System and method for controlling dynamic output impedance of an inverter
View Patent ↗A control circuit is described herein. The control circuit includes an oscillator and a processor. The oscillator is configured to generate a reference signal. The processor is coupled to the oscillator. The processor is configured to receive a first output current sample, a second output current sample, and a third output current sample, all of an output current. The first output current sample is first-in-time, the second output current sample is second-in-time, and the third output current sample is third-in-time. The processor is further configured to compute a time-derivative of the output current. The processor is further configured to compute a command variable based on the reference signal, a time-derivative of the reference signal, the third output current sample, and the time-derivative of the output current.
1. A control circuit, comprising:
an oscillator configured to generate a reference signal; and
a processor coupled to said oscillator and configured to:
receive a first output current sample, a second output current sample, and a third output current sample, wherein the first, second, and third samples are samples of an output current,
compute a time-derivative of the output current based on the samples, and
compute a command variable based on the reference signal, a time-derivative of the reference signal, the output current, and the time-derivative of the output current, and
operate an inverter circuit based on the command variable.
2. The control circuit of claim 1 , wherein said processor is further configured to apply respective gains to the reference signal, the time-derivative of the reference signal, the output current, and the time-derivative of the output current.
3. The control circuit of claim 1 , wherein said processor is further configured to receive an output voltage sample and a bridge current sample.
4. The control circuit of claim 3 , wherein said processor is further configured to compute the command variable based on the output voltage sample and the bridge current sample.
5. The control circuit of claim 1 , wherein said processor comprises a state controller for computing the time-derivative of the output current.
6. The control circuit of claim 1 , wherein said processor is further configured to compute the time-derivative of the output current based on the first output current sample, the second output current sample, and the third output current sample.
7. A method of controlling an inverter circuit, said method comprising:
receiving three output current samples of an output current;
computing a time-derivative of the output current based on the three output current samples;
generating a command variable based on the reference signal and time-derivative thereof, the output current, and the time-derivative of the output current; and
operating the inverter circuit based on the command variable.
8. The method of claim 7 further comprising receiving a sample of a bridge current supplied by the inverter circuit.
9. The method of claim 8 , wherein generating the command variable is further based on the sample of the bridge current.
10. The method of claim 7 wherein computing the time-derivative of the output current comprises calculating (2x[k]−3x[k−1]+x[k−2])/T, wherein:
x[k] is a last-in-time sample of the three output current samples,
x[k−1] is a second-to-last-in-time sample of the three output current samples,
x[k−2] is a third-to-last-in-time sample of the three output current samples, and
T is a time period over which the three output current samples are taken.
11. The method of claim 7 further comprising amplifying the reference signal, the time derivative of the reference signal, the output current, and the time-derivative of the output current using respective gains.
12. The method of claim 11 further comprising retrieving the respective gains from a non-transitory memory device.
13. The method of claim 7 wherein computing the time-derivative of the output current comprises employing a state controller.