{"id":2170,"date":"2026-08-22T07:50:13","date_gmt":"2026-08-22T07:50:13","guid":{"rendered":"https:\/\/zeeyielec.com\/?p=2170"},"modified":"2026-08-22T07:54:08","modified_gmt":"2026-08-22T07:54:08","slug":"solid-state-transformer","status":"publish","type":"post","link":"https:\/\/zeeyielec.com\/ko\/solid-state-transformer\/","title":{"rendered":"\uace0\uccb4 \ubcc0\uc555\uae30: \uc815\uc758, \uc791\ub3d9 \uc6d0\ub9ac \ubc0f \uacf5\ud559\uc801 \ud604\uc2e4"},"content":{"rendered":"\n

Solid state transformers (SSTs) replace the passive distribution transformer with an actively controlled power-electronics system. This guide covers how they work, where they fit, and why conventional transformers usually remain the practical choice.<\/p>\n\n\n\n

What Is a Solid State Transformer? Core Definition and System Architecture<\/h2>\n\n\n\n

A solid state transformer (SST) is a power-electronics conversion device replacing the passive line-frequency magnetic coupling of a conventional distribution transformer with an actively switched converter chain around a medium-frequency transformer (MFT). It steps MV supply down to LV with galvanic isolation, adding bidirectional power flow, fast voltage regulation, DC output ports, and power-quality functions. Commercial MV deployment remains limited; most figures come from prototypes and pilots. The engineering reference literature on solid-state transformers<\/a> summarizes the IEEE research stream.<\/p>\n\n\n\n

\"Three-stage
Figure 1. Block diagram of the three-stage solid-state transformer architecture, showing the MV-side converter, the medium-frequency transformer, and the LV-side converter that together provide galvanic isolation and bidirectional power flow.<\/figcaption><\/figure>\n\n\n\n

The Three-Stage Conversion Chain: MVAC \u2192 MFT \u2192 LVDC<\/h3>\n\n\n\n

Stage 1 rectifies the MVAC supply \u2014 typically 10\u201336 kV \u2014 into a DC link; Stage 2 transfers energy across the galvanic boundary via the MFT at 1\u201320 kHz; Stage 3 synthesizes LVAC output (commonly 400 V three-phase) or LVDC (often 750\u20131500 V DC for EV charging and DC microgrids).<\/p>\n\n\n\n

How an SST Differs from a Conventional Distribution Transformer<\/h3>\n\n\n\n

A conventional distribution transformer is a passive, unidirectional, 50\/60 Hz magnetic device tested against the IEC 60076 series, supported by a mature accessory ecosystem \u2014 bushings, tap changers, fuse assemblies. An SST replaces that passive coupling with active switching, enabling dynamic voltage regulation, bidirectional flow, and harmonic filtering. For projects that continue on conventional transformers, the established transformer accessories<\/a> ecosystem remains the practical specification path.<\/p>\n\n\n\n

The Physics: Why Higher Frequency Shrinks the Transformer and Enables Bidirectional Power Flow<\/h2>\n\n\n\n

A conventional transformer is locked to 50\/60 Hz; an SST’s converters generate their own internal frequency \u2014 typically 1\u201320 kHz \u2014 cascading through core size, isolation design, and controllability.<\/p>\n\n\n\n

Why Operating at Kilohertz Frequencies Reduces Core and Winding Volume<\/h3>\n\n\n\nFor a transformer operating at frequency\u00a0f, the induced voltage per turn scales as\u00a0V\u00a0\u221d\u00a0B\u00a0\u00d7\u00a0A\u00a0\u00d7\u00a0f, where\u00a0B\u00a0is the core flux density and\u00a0A\u00a0the core cross-section. Raising\u00a0f\u00a0from 50\/60 Hz to the 1\u201320 kHz range therefore allows a much smaller magnetic core to support the same voltage transformation \u2014 the core reason an SST can be substantially lighter and more compact than a line-frequency unit of equal rating.\n\n\n\n

Prototype literature for MV SSTs reports 30\u201350% weight reductions versus line-frequency units, depending on cooling and packaging. The smaller core does not automatically mean a smaller enclosure \u2014 power electronics and thermal management occupy much of it.<\/p>\n\n\n\n

Galvanic Isolation and the Role of the Medium-Frequency Transformer<\/h3>\n\n\n\n

The MFT is the only component crossing the galvanic boundary between MV and LV, so it carries the full insulation duty at kilohertz rates. High dv\/dt changes insulation behavior versus 50\/60 Hz \u2014 creepage, partial-discharge inception, and inter-layer voltage distribution need dedicated attention. This insulation burden, not the magnetic core, sets the ceiling on internal frequency.<\/p>\n\n\n\n

Switching Devices in SST Design: SiC MOSFETs and IGBTs<\/h3>\n\n\n\n

SiC MOSFETs (1.2\/3.3\/10 kV; junction 150\u2013175\u00b0C) suit fast switching with low losses; IGBTs (to 6.5 kV; 125\u2013150\u00b0C) carry higher current at medium frequency. Choice depends on power level, frequency, and thermal budget.<\/p>\n\n\n\n

Because both converters are actively switched, current can reverse direction on command \u2014 enabling regenerative operation and backfeed no passive transformer can perform. The electromagnetic induction fundamentals in our transformer fundamentals<\/a> guide provide the base physics.<\/p>\n\n\n\n

SST vs Conventional Transformer: Engineering Comparison<\/h2>\n\n\n\n

This is not a “better versus worse” question but one of operating envelope \u2014 the conventional unit is a proven commodity; the SST’s advantages appear only where usable.<\/p>\n\n\n\n

\"SST
Figure 2. Side-by-side comparison of conventional distribution transformer and solid-state transformer characteristics, including operating frequency, efficiency bands, voltage-regulation response, and maintenance profile at distribution-class ratings.<\/figcaption><\/figure>\n\n\n\n

SST vs Conventional Transformer: Key Parameters at a Glance<\/h3>\n\n\n\n
Parameter<\/th>Conventional distribution transformer<\/th>SST (current state)<\/th><\/tr><\/thead>
Operating frequency<\/td>50\/60 Hz (grid-locked)<\/td>1\u201320 kHz internal (converter-generated)<\/td><\/tr>
Typical voltage class<\/td>LV to 36 kV (IEC 60076 ecosystem)<\/td>10\u201336 kV in demonstrations<\/td><\/tr>
Efficiency at rated load<\/td>~98\u201399.5%<\/td>96\u201399% in pilots, test-condition dependent<\/td><\/tr>
Voltage regulation<\/td>Passive; tap-changer dependent<\/td>Dynamic, sub-cycle-class response<\/td><\/tr>
Bidirectional power flow<\/td>Not possible<\/td>Yes, inherent<\/td><\/tr>
Harmonics and power quality<\/td>None (passes system harmonics)<\/td>Active filtering capability<\/td><\/tr>
Maintenance profile<\/td>Mature utility practice<\/td>Power-electronics spares, specialist skills<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Efficiency, Size, and Weight at Distribution-Class Ratings<\/h3>\n\n\n\n

At rated load, conventional units reach roughly 98\u201399.5% efficiency; SST prototypes report 96\u201399%. The comparison is load-point dependent \u2014 converter losses are relatively constant and dominate at light load.<\/p>\n\n\n\n

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Expert Insight \u2014 comparing efficiency claims in procurement<\/p>\n\n\n\n