Control apparatus for AC motor

Patent metadata

Field	Value
Publication number	US-9998058-B2
Application number	US-201715484574-A
Country	US
Kind code	B2
Filing date	Apr 11, 2017
Priority date	Apr 12, 2016
Publication date	Jun 12, 2018
Grant date	Jun 12, 2018

Abstract

In a control apparatus for an AC motor, a voltage waveform specifying unit of an inverter control unit specifies a voltage waveform for operating the inverter, based on a voltage vector calculated by a voltage command calculation unit. A spectrum amplitude extraction unit acquires values of bus current of the inverter and extracts the spectrum amplitude of the specific frequency that corresponds to the LC resonance frequency of the converter. A boost/non-boost state judgement unit of a converter control unit determines whether the state required by the converter in the next control cycle is the boost state or the non-boost state. When the spectrum amplitude of the specific frequency, correlated with the voltage waveform, is higher than the judgement threshold value and the converter is in the non-boost state, a voltage command value alteration unit changes the voltage command reference value such that the converter transitions to the boost state.

First claim

What is claimed is:

1. A control apparatus for an AC motor, comprising:
a converter capable of boosting a power source voltage supplied from a battery to a required system voltage by operation of a high-potential side switching element and a low-potential side switching element;
an inverter for converting DC power which is at the system voltage, outputted from the converter, to AC power by operation of a plurality of switching elements, and supplying the AC power to an AC motor;
a converter control unit for calculating a voltage command value of the system voltage, and controlling the operation of the converter;
an inverter control unit having a voltage command calculation unit for calculating a voltage vector that is notified to the inverter, and a voltage waveform specifying unit that specifies a voltage waveform, for operating the inverter based on the voltage vector; and
a spectrum amplitude extraction unit for acquiring a bus current of the inverter and extracting a spectrum amplitude of the bus current at a specific frequency, the specific frequency corresponding to a resonance frequency of an LC circuit of the converter, through which the bus current flows,
wherein the converter control unit comprises:
a voltage command reference value calculation unit for calculating a voltage command reference value as a reference value of the voltage command value, based on a torque and a rotation speed of the AC motor;
a boost state/non-boost state judgement unit for judging whether a control state requested for a succeeding control cycle of the converter is a boost state, in which the power source voltage is boosted and outputted, or is a non-boost state, in which the power source voltage is outputted without being boosted; and
a voltage command value alteration unit for changing a voltage command reference value such as to set the converter in the boost state when the spectrum amplitude at the specific frequency, correlated with the voltage waveform, exceeds a judgement threshold value while also the judgement result from the boost state/non-boost state judgement unit is the non-boost state.

2. The control apparatus for an AC motor according to claim 1 , wherein the voltage command value alteration unit changes the voltage command reference value to a value that is higher than the power source voltage, when the converter is to transition from the non-boost state to the boost state.

3. The control apparatus for an AC motor according to claim 1 , wherein
when the detected value of the system voltage becomes lower than the system voltage threshold value, the boost/non-boost state judgement unit judges that there is a request for the converter to transition from the boost state to the non-boost state, and
when the spectrum amplitude at the specific frequency is equal to or higher than the judgement threshold value, the voltage command value alteration unit changes the voltage command reference value to a value higher than a system voltage threshold value.

4. The control apparatus for an AC motor according to claim 1 , wherein
when the voltage command reference value becomes lower than a system voltage threshold value, the boost/non-boost state judgement unit judges that there is a request for the converter to transition from the boost state to the non-boost state, and
when the spectrum amplitude at the specific frequency exceeds the judgement threshold value, the voltage command value alteration unit changes the voltage command reference value to a value higher than the reference threshold value.

5. The control apparatus for an AC motor according to claim 1 , wherein
a dead time is set by the converter, between an ON period of the high-potential side switching element and an ON period of the low-potential side switching element, and
the voltage command value alteration unit changes the voltage command reference value to a value that is greater than or equal to a value required to provide a voltage boost which compensates for a voltage drop caused by the dead time.

6. The control apparatus for an AC motor according to claim 1 , wherein
the voltage command calculation unit comprises a current feedback control unit for calculating a voltage vector as an operation quantity for feedback control of current flowing in the AC motor,
the voltage waveform specifying unit comprises at least one of a pulse pattern generating unit and a PWM signal generating unit,
the pulse pattern generating unit selects one of a plurality of predetermined pulse patterns that have been stored beforehand, the selection being based upon a modulation factor that is calculated from values of voltage amplitude and system voltage that are outputted from the current feedback control unit and upon the rotation speed of the AC motor, and
the PWM signal generating unit generates a PWM signal by comparing a phase voltage with a carrier wave, the phase voltage being calculated based on an output of the current feedback control unit.

7. The control apparatus for an AC motor according to claim 6 , wherein
the voltage command calculation unit further comprises a torque feedback control unit, for calculating the phase of the voltage vector, as an operation amount for feedback control of the torque of the AC motor,
the voltage waveform specifying unit comprises a pulse pattern setting unit, and
when the voltage vector is calculated by the torque feedback control unit, the pulse pattern setting unit selects a rectangular-waveform pulse pattern having one pulse in each period.

8. The control apparatus for an AC motor according to claim 7 , wherein when the voltage waveform specified by the voltage waveform specifying unit is a rectangular waveform, the voltage command calculation unit halts control by the current feedback control unit and effects calculation of the voltage vector by the torque feedback control unit.

9. The control apparatus for an AC motor according to claim 8 , wherein the AC motor is a three-phase AC motor, and wherein
when the voltage waveform specified by the voltage waveform specifying unit is a rectangular waveform, and the rotation speed of the AC motor is such that the frequency of the 6th- order harmonic component of the bus current coincides with the resonance frequency of the LC circuit, the voltage command value alteration unit changes the voltage command reference value such that the converter transitions to the boost state.

10. The control apparatus for an AC motor according to claim 1 ,
wherein the boost state of the converter is a state in which the ON state and the OFF state of the high-potential side switching element continuously alternate.

Assignees

• Denso Corp

Inventors

• Takahashi Hidekazu

Classifications

• H02P2201/07

  DC-DC step-up or step-down converter inserted between the power supply and the inverter supplying the motor, e.g. to control voltage source fluctuations, to vary the motor speed · CPC title

• H02P27/06

  using DC to AC converters or inverters (H02P27/05 takes precedence) · CPC title

• H02M1/44 Primary

  Circuits or arrangements for compensating for electromagnetic interference in converters or inverters · CPC title

• H02P27/08 Primary

  with pulse width modulation · CPC title

• B60L50/13

  using AC generators and AC motors · CPC title