Method and apparatus for controlling a cascaded inverter circuit and an electric machine

Patent metadata

Field	Value
Publication number	US-10826424-B2
Application number	US-201816031632-A
Country	US
Kind code	B2
Filing date	Jul 10, 2018
Priority date	Jul 10, 2018
Publication date	Nov 3, 2020
Grant date	Nov 3, 2020

Abstract

A cascaded inverter system is described and includes an electric machine that is electrically connected in series between first and second inverters. A controller is in communication with the first and second inverters, and includes an executable instruction set. A first dead-time compensation term and a first voltage compensation term are determined based upon an initial phase current and a switching frequency for the first inverter, and a final first duty cycle is determined based thereon. Simultaneously, a second dead-time compensation term and a second voltage compensation term are determined based upon the inverted initial phase current and a switching frequency for the second inverter, and a final second duty cycle is determined based thereon. Operation of the first and second inverters are dynamically controlled based upon the final first duty cycle and the final second duty cycle, respectively.

First claim

What is claimed is:

1. A device for operating a multi-phase electric machine, comprising:
a first multi-phase pulsewidth-modulated inverter circuit (first inverter) and a second multi-phase pulsewidth-modulated inverter circuit (second inverter), wherein the multi-phase electric machine is electrically connected in series therebetween; and
a controller in communication with the first and second inverters, the controller including an instruction set, the instruction set executable to:
determine an initial phase current,
determine a first initial duty cycle for controlling the first inverter based upon the initial phase current,
determine a switching frequency for the first inverter,
determine a cycle period for the first inverter based upon the switching frequency,
determine a first dead-time period associated with operation of the first inverter,
determine a first dead-time compensation term based upon a comparison of the first dead-time period and the cycle period,
determine a first voltage compensation term based upon a voltage drop across the first inverter,
determine a final first duty cycle based upon the first initial duty cycle, the first dead-time compensation term and the first voltage compensation term,
invert the initial phase current,
determine a second initial duty cycle for controlling the second inverter based upon the inverted initial phase current,
determine a second dead-time compensation term,
determine a second voltage compensation term based upon a voltage drop across the second inverter,
determine a final second duty cycle based upon the second initial duty cycle, the second dead-time compensation term and the second voltage compensation term, and
control operation of the first inverter based upon the final first duty cycle and simultaneously control operation of the second inverter based upon the final second duty cycle.

2. The device of claim 1 , wherein the first and second inverters are configured to operate in a linear modulation mode, and wherein the controller is disposed to control operation of the first inverter based upon the final first duty cycle and simultaneously control operation of the second inverter based upon the final second duty cycle when the controller is operating the first and second inverters in the linear modulation mode.

3. The device of claim 1 , further comprising the controller in communication with the first inverter via a first gate driver and the controller in communication with the second inverter via a second gate driver.

4. The device of claim 1 , wherein the multi-phase electric machine comprises a synchronous permanent magnet electric machine.

5. The device of claim 1 , wherein the instruction set executable to determine the first voltage compensation term based upon the voltage drop across the first inverter comprises the instruction set executable to:
determine an average voltage drop across the first inverter,
determine a dc link voltage, and
determine the first voltage compensation term based upon a ratio of the voltage drop across the first inverter and the dc link voltage.

6. The device of claim 1 , wherein the instruction set executable to determine the second voltage compensation term based upon the voltage drop across the second inverter comprises the instruction set executable to:
determine an average voltage drop across the second inverter,
determine a dc link voltage, and
determine the second voltage compensation term based upon a ratio of the voltage drop across the second inverter and the dc link voltage.

7. The device of claim 1 , wherein the instruction set executable to determine the second dead-time compensation term comprises the instruction set executable to:
determine a switching frequency for the second inverter,
determine a cycle period for the second inverter based upon the switching frequency;
determine a second dead-time period associated with operation of the second inverter, and
determine the second dead-time compensation term based upon a comparison of the second dead-time period and the cycle period.

8. The device of claim 1 , further comprising a current sensor disposed to monitor electric current between the first inverter and a phase winding of the multi-phase electric machine to determine the initial phase current.

9. A method for operating a multi-phase electric machine that is electrically connected in series between a first multi-phase pulsewidth-modulated inverter circuit (first inverter) and a second multi-phase pulsewidth-modulated inverter circuit (second inverter), the method comprising:
determining an initial phase current;
determining a first initial duty cycle for controlling the first inverter based upon the initial phase current;
determining a first dead-time compensation term, including:
determining a switching frequency for the first inverter,
determining a cycle period for the first inverter based upon the switching frequency,
determining a first dead-time period associated with operation of the first inverter, and
determining the first dead-time compensation term based upon a comparison of the first dead-time period and the cycle period;

determining a first voltage compensation term based upon a voltage drop across the first inverter;
determining a final first duty cycle based upon the first initial duty cycle, the first dead-time compensation term and the first voltage compensation term;
inverting the initial phase current;
determining a second initial duty cycle for controlling the second inverter based upon the inverted initial phase current;
determining a second dead-time compensation term;
determining a second voltage compensation term based upon a voltage drop across the second inverter;
determining a final second duty cycle based upon the second initial duty cycle, the second dead-time compensation term and the second voltage compensation term; and
dynamically operating the first inverter based upon the final first duty cycle and simultaneously dynamically operating the second inverter based upon the final second duty cycle.

10. The method of claim 9 , comprising operating the first inverter in a linear modulation mode based upon the final first duty cycle and simultaneously operating the second inverter in a linear modulation mode based upon the final second duty cycle.

11. The method of claim 9 , wherein determining the first voltage compensation term based upon the voltage drop across the first inverter comprises:
determining an average voltage drop across the first inverter;
determining a dc link voltage; and
determining the first voltage compensation term based upon a ratio of the voltage drop across the first inverter and the dc link voltage.

12. The method of claim 9 , wherein determining the second voltage compensation term based upon the voltage drop across the second inverter comprises:
determining an average voltage drop across the second inverter;
determining a dc link voltage; and
determining the second voltage compensation term based upon a ratio of the voltage drop across the second inverter and the dc link voltage.

13. The method of claim 9 , wherein determining the second dead-time compensation term comprises:
determining a switching frequency for the second inverter;
determining a cycle period for the second inverter based upon the switching frequency;
determining a second dead-time period associated with operation of the second inverter; and
determining the second dead-time compensation term based upon a comparison of the second dead-time period and the cycle period.

14. The method of claim 9 , wherein determining the init

Assignees

• Gm Global Tech Operations Llc

Inventors

• Welchko Brian A
• Gagas Brent S

Classifications

• H02M1/385

  with means for correcting output voltage deviations introduced by the dead time · CPC title

• H02P27/085 Primary

  wherein the PWM mode is adapted on the running conditions of the motor, e.g. the switching frequency · CPC title

• H02M7/5395

  by pulse-width modulation · CPC title

• H02P29/50

  Reduction of harmonics · CPC title

• H02M7/5387 Primary

  in a bridge configuration · CPC title