Power converter

Abstract

A power conversion device is provided. Switching elements are connected in series, currents IU and IL flowing in respective elements are switched, and an output current IO is supplied to a load, such as a motor, from an output terminal O. In this case, a MOSFET having a mirror element, where mirror elements are provided in main switching elements, is used as the switching elements; current detection circuits are provided in respective mirror elements each; the current detection circuits extract mirror currents IU, IL flowing in the mirror elements as detection signals S< IU>, S; the detection signals are inputted into a comparison circuit 9 as a difference signal S of the detection signals S, S; the difference signal is input to a control operation section 6 as a signal indicating the output current IO; and the switching timing of the switching elements and switching time are controlled. Therefore, a compact, low-loss, and low-cost power conversion device for detecting current is provided, where there is no risk of restriction on output voltage performance.

Description

technical field [0001] The present invention relates to a power conversion device with an output current detection function, in particular to a power conversion device suitable for a servo system, a DC / DC converter or a three-phase AC inverter. Background technique [0002] It is common practice to detect the output current for the control of power conversion devices such as servo systems, DC / DC converters, or three-phase AC inverters, and various current sensors have been proposed. (core) insulated current sensor is the so-called Hall sensor. Here, the Hall sensor means that a conductor through which the current to be measured is passed through a ring-shaped magnetic core, and the Hall sensor installed on the magnetic circuit of the magnetic core reads the magnetic field generated by the current and detects it as a current. [0003] In addition, in addition to the Hall sensor, there is also known a shunt resistance type current sensor in which a shunt resistance is inserte...

AI Technical Summary

Problems solved by technology

[0004] Current sensors used in power conversion devices are generally required to be small, low-loss, low-cost, and high-precision. It cannot be said that these aspects have been fully considered in the prior art

[0005] In the prior art described above, in addition to the high price of the current sensor with the insulated magnetic core itself, as a path for the primary current, it is necessary to pass through structures such as the bus bar of the sensor, so the number of parts increases and the structure is enlarged. , thus further increasing the cost

[0006] Furthermore, from the viewpoint of system protection against overcurrent such as short circuits, it is necessary to provide a current detection circuit for detecting overcurrent of switching elements in addition to a current sensor for detecting output current, which not only increases the number of parts, but also makes it impossible Avoid further escalation of costs

[0007] In addition, since the current sensor based on the shunt resistance increases the power loss in equipment that controls a large current such as a power conversion device, it is necessary to consider the increase in the size of the shunt resistor and suppress the temperature rise due to heat generation. Unavoidable increase in size and cost

[0008] From these aspects, in the above-mentioned prior art, although it is expected to perform current detection using the on-voltage of the MOSFET, at this time, it is necessary to make the element in the on-state at the timing (timing) to detect the current, so the cycle of current detection and on-off duty will be mutually limited

[0009] For example, when the current detection is performed by the lower arm, the lower arm needs to be fully turned on every current detection cycle, so the current detection cannot be performed in the state where the upper arm is 100% turned on.

Moreover, it takes time from the moment the lower arm is turned on until the output of the current value stabilizes, and the sampling of the current value also takes time, so it is necessary to lengthen the on-period of the lower arm. more restrictive

[0010] Thus, when the duty ratio has an upper limit value, the output voltage performance of the power conversion device is limited, for example, in the case of an inverter driving a three-phase motor, the voltage applied to the motor is limited, resulting in The disadvantage that current does not flow under high-speed rotation

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