Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
1999-07-07
2001-02-27
Masih, Karen (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S812000, C318S139000, C318S432000, C318S434000, C318S132000, C318S254100, C318S721000
Reexamination Certificate
active
06194865
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control apparatus and method for driving an electric rotary machine such as a motor or a generator which is mounted on an electric vehicle.
2. Related Background Art
Not only industrial synchronous machines but also synchronous machines which have been widely used have a tendency that the terminal voltage of the synchronous machine, caused by a speed electromotive force, generally goes higher as the rotational speed of the synchronous machine increases. If this terminal voltage Vac goes over the maximum applied voltage Vtmax, the difference between Vac and Vtmax is applied to an inverter or power supply, which may damage a component. To prevent this, a field weakening control is performed which applies a predetermined negative field weakening current to the d axis to keep Vac equal to or less than Vtmax. This field weakening current is predetermined according to torques and rotational speeds of the machine so that Vac may not exceed Vtmax even when the battery voltage is low.
When the inverter-on voltage is ignored, the maximum A.C.(alternating current) voltage Vtmax which the power converter can apply is determined by a battery voltage VB as shown by Equation (1). Accordingly, if the battery voltage VB is high enough, the efficiency can be increased by reducing the magnitude of the field weakening current and the quantity of current flow.
Vtmax
=({square root over (3)}/2{square root over (2)})
VB
(1)
With regard to this point, Japanese Non-examined Patent Publication No.07-107772 discloses a method for increasing the efficiency without applying an excessive field weakening current. This method consists of always detecting a battery voltage, calculating a maximum impression voltage of the voltage converter by Equation (1), and determining the d-axis current command value Id* that makes the terminal voltage Vac of the synchronous motor equal to Vtmax by Equations (2) and (3) which represent a steady status. In Equation (2), R is a primary resistance, &ohgr; is an electric angular velocity of a motor, Ld is a d-axis inductance, Lq is a q-axis inductance, E0 is a number of flux interlinkages, Vd is a d-axis voltage, and Vq is a q-axis voltage.
[
Vd
Vq
]
=
[
R
-
ω
·
Lq
ω
·
Lq
R
]
[
ld
lq
]
+
[
0
ω
·
E0
]
(
2
)
Vac
={square root over ( )}(
Vd
2
+Vq
2
) (3)
An electric vehicle has two problems as the D.C. input voltage value temporarily varies due to consumption of battery power, driving of auxiliary units, and torque motoring/regeneration, and the dq-axis currents transit repeatedly and frequently.
First, a method disclosed in Japanese Non-examined Patent Publication No.07-107772 does not include the current transition status. At the time of a current transition, said Equation (2) has a term expressed by Equation (4) on its right side. Accordingly, the actual terminal voltage V
1
of the synchronous motor becomes higher than Vac calculated by Equations (2) and (3) and it temporarily exceeds Vtmax.
[
VdL
VqL
]
=
[
s
·
Ld
·
ld
s
·
Lq
·
lq
]
(
4
)
The second problem of the prior art is that the dq-axis currents are disturbed by a change of a D.C. input voltage value and a requested torque (torque command) cannot be accomplished exactly. For instance, when the D.C. input voltage drops down to 400V while a predetermined dq-axis current is applied at 500V of the D.C. input voltage, the A.C. voltage actually output from the power converter is multiplied by 400/500. Consequently, the dq-axis current value deviates from the predetermined value for a time period until the dq-axis compensating voltage command in the control equipment takes a value fit for the D.C. input voltage of 400V. Necessarily, the requested torque cannot be accomplished exactly.
In relation to the first problem, also when only a field weakening control is performed to keep the terminal voltage of the synchronous motor under a predetermined value, a battery power equivalent to the losses of the power converter and the synchronous motor is consumed, which reduces the distance per charging that the vehicle can run.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to solve the above problems and provide a control apparatus and method of controlling an electric rotary machine efficiently and steadily.
The features of the present invention are to provide 1) a function for generating dq-axis current commands so that the terminal voltage of the synchronous motor may not exceed the voltage which a power converter can output even at a current transition time, 2) a voltage command correcting function for correcting a fluctuation of a D.C. input voltage, and 3) a function for eliminating the D.C. input power to zero when performing field weakening control.
A control apparatus for controlling an electric rotary machine which is connected to a battery via a power converter in accordance with the present invention comprises: a D.C. input voltage detecting means for detecting a D.C. input voltage of said power converter, a current and rotational speed detecting means for detecting a 3-phase Alternating current and the rotational speed of said electric rotary machine, a dq-axis current command generating means for generating dq-axis current commands of said electric rotary machine such as operation commands to control the output of said electric rotary machine according to input signals, a dq-axis voltage correction value calculating means for calculating a dq-axis voltage correction value from said dq-axis current command and a dq-axis current detection value of said electric rotary machine, a 3-phase A.C. voltage command value generating means for generating a 3-phase A.C. voltage command value from said dq-axis voltage correction value and phases of said electric rotary machine, and a PWM control means for outputting a PWM signal to drive said power converter from said A.C. voltage command value. Said dq-axis current command generating means consists of a maximum impression voltage calculating means for generating the maximum impression voltage of said power converter from said D.C. input voltage value, a permissible maximum voltage calculating means for calculating a permissible maximum voltage by subtracting a preset value from said maximum impression voltage, and a dq-axis voltage command calculating means for calculating a dq-axis voltage command to increase the efficiency of said electric rotary machine and said power converter from said input signal and said rotational speed of said electric rotary machine under conditions that the terminal voltage of said electric rotary machine is under said permissible maximum voltage.
More concrete features of the present invention to generate dq-axis current commands so that the terminal voltage of the synchronous motor may not exceed the voltage which a power converter can output even at a current transition time in accordance with said first function: Said dq-axis current command generating means consists of a maximum impression voltage calculating means for generating the maximum impression voltage of said power converter from said D.C. input voltage value, a permissible maximum voltage calculating means for calculating a permissible maximum voltage by subtracting a preset value from said maximum impression voltage, and a dq-axis voltage command calculating means for calculating a dq-axis voltage command to increase the efficiency of said electric rotary machine and said power converter from said input signal and said rotational speed of said electric rotary machine under conditions that the terminal voltage of said electric rotary machine is under said permissible maximum voltage.
Even at a transition time when current commands are changed, it is possible to drive the electric rotary machine in the range of an impression voltage that the power converter outputs by selecting an optimum dq-axis current command table by a differen
Matsudaira Nobunori
Mitsui Toshisada
Ohtsu Eiichi
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Hitachi , Ltd.
Masih Karen
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