Electric power conversion systems – Current conversion – Having plural converters for single conversion
Reexamination Certificate
2002-07-25
2004-06-15
Patel, Rajnikant B (Department: 2838)
Electric power conversion systems
Current conversion
Having plural converters for single conversion
C363S098000
Reexamination Certificate
active
06751106
ABSTRACT:
BACKGROUND OF INVENTION
Paralleling multiple power converters is a common practice in the telecom and UPS (uninterruptible power supply) industries to increase overall system power capacities and to enhance system reliabilities by building redundancy. Typical examples of such power converters are single phase or three phase converters comprising inverters, rectifiers and DC/DC converters. Typically all the parallel power converters are gated synchronously and are tied together through isolation transformers to limit the cross current. Synchronous gating implies that the gate controls for the parallel converters are perfectly aligned.
Another way to operate the parallel power converters is through interleaved gating. Interleaved gating means that the switching patterns of the parallel converters are uniformly phase shifted, rather than synchronized. Interleaved gating has several advantages such as having reduced harmonic filter size, increased system efficiency, greatly enhanced control bandwidth (and thus improved dynamic performance), and potentially reduced EMI (electromagnetic interference).
Common mode current that circulates among the paralleled multiple converters or within paralleled converter systems that does not contribute to the output to the load is typically referred to as “cross current.” Both synchronous and interleaved gating control embodiments typically result in undesirable cross current with the cross current being more severe in interleaved embodiments. In ideal conditions synchronous gating does not lead to cross current, but in actual circuits using synchronous gating cross current exists due to mismatched circuit parameters. One way to reduce the cross current is by using an isolation transformer. In embodiments with isolation transformers, these isolation transformers account for almost one third of the system cost.
The existing techniques for controlling cross current without using an isolation transformer all suffer from certain inherent disadvantages. For example, using current balancers or inter-phase reactors for controlling cross current requires design of an inter-phase reactor. Such design cannot be standardized for arbitrary numbers of converters in parallel.
Another technique of controlling cross current without using isolation transformers is through use of “combined-mode” current control by treating two parallel converters as one converter, selecting the “optimum” switching vector, and adding a current balancer. The “combined-mode approach” is not suitable for more than two converters in parallel because the modulator complication level increases drastically when dealing with more than two parallel converters.
It would therefore be desirable to have an improved cross control system for interleaved or synchronous operation of multiple power converters, arranged in parallel, without using isolation transformers.
SUMMARY OF INVENTION
Briefly, in accordance with one embodiment of the present invention, a cross current control system for multiple, parallel-coupled power converters comprises common mode chokes, local cross current detectors, local cross current feedback controllers and local converter controllers. Each of the common mode chokes is coupled to a respective power converter. Each local cross current detector is configured for obtaining common mode cross currents from a respective output line of a respective power converter. Each of the local cross current feedback controllers is configured for receiving the common mode cross currents from respective local cross current detectors, calculating a resultant cross current, and generating a local feedback control signal. Each of the local converter controllers is configured for using a respective local feedback control signal to drive the respective power converter in accordance with a coordinated switching pattern which may comprise either an interleaved or a synchronous switching pattern with respect to the other power converters.
In accordance with another embodiment of the invention, a method of controlling cross-current through multiple, parallel-coupled power converters comprises providing common mode chokes, each coupled to a respective power converter; and obtaining common mode cross currents from output lines of the power converters. The method further comprises for each respective power converter, calculating a resultant cross current by using the respective common mode cross currents, generating a local feedback control signal by using the resultant cross current, and driving the respective power converter by using the respective local feedback control signal in accordance with a coordinated switching pattern with respect to the other power converters.
In accordance with another embodiment of the invention, an integral choke assembly comprises a common mode choke and a differential mode choke. The common mode choke comprises a common mode core wound with at least two common mode coils and a differential mode choke comprises a differential mode core wound with at least one differential mode coil. The common and differential mode choke cores are configured so that at least one magnetic path is shared by magnetic flux generated by common and differential mode coils.
REFERENCES:
patent: 5212630 (1993-05-01), Yamamoto et al.
patent: 5319343 (1994-06-01), Jeffries
patent: 5446645 (1995-08-01), Shirahama et al.
patent: 5726615 (1998-03-01), Bloom
patent: 5909367 (1999-06-01), Change
patent: 6169677 (2001-01-01), Kitahata et al.
Hiroshi Ohshima and Kazuto Kawakami, “Large Capacity 3-Phase UPS with IGBT PWM Inverter”, 1991 IEEE, pp. 117-122, no date.
Tako Kawabata, Shigenori Higashino, “Parallel Operation Of Voltage Source Inverters,” IEEE Transactions on Industry Applications, vol. 24, No. 2, Mar./Apr. 1988, pp. 281-287.
J.F.Chen, C.L.Chu, C.L. Huang, “The Parallel Operation Of Two UPS By The Coupled-Inductor Method,” IEEE, pp. 733-736, no date.
Keiju Matsui, Yoshihiro Murai, Makoto Watanabe, Mitsutaka Kaneko, and Fukashi Ueda, “A Pulsewidth-Modulated Inverter with Parallel Connected Transistors Using Current-Sharing Reactor,” IEEE Transactions on Power Electronics, vol. 8, No. 2, Apr. 1993, pp. 186-191.
Satoshi Ogasawara, Jin Takagaki, Hirofumi Akagi, and Akira Nabae, “A Novel Control Scheme of a Parallel Current-Controlled PWM Inverter,” IEEE Transactions on Industry Applications, vol. 28, No. 5, Sep./Oct., 1992, pp. 1023-1030.
Yoshihiro Komatsuzako, “Cross Current Control for Parallel Operating Three Phase Inverter,” 1994 IEEE,pp. 943-950, no date.
Kun Xing, Fred C. Lee, Dusan Borojevic, Zhihong Ye, and Sudip Mazumder, “Interleaved PWM with Discontinuous Space-Vector Modulation,” IEEE Transactions on Power Electronics, vol. 14, No. 5, Sep. 1999, pp. 906-917.
Garces Luis Jose
Lyons James Patrick
Yuan Xiaoming
Zhang Richard S.
Agosti Ann M.
General Electric Company
Patel Rajnikant B
Patnode Patrick K.
LandOfFree
Cross current control for power converter systems and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Cross current control for power converter systems and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Cross current control for power converter systems and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3363739