Parallel redundant power system and the control method for the same

• US 7,425,779 B2
• Filed: 08/21/2006
• Issued: 09/16/2008
• Est. Priority Date: 10/02/2003
• Status: Expired due to Fees

• Current Assignee: Phoenixtec Power Co Ltd (Eaton Corporation PLC.)
• Original Assignee: Phoenixtec Power Co Ltd (Eaton Corporation PLC.)
• Inventors: Tsai, Chia-Ming, Luo, Han-Sheng, Tian, Shou-Long
• Primary Examiner(s): Sherry; Michael J
• Assistant Examiner(s): Parries; Dru M
• Application Number:
  US11/507,425
• Publication Number:
  US 20060293798A1
• Time in Patent Office: 757 Days
• Field of Search: 307/82
• US Class Current: 307/82
• CPC Class Codes: H02M 7/493 the static converters being arranged for operation in parallel

Abstract

A power redundant power system and a method for controlling the power system are presented, wherein the power system is composed of at least one inverter for supplying AC power to a load through a bus, a phase lock system to synchronize all output voltages of the inverters and a current sharing circuit to properly distribute the load current among all inverters. Each inverter is controlled by an unbalanced power to limit the increase of its cross current. Moreover, the information related to DC bus voltage is further applied to control the inverters, whereby the cross current is mitigated and entire power system is operated steadily.

Claims

1. A load sharing control method by using an unbalanced power to adjust active power, the method applying for a power system composed of at least two inverters coupled in parallel to provide AC power to a load through a bus, the method comprising the steps of:

sampling an output voltage v_o(t), a load current i_load(t), and a current sharing command i_load*(t) generated from a current sharing circuit;

calculating a difference value i_e(t) by comparing the sampled load current with the sampled current sharing command, wherein the difference value is expressed by i_c(t)=i_load*(t)−

i_load(t);

integrating the product of the difference value i_e(t) and the output voltage v_o(t) during an output voltage cycle T, and then calculating an unbalanced power P_unbal according to an equation

$P_{\mathrm{unbal}}=\frac{1}{T}<br><br>{\int <br><br>}_T<br><br>i_e<br><br>\left(t\right)\times <br><br>v_o<br><br>\left(t\right)<br><br>d<br><br>t;<br><br>$

establishing a relationship between the unbalanced power P_unbal and a reference voltage V_ref, wherein the relationship is expressed by an equation V_ref=V_setting+K₁×

P_unbal, and V_setting is a preset initial voltage of the reference voltage V_ref and K₁ is a gain value that is inversely proportional to the difference value i_e(t); and

adjusting the output voltage v_o(t) of the inverter based on the unbalanced ∞

power P_unbal.

2. The method as claimed in claim 1, wherein the unbalanced power is generated when the amplitude of the output voltages, the output impedance, or the phases of the output voltages of the at least two inverters are different to each other.