Electrical power sources and systems for heating in or adjacent to an oil well or other mineral well, or for heating other earth media, each comprising an A.C. heating generator that generates an A.C. heating current at a selected heating frequency substantially different from the conventional 50/60 Hz frequency used by power companies; the heating generator may comprise an A.C. to D.C. converter for developing an intermediate D.C. output of predetermined amplitude from a conventional 50/60 Hz A.C. input, and a solid state switching circuit for repetitively sampling the D.C. output of the converter at the selected heating frequency, usually in a range of 0.01 Hz (or even lower) up to about 35 Hz. A heating rate control varies the energy content and the frequency of the A.C. output to suit well requirements. Each power source or system includes output connections for connecting the output of the heating generator to a normally inaccessible main heating electrode, usually located downhole in a well, and to a return electrode; most have the capability of including a very small controllable D.C. component in the output.

Power sources for downhole electrical heating

A motor driving apparatus capable of drivingly controlling a plurality of inverter units (IV1-IV4) with a single motor driving command S from a motor control unit (1), to thereby control a large-capacity motor or the like. The motor control unit (1) sends out a single motor driving command (torque command) S. An intermediary unit (3) obtains motor driving commands SxA1 to SxA4 for the inverter units (IV1-IV4) by multiplying the motor driving command S by each of coefficients A1 to A4 set in advance. The inverter units (3) are fed with the motor driving commands SxA1 to SxA4 individually and drive a single motor (2). Since the motor (2) is driven by the total current supplied by the inverter units (IV1-IV4), the motor can generate a large torque. The motor control unit (1) only needs to generate a single motor driving command S, and hence only needs to operate a single processing part. Alternatively, the single motor (2) may be replaced by a plurality of motors, each associated with a respective one of the inverter units (IV1 to IV4). Also, the intermediary unit (3) may generate the individual motor driving commands in the form of parallel or serial data.

Motor driving apparatus

A method, voltage source converter and computer program product for limiting the current in a DC power transmission system are disclosed. The voltage source converter has an AC side and a DC side and a fault current path between these sides. It furthermore includes a control unit and at least one switching unit of a first type provided in the fault current path and that includes a primary switching element together with an anti-parallel secondary controllable rectifying element. Based on a fault being detected in the DC power system when the primary switching elements of the converter are blocked, the control unit changes the control of the controllable rectifying element from acting as a non-controllable rectifying to acting as a controllable rectifying element.

Fault current limitation in dc power transmission systems

In a discharge control section of an inverter control device, when the connection of the battery and the smoothing capacitor is disconnected by means of a contactor, the charge accumulated on the smoothing capacitor is discharged by applying high-frequency voltage to the stator windings of the motor by controlling the main inverter circuit.

Inverter control device and electric vehicle thereof

A variable speed drive (VSD) having a rectifier, an inverter, an inverter modulator, an inverter controller, and a control loop, for controlling a motor load, wherein the control loop reduces an amount of power transferred to the inverter during a voltage sag. The control loop may include a reference generator, a filter, a regulator, and a ride-through corrective algorithm. A method for controlling a VSD to improve voltage sag ride-through by monitoring a voltage applied to the VSD, generating a control signal representative of losses in a motor load when a voltage sag is detected in the voltage applied to the VSD and applying less power to the load of the inverter.

Control loop and method for variable speed drive ride-through capability improvement

A power converter having a thyristor converter connected to an AC power source to rectify its AC output, a DC intermediate circuit including a smoothing capacitor and receiving a rectified output from the thyristor rectifier and a voltage type inverter for converting a DC voltage applied from the DC intermediate circuit into an AC output voltage of a variable voltage and a variable frequency. The DC intermediate circuit has two series circuits, each having a diode and a transistor switch, connected in parallel with each other and to the both terminals of the thyristor converter. The junctions, each between the diode and the resistor, are connected to the both terminals of the smoothing capacitor. The two series circuits function to switch the connection polarities of the thyristor converter and the smoothing capacitor and to regulate the voltage across the capacitor with a limited current by a voltage step-up or step-down operation by the transistor switch.

Takashi Tsukahara

Papers

Power converter for driving an AC motor at a variable speed