Aspects of the invention overcome a monolithic approach to conventional low-frequency LPTs by using a high-frequency solid-state alternating current ac/ac modular powerconversion approach. Embodiments of the invention enable the ability to incorporate new technologies without in all cases redoing a LPT design from scratch. Furthermore, given that LPTs are for the long term, aspects of the invention ensure that they are durable, efficient, and fault tolerant with overloading capability.

A direct current (DC) power secondary distribution system is provided. The system comprises at least one first conversion unit and a one or more second conversion units. The first conversion unit receives alternating current (AC) electrical voltage from a distribution transformer of an AC power distribution system and converts the AC electrical voltage to DC electrical voltage output. The one or more second conversion units are connected downstream of the first conversion unit, and each second conversion unit converts the DC electrical voltage output from the first conversion unit to a respective AC electrical voltage output for a respective one or more loads. The one or more loads may be associated with a household.

Disclosed is an optimized energy interconnection system for an urban railway train in the technical field of urban railway transportation power supply, for addressing the technical problem that distribution of regenerative braking energy flows cannot be accurately determined. The system includes a DC intermediate bus and a multi-port flow controllable energy router. The multi-port flow controllable energy router can comprehensively control a source and a load connected in parallel on the DC intermediate bus and thus can accurately determine the distribution of regenerative braking energy flows, thereby forming a well-developed system for evaluating usage of the braking energy.

Aspects of the invention overcome a monolithic approach to conventional low-frequency LPTs by using a high-frequency solid-state alternating current ac/ac modular power-conversion approach. Embodiments of the invention enable the ability to incorporate new technologies without in all cases redoing a LPT design from scratch. Furthermore, given that LPTs are for the long term, aspects of the invention ensure that they are durable, efficient, and fault tolerant with overloading capability.

In one embodiment, an apparatus includes a surge voltage blocker circuit to couple between a distribution grid network and a grid-side power converter of a power conversion system. The surge voltage blocker circuit may include a plurality of series-coupled AC switch circuits, each including: a bidirectional switch formed of a first power transistor and a second power transistor; and a transient voltage suppression device coupled in parallel with the bidirectional switch.

A power converter, includes: a first terminal, a second terminal, a third terminal and a fourth terminal; stored-energy-source terminals, to which a stored energy source can be connected; four inverter bridge branches, which are formed from semiconductor switching devices, the inverter bridge branches each having a center tap, each center tap being assigned to one of the terminals, and the inverter bridge branches being interconnected and controllable such that electrical energy can be transferred bidirectionally between the stored-energy-source terminals and the first terminal, the second terminal, the third terminal and/or the fourth terminal; and a control unit, which is designed to control the semiconductor switching devices of the inverter bridge branches.

An apparatus includes a DC-to-AC converter comprising a first output terminal and a second output terminal. The apparatus also includes a DC-to-DC converter comprising a third output. The DC-to-AC converter is configured to receive a DC input voltage from a DC power source, and to produce a first alternating output voltage at the first output terminal, and a second alternating output voltage at the second output terminal. The DC-to-DC converter is configured receive a DC input voltage from the DC power source, and to step down the DC input voltage at the third output.

A power transmission unit includes an alternating-current power source that outputs alternating-current power, a clock generation unit that generates a clock signal higher in frequency than the alternating-current power, and a power transmission antenna that wirelessly transmits the power. A power reception unit includes, a power reception antenna that receives wirelessly the power from the power transmission antenna, and a rectification circuit that rectifies a voltage output from the power reception antenna and outputs the alternating-current power. A control system includes a correction unit that estimates a property change in one or more passive elements included in at least one of the power transmission unit or the power reception unit, and corrects a phase of the clock signal or the alternating-current power output from the alternating-current power source to maintain linearity between the alternating-current power output from the alternating-current power source and the alternating-current power output from the rectification circuit.

An AC-AC converter can include a stack of four switches. An input of the converter can be coupled across the stack of four switches, and an output of the converter can be taken from first terminal coupled to a connection point of first and second switches of the stack and a second terminal coupled to a connection point of third and fourth switches of the stack. The converter can further include a controller that operates the switches such that during a positive half cycle of an AC input voltage, the first and second switches are operated with an alternating 50% duty cycle and the third and fourth switches are constantly on, and during the negative half cycle of the AC input voltage, the third and fourth switches are operated with an alternating 50% duty cycle and the first and second switches are constantly on.

Transformer assembly including a first transformer stage having a plurality of first-stage transformer cells; and a second transformer stage. An input of the second transformer stage is connected to an output of the first transformer stage. A lightning impulse breakdown voltage of a transformer cell of the second stage is at least double of a lightning impulse breakdown voltage of transformer cells of the first stage.