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CN-122017682-A - Neutral line connection detection device of split-phase power grid inverter

CN122017682ACN 122017682 ACN122017682 ACN 122017682ACN-122017682-A

Abstract

The invention discloses a neutral line connection detection device of a split-phase power grid inverter, which relates to the technical field of split-phase power grid inverters, and comprises a relay group, a filtering unit, a voltage sampling unit and a control unit, wherein the relay group is an inherent switching element of an inverter grid-connected loop, and the filtering unit adopts an inherent output filter capacitor of a direct current-alternating current conversion module; the control unit can control the on-off of the corresponding relay, the inherent filter capacitor is connected into the power grid to form an asymmetric load, and the neutral line connection state is judged by comparing the two-phase voltage difference value. According to the invention, no additional detection hardware is needed, the system cost and the power grid disturbance are reduced, the detection reliability is improved, and the overvoltage damage of the electric equipment can be effectively avoided.

Inventors

  • HU YONGFENG
  • FANG XIAOFENG
  • HU PENGFENG

Assignees

  • 上海铂科电子有限公司

Dates

Publication Date
20260512
Application Date
20260330

Claims (7)

  1. 1. The neutral line connection detection device of the split-phase power grid inverter is characterized by comprising a relay group, wherein the relay group comprises a first relay (1), a second relay (2) and a third relay (3), the split-phase power grid comprises a first phase line (4), a second phase line (6) and a power grid neutral line (5), the inverter comprises a grid-connected interface connected with the split-phase power grid and a direct current-alternating current conversion module (9), the first relay (1) is connected in series between the first phase line (4) and a first phase input end of the direct current-alternating current conversion module (9), the second relay (2) is connected in series between the power grid neutral line (5) and a neutral line input end of the direct current-alternating current conversion module (9), and the third relay (3) is connected in series between the second phase line (6) and a second phase input end of the direct current-alternating current conversion module (9); The filter unit comprises a first filter capacitor (7) and a second filter capacitor (8), wherein the first filter capacitor (7) is connected in parallel between a first phase input end and a neutral line input end of the direct current-alternating current conversion module (9), and the second filter capacitor (8) is connected in parallel between a second phase input end and a neutral line input end of the direct current-alternating current conversion module (9), and the first filter capacitor (7) and the second filter capacitor (8) are inherent output filter elements of the direct current-alternating current conversion module (9); the voltage sampling unit is respectively and electrically connected with the first phase line (4), the second phase line (6) and the power grid neutral line (5) and is used for collecting the first phase voltage between the first phase line (4) and the power grid neutral line (5) and the second phase voltage between the second phase line (6) and the power grid neutral line (5) in real time; The control unit is used for controlling the first relay (1) and the second relay (2) to be closed or controlling the second relay (2) and the third relay (3) to be closed before grid connection start of the inverter or during system self-checking, connecting the corresponding filter capacitor between the corresponding phase line and the neutral line (5) of the power grid, receiving the voltage acquired by the voltage sampling unit and judging the connection state of the neutral line of the inverter and the neutral line (5) of the power grid according to the voltage variation or the voltage difference value.
  2. 2. The neutral line connection detection device of the split-phase power grid inverter is characterized in that the initial states of the first relay (1), the second relay (2) and the third relay (3) are all normally open.
  3. 3. The neutral line connection detection device of the split-phase power grid inverter according to claim 1, wherein the voltage sampling unit comprises a first voltage sampling branch circuit (10) and a second voltage sampling branch circuit (11), the first voltage sampling branch circuit (10) is connected in parallel between a first phase line (4) and a power grid neutral line (5), and the second voltage sampling branch circuit (11) is connected in parallel between a second phase line (6) and the power grid neutral line (5).
  4. 4. The neutral line connection detection device for the split-phase power grid inverter is characterized in that when the control unit judges that the neutral line of the inverter is normally connected with the neutral line (5) of the power grid, the relay group is controlled to be closed so that the inverter enters a grid-connected operation state, and when the control unit judges that the neutral line of the inverter is not reliably connected with the neutral line (5) of the power grid, a protection action is triggered, an alarm signal is sent, and grid connection of the inverter is forbidden.
  5. 5. The neutral line connection detection device of the split-phase power grid inverter is characterized in that the first relay (1), the second relay (2) and the third relay (3) are inherent switching elements of an inverter grid-connected loop.
  6. 6. A split-phase grid inverter neutral connection detection method based on the device of any one of claims 1-5, comprising the steps of: The method comprises the following steps that S1, a control unit controls a first relay (1), a second relay (2) and a third relay (3) to be kept open, and a first phase voltage effective value between a first phase line (4) and a power grid neutral line (5) and/or a second phase voltage effective value between a second phase line (6) and the power grid neutral line (5) and/or a line voltage effective value between the first phase line (4) and the second phase line (6) are collected through a voltage sampling unit to serve as initial voltage values; Step S2, the control unit controls the first relay (1) and the second relay (2) to be closed, and the first filter capacitor (7) is connected between the first phase line (4) and the neutral line (5) of the power grid, or controls the second relay (2) and the third relay (3) to be closed, and the second filter capacitor (8) is connected between the second phase line (6) and the neutral line (5) of the power grid; step S3, after the system is stabilized, acquiring corresponding first phase voltage effective values and/or second phase voltage effective values and/or line voltage effective values again through a voltage sampling unit to serve as detection voltage values; And S4, the control unit judges the connection state of the neutral line of the inverter and the neutral line (5) of the power grid according to the voltage variation of the initial voltage value and the detection voltage value or the variation of the voltage combination difference value obtained by calculation of the initial voltage value and the detection voltage value.
  7. 7. The method for detecting the neutral-line connection of a split-phase grid inverter according to claim 6, wherein the method for determining the connection state in step S4 includes any one of the following: Calculating the absolute value of the difference value of the first phase voltage before and after the step S1 and the step S2, if the difference value is larger than a preset threshold value, judging that the neutral line of the inverter is not reliably connected with the neutral line (5) of the power grid, otherwise, judging that the connection is normal; calculating the absolute value of the difference value of the second phase voltage before and after the step S1 and the step S2, if the difference value is larger than a preset threshold value, judging that the neutral line of the inverter is not reliably connected with the neutral line (5) of the power grid, otherwise, judging that the connection is normal; Calculating the variation of the absolute value of the difference between the first phase voltage and the line voltage before and after the step S1 and the step S2, if the variation is larger than a preset threshold value, judging that the neutral line of the inverter is not reliably connected with the neutral line (5) of the power grid, otherwise, judging that the connection is normal; And step four, calculating the variation of the absolute value of the difference between the second phase voltage and the line voltage before and after the step S1 and the step S2, if the variation is larger than a preset threshold value, judging that the neutral line of the inverter is not reliably connected with the neutral line (5) of the power grid, otherwise, judging that the connection is normal.

Description

Neutral line connection detection device of split-phase power grid inverter Technical Field The invention relates to the technical field of split-phase power grid inverters, in particular to a neutral line connection detection device and a neutral line connection detection method for a split-phase power grid inverter. Background The split-phase power grid is used as a common residential power supply system and widely applied to North America, two phase lines with 180-degree phase difference are led out from a distribution transformer, and two voltage levels can be respectively provided by matching with a neutral line, wherein the low voltage is mainly used for general household appliances such as illumination and common sockets, and the high voltage is used for high-power equipment such as air conditioners, electric water heaters and the like. In this system, the inverter, as a key device for accessing a distributed energy source or backup power source, has to be reliably connected with the output neutral line of the split-phase grid. If the neutral line of the inverter is not reliably connected with the neutral line of the split-phase power grid, abnormal system voltage reference points are caused, voltage drift of each phase is caused, overvoltage damage of electric equipment connected to a low-voltage line is possibly caused, and obvious potential safety hazards exist. In the prior art, in order to solve the problem of abnormal voltage caused by the disconnection of the neutral line, a detection circuit scheme based on external impedance is generally adopted, as shown in fig. 1, in the scheme, an additional detection circuit is arranged in an inverter, a specific impedance is connected in parallel to a voltage port of one phase by utilizing the closing action of a relay, an asymmetric impedance load is manufactured between two phases artificially, then the effective value of the voltage of the two phases is detected, if a significant voltage difference exists between the two phases is detected, the neutral line of the inverter is judged to be not connected with the neutral line of a power grid, and if the effective values of the voltage of the two phases are basically equal, the neutral line is judged to be in a normal connection state. However, this prior art has several significant drawbacks, firstly, it relies on additional hardware circuitry, not only increasing the complexity and number of components of the system, but also increasing the manufacturing costs and potential points of failure, secondly, it belongs to active detection, it requires the application of asymmetric loads by switching relay states at specific moments, this process may cause transient disturbances of the grid side voltage, affecting connected sensitive devices, and furthermore, the decision logic relies on artificially manufactured unbalanced conditions, which still have insufficient distinguishing capability and reliability under certain specific load conditions. Therefore, there is a need to develop a new detection device that is more compact, reliable and does not require the introduction of additional disturbances to overcome the deficiencies of the prior art. Disclosure of Invention In view of the problems existing in the prior art, the invention aims to provide a neutral line connection detection device and a detection method for a split-phase power grid inverter, which can realize reliable detection of a neutral line connection state by utilizing the existing elements in an inverter system without adding special detection hardware, reduce power grid disturbance and improve the running stability of the system. The neutral line connection detection device of the split-phase power grid inverter comprises a first phase line, a second phase line and a power grid neutral line, the inverter comprises a grid-connected interface connected with the split-phase power grid and a direct current-alternating current conversion module, and the detection device comprises a relay group, a filtering unit, a voltage sampling unit and a control unit; The relay group comprises a first relay, a second relay and a third relay, wherein the first relay is connected in series between a first phase line and a first phase input end of the direct current-alternating current conversion module, the second relay is connected in series between a neutral line of a power grid and a neutral line input end of the direct current-alternating current conversion module, and the third relay is connected in series between a second phase line and a second phase input end of the direct current-alternating current conversion module; the filter unit comprises a first filter capacitor and a second filter capacitor, wherein the first filter capacitor is connected in parallel between a first phase input end and a neutral line input end of the direct current-alternating current conversion module, and the second filter capacitor is connected in parallel between a second p