Electric power conversion systems – Current conversion – Including an a.c.-d.c.-a.c. converter
Reexamination Certificate
2000-04-06
2001-09-25
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including an a.c.-d.c.-a.c. converter
C363S034000, C363S124000
Reexamination Certificate
active
06295215
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to power supply apparatus and methods of operation thereof, and more particular, to AC power supply apparatus and methods.
Power supply circuits are commonly used in equipment such as uninterrupted (or “uninterruptible”) power supplies (UPSs), motor drives, and other applications. Conventional UPSs use a variety of different circuit topologies, including standby, line-interactive and on-line topologies. Generally, each of these topologies has advantages and disadvantages and, accordingly, selection of a particular topology is typically governed by the needs of the application.
For example, a typical standby UPS topology includes a transfer switch that directly connects the load to a primary AC power source under normal conditions and that transfers the load to a secondary AC source derived from a battery or other auxiliary source when the primary AC power source fails. Due to the time needed to operate the transfer switch, such a standby UPS often exhibit a significant interruption in power delivered to the load, which may be unacceptable for data processing or other critical tasks. In addition, standby UPSs often do not compensate for power quality, e.g., voltage degradation, harmonic distortion and low power factor. Nonetheless, the standby topology is often used for low-cost UPSs, as it is often cheaper to produce than other topologies. A line interactive UPS may use a transfer switch arrangement similar to that of the standby topology, but may also include means for regulating and conditioning the AC power source to improve power quality.
Many UPSs use an online topology. For example, a typical online series train UPS includes a series train AC/AC converter that produces an AC output voltage at a load from an AC input voltage provided by an AC power source such as a utility, but includes a DC link that is used to isolate the load from disturbance and other degradation of the AC power source. The intermediate DC bus is typically coupled to an inverter that inverts the DC voltage on the DC bus to produce an AC output. Other circuits, such as filters and regulators, may be included in the path with the rectifier and the inverter. Typically, the DC bus is also coupled to an auxiliary source of power, such as a battery, which maintains the DC voltage on the DC bus in the event the AC power source fails. Some online UPSs use circuit topologies other than a series train, including more complex topologies, such as delta converters, or other techniques.
Under normal operating conditions, online UPS's supply power to a load through a rectifier/inverter chain or similar regulating circuitry, providing relatively clean and regulated power at the output of the UPS. When the AC power source fails, the UPS may achieve an uninterrupted transition to battery power, as there typically is no need to change the state of a transfer switch. Some online series train UPSs also include a bypass feature such that, in the event of a failure, the inverter is prevented from supplying power to the load (e.g., by disconnecting it from the load or placing it into an inactive standby state) while the load is connected to the AC power source via a bypass path. Such a feature may also be used to provide an “economy” mode of operation, as power dissipation associated with the operation of the rectifier/inverter chain may be reduced when the load is transferred to the bypass path.
However, such an approach may be compromised if the AC power source is subject to small but frequent excursions outside of the power quality criteria, as may be the case, for example, in systems powered by an unsteady AC power source, Such as an auxiliary generator set. In such a case, the UPS may be forced to power the load through the inverter in order to meet the power quality requirements of the load, thus reducing the opportunity for greater efficiency through bypass operation.
SUMMARY OF THE INVENTION
According to embodiments of the invention, improved efficiency may be achieved in a power supply apparatus (e.g., a UPS circuit) that incorporates an AC/DC converter that produces an intermediate DC voltage from an AC input voltage. The power supply apparatus includes a multi-mode DC/AC converter circuit that provides a first component of power, for example, a real power component, while a bypass circuit provides a second component of power, for example, a harmonic power component and/or a reactive power component, to the load from an AC power source. The DC/AC converter circuit may include a current mode controlled inverter that provides reactive and harmonic currents to the load such that the bypass circuit predominantly transfers real power between the AC source and the load. In this manner, power factor and other power quality parameters at the AC source may be maintained at desired levels.
In particular, in embodiments of the invention, a power supply apparatus includes an AC input port, an output port, and a bypass circuit that couples the AC input port to the output port. An AC/DC converter circuit, coupled to the AC input port, produces a DC voltage from an AC input voltage at the AC input port. A DC/AC converter circuit, coupled to the AC/DC converter circuit, controls current transfer between the output port and the AC/DC converter circuit responsive to a control input such that respective first and second component currents of a current delivered to a load coupled to the output port pass via respective ones of the bypass circuit and the DC/AC converter circuit. The DC/AC converter circuit may be operated such that current passing through the bypass circuit is constrained to be substantially in phase with the AC input voltage.
In other embodiments of the invention, a power supply apparatus includes an AC input port, first and second voltage busses, and an output port. An AC/DC converter circuit, coupled to the AC output port and to the first and second voltage busses, produces a DC voltage across the first and second voltage busses from an AC input voltage at the AC input port. A first switching circuit selectively couples the AC input port and the output port responsive to a first control input. A second switching circuit selectively couples the output port and the first and second voltage busses responsive to a second control input. A control circuit generates the first and second control inputs such that, in a first mode of operation, the first switching circuit decouples the AC input port from the output port while the second switching circuit supplies power to the output port. In a second mode of operation, the first switching circuit couples the AC input port to the output port and supplies a first component of a power at the output port while the second switching circuit supplies a second component of the power at the output port. In the second mode of operation, the control circuit may generate the second control input such that the current passing through the first switching circuit is substantially in phase with the AC input voltage.
In yet other embodiments of the invention, an uninterruptible power supply (UPS) apparatus includes an AC input port, an AC output port, and a bypass circuit that couples and decouples the AC input port to and from the AC output port responsive to a first control input. A series train AC/AC conversion circuit, coupled to the AC input port and to the AC output port, transfers power between the AC input port and the AC output port such that, in a first mode of operation, the series train AC/AC conversion circuit transfers a first component of power from the AC input port to the AC output port while the bypass circuit transfers a second component of power from the AC input port to the AC output port. In a second mode of operation, the series train AC/AC conversion circuit transfers power from the AC input port to the AC output port while the bypass circuit decouples the AC input port from the AC output port. In the first mode of operation, the series train AC/AC conversion circuit may be operated such that it causes the
Akbari Edward
Faria Des
Grudzinski Piotr
Ohman Ove
Zhang Hong
Berhane Adolf Deneke
Myers Bigel & Sibley & Sajovec
Powerware Corporation
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