EP4652657A1

EP4652657A1 - Method for operating a resistor-less high voltage precharge circuit

Info

Publication number: EP4652657A1
Application number: EP24700844.4A
Authority: EP
Inventors: Jacob William Green; Tissaphern Mirfakhrai; Rocendo Bracamontes Del Toro; Payam Naghshtabrizi; Tae Hyung Kim
Original assignee: Eaton Intelligent Power Ltd
Current assignee: Eaton Intelligent Power Ltd
Priority date: 2023-01-18
Filing date: 2024-01-12
Publication date: 2025-11-26
Also published as: WO2024153457A1

Abstract

A bidirectional circuit system that enables a bidirectional current flow between an input and output of a precharge circuit and methods of operating the bidirectional circuit system are provided. The bidirectional circuit system includes a resistor-less precharge circuit including a high-side switch and a low-side switch that provides as an output a constant DC current. The bidirectional circuit system also includes a controller coupled to the resistor-less precharge circuit and including control logic to control the high-side switch and the low-side switch to allow a bidirectional current flow between an input to the precharge circuit and the output. A method of operating the resistor-less precharge circuit in an open circuit condition is provided as well as a method of operating the resistor-less precharge circuit when the precharge circuit is connected to DC link capacitor and a load.

Description

METHOD FOR OPERATING A RESISTOR-LESS HIGH VOLTAGE PRECHARGE

CIRCUIT

Statement Regarding Government Funding:

[0001] This invention was made with government support under U.S. Army TARDEC Phase II project, contract number 2019140-141043. The Federal Government has certain rights to this invention.

BACKGROUND

[0002] Precharge circuits are often used to limit an inrush of current into a circuit of a high voltage system, for example. In the context of this application, high voltage is defined as 600 to 1200 V DC. Such high voltage systems include, but are not limited to, electric vehicles, on-board chargers, power supplies, DC microgrid controllers, and power distribution units. If not limited by a precharge circuit or other mechanism, the inrush of current may damage the system components of the circuit. For example, a current spike can cause contacts of a contactor to weld closed.

[0003] Precharge circuits for high voltage systems may be resistive or non-resistive. Resistive precharge circuits utilize a resistor to slowly charge a capacitor inside the circuit before powering up. Non-resistive precharge circuits, or resistor-less precharge circuits, use alternative methods and systems for charging the capacitor without utilizing a resistor which may introduce a lossy element that consumes power during normal operation. For example, a Tess lossy’, but energy limiting element, such as an inductor may be used in a non-resistive precharge circuit.

BRIEF SUMMARY

[0004] A bidirectional circuit system that enables a bidirectional current flow between an input and output of a precharge circuit and methods of operating the bidirectional circuit system are described.

[0005] A bidirectional circuit system includes a resistor-less precharge circuit including a high-side switch and a low-side switch that provides as an output a constant DC current. The bidirectional circuit system also includes a controller coupled to the resistor-less precharge circuit and including control logic to control the high-side switch and the low-side switch to allow a bidirectional current flow between an input to the precharge circuit and the output.

[0006] A method to control a precharge voltage at an output of a resistor-less precharge circuit is provided. The resistor-less precharge circuit includes a high-side switch, a low- side switch, and a charge storage device. The method includes measuring a voltage utilizing a voltage sensor at the output of the precharge circuit, precharging the charge storage device in the precharge circuit, wherein the charge storage device is connected at the output of the precharge circuit, and detecting, by a control system coupled to the precharge circuit, based on the measured voltage at the output of the resistor-less precharge circuit, an open circuit condition at the output of the precharge circuit. Responsive to the open circuit condition, operating by the control system the high-side switch and low-side switch to turn-off.

[0007] A method to operate a bidirectional circuit system is provided. The bidirectional circuit system includes a resistor-less precharge circuit including a high-side switch and a low-side switch connected to an inductor, a high voltage battery and an DC link capacitor. The method includes measuring an output voltage at an output of the resistor-less precharge circuit utilizing a voltage sensor, measuring a precharge current at the output of the resistorless precharge circuit utilizing a current sensor, connecting the DC link capacitor to the output of the resistor-less precharge circuit to receive the output voltage, controlling, by a control system coupled to the resistor-less precharge circuit, a current through the inductor by operating the high-side switch and the low-side switch based on the measured precharge current.

[0008] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0009] To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0010] FIG. 1 illustrates a circuit diagram of a resistor-less precharge circuit. [0011] FIG. 2 illustrates a method to control a precharge voltage at the output of a resistor-less precharge circuit in accordance with one embodiment.

[0012] FIG. 3 illustrates a method to operate a bidirectional circuit system in accordance with one embodiment.

DETAILED DESCRIPTION

[0013] A bidirectional circuit system that enables a bidirectional current flow between an input and output of a precharge circuit is described. The precharge circuit is resistor-less such that it uses an inductor to control the flow of current through the precharge circuit instead of a resistor. Methods of operating and controlling the bidirectional circuit system are also provided. In a resistive precharge circuit, there is no control of power to the load which is dictated by RC time constant of the precharge circuit. With the presented resistorless precharge circuit, because the current can be controlled through the inductor utilizing switches in the precharge circuit, the same time constant can be achieved independent of the load capacitance, e.g., a DC link capacitor. A broad range of load capacitances can be supported with the same time constant by operating the switches based on real-time measurements.

[0014] FIG. 1 illustrates a bidirectional circuit system. The bidirectional circuit system 102 includes a resistor-less precharge circuit 104 (shown to the left of dotted line) controlled by a control system 106. Referring to FIG. 1, bidirectional circuit system 102 can also include a battery 108, or other power source, that provides a high voltage, such as 600V DC, to the resistor-less precharge circuit 104. The bidirectional circuit system 102 is suitable for precharging a high voltage system such as an electric vehicle. The battery 108 provides DC power at the DC output 110 to a DC link capacitor 112 via circuitry controlled by the control system 106. In some cases, the capacitance of the DC link capacitor 112 is in a range of 1-1 OmF. An electromechanical switch 114 is included to provide selective galvanic isolation between battery 108 and the DC link capacitor 112 and a load 116 connected to the output of the bidirectional circuit system 102. The electromechanical switch 114 can be a relay, a contactor, a semiconductor device, etc. The opening and closing of electromechanical switch 114 are performed by the control system 106. In an embodiment, the resistor-less precharge circuit 104 is a solid state precharge circuit. [0015] Instead of a resistor, the bidirectional circuit system 102 includes switches 118 (high-side switch QI and low-side switch Q2), inductor 120, and a small (e.g., on the order of 10 pF) capacitor 122. The high-side switch QI and the low-side switch Q2 may be MOSFET devices. The high-side switch QI and the low-side switch QI may be positioned in a buck converter configuration. The high-side switch QI is connected to the positive terminal of the high voltage battery 108. The low-side switch Q2 is connected to ground. These electrical components (switches 118, inductor 120, and capacitor 122) enable a bidirectional current flow that can pull energy back into battery 108.

[0016] The control system 106 is coupled to the resistor-less precharge circuit 104. The control system 106 can control the high-side switch QI and the low-side switch Q2 to limit a flow of current through the inductor 120. Limiting the flow of current through the inductor 120 affects rate of voltage increase across the DC link capacitor 112. The control system 106 may be a microprocessor that can control the operation of the resistor-less precharge circuit 104. In some cases, the microprocessor can include state machines and other components.

[0017] For a bidirectional circuit system 102 such as shown in FIG. 1, in precharging operation, the DC link capacitor 112 receives the DC power from the battery 108 as filtered by electrical components controlled by control system 106 when the electromechanical switch 114 is closed. After sufficient charging of the DC link capacitor 112, the electromechanical switch 114 is opened and the bidirectional circuit system 102 is then ready to provide precharge to its load 116, at the DC output 110. Through operations of the control system 106, the DC link capacitor 112 can be charged according to method 300.

[0018] Capacitor 122 is also positioned to receive DC power from the battery 108.

However, capacitor 122 is mostly utilized for “no load” situations when the electromechanical switch 114 is closed into a no load condition. A current sensor 124 and/or a voltage sensor 126 each having a corresponding power source (not shown) may be positioned at the DC output 110 to measure a respective output current or output voltage at the DC output 110. The current sensor/voltage sensor provides a signal to the control system 106 to indicate the current/voltage, respectively, at the DC output 110. The output current and/or output voltage can be used by control system 106 in operating the switches 118. A voltage sensor (not shown) may also be positioned at the input of the resistor-less precharge circuit 104 to measure an input voltage, or voltage coming from the high voltage battery.

[0019] FIG. 2 illustrates a method to control the precharge voltage at the output of a resistor-less precharge circuit. Method 200 can be performed utilizing the resistor-less precharge circuit such as described in FIG. 1. The method 200 includes measuring (202) a voltage utilizing a voltage sensor at the output of the resistor-less precharge circuit, precharging (204) a charge storage device in the precharge circuit, wherein the charge storage device is connected at the output of the precharge circuit, and detecting, (206) by a control system coupled to the precharge circuit, based on the measured voltage, an open circuit condition at the output of the precharge circuit. Responsive to the open circuit condition, operating (208) by the control system, based on the measured voltage at the output of the resistor-less precharge circuit, the high-side switch to turn-off.

[0020] As described previously, when there is a no-load condition, e.g., the electromechanical switch 114 is in a closed state, and an open circuit condition exists, a charge storage device, such as capacitor 122, can be utilized to slow the precharge voltage ramp at the output of the resistor-less precharge circuit 104. The open circuit condition of the bidirectional circuit system 102 may be defined as when the high voltage battery 108 is connected to the precharge circuit and the high-side switch is turned-on such that the voltage at the output is increasing and there is no load. This situation can be a dangerous condition for a person that may not realize that the unconnected output of the precharge circuit has a high voltage. Thus, for safety purposes, the method 200 includes utilizing a small capacitor 122, e.g., approximately 10 pF, in the resistor-less precharge circuit 104 to precharge against until the control system 106 can detect the open circuit condition and react to the situation. The small capacitor 122 allows the inductor 120 to limit the current to the DC output 110. Once the control system 106 detects the open circuit condition, the control system 106 can turn-off the switching operation by opening the switches 118, high- side switch QI and low side switch Q2.

[0021] In order to detect the open circuit condition, the control system 106 utilizes the measured voltage, e.g., by voltage sensor 126, at the output of the resistor-less precharge circuit 104. For example, the control system 106 can detect a rapid increase of the output voltage as an indication of an open circuit condition. The control system 106 can determine the rapid increase in the output voltage by calculating a difference between a first voltage measured at a first time and a second voltage measured at a second time. For example, a rapid increase could mean that the difference between the second voltage at a second time and a first voltage measured at the first time divided by the elapsed time is approximately 100 V/ms. If the difference is above a threshold indicating the rapid increase in the output voltage, the control system 106 turns-off the high-side switch QI preventing a current flow to the DC output 110.

[0022] FIG. 3 illustrates a method to operate a bidirectional circuit system. Method 300 can be performed when utilizing the bidirectional circuit system such as described in FIG. 1. Method 300 includes measuring (302) an output voltage at the output of the precharge circuit utilizing a voltage sensor and measuring (304) a precharge current at the output of the precharge circuit utilizing a current sensor. Method 300 further includes connecting (306) the DC link capacitor 112 to the output of the resistor-less precharge circuit 104 to receive the output voltage. Method 300 further includes controlling (308) by a control system coupled to the resistor-less precharge circuit, a current through the inductor by operating the high side switch and the low side switch based on the measured precharge current.

[0023] Once the electromechanical switch 114 is closed by the control system 106, operation of the bidirectional circuit system 102 to control a flow of current through the resistor-less precharge circuit 104 can begin. Communication from other systems, e.g., other systems of an electric vehicle, are made to the control system 106 via CAN (computer aided network) messages. For example, a CAN message can be sent to the control system 106 to operate the bidirectional circuit system 102 to adjust a rate of charge to a load, e.g., DC link capacitor 112, in at least two different modes: a fixed rate precharge mode which specifies charging the DC link capacitor 112, to a precharge voltage over a period of time or a fixed voltage mode which charges the DC link capacitor 112 to a setpoint (fixed) voltage.

[0024] Operating the bidirectional circuit system 102 begins by measuring an input voltage to resistor-less precharge circuit 104 across the battery 108. A voltage sensor (not shown) is positioned between the positive terminal of the high voltage battery and ground may be utilized to measure the input voltage. The input voltage is communicated by the voltage sensor to the control system 106. [0025] A duty cycle is generated by the control system 106 for the switches 118, e.g., the high-side switch QI and the low-side switch Q2. A switching frequency, for example 100 kHz, can also be set by the control system 106. In the fixed rate precharge mode, the duty cycle is initially set to a minimum duty cycle, for example, approximately 5-7%, in order to limit the heat dissipation through the electrical devices. The duty cycle can be defined as the amount of time in a given time period that the device, e.g., the high-side switch QI and the low-side switch Q2, is turned-on. In some cases, the duty cycle is approximately 1 ms. In the fixed rate precharge mode, the duty cycle is increased over the requested period of time to 100% so that the switches 118 are completely turned-on. In the fixed voltage mode, the duty cycle is calculated to be the requested output voltage (as sent to the control system 106 by the CAN message) divided by the input voltage. The current at the DC output 110 is measured by the current sensor 124 every duty cycle.

[0026] The control system 106 controls the current through the inductor 120 by operating the high-side switch QI and the low-side switch Q2 based on the measured precharge current. Once the electromechanical switch 114 is closed, the control system 106 utilizes pulse width modulation (PWM) to operate the high-side switch QI and the low- side switch Q2 from the bidirectional resistor-less precharge circuit 104. In the fixed rate precharge mode, the control system 106 utilizes the PWM to adjust a rate of charge to the DC link capacitor 112 at the output of the resistor-less precharge circuit. This operational mode is replicated in the fixed voltage mode except the feedback control is changed from charging at a rate voltage versus time to a voltage hold setpoint mode.

[0027] The PWM includes operating, by the control system 106, the switches 118, during each duty cycle, by turning-on the high-side switch QI and turning-off the low side switch Q2 to allow the current to flow through the inductor 120 in a direction from the high-side switch QI to the output of the precharge circuit until the measured precharge current reaches a predetermined value. When the measured precharge current reaches the predetermined value at the output of the precharge circuit, the control system 106 operates the high-side switch QI and the low-side switch Q2 by turning-off the high side switch QI off and turning-on the low side switch Q2 on to allow the current to flow through the inductor 120 in a direction from the output of the precharge circuit to the low side switch Q2. The PMW is repeated for each duty cycle until the output voltage equals the setpoint voltage or the output voltage equals a precharge voltage for the set period of time. [0028] The output voltage is measured at the DC output 110 by voltage sensor 126 which communicates the value of the output voltage to the control system 106. The output voltage is measured approximately once every 100ms-l sec and communicated to the control system 106. For the fixed rate precharge mode, based on the measured output voltage, the PWM parameters, such as the duty cycle, can be adjusted to allow more or less current to flow through the inductor 120 in order to meet the rate of precharge voltage.

[0029] In some cases, the voltage rate, e.g., volts per second, is calculated. A first voltage is measured at a first time and a second voltage is measured at a second time. The voltage rate is calculated by taking a difference between the second voltage and the first voltage and dividing it by the elapsed time. When the voltage rate is above a threshold indicating a rapid increase, similar to the open circuit condition described with respect to method 200, the control system 106 turns-off the high-side switch QI and the low-side switch Q2 preventing a current flow to the DC output 110. In some cases, a short condition can be detected. For the short condition, the difference between the second voltage and the first voltage is close to zero over a plurality of duty cycles. In this case, the control system 106 turns-off the high-side switch QI and the low-side switch Q2 preventing a current flow to the DC output 110.

[0030] For the fixed rate precharge mode, when the output voltage is approximately, e.g., 95-99%, the measured input voltage the control system 106 turns-off the high-side switch QI and the low-side switch Q2 preventing a current flow to the DC output 110. In the fixed voltage mode, when the output voltage is the setpoint voltage, the control system 106 turns-off the high-side switch QI and the low-side switch Q2 preventing a current flow to the DC output 110. In some cases, in the fixed voltage mode, once the output voltage equals the setpoint voltage, the control system 106 will wait until a CAN message is received, before turning-off the high side switch QI and the low side switch Q2.

[0031] Although the subject matter has been described in language specific to structural features and/or acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims.

Claims

CLAIMS What is claimed is:

1. A bidirectional circuit system, comprising: a resistor-less precharge circuit including a high-side switch and a low-side switch that provides as an output a constant DC current; and a controller coupled to the resistor-less precharge circuit and including control logic to control the high-side switch and the low-side switch to allow a bidirectional current flow between an input to the precharge circuit and the output.

2. The bidirectional circuit system of claim 1, further comprising a high voltage battery connected to the input of the resistor-less precharge circuit.

3. The bidirectional circuit system of claim 2, wherein precharge circuit comprises an electromechanical switch electrically connected to the high voltage battery, and wherein the high voltage battery provides a voltage in a range of 600 to 1200 V DC.

4. The bidirectional circuit of claim 2, wherein the precharge circuit includes a capacitor connected to receive DC power from the high voltage battery.

5. The bidirectional circuit of claim 2, wherein each of the high-side switch and the low- side switch comprise a transistor, and wherein the high-side switch is connected to a positive terminal of the high voltage battery and the low-side switch is connected to ground.

6. The bidirectional circuit of claim 1, wherein the bidirectional circuit further comprises a current sensor to measure a current at the output of the precharge circuit.

7. The bidirectional circuit of claim 1, wherein the bidirectional circuit further comprises a voltage sensor to measure a voltage at the output of the precharge circuit.

8. The bidirectional circuit of claim 1, wherein the precharge circuit includes an inductor that connects the high-side switch and the low-side switch to the output of the precharge circuit.

9. A method to control a precharge voltage at an output of a resistor-less precharge circuit comprising a high-side switch, a low-side switch, and a charge storage device, the method comprising: measuring a voltage utilizing a voltage sensor at the output of the precharge circuit; precharging the charge storage device in the precharge circuit, wherein the charge storage device is connected at the output of the precharge circuit; detecting, by a control system coupled to the precharge circuit, based on the measured voltage at the output of the resistor-less precharge circuit, an open circuit condition at the output of the precharge circuit; and responsive to the open circuit condition, operating by the control system the high- side switch and low-side switch to turn-off.

10. The method of claim 9, wherein the control system detects that an open circuit condition exists by: measuring a first voltage utilizing the voltage sensor at a first time; measuring a second voltage utilizing the voltage sensor at a second time; determining a voltage rate by calculating a difference, by the control system, between the second voltage and the first voltage and dividing by the first time subtracted from the second time; and responsive to the voltage rate being above a threshold indicating a rapid rate of increase in the measured voltage, detecting the open circuit condition.

11. A method of operating a bidirectional circuit system, the bidirectional circuit system including a resistor-less precharge circuit including a high-side switch and a low-side switch connected to an inductor, a high voltage battery and an DC link capacitor, the method comprising: measuring an output voltage at an output of the resistor-less precharge circuit utilizing a voltage sensor; measuring a precharge current at the output of the resistor-less precharge circuit utilizing a current sensor; connecting the DC link capacitor to the output of the resistor-less precharge circuit to receive the output voltage; and controlling, by a control system coupled to the resistor-less precharge circuit, a current through the inductor by operating the high-side switch and the low-side switch based on the measured precharge current.

12. The method of claim 11, further comprising generating, by the control system, a duty cycle for the high-side switch and low-side switch.

13. The method of claim 12, wherein the controlling includes utilizing pulse width modulating to operate the high-side switch and the low-side switch from the bidirectional resistor-less precharge circuit.

14. The method of claim 13, wherein the pulse width modulating includes operating, by the control system, during the duty cycle, the high-side switch and the low-side switch by turning-on the high-side switch and turning-off the low-side switch to allow the current to flow through the inductor in a direction from the high-side switch to the output of the precharge circuit until the measured precharge current reaches a predetermined value, and wherein when the measured precharge current reaches the predetermined value at the output of the precharge circuit, the control system operates the high-side switch and the low-side switch by turning-off the high-side switch off and turning-on the low-side switch on to allow the current to flow through the inductor in a direction from the output of the precharge circuit to the low-side switch.

15. The further of claim 12, further comprising: measuring a first voltage utilizing the voltage sensor at a first time; measuring a second voltage utilizing the voltage sensor at a second time; calculating a difference, by the control system, between the second voltage and the first voltage; responsive to the difference being above a threshold indicating a rapid rate of increase in the measured voltage, turning-off the high side switch and turning-off the low side switch; and responsive to the difference in the measured voltage being zero over a plurality of duty cycles, turning-off the high side switch and turning-off the low side switch.