Inverter of new and renewable energy storage system
Provided is an inverter of a renewable energy storage system, which has an input port and an output port electrically insulated, and is compact and low-priced, while having a simplified circuit. The inverter includes a DC-DC converting unit connected to the DC link, and an inverting unit connected between the DC-DC converting unit and the power system, wherein the DC-DC converting unit is an unregulated DC-DC bus converter.
1. A renewable energy storage system for a renewable energy source, the renewable energy storage system comprising:
a maximum power point tracking (MPPT) converter connected to the renewable energy source;
a DC link connected to the MPPT converter;
a DC-DC converting unit connected to the DC link; and
an inverting unit connected to the DC-DC converting unit, wherein the DC-DC converting unit includes:
a half-bridge circuit including first and second unregulated switches;
an oscillator that oscillates power output from the half-bridge circuit, and
a transformer that converts power from the oscillator into power of a different level, wherein the first and second switches are complementary switches that operate based on a duty cycle and an operating frequency that are substantially fixed;
wherein the MPPT converter extracts maximum available power from the new renewable energy and provides an output voltage that varies less than 10% for a predetermined operational power range of the renewable energy source, and wherein the output voltage of the DC link remains substantially constant in the predetermined operation range of the renewable energy source.
2. The renewable energy storage system as claimed in claim 1 , wherein the first and second switches of the half-bridge circuit in the DC-DC converting unit operate with a fixed duty cycle of 50%.
3. The renewable energy storage system as claimed in claim 1 , wherein the DC-DC converting unit comprises: a full-bridge diode rectifier that rectifies the converted power output from the transformer into DC power and outputs the rectified power.
4. The renewable energy storage system as claimed in claim 3 , wherein:
the first switch is connected to a first electrode of the DC link; and
the second switch is connected to the first switch and a second electrode of the DC link.
5. The renewable energy storage system as claimed in claim 3 , wherein the oscillator comprises:
an input capacitor connected to the half-bridge circuit;
a first inductor connected to the input capacitor; and
a second inductor connected to first inductor and the DC link.
6. The renewable energy storage system as claimed in claim 5 , wherein the transformer comprises:
a primary coil connected in parallel to the second inductor; and
a secondary coil insulated from the primary coil.
7. The renewable energy storage system as claimed in claim 3 , wherein the fixed duty cycle is 50%.
8. The renewable energy storage system as claimed in claim 3 , wherein the inverting unit includes a full-bridge switch connected to the DC-DC converting unit.
9. The renewable energy storage system as claimed in claim 1 , wherein the inverting unit includes a full-bridge switch connected to the DC-DC converting unit.
10. The renewable energy storage system as claimed in claim 1 , wherein the DC-DC converting unit is coupled to receive electric energy produced from a solar cell, a wind power generator, a geothermal generator, or a tidal power generator.
11. The renewable energy storage system as claimed in claim 1 , wherein the first and second switches are controlled to perform zero voltage switching.
12. The renewable energy storage system as claimed in claim 1 , wherein the predetermined operational range of the renewable energy source includes 70 W to 1 kW.
13. The renewable energy storage system as claimed in claim 1 , wherein a ratio of the predetermined operational range of the renewable energy source to the voltage output from the MPPT is approximately 130.
14. The renewable energy storage system as claimed in claim 1 , wherein the MPPT converter provides an output voltage that varies approximately 2%.
15. The renewable energy storage system as claimed in claim 1 , wherein a circulating current is suppressed at an input port of the inverting unit as a result of the output voltage of the MPPT varying approximately 2% for the predetermined operational power range of the renewable energy source.
16. The renewable energy storage system as claimed in claim 1 , wherein the MPPT converter provides an output voltage that varies less than 5%.