| CPC H02J 7/0019 (2013.01) [H01M 10/0525 (2013.01); H01M 10/441 (2013.01)] | 2 Claims |
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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*Vij+R*Iij,
where j is a serial number of the equalizer, and j=1, 2, 3, . . . , n; Vij 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; Iij 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+=Imax−I, and I−=−I−Imax,
where Imax 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 Ioff and an absolute value of a difference between the voltage loop reference value and the output voltage of the equalizer is less than Voff, 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 Von, turning on the drive circuit and PID regulator of the equalizer, so as to re-enable the equalization, wherein Ioff is a threshold current for disabling the equalization, Voff is a threshold voltage for disabling the equalization, Von is a threshold voltage for re-enabling the equalization, the three are all determined by actual demand, and Von>Voff.
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