TECHNICAL FIELD

[0001] The present subject matter generally relates to a vehicle. More particularly but not exclusively the present subject matter relates to a system to a pre-charging system for the vehicle.

BACKGROUND

[0002] Vehicles which uses battery as energy source for running vehicle generally uses high voltage battery pack owing to the large requirement to generate adequate traction force. The battery pack generally includes a main contactor in order to switch the battery power to the load. The circuit comprises some capacitance which is responsible for large amount of inrush current when the contactor is closed. In order to overcome the inrush current the circuit is provided with a pre-charge circuit. The pre-charge circuit may comprise of a resistor in series with the contactor connected across a contactor or a combination of inductor and a semiconductor device such as a unijunction diode.

[0003] Other pre-charging techniques may include increasing the firing angle of a semiconductor device (e.g, a thyristor) in a rectifier until capacitor on a DC bus is charged to some level or connecting a resistor with a contactor in parallel with a resistor in bypass via the contactor after the DC capacitors gets charged. In another type of pre-charge circuit that may involve a three-way switch which may connect to the DC bus to pre-charge the DC bus or disconnect the DC bus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Figure 1 illustrates an exemplary vehicle with a left side view which incorporates the present subject matter.

[0005] Figure 2 illustrates a block diagram depicting the essential components of the [resent subject matter. [0006] Figure 3 illustrates a circuit level diagram incorporating the present subject matter.

[0007] Figure 4 illustrates a flow chart of the system used in the present subject matter. DETAILED DESCRIPTION

[0008] Typically, during charging or discharging of an energy source of an electrical device, the maximum instantaneous input current drawn by an electrical device when switched ON may be multiple times of the normal full-load current when first energized for a certain number of cycles of the input waveform. This is often called input surge current or inrush current and this input surge current occurs for a short duration of time due to a high capacitor initial power load. Therefore, many circuits need protection against such inrush current. Under situations of frequent switching ON or OFF of the electrical device, the possibility of inrush currents increases which can be adverse to the durability & safety of the system.

[0009] A DC (Direct current) Bus Capacitors generally will be present alongside all high power sources to supply ripple currents. These DC Bus capacitors will consume high inrush currents while closing the main relay contactor which connects high power source to DC bus having inverter circuitry bridge. This inrush current can cause high peaks in contactor and source typically battery which causes damage or reduce life of both the systems. Also, high inrush current in contactor can cause permanent weld of the contactor material. Problem of frequent high inrush current can cause reduction in battery life due to over current strain on the cells. Hence, to avoid these high inrush currents a pre-charge circuit is often used in parallel with the main contactor.

[00010] A typical pre-charge circuit may consist of a switch in series with a resistor connected parallel to main contactor. Before switching on the main contactor the pre-charge switch is closed and current flows through pre-charge switch and resistor. It is expected that pre-charging process finishes in short duration so other process finishes in time without incurring any losses or damage. The charging time is dependent on RC (resistance-capacitance) time constant. The pre-charging resistor must be large enough to limit inrush current which causes an undesirably long delay and DC Bus capacitance necessarily has a relatively large capacitance which causes high capacitive potential energy losses which is given by equation 1/2CV ^A 2. Furthermore, the presence of additional loads on the main DC bus can affect the pre-charging by increasing the impedance.

[00011] Devices and methods which incorporate use of a resistor and technique such as increasing the firing angle of the semi-conductor devices leads to increase in the consumption of power and dissipation of heat. Techniques involving one or more circuit breakers to connect or to disconnect a drive from the DC bus increases the overall size. Thus, there is a need to provide an improved pre-charging system which is compact, cost effective & efficient overcoming all the above problems & other problems of known art.

[00012] the present subject matter provides a pre-charging system and method which is configured to automatically detect the voltage of the DC bus, compare the DC bus voltage with the battery voltage and prevent the sudden inrush current caused due to the presence of one or more capacitor thereby preventing potential damage to the contactor relay switch. Further, the present subject matter provides a controller to monitor the charging of the capacitor which is coupled to the inverter circuitry.

[00013] Another embodiment of the present subject matter is to control the duty cycle through a controller by providing a pulse width modulation (PWM) signal to limit the peak current coming from the battery and also controlling the charging rate.

[00014] Still another embodiment of the present subject matter provides a pre-charging circuit with two MOSFET switches. One of the switches is the switching MOSFET which is fed with the PWM (pulse width modulation signal) (310) and the same is controlled by the controller. Another switch is a bypass MOSFET switch. The switching between the two switches is controlled by the controller.

[00015] Another embodiment of the present subject matter is to provide a relay type contactor connected in parallel with the pre-charging circuit. The relay type contactor starts functioning once the DC bus voltage becomes equivalent to the battery voltage. The relay type contactor is provided with a relay switch which switches ON/OFF when the relay coil gets energized or de-energized respectively by the battery. The relay is controlled by the relay control signal provided by the controller.

[00016] Another embodiment of the present subject matter is to provide automatic switching between the pre-charging circuit and the bypass circuit through the controller and to control the relay switch from any potential damage which may be caused due to the inrush current.

[00017] Still another embodiment of the present subject matter is to provide automatic detection of the voltage of the DC bus. If the DC bus voltage falls below the battery voltage the pre-charging circuits gets activated to allow the DC bus voltage to rise up to the level of the battery voltage. In case of quick ignition ON/OFF sequence, the DC bus voltage will be at a potential level above zero volt but below the battery voltage. Hence, the pre-charging starts and the bypass switch gets turned OFF after the completion of the pre-charging process. At, the time of pre-charging process the inverter circuitry operation circuit remains dormant in order to prevent any damage to the circuit including a microprocessor from sudden inrush of current.

[00018] Another embodiment of the present subject matter provides a pre charging circuitry which completely eliminates the requirement of manual operation of switches and high power consuming circuit comprising passive devices such as a resistor.

[00019] Yet another embodiment of the subject matter is to provide a small size inductor without compromising the duty cycle as the duty cycle is being monitored and controlled by the controller.

[00020] These and other advantages of the present subject matter would be described in greater detail in conjunction with an embodiment of a two wheeled scooter type hybrid vehicle with the figures in the following description.

[00021] Fig. 1 illustrates a left side view of an exemplary motor vehicle (100), in accordance with an embodiment of the present subject matter. The vehicle (100) illustrated, has a frame member (105). In the present embodiment, the frame member (105) is step-through type including a head tube (105 A), and a main frame (105B) that extend rearwardly downward from an anterior portion of the head tube (105 A). The main frame (105B) extends inclinedly rearward to a rear portion of the vehicle (100).

[00022] The vehicle (100) includes one or more prime movers that are connected to the frame member (105). In the present implementation, one of the prime movers is an internal combustion (IC) engine (115) mounted to the frame member (105). In the depicted embodiment, the IC engine (115) is mounted to a structural member (135) that is pivoted to the frame member (105). In one embodiment, the structural member (135) is a rigid member made including metal. The vehicle (100) also includes another prime mover, which is an electric motor (120). In a preferred embodiment, the electric motor (120) is hub mounted to one wheel of the vehicle (100). In another embodiment, one or more than one electric motor is mounted to wheels or to the frame of the vehicle. In the depicted embodiment, the vehicle (100) includes at least two-wheels and the electric motor (120) is hub mounted to the rear wheel (125) of the vehicle. A front wheel (110) is rotatably supported by the frame member (105) and is connected to a handle bar assembly (130) that enables maneuvering of the vehicle (100).

[00023] Further, the vehicle (100) includes a high capacity on-board battery (not shown) that drives the electric motor (120). The high capacity battery may include one or more high capacity battery packs or one or more low capacity cells. The high capacity battery can be disposed at a front portion, a rear portion, or at the center of the vehicle (100). The high capacity battery is supported by the frame member (105) and the vehicle (100) includes plurality of body panels, mounted to the frame member (105) for covering various components of the vehicle (100). The plurality of panels includes a front panel (140A), a leg shield (140B), an under-seat cover (140C), and a left and a right-side panel (140D). A glove box may be mounted to a leg shield (140B).

[00024] A floorboard (145) is provided at the step-through portion defined by the main tube (105B). A seat assembly (150) is disposed rearward to the step- through portion and is mounted to the main frame (105B). The seat assembly (150) that is elongated in a longitudinal direction F-R of the vehicle (100) enables the user to operate the vehicle in a saddle ride-type posture. One or more suspension(s) connect the wheels (110), (125) to the vehicle (100) and provide a comfortable ride. The vehicle (100) comprises of plurality of electrical and electronic components including a headlight (155A), a taillight (155B), a starter motor (not shown), a horn etc. Also, the vehicle (100) includes a master control unit (not shown) that takes control of the overall operation of the vehicle (100) including the function of the IC engine (115), the electric motor (120), charging of the batteries from a magneto/integrated starter generator (ISG), driving of loads by the magneto/ISG, charging of the high capacity batteries by the electric motor operating in generator mode, and any other operations associated with the operation of the vehicle (100). The vehicle (100) shown in fig. 1 is an exemplary vehicle and the present subject matter can be used in a two-wheeled vehicle, three-wheeled vehicle or a four- wheeled vehicle.

[00025] Fig. 2 illustrates a block diagram of an embodiment of the present subject matter. The vehicle needs to be started as soon as the driver switches ON the vehicle and therefore it is desirable to complete the pre-charging process in a short time. The electric drive of the electrical or hybrid vehicle is provided with a DC (direct current) power source (201) e.g. a battery (201) of about 48 volt (may be higher depending on the vehicle requirement). The power coming from the battery (201) need to be step down depending on the requirement of various inputs present in the vehicle. Also, the power may be converted from DC to AC depending on the type of load. An inverter circuitry (206) which converts the DC power into AC power of a particular frequency to drive the traction motor at a specific speed & other applicable electrical loads is also configured to the contactor (202). The inverter circuitry (206) is coupled with at least one capacitor load (304) (refer fig. 3) to remove the ripple that is being carried with the power signal from the battery. Hence, the pre-charging circuit (300) which charges the capacitor load (304), when coupled with the inverter circuitry (206) is called as the Pre-charging of the DC bus (305) (refer fig. 3). When the DC bus (305) gets charged only then the battery voltage is applied to the load (207). The DC bus (305) may be again recharged when the DC bus potential falls below a certain level. After the pre-charging function gets completed the inverter circuitry (206) starts operating by switching OFF the pre charging circuit (300) through a controller (205).

[00026] The battery (201) is connected to a contactor (202) which is responsible providing power to the load (207) like traction motor and electrical loads like head lamp, tail lamp, turn signal lamp, speedometer, several input switches and sensors. The contactor (202) has an input adapted to be connected with the battery (201) and the output connected to the loads (207). The contactor (202) is of relay contactor type which gets energized and de-energized in order to switch between an open state and a closed state enabled by the relay switch (313) (refer fig. 3). The energization and de-energization is controlled by the controller (205). A DC bus (305) is coupled to the capacitor load (304) and the output of the relay based contactor (202).

[00027] A pre-charge circuit has been electrically configured between the battery (DC power source) and the capacitor in shunt arrangement in order to prevent the contactor (202) from getting damaged from the sudden spike of current for few seconds due to the inrush current. The pre-charging circuit (300) provides a supply of controlled current from the battery (201) to the capacitor load (304). The amount of current being given to the load (207) is controlled by the controller (205).

[00028] The pre-charging circuit (300) comprises of a pre-charging switch

(204) and a bypass switch (203). The switching between the bypass switch (203) and pre-charging switch (204) is controlled by the controller (205). The controller

(205) gives signal to the contactor (202) based on the DC bus voltage to start transferring power to the inverter circuitry (206) in order to run the loads (207) and simultaneously the pre-charging switch (204) gets switched OFF.

[00029] Fig. 3 illustrates an embodiment of the pre-charging circuit (300). The bypass switch (203) and the pre-charging switch (204) are active devices such as a MOSFET. The source of the pre-charging switch (204) is electrically connected to the positive terminal of the battery (201). Similarly, the source of the bypass switch (203), also called the ON/OFF controlling MOSFET switch, is connected to the positive terminal of the battery (201). The active solid state device MOSFET can be either a depletion type MOSFET or an enhancement type MOSFET. The gate of the pre-charging switch (204) is connected to a controller (205) which provides series of pulses. The pulses given by the controller (205) to the gate of the pre-charging switch (204) is a pulse width modulation (PWM) signal (310). Similarly, the gate of the bypass switch (203) receives a control signal (309) from the controller (205). Through bypass switch (203) the switching ON/OFF function of the pre-charging switch (204) can be controlled. When the pre-charging circuit (300) matches the DC bus voltage with the battery voltage, the pre-charging process gets turned OFF by the controller (205) and the bypass switch (203) gets turn ON by the controller. The source of energy can either be a battery or any other rectified AC power. Both the capacitor load (304) and the inverter circuitry (206) are connected in parallel and the DC bus connected to both capacitor load (304) and inverter circuitry (206).

[00030] The drain of pre-charging switch (204) is connected to the n- side of the unijunction diode (303) and to an inductor (302). The drain of the bypass switch (203) controlling the ON/OFF control of the pre-charging switch (204) is electrically connected to the inverter circuitry (206), at least one capacitor load (304) and the inductor (302). Diode (303) has been reversed biased with its positive terminal (p-side) connected to the negative terminal of the battery (201) and the p- side of the diode (303) connected to the drain of the pre-charging switch (204) and the inductor (302).

[00031] The circuit is further provided with a contactor (202) which is electrically configured in shunt with the pre-charging switch (204). The source of the bypass switch (203) and source of the pre-charging switch (204) is electrically connected to the relay input (306) of the contactor (202). The contactor (202) comprises a relay coil (314) with terminal A and the relay is controlled by providing a relay control signal (312) from the controller (205) to control the function of the contactor (202) by first monitoring the pre-charging process and depending on the DC bus voltage. Other input of the contactor (202) is terminal B which is connected to the ground at zero potential. The relay coil (314) gets energized, relay coil (314) enables switching of the relay switch (313). When the relay switch (313) closes or gets switched ON, the current flows from the contactor (202) to the load (207). The controller (205) sends the relay control signal (312) in order to energized and de energize the relay coil (314) in order to control the current flow through the relay switch (313) to the load (207). Therefore, the relay based contactor (202) works on the basis of the relay control input received from the controller (205).

[00032] Fig. 4 illustrates an methodology of implementing the system of pre charging as described. In order to initiate the pre-charging process, the pre-charging switch (204) is enabled by the controller (205) in step 401. The voltage level of the DC bus is detected and gate of pre-charging switch (204) receives the pulse width modulation (PWM) signal (310) and controls the current flowing to the capacitor load (305) by controlling the duty cycle and limiting the peak value of the current in step 402. The pre-charging switch (204) delivers a controlled small amount of constant current to raise the level of the DC bus voltage. The duty cycle and the switching frequency is appropriately chosen based on at least one of the rise time of the voltage and the inductance. The duty cycle is controlled on the basis of voltage rise of the DC bus capacitor load (304) in step 403.

[00033] In step the 404 DC bus voltage is compared with the battery voltage in step 404. The method is repeated continuously till the DC bus voltage reaches the battery voltage. When the voltage matching is satisfied then the pre-charging switch (204) is switched OFF in step 405. The pulse width modulation signal (310) provided to the gate of the pre-charging switch (204) which is used to vary the duty cycle thereby regulating the output peak current and controlling the charging rate gets snapped by the controller. The pulse width modulation (PWM) (310) provides a time delay to prevent any surge in the current.

[00034] Further, in step 406 the bypass switch (406) gets activated and in step 407 the relay switch (313) closes the circuit by closing relay input (306) and relay output (307). When the contactor (202) is closed and the capacitor load (304) is fully charged then inverter circuitry (206) receives the power. [00035] In order to prevent the damage, the pre-charging circuit (300) is configured to continuously monitor the duty cycle with the help of the controller (205) using the pulse with modulation (PWM) signal (310) given to the MOSFET based re-charging circuit. Implementing a resistor in the pre-charging circuit (300) increases the undesirable delay & hence to avoid the delay an inductor is implemented. Incorporating a big size inductor reduces the delay time but the overall material cost spikes up and using a small inductor causes more delay but small duty cycle. So, to control the duty cycle by incorporating a small inductor the pre-charging switch (204) is utilized and a PWM (Pulse width modulation) signal (310) is provided by the controller (205). The PWM signal helps in faster switching frequency of the pre-charging switch (204) and at the same time the duty cycle is kept under control to limit the peak current.

[00036] The controlled current keeps on flowing to the pre-charge circuit till the voltage across the DC bus becomes equivalent to the battery voltage. The moment the DC bus attains a voltage equivalent to the voltage of the battery (201) then the bypass switch (203) is switched ON and the pre-charging switch (204) is switched OFF.