Parallel redundant power system and the control method for the same

• US 20060293798A1
• Filed: 08/21/2006
• Published: 12/28/2006
• Est. Priority Date: 10/02/2003
• Status: Active Grant

• Current Assignee: Eaton Phoenixtec MMPL Co. Ltd. (Eaton Corporation PLC.)
• Original Assignee: Eaton Phoenixtec MMPL Co. Ltd. (Eaton Corporation PLC.)
• Inventors: Tsai, Chia-Ming, Luo, Han-Sheng, Tian, Shou-Long
• Granted Patent: US 7,425,779 B2
• Time in Patent Office: Days
• US Class Current: 700/286
• 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_e(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

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

 

and

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

2. The method as claimed in claim 1 further comprising the steps of:

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;

wherein 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).

3. The method as claimed in claim 2, 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.

4. A load sharing control method for adjusting 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:

detecting a DC bus voltage V_realBUS;

comparing the detected DC bus voltage V_realBUS with a preset DC bus voltage V_BUSsetting to obtain a difference value Δ

V_BUS, where the difference value is expressed by Δ

V_BUS=V_realBUS−

V_BUSsetting;

establishing a relationship between the difference value Δ

V_BUS and a reference voltage V_ref, where the relationship is expressed by an equation V_ref=V_setting+K₂×

Δ

V_BUS, wherein V_setting is a preset initial voltage of the reference voltage V_ref and K₂ is a gain value.

5. The method as claimed in claim 4, wherein the gain value is inversely proportional to the current sharing difference.

6. A load sharing control method by using a current sharing error to adjust a transient current of a power system composed of at least two inverters coupled in parallel so as to provide AC power to a load through a bus, the method comprising the steps of:

sampling a load current i_load(t) and a current sharing command i_avg(t) generated from a current sharing circuit;

comparing the sampled load current i_load(t) and the current sharing command i_avg(t) to obtain a current sharing difference and then multiplying the current sharing difference by a gain value K_i2 to derive a compensation command i_com(t), where the compensation command is expressed by an equation i_com(t)=K_i2*(i_avg(t)−

i_load(t)); and

applying the compensation command i_com(t) to adjust the load current i_load(t).

7. The method as claimed in claim 6, wherein the gain value K_i2 is inversely proportional to the current sharing difference.