A direct-current power supply apparatus includes: a reactor having one end connected to an alternating-current power supply; a bridge circuit, connected to an opposite end of the reactor, converting an alternating-current first voltage output from the alternating-current power supply into a direct-current voltage; and a current detector detecting an alternating current flowing between the alternating-current power supply and the bridge circuit. The reactor reduces an inductance in accordance with an increase of the alternating current and, when the alternating current exceeds a first current, has an inductance lower than one third of an inductance at which a current does not flow in the reactor. The bridge circuit performs an active operation when the detection value of the alternating current is larger than or equal to the first current and performs a passive operation when the detection value of the alternating current is lower than the first current.

A motor drive device has an abnormality detection function for a power supply unit between its own device and a power supply, and includes: a forward converter that is inputted AC power from the power supply via the power supply input part, and converts the AC power into DC power; a reverse converter that converts the DC power from the forward converter into AC power; a DC link capacitor provided to a DC link between the forward converter and the reverse converter; a voltage detection part that detects voltage of the DC link capacitor; and an abnormality detection part that obtains a voltage change amount for a predetermined time of the DC link capacitor based on voltage values detected by the voltage detection part, and performs abnormality detection on the power supply input part based on the voltage change amount thus obtained.

A motor drive comprises a rectifier arranged to receive an externally supplied AC voltage and to generate a DC bus voltage. An inverter is arranged to receive the DC bus voltage and to generate an AC output voltage for supply to an external load. A DC bus portion is connected between the rectifier and the inverter. The DC bus comprises first and second conductors, wherein an inductor is connected in series along the first conductor between the rectifier and the inverter. A DC link capacitor is connected in parallel between the conductors. A controller is arranged to supply a plurality of perturbation signals at a first node between the rectifier circuit portion and the DC bus portion, to measure a respective response signal at a second node between the DC bus and the inverter and is is arranged to generate a parameterised model of a transfer function of the DC.

A pulse pattern generation device generating a pulse pattern for controlling switching elements provided in an inverter that operates a motor, the pulse pattern generation device includes a current calculation unit that calculates a current flowing through a coil when a voltage that is applied to the motor during the operation of the motor is virtually applied to the coil of the motor, an effective current calculation unit that calculates an effective current from the current calculated by the current calculation unit, an iron loss estimation unit that estimates an iron loss which originates in a core of the motor, and a pattern generation unit that generates a pulse pattern using an evaluation function including the iron loss estimated by the iron loss estimation unit and the effective current calculated by the effective current calculation unit as evaluation items.

A motor drive comprises a rectifier circuit portion arranged to receive an externally supplied AC voltage and to generate a DC bus voltage. An inverter circuit portion is arranged to receive the DC bus voltage (V.sub.DC_Bus) and to generate an AC output voltage (V.sub.out) for supply to an external load. A DC bus portion is connected between the rectifier and the inverter. An inductor (L.sub.1) is connected in series along a bus conductor between the rectifier and inverter, and a DC link capacitor (C.sub.1) is connected in parallel between the bus conductors. A voltage across the DC link capacitor (C.sub.1) is input to a tuneable notch filter arranged to supply a filtered signal. A controller varies the resonant frequency of the notch filter to a plurality of values across an operational range and modulates a supply current provided by the inverter with a probe current signal at the resonant frequency.

An electric motor drive device includes: a main substrate mounted with a power supply circuit that generates, on the basis of alternating-current power supplied from an alternating-current power supply, a drive power to drive a compressor motor; a plurality of connection switching relays that perform switching between connections for the compressor motor; a small substrate mounted with the connection switching relays; a relay drive circuit that switches the connection switching relays; lead wires that connect the compressor motor and the small substrate to the power supply circuit; and lead wires that connect the small substrate and the compressor motor.

A power converting apparatus includes: a rectifying unit configured to rectify an input AC power, a buck converter that is configured to step down a voltage of the rectified power and that is configured to output DC power having the step down voltage, a first inverter that is connected to an output terminal of the buck converter and that is configured to convert the DC power into AC power to drive a first motor, a second inverter that is connected to the output terminal of the buck converter, that is disposed in parallel to the first inverter, and that is configured to convert the DC power into AC power to drive a second motor, and a converter controller configured to control an output voltage of the DC power of the buck converter.

Examples include a method for controlling a variable speed drive driving an electric motor. The variable speed drive is connected to an electric power source and comprises a passive DC-link and an inverter stage controlled by a first controller of the variable speed drive. The passive DC-link is connected to the inverter stage. The method comprises running the electric motor to reach a steady-state operating point, measuring a plurality of values of current or voltage of the passive DC-link, and computing, by a second controller, a frequency spectrum of the DC-link based on the plurality of values of current or voltage measured. The method further comprises detecting a specific resonance frequency by comparing amplitudes of the frequency spectrum to a predetermined pattern, and modifying filter parameters of a digital filter of the DC-link or control parameters of a control law of the electric motor based on the specific resonance frequency.

Provided is a power conversion unit, in which a power smoothing capacitor is configured such that a plurality of unit capacitors as conductive polymer hybrid aluminum electrolytic capacitors are arrayed in a grid pattern and connected in parallel on a circuit board, and also connected to a plurality of unit modules of different phases via positive and negative bus bars arranged on both sides of the circuit board so that each group of several unit capacitors and each unit module are arranged close to each other, to thereby reduce wiring impedance of a power supply circuit and suppress noise generation.

A control device for drives of a machine switches between normal operation and special operation depending on power demand from a power supply. In both operating modes, the control device cyclically determines preliminary current setpoint values. In normal operation, the current setpoint values match the preliminary setpoint values. In special operation, the control device dynamically determines a proportional factor for the drives depending on nominal and/or actual operating states of the drives. The control device determines current setpoint values by modifying the preliminary current setpoint values so that a respective drive draws no more power than the product of the respective proportional factor and the available total power. The current setpoint values and the current actual values are fed to drive controllers for the first drives, by means of which the preliminary first current setpoint values are determined. The control characteristics of the drive controllers include an integral part.