Integrating renewable generation and storage while designing, modelling, and controlling resilient DC and AC microgrids.
A microgrid is a bounded set of sources, storage and loads that can operate connected to the utility or on its own. That single capability — islanding — is what makes the architecture choice consequential: everything about control, protection and power quality follows from which bus the energy actually sits on.
Efficient DC power distribution systems with advanced control strategies for optimal energy management and reliability.
Grid-connected and islanded AC microgrid architectures with seamless transition capabilities and power quality management.
Integrated systems combining the benefits of both AC and DC distribution for maximum efficiency and flexibility.
A microgrid brings energy resources with very different electrical characteristics into one distribution and control system. Wind, solar and fuel cells supply energy; storage manages the timing mismatch between generation and demand. Each resource needs a power-conversion, control and protection interface matched to its behaviour.
A wind turbine produces AC whose voltage and frequency move with rotor speed. A full-scale or doubly-fed converter decouples that mechanical speed from the microgrid, enabling maximum-power tracking while meeting active-power, reactive-power and fault-ride-through requirements. The rectified link can feed a DC bus, or a grid-side inverter can synchronise it to an AC bus.
A PV array is natively DC, with an operating point that moves with irradiance and temperature. On a DC bus, a DC–DC stage performs maximum-power-point tracking and bus matching; on an AC bus, an inverter also manages synchronisation, power factor and power quality. The energy manager coordinates curtailment, forecast error and the storage available to smooth production.
A fuel cell is a dispatchable DC source, but stack voltage changes with current and its reactant and thermal systems respond more slowly than electrical loads. A boost-derived DC–DC interface regulates voltage and limits current, while a battery or supercapacitor absorbs fast power steps. Dispatch must balance fuel use, stack life and the microgrid's power request.
Storage is the microgrid's bidirectional flexibility layer: it absorbs renewable surplus and releases energy during deficits, islanding transitions and load steps. Batteries provide minutes-to-hours energy, while high-power devices such as supercapacitors handle faster transients. Their bidirectional converters can also regulate the bus, form the grid and support black start, subject to state-of-charge, thermal and ageing limits.
The bus is the architecture. Choosing DC, AC or both decides how many conversion stages sit between a panel and a load, what quantity carries power-balance information, and what you have to do to clear a fault.
PV, batteries, fuel cells, LED lighting, variable-speed drives and EV charging are all natively DC. Putting them on a DC bus removes a conversion stage each way, and with it the losses and the hardware.
There is no frequency, no phase angle, no reactive power and no synchronisation. Power sharing needs one variable — bus voltage.
DC fault current has no natural zero crossing, so interruption needs solid-state or hybrid breakers and deliberate fault-current limiting, with selectivity designed rather than inherited.
Tightly regulated converters look like constant-power loads. Their negative incremental impedance destabilises the bus unless source impedance and bus capacitance are designed against it.
Protection practice, switchgear, transformers, metering and motor loads all already exist and are certified. Voltage transformation is a passive component.
The cost is control: frequency and voltage both carry power balance, at least one converter has to be grid-forming, and islanding and reconnection have to happen without a phase step.
A microgrid has no infinite bus to lean on. In island mode the converters themselves have to set voltage and frequency, share load without fighting each other, and hand back to the utility cleanly when it returns.
A grid-following converter needs an existing voltage to lock a PLL onto — perfect when the utility is present, useless the instant it is not. A grid-forming converter behaves as a voltage source behind an impedance and establishes the reference itself. An islandable microgrid needs at least one, and usually needs them to share.
Detecting the island, transferring without a load interruption, then matching voltage, phase and frequency before reclosing. Passive detection has a non-detection zone; active methods inject a small perturbation. The transfer is where most commissioning problems appear.
A converter-dominated microgrid has almost no rotating inertia, so the rate of change of frequency after a disturbance is high. Virtual synchronous machine and synthetic inertia schemes emulate it, trading storage headroom and bandwidth for a slower, more forgiving frequency response.
Converters cannot supply the multiples of rated current that overcurrent protection assumes. Islanded settings differ from grid-connected ones, and coordination often needs directional, differential or communication-assisted schemes rather than time grading.
Switching converters supply the harmonics, and weak islanded networks have high grid impedance, so distortion and resonance interact. Filter design and converter output impedance shaping stop being independent problems.
Above the fast loops, the dispatch problem: forecast, state of charge, degradation cost, tariffs, and the exchange schedule with the utility. This layer decides economics; the layers below decide whether the system stays up.
An SST is the clearest answer to the hybrid question. Instead of a line-frequency transformer plus separate converters bolted around it, one multistage device provides the medium-voltage connection, the isolation and every port the microgrid needs — with controllable power flow between them.
The line-frequency transformer. Isolation moves to a high-frequency transformer inside the isolated DC–DC stage, which is why the magnetics shrink by an order of magnitude in volume.
Bidirectional power flow, voltage regulation independent of turns ratio, a native DC port at the internal link, reactive support and harmonic control at the MV side, and ride-through behaviour that a passive transformer cannot offer.
Series-connected medium-voltage cells, isolation coordination, cell-voltage balancing, distributed control, and efficiency that must beat a 99 %-efficient passive component to justify itself.
The full series works through it stage by stage: applications and motivation · architecture · AC–DC front end · DAB isolation stage · DC–AC output stage · modular integration and testing.