Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-07-06
2002-02-26
Nguyen, Matthew (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S289000
Reexamination Certificate
active
06351107
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a switching element driving device for a power conversion device including current control semiconductor switching elements. In particular, the present invention relates to a technology of achieving an improved power conversion efficiency in such power conversion device including semiconductor switching elements.
BACKGROUND OF THE INVENTION
A power conversion device including semiconductor switching elements has widely been used from the standpoint of efficient utilization of energy due to its excellent characteristics in power conversion efficiency. Example of the semiconductor switching elements include voltage-driven type elements, such as insulated-gate bipolar transistors (IGBT), static-induction type transistors, field-effect transistors (FET), and current-driven type elements, such as bipolar-mode static-induction type transistors (BSIT) and bipolar junction transistors (BJT).
The voltage driven type elements can be directly driven by voltage signals, so that their driving circuit may readily be simplified and their drive frequency may also be set higher. In applications which require 250V or more of withstand voltage, several types of switching elements are selectively used depending on the capacity and drive frequency required. Specifically, as switching elements for use in the drive frequency range of several KHz to several hundred KHz, use has widely been made of IGBTs which have an excellent overall balance between a voltage drop under ON state and a switching performance and of FETs which have a small current capacity but capable of high speed operation.
On the other hand, since the current-driven switching element is driven by applying current to its control terminal, the driving circuit often becomes complicated and the switching speed is generally lower as compared with a voltage-driven type element. However, the current-driven switching elements have a characteristic that the voltage drop under ON state is about one-third to one-sixth of the voltage-driven element. Therefore, it can be concluded that the current-driven switching element is suited to reduction in size of the power conversion device.
Thus, semiconductor switching elements usable for power conversion devices can be classified broadly into two types. Among these types, from the standpoint of size reduction of components, simplification of circuits, size reduction by high frequency driving, and cost reduction and so on, there is an increasing tendency of using voltage-driven switching elements which have a lower switching loss and a capability of being easily driven in high frequency range. However, in order to comply with social needs for achieving further improvements in efficiency and size reduction over the future, the level of voltage drop under ON state of the voltage-driven type element would be an obstacle as long as the current technologies using the voltage-driven switching elements are continued to be adopted. In particular, observing the current situation, the voltage drop under an ON state of an IGBT or the like, which is the most widely used one among voltage-driven switching elements, has already been improved closely up to a theoretical value. Thus, the technology has already been reached a highest accomplishment, so that there would be no hope in an effort to achieve a substantial reduction in the conduction loss.
As to the switching loss, developments have been made in a loss recovery technology utilizing a resonance phenomenon and a soft switching technology for the purpose of both the prevention of electromagnetic environmental pollution and the reduction of power loss. On the other hand, a conduction loss is always produced in a semiconductor switching element whenever current passes through the element and the amount of the loss depends on the characteristics of the element, so that it would not be easy to reduce the conduction loss only through a simple improvement but would require radical review of circuit topology.
In the technical field of the power conversion device, various efforts are still continued with aiming at size reduction of the device as a whole, obtaining a high power/high density device, and accomplishing a higher efficiency, and so on.
There are two primary losses produced in semiconductor switching elements of a power conversion device, one being a switching loss generated while the semiconductor switching element is moved from an ON state to an OFF state or from an OFF state to an ON state, the other being a conduction loss caused by a voltage drop produced in the semiconductor switching element when the semiconductor switching element is in the ON state. In order to comply with the requirements of making a power conversion device more compact than existing ones provide a device of higher output power and higher density, to thereby obtain a power conversion device meeting with the needs, it is necessary to develop a technology capable of accomplishing high efficiency by comprehensively reducing both the aforementioned conduction loss caused by the voltage drop under ON state of the semiconductor switching element and the switching loss which together lead to a power loss.
Under the above circumstances, there are very few examples reporting that the conduction loss in a semiconductor switching element has been reduced through an effective improvement in circuitry. Referring to examples among these reports, Japanese Patent Laid-Open Publication No. Hei 1-97173 discloses a technology for reducing both switching loss and conduction loss in a PWM full bridge power conversion device such as a PWM inverter by providing a semiconductor switching element having small conduction loss, such as a bipolar transistor, in an arm adapted to be switched under a commercial-frequency, and a semiconductor switching element having small switching loss, such as static-induction transistor, in an arm adapted to be switched under a high-frequency. The Transactions of the Institute of Electrical Engineering of Japan (T. IEE Japan), Vol. 116D, No12 (1996), also discloses a circuitry improvement for reducing conduction losses in a power conversion device using semiconductor switching elements. However, these prior art technologies still include problems in that adequate investigations have not been made in respect of optimization of conduction loss, reduction of loss in the driving circuit and size reduction, and that there is practically limitations in the driving frequency. For example, the aforementioned Japanese Laid-Open Publication includes no specific teaching about method for driving the bipolar transistor which is of a current control type switching element. However, when a constant current is applied to the base as in a conventional method for driving a transistor, the efficiency under a light load condition would particularly become low due to the driving loss in no load condition or light load condition. In the technology described in the aforementioned Transactions of the Institute of Electrical Engineers of Japan, drive power is supplied to a transistor by a CT (current transformer) which is connected to the collector of the transistor, so that the base current is determined by the winding ratio of the aforementioned CT. Therefore, it is required that the circuit is to be designed in consideration of the minimum value of current amplification factor of the semiconductor switching element. As the result, there is a possibility that the CT is driven up to a supersaturated state in low load. Besides, the technology is effective only under a relatively high frequency due the use of the CT.
SUMMARY OF THE INVENTION
Under these circumstances, it is an object of the present invention to provide a power conversion device including a semiconductor switching element and capable of achieving high efficiency by totally reducing the switching loss and the conduction loss produced at the switching element.
In order to accomplish the above and other objects, the present invention proposes to detect the collector current or dra
Nguyen Matthew
TDK Corporation
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