Power semiconductor device, power arm and inverter circuit

Details Power semiconductor device, power arm and inverter circuit Power semiconductor device, power arm and inverter circuit

2001-06-15

2003-11-04

Han, Jessica (Department: 2838)

Electric power conversion systems

Current conversion

Using semiconductor-type converter

C363S056020, C363S056120

Reexamination Certificate

active

06643155

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to an inverter circuit for converting DC power and AC power into AC power having arbitrary frequency, a power arm for forming the inverter circuit and a power arm element for forming the power arm.
2. Description of the Background Art
FIG. 8
shows a three-phase inverter circuit as an example of an inverter circuit using a power arm in the background art. In
FIG. 8
, the reference number V
1
represents a DC voltage generating circuit such as a DC voltage source consisting of a commercial AC power supply and a diode bridge circuit or a battery. The reference numbers HB
1
, HB
2
and HB
3
represent half bridge circuits including a single-phase power arm for generating an AC voltage from a DC voltage Vcc generated at the DC voltage generating circuit V
1
.
A power arm of the half bridge circuit HB
1
consists of a power arm element including a switching element
1
a
and a free wheeling diode
2
a
connected in inverse-parallel connection and another power arm element including a switching element
1
b
and a free wheeling diode
2
b
. These power arm elements are connected in series at a node U. An IGBT (insulated gate bipolar transistor), a power bipolar transistor, a power MOSFET (metal oxide semiconductor field effect transistor) and the like are applicable as the switching elements
1
a
and
1
b.
More particularly, an electrode for inputting current of the switching element
1
a
(corresponding to a collector when the switching element
1
a
is an N-channel type IGBT) is connected to a cathode of the free wheeling diode
2
a
and an electrode for outputting current of the switching element
1
a
(corresponding to an emitter when the switching element
1
a
is an N-channel type IGBT) is connected to an anode of the free wheeling diode
2
a
. The switching element
1
b
and the free wheeling diode
2
b
are constituted similarly. The electrode for outputting current of the switching element
1
a
is connected to an electrode for inputting current of the switching element
1
b
at the node U.
The electrode for inputting current of the switching element
1
a
is connected to a terminal of high potential side of the DC voltage generating circuit V
1
at a node N
1
. An electrode for outputting current of the switching element
1
b
is connected to a terminal of low potential side of the DC voltage generating circuit V
1
at a node N
2
.
Similar to the half bridge circuit HB
1
, the half bridge circuits HB
2
and HB
3
respectively include two power arm elements connected in series at nodes V and W. Switching elements of each power arm element are connected to the terminal of high potential side and the terminal of low potential side of the DC voltage generating circuit V
1
at the nodes N
1
and N
2
. For brevity, the power arm elements of the half bridge circuits HB
2
and HB
3
are omitted in FIG.
8
.
Three-phase loads (not shown) including three connecting terminals having shapes such as Y shape or &Dgr; shape are connected to the nodes U, V and W.
A control signal such as a PWM (pulse width modulation) signal is applied from an HVIC (high voltage integrated circuit)
3
acting as a control circuit to control electrodes (corresponding to a gate when the switching elements
1
a
and
1
b
are IGBTs) of the switching elements
1
a
and
1
b
of the half bridge circuits HB
1
. On receipt of the control signal in predetermined timing, each of the switching elements
1
a
and
1
b
is turned on and off to generate an AC voltage having arbitrary frequency to be applied to the terminal of the three-phase load connected to the node U. Similar to the half bridge circuit HB
1
, control electrodes of the switching elements of the half bridges HB
2
and HB
3
receive a control signal from the HVIC
3
to apply an AC voltage having arbitrary frequency to the terminals of the three-phase loads connected to the nodes V and W.
Peripheral circuits such as a voltage source V
2
for operating the HVIC
3
, a resistor R
1
and a capacitor C
1
are connected to the HVIC
3
. The HVIC
3
and its peripheral circuits may be individually provided to each of the half bridge circuits HB
1
, HB
2
and HB
3
. Alternatively, each of the half bridge circuits HB
1
, HB
2
and HB
3
can be controlled by a single set of the HVIC
3
and its peripheral circuits.
FIG. 8
shows an example in which the HVIC
3
and the capacitor C
1
are individually provided to each of the half bridge circuits HB
1
, HB
2
and HB
3
and the voltage source V
2
and the resistor R
1
are shared among the half bridge circuits HB
1
, HB
2
and HIB
3
.
A ground potential terminal of the HVIC
3
is connected to the node N
2
for receiving a ground potential GND from the terminal of low potential side of the DC voltage generating circuit V.
The problems of each of the half bridge circuits of the three-phase inverter circuit shown in
FIG. 8
will be described below in reference to
FIGS. 9
,
10
and
11
taking the half bridge circuit HB
1
as an example.
When the switching element
1
a
is in ON state and the switching element
1
b
is in OFF state, a current Ic flows from the terminal of high potential side of the DC voltage generating circuit V
1
into the terminal of low potential side thereof through the switching element
1
a
and a three-phase load LD (shown as an inductor in
FIG. 9
) as shown in FIG.
9
.
Next, when the switching element
1
a
is switched to be in OFF state and the switching element
1
b
is switched to be in ON state, the flow of the current Ic stops. However, as the current flowing so far is induced to continue flowing by the three-phase load LD, a free wheeling current Ir temporarily flows into the three-phase LD through the free wheeling diode
2
b.
FIG. 10
shows time variation of a potential Vs at the node U considering the ground potential GND as zero. When the switching element
1
a
is in ON state and the switching element
1
b
is in OFF state, the potential Vs is approximately the same as the power supply potential Vcc to be provided from the terminal of high potential side of the DC voltage generating circuit V
1
. However, after time t
1
at which the switching element
1
a
is switched to be in OFF state and the switching element
1
b
is switched to be in ON state, the flow of the current Ic is suspended until these switching elements are switched again. Due to this, the potential Vs suddenly drops from the power supply potential Vcc.
After transient drop of the potential Vs to a potential Vtr
2
having a large degree of a negative value, the potential Vs rises to a potential Vst having a negative value calculated by subtracting a threshold voltage of the free wheeling diode
2
b
from the ground potential GND and maintains its stationary state until the switching elements are switched again.
When transient increase in a value of the free wheeling current Ir occurs to increase an absolute value of its potential Vtr
2
to a certain value or more, the potential Vs at the node U excessively drops. Due to this, increase in a voltage between the control electrode and the electrode for outputting current of the switching element
1
a
occurs, resulting in the problem of erroneous turn-on of the switching element
1
a
. As a result of this problem, another problem of malfunction of the HVIC
3
is also caused.
These problems can be avoided by controlling the absolute value of the potential Vtr
2
which corresponds to a transient voltage characteristic of the free wheeling diode at a low value. However, in the free wheeling diode of the power arm element in the background art, a thickness of an n
−
drift region has been defined to be large to ensure its breakdown voltage having a value approximately the same as that of a breakdown voltage of the switching element. That is, the breakdown voltage of the free wheeling diode, consisting of a cathode electrode CT, n-type semiconductor layers S
1
a
and S
1
b
, a p-type semiconductor layer S
2
and an anode electrode AN as shown in
FIG. 11
, has been ens

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