Universal AC high power inveter with galvanic isolation for linear and non-linear loads

• US 7,660,135 B2
• Filed: 05/23/2007
• Issued: 02/09/2010
• Est. Priority Date: 05/23/2007
• Status: Active Grant

• Current Assignee: Hamilton Sundstrand Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: Hamilton Sundstrand Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Fang, Si Jian
• Primary Examiner(s): HAN, YOUNGHUIE JESSICA
• Application Number:
  US11/805,489
• Publication Number:
  US 20080291707A1
• Time in Patent Office: 993 Days
• Field of Search: 363/17, 363 24- 26, 363/98, 363/132
• US Class Current: 363/17
• CPC Class Codes: H02M 1/007 Plural converter units in cascade push-pull DC/DC converters with pre-regulator H02M3/3374; DC-AC converters following a DC-DC stage including a high frequency transformer H02M7/4807; DC-AC converters following a DC-DC conversion stage generating periodically varying voltages H02M7/4826
• CPC Class Codes: H02M 1/40 Means for preventing magnetic saturation
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: H02M 7/53871 with automatic control of output voltage or current

Abstract

A universal alternating current (AC) inverter system with galvanic isolation takes an unregulated direct current (DC) input and provides a high-quality AC output that may be used in conjunction with both linear and non-linear loads. The universal AC inverter system includes a DC-DC converter for converting an unregulated DC input to a regulated DC output, and a DC-AC inverter for converting the regulated DC output to a high-quality AC output. The DC-DC converter includes a DC link isolation high frequency transformer that provides galvanic isolation between the unregulated DC input and the AC output. To avoid saturation of the transformer, the controller for the DC-DC converter employs a DC offset correction loop that prevents accumulation of DC content on the primary side of the transformer. The universal AC inverter system includes a 4-phase inverter topology that converts the regulated DC voltage provided by the DC-DC converter to an AC output. An inverter controller employs a number of feedback loops that are used to control switches within the 4-phase inverter topology to provide a high-quality AC output voltage for both linear and non-linear loads, including a fast voltage control loop, a slow voltage control loop, a AC output capacitor current control loop, and a DC content control loop.

Claims

1. A alternating current (AC) generator system comprising:

a direct-current (DC) to DC converter that includes a first switch, a second switch, a transformer, and a full wave rectifier to convert a DC input voltage to a DC output voltage;

a DC to DC controller that provides a first pulse width modulation (PWM) signal to the first switch and a second PWM signal to the second switch in response to a monitored output voltage to regulate the DC output voltage to a desired magnitude, wherein the DC to DC controller includes a DC offset control loop that monitors current on a primary side of the transformer, isolates DC content within the monitored current, and generates a DC content compensation signal in response to the isolated DC content that is combined with the monitored output voltage to modify the first PWM signal provided to the first switch such that DC content is minimized within the transformer;

an inverter that includes a network of switches, at least one output inductor, and at least one output capacitor for converting the DC output voltage provided by DC to DC converter to an AC output voltage of desired magnitude and frequency; and

an inverter controller that provides control signals to the network of switches based on monitored AC output voltage of the inverter and a reference voltage defining the desired magnitude and frequency, wherein the inverter controller employs a plurality of control loops to generate the control signals provided to the network of switches to provide regulation of the AC output voltage.

2. The system of claim 1, wherein the DC to DC converter provides galvanic isolation between the DC input voltage and the AC output voltage.

3. The system of claim 1, wherein the DC offset control loop includes:

a low pass filter that isolates DC content within the current monitored on the primary side of the transformer; and

a volt-second correction network that generates the DC content compensation signal in response to detected DC content provided by the low-pass filter.

4. The system of claim 3, wherein the DC to DC controller includes:

a voltage feedback loop that provides a feedback signal based on a comparison of the DC output voltage to a DC reference voltage;

a modulating ramp signal generator that generates a ramp signal;

a first combiner that adds the voltage feedback signal generated by the voltage feedback loop to the DC content compensation signal to generate a combined signal;

a first half-cycle peak current controller that compares the combined signal to the ramp signal to generate the first PWM signal; and

a second half-cycle peak current controller that compares the feedback signal to the modulating ramp signal to generate the second PWM signal.

5. The system of claim 4, wherein the modulating ramp signal generator includes:

a second combiner for adding a slope compensation signal to a monitored feedback current representing current provided to the first switch and the second switch to generate the modulating ramp signal that is provided to the first half-cycle peak current controller and the second half-cycle peak current controller.

6. The system of claim 1, wherein the inverter controller includes:

a fast voltage control loop that provides a first compensated signal to regulate differences between the AC output voltage and the AC reference voltage;

a slow voltage control loop that provides a second compensated signal to regulate differences between a root mean square (RMS) value of the AC output voltage and an RMS value of the AC reference voltage;

an AC output capacitor current control loop that derives an AC output capacitor current through the at least one capacitor based on the AC output voltage and derives an AC reference current based on the AC reference voltage and provides a third compensation signal to regulate differences between the AC output capacitor current and the AC reference current;

a DC content control loop that provides a fourth compensation signal to regulate detected DC content within the AC output voltage; and

a PWM generator that provides PWM control signals to the second network of switches based on the combination of the first, second, third, and fourth compensation signals.

7. The system of claim 6, wherein the fast voltage control loop includes:

a differentiator for applying a time derivative to the AC output voltage;

a comparator for comparing the result of the differentiator to the AC reference voltage to generate a first difference signal; and

a pole-zero compensation network that generates the first compensation signal in response to the difference signal.

8. The system of claim 6, wherein the slow voltage control loop includes:

a first root mean square calculator for calculating the root mean square of the AC output voltage;

a second root mean square calculator for calculating the root mean square of the AC reference voltage;

a comparator for comparing the RMS of the AC output voltage to the RMS of the AC reference voltage to generate a second difference signal; and

an integrator compensation network that generates the second compensation signal in response to the signal representing the difference between the RMS of the AC output voltage and the RMS of the AC reference voltage.

9. The system of claim 6, wherein the AC output capacitor current control loop includes:

a first differentiator that derives the AC output capacitor current through the at least one capacitor by applying a time-based derivative to the AC output voltage;

a second differentiator that derives the AC reference current by applying a time-based derivative to the AC reference voltage;

a comparator for comparing the derived AC output capacitor current to the derived AC reference current to generate a difference signal; and

a pole-zero compensation network that generates the third compensation signal in response to the difference between the derived AC output capacitor current and the derived AC reference current.

10. The system of claim 6, wherein the DC content control loop includes:

a low-pass filter that isolates DC content in the AC output voltage;

a comparator for comparing the isolated DC content to a desired value to generate a difference signal; and

a integrator compensation network that generates the fourth compensation signal in response to the difference between the isolated DC content and the desired value.

11. A direct-current (DC) to DC controller connectable to a DC to DC converter that includes a first power transistor, a second power transistor and a transformer, the DC to DC controller comprising:

a modulating ramp signal generator that generates a modulating ramp signal;

a voltage compensation loop that monitors a DC output voltage generated by the DC to DC converter and generates an output voltage control signal based on a comparison of the DC output voltage to a DC reference voltage;

a volt-second correction loop that monitors alternating current (AC) current on a primary side of the transformer, detects DC content within the AC current, and generates a DC content compensation signal based on the detected DC content;

a combiner that combines the output voltage control signal and the DC content compensation signal to generate a combined signal;

a first half-cycle peak current controller that generates control signals provided to the first power transistor based on a comparison of the modulating ramp signal to the combined signal; and

a second half-cycle peak current controller that generates controls signals provided to the second power transistor based on a comparison of the modulating ramp signal to the output voltage control signal.

12. The DC-DC controller of claim 11, wherein the volt-second connection loop includes:

a low pass filter that isolates the DC content within the AC current monitored on the primary side of the transformer; and

a volt-second correction network that generates the DC content compensation signal in response to the isolated DC content provided by the low-pass filter.

13. The DC-DC converter of claim 12, wherein the volt-second correction network includes a proportional-integral-derivative (PD) controller that generates the DC content compensation signal in response to the isolated DC content.

14. An alternating current (AC) controller that provides control signals to an inverter topology to regulate an AC output voltage to a desired magnitude and frequency represented by an AC reference signal, the AC controller comprising:

a fast voltage control loop that provides a first compensated signal to regulate differences between the AC output voltage and the AC reference voltage;

a slow voltage control loop that provides a second compensated signal to regulate differences between a root mean square (RMS) value of the AC output voltage and an RMS value of the AC reference voltage;

an AC output capacitor current control loop that derives an AC output capacitor current through the at least one capacitor based on the AC output voltage and derives an AC reference current based on the AC reference voltage and provides a third compensation signal to regulate differences between the AC output capacitor current and the AC reference current; and

a DC content control loop that provides a fourth compensation signal to regulate detected DC content within the AC output voltage; and

a combiner that combines the first, second, third, and fourth compensation signals to generate a single compensation signal used by the inverter controller to generate the control signals provided to the inverter topology to regulate the AC output voltage to the desired magnitude and phase.

15. The system of claim 14, wherein the fast voltage control loop includes:

a differentiator for applying a time derivative to the AC output voltage;

a comparator for comparing the result of the differentiator to the AC reference voltage to generate a first difference signal; and

a pole-zero compensation network that generates the first compensation signal in response to the difference signal.

16. The system of claim 14, wherein the slow voltage control loop includes:

a first root mean square calculator for calculating the root mean square of the AC output voltage;

a second root mean square calculator for calculating the root mean square of the AC reference voltage;

a comparator for comparing the RMS of the AC output voltage to the RMS of the AC reference voltage to generate a second difference signal; and

an integrator compensation network that generates the second compensation signal in response to the signal representing the difference between the RMS of the AC output voltage and the RMS of the AC reference voltage.

17. The system of claim 14, wherein the AC output capacitor current control loop includes:

a first differentiator that derives the AC output capacitor current through the at least one capacitor by applying a time-based derivative to the AC output voltage;

a second differentiator that derives the AC reference current by applying a time-based derivative to the AC reference voltage;

a comparator for comparing the derived AC output capacitor current to the derived AC reference current to generate a difference signal; and

a pole-zero compensation network that generates the third compensation signal in response to the difference between the derived AC output capacitor current and the derived AC reference current.

18. The system of claim 14, wherein the DC content control loop includes:

a low-pass filter that isolates DC content in the AC output voltage;

a comparator for comparing the isolated DC content to a desired value to generate a difference signal; and

a integrator compensation network that generates the fourth compensation signal in response to the difference between the isolated DC content and the desired value.

19. The system of claim 14, wherein the magnitude and frequency of the AC output voltage is selectively controlled by modifying the AC reference voltage provided to the inverter controller.