Approach constant delay comparator for closed loop systems

Abstract

A voltage comparator and a programmable counter coupled to a high speed clock are used to provide a near constant delay time for a closed loop system. The voltage comparator input-output time delay is characterized at certain temperatures and operating voltages, and then the voltage comparator delay time variation over a range of operating temperatures and voltages is measured and / or extrapolated. A number of clock pulses for the delay time count are programmed into the programmable counter to provide a near constant delay time from a change at the input of the voltage comparator to a change at the output of the programmable counter.

Description

[0001] Related patent applications

[0002] This application claims priority to co-owned U.S. Provisional Patent Application Serial No. 63 / 007,843, filed April 9, 2020, entitled “Near Constant Delay Comparator for Closed-Loop System,” which is incorporated herein by reference for all purposes. Technical Field

[0003] This disclosure relates to closed-loop protection circuits and systems, and more specifically, to closed-loop protection circuits and systems for electric motors. Background Technology

[0004] In electric motor protection and control system applications, voltage comparators are commonly used in overcurrent / overdrive protection circuits. These circuits use a current-to-voltage converter (e.g., a resistor) to sense the motor current. This converter provides a voltage proportional to the motor current, which is coupled to a voltage comparator. The comparator compares the sensed motor current (the voltage across the resistor) with a voltage reference (voltage threshold). When the motor current exceeds a certain value, the comparator output changes its logic state, potentially leading to a reduction in motor load or shutdown.

[0005] Traditional motor protection and control systems must trade reliability for efficiency. A typical voltage comparator (analog device) can have an operating delay variation of plus or minus fifty percent (50%). Therefore, the current sensing resistor must be selected with fifty percent (50%) of the delay subtracted for the worst-case scenario, and the motor protection system must be able to protect the motor with fifty percent (50%) of the delay added for the worst-case scenario. This margin leads to inefficient or over-designed motor protection systems. Summary of the Invention

[0006] Therefore, there is a need for a way to minimize the changes in operating delay caused by analog voltage comparators when used in protection circuits.

[0007] According to one embodiment, a comparator with a near-constant input-to-output delay time is disclosed. The comparator may include: a voltage comparator having a measurement delay time between an input change and a subsequent output change at a given temperature and operating voltage; and a programmable delay counter having a first input, a second input, and a third input, the first input coupled to the output of the voltage comparator, the second input coupled to a clock that generates a plurality of clock pulses, and the third input for programming a count of the plurality of clock pulses used to determine a time delay of a logic level change at the first input, the logic level change at the first input causing a subsequent logic level change at the output of the programmable delay counter, wherein the first input logic level can be programmed into the count of the plurality of clock pulses in the programmable delay counter via the third input delay of the programmable delay counter, such that the total delay from the input of the voltage comparator to the output of the programmable delay counter is the input-to-output delay time of the voltage comparator plus the time associated with the count of the plurality of clock pulses programmed into the programmable delay counter.

[0008] According to another embodiment, a microcontroller is disclosed that may include a digital processor and memory coupled to the programmable delay counter, wherein the microcontroller programs the counting of a plurality of clock pulses into the programmable delay counter. According to another embodiment, a temperature sensor and a voltage sensor are provided within the microcontroller for measuring the temperature and voltage of the voltage comparator, wherein the digital processor and memory adjust the counting of the plurality of clock pulses programmed into the programmable delay counter based on the measured temperature and voltage. According to another embodiment, a first input of the voltage comparator may be adapted to be coupled to a motor current sensor. According to another embodiment, the microcontroller may further include a digital-to-analog converter coupled to the digital processor and memory and having an output for providing a reference voltage coupled to a second input of the voltage comparator.

[0009] According to another embodiment, a system for overcurrent protection of an electric motor is disclosed, the system comprising: a current sensor coupled to a coil of the electric motor for measuring its current and having a voltage output proportional to the current of the electric motor; a voltage comparator having a first input coupled to the current sensor and a second input coupled to a reference voltage, wherein the voltage comparator has a known time delay between an input change and a subsequent output change at a given temperature and operating voltage; and a programmable delay counter having a first input, a second input, and a third input, the first input being coupled to the output of the voltage comparator, and the second input being coupled to the generation of a plurality of clock pulses. The clock, the third input being used to program a count of a plurality of clock pulses for determining a time delay of a logic level change at the first input, the logic level change at the first input causing a subsequent logic level change at the output of the programmable delay counter, wherein the first input logic level can be programmed into the count of the plurality of clock pulses in the programmable delay counter via the third input delay of the programmable delay counter; and a motor power control circuit having an input coupled to the output of the programmable delay counter, wherein the output of the programmable delay counter causes the motor power control circuit to modify the operation of the electric motor when the voltage from the current sensor is greater than the reference voltage.

[0010] According to another embodiment, modifying the operation of the electric motor can shut it off. According to another embodiment, modifying the operation of the electric motor can reduce the power used by the motor. According to another embodiment, a microcontroller is disclosed that may include a digital processor and a memory coupled to the programmable delay counter, whereby the digital processor and memory program the counting of a plurality of clock pulses into the programmable delay counter. According to another embodiment, the microcontroller may include a voltage comparator and a programmable delay counter. According to another embodiment, the comparator may include a temperature sensor and a voltage sensor located in the microcontroller for measuring the temperature and operating voltage of the voltage comparator, wherein the digital processor and memory adjust the counting of the plurality of clock pulses programmed into the programmable delay counter based on the measured temperature and voltage.

[0011] According to another embodiment, the microcontroller may include a digital-to-analog converter coupled to the digital processor and having an output for providing a reference voltage to a second input of the voltage comparator. According to another embodiment, the current sensor may include a resistor connected in series between an electrical terminal of the motor's coil and a power source. According to another embodiment, the current sensor may include a current transformer having a first winding connected in series between an electrical terminal of the motor's coil and a power source, and a second winding coupled in parallel with the resistor.

[0012] According to another embodiment, a method for providing a near-constant input-output delay for a comparator is disclosed, the method comprising the steps of: providing a voltage comparator having a known time delay between an input change and a subsequent output change at a given temperature and operating voltage; coupling a programmable delay counter to the voltage comparator; coupling a clock suitable for generating a plurality of clock pulses to the programmable delay counter; and programming the counting of the plurality of clock pulses to determine the time delay of the programmable delay counter, wherein the time delay from an input change to the voltage comparator to a subsequent output change from the programmable delay counter may be the input-output delay time of the voltage comparator plus the time associated with the count of the plurality of clock pulses programmed into the programmable delay counter.

[0013] According to another embodiment of the method, a step of modifying the programmed count based on the temperature of the voltage comparator may be included. According to another embodiment of the method, a step of modifying the programmed count based on the operating voltage of the voltage comparator may be included. According to another embodiment of the method, the step of programming the count of the plurality of clock pulses to determine the time delay of the programmable delay counter can be performed using a digital processor and memory. Attached Figure Description

[0014] A more complete understanding of this disclosure can be obtained by referring to the following description taken in conjunction with the accompanying drawings, in which:

[0015] Figure 1 A schematic block diagram of an overcurrent protection circuit and system for motors connected in series and in parallel, according to a specific exemplary embodiment of the present disclosure, is shown.

[0016] Figure 2 A schematic block diagram of an overcurrent protection circuit and system for a three-phase motor with delta and Y connections according to a specific exemplary embodiment of the present disclosure is shown.

[0017] Figure 3 The teachings of this disclosure are shown to be applicable to [various situations]. Figure 1, Figure 2 and Figure 4 A schematic diagram of the current sensor in the circuit shown; and

[0018] Figure 4 A specific exemplary embodiment of the present disclosure is shown for use in Figure 1 and Figure 2 The diagram shows a schematic block diagram of a microcontroller implementation of the overcurrent protection circuit shown.

[0019] While this disclosure is susceptible to various modifications and alternatives, specific exemplary embodiments thereof have been shown in the accompanying drawings and described in detail herein. However, it should be understood that the description of specific exemplary embodiments herein is not intended to limit this disclosure to the forms disclosed herein. Detailed Implementation

[0020] Motor protection circuits, such as overcurrent protection circuits, use a voltage comparator in conjunction with a reference voltage Vref to detect overcurrent. One input of the voltage comparator is coupled to a current-to-voltage converter (resistor) (whose voltage represents the motor current), and the other input is coupled to the reference voltage Vref. When the voltage representing the motor current changes from less than the reference voltage to greater than the reference voltage, or vice versa, the comparator's logic output changes its logic state, for example, from 0 to 1 or from 1 to 0. However, this output logic state change varies over time depending on the comparator circuit process, voltage, and / or temperature (PVT). Therefore, the overload protection actuation time of the control loop is thus affected.

[0021] The motor can only be used in a very short time (T motor_ovd It can withstand large overload currents. The overload protection actuation time (T) of the control circuit... resp_ovd It must be less than T. motor_ovd A fast comparator response can be achieved by using a large voltage drop (IR) across the current sensing resistor (a large resistance value). As used below, nanoseconds are abbreviated as "ns" and millivolts as "mV". For example, the response time of a voltage comparator for a 200mV change could be t. comp =50ns + / -50%, and for a 20mV change, this response time can be t. comp = 250ns + / - 50%. Therefore, the response time for a 200mV change can be 25ns to 75ns (a 50ns change), while the response time for a 20mV change can be 125ns to 375ns (a 250ns change).

[0022] For a high-efficiency motor system with a 20mV current sensor variation, the control loop will compensate for the 125ns voltage comparator response time variation, but there is a 250ns protection time variation greater than T.motor_ovd The risk is that for motor systems using a 200mV current sensor for higher protection reliability, the control loop will compensate for the 25ns voltage comparator response time variation. A 50ns protection time variation will be greater than T. motor_ovd The probability of this is very low, and it can be up to 200 ns faster than a high-efficiency motor system. Unfortunately, the efficiency of the motor system decreases when using a larger voltage for current sensing. Therefore, as long as the voltage comparator's response time t... comp Less than the motor overload time T motor_ovd The change in the response time of the voltage comparator can be compensated for.

[0023] Embodiments of this disclosure may include an analog voltage comparator and a programmable counter coupled to a high-speed clock. The programmable counter can provide an adjustable time delay that can be used to compensate for the variable time delay of the voltage comparator caused by process, voltage, and / or temperature (PVT) variations within the voltage comparator circuitry. The programmable counter can be programmed based on a process characterization of the voltage comparator delay time, such as the measured time delay of the manufacturing voltage comparator circuitry, and the variation of the measured voltage comparator delay time based on variations in its operating temperature and voltage. A baseline process-dependent delay time can be determined using a given temperature and voltage, and then the deviation of this baseline process-dependent delay time over a certain temperature and voltage range can be determined. Once the voltage comparator delay time has been characterized for all PVT values ​​of interest, a lookup table can be defined and associated with the desired additional time delay introduced by the programmable counter. Therefore, the resulting compensated comparator delay time (t...) comp The counter delay time will always be less than the motor overload time T. motor_ovd .

[0024] The advantage of the implementation disclosed herein is that the comparator delay remains nearly constant as temperature and voltage change. This allows for motor current sensing using smaller current sensing (smaller resistor) values, thereby reducing power losses and improving motor operating efficiency without sacrificing motor reliability.

[0025] Referring now to the accompanying drawings, details of an exemplary embodiment are schematically illustrated. Similar elements in the drawings will be represented by similar numerals, and similar elements will be represented by similar numerals with different lowercase letter suffixes.

[0026] refer to Figure 1 It shows a schematic block diagram of an overcurrent protection circuit and system for motors connected in series and in parallel, according to a specific exemplary embodiment of the present disclosure. Figure 1 (a) shows a coil 104 and a motor armature 102 connected in series with a current sensor 106. Figure 1(b) shows the coil 104 and the motor armature 102 connected in parallel with the current sensor 106.

[0027] A voltage comparator 108 can be used to compare the voltage generated by the current sensor 106 with a reference voltage Vref. The comparator output can be at logic 1 when the reference voltage is greater than the voltage from the current sensor 106, and at logic 0 when the reference voltage is less than the voltage from the current sensor 106. The output of comparator 108 can be used to indicate the motor overcurrent condition measured by coils 104 / 104a.

[0028] refer to Figure 2 It shows a schematic block diagram of an overcurrent protection circuit and system for a three-phase motor with delta and Y-connections according to a specific exemplary embodiment of the present disclosure. Figure 2 (a) shows a motor in a delta connection with a current sensor 106, the motor including three-phase coils 204 shown as coils 204a, 204b and 204c respectively. Figure 2 (b) shows a motor connected in a Y-shape in combination with a current sensor 106, the motor including a three-phase coil 210 shown as coils 210a, 210b and 210c respectively.

[0029] A voltage comparator 108 can be used to compare the voltage generated by the current sensor 106 with a reference voltage Vref. When the reference voltage is greater than the voltage from the current sensor 106, the comparator output can be at logic 1. When the reference voltage is less than the voltage from the current sensor 106, the comparator output can be at logic 0. The output of comparator 108 can be used to indicate motor overcurrent.

[0030] refer to Figure 3 It demonstrates that the teachings of this disclosure can be used to... Figure 1 , Figure 2 and Figure 4 The diagram shows a current sensor in the circuit shown. Figure 3 (a) shows resistor 326 through which the motor current flows directly. The voltage drop across resistor 326 is proportional to the motor current. The voltage at the motor side of resistor 326 is compared to a reference voltage Vref, and the output of comparator 108 can be at logic 0 when the voltage is greater than Vref. Figure 3(b) A resistor 328 is shown connected in parallel with the winding of the current transformer (CT) 330. A diode 340 is used to convert the AC voltage to a DC voltage, and a smoothing capacitor, not shown, will also be used to convert the AC voltage to a DC voltage. As the power lead from the power source to the motor passes through CT 330, the current flowing through that power lead gradually decreases proportionally to the turns ratio of CT 330 to the power lead to the motor. The winding of CT 330, combined with resistor 328, produces a voltage proportional to the motor current divided by the turns ratio of CT 330. The voltage from resistor 328 is compared to a reference voltage Vref, and when this voltage is greater than Vref, the output of comparator 108 can be at logic 0. The output of comparator 108 can be used to indicate an overcurrent.

[0031] refer to Figure 4 It illustrates a specific exemplary embodiment of the present disclosure for use with Figure 1 and Figure 2 The diagram shows a schematic block diagram of a microcontroller implementation of the overcurrent protection circuit. The microcontroller 410 may include a comparator 108, a digital-to-analog converter (DAC) 412, a digital processor and memory 414, a programmable delay counter 416, and a clock 418. A first input of the comparator 108 may be coupled to a current sensor 106, and a second input may be coupled to the output of the DAC 412. The DAC 412 may be used to provide a programmable reference voltage Vref from the digital processor and memory 414. The output from the programmable delay counter 416 may be coupled to a motor power control 424 for shutting off and / or reducing the power used by the coils 104, 104a, 204, 210 of the target motor. The programmable delay counter 416 may be programmed with a count n such that a change in the input logic level indicating overcurrent at its input (coupled to the output of the comparator 108) may be delayed by n clock pulses (clock pulses from the clock 418). The delayed output from the programmable delay counter 416 may be coupled to the motor power control 424 as a motor trip signal. Temperature sensor 420 and voltage sensor 422 can be housed in microcontroller 410 for measuring temperature and voltage of comparator 108. If temperature sensor 420 and voltage sensor 422 have analog outputs instead of digital outputs, an analog-to-digital converter (not shown) can also be placed between these sensors and digital processor and memory 414.

[0032] The count n can be used to characterize the time delay of the voltage comparator 108 under test when operating at a certain temperature and voltage. An inference test of the time delay of the voltage comparator 108 can then be performed within the operating range of temperature and operating voltage. How temperature and voltage variations affect the time delay of the voltage comparator 108 can be determined. The measured time delay and how it varies with temperature and voltage can be stored in the memory of the digital processor 414. During operation of the microcontroller 410, temperature sensor 420 and voltage sensor 422 can be used to provide temperature and voltage values, which can be used to look up corresponding temperature and voltage variation tables and / or infer how they affect the time delay of the comparator 108. This provides a more accurate fixed time delay compared to voltage comparator circuit processes, voltage and / or temperature (PVT) variations.

[0033] For example, the process delay may vary by + / -35%, and the temperature-induced delay may vary by + / -15%. A fixed 400ns comparator output logic change is provided to signal motor tripping in response to the output of current sensor 106 exceeding Vref, and assuming a clock time of 6ns,

[0034] A typical comparator delay of 250ns + a counter delay of 150ns = 400ns, meaning the counter takes 25 clock cycles to reach its destination.

[0035] The slow comparator has a delay of 330ns + the counter has a delay of 70ns = 400ns, taking 12 clock cycles to reach the counter. The fast comparator has a delay of 170ns + the counter has a delay of 230ns, taking 38 clock cycles to reach the counter.

[0036] Temperature delay can be adjusted and corrected:

[0037] Room temperature delay count = 25 clock cycles

[0038] Low-temperature delay count = 28 clock cycles

[0039] High-temperature delay count = 22 clock cycles

[0040] This disclosure has been described according to one or more embodiments, and it should be understood that many equivalents, alternatives, variations, and modifications are possible and within the scope of this disclosure, in addition to those expressly stated. While this disclosure is susceptible to various modifications and alternatives, specific exemplary embodiments thereof have been shown in the accompanying drawings and described in detail herein. However, it should be understood that the description of specific exemplary embodiments herein is not intended to limit this disclosure to the specific forms disclosed herein.

Claims

1. A microcontroller, the microcontroller comprising: A voltage comparator that has a measurement delay time between an input change and a subsequent output change at a given temperature and operating voltage; A programmable delay counter has a first input, a second input, and a third input. The first input is coupled to the output of a voltage comparator. The second input is coupled to a clock that generates a plurality of clock pulses. The third input is used to program a count of the plurality of clock pulses for determining a time delay of a logic level change at the first input. A logic level change at the first input causes a subsequent logic level change at the output of the programmable delay counter. The logic level change at the first input is delayed by the count of the plurality of clock pulses. The count of the plurality of clock pulses is programmed into the programmable delay counter via the third input, such that the total delay from the input of the voltage comparator to the output of the programmable delay counter is the input-output delay time of the voltage comparator plus the time associated with the count of the plurality of clock pulses programmed into the programmable delay counter. A digital processor and a memory are coupled to the programmable delay counter, wherein the digital processor programs the counts of the plurality of clock pulses into the programmable delay counter, and The microcontroller includes a temperature sensor and a voltage sensor for measuring the temperature and voltage of the voltage comparator, wherein the digital processor and memory adjust the count of the plurality of clock pulses programmed into the programmable delay counter based on the measured temperature and voltage.

2. The microcontroller of claim 1 further includes a first input of the voltage comparator, the first input being adapted to be coupled to a motor current sensor.

3. The microcontroller of claim 2, wherein the microcontroller further comprises a digital-to-analog converter coupled to the digital processor and the memory and having an output for providing a reference voltage coupled to a second input of the voltage comparator.

4. A system for overcurrent protection of an electric motor, the system comprising: A current sensor, coupled to a coil of an electric motor, is used to measure the current of the electric motor and has a voltage output proportional to the current of the electric motor. A voltage comparator having a first input coupled to the current sensor and a second input coupled to a reference voltage, wherein the voltage comparator has a measurement delay time between a change in the input and a subsequent change in the output at a given temperature and operating voltage. A programmable delay counter has a first input, a second input, and a third input. The first input is coupled to the output of the voltage comparator, the second input is coupled to a clock that generates a plurality of clock pulses, and the third input is used to program a count of the plurality of clock pulses for determining a time delay of a logic level change at the first input. A logic level change at the first input causes a subsequent logic level change at the output of the programmable delay counter, wherein the logic level at the first input is delayed by the count of the plurality of clock pulses, and the count of the plurality of clock pulses is programmed into the programmable delay counter via the third input. as well as A motor power control circuit having an input coupled to the output of a programmable delay counter, wherein the output of the programmable delay counter causes the motor power control circuit to modify the operation of the electric motor when the voltage from the current sensor is greater than the reference voltage.

5. The system according to claim 4, wherein the operation of modifying the electric motor is to turn off the motor.

6. The system of claim 4, wherein the operation of modifying the electric motor is to reduce the power used by the motor.

7. The system of claim 4, further comprising a microcontroller including a digital processor and a memory coupled to the programmable delay counter, wherein the digital processor programs the counting of the plurality of clock pulses into the programmable delay counter.

8. The system of claim 7, wherein the microcontroller further includes the voltage comparator and the programmable delay counter.

9. The system of claim 8, further comprising a temperature sensor and a voltage sensor in the microcontroller for measuring the temperature and operating voltage of the voltage comparator, wherein the digital processor and memory adjust the counting of the plurality of clock pulses programmed into the programmable delay counter based on the measured temperature and voltage.

10. The system of claim 8, wherein the microcontroller further comprises a digital-to-analog converter coupled to the digital processor and having an output for providing the reference voltage to a second input of the voltage comparator.

11. The system of claim 4, wherein the current sensor comprises a resistor connected in series between an electrical terminal of the motor coil and a power source.

12. The system of claim 4, wherein the current sensor comprises a current transformer having a first winding connected in series between an electrical terminal of the motor coil and a power source, and a second winding coupled in parallel with a resistor.

13. A method for providing a near-constant input-output delay for a comparator, the method comprising the steps of: A voltage comparator is provided, which has a known time delay between a change in the input and a subsequent change in the output at a given temperature and operating voltage; Couple a programmable delay counter to the voltage comparator; A clock suitable for generating multiple clock pulses is coupled to the programmable delay counter; Measure the temperature and voltage of the voltage comparator; as well as Based on the measured temperature and voltage, the counting of multiple clock pulses is programmed to determine the time delay of the programmable delay counter, wherein the time delay from a change to the input of the voltage comparator to a subsequent change to the output of the programmable delay counter is the input-output delay time of the voltage comparator plus the time associated with the count of the multiple clock pulses programmed into the programmable delay counter.

14. The method of claim 13, wherein the step of programming the counts of the plurality of clock pulses to determine the time delay of the programmable delay counter is performed using a digital processor and a memory.

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