Resonant inverter control system

Details Resonant inverter control system Resonant inverter control system

2002-04-30

2003-05-27

Nguyen, Matthew (Department: 2838)

Electric power conversion systems

Current conversion

With condition responsive means to control the output...

C363S132000

Reexamination Certificate

active

06570780

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inverter control system that controls an inverter circuit in order to drive a load such as a motor, in particular, relates to a resonant inverter control system that controls an inverter circuit provided with snubber capacitors for carrying out soft switching, and also relates to a resonant inverter apparatus that carries out soft switching in order to drive a motor used in an electric vehicle (EV), a hybrid vehicle (HEV), or the like.
2. Description of the Related Art
Technology for conventional inverter circuits for driving a load such as a motor is disclosed in U.S. Pat. Nos. 5,710,698, 5,642,273, and 5,047,913. According to these patents, as shown in
FIG. 15
, for example, a conventional example of a soft switching inverter comprises an inverter part using as switching elements IGBTs (insulated gate bipolar transistors) Q
101
to Q
106
connected to the motor
1
, which comprises a three phase induced motor or a direct current brushless motor that serves as a load.
In the inverter, the IGBT Q
101
to Q
106
are connected at both terminals of the direct current power source
3
to form a three-phase bridge structure comprising a U phase, a V phase, and a W phase, and free wheeling diodes (FWD) D
101
to D
106
are connected between the collector terminals and emitter terminals of each of the IGBTs, with the object of circulating the regeneration energy that the load of the inductance of the motor
101
generates and the current energy accumulated in the load of the inductance. In addition, snubber capacitors C
101
to C
106
, which are for absorbing a surge voltage applied across the collector terminal and the emitter terminal of the IGBTs during the turn-ON and turn-OFF of the IGBTs, are also connected between the collector terminals and emitter terminals of each of the IGBTs.
Furthermore, in the inverter, a smoothing capacitor C
109
is connected to the direct current power source
103
, and at the connection points of the center-taped voltage maintaining capacitors C
107
and C
108
that are connected serially to both terminals of the smoothing capacitor C
109
, from the respective connecting points of the U phase snubber capacitors C
101
and C
102
, the V phase snubber capacitors C
103
and C
104
, and the W phase snubber capacitors C
105
and C
106
, bi-directional switch units SU
101
to SU
103
for running resonant current via the inductor are respectively connected to the inductor L
101
that resonates with the snubber capacitors C
101
and C
102
, the inductor L
102
that resonates with the snubber capacitors C
103
and C
104
, and inductor L
103
that resonates with the snubber capacitors C
105
and C
106
.
The structure described is also called an auxiliary free-wheeling arm linked snubber inverter, and in the soft switching inverter having the structure described above, when, for example, the IGBT Q
102
is to be turned ON slightly after the IGBT Q
101
is to be turned OFF, the charging current of the snubber capacitor C
101
and the discharge current of the snubber capacitor C
102
flow to the center-taped voltage maintaining capacitors C
108
and C
108
via the inductor L
101
, and at the same time, when the IGBTs Q
103
and Q
105
are to be turned ON slightly after the IGBTs Q
104
and Q
106
are to be turned OFF, the charging current of the snubber capacitors C
104
and C
106
and the discharge current of the snubber capacitors C
103
and C
105
is supplied from the center-taped voltage maintaining capacitors C
107
and C
108
via the inductors L
102
and L
103
.
Therefore, the snubber capacitor will charge and discharge due to the resonant current of the snubber capacitor and the inductor, and thus in the case that the IGBT turns OFF and the snubber capacitor is charged, because of the delay in the rise of the voltage applied to the IGBT provided by the snubber capacitor due to the time constant, ZVS (Zero Voltage Switching) of the IGBTs is realized. In contrast, in the case that before the IGBT is turned ON the snubber capacitor discharges, the voltage and current applied to the IGBTs due to the free wheeling diode conduction falls to zero. Thereby, the loss that occurs during the turn-ON and the turn-OFF of the switching elements can be reduced because ZVS (Zero Voltage Switching) and ZCS (Zero Current Switching) of the IGBTs are realized.
FIG. 16
is also a conventional example of a soft switching inverter, also called an auxiliary resonant AC linked snubber inverter, and like the auxiliary resonant commutation arm linked snubber inverter in
FIG. 16
, comprises an inverter part in which the IGBTs Q
101
to Q
106
connected to free wheeling diodes D
101
to D
106
and snubber capacitors C
101
to C
106
are connected at both terminals of the direct current source
103
to form a three-phase bridge structure comprising a U phase, a V phase, and a W phase and a structure wherein the inductor L
104
that resonates with the snubber capacitors C
101
and C
102
, the inductor L
105
that resonates with the snubber capacitors C
103
and C
104
, and the inductor L
106
that resonates with the snubber capacitors C
105
and C
106
are respectively connected between the connecting point between the U phase snubber capacitors C
101
and C
102
, the connection point between the snubber capacitors C
103
and C
104
of the V phase, the connecting point between the snubber capacitors C
105
and C
106
of the W phase of the inverter and the bi-direction switching units SU
104
to SU
106
for providing a resonant current to flow via the inductors.
The difference in operation between the auxiliary resonant AC linked snubber inverter in FIG.
16
and the auxiliary resonant snubber inverter in
FIG. 15
is only the paths of the current that charges and discharges the snubber capacitor, and the principle that the IGBTs, which comprise each of the switching elements, attain ZVS and ZCS is identical.
In the conventional example of a soft switching inverter such as that described above, forming the resonant circuit by snubber capacitors and each of the inductors is effective for making the loss during the turn ON and the turn OFF that occurs in the switching elements small because the current flowing to the IGBTs (switching elements) and the voltage applied to the IGBTs can be controlled.
However, because the core capacity required by the inductors is determined by the conducting peak current, the weight of the inductors and the volume of the inductors increases along with an increase in the controlled load current, and in particular, in the conventional example of the soft switching inverter that required three inductors through which a current equal to or greater than the load current can flow, there are the problems that decreasing the weight and down-sizing are not possible due to the increase in the weight and volume of the inductors.
In addition, clearly decreasing the weight and down-sizing is most effectively attained by reducing the number of inductors, but in carrying out soft switching after the number of inductors have been reduced, inverter control that is different from conventional technology is required, and thus there is the problem that the control device must be clarified.
In consideration of the problems described above, an object of the first embodiment of the present invention is to provide a resonant inverter control apparatus that can concretely control the resonant inverter having a reduced number of resonant inductors according to this operating principle to realize soft switching.
Furthermore, in a soft switching inverter apparatus of the first embodiment, during the turn-ON operation and turn-OFF operation of the main switching elements, by establishing resonance across the resonant inductor in the auxiliary circuit and the resonant capacitors connected in parallel to the main switching elements, the slope of the change of the voltage across terminals of the main switching elements becomes gentle and soft switching is realized.
However, in the case that the ma

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