The present invention relates to the operation of power MOSFETs in switching applications to reduce in-rush currents in cell/battery charging applications. The present invention is applicable with multiple cells that are present in a single battery module or multiple batteries connected in series or parallel. The present invention is also applicable in a central power supply module for managing multiple loads and for simultaneously charging multiple batteries. The present invention therefore adds more flexibility to generate multiple voltage sources from a single cell.
In many battery charging applications and in central power supply modules, a switching element is used to connect and disconnect a battery cell or a power supply module. For example, when a power supply module is replaced, the central power supply is ordinarily turned off. The input stage of the power supply module generally contains several initially uncharged bulk capacitors and EMI capacitors. Without any control, during first contact, these capacitors would experience a high surge current similar to a short circuit event. The current is only limited by the PCB parasitics of any other connected components such as resistances and inductances, with in-rush current being able to reach several hundred amperes or more. Although the energy is mainly drawn from the capacitor bank, the central power supply may collapse below a permissible level during this in-rush phase.
As a further example, assume an electric vehicle includes a power supply module having a battery cell/module at 14.5 V and a battery cell/module at 13 V. The power supply includes a first set of switches to couple the cells/modules in series and a second set of switches to couple the battery cells/modules in parallel, as generally set forth in US2018/0254658 to Koerner et al, the disclosure of which is incorporated by reference in its entirety. When the battery cells/modules are connected in parallel, there will be a high amount of current conducting between the two battery cells/modules.
Prior art solutions to the foregoing technical problems included the use of a dedicated charger for each battery module and/or the use of switches with an extremely high current rating. However, these prior art solutions are costly and can increase the size of the power supply beyond what is otherwise desired. Accordingly, there remains a continued need for an improved system and method for preventing in-rush currents in these and other applications.
A system and a method for limiting in-rush currents to a battery module is provided. The system and the method include operating a power MOSFET with a pulse-width-modulated (PWM) gate voltage (VGS). The frequency and the duty cycle of the PWM gate voltage (VGS) are iteratively selected such that the current through the battery module does not exceed a current limit value, the battery module being series connected with the MOSFET load path. For example, the frequency and the duty cycle of the PWM gate voltage can be alternatively varied to gradually increase the current in the load path until a desired current limit value is reached. By controlling the input current to the battery module, the central power supply will not collapse and will instead allow charging of the battery module on-the-go, e.g., without a power down condition. An effective current limitation with an instant hot-swap capability is achieved by interposing the power MOSFET between a power supply and the battery module, the power MOSFET operating in the linear region and the saturation region during this short duration event. In series-to-parallel switching operations, a current-limiting behavior of the power MOSFET is utilized in the saturation region. As a result, the current can be controlled and slowly charge the battery cell having a lower voltage without the need of a buck converter. As the power MOSFET is activated, a thermal source is generated. This thermal source can be used to warm up the battery modules in cold temperatures to improve their reliability. If cranking fails due to low voltage, the present invention includes balancing the battery modules and thereby warming the battery modules to support the cranking current.
These and other features and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the accompanying drawings and the appended claim.
In the present embodiment, a power MOSFET is used as a switch to control the flow of power to an electrical load, and in particular, a battery module. As is known in the art, a MOSFET is a three-terminal device in which the gate voltage controls the flow of current between a source and a drain. The system and method of the present invention limit in-rush currents to a battery module by iteratively varying the duty cycle (D) and frequency (f) of a pulse-width-modulated (PWM) gate voltage (VGS), such that the frequency and duration of the individual control pulses and the time interval between two successive pulses can vary over time.
Referring now to
Operation of the above control circuits to limit in-rush currents is illustrated in connection with the functional block diagram of
In particular, if the measured current (IDS) is less than the current limit value (IDS-Limit), the method includes decreasing the baseline frequency of the PWM gate voltage (VGS) (step 38). The load current (IDS) is again measured (step 40) and compared with the current limit value (IDS-Limit) (step 42). If the measured current (IDS) is less than the current limit value (IDS-Limit), the method includes decreasing the baseline frequency (f) of the PWM gate voltage (VGS) (step 44); otherwise, the PWM gate voltage (VGS) reverts to the prior frequency (f) (step 46). The load current (IDS) is again measured (step 48) and compared with the current limit value (IDS-Limit) (step 50). If the measured current (IDS) is less than the current limit value (IDS-Limit), the method includes decreasing the duty cycle (D) of the PWM gate voltage (VGS) (step 38); otherwise, the PWM gate voltage (VGS) reverts to the prior frequency (f) (step 52). In this respect, the load current (IDS) through the battery module 14 is allowed to gradually increase until reaching the current limit value (IDS-Limit) without a short circuit event that might otherwise damage the battery module 14.
The foregoing control circuit and method can be used to limit the in-rush current to an acceptable range. The forgoing control circuit and method can also be used in a central power supply module for managing multiple loads, for example when simultaneously charging multiple batteries. By controlling the input current, the central power supply will not collapse, and the changing of power modules on-the-go (e.g., without a power down condition) is made possible. In series-to-parallel switching operations, the current can be controlled and slowly charge the battery module having a lower voltage without the need of a buck converter. As the power MOSFET is activated, a thermal source is also generated. This thermal source can be used to warm up the battery modules in cold temperatures to improve their reliability. If cranking fails due to low voltage, the present invention includes balancing the battery modules and thereby warming the battery modules to support the cranking current.
As further illustrated in
The above description is that of a current embodiment of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention. This disclosure is presented for illustrative purposes and should not be interpreted as an exhaustive description of all embodiments of the invention or to limit the scope of the claims to the specific elements illustrated or described in connection with these embodiments. Any reference to elements in the singular, for example, using the articles “a,” “an,” “the,” or “said,” is not to be construed as limiting the element to the singular.
This application claims the benefit of U.S. Provisional Application 63/059,223, filed Jul. 31, 2020, the disclosure of which is incorporated by reference in its entirety.
Filing Document | Filing Date | Country | Kind |
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PCT/IB2021/056934 | 7/29/2021 | WO |
Number | Date | Country | |
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63059223 | Jul 2020 | US |