Automatic detection method for CT (Computed Tomography) installation state

Abstract

The invention relates to the technical field of energy storage inverters, in particular to an automatic detection method of a CT installation state. Comprising the following steps: periodically outputting a preset power pulse to a power grid end through an inverter; adjusting the output power of the inverter, and collecting and calculating the power change of the power grid end CT; judging the installation direction of the CT based on the change of the output power of the inverter and the change of the power of the power grid end CT; based on the change of the power grid end CT power along with the change of the output power of the inverter, whether the external CT of the energy storage mixed network inverter is installed and the installation direction are automatically detected by continuously adjusting the output power of the inverter and collecting the change of the power grid end CT power, so that the difficulty of field installation is reduced, the installation efficiency is improved, and the installation cost is reduced. And meanwhile, the situation that the CT cannot work due to the wrong CT installation direction is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of energy storage inverters, in particular to an automatic detection method for a CT installation state. Background Art

[0002] In energy storage hybrid grid inverter products, the external CT (current transformer) is a relatively important component as a sensor device for sampling the current at the grid end. The CT sensor samples the current at the household grid end to control the output power of the inverter, which is used to realize the function of hybrid grid load (the inverter power is provided to the load and not fed into the grid). In traditional use, there is either no CT setting option, and the installation direction of the CT must be exactly the same as the preset direction of the inverter to work; or after the CT wiring is installed, the direction of the CT needs to be manually set, and the direction set by the device must be exactly the same as the actual installation direction to work normally. However, the on-site installation environment is complex and the installation personnel have different levels. It is easy for the machine to fail to work properly due to the wrong CT installation direction.

[0003] At present, there are two main installation directions for external CTs: fixed and parameter setting. In the fixed method, the inverter device assumes that the CT installation direction is correct by default without any processing. This method is not flexible enough. When the CT installation direction is incorrect, it is necessary to manually change the CT installation direction on site. The parameter setting is to set the CT direction through the setting parameters on the inverter screen. Although this solution does not require on-site processing, it also requires determining the installation direction of the CT before it can be set correctly. There is a problem of setting errors, and when the external CT has not been installed, if the inverter parameters are set to enable, the inverter cannot work normally.

[0004] Therefore, it is very important for those skilled in the art to design an automatic detection method that can quickly and conveniently detect the installation status of a CT. Summary of the invention

[0005] The technical problem to be solved by the embodiments of the present invention is to provide an automatic detection method that can quickly and conveniently detect the installation status of a CT, so as to solve the problem in the prior art that the operation is complicated and prone to errors.

[0006] The present invention discloses an automatic detection method for CT installation status, which is used in an energy storage hybrid grid inverter system, and the method comprises the following steps:

[0007] The inverter periodically outputs preset power pulses to the grid;

[0008] Adjust the inverter output power, and collect and calculate the changes in CT power at the grid end;

[0009] The installation direction of the CT is determined based on the changes in the inverter output power and the changes in the CT power at the grid end.

[0010] Optionally, the “determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power” comprises the following steps:

[0011] Set the power flowing from the inverter to the grid as positive, and the power flowing from the grid to the inverter as negative;

[0012] When the inverter output power increases, if the grid-side CT power decreases accordingly, it is determined that the installation direction of the CT points to the inverter;

[0013] If the CT power at the grid end increases accordingly, it is determined that the installation direction of the CT points to the grid end.

[0014] Optionally, the “determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power” further includes the following steps:

[0015] Set the power flowing from the inverter to the grid as positive, and the power flowing from the grid to the inverter as negative;

[0016] When the inverter output power decreases, if the grid-side CT power increases accordingly, it is determined that the installation direction of the CT points to the inverter;

[0017] If the CT power at the grid end decreases accordingly, it is determined that the installation direction of the CT points to the grid end.

[0018] Optionally, the “determining the installation direction of the CT based on the change in the inverter output power and the change in the CT power” further includes calculating the change in the inverter output power according to the following formula:

[0019] ΔP 逆变 =P 逆变_N -P 逆变_N-1

[0020] Among them, ΔP 逆变 is the change in inverter output power, P 逆变_N is the inverter output power of the current cycle, P 逆变_N-1 is the inverter output power of the previous cycle.

[0021] Optionally, the “determining the installation direction of the CT based on the change in the inverter output power and the change in the CT power” further includes calculating the change in the grid-side CT power according to the following formula:

[0022] ΔP CT =P CT_N -P CT_N-1

[0023] Among them, ΔP CT is the change in CT power at the grid end, P CT_Nis the grid-side CT power sampled in the current cycle, P CT_N-1 It is the grid-side CT power sampled in the previous cycle.

[0024] Optionally, the “determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power” further includes the following steps:

[0025] When ΔP 逆变 >P TH , and ΔP CT <-P TH , or ΔP 逆变 <-P TH , and ΔP CT >P TH When , it is determined that the installation direction of CT is pointing to the inverter; where P TH As the judgment threshold, let P TH =0.5×P 逆变 .

[0026] Optionally, the “determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power” further includes the following steps:

[0027] When ΔP 逆变 <-P TH , and ΔP CT <P TH , or ΔP 逆变 <-P TH , and ΔP CT <-P TH When , it is determined that the installation direction of CT is toward the grid end; where P TH As the judgment threshold, let P TH =0.5×P 逆变 .

[0028] Optionally, the “determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power” further includes the following steps:

[0029] When |ΔP 逆变 |>P TH , and |ΔP CT |<0.5×P TH When , it is judged that CT is not installed; among them, P TH As the judgment threshold, let P TH =0.5×P 逆变 .

[0030] Optionally, the method further comprises the following steps:

[0031] The installation direction of the CT is judged based on the change of the inverter output power and the change of the CT power at the grid end for many times, and the judgment results are counted. If the count of the same result is greater than the preset number of times, the judgment is considered successful;

[0032] After the judgment is successful, the detection result is written into the CT enable register and the CT installation direction register in the energy storage hybrid inverter system, and the CT automatic detection function is automatically turned off.

[0033] Optionally, the energy storage hybrid grid inverter is a single-phase inverter or a split-phase inverter; the inverter output power is active power.

[0034] Compared with the prior art, the beneficial effect of the automatic detection method of the CT installation status provided by the embodiment of the present invention is that: by designing an automatic detection method of the CT installation status, it is used in the energy storage hybrid grid inverter system, including periodically outputting preset power pulses to the grid end through the inverter; adjusting the inverter output power, and collecting and calculating the change of the CT power at the grid end; judging the installation direction of the CT based on the change of the inverter output power and the change of the CT power at the grid end; based on the change of the CT power at the grid end with the change of the inverter output power, the present invention automatically detects whether the external CT of the energy storage hybrid grid inverter is installed and the installation direction by continuously adjusting the inverter output power and collecting the change of the CT power at the grid end, thereby reducing the difficulty of on-site installation, improving installation efficiency, and avoiding the CT from failing to work due to the wrong installation direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments, in which:

[0036] Figure 1 The following is a flow chart of the automatic detection method of CT installation status provided by the embodiment of the present invention. Figure 1 ;

[0037] Figure 2 The structure of the photovoltaic energy storage system provided by the embodiment of the present invention is Figure 1 ;

[0038] Figure 3 The structure of the photovoltaic energy storage system provided by the embodiment of the present invention is Figure 2 ;

[0039] Figure 4 The following is a flow chart of the automatic detection method of CT installation status provided by the embodiment of the present invention. Figure 2 ;

[0040] Figure 5 The following is a flow chart of the automatic detection method of CT installation status provided by the embodiment of the present invention. Figure 3 . DETAILED DESCRIPTION

[0041] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. Now, in conjunction with the accompanying drawings, the preferred embodiments of the present invention are described in detail.

[0042] like Figures 1 to 5 As shown, the present invention provides a specific embodiment of a method for automatically detecting the installation status of a CT.

[0043] An automatic detection method for CT installation status, used in energy storage hybrid grid inverter system, reference Figure 1 , including the following steps:

[0044] S1, periodically outputting preset power pulses to the grid through the inverter;

[0045] S2, adjust the inverter output power, and collect and calculate the change of CT power at the grid end;

[0046] S3. Determine the installation direction of the CT based on the change of the inverter output power and the change of the CT power at the grid end.

[0047] Specifically, a common application of photovoltaic energy storage hybrid inverter is anti-backflow application, that is, the inverter is in the state of grid connection, refer to Figure 2 The power of the photovoltaic 100 and battery 200 sides is output through the inverter 300 and fed back to the local load 400. The power output by the inverter 300 is usually less than or equal to the power of the local load 400, that is, the power fed back by the inverter 300 to the power grid 500 needs to be less than or equal to 0. The CT600 (current transformer) is a sensor, and its function is to detect the current at the end of the power grid 500 to help the inverter system control the size and stability of the output current so that the system operates within a safe range. After detecting the current at the power grid end, the CT can also be used as an overload protection to prevent equipment damage or other accidents.

[0048] Further, refer to Figure 3 CT600 has an installation direction during the installation process. Generally speaking, there is an arrow on CT600, and the direction of the arrow is the positive current detection direction of CT600. That is to say, when the current direction is consistent with the direction of CT600, the detected power will be greater than or equal to 0, and when the current direction is opposite to the direction of CT600, the detected power will be less than 0. In practical applications, the arrow direction of CT600 is required to be consistent with the default direction of inverter 300, and the positive current detection direction of CT600 is required to be consistent with the default direction of inverter 300.

[0049] At present, there are generally two types of detection of CT installation direction, a fixed solution and a parameter setting solution. In the fixed solution, the inverter device generally assumes that the CT installation direction is correct and no processing is required. This solution is not flexible enough. When the CT installation direction on site is inconsistent with the correct installation direction of the inverter device by default, the CT installation direction must be changed manually on site. Although the parameter setting solution does not require on-site changes, it is also necessary to confirm the installation direction of the CT before the correct parameters can be set. It is also easy to have setting errors during the setting process. In addition, when the external CT has not been installed, if the enable is set in the inverter parameters, the inverter will not work properly.

[0050] The present invention provides an automatic detection method for the installation status of a CT, which uses inverter software to automatically detect whether an external CT of an energy storage hybrid grid inverter is installed and the installation direction, thereby reducing the difficulty of on-site installation, improving installation efficiency, and avoiding CT failure to work due to incorrect CT installation direction.

[0051] The automatic detection method of the CT installation status is to first periodically output low-power pulses to the grid end through the inverter. At this time, the CT will detect the current at the grid end. The installation status and installation direction of the CT can be determined by detecting the power change of the CT.

[0052] In the initial state, when the power of the inverter is 0, the absolute value of the CT power will be equal to the absolute value of the load power. When the power of the inverter is 0 and the CT direction points to the inverter, the CT power value will be equal to the load power value. When the power of the inverter is 0 and the CT direction points to the grid end, the CT power value will be equal to the negative of the load power value. When the power of the inverter increases and the CT direction points to the inverter, the CT power at the grid end will decrease. When the power of the inverter increases and the CT direction points to the grid end, the CT power at the grid end will increase. When the output power of the inverter decreases and the CT direction points to the inverter, the CT power at the grid end will increase. When the output power of the inverter decreases and the CT direction points to the inverter, the CT power at the grid end will decrease.

[0053] Therefore, the inverter periodically outputs preset power pulses to the grid end, and continuously adjusts the output power of the inverter to increase or decrease the output power of the inverter. At the same time, the grid-end CT power is collected and calculated to increase or decrease. By analyzing the changes in the grid-end CT power as the inverter output power changes, the installation direction of the CT can be determined.

[0054] In one embodiment, reference Figure 4 , the “determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power” comprises the following steps:

[0055] S110, setting the power flowing from the inverter to the grid to be positive, and the power flowing from the grid to the inverter to be negative;

[0056] S111. When the output power of the inverter increases, if the power of the CT at the grid end decreases accordingly, the installation direction of the CT points to the inverter;

[0057] S112. If the power of the CT at the grid end increases accordingly, the installation direction of the CT points to the grid end.

[0058] S121, when the output power of the inverter decreases, if the power of the CT at the grid end increases accordingly, it is determined that the installation direction of the CT points to the inverter;

[0059] S122: If the power of the CT at the grid end decreases accordingly, it is determined that the installation direction of the CT points to the grid end.

[0060] Specifically, based on the principle that "when the power of the inverter is 0 and the CT direction points to the grid end, the CT power value will be equal to the negative of the load power value; when the power of the inverter increases and the CT direction points to the inverter, the CT power at the grid end will decrease, and when the power of the inverter increases and the CT direction points to the grid end, the CT power at the grid end will increase; when the output power of the inverter decreases and the CT direction points to the inverter, the CT power at the grid end will increase, and when the output power of the inverter decreases and the CT direction points to the grid end, the CT power at the grid end will decrease", the output power of the inverter is increased and then the change of the CT power at the grid end is obtained, so that the installation direction of the CT can be automatically detected. If the output power of the inverter increases and the CT power at the grid end decreases, the installation direction of the CT points to the inverter; if the output power of the inverter increases and the CT power at the grid end increases, the installation direction of the CT points to the grid end; if the output power of the inverter decreases and the CT power at the grid end increases, the installation direction of the CT points to the inverter, and if the output power of the inverter decreases and the CT power at the grid end decreases, the installation direction of the CT points to the grid end.

[0061] In one of the embodiments, the “determining the installation direction of the CT based on the change in the inverter output power and the change in the CT power” further includes calculating the change in the inverter output power according to the following formula:

[0062] ΔP 逆变 =P 逆变_N -P 逆变_N-1

[0063] Among them, ΔP 逆变 is the change in inverter output power, P 逆变_N is the inverter output power of the current cycle, P 逆变_N-1 is the inverter output power of the previous cycle.

[0064] Specifically, the change in inverter output power can be obtained by collecting the inverter output power values ​​within multiple cycles of the inverter, and subtracting the inverter output power value of the previous cycle relative to the current cycle from the inverter output power value of the current cycle to obtain the change value of the inverter output power from the previous cycle to the current cycle.

[0065] In one of the embodiments, the “determining the installation direction of the CT based on the change in the inverter output power and the change in the CT power” further includes calculating the change in the grid-side CT power according to the following formula:

[0066] ΔP CT =P CT_N -P CT_N-1

[0067] Among them, ΔP CT is the change in CT power at the grid end, P CT_N is the grid-side CT power sampled in the current cycle, P CT_N-1 It is the grid-side CT power sampled in the previous cycle.

[0068] Specifically, the change in grid-end CT power can be obtained by collecting the grid-end CT power values ​​of the grid-end CT in multiple cycles, and subtracting the grid-end CT power value of the previous cycle relative to the current cycle from the grid-end CT power value of the current cycle to obtain the change value of the grid-end CT power from the previous cycle to the current cycle.

[0069] The installation direction of the CT can be automatically detected and determined by analyzing the change value of the inverter output power and the change value of the CT power at the grid end.

[0070] In one of the embodiments, the “determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power” further includes the following steps:

[0071] When ΔP 逆变 >P TH , and ΔP CT <-P TH , or ΔP 逆变 <-P TH , and ΔP CT >P TH When , it is determined that the installation direction of CT is pointing to the inverter; where P TH As the judgment threshold, let P TH =0.5×P 逆变 .

[0072] That is, half of the inverter's output power in the current cycle is used as the judgment threshold of the inverter power change value. When the change value of the inverter output power is greater than the judgment threshold and the change value of the grid-side CT power is less than the negative number of the judgment threshold, it is judged that the installation direction of the CT is pointing to the inverter.

[0073] In one of the embodiments, the “determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power” further includes the following steps:

[0074] When ΔP 逆变 <-P TH , and ΔP CT <P TH , or ΔP 逆变 <-P TH , and ΔP CT <-P TH When , it is determined that the installation direction of CT is toward the grid end; where P TH As the judgment threshold, let P TH =0.5×P 逆变 .

[0075] That is, half of the inverter's output power in the current cycle is used as the judgment threshold of the inverter power change value. When the change value of the inverter output power is less than the negative number of the judgment threshold and the change value of the grid-end CT power is less than the judgment threshold, it is judged that the installation direction of the CT is pointing to the grid end.

[0076] In one of the embodiments, the “determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power” further includes the following steps:

[0077] When |ΔP 逆变 |>P TH , and |ΔP CT |<0.5×P TH When , it is judged that CT is not installed; among them, P TH As the judgment threshold, let P TH =0.5×P 逆变 .

[0078] That is, half of the inverter's output power in the current cycle is used as the judgment threshold of the inverter power change value. When the absolute value of the inverter output power change value is greater than the judgment threshold and the absolute value of the grid-side CT power change value is less than half of the judgment threshold, it is judged that the CT is not installed.

[0079] In one embodiment, reference Figure 5 , further comprising the following steps:

[0080] S4, judging the installation direction of the CT based on the change of the inverter output power and the change of the CT power at the grid end for multiple times, and counting the judgment results. If the count of the same result is greater than the preset number of times, it is considered that the judgment is successful;

[0081] S5. After the judgment is successful, the detection result is written into the CT enable register and the CT installation direction register in the energy storage hybrid inverter system, and the CT automatic detection function is automatically turned off.

[0082] Specifically, by repeatedly judging the installation direction of the CT based on the change of the inverter output power and the change of the grid-side CT power, interference and misjudgment can be avoided to improve the accuracy, credibility and stability of the judgment result.

[0083] In one embodiment, the energy storage hybrid grid inverter is a single-phase inverter or a split-phase inverter.

[0084] Specifically, a single-phase inverter is an electronic device that converts direct current into single-phase alternating current. It converts the input direct current into single-phase alternating current with a specified frequency and voltage, and is able to provide continuous power supply when the power grid is out of power. A split-phase inverter is used to convert direct current into alternating current. It is able to split the input direct current into two paths, and then convert it into two alternating current phases through an inverter, usually alternating current with a phase difference of 120 degrees, to provide additional power output and better power balance.

[0085] In one of the embodiments, the inverter output power is active power.

[0086] Specifically, active power can actually perform power conversion in the circuit to generate actual functions such as light, heat, and mechanical movement. Active power is used to enable a device or system to perform actual functions. It can make the current and voltage in phase, and make the current and voltage reach the maximum or minimum value at the same time. By injecting active power for detection, better change value measurement can be performed.

[0087] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. For those skilled in the art, the technical solutions described in the above embodiments can be modified, or some of the technical features therein can be replaced by equivalents; and all these modifications and replacements should fall within the protection scope of the claims attached to the present invention.

Claims

1. A method for automatically detecting the installation status of a CT, used in an energy storage hybrid grid inverter system, characterized in that: The following steps are involved: The inverter periodically outputs preset power pulses to the grid; Adjust the inverter output power, and collect and calculate the changes in CT power at the grid end; The installation direction of the CT is determined based on the changes in the inverter output power and the changes in the CT power at the grid end.

2. The automatic detection method of CT installation status according to claim 1, characterized in that: The “determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power” comprises the following steps: Set the power flowing from the inverter to the grid as positive, and the power flowing from the grid to the inverter as negative; When the inverter output power increases, if the grid-side CT power decreases accordingly, the CT installation direction points to the inverter; If the CT power at the grid end increases accordingly, the installation direction of the CT should point to the grid end.

3. The automatic detection method of CT installation status according to claim 2, characterized in that: The "determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power" also includes the following steps: Set the power flowing from the inverter to the grid as positive, and the power flowing from the grid to the inverter as negative; When the inverter output power decreases, if the grid-side CT power increases accordingly, the CT installation direction points to the inverter; If the CT power at the grid end decreases accordingly, the installation direction of the CT should point to the grid end.

4. The automatic detection method of CT installation status according to claim 3, characterized in that: The “determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power” also includes calculating the change of the inverter output power according to the following formula: ΔP 逆变 =P 逆变_N -P 逆变_N-1 Among them, ΔP 逆变 is the change in inverter output power, P 逆变_N is the inverter output power of the current cycle, P 逆变_N-1 is the inverter output power of the previous cycle.

5. The automatic detection method of CT installation status according to claim 4, characterized in that: The “determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power” also includes calculating the change of the grid-side CT power according to the following formula: ΔP CT =P CT_N -P CT_N-1 Among them, ΔP CT is the change in CT power at the grid end, P CT_N is the grid-side CT power sampled in the current cycle, P CT_N-1 It is the grid-side CT power sampled in the previous cycle.

6. The automatic detection method of CT installation status according to claim 5, characterized in that: The "determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power" also includes the following steps: When ΔP 逆变 >P TH , and ΔP CT <-P TH , or ΔP 逆变 <-P TH , and ΔP CT >P TH When , it is determined that the installation direction of CT is pointing to the inverter; where P TH As the judgment threshold, let P TH =0.5×P 逆变 .

7. The automatic detection method of CT installation status according to claim 5, characterized in that: The "determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power" also includes the following steps: When ΔP 逆变 <-P TH , and ΔP CT <P TH , or ΔP 逆变 <-P TH , and ΔP CT <-P TH When , it is determined that the installation direction of CT is toward the grid end; where P TH As the judgment threshold, let P TH =0.5×P 逆变 .

8. The automatic detection method of CT installation status according to claim 5, characterized in that: The "determining the installation direction of the CT based on the change of the inverter output power and the change of the CT power" also includes the following steps: When ΔP 逆变 >P TH , and ΔP CT <0.5×P TH When , it is judged that CT is not installed; among them, P TH As the judgment threshold, let P TH =0.5×P 逆变 .

9. The automatic detection method of CT installation status according to claim 1, characterized in that: The following steps are also included: The installation direction of the CT is judged based on the change of the inverter output power and the change of the CT power at the grid end for many times, and the judgment results are counted. If the count of the same result is greater than the preset number of times, the judgment is considered successful; After the judgment is successful, the detection result is written into the CT enable register and the CT installation direction register in the energy storage hybrid inverter system, and the CT automatic detection function is automatically turned off.

10. The automatic detection method of CT installation status according to claim 1, characterized in that: The energy storage hybrid grid inverter is a single-phase inverter or a split-phase inverter; the inverter output power is active power.

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