Method and apparatus for controlling an inverter

• US 5,502,633 A
• Filed: 09/15/1994
• Issued: 03/26/1996
• Est. Priority Date: 01/24/1992
• Status: Expired due to Term

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Ben-Brahim, Lazhar, Miyazaki, Satoshi, Kurosawa, Ryoichi
• Primary Examiner(s): NGUYEN, MATTHEW VAN
• Application Number:
  US08/306,579
• Time in Patent Office: 558 Days
• Field of Search: 363/95, 363/96, 363/98, 363/132, 363/136
• US Class Current: 363/98
• CPC Class Codes: H02M 7/4833 Capacitor voltage balancing
• CPC Class Codes: H02M 7/487 Neutral point clamped inverters

Abstract

An inverter control apparatus comprises a controller, a mode decision circuit and a voltage reference conversion circuit. The mode decision circuit determines one of three kinds of modes which may be used to control the inverter, namely, a normal mode, a rectangle mode and zero correction mode selected according to values and polarities of multi-phase voltage reference signals. The voltage reference conversion circuit corrects the voltage reference signals according to the determined mode in the mode decision circuit. In the case of the normal mode, the mode decision circuit outputs the previous voltage reference signal V* without change as the new or corrected voltage reference signals. In the case of the rectangle mode, the circuit fixes the voltage reference signal V* having the greatest value of the three phase (U-phase, V-phase and W-phase) to a minimum voltage reference V_min which is of opposite polarity to the selected greatest value signal, or, in another embodiment, to a zero value. Further the circuit converts the others voltage reference signals to corrected voltage reference signals without change of line voltage. The control circuit permits control of the inverter even in a regime of low reference voltage which would otherwise result in an uncontrolled region of the inverter.

Claims

1. A method of controlling an inverter generating a plurality of phase voltages and a corresponding plurality of line voltages defined as the differences between said phase voltages, said method comprising the steps of:

generating voltage reference signals having waveforms with a plurality of phases;

determining one of (1) a normal mode, (2) a rectangle mode and (3) a zero correction mode of operation of said inverter in response to values and polarities of said voltage reference signals;

wherein

the normal mode is determined when the amplitude of the waveforms of all three phases of the voltage reference signals are over a preset value;

the rectangle mode is determined when at least one of the following conditions exist;

(1) the amplitudes of the waveforms of at least two phases of the voltage reference signals are less than or equal to the preset value, and (2) the amplitudes of the waveforms of at least two phases of the voltage reference signals are less than or equal to twice the preset value and the signs of said at least two phases of the voltage reference signals are of different polarities with respect to each other; and

the zero correction mode is determined when the amplitude of the waveform of one phase of the voltage reference signals is less than or equal to the preset value, and the amplitudes of the waveforms of the other two phases of the voltage reference signals are less than or equal to twice the preset value and the other two phases have the same polarity;

using the voltage reference signals during the normal mode as a reference value for controlling said inverter; and

in at least one of said determined rectangle and zero correction modes, converting the voltage reference signals to converted voltage reference signals in accordance with a preset algorithm such that each phase voltage based on said converted voltage reference signals has a controlled pulse width greater than or equal to predetermined minimum width and such that the resulting line voltages do not change when compared to said line voltages generated using said voltage reference signals;

wherein the step of converting said voltage reference signals to said converted voltage reference signals in said rectangle mode takes place at one of (1) a fixed time when the frequency of said voltage reference signals is less than a prefixed value, and (2) at a time which is determined by a predetermined phase of said voltage reference signals when the frequency of said voltage reference signals is greater than or equal to said prefixed value.

2. A method of controlling an inverter generating a plurality of phase voltages and a corresponding plurality of line voltages defined as the differences between said phase voltages, said method comprising the steps of:

generating voltage reference signals having waveforms with three phases;

determining one of (1) a normal mode, (2) a rectangle mode and (3) a zero correction mode of operation of said inverter in response to values and polarities of said voltage reference signals;

wherein

the normal mode is determined when the amplitude of the waveforms of all three phases of the voltage reference signals are over a preset value;

the rectangle mode is determined when at least one of the following conditions exists;

(1) the amplitudes of the waveforms of at least two phases of the voltage reference signals are less than or equal to the preset value, and (2) the amplitudes of the waveforms of at least two phases of the voltage reference signals are less than or equal to twice the preset value and the signs of said at least two phases of the voltage reference signals are of different polarities with respect to each other;

the zero correction mode is determined when the amplitude of the waveform of one phase of the voltage reference signals is less than or equal to the preset value, and the amplitudes of the waveforms of the other two phases of the voltage reference signals are less than or equal to twice the preset value and the other two phases have the same polarity;

using the voltage reference signals during the normal mode as a reference value for controlling said inverter;

in at least one of said determined rectangle and zero correction modes, converting the voltage reference signals to converted voltage reference signals in accordance with a preset algorithm such that each phase voltage based on said converted voltage reference signals has a controlled pulse width greater than or equal to predetermined minimum width and such that the resulting line voltages do not change when compared to said line voltages generated using said voltage reference signals; and

wherein the step of converting said voltage reference signals to said converted voltage reference signals in said rectangle mode takes place at one of (1) a fixed time when the frequency of said voltage reference signals is less than a prefixed value, and (2) at a time which is determined by a predetermined phase of said voltage reference signals when the frequency of said voltage reference signals is greater than or equal to said prefixed value.

3. A method of controlling an inverter generating a plurality of phase voltages and a corresponding plurality of line voltages defined as the differences between said phase voltages, said method comprising the steps of:

generating voltage reference signals having waveforms with a plurality of phases;

determining one of (1) a normal mode, (2) a rectangle mode and (3) a zero correction mode of operation of said inverter in response to values and polarities of said voltage reference signals;

wherein

the normal mode is determined when the amplitude of the waveforms of all three phases of the voltage reference signals are over a preset value;

the rectangle mode is determined when at least one of the following conditions exist;

(1) the amplitudes of the waveforms of at least two phases of the voltage reference signals are less than or equal to the preset value, and (2) the amplitudes of the waveforms of at least two phases of the voltage reference signals are less than or equal to twice the preset value and the signs of said at least two phases of the voltage reference signals are of different polarities with respect to each other; and

the zero correction mode is determined when the amplitude of the waveform of one phase of the voltage reference signals is less than or equal to the preset value, and the amplitudes of the waveforms of the other two phases of the voltage reference signals are less than or equal to twice the preset value and the other two phases have the same polarity;

using the voltage reference signals during the normal mode as a reference value for controlling said inverter; and

in at least one of said determined rectangle and zero correction modes, converting the voltage reference signals to converted voltage reference signals in accordance with a preset algorithm such that each phase voltage based on said converted voltage reference signals has a controlled pulse width greater than or equal to a predetermined minimum width and such that the resulting line voltages do not change when compared to said line voltages generated using said voltage reference signals;

wherein said converted voltage reference signals have phases corresponding to the phases of said voltage reference signals and wherein said step of converting said voltage reference signals to said converted voltage reference signals in said rectangle mode comprises the steps of;

selecting the waveform of the phase of said voltage reference signals which has the greatest absolute value, and

fixing the amplitude of the waveform of the converted voltage reference signal corresponding to said selected phase to a predetermined value, V_min, where V_min has the opposite sign as said selected phase, and adjusting the amplitude of the waveforms of the other phases of the converted voltage reference signals such that the resulting line voltages do not change when compared to said line voltages generated using said voltage reference signals; and

wherein the step of converting said voltage reference signals to said converted voltage reference signals in said rectangle mode takes place at one of (1) a fixed time when the frequency of said voltage reference signals is less than a prefixed value, and (2) at a time which is determined by a predetermined phase of said voltage reference signals when the frequency of voltage reference signals is greater than or equal to said prefixed value.

4. A method of controlling an inverter generating a plurality of phase voltages and a corresponding plurality of line voltages defined as the differences between said phase voltages, said method comprising the steps of:

generating voltage reference signals having waveforms with a plurality of phases;

determining one of (1) a normal mode, (2) a rectangle mode and (3) a zero correction mode of operation of said inverter in response to values and polarities of said voltage reference signals;

using the voltage reference signals during the normal mode as a reference value for controlling said inverter; and

in at least one of said determined rectangle and zero correction modes, converting the voltage reference signals to converted voltage reference signals in accordance with a preset algorithm such that each phase voltage based on said converted voltage reference signals has a controlled pulse width greater than or equal to a predetermined minimum width and such that the resulting line voltages do not change when compared to said line voltages generated using said voltage reference signals;

wherein the step of generating voltage reference signals comprises generating voltage reference signals having waveforms with three phases, and the method further comprising the steps of;

determining the normal mode when the amplitude of the waveforms of all three phases of the voltage reference signals are over a preset value;

determining the rectangle mode when at least one of the following conditions exist;

(1) the amplitudes of the waveforms of at least two phases of the voltage reference signals are less than or equal to the preset value, and (2) the amplitudes of the waveforms of at least two phases of the voltage reference signals are less than or equal to twice the preset value and the signs of said at least two phases of the voltage reference signals are of different polarities with respect to each other; and

determining the zero correction mode when the amplitude of the waveform of one phase of the voltage reference signals is less than or equal to the preset value, and the amplitudes of the waveforms of the other two phases of the voltage reference signals are less than or equal to twice the preset value and the other two phases have the same polarity;

wherein said converted voltage reference signals have phases corresponding to the phases of said voltage reference signals and wherein said step of converting said voltage reference signals to said converted voltage reference signals in said rectangle mode comprises the steps of;

selecting the waveform of the phase of said voltage reference signals which has the greatest absolute value, and

fixing the amplitude of the waveform of the converted voltage reference signal corresponding to said selected phase to a predetermined value, V_min, where V_min has the opposite sign as said selected phase, and adjusting the amplitude of the waveforms of the other phases of the converted voltage reference signals such that the resulting line voltages do not change when compared to said line voltages generated using said voltage reference signals; and

wherein the step of converting said voltage reference signals to said converted voltage reference signals in said rectangle mode takes place at one of (1) a fixed time when the frequency of said voltage reference signals is less than a prefixed value, and (2) at a time which is determined by a predetermined phase of said voltage reference signals when the frequency of voltage reference signals is greater than or equal to said prefixed value.

5. A method of controlling an inverter generating a plurality of phase voltages and a corresponding plurality of line voltages defined as the differences between said phase voltages, said method comprising the steps of:

generating voltage reference signals having waveforms with a plurality of phases;

determining one of (1) a normal mode, (2) a rectangle mode and (3) a zero correction mode of operation of said inverter in response to values and polarities of said voltage reference signals;

wherein

the normal mode is determined when the amplitude of the waveforms of all three phases of the voltage reference signals are over a preset value;

the rectangle mode is determined when at least one of the following conditions exist;

(1) the amplitudes of the waveforms of at least two phases of the voltage reference signals are less than or equal to the preset value, and (2) the amplitudes of the waveforms of at least two phases of the voltage reference signals are less than or equal to twice the preset value and the signs of said at least two phases of the voltage reference signals are of different polarities with respect to each other; and

the zero correction mode is determined when the amplitude of the waveform of one phase of the voltage reference signals is less than or equal to the preset value, and the amplitudes of the waveforms of the other two phases of the voltage reference signals are less than or equal to twice the preset value and the other two phases have the same polarity;

using the voltage reference signals during the normal mode as a reference value for controlling said inverter; and

in at least one of said determined rectangle and zero correction modes, converting the voltage reference signals to converted voltage reference signals in accordance with a preset algorithm such that each phase voltage based on said converted voltage reference signals has a controlled pulse width greater than or equal to predetermined minimum width and such that the resulting line voltages do not change when compared to said line voltages generated using said voltage reference signals;

wherein said converted voltage reference signals have three waveforms with phases V_U **,V_V **, and V_W ** corresponding respectively to three waveforms with phases V_U *, V_V *, and V_W * of said voltage reference signals and wherein said step of converting said voltage reference signals to said converted voltage reference signals in said rectangle mode comprises the steps of;

a) when the voltage reference signal with the phase V_U * has an amplitude which is the greatest of the three waveforms and is positive, setting the values of the corrected voltage reference signals according to the following relations;

V_U **=-V_min

V_V **=-V_min -(V_U *-V_V *)

V_W **=-V_min -(V_U *-V_W *), and

b) when the voltage reference signal V_U * is the greatest of the three phases and is negative, setting the values of the corrected voltage reference signals according to the following relations;

V_U **=V_min

V_V **=V_min -(V_U *-V_V *)

V_W **=V_min -(V_U *-V_W *)

where V_min is a predetermined value; and

wherein the step of converting said voltage reference signals to said converted voltage reference signals in said rectangle mode takes place at one of (1) a fixed time when the frequency of said voltage reference signals is less than a prefixed value, and (2) at a time which is determined by a predetermined phase of said voltage reference signals when the frequency of voltage reference signals is greater than or equal to said prefixed value.

6. A method of controlling an inverter generating a plurality of phase voltages and a corresponding plurality of line voltages defined as the differences between said phase voltages, said method comprising the steps of:

generating voltage reference signals having waveforms with a plurality of phases;

determining one of (1) a normal mode, (2) a rectangle mode and (3) a zero correction mode of operation of said inverter in response to values and polarities of said voltage reference signals;

using the voltage reference signals during the normal mode as a reference value for controlling said inverter; and

in at least one of said determined rectangle and zero correction modes, converting the voltage reference signals to converted voltage reference signals in accordance with a preset algorithm such that each phase voltage based on said converted voltage reference signals has a controlled pulse width greater than or equal to predetermined minimum width and such that the resulting line voltages do not change when compared to said line voltages generated using said voltage reference signals;

wherein the step of generating voltage reference signals comprises generating voltage reference signals having waveforms with three phases, and the method further comprising the steps of;

determining the normal mode when the amplitude of the waveforms of all three phases of the voltage reference signals are over a preset value;

determining the rectangle mode when at least one of the following conditions exist;

(1) the amplitudes of the waveforms of at least two phases of the voltage reference signals are less than or equal to the present value, and (2) the amplitudes of the waveforms of at least two phases of the voltage reference signals are less than or equal to twice the preset value and the signs of said at least two phases of the voltage reference signals are of different polarities with respect to each other; and

determining the zero correction mode when the amplitude of the waveform of one phase of the voltage reference signals is less than or equal to the preset value, and the amplitudes of the waveforms of the other two phases of the voltage reference signals are less than or equal to twice the preset value and the other two phases have the same polarity;

wherein said converted voltage reference signals have three waveforms with phases V_U **, V_V **, and V_W **, corresponding respectively to three waveforms with phases V_U *, V_V *, and V_W * of said voltage reference signals and wherein said step of converting said voltage reference signals to said converted voltage reference signals in said rectangle mode comprises the steps of;

a) when the voltage reference signal with the phase V_U * has an amplitude which is the greatest of the three waveforms and is positive, setting the values of the corrected voltage reference signals according to the following relations;

V_U **=-V_min

V_V **=-V_min -(V_U *-V_V *)

V_W **=-V_min -(V_U *-V_W *), and

b) when the voltage reference signal V_U * is the greatest of the three phases and is negative, setting the values of the corrected voltage reference signals according to the following relations;

V_U **=V_min

V_V **=V_min -(V_U *-V_V *)

V_W **=V_min -(V_U *-V_W *)

where V_min is a predetermined value; and

wherein the step of converting said voltage reference signals to said converted voltage reference signals in said rectangle mode takes place at one of (1) a fixed time when the frequency of said voltage reference signals is less than a prefixed value, and (2) at a time which is determined by a predetermined phase of said voltage reference signals when the frequency of voltage reference signals is greater than or equal to said prefixed value.