Insulation monitoring method, device and new energy power generation system

Abstract

The present invention discloses an insulation monitoring method, device and new energy power generation system. Usually, the inverter is shut down at night and connected to the grid during the day. The present invention divides the switching process of the anti-PID device and the insulation monitoring device into two periods: inverter shutdown and inverter grid connection for insulation monitoring, thereby achieving insulation monitoring throughout the day while suppressing the PID effect. Specifically, when the inverter is monitored to be shut down, AC insulation monitoring is continuously performed on the AC side. When the monitored AC insulation resistance meets the preset normal AC resistance condition, the inverter is working and meets the grid connection condition, DC insulation monitoring is performed before the inverter is connected to the grid. When the DC insulation resistance meets the preset normal DC resistance condition, the inverter is controlled to be connected to the grid and the AC and DC insulation monitoring is stopped. During the inverter grid connection, the anti-PID device and the AC insulation monitoring device are controlled to be executed alternately.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic power generation, and more specifically, to an insulation monitoring method, device and a new energy power generation system. Background Art

[0002] In the process of photovoltaic power generation, the inverter converts photovoltaic energy into a sinusoidal current with the same frequency and phase as the power grid and feeds it into the power grid. Due to the characteristics of photovoltaic panels, the photovoltaic energy conversion process will produce a PID (Potential Induced Degradation) effect on the photovoltaic panels. The PID effect will gradually reduce the working performance of the photovoltaic panels and eventually cause the photovoltaic panels to lose their power generation capacity. Therefore, the PID effect needs to be suppressed.

[0003] In the prior art, anti-PID equipment is usually used to raise the voltage of the negative pole of the photovoltaic string relative to the ground to suppress the PID effect of the photovoltaic panel. During the anti-PID operation, since there is a grounding loop between the anti-PID equipment and the ground, the insulation monitoring device (IMD) installed on the AC side cannot monitor the ground insulation resistance. Based on this, the prior art generally only turns on the insulation monitoring device at night. However, according to the requirements of the IEC standard, the insulation monitoring device needs to run 24 hours a day to perform insulation monitoring.

[0004] Therefore, how to achieve all-day insulation monitoring while suppressing the PID effect has become a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0005] In view of this, the present invention discloses an insulation monitoring method, device and new energy power generation system, so as to realize insulation monitoring throughout the day while suppressing the PID effect.

[0006] An insulation monitoring method, comprising:

[0007] When the inverter is detected to be shut down, the AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring;

[0008] When the monitored AC insulation resistance meets the preset normal AC resistance condition, the inverter is working and meets the grid connection condition, performing DC insulation monitoring before the inverter is connected to the grid;

[0009] When the monitored DC insulation resistance meets the preset normal DC resistance condition, the inverter is controlled to be connected to the grid, and the AC insulation monitoring and the DC insulation monitoring are stopped. At the same time, during the inverter being connected to the grid, the anti-PID device and the AC insulation monitoring device are controlled to be executed alternately.

[0010] Optionally, when the inverter is shut down, the method further includes:

[0011] If it is monitored that the AC insulation resistance is lower than the first fault threshold value for a first preset time period, it is determined that an AC insulation fault occurs on the AC side;

[0012] Output first AC insulation fault prompt information, and disconnect the low-voltage side system where the inverter is located from the power grid.

[0013] Optionally, when the inverter is shut down, the method further includes:

[0014] If it is monitored that the AC insulation resistance is higher than the first fault threshold and lower than the first alarm threshold for a second preset time period, it is determined that the AC insulation resistance is abnormal;

[0015] Outputs the first alarm information of abnormal AC insulation resistance.

[0016] Optionally, when the inverter is shut down, the method further includes:

[0017] When the AC insulation resistance is lower than the first alarm threshold, if the AC insulation resistance monitored at any time is higher than the first recovery threshold, it is determined that the AC insulation resistance has returned to normal, and the first alarm information is stopped from being output, and the continuous monitoring operation of the AC insulation resistance is exited.

[0018] Optionally, after the inverter is connected to the grid, the method further includes:

[0019] If it is monitored that the AC insulation resistance is lower than the second fault threshold value for a second preset time period, it is determined that an insulation fault occurs;

[0020] According to a preset fault location scheme, it is determined whether the insulation fault occurs on the AC side or the DC side.

[0021] Optionally, determining that the insulation fault occurs on the AC side or the DC side according to a preset fault location scheme includes:

[0022] Controlling the inverter to shut down and triggering DC insulation monitoring;

[0023] If any one of the insulation resistance between the positive pole and the ground and the insulation resistance between the negative pole and the ground of the photovoltaic string is less than the protection threshold, it is determined that the insulation fault occurs on the DC side;

[0024] as well as,

[0025] Triggering AC insulation monitoring;

[0026] If the monitored current AC insulation resistance is lower than the third fault threshold, it is determined that the insulation fault occurs on the AC side.

[0027] Optionally, also include:

[0028] When the insulation fault occurs on the AC side, outputting second AC insulation fault prompt information;

[0029] The connection between the low-voltage side system where the inverter is located and the power grid is disconnected.

[0030] Optionally, also include:

[0031] When the connection between the low-voltage side system and the power grid is not disconnected, the inverter is controlled to shut down and insulation resistance monitoring is continuously performed;

[0032] If the insulation fault returns to normal, the output of the second AC insulation fault prompt information stops, and the inverter is restored to be connected to the grid.

[0033] Optionally, after the inverter is connected to the grid, the method further includes:

[0034] If it is monitored that the AC insulation resistance is higher than the second fault threshold and lower than the second alarm threshold for a third preset time period, it is determined that the AC insulation resistance is abnormal;

[0035] Outputs the second alarm information of abnormal AC insulation resistance.

[0036] Optionally, after the inverter is connected to the grid, the method further includes:

[0037] When the AC insulation resistance is lower than the second alarm threshold, if the AC insulation resistance monitored at any time is higher than the second alarm threshold, it is determined that the AC insulation resistance has returned to normal, and the output of the second alarm information is stopped, and the continuous monitoring operation of the AC insulation resistance is exited.

[0038] Optionally, after the inverter is connected to the grid, the method further includes:

[0039] When the low insulation resistance alarm flag is detected to be in the effective state, the timing time of the insulation monitoring cycle timer is cleared, and AC insulation monitoring is forced to be performed continuously;

[0040] When the AC insulation resistance is higher than the second recovery threshold value for a preset AC insulation alarm recovery time, it is determined that the AC insulation resistance has returned to normal, the low insulation resistance alarm flag is switched to an invalid state, and continuous AC insulation monitoring is stopped.

[0041] Optionally, also include:

[0042] During the inverter grid-connection period, if the inverter is shut down or a non-insulation fault occurs in the inverter, the insulation monitoring logic during the inverter grid-connection period is switched to the insulation monitoring logic when the inverter is shut down.

[0043] Optionally, when the inverter is detected to be shut down, controlling an AC insulation monitoring device on the AC side to continuously perform AC insulation monitoring specifically includes:

[0044] If the anti-PID device is installed on the AC side, when it is detected that the inverter is shut down, the AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring, and the anti-PID device is controlled to stop working;

[0045] If the anti-PID device is installed on the DC side, when it is detected that the inverter is shut down, the AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring, and the anti-PID device is controlled on the DC side to operate.

[0046] An insulation monitoring device, comprising:

[0047] The AC insulation monitoring unit is used to control the AC insulation monitoring device on the AC side to continuously perform AC insulation monitoring when the inverter is detected to be shut down;

[0048] A DC insulation monitoring unit, used for performing DC insulation monitoring before the inverter is connected to the grid when the monitored AC insulation resistance meets the preset normal AC resistance condition and the inverter is working and meets the grid connection condition;

[0049] The control unit is used to control the inverter to be connected to the grid and stop the AC insulation monitoring and the DC insulation monitoring when the monitored DC insulation resistance meets the preset normal DC resistance condition, and at the same time, control the anti-PID device and the AC insulation to be executed alternately during the inverter being connected to the grid.

[0050] A new energy power generation system includes: an anti-PID device, an AC insulation monitoring device and a control device, wherein the control device includes a memory, a processor and a computer program stored in the memory and executable on the processor, and the processor implements the steps of the insulation monitoring method when executing the computer program.

[0051] From the above technical solution, it can be seen that the present invention discloses an insulation monitoring method, device and new energy power generation system. When it is monitored that the inverter is shut down, the AC insulation monitoring equipment is controlled on the AC side to continuously perform AC insulation monitoring. When the monitored AC insulation resistance meets the preset normal AC resistance condition, the inverter works and meets the grid-connected condition, DC insulation monitoring is performed before the inverter is connected to the grid. When the monitored DC insulation resistance meets the preset normal DC resistance condition, the inverter is controlled to be connected to the grid, and the AC insulation monitoring and DC insulation monitoring are stopped. At the same time, during the inverter grid connection, the anti-PID device and the AC insulation monitoring equipment are controlled to be executed alternately. Usually, the inverter is shut down at night and connected to the grid during the day. Therefore, the present invention divides the switching process of the anti-PID device and the insulation monitoring device into two periods: inverter shutdown and inverter grid connection. When the inverter is shut down, the AC insulation monitoring device continuously performs AC insulation monitoring. When the inverter is grid-connected, the anti-PID device and the AC insulation monitoring device are executed alternately to achieve compatibility between anti-PID operation and AC insulation monitoring. Therefore, the present invention realizes insulation monitoring throughout the day while suppressing the PID effect, solving the problem that the current insulation monitoring device cannot operate throughout the day. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the disclosed drawings without paying creative work.

[0053] Figure 1 A flow chart of an insulation monitoring method disclosed in an embodiment of the present invention;

[0054] Figure 2 A schematic diagram of a low-voltage side system of an inverter when a PID device disclosed in an embodiment of the present invention is installed on a DC side;

[0055] Figure 3 A schematic diagram of a low-voltage side system of an inverter when a PID device disclosed in an embodiment of the present invention is installed on the AC side;

[0056] Figure 4 A schematic diagram of a full-day switching solution for anti-PID equipment operation and insulation monitoring equipment disclosed in an embodiment of the present invention;

[0057] Figure 5 A flow chart of an insulation monitoring method when an inverter is shut down disclosed in an embodiment of the present invention;

[0058] Figure 6 A flow chart of an insulation monitoring method after an inverter is connected to the grid disclosed in an embodiment of the present invention;

[0059] Figure 7 A schematic diagram of the structure of an insulation monitoring device disclosed in an embodiment of the present invention;

[0060] Figure 8 The present invention is a schematic diagram of the structure of a control device in a new energy power generation system disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0061] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] The embodiment of the present invention discloses an insulation monitoring method, device and new energy power generation system. When it is monitored that the inverter is shut down, an AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring. When the monitored AC insulation resistance meets the preset normal AC resistance condition and the inverter is working and meets the grid-connected condition, DC insulation monitoring is performed before the inverter is grid-connected. When the monitored DC insulation resistance meets the preset normal DC resistance condition, the inverter is controlled to be grid-connected, and the AC insulation monitoring and DC insulation monitoring are stopped. At the same time, during the inverter grid-connected period, the anti-PID device and the AC insulation monitoring device are controlled to be executed alternately. Usually, the inverter is shut down at night and connected to the grid during the day. Therefore, the present invention divides the switching process of the anti-PID device and the insulation monitoring device into two periods: inverter shutdown and inverter grid connection. When the inverter is shut down, the AC insulation monitoring device continuously performs AC insulation monitoring. When the inverter is grid-connected, starting from the operation of the anti-PID device, the anti-PID device and the AC insulation monitoring device are executed alternately to achieve compatibility between anti-PID operation and AC insulation monitoring. Therefore, the present invention realizes insulation monitoring throughout the day while suppressing the PID effect, solving the problem that the current insulation monitoring device cannot operate all day.

[0063] See also Figure 1 , a flow chart of an insulation monitoring method disclosed in an embodiment of the present invention, the method is applied to a control device in a new energy power generation system, the method comprising:

[0064] Step S101: When it is detected that the inverter is shut down, the AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring;

[0065] In actual applications, when the AC switch inside the inverter is disconnected, the inverter stops, and the AC and DC insulation to ground are decoupled. On the AC side, AC insulation monitoring equipment is used to continuously perform AC insulation monitoring.

[0066] It should be noted that if the anti-PID device is installed on the DC side (see Figure 2 ), when the inverter is detected to be shut down, the AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring, and the anti-PID device is controlled on the DC side (it can be controlled according to the original settings). At this time, the DC side and the AC side do not interfere with each other.

[0067] If the PID device is installed on the AC side (see Figure 3 ), when the inverter is detected to be shut down, the AC insulation monitoring equipment can be controlled on the AC side to continuously perform AC insulation monitoring.

[0068] To facilitate understanding of the location of AC insulation monitoring equipment and anti-PID equipment, Figure 2 Taking an example for explanation, the inverter low-voltage side system includes: a photovoltaic panel 11 , an inverter 12 , an anti-PID device 13 , an AC insulation monitoring device 14 and a transformer 15 .

[0069] The photovoltaic panel 11 is connected to the inverter 12 via a switch K, one end of the anti-PID device 13 is connected to the DC side of the inverter 12, and the other end of the anti-PID device 13 is grounded.

[0070] The AC insulation monitoring device 14 is connected to the AC side of each AC inverter 12 .

[0071] One end of the transformer 15 is connected to the AC side of each AC inverter 12 , and the other end ( L1 , L2 , and L3 ) of the transformer 15 is connected to the power grid.

[0072] Step S102: When the monitored AC insulation resistance meets the preset normal AC resistance condition, the inverter is working and meets the grid connection condition, DC insulation monitoring is performed before the inverter is connected to the grid;

[0073] When the AC insulation resistance meets the preset normal AC resistance condition, it indicates that the AC insulation is normal and no AC insulation fault occurs, wherein the preset normal AC resistance condition refers to the value range of the AC insulation resistance corresponding to the normal AC insulation. The value range is determined according to actual needs and the present invention is not limited here.

[0074] In this embodiment, when the AC insulation is normal and the inverter meets the grid-connected conditions, the grid-connected operation is not performed on the inverter immediately. Instead, DC insulation monitoring is performed before the inverter is grid-connected, that is, DC insulation monitoring is performed through a DC insulation monitoring device, and the inverter is controlled to be grid-connected when it is detected that the DC insulation is normal.

[0075] Step S103: When the monitored DC insulation resistance meets the preset normal DC resistance condition, the inverter is controlled to be connected to the grid, the AC insulation monitoring and the DC insulation monitoring are stopped, and during the inverter being connected to the grid, the anti-PID device and the AC insulation monitoring device are controlled to be executed alternately.

[0076] When the DC insulation resistance meets the preset normal DC resistance condition, it indicates that the DC insulation is normal and no DC insulation fault occurs. At this time, the inverter is controlled to be connected to the grid, so that the inverter enters the grid-connected stage from the shutdown stage. At the same time, the AC insulation monitoring and DC insulation monitoring are stopped.

[0077] The preset normal DC resistance condition refers to a value range of the DC insulation resistance corresponding to normal DC insulation. The value range is determined according to actual needs and is not limited in the present invention.

[0078] In actual applications, during the inverter grid-connected period, the anti-PID device and the AC insulation monitoring device can be controlled to execute alternately starting from the operation of the anti-PID device; or the anti-PID device and the AC insulation monitoring device can be controlled to execute alternately starting from the AC insulation monitoring device. The specific operation depends on the actual situation and the present invention is not limited here.

[0079] For details, see Figure 4 , a schematic diagram of a full-day switching scheme of an anti-PID device operation and an insulation monitoring device disclosed in an embodiment of the present invention is divided into daytime and nighttime. At night, due to the lack of sunlight, the photovoltaic panel does not work. To reduce energy consumption, the inverter is in a shutdown state. To achieve full-day insulation monitoring, the present invention still performs insulation monitoring after the inverter is shut down. The specific insulation monitoring process can be referred to step S101 and step S102.

[0080] When the inverter is connected to the grid, stop AC insulation monitoring and DC insulation monitoring. During the inverter connection, the anti-PID device can be controlled to run first, and the timer starts to count. When the timer reaches T1 time, turn off the anti-PID device to disconnect the grounding loop and start AC insulation monitoring. After T2 time, if the AC insulation resistance is normal, turn off AC insulation monitoring and resume PID operation, so as to achieve the alternating execution of the anti-PID device and AC insulation monitoring device (see Figure 4 In practical applications, each time the anti-PID device and the AC insulation monitoring device are alternated, it can be determined that the timer has completed a preset cycle and restarted the timing. The preset cycle includes T1 and T2, T1 is the anti-PID cycle, and T2 is the insulation monitoring cycle.

[0081] It should be noted that after the inverter is shut down, the AC side and the DC side are physically isolated. AC insulation monitoring and DC insulation monitoring require two sets of equipment, namely: AC insulation monitoring equipment and DC insulation monitoring equipment. There are differences in the working principles of AC insulation monitoring equipment and DC insulation monitoring equipment. The DC insulation monitoring equipment only operates after the inverter is shut down, while the AC insulation monitoring equipment can operate when the inverter is shut down and connected to the grid.

[0082] In summary, the present invention discloses an insulation monitoring method. When it is detected that the inverter is shut down, the AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring. When the monitored AC insulation resistance meets the preset normal AC resistance condition and the inverter is working and meets the grid-connected condition, DC insulation monitoring is performed before the inverter is connected to the grid. When the monitored DC insulation resistance meets the preset normal DC resistance condition, the inverter is controlled to be connected to the grid, and the AC insulation monitoring and DC insulation monitoring are stopped. At the same time, during the inverter being connected to the grid, the anti-PID device and the AC insulation monitoring device are controlled to be executed alternately. Usually, the inverter is shut down at night and connected to the grid during the day. Therefore, the present invention divides the switching process of the anti-PID device and the insulation monitoring device into two periods: inverter shutdown and inverter grid connection. When the inverter is shut down, the AC insulation monitoring device continuously performs AC monitoring. When the inverter is grid-connected, starting from the operation of the anti-PID device, the anti-PID device and the AC insulation monitoring device are executed alternately to achieve compatibility between anti-PID operation and AC insulation monitoring. Therefore, the present invention realizes insulation monitoring throughout the day while suppressing the PID effect, solving the problem that the current insulation monitoring device cannot operate throughout the day.

[0083] In addition, the present invention does not require equipment modification of the existing inverter system, and only requires changing the control logic of the controller. Therefore, the cost is low and the implementation is convenient.

[0084] It should also be noted that the present invention is compatible with all insulation monitoring devices, and there is no need to specifically distinguish the models of insulation monitoring devices.

[0085] To further optimize the above embodiment, the present invention can also monitor insulation anomalies during inverter shutdown and inverter grid connection, and can locate faults.

[0086] Therefore, see Figure 5 , a flow chart of a method for insulation monitoring when an inverter is shut down disclosed in an embodiment of the present invention, the method comprising:

[0087] Step S201: When it is detected that the inverter is shut down, the AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring;

[0088] Step S202: if it is monitored that the AC insulation resistance is lower than the first fault threshold value for a first preset time period, it is determined that an AC insulation fault occurs on the AC side, a first AC insulation fault prompt message is output, and the connection between the low-voltage side system where the inverter is located and the power grid is disconnected;

[0089] Specifically, if the AC insulation resistance value monitored by the AC insulation monitoring device is lower than the first fault threshold value and the time lasts for the first preset time period, it is determined that the AC insulation resistance value is low and an AC insulation fault occurs on the AC side. At this time, while reporting the fault by outputting the first AC insulation fault prompt information, the AC insulation fault is removed by disconnecting the connection between the low-voltage side system where the inverter is located and the power grid.

[0090] In practical applications, the AC insulation fault can be removed by controlling the vacuum circuit breaker (VCB) of the ring cabinet disposed between the inverter and the power grid to trip.

[0091] The values ​​of the first fault threshold and the first preset time period are determined according to actual needs, and the present invention does not limit them here.

[0092] Step S203: if it is monitored that the AC insulation resistance is higher than the first fault threshold and lower than the first alarm threshold for a second preset time period, it is determined that the AC insulation resistance is abnormal, and a first alarm message of abnormal AC insulation resistance is output;

[0093] Among them, the first fault threshold is less than the first alarm threshold, and the values ​​of the first fault threshold, the first alarm threshold and the second preset time period are determined according to actual needs, and the present invention is not limited here.

[0094] Step S204: When the AC insulation resistance is lower than the first alarm threshold, if any monitored AC insulation resistance is higher than the first recovery threshold, it is determined that the AC insulation resistance has returned to normal, and the first alarm information is stopped from being output, and the continuous monitoring operation of the AC insulation resistance is exited.

[0095] The first recovery threshold in this embodiment refers to the lowest limit value of the normal AC insulation resistance. The value of the first recovery threshold depends on actual needs and is not limited in the present invention.

[0096] See also Figure 6 , a flow chart of a method for insulation monitoring after an inverter is connected to the grid is disclosed in an embodiment of the present invention, the method comprising:

[0097] Step S301: When the monitored DC insulation resistance meets the preset normal DC resistance condition, the inverter is controlled to be connected to the grid, and the AC insulation monitoring and DC insulation monitoring are stopped. Meanwhile, during the inverter being connected to the grid, the anti-PID device and the AC insulation monitoring device are controlled;

[0098] Step S302: if it is monitored that the AC insulation resistance is lower than the second fault threshold value for a second preset time period, it is determined that an insulation fault occurs;

[0099] Step S303: Determine whether the insulation fault occurs on the AC side or the DC side according to a preset fault location scheme.

[0100] Specifically, if the AC insulation resistance is monitored to be lower than the second fault threshold, in order to avoid misjudgment, the AC insulation resistance is continuously monitored, and whether the insulation monitoring cycle T2 timer has expired during this period is ignored. If the AC insulation resistance is lower than the second fault threshold for a second preset period of time, it is determined that an insulation fault has occurred, and the subsequent fault location solution is executed at this time; otherwise, the timing logic of the timer continues to be executed.

[0101] It should be noted that, in this embodiment, during the inverter grid connection period, the fault location scheme mainly determines whether the insulation fault occurs on the AC side or the DC side. The specific fault location scheme is as follows:

[0102] The inverter is controlled to shut down and DC insulation monitoring is triggered; if any of the insulation resistance between the positive pole and the negative pole of the PV string and the ground is less than the protection threshold, it is determined that the insulation fault occurs on the DC side;

[0103] And, triggering AC insulation monitoring; if the monitored current AC insulation resistance is lower than the third fault threshold, it is determined that the insulation fault occurs on the AC side.

[0104] The values ​​of the protection threshold and the third fault threshold are determined according to actual needs, and the present invention does not limit them here.

[0105] When an insulation fault occurs on the AC side, a second AC insulation fault prompt message is output;

[0106] Disconnect the low-voltage side system where the inverter is located from the grid.

[0107] In this embodiment, when an insulation fault occurs on the AC side, an AC insulation fault actually occurs. At this time, while reporting the fault by outputting a second AC insulation fault prompt message, the AC insulation fault is removed by disconnecting the connection between the low-voltage side system where the inverter is located and the power grid.

[0108] In practical applications, the AC insulation fault can be removed by controlling the ring cabinet vacuum circuit breaker VCB set between the inverter and the power grid to trip.

[0109] When the connection between the low-voltage side system and the grid is not disconnected, the inverter is controlled to shut down and the insulation resistance is continuously monitored; if the insulation fault (AC / DC insulation fault) returns to normal, the output of the second AC insulation fault prompt information is stopped.

[0110] In this embodiment, if the ring cabinet vacuum circuit breaker VCB does not trip, the insulation resistance monitoring is continuously performed after the inverter is shut down. If the insulation fault returns to normal, the output of the second AC insulation fault prompt information is stopped, and the inverter is restored to the grid.

[0111] It should be noted that the number of insulation fault recovery is allowed to exceed the preset number in one day. If the number of insulation fault recovery exceeds the preset number, it is determined that an insulation fault exists and the insulation fault will no longer be recovered.

[0112] (2) After the inverter is connected to the grid, if it is monitored that the AC insulation resistance is higher than the second fault threshold and lower than the second alarm threshold for a third preset time period, it is determined that the AC insulation resistance is abnormal;

[0113] Outputs the second alarm information of abnormal AC insulation resistance.

[0114] Among them, the second fault threshold is less than the second alarm threshold, and the values ​​of the second fault threshold, the second alarm threshold and the third preset time period are determined according to actual needs, and the present invention is not limited here.

[0115] In this embodiment, after the inverter is connected to the grid, if it is monitored that the AC insulation resistance is higher than the second fault threshold and lower than the second alarm threshold, in order to avoid misjudgment, AC insulation monitoring is continuously performed, and whether the insulation monitoring cycle T2 timer has expired during this period is ignored. If it is monitored that the AC insulation resistance is higher than the second fault threshold and lower than the second alarm threshold for a third preset time period, it is determined that the AC insulation resistance is abnormal, and the second alarm information of the abnormal AC insulation resistance is output.

[0116] (3) After the inverter is connected to the grid, when the AC insulation resistance is lower than the second alarm threshold, if the AC insulation resistance monitored at any time is higher than the second alarm threshold, it is determined that the AC insulation resistance has returned to normal, and the second alarm information is stopped from being output, and the continuous monitoring operation of the AC insulation resistance is exited.

[0117] The value of the second alarm threshold is determined according to actual needs, and the present invention does not limit it here.

[0118] (4) After the inverter is connected to the grid, when the low insulation resistance alarm flag is detected to be in the effective state, the timing time of the insulation monitoring cycle timer is cleared and AC insulation monitoring is forced to be performed continuously;

[0119] When the AC insulation resistance is higher than the second recovery threshold value for a preset AC insulation alarm recovery time, it is determined that the AC insulation resistance has returned to normal, the low insulation resistance alarm flag is switched to an invalid state, and continuous AC insulation monitoring is stopped.

[0120] The value of the preset AC insulation alarm recovery time is determined according to actual needs, such as 10 minutes, and the present invention does not limit this.

[0121] The value of the second restoration threshold is determined according to actual needs, for example, 20k, and the present invention does not limit this.

[0122] It should be noted that during the inverter grid connection period, if the inverter is shut down or a non-insulation fault occurs in the inverter, the insulation monitoring logic when the inverter is shut down is switched to. That is to say, during the inverter grid connection period, when the inverter is shut down or a non-insulation fault occurs in the inverter (i.e., a fault other than the fault shown in the present invention), the timer is reset and the insulation monitoring logic during the inverter grid connection period is switched to the insulation monitoring logic when the inverter is shut down. The insulation monitoring logic when the inverter is shut down can be found in Figure 5 As shown, the insulation monitoring logic during inverter grid connection can be found in Figure 6 shown.

[0123] Corresponding to the above method embodiment, the present invention also discloses an insulation monitoring device.

[0124] See also Figure 7 , a schematic diagram of the structure of an insulation monitoring device disclosed in an embodiment of the present invention, the device is applied to a control device in a new energy power generation system, and the insulation monitoring device includes:

[0125] The AC insulation monitoring unit 401 is used to control the AC insulation monitoring device on the AC side to continuously perform AC insulation monitoring when the inverter is detected to be shut down;

[0126] In actual applications, when the AC switch inside the inverter is disconnected, the inverter stops, and the AC and DC insulation to ground are decoupled. On the AC side, AC insulation monitoring equipment is used to continuously perform AC insulation monitoring.

[0127] The AC insulation monitoring unit 401 is specifically used to control the AC insulation monitoring device on the AC side to continuously perform AC insulation monitoring when the inverter is detected to be shut down if the PID device is installed on the AC side;

[0128] If the anti-PID device is installed on the DC side, when it is detected that the inverter is shut down, the AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring, and the anti-PID device is controlled on the DC side to operate. At this time, the DC side and the AC side do not interfere with each other.

[0129] On the DC side, the anti-PID device is controlled according to the original settings, and the DC side and the AC side complement each other.

[0130] A DC insulation monitoring unit 402 is used to perform DC insulation monitoring before the inverter is connected to the grid when the monitored AC insulation resistance meets the preset normal AC resistance condition and the inverter is working and meets the grid connection condition;

[0131] When the AC insulation resistance meets the preset normal AC resistance condition, it indicates that the AC insulation is normal and no AC insulation fault occurs, wherein the preset normal AC resistance condition refers to the value range of the AC insulation resistance corresponding to the normal AC insulation. The value range is determined according to actual needs and the present invention is not limited here.

[0132] In this embodiment, when the AC insulation is normal and the inverter meets the grid-connected conditions, the grid-connected operation is not performed on the inverter immediately. Instead, DC insulation monitoring is performed before the inverter is grid-connected, that is, DC insulation monitoring is performed through a DC insulation monitoring device, and the inverter is controlled to be grid-connected when it is detected that the DC insulation is normal.

[0133] The control unit 403 is used to control the inverter to be connected to the grid, stop the AC insulation monitoring and the DC insulation monitoring when the monitored DC insulation resistance meets the preset normal DC resistance condition, and control the anti-PID device and the AC insulation to be executed alternately during the inverter being connected to the grid.

[0134] When the DC insulation resistance meets the preset normal DC resistance condition, it indicates that the DC insulation is normal and no DC insulation fault occurs. At this time, the inverter is controlled to be connected to the grid, so that the inverter enters the grid-connected stage from the shutdown stage. At the same time, the AC insulation monitoring and DC insulation monitoring are stopped.

[0135] The preset normal DC resistance condition refers to a value range of the DC insulation resistance corresponding to normal DC insulation. The value range is determined according to actual needs and is not limited in the present invention.

[0136] The all-day switching scheme for anti-PID equipment operation and insulation monitoring equipment is detailed in the method embodiment and Figure 3 , I will not go into details here.

[0137] It should be noted that after the inverter is shut down, the AC side and the DC side are physically isolated. AC insulation monitoring and DC insulation monitoring require two sets of equipment, namely: AC insulation monitoring equipment and DC insulation monitoring equipment. There are differences in the working principles of AC insulation monitoring equipment and DC insulation monitoring equipment. The DC insulation monitoring equipment only operates after the inverter is shut down, while the AC insulation monitoring equipment can operate when the inverter is shut down and connected to the grid.

[0138] In summary, the present invention discloses an insulation monitoring device. When it is detected that the inverter is shut down, the AC insulation monitoring equipment is controlled on the AC side to continuously perform AC insulation monitoring. When the monitored AC insulation resistance meets the preset normal AC resistance condition and the inverter is working and meets the grid-connected condition, DC insulation monitoring is performed before the inverter is connected to the grid. When the monitored DC insulation resistance meets the preset normal DC resistance condition, the inverter is controlled to be connected to the grid, and the AC insulation monitoring and DC insulation monitoring are stopped. At the same time, during the inverter being connected to the grid, the anti-PID equipment and the AC insulation monitoring equipment are controlled to be executed alternately. Usually, the inverter is shut down at night and connected to the grid during the day. Therefore, the present invention divides the switching process of the anti-PID device and the insulation monitoring device into two periods: inverter shutdown and inverter grid connection. When the inverter is shut down, the AC insulation monitoring device continuously performs AC insulation monitoring. When the inverter is grid-connected, starting from the operation of the anti-PID device, the anti-PID device and the AC insulation monitoring device are executed alternately to achieve compatibility between anti-PID operation and AC insulation monitoring. Therefore, the present invention realizes insulation monitoring throughout the day while suppressing the PID effect, solving the problem that the current insulation monitoring device cannot operate all day.

[0139] In addition, the present invention does not require equipment modification of the existing inverter system, and only requires changing the control logic of the controller. Therefore, the cost is low and the implementation is convenient.

[0140] It should also be noted that the present invention is compatible with all insulation monitoring devices, and there is no need to specifically distinguish the models of insulation monitoring devices.

[0141] To further optimize the above embodiment, the present invention can also monitor insulation anomalies during inverter shutdown and inverter grid connection, and can locate faults.

[0142] Therefore, the insulation monitoring device may further include: a shutdown inverter fault monitoring unit.

[0143] A shutdown inverter fault monitoring unit, used for determining that an AC insulation fault occurs on the AC side when the inverter is shut down if it is detected that the AC insulation resistance value is lower than the first fault threshold value for a first preset time period;

[0144] Output first AC insulation fault prompt information, and disconnect the low-voltage side system where the inverter is located from the power grid.

[0145] The shutdown inverter fault monitoring unit is further used to determine that the AC insulation resistance is abnormal if it is monitored that the AC insulation resistance is higher than the first fault threshold and lower than the first alarm threshold for a second preset time period when the inverter is shut down;

[0146] Outputs the first alarm information of abnormal AC insulation resistance.

[0147] The shutdown inverter fault monitoring unit is also used for, when the inverter is shut down, when the AC insulation resistance is lower than the first alarm threshold, if the AC insulation resistance monitored at any time is higher than the first recovery threshold, it is determined that the AC insulation resistance has returned to normal, and the output of the first alarm information is stopped, and the continuous monitoring operation of the AC insulation resistance is exited.

[0148] To further optimize the above embodiment, the insulation monitoring device may further include: a grid-connected inverter fault monitoring unit and a fault locating unit.

[0149] A grid-connected inverter fault monitoring unit, configured to determine that an insulation fault occurs if it is detected that the AC insulation resistance is lower than a second fault threshold value for a second preset time period after the inverter is connected to the grid;

[0150] The fault locating unit is used to determine whether the insulation fault occurs on the AC side or the DC side according to a preset fault locating scheme.

[0151] The fault location unit is specifically used for:

[0152] Controlling the inverter to shut down and triggering DC insulation monitoring;

[0153] If any one of the insulation resistance between the positive pole and the ground and the insulation resistance between the negative pole and the ground of the photovoltaic string is less than the protection threshold, it is determined that the insulation fault occurs on the DC side;

[0154] and, triggering AC insulation monitoring;

[0155] If the monitored current AC insulation resistance is lower than the third fault threshold, it is determined that the insulation fault occurs on the AC side.

[0156] The fault location unit is also specifically used for:

[0157] When the insulation fault occurs on the AC side, outputting second AC insulation fault prompt information;

[0158] The connection between the low-voltage side system where the inverter is located and the power grid is disconnected.

[0159] The fault location unit is also specifically used for:

[0160] When the connection between the low-voltage side system and the power grid is not disconnected, the inverter is controlled to shut down and insulation resistance monitoring is continuously performed;

[0161] If the insulation fault returns to normal, the output of the second AC insulation fault prompt information stops, and the inverter is restored to be connected to the grid.

[0162] To further optimize the above embodiment, the grid-connected inverter fault monitoring unit may also be used for:

[0163] After the inverter is connected to the grid, if it is monitored that the AC insulation resistance is higher than the second fault threshold and lower than the second alarm threshold for a third preset time period, it is determined that the AC insulation resistance is abnormal;

[0164] Outputs the second alarm information of abnormal AC insulation resistance.

[0165] To further optimize the above embodiment, the grid-connected inverter fault monitoring unit may also be used for:

[0166] After the inverter is connected to the grid, when the AC insulation resistance is lower than the second alarm threshold, if the AC insulation resistance monitored at any time is higher than the second alarm threshold, it is determined that the AC insulation resistance has returned to normal, and the output of the second alarm information is stopped, and the continuous monitoring operation of the AC insulation resistance is exited.

[0167] To further optimize the above embodiment, the grid-connected inverter fault monitoring unit may also be used for:

[0168] After the inverter is connected to the grid, when the low insulation resistance alarm flag is detected to be in the effective state, the timing time of the insulation monitoring cycle timer is cleared, and AC insulation monitoring is forced to be performed continuously;

[0169] When the AC insulation resistance is higher than the second recovery threshold value for a preset AC insulation alarm recovery time, it is determined that the AC insulation resistance has returned to normal, the low insulation resistance alarm flag is switched to an invalid state, and continuous AC insulation monitoring is stopped.

[0170] The insulation monitoring device may further include: a switching unit.

[0171] The switching unit is used to switch from the insulation monitoring logic during the inverter grid connection period to the insulation monitoring logic when the inverter is shut down if the inverter is shut down or a non-insulation fault occurs in the inverter during the inverter grid connection period.

[0172] It should be noted that the specific working principles of the various components in the insulation monitoring device can be found in the corresponding part of the method embodiment, which will not be repeated here.

[0173] The present invention also discloses a new energy power generation system, which includes an anti-PID device, an AC insulation monitoring device and a control device, see Figure 6 The control device shown includes a processor 1, a memory 2, and a computer program stored in the memory 2 and executable on the processor.

[0174] The processor 1 and the memory 2 communicate with each other via a communication bus 3 .

[0175] The processor 1 may be a central processing unit (CPU), or an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the embodiments of the present invention.

[0176] The memory 2 may include a high-speed RAM memory, and may also include a non-volatile memory (non-volatile memory), such as at least one disk memory.

[0177] When the processor 1 executes the computer program, the following functions are realized:

[0178] When the inverter is detected to be shut down, the AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring;

[0179] When the monitored AC insulation resistance meets the preset normal AC resistance condition and the inverter meets the grid connection condition, performing DC insulation monitoring before the inverter is connected to the grid;

[0180] When the monitored DC insulation resistance meets the preset normal DC resistance condition, the inverter is controlled to be connected to the grid, and the AC insulation monitoring and the DC insulation monitoring are stopped;

[0181] During the inverter being connected to the grid, the anti-PID device and the AC insulation monitoring device are controlled to be executed alternately.

[0182] In summary, the present invention discloses a new energy power generation system. When the control device in the new energy power generation system detects that the inverter is shut down, the control device controls the AC insulation monitoring equipment on the AC side to continuously perform AC insulation monitoring, and controls the anti-PID equipment on the DC side to operate. When the monitored AC insulation resistance meets the preset normal AC resistance condition, the inverter works and meets the grid-connected condition, DC insulation monitoring is performed before the inverter is connected to the grid. When the monitored DC insulation resistance meets the preset normal DC resistance condition, the inverter is controlled to be connected to the grid, and the AC insulation monitoring and DC insulation monitoring are stopped. At the same time, during the inverter being connected to the grid, the anti-PID equipment and the AC insulation monitoring equipment are controlled to be executed alternately. Usually, the inverter is shut down at night and connected to the grid during the day. Therefore, the present invention divides the switching process of the anti-PID device and the insulation monitoring device into two periods: inverter shutdown and inverter grid connection. When the inverter is shut down, the AC insulation monitoring device continuously performs AC insulation monitoring. When the inverter is grid-connected, starting from the operation of the anti-PID device, the anti-PID device and the AC insulation monitoring device are executed alternately to achieve compatibility between anti-PID operation and AC insulation monitoring. Therefore, the present invention realizes insulation monitoring throughout the day while suppressing the PID effect, solving the problem that the current insulation monitoring device cannot operate all day.

[0183] Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0184] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0185] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An insulation monitoring method, characterized in that: include: When the inverter is detected to be shut down, the AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring; When the monitored AC insulation resistance meets the preset normal AC resistance condition, the inverter is working and meets the grid connection condition, performing DC insulation monitoring before the inverter is connected to the grid; When the monitored DC insulation resistance meets the preset normal DC resistance condition, the inverter is controlled to be connected to the grid, and the AC insulation monitoring and the DC insulation monitoring are stopped. At the same time, during the inverter being connected to the grid, the anti-PID device and the AC insulation monitoring device are controlled to be executed alternately.

2. The insulation monitoring method according to claim 1, characterized in that: When the inverter is shut down, the method further includes: If it is monitored that the AC insulation resistance is lower than the first fault threshold value for a first preset time period, it is determined that an AC insulation fault occurs on the AC side; Output first AC insulation fault prompt information, and disconnect the low-voltage side system where the inverter is located from the power grid.

3. The insulation monitoring method according to claim 2, characterized in that: When the inverter is shut down, the method further includes: If it is monitored that the AC insulation resistance is higher than the first fault threshold and lower than the first alarm threshold for a second preset time period, it is determined that the AC insulation resistance is abnormal; Outputs the first alarm information of abnormal AC insulation resistance.

4. The insulation monitoring method according to claim 3, characterized in that: When the inverter is shut down, the method further includes: When the AC insulation resistance is lower than the first alarm threshold, if the AC insulation resistance monitored at any time is higher than the first recovery threshold, it is determined that the AC insulation resistance has returned to normal, and the first alarm information is stopped from being output, and the continuous monitoring operation of the AC insulation resistance is exited.

5. The insulation monitoring method according to claim 1, characterized in that: When the inverter is connected to the grid, the invention further comprises: If it is monitored that the AC insulation resistance is lower than the second fault threshold value for a second preset time period, it is determined that an insulation fault occurs; According to a preset fault location scheme, it is determined whether the insulation fault occurs on the AC side or the DC side.

6. The insulation monitoring method according to claim 5, characterized in that: Determining that the insulation fault occurs on the AC side or the DC side according to a preset fault location scheme includes: Controlling the inverter to shut down and triggering DC insulation monitoring; If any one of the insulation resistance between the positive pole and the negative pole of the photovoltaic string and the insulation resistance between the positive pole and the ground is less than the protection threshold, it is determined that the insulation fault occurs on the DC side; as well as, Triggering AC insulation monitoring; If the monitored current AC insulation resistance is lower than the third fault threshold, it is determined that the insulation fault occurs on the AC side.

7. The insulation monitoring method according to claim 6, characterized in that: Also includes: When the insulation fault occurs on the AC side, outputting second AC insulation fault prompt information; The connection between the low-voltage side system where the inverter is located and the power grid is disconnected.

8. The insulation monitoring method according to claim 7, characterized in that: Also includes: When the connection between the low-voltage side system and the power grid is not disconnected, the inverter is controlled to shut down and insulation resistance monitoring is continuously performed; If the insulation fault returns to normal, the output of the second AC insulation fault prompt information is stopped, and the inverter is restored to be connected to the grid.

9. The insulation monitoring method according to claim 5, characterized in that: When the inverter is connected to the grid, the invention further comprises: If it is monitored that the AC insulation resistance is higher than the second fault threshold and lower than the second alarm threshold for a third preset time period, it is determined that the AC insulation resistance is abnormal; Outputs the second alarm information of abnormal AC insulation resistance.

10. The insulation monitoring method according to claim 9, characterized in that: When the inverter is connected to the grid, the invention further comprises: When the AC insulation resistance is lower than the second alarm threshold, if the AC insulation resistance monitored at any time is higher than the second alarm threshold, it is determined that the AC insulation resistance has returned to normal, and the output of the second alarm information is stopped, and the continuous monitoring operation of the AC insulation resistance is exited.

11. The insulation monitoring method according to claim 1, characterized in that: When the inverter is connected to the grid, the invention further comprises: When the low insulation resistance alarm flag is detected to be in the effective state, the timing time of the insulation monitoring cycle timer is cleared, and AC insulation monitoring is forced to be performed continuously; When the AC insulation resistance is higher than the second recovery threshold value for a preset AC insulation alarm recovery time, it is determined that the AC insulation resistance has returned to normal, the low insulation resistance alarm flag is switched to an invalid state, and continuous AC insulation monitoring is stopped.

12. The insulation monitoring method according to claim 1, characterized in that: Also includes: During the inverter grid-connection period, if the inverter is shut down or a non-insulation fault occurs in the inverter, the insulation monitoring logic during the inverter grid-connection period is switched to the insulation monitoring logic when the inverter is shut down.

13. The insulation monitoring method according to claim 1, characterized in that: When the inverter is detected to be shut down, the AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring, specifically including: If the anti-PID device is installed on the AC side, when it is detected that the inverter is shut down, the AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring, and the anti-PID device is controlled to stop working; If the anti-PID device is installed on the DC side, when it is detected that the inverter is shut down, the AC insulation monitoring device is controlled on the AC side to continuously perform AC insulation monitoring, and the anti-PID device is controlled on the DC side to operate.

14. An insulation monitoring device, characterized in that: include: The AC insulation monitoring unit is used to control the AC insulation monitoring device on the AC side to continuously perform AC insulation monitoring when the inverter is detected to be shut down; A DC insulation monitoring unit, used for performing DC insulation monitoring before the inverter is connected to the grid when the monitored AC insulation resistance meets the preset normal AC resistance condition and the inverter is working and meets the grid connection condition; The control unit is used to control the inverter to be connected to the grid and stop the AC insulation monitoring and the DC insulation monitoring when the monitored DC insulation resistance meets the preset normal DC resistance condition, and at the same time, control the anti-PID device and the AC insulation to be executed alternately during the inverter being connected to the grid.

15. A new energy power generation system, comprising: An anti-PID device, an AC insulation monitoring device and a control device, wherein the control device includes a memory, a processor and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the insulation monitoring method as described in any one of claims 1 to 13 when executing the computer program.

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