A pre-charge control method for a hybrid multilevel power converter comprises steps of: (a) controlling access of the current-limiting resistor unit, limiting current from the AC power via the current-limiting resistor unit, and outputting the current; (b) controlling the second capacitor unit to bypass, and charging the first capacitor unit; (c) controlling the access of the second capacitor unit when the first capacitor unit is charged to a third preset voltage, and charging the first and second capacitor units at the same time; (d) controlling the first capacitor unit to bypass when the second capacitor unit is charged to a fourth preset voltage, or the first capacitor unit is charged to a first preset voltage, and charging the second capacitor unit; and (e) controlling the access of the first capacitor units and the current-limiting resistor unit to bypass when the second capacitor unit is charged to a second preset voltage.

A protection and attenuation circuit for sensitive AC loads is described. The circuit provides AC power protection and attenuation utilizing high-efficiency switch-mode techniques to attenuate an AC power signal by incorporating a bidirectional, transistorized switch driven from a pulse width modulation signal, PWM. The circuit monitors characteristics of the AC power signal driving a known load and characteristics of the load or other elements and determines the duty cycle of the pulse width modulated signal, PWM, based upon the duration and amplitude of the over-voltage, over-current, over-limit or other event.

A protection and attenuation circuit for sensitive AC loads is described. The circuit provides AC power protection and attenuation utilizing high-efficiency switch-mode techniques to attenuate an AC power signal by incorporating a bidirectional, transistorized switch driven from a pulse width modulation signal, PWM. The circuit monitors characteristics of the AC power signal driving a known load and characteristics of the load or other elements and determines the duty cycle of the pulse width modulated signal, PWM, based upon the duration and amplitude of the over-voltage, over-current, over-limit or other event.

A testing device is provided. The testing device comprises a processor and a switching AC to AC power converter that has no DC link. The processor is configured to set a plurality of bi-directional switches in the power converter in a configuration of on/off states that cause a substantially set electric current to flow through a component being tested by the testing device.

A testing device is provided. The testing device comprises a processor and a switching AC to AC power converter that has no DC link. The processor is configured to set a plurality of bi-directional switches in the power converter in a configuration of on/off states that cause a substantially set electric current to flow through a component being tested by the testing device.

A transformer includes a front stage circuit and a rear stage circuit. As a front stage circuit, a switch series unit, which is connected in parallel to a power supply, includes odd-numbered switches and even-numbered switches alternately turned ON. Mutual connection points of the respective switches and points at both ends of the switch series unit are regarded as m nodes in total. Capacitors are provided on at least one of a first electrical path combining odd nodes to lead them to a first output port, and a second electrical path combining even nodes to lead them to a second output port. The capacitors are present so as to correspond to at least (m−1) nodes. The rear stage circuit includes an element series unit, which is composed of a pair of semiconductor elements connected in series to each other for conducting operations of mutually opposite polarities, and necessary inductors.

Power converters, and microgrids driven by such a power converter, in which the converter is controlled by a proportional controller which operates directly on AC waveforms, preferably without conversion to a DC type signal; preferably with use of voltage compensation to remove inherent error of proportional controller; and preferably with use of individual phase RMS voltages in the voltage compensation, to allow for normal operation under any load condition. Undervoltage of one or two phases is automatically compensated by adjusting the voltage of all phases, to retain balance. Line-starting of a motor load is automatically detected, and frequency droop is driven, apart from the other control relations in the system, to complete the line-starting operation as quickly as possible.

Power converters, and microgrids driven by such a power converter, in which the converter is controlled by a proportional controller which operates directly on AC waveforms, preferably without conversion to a DC type signal; preferably with use of voltage compensation to remove inherent error of proportional controller; and preferably with use of individual phase RMS voltages in the voltage compensation, to allow for normal operation under any load condition. Undervoltage of one or two phases is automatically compensated by adjusting the voltage of all phases, to retain balance. Line-starting of a motor load is automatically detected, and frequency droop is driven, apart from the other control relations in the system, to complete the line-starting operation as quickly as possible.

A substrate and a first circuit board each have an upper side and a lower side. The substrate lower side is connected to a cooling body. On the upper side of the substrate, first electronic switching elements connect an alternating current potential at a phase terminal to a high direct current potential at a first potential terminal and to a low direct current potential at a second potential terminal. Second electronic switching elements connect the alternating current potential to a middle direct current potential at a third potential terminal. The substrate is spaced from the first circuit board under the first circuit board lower side. The upper side of the substrate faces toward the first circuit board. The second switching elements are at least on the upper side of the first circuit board, possibly additionally also on the lower side of the first circuit board.

A converter includes a transformer including primary windings and secondary windings, switches connected to the primary windings, an output inductor connected to the secondary windings, and a controller connected to the switches. The controller turns the switches on and off based on dwell times calculated using space vector modulation with a reference current {right arrow over (I)}.sub.ref whose magnitude changes with time.