Bidirectional Converter for Battery Management Systems

Abstract

The present invention relates to a battery management system for an electric vehicle, including a high-voltage battery, a low-voltage battery, and a bidirectional converter. The bidirectional converter is configured to connect the high-voltage battery to a low-voltage battery and to generate a power flow between the high-voltage battery and the low-voltage battery. The bidirectional converter is further configured to monitor a first voltage associated with the high-voltage battery and a second voltage associated with the low-voltage battery, and to control the voltage ratio between the first voltage and the second voltage to remain within a predetermined range by controlling the power flow between the high-voltage battery and the low-voltage battery.

Description

[Technical Field]

[0001] The present invention relates to a vehicle battery management system, a method for controlling a battery management system, and a computer-implemented method for controlling a bidirectional converter. [Background technology]

[0002] The market for electric and / or hybrid vehicles (cars, bikes, boats, ...) is booming. An example of a hybrid vehicle is a vehicle that requires energy input from at least two different types of energy sources, for example, an electric power source or an electric engine and a fuel power source or a combustion engine. The electric power source can be, for example, a solar power source, which can be, for example, integrated into the vehicle itself, for example, by integrating photovoltaic solar cells into the vehicle. The performance of the vehicle is highly dependent on the energy storage capacity, for example, batteries. One of the key factors is the management of energy storage, which enhances the efficiency and performance of these systems.

[0003] In this system, the electric and / or hybrid vehicle may include a high-voltage energy storage device and a low-voltage energy storage device, where an energy converter is connected between the high-voltage energy storage device and the low-voltage energy storage device. The energy converter is configured to transfer energy from one to the other. For example, when the vehicle is stationary and multiple accessories, such as audio, air conditioning, etc., are consuming power via the low-voltage battery, the converter may extract energy from the high-voltage source and transfer it to the low-voltage battery.

[0004] Because battery voltage varies significantly with state of charge, the energy converter in this system must typically operate over a wide input voltage range. However, the wide operating range results in the converter not always being able to operate in an optimal manner. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a battery management system for a vehicle, the battery management system comprising: ●High voltage battery and Low voltage battery and a bidirectional converter configured to connect the high-voltage battery to the low-voltage battery and to generate a power flow between the high-voltage battery and the low-voltage battery, the bidirectional converter comprising: monitoring a first voltage associated with the high voltage battery and a second voltage associated with the low voltage battery; By controlling the power flow between the high voltage battery and the low voltage battery, the voltage ratio between the first voltage and the second voltage is controlled to remain within a predetermined range; When the voltage ratio exceeds a predetermined range, a power flow is generated from the high-voltage battery to the low-voltage battery. Further configured to cause power flow from the low voltage battery to the high voltage battery when the voltage ratio falls below a predetermined range. [Means for solving the problem]

[0006] Because battery voltage varies significantly with the state of charge, battery management systems must operate over a wide input voltage range. However, a consequence of this wide operating range is that the bidirectional converter in a battery management system cannot always operate at zero voltage switching (ZVS) and zero current switching (ZCS). The bidirectional converter cannot be optimized for one fixed operating point. In the present system, this can be solved by varying the switching frequency to change the voltage gain. However, this process is often complicated and inefficient.

[0007] With the introduction of the present invention, the above problems can be alleviated through easier control and enhanced efficiency of the bidirectional converter of the battery management system.

[0008] The present invention further comprises a bi-directional converter for a battery management system, wherein the bi-directional converter comprises a first terminal for connecting to a high voltage battery and a second terminal for connecting to a low voltage battery, wherein the bi-directional converter is configured to connect the high voltage battery to the low voltage battery and to generate a power flow between the high voltage battery and the low voltage battery, the bi-directional converter comprising: monitoring a first voltage associated with the high voltage battery and a second voltage associated with the low voltage battery; controlling a voltage ratio between the first voltage and the second voltage to remain within a predetermined range by controlling power flow between the high voltage battery at the first terminal and the low voltage battery at the second terminal; When the voltage ratio exceeds a predetermined range, a power flow is generated from the high-voltage battery to the low-voltage battery. • further configured to cause a power flow from the low voltage battery to the high voltage battery when the voltage ratio falls below a predetermined range.

[0009] The battery management system according to the present invention can be applied to electric vehicles, for example electric vehicles that can be at least partially charged by on-board solar panels, which may be integrated into the roof of the vehicle, and further, the electric vehicle may be equipped with in-wheel motors.

[0010] Generally, the high-voltage battery and the low-voltage battery of the battery management system are utilized to power one or more electric traction motors and devices that operate at low voltages, such as car audio systems, airbags, heated seats, etc., respectively. High voltage is generally greater than 60 volts. Typically, high voltage is defined as a voltage in the range of 300V to 430V, and by low voltage it is meant operating at a safe voltage, typically 12 volts, 24 volts, or 48 volts.

[0011] The battery management system further includes a bidirectional converter configured to connect the high-voltage battery to the low-voltage battery and to generate a power flow between the high-voltage battery and the low-voltage battery, and vice versa, so that the high-voltage battery can supply the low-voltage battery, for example, when the low-voltage battery's state of charge (SOC) becomes low. SOC is the level of charge of a battery relative to its capacity. SOC can be expressed, for example, as a percentage.

[0012] In one embodiment, the high voltage battery can be configured to be charged by a photovoltaic device, which can be solar cells grouped into modules and integrated into or mounted on the roof of the electric vehicle.

[0013] Furthermore, the bidirectional converter is configured to monitor a first voltage associated with the high-voltage battery and a second voltage associated with the low-voltage battery. The first and second voltages may correspond, for example, to the voltages at the terminals of the high-voltage battery and the low-voltage battery, respectively. The first and second voltages are related to the respective state of energy (SoE) of each battery. Generally, because battery voltage varies significantly with SoE, the bidirectional converter must operate over a wide input voltage range.

[0014] The bidirectional converter of the present invention further controls the voltage ratio of the first voltage to the second voltage to stay within a predetermined range. To stay within the predetermined range, the bidirectional converter controls the power flow between the high-voltage battery and the low-voltage battery. The most suitable condition for operating the bidirectional converter is when the voltage ratio is substantially fixed. By introducing the predetermined range, the bidirectional converter is prevented from continuously working to control the voltage ratio to a fixed point. To make it more practical, there is some room for the voltage ratio to fluctuate within the predetermined range. For example, the predetermined range has an upper limit of +10 percent and a lower limit of -10 percent relative to the nominal or reference voltage ratio. Suppose the reference or nominal voltage on the high battery side is 200 V and the reference or nominal voltage on the low battery side is 50 V. Therefore, the nominal voltage ratio is 4. The predetermined range can then be specified, for example, as ranging from 3.6 to 4.4 (i.e., a range from +10% to -10% relative to the nominal voltage ratio).

[0015] By introducing the predetermined range, it is avoided that the bidirectional converter has to operate continuously by controlling the voltage ratio, which is not practical and efficient. It can be noted that the predetermined range can be related to the minimum power that the bidirectional converter has to deliver. In this way, the bidirectional converter is only turned on when it has to deliver a minimum amount of power, for example 100 watts, between 50 and 200 watts, for example. There are various possibilities for controlling the voltage ratio by the bidirectional converter, which will become clear in the further description.

[0016] The bidirectional converter is further configured to generate a power flow from the high-voltage battery to the low-voltage battery when the voltage ratio is higher than a predetermined range. For example, when a stationary vehicle is turned on and using some of the vehicle's functional subsystems (such as the radio system, climate control system, and light system), the SOC of the low-voltage battery obviously drops rapidly compared to the SOC of the high-voltage battery. Therefore, the second voltage may steadily decrease while the first voltage remains generally unchanged. To control the voltage ratio between the high-voltage battery and the low-voltage battery, the bidirectional converter can extract power from the high-voltage battery and supply it to the low-voltage battery.

[0017] Similarly, the bidirectional converter can be configured to generate a power flow from the low-voltage battery to the high-voltage battery when the voltage ratio (i.e., the ratio of the voltage at the high-voltage battery to the voltage at the low-voltage battery) falls below a predetermined range, which may occur, for example, during extreme weather conditions.

[0018] An advantage of the present invention is that the bidirectional converter is enabled to operate at a substantially fixed voltage gain or essentially fixed frequency. This results in the converter operating more efficiently with ZVS and ZCS across the entire SoE range without the need for complex operations or procedures. Another advantage is lower peak currents and therefore lower power losses.

[0019] Note that the voltage ratio can also be the ratio of the voltage associated with the low voltage battery to the voltage associated with the high voltage battery.

[0020] In one embodiment, the battery management system is configured to maintain a voltage ratio that remains substantially constant. Preferably, the voltage ratio is an integer or a fraction of an integer, such as 4 or 1 / 4. Assuming both batteries have similar chemistries, the SOC will also remain similar. Choosing an integer voltage ratio can reduce inductor cost and leakage.

[0021] In one embodiment, the bidirectional converter is an LLC converter or a CCL converter. Both types of converters are resonant converters. What is unique about these converters is that the voltage gain is fixed at the resonant frequency regardless of load variations. LLC converters use a magnetizing inductance to induce resonance. The advantage of LLC resonant converters is a narrow frequency variation range over a wide load range. Even ZVS is possible under no load conditions. A disadvantage of current LLC converters is the difficulty of optimizing performance over a wide input voltage range. However, this problem can be alleviated by the present invention.

[0022] In addition to LLC converters, the present invention is applicable to CCL converters, which operate in a similar manner to LLC converters, however, instead of using a magnetizing inductance for resonance, CCL converters use a separate parallel inductor for resonance.

[0023] In one embodiment, the bidirectional converter operates at a fixed switching frequency when power flows between the low-voltage battery and the high-voltage battery. Operating at a fixed frequency essentially means operating at a fixed voltage gain. The SOC of both batteries is kept similar. An advantage of this embodiment is that the converter can efficiently operate with ZVS and ZCS.

[0024] In one embodiment, the bidirectional converter comprises a first terminal for connection to a high-voltage battery and a second terminal for connection to a low-voltage battery. As described above, the high-voltage battery can be configured to be charged by a photovoltaic device, where the high-voltage battery can be connected to the photovoltaic device, for example, an on-board solar panel. Alternatively, the low-voltage battery can be charged by the photovoltaic device. Optionally, the photovoltaic device is configured to charge both the high-voltage battery and the low-voltage battery.

[0025] In one embodiment, the bidirectional converter may include a control unit that monitors the voltage ratio, e.g., on a substantially continuous basis. Based on the monitored voltage ratio and a predetermined range, the control unit controls the bidirectional converter to generate the required or desired power flow, e.g., as soon as the voltage ratio falls outside the predetermined range. There are various options for regulating the bidirectional converter and generating the power flow.

[0026] The first possible option is for the bidirectional converter to generate power flow only when the voltage ratio falls outside a predetermined range. The bidirectional converter is, in effect, passive or inactive when the voltage ratio remains substantially constant, for example, or within a predetermined range. To resume the example above, suppose the (nominal) voltage ratio is 4, and the limits of the predetermined range are 3.6 to 4.4. The moment the voltage ratio increases beyond 4.4, for example to 4.5, the bidirectional converter generates power flow from the high-voltage side to the low-voltage side until the voltage ratio reaches the upper limit of the predetermined range.

[0027] The disadvantage of this regulation is that the efficiency of the bidirectional converter is not optimal in situations where one of the battery sources is significantly powering. In that case, the voltage ratio will steadily move towards a value outside the predetermined range. As a result, the bidirectional converter is active most of the time.

[0028] Another option is for the bidirectional converter to generate power flow between the high-voltage battery and the low-voltage battery as soon as the voltage ratio falls outside a predetermined range. The bidirectional converter controls the power flow so that the voltage ratio is restored to the nominal voltage ratio. In other words, the bidirectional converter does not immediately shut off as soon as the voltage ratio falls back within the predetermined range, but remains active until the nominal voltage ratio is reached.

[0029] Continuing with the example above, the (nominal) voltage ratio is 4 and the limits of the predetermined range are 3.6 to 4.4. At the moment when the voltage ratio increases beyond 4.4, for example to 4.5, the bidirectional converter will generate a power flow from the high voltage side to the low voltage side until the voltage ratio reaches the nominal voltage ratio of 4. The advantage is that the active control time of the bidirectional converter is reduced, especially when the voltage ratio increases or decreases systematically.

[0030] It can be noted that the transfer of power may be a function of both the voltage difference between the two batteries and the power consumption associated with the power supply of the high-voltage battery and / or the low-voltage battery. The rate at which the voltage of a battery decreases is a measure of the battery's power supply. If the rate of decrease is high enough, it is an indication that the battery is dominating the power supply. By monitoring the voltage fluctuations of the high-voltage battery and / or the low-voltage battery as a function of time, and therefore the power consumption, the battery management system is configured to predict the moment when the voltage ratio may fall outside a predetermined range. The system is configured to anticipate even faster regarding deviations in the voltage ratio.

[0031] A variation of the above adjustment of the voltage ratio is that the bidirectional converter remains active for a predetermined period of time by keeping the voltage ratio at the nominal voltage ratio, at the moment when the voltage ratio is restored to the nominal voltage ratio.

[0032] Continuing with the example above, the (nominal) voltage ratio is 4, and the limits of the predetermined range are 3.6 to 4.4. At the moment the voltage ratio increases beyond 4.4, e.g., to 4.5, the bidirectional converter generates a power flow from the high-voltage side to the low-voltage side until the voltage ratio reaches the nominal voltage ratio of 4. The bidirectional converter remains active by regulating the power flow between the high-voltage battery and the low-voltage battery for a predetermined period, e.g., 1 second, to keep the voltage ratio at 4.

[0033] Alternatively, if the voltage ratio falls outside the predetermined range, the bidirectional converter controls the power flow such that the voltage ratio is restored to the farthest limit of the predetermined range.

[0034] Continuing with the example above, the (nominal) voltage ratio is 4, and the limits of the predetermined range are 3.6 to 4.4. At the moment the voltage ratio increases above 4.4, for example to 4.5, the bidirectional converter will generate a power flow from the high voltage side to the low voltage side until the voltage ratio reaches the lower limit of the predetermined range, 3.6.

[0035] In one embodiment, the bidirectional converter is configured to monitor a first voltage associated with the high-voltage battery and a second voltage associated with the low-voltage battery by receiving a first voltage signal associated with the first voltage and a second voltage signal associated with the second voltage, and control power flow based on the first voltage signal and the second voltage signal.

[0036] In an alternative embodiment, the bidirectional converter may include a voltage measurement device. The voltage measurement device may be connected to the first voltage battery and / or the low voltage battery. The voltage measurement device is configured to measure the first voltage and / or the second voltage. The voltage measurement device then provides the bidirectional converter with a first voltage signal associated with the first voltage and / or a second voltage signal associated with the second voltage.

[0037] In accordance with the present invention, the present invention further relates to a method of controlling a battery management system for an electric vehicle comprising a high voltage battery, a low voltage battery, and a bidirectional converter configured to connect the high voltage battery to the low voltage battery and to generate a power flow between the high voltage battery and the low voltage battery, the method comprising: monitoring a first voltage associated with the high voltage battery and a second voltage associated with the low voltage battery; controlling a voltage ratio of the first voltage to the second voltage to remain within a predetermined range by controlling power flow between the high voltage battery and the low voltage battery; generating a power flow from the high voltage battery to the low voltage battery when the voltage ratio is higher than a predetermined range; and - causing power flow from the low voltage battery to the high voltage battery when the voltage ratio is below a predetermined range.

[0038] In the method of the present invention, a first voltage associated with a high-voltage battery and a second voltage associated with a low-voltage battery are monitored. The high-voltage battery and the low-voltage battery can be connected via a bidirectional converter. By monitoring the first voltage and the second voltage, a voltage ratio is determined. For example, both voltages can be determined by voltage measurement via a control unit. The control unit can be part of the bidirectional converter. Alternatively, there can be a distributed control unit that determines the voltages of both batteries, where the control unit controls the bidirectional converter.

[0039] The next step in the method of the present invention is to control the voltage ratio of the first voltage to the second voltage to remain within a predetermined range. The bidirectional converter thereby controls the power flow between the high-voltage battery and the low-voltage battery. Power flow is generated from the high-voltage battery to the low-voltage battery when the voltage ratio is higher than the predetermined range. For example, when a stationary vehicle is turned on and using some of the vehicle's functional subsystems (radio system, climate control system, light system, etc.), the SOC of the low-voltage battery obviously drops rapidly compared to the SOC of the high-voltage battery. Therefore, the second voltage may steadily decrease while the first voltage remains generally unchanged. To control the voltage ratio between the high-voltage battery and the low-voltage battery, power is extracted from the high-voltage battery and supplied to the low-voltage battery.

[0040] Similarly, power flow is generated from the low voltage battery to the high voltage battery when the voltage ratio falls below a predetermined range, which may occur, for example, during extreme weather conditions.

[0041] The predetermined range may include, for example, upper and lower limits between which the voltage ratio must be controlled. The following example will make this clear.

[0042] Assume the desired voltage ratio is 4, meaning the SOC of each battery is equal. In this example, the predetermined range has an upper limit of 4.4 and a lower limit of 3.6. In other words, there is a built-in deviation of 10 percent from the desired voltage ratio. During operation, the bidirectional converter monitors the first and second voltages. A high load on the high-voltage battery results in a higher power demand on the high-voltage battery compared to the low-voltage battery. The balance between the batteries is disturbed, and the voltage ratio drops below 4. When the voltage ratio reaches the lower limit of the predetermined range, i.e., 3.6, the bidirectional converter converts power from the low-voltage battery to the high-voltage battery. The power flow ensures that the voltage ratio remains within the predetermined range.

[0043] The invention will be described in more detail below with reference to the figures, which show, in a non-limiting manner, exemplary embodiments of the invention, and in which the same reference numerals in different figures indicate the same features in the different figures. [Brief explanation of the drawings]

[0044] [Figure 1] 1 is a diagram illustrating a schematic of a battery management system according to an embodiment of the present invention, comprising a high-voltage battery, a low-voltage battery, and a bidirectional converter; [Figure 2] FIG. 1 is a diagram illustrating a bidirectional converter for a battery management system, the bidirectional converter comprising a first terminal for connecting to a high-voltage battery and a second terminal for connecting to a low-voltage battery. [Figure 2a] FIG. 1 is a diagram illustrating an embodiment of a bi-directional converter, where the bi-directional converter has an LLC configuration. [Figure 3a] FIG. 10 is a diagram illustrating various control schemes for controlling the voltage ratio between a first voltage and a second voltage to remain within a predetermined range by controlling the power flow between a high-voltage battery and a low-voltage battery. [Figure 3b]FIG. 10 is a diagram illustrating various control schemes for controlling the voltage ratio between a first voltage and a second voltage to remain within a predetermined range by controlling the power flow between a high-voltage battery and a low-voltage battery. [Figure 3c] FIG. 10 is a diagram illustrating various control schemes for controlling the voltage ratio between a first voltage and a second voltage to remain within a predetermined range by controlling the power flow between a high-voltage battery and a low-voltage battery. [Figure 4] FIG. 1 is a schematic illustration of one embodiment of a flow diagram of a computer-implemented method for controlling a bidirectional converter in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0045] 1 illustrates a schematic diagram of a solar car electrical system, in which a battery management system 120 is shown comprising a high-voltage battery 122, a low-voltage battery 130, and a bidirectional converter 126. The battery management system 120 is applied to an electric vehicle that is at least partially rechargeable by an on-board solar panel comprising solar cells. Typically, the solar cells are integrated into the roof of the electric vehicle.

[0046] 1 illustrates several groups of solar cells 102, each connected to an associated distributed maximum power point tracker 104. The groups 102 are connected in series, thereby forming strings, with the outputs of the strings connected to a string voltage bus 106.

[0047] One side of each distributed maximum power point tracker 104, the primary side, is connected to the group associated with that distributed maximum power point tracker. The other side, the secondary side, is connected to an energy exchange bus 108. For other possible uses, such as diagnostics and current monitoring, the distributed maximum power point trackers exhibit a communication bus 110. The string voltage bus 106 is connected via a DC / DC converter 112.

[0048] A distributed maximum power point tracker controller 134 controls the distributed maximum power point tracker 104 via the communication bus 110, for example, to disable the group 102 during service or error conditions (indicated by, for example, an deployed airbag), etc. A DC / DC converter 112 loads the string bus 106.

[0049] Also shown is a motor controller 116 that is connected to the high voltage bus and generates voltage for an (electric) traction motor 118, e.g., a permanent magnet motor. It is noted that more than one motor may be used (typically each motor having its own motor controller). It is also noted that the motor may be any type of motor, brushed or brushless, for propelling a vehicle (or boat), as long as it is an electric motor.

[0050] It should be noted that most of the above components are optional with respect to the present invention.

[0051] A bidirectional converter 126 connects the high-voltage battery 122 with a low-voltage battery 130. The bidirectional converter is configured to generate a power flow between the high-voltage battery and the low-voltage battery. The low-voltage battery 130 (typically a lead-acid battery) powers a number of low-voltage users 132 (air conditioner, audio system, lighting, etc.). Typically, high voltage is defined as greater than 60 volts. Typically, high voltage is defined as a voltage in the range of 300V to 430V. By low voltage, it is meant operating at a safe voltage, typically 12 volts or 24 volts.

[0052] The bidirectional converter 126 is configured to power the low-voltage battery 130 from the high-voltage battery 122, or vice versa, for example, when the low-voltage battery demands a load. The high-voltage battery and / or the low-voltage battery are configured to be charged by a solar cell.

[0053] 2 schematically illustrates a bidirectional converter for a battery management system according to the present invention. The bidirectional converter 202 includes a first terminal 204 for connection to a high-voltage battery 201 and a second terminal 205 for connection to a low-voltage battery 203. The bidirectional converter 202 is configured to connect the high-voltage battery 201 to the low-voltage battery 203 and to generate a power flow (indicated by arrows 201a, 201b, 203a, and 203b) between the high-voltage battery 201 and the low-voltage battery 203. The transfer of power from the high-voltage battery 201 to the low-voltage battery 203 through the bidirectional converter 202 is illustrated by arrows 201a and 203a. The transfer of power from the low-voltage battery 203 to the high-voltage battery 201 is illustrated by arrows 203b and 201b.

[0054] The bidirectional converter 202 is configured to monitor a first voltage associated with the high-voltage battery 201 at a first terminal 204 and a second voltage associated with the low-voltage battery 203 at a second terminal 205. The bidirectional converter receives a first signal 207 corresponding to the first voltage 207 and a second signal 208 corresponding to the second voltage 208. The first and second voltages may correspond to the voltages at the terminals of the high-voltage battery and the low-voltage battery, respectively, for example. The first and second voltages are related to the respective SOCs of each battery.

[0055] The bidirectional converter 202 further controls the voltage ratio of the first voltage to the second voltage to remain within a predetermined range. To remain within the predetermined range, the bidirectional converter controls the power flow between the high-voltage battery 201 and the low-voltage battery 203. The most suitable condition for operating the bidirectional converter is when the voltage ratio is substantially fixed. By introducing the predetermined range, the bidirectional converter is prevented from having to continuously work to control the voltage ratio to a fixed point. To make it more practical, there is some room for the voltage ratio to fluctuate within the predetermined range. By introducing the predetermined range, the bidirectional converter is prevented from having to continuously work by controlling the voltage ratio, which is both practical and inefficient.

[0056] The bidirectional converter is further configured to generate a power flow from the high-voltage battery to the low-voltage battery when the voltage ratio is higher than a predetermined range. For example, when a stationary vehicle is turned on and using some of the vehicle's functional subsystems (radio system, climate control system, light system, etc.), the SOC of the low-voltage battery will obviously rapidly become zero compared to the SOC of the high-voltage battery. The second voltage will steadily decrease, while the first voltage will remain generally unchanged. To control the voltage ratio between the high-voltage battery and the low-voltage battery, the bidirectional converter can extract power from the high-voltage battery to the low-voltage battery.

[0057] On the other hand, the bidirectional converter is configured to generate power flow from the low-voltage battery to the high-voltage battery when the voltage ratio falls below a predetermined range, which may occur, for example, during extreme weather conditions.

[0058] In FIG. 2 , the bidirectional converter includes a control unit 206 that constantly monitors the voltage ratio. The control unit 206 receives a first signal 207 representing a first voltage and a second signal 208 representing a second voltage to determine the voltage ratio. Based on the monitored voltage ratio and a predetermined range, the control unit 206 controls the bidirectional converter 202 to generate the required power flow, for example, as soon as the voltage ratio falls outside the predetermined range. There are various options for regulating the bidirectional converter 202 and generating the power flow. In one embodiment, the control unit may be a separate controller or control unit, i.e., a controller or control unit separate from the bidirectional converter. Such a separate control unit may be, for example, a central master control unit of a vehicle, controlling the bidirectional converter.

[0059] An advantage of the present invention is that the converter is allowed to operate at a fixed voltage gain or essentially a fixed frequency. This results in the converter operating more efficiently with ZVS and ZCS without the need for complex actions or procedures. Another advantage is lower peak currents and therefore lower power losses.

[0060] Figure 2a illustrates one embodiment of a bidirectional converter, called an LLC resonant converter. What is unique about these converters is that the voltage gain is fixed at the resonant frequency regardless of load variations. LLC converters use a magnetizing inductance to induce resonance. The advantage of LLC resonant converters is their narrow frequency variation range over a wide load range. Even ZVS is possible at no load conditions. Another possible configuration is the CCL resonant converter, which is exactly the same as the LLC resonant converter.

[0061] 3a-3c schematically illustrate various control schemes for controlling the power flow between the high-voltage battery and the low-voltage battery so that the voltage ratio between the first voltage VH and the second voltage VL remains within a predetermined range. The ratio of the first voltage VH to the second voltage VL is described as a function of time t.

[0062] The bidirectional converter according to the present invention is configured to monitor a first voltage VH associated with a high-voltage battery and a second voltage VL associated with a low-voltage battery, where the first and second voltages may correspond to the voltages at the terminals of the high-voltage battery and the low-voltage battery, respectively.

[0063] The bidirectional converter controls the voltage ratio Vrat of the first voltage VH to the second voltage VL so that it remains within a predetermined range. The predetermined range is specified by an upper limit Ulim and a lower limit Llim. The voltage ratio Vrat and the predetermined range are plotted on the vertical axis of Figures 3a to 3c.

[0064] In Figures 3a-3c, the predetermined ranges are defined symmetrically with respect to the voltage ratio, meaning that the voltage ratio is the center of the predetermined range. As an example, the nominal value of the first voltage VH on the high battery side can be, for example, 200 V, and the nominal value of the second voltage VL on the low battery side can be, for example, 50 V. Therefore, the nominal or desired voltage ratio Vrat is set to 4. The predetermined range has an upper limit of +10 percent and a lower limit of -10 percent, determined from the voltage ratio. The upper limit Ulim is therefore specified as 4.4, and the lower limit Llim is specified as 3.6. Introducing the predetermined ranges avoids the need for the bidirectional converter to operate continuously by controlling the voltage ratio, which is both practical and inefficient.

[0065] The bidirectional converter monitors the voltage ratio VH / VL. As soon as the voltage ratio falls outside a predetermined range, the bidirectional converter generates a power flow between the high-voltage battery and the low-voltage battery. In FIG. 3a, the voltage ratio is assumed to increase and reaches an upper limit at time t1. Consequently, the bidirectional converter begins to generate a power flow from the high-voltage side to the low-voltage side at time t2 until the voltage ratio VH / VL reaches a voltage ratio Vrat of 4. During the period t1-t2, the low-voltage battery is therefore receiving power from the high-voltage battery. In the example given in FIG. 3a, the bidirectional converter stops the power flow once the voltage ratio Vrat reaches its nominal value.

[0066] 3a, the active control periods of the bidirectional converter are during time intervals t1-t2, t3-t4, t5-t6, and t7-t8. The advantage of generating power flow only during specific time intervals is that the active control time of the bidirectional converter is reduced, especially when the voltage ratio increases or decreases systematically.

[0067] Another option is for the bidirectional converter to generate power flow only when the voltage ratio falls outside a predetermined range. This regulation mode is visualized in Figure 3b. The bidirectional converter is, in fact, passive or inactive when the voltage ratio remains substantially constant, for example, or within a predetermined range. Resuming the example of Figure 3a, the (nominal) voltage ratio Vrat is 4, and the limits of the predetermined range, Llim, Ulim, are 3.6 to 4.4. At time t1, the voltage ratio increases beyond 4.4, for example to 4.5, meaning that the low-voltage battery provides power predominantly compared to the high-voltage side. As a result, the bidirectional converter generates power flow from the high-voltage side to the low-voltage side until the voltage ratio reaches the upper limit, Ulim, of the predetermined range. In Figure 3b, it is assumed that during the time interval t1 to t8, the low-voltage battery continuously uses power, such that the second voltage associated with the low-voltage battery steadily decreases while the first voltage associated with the high-voltage battery remains roughly unchanged. The bidirectional converter continues to transfer power from the high voltage battery to the low voltage battery to stay within the upper limit Ulim of the predetermined range.

[0068] The disadvantage of this regulation is that the efficiency of the bidirectional converter is not optimal in situations where one of the battery sources is significantly powering. As a result, the bidirectional converter is active most of the time. The active control period of the bidirectional converter is during the time interval t1-t8. The regulation of Figure 3b is less efficient than the situation of Figure 3a.

[0069] Alternatively, if the voltage ratio strays outside the predetermined range, the bidirectional converter controls the power flow so that the voltage ratio is restored to the furthest limit of the predetermined range. This control scheme is visualized in Figure 3c.

[0070] 3a-3b, the (nominal) voltage ratio Vrat is 4, and the predetermined range limits Llim, Ulim are between 3.6 and 4.4. In Fig. 3c, at time t1, the voltage ratio increases beyond 4.4, e.g., to 4.5, and the bidirectional converter generates power flow from the high-voltage side to the low-voltage side until the voltage ratio reaches the lower limit Llim of the predetermined range of 3.6.

[0071] As can be seen from Figure 3c, the active control periods of the bidirectional converter are during time intervals t1-t2, t4-t5, and t7-t8. During these intervals, the bidirectional converter controls power flow from the high-voltage battery to the low-voltage battery until the voltage ratio reaches a lower limit Llim. This type of regulation is very efficient in situations where only one of the battery sources is significantly supplying power and the voltage associated with the other battery source remains largely unchanged, such as when the battery source is not supplying power or is being charged by solar power.

[0072] Alternatively, the power transfer may be a function of both monitored voltage and operational data associated with the battery. The operational data may relate to all different types of data, such as power consumption associated with powering the high-voltage and / or low-voltage batteries, vehicle usage, GPS data, etc. For example, power consumption is a measure of the rate at which the battery's voltage decreases. If the rate of decrease becomes high enough, it is an indication that the battery is dominating the supply of power. By monitoring the voltage fluctuations of the high-voltage and / or low-voltage batteries as a function of time, and therefore power consumption, the battery management system is configured to predict moments when the voltage ratio may fall outside a predetermined range. The system is configured to anticipate more quickly regarding deviations in the voltage ratio.

[0073] In one embodiment, the vehicle or controller logs operational data. Based on the operational data, the system is configured to select the most efficient control mechanism for the bidirectional converter. The system is configured to more accurately and quickly predict deviations in the voltage ratio.

[0074] 4 schematically depicts a flow diagram of one embodiment of a computer-implemented method according to the present invention for controlling a bidirectional converter. The bidirectional converter is configured to generate a power flow between a high-voltage battery and a low-voltage battery. The bidirectional converter is further configured to connect the high-voltage battery to the low-voltage battery.

[0075] The computer-implemented method of the present invention includes receiving 401 a first voltage signal representing a first voltage associated with a high voltage battery.

[0076] In step 402, a second voltage signal representing a second voltage associated with the low voltage battery is received. Note that the sequence in which steps 401 and 402 occur can vary and is therefore not fixed. Both steps 401 and 402 can be performed simultaneously.

[0077] The first and second voltage signals can be derived from the voltages, for example, by monitoring the first and second voltages using a voltage measurement system or device. Such voltage measurement or monitoring can be performed, for example, by a voltage measurement device associated with the bidirectional converter. The voltage measurement device can have, for example, an output or output terminal at which a signal representing the measured voltage can be made available. In one embodiment, the bidirectional converter can include a control unit configured to control the voltage measurement device. In one embodiment, the voltage measurement device is configured to measure the first voltage and / or the second voltage. The voltage measurement device can generate a first voltage signal associated with the first voltage and / or a second voltage signal associated with the second voltage.

[0078] The computer-implemented method further includes determining 403 a voltage ratio based on the first voltage signal and the second voltage signal, the voltage ratio representing the ratio of the first voltage and the second voltage.

[0079] The computer-implemented method further includes determining 404 a control signal for controlling the bi-directional converter. The control signal is based on the voltage ratio. In one embodiment, the control signal is configured to control operation of the bi-directional converter such that the voltage ratio is controlled toward a target value or maintained within a predetermined range.

[0080] The computer-implemented method of the present invention further includes outputting a control signal at step 405. The control signal may be output directly to the bidirectional converter. For example, the control signal may ensure that the bidirectional converter generates the necessary or desired power flow between the high-voltage battery and the low-voltage battery when the voltage ratio deviates from its nominal or target value.

[0081] It should be understood that the disclosed embodiment of FIG. 4 can also be implemented in a method for controlling a battery management system according to the present invention. Such a battery management system can be used, for example, in a vehicle and can include a high-voltage battery, a low-voltage battery, and a bidirectional converter configured to connect the high-voltage battery to the low-voltage battery and to generate a power flow between the high-voltage battery and the low-voltage battery. Such a battery management system can further include, for example, a control unit for controlling the bidirectional converter. Such a control unit can have, for example, one or more input terminals for receiving voltage signals, for example, of steps 401 and 402 shown in FIG. 4 , and one or more output terminals for outputting control signals, for example, determined in step 404. Such a control unit can be further configured to execute a computer-implemented method according to the present invention. In such an embodiment, the control unit can include, for example, a memory unit and a processing unit. In such an embodiment, the memory unit can be configured, for example, to store the received voltage signals and, optionally, to store any further operating data received. The processing unit of such a control unit can be configured, for example, to process the stored data, for example, the voltage signals, and, based on the voltage signals, determine a voltage ratio and a control signal to be output to control the bidirectional converter.

[0082] It should be understood that the disclosed embodiments are used as examples, and that the present invention may be implemented in other forms. Accordingly, the specific structural aspects disclosed herein should not be considered as limitations on the present invention, but merely as a basis for the claims and for enabling the invention to be implemented by those skilled in the art.

[0083] Furthermore, various terms used in the description should not be construed as limiting, but rather as a comprehensive description of the invention.

[0084] As used herein, the word "a" means one or more than one unless otherwise specified. The phrase "plurality" means two or more than two. The words "comprising" and "having" constitute open language and do not exclude the presence of additional elements.

[0085] Reference numerals in the claims should not be construed as limiting the invention, and it is not necessary for a particular embodiment to achieve all of the objectives described.

[0086] The mere fact that certain technical measures are recited in different dependent claims further allows the possibility that a combination of these technical measures can be applied to advantage. [Explanation of symbols]

[0087] 102 Solar Cell 104 Distributed Maximum Power Point Tracker 106 String Voltage Bus 108 Energy Exchange Bus 110 Communication Bus 112 DC / DC converter 116 Motor Controller 118 Drive motor 120 Battery Management System 122 High Voltage Battery 126 Bidirectional Converter 130 Low Voltage Battery 132 Low Voltage Users 134 Distributed Maximum Power Point Tracker Controller 201 High Voltage Battery 201a, 201b power flow 202 Bidirectional Converter 203 Low Voltage Battery 203a, 203b power flow 204 First terminal 205 Second Terminal 206 Control Unit 207 First voltage, first signal 208 Second voltage, second signal

Claims

1. 1. A battery management system for an electric vehicle, comprising: High voltage battery and Low voltage battery and a bi-directional converter configured to connect the high voltage battery to the low voltage battery and to generate a power flow between the high voltage battery and the low voltage battery, the bi-directional converter comprising: monitoring a first voltage associated with the high voltage battery and a second voltage associated with the low voltage battery; controlling the voltage ratio between the first voltage and the second voltage to remain within a predetermined range by controlling the power flow between the high voltage battery and the low voltage battery; generating the power flow from the high voltage battery to the low voltage battery when the voltage ratio is higher than the predetermined range; further configured to cause the power flow from the low voltage battery to the high voltage battery when the voltage ratio falls below the predetermined range. Battery management system.

2. The battery management system of claim 1 , wherein the voltage ratio is the first voltage divided by the second voltage.

3. The battery management system of claim 1 , wherein the voltage ratio is the second voltage divided by the first voltage.

4. The battery management system of claim 1 , wherein the voltage ratio is substantially constant.

5. The battery management system of claim 1 , wherein the voltage ratio is an integer.

6. The battery management system of claim 1 , wherein the predetermined range is between 5 and 15 percent of the voltage ratio.

7. The battery management system of claim 1 , wherein a photovoltaic device is integrated into a roof of the vehicle.

8. The battery management system of claim 1 , wherein the low voltage battery operates in the range of 12-48 volts and the high voltage battery operates above 60 volts.

9. The battery management system of claim 1 , wherein the bidirectional converter is operating in ZVS and / or ZCS.

10. The battery management system of claim 1 , wherein the bidirectional converter is an LLC converter or a CCL converter.

11. 2 . The battery management system of claim 1 , wherein the bi-directional converter operates at a fixed switching frequency when the power flow is generated between the low-voltage battery and the high-voltage battery.

12. The bidirectional converter, a first terminal for connection to the high voltage battery; a second terminal for connection to the low voltage battery; and The battery management system of claim 1 , comprising:

13. A vehicle comprising the battery management system according to claim 1.

14. The vehicle of claim 13 , wherein the vehicle further comprises a solar panel and an in-wheel motor.

15. 1. A bi-directional converter for a battery management system, the bi-directional converter comprising a first terminal for connecting to a high voltage battery and a second terminal for connecting to a low voltage battery, the bi-directional converter configured to connect the high voltage battery to the low voltage battery and to generate a power flow between the high voltage battery and the low voltage battery, the bi-directional converter comprising: monitoring a first voltage associated with the high voltage battery and a second voltage associated with the low voltage battery; controlling the voltage ratio of the first voltage to the second voltage to remain within a predetermined range by controlling the power flow between the high voltage battery at the first terminal and the low voltage battery at the second terminal; generating the power flow from the high voltage battery to the low voltage battery when the voltage ratio is higher than the predetermined range; • A bidirectional converter further configured to cause the power flow from the low voltage battery to the high voltage battery when the voltage ratio falls below the predetermined range.

16. 16. The bi-directional converter of claim 15, wherein the bi-directional converter is configured to monitor the first voltage associated with the high voltage battery and the second voltage associated with the low voltage battery by receiving a first voltage signal associated with the first voltage and a second voltage signal associated with the second voltage, and to control the power flow based on the first voltage signal and the second voltage signal.

17. 17. The bi-directional converter of claim 16, wherein the bi-directional converter comprises a voltage measurement device configured to measure the first voltage and / or the second voltage and to provide a first voltage signal associated with the first voltage and / or a second voltage signal associated with the second voltage to the bi-directional converter.

18. 1. A method of controlling a battery management system for an electric vehicle comprising a high voltage battery, a low voltage battery, and a bi-directional converter configured to connect the high voltage battery to the low voltage battery and to generate a power flow between the high voltage battery and the low voltage battery, comprising: monitoring a first voltage associated with the high voltage battery and a second voltage associated with the low voltage battery; controlling the voltage ratio between the first voltage and the second voltage to remain within a predetermined range by controlling the power flow between the high voltage battery and the low voltage battery; causing the power flow from the high voltage battery to the low voltage battery when the voltage ratio is higher than the predetermined range; and causing said power flow from said low voltage battery to said high voltage battery when said voltage ratio is below said predetermined range.

19. 20. The method of claim 18, wherein the low voltage battery operates in the range of 12-48 volts and the high voltage battery operates above 60 volts.

20. 20. The method of claim 18, wherein the monitoring step comprises providing a voltage ratio signal to the bi-directional converter based on the first voltage and the second voltage.

21. The method of claim 18 , wherein the first voltage and the second voltage are determined by voltage measurements.

22. The method of claim 18 , wherein the voltage ratio is substantially constant.

23. The method of claim 18 , wherein the voltage ratio is an integer.

24. 20. The method of claim 18, wherein the predetermined range is between 5 and 15 percent of the voltage ratio.

25. 1. A computer-implemented method for controlling a bi-directional converter configured to generate a power flow between a high voltage battery and a low voltage battery, comprising: receiving a first voltage signal representative of a first voltage associated with the high voltage battery; receiving a second voltage signal representative of a second voltage associated with the low voltage battery; determining a voltage ratio based on the first voltage signal and the second voltage signal, the voltage ratio representing a ratio between the first voltage and the second voltage; determining a control signal for controlling the bidirectional converter, the control signal being based on the voltage ratio; - outputting said control signal.

26. 26. The method of claim 25, wherein the control signal is configured to control the power flow of the bi-directional converter to maintain the voltage ratio between the first voltage and the second voltage within a predetermined range.

27. 26. A computer program comprising instructions which, when said program is executed by a computer, cause said computer to perform the method of claim 25.

28. A controller for a bi-directional converter, the controller being configured to implement the method of claim 25.