Design and implementation of energy storage inverter test platform

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Design and implementation of energy storage inverter test platform [Copy link]

The energy storage industry has exploded, and energy storage inverters, as an important link in the industry chain, are also rapidly increasing in value. Therefore, it is particularly important to develop a systematic testing and debugging platform for energy storage inverters.

With the diversified development of new energy electronic devices, the complexity of control program algorithms requires more data to be obtained through test platforms. Although traditional test platforms can meet basic test needs, they cannot better meet the requirements for data transmission speed.

The test platform has high requirements for data transmission rate in the process of acquiring data, and also needs to have more practical functions.

Based on this, the current research focus is to build to the platform's actual needs for human-computer interaction of energy storage inverters .

1. Test platform requirements analysis

1.1 Energy Storage Inverter

In the construction of smart grids, energy storage inverters can perform some special functions with their bidirectional conversion function. As a bidirectional converter, it can not only complete the energy transmission between grid power, but also complete the energy transmission between energy storage power, and is suitable for a variety of DC energy storage units.

In the DC energy storage unit, the energy storage inverter can quickly complete the function of distributed power generation and improve the grid's acceptance of renewable energy. According to the characteristics of the system, during the low load period, more power generation needs to be stored for emergency use. The energy released during the peak load period can effectively improve the power supply quality of the grid. Figure 1 shows the structural network of the energy storage inverter in the grid.

Energy storage inverters are suitable for charging and discharging large-capacity energy storage batteries. When used in charging and discharging systems, they can achieve bidirectional flow, realizing advantages such as intelligence, stability and safety.

During the entire development process of the energy storage inverter, an oscilloscope is used to complete a comprehensive test of the electrical signal. The actual electrical signal quantity obtained by using the energy storage inverter control algorithm is relatively small. In the process of using an oscilloscope to detect a large amount of data, there will be some problems. Although the electrical signal of the energy storage inverter can be obtained, after the signal is converted by the sensor, the accuracy of the collected quantity cannot be guaranteed by AD.

Therefore, in order to ensure the normal operation of the system, it is very necessary to observe the variables of the program. In the process of program observation, there are many ways to use breakpoint observation . When debugging and applying weak current circuit programs, breakpoint observation is a very effective debugging method. However, in the debugging of high-power equipment, breakpoint observation cannot better predict the status of high-power equipment, which is easy to cause short-circuit failures and has certain safety hazards, which is very unfavorable for the safe operation of workers.

By debugging the software, the refresh function can be guaranteed while reducing safety risks . During the testing of high-power equipment of energy storage inverters, many fault problems will be encountered. After a fault occurs, if the variable information of the algorithm is not saved in time, the location and cause of the fault point cannot be accurately obtained.

Therefore, in the process of testing and debugging the energy storage inverter, the size of the harmonic content is an important indicator of the test . The harmonic content of the energy storage inverter can be obtained in real time, which is very important for the testing of the energy storage inverter. Based on the above problems, it is necessary to develop an energy storage inverter test software platform.

1.2 Requirements Analysis

The design of the energy storage inverter test software platform consists of two parts: the human-computer interaction test platform and the data acquisition module . The test platform is shown in Figure 2.

For the sensor module of the energy storage inverter, completing the signal conversion is a highlight . By acquiring the data of the AD small signal, the DSP controller is used to process it and then the data is sent to the PC through the Ethernet communication module.

The test software platform reads the data information in the Ethernet through the PC port, realizes the data processing, and completes the comprehensive analysis of the data results through the test platform.

Based on the above overall design of the energy storage inverter test software platform, the functional module requirements analysis is carried out:

(1) High-speed communication between upper and lower computers: The traditional bus communication rate is 460800bps[4]. In order to improve the accuracy of communication, the most commonly used rate is 9600bps. The communication rate of the CAN bus is 1Mbps, which is quite different from the bus of industrial Ethernet.

The reliability of traditional buses is low, and only CAN or industrial Ethernet can meet the design requirements of communication transmission stability. Since the host computer generally uses a PC in the communication between the upper and lower computers, the CAN bus needs to process data through an interface card when communicating between the upper and lower computers, so the cost of using CAN is relatively high.

(2) Background data processing : After receiving data through the test software platform, the data is processed, which is mainly completed by the background of the energy storage inverter.

(3) Data display and human-computer interaction: The background of the energy storage inverter test software platform is mainly responsible for processing data, completing data operations by displaying data, and realizing the final human-computer interaction.

2 Test platform structure and algorithm design

2.1 Overall structure

After the energy storage inverter test software platform obtains data through industrial Ethernet, it needs to perform calculations and analysis on the data. While displaying the data, it can also store historical data according to the user's setting requirements. The data processing flow of the test platform is shown in Figure 3.

When developing the test software platform for the energy storage inverter, a three-layer structure system is adopted, including the application layer, business logic layer and control layer, which divides the tasks at each level in the software and facilitates the development of the software.

2.2 Harmonic Detection Algorithm

2.3 Efficiency calculation method

2.4 High-speed communication protocol

3. Test platform module implementation

3.1 The process of data acquisition module implementation is:

Voltage and current sensor → signal conditioning circuit → AD → DSP, the sensor converts the strong electric signal into a weak signal, and after AD collection, the data is sent to the test platform via Ethernet.

In the design of this system, the data acquisition module mainly completes the sampling of the input signal through the 8-channel, 16-bit chip AD7606 produced by AD Company, so that the acquisition rate of all channels can reach 200kSPS.

3.2 Implementation of Ethernet communication module The implementation process is:

Data acquisition module → DSP → RTL → energy storage inverter test software platform. The data transmission of the test software platform is carried out using industrial Ethernet. The data in the data acquisition module is transmitted to the Ethernet controller through DSP, and Ethernet transmits it to the test platform.

The data communication between the upper and lower computers uses RTL8019AS. The controller has a simple circuit, easy operation, and high communication rate, which can meet the design requirements of the platform.

3.3 Implementation of harmonic detection module using radix-2 FFT algorithm

The harmonic detection and analysis of the FFT algorithm is completed through butterfly operation. The effective value calculation module is realized by adding DC and AC to the same resistance, and through the cycle of traffic flow, the heat of DC and AC is equal to obtain the effective value of traffic flow.

4 Conclusion

The test software platform design for energy storage inverter is mainly developed for energy storage inverter. This software can also be used for debugging in other inverters .

By analyzing the harmonic detection algorithm, the principle of suppressing spectrum leakage is obtained, which plays a significant role in further improving the real-time performance of the test platform.

After analyzing the functional implementation of each module, it was found that C++ can be used to implement the design of the test software platform for energy storage inverters, complete the analysis of harmonic analysis, detection, acquisition, calculation, display and storage functions, and verify the feasibility of the design scheme.

Reference: Design and implementation of energy storage inverter test platform; Author: Li Chun, Chen Guodong Shanghai Electric Power Transmission and Distribution Group Technology Center

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