China has a vast territory, and the resource end and power demand end of traditional and new energy are geographically separated from the west to the east. Just like the South to North Water Transfer Project, the west to east power transmission is required. Therefore, the UHV power transmission mode, which meets the requirements of large scale, long distance and high efficiency, was once one of the representatives of China’s old infrastructure.
As the name implies, UHV is a very high voltage, which refers to ± 800 kV and above DC and 1000 kV and above AC. For ultra-high voltage, people know little about it except for the overhead lines that shuttle across the sky. However, in 2019, under the dual carbon background of developing clean energy, UHV was endowed with the attribute of new infrastructure, and took on the strategic mission of “national pillar” again, becoming the focus of attention.
According to CCID data, in 2020, the total investment scale driven by China’s ultra-high voltage industry and its upstream and downstream supporting links in the industrial chain will exceed 300 billion yuan, including nearly 100 billion yuan of ultra-high voltage industry investment and more than 200 billion yuan of social investment. By 2022, the total investment scale driven by China’s ultra-high voltage industry and its upstream and downstream supporting links in the industrial chain will reach 414 billion yuan; By 2025, the overall investment scale of UHV industry and its driven industries will reach 587 billion yuan. These figures show that UHV has increasingly become an indispensable infrastructure from people’s livelihood to production.
The power system includes five major parts of “power generation, transmission and transformation allocation”, and the UHV is mainly composed of two parts of “power transmission and transformation”. The converter station and substation are the core, and the electrical equipment accounts for more than half of the total investment. The advantages of UHV are realized from conversion, protection, control, detection and other aspects. Whether it is DC converter valve, DC control and protection equipment, or AC GIS, transformer, are inseparable from the integrated circuit.
Complex power systems, from components, board level systems to equipment, have some special requirements to ensure the conversion, measurement, control and protection processes. Reliability is the most basic and important requirement of power system. Once a fault occurs, it will affect people’s production and life; Secondly, it is required to be real-time. The voltage and current are changing all the time and must be adjusted in real time to ensure stability; Thirdly, it is high efficiency, because the whole transmission link involves a lot of power conversion, and the loss needs to be reduced; The fourth is anti-interference. The complex environment of power system will produce a lot of electromagnetic noise. Therefore, high efficiency, reliability, real-time and anti-interference are the most difficult points in power system design, and UHV system has higher requirements due to its particularity.
In addition, although China is far ahead in ultra-high voltage technology, every project has new requirements and needs to innovate constantly to try to explore new technologies. At the same time, with the increasing complexity of ultra-high voltage system, the demand for integration and intelligence has penetrated into each subsystem. The chip is a carrier to realize these innovations. What kind of chip can solve many challenges in ultra-high voltage system?
High reliability and real-time
In fact, high reliability is to reduce the failure rate. To control and protect the transmission system, it is necessary to have perfect monitoring capability. This is naturally inseparable from the signal chain connecting analog and digital domain bridges, in which the sensing, collection, conversion and transmission of voltage, current and other parameters to the ADC of the system is crucial. For the power system, there are usually three-phase voltages, three-phase currents, and voltages and currents of the central line. There is a phase relationship between these signals. Therefore, in addition to the amplitude information, the system must be able to acquire the phase relationship in real time and accurately, so that the system can perform protection and control. In addition, the dynamic range of signals in the power system, especially the current signal, is very wide, and the requirements for the accuracy of signal acquisition are very high, so that the fault can be accurately located.
TI provides 16 bit ADC specially designed for power system, with multi-channel, synchronous sampling, high precision and high accuracy, wide dynamic range up to 90dB, and can quickly find short circuit or open circuit faults. These two ADCs are integrated with amplifiers and have precise calibration circuits inside, so no additional signal chain integration or calibration is required. An error correction mechanism is also integrated at the interface with the CPU to ensure the reliable communication process transmitted to the processing system through the monitoring mechanism. In other words, TI’s ADC products have high reliability from analog domain to digital domain and then to interfaces.
In fact, the reliability of the whole system is reflected through the implementation of the system chip and scheme. It is worth mentioning that all power grid application products of TI have passed the professional and strict quality management process in the production and testing links, so as to ensure the high reliability of the products. In the whole temperature range, the temperature drift is very low, which is very suitable for complex power grid environment.
High efficiency, anti-interference and high integration
The efficiency of power system refers to the conversion efficiency. All kinds of equipment, from converter valves to transmission stations, can not be separated from power conversion. One by one, power tubes convert and transmit power sources endlessly. Whether IGBT or SiC is required for power conversion, efficient and reliable drive is required to control these core components.
Due to the lack of highly integrated chips, IGBT drivers are traditionally implemented with modules, which is expensive. The latest UCC5870-Q1 launched by TI is an isolated, configurable single channel gate driver. The internally integrated ADC can support a variety of analog input monitoring, and also integrate temperature control and other protection functions, supporting SPI interface configuration, so as to achieve more efficient conversion and detection functions, which is applicable to any SiC or IGBT. In this way, customers can replace the functions that can be realized by two modules with a single chip, thus simplifying the design of the drive system and greatly reducing the cost.
The electromagnetic characteristics of devices are of great concern to the power system, which should not only reduce the radiation generated by devices, but also resist external interference. Many TI devices, such as op amps, have integrated filters, which can still maintain high-precision signal processing under strong external electromagnetic interference. Isolation technology is also an important anti-interference method. TI is one of the earliest manufacturers of capacitive isolation, which is much superior to the traditional optocoupler, magnetic coupler and other competitors in terms of anti-interference capability. For example, UCC5870-Q1 uses silicon dioxide isolation technology to achieve dv/dt of up to 150 kV/ns, which is far superior to competitors.
With the further development of UHV technology, a series of advanced technologies including flexible DC transmission are developing rapidly, from control, drive, protection to the operation and requirements of the whole system. For chip companies, this means more opportunities, but also higher requirements. We can see that in order to cope with the increasingly complex UHV power grid system, TI products have been accelerating their iteration, providing the market with products with high reliability and high integration to simplify the application of customers.