How does a solid-state transformer improve smart grid efficiency?

Solid-state transformers (SST), also known as "smart transformers," are modern electrical devices capable of providing bidirectional power flow. They integrate high-power semiconductor components, control circuits, and conventional high-frequency transformers, offering multiple functions such as reactive power compensation and harmonic suppression. SSTs meet a wide range of application needs, from distributed generation to traction locomotives, power grids, and industrial power systems. Their applications extend beyond voltage conversion, enabling smooth transitions from AC to DC and from DC to AC. However, distributed generation is the primary application of solid-state transformers.

Unlike traditional transformers, solid-state transformers can provide DC output at the required voltage levels. In a typical SST, an input voltage is converted into a high-frequency AC signal via a power electronic converter and then fed into the primary side of a high-frequency transformer. On the secondary side, the reverse process is performed to produce the desired AC, DC, or both outputs for the load. High-frequency power transfer significantly reduces the transformer's weight and size.

Many advantages of solid-state transformers stem from this size reduction. Today, installing conventional transformers is no simple task—considerations such as transportation, site preparation, installation, and transmission costs all add to project budgets. In contrast, smaller and more cost-effective solid-state transformers can be easily installed in small solar farms or storage containers. The faster switching speed of solid-state devices also enables utility companies to better manage multiple power sources feeding into the grid, as more transformers can be deployed to control and fine-tune power quality.

SSTs are also referred to as Power Electronic Transformers (PET) or Electronic Power Transformers (EPT). They are intelligent devices that use power electronic conversion technology to achieve voltage level transformation and power transmission.

Their basic principle is illustrated as follows: First, a power-frequency AC signal is converted into a high-frequency square wave by a power electronic converter. The signal is transmitted through a high-frequency isolation transformer, then converted back into a power-frequency AC signal by another power electronic converter. This entire process is controlled by adjusting the power electronic switching devices via a controller.

Based on this operating principle, the advantages of solid-state transformers over traditional transformers are evident:

• The use of high-frequency transformers instead of power-frequency transformers greatly reduces the size and weight.

• With appropriate control, the input side can achieve unity power factor, absorb reactive power from the load side, block harmonic currents, suppress bidirectional harmonic propagation, and effectively improve power quality.

• It can eliminate the impact of overvoltage or undervoltage on the source side on the load-side voltage, ensuring stable load-side voltage magnitude, frequency, and waveform.

• It features AC and DC interfaces, facilitating grid integration of distributed generation systems and connection of DC loads.

• Full digital control enables easy collection of grid data and network communication, allowing power flow control. It can also work in coordination with Flexible AC Transmission Systems (FACTS) to enhance grid stability and reliability.

Clearly, solid-state transformers are better suited to meet the requirements of smart grids and can more effectively satisfy users' personalized demands for power systems.