Dissipation circuit for electric vehicles

A method for dissipating power of an automotive electric drive system that includes a traction battery, and an inverter, wherein the inverter includes a DC bus between, and a dissipation circuit between the traction battery and DC bus, wherein the dissipation circuit includes a plurality of resistors connected in series between positive and negative terminals of the DC bus and a dissipation resistor and switch connected in series between the positive and negative terminals, the method includes responsive to a voltage across one of the plurality of resistors being less than a threshold value, deactivating the switch to prevent current flow from the positive terminal to the negative terminal through the dissipation resistor, and responsive to the voltage exceeding the threshold value, activating the switch to permit current flow from the positive terminal to the negative terminal through the dissipation resistor.

TECHNICAL FIELD

The present disclosure generally relates to a bleeding circuit for bleeding/dissipating a high-voltage bus of an electrified vehicle.

BACKGROUND

Electric vehicles (EVs) and hybrid electric vehicles (HEVs) often use regenerative mode (re-gen mode) to convert a kinetic energy into electric energy to charge a traction battery. For instance, electric power generated by an electric motor flows from the motor to the battery through an inverter in the re-gen mode. However, a “load dump” condition may occur in the regenerative mode when a main contactor for the traction battery is open, separating the battery from the high voltage bus. Under such condition, since the battery is disconnected from the inverter, the power generated may be “dumped” in to a DC capacitor connected with the high-voltage bus.

SUMMARY

In one or more illustrative embodiments of the present disclosure, a vehicle includes an electric drive system including a traction battery and an inverter, wherein the inverter includes a DC bus, and a dissipation circuit between the traction battery and DC bus, wherein the dissipation circuit includes discharge and sensing resistors connected in series between positive and negative terminals of the DC bus and a dissipation resistor and switch connected in series between the positive and negative terminals, wherein the discharge resistor, sensing resistor, and gate of the switch share a common terminal, and wherein the switch is configured such that responsive to a voltage across the sensing resistor being less than a threshold value, the switch remains off to prevent current flow from the positive terminal to the negative terminal through the dissipation resistor, and responsive to the voltage exceeding the threshold value, the switch turns on to permit current flow from the positive terminal to the negative terminal through the dissipation resistor.

In one or more illustrative embodiments of the present disclosure, a method for dissipating power of an automotive electric drive system that includes a traction battery, and an inverter including a DC bus and a dissipation circuit between the traction battery and DC bus, wherein the dissipation circuit includes a plurality of resistors connected in series between positive and negative terminals of the DC bus and a dissipation resistor and switch connected in series between the positive and negative terminals, the method includes responsive to a voltage across one of the plurality of resistors being less than a threshold value, deactivating the switch to prevent current flow from the positive terminal to the negative terminal through the dissipation resistor, and responsive to the voltage exceeding the threshold value, activating the switch to permit current flow from the positive terminal to the negative terminal through the dissipation resistor.

In one or more illustrative embodiments of the present disclosure, an automotive electric drive system includes a traction battery; an inverter; a DC bus between the traction battery and inverter; and a dissipation circuit, between the traction battery and DC bus, including one or more Zener diodes, a limiting resistor, and sensing resistor connected in series between positive and negative terminals of the DC bus and a dissipation resistor and switch connected in series between the positive and negative terminals, wherein the limiting resistor, sensing resistor, and gate of the switch share a common terminal, and wherein the switch is configured such that responsive to a voltage across the sensing resistor being less than a threshold value, the switch remains off to prevent current flow from the positive terminal to the negative terminal through the dissipation resistor, and responsive to the voltage exceeding the threshold value, the switch turns on to permit current flow from the positive terminal to the negative terminal through the dissipation resistor.

DETAILED DESCRIPTION

FIG.1depicts an electrified vehicle112that may be referred to as a plug-in hybrid-electric vehicle (PHEV). A plug-in hybrid-electric vehicle112may comprise one or more electric machines114mechanically coupled to a hybrid transmission116. The electric machines114may be capable of operating as a motor or a generator. In addition, the hybrid transmission116is mechanically coupled to an engine118. The hybrid transmission116is also mechanically coupled to a drive shaft120that is mechanically coupled to the wheels122. The electric machines114can provide propulsion and braking capability when the engine118is turned on or off. The electric machines114may also act as generators and can provide fuel economy benefits by recovering energy that would normally be lost as heat in a friction braking system. The electric machines114may also reduce vehicle emissions by allowing the engine118to operate at more efficient speeds and allowing the hybrid-electric vehicle112to be operated in electric mode with the engine118off under certain conditions. An electrified vehicle112may also be a battery electric vehicle (BEV). In a BEV configuration, the engine118may not be present.

A traction battery or battery pack124stores energy that can be used by the electric machines114. The vehicle battery pack124may provide a high voltage direct current (DC) output. The traction battery124may be electrically coupled to one or more power electronics modules126(may also be referred to as a traction inverter). One or more contactors142may isolate the traction battery124from other components when opened and connect the traction battery124to other components when closed. The power electronics module126is also electrically coupled to the electric machines114and provides the ability to bi-directionally transfer energy between the traction battery124and the electric machines114. For example, a traction battery124may provide a DC voltage while the electric machines114may operate with a three-phase alternating current (AC) to function. The power electronics module126may convert the DC voltage to a three-phase AC current to operate the electric machines114. In a regenerative mode, the power electronics module126may convert the three-phase AC current from the electric machines114acting as generators to the DC voltage compatible with the traction battery124.

The vehicle112may include a variable-voltage converter (VVC) (not shown) electrically coupled between the traction battery124and the power electronics module126. The VVC may be a DC/DC boost converter configured to increase or boost the voltage provided by the traction battery124. By increasing the voltage, current requirements may be decreased leading to a reduction in wiring size for the power electronics module126and the electric machines114. Further, the electric machines114may be operated with better efficiency and lower losses.

In addition to providing energy for propulsion, the traction battery124may provide energy for other vehicle electrical systems. The vehicle112may include a DC/DC converter module128that converts the high voltage DC output of the traction battery124to a low voltage DC supply that is compatible with low-voltage vehicle loads. An output of the DC/DC converter module128may be electrically coupled to an auxiliary battery130(e.g., 12V battery) for charging the auxiliary battery130. The low-voltage systems may be electrically coupled to the auxiliary battery130. One or more electrical loads146may be coupled to the high-voltage bus/rail. The electrical loads146may have an associated controller that operates and controls the electrical loads146when appropriate. Examples of electrical loads146may be a fan, an electric heating element and/or an air-conditioning compressor.

The electrified vehicle112may be configured to recharge the traction battery124from an external power source136. The external power source136may be a connection to an electrical outlet. The external power source136may be electrically coupled to a charger or electric vehicle supply equipment (EVSE)138. The external power source136may be an electrical power distribution network or grid as provided by an electric utility company. The EVSE138may provide circuitry and controls to regulate and manage the transfer of energy between the power source136and the vehicle112. The external power source136may provide DC or AC electric power to the EVSE138. The EVSE138may have a charge connector140for plugging into a charge port134of the vehicle112. The charge port134may be any type of port configured to transfer power from the EVSE138to the vehicle112. The charge port134may be electrically coupled to a charger or on-board power conversion module132. The power conversion module132may condition the power supplied from the EVSE138to provide the proper voltage and current levels to the traction battery124. The power conversion module132may interface with the EVSE138to coordinate the delivery of power to the vehicle112. The EVSE connector140may have pins that mate with corresponding recesses of the charge port134. Alternatively, various components described as being electrically coupled or connected may transfer power using a wireless inductive coupling.

One or more wheel brakes144may be provided for braking the vehicle112and preventing motion of the vehicle112. The wheel brakes144may be hydraulically actuated, electrically actuated, or some combination thereof. The wheel brakes144may be a part of a brake system150. The brake system150may include other components to operate the wheel brakes144. For simplicity, the figure depicts a single connection between the brake system150and one of the wheel brakes144. A connection between the brake system150and the other wheel brakes144is implied. The brake system150may include a controller to monitor and coordinate the brake system150. The brake system150may monitor the brake components and control the wheel brakes144for slowing the vehicle. The brake system150may respond to driver commands and may also operate autonomously to implement features such as stability control. The controller of the brake system150may implement a method of applying a requested brake force when requested by another controller or sub-function.

Electronic modules in the vehicle112may communicate via one or more vehicle networks. The vehicle network may include a plurality of channels for communication. One channel of the vehicle network may be a serial bus such as a Controller Area Network (CAN). One of the channels of the vehicle network may include an Ethernet network defined by Institute of Electrical and Electronics Engineers (IEEE) 802 family of standards. Additional channels of the vehicle network may include discrete connections between modules and may include power signals from the auxiliary battery130. Different signals may be transferred over different channels of the vehicle network. For example, video signals may be transferred over a high-speed channel (e.g., Ethernet) while control signals may be transferred over CAN or discrete signals. The vehicle network may include any hardware and software components that aid in transferring signals and data between modules. The vehicle network is not shown inFIG.1but it may be implied that the vehicle network may connect to any electronic module that is present in the vehicle112. A vehicle system controller (VSC)148may be present to coordinate the operation of the various components.

The electric machines114may be coupled to the power electronics module126via one or more conductors that are associated with each of the phase windings.FIG.2depicts a block diagram of a portion of an electric drive system for a vehicle. The vehicle112may include one or more power electronics controllers200configured to monitor and control the components of the power electronics module126. The power electronics controllers200may be under a global control or coordination of the VSC148. Further coordinated by the VSC148may be the main contactor142connected between the power electronics module126and the traction battery124. As illustrated in the present example, the main contactor142may be connected on a positive terminal of a high-voltage rail (a.k.a. DC rail)152. Under normal discharge and regenerative operating conditions, the main contactor124may be closed by the VSC148to connect the traction battery124to the rest of the circuit allowing the traction battery124to be discharged or charged.

The conductors may be part of a wiring harness between the electric machine114and the power electronics module126. A three-phase electric machine114may have three conductors coupled to the power electronics module126. The power electronics module126may be configured to switch positive and negative terminals of the high-voltage rail152to phase terminals of the electric machines114. The power electronics module126may be controlled to provide a pulse-width modulated (PWM) voltage and sinusoidal current signals to the electric machine114. The frequency of the signals may be proportional to the rotational speed of the electric machine114. The controller200may be configured to adjust the voltage and current output of the power electronics module126at a predetermined switching frequency. The switching frequency may be the rate at which the states of switching devices within the power electronics module126are changed.

The power electronics module126may interface with a position/speed feedback device202that is coupled to the rotor of the electric machine114. For example, the position/speed feedback device202may be a resolver or an encoder. The position/speed feedback device202may provide signals indicative of a position and/or speed of the rotor of the electric machine114. The power electronics126may include a power electronics controller200that interfaces to the speed feedback device202and processes signals from the speed feedback device202. The power electronics controller200may be programmed to utilize the speed and position feedback to control the power electronics module126to operate the electric machine114.

The traction inverter or power electronics module126may include power switching circuitry240that includes a plurality of switching devices210,212,214,216,218,220. The switching devices210,212,214,216,218,220may be Insulated Gate Bipolar Transistors (IGBT), Metal Oxide Semiconductor Field Effect Transistors (MOSFET), or other solid-state switching devices. The switching devices210,212,214,216,218,220may be configured to selectively couple a positive terminal and a negative terminal of the high-voltage rail152to each phase terminal or leg (e.g., labeled U, V, W) of the electric machine114. The power electronics126may be configured to provide a U-phase voltage, a V-phase voltage and a W-phase voltage to the electric machine114. Each of the switching devices210,212,214,216,218,220within the power switching circuitry240may have an associated diode222,224,226,228230,232connected in parallel to provide a path for inductive current when the switching device is in a non-conducting state. Each of the switching devices210,212,214,216,218,220may have a control terminal for controlling operation of the associated switching device. The control terminals may be electrically coupled to the power electronics controller200. The power electronics controller200may include associated circuitry to drive and monitor the control terminals. For example, the control terminals may be coupled to the gate input of the solid-state switching devices.

A phase leg of the inverter126may include switching devices and circuitry configured to selectively connect a phase terminal of the electric machine114to each terminal of the high-voltage rail152. A first switching device210may selectively couple the HV-rail positive terminal to a first phase terminal (e.g., U) of the electric machine114. A first diode222may be coupled in parallel to the first switching device210. A second switching device212may selectively couple the HV-rail negative terminal to the first phase terminal (e.g., U) of the electric machine114. A second diode224may be coupled in parallel to the second switching device212. A first inverter phase leg may include the first switching device210, the first diode222, the second switching device212, and the second diode224.

A third switching device214may selectively couple the HV-rail positive terminal to a second phase terminal (e.g., V) of the electric machine114. A third diode226may be coupled in parallel to the third switching device214. A fourth switching device216may selectively couple the HV-rail negative terminal to the second phase terminal (e.g., V) of the electric machine114. A fourth diode228may be coupled in parallel to the fourth switching device216. A second inverter phase leg may include the third switching device214, the third diode226, the fourth switching device216, and the fourth diode228.

A fifth switching device218may selectively couple the HV-rail positive terminal to a third phase terminal (e.g., W) of the electric machine114. A fifth diode230may be coupled in parallel to the fifth switching device218. A sixth switching device220may selectively couple the HV-rail negative terminal to the third phase terminal (e.g., W) of the electric machine114. A sixth diode232may be coupled in parallel to the sixth switching device220. A third inverter phase leg may include the fifth switching device218, the fifth diode230, the sixth switching device220, and the sixth diode232.

The power switching devices210,212,214,216,218,220may include two terminals that handle the high-power current through the power switching device. For example, an IGBT includes a collector (C) terminal and an emitter (E) terminal and a MOSFET includes a drain terminal (D) and a source (S) terminal. The power switching devices210,212,214,216,218,220may further include one or more control inputs. For example, the power switching devices210,212,214,216,218,220may include a gate terminal (G) and a Kelvin source/emitter (K) terminal. The G and K terminals may comprise a gate loop to control the power switching device.

The traction inverter126may be configured to flow a rated current and have an associated power rating. Some applications may demand higher power and/or current ratings for proper operation of the electric machine114. The power switching circuitry240may be designed to include power switching devices210,212,214,216,218,220that can handle the desired power/current rating. The desired power/current rating may also be achieved by using power switching devices that are electrically coupled in parallel. Power switching devices may be electrically coupled in parallel and controlled with a common control signal so that each power switching device flows a portion of the total current flowing to/from the load.

The power electronics controller200may be programmed to operate the switching devices210,212,214,216,218,220to control the voltage and current applied to the phase windings of the electric machine114. The power electronics controller200may operate the switching devices210,212,214,216,218,220so that each phase terminal is coupled to only one of the HV-rail positive terminal or the HV-rail negative terminal at a particular time.

Various motor control algorithms and strategies are available to be implemented in the power electronics controller200. The power electronics module126may also include current sensors204. The current sensors204may be inductive or Hall-effect devices configured to generate a signal indicative of the current passing through the associated circuit. In some configurations, two current sensors204may be utilized and the third phase current may be calculated from the two measured currents. The controller200may sample the current sensors204at a predetermined sampling rate. Measured values of the phase currents of the electric machine114may be stored in controller memory for later computations.

The power electronics module126may include one or more voltage sensors. The voltage sensors may be configured to measure an input voltage to the power electronics module126and/or one or more of the output voltages of the power electronics module126. The power electronics module126may include a line voltage sensor250that is configured to measure a line voltage across the V and W phase outputs. The voltage may be a voltage difference between the V-phase voltage and the W-phase voltage. The voltage sensors may be resistive networks and include isolation elements to separate high-voltage levels from the low-voltage system. In addition, the power electronics module126may include associated circuitry for scaling and filtering the signals from the current sensors204and the voltage sensors. In some configurations, each phase leg of the inverter may have corresponding voltage and current sensors.

Under normal/discharge operating conditions, the power electronics controller200controls operation of the electric machine114. For example, in response to torque and/or speed setpoints, the power electronics controller200may operate the switching devices210,212,214,216,218,220to control the torque and speed of the electric machine114to achieve the setpoints. The torque and/or speed setpoints may be processed to generate a desired switching pattern for the switching devices210,212,214,216,218,220. The control terminals of the switching devices210,212,214,216,218,220may be driven with PWM signals to control the torque and speed of the electric machine114. The power electronics controller200may implement various well-known control strategies to control the electric machine114using the switching devices such as vector control and/or six-step control. During discharge operating conditions, the switching devices210,212,214,216,218,220are actively controlled to achieve a desired current through each phase of the electric machine114.

Under regenerative/charge operating conditions (e.g. regenerative mode), the power electronics controller200may control the power electronics module126to accommodate power generated by the electric machine114. For example, the power electronics controller200may operate the switching devices210,212,214,216,218,220to convert AC power generated by the electric machine114to DC current to charge the traction battery124via the high-voltage rail152. The power electronics controller200may implement various well-known control strategies to perform the regenerative operation.

The power electronics module126may also include one or more bus capacitors260that are coupled across the positive and negative terminals of the high-voltage rail152via a high-voltage bus (a.k.a. DC bus)266. As illustrated inFIG.2, a positive terminal of the high-voltage bus266connects the positive terminal of the high-voltage rail152to a first terminal of the bus capacitor260, and a negative terminal of the high-voltage bus266connects the negative terminal of the high-voltage rail152to a second terminal of the bus capacitor260. Here, since the high-voltage bus266is directly connected to the high-voltage rail152, voltage on the high-voltage bus266may be substantially the same as voltage on the high-voltage bus152. The bus capacitors260may smooth the voltage of the high-voltage bus266as well as the voltage of the high-voltage rail152. As illustrated inFIG.2, the high-voltage bus266and the bus capacitor260may be integrated with the power electronics module126. Alternatively, the high-voltage bus266and the bus capacitor260may be independent components outside with the power electronics module126. A bleeding circuit (a.k.a. dissipation circuit)270may be connected in parallel with the capacitor260between the positive and negative terminals of the high-voltage rail152configured to discharge a load dump on the high-voltage bus266. Alternatively, the bleeding circuit270may be directly connected to the high-voltage bus266instead of being connected to the high-voltage rail152depending on specific design need. Similar to the high-voltage bus266, The bleeding circuit270may be implemented as a part of the power electronics module126or alternatively as a individual component outside the power electronics module126. For instance, a load dump may include a fault condition when the main contactor142is open while the electric machine114is in a regenerative mode. Under such condition, since the traction battery124is disconnected from the inverter126, the electric power generated by the electric machine114may be dumped into the capacitor260and cause the voltage of the high-voltage bus266to rise rapidly. In severe cases, the rapid rising voltage on the high-voltage bus266may surpass the breakdown voltage of the switching devices210,212,214,216,218,220and the capacitor260without a protection mechanism. The bleeding circuit270may be used as a protection mechanism to discharge the high-voltage bus266in the load dump situation.

FIG.3depicts a bleeding circuit of one embodiment of the present disclosure. The bleeding circuit270ain the present example may include a switching device (a.k.a. bleeding switch)302. The bleeding switch302may be an IGBT, a MOSFET, or another solid-state switching device. For the simplicity of the illustration, an IGBT having a gate terminal, a collector terminal and an emitter terminal will be used to describe the bleeding switch302in the present example. As illustrated, the emitter terminal of the bleeding switch302may be connected to the negative terminal of the high-voltage rail152. A bleeding resistor (a.k.a. dissipation resistor)304may be connected between the collector terminal of the bleeding switch302and the positive terminal of the high-voltage rail152. The gate terminal of the bleeding switch302is connected to the positive terminal of the high-voltage rail152via a discharge resistor306, and to the negative terminal of the high-voltage rail152via a sensing resistor308respectively.

During normal operation, the high-voltage rail152may be discharged through the discharge resistor306and the sensing resister308connected in series. The resistance of the sensing resistor308may be selected significantly smaller than the resistance of the discharge resistor306. Therefore, the voltage-drop across the sensing resistor308may be small and not enough to switch on the bleeding switch302via the gate terminal. When the bleeding switch302is OFF, there is no current flowing through the bleeding resistor304and therefore no additional power loss is generated during normal operation. When the load dump occurs, the voltage across the high-voltage bus266and high-voltage rail152may increase rapidly, eventually causing the voltage-drop across the sensing resistor308to surpass the threshold voltage of the bleeding switch302. When the bleeding switch302turns ON, power across the high-voltage rail152and high-voltage bus266may be discharged via the bleeding switch304. The value of the bleeding resistor304may be smaller than the discharge resistor, allowing a quick discharge of the high-voltage bus266. As the voltage across the DC bus266reduces, the voltage-drop across the sensing resistor308may eventually decrease below the threshold voltage of the bleeding switch and the circuit270areturns to normal operation.

The following is an example to determine a value for each component of the bleeding circuit270a. The high-voltage bus266may have a maximum operating DC voltage of 400V, while the inverter126may have a breakdown voltage of 800V. Therefore, the bleeding circuit270aneeds to be activated when the voltage on the high-voltage bus266is between 400V and 800V. In the present example, the high-voltage bus threshold voltage may be set to 500V. The discharging resistor306may be selected to meet a discharge regulatory requirement. For the 400V DC bus configuration of the present example, the discharging resistor may have a value of RD=40 kΩ. For instance, a 5% accuracy resistor may be used with a minimum, typical, and maximum values at 36.1 kΩ, 38 kΩ and 39.9 kΩ respectively. The bleeding switch302may have a gate terminal threshold VGE_thresholdat around 0.7V (with a minimum and maximum value of 0.67V and 0.73V respectively). The sensing resistor308connected between the collector and gate of the bleeding switch302may be selected to meet the following conditions. When the voltage on the high-voltage bus266is below 500V, the sensing resistor needs 308 to keep the bleeding switch302in OFF state. Therefore,
RS_Max/(RS_Max+RD_min)×500 V<VGE_Threshold_Min(1)
Based on formula (1), the maximum value of the sensing resistor308may be calculated as
RS_Max<48.44 Ω  (2)
When the voltage of the high-voltage bus266is above 800V, the sensing resistor308needs to keep the bleeding switch302in ON state. Therefore,
RS_Min/(RS_Min+RD_Max)×800 V>VGE_Threshold_Max(3)
Based on formula (2), the minimum value of the sensing resistor308may be calculated as
RS_min>36.44 Ω  (4)
Based on the above calculations, a value range of the sensing resistor308may be determined. In the present example, the sensing resistor308may be selected to have a 5% accuracy with the minimum, typical, and maximum values of 42.75Ω, 45Ω, and 47.25Ω which meet the above range requirement. The value of the bleeding resistor304may be application dependent and selected to be small enough to quickly bleed the energy being injected into the high-voltage bus266. As an example, the value of the bleeding resistor304may be around 80-100Ω.

FIG.4depicts a bleeding circuit of another embodiment of the present disclosure. Compared with the example illustrated inFIG.3, the bleeder circuit270bin the present example uses multiple Zener diodes406and a limiting resistor410connected in series in lieu of the discharging resistor306. As illustrated, the bleeding switch402may be an IGBT having a gate terminal, a collector terminal and an emitter terminal. The emitter terminal of the bleeding switch402may be connected to the negative terminal of the high-voltage rail152. A bleeding resistor (a.k.a. dissipation resistor)404may be connected between the collector terminal of the bleeding switch402and the positive terminal of the high-voltage rail152. The gate terminal of the bleeding switch402is connected to the positive terminal of the high-voltage rail152via the limiting resistor410and at least one Zener diode406connected in series. The gate terminal of the bleeding switch402may be further connected to the negative terminal of the high-voltage rail152via a sensing resistor408.

During normal operation, the Zener diodes406may block the DC voltage across the positive and negative terminals of the high-voltage bus266to prevent power loss. In this situation, there is no current passing through the limiting resistor410and the sensing resistor408. The bleeding switch402may be in OFF state because the threshold voltage is not reached across the sensing resistor408. When the load dump condition occurs, the voltage on the high-voltage bus266may increase rapidly. Once the voltage exceeds the breakdown voltage of the Zener diodes406, current may flow through the Zener diodes406, the limiting resistor410and the sensing resistor. The voltage-drop across the sensing resistor308may surpass the threshold voltage of the bleeding switch302. When the bleeding switch402turns ON, power across the high-voltage bus266may be discharged via the bleeding switch404. The value of the bleeding resistor404may be smaller than the discharge resistor, allowing a quick discharge of the high-voltage bus266. As the voltage across the DC bus266reduces, the voltage-drop across the Zener diodes406may drop below the breakdown voltage and the Zener diodes406once again block the DC voltage. The voltage-drop across the sensing resistor408may decrease below the threshold voltage of the bleeding switch and the circuit270breturns to normal operation.

The following is an example to determine a value for each components of the bleeding circuit270b. The high-voltage bus266may have a maximum operating DC voltage of 400V, while the inverter126may have a breakdown voltage of 800V. Therefore, the bleeding circuit270bneeds to be activated when the voltage on the high-voltage bus266is between 400V and 800V. In the present example, the high-voltage bus threshold voltage may be set to 600V. A Zener diode406with 3 W power rating may be used. The number (i.e. n) of the Zener diodes406to form the diode chain may be application dependent. For instance, three Zener diodes406are used in the present example (i.e. n=3). Each Zener diode406may have a breakdown voltage (a.k.a. Zener voltage) ranges within 228V minimum, 240V typical, and 256V maximum. Similar to the example illustrated inFIG.3, the bleeding switch402may have a gate terminal threshold VGE_thresholdat around 0.7V (with a minimum and maximum value of 0.67V and 0.73V respectively). The sensing resistor408and the limiting resistor are selected to limit the current flowing through the Zener diodes406using the following formulas:
((800 V−VZener_Min×n)−VGE_Threshold_Min)/RL_Min<3W/VZener_Max(5)
which gives
RL_Min>9.86 Ω  (6)
To make sure the bleeding switch402turns ON when the high-voltage bus266is 800V or above,
(800 V−VZener_Max×n)×RS_min/(RS_min+RL_max)>VGE_Threshold_Max(7)
Therefore,
RL_Max<42.84×RS_min(8)
Based on formulas (6) and (8) presented above, a general range of the sensing resistor408and the limiting resistor410may be calculated. In the present example, a 5% accuracy resistor with minimum, typical, and maximum values of 285Ω, 300Ω, 315Ω may be selected for the sensing resistor408, and a 5% accuracy resistor with minimum, typical, and maximum values of 10.93 kΩ, 11.5 kΩ, 12.08 kΩ may be selected for the limiting resistor410to meet the requirement of formulas (6) and (8). The value of the bleeding resistor404may be application dependent and selected to be small enough to quickly bleed the energy being injected into the high-voltage bus266. As an example, the value of the bleeding resistor404may be around 80-100Ω.