Solid-state transformers could make electricity infrastructure smaller, more controllable and potentially more efficient by combining traditional voltage conversion with semiconductor-based power electronics. Srdjan Lukic, a professor of electrical and computer engineering at North Carolina State University, says a device developed in his laboratory has now undergone a 1-megawatt test under realistic operating conditions.
Why conventional transformers are difficult to replace
Transformers are central to electricity transmission and distribution. In addition to stepping voltage up or down, they often provide galvanic isolation, meaning there is no direct current electrical path through the transformer. This helps limit disturbances moving through the grid and improves safety.
However, today’s transformers are large and bulky, making them difficult and expensive to replace, Lukic said.
How solid-state transformers work
Solid-state transformers follow the basic design of conventional transformers but add semiconductors, also known as power electronics, to convert and control electricity.
Traditional transformers operate at the frequency of the grid to which they are connected. Solid-state transformers can control the frequency of the current. They typically first convert incoming alternating-current (AC) power from the grid into direct-current (DC) power. Semiconductor switches, including devices made with silicon carbide, then convert that electricity into high-frequency AC power.
A magnetic component subsequently changes the voltage. Because advanced semiconductors provide greater control over the current’s frequency and stability, the magnetic core can be much smaller than the core in a conventional transformer. Lukic said some solid-state transformers are about one-tenth the size while providing the same capacity.
Additional power electronics then convert the high-frequency AC into the required form, usually first returning it to DC and then converting it into low-frequency AC.
More than voltage conversion
Many conventional transformers primarily step voltage up or down. Solid-state transformers can also incorporate the functions of devices such as rectifiers and inverters, which convert AC power to DC and vice versa.
Combining these functions could reduce the overall footprint of electrical equipment and lower the amount of power lost within the system.
1-megawatt test
In August, the New York Electric Power Administration and the Electric Power Research Institute (EPRI) tested a 1-megawatt solid-state transformer under realistic working conditions at EPRI’s test site.
The device was created in Lukic’s laboratory, and the test marked the first time a transformer of this capacity had been tested.
Source: www.technologyreview.com