Maximum power point tracking (MPPT) efficiency measuring system of string inverter and measuring method thereof

Abstract

The invention relates to an MPPT efficiency measuring system of a string inverter and a measuring method thereof. The measuring system comprises an integrated testing device and a measuring device. The integrated testing device comprises multiple paths of first connecting terminals used for being connected with a direct-current power supply, multiple paths of second connecting terminals used for being connected with the direct-current input end of the string inverter, and a plurality of direct-current testing modules connected between at least one path of second connecting terminal and the first connecting terminals. The direct current test module jointly measures the direct current input power of the string inverter when the MPPT unit stops working, and the measuring device is used for being connected with the string inverter so as to measure the total efficiency of the string inverter under the normal working condition and the alternating current output power of the string inverter when the MPPT unit stops working, and then the total MPPT efficiency is obtained. By using the measuring system, the MPPT efficiency of the inverter can be simply, conveniently and indirectly tested on site.

Description

Technical Field

[0001] This invention relates to the field of inverter technology, and more particularly to an MPPT efficiency measurement system and method for string inverters. Background Technology

[0002] Under standard or specific operating conditions, each inverter has an MPPT (Maximum Power Point Tracking) unit at the DC input string terminal to maintain the DC input power at the maximum power point. In particular, string inverters have multiple MPPT units.

[0003] Generally, to obtain MPPT efficiency, it is necessary to use a matrix simulator under laboratory conditions to collect MPPT inputs and outputs for calculation. However, this method places a significant cost burden on the testing facility's equipment configuration and power supply (at least 500kW of power). Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an MPPT efficiency measurement system and method for string inverters.

[0005] The technical solution adopted by the present invention to solve its technical problem is: to construct an MPPT efficiency measurement system for string inverters, including an integrated testing device and a measuring device; The integrated testing device includes multiple first connection terminals, multiple second connection terminals, and several DC testing modules; The first connection terminal is used to connect to a DC power supply, and the second connection terminal is used to connect to the DC input terminal of the string inverter, and each second connection terminal is connected to a corresponding first connection terminal. Each of the DC test modules is connected between at least one of the second connection terminals and the first connection terminal to measure the DC input power of the string inverter when the MPPT unit stops working. The measuring device is used to connect to the string inverter to measure the total efficiency of the string inverter under normal operating conditions and its AC output power when the MPPT unit stops working, thereby obtaining the total MPPT efficiency.

[0006] In some embodiments, the integrated testing device further includes a parallel control module for controlling the switching of each of the second connection terminals between a parallel state and an independent state; In the parallel connection state, all positive terminals of the second connection terminals are connected in parallel to stop the MPPT unit of the string inverter from operating.

[0007] In some embodiments, any of the DC test modules includes a current loop and a voltage test module; the integrated test device also includes a power supply module for supplying power to the current loop, and the power supply module is connected to each of the current loops respectively.

[0008] In some embodiments, every two second connection terminals are configured to correspond to one MPPT unit of the string inverter; In each pair of second connection terminals, the positive terminals of the two second connection terminals are first connected to the same current loop and the positive terminal of the same voltage test module in sequence, and then connected to the positive terminal of the first connection terminal on their respective circuits; moreover, the negative terminals of the two second connection terminals are connected to the negative terminal of the first connection terminal on their respective circuits, and the negative terminal of one of the second connection terminals is also connected to the negative terminal of the voltage test module.

[0009] In some embodiments, the current loop is a closed-loop current loop.

[0010] In some embodiments, the current loop has a range of 0–100A and a measurement accuracy of no more than ±0.5%.

[0011] In some embodiments, the voltage measurement range of the voltage testing module is 0 to 2000V, and the measurement accuracy is no higher than ±0.1%.

[0012] In some embodiments, the integrated testing device is provided with an indicator light, which is electrically connected to the signal output terminal of the current loop to provide feedback on the working status of the current loop or the line connection status.

[0013] In some embodiments, the measuring device is a waveform recorder, which has multiple acquisition terminals configured to be connected to the DC input terminal and AC output terminal of the string inverter, respectively.

[0014] This invention also constructs a method for measuring the MPPT efficiency of a string inverter, which utilizes the aforementioned MPPT efficiency measurement system for string inverters. The measurement method includes the following steps: The string inverter is connected to the DC input via an integrated testing device. The overall efficiency of the string inverter in independent state was measured using a measuring device; The inverter is switched to parallel mode by a parallel control module, and then the conversion efficiency of the string inverter is obtained by a DC test module and a measuring device. The total MPPT efficiency of the string inverter is obtained based on the total efficiency of the string inverter in the independent state and the conversion efficiency of the string inverter in the parallel state.

[0015] The present invention has the following advantages: the MPPT efficiency of the inverter can be easily and indirectly tested on site using this measurement system. Compared with traditional laboratory testing, it saves a lot of equipment investment and power supply, and is simple and efficient. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a logic block diagram of the MPPT efficiency measurement system of the string inverter of the present invention, which is connected to the DC power supply and the string inverter. Figure 2 This is a simplified structural diagram of the integrated testing device of the present invention in some embodiments. The diagram shows the internal structure of the integrated testing device, in which connecting wires are omitted. Figure 3 This is a simplified connection diagram between the integrated testing device, string inverter, and waveform recorder of this invention.

[0017] Reference numerals: Integrated test device 1; Housing 11; First connection terminal 12; Second connection terminal 13; Current loop 14; Voltage test module 15; Parallel control module 16; Power supply module 17; Indicator light 18; Measuring device 2; Waveform recorder 21; DC current acquisition terminal 211; DC voltage acquisition terminal 212; AC voltage acquisition terminal 213; AC current acquisition terminal 214; String inverter 200; DC power supply 300. Detailed Implementation

[0018] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0019] It should be noted that the flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0020] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0021] Please refer to Figure 1This invention constructs an MPPT efficiency measurement system for a string inverter 200, which mainly includes an integrated testing device 1 and a measuring device 2. The integrated testing device 1 is connected to a DC power supply 300 and the DC input string of the string inverter 200, respectively, and the measuring device 2 is indirectly / directly connected to the DC input string and the AC output terminal of the string inverter 200.

[0022] Please refer to Figure 2 The integrated test device 1 includes a housing 11, multiple first connection terminals 12, multiple second connection terminals 13, several current loops 14, several voltage test modules 15, and a parallel control module 16.

[0023] The first connection terminal 12 and the second connection terminal 13 are respectively installed on the housing 11, for example, they are respectively inserted into two opposite side walls of the housing 11. The second connection terminal 13 is used to connect to the DC input terminal of the string inverter 200. The second connection terminal 13 has multiple channels, and each channel of the second connection terminal 13 includes a pair of positive and negative connection terminals, which will be referred to as the positive terminal and the negative terminal below. In this embodiment, as shown... Figure 2 As shown, the second connection terminal 13 has a total of 24 channels. The first connection terminal 12 is used to connect to the DC power supply 300. The number of first connection terminals 12 is the same as that of the second connection terminals 13, and they are connected one-to-one.

[0024] Continue to refer to Figure 2 The DC test module is installed inside the housing 11 and connected between the second connection terminal 13 and the first connection terminal 12, which belong to at least one circuit, for collecting the DC input power of the string inverter 200.

[0025] like Figure 2 As shown, the DC test module may include a current loop 14 and a voltage test module 15. The current loop 14 is used to control the current output and achieve accurate current tracking. In some embodiments, the current loop 14 is a closed-loop current loop, which offers higher accuracy and improves the accuracy of the measurement results. Furthermore, the current loop 14 can be a current loop with a current range of 0-100A and an accuracy of ≤0.5%. The voltage test module 15 is used to acquire and obtain the DC input voltage of the string inverter 200. In some embodiments, the voltage test module 15 can be a voltage test module with a voltage range of 0-2000V and an accuracy of ≤0.1%.

[0026] The positive terminals of every two second connection terminals 13 are first connected sequentially to the same current loop 14 and the positive terminal of the same voltage test module 15, and then each is connected to its respective first connection terminal 12 (positive terminal). At the same time, the negative terminals of every two second connection terminals 13 are directly connected to their respective first connection terminals 12 (negative terminals) without passing through the current loop 14; one of the negative terminals of the second connection terminal 13 is also connected to the negative terminal of the voltage test module 15.

[0027] Understandably, the positive terminals of every two second connection terminals 13 are converged by wires and pass through the sensing hole of the same current loop 14. This two-in-one sampling method reduces the number of sensors, lowers the size and cost of the equipment, and, through the synergistic effect of the parallel control module 16, ensures that the total input current of the two channels can be accurately captured in parallel mode.

[0028] Adding a current loop 14 to each channel would require numerous sensors, doubling the cost and causing extreme congestion in the internal wiring of the testing equipment, as well as increasing signal interference. Furthermore, connecting more channels (e.g., 4 or 8 channels) to a single current loop 14 would lead to unclear fault location. If a string in one channel experiences aging, obstruction, or a short circuit, the current data from multiple channels connected in parallel would mask the anomaly in that single channel, resulting in inaccurate test results. Moreover, if more positive lines are connected, the total current may exceed the range of the current loop 14.

[0029] Taking a string inverter 200 with 24 inputs as an example, under normal circumstances, 24 inputs correspond to 12 MPPT units. By passing the positive terminals of every two strings through a current loop 14, the measured current is exactly the total input current of that MPPT.

[0030] The negative terminal of the second connection terminal 13 does not pass through the current loop 14 because the DC loop current is equivalent. Only one negative terminal is connected to the negative terminal of the voltage test module 15 because the potentials of the negative branches are the same. This configuration simplifies the wiring structure, effectively reduces the size of the integrated test device 1, and lowers magnetic field and common-mode interference.

[0031] Continue to refer to Figure 2 The integrated test device 1 also includes a power supply module 17 connected to the current loop 14, which converts the external power supply into a low-voltage power supply suitable for the operation of the current loop 14.

[0032] An indicator light 18 can also be installed on the housing 11 to provide feedback on the operating status of the current loop 14. When the line coupled to the current loop 14 is loose or misconnected, the indicator light 18 will turn off. For example, the indicator light 18 is electrically connected to the signal output terminal of the current loop 14, and a comparator circuit determines whether the signal is within the normal range; when a loose connection occurs in the line, resulting in excessive impedance or no current flow, the state of the indicator light 18 will change.

[0033] The parallel control module 16 is used to control the switching between parallel and independent states of each of the second connection terminals 13. The parallel state can be understood as all the positive terminals of the second connection terminals 13 being connected in parallel, which prevents the MPPT unit of the string inverter 200 from operating. The independent state can be understood as all the positive terminals of the second connection terminals 13 being independently connected, which allows the string inverter 200 to operate normally. It can be understood that the connection methods of the negative terminals of the current string inverter 200 are divided into two mainstream topologies: common negative terminal connection (non-isolated mainstream scheme) and independent negative terminal connection (isolated scheme). For the string inverter 200 with common negative terminal connection, the integrated test device 1 is configured such that all the negative terminals of the second connection terminals 13 are connected together in both parallel and independent states. For the string inverter 200 with independent negative terminal connection, the integrated test device 1 is configured such that all the negative terminals of the second connection terminals 13 are independently connected in the independent state, and connected together in the parallel state.

[0034] In some embodiments (not shown in the figure), the parallel control module 16 includes several sets of contactors and a control bus. The positive and negative terminals of each second connection terminal 13 are connected to the internal DC parallel copper bus via normally open contacts of the contactors. When a trigger signal (e.g., a manual switch or logic level) is received, all contactor coils are energized, forcing all DC positive and negative inputs to physically converge to the same potential point. In other embodiments, switching transistors can be used instead of contactors, and the switching transistors can be controlled to turn on and off by outputting PWM signals or high and low levels.

[0035] The measuring device 2 is used to acquire and obtain the AC output power and total efficiency of the string inverter 200. In some embodiments, the measuring device 2 can be a specially constructed waveform recorder 21 with extended channels. It should be noted that a typical waveform recorder 21 has limited channels, generally only two DC inputs and three AC outputs, far fewer than the requirements of this test, thus necessitating additional expansion of the connection channels. Current string inverters commonly have 12 DC inputs, therefore this waveform recorder 21 is configured to have more than 15 channels (12 DC inputs + 3 AC outputs).

[0036] refer to Figure 3The DC current acquisition terminal 211 of the waveform recorder 21 is configured to acquire the current in the connection circuit between the first connection terminal 12 and the second connection terminal 13, and the DC voltage acquisition terminal 212 of the waveform recorder 21 is configured to acquire the voltage at the second connection terminal 13. The AC voltage acquisition terminal 213 of the waveform recorder 21 is configured to acquire the output voltage of the string inverter 200, and the AC current acquisition terminal 214 of the waveform recorder 21 is configured to acquire the output current of the string inverter 200. As for the measurement method of the waveform recorder 21, existing technology can be referenced, and it will not be elaborated here.

[0037] Overall, with Figure 2 The illustrated embodiment illustrates this example. The string inverter has a total of 24 DC input terminals, each with a pair of positive and negative terminals. The positive terminal of every two terminals is first connected to the current loop 14 (closed loop), and then to the positive terminal of the voltage testing device. The negative terminal of every two terminals does not pass through the current loop 14, and one of them is connected to the negative terminal of the voltage testing device. The power supply provides low-voltage power to the 12 current loops 14. During measurement, the integrated testing device 1, in conjunction with the waveform recorder 21, first measures the total efficiency of the string inverter 200 under normal operating conditions. Then, through the parallel control module 16, the DC inputs of all string terminals are forced into parallel connection. At this time, the MPPT unit no longer operates. Measurement is taken again. The DC power of the string inverter 200 after the terminals are connected in parallel is obtained through the current loop 14, and the total AC output power of the string inverter 200 after the terminals are connected in parallel is obtained through the voltage testing device. Thus, the conversion efficiency of the string inverter 200 under MPPT non-operational conditions (pure hardware circuit condition) is obtained. Finally, the total MPPT efficiency is obtained based on the total efficiency and conversion efficiency of the string inverter 200.

[0038] The relevant formulas for calculating the overall efficiency, conversion efficiency, and MPPT efficiency of an inverter include: Conversion efficiency: (1) AC output power of the inverter DC power of the inverter Overall efficiency of the inverter: (2) If the inverter is a string inverter with n MPPT inputs, the total efficiency of the string inverter 200 is: (3) in, For the string inverter 200 to operate normally, during the cycle Overall MPPT efficiency within; Let be the instantaneous efficiency of the i-th MPPT of the string inverter 200 at a certain moment.

[0039] Additionally, the formula for calculating MPPT efficiency from related technologies is attached here: (4) MPPT input power to inverter main unit (kW); : Instantaneous power (kW) of the i-th string input of the inverter; Inverter power monitoring cycle.

[0040] In some embodiments, the measurement system may further include a computation module for data processing. The data measured by the current loop 14 and voltage test module 15 of each group can be transmitted to the computation module to obtain the total DC input power; then, the computation module combines the total efficiency of the string inverter 200 in the independent state measured by the measurement device 2 with its AC output power in the parallel state to calculate the total MPPT efficiency.

[0041] It should be noted that the calculation module can be a device independent of the integrated test device 1, or it can be integrated into a module of the integrated test device 1; there is no limitation on this. The calculation module is not a necessary component of this measurement system and can also be calculated manually after obtaining the relevant measurement data.

[0042] This invention also provides a method for measuring the MPPT efficiency of a string inverter 200, characterized in that the measurement is performed using the aforementioned MPPT efficiency measurement system for the string inverter 200. Specifically, it includes: S1: Connect the DC input to the string inverter 200 through the integrated test device 1; S2: Using measuring device 2, the total efficiency of string inverter 200 in independent state is measured; S3: Switch to parallel state through parallel control module 16, and then obtain the conversion efficiency of string inverter 200 using DC test module and measuring device 2; S4: Based on the total efficiency of the string inverter 200 in the independent state and the conversion efficiency of the string inverter 200 in the parallel state, the total MPPT efficiency of the string inverter 200 is calculated.

[0043] S1 includes: connecting the DC input terminal of the string inverter 200 to the second connection terminal 13 of the integrated test device 1, and connecting the first connection terminal 12 of the integrated test device 1 to the DC power supply 300.

[0044] The operations in S3 and S4 can be performed by the calculation module or manually, and there is no limitation on this; the conversion efficiency is based on the measured AC output power and DC input power.

[0045] In summary, this system allows for convenient and indirect on-site testing of inverter MPPT efficiency (e.g., at photovoltaic power plants), saving significant equipment investment and power requirements compared to traditional laboratory testing. It is simple, efficient, and cost-effective. Furthermore, this integrated testing device 1 greatly reduces the wiring layout required for on-site testing, allows for rapid test results, and minimizes the risk of equipment damage during transport.

[0046] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. An MPPT efficiency measurement system for string inverters, characterized in that, It includes an integrated testing device (1) and a measuring device (2); The integrated test device (1) includes multiple first connection terminals (12), multiple second connection terminals (13), and several DC test modules; The first connection terminal (12) is used to connect to the DC power supply (300), and the second connection terminal (13) is used to connect to the DC input terminal of the string inverter, and each second connection terminal (13) is connected to the corresponding first connection terminal (12). Each of the DC test modules is connected between at least one of the second connection terminals (13) and the first connection terminal (12) to measure the DC input power of the string inverter when the MPPT unit stops working. The measuring device (2) is used to connect to the string inverter to measure the total efficiency of the string inverter under normal operating conditions and its AC output power when the MPPT unit stops working, thereby obtaining the total MPPT efficiency.

2. The MPPT efficiency measurement system for string inverters according to claim 1, characterized in that, The integrated test device (1) also includes a parallel control module (16) for controlling the switching of each of the second connection terminals (13) between parallel and independent states; In the parallel state, all positive terminals of the second connection terminals (13) are connected in parallel to stop the MPPT unit of the string inverter from working.

3. The MPPT efficiency measurement system for string inverters according to claim 1 or 2, characterized in that, Each of the DC test modules includes a current loop (14) and a voltage test module (15); the integrated test device (1) is also provided with a power supply module (17) for supplying power to the current loop (14), and the power supply module (17) is connected to each of the current loops (14).

4. The MPPT efficiency measurement system for string inverters according to claim 3, characterized in that, Each pair of second connection terminals (13) is configured to correspond to one MPPT unit of the string inverter; In each pair of second connection terminals (13), the positive terminals of the two second connection terminals (13) are first connected to the same current loop (14) and the positive terminal of the same voltage test module (15) in sequence, and then connected to the positive terminal of the first connection terminal (12) on their respective paths; moreover, the negative terminals of the two second connection terminals (13) are connected to the negative terminal of the first connection terminal (12) on their respective paths, and the negative terminal of one of the second connection terminals (13) is also connected to the negative terminal of the voltage test module (15).

5. The MPPT efficiency measurement system for string inverters according to claim 3, characterized in that, The current loop (14) is a closed-loop current loop.

6. The MPPT efficiency measurement system for string inverters according to claim 3, characterized in that, The current loop (14) has a range of 0 to 100A and a measurement accuracy of no more than ±0.5%.

7. The MPPT efficiency measurement system for string inverters according to claim 3, characterized in that, The voltage measurement range of the voltage test module (15) is 0 to 2000V, and the measurement accuracy is no higher than ±0.1%.

8. The MPPT efficiency measurement system for string inverters according to claim 3, characterized in that, The integrated test device (1) is equipped with an indicator light (18), which is electrically connected to the signal output terminal of the current loop (14) to provide feedback on the working status or line connection status of the current loop (14).

9. The MPPT efficiency measurement system for string inverters according to claim 3, characterized in that, The measuring device (2) is a waveform recorder (21), which has multiple acquisition terminals and is configured to be connected to the DC input terminal and AC output terminal of the string inverter respectively.

10. A method for measuring the MPPT efficiency of a string inverter, characterized in that, The MPPT efficiency measurement system for string inverters according to any one of claims 2-9 is used for measurement, and the measurement method includes the following steps: The string inverter is connected to the DC input via an integrated test device (1); The overall efficiency of the string inverter in independent state was measured using the measuring device (2); The parallel control module (16) switches to the parallel state, and then the DC test module and measuring device (2) are used to obtain the conversion efficiency of the string inverter. Based on the total efficiency of the string inverter in independent state and the conversion efficiency of the string inverter in parallel state, the total MPPT efficiency of the string inverter is calculated.

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