Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-09-07
2002-07-02
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
Reexamination Certificate
active
06414854
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a power conversion apparatus using a current-controlled semiconductor element as a switching element. In particular, the present invention relates to a switching-element driving device in such a power conversion apparatus. More specifically, the present invention relates to a technique for enhancing the power conversion efficiency of a power conversion apparatus using a semiconductor element as a switching element.
BACKGROUND ART
In view of efficient utilization of energy, a power conversion apparatus using a semiconductor switching element as a switching element has an extremely widespread availability due to its excellent characteristics in power conversion efficiency. The semiconductor switching element includes a voltage-driven type element, such as an isolated-gate bipolar transistor (IGBT), static-induction transistor and field-effect transistor (FET), and a current-driven type element, such as a bipolar-mode static-induction transistor (BSIT) and bipolar junction transistor (BJT).
The voltage driven type element may be driven directly by a voltage signal so that a driving circuit may be readily simplified and its driving frequency may also be arranged higher. In applications requiring a withstand voltage of 250V or more, several types of switching elements are selectively used depending on requirements for capacity and driving frequency. Specifically, in case of using the switching elements in a driving frequency range of several KHz to several hundred KHz, the IGBT excellent in overall balance of voltage drop in ON state and switching performance and the FEA having small current capacity but capable of high speed operation are widely employed in the power conversion apparatus.
On the other hand, since the current-driven switching type element is driven by applying current to a control terminal, a driving circuit tends to be complexified and to have a lower operation speed than that of the voltage-driven type element. However, the current-driven type switching element has an advantageous feature that the voltage drop in ON state is about one-third to one-sixth of that of the voltage-driven type element, and thereby provides a lower conduction loss. This proves that the current-driven type switching element is more suitable for providing a downsized power conversion apparatus.
While there are broadly classified two types of semiconductor switching elements available for the power conversion apparatus, as described above, it has been often the case that the voltage-driven type switching element having a low switching loss and facilitating a high frequency driving was employed in view of downsizing of components, simplification of circuits, downsizing based on high driving frequency, cost reduction and other. However, considering how to coping with social needs for achieving an enhanced efficiency and downsizing with an eye to the future, the level of voltage drop in ON state of the voltage-driven type element will be an obstacle as long as holding over the technique using the current voltage-driven switching element. For instance, observing the current situation, the voltage drop in ON state of the IGBT et al. being a mainstream voltage-driven switching element has already been improved closely up to the theoretical value. All the more because of its current high percentage of completion, it cannot be expected to reduce the conduction loss drastically.
As to switching loss, loss recovery techniques utilizing resonance phenomenon and soft switching techniques have been developed for preventing electromagnetic environment pollution and reducing power loss. In contrast, a conduction loss in the semiconductor switching element inevitably arises when a current is passed through the element and the level of the loss depends on the performance of the element. Thus, the conduction loss cannot be readily reduced only by a simple modification but a radical review of circuit topology.
Two primary losses arise in the semiconductor switching element of the power conversion apparatus; one is a switching loss arising in the course of changing the state of the semiconductor switching element from ON state to OFF state or from OFF state to ON state; and the other is a conduction loss caused by a voltage drop arising in the semiconductor switching element when this semiconductor switching element is in ON state. Thus, in order to provide a power conversion apparatus capable of meeting the need in response to the demand for further downsizing the current power conversion apparatus and enhancing its power density, it is necessary to develop a technique capable of achieving higher efficiency by comprehensively reducing both of the conduction loss caused by the voltage drop in ON state of the semiconductor switching element and the switching loss which lead to a power loss.
Heretofore, there have been very few cases reporting that the conduction loss in the semiconductor switching element was reduced by an effective improvement in circuit. Giving some examples from among such few cases, Japanese Patent Laid-Open Publication No. Hei 1-97173 discloses a technology for reducing both a switching loss and conduction loss in a PWM full-bridge power conversion apparatus, such as a PWM inverter, by applying a semiconductor switching element having a small conduction loss, such as a bipolar transistor, to an arm switched by commercial frequency, and a semiconductor switching element having a small switching loss, such as a static-induction transistor, to an arm switched by high-frequency, so as to make up a bridge circuit in the apparatus. The Journal of the Institute of Electrical Engineers of Japan, Section D, vol. 116, No. 12, 1996, pp. 1205-1210, also discloses a modification in circuit for reducing a conduction loss in a power conversion apparatus using semiconductor switching elements. However, these prior arts involve insufficient studies in terms of optimization of the conduction loss, reduction of the loss in their driving circuit, downsizing et al. For example, the aforementioned Japanese Patent Laid-Open Publication includes no specific teaching about how to drive the bipolar transistor serving as a current controlled switching element. However, when a constant current is applied to a base of the transistor as in conventional methods for driving transistors, the efficiency in low load will be particularly deteriorated due to the driving loss in no load state or low load state. In the technique described in the aforementioned Journal of the Institute of electrical Engineers of Japan, since a driving current is supplied to the transistor by a current transformer (CT), a base current is defined by the coil ratio of the CT. Thus, it is necessary for the circuit to be designed in consideration of the minimum current amplification factor of the semiconductor switching element. As a result, the semiconductor switching element will be driven to its oversaturated state during the low load state. In addition, the driving current may be effectively supplied only by relatively high driving frequency because of using the CT.
DISCLOSURE OF THE INVENTION
In view of the above problems, it is an object of the present invention to provide a power conversion apparatus using a semiconductor switching element and a method therefor, capable of reducing a power loss by regenerating power, and comprehensively reducing a switching loss and conduction loss arising in the switching element so as to achieve high efficiency.
It is another object of the present invention to provide a power conversion apparatus using a semiconductor switching element, capable of comprehensively reducing a switching loss and conduction loss arising in the switching element so as to achieve high efficiency.
In order to achieve the above objects, according to one aspect of the present invention, in a power conversion apparatus including a current-controlled semiconductor switching element having a collector, an emitter and a base, a switching-element driving device is provided with a current
Itoh Kazuyuki
Okita Yoshihisa
Takayanagi Yoshinobu
Tanaka Katsuaki
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Riley Shawn
TDK Corporation
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