Amid the trend of larger new energy vessels, the demand for megawatt-class charging has become increasingly urgent. Traditional line-frequency transformers, constrained by inherent bottlenecks such as large size, low efficiency, and harmonic pollution, can no longer support the rapid energy supplement system for modern shipping. At this critical juncture of industrial upgrading, high-voltage solid-state transformer (SST) technology, as a revolutionary breakthrough in the field of energy conversion, is driving a fundamental systemic transformation of port energy systems.
Through the in-depth integration of semiconductor devices and high-frequency topological structures, this technology enables the intelligent direct conversion of 10kV high-voltage alternating current (AC) to ship direct current (DC). Leveraging high-frequency isolation and rapid dynamic response characteristics, it significantly improves charging efficiency, achieving breakthrough progress with an end-to-end efficiency exceeding 98% and a 50% reduction in equipment size. Its intelligent power regulation and multi-energy interface capabilities upgrade ports from single energy supply nodes to regional energy hubs with dynamic balancing capabilities, providing key infrastructure support for building an integrated “zero-carbon port – zero-carbon vessel” ecosystem.
Chengrui Power Technology has targeted this strategic track with a forward-looking technological vision. Through independent R&D, it has launched a high-voltage SST solution integrating compact structure, excellent energy efficiency, and flexible expansion. This not only addresses the current space constraints and energy consumption challenges of ports but also demonstrates Chengrui Power Technology’s innovative leadership in the global green shipping revolution by promoting the trinity transformation of the port and shipping system towards “energy interconnection – intelligent dispatching – zero-carbon operation.”
Overview of Cascaded SST System for Port and Shipping Charging
The cascaded SST (Solid-State Transformer) system for port and shipping charging directly shares the grid voltage by connecting multiple power modules in series on the high-voltage side, thereby eliminating the bulky line-frequency transformer and enabling direct high-voltage grid connection. Each module can independently process a portion of electrical energy, and system control ensures voltage and power balance among the modules.
- Module Level: Adopts high-frequency conversion circuits based on SiC devices. SiC devices support high-frequency switching, and combined with high-frequency transformers, they achieve efficient isolation and transmission of electrical energy, improving the system’s size, efficiency, and power density.
- System Level: Employs a modular cascaded design, allowing flexible adjustment of the number of connected modules according to grid conditions and power requirements. Without the need for custom transformers, prefabricated stock and rapid system installation can be achieved, significantly shortening the product delivery cycle.
Topology Diagram of Cascaded SST System for Port and Shipping Charging
Technical Features of High-Voltage SST
Fault-Tolerant Control Strategy
The fault-tolerant control strategy aims to maintain basic operation and retain system functions as much as possible when a fault occurs through redundant design. Specifically, when a component, module, or even the entire solid-state transformer malfunctions, the system can block or bypass the faulty part through fault location and characteristic analysis technology, while activating the corresponding redundant module to take over its operation. This achieves uninterrupted fault-tolerant operation and effectively improves the reliability of the system and the associated power grid.
Carrier Phase-Shifted Modulation Technology
The core of carrier phase-shifted modulation technology is to make n cascaded H-bridge rectifier modules adopt the same sine wave modulation, but the phase of each triangular carrier lags by 1/n cycle in sequence. Through this carrier phase-shifting processing, the SPWM waveforms output by each cascaded module on the AC side are superimposed on each other, resulting in (2n+1) levels in the final synthesized total output voltage, and its equivalent switching frequency is increased to n times that of a single module. This can significantly reduce the harmonic content of the system’s total output waveform without increasing actual switching losses.
DC-Side Capacitor Voltage Balance Control Strategy
The DC-side capacitor voltage balance control strategy aims to solve the DC-side capacitor voltage imbalance problem of cascaded H-bridge rectifiers caused by their inherent topological structure. Its core principle is: on the basis of the system’s total voltage closed-loop control, only introduce independent duty cycle deviation adjustment loops for the first (n-1) H-bridge units. Generate d-axis deviation through PI controllers to accurately correct the PWM commands of each module, thereby achieving capacitor voltage balance. The nth unit serves as an open-loop adjustment reference. This design ensures that the (n-1) voltage balance closed loops and the total voltage closed loop are independent of each other, maintaining the stability of the system’s total voltage while ensuring all power devices operate within a safe voltage range.
DC/DC Stage Voltage Balance Control Strategy
The DC/DC stage voltage balance control strategy is applied to the latter-stage DC/DC link of the cascaded SST system for port and shipping charging. Its core is to utilize the approximately constant power characteristics of the input side. On the premise that the DC-side voltage of the front-stage H-bridge is already balanced, all DAB converters operate in open loop with the same control signal. When the output voltage of a module deviates from the equilibrium point due to disturbances, the system automatically adjusts its input current to change the charging and discharging state of the output capacitor, thereby generating a reverse adjustment effect to return its voltage to the equilibrium point. Ultimately, automatic voltage balance on the output side of all modules is achieved without the need to add independent voltage closed-loop control for each module.