Balancing control for rechargeable energy storage systems

Abstract

Balancing control for a rechargeable energy storage system (RESS) having a plurality of power modules. Balancing control may include determining a state deviation for each of the power modules and implementing a balancing control strategy to individually control the power transfer capabilities of the power modules to drive the associated state deviation toward a state target.

Description

INTRODUCTION

[0001] The present disclosure relates to providing balancing regulation for rechargeable energy storage systems (RESS), such as, but not necessarily limited to, providing balancing regulation for a RESS configured to store and deliver electrical energy to a traction motor of a vehicle.

[0002] A rechargeable energy storage system (RESS) can be configured to store and deliver electrical energy for a variety of applications, with one of the more common types of RESSs comprising a plurality of battery cells arranged in one or more battery modules. Such a RESS can be installed onboard a vehicle to store and deliver electrical energy to a traction motor, which converts the electrical energy into mechanical energy to propel the vehicle. To achieve and maintain the desired performance level of the RESS, it may be advantageous to minimize operating differences and imbalances between the battery modules. DESCRIPTION

[0003] One non-limiting aspect of the present disclosure relates to providing balancing regulation for a rechargeable energy storage system (RESS). Balancing regulation may be beneficial to minimize operating differences and imbalances between energy sources, modules, etc., of the RESS configured to store and deliver electrical energy. Balancing regulation may be used to normalize, balance, equalize, or otherwise adjust operating differences between the power sources toward a normalized or common target. Accordingly, the present disclosure encompasses systems and methods for controlling power flow between the power sources, which may include controlling associated power conversion systems according to adjustable current, voltage, and / or power limits.

[0004] One non-limiting aspect of the present disclosure relates to a method for balancing a plurality of power modules configured to store and deliver electrical energy as part of a rechargeable energy storage system (RESS). The method may include determining a state for each of the power modules, determining a state deviation for each of the power modules to quantify a deviation of the state of the associated power module relative to a state target, and implementing a balancing regulation strategy to balance the power modules. The balancing regulation strategy may select a maximum current threshold for each of the power modules to individually normalize the state of the associated power module toward the state target.

[0005] The method may include implementing the balancing regulation strategy based on the state representing a state of charge (SOC) and the state target representing a SOC target.

[0006] The method may include implementing the balancing regulation strategy based on the state representing a voltage and the state target representing a voltage target.

[0007] The method may include implementing the balancing regulation strategy based on the condition representing a state of health (SOH) and the condition goal representing an SOH goal.

[0008] The method may include implementing the balancing regulation strategy based on the state representing a state of energy (SOE) and / or a state of performance (SOP) and the state target representing an SOE and / or an SOP target.

[0009] The method may include determining a combined power of the power modules during operation according to the balancing regulation strategy to be less than a power demand of the low-voltage busbar, and implementing a maximum power strategy instead of the balancing regulation strategy. The maximum power strategy may allow the power modules to operate above the maximum LV current thresholds specified in the balancing regulation strategy.

[0010] The method may include implementing the balancing regulation strategy in coordination with the power modules that supply high voltage (HV) electrical power to an electric motor to convert the HV electrical power into mechanical power that can be used to propel a vehicle.

[0011] The method may include the power modules being connected in series and the RESS comprising a plurality of power converters, wherein an input of each power converter is connected in parallel with one of the power modules and an output of each power converter is connected together in parallel.

[0012] The method may include the power converters as direct current (DC-DC) converters.

[0013] One non-limiting aspect of the present disclosure relates to a method for balancing a plurality of power modules configured to store and deliver electrical energy as part of a rechargeable energy storage system (RESS) included onboard a vehicle. The RESS is operable to deliver high voltage (HV) to a traction motor and low voltage (LV) to a low voltage rail. The method may include determining a state for each of the power modules, determining a state deviation for each of the power modules to quantify a deviation of the state of the associated power module relative to a state target, and implementing a balancing regulation strategy to balance the power modules.The balancing regulation strategy can individually control the power transfer capabilities of the power module to control the associated state deviation towards the state target.

[0014] The Method One non-limiting aspect of the present disclosure relates to the balancing regulation strategy that establishes a current limit for each of the power modules. The current limits may indicate a maximum available current output for the associated power module.

[0015] The method may include implementing the balancing regulation strategy based on the state representing a state of charge (SOC) and the state target representing a SOC target.

[0016] The method may include setting the current limits for the power modules whose SOC is less than the SOC target to be greater than the current limits for the power modules whose SOC is equal to or greater than the SOC target.

[0017] The method may include overriding the current limit in response to determining a combined power output of the power modules that is less than the power demand of a load connected to the low voltage bus. The method may include the balancing regulation strategy setting a current limit and a voltage limit for each of the power modules.

[0018] The method may include setting the current limits in proportion to the state deviation of the associated power module and adjusting the voltages to be approximately equal to each other.

[0019] One non-limiting aspect of the present disclosure relates to a vehicle. The vehicle may include an electric motor configured to convert high voltage (HV) power into mechanical energy suitable for propelling the vehicle, a low voltage (LV) bus operable to distribute LV power to one or more loads onboard the vehicle, and a rechargeable energy storage system (RESS) operable to supply the HV power to the electric motor and the LV power to the LV bus. The RESS may include a plurality of battery cells arranged in a plurality of battery modules, each of the battery modules connected in series and individually in parallel to one of a plurality of power converters operable to control the LV power transfer between the associated battery module and the LV bus.The vehicle may include a controller that controls the power converters according to a balancing regulation strategy. The balancing regulation strategy may individually control the LV power transfer through each of the power converters to balance the battery modules toward a normalized target.

[0020] The controller may be operable to determine a state for each of the power modules, determine a state deviation for the state of each power module with respect to the normalized target, and implement the balancing regulation strategy to individually control the power transfer capabilities of the power modules with respect to the associated state deviation.

[0021] The balancing regulation strategy may include setting a maximum current threshold individually for each of the power converters and then iteratively adjusting the maximum current thresholds to drive the state deviation of the associated power module towards the normalized target.

[0022] This can be used to determine a combined power of the power converters during operation according to the balancing regulation strategy so that it is lower than a power demand of the low-voltage busbar, and to implement a maximum power strategy instead of the balancing regulation strategy in order to enable the power modules to operate above the maximum current thresholds defined in the balancing regulation strategy.

[0023] These features and advantages, along with other features and advantages of the present teachings, can be readily appreciated from the following detailed description of modes for carrying out the present teachings when considered in conjunction with the accompanying drawings. It should be understood that, although the following figures and embodiments may be described separately, individual features thereof may be combined to form additional embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which may be incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. Fig. 1 shows a vehicle according to a non-limiting aspect of the present disclosure. Fig. 2 shows a partial schematic view of a RESS according to a non-limiting aspect of the present disclosure. Fig. 3 shows a flowchart of a method for balancing the energy conversion systems in accordance with a non-limiting aspect of the present disclosure. Fig. 4 shows an operational diagram of the capabilities of an energy conversion system according to a non-limiting aspect of the present disclosure. DETAILED DESCRIPTION

[0025] As appropriate, detailed embodiments of the present disclosure may be disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the disclosure that may be embodied in various and alternative forms. The drawings are not necessarily to scale; some features may be exaggerated or reduced in size to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for showing one skilled in the art how to variously employ the present disclosure.

[0026] Fig. 1 shows a vehicle 12 in accordance with one non-limiting aspect of the present disclosure. The vehicle 12, which may be interchangeably referred to as an electric or hybrid vehicle 12, may include an electric traction motor 14 operable to convert electrical energy into mechanical energy for the purpose of performing work, such as mechanically driving a drivetrain 16 to propel the vehicle. The vehicle 12 is depicted as a hybrid vehicle because the drivetrain 16 optionally includes an internal combustion engine (ICE) 18 for generating mechanical energy. The drivetrain 16 may include components that facilitate the transfer of rotational power from the traction motor 12 to one or more of the wheels 20, 22, 24, 26. The vehicle 10 may include a rechargeable energy storage system (RESS) 30 configured to store electrical energy for the traction motor 12 and / or other components, systems, etc.to store and deliver. 32 on board the vehicle 10, e.g., via a first bus bar 34 and a second bus bar 36. The vehicle 10 may include a vehicle controller 38 to facilitate monitoring, controlling, measuring, and otherwise controlling the operation, performance, etc. on board the vehicle 10, which may include taking measurements, taking readings, or otherwise collecting data to facilitate balancing regulation for the RESS 30.

[0027] Fig. 2 shows a partial schematic view of the RESS 30 according to one non-limiting aspect of the present disclosure. The RESS 30 may include a plurality of energy sources, cells, or other storage units (not shown) arranged in a plurality of power modules, packs, or other groupings 40. The present disclosure contemplates that the power modules 40 may be comprised of a plurality of components that may be employed to store and deliver electrical energy. The power modules 40 may, for example, include various combinations of battery cells, battery packs, capacitors, supercapacitors, fuel cells, or other types of energy components used to store and deliver electrical energy.Although the present disclosure contemplates the use of balance regulation in other environments and for other systems, the described use of balance regulation with the vehicle 12 may be particularly advantageous in minimizing operational differences and imbalances between the power modules 40 while operating in an environment where the RESS 30 may regularly be subject to relatively high power demands and long-term operational requirements.

[0028] The RESS 30 is illustrated by way of example with the power modules 40 connected in series such that the series connection can provide a main or high-voltage output to the first bus bar 34, which may be referred to as the main or high-voltage bus bar, respectively. The RESS 30 is also illustrated by way of example as including power modules 40 individually connected in parallel with one of a plurality of power converters 44. The power converters 44 may consist of power electronics capable of controlling the power exchange with the associated modules 40, with each power converter 44 optionally having an input and an output that may be interchangeable or reversible.The power converters 44 may, for example, be direct current (DC-DC) converters 44 connected as shown, with the inputs connected in parallel with one or more of the modules 40 and the outputs connected in parallel to provide an auxiliary or low-voltage output to the second busbar, which may be referred to as the auxiliary or low-voltage busbar, respectively. The power modules 40 and their associated power converters 44 may together form an individual power 34, 36, i.e., a power converter system 46 for each combination of power module 40 and power converter 44.The first and second bus bars 34, 36 are shown separately for illustrative purposes, as the present disclosure fully contemplates that the bus bars 34, 36 may be joined or connected together and / or that one bus bar 34, 36 may be used to provide or exchange electrical energy with the other bus bar 34, 36 or additional bus bars (not shown).

[0029] A plurality of circuit representations for resistance (R) and inductance (L) are shown to reflect equivalent factors that affect power distribution, i.e., the resistance, impedance, etc., associated with the power conversion systems 46, the power converters 44, the busbars 34, 36, and / or the corresponding wires, busbars, traces, etc. that affect power transfer. Even with ideal manufacturing, the resistances, inductances, etc. associated with each of the power conversion systems 46 may vary somewhat, so that the power conversion systems 46 may individually operate slightly differently even with the same control or operating instructions and parameters, which may result in operating differences and imbalances between the power conversion systems 46.To prevent one or more of the energy conversion systems 46 from wearing out or deteriorating faster than another energy conversion system 46, and for a variety of other reasons, it may be advantageous to control the energy conversion systems 46 according to the balancing regulation described herein. The balancing regulation may serve to regulate the utilization of the individual energy conversion systems 46 relative to a normalized or desired target.

[0030] The controller 38 may be configured to control the power converters 44 to, in turn, regulate the power exchanged with the power conversion systems 46 such that imbalances and differences between the power conversion systems 46 are minimized overall or converge toward the common goal over time. For example, the controller 38 may be configured to individually adjust the current, voltage, and power exchange for each of the power conversion systems 46 relative to the other power conversion systems 46, with some power conversion systems 46 possibly being controlled differently than some other power conversion systems 46.This ability to individually adjust power delivery for each power conversion system 46 may be useful for managing the load, stress, and other constraints for each power conversion system 46 relative to the other power conversion systems 46, so that overall differences and imbalances between the power conversion systems 46 can be limited and relatively balanced over time. The controller 38 may be configured to balance the power conversion systems 46 with respect to a variety of objectives, including objectives based on current, voltage, power, temperature, state of charge (SOC), state of health (SOH), state of energy (SOE), state of performance (SOP), etc.

[0031] Fig. 3 shows a flowchart 60 of a method for balancing the energy conversion systems 46 according to one non-limiting aspect of the present disclosure. The method may be implemented with the controller 38 and / or other devices onboard and / or off-board the vehicle 12 that control the RESS 30, and in particular the power converter 44, to implement various control strategies. The controller 38 and / or other devices used to implement the control strategies may perform calculations, issue instructions, and / or execute other operations according to logic, software, algorithms, etc., which may be based on one or more associated processors executing a plurality of non-transitory instructions stored on one or more computer-readable storage media.Although the RESS 30 may be controlled according to other and / or additional strategies without departing from the scope and contemplation of the present disclosure, the method is primarily described in terms of controlling the RESS 30 to meet electrical power demand while selectively operating according to a balance regulation strategy and a maximum power strategy.

[0032] The balancing regulation strategy may generally refer to setting limits or other individual adjustment of the power transfer capabilities of the energy conversion systems 46 so that each of the energy conversion systems 46 is collectively controlled toward a normalized target. The maximum power strategy may generally refer to removing limits or other constraints used to intentionally drive the energy conversion systems 46 toward the normalized target so that the energy conversion systems 46 are available to deliver energy without being metered to maintain balance among each other. Block 62 refers to a goal setting process in which the controller 38 may determine a normalized state target for the energy conversion systems 46.The normalized state target may be selected as a benchmark to which the operation of the energy conversion systems 46 can be individually aligned to create a collective commonality for the energy conversion systems 46. The state-normalized target may, for example, be defined in terms of one or more targets based on current, voltage, power, temperature, SOC, SOH, SOE, SOP, etc. For simplicity, the method will be described primarily in terms of defining the normalized state-normalized target in terms of SOC, which may be referred to as the SOC target. The SOC target may represent a common SOC level desired for each of the energy conversion systems 46.

[0033] Block 64 refers to a state process in which the controller 38 may determine a state for each of the power conversion systems 46. The state may include a state value or other metric to independently relate the power conversion systems 46 or the power modules 40 and / or the power converters 44 to the normalized target state. The state may be representative of current or active measurements, calculations, or other metrics performed individually for each of the power conversion systems 46 to quantify the operation of the associated power conversion system 46 relative to the state-normalized target. Block 66 refers to a deviation process in which the controller 38 may determine a state deviation for each of the power conversion systems 46.The state deviations can be used to quantify a deviation of the state of each energy conversion system 46 relative to the state target. For example, the state deviation can be based on a mathematical representation suitable for quantifying individual differences between the state of each energy conversion system 46 relative to the state target. With respect to the exemplary use of the SOC target, the state deviation determined for each of the energy conversion systems 46 can be based on a relative difference between the state of the associated energy conversion system 46 and the normalized target. For example, if the SOC target is a percentage value, such as 70%, the state deviation can be based on subtracting the SOC state value from the state target, such that the state deviation can correspond to a percentage value by which the SOC of the corresponding energy conversion system 46 deviates from the SOC target.

[0034] Block 68 relates to a strategy selection process in which the controller 38 may determine whether to use the balancing regulation strategy or the maximum power strategy to meet the energy demand. While the present disclosure contemplates other thresholds or triggers for switching between the balancing regulation strategy and the maximum power strategy, the method may differentiate between the strategies depending on the power available from the power conversion systems 46. This may include, for example, determining a power threshold based on a power demand of one or more loads connected to the LV bus 36 and / or the HV bus 34 and / or other elements requiring electrical power from the RESS 30, and determining whether the power available from the power conversion systems 46, i.e.the combined power of the power conversion systems 46 is sufficient to meet the power demand. Block 70 refers to a maximum power process for implementing the maximum power strategy when the power available from the energy conversion systems 46 is insufficient to meet the power demand, i.e., when the power available from the RESS 30 is below the power threshold. Block 72 refers to a balancing regulation method for implementing the balancing regulation strategy when the power available from the energy conversion systems 46 can meet the power demand, i.e., when the power available from the RESS 30 is greater than the power threshold.

[0035] The balancing regulation strategy may correspond to the controller 38 establishing limits, constraints, parameters, or other requirements for the power conversion systems 46 to collectively control the power conversion systems 46 toward the SOC target. One non-limiting aspect of the present disclosure contemplates implementing the balancing regulation strategy by selecting the maximum balancing current limit for each of the power converters 44. The maximum balancing current limits may be used to limit the amount of power that can be drawn from the associated power conversion system 46. The maximum balancing current limits may be set differently for the power conversion systems 46 depending on the state deviation determined for the associated power conversion system 46.This may include, for example, setting the maximum compensating current limits for the power conversion systems 46 with an SOC above the SOC threshold to a lower maximum compensating current limit than for the power conversion systems 46 with an SOC below the SOC threshold. The maximum compensating current limits may be set and then iteratively increased or decreased depending on whether the SOC of the corresponding power conversion system 46 increases or decreases relative to the target SOC. Similar limits may be set for voltage, voltage and current, power, temperature, etc., e.g., a maximum power flow or maximum transfer capability may be set for each of the power conversion systems 46 by appropriately controlling the power converter 44.

[0036] The balancing regulation strategy can be used in the manner mentioned so that some power conversion systems 46 can be allowed to provide more power than other power conversion systems 46, for example, to increase the use of certain power conversion systems 46 over the use of other power conversion systems 46. This differential control of the power conversion systems 46 can be advantageous in adjusting the relative operation of the power conversion systems 46 so that each power conversion system 46 can be utilized more or less depending on the state deviation of the associated power conversion system 46. However, the power conversion systems 46 can have additional limits or maximum values ​​for their capabilities, e.g.The power conversion systems 46 may have maximum capabilities or design limits for the amount of current, voltage, and / or power they can provide. Fig. 4 shows an operating characteristics chart 76 providing a representation of the capabilities of the power conversion system 46 according to one non-limiting aspect of the present disclosure. The chart 76 may include a vertical axis 78 representing voltage and a horizontal axis 80 representing current available from one of the power conversion systems 46.

[0037] Diagram 76 illustrates the ability of power conversion system 46 to distribute power at a maximum voltage that decreases once the current reaches a first current threshold 84 and then continues to decrease until the current reaches a second, or maximum, current threshold 86. As one skilled in the art will appreciate, the voltage may experience a dip or otherwise decrease from left to right, but this detail is omitted for simplicity. The balancing regulation strategy may exploit the operating characteristics of power conversion systems 46 to implement the balancing regulation strategy contemplated herein. This may include, for example, setting the maximum balancing current limit, which may be referenced to a location 90, individually and separately for each of power conversion systems 46 such that the maximum balancing current limit is to the left of the first and / or second current thresholds 84, 86.For example, by setting the compensating current limit to values ​​below the first current threshold, the power transfer capabilities of the power converter systems 46 may be dosed or restricted with respect to the maximum capabilities, optionally restricting some power converter systems 46 more than others to collectively steer the power converter systems 44 toward the normalized target state.

[0038] In order to Fig.3, implementing the balancing regulation strategy may involve iteratively returning to block 62 and repeating the process thereafter to maintain, increase, and / or decrease the maximum balancing current limits and / or other constraints imposed on the power conversion systems 46 to adjust power transfer accordingly to account for ongoing changes in the relative operation of the power conversion systems 46 toward the normalized target state. In this way, it may be advantageous to perform the iterative adjustments to account for some power modules 40 temporarily delivering more and less power than other power modules 40, after which fewer constraints may be required to adjust the power conversion systems 46 toward the normalized threshold state.Once the differences and / or imbalances between the power conversion systems 46 are minimized or approach the normalized target state, the extent of the constraints imposed on the power conversion system 46 can be reduced.

[0039] As shown in block 70, in the event that the constraints imposed on the power conversion systems 46 are unable to meet the power demand, the maximum power strategy may be implemented. The maximum power strategy may correspond to removing the maximum balancing current limit or other constraints imposed on the power conversion systems 46 so that the power conversion systems 46 can operate at their maximum capacity in an attempt to meet the power demand. The maximum power strategy may, for example, consist of controlling the power conversion systems 46 according to the characteristics illustrated in the diagrams above. In the event that the power demand decreases or the power conversion systems 46 are otherwise able to provide power above the power threshold established in block 68, the balancing regulation strategy may be implemented again in block 72.The previous sections primarily described adjusting the current limit for the power conversion systems 46 in proportion to the state deviation determined for them. However, other calculations may also be performed to determine how much each of the power conversion systems 46 should be limited in order to collectively or evenly balance the RESS 30. Such a method may include determining a maximum value signal for an output voltage at at least one power conversion system 46 or the at least one load and measuring this power conversion relative to lower-power power conversion systems 46.

[0040] In one aspect, the controller 38 may derive control signals for implementing the balancing regulation strategy depending on a threshold value (Δ), wherein the at least one transmitted signal may have at least one value when the threshold value (Δ) is greater than or equal to zero, and the at least one transmitted signal may have at least one other value when the threshold value (Δ) is less than zero. In another aspect, the transmitted value may be a maximum balancing current limit when the threshold value (Δ) is greater than or equal to zero, or the transmitted value is a minimum current limit when the threshold value (Δ) is less than zero. In another aspect, control signals corresponding to at least one power conversion system 46 are derived according to a relationship between at least one battery state and a function in all battery states, ie, SOC i / (SOC 1 + SOC 2 + ... SOC N), so that the normalized battery state is the maximum battery state, i.e. ΔSOC i = SOC i / max (SOC), the minimum battery state, i.e. ΔSOC i = SOC i / min (SOC), or the average battery state, i.e. ΔSOC i = SOC i / mean(SOC). In another aspect, the controller 38 may use a low-pass filter (moving average) or hysteresis logic to prevent chatter in individual current limits of the converter 44 determined according to the threshold (Δ). In another aspect, the controller 38 may use at least one proportional (P) or proportional-integral (PI) or proportional-integral with derivative gain (PID) compensator or advanced arithmetic controllers such as model predictive controllers (MPC) or neural networks to derive the at least one communication signal for the at least one power converter system 46.In another aspect, the power conversion systems 46 may optionally ignore the current limit or power limit signal when the measured voltage at the output of the DC / DC converter 44 falls below a certain threshold and choose to use the current or power limit signal when the voltage exceeds a certain threshold.

[0041] While various embodiments have been described, the description is intended to be exemplary and not restrictive, and it will be apparent to those skilled in the art that many other embodiments and implementations are possible that fall within the scope of the embodiments. Any feature of one embodiment may be used in combination with, or in place of, another feature or element in another embodiment, unless expressly limited. Accordingly, the embodiments are not to be limited except in accordance with the appended claims and their equivalents. Also, various modifications and changes may be made within the scope of the appended claims.Although various modes for carrying out the many aspects of the present teachings have been described in detail, those familiar with the art to which these teachings relate will recognize various alternative aspects for carrying out the present teachings that fall within the scope of the appended claims. It is intended that everything contained in the above description or shown in the accompanying drawings be considered illustrative and exemplary of the entire range of alternative embodiments that one of ordinary skill in the art would recognize as being implied, structurally and / or functionally equivalent, or otherwise obvious based on the content contained therein, and not as limited solely to the embodiments expressly shown and / or described.

Claims

[1] A method for balancing a plurality of power modules configured to store and deliver electrical energy as part of a rechargeable energy storage system (RESS), the method comprising: Determining a state for each of the power modules; Determining a state deviation for each of the power modules to quantify a deviation of the state of each respective power module relative to a state target; and Implementing a balancing regulation strategy to balance the power modules, the balancing regulation strategy comprising selecting a maximum current threshold for each of the power modules to individually normalize the state of each respective power module toward the state target. [2] The method of claim 1, further comprising: Implementing the balancing regulation strategy based on the state representing a state of charge (SOC) and the state target representing a SOC target. [3] The method of claim 1, further comprising: Implement the balancing regulation strategy based on the state representing a voltage and the state target representing a voltage target. [4] The method of claim 1, further comprising: Implement the balancing control strategy based on the state representing a state of health (SOH) and the state target representing an SOH target. [5] The method of claim 1, further comprising: Implementing the balancing regulation strategy based on the state representing a state of energy (SOE) and / or a state of power (SOP) and the state target representing an SOE and / or an SOP target. [6] The method of claim 1, further comprising: Determining a combined power of the power modules during operation according to the balancing regulation strategy that is less than a power demand of the LV busbar; and Implementing a maximum power strategy instead of the balancing regulation strategy, wherein the maximum power strategy allows the power modules to operate above the maximum current threshold specified as part of the balancing regulation strategy. [7] The method of claim 1, further comprising: Implementing the balancing regulation strategy in coordination with the provision of high voltage (HV) electrical power from the power modules to an electric motor, wherein the electric motor converts the HV electrical power into mechanical power that can be used to propel a vehicle. [8] The method of claim 7, wherein: the power modules are connected in series; and the RESS comprises a plurality of power converters, wherein an input of each power converter is connected in parallel with one of the power modules and an output of each power converter is connected together in parallel. [9] The method of claim 8, wherein: the power converters are direct current converters (DC-DC). [10] A method for balancing a plurality of power modules configured to store and deliver electrical energy as part of a rechargeable energy storage system (RESS) on board a vehicle, the RESS being operable to deliver high voltage (HV) power to a traction motor and low voltage (LV) power to a LV busbar, the method comprising: Determining a state for each of the power modules; Determining a state deviation for each of the power modules to quantify a deviation of the state of each respective power module relative to a state target; and Implementing a balancing regulation strategy to balance the power modules, wherein the balancing regulation strategy individually controls the power transfer capabilities of the power modules to drive each respective state deviation towards the state target.

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