DESC:SWITCHED MODE POWER SUPPLY SUITABLE FOR USE IN A POWER DISTRIBUTION UNIT FOR ELECTRIC OR HYBRID VEHICLES

CONTINUITY INFORMATION
This application claims priority from Indian Provisional Application no. 201941018441 filed on 8th May 2019.

FIELD OF THE INVENTION
The present disclosure relates to an improved switched mode power supply (SMPS). More particularly, the present disclosure relates to a high power SMPS with improved efficiency during low power operation. The SMPS of the present disclosure is suitable for use in a power distribution unit (PDU) of an electric or hybrid vehicle.

BACKGROUND
A switched mode power supply (SMPS) is an electronic power supply that uses a switching regulator to convert electrical power efficiently. An SMPS transfers power from a direct current (DC) or alternating current (AC) source supply to DC loads, while converting voltage and current characteristics. Voltage regulation is achieved by varying a duty cycle (i.e. the ratio of ON-time to time-period). Power is drawn from the source supply during the ON-time of the duty cycle, and the source supply is switched off or disconnected from SMPS during the remainder of the time-period of the duty cycle. This allows an SMPS to achieve a higher power conversion efficiency than prior solutions. Further, an SMPS is typically smaller and lighter than prior solutions such as a linear supply, due to the smaller transformer size and weight.

The SMPS is used to supply power to electronic equipment in a wide-variety of applications. For example, an SMPS may be used in power supplies of personal computing devices such as personal computers, laptops, and mobile phones. Additionally, an SMPS may be used in power supplies for data centers to power servers, networking devices, storage devices, and so on. More recently, with an increase in popularity of electric and hybrid vehicles, SMPSs are increasingly used to supply power in various types of vehicles such as cars, scooters, motorcycles, buses and trucks.

In order to supply power to multiple devices, an SMPS is often incorporated in a power distribution unit (PDU). A PDU is a device that provides multiple power outputs to distribute electrical power to one or more load devices. In addition to power distribution, a PDU may provide functionality to facilitate power protection and management. For example, various PDUs provide features such as remote monitoring of power consumption, remote management (e.g. turning on or off power supply to particular outputs), and metering of power drawn from the source supply and/or power supplied to various outputs. Additionally, they may provide features to protect the electrical network from local electrical faults (e.g. electrical faults in individual devices on the network).

In vehicles, PDUs are used to supply power to various devices within the vehicle, such as its motor controller unit (MCU), various control units and microprocessors, air conditioner, steering system, heater, defogger, windshield wipers, lights, displays, entertainment system, brakes, anti-theft system, and so on. Additionally, PDUs also provide features to manage the charging of the vehicle’s battery. As such, PDUs in vehicles are expected to operate for long durations or even continuously, depending upon the design of the vehicle. However, the power demand on the PDU is expected to vary significantly over time, depending on the use of the vehicle. Typically, the load on the PDU is quite low when the vehicle is not in use, or is idling. For example, when the vehicle is not in use, systems such as access control systems to lock or unlock the vehicle, anti-theft systems, etc. may still need to draw power from the PDU. On the other hand, during use of the vehicle, the load goes up significantly to power the MCU, particularly when the vehicle accelerates or maintains high speeds. The load further varies with use of devices such as air conditioners, headlights, heaters, and so on. Therefore, a PDU in a vehicle is typically required to provide high power output to cater to peak loads, but also operate in a low power mode for long durations.

An important characteristic of a power supply, such as an SMPS or a PDU, is its efficiency. Efficiency is defined as the ratio of total output power to total input power. A low efficiency means greater power loss, typically due to factors such as switching losses and dissipation of power as heat. Traditional PDUs are usually efficient in a certain power band. For example, a traditional SMPS rated to provide a maximum steady state power of 120 Watt typically has a high or acceptable efficiency (about 85% or more) in the range of 30 to 120 Watt. However, if the load demand falls below 30 Watt, the efficiency of a traditional high power SMPS falls steeply. For various traditional SMPSs, the efficiency is as low as 19% when operating at about 0.5 Watt. Some of the reasons for this fall in efficiency are the constant power consumption by the control circuitry of the PDU, switching losses at the switches, and magnetic losses. In high load conditions, the conduction losses in the SMPS are higher and gate driving or switching losses are smaller in comparison. However, during low power operation, conduction losses are lower, but the gate driving or switching losses dominate and are responsible for reducing efficiency.
Also, existing SMPS have good low power efficiency but then they are inefficient at high power, similarly vice versa.

Therefore, in light of the aforementioned drawbacks and several other inherent in the traditional SMPSs in general and PDUs in particular, there exists a need of an SMPS with improved efficiency characteristics. Particularly, there exists a requirement of an SMPS with improved efficiency during both high power and low power operation.

OBJECTS OF THE INVENTION
It is an objective of the present disclosure to provide a high power SMPS with improved efficiency characteristics at low power.
It is another objective of the present disclosure to provide a high power SMPS with improved performance characteristics during low power operation.
It is another objective of the present disclosure to provide a high power SMPS suitable for use in a power distribution unit (PDU).
It is yet another objective of the present disclosure to provide a high power SMPS suitable for use in an electric or hybrid vehicle.

DESCRIPTION OF THE DRAWINGS
The drawings shown in the present disclosure are exemplary and the present disclosure may be understood when read in conjunction with the following drawings:
Fig. 1 illustrates exemplary environment for working of the invention according to an embodiment of the present disclosure.
Fig. 2 illustrates an exemplary circuit diagram showing a switched mode power supply according to an embodiment of the present disclosure.
Fig. 3 illustrates an exemplary block diagram showing an efficiency tracking module according to an embodiment of the present disclosure.
Fig. 4 illustrates an efficiency chart comparing the efficiency of a traditional SMPS with that of a high power according to an embodiment of the present disclosure.
Fig. 5 illustrates plots of duty cycle signal showing the working of an exemplary
embodiment of the present disclosure

BRIEF DESCRIPTION OF THE DISCLOSURE
The present disclosure relates to an improved switched mode power supply (SMPS). The present disclosure relates to a switched mode power supply (SMPS) with improved efficiency during low power operation. The present disclosure also relates to a high power SMPS that uses a supercapacitor. The present disclosure also relates to a high power SMPS that uses a cascaded proportional-integral-derivative (PID) controller. The present disclosure also relates to a high power SMPS that is suitable for use in a power distribution unit (PDU) of an electric or hybrid vehicle.

A high power SMPS, in accordance with various embodiments of the present disclosure, uses a switching power convertor topology. During the ON time of the SMPS, power is supplied to a load and also used to charge a supercapacitor. On the other hand, during the OFF time of the SMPS, the power stored in the supercapacitor is used to power the load.

A high power SMPS, in accordance with various embodiments of the present disclosure, is designed to provide fast charging of the supercapacitor. For example, the supercapacitor may be charged at 30 Watt. Thus, during the ON time of the SMPS, when it supplies power to the load as well as the supercapacitor, the demand on it is at least 30 W thereby ensuring that it works at high efficiency. When the output load is low (e.g. 5 Watt), the supercapacitor discharges slowly, and control logic provided in the SMPS keeps the SMPS in OFF state until the supercapacitor discharges and output voltage falls below a desired range. Since supercapacitors store relatively large amounts of power, the SMPS remains in OFF state for long periods during low power operation. In this way, gate driving and switching losses are minimized, and a higher efficiency is achieved even during low power operation.

Control logic is provided to generate a duty cycle signal in a manner that optimizes efficiency even during low power operation, while maintaining the required output voltage, and controlling the rate of charge of the supercapacitor in accordance with its maximum constant working current.

Thus, a high power SMPS in accordance with the present disclosure implements a power averaging technique, where the SMPS consumes power in short, high-power (and therefore high-efficiency) bursts and stores the received energy in a supercapacitor. The SMPS delivers the energy stored in the supercapacitor to the load. While the supercapacitor retains enough energy to supply power to the load, the SMPS is maintained in an OFF state. During low power operation, the energy stored in the supercapacitor lasts for longer time. Thus, the SMPS is maintained in OFF state for a longer time; gate driving and switching losses are thereby reduced, leading to increased efficiency of the SMPS.

The foregoing principles are illustrated hereunder with the example of a buck converter.
Fig. 1 illustrates an exemplary environment [10] or functioning of the invention. The exemplary environment [10] mat be an electric or a hybrid two wheeler or our wheeler. The environment [10[ includes a power source [104] in connection with a plurality of loads [106A, 106B, 106C, 106D] (to be referred to as load [106] from here on). through a switched mode power supply (SMPS) [102]. According to an embodiment of the invention, there may be other electronic components within the SMPS [102] as will be explained later in the description. According to anther embodiments of the invention, the load [106], may be however, not limiting to, wipers, infotainment units, headlight, taillight, stand sensor, door sensor, steering/handle lock arrangement sensor, anti-theft systems etc.

Fig. 2 illustrates an exemplary circuit diagram [100] showing a switched mode power supply [102] according to an embodiment of the present disclosure. SMPS [102] draws DC power from a source [104] and supplies DC power to a load [106]. In the illustrated embodiment, SMPS [102] incorporates a buck convertor as shown in circuit diagram [100]. However, it will be apparent to a person skilled in the art that the teachings of the present disclosure may be applied to any kind of SMPS without limitation, such as to a boost convertor, buck-boost convertor, boost-buck or split-pi convertor, a Cuk convertor, and so on.

Source [104] is connected to the circuit via complementary switches [108] and [110], which are operated by a duty cycle signal [112]. Duty cycle signal [112] is fed to switch [108] directly and to switch [110] via NOT gate [114]. When duty cycle signal [112] is ON, switch [108] is ON and switch [110] is OFF, and source [104] is connected between points [116] and [118] to supply power to the circuit. On the other hand, when duty cycle signal [112] is OFF, switch [108] is OFF and switch [110] is ON, and source [104] is effectively disconnected from the circuit and points [116] and [118] are directly connected or shorted. Power drawn by the circuit from source [104] is thus controlled by varying the ratio of ON-time to time-period of duty cycle signal [112]. In the illustrated embodiment, switches [108] and [110] are metal oxide semiconductor field effect transistors (MOSFETs). However, it will be apparent to a person skilled in the art that many techniques of implementing electronically operated switches are known in the art, and any suitable technique may be used without deviating from the teachings of the present disclosure.

Power drawn from source [104] is supplied via an inductor [120] to a supercapacitor [122]. Supercapacitor [122] is further connected to load [106] as shown.

When duty cycle signal [112] is ON, source [104] drives power to load [106], and charges supercapacitor [122]. When duty cycle signal [112] is OFF, supercapacitor [122] drives power to load [106] and gets discharged in the process.

Voltmeters and ammeters are used to measure various voltages and currents in the circuit. A voltmeter [124] measures input voltage V_in of SMPS [102] and an ammeter [126] measures the input current I_in. Similarly, a voltmeter [128] measures output voltage V_out and an ammeter [130] measures the output current I_out. A voltmeter [132] measures the voltage across supercapacitor [122], shown as V_C. An ammeter [134] measures the current through inductor [120], also referred to as the load current and shown as I_L.

The value of V_C, as measured by voltmeter [132], is fed to a differentiator [144] to obtain a supercapacitor derivative voltage [146]. Supercapacitor derivative voltage [146] is used in the cascaded PID control as described later.

Further, an output voltage monitor [148] monitors whether the value of output voltage V_out is within a desired range. In output voltage monitor [148], the value of output voltage V_out, as measured by voltmeter [128], is fed to a comparator [150] with hysteresis whose output is in turn fed to a compare-to-zero block [152]. Compare-to-zero block [152] outputs an output-voltage-in-range signal [154], which is a binary signal indicating whether output voltage V_out is within the desired range or not.

SMPS [102] uses a two-stage cascaded PID controller. At a first PID stage [156], a derivative voltage constant V_der is used as the set point for a first PID controller [158]. Derivative voltage constant V_der is a constant voltage and represents the desired value of supercapacitor derivative voltage [146]. In the illustrated embodiment, first PID stage [156] has derivative voltage constant V_der of 0.8 Volt. The difference between derivative voltage constant V_der and supercapacitor derivative voltage [146] is fed to first PID controller [158]. First PID controller [158] maintains the rate of charge of supercapacitor [122] at a desired rate, which leads to prolonged life expectancy of supercapacitor [122].
Further, output-voltage-in-range signal [154] is also fed to first PID controller [158]. Output-voltage-in-range signal [154] powers the first PID controller [158] when SMPS [102] is operational.

At a second PID stage [160], the output of first PID controller [158] is used as the set point for a second PID controller [162]. The difference or error between the output of first PID controller [158] and the value of load current I_L is fed to second PID controller [162]. Further, output-voltage-in-range signal [154] is also fed to second PID controller [162]. Output-voltage-in-range signal [154] powers the second PID controller [162] when SMPS [102] is operational.

At a duty cycle signal generator [164], a duty cycle reference generator [166] generates a constant DC voltage D that represents the reference value for the duty cycle. The sum of the outputs of second PID controller [162] and duty cycle reference generator [166] is in turn fed to a comparator [168]. Comparator [168] compares the received sum with a sawtooth waveform received from a sawtooth generator [170] to generate a reference duty cycle signal [172].

Finally, at driver circuit [174], reference duty cycle signal [172] and output-voltage-in-range signal [154] are used to generate duty cycle signal [112], which is supplied to switches [108] and [110] as described earlier. Driver circuit [174] generates duty cycle signal [112] by selectively passing on reference duty cycle signal [172] only when output-voltage-in-range signal [154] indicates that the output voltage V_out is not within the desired range. Consequently, duty cycle signal [112] operates switches [108] and [110] to draw power from source [104] only when the output voltage V_out is not within the desired range.

During periods when the demand on SMPS [102] is low, the energy stored in supercapacitor [122] can drive load [106] for relatively long durations without need for replenishment from source [104]. During such periods, while the output voltage V_out is within the desired range, output-voltage-in-range signal [154] prevents driver circuit [174] from passing on reference duty cycle signal [172], and duty cycle signal [112] remains in a state where no power is drawn from source [104].

As the energy in supercapacitor [122] gets depleted, output voltage V_out falls below the desired range, and output-voltage-in-range signal [154] causes driver circuit [174] to pass on reference duty cycle signal [172] as duty cycle signal [112]. Duty cycle signal [112], in turn, drives switches [108] and [110] to draw power from source [104] to supply load [106] as well as charge supercapacitor [122].

SMPS [102] keeps the charge rate of supercapacitor [122] constant while varying the output current I_out based on power demand at load [106]. SMPS [102] is thereby able to maintain a constant output voltage V_out and charge rate of supercapacitor [122], while catering to varying demand at load [106].

The desired input voltage of load [106] determines the desired output characteristics of output voltage V_out. For example, it is desired that SMPS [102] produces an average output voltage of 11 Volt, which may vary between a minimum of 10 Volt and a maximum of 12 Volt no faster than 0.4 Hz, since a supply within these parameters enables load [106] to operate within specifications.

Further, the desired supply characteristics of load [106] are used to select a suitable supercapacitor [122]. The characteristics of supercapacitor [122] are used to select a suitable desired charge rate of supercapacitor [122], and in turn a suitable value of reference voltage V_ref. In an example, the capacitance of supercapacitor [122] is 2.5 F, and characteristics of supercapacitor [122] specify a maximum constant working current of 2 A. Then, a charge rate of 0.8 V/sec is selected by setting derivative voltage constant V_der to 0.8 V to prolong the life cycle and reduce losses at supercapacitor [122].

A person skilled in the art may, without undue experimentation, use the foregoing information to design various parameters of SMPS [102] such as, but not limited to, inductance of inductor [120], capacitance of supercapacitor [122], derivative voltage constant V_der, parameters of first PID controller [158] and second PID controller [162], parameters of comparator [150], output voltage of duty cycle reference generator [166], and parameters of sawtooth generator [170].

Fig. 2 illustrates an exemplary block diagram [200] showing an efficiency tracking module [202] (ETM [202]) according to an embodiment of the present disclosure. In various embodiments, ETM [202] is used to monitor the efficiency of SMPS [102]. ETM [202] comprises a first multiplier [204], a second multiplier [206], and a divider [208]. First multiplier [204] multiplies values of V_out and I_out, as observed at voltmeter [128] and ammeter [130] respectively, to calculate an output power [210]. Similarly, second multiplier [206] multiplies values of V_in and I_in, as observed at voltmeter [124] and ammeter [126] respectively, to calculate an input power [212]. Divider [208] divides output power [210] by input power [212] to calculate an efficiency [214]. Various analog and digital techniques of implementing multipliers [204] and [206] and divider [208] are known in the art.

In the illustrated embodiment, efficiency [214] is then shown on an efficiency display [216]. However, it will be apparent to one skilled in the art that the calculated value of efficiency [214] may be used in a variety of ways, without limitation. For example, in an embodiment where SMPS [102] is deployed in a PDU of an electric or hybrid vehicle, efficiency [214] may be displayed to the operator of the vehicle, periodically stored in a system health log, provided to a mobile phone application, and so on.

Fig. 3 illustrates an efficiency chart [300] comparing the efficiency of a traditional SMPS with that of SMPS [102]. Efficiency values are plotted for operation with an input voltage (V_in) of 48 Volt with output power (V_out* I_out) varying between 5 Watt and 55 Watt. Both the traditional SMPS and SMPS [102] incorporate a buck convertor. The traditional SMPS employs a traditional capacitor with a capacitance of 540 µF and uses a single stage PID controller. On the other hand, SMPS [102] uses supercapacitor [122] with a capacitance of 2.5 F and uses a cascaded PID controller as described earlier.
Table 1 below presents various design characteristics of the traditional SMPS and SMPS [102]:
Traditional SMPS SMPS [102]
Type Buck Convertor Buck Convertor
Controller Single Stage PID 2-stage Cascaded PID
Input Voltage (V_in) 48 V 48 V
Buck Inductor 21 µH 21 µH
Buck Capacitor 540 µF 2.5 F
Duty Cycle Period 10 µsec 10 µsec

In efficiency chart [300], the efficiency of the traditional SMPS is shown as a first plot [302] and the efficiency of SMPS [102] is shown as a second plot [304]. As shown in the efficiency chart [300], both the traditional SMPS and SMPS [102] operate at a high efficiency for medium or high output power (20 W and above). However, in low power operation (below 20 W), the efficiency of the traditional SMPS falls drastically to undesirable levels of about 50%. In stark contrast, the efficiency of SMPS [102] sees a slight increase and remains in a desirable range of about 85% even for very low output power.

Fig. 4 illustrates plots of duty cycle signal [112] showing the working of an exemplary embodiment of the present disclosure. The figure presents a first plot [402] that shows duty cycle signal [112] over a time span of 70 seconds, and a second plot [410] showing a zoomed-in view of first plot [402].

In a first period [404], between about 0 and 16 seconds in first plot [402], duty cycle signal [112] is activated by output-voltage-in-range signal [154], and reflects reference duty cycle signal [112], and switches [108] and [110] are operated to draw power from source [104]. Similarly, duty cycle signal [112] is active in a second period [406] and a third period [408] as shown. For the remaining times shown in first plot [402], duty cycle signal [112] is inactive, and switches [108] and [110] are not operated to draw power from source [104].

The figure further presents a second plot [410] which shows a zoomed-in view of first plot [402] around time 36.59651 seconds in second period [406] when duty cycle signal [112] is active. As is more clearly seen in second plot [410], during time periods when duty cycle signal [112] is active, it reflects reference duty cycle signal [172], and performs switching of switches [108] and [110] to draw power from source [104].

It will be apparent to a person skilled in the art that all isolated switching power converter topologies have constant switching losses of its devices and transformer core, and therefore the teachings of the present disclosure may be applied to any high power system, without limitation, to improve low power efficiency.

In a nutshell, the present disclosure provides an improved SMPS. The present disclosure also provides a high power SMPS with improved efficiency during low power operation. The present disclosure also provides a high power SMPS that uses a supercapacitor. The present disclosure also provides a high power SMPS that uses a cascaded proportional-integral-derivative (PID) controller. The present disclosure also provides a high power SMPS that is suitable for use in a power distribution unit (PDU) of an electric or hybrid vehicle.

Although the present disclosure has been described with reference to certain preferred embodiments and examples thereof, other embodiments and equivalents are also possible and are encompassed by this disclosure. Despite the fact that various characteristics and advantages of the present disclosure have been laid down in the description, various modifications are still possible in the presently disclosed system without deviating from the intended scope and spirit of the present disclosure.

,CLAIMS:Claims
What is claimed is:
1. A power distribution unit (PDU) of an electric vehicle comprising:
a power source;
a load; and
a switched mode power supply system (SMPS), connected to the power source on one side and the load on the other side through a plurality of complementary switches, the SMPS comprising:
a driver module configured to control generation of a driver duty cycle signal;
an output voltage monitor module configured to measure an output voltage of the SMPS and output an output voltage in range signal to indicate whether output voltage is within range or not;
a controller module, operably connected to the output voltage monitor module output of a current monitor on one side and the driver module on the other side, configured to maintain a rate of charge of a supercapacitor, operably connected to the SMPS;
wherein, when the output voltage in range signal indicates that the output voltage is within range, the output voltage in range signal prevents the driver module from generating the driver duty cycle signal and the load is powered by the supercapacitor, whereas when the output voltage in range signal indicates that the output voltage is not within the range, the output voltage in range signal causes the driver module to generate the driver duty cycle signal and consequently connecting the load to the power source and the supercapacitor simultaneously.
2. The PDU of claim 1, wherein the power source is an alternating current or direct current power source.
3. The PDU of claim 1, wherein the plurality of complementary switches are metal oxide semiconductor field effect transistors (MOSFET) switches.
4. The PDU of claim 1, wherein the current monitor is an inductor.
5. The PDU of claim 1, wherein the controller module includes at least two proportional-integral-derivative (PID) controllers.
6. The PDU of claim 5, wherein a first PID controller of the at least two PID controllers controls a second PID controller of the at least two PID controllers.
7. The PDU of claim 1, wherein the output voltage in range signal is a binary signal.
8. The PDU of claim 1, wherein the output voltage is measure using a voltmeter.
9. The PDU of claim 1, wherein the rate of charge of the supercapacitor is maintained at a constant rate.
10. The PDU of claim 1, wherein the plurality of complementary switches are operated by the duty signal cycle.
11. The PDU of claim 10, wherein the plurality of complementary switches are two in number.
12. The PDU of claim 11, wherein the driver duty cycle signal is fed directly to a first switch of the two switches.
13. The PDU of claim 12, wherein the driver duty cycle signal is fed through a NOT gate to a second switch of the two switches.
14. The PDU of claim 13, wherein when the driver duty cycle signal is generated, the first switch is on and the second switch is off and the power source is connected to the SMPS.
15. The PDU of claim 13, wherein when the driver duty cycle signal is not generated, the first switch is off and the second switch is on and the power source is disconnected from the SMPS.
16. The PDU of claim 1, wherein a power drawn by the SMPS from the power source is controlled by varying a ratio of ON-time to time period of the driver duty cycle signal.