Electricity: single generator systems – Automatic control of generator or driving means – Current output
Reexamination Certificate
2002-11-07
2004-09-21
Ponomarenko, Nicholas (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
Current output
C322S038000, C322S017000, C338S049000
Reexamination Certificate
active
06794854
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a power converter such as an inverter or a power storage, and particularly relates to a power converter of a pulse width modulation control system with an electric current detector using a shunt resistor.
Inverters have been used widely for operating AC motors such as induction motors, and recently used also as controllers for power sources of carriages. Thus, the advantage of adjustable speed operation by using the inverters may be enjoyed sufficiently.
For the control of an inverter, detection of a load current may be required. A hall element type current sensor
28
or a shunt resistor
13
with a detection circuit
18
has been conventionally adopted for the detection of the load current.
The hall element type current sensor
28
is a current sensor in which a hall element is provided in a part of an annular magnetic substance, and an electric wire supplied with a load current is wound around or passed through the magnetic substance so that magnetic flux generated by the load current is converted into a voltage by the hall element. In this case, there is a merit that a detection signal electrically isolated from an electric circuit which is a target to be detected can be obtained.
Similarly, the shunt resistor
13
and the detection circuit
18
are defined as follows. That is, a resistor inserted in series into an electric circuit in which a load current flows is a shunt resistor. A voltage drop appearing between the opposite terminals of the shunt resistor
13
due to the load current. In order to form a detection signal from the voltage drop, a circuit is used as the detection circuit
18
. The shunt resistor
13
with the detection circuit
18
can be provided with considerably low cost. Thus, such circuits have been conventionally used widely.
FIG. 11
shows an example of the background art in which both the hall element type current sensor
28
and the shunt resistor
13
with the detection circuit
18
have been applied to a power converter of a PWM (Pulse Width Modulation) control system as a target. Here, both the hall element type current sensor
28
and the shunt resistor
13
with the detection circuit
18
are illustrated for the sake of description. Actually, it will go well if either the hall element type current sensor
28
or the shunt resistor
13
with the detection circuit
18
is provided.
In
FIG. 11
, a main circuit is constituted by a converter (power rectification portion)
14
, an inverter (power inversion portion)
15
of a PWM control system, and a smoothing capacitor
16
. The converter
14
is constituted by a diode rectifier. DC power outputted from the converter
14
is supplied to the inverter
15
. The capacitor
16
is connected to a DC circuit between the converter
14
and the inverter
15
.
Then, when AC power is supplied to the converter
14
from a commercial power source
29
as a power source, DC power smoothed by the capacitor
16
is supplied to the inverter
15
. Here, semiconductor switching devices
5
represented by IGBTs (Insulated Gate Bipolar Transistors) in the inverter
15
are PWM-controlled so that the DC power is converted into AC power with a specific voltage and a specific frequency. As a result, power with a variable voltage and a variable frequency is supplied to a load such as an induction motor.
As shown in
FIG. 12
, also in a power converter in which DC power outputted by a power storage
30
such as a battery is supplied to the inverter
15
, semiconductor switching devices
5
of the inverter
15
are PWM-controlled in the aforementioned manner so that DC power is converted into AC power with a specific voltage and a specific frequency. As a result, power with a variable voltage and a variable frequency is supplied to a motor
17
as a load, such as a power source for a carriage, a cooling fan of a cooler, a pump driving motor for circulating cooling water, a hydraulic pump driving motor for hydraulic apparatus, or a compressor driving motor for an air conditioner.
At this time, on (conduction) and off (interruption) of the semiconductor switching devices
5
in the inverter
15
are controlled in accordance with PWM signals by a computer
19
through a driver circuit as shown in FIG.
11
. To this end, the value of a current flowing in the motor
17
which is a load, that is, the value of a load current is required for the control by the computer
19
.
To detect the value of the load current, there are two methods as described previously. That is, one is a method using the hall element type current sensor
28
and the other is a method using the shunt resistor
13
and the detection circuit
18
.
First, when the hall element type current sensor
28
is used, this current sensor is connected in series between the inverter
15
and the motor
17
which is a load. The detection result by the current sensor
28
is A/D converted and supplied to the computer
19
.
On the other hand, when the shunt resistor
13
and the detection circuit
18
are used, the shunt resistor
13
is connected in series between the capacitor
16
and the inverter
15
. A voltage drop appearing due to a load current flowing in the shunt resistor
13
is A/D converted through a filter, an amplifier and so on, and supplied to the computer
19
. The shunt resistor
13
may be connected in series between the inverter
15
and the motor
17
.
The shunt resistor
13
is, generally, of a sheet-like resistive material
6
made of manganin material (alloy of copper and manganese) excellent in temperature characteristics. The sheet-like resistive material
6
is formed into a predetermined shape by punching or by etching after fixed attachment to an insulating layer
4
. A shunt resistance
8
, main electrodes
7
for making a load current flow into the shunt resistance
8
, and detection electrodes
31
for detecting a voltage generated in the shunt resistance
8
are formed from the same resistive material. As shown in
FIGS. 13A and 13B
, the shunt resistance
8
, the main electrodes
7
and the detection electrodes
31
are mounted on a heat radiating base plate
1
of a power module through the insulating layer
4
. The heat radiating base plate
1
is superior in heat radiation characteristics, and the semiconductor switching device
5
of the inverter
15
is mounted on the base plate
1
.
Heat generation in the shunt resistor
13
occurs in both the shunt resistance
8
and the main electrodes
7
because the load current flows into the shunt resistance
8
and the main electrodes
7
. The generated heat flows into the heat radiating base plate
1
so that the temperature increase is suppressed.
The length, width and thickness of the shunt resistor
13
using the sheet-like resistive material
6
are defined as follows. That is, the length direction of the shunt resistor
13
is defined as the direction in which a detection current flows. The width direction of the shunt resistor
13
is defined as the direction perpendicular to the length direction. The thickness direction of the shunt resistor
13
is defined as the direction perpendicular to the insulating layer
4
.
SUMMARY OF THE INVENTION
In the background art, the hall element type current sensor
28
or the shunt resistor
13
with the detection circuit
18
is used for PWM control of a power converter. However, in the case of the hall element type current sensor
28
, a comparatively expensive hall element and a large magnetic substance are required. Accordingly, there is a problem in cost reduction and miniaturization.
On the other hand, the shunt resistor
13
and the detection circuit
18
can be constituted by small and inexpensive electronic parts. However, the shunt resistor
13
and the detection circuit
18
are connected in series with a power line so as to detect a load current ranging from several amperes to several thousands of amperes. Thus, heat is generated. Although manganin material or the like having a low rate of resistance temperature change is used to improve the accuracy, the resistivity of the m
Ibori Satoshi
Nakatsu Kinya
Saito Ryuichi
Sasaki Masataka
Takase Masato
Cuevas Pedro J.
Hitachi , Ltd.
Hogan & Hartson LLP
Ponomarenko Nicholas
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