Method for estimating an output electric current of a power converter

Abstract

The present invention targets a power converter, in particular configured to be housed on board an electric or hybrid motor vehicle, comprising at least one arm through which an output current of the power converter flows, a switch system arranged in series with said at least one arm such that the output current flows through the switch system, a voltage-measuring device designed to measure a voltage drop (Vss) across the terminals of the switch system, a temperature-measuring device designed to measure a representative temperature (T) corresponding to the junction temperature (Tss) of the switch system or to the temperature of an element in thermal contact with the switch system, and a computing module configured to estimate the strength of the output current (Iout) on the basis of the representative temperature (T) and of the voltage drop (Vss) across the terminals of the switch system.

Description

DESCRIPTION Title of the invention: Method for estimating the output electrical current of a power converter TECHNICAL FIELD

[0001] The present invention relates to the field of electrical equipment, particularly for electric or hybrid motor vehicles. Specifically, the present invention concerns a power converter comprising a device for measuring an electric current, and an associated method for measuring an electric current. STATE OF THE ART

[0002] As is well known, an electric or hybrid vehicle includes an electric motor system, enabling vehicle propulsion, powered by a high-voltage battery via a high-voltage onboard electrical system. In addition, an electric or hybrid vehicle also includes a variety of auxiliary electrical equipment, such as onboard computers or windshield motors, powered by a low-voltage battery via a low-voltage onboard electrical system. The main battery typically delivers a voltage between 100 V and 900 V, preferably between 100 V and 500 V, or between 400 V and 800 V, while the low-voltage battery typically delivers a voltage of around 12 V, 24 V, or 48 V.

[0003] More specifically, the high-voltage power supply battery provides a power supply function for the low-voltage power supply battery, notably via a DC-DC power converter. However, the voltage reduction performed by the DC-DC power converter involves managing a high current. Consequently, the DC-DC power converter generally includes a safety switch located at the converter output to protect the converter from a potential short circuit, and a device for measuring the output electrical current for diagnostic and control purposes.

[0004] In this context, a conventional solution for measuring the output current of a power converter involves using a measuring shunt, located at the converter's output. The measuring shunt is a calibrated resistor. By measuring the voltage across the resistor and applying Ohm's law, the electric current flowing through the resistor can be deduced. This solution allows for a precise measurement of the output current, but it does introduce power losses that impact the converter's efficiency and affect its compactness.

[0005] Alternatively, current measurement can be performed by measuring the magnetic field, typically using a Hall effect sensor. The sensor is preferably positioned as close as possible to the electrical conductor carrying the output current to achieve the desired measurement accuracy. This solution has the advantage of not affecting the converter's efficiency. However, the mechanical integration of the sensor into the converter can be complex and may even require the use of a magnetic field concentrator, often C- or U-shaped, with an air gap, thus increasing the converter's overall size.

[0006] However, today, particularly in the automotive sector, the constraints related to size and efficiency for power converters are significant. Therefore, there is a need for a power converter with a means of measuring electrical current and an associated process that reduces size while limiting the impact of the current measurement device on the power converter's efficiency. PRESENTATION OF THE INVENTION

[0007] More specifically, according to one aspect of the invention, the invention relates to a power converter, particularly configured for installation in an electric or hybrid motor vehicle. The power converter according to the invention comprises at least one arm through which an output current from the power converter flows and which is configured to be connected to a load, and a switching system arranged in series with said at least one arm such that the output current flows through the switching system.Furthermore, the power converter according to the invention includes a voltage measuring device adapted to measure a voltage drop Vss across the terminals of the switching system, a temperature measuring device adapted to measure a representative temperature T corresponding to the junction temperature Tss of the switching system or to the temperature of an element in thermal contact with the switching system, and a calculation module configured to estimate the intensity of the output current lout as a function of the representative temperature T and the voltage drop Vss across the terminals of the switching system.

[0008] The present invention therefore offers the considerable advantage of allowing the measurement of the output current intensity of the power converter without requiring the addition of a measuring shunt or a Hall effect sensor, but by using a switching system, in particular the safety switch(es) and temperature measuring devices that are already present in the majority of power converters. Consequently, compared to the use of a measuring shunt, the present invention does not induce additional power losses, and therefore does not impact, or only minimally impacts, the efficiency of the power converter. Furthermore, compared to the solution using a Hall effect sensor, the implementation of The invention does not require mechatronic integration, improving the compactness of the power converter. Thus, the solution proposed in the invention is inexpensive and easy to implement from an industrial manufacturing perspective.

[0009] Advantageously, the switching system includes at least one safety switch, for example, one or two safety switches in series. The invention therefore allows the use of the safety switch or switches to measure the output current, the safety switch being a very common device used at the output of power converters.

[0010] Advantageously, the temperature measuring device is configured to measure the temperature of a Tfluid cooling fluid suitable for cooling the switch system.

[0011] Advantageously, the said at least one arm consists of three arms.

[0012] Advantageously, the switching system consists of a MOSFET.

[0013] Advantageously, the power converter according to the invention is a DC-DC power converter.

[0014] According to another aspect of the invention, the invention relates to a method for estimating the output current of the power converter as described above. The method according to this aspect of the invention, implemented by the calculation module, comprises: - the acquisition of the voltage drop Vss and the representative temperature T; - during a first measurement, the initialization of the junction temperature Tss of the switch system as a function of the representative temperature T; - the determination of the resistance Rss of the switching system, the resistance Rss being estimated as a function of the junction temperature Tss of the switching system; - the determination of the intensity of the output current lout from the voltage drop Vss and the resistance Rss of the switching system.

[0015] The method according to the invention has the advantage of implementing simple calculation operations, which consequently are economical in terms of computing resources.

[0016] Advantageously, the determination of the resistance Rss of the switch system is carried out according to the equation [Math 1] Rss = Rss_ref x (1 + C x (Tss - Tref)), where C is a temperature constant of the switch system and Rss_ref is a reference value of the resistance of the switch system corresponding to a reference temperature.

[0017] The representative temperature T can, in particular, correspond to the temperature of an element in thermal contact with the switching system. Then, the process according to The invention advantageously comprises, after the step of acquiring the voltage drop Vss and the representative temperature T, the successive execution of the following steps by the calculation module for a number of iterations N: - during a first execution following the acquisition step, the initialization of the junction temperature T ss of the switch system to a value T ss0 equal to the representative temperature T, or during an iteration i, the initialization of the junction temperature Tss to a value Tssi determined at the end of the previous iteration; - the determination of the resistance Rssj of the switch system estimated as a function of the junction temperature Tssi of the switch system according to the following equation: [Math 2] RsSj = Rss_ref x (1 + C x (Tssj — Tref)); - the determination of the output current intensity loutj according to the following equation: Vss [Math 3] lout j = — ; Rs sj - the determination of the power dissipated Pssi by the switching system as a function of the output current intensity loutj and the resistance Rssi of the switching system according to the following equation: [Math 4] Pssj = (louti) 2 x RSS; - the update of the junction temperature Tssj according to the following equation [Math 5] Tss i+1 = T + Pssj x Rth, where Rth is a given thermal resistance between the junction of the switching system and the element in thermal contact with the switching system having the representative temperature T. This iterative update of the estimated junction temperature Tss advantageously allows convergence towards the real value of the output current intensity of the power converter. PRESENTATION OF THE FIGURES

[0018] The invention will be better understood upon reading the following description, given solely by way of example, and referring to the accompanying drawings given by way of non-limiting examples, in which identical references are given to similar objects and on which:

[0019] [Fig. 1]: Figure 1 is a schematic representation of a method, according to one aspect of the invention, for estimating an electrical output current of a power converter;

[0020] [Fig. 2]: Figure 2 is a schematic representation of an example of a power converter according to another aspect of the invention;

[0021] [Fig. 3]: Figure 3 is a schematic representation of another example of a power converter according to one aspect of the invention;

[0022] [Fig. 4]: Figure 4 is a schematic representation of another example of a power converter according to one aspect of the invention.

[0023] It should be noted that the figures set out the invention in detail to allow the invention to be implemented, said figures being able of course to serve to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0024] According to one aspect of the invention, the invention relates to a power converter comprising a means for measuring the output current of the power converter, particularly for control purposes. The converter is specifically configured to be connected on one side to a voltage source and on the other to a load, and adapted for installation in an electric or hybrid motor vehicle. The present invention will be described below in the context of a DC-DC power converter but can be applied to any power converter, in particular an inverter or an electric charger, especially an on-board charger, also known as an OBC (for "On-Board Charger"). More specifically, in the context of the DC-DC power converter, the voltage source corresponds to the high-voltage supply battery, and the load to the low-voltage supply battery.

[0025] With reference to Figures 2 to 4, the power converter 1 according to the invention comprises at least one arm 11 carrying an output current from the power converter 1 and configured to be connected to the load, and a switching system Qss arranged in series with said at least one arm 11 such that the output current flows through the switching system Qss. The switching system preferably comprises at least one safety switch. In the following description, the invention will be described in the non-limiting context of the use of the safety switch. However, the present invention can be applied to any switching system carrying the output current.

[0026] The safety switch, commonly referred to as a "safety switch" in English, protects electrical equipment when the output current becomes too high. The safety switch is located either directly at the output of the power converter or in a feedback loop of the power converter's output current. When power conversion is active, the safety switch is closed. In case of a malfunction, such as a battery polarity reversal or an overvoltage, the safety switch opens.

[0027] Figures 2 to 4 represent different possible configurations of the Qss switch system. In the examples shown in Figures 2 and 3, the switch system Qss is electrically connected on one side to the output of the power converter and on the other side to ground. Alternatively, in the example in Figure 4, the Qss switching system is electrically connected on one side to the output of the power converter and on the other side to the load. Furthermore, the switching system may preferably include one (illustrated in Figure 2) or two safety switches in series (illustrated in Figures 3 and 4). The safety switch may consist of a transistor, in particular a MOSFET. In Figures 2 and 3, the Qss switching system is positioned to loop back the output current of the power converter; for this purpose, the Qss switching system is connected between a ground of the voltage converter and a ground of the component at the converter's output, in particular a ground of a low-voltage vehicle battery.In Figure 4, the Qss switch system is positioned directly at the output of the power converter, with the connection of the voltage converter ground and the ground of the component at the converter output being made elsewhere (not shown). Furthermore, in Figures 2 and 3, the Qss switch system is, for example, connected between the terminals of two capacitors of a 2TT-type differential mode filter. In Figure 4, the Qss switch system is, for example, connected at the output of a TT-type differential mode filter.

[0028] As illustrated in Figures 2 to 4, the invention proposes, in particular, to use the safety switch(s), the safety switch being a very common device at the output of power converters, to measure the output current intensity lout. Specifically, by estimating the resistance of the switching system Qss and measuring a voltage drop Vss across the terminals of the switching system Qss, it is possible to deduce the output current intensity lout by applying Ohm's law.

[0029] However, the resistance of the switching system Qss is generally variable depending on the junction temperature of the switching system Qss. For example, a realistic temperature range for the switching system is between 25°C and 150°C. Over this temperature range, the resistance of the switching system can double. It is therefore necessary to consider the influence of the junction temperature when estimating the output current.

[0030] To this end, as illustrated in Figures 2 to 4, the power converter 1 according to the invention comprises a voltage measuring device adapted to measure the voltage drop Vss across the terminals of the switching system Qss, a temperature measuring device 12 adapted to measure a representative temperature corresponding to the junction temperature of the switching system Qss or to the temperature of an element in thermal contact with the switching system Qss, and a calculation module 13 configured to estimate the current intensity output current lout as a function of representative temperature and voltage drop Vss across the terminals of the switching system Qss.

[0031] The present invention therefore offers the considerable advantage of enabling the measurement of the output current of the power converter without requiring the addition of a measuring shunt or a Hall effect sensor, but rather by using the safety switches and temperature measurement devices already present in most power converters. Consequently, compared to using a measuring shunt, the present invention does not induce additional power losses, and therefore has little or no impact on the efficiency of the power converter. Furthermore, compared to the solution using a Hall effect sensor, the implementation of the invention does not require mechatronic integration, thus improving the compactness of the power converter. Therefore, the solution proposed in the invention is inexpensive and easy to implement from an industrial manufacturing perspective.

[0032] Advantageously, the representative temperature of the power converter measured by the temperature measuring device corresponds directly to the junction temperature of the switching system.

[0033] Alternatively, the temperature measurement device can advantageously be configured to measure the temperature, known as the representative temperature, of an element in direct thermal contact with the switching system, such as a suitable coolant for cooling the switching system, an electronic board to which the switching system is mounted, or a housing covering the switching system. It is important to note that at thermal equilibrium, the representative temperature is, in particular, equivalent to the junction temperature of the switching system. An equivalent temperature is understood to mean that the junction temperature depends on the representative temperature. Thus, the junction temperature can be equal to, or a function of, the representative temperature, notably through the use of a suitable model of the junction temperature as a function of the representative temperature.

[0034] In general, with reference to Figures 2 to 4, the power converter 1 comprises a switching cell arranged in a half-H-bridge structure, the half-H-bridge being a circuit for controlling the polarity across the load. As is known, a half-H-bridge has an upper and a lower branch. An upper branch of a half-H-bridge connects a terminal of the circuit controlled by the half-H-bridge to an upper terminal of the half-H-bridge, via an upper switching element Q1, the upper terminal of the half-H-bridge being connected to an upper terminal of the voltage source. Conversely, a lower branch of a half-H-bridge connects the terminal of the circuit controlled by the half-H-bridge to A lower terminal of the H-bridge is connected via a lower switching element Q2, the lower terminal of the H-bridge being connected to ground. The H-bridge is supplied with a voltage between ground and its upper terminal to deliver an output voltage to the system. At least one arm 11 is connected on one side to the circuit terminal controlled by the H-bridge and on the other side to the load.

[0035] This at least one arm may advantageously consist of three arms. In this case, the current measurement can be performed on a portion or all of the output currents of the three arms.

[0036] According to another aspect of the invention, the invention relates to a method for estimating the output current of the power converter described above.

[0037] With reference to Figure 1, the method according to the invention, implemented by the calculation module, comprises: - the acquisition E1 of the voltage drop Vss and the representative temperature T, the voltage drop Vss and the representative temperature T being in particular recorded in the calculation module as variables; - during a first measurement, the initialization E2 of the junction temperature Tss of the switch system as a function of the representative temperature T, in particular by setting that Tss is equal to T; - the determination E3 of the resistance Rss of the switch system, the resistance Rss being estimated as a function of the junction temperature Tss of the switch system; - the determination E4 of the intensity of the output current lout from the voltage drop Vss and the resistance Rss of the switching system, in particular using Ohm's law according to the following equation lout = Vss / Rss.

[0038] The process has the advantage of implementing simple calculation operations, which consequently are economical in terms of computing resources.

[0039] As illustrated in Figure 1, the resistance Rss of the switch system is determined as a function of the junction temperature Tss, notably from thermoelectric behavior data of the switch system provided by the manufacturer. A common approximation for the resistance Rss of the switch system is to assume that the resistance Rss of the switch system varies linearly with the junction temperature Tss of the switch system. Thus, the resistance Rss of the switch system can be calculated using the following equation: [Math 1] Rss = Rss_ref x (1 + C x (Tss — Tref)) where C is a predefined temperature constant of the switch system and Rss_ref is a reference value of the resistance of the switching system corresponding to a reference temperature Tref, for example 25°C. The constant C is preferably a temperature coefficient of resistance, representing the change in the electrical resistance of the switching system per unit change in temperature.

[0040] According to an example of the invention where the representative temperature, measured by the temperature measuring device, corresponds to the junction temperature of the switch system, the intensity of the output current lout is directly calculated.

[0041] According to another example of the invention, the representative temperature corresponds to the temperature of an element in thermal contact with the switching system. Therefore, in the case of thermal equilibrium, the representative temperature is equivalent to the junction temperature of the switching system. As a reminder, the equivalent temperature means that the junction temperature can be estimated based on the representative temperature. In this case, the calculated output current intensity is assumed to be correct.

[0042] However, under certain conditions, there may be an initial lack of thermal equilibrium between the switching system and the element in thermal contact with the switching system whose temperature is being measured. For example, in the case of a power conversion shutdown followed by a rapid restart, there may be a discrepancy between the junction temperature and the representative temperature. Thus, the initial value of the junction temperature Tss may be incorrect, which affects the determination of the output current lout. Therefore, it may be advantageous to adjust the estimated junction temperature Tss.

[0043] To this end, with reference to Figure 1, the method for estimating the output current of the power converter may preferably include the acquisition E1 of the voltage drop Vss across the terminals of the switching system Qss and the representative temperature T.

[0044] Then, the method for estimating the output current preferably includes the successive execution of the following steps for a number of iterations N: - the initialization E2 of the junction temperature Tss of the switch system to a value Tsso equal to the representative temperature (Tss0=T) during a first execution following the acquisition step E1; or during an iteration i, to a value Tssi determined at the end of the previous iteration; - the determination E3 of the resistance Rssi of the switch system estimated as a function of the junction temperature Tssi according to the following equation: [Math 2] RsSj = Rss_ref x (1 + C x (Tssj — Tref)); - the determination E4 of the intensity of the output current loutj according to the following equation: [Math 3] loutj = — ; RSSJ - the determination E5 of the power dissipated Pssi by the switching system as a function of the output current intensity lout and the resistance Rssi of the switching system Qss, in particular according to the equation [Math 4] Pssj = (louti) 2 x RSS ( ; - the E6 update of the Tss junction temperature i+i estimated according to the following equation, [Math 5] Tss i+1= T + Pssj x Rth, where Rth is a given thermal resistance between the junction of the switching system and the element in thermal contact with the switching system at the representative temperature T. Such a thermal resistance can be determined beforehand during a circuit calibration step, or from information regarding the dimensions of the contact surface between the switching system and the element in thermal contact with the switching system, and / or the material of the switching system and the element in thermal contact with the switching system, and / or a cooling fluid flowing through the element in thermal contact with the switching system. Thermal resistance is generally expressed in °C / W or K / W.

[0045] This iterative update of the estimated junction temperature Tss advantageously allows convergence towards the actual value of the power converter's output current. Furthermore, the number of iterations N is preferably between 5 and 15, preferably 10.

[0046] In summary, the present invention proposes a power converter having a means for measuring electric current and an associated method, using the safety switch(es), thus making it possible to reduce the size of the power converter while limiting the impact of the current measurement means on the efficiency of the power converter.

Claims

DEMANDS 1. Power converter (1), in particular configured for installation in an electric or hybrid motor vehicle, comprising: at least one arm (11) through which an output current from the power converter (1) flows and which is configured to be connected to a load; a switching system (Qss) arranged in series with said at least one arm (11) such that the switching system (Qss) is through which the output current flows; a voltage measuring device adapted to measure a voltage drop Vss across the terminals of the switching system (Qss); a temperature measuring device (12) adapted to measure a representative temperature T corresponding to the junction temperature Tss of the switching system (Qss) or to the temperature of an element in thermal contact with the switching system (Qss);a calculation module (13) configured to estimate the intensity of the output current lout as a function of the representative temperature T and the voltage drop Vss across the terminals of the switching system (Qss).; 2. Power converter (1), according to claim 1, characterized in that the switching system (Qss) comprises at least one safety switch.

3. Power converter (1), according to any one of the preceding claims, characterized in that the temperature measuring device (12) is configured to measure the temperature of a cooling fluid Tfluid suitable for cooling the switching system (Qss).

4. Power converter (1) according to any one of the preceding claims, characterized in that said at least one arm (11) consists of three arms.

5. Power converter (1) according to any one of the preceding claims, characterized in that the switching system (Qss) consists of a MOSFET.

6. Power converter (1) according to any one of the preceding claims, being a DC-DC power converter.

7. Method for estimating the output current of a power converter (1) comprising a switching system (Qss) through which the output current flows, a device voltage measurement adapted to measure a voltage drop Vss across the terminals of the switching system (Qss), a temperature measurement device (12) adapted to measure a representative temperature corresponding to the junction temperature Tss of the switching system (Qss) or to the temperature of an element in thermal contact with the switching system (Qss), a calculation module (13), the method, implemented by the calculation module (13), comprising: the acquisition (E1) of the voltage drop Vss and the representative temperature T; during a first measurement, the initialization (E2) of the junction temperature Tss of the switching system (Qss) as a function of the representative temperature T; the determination (E3) of the resistance Rss of the switching system (Qss), the resistance Rss being estimated as a function of the junction temperature Tss of the switching system (Qss);the determination (E4) of the intensity of the output current lout from the voltage drop Vss and the resistance Rss of the switching system (Qss).; 8. Method according to the preceding claim, characterized in that the determination of the resistance Rss of the switch system is carried out according to the equation [Math 1] Rss = Rss_ref x (1 + C x (Tss - Tref)) , where C is a temperature constant of the switch system (Qss) and Rss_ref is a reference value of the resistance of the switch system (Qss) corresponding to a reference temperature.

9. Method according to claims 7 or 8, the representative temperature T corresponding to the temperature of an element in thermal contact with the switching system (Qss), characterized in that it comprises, after the acquisition step (E1) of the voltage drop Vss and the representative temperature T, the successive execution of the following steps by the calculation module (13) for a number of iterations N: during a first execution following the acquisition step (E1), the initialization (E2) of the junction temperature Tss of the switching system (Qss) to a value Tsso equal to the representative temperature T, or during an iteration i, the initialization (E2) of the junction temperature Tss to a value Tssi determined at the end of the previous iteration; the determination (E3) of the resistance Rssi of the switch system (Qss) estimated as a function of the junction temperature Tssi of the switch system (Qss) according to the equation [Math 2] Rss;= Rss_ref x (1 + C x (Tssj - Tref)); the determination (E4) of the intensity of the output current I or according to the equation [Math 3] T tou 4t- ; Vss ■ 1 = — Rssj, the determination (E5) of the power dissipated Pssi by the switching system (Qss) as a function of the output current intensity lou and the resistance Rssi of the switching system (Qss); the update (E6) of the junction temperature Tssi according to the following equation, [Math 4] Tss i+1 = T + Pss jx Rth , where Rth is a given thermal resistance between the junction of the switching system (Qss) and the element in thermal contact with the switching system (Qss) exhibiting the representative temperature T.

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