral line access of a three-phase inverter. The three-phase inverter includes a three-phase inverter circuit and a fault detection circuit. The fault detection circuit includes three detection branches with the same impedance. The AC port of the three-phase inverter circuit includes three phase terminals and a neutral terminal. Each phase terminal is connected to the neutral terminal through a corresponding detection branch. The first detection branch of the three detection branches includes a first switch unit for disconnecting the first detection branch. The method includes: when the AC port is connected to a three-phase power distribution system, closing the first switch unit and obtaining the voltage between the phase terminal where the first detection branch is located and the neutral terminal as the first voltage; disconnecting the first switch unit and obtaining the voltage between the phase terminal where the first detection branch is located and the neutral terminal as the second voltage; and determining the neutral line access detection result according to the relationship between the first voltage and the second voltage.

[0005] In one embodiment, a neutral line access detection result is determined based on the relationship between a first voltage and a second voltage, including: obtaining a voltage deviation value between the first voltage and the second voltage; when the voltage deviation value is less than a preset voltage threshold, determining that the neutral line access detection result is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system; when the voltage deviation value is greater than or equal to the preset voltage threshold, determining that the access detection result is that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system.

[0006] In one embodiment, obtaining a voltage deviation value between a first voltage and a second voltage includes: obtaining a difference value obtained by subtracting the second voltage from the first voltage; and using an absolute value of the difference value as the voltage deviation value.

[0007] In one embodiment, the neutral line connection detection result is determined based on the relationship between the first voltage and the second voltage, including: when the first voltage is equal to the second voltage, determining that the neutral line connection detection result is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system.

[0008] In one embodiment, a neutral line connection detection result is determined based on the relationship between the first voltage and the second voltage, including: when the second voltage is greater than the first voltage and the ratio of the second voltage to the first voltage meets a preset ratio condition, determining that the neutral line connection detection result is that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system.

[0009] In one embodiment, the method also includes: when the neutral line access detection result is that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system, returning to execute the step of closing the first switch unit to perform the next neutral line access detection; when consecutive preset neutral line access detection results are all that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system, determining that the final detection result of the neutral line access detection is that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system.

[0010] In one embodiment, the method also includes: when the number of consecutive detections does not exceed a preset number of times, if the result of any neutral line access detection is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system, determining that the final detection result of the neutral line access detection is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system.

[0011] In one embodiment, the three-phase inverter further includes a second switch unit, a first end of the second switch unit is connected to the AC port, and a second end of the second switch unit is used to connect to the load. Before closing the first switch unit, the method further includes: opening the second switch unit.

[0012] The second aspect of the present application provides a three-phase inverter, including a three-phase inverter circuit, a fault detection circuit and a controller. The fault detection circuit includes three detection branches with the same impedance. The AC port of the three-phase inverter circuit includes three phase line terminals and a neutral line terminal, and each phase line terminal is connected to the neutral line terminal through a corresponding detection branch. The first detection branch of the three detection branches includes a first switch unit for disconnecting the first detection branch. The controller is connected to the three-phase inverter circuit and the fault detection circuit respectively. The controller is used to execute the neutral line access detection method of the three-phase inverter as described in any of the above items.

[0013] The third aspect of the present application provides an energy storage inverter, including a three-phase inverter circuit, a fault detection circuit, an energy storage battery pack and a controller. The three-phase inverter circuit is a bidirectional inverter circuit, the energy storage battery pack is connected to the DC end of the three-phase inverter circuit, and the fault detection circuit includes three detection branches with the same impedance. The AC port of the three-phase inverter circuit includes three phase line terminals and a neutral line terminal, and each phase line terminal is connected to the neutral line terminal through a corresponding detection branch. The first detection branch of the three detection branches includes a first switch unit for disconnecting the first detection branch. The controller is respectively connected to the three-phase inverter circuit and the fault detection circuit, and the controller is used to execute the neutral line access detection method of the three-phase inverter as described in any of the above items.

[0014] The neutral line access detection method of the three-phase inverter provided in the present application can be applied to the three-phase inverter provided with the three-phase inverter circuit and the fault detection circuit. Among them, the fault detection circuit includes three detection branches with the same impedance, and each phase line terminal of the AC port of the three-phase inverter circuit is connected to the neutral terminal of the three-phase inverter circuit through the corresponding detection branch, wherein the first detection branch also includes a first switch unit for disconnecting the first detection branch. In the neutral line access detection method, when the AC port is connected to the three-phase power distribution system, the first switch unit is closed and the voltage between the phase line terminal and the neutral line terminal where the first detection branch is located is obtained as the first voltage. Then the first switch unit is disconnected and the voltage between the phase line terminal and the neutral line terminal where the first detection branch is located is obtained as the second voltage. It can be understood that the impedance (detection load) of the three detection branches is the same, therefore, when the first switch unit is disconnected, the impedance of the first detection branch is not connected between the phase line terminal and the neutral line terminal where the first detection branch is located, at this time, the three-phase detection load is unbalanced, on the contrary, when the first switch unit is closed, the three-phase detection load is balanced. When the neutral line terminal of the three-phase inverter circuit is connected to the neutral line of the three-phase power distribution system, due to the clamping effect of the neutral line of the three-phase power distribution system, regardless of whether the first switch unit is disconnected or the three-phase detection load is balanced, the voltage between each phase line terminal and the neutral line terminal (i.e., the phase voltage) is equal, and is equal to the single-phase voltage of the three-phase power distribution system. Therefore, the first voltage and the second voltage are both approximately equal to the single-phase voltage of the three-phase power distribution system. When the neutral line terminal of the three-phase inverter circuit is disconnected from the neutral line of the three-phase power distribution system, the first switch unit is closed, and the three-phase detection load is balanced, then the neutral line terminal potential of the three-phase inverter circuit is not affected, and the phase voltage (first voltage) of the three phase line terminals is still equal to the single-phase voltage of the three-phase power distribution system; and when the first switch unit is disconnected and the three-phase detection load is unbalanced, due to the loss of the clamping of the neutral line of the three-phase power distribution system, the neutral line terminal potential changes at this time, thereby affecting the phase voltages of the three phase line terminals, but the voltage between two phase line terminals (i.e., the line voltage) is not affected. At this time, according to the voltage vector diagram, it can be calculated that the phase voltage (second voltage) of the phase line terminal where the first detection branch is located is approximately equal to 1.5 times the single-phase voltage of the three-phase power distribution system. In this way, the neutral line access detection result can be determined based on the relationship between the first voltage and the second voltage. For example, when the second voltage is greater than the first voltage, it is determined that the neutral line of the three-phase inverter is disconnected from the neutral line of the three-phase power distribution system. In this way, the neutral line access detection method provided by the present application does not rely on user loads and does not require complex calculations. It can quickly detect whether the neutral line terminal of the three-phase inverter is connected to the neutral line of the three-phase power distribution system based on the measured first voltage and second voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present application and should not be regarded as limiting the scope of protection of the present application. In each of the drawings, similar components are numbered similarly.

[0016] Figure 1 A schematic diagram of the connection between a three-phase inverter, a three-phase power distribution system and a load provided in one embodiment of the present application.

[0017] Figure 2 A schematic diagram of the flow of a neutral line access detection method for a three-phase inverter provided in an embodiment of the present application.

[0018] Figure 3 It is a voltage vector diagram of three phase terminals and a neutral terminal of the AC port when the AC port of the three-phase inverter circuit is connected to a three-phase power distribution system and the first switch unit is closed.

[0019] Figure 4 It is a voltage vector diagram of three phase terminals and a neutral terminal of the AC port when the AC port of the three-phase inverter circuit is connected to a three-phase power distribution system and the first switch unit is disconnected, if the neutral terminal is not connected to the neutral line of the three-phase power distribution system.

[0020] Figure 5 A flowchart of the sub-steps of step S203 provided for implementation of the present application.

[0021] Figure 6 A flowchart of the sub-steps of step S501 provided in an embodiment of the present application.

[0022] Figure 7 A circuit block diagram of a three-phase inverter provided in one embodiment of the present application.

[0023] Figure 8 A circuit block diagram of an energy storage converter provided in one embodiment of the present application.

[0024] Fig. 9 A functional block diagram of a control device provided in one embodiment of the present application.

[0025] Fig.10 A functional block diagram of a computer-readable storage medium provided for one embodiment of the present application. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0027] It should be noted that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be a central component at the same time. When a component is considered to be "located on" another component, it may be directly located on the other component or there may be a central component at the same time. The terms "top", "bottom", "upper", "lower", "left", "right", "front", "back", and similar expressions used herein are for illustrative purposes only.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0029] Some embodiments will be described below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0030] In the related art, the N-phase missing detection scheme of the power grid is generally based on the voltage difference between the neutral point voltage calculated by the three phase line terminals of the device and the N-phase voltage of the power grid, or the magnitude and phase of the phase voltage measured by the device end, to determine whether the N-phase of the external power supply connected to the device is missing. In this way, the voltage difference between the neutral point voltage and the N-phase voltage of the power grid or the abnormal phase voltage can only be detected when the three phase line terminals of the device are connected to the user load and the three-phase load is unbalanced. However, on the one hand, when the load imbalance of the three phase line terminals of the device is small, the fault cannot be detected. On the other hand, when the abnormality is detected, if the load imbalance of the three phase line terminals of the device is large, the device may have been subjected to 2 to 3 times the rated voltage of the device, and it is very likely that the device will be damaged due to overvoltage, and the effect of protecting the device in advance cannot be achieved. In addition, the calculation process of calculating the voltage difference between the neutral point voltage and the N-phase voltage of the power grid, or the phase of the phase voltage measured by the device, is complicated and the calculation amount is relatively large, the risk of false alarm is large, and the reliability is not high.

[0031] Based on this, the present application provides a neutral line access detection method for a three-phase inverter, a three-phase inverter and an energy storage converter, which can quickly detect whether the neutral line terminal is connected to the neutral line of the three-phase power distribution system without relying on the load.

[0032] First, see Figure 1 , Figure 1 The three-phase inverter 10 is used to connect to the three-phase power distribution system 20 and supply power to the load 30. Figure 1The three-phase inverter 10 shown includes a three-phase inverter circuit 11 and a fault detection circuit 12. The fault detection circuit 12 includes three detection branches with the same impedance. The AC port of the three-phase inverter circuit 11 includes three phase terminals and a neutral terminal, and each phase terminal is connected to the neutral terminal through a corresponding detection branch.

[0033] The DC port of the three-phase inverter circuit 11 can also be connected to a DC device ( Figure 1 The three-phase inverter circuit 11 is used to convert the AC power output by the three-phase power distribution system 20 into DC power, or to convert the received DC power into AC power to power the load 30 and / or feed it to the three-phase power distribution system 20 through the AC port. It can be understood that the three-phase inverter circuit 11 can be a bidirectional inverter circuit. The three-phase inverter circuit 11 can also be replaced by a unidirectional conversion circuit, for example, a DC-AC conversion circuit or an AC-DC conversion circuit, and the present application is not limited to this. The three phase line terminals of the three-phase inverter circuit 11 may include an A terminal, a B terminal and a C terminal, and the neutral line terminal may be an N terminal.

[0034] The fault detection circuit 12 includes a first detection branch 121, a second detection branch 122, and a third detection branch 123. In some embodiments, the first detection branch 121 includes a first impedance R1 and a first switch unit 1211 for disconnecting the first detection branch 121. The second detection branch 122 includes a second impedance R2, and the third detection branch 123 includes a third impedance R3. The impedance values ​​of the first detection branch 121, the second detection branch 122, and the third detection branch 123 are equal. Considering that the impedance is approximately equal to 0 when the switch unit is closed, the first impedance R1 in the first detection branch 121 is the same as the second impedance R2 of the second detection branch 122 or the third impedance R3 of the third detection branch 123. In some embodiments, the first impedance R1, the second impedance R2, and the third impedance R3 may include at least one of a resistor, an inductor, and a capacitor. The present application does not limit the specific electronic components in the first detection branch 111, the second detection branch 122, and the third detection branch 123, and only requires that the impedance value of each detection branch is equal.

[0035] Further, the C terminal is connected to the N terminal through the first detection branch 121, the B terminal is connected to the N terminal through the second detection branch 122, and the A terminal is connected to the N terminal through the third detection branch 123. Specifically, the first end of the first switch unit 1211 is connected to the C terminal, the second end of the first switch unit 1211 is connected to the first end of the first impedance R1, and the second end of the first impedance R1 is connected to the N terminal. The first end of the second impedance R2 is connected to the B terminal, and the second end of the second impedance R2 is connected to the N terminal. The first end of the third impedance R3 is connected to the C terminal, and the second end of the third impedance R3 is connected to the N terminal. In this embodiment, the second end of the first impedance R1, the second end of the second impedance R2, and the second end of the third impedance R3 are all connected to the N terminal through the middle point O.

[0036] The three-phase power distribution system 20 can be, for example, a three-phase power grid, a three-phase power transformer, a three-phase power distribution station or other voltage output device for outputting three-phase power. Among them, the A terminal on the AC port of the three-phase inverter 10 is used to connect the first phase line a of the three-phase power grid, the B terminal is used to connect the second phase line b of the power grid, and the C terminal is used to connect the third phase line b of the power grid. The N terminal is used to connect the neutral line n of the power grid. The first switch unit 1211 includes but is not limited to switching devices such as switch tubes and relays. The switch tube can be, for example, a triode or a field effect tube. In one embodiment, the first switch unit 1211 is a controllable relay S1 to illustrate the neutral line access detection method of the three-phase inverter provided in the present application.

[0037] The load 30 may be an AC load such as a motor or a transformer, or a DC load equipped with an AC-DC conversion module.

[0038] It is understandable that in other embodiments, the first switch unit 1211 can also be set in the second detection branch 122 or the third detection branch 123. This application only takes the first switch unit 1211 set in the first detection branch 121 as an example to illustrate the neutral line access detection method of the three-phase inverter.

[0039] See also Figure 2 , Figure 2 A schematic flow chart of a neutral line connection detection method for a three-phase inverter provided in an embodiment of the present application. It can be understood that the method can be executed by a controller of the three-phase inverter. The method includes:

[0040] Step S201: when the AC port is connected to a three-phase power distribution system, the first switch unit is closed and the voltage between the phase terminal and the neutral terminal where the first detection branch is located is obtained as the first voltage.

[0041] Please also read Figure 1In step S201, the first voltage is the voltage between the C terminal and the N terminal when the first switch unit 1211 is closed, and is also the C-phase voltage of the three-phase inverter circuit when the first switch unit 1211 is closed. Since the potential of the middle point O is the same as the potential of the N terminal, the first voltage may also be the voltage between the C terminal and the middle point O when the first switch unit 1211 is closed. In some embodiments, the first voltage may be obtained by a voltage sensor or a voltage detection circuit.

[0042] In some embodiments, whether the AC port is connected to the three-phase power distribution system can be determined by detecting the voltage of the AC port. For example, when it is detected that the voltage of the AC port is greater than or equal to a preset voltage, it is determined that the AC port is connected to the three-phase power distribution system 20, and then the controller controls the first switch unit 1211 to close and obtain the first voltage.

[0043] It can be understood that when the AC port of the three-phase inverter circuit 11 is connected to the three-phase power distribution system 20 and the first switch unit 1211 is closed, since the impedance of each detection branch is equal, the three-phase detection load of the three-phase inverter circuit 11 is balanced. Therefore, regardless of whether the neutral line terminal is connected to the neutral line of the three-phase power distribution system 20, the potential of the N terminal is the same as the neutral line potential of the three-phase power distribution system 20. Since the potential of the middle point O is the same as the potential of the N terminal, the three phase line terminals and the neutral line terminal of the AC port can form a Figure 3 The voltage vector diagram is shown. Figure 3 The voltage vector diagram shown is an equilateral triangle, and point O1 represents the potential of the middle point O when the AC port is connected to the three-phase power distribution system 20 and the first switch unit 1211 is closed.

[0044] See also Figure 3 That is, in step S201, when the AC port is connected to the three-phase power distribution system and the first switch unit 1211 is closed, the potential of the N terminal is the same as the potential of the neutral line n of the three-phase power distribution system 20; the voltage U between the A terminal and the middle point O is AO1 , the voltage U between terminal B and the middle point O BO1 , and the voltage U between the C terminal and the midpoint O CO1 When the single-phase voltage of the three-phase power distribution system 20 is U grid When

[0045] U AO1 =U BO1 =U CO =U an =U bn =U cn =U grid

[0046] Among them, U anis the voltage between the first phase line a and the neutral line n of the three-phase power distribution system 20; U bn is the voltage between the second phase line b and the neutral line n of the three-phase power distribution system 20; U cn It is the voltage between the third phase line c and the neutral line n of the three-phase power distribution system 20.

[0047] In this way, when the AC port is connected to the three-phase power distribution system and the first switch unit 1211 is closed, the first voltage obtained is equal to the single-phase voltage U grid Roughly equal.

[0048] Step S202: disconnect the first switch unit and obtain the voltage between the phase terminal and the neutral terminal where the first detection branch is located as the second voltage.

[0049] After the first voltage is acquired, the first switch unit 1211 is turned off, and the voltage between the C terminal and the neutral line terminal (midpoint O or N terminal) is acquired as the second voltage.

[0050] Step S203: determining a neutral line connection detection result according to a relationship between the first voltage and the second voltage.

[0051] Please refer again Figure 1 , it can be understood that after the first switch unit 1211 is disconnected, the first detection branch 121 is disconnected, at this time the first impedance R1 is not connected between the C terminal and the N terminal, and the impedance R2 / R3 of the same impedance value is connected between the A terminal, the B terminal and the N terminal. If the neutral line terminal is not connected to the neutral line of the three-phase power distribution system 20, that is, when the connection between the N terminal and the neutral line n of the three-phase power distribution system 20 is disconnected, at this time the potential of the N terminal loses the clamping of the neutral line n, then the phase line terminals (that is, the B terminal and the A terminal) where the second detection branch 122 and the third detection branch 123 are located affect the potential of the N terminal. When the three-phase power distribution system 20 is connected, but the neutral line n is not connected, when the power supply of the three-phase power distribution system 20 is stable, the line voltage is stable, and there is Since the three phase terminals A, B, and C are connected to phase lines a, b, and c respectively, In this way, a Figure 4 The voltage vector diagram is shown. Point O2 represents the potential of the middle point O when the AC port is connected to the three-phase power distribution system 20 and the first switch unit 1211 is disconnected. Since the impedance of the second detection branch 122 and the third detection branch 123 are the same, the voltage U between the A terminal and the middle point O is AO2 , and the voltage U between terminal B and the middle point O BO2 equal, and the potential of the middle point O is between points A and B (i.e. Figure 4 Point O2 in the middle, between vectors AB), from and in Figure 4In the voltage vector diagram shown, vector O2C is perpendicular to vector AB, and vector O2C intersects vector AB at the midpoint of vector AB. Figure 4 And the Pythagorean theorem of a right triangle (where ∠AO2C is a right angle, ∠O2AC is 60°, and ∠ACO2 is 30°) can be calculated to obtain:

[0052]

[0053]

[0054] At this time, U CO That is, the voltage between the C terminal and the middle point O, that is, the voltage between the C terminal and the neutral line terminal, the second voltage. That is, when the AC port is connected to the three-phase power distribution system and the first switch unit 1211 is disconnected, if the neutral line terminal is not connected to the neutral line of the three-phase power distribution system 20, the second voltage obtained is close to 1.5U grid That is, the second voltage is greater than the first voltage.

[0055] When the first switch unit 1211 is disconnected, if the neutral line terminal is connected to the neutral line of the three-phase power distribution system 20, that is, the N terminal is connected to the neutral line n of the three-phase power distribution system 20, the potential of the N terminal will always be clamped by the neutral line n, and the potential of the middle point O is the same as the potential of the N terminal, and both are the same as the potential of the neutral line of the three-phase power distribution system 20. At this time, the voltage vector diagram between the A terminal, the B terminal, the C terminal and the middle point O is still Figure 3 In the voltage vector diagram shown, the second voltage is substantially equal to the first voltage.

[0056] Therefore, in step S203, when the second voltage increases significantly compared to the first voltage, it can be determined that the neutral line of the three-phase inverter 10 is not connected to the neutral line of the three-phase power distribution system 20; when the second voltage is approximately equal to the first voltage, it can be determined that the neutral line of the three-phase inverter 10 is connected to the neutral line of the three-phase power distribution system 20.

[0057] In summary, the neutral line access detection method of the three-phase inverter provided in the present application can be applied to the three-phase inverter 10 provided with the three-phase inverter circuit 11 and the fault detection circuit 12. Among them, the fault detection circuit 12 includes three detection branches with the same impedance, and each phase line terminal of the AC port of the three-phase inverter circuit 11 is connected to the neutral terminal of the three-phase inverter circuit 11 through the corresponding detection branch, wherein the first detection branch 121 also includes a first switch unit 1211 for disconnecting the first detection branch 121. In the neutral line access detection method, when the AC port is connected to the three-phase power distribution system 20, the first switch unit 1211 is closed and the voltage between the phase line terminal (C terminal) and the neutral line terminal (N terminal) where the first detection branch 121 is located is obtained as the first voltage. Then the first switch unit 1211 is disconnected and the voltage between the phase line terminal (C terminal) and the neutral line terminal (N terminal) where the first detection branch is located is obtained as the second voltage. It can be understood that the impedances of the three detection branches are the same. Therefore, when the first switch unit 1211 is disconnected, the impedance of the first detection branch 121 is not connected between the phase terminal and the neutral terminal where the first detection branch 121 is located. At this time, the three-phase detection load is unbalanced. On the contrary, when the first switch unit 1211 is closed, the three-phase detection load is balanced. When the neutral terminal of the three-phase inverter circuit 11 is connected to the neutral line of the three-phase power distribution system 20, due to the clamping effect of the neutral line of the three-phase power distribution system 20, regardless of whether the first switch unit 1211 is disconnected or not, and whether the three-phase detection load is balanced or not, the voltage (i.e., phase voltage) between each phase terminal and the neutral terminal is equal, and is equal to the single-phase voltage of the three-phase power distribution system. Therefore, the first voltage and the second voltage are both approximately equal to the single-phase voltage of the three-phase power distribution system. When the neutral line terminal of the three-phase inverter circuit 11 is disconnected from the neutral line of the three-phase power distribution system 20, the first switch unit 1211 is closed, and the three-phase detection load is balanced, then the neutral line terminal potential of the three-phase inverter circuit 11 is not affected, and the phase voltage (first voltage) of the three phase line terminals is still equal to the single-phase voltage of the three-phase power distribution system 20; and when the first switch unit 1211 is disconnected and the three-phase detection load is unbalanced, due to the loss of the clamping of the neutral line of the three-phase power distribution system 20, the neutral line terminal potential changes at this time, thereby affecting the phase voltage of the three phase line terminals, but the voltage between the two phase line terminals (i.e., the line voltage) is not affected. At this time, according to the voltage vector diagram, it can be calculated that the phase voltage (second voltage) of the phase line terminal where the first detection branch 121 is located is approximately equal to 1.5 times the single-phase voltage of the three-phase power distribution system 20. In this way, the neutral line access detection result can be determined according to the relationship between the first voltage and the second voltage. For example, when the second voltage is greater than the first voltage, it is determined that the neutral line of the three-phase inverter 10 is disconnected from the neutral line of the three-phase power distribution system 20 .In this way, the neutral line connection detection method provided in the present application does not rely on the connection of the load 30 and does not require complex calculations. It can quickly detect whether the neutral line terminal of the three-phase inverter 10 is connected to the neutral line of the three-phase power distribution system 20 based on the measured first voltage and second voltage.

[0058] See also Figure 5 In some embodiments, step S203 includes the following sub-steps:

[0059] Step S501: obtaining a voltage deviation value between a first voltage and a second voltage.

[0060] The voltage deviation value is used to represent the voltage value difference between the first voltage and the second voltage.

[0061] Step S502: When the voltage deviation value is less than the preset voltage threshold, it is determined that the neutral line connection detection result is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system.

[0062] Among them, the preset voltage threshold is used to represent the critical value of the voltage deviation value when the neutral line of the three-phase inverter 10 is not connected to the three-phase power distribution system 20. It can be understood that due to the voltage detection error, the detected second voltage may be less than the ideal value, resulting in the deviation value between the second voltage and the first voltage being less than 0.5 times the single-phase voltage of the three-phase power distribution system 20. Therefore, in order to reduce the probability of misjudgment, the preset voltage threshold can be configured to be less than or equal to 0.5 times the single-phase voltage of the three-phase power distribution system 20, and the preset voltage threshold is greater than 0. For example, in some embodiments, the preset voltage threshold can be 0.1 times the single-phase voltage of the three-phase power distribution system 20.

[0063] Thus, in step S502, when the voltage deviation value is less than the preset voltage threshold, it indicates that the second voltage is closer to the first voltage, so it can be determined that the neutral line terminal is connected to the neutral line of the three-phase power distribution system.

[0064] Step S503: When the voltage deviation value is greater than or equal to the preset voltage threshold, it is determined that the connection detection result is that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system.

[0065] In step S503, when the voltage deviation value is greater than or equal to the preset voltage threshold, it indicates that the deviation between the second voltage and the first voltage is large, so it can be determined that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system.

[0066] In summary, in this embodiment, the neutral line connection detection result is determined by obtaining the voltage deviation value between the first voltage and the second voltage and comparing the voltage deviation value with the preset voltage threshold.

[0067] Understandably, in some embodiments, after the three-phase inverter 10 is powered on, the neutral line connection detection method of the three-phase inverter provided in the present application is first executed, and after determining that the neutral line connection detection result is that the neutral line terminal of the three-phase inverter 10 is connected to the neutral line of the three-phase power distribution system 20, the operation of feeding power to the three-phase power distribution system 20, supplying power to the load 30, or converting AC power into DC power to supply power to DC devices is executed. In this way, the power safety of the three-phase inverter 10 can be guaranteed.

[0068] See also Figure 6 In some embodiments, step S501 includes the following sub-steps:

[0069] Step S601: obtaining a difference value obtained by subtracting a second voltage from a first voltage.

[0070] Step S602: taking the absolute value of the difference as the voltage deviation value.

[0071] Understandably, since the first voltage is always less than or equal to the second voltage, the difference obtained by subtracting the second voltage from the first voltage may be a negative number. Thus, further obtaining the absolute value of the difference as the voltage deviation value can better measure the degree of deviation between the first voltage and the second voltage.

[0072] In summary, in this embodiment, by executing step S601 to step S602 , a voltage deviation value that better measures the degree of deviation between the first voltage and the second voltage can be obtained.

[0073] In some embodiments, step S203 further includes:

[0074] When the first voltage is equal to the second voltage, it is determined that the neutral line connection detection result is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system.

[0075] As described above, when the AC port is connected to the three-phase power distribution system 20 and the first switch unit 1211 is disconnected, if the neutral line terminal is connected to the neutral line of the three-phase power distribution system 20, the potential of the middle point O is the same as the potential of the N terminal, and both are the same as the potential of the neutral line of the three-phase power distribution system 20. At this time, the voltage vector diagram between the A terminal, the B terminal, the C terminal and the middle point O is still Figure 3 The voltage vector diagram is shown. In this way, the second voltage is equal to the first voltage. Therefore, when the first voltage is equal to the second voltage, it is determined that the neutral line connection detection result is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system.

[0076] In some embodiments, step S203 further includes:

[0077] When the second voltage is greater than the first voltage and the ratio of the second voltage to the first voltage meets a preset ratio condition, it is determined that the neutral line connection detection result is that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system.

[0078] As described above, when the AC port is connected to the three-phase power distribution system 20 and the first switch unit 1211 is disconnected, if the neutral line terminal is connected to the neutral line of the three-phase power distribution system 20, the second voltage is approximately 1.5 times the first voltage. In this way, the neutral line access detection result can be determined based on the proportional relationship between the second voltage and the first voltage. However, due to voltage detection errors, the second voltage may be less than the ideal value. Therefore, the preset proportional condition can be configured to be less than or equal to 1.5 and greater than 1.1. This application does not limit the specific preset proportional conditions.

[0079] In some embodiments, the neutral line connection detection method of the three-phase inverter further includes:

[0080] When the neutral line connection detection result is that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system, returning to the step of closing the first switch unit to perform the next neutral line connection detection;

[0081] When consecutive preset secondary neutral line access detection results are all that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system, it is determined that the final detection result of the neutral line access detection is that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system.

[0082] Thus, in this embodiment, when the neutral line connection detection result is that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system, multiple executions of the neutral line connection detection can be performed on the three-phase inverter 10 to further reduce the probability of misjudgment and improve the detection accuracy.

[0083] The present application does not limit the specific number of preset times, for example, the preset number of times can be 3 times.

[0084] In some embodiments, the neutral line connection detection method of the three-phase inverter further includes:

[0085] When the number of consecutive detections does not exceed the preset number of times, if the result of any neutral line access detection is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system, the final detection result of the neutral line access detection is determined to be that the neutral line terminal is connected to the neutral line of the three-phase power distribution system.

[0086] In other embodiments, the neutral line connection detection method of the three-phase inverter further includes: when the number of consecutively acquired neutral line connection detection results is less than or equal to a first preset number, returning to execute the step of closing the first switch unit to perform the next neutral line connection detection, and stopping when the number of consecutively acquired neutral line connection detection results is equal to the first preset number. Furthermore, when the neutral line connection detection result is that the number of times the neutral line terminal is not connected to the neutral line of the three-phase power distribution system is greater than or equal to a second preset number, the neutral line terminal is not connected to the neutral line of the three-phase power distribution system as the final detection result.

[0087] Please refer again Figure 1 In some embodiments, the three-phase inverter 10 further includes a second switch unit 13. A first end of the second switch unit 13 is connected to the AC port. A second end of the second switch unit 13 is used to connect the load 30. Before closing the first switch unit 1211, the method further includes: disconnecting the second switch unit 13.

[0088] Understandably, when the AC port of the three-phase inverter 10 is connected to the three-phase power distribution system 20, and the neutral line of the three-phase inverter 10 is not connected to the neutral line of the three-phase power distribution system 20, if the load 30 is directly connected to the three-phase inverter 10 at this time, if the load 30 is connected as an unbalanced load, the load on the unbalanced phase may be subjected to 2 to 3 times the rated voltage, which may easily damage the load 30. In this way, by disconnecting the second switch unit 13 before executing step S201, when the neutral line connection detection is performed after the three-phase inverter 10 is connected to the three-phase power distribution system 20 and powered on, the AC port overvoltage caused by the loss of N phase can be avoided to damage the load 30, thereby ensuring power safety.

[0089] Understandably, when the neutral line connection detection result is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system 20 , the second switch unit 13 is turned on to supply power to the load 30 normally.

[0090] In some embodiments, the second switch unit 13 may include four switch devices S2. The input interface of the load 30 includes three phase terminals and one neutral terminal. Each terminal of the load 30 is connected to the AC port of the three-phase inverter circuit 11 through a corresponding switch device S2. The switch device S2 includes but is not limited to switch devices such as switch tubes and relays. The switch tube may be, for example, a triode or a field effect tube.

[0091] See also Figure 7, an embodiment of the present application also provides a three-phase inverter 10. The three-phase inverter 10 includes a three-phase inverter circuit 11, a fault detection circuit 12 and a controller 14. The fault detection circuit 12 includes three detection branches with the same impedance. The AC port of the three-phase inverter circuit 11 includes three phase line terminals and a neutral line terminal, and each phase line terminal is connected to the neutral line terminal through a corresponding detection branch. The first detection branch 121 of the three detection branches includes a first switch unit 1211 for disconnecting the first detection branch 121. The controller 14 is connected to the three-phase inverter circuit 11 and the fault detection circuit 12, respectively. The controller 14 is used to execute the neutral line access detection method of the three-phase inverter provided in any of the above embodiments.

[0092] In some embodiments, the three-phase inverter 10 further includes a second switch unit 13. A first end of the second switch unit 13 is connected to an AC port. A second end of the second switch unit 13 is used to connect a load 30. Before closing the first switch unit 1211, the controller 14 disconnects the second switch unit 13 to avoid damage to the load 30 due to overvoltage of the AC port caused by the loss of the N phase, thereby ensuring power safety. When the controller 14 determines that the neutral line access detection result is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system 20, the controller 14 controls the second switch unit 13 to turn on to supply power to the load 30 normally.

[0093] Among them, the three-phase inverter circuit 11 can be a bidirectional inverter circuit; it can also be replaced by a unidirectional conversion circuit, for example, a DC-AC conversion circuit or an AC-DC conversion circuit, and the present application does not limit this.

[0094] See also Figure 8 , an embodiment of the present application also provides an energy storage converter (Power Control System, PCS) 100. The energy storage converter 100 includes a three-phase inverter circuit 11, a fault detection circuit 12, an energy storage battery pack 15 and a controller 14. The three-phase inverter circuit 11 is a bidirectional inverter circuit. The energy storage battery pack 15 is connected to the DC end of the three-phase inverter circuit 11. The fault detection circuit 12 includes three detection branches with the same impedance. The AC port of the three-phase inverter circuit 11 includes three phase terminals and a neutral terminal. Each phase terminal is connected to the neutral terminal through a corresponding detection branch. The first detection branch 121 of the three detection branches includes a first switch unit 1211 for disconnecting the first detection branch 121. The controller 14 is connected to the three-phase inverter circuit 11 and the fault detection circuit 12, respectively. The controller 14 is used to execute the neutral line access detection method of the three-phase inverter provided in any of the above embodiments.

[0095] The energy storage battery pack 15 is used to store electrical energy and includes at least one battery cell. In some embodiments, the controller 14 is also loaded with a battery management system BMS (Battery Management System) (not shown), and the controller 14 is also connected to the energy storage battery pack 15 for protecting and managing the energy storage battery pack 15. In other embodiments, the controller of the energy storage battery pack 15 and the controller 15 may also be independent control devices, and this application does not limit this.

[0096] In some embodiments, the energy storage converter 100 further includes a second switch unit 13. The first end of the second switch unit 13 is connected to the AC port. The second end of the second switch unit 13 is used to connect the load 30. Before closing the first switch unit 1211, the controller 14 disconnects the second switch unit 13 to avoid damage to the load 30 due to overvoltage of the AC port caused by the loss of the N phase, thereby ensuring the safety of electricity use. When the controller 14 determines that the neutral line access detection result is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system 20, the controller 14 controls the second switch unit 13 to turn on to supply power to the load 30 normally.

[0097] It is understandable that in other embodiments, the three-phase inverter circuit 11 may also be replaced by a unidirectional conversion circuit, for example, a DC-AC conversion circuit or an AC-DC conversion circuit.

[0098] See also Fig. 9 The present application also provides a control device, which is applied to the three-phase inverter 10 or an electronic device integrated with the three-phase inverter 10. Fig. 9 The structure block diagram of the control device 200 provided in the embodiment of the present application is schematically shown. Fig. 9 As shown, the control device 200 includes:

[0099] The first execution module 210 is used to close the first switch unit and obtain the voltage between the phase terminal and the neutral terminal where the first detection branch is located as the first voltage when the AC port is connected to the three-phase power distribution system.

[0100] The second execution module 220 is used to disconnect the first switch unit and obtain the voltage between the phase terminal and the neutral terminal where the first detection branch is located as the second voltage.

[0101] The determination module 230 is used to determine the neutral line connection detection result according to the relationship between the first voltage and the second voltage.

[0102] The specific details of the control device 200 provided in the embodiment of the present application to implement the neutral line access detection method of the three-phase inverter have been described in detail in the embodiment of the corresponding neutral line access detection method of the three-phase inverter, and will not be repeated here.

[0103] The present application also provides a computer-readable storage medium 300 on which a computer program 310 is stored. When the computer program 310 is executed by a processor, the neutral line connection detection method of the three-phase inverter in the above technical solution is implemented. The computer-readable storage medium 300 can be a portable compact disk read-only memory (CD-ROM) and include program code, and can be run on a terminal device, such as a personal computer. However, the program product of the present invention is not limited to this. In this document, the computer-readable storage medium 300 can be any tangible medium containing or storing a program, which can be used by or in combination with an instruction execution system, an apparatus or a device.

[0104] The above program product can adopt any combination of one or more readable media. The readable medium can be a readable signal medium or a readable storage medium. The readable storage medium can be, for example, but not limited to, a system, device or device of electricity, magnetism, light, electromagnetic, infrared, or semiconductor, or any combination of the above. More specific examples (non-exhaustive list) of readable storage media include: an electrical connection with one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the above.

[0105] Computer readable signal media may include data signals propagated in baseband or as part of a carrier wave, in which readable program code is carried. Such propagated data signals may take a variety of forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination of the above. Readable signal media may also be any readable medium other than a readable storage medium, which may send, propagate, or transmit a program for use by or in conjunction with an instruction execution system, apparatus, or device.

[0106] The program code embodied on the readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wired, optical cable, RF, etc., or any suitable combination of the foregoing.

[0107] Program code for performing the operations of the present invention may be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java, C++, etc., and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code may be executed entirely on the user computing device, partially on the user device, as a separate software package, partially on the user computing device and partially on a remote computing device, or entirely on a remote computing device or server. In cases involving a remote computing device, the remote computing device may be connected to the user computing device through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computing device (e.g., through the Internet using an Internet service provider).

[0108] In addition, the above-mentioned figures are only schematic illustrations of the processes included in the method according to an exemplary embodiment of the present invention, and are not intended to be limiting. It is easy to understand that the processes shown in the above-mentioned figures do not indicate or limit the time sequence of these processes. In addition, it is also easy to understand that these processes can be performed synchronously or asynchronously, for example, in multiple modules.

[0109] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A neutral line access detection method for a three-phase inverter, characterized in that: The three-phase inverter comprises a three-phase inverter circuit and a fault detection circuit, wherein the fault detection circuit comprises three detection branches with the same impedance, an AC port of the three-phase inverter circuit comprises three phase terminals and a neutral terminal, each of the phase terminals is connected to the neutral terminal through the corresponding detection branch, and a first detection branch of the three detection branches comprises a first switch unit for disconnecting the first detection branch; the method comprises: When the AC port is connected to a three-phase power distribution system, the first switch unit is closed and a voltage between a phase terminal where the first detection branch is located and the neutral terminal is obtained as a first voltage; Disconnecting the first switch unit and acquiring a voltage between the phase line terminal and the neutral line terminal where the first detection branch is located as a second voltage; A neutral line connection detection result is determined according to a relationship between the first voltage and the second voltage.

2. The method according to claim 1, characterized in that The determining a neutral line connection detection result according to a relationship between the first voltage and the second voltage includes: Acquire a voltage deviation value between the first voltage and the second voltage; When the voltage deviation value is less than a preset voltage threshold, determining that the neutral line connection detection result is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system; When the voltage deviation value is greater than or equal to the preset voltage threshold, it is determined that the connection detection result is that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system.

3. The method according to claim 2, characterized in that The obtaining a voltage deviation value between the first voltage and the second voltage includes: Obtaining a difference value obtained by subtracting the second voltage from the first voltage; The absolute value of the difference is used as the voltage deviation value.

4. The method according to claim 1, characterized in that: The determining a neutral line connection detection result according to a relationship between the first voltage and the second voltage includes: When the first voltage is equal to the second voltage, it is determined that the neutral line connection detection result is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system.

5. The method according to claim 1, characterized in that The determining a neutral line connection detection result according to a relationship between the first voltage and the second voltage includes: When the second voltage is greater than the first voltage and a ratio of the second voltage to the first voltage satisfies a preset ratio condition, it is determined that the neutral line connection detection result is that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system.

6. The method according to claim 1, characterized in that The method further comprises: When the neutral line connection detection result is that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system, returning to the step of closing the first switch unit to perform the next neutral line connection detection; When consecutive preset secondary neutral line access detection results are all that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system, it is determined that the final detection result of the neutral line access detection is that the neutral line terminal is not connected to the neutral line of the three-phase power distribution system.

7. The method according to claim 6, characterized in that The method further comprises: When the number of consecutive detections does not exceed the preset number of times, if the result of any neutral line access detection is that the neutral line terminal is connected to the neutral line of the three-phase power distribution system, the final detection result of the neutral line access detection is determined to be that the neutral line terminal is connected to the neutral line of the three-phase power distribution system.

8. The method according to claim 1, characterized in that: The three-phase inverter further includes a second switch unit, a first end of the second switch unit is connected to the AC port, and a second end of the second switch unit is used to connect a load. Before closing the first switch unit, the method further includes: The second switch unit is turned off.

9. A three-phase inverter, characterized in that: The three-phase inverter includes a three-phase inverter circuit, a fault detection circuit and a controller, the fault detection circuit includes three detection branches with the same impedance, the AC port of the three-phase inverter circuit includes three phase line terminals and a neutral line terminal, each of the phase line terminals is connected to the neutral line terminal through the corresponding detection branch, and the first detection branch of the three detection branches includes a first switch unit for disconnecting the first detection branch; the controller is respectively connected to the three-phase inverter circuit and the fault detection circuit, and the controller is used to execute the neutral line access detection method of the three-phase inverter as described in any one of claims 1-8.

10. An energy storage converter, characterized in that: The energy storage inverter includes a three-phase inverter circuit, a fault detection circuit, an energy storage battery pack and a controller. The three-phase inverter circuit is a bidirectional inverter circuit. The energy storage battery pack is connected to the DC end of the three-phase inverter circuit. The fault detection circuit includes three detection branches with the same impedance. The AC port of the three-phase inverter circuit includes three phase line terminals and a neutral line terminal. Each of the phase line terminals is connected to the neutral line terminal through the corresponding detection branch. The first detection branch of the three detection branches includes a first switch unit for disconnecting the first detection branch. The controller is connected to the three-phase inverter circuit and the fault detection circuit respectively, and the controller is used to execute the neutral line access detection method of the three-phase inverter according to any one of claims 1 to 8.

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