Multi switch inverter, personal power plant system using thereof and method to generate AC power sine wave

1. A power inverter having AC over current protection, the power inverter comprising:

a plurality of DC input terminals wherein each DC input terminal is electrically coupled to respective battery cassettes of the battery bank;

a bridge circuit configured to switch a polarity of a voltage applied to a load electrically coupled thereto;

a modulator comprising a plurality of semiconductor switches comprising MOS-FETS electrically coupled to respective DC input terminals, wherein the plurality of semiconductor switches are electrically coupled to the bridge circuit; and

a plurality of Schottky diodes to prevent backward current flow, wherein an anode of each Schottky diode is electrically coupled to a corresponding semiconductor switch of the plurality of semiconductor switches and a cathode of each Schottky diode is electrically coupled to the bridge circuit;

wherein the plurality of semiconductor switches connect and disconnect DC current from the respective DC input terminals to the bridge circuit according to received switching sequences such that a multi-level stepped voltage waveform is generated, each step of the multi-level stepped waveform having a modulated width of a selected voltage; and

a soft fuse system comprising:

a load current sensor disposed between the bridge circuit and ground to continuously monitor an inverter current;

a circuit breaker electronically coupled to the bridge circuit; and

a controller configured to:

monitor the inverter current by the load current sensor;

monitor an output voltage from the modulator; and

disable the modulator by turning off the plurality of semiconductor switches within a prescribed period of time, when the inverter current exceeds a predetermined value.

2. The power inverter according to claim 1 , wherein the predetermine value is determined based at least on the inverter current detected by the load current sensor, the output voltage from the modulator and a rated current of the circuit breaker, and the prescribed period of time is 2 milliseconds or less.

3. The power inverter according to claim 1 , wherein the bridge circuit is an H-bridge comprising MOS-FETs.

4. The power inverter according to claim 1 , wherein the controller further configured to:

turn on one of the plurality of semiconductor switches for an enough period of time to detect the inverter current by the load sensor after removal of a cause of the exceeding inverter current, and

enable the modulator when the invertor load current is less than the predetermined value.

5. The power inverter according to claim 1 , wherein the modulator and the bridge circuit are disabled when the inverter current exceeds the predetermined value.

6. A method to prevent AC over current for a power inverter, the method comprising:

with an inverter including a plurality of DC input terminals, a modulator including a plurality of semiconductor switches electrically coupled to respective DC input terminals, a bridge circuit configured to switch a polarity of a voltage applied to a load coupled thereto, and a load current sensor disposed between the bridge circuit and ground to continuously monitor an inverter current,

connecting a plurality of battery cassettes in series to form a battery bank, wherein a center tap is provided between the adjacent battery cassettes;

connecting the center taps and a positive electrode of the battery bank to respective DC input terminals;

operating the plurality of semiconductor switches according to predetermined switching sequences such that a multi-level stepped voltage waveform with a modulated width of selected step thereof is generated;

applying the multi-level stepped voltage waveform to the bridge circuit;

switching the polarity of the voltage applied to the load coupled to the bridge circuit to generate an AC power sine wave with reduced harmonic distortion;

continuously monitoring an inverter current by the load current sensor and an output voltage from the modulator, and

disabling the modulator by turning off the plurality of semiconductor switches within a prescribed period of time, when the inverter current exceeds a predetermined value.

7. The method according to claim 6 , wherein the predetermine value is determined based at least on the inverter current detected by the load current sensor, the output voltage from the modulator and a rated current of a circuit breaker electronically coupled to the bridge circuit, and the prescribed period of time is 2 milliseconds.

8. The method according to claim 6 further comprising:

turning on one of the plurality of semiconductor switches for a enough period of time to detect the inverter current by the load sensor after removal of a cause of the exceeding inverter current, and

enabling the modulator when the load current is less than the predetermined value.

9. The method according to claim 6 , wherein the modulator and the bridge circuit are disabled when the inverter current exceeds the predetermined value.

10. A personal power plant system comprising:

an input selector configured to select a power source;

a battery bank comprising a plurality of battery cassettes coupled in series, wherein each battery cassette comprises a plurality of batteries connected in series;

a charger configured to charge the battery bank using electrical energy from the selected power source;

a battery selector comprising a plurality of switches configured to select one or more of the plurality of battery cassettes to charge;

a plurality of solar panels electrically coupled to respective battery cassettes of the battery bank, wherein ones of the plurality of solar panels are selectively coupled to the input selector;

an inverter, wherein said inverter comprises:

a plurality of DC input terminals wherein each DC input terminal is electrically coupled to respective battery cassettes of the battery bank;

a bridge circuit configured to switch a polarity of a voltage applied to a load electrically coupled thereto;

a plurality of semiconductor switches comprising MOS-FETS electrically coupled to respective DC input terminals, wherein the plurality of semiconductor switches are electrically coupled to the bridge circuit; and

a plurality of Schottky diode to prevent back backward current flow, wherein an anode of each Schottky diode is electrically coupled to a corresponding semiconductor switch of the plurality of semiconductor switches and a cathode of each Schottky diode is electrically coupled to the bridge circuit; and

a load current sensor disposed between the bridge circuit and ground to continuously monitor an inverter current; and

a controller configured to:

generate a predetermined switching sequence to be applied to the plurality of semiconductor switches,

connect and disconnect the MOS-FETS of the plurality of semiconductor switches to apply a multi-level stepped voltage waveform with a modulation of a selected step thereof across the bridge circuit such that an output from the bridge circuit approximates an AC power sine wave with reduced harmonic distortion;

monitor the inverter current by the load current sensor;

monitor an output voltage from the modulator; and

disable the modulator by turning off the plurality of semiconductor switches within a prescribed period of time, when the inverter current exceeds a predetermined value.

11. The personal power plant system according to claim 10 , wherein the predetermine value is determined based at least on the inverter current detected by the load current sensor, the output voltage from the modulator and a rated current of a circuit breaker electronically coupled to the bridge circuit, and the prescribed period of time is 2 milliseconds or less.

12. The personal power plant system according to claim 10 , wherein the bridge circuit is an H-bridge comprising MOS-FETs.

13. The personal power plant system according to claim 10 , wherein the controller further configured to:

turn on one of the plurality of semiconductor switches for an enough period of time to detect the inverter current by the load sensor after removal of a cause of the exceeding inverter current, and

enable the modulator when the invertor load current is less than the predetermined value.

14. The personal power plant system according to claim 10 , wherein the power source comprising an electric grid, a gas generator, a wind turbine, the solar panels, and fuel cells.

15. The personal power plant system according to claim 10 , wherein the battery bank comprises four batteries.

16. The personal power plant system according to claim 10 , wherein the plurality of solar panels are configured to charge respective battery cassette and an output voltage of each solar panels is greater than an output voltage of each of the plurality of battery cassette.

17. The personal power plant system according to claim 10 , wherein each battery cassette of the plurality of battery cassette has approximately a same terminal voltage.

18. The personal power plant system according to claim 10 , further comprises a watt-hour meter electrically coupled to the bridge circuit.

19. The personal power plant system according to claim 18 , wherein the controller is configured to modify the predetermined switching sequences based at least in part on feedback from the load current sensor and the watt-hour meter.

20. The personal power plant system according to claim 10 , further comprising a circuit breaker electronically coupled to the bridge circuit.