Pulse width modulation (PWM) rectifier with variable switching frequency
A method for controlling a device including a plurality of switching devices operated in accordance with a pulse width modulation technique includes receiving a reference voltage signal associated with a first pair of the switching devices. A switching signal is generated. The first pair of switching devices are controlled based on the reference voltage signal and the switching signal in accordance with the pulse width modulation technique. A frequency of the switching signal is varied based on the value of the reference voltage signal.
1. A rectifier operable to receive a plurality of input voltages each having a phase, comprising:
a positive bus;
a negative bus;
a plurality of main inductors, each coupled to one of the input voltage phases;
a switching circuit coupled between the positive and negative buses and the main inductors, the switching circuit including a plurality of pairs of switching devices, each pair being associated with one of the input voltage phases;
a controller operable to control the pairs of switching devices for each phase based on a reference voltage signal for each phase and a switching signal for each phase, the controller varying the frequency of the switching signal for a selected phase based on the value of the reference voltage signal for the selected phase to control ripple currents and power losses associated with switching the plurality of pairs of switching devices; and
wherein the reference voltage signal for the selected phase has a maximum magnitude and a minimum magnitude, and the controller is operable to set the frequency of the switching signal to a first value during a first interval including the maximum magnitude and set the frequency of the switching signal to a second value during a second interval including the minimum magnitude.
2. A rectifier operable to receive a plurality of input voltages each having a phase, comprising:
a positive bus;
a negative bus;
a plurality of main inductors, each coupled to one of the input voltage phases;
a switching circuit coupled between the positive and negative buses and the main inductors, the switching circuit including a plurality of pairs of switching devices, each pair being associated with one of the input voltage phases;
a controller operable to control the pairs of switching devices for each phase based on a reference voltage signal for each phase and a switching signal for each phase, the controller varying the frequency of the switching signal for a selected phase based on the value of the reference voltage signal for the selected phase; and
wherein the reference voltage signal for the selected phase has a maximum magnitude and a minimum magnitude, and the controller is operable to set the frequency of the switching signal to a first value during a first interval including the maximum magnitude and set the frequency of the switching signal to a second value during a second interval including the minimum magnitude.
3. The rectifier of claim 2 , wherein the minimum magnitude comprises zero.
4. The rectifier of claim 2 , wherein the second value is greater than the first value.
5. The rectifier of claim 2 , wherein the second value is between about 2 and 6 times the first value.
6. The rectifier of claim 2 , wherein the controller is operable to set the frequency of the switching signal to a third value during a third interval including neither the maximum magnitude nor the minimum magnitude.
7. The rectifier of claim 6 , wherein the first value comprises zero, and the second value is greater than the third value.
8. The rectifier of claim 2 , wherein the controller is operable to implement one of a space vector pulse width modulation technique and a discrete pulse width modulation technique.
9. The rectifier of claim 2 , further comprising an LCL filter disposed between the main inductors and the phase input voltages.
10. A motor control system, comprising:
a power supply operable to provide three input signals each having a phase;
a rectifier operable to receive the three phase input signals and generate a direct current output signal over positive and negative buses, the rectifier implementing a pulse width modulation technique based on a switching signal and a reference voltage signal associated with each of the phases, wherein the rectifier is operable to vary the switching frequency for a selected phase based on a value of the reference voltage signal for the selected phase to reduce ripple currents injected into the positive and negative buses and switching losses associated with pulse width modulation technique;
an inverter operable to switch between the positive and negative buses to generate a plurality of motor drive signals;
a motor operable to rotate responsive to the plurality of motor drive signals; and
wherein the reference voltage signal for the selected phase has a maximum magnitude and a minimum magnitude, and the controller is operable to set the frequency of the switching signal to a first value during a first interval including the maximum magnitude and set the frequency of the switching signal to a second value during a second interval including the minimum magnitude.
11. The rectifier of claim 10 , wherein the minimum magnitude comprises zero.
12. The rectifier of claim 10 , wherein the second value is greater than the first value.
13. The rectifier of claim 10 , wherein the second value is between about 2 and 6 times the first value.
14. The rectifier of claim 10 , wherein the controller is operable to set the frequency of the switching signal to a third value during a third interval including neither the maximum magnitude nor the minimum magnitude.
15. The rectifier of claim 14 , wherein the first value comprises zero, and the second value is greater than the third value.
16. The rectifier of claim 10 , wherein the controller is operable to implement one of a space vector pulse width modulation technique and a discrete pulse width modulation technique.
17. The rectifier of claim 10 , wherein the rectifier comprises:
a plurality of main inductors, each coupled to one of the input voltage phases;
a switching circuit coupled between the positive and negative buses and the main inductors, the switching circuit including a plurality of pairs of switching devices, each pair being associated with one of the input voltage phases; and
a controller operable to control the pairs of switching devices for each phase based on the reference voltage signal for each phase and the switching signal for each phase.
18. The rectifier of claim 17 , wherein the rectifier further comprises an LCL filter disposed between the main inductors and the phase input voltages.
19. A device, comprising:
a plurality of switching devices;
a controller operable to receive a reference voltage signal associated with a first pair of the switching devices, generate a switching signal, control the first pair of switching devices based on the reference voltage signal and the switching signal in accordance with a pulse width modulation technique, and vary a frequency of the switching signal based on the value of the reference voltage signal to control ripple currents and power losses associated with switching the first pair of switching devices; and
wherein the reference voltage signal has a maximum magnitude and a minimum magnitude and, wherein the controller varies the frequency of the switching signal to have a first frequency during a first interval associated with the maximum magnitude of the reference voltage signal and a second frequency during a second interval associated with the minimum magnitude of the reference voltage signal.
20. A method for controlling a device including a plurality of switching devices operated in accordance with a pulse width modulation technique, comprising:
receiving a reference voltage signal associated with a first pair of the switching devices;
generating a switching signal;
controlling the first pair of switching devices based on the reference voltage signal and the switching signal in accordance with the pulse width modulation technique;
varying a frequency of the switching signal based on the value of the reference voltage signal to control ripple currents and power losses associated with switching the plurality of pairs of switching devices; and
wherein the reference voltage signal has a maximum magnitude and a minimum magnitude, and varying the frequency further comprises setting the frequency of the switching signal to a first value during a first interval including the maximum magnitude and setting the frequency of the switching signal to a second value during a second interval including the minimum magnitude.