Decentralized active equalization method for cascaded lithium-ion battery pack

Patent metadata

Field	Value
Publication number	US-12206265-B2
Application number	US-202217589103-A
Country	US
Kind code	B2
Filing date	Jan 31, 2022
Priority date	Feb 8, 2021
Publication date	Jan 21, 2025
Grant date	Jan 21, 2025

Abstract

The present disclosure provides a decentralized active equalization method for a cascaded lithium-ion battery pack. The method includes: connecting each battery cell in the cascaded lithium-ion battery pack to a direct current (DC) bus through an equalizer respectively, where each equalizer includes an independent controller, a sampling circuit, a power supply circuit, a drive circuit, and a main circuit; connecting an input terminal of the main circuit to a corresponding battery cell, and connecting an output terminal of the main circuit to the DC bus. The present disclosure solves the technical problem that an existing cascaded lithium-ion battery pack equalization method cannot achieve equalization when a centralized controller failure or a communication failure occurs, improves the reliability of the equalization method, can make the equalizer work at high efficiency by configuring parameters of C, K, and R, and speeds up the equalization or improves the equalization accuracy. The present disclosure uses a bus structure, which can achieve the equalization of all battery cells at the same time, thereby greatly improving the equalization speed. The present disclosure uses a modular design and can be arbitrarily configured according to the scale of the cascaded lithium battery pack, and has strong scalability.

First claim

What is claimed is:

1. A decentralized active equalization method for a cascaded lithium-ion battery pack, comprising:
connecting each battery cell in the cascaded lithium-ion battery pack to a direct current (DC) bus through an equalizer respectively, wherein each equalizer comprises a controller, a sampling circuit, a power supply circuit, a drive circuit, and a main circuit;
connecting an input terminal of the main circuit to a corresponding battery cell,
connecting an output terminal of the main circuit to the DC bus,
supplying power to the controller and the sampling circuit by the power supply circuit,
sampling an input voltage, an input current, and an output voltage of the equalizer by the sampling circuit,
processing sampling data of the sampling circuit and sending a control signal to the drive circuit by the controller, and
generating a drive signal by the drive circuit to drive the main circuit,
wherein the equalizer uses voltage and current double closed-loop control, and a voltage loop reference value V* Oj is calculated according to the following formula:
V* Oj =C+K*V ij +R*I ij ,

where j is a serial number of the equalizer, and j=1, 2, 3, . . . , n; V ij is the input voltage of the equalizer and a real-time terminal voltage of a corresponding battery cell, and is acquired by the sampling circuit; I ij is an average input current of the equalizer, the average input current is obtained by digital low-pass filtering of the input current acquired by the sampling circuit, the average input current is an equalizing current, and a battery cell discharge direction is positive; C, K, and R are constants;
the voltage loop reference value is compared with the sampled input voltage, a difference is input to a proportional-integral-derivative (PID) regulator of the controller, an output value of the PID regulator is limited and a value after limiting is used as a current loop reference value, and the limit value is:
I + =I max −I , and I − =−I−I max ,

where I max is a maximum charge and discharge current of the battery cell, I is a current of the cascaded lithium-ion battery pack, I + is a positive limit value, and L is a negative limit value;
the current loop reference value is compared with the average input current, a difference is input to the PID regulator of the controller, an output value of the PID regulator is sent to a pulse width modulation (PWM) generator of the controller, and the PWM generator generates a PWM signal and then inputs the PWM signal to the drive circuit so as to generate a drive signal to drive the main circuit; and
a control strategy of the equalizer comprises the following steps:
when an absolute value of the equalizing current is less than I off and an absolute value of a difference between the voltage loop reference value and the output voltage of the equalizer is less than V off , turning off the drive circuit and the PID regulator of the equalizer, so as to disable equalization;
when the absolute value of the difference between the voltage loop reference value and the output voltage of the equalizer is greater than V on , turning on the drive circuit and PID regulator of the equalizer, so as to re-enable the equalization, wherein I off is a threshold current for disabling the equalization, V off is a threshold voltage for disabling the equalization, V on is a threshold voltage for re-enabling the equalization, the three are all determined by actual demand, and V on >V off .

2. The decentralized active equalization method for a cascaded lithium-ion battery pack according to claim 1 , wherein:
the main circuit has a structure of a bidirectional isolated converter, and
the drive circuit is a switch tube circuit converting a low-voltage PWM signal output from the controller into an isolated high-voltage PWM signal to drive the bidirectional isolated converter.

Assignees

• Univ Chongqing
• Star Insitiute Of Intelligent Systems
• Db Chongqing Intelligent Tech Research Institute Co Ltd
• Star Inst Of Intelligent Systems

Inventors

• Song Yongduan
• Chen Jiawei
• Chen Li
• Song Qingchao

Classifications

• H02J7/56 Primary

  Active balancing, e.g. using capacitor-based, inductor-based or DC-DC converters · CPC title

• H02J7/82

  Control of state of charge [SOC] · CPC title

• H02J7/54 Primary

  Passive balancing, e.g. using resistors or parallel MOSFETs · CPC title

• H01M10/441

  for several batteries or cells simultaneously or sequentially · CPC title

• H01M10/0525

  Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries · CPC title