Commutation technique for an ac-to-ac converter based on state machine control

This invention is a technique that resolves current commutation challenges in various types of ac-ac switching power converters. It also applies to inverters and rectifiers with high-frequency links. Direct ac-ac converters such as matrix converters and cycloconverters benefit from the approach. This technology commutates load current without inserting dead-time into the switching sequence or using large inductors to limit shoot-through current. Both of these prior techniques intrinsically compromise a converter's performance and efficiency.

The new technology provides a continuous path for load current and control of ac-ac converter switching so voltage sources do not short-circuit during commutation. If input voltage sources short-circuit they result in dangerously high shoot-through currents, while a disruption in the load current results in dangerously high voltages.Either scenario can damage or destroy equipment. In the past, additional components or timing constraints have been required to address current commutation. This new technology prevents both shoot-through and load current disruption, and allows load-current zero-crossings to occur naturally without the distortion associated with prior techniques. The preferred embodiment of the new invention is a state-machine-based controller that tracks the switch sequencing needed to avoid trouble.

Applications

  • Link inverters - The high-frequency link pulse width modulation (HF PWM) topology is a reduced-cost solution ideal for producing ac voltage from alternative energy sources such as solar panels and fuel cells. Other applications include uninterruptible power supplies (UPS), portable generators, and inverters for automobiles.
  • Matrix converters - ac-ac converters based on direct switch matrix circuits are difficult to implement with conventional commutation methods. The invention facilitates the design and operation of matrix converters.
  • Cycloconverters - Applications for cycloconverter-type ac-ac converters have traditionally been limited to relatively low frequencies, in part because of complicated current management. Effective commutation has been a significant barrier to wider application of these circuits. This invention resolves the commutation challenge and greatly expands the application range of cycloconverters.

Benefits

  • Smooth half-cycle transitions - Proper selection of switch sequencing allows a load current to transition smoothly from one half-cycle to the next without disruptions.
  • Reduced distortion and EMI - Smooth current zero-cross transitions eliminate distortion inherent with dead-time techniques. Natural current commutation provides superior EMI performance compared with forced current commutation.
  • Increased conversion and cost efficiency - The new technology facilitates increased power conversion efficiency while supporting miniaturization. It reduces cost by reducing the need for commutation chokes or large snubbers.
  • Protects equipment - This technology prevents current shoot-through and load current disruptions that damage equipment.

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