Feedforward control of motor drives with output sinewave filter
Disclosed examples include power conversion systems and methods to operate an inverter to drive a motor load through an intervening output filter, a transformer and a cable, including a current regulator to compute a command value according to a current reference value and a motor current feedback value, a cross-coupled feedforward component to compensate the command value by an estimated cross-coupled voltage value to compute a control output value, a cross-coupled object component to compute the motor current feedback value according to a voltage value using a plant transfer function representing the output filter, the transformer, the cable and the motor load, and a controller to provide the inverter switching control signals to control the inverter according to the control output value.
1. A power conversion system, comprising:
an inverter comprising a DC input, an AC output, and a plurality of switching devices coupled between the DC input and the AC output and operative according to inverter switching control signals to convert DC electrical power received at the DC input to provide AC electrical output power at the AC output to drive a motor load through an intervening output filter, a transformer and a cable; and
a controller, including:
a current regulator component implemented by a processor to compute a command value according to a current reference value and a motor current feedback value,
a cross-coupled feedforward component implemented by the processor to compensate the command value by an estimated cross-coupled voltage value to compute a control output value, and
a cross-coupled object component implemented by the processor to compute the motor current feedback value according to a voltage value using a plant transfer function representing the output filter, the transformer, the cable and the motor load;
the controller being operative to provide the inverter switching control signals to control the inverter according to the control output value;
wherein the current regulator component computes a d-axis command value according to a d-axis current reference value and a d-axis motor current feedback value, and computes a q-axis command value according to a q-axis current reference value and a q-axis motor current feedback value; and
wherein the cross-coupled feedforward component compensates the d-axis command value by subtracting an estimated q-axis voltage value from the d-axis command value to compute a d-axis control output value, and wherein the cross-coupled feedforward component compensates the q-axis command value by adding an estimated d-axis voltage value to the q-axis command value to compute a q-axis control output value.
2. The power conversion system of claim 1 , wherein the cross-coupled feedforward component computes the estimated q-axis voltage value according to an estimated q-axis motor back EMF value.
3. The power conversion system of claim 1 , wherein the cross-coupled feedforward component computes the estimated d-axis voltage value according to a reference or feedback q-axis motor current value and an estimated inverter electrical frequency, and wherein the cross-coupled feedforward component computes the estimated q-axis voltage value according to a reference or feedback d-axis motor current value and the estimated inverter electrical frequency.
4. The power conversion system of claim 3 , wherein the cross-coupled feedforward component computes the estimated d-axis voltage value according to a reference or feedback q-axis inverter current value and the estimated inverter electrical frequency, and wherein the cross-coupled feedforward component computes the estimated q-axis voltage value according to a reference or feedback d-axis inverter current value and the estimated inverter electrical frequency.
5. The power conversion system of claim 1 ,
wherein the cross-coupled object component computes a d-axis output voltage value by adding a q-axis motor voltage value to a d-axis inverter voltage value;
wherein the cross-coupled object component computes a d-axis motor current feedback value according to the d-axis output voltage value using the plant transfer function;
wherein the cross-coupled object component computes a q-axis output voltage value by subtracting a d-axis motor voltage value from a q-axis inverter voltage value; and
wherein the cross-coupled object component computes a q-axis motor current feedback value according to the q-axis output voltage value using the plant transfer function.
6. The power conversion system of claim 5 , wherein the cross-coupled object component computes the d-axis motor voltage value according to a q-axis motor back EMF value.
7. The power conversion system of claim 5 , wherein the cross-coupled object component computes the d-axis motor voltage value according to the d-axis motor current feedback value, and wherein the cross-coupled object component computes the q-axis motor voltage value according to the q-axis motor current feedback value.
8. The power conversion system of claim 7 , wherein the cross-coupled object component computes the d-axis motor voltage value according to a d-axis inverter current feedback value (I inv.d ), and wherein the cross-coupled object component computes the q-axis motor voltage value according to a q-axis inverter current feedback value.
9. A method of operating an inverter to drive a motor load through an output filter and a transformer, the method comprising:
implementing a current regulator component to compute a command value according to a current reference value and a motor current feedback value;
implementing a cross-coupled feedforward component to compensate the command value by an estimated cross-coupled voltage value to compute a control output value;
implementing a cross-coupled object component to compute the motor current feedback value according to a voltage value using a plant transfer function representing the output filter, the transformer, the cable and the motor load; and
providing inverter switching control signals to control the inverter according to the control output value;
further comprising implementing the current regulator component to compute a d-axis command value according to a d-axis current reference value and a d-axis motor current feedback value, and to compute a q-axis command value according to a q-axis current reference value and a q-axis motor current feedback value; and
further comprising implementing the cross-coupled feedforward component to compensate the d-axis command value by subtracting an estimate q-axis voltage value from the d-axis command value to compute a d-axis control output value, and implementing the cross-coupled feedforward component to compensate the q-axis command value by adding an estimated d-axis voltage value to the q-axis command value to compute a q-axis control output value.
10. The method of claim 9 , wherein the cross-coupled feedforward component computes the estimated q-axis voltage value according to an estimated q-axis motor back EMF value.
11. The method of claim 9 , further comprising implementing the cross-coupled feedforward component to compute the estimated d-axis voltage value according to a reference or feedback q-axis motor current value and an estimated inverter electrical frequency, and implementing the cross-coupled feedforward component to compute the estimated q-axis voltage value according to a reference or feedback d-axis motor current value and the estimated inverter electrical frequency.
12. The method of claim 11 , further comprising implementing the cross-coupled feedforward component to compute the estimated d-axis voltage value according to a reference or feedback q-axis inverter current value and the estimated inverter electrical frequency, and implementing the cross-coupled feedforward component to compute the estimated q-axis voltage value according to a reference or feedback d-axis inverter current value and the estimated inverter electrical frequency.
13. The method of claim 9 , further comprising:
implementing the cross-coupled object component to compute a d-axis output voltage value by adding a q-axis motor voltage value to a d-axis inverter voltage value;
implementing the cross-coupled object component to compute a d-axis motor current feedback value according to the d-axis output voltage value using the plant transfer function;
implementing the cross-coupled object component to compute a q-axis output voltage value by subtracting a d-axis motor voltage value from a q-axis inverter voltage value; and
implementing the cross-coupled object component to compute a q-axis motor current feedback value according to the q-axis output voltage value using the plant transfer function.
14. The method of claim 13 , further comprising implementing the cross-coupled object component to compute the d-axis motor voltage value according to a q-axis motor back EMF value.
15. The method of claim 13 , further comprising implementing the cross-coupled object component to compute the d-axis motor voltage value according to the d-axis motor current feedback value, and comprising implementing the cross-coupled object component to compute the q-axis motor voltage value according to the q-axis motor current feedback value.
16. A non-transitory computer readable medium including computer executable instructions which, when executed by a processor, cause the processor to:
compute a command value according to a current reference value and a motor current feedback value;
compensate the command value by an estimated cross-coupled voltage value to compute a control output value;
compute the motor current feedback value according to a voltage value using a plant transfer function representing the output filter, the transformer, the cable and the motor load; and
control the inverter according to the control output value i , compute a d-axis command value according to a d-axis current reference value and a d-axis motor current feedback value, and compute a q-axis command value according to a q-axis current reference value and a q-axis motor current feedback value; and
compensate the d-axis command value by subtracting an estimated q-axis voltage value from the d-axis command value to compute a d-axis control output value, and compensate the q-axis command value by adding an estimated d-axis voltage value to the q-axis command value to compute a q-axis control output value.