Wu Hengliang: Reconstructing the key technologies of photovoltaic inverters from the three aspects of "efficiency, safety, and operation and maintenance"

In 2020, my country announced that it would strive to achieve carbon peak by 2030 and carbon neutrality by 2060. Under the background of the "dual carbon" strategy, the new energy industry has ushered in a huge opening. Among them, the photovoltaic industry has become the leader and leader in the green and low-carbon development boom.

Zhuzhou CRRC Times Electric Co., Ltd. (hereinafter referred to as "Zhuzhou CRRC Times Electric") is the only central enterprise in the photovoltaic inverter market. In recent years, it has actively promoted the integration of solar energy utilization and conventional energy systems, and strived to achieve large-scale and leapfrog development of the photovoltaic industry. It successfully won the "2023 Good Photovoltaic·Top Ten Photovoltaic Inverter Brands of the Year" award at the 2023 Eighth Good Photovoltaic Brand Ceremony.

At the 2023 8th China Photovoltaic Industry Forum on November 7, Wu Hengliang, deputy chief engineer of Zhuzhou CRRC Times Electric Green Energy Business Unit, delivered a speech entitled "Focusing on power electronics technology to lead the efficient conversion of "wind, light and hydrogen storage" - CRRC photovoltaic inverters ensure high-quality operation of power stations". Through the analysis of the development trend of photovoltaic power stations, he focused on introducing the key technologies of photovoltaic inverters from three aspects: efficiency, safety and operation and maintenance.

Wu Hengliang, Deputy Chief Engineer of Green Energy Division, Zhuzhou CRRC Times Electric Co., Ltd.

The PV Inverter Dilemma

——Chip shortage, supply interruption, and delivery difficulties

In recent years, the National Energy Administration has made the construction of large-scale wind and solar bases a top priority for the development of new energy in the "14th Five-Year Plan", and the construction of large bases has become the main theme of new energy development.

According to the "Planning and Layout Plan for Large-scale Wind and Photovoltaic Bases Focusing on Deserts, Gobi and Arid Areas" issued by the National Development and Reform Commission and the National Energy Administration, three batches of wind and solar bases with a total installed capacity of about 455 million kilowatts are planned to be built by 2030. At present, the first batch of 97.05 million kilowatts of large base projects have been fully started, the second batch of large base projects have been gradually started, and the list of the third batch of base projects has been officially issued and implemented.

Wu Hengliang pointed out that with the acceleration of the construction of large-scale wind power and photovoltaic bases, the increase in photovoltaic ground power stations will gradually improve. However, what comes with it is that the main body of the power supply will undergo a fundamental change, and the random volatility of both the source and the load will bring huge challenges to the balance of power and electricity. At the same time, the insufficient frequency regulation capacity caused by the high proportion of new energy grid connection makes the power grid face problems such as reduced system inertia, transient overvoltage disconnection and broadband oscillation.

In the photovoltaic field, due to the diversification and complexity of "photovoltaic +" scenarios and the scale of power station capacity, the scope of fault impact is large, resulting in increased difficulty in equipment selection, design, construction, and operation and maintenance. In addition, at the end of 2022, the photovoltaic inverter market experienced a "chip shortage" and "supply interruption", and many projects were forced to postpone grid connection. Difficult delivery has become a development dilemma for the photovoltaic industry.

Wu Hengliang said that since the large bases are mainly located in deserts, Gobi deserts and wastelands, how to transmit new energy over long distances at high voltage and better absorb it without causing power waste has become a difficult problem that needs to be solved in the industry. He also further emphasized the importance of energy storage, and Zhuzhou CRRC Times Electric is currently working on this aspect.

Three core technologies of photovoltaic inverter

——Efficiency, safety, operation and maintenance

As a conversion device in a photovoltaic power station, the photovoltaic inverter plays an important role in the entire photovoltaic power station. At the forum, Wu Hengliang focused on introducing the key technologies of photovoltaic inverters from three aspects: efficiency, safety, and operation and maintenance.

In terms of efficiency, Wu Hengliang introduced a PWM modulation strategy based on global efficiency optimization, a patented technology for maximum power point tracking (MPPT) of photovoltaic inverters, a synchronous phase-locked intelligent grid-connected control technology based on rapid extraction of positive sequence components, and a grid structural grid-connected control technology based on a power synchronization loop.

Wu Hengliang said that due to the large fluctuation in the output power of new energy inverters, the use of a globally optimized segmented modulation strategy can increase the conversion efficiency by more than 0.2%, and the use of patented power prediction technology can achieve a maximum power tracking efficiency of 99.9%.

At present, due to the influence of the power grid support capacity, especially in the remote areas of large bases, in order to meet the needs of new energy converters to quickly respond to the power grid and support the stable operation of the power grid, the synchronous phase-locked intelligent grid-connected control technology with rapid extraction of positive sequence components is adopted, which can make the reactive response time reach <30ms.

In terms of safety, how to quickly detect arcing and quickly isolate it is a problem currently faced by the industry. Based on this, Wu Hengliang launched arc detection technology based on a neural network model. This technology can accurately identify series, parallel, and grounding arc faults, effectively identify weak arc signals under strong interference noise and long line impedance, and can identify arcs within 100ms and disconnect the DC disconnect switch to prevent fires. In this regard, Zhuzhou CRRC Times Electric has launched the first 320kW inverter in China that has passed L4 arc detection.

Wu Hengliang said that since arcing cannot be completely eliminated, intelligent DC disconnect switches are used in the DC input of photovoltaic string inverters to actively disconnect DC faults, effectively block DC hazards, and prevent faults from spreading. In photovoltaic centralized inverters, combiner box DC switches with built-in shunt tripping are used to support coordinated control with the inverter, effectively block DC hazards, and ensure the safety of the power station.

In traditional DC side mechanical switches, due to their slow breaking, difficult arc extinguishing and high system delay, Zhuzhou CRRC Times Electric has launched a DC breaking protection solution that can realize intelligent equipment detection, us-level protection, ms-level breaking, and protect the power electronics of equipment.

In terms of operation and maintenance, Wu Hengliang launched an intelligent operation and maintenance system based on device-level health status prediction, an intelligent operation and maintenance solution for centralized inverter power stations, and string status monitoring and diagnosis based on branch power energy.

Wu Hengliang said that the introduction of these solutions has reconstructed the operation and maintenance experience, allowing new energy power stations to leap from "regular maintenance" and "fault repair" to "condition maintenance", effectively solving the pain points of centralized operation and maintenance, scientifically guiding power station operation and maintenance, and increasing power generation by more than 3%.

Source: International Energy Network/Photovoltaic Headlines