Abstract: Method for controlling an electric drive motor coupled to a reciprocating mechanical system such as an oil well walking beam pump by inserting a pair of power-off pulses in a reciprocation period of the pump motor energization cycle, with one pulse in a top-of-cycle region and the other pulse in a bottom-of-cycle region to reduce rod stress and motor electrical power consumption and increase pump displacement and efficiency.

Abstract: A motor drive system for direct current motors and other similar loads in which the power factor presented to the line by the system remains close to unity for all operating conditions (e.g., all motor speeds). This is accomplished by rectifying an alternating current input voltage and thereafter chopping it to vary power input to the load. An important feature of the invention is the use of a choke at the output of the rectifier of sufficient size to insure that current pulses flowing from the rectifier will be continuous (i.e., will not drop to the zero voltage level) during the sequential ON periods of the rectifier elements.

Abstract: A mounting assembly for press-pack semiconductive controlled rectifiers wherein the rectifiers are all thermally connected to the same heat sink using an insulating medium, the rectifiers being electrically interconnected using common bus bars as required to provide a desired alternating current or direct current connection. A common spring arrangement is used to apply appropriate pressure to at least two semiconductors at once to hold them in contact with their associated bus bars. At least one of the interconnecting bus bars for the rectifiers is formed of a malleable conducting medium, such as copper, formed and used in a manner to provide load equalizing and surface alignment such that the spring can transmit uniform pressure to the heat sink and the semiconductive controlled rectifiers.