DC converters with modified droop control and method of use
A variable frequency resonant converter includes an inverter stage, a resonant circuit, a transformer, a rectifier stage, and a controller. The inverter and rectifier stages include first and second FET devices. The inverter converts a DC input signal to a first AC signal. The resonant circuit is coupled to the inverter stage and filters the first AC signal. The transformer is coupled to the resonant circuit and converts the first AC signal to a second AC signal. The rectifier stage is coupled to the transformer and converts the second AC signal to a DC output signal. The controller is configured to operate both of the first and second FET devices substantially at a resonant frequency at least partially defined by the resonant circuit to generate the DC output signal according to a voltage setpoint.
1. A variable frequency resonant converter comprising:
an inverter stage configured to convert a direct current (DC) input signal to a first alternating current (AC) signal, said inverter stage comprising a first switching device;
a resonant circuit coupled to said inverter stage, said resonant circuit configured to filter the first AC signal and at least partially define a resonant frequency;
a transformer coupled to said resonant circuit, said transformer configured to convert the first AC signal to a second AC signal;
a rectifier stage coupled to said transformer, said rectifier stage configured to convert the second AC signal to a DC output signal, said rectifier stage comprising a second switching device;
a controller configured to operate both of said first switching device and said second switching device substantially at the resonant frequency to generate the DC output signal according to a reference voltage; and
wherein said controller comprises a droop control system configured to generate the reference voltage based on a variable-voltage DC input signal and a measured output current, said controller further configured to tune the reference voltage to produce the resonant frequency.
2. The variable frequency resonant converter in accordance with claim 1 , wherein said inverter stage is further configured to receive a variable-voltage DC input signal.
3. The variable frequency resonant converter in accordance with claim 1 , wherein said rectifier stage is further configured to generate the DC output signal according to the reference voltage defined within a range of 22 volts DC to 29 volts DC, inclusively.
4. The variable frequency resonant converter in accordance with claim 1 , wherein said resonant circuit comprises a first capacitor and a first inductor coupled in series with said transformer.
5. The variable frequency resonant converter in accordance with claim 4 , wherein said resonant circuit further comprises a second inductor coupled in parallel with said transformer.
6. The variable frequency resonant converter in accordance with claim 1 , wherein said transformer comprises a high-frequency transformer.
7. An electrical power system, comprising:
a DC bus configured to be coupled to an electrical load;
a first DC converter defining a first droop characteristic and a first resonant frequency, said first DC converter coupled to said DC bus, said first DC converter configured to operate substantially at the first resonant frequency to generate a DC output voltage on said DC bus according to a first variable reference voltage;
a second DC converter defining a second droop characteristic and a second resonant frequency, said second DC converter coupled to said DC bus, said second DC converter configured to operate substantially at the second resonant frequency to generate the DC output voltage on said DC bus according to a second variable reference voltage, said second DC converter further configured to share the electrical load with said first DC converter; and
wherein said DC bus is operable in a range of 22 volts DC to 29 volts DC, inclusively.
8. The electrical power system in accordance with claim 7 , wherein said first DC converter further comprises a droop control system configured to:
measure a first output current of said first DC converter;
generate the first variable reference voltage according to an input voltage, the first output current, and a first voltage setpoint;
tune the first variable reference voltage such that an output frequency is substantially constant and substantially equal to the first resonant frequency; and
operate said first DC converter substantially at the first resonant frequency, the first resonant frequency corresponding to the first variable reference voltage.
9. The electrical power system in accordance with claim 8 , wherein said first converter is configured to receive a variable input voltage.
10. The electrical power system in accordance with claim 9 , wherein said droop control system is further configured to generate the first variable reference voltage according to the variable input voltage.
11. The electrical power system in accordance with claim 7 , wherein said first DC converter comprises a variable frequency resonant converter.
12. The electrical power system in accordance with claim 7 further comprising a third DC converter defining a third droop characteristic and a third resonant frequency, said third DC converter coupled to said DC bus and configured to operate substantially at the third resonant frequency to generate the DC output voltage on said DC bus according to a third variable reference voltage, said third DC converter further configured to share the electrical load with said first DC converter and said second DC converter.
13. A method of controlling a direct current (DC) to DC converter, said method comprising:
measuring an output current of the DC to DC converter;
generating a reference voltage as a function of the output current, an input voltage of the DC to DC converter, and a voltage setpoint for the DC to DC converter;
computing the reference voltage such that the reference voltage produces a substantially constant switching frequency substantially equal to a resonant frequency of the DC to DC converter;
operating the DC to DC converter substantially at the resonant frequency according to the reference voltage to generate a DC output voltage;
receiving a variable input voltage; and
generating the reference voltage as a function of the output current, the variable input voltage, and the voltage setpoint.
14. The method in accordance with claim 13 further comprising computing a resonant frequency for the DC to DC converter.
15. The method in accordance with claim 13 further comprising:
operating the DC to DC converter at the resonant frequency in an open-loop;
determining a droop characteristic for the DC to DC converter; and
computing the reference voltage according to the droop characteristic.
16. The method in accordance with claim 13 , wherein operating the DC to DC converter comprises generating the DC output voltage within a range of 22 volts DC to 29 volts DC, inclusively.
17. The method in accordance with claim 13 , wherein operating the DC to DC converter at the resonant frequency comprises operating at least one switching device of the DC to DC converter at a switching frequency substantially equal to the resonant frequency.