High voltage, high efficiency sine wave generator with pre-set frequency and adjustable amplitude
View Patent ↗An apparatus for generating a sinusoid at a pre-set frequency f includes a DC power source with a controllable output voltage, a transformer, a power switch, a sequencer, and an output filter. The power switch is configured to apply the output of the DC power source to the primary of the transformer in either direction or to remain off based on control signals that are applied to its control input. The sequencer applies control signals to the control input in a choreographed sequence to form an oversampled version of a sine wave. The output filter is connected to the secondary of the transformer, and it passes the pre-set frequency f and attenuates frequencies above a cut-off frequency. In some preferred embodiments, the cut-off frequency is 3f and the transfer function of the output filter has a zero at 5f.
1. An apparatus for generating a sinusoid at a pre-set frequency f, the apparatus comprising:
a DC power source having a voltage-control input that sets an output voltage of the DC power source;
a transformer having a primary and a secondary;
a power switch having a control input, wherein the power switch is configured to apply the output of the DC power source to the primary of the transformer in a first direction when a first control signal is applied to the control input, apply the output of the DC power source to the primary of the transformer in a second direction when a second control signal is applied to the control input, and remain off when neither the first control signal nor the second control signal is applied to the control input, wherein the second direction is opposite to the first direction;
a sequencer configured to (a) apply the first control signal to the control input for a duration of T/3, then (b) to wait for a duration of T/6, then (c) to apply the second control signal to the control input for a duration of T/3, and then (d) to wait for a duration of T/6, then to continuously repeat the sequence (a), (b), (c), and (d), wherein T is the reciprocal of the pre-set frequency f; and
an output filter connected to the secondary of the transformer, wherein the output filter passes the pre-set frequency f and attenuates frequencies above a cut-off frequency, wherein the cut-off frequency is between 2f and 4f, and wherein the output filter has a transfer function with a zero at 5f.
2. The apparatus of claim 1 , further comprising a controller programmed to control an amplitude of the sinusoid at the pre-set frequency by adjusting a third control signal that is applied to the voltage-control input of the DC power source.
3. The apparatus of claim 2 , further comprising a sensor that detects an output current of the apparatus, wherein the controller is programmed to increase the amplitude of the sinusoid when the detected output current is lower than a desired current, and to decrease the amplitude of the sinusoid when the detected output current is higher than the desired current.
4. The apparatus of claim 3 , wherein the sequencer inhibits generation of both the first control signal and the second control signal when the output current detected by the sensor is indicative of an error condition.
5. The apparatus of claim 1 , wherein the transfer function of the output filter has an additional zero at 7f.
6. The apparatus of claim 5 , wherein the output filter comprises a low pass elliptic filter.
7. The apparatus of claim 6 , wherein the cut-off frequency of the output filter is at or near 3f.
8. The apparatus of claim 1 , wherein the cut-off frequency of the output filter is at or near 3f.
9. The apparatus of claim 1 , wherein the output filter is a multi-stage low pass LC filter, and a leakage inductance of the transformer provides at least half of the inductance of a first stage of the low pass LC filter.
10. The apparatus of claim 1 , wherein the output filter is a multi-stage low pass LC filter, and a leakage inductance of the transformer provides all of the inductance of a first stage of the low pass LC filter.
11. The apparatus of claim 1 , wherein the output filter has an output impedance of 70 ohms.
12. The apparatus of claim 1 , wherein the output filter has an output impedance between 40 and 120 ohms.
13. The apparatus of claim 1 , wherein the pre-set frequency f is 200 kHz.
14. The apparatus of claim 1 , wherein the pre-set frequency f is 150 kHz.
15. The apparatus of claim 1 , wherein the power switch has an H-bridge configuration.
16. An apparatus for generating a sinusoid at a pre-set frequency f, the apparatus comprising:
n DC power sources, each of the n DC power sources having a voltage-control input that sets an output voltage of the respective power source, wherein n is a positive integer;
a transformer having a primary and a secondary;
a power switch having a control input, wherein the power switch is configured to either (a) apply the output of a selected one of the n DC power sources to the primary of the transformer in a selected direction in response to 2n states of a control signal that is applied to the control input or (b) remain off in response to an additional state of the control signal;
a sequencer configured to control the generation of an oversampled version of a sine wave that is sampled N times per cycle using evenly spaced samples that include a sampling point at 0°, where N=2+4n, by setting the output voltages of the n DC power sources to levels that are present on the oversampled version of the sine wave, and then sequencing the control signal through the 2n states and the additional state, so that each of the n DC power sources is applied to the primary of the transformer in each direction at appropriate times in a sequence so as to generate the oversampled version of the sine wave; and
an output filter connected to the secondary of the transformer, wherein the output filter passes the pre-set frequency f and attenuates frequencies above a cut-off frequency, and wherein the output filter has a transfer function with a zero at a frequency where a harmonic of the pre-set frequency f is expected to contain power, and
wherein a controller is configured to control an amplitude of the sinusoid by adjusting the output voltages of the n DC power sources via the voltage-control inputs, while maintaining a fixed ratio between the output voltages of each of the n DC power sources.
17. The apparatus of claim 16 , wherein the transfer function of the output filter has an additional zero at a next frequency where a harmonic of the pre-set frequency f is expected to contain power.
18. The apparatus of claim 16 , wherein the cut-off frequency of the output filter is at or near 3f.
19. The apparatus of claim 16 , wherein the output filter is a multi-stage low pass LC filter, and a leakage inductance of the transformer provides at least half of the inductance of a first stage of the low pass LC filter.
20. The apparatus of claim 16 , wherein the output filter is a multi-stage low pass LC filter, and a leakage inductance of the transformer provides all of the inductance of a first stage of the low pass LC filter.
21. The apparatus of claim 16 , further comprising:
a second output filter that passes a second pre-set frequency f2 and attenuates frequencies above a second cut-off frequency, wherein the second output filter has a transfer function with a zero at a frequency where a harmonic of the second pre-set frequency f2 is expected to contain power; and
a switch that selectively connects either the output filter or the second output filter to the secondary of the transformer.
22. The apparatus of claim 16 , wherein the output filter includes at least one component with a tunable reactance.
23. An apparatus for generating a sinusoid at a pre-set frequency f, the apparatus comprising:
n DC power sources, each of the n DC power sources having a voltage-control input that sets an output voltage of the respective power source, wherein n is a positive integer;
a power switch having output terminals and a control input, wherein the power switch is configured to either (a) switch the output of a selected one of the n DC power sources across the output terminals in a selected direction in response to 2n states of a control signal that is applied to the control input or (b) remain off in response to an additional state of the control signal;
a sequencer configured to control the generation of an oversampled version of a sine wave that is sampled N times per cycle using evenly spaced samples that include a sampling point at 0°, where N=2+4n, by setting the output voltages of the n DC power sources to levels that are present on the oversampled version of the sine wave, and then sequencing the control signal through the 2n states and the additional state, so that each of the n DC power sources is switched across the output terminals in each direction at appropriate times in a sequence so as to generate the oversampled version of the sine wave; and
an output filter that filters a signal received from the output terminals of the power switch, wherein the output filter passes the pre-set frequency f and attenuates frequencies above a cut-off frequency, and wherein the output filter has a transfer function with a zero at a frequency where a harmonic of the pre-set frequency f is expected to contain power,
wherein a controller controls an amplitude of the sinusoid by adjusting the output voltages of the n DC power sources via the voltage-control inputs, while maintaining a fixed ratio between the output voltages of each of the n DC power sources.
24. The apparatus of claim 23 , wherein the transfer function of the output filter has an additional zero at a next frequency where a harmonic of the pre-set frequency f is expected to contain power.
25. The apparatus of claim 23 , wherein the cut-off frequency of the output filter is at or near 3f.
26. The apparatus of claim 23 , further comprising:
a second output filter that passes a second pre-set frequency f2 and attenuates frequencies above a second cut-off frequency, wherein the second output filter has a transfer function with a zero at a frequency where a harmonic of the second pre-set frequency f2 is expected to contain power; and
a switch that selectively connects either the output filter or the second output filter to the secondary of the transformer.
27. The apparatus of claim 23 , wherein the output filter includes at least one component with a tunable reactance.
28. A method for generating a sinusoid at a pre-set frequency f, the method comprising:
setting n DC power sources to respective output voltages, wherein n is a positive integer;
generating an oversampled version of a sine wave that is sampled N times per cycle using evenly spaced samples that include a sampling point at 0°, where N=2+4n, by setting the output voltages of the n DC power sources to levels that are present on the oversampled version of the sine wave, and then switching the outputs of the n DC power sources to an output in a controlled sequence such that each of the n DC power sources is switched to the output in each direction at appropriate times in the sequence so as to generate the oversampled version of the sine wave; and
filtering the oversampled version of the sine wave to pass the pre-set frequency f and attenuate frequencies above a cut-off frequency, wherein the filtering implements a transfer function with a zero at a frequency where a harmonic of the pre-set frequency f is expected to contain power,
wherein the amplitude of the sinusoid is controlled by adjusting the output voltages of the n DC power sources.
29. The method of claim 28 , wherein n equals 1.
30. The method of claim 29 , wherein the cut-off frequency is at or near 3f.
31. The method of claim 28 , wherein n is greater than 1, and the amplitude of the sinusoid is controlled by adjusting the output voltages of the n DC power sources, while maintaining a fixed ratio between the output voltages of each of the n DC power sources.
32. The method of claim 28 , wherein the transfer function has an additional zero at a next frequency where a harmonic of the pre-set frequency f is expected to contain power.