Patent Application
20160380570
Field
The disclosed concept relates generally to motor control drives, and, more particularly, to a fully integrated medium voltage motor drive system that includes an integrated dual bus configuration.
Background Information
There are numerous situations where multiple alternating current (AC) motors are employed to drive heavy machinery. For example, multiple high horsepower electric AC motors are used in a pumping system, such as, without limitation, a water pumping system. As is known in the art, in such settings, there are a number of devices that can be used to control the AC motors. In particular, contactors, soft starters, and variable frequency drives (VFDs) (also referred to as adjustable frequency drives or AFDs) are different types of devices that can be used to control an AC motor in such a setting.
A contactor simply connects the motor directly across the AC line. A motor connected to the AC line will accelerate very quickly to full speed and draw a large amount of current during acceleration. A soft starter is a device used to slowly ramp a motor up to full speed, and/or slowly ramp the motor down to a stop. Reducing both current draw and the mechanical strain on the system are big advantages of using a soft starter in place of a contactor. A VFD is a solid state electronic power converting device used for controlling the rotational speed of an AC motor by controlling the frequency of the electrical power supplied to the motor. Typically, a VFD first converts an AC input power to a DC intermediate power. The DC intermediate power is then converted to a quasi-sinusoidal AC power for driving the motor. Thus, the main components of a typical VFD include a number of input isolation transformers coupled to the source of AC power, a converter, such as a number of rectifier bridge assemblies, for converting the AC source power into the DC intermediate power, a direct current (DC) bus and associated DC bus capacitors for storing the DC intermediate power, and an inverter for converting the stored DC intermediate power into a variable voltage, variable frequency AC voltage for driving the motor.
There are currently no integrated medium voltage motor control systems wherein multiple AC motors may be driven using a common AC bus while allowing multiple inverters to share a common DC bus. There is thus room for improvement in the field of motor control centers.
In one embodiment, a medium voltage drive and control system is provided that includes a dual bus configuration including an AC bus and a DC bus, the AC bus being structured to be coupled to an AC power source. The system also includes a converter module connected to the AC bus and structured to receive AC power from the AC bus and convert the AC power to DC power, a DC link module coupled to the converter module and to the DC bus, wherein the DC link module is structured to store the DC power and provide the DC power to the DC bus, and a plurality of inverter modules, each inverter module being coupled to the DC bus and being structured to receive at least a portion of the DC power from the DC bus and convert the at least a portion of the DC power to quasi-sinusoidal AC output power for provision to a load associated with the inverter module.
In another embodiment, a method of driving a plurality of loads is provided. The method includes receiving AC power from an AC bus coupled to an AC power source, converting the AC power to DC power in a converter module coupled to the AC bus, providing the DC power to a DC bus, receiving at least a portion of the DC power in a plurality of inverter modules, each inverter module being coupled to the DC bus, and in each inverter module, converting the received at least a portion of the DC power to quasi-sinusoidal AC output power for provision to a particular one of the loads associated with the inverter module.
A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
Directional phrases used herein, such as, for example, left, right, front, back, top, bottom and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.
As employed herein, the statement that two or more parts are “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts.
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the terms “hard bus”, “hard bussed” or “hard bussing” shall refer to a system of one or more electrical conductors that makes a common connection between a number of circuits or circuit components and that employs metallic, e.g., copper, brass or aluminum, strips or bars that are connected, e.g., bolted, together, as opposed to a cable or cables that are strung together to interconnect a number of circuits or circuit components (which is usually used for field connections).
As employed herein, the term “medium voltage” shall mean 1000V-15,000V.
The disclosed concept provides a medium voltage motor control system which uses one or more large converter sections interconnected with an integrated dual AC and DC bus. Multiple inverters, bypasses, or other motor control devices can then be connected to the dual buses to provide a system that shares the large pool of direct current and the common connection to the AC line.
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Moreover, according to a further aspect of the disclosed concept, a number of additional motor control devices may be coupled to the common AC bus 18 for driving a number of additional motors 16. For example, motor 16D shown in
In the non-limiting illustrated exemplary embodiment, at least AC bus 18, DC bus 20, converter module 22, DC link capacitor bank 24, inverter modules 26, inverter contactors 28, bypass contactors 30, FVNR 32 and FVNR contactor 34 are provided in an enclosure 36. In alternative embodiments, isolation switch 8, fuse 10, main contactor 12, and main transformer 4 they also be provided in enclosure 36. In the exemplary embodiment, enclosure 36 is an arc resistant enclosure that is structured to withstand an internal fault without endangering an operator who is standing in front of the equipment. In the exemplary embodiment, arc resistant enclosure 8 is structured to meet IEEE C37.20.7 standards, and thus be arc resistant at the front, sides and rear thereof, and to have the following arc resistant ratings: 50 kA-0.5 s, Type 2B.
While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.
