DESC:TECHNICAL FIELD

The present invention relates generally to pulse width modulation (PWM) digital to analog conversion and, particularly, to a circuit and method that provides increased accuracy for a microcontroller-based PWM digital to analog conversion

BACKGROUND

The electronic circuit breakers include Molded Case Circuit Breakers (MCCB) and Air Circuit Breakers (ACB) where self generated power supply is required to drive the electronic circuit. The power supply for the electronic circuit is derived from the current transformers which are connected on poles of the circuit breaker.

The power supply can be generated by single phase system or three phase system also. Here the MOSFET is used as a current switching element. The PWM (Pulse Width Modulation) pulses from the microcontroller are given to the gate of the MOSFET for controlling the power supply using some extrahardware.

For regulation of power supply using hardware, additional component like Zener diode has to be included which gives gate pulses to MOSFET when supply voltage go above certain threshold. This adds to the cost of the electronic trip unit as well as zener leakage current gets added to overall power consumption. This becomes key parameter for low power trip unit design. Also, the pulses generated using this method will have constant width. Hence, the pulse width does not vary depending on the supply voltage. The ripple in the supply voltage using method is in the range of 1V-2V.

For regulation of power supply using firmware, typical implementation involves use of an analog to digital converter (ADC) and a timer. The step-down supply voltage value(sense voltage) is checked at regular interval in the timer interrupt by ADC sampling. When the supply voltage is above threshold, the PWM output is made high to switch on the MOSFET and discharge the capacitor. This method involves latencies due to timer response time, ADC initialization in the firmware, ADC sampling time and timer interrupt priority. These latencies lead to high response time at startup. Hence, there is a need of PWM generation using hardware component like zener diode during such condition. This method involving use of ADC provides variable pulse width depending on the supply voltage and it leads to better regulation of supply voltage and reduce ripple as compared to only hardware implementation. But the hardware component will be required to take care of the startup condition. This will again increase overall cost of implementation.

The prior-art document, US 20090184854 A1 by Honeywell International, Inc. discloses a precision digital to analog conversion circuit and method. A regulated direct current (DC) voltage having a DC voltage magnitude is supplied to a device, such as a processor. The processor generates a pulse width modulation (PWM) output signal based, at least in part, on the regulated DC voltage. An analog output signal is generated from the PWM output signal. The regulated DC voltage is compared to a precision reference DC voltage; the DC voltage magnitude is selectively adjusted based on the comparison.

The prior-art document, US 5189421 A by National Semiconductor Corporation, discloses a microcontroller based analog-to-digital converter is disclosed. Themicrocontroller is coupled to an output of a comparator. The comparator includes an input for receiving an unknown analog voltage and an input coupled to a capacitor. The capacitor is also coupled to the microcontroller through a resistor.Based upon the output of the comparator, the microcontroller provides a pulsed input signal with a predetermined duty cycle to the capacitor. The duty cycles for "high" pulses and "low" pulses are individually set to match a selected input voltage range. The rate at which pulses are applied to the capacitor is adjusted until the voltage on the capacitor matches the input voltage being measured. The pulsed input signal is monitored to establish a pulse count. Based upon the pulsecount, the unknown analog voltage value is converted to a corresponding digital voltage value.

In the view of the above mentioned problems and the other existing problems, there exists a need to provide an improved microcontroller based pulse width modulation power supply for a circuit breaker that overcomes some or all the drawbacks of the prior art

SUMMARY

This summary is provided to an improved microcontroller based pulse width modulation circuit and method thereof for a circuit breaker. This summary is not intended to identify essential features of the subject matter nor is it intended for use in determining or limiting the scope of the subject matter.

In one implementation, the invention helps to overcome the limitation in the previous techniques of power supply regulation in electronic trip unit.

In one implementation,the present invention helps to resolve the problems of prior-art mentioned and the other related issues in above section, as it uses internal comparator of microcontroller and the response time is very less. It responds faster than hardware in case of short circuit condition and hence, hardware component can be completely eliminated.

In one implementation, the disclosed invention consists of a firmware for supply voltage regulation in microcontroller based electronic trip unit of circuit breakers.
In one implementation, the microcontroller used has an internal analog comparator and digital to analog converter (DAC).

In one implementation, the potential divider circuit is used to step down the supply voltage and this is given to the positive terminal of the comparator. The internal DAC of microcontroller is used to generate a threshold voltage and it is given as input to the negative terminal of the comparator.

In one implementation, the output of the comparator is given to MOSFET gate. The PWM pulses generated by comparator are used for power supply regulation.

In one implementation, an improved technique for power supply regulation in case of electronic trip unit of circuit breakers is disclosed.

In one implementation, the present invention deals with regulation of supply voltage using internal analog comparator of the microcontroller.

In one implementation, the present invention makes use of internal analog comparator of microcontroller which helps to reduce cost and space. The present invention also discusses the use of microcontroller for adjusting pulse width according to MOSFET parameters.

In one implementation, an efficient implementation of power supply regulation using analog comparator in microcontroller will help to eliminate hardware circuit and hence, reduction in power consumption and cost is disclosed. Due to the fast response time of the analog comparator, the present invention also works in short circuit condition (6kA - 50kA).The analog comparator of microcontroller provides additional settings for sampling and filtering of the comparator output signal.Hence, the minimum pulse width can be adjusted depending on MOSFET parameters. Such a method will ensure operation of MOSFET in saturation and cut-off region thereby reducing power dissipation across MOSFET. So, MOSFET does not work in active region. This power supply regulation technique provides an advantage of variation in pulse width according to power supply voltage. This leads to lower ripple(100mV- 800mV) in supply voltage as compared to ripple achieved by power supply regulation using hardware (1V- 2V).

Accordingly, in one implementation, a microcontroller based pulse width modulation power supply for a circuit breaker is disclosed. The microcontroller of said circuit breaker comprises aninternal comparator (present in the microcontroller) with a specific response time configured to generate a pulse width modulation (PWM) power supply characterized in that a said step down supply voltage (sense voltage) is provided as input at a positive terminal of said internalcomparator and a threshold voltage (Vref) is provided as input at a negative terminal of said internal comparator. In one impledmentnantion, said specific response time is preferably selected from a range of 40microseconds to 100 microseconds.

In one implementation, a method for supply voltage regulation in microcontroller based electronic trip unit of a circuit breaker is disclosed. The method comprises the steps of: generating, by using aninternalcomparator with a high response time, a pulse width modulation (PWM) power supply characterized in that a said step down supply voltage (sense voltage) is provided as input at a positive terminal of said internalcomparator and a threshold voltage (Vref) is provided as input at a negative terminal of said internalcomparator.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The detailed description is described with reference to the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to refer like features and components.

Figure 1 illustrates a circuit for prior art is shown, in accordance with an embodiment of the present subject matter.

Figure 2 illustrates a proposed circuit for present inventionis shown, in accordance with an embodiment of the present subject matter.

Figure 3 illustrates amethod for supply voltage regulation in microcontroller based electronic trip unit of a circuit breakeris shown, in accordance with an embodiment of the present subject matter.

DETAILED DESCRIPTION OF THE PRESENT INVNENTION

Preferred embodiments of the present disclosure will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail.

The terms and words used in the following description are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention.

It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

By the term “substantially” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

In one implementation, the present invention is related to an improved microcontroller based pulse width modulation circuit and method thereof for a circuit breaker.

In one implementation, the present invention consists of a firmware for supply voltage regulation in microcontroller based electronic trip unit of circuit breakers. The microcontroller used has an internal analog comparator and digital to analog converter (DAC). The potential divider circuit is used to step down the supply voltage and this is given to the positive terminal of the comparator. The internal DAC of microcontroller is used to generate a threshold voltage and it is given as input to the negative terminal of the comparator. The output of the comparator is given to MOSFET gate. The PWM pulses generated by comparator are used for power supply regulation.

In one implementation, an improved technique for power supply regulation in case of electronic trip unit of circuit breakers is disclosed.

Referring now to figure 1 illustrates a circuit for prior art is shown, in accordance with an embodiment of the present subject matter. In one implementation, figure 1 is an exemplary embodiment of the present invention wherein, T1 is the current transformer 1. P1 is the primary winding and S1 is the secondary winding. I1 is the secondary current of transformer 1. This AC secondary current is converted into pulsating DC current by using bridge rectifier BR1. This DC current charges the capacitor C1 so that the rail voltage will appear on the line 1. The same rail voltage is available on rail line 2. The MOSFET M1 is connected across the bridge rectifier BR1. For power supply regulation using hardware, the zener diode Z1 is provided in the circuit. The resistor R4 is to limit the current to the zener diode Z1. In case of an over-current, the voltage across R4 drives the gate of the MOSFET M1 and the MOSFET gets turn on.

The regulator REG converts the rail voltage into the suitable voltage which is required by the microcontroller M. The voltage for the controller operation is available at line 3.

The resistor R1 is to limit the gate current and the resistor R7 is to discharge the gate capacitance of the MOSFET.

Referring now to figure 2 illustrates a proposed circuit for present invention is shown, in accordance with an embodiment of the present subject matter. In one implementation, the figure 2 is an exemplary embodiment of the present invention wherein, the present invention provides a method to eliminate hardware circuitry involving Zener diode Z1.

In figure 2, the resistor divider consisting of resistors R2 and R3 are connected across capacitor C1. The resistor divider voltage (sense voltage) is available at node 5. The value of sense voltage can be adjusted by adjusting the values of R2 and R3. The sense voltage (5) is given to analog comparator of microcontroller M. The analog comparator is configured to used sense voltage at the positive terminal and output of digital to analog comparator (DAC) at negative terminal.

The DAC is configured for certain threshold voltage Vref. The comparator gives high output when the sense voltage is above Vref and low output when the sense voltage is below Vref. Additionally, a hysteresis band is defined in the comparator settings in which the comparator output will not change. This pulse is given to the gate of the MOSFET M1.The MOSFET M1 get turned on to limit the value of secondary current and hence controlling the rail voltage on line 2.

In one implementation, a microcontroller based pulse width modulation power supply for a circuit breaker is disclosed. The microcontroller of said circuit breaker comprises aninternal comparator with a high response time configured to generate a pulse width modulation (PWM) power supply characterized in that a said step down supply voltage (sense voltage) is provided as input at a positive terminal of said internal comparator and a threshold voltage (Vref) is provided as input at a negative terminal of said internalcomparator.

In one implementation, said circuit breaker comprises a potential divider circuit to step down said supply voltage; anda digital to analog converter (DAC) configured to generate said threshold voltage (Vref), wherein said internal comparatorprovides a variable pulse width depending on said supply voltage thereby leading to better regulation of supply voltage.

In one implementation, said pulse width modulation (PWM) is based on said threshold voltage (Vref) generated.

In one implementation, said internal comparator with a specific response time is characterized with a certain pre-determined hysteresis band value, wherein said pulse width modulation (PWM) power supply remains constant in said certain pre-determined hysteresis band value.For example, if the hysteresis band of 10 mV is defined then the fluctuation of 10mV above and below the threshold voltage (Vref) does not cause any change in comparator output.

In one implementation, said internal comparator with a specific response time is characterized for sampling and filtering.In filtering, the output of internal comparator goes high only when the sense voltage is greater than threshold voltage for a defined filter period. In sampling, the output of internal comparator goes high only when the sense voltage is greater than threshold voltage for a defined number of samples of sense voltage.
In one implementation, said internal comparator with a high response time is characterized to change its output only if said step down supply voltage (sense voltage) is above a certain pre-determined threshold for a certain number of samples. Pre-determined threshold is computed on the basis of value of supply voltage (Vcap) to be achieved.
Threshold Voltage = (R3/ (R2+R3))*Vcap

The number of sample of sense voltage to be taken depends on MOSFET parameters like minimum pulse width to be given to gate of MOSFET.

In one implementation, said pulse width modulation (PWM) power supply is given to a MOSFET gate and is used for power supply regulation.

Another advantage of using analog comparator is controlling the minimum width of the PWM pulses given to the gate of the MOSFET. The analog comparator of the microcontroller can configured for sampling and filtering. Hence, the pulse width can be varied depending on the MOSFET parameters. Such a method will ensure operation of MOSFET in saturation and cut-off region thereby reducing power dissipation across MOSFET. So, MOSFET does not work in active region.

In one implementation, the internal digital to analog converter (DAC) of the microcontroller is configured to give Vref (threshold voltage above which PWM output will be high) as output.

In one implementation, the internal analog comparator of the microcontroller is configured with step-down supply voltage (sense voltage) at positive terminal and DAC output at negative terminal.

In one implementation, the analog comparator is configured with certain hysteresis band value. The comparator output will not change in this band region. For example, if the hysteresis band of 10 mV is defined then the fluctuation of 10mV above and below the threshold voltage (Vref) does not cause any change in comparator output.

Also, the analog comparator is configured for sampling and filtering. The comparator output will change only if sense voltage is above certain threshold for certain number of samples.

Referring now to figure 3, the method for supply voltage regulation in microcontroller based electronic trip unit of a circuit breakeris shown, in accordance with an embodiment of the present subject matter.

In one implementation, a method for supply voltage regulation in microcontroller based electronic trip unit of a circuit breaker is disclosed. The method comprises the steps of: generating, by using aninternal comparator with a high response time, a pulse width modulation (PWM) power supply characterized in that a said step down supply voltage (sense voltage) is provided as input at a positive terminal of said internal comparator and a threshold voltage (Vref) is provided as input at a negative terminal of said internal comparator.

In one implementation, said method further comprises of performing, using a potential divider circuit, a step down of said supply voltage; andgenerating, using a digital to analog converter (DAC), said threshold voltage (Vref), wherein internal comparatorprovides a variable pulse width depending on said supply voltage thereby leading to better regulation of supply voltage.

In one implementation, said internal comparator with a high response time is characterized with a certain pre-determined hysteresis band value, wherein said pulse width modulation (PWM) power supply remains constant in said certain pre-determined hysteresis band value.

In one implementation, the method further comprises of comprises providing said pulse width modulation (PWM) power supply to a MOSFET gate and is used for power supply regulation.

In one impledmentnantion, said specific response time is preferably selected from a range of 40microseconds to 100 microseconds.

In one implementation, it will be understood by the person skilled in the art that the above mentioned method may be performed by said microcontroller and the set of instruction or module may be stored in the available memory of the micro controller or the circuit breaker. Further, said firmware may be available for performing the above motioned steps when coupled with the micro controller.

Exemplary embodiments discussed above may provide certain advantages. Though not required to practice aspects of the disclosure, these advantages may include those provided by the following features:

One feature of the invention is that,an efficient implementation of power supply regulation using analog comparator in microcontroller is proposed. The proposed mechanism will help to eliminate hardware circuit and hence, reduction in power consumption and cost.

Another feature of the invention is that, due to the fast response time of the analog comparator, the present invention also works in short circuit condition (6kA – 50kA).

Yet another feature of the invention is that, the analog comparator of microcontroller provides additional settings for sampling and filtering of the comparator output signal. Hence, the minimum pulse width can be adjusted depending on MOSFET parameters. Such a method will ensure operation of MOSFET in saturation and cut-off region thereby reducing power dissipation across MOSFET. So, MOSFET does not work in active region.

Still another feature of the invention is that, this power supply regulation technique provides an advantage of variation in pulse width according to power supply voltage. This leads to lower ripple(100mV- 800mV) in supply voltage as compared to ripple achieved by power supply regulation using hardware (1V- 2V).

Although an improved microcontroller based pulse width modulation circuit and method thereof for a circuit breaker has been described in language specific to structural features and/or methods, it is to be understood that the embodiments disclosed in the above section are not necessarily limited to the specific features or methods or devices described. Rather, the specific features are disclosed as examples of implementations an improved microcontroller based pulse width modulation circuit and method thereof for a circuit breaker.

The illustrations of arrangements described herein are intended to provide a general understanding of the structure of various embodiments, and they are not intended to serve as a complete description of all the elements and features of apparatus and systems that might make use of the structures described herein. Many other arrangements will be apparent to those of skill in the art upon reviewing the above description. Other arrangements may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. Figures are also merely representational and may not be drawn to scale. Certain proportions thereof may be exaggerated, while others may be minimized. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

Thus, although specific arrangements have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific arrangement shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments and arrangements of the invention. Combinations of the above arrangements, and other arrangements not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description. Therefore, it is intended that the disclosure not be limited to the particular arrangement(s) disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments and arrangements falling within the scope of the appended claims.

A person of ordinary skill in the art may understand that all or a part of the processes of the methods in the embodiments may be implemented by a computer program instructing relevant hardware. The program may be stored in a computer readable storage medium. When the program runs, the processes of the methods in the embodiments are performed. The foregoing storage medium may include: a magnetic disk, an optical disc, a read-only memory (Read-Only Memory, ROM), or a random access memory (Random Access Memory, RAM).

The foregoing descriptions are merely exemplary embodiments of the present invention, but are not intended to limit the present invention. Any modification, equivalent replacement, or improvement made within the principle of the present invention shall fall within the protection scope of the present invention.
,CLAIMS:1. A microcontroller based pulse width modulation power supply for a circuit breaker, said microcontroller of said circuit breaker comprising:
an internal comparator with a specific response time configured to generate a pulse width modulation (PWM) power supply characterized in that a said step down supply voltage(sense voltage)is provided as input at a positive terminal of said internal comparator and a threshold voltage (Vref) is provided as input at a negative terminal of said internal comparator

2. The microcontroller based pulse width modulation power supply as claimed in claim 1, comprises
a potential divider circuit to step down said supply voltage; and
an internal comparatorconfigured to generate said threshold voltage (Vref), wherein saidinternal comparatorprovides a variable pulse width depending on said supply voltage thereby leading to aregulation of supply voltage.

3. The microcontroller based pulse width modulation power supply as claimed in claims 1 and 2, wherein said pulse width modulation (PWM) is based on said threshold voltage (Vref) generated.

4. The microcontroller based pulse width modulation power supply as claimed in claims 1 to 3, wherein said internal comparator with a high response time is characterized with a certain pre-determined hysteresis band value, wherein said pulse width modulation (PWM) power supply remains constant in said certain pre-determined hysteresis band value.

5. The microcontroller based pulse width modulation power supply as claimed in claims 1 to 4, wherein said internal comparator with a high response time is characterized for sampling and filtering.

6. The microcontroller based pulse width modulation power supply as claimed in claims 1 to 5, wherein said internal comparator with a high response time is characterized to change its output only if said step down supply voltage (sense voltage) is above a certain pre-determined threshold for a certain number of samples.

7. The microcontroller based pulse width modulation power supply as claimed in claims 1 to 6, wherein said pulse width modulation (PWM) power supply is given to a MOSFET gate and is used for power supply regulation.

8. The microcontroller based pulse width modulation power supply as claimed in claims 1 to 7, wherein said specificresponse time is preferably selected from a range of 40microseconds to 100 microseconds.

9. A method for supply voltage regulation in microcontroller based electronic trip unit of a circuit breaker, said method comprising the steps of:
generating, by using a internal comparator with a specific response time, a pulse width modulation (PWM) power supply characterized in that a said step down supply voltage (sense voltage) is provided as input at apositiveterminal of said internal comparator and a threshold voltage (Vref) is provided as input at a negative terminal of said internal comparator.

10. The method as claimed in claim 9, comprises:
performing, using a potential divider circuit, a step down of said supply voltage; and
generating, using an internal comparator, said threshold voltage (Vref), wherein said internal comparatorprovides a variable pulse width depending on said supply voltage thereby leading to better regulation of supply voltage.

11. The method as claimed in claims 9 and 10, wherein said internal comparator with a high response time is characterized with a certain pre-determined hysteresis band value, wherein said pulse width modulation (PWM) power supply remains constant in said certain pre-determined hysteresis band value.

12. The method as claimed in any of the preceding claims comprises: providing said pulse width modulation (PWM) power supplyto a MOSFET gate and is used for power supply regulation.

13. The method as claimed in any of the preceding claims, wherein said specific response time is preferably selected from a range of 40 microseconds to 100 microseconds.