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SYSTEM AND METHOD FOR IMPLEMENTING A STARTUP CIRCUIT FOR SOLAR INVERTER

IP.com Disclosure Number: IPCOM000246400D
Publication Date: 2016-Jun-03
Document File: 6 page(s) / 302K

Publishing Venue

The IP.com Prior Art Database

Abstract

The invention proposes a system and method for implementing a startup circuit for a solar inverter test setup. The startup circuit comprises resistor, protection fuse and control relay. The startup resistor and protection fuse are connected in the test transformer feed circuit, and a bypass contactor is connected in parallel with the startup resistor. The fuse is serially connected with the startup resistor for short circuit protection. The resistor is connected in series with the circuit during the startup stage, which limits the current to a small value and prevents the high inrush current while the transformers are energized. After steady state is reached, contactor K1 shorts the resistor R1, which returns to the original circuit. Using this circuit, one source transformer could energize two test transformers. The method is a simple and cost-effective solution for energizing a solar inverter test system.

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Page 01 of 6

SYSTEM AND METHOD FOR IMPLEMENTING A STARTUP CIRCUIT FOR SOLAR INVERTER

BACKGROUND

The invention is in general related to power controls and in particular to a system and method for implementing a startup circuit for solar inverter. The solar inverter is a unit under test, while photovoltaic (PV) emulator is another solar inverter used to simulate a PV panel. A solar inverter connected with a test circuit is shown in FIG. 1. PV emulator gets power from test transformer T2 and provides power to the solar inverter. Solar inverter feeds power to test transformer T3. So, most of the power will flow through T2 and T3 in the circuit and source transformer T4 only feeds the power loss for T2, T3, solar inverter and PV emulator.

FIG. 1: Solar inverter connected with a test circuit

A large flow of inrush current occurs when the transformers are charged. The simulation of inrush current of the transformer T2 during startup is shown in FIG. 2, if a contactor K2 is closed at zero degree phase based on transformer parameter. The maximum inrush current is about 10 times the rated current. The instantaneous pick up current of the circuit breakers MVCB1, LVCB1, MVCB2 and MVCB3 is about 8 times the rated current. If K2 and K3 are closed simultaneously, the inrush current is even bigger, about 20 times the rated current. The inrush current may trip upstream circuit breakers while T2 and T3 could not be energized. Thus, there is a need for a solution for energizing large capacity transformers without tripping the upstream protection devices.

 


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XFMR current - t


0.08

800.0

700.0

600.0

500.0

400.0

300.0

200.0

100.0


0.0

Current (A)

-100.0

0


0.02

0.04

0.06

0.12

0.14

0.16

0.18


0.1

t (sec)


0.2

FIG. 2: Inrush current during transformer startup

BRIEF DESCRIPTION OF DRAWINGS

The invention discloses a system and method for implementing a startup circuit for solar inverter, wherein:

FIG. 1 shows a solar inverter connected with a test setup.

FIG. 2 shows inrush current during transformer startup.

FIG. 3 shows a startup circuit for solar inverter test system.

FIG. 4 shows a comparison between regression B-H curve and real B-H curve.

FIG. 5 shows inrush current variation with different values of startup resistor.

FIG. 6 shows an alternative design of the startup circuit for the solar inverter test system.

DETAILED DESCRIPTION

The invention proposes a system and method for implementing a startup circuit to energize large capacity test transformers in a solar inverter test setup. The startup circuit comprises resistors, protection fuses and control relays. The startup resistors and protection fuses are connected in the test transformer feed circuit, and a bypass contactor is connected in parallel with startup resistors. The startup circuit comprises startup resistor R1 and contactor K1 as shown in FIG. 3. Fuse FU3 is serially connected with the startup resistor R1 for short circuit protection. The resistor R1 is connected in series with the circui...