Power converter and electric vehicle

Abstract

The present disclosure describes an electric vehicle comprising: an electric machine for propelling the vehicle; a battery providing electric power for powering the electric machine; and a powertrain coupling the electric power of the battery to the electric machine, wherein the powertrain comprises a switched mode voltage converter for converting the voltage of at least a portion of the electric power, the switched mode voltage converter comprising at least one pair of transistors coupled to an inductor operating as a switched energy storage element for converting the voltage and an overcurrent monitor configured to detect an overcurrent condition in at least one of the pair of transistors, the overcurrent monitor configured to compare an electrical measurement of the at least one of the transistors to a threshold value and generate a fault signal when the overcurrent monitor receives an indication that the at least one of the transistors is conducting and the electrical measurement exceeds the threshold value.

Description

Technical Field

[0001] The present invention relates to a power converter and an electric vehicle including the power converter, and particularly to a switch-mode power converter, for example, which can be arranged to convert at least a portion of the kinetic electrical power of an electric vehicle. Background Technology

[0002] Electric power systems consisting of one or more battery modules are typically used to power vehicles, boats, small aircraft and other modes of transportation, as well as industrial applications such as mining vehicles and equipment. The flexibility of such systems also makes them attractive as mobile power sources for both home and industrial use. In all these systems, it is generally desirable to convert the local DC voltage output from one or more battery modules to a different DC voltage required by the power unit in the vehicle or other load units in the home and industrial systems. It may also be desirable to convert the DC voltage output from one or more batteries to AC voltage, which can occur in inverters that supply AC voltage to the drive motors in electric vehicles.

[0003] Figure 1 An electric vehicle 10 is schematically shown in a plan view. The electric vehicle 10 includes a powertrain 12 comprising one or more electric motors 14 for driving wheels 16 or other drive elements of the vehicle, optionally via a mechanical transmission 18, and one or more batteries 20 for providing power current to the motors 14. To regulate the power current delivered to the one or more motors 14 in the correct manner, the powertrain 12 also includes power electronics 22, which may itself include one or more DC-DC converters 23, one or more DC-AC inverters 24, and other components. Various electronic systems may be located within the electric vehicle 10 and optionally at least partially outside the electric vehicle 10 to provide proper monitoring and / or control of the powertrain; for example, a battery management system 25 may monitor and maintain the state of the battery 20, and a powertrain electronic control unit 26 may control the power electronics 22 and the motors 14.

[0004] More specifically, such as Figure 1As shown, one or more batteries 20 provide DC power to one or more DC-DC power converters 23. Each of the one or more power converters 23 provides a DC-DC conversion from a first voltage to a second voltage of the battery 20 for use by one or more inverters 24. In a vehicle, the first voltage is typically higher than the second voltage, and the voltage conversion is typically achieved by carefully controlling the switching operation of power semiconductors such as MOSFETs. The inverters 24 convert the second DC voltage output from the power converters 23 into an AC voltage to supply to the motor 14 used for vehicle power drive. Typically, the inverters and DC-DC power converters can be arranged to operate in both directions to provide power using battery power or to charge the battery using the movement of the vehicle.

[0005] A key component of DC-DC power converters and inverters is the switching power semiconductor. Failure of these power semiconductors can be caused by a variety of reasons. The aim is to address the problems and limitations of existing technologies. Summary of the Invention

[0006] This disclosure relates to apparatus and methods for preventing the drain-source current of a MOSFET from exceeding safe or desired values, for example, in the event of a fault in the surrounding circuitry. The apparatus can be implemented in electric vehicles.

[0007] Therefore, the present invention provides an electric vehicle comprising: an electric motor for propelling the vehicle; a battery for providing electrical power to the electric motor; and a power transmission system for coupling the electrical power from the battery to the electric motor. The power transmission system includes a switch-mode voltage converter arranged to convert the voltage of at least a portion of the electrical power. The switch-mode voltage converter includes at least one pair of transistors coupled to an inductor operating as a switching energy storage element for voltage conversion. An overcurrent monitor is configured to detect an overcurrent condition in at least one of the transistors in the pair, the overcurrent monitor being configured to compare an electrical measurement or sensed value of at least one of the transistors in the pair with a threshold, and to generate a fault signal when the overcurrent monitor receives a signal and / or indication that the transistor is conducting and the electrical measurement or sensed value exceeds the threshold. The electrical measurement can be a sensed voltage or current indicating the voltage or current of at least one of the transistors in the pair. In embodiments, the electrical measurement can be a sensed voltage or current based on the voltage or current at the drain terminal of at least one of the transistors in the pair. The threshold can be based on the voltage or current sensed at the source terminal of at least one of the transistors in the pair. In this way, the drain-source voltage or current on at least one of the transistors in the pair can be monitored.

[0008] The overcurrent monitor can also be configured to shut down the voltage converter when a fault signal is generated.

[0009] Fault signals may be latched. For example, a fault signal can be latched by storing it in a memory element such as a trigger. The latched fault signal can continue to shut down the power stage until it is reset by the main system controller.

[0010] A voltage converter controller or PWM controller can be arranged to control the switching of transistors in the voltage converter. The voltage converter controller or PWM controller can be arranged to send an indication or signal indicating that at least one transistor is on to an overcurrent monitor. The indication of at least one transistor being on can be a desaturation enable signal.

[0011] The indication that at least one transistor is turned on may include a windowed signal between at least one transistor in a pair of transistors of the voltage converter and the voltage converter controller turning off at least one transistor in the pair of transistors of the voltage converter.

[0012] A signal indicating that at least one transistor is turned on can be provided after a time delay following the turn-on of the voltage converter transistor by the voltage converter controller.

[0013] The time delay can be less than or equal to 20 ns (nanoseconds), less than or equal to 50 ns, or less than or equal to 100 ns.

[0014] The time interval can be adjusted.

[0015] The voltage converter controller can be configured to receive a fault signal from an overcurrent monitor and shut down the voltage converter when the fault signal is received.

[0016] A voltage converter controller can be configured to receive control signals to control the on and off states of transistors in a voltage converter for voltage conversion. The voltage converter controller may include logic circuitry arranged to invert a fault signal and perform an AND operation on the control signal and the inverted fault signal, such that the voltage converter controller turns off the transistor when the fault signal indicates an overcurrent condition at the transistor.

[0017] The electrical measurement or sensed value of at least one of the transistors in the pair may include sensing or measuring the voltage indication or current or voltage at the transistor input.

[0018] An overcurrent monitor may include a comparator for comparing the measured or sensed voltage with a threshold.

[0019] An overcurrent monitor may include a logic gate configured to perform an AND function. The logic gate may be configured to receive a first input and a second input from a comparator, the second input being an indication of transistor on. The logic gate may be configured to provide an output, such as a high or 1 output, as a fault signal when the measured or sensed value exceeds the threshold and an indication or signal of transistor on is received.

[0020] The voltage measurement or sensed value at the transistor input terminal can be the voltage measurement at the transistor drain terminal. This measurement or sense can be performed using a blocking diode in a voltage divider.

[0021] An overcurrent monitor can be configured to provide a test voltage lower than the voltage conversion voltage to perform electrical measurements or sensing and test at least one transistor when the battery is not supplying power to the voltage converter. The test voltage can be pulsed on at any time, regardless of whether the battery is powered on. This can be combined with a pulse signal indicating transistor on. In this way, the transistor can be pulse-tested even when the battery is off, thus enabling effective continuous monitoring of the power converter.

[0022] The test voltage can be less than 50V, for example, between 10V and 30V, or about 20V.

[0023] The transistor can be a MOSFET, such as a SiC MOSFET.

[0024] The voltage converter can be a buck-boost voltage converter.

[0025] The voltage converter can be a DC-DC converter or an inverter.

[0026] The present invention also provides a switch-mode voltage converter, comprising: at least one pair of transistors coupled to an inductor that operates as a switching energy storage element for voltage conversion; and an overcurrent monitor configured to detect an overcurrent condition in at least one of the transistors in the pair, the overcurrent monitor being configured to compare an electrical measurement or sensed value of at least one of the transistors in the pair with a threshold value, and to generate a fault signal when the overcurrent monitor receives a signal or indication that at least one of the transistors in the pair is turned on and the electrical measurement or sensed value exceeds the threshold value. The voltage converter may also include any one or more of the features listed in the preceding paragraphs related to a voltage converter in a vehicle.

[0027] The present invention also provides a method for overcurrent control in a switch-mode voltage converter for converting at least a portion of the power in an electric vehicle powertrain system, the switch-mode voltage converter including at least a pair of transistors coupled to an inductor operating as a switching energy storage element for voltage conversion, the method comprising: comparing an electrical measurement value of at least one of the transistors in the pair with a threshold; and generating a fault signal when an enable signal indicates that at least one of the transistors in the pair is turned on and the electrical measurement value exceeds the threshold.

[0028] The method may also include: turning off at least one of the transistors in the pair when a fault signal is generated.

[0029] The present invention also provides an electric vehicle, comprising: an electric motor for propelling the vehicle; a battery for providing motive power to the electric motor; and a powertrain system for coupling the motive power from the battery to the electric motor, wherein the powertrain system includes a switch-mode voltage converter arranged to convert the voltage of at least a portion of the motive power, the switch-mode voltage converter including at least a pair of transistors coupled to an inductor operating as a switching energy storage element for voltage conversion, and an overcurrent monitor configured to continuously detect overcurrent in at least one of the transistors in the pair, the overcurrent monitor being configured to compare an electrical measurement value of at least one of the transistors in the pair with a threshold value, the overcurrent monitor providing a test voltage for performing an electrical measurement on at least one of the transistors in the pair when the battery (or motor) is not supplying power to the voltage converter, performing the electrical measurement when the transistor is turned on by a controller pulse, and generating a fault signal when the transistor is turned on and the electrical measurement value exceeds the threshold value. The voltage converter with overcurrent control can alternatively be used in scenarios different from the electric vehicle powertrain system.

[0030] This invention can be applied to various MOSFET applications, including switch-mode power converters such as DC-DC buck-boost, AC-AC, AC-DC, and DC-AC converters. Applications include automotive and mining vehicle powertrains, solar and wind power conversion, and large-scale energy storage systems. Attached Figure Description

[0031] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, wherein: Figure 1 An electric vehicle is shown, along with its powertrain system; Figure 2 This is a detailed circuit diagram of a DC-DC voltage converter; Figure 3 This is a circuit diagram of an overcurrent monitor according to an embodiment of the present invention; Figure 4It is a logic table that displays the combination of the output of the PWM controller's 0 / 1 inputs and the 0 / 1 values ​​of the fault signal; Figure 5 It is a timing diagram showing the on and off of various voltages related to PWM control and overcurrent detection; Figure 6 This is a flowchart of a method for detecting overcurrent in a power converter according to an embodiment of the present invention; and Figure 7 It is a logic table that shows when a fault signal (high) is generated based on the values ​​of the enable signal and the drain voltage. Detailed Implementation

[0032] As previously stated, this disclosure addresses the challenge of preventing current through one or more transistors from exceeding safe or ideal values ​​in voltage converter circuits, as may be found in electric vehicles. In a particular example, the transistor is a MOSFET, and the current is a drain-source current. In the event of a fault in the surrounding circuitry, the drain-source current may exceed the safe voltage. The result of such a fault is an increase in the drain-source current, and therefore an increase in the drain-supply voltage across the MOSFET. This disclosure provides a solution for detecting a voltage rise to a level indicating a fault that requires action in the form of turning off the MOSFET (preferably keeping it off). However, simply detecting the overvoltage is insufficient, as the voltage is already high as long as the MOSFET is off.

[0033] Before describing the invention in detail, it is necessary to consider the circuit diagram of the DC-DC voltage converter 23, such as... Figure 2 As shown. Multiple such voltage converters can be arranged in parallel to either step down or step up the voltage. By arranging the voltage converters in parallel, the voltage processed by the converters can be distributed across the converters, such that the total voltage processed by all the converters in parallel is greater than the voltage processed by each individually. This allows for the processing of higher voltages without damaging the voltage converters.

[0034] exist Figure 2 In the circuit diagram, the voltage converter is shown as a buck-boost converter. Other voltage converters can be used, and the invention described herein can be applied accordingly. Although we generally consider... Figure 2 The converter shown provides voltage conversion from voltage rail V1 on the left to voltage rail V2 on the right, which is the case when providing power to drive a motor, but the voltage converter can also operate in reverse to charge a battery.

[0035] The buck-boost converter can be a four-transistor buck-boost converter, and preferably a four-MOSFET buck-boost converter. Other power converter components or switching units can be used instead of MOSFETs, such as other types of transistors. However, for the applications described herein, MOSFETs are preferred, especially SiC MOSFETs, because their switching speed is faster than that of Si MOSFETs, resulting in higher power delivery efficiency. Figure 2 In the diagram, the four MOSFETs are identified by reference numerals 112, 113, 142, and 143. Another key component of the buck-boost converter is the reactance component. Figure 2 The middle one is inductor 120.

[0036] Four MOSFETs are arranged in two pairs. MOSFET module 110 includes a first pair of MOSFETs 112 and 113. Second MOSFET module 140 includes a second pair of MOSFETs 142 and 143. Two voltage converter controllers, VCC1 and VCC2, are shown in the figure and are identified by reference numerals 104 and 106. These may also be referred to as power converter controllers.

[0037] Voltage converter controller 104 sends signals to the first MOSFET module 110 to control the on / off switching of MOSFETs 112 and 113 for switch-mode voltage conversion. Voltage converter controller 106 sends signals to the second MOSFET module 140 to control the on / off switching of MOSFETs 142 and 143 for switch-mode voltage conversion. Voltage converter controllers 104 and 106 receive signals regarding the voltage required by the main controller in response to vehicle and driver requests. The voltage converter controllers may form part of a PWM controller.

[0038] The MOSFETs in each pair are connected in series. One side of inductor 120 is connected to the first node n1 between the two MOSFETs 112 and 113 of the first MOSFET module. The other side of the inductor is connected to the second node n2 between the two MOSFETs 142 and 143 of the second MOSEFT module.

[0039] The buck-boost converter device is configured to convert from a first voltage V1 to a second voltage V2, wherein the first voltage V1 is at... Figure 2 The left side displays the voltage on the power rail / line in the upper left corner, and the second voltage V2 is... Figure 2The right side shows the voltage on the power rail / line in the upper right corner. The drain terminal of MOSFET 112 is connected to the V1 voltage, and its source terminal is connected to node n1, which in turn is connected to the drain of MOSFET 113. The source of MOSFET 113 is connected to the ground rail / line 130. The gates of MOSFETs 112 and 113 are controlled by a signal from the voltage converter controller 104, which can be provided to the MOSFETs via a MOSFET module board forming part of the MOSFET module 110. On the left side of the circuit diagram is a capacitor C3 connected between the V1 voltage rail and the ground rail 130. Capacitor C3 is an output smoothing capacitor used to smooth voltage ripple on the V1 rail, especially when power returns to the V1 rail. Additionally, capacitor C1 is connected from the drain terminal of MOSFET 112 to the source terminal of MOSFET 113. Capacitor C1 is a buffer capacitor used to suppress voltage spikes and ripples that may occur when the MOSFET is turned on and off.

[0040] Figure 2 The right side is a partial mirror image of the left side. MOSFET module 140 includes MOSFETs 142 and 143. The drain terminal of MOSFET 142 is connected to the V2 voltage, and its source terminal is connected to node n2, which in turn is connected to the drain of MOSFET 143. The source terminal of MOSFET 143 is connected to the ground rail / line 130. The gates of MOSFETs 142 and 143 are controlled by a signal from voltage converter controller 106, which can be provided to the MOSFETs via a MOSFET module board forming part of MOSFET module 140. The far right of the circuit diagram may be capacitor C4 connected between the V2 voltage rail and the ground rail 130. Capacitor C4 is an output smoothing capacitor used to smooth voltage ripple on the V2 rail when power is supplied to it. Additionally, capacitor C2 is connected from the drain terminal of MOSFET 142 to the source terminal of MOSFET 143. Capacitor C2 is also a buffer capacitor used to suppress voltage spikes and ripples that may occur when the MOSFETs are turned on and off. Sensors may be provided on both sides of the circuit for measuring various voltages, currents, and temperatures.

[0041] Figure 2 The control line or bus 102 used to send control signals from the main controller to the voltage converter controllers 104, 106 is also shown.

[0042] We now describe the operation of the buck-boost converter. MOSFETs are turned on in pairs. When MOSFETs 112 and 143 are on, voltage V1 is applied across inductor 120, and energy is stored in the inductor. Current flows and increases after turn-on, flowing through MOSFET 112, inductor 120, and MOSFET 143. During this period, MOSFETs 113 and 142 are off. The switching of the MOSFET pairs is complementary, so when MOSFETs 112 and 143 are off, MOSFET 113 is on with MOSFET 142. When this occurs, the energy stored in the inductor causes current to flow through MOSFETs 113 and 144. After MOSFETs 113 and 142 are turned on (and MOSFETs 112 and 143 are turned off), the current will slowly decrease. Through this and other switching operations, the buck-boost converter operates similarly to a switch-mode power supply, which can be used to increase or decrease voltage. Specifically, the operation is that of a buck-boost bidirectional converter, and it can operate in voltage, current, or power control modes.

[0043] Figure 2 The converter device can be used to output a voltage on the V2 rail that is higher or lower than the input voltage rail V1 (i.e., boost or buck), and power can flow in either direction. Example voltages for V1 and V2 can be 1500V and 2100V, or 1500V and 700V. Multiple stages can be configured to handle power from 100kW (kilowatts) to 10MW (megawatts), such as a peak power of 600kW or 3MW.

[0044] Figure 2 One challenge in circuitry is preventing the MOSFET drain-source current from exceeding safe or ideal values, which can occur if the surrounding circuitry fails. Possible failures could include electrical short circuits or other faults in the load, transient or other overvoltage events in the battery power supply, controller malfunction causing the MOSFET to turn on in both branches simultaneously (a phenomenon known as "shoot-through"), inductor saturation, excessively long switching cycles causing the inductor to be built too far, and potential failure of another MOSFET in the converter (such as another branch).

[0045] Prior to the use of SiC-MOSFETs, Si insulated-gate bipolar transistors (IGBTs) were used. However, the high switching speed and power handling capability of SiC MOSFETs mean they are increasingly being preferred over Si IGBTs. SiC MOSFETs have different, more stringent short-circuit protection requirements. The smaller device area of ​​the SiC MOSFET die means it has poorer heat dissipation during overcurrent events, which can lead to die damage. Furthermore, SiC MOSFETs operate differently from IGBTs. IGBTs operate in the saturation region during normal operation. Under overcurrent conditions, the current increases in the desaturation region, but is somewhat self-limiting. IGBTs have better heat dissipation characteristics than MOSFETs, which also means that overcurrent protection circuits have sufficient time to conduct.

[0046] Traditionally, IGBT overcurrent protection circuits are based on RC circuits. This means the protection circuit can be configured to turn on relatively slowly. Fast turn-on is undesirable because the voltage level is high whenever the IGBT turns off. Therefore, the RC circuit arrangement for desaturation detection provides a time delay when reading the drain voltage. The sensed drain voltage is input to a comparator to check if the voltage exceeds a threshold. Desaturation detection techniques for IGBTs are well studied, but the delay is hardwired into the circuit and can be affected by drift, errors, and inaccuracies.

[0047] SiC MOSFETs operate differently from IGBTs. SiC MOSFETs operate in the linear ohmic region during normal turn-on operation, but current accumulates rapidly during overcurrent events. Furthermore, the smaller chip size means the device heats up more quickly. This means that the RC protection circuitry used in IGBTs needs to react faster and have reduced delays. However, MOSFETs can exhibit switching noise lasting for several nanoseconds after turn-on, meaning that if the time constant of the RC circuit is reduced too much, the transient switching noise will be detected as an overcurrent condition. Therefore, improved overcurrent protection circuitry for SiC-MOSFETs is desired.

[0048] Figure 3 An overcurrent monitor 200 according to an embodiment of the present invention is shown. The overcurrent monitor may include two parts. The first part 200a of the overcurrent monitor may be a monitor or an overcurrent detection side. The second part 200b of the overcurrent monitor may be used to provide feedback to control the switching of a MOSFET. Although MOSFETs do not have a desaturation region like IGBTs, the term desaturation is commonly used in the context of appropriate overcurrent conditions.

[0049] like Figure 3The overcurrent monitor 200 shown can be applied to any MOSFET, transistor, or other power converter unit in a switch-mode voltage converter. For example, the overcurrent monitor 200 can be applied to... Figure 2 Any one of MOSFETs 112, 113, 142, and 143. Figure 3 In the example, an overcurrent monitor is applied to MOSFET 112 of MOSFET module 110. Figure 3 Not shown in the middle Figure 2 The voltage converter includes various other components, including an inductor, a capacitor, and two other MOSFETs. The overcurrent monitor 200 includes a comparator 202 arranged to receive two inputs. The first input is the voltage V at the drain terminal of MOSFET 112. d The measured value. This is measured using a voltage divider that includes a resistor R and a diode D, such as... Figure 3 As shown. One side of resistor R is connected to voltage source V. TEST The voltage source V TEST For example, the drain voltage V when the battery is on can be approximately 20V higher than the expected voltage at the source terminal of the MOSFET 112. d It can be approximately 1500-2000V. The other side of the resistor is connected to node p, which is connected to the first input of the comparator and diode D. Diode D is a blocking diode, such as a Zener diode, which is connected to the drain terminal of MOSFET 112. The diode is reverse-connected to prevent the comparator from seeing drain voltage when the MOSFET is off (battery on). The second input of the comparator is connected to a voltage source. Figure 3 The middle is represented as V TH The voltage source is relative to the voltage V at the source terminal of MOSFET 112. s This setting is used to compare the voltage measured by the voltage divider at node p. V TH The value can be set to around 4V (when the battery and MOSFET are conducting under normal use). Although 4V is V TH This is the normal value, but it can be changed to set the exact current level required to trigger a fault. Voltage V TH A second voltage divider can be used for this purpose. The comparator can be configured such that when the first input from node p of the voltage divider is greater than (or equal to) the second input V... TH When the voltage exceeds a certain value, the logic output is high. This allows the comparator to detect when the voltage between the drain and source terminals of the MOSFET exceeds a certain value, which may indicate a high current level through the MOSFET, for example, a short circuit elsewhere in the voltage converter.

[0050] The overcurrent monitor also includes an AND gate 204. The output of comparator 202 is fed to one of the inputs of the AND gate. The other input of the AND gate provides an enable signal. The enable signal can be turned on and off and can be received from a controller, such as the controller of a voltage converter or a PWM controller. When the enable signal is on or goes high, the output of the AND gate is the same as the output of the comparator (high or low). When the enable signal goes low, the output of the AND gate also goes low. Figure 7 The logical table summarizes this operation. Figure 3 In this configuration, the output of AND gate 204 is marked as faulty. Therefore, it will only fail to register a fault if an enable signal is received and the detected drain voltage is higher than voltage V. TH A fault signal will only be output when the time is right.

[0051] On the input side of MOSFET module 110, a pulse-width modulation (PWM) signal is applied to MOSFET 112 to turn the MOSFET on / off, thereby providing the necessary power to the inductor and voltage converter. Back Figure 2 Each of the four MOSFETs will receive a properly timed PWM signal to turn the MOSFETs on or off as needed for the required voltage conversion. Figure 3 In this arrangement, the PWM signal is sent via AND gate 208. The fault signal received from AND gate 204 at the monitoring side 200a of the overcurrent monitor is provided to the control side of the MOSFET at overcurrent monitor 200b. The control side 200b of the overcurrent monitor includes an inverter or NOT gate 206 and another AND gate 208. The fault signal is inverted by the NOT gate and then reaches one input of AND gate 208. The other input of the AND gate is the PWM on / off signal of MOSFET 112. As previously mentioned, the fault signal is high when the MOSFET is turned on and the voltage at the MOSFET drain terminal exceeds a threshold. After the signal is inverted and combined with the PWM on / off signal at AND gate 208, the effect is as follows: Figure 4 The logic table is shown. The PWM signal is modified by AND gate 208. The PWM signal is typically turned on and off as needed for voltage conversion. However, AND gate 208 is modified so that the MOSFET will not turn on if an overcurrent fault is detected. This can... Figure 4 The table shows that when the "PWM input" signal is high and a fault exists, the "PWM output" signal is low. By applying the overcurrent monitor result to the MOSFET PWM control signal of the same MOSFET, the control is local and direct, meaning that other MOSFETs or power converters can continue to operate.

[0052] The enable signal applied to the AND gate 204 in the detector and detection section 200a of the overcurrent monitor can be set at a specific timing. As previously mentioned, the MOSFET may require time to stabilize after being turned on, so detecting an overcurrent condition directly after turn-on may result in a false alarm. The enable signal can be provided from the voltage converter controller (PWM controller) and timed to precisely follow the PWM turn-on specified time interval or delay. In a preferred arrangement, the delay can be approximately 50 ns, although shorter or longer delays, such as approximately 20 ns or approximately 100 ns, can be used. The delay can be set to a fixed time interval and can be set after testing to determine the optimal delay for a specific design of the power converter within the design load range. In some embodiments, the delay can be dynamically set and can be adapted to, for example, load and other conditions.

[0053] Figure 5 This is a timing diagram showing the on and off states of various voltages. At time t0, the MOSFET is off, as can be seen from the high drain voltage and the low gate driver signal PWM GD. At time t1, the PWM signal is on, as shown by the PWM GD going high, and the MOSFET drain voltage drops. The MOSFET drain voltage continues to drop and falls below V... TH This fall time is likely around 30ns. At time t2, after the MOSFET voltage stabilizes and the drain voltage decreases, the enable signal is turned on (e.g., ...). Figure 5 (The desaturation enable signal is shown in the diagram). This enable signal is asynchronous with the conduction of the PWM GD signal. The overcurrent monitor is now monitoring the overcurrent of the MOSFET. The drain voltage increases slightly after time t2. This could be due to heating in the device, or more typically, an increase in inductor current, thus increasing the drain current of the MOSFET. At time t3, the PWM signal turns off the MOSFET, as indicated by the PWM gate driver signal PWM GD going low. The drain voltage rises back to high, and the enable signal is also turned off as the gate driver signal goes low. At time t1', the cycle starts again, and the gate driver PWM GD signal turns on the MOSFET. The overcurrent monitor turns on after a delay of time t2'. However, in this cycle, the drain voltage increases to V. TH A current reading above the monitor threshold voltage indicates an overcurrent condition in the MOSFET. At time t4, when the overcurrent monitor detects that the drain voltage has exceeded V... TH When an overcurrent monitor generates or conducts a fault signal, the PWM gate driver signal is turned off to shut down the MOSFET. The enable signal can remain on until the PWM cycle ends and is turned off by the voltage converter controller.

[0054] Typical MOSFET switching time is approximately 10-25 kHz, while the typical rise time for current to turn on in SiC devices is approximately 30 ns.

[0055] As described above, once the overcurrent monitor is turned on by the enable signal, it remains active. This means the MOSFET can be turned off very quickly. This reduces any settling time and increases the speed at which overcurrent conditions are eliminated, compared to RC circuits, which may require time to react due to their time constant. This improved response speed is a particular advantage of the present invention, providing faster turn-off in overcurrent conditions.

[0056] In this embodiment, the overcurrent monitor does not use the RC circuit of the prior art. Instead, the monitor voltage source V... TEST The comparator can always be active. When the MOSFET is turned off, the blocking diode isolates the comparator from the drain voltage (which may be 1500V-2000V), which increases the stability of the control.

[0057] In another aspect of the invention, the same overcurrent monitoring circuit can also be used to perform power converter startup testing when no battery provides any high voltage. In this case, refer to Figure 2 The voltage on voltage rail V1 may be zero, just like before the battery is turned on. We mentioned before that V... TEST It can be set to be approximately 20V higher than the voltage at the MOSFET source terminal. V acts as an overcurrent monitor. TEST A power supply of approximately 20V is sufficient to turn on the MOSFET. Therefore, when an on-signal is applied to the gate from the PWM control, it can be effectively used to check if the MOSFET is turning on as expected. Approximately 20V can be applied to the drain of the MOSFET because the conduction direction of diode D allows this. Thus, by sequentially providing each MOSFET with a single short PWM pulse, for example, only a few milliseconds, they can be used to check if each MOSFET is responding correctly to the gate driver PWM GD signal and is not entering an overcurrent condition, such as when the battery is off. The power converter can turn its MOSFETs on and off to detect if 20V is grounded via a resistor divider to check if each MOSFET is operating correctly. As in normal operation, if an overcurrent is detected, a high fault signal is sent to AND gate 208. When the MOSFET is turned on with the PWM ON / OFF or PWM GD signal, the output of AND gate 208 will be low, thus stopping the gate from conducting.

[0058] The effect of normal and startup operation of an overcurrent monitor is that, when a fault is detected, a fault signal can continue to be supplied to the gate driver or PWM control signal (to prevent the MOSFET from turning on), thus the fault signal can be considered latched. This can be achieved by storing the fault signal in memory. For example, the fault signal can be fed into a flip-flop, which latches the fault signal until it is reset by the main system controller (e.g., when the fault is corrected). Another difference from the prior art is that the prior art effectively turns on the MOSFET every time and waits for the RC time to pass before detecting the fault and turning it off. Therefore, the prior art method is more likely to cause further and continuous damage to the MOSFET.

[0059] In the above arrangement, comparator 202 may be an operational amplifier. Other embodiments may use other components to perform the comparison and function of logic gates, such as a microprocessor and an AD converter.

[0060] We have already described the overcurrent monitor for MOSFET 112. A separate overcurrent monitoring circuit can be provided for each MOSFET. For example, a second overcurrent monitoring circuit can be provided for another MOSFET 113 in MOSFET module 110. Figure 2 The voltage converter 23 provides four overcurrent circuits, and each such converter can similarly have such monitoring circuitry.

[0061] As previously mentioned, MOSFETs are typically implemented in pairs of two MOSFETs or clusters of MOSFETs in a MOSFET module (in the latter, each MOSFET is actually composed of several identical MOSFETs controlled in parallel), with high-voltage / power connections for the drain, source, and inductor. The gate drive signal can originate from an interface board, which includes MOSFET driver circuitry (which may include amplifiers) located on the MOSFET module. Lower-power gate driver boards can be provided to receive control signals from a remote controller and pass them to the interface board; these control signals may include, for example, PWM timing passed to the interface board. Overcurrent detection circuitry and associated PWM control can be configured on the gate driver board, but can also be formed as part of the interface board, or as a board combining both.

[0062] Figure 6This is a flowchart of the overcurrent detection method of the present invention. In step 610, the overcurrent monitor compares the electrical measurement value of at least one transistor in a pair of transistors with a threshold. The measurement value may be a voltage measurement value to determine the voltage at the drain terminal of the MOSFET. The threshold may be a voltage corresponding to the condition of reaching or about to reach an overcurrent condition. In step 620, a fault signal is generated when the electrical measurement value exceeds the threshold and the overcurrent monitor receives an indication that the voltage converter is turned on. The indication that the voltage converter is turned on may be provided as an enable signal, for example from a voltage converter controller or PWM control. If a fault signal is generated, then in step 630, the transistor in the pair of transistors is turned off.

[0063] Although we have described a four-MOSFET buck-boost converter providing bidirectional power conversion above, an alternative converter with only two MOSFETs and a unidirectional configuration can also be provided. This converter is similar to... Figure 3 The converter shown excludes MOSFETs 142 and 143. The inductor output is directly connected to the output voltage line V2 across the smoothing capacitor C4. This type of converter can be called a buck converter. The unidirectional nature of the dual MOSFET converter means that power conversion is provided to the second voltage rail V2. Using a buck converter also reduces the voltage at V2 compared to V1.

[0064] Although specific embodiments of the invention have been described with reference to the accompanying drawings, those skilled in the art will recognize that variations and modifications can be made to these embodiments without departing from the scope of the invention as defined in the claims. For example, although the invention has been described in the context of vehicles, it can be applied to household and industrial mobile power supplies. Furthermore, while the invention has been described with reference to a DC-DC voltage converter, it is also applicable to other converters including inverters, such as inverters for converting DC voltage to AC to drive vehicle motors.

Claims

1. An electric vehicle, comprising: The electric motor used to propel the vehicle; A battery that provides power to the motor; as well as The power of the battery is coupled to the power transmission system of the motor. The powertrain system includes a switch-mode voltage converter arranged to convert the voltage of at least a portion of the power output. The switch-mode voltage converter includes at least one pair of transistors coupled to an inductor operating as a switching energy storage element for voltage conversion. An overcurrent monitor is configured to detect overcurrent in at least one of the pair of transistors, the overcurrent monitor being configured to compare an electrical measurement value of at least one of the pair of transistors with a threshold, and to generate a fault signal when the overcurrent monitor receives an indication that at least one of the pair of transistors is turned on and the electrical measurement value exceeds the threshold.

2. The electric vehicle according to claim 1, wherein, The overcurrent monitor is also configured to shut down the voltage converter or at least one of the pair of transistors when the fault signal is generated.

3. The electric vehicle according to claim 1 or 2, wherein, A voltage converter controller is configured to control the switching of transistors in the voltage converter, and the voltage converter controller is configured to send an indication to the overcurrent monitor that the voltage converter is turned on.

4. The electric vehicle according to claim 3, wherein, The indication of the voltage converter being turned on includes a windowed signal between at least one of the pair of transistors of the voltage converter being turned on by the voltage converter controller and at least one of the pair of transistors of the voltage converter being turned off by the voltage converter controller.

5. The electric vehicle according to claim 4, wherein, After a time delay following the turn-on of at least one of the pair of transistors of the voltage converter by the voltage converter controller, a signal indicating that the voltage converter is turned on is sent.

6. The electric vehicle according to claim 5, wherein, The time delay is less than or equal to 20ns, less than or equal to 50ns, or less than or equal to 100ns.

7. The electric vehicle according to claim 5 or 6, wherein, The time interval is adjustable.

8. The electric vehicle according to any one of claims 3 to 7, wherein, The voltage converter controller is configured to receive the fault signal from the overcurrent monitor and, upon receiving the fault signal, turn off at least one of the pair of transistors.

9. The electric vehicle according to claim 8, wherein, The voltage converter controller is configured to receive or generate a control signal to control the on and off of at least two transistors in the voltage converter for voltage conversion, and the voltage converter controller includes logic circuitry arranged to invert the fault signal and perform an AND function on the control signal and the inverted fault signal, such that when the fault signal indicates the overcurrent condition, the voltage converter controller turns off the transistors.

10. The electric vehicle according to any one of the preceding claims, wherein, The electrical measurements of at least one of the transistors in the pair include voltage measurements indicating the input current of the transistor.

11. The electric vehicle according to claim 10, wherein, The overcurrent monitor includes a comparator for comparing the measured voltage with a threshold.

12. The electric vehicle according to claim 10 or 11, wherein, The overcurrent monitor includes a logic gate configured to perform an AND function, the logic gate being configured to receive a first input and a second input from the comparator, the second input being an indication of the transistor being turned on, wherein the logic gate is configured to provide an output, the output being the fault signal, when the measured electrical value exceeds the threshold and an indication of the voltage converter being turned on is received.

13. The electric vehicle according to any one of claims 10 to 12, wherein, The voltage measurement at the input terminal of the transistor is the voltage measurement at the drain terminal of the transistor, and optionally, the measurement is performed using a blocking diode of a voltage divider.

14. The electric vehicle according to any one of the preceding claims, wherein, The overcurrent monitor is configured to provide a test voltage lower than the voltage conversion voltage to perform electrical measurements and test the at least one transistor when the battery is not supplying electrical power to the voltage converter.

15. The electric vehicle according to claim 14, wherein, The amplitude of the test voltage is less than 50V.

16. The electric vehicle according to any one of the preceding claims, wherein, The transistor is a MOSFET, such as a SiCMOSFET.

17. The electric vehicle according to any one of the preceding claims, wherein, The voltage converter is a buck-boost voltage converter.

18. The electric vehicle according to any one of the preceding claims, wherein, The voltage converter is a DC-DC converter or an inverter.

19. A switch-mode voltage converter, comprising: At least one pair of transistors coupled to an inductor, the inductor operating as a switching energy storage element for voltage conversion, and An overcurrent monitor is configured to detect overcurrent in at least one of the pair of transistors, the overcurrent monitor being configured to compare an electrical measurement value of at least one of the pair of transistors with a threshold, and to generate a fault signal when the overcurrent monitor receives an indication that at least one of the pair of transistors is turned on and the electrical measurement value exceeds the threshold.

20. A method for overcurrent control in a switch-mode voltage converter for converting at least a portion of the kinetic power in a powertrain system of an electric vehicle, the switch-mode voltage converter comprising at least a pair of transistors coupled to an inductor operating as a switching energy storage element for voltage conversion, the method comprising: The electrical measurement value of at least one of the pair of transistors is compared with a threshold. A fault signal is generated when the enable signal indicates that at least one of the pair of transistors is turned on and the electrical measurement value exceeds the threshold.

21. The method of claim 20, further comprising turning off at least one of the pair of transistors when the fault signal is generated.

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