Kong-Soon Ng

An enhanced coulomb counting method for estimating state-of-charge and state-of-health of lead-acid batteries

This paper proposes an enhanced coulomb counting method based on the depth-of-discharge (DOD) to estimate the state-of-charge (SOC) and state-of-health (SOH) for valve regulated lead-acid (VRLA) batteries. The losses at different discharging currents are accounted for compensation to the releasable capacities. Furthermore, the SOH is revaluated at the depletion and fully charged states by the maximum releasable capacity and the charged capacity, consequently leading to more accurate SOC estimation. Through the experiments that emulate practical operations, the experimental results reveal that the maximum error is less than 6 %.

State-of-charge estimation for lead-acid batteries based on dynamic open-circuit voltage

The charging and discharging characteristics of lead-acid batteries are investigated to learn the relationship between the state-of-charge (SOC) and the dynamically changed open-circuit voltage. Experimental results indicate that the open-circuit voltage of the lead-acid battery varies methodically with the charging or discharging rates and the duration since they have been disconnected from the load or charger. Accordingly, a dynamic open-circuit voltage method by taking account of the open-circuit time and the previous charging/discharging rate is capable of more precisely estimating the SOC in a shorter time. Experiments that emulate practical operations are carried out to demonstrate the effectiveness and accuracy of the proposed method.

Charge equalization of battery power modules in series

Battery power modules (BPMs) with associated power converters are connected in series to comply with a high load voltage. With bidirectional power converters, BPMs can perform buck conversion for the charging operation. The continuous conduction mode (CCM) and the discontinuous conduction mode (DCM) of buck converters in series are analyzed. According to the analyzed results, an equalization strategy is proposed to solve the charge imbalance problem by scheduling the individual battery current. Experiments are carried out to demonstrate the effectiveness of the balance charging method.

State-of-Charge Estimation with Open-Circuit-Voltage for Lead-Acid Batteries

A state-of-charge (SOC) estimation method is proposed based on the relationship between the state-of-discharge (SOD) and the dynamically changed open-circuit-voltage. The variation of the open-circuit-voltage is observed experimentally on the lead-acid batteries and, by considering the open-circuit time and the previous discharging current, an estimation equation based on the equivalent circuit of the battery is derived. With an accurate SOD estimation, a precise prediction of the SOC is achievable. The estimation accuracy is verified by coulomb counting on experiments with intermittent discharging test.

Operation of battery power modules with series output

This paper presents the operation of battery power modules (BPMs) connected in series for the high voltage output applications. As compared to the conventional applications of the battery banks with a single converter, the configuration has lower component stresses leading to a higher operating efficiency. The batteries can be substantially controlled independently, so that the advantages with parallel operation more efficient utilization of battery power and extensive battery management as well as charge equalization can be realized. Circuit operations and theoretical analyses are discussed on the boost-typed BPMs with series output configuration. Practical measurements are made to demonstrate the effectiveness of charge equalization.

DC-to-DC converter with hybrid input sources

This paper proposes a three-port dc-to-dc power conversion circuit for small-scale distributed generation systems. With the three-port converter, the load can be powered from two different dc sources, which can be a combination of two from a solar-cell panel, a fuel-cell set, a battery bank, etc. The power conversion circuit consists of two active power switches by commonly using an inductor and an output filter capacitor. By adjusting the duty-ratio of the active power switch, the voltage regulation at the output as well as the power coordination between two input sources can be made. The circuit operation is described in detail with the theoretical analysis and computer simulation. An experimental circuit has been built and tested to verify the analyzed and simulated results.

Charge equalization circuit for discharging series‐connected batteries with regulated output

Abstract Charge equalization during the charging process has been extensively discussed for series‐connected batteries. However, charge inequality may also happen to batteries during discharging. The imbalance among batteries may result in over‐discharging and consequently damage to the batteries. To solve the problem, a balanced discharging method for a series‐connected battery bank is proposed. A flyback conversion circuit is designed with a pulse‐width‐modulation controller to achieve output voltage regulation as well as balanced discharging. The applicability of the proposed method is confirmed by experiments.

Intermittent Discharging for Lead-Acid Batteries

Experiments are carried out to demonstrate that the stored energy in lead-acid batteries can be efficiently exploited if the discharge periods are interleaved with the rest periods. The experimental results reveal that an intermittent discharging current with a longer rest time at a higher frequency can release more charge to the load. It is interesting to find a significant increase in releasable capacity by executing an intermittent discharging current at the deeper discharge state but a negative effect at the earlier stage of a discharging cycle. An efficient discharging profile with intermittent current is figured out based on the investigation results.

Single-switch dual-source tri-port DC-to-DC converter

This paper proposed a three-port dc-to-dc converter, by which the load can be powered from two different dc sources. The power conversion circuit consists of only an active power switch with associated passive components. By adjusting the duty-ratio of the active power switch, the power sharing between two power sources as well as the output voltage regulation can be made. Theoretical analyses are verified by experimental results conducted in a laboratory circuit.

Investigation on intermittent discharging for lead‐acid batteries

Abstract This paper studies the operating characteristics of lead‐acid batteries under intermittent current discharge. A resting time is added on purpose in each discharging cycle to observe its impact on the batterys releasable capacity. Experimental results reveal that the batteries subject to intermittent discharge recover higher loaded voltages and thus can release more capacity. This effect is found to be more significant for an intermittent current at a higher frequency and at a stage when the battery is deeply discharged. A two‐stage discharging profile can be scheduled to deliver the most capacity. However, experimental results show that the average current plays the most important role in current discharge. With the same average current, the largest capacity with intermittent discharge is approximately equal to that with constant current discharge.