Systems and methods for error compensation in pulse width modulation systems

Abstract

An airflow conditioning system is provided, the system comprising a solenoid valve configured to transition between an open position and a closed position, the solenoid valve comprising a solenoid; a power source; a switch configured to connect or disconnect the power source to or from the solenoid valve according to a duty cycle of the system; and a controller including a memory storing: a mathematical model of a circuit including the solenoid valve, the power source, and the switch; and instructions to execute the steps of: determining a required value of the current through the solenoid; measuring the response of the circuit to the test signal; calculating a compensation value for the duty cycle of the system based on the required value of the current through the solenoid, the response of the circuit to the test signal, and the mathematical model of the circuit; and adjusting the duty ratio of the system based on the compensation value.

Description

Technical Field

[0001] The present invention relates to systems and methods for error compensation in pulse width modulation (PWM) systems, particularly solenoid valves. Background Art

[0002] Many systems are based on pulse width modulation (PWM) technology. PWM is a method of reducing the average power delivered by an electrical signal, and it is a simple and effective way to achieve a specific output value of a process at a low cost. The average value of the voltage (and current) fed to the load is controlled by quickly turning on and off the switch between the supply and the load. The total power supplied to the load depends on the on / off time (active and inactive phases) of the switch.

[0003] One specific application of PWM systems is the solenoid valve. A solenoid valve can be used to control (regulate) the flow of a fluid (e.g., a gas). In a solenoid valve, the magnetic field strength that produces the force for the valve to open is equivalent to the average value of the current in the winding. The valve usually has a spring or other element that resists this force to close the valve when no current is supplied to the valve.

[0004] The current through the solenoid valve must meet a certain minimum value to ensure that the valve is open. Existing systems usually compensate for the effects of, for example, supply voltage variations or the effects of ambient temperature. This is mainly achieved through simple voltage feedback, which allows the current to be adjusted (proportional to the voltage and the force to open the valve).

[0005] One problem with existing PWM systems as applied to solenoid valves is that the components of the circuit modules are not ideal. Existing systems that compensate for the non-ideal behavior of the components typically utilize tables with characteristic data of the system (thus being non-adaptive systems), and / or they require complex signal processing, and / or they require additional components such as pressure sensors, temperature sensors, etc.

[0006] Therefore, there is a need to provide a simple and accurate system and method for regulating a PWM system which will alleviate the above situation. Summary of the invention

[0007] In a first aspect of the present invention, an airflow regulation system is provided, the system comprising a solenoid valve configured to transition between an open position and a closed position, the solenoid valve comprising a solenoid; a power source; a switch configured to connect the power source to the solenoid valve or disconnect it from the solenoid valve according to a duty cycle of the system; and a controller comprising a memory storing: a mathematical model of a circuit including the solenoid valve, the power source and the switch; and instructions for performing the following steps: determining a required value of current through the solenoid; measuring a response of the circuit to a test signal; calculating a compensation value for the duty cycle of the system based on the required value of current through the solenoid, the response of the circuit to the test signal and the mathematical model of the circuit; and adjusting the duty cycle of the system based on the compensation value.

[0008] In an embodiment of the first aspect, the compensation value in the air flow regulation system depends on the difference between the on-time and the off-time of the switch.

[0009] In a second aspect of the present invention, a method for controlling an airflow regulation system includes a solenoid valve configured to move between an open position and a closed position, the solenoid valve including a solenoid; a power source; a switch configured to connect the power source to the solenoid valve or disconnect it from the solenoid valve according to a duty cycle of the system; and a controller including a memory storing: a mathematical model of a circuit including the solenoid valve, the power source and the switch; the method includes: determining, by the controller, a required value of current passing through the solenoid; measuring, by the controller, a response of the circuit to a test signal; calculating, by the controller, a compensation value for the duty cycle of the system based on the required value of current passing through the solenoid, the response of the circuit to the test signal and the mathematical model of the circuit; and adjusting, by the controller, the duty cycle of the system based on the compensation value.

[0010] In an embodiment of the second aspect, the method may further include: measuring a dependency of a difference between a duty cycle indicated by the controller and a duty cycle of the system on a difference between an on-time and an off-time of the switch; and determining a compensation value based on the measured dependency.

[0011] Other embodiments are defined in the claims and described in the detailed description below. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0013] Figure 1 It is a schematic diagram of the PWM regulation system;

[0014] Figure 2 is a schematic diagram of the regulator circuit module;

[0015] Figure 3is an example of PWM with a 32kHz frequency and corresponding current through the solenoid coil;

[0016] Figure 4 Relating to the illustration of the model according to the invention;

[0017] Figure 5 A flow chart of an example method according to the invention is shown. DETAILED DESCRIPTION

[0018] The following description is for illustrative purposes only and is not intended to be limiting. Where appropriate, various elements of the following embodiments may be combined into embodiments not explicitly described.

[0019] Figure 1 A block diagram of an example PWM regulation system is shown. A microcontroller 101 receives a request value for an output current and outputs a first duty cycle. The first duty cycle corresponds to an ideal duty cycle, i.e., a duty cycle in an ideal circuit. A switch 102 operates according to the first (ideal) duty cycle output by the microcontroller 101, changing its state between on and off (active and inactive phases, i.e., where the switch is conducting and non-conducting, respectively) according to the first (ideal) duty cycle.

[0020] In order to compensate for differences in various external parameters (e.g., power supply voltage fluctuations, environmental influences such as ambient temperature, etc.), a feedback loop is provided including an integrator 104. The integrator 104 receives a feedback signal from the solenoid valve 103 and outputs an integrated analog voltage feedback signal to the controller 101. Upon receiving the feedback signal, the feedback signal is processed by the controller 101 and the duty cycle is adjusted accordingly.

[0021] Figure 2 An example PWM regulation system is shown in more detail. The system includes a power source 211, a switch 202 between the power source 201 and the solenoid valve 203, a microcontroller 201, a diode 212, an integrator 204 and a shunt resistor 213. It will be appreciated that other components may be present in the circuit.

[0022] The switch 202 is controlled by the microcontroller 201. The microcontroller 201 generates a duty cycle of pulse width modulation. Based on the duty cycle of pulse width modulation generated by the microcontroller 201, the switch 202 selectively supplies power to the solenoid valve 203.

[0023] There is a diode 212 in parallel with the solenoid valve. The diode 212 provides continuity of the solenoid current during the inactive phase of the switch 202. The average current is proportional to the activation time of the switch 202 (ie the time the switch is on and conducting current).

[0024] The integrator 204 provides a feedback signal. The integrator 204 is connected in parallel to the shunt resistor 213. The voltage drop at the shunt resistor 213 represents the current through the load (solenoid 203 and / or diode 212); based on the information about the voltage at the shunt resistor 213 and the information about the duty cycle generated by the microcontroller 201, the output current can be calculated.

[0025] exist Figure 3 The activated and deactivated phases of the switch 202 are shown in FIG. Figure 3 The upper part of FIG. 3 shows two PWM cycles with an example frequency of 32 kHz (curve 314; “rising” is the active phase of the switch 202 and “falling” is the inactive phase of the switch 202), while Figure 3 The lower portion of (curve 315) shows the corresponding current through the solenoid valve 203. Any other suitable PWM frequency may be used.

[0026] During the active phase of the PWM cycle, the switch 202 is turned on. The power supply device 211 supplies current through the switch 202. The current flows through the solenoid valve 203 and the shunt resistor 213 and returns to the power source 211.

[0027] During the inactive phase of the PWM cycle, switch 202 is non-conductive. Since switch 202 cannot carry current, the current source is the solenoid (coil) of solenoid valve 203. The energy stored in the magnetic field of the solenoid is converted into a current flowing through diode 212. The current steadily decreases until the next active phase of switch 202 occurs or the current decreases to zero (i.e., until the current disappears if the magnetic field energy is too low).

[0028] Components of the system, such as switch 202, are not ideal components. Therefore, the current supplied to the solenoid valve 203 does not necessarily exactly match the first (ideal) duty cycle output by the controller 201. Instead, the solenoid valve 203 operates according to a second (actual) duty cycle, which may be different from the first duty cycle generated by the microcontroller 201. Therefore, the expected (ideal) current through the solenoid may be different from the actual current through the solenoid. The difference in duty cycle and / or current is due to the difference between the ideal component and the real component. In other words, due to its construction, the switch 202 can change the duty cycle from the first (ideal) duty cycle to the second (actual) duty cycle. This change may be small, but it is still important from a gas safety perspective.

[0029] For example, the switch 202 may have specific on and off times, i.e., the switch 202 does not go from an active state to an inactive state in zero time. These on / off times may not be equal (e.g., the switch may take longer to go from an active phase to an inactive phase than from an inactive phase to an active phase). This may result in the above-mentioned difference between the first and second duty cycles, and therefore in a difference between the expected current flowing through the solenoid valve 103 and the actual current flowing through the solenoid valve 103. This is a risk for a solenoid valve regulating a gas flow; generally, the safety of a gas system including a solenoid valve is improved if there is no delay between the theoretical cut-off and the actual cut-off.

[0030] exist Figure 5 An example method of compensating for the above-mentioned current difference (caused by unequal on / off times) is shown in FIG. The circuit can be analyzed to construct a mathematical model of the circuit (step S1). A test signal can be used to measure the system response (step S2), and an appropriate compensation value can be calculated based on the system response to the test signal and the mathematical model (step S3). The compensation value can then be applied to improve the accuracy of the system regulation (step S4).

[0031] This method is simpler than existing compensation methods and can be used at any time, not just during the installation or calibration phase. This method can be used even in situations where full-scale calibration cannot be used (for example, where a significant change in the output value would be unacceptable) because the changes necessary for on / off compensation may be so small that the overall output response of the system is minimal.

[0032] The method minimizes or even eliminates the need to use a look-up table with system characteristics. The method also minimizes or even eliminates the need for complex signal analysis.

[0033] The correction calculated according to the method can be applied during standard operation of the system without any negative impact on the system. The method does not require additional components (such as pressure or temperature sensors, etc.).

[0034] The correction calculated according to this method can provide a more accurate current set point for the solenoid valve. As a result, energy consumption can be lower and the solenoid valve can be more reliable. This method can provide a cost-effective solution to reliability issues because it does not require adding components to the system.

[0035] Compensating for the on / off time difference can improve gas safety. In particular, after applying the compensation, the delay of opening / closing the valve is minimized or even eliminated. This improves the accuracy of the solenoid gas valve and can therefore improve gas safety.

[0036] Those skilled in the art will appreciate that the improvement of the reliability and / or safety of the solenoid valve may depend on the mathematical model of the system, for example on its complexity.

[0037] The model may be specially constructed, or it may be pre-stored in a memory (not shown) of the controller 201 .

[0038] refer to Figure 4 , an example mathematical model and the corresponding compensation can be calculated as follows. Figure 4 The circuit components correspond to Figure 2 Components in ; for simplicity, Figure 4 The circuit includes a power source 411, a switch 402, a solenoid valve 403, a controller 401, an integrator 404 and a shunt resistor 413. The following example is based on the difference between the on / off times of the switch 402, but it will be understood that this is merely an illustrative example.

[0039] In the following, the parameters included in the model are the solenoid valve inductance L and the series resistance R L ; Shunt resistance R sense ; Supply voltage V source ; Anti-parallel diode forward voltage V diode ; and the active and inactive phases of the PWM cycle (i.e., the duty cycle, a number between 0 and 1).

[0040] In the following model, the equations for charging the coil through a resistor from a voltage supply during the active phase of PWM (Equation 1) and discharging the coil through a diode during the inactive phase of PWM (Equation 2) are used:

[0041]

[0042] where (the corresponding units of measurement are given in [square brackets]):

[0043] i RISING (t) is the current during coil charging in the activation phase [A];

[0044] i FALLING (t) is the current during coil discharge in the non-activated phase [A];

[0045] i o is the initial condition of the current [A];

[0046] V SOURCE is the supply voltage [V];

[0047] V DIODE is the forward voltage of the diode [V];

[0048] R SENSEis the shunt resistance value [Ohm];

[0049] R L is the solenoid winding resistance [Ohm];

[0050] L is the solenoid winding inductance [H];

[0051] t is the time [s]; t1 is the activation phase time [s]; and

[0052] t2 is the inactive phase time [s].

[0053] The calculation of the average current value under steady-state conditions can be performed by following the steps below. (Symbols are explained below; the numbering of the steps and the numbering of the equations are provided for ease of reference only.)

[0054] 1. Test whether the current drops to zero during the inactive phase:

[0055] a. Calculate the current level reached after the first activation phase with zero initial current:

[0056]

[0057] b. Calculate the time before the current disappears:

[0058]

[0059] c. Based on the results of steps 1a and 1b, select the appropriate model for further calculations. If the current flows during the entire PWM period (including the entire inactive phase of the switch), then select model 1. If the current drops to zero before the next active phase of the switch, then select model 2.

[0060] 2. Model 1 (preferably used if current flows during the entire PWM period):

[0061] a. Find the minimum and maximum currents in steady state using Equations 5 and 6:

[0062]

[0063] b. Calculate the average current during the activation and deactivation phases:

[0064]

[0065] c. Calculate the average current over time:

[0066]

[0067] 3. Model 2 (preferably used when the current drops to zero during the switch inactive phase):

[0068] a. Calculate the average current (current flowing through the coil) during the activation phase:

[0069]

[0070] b. Calculate the average current value during the inactive phase (until the current drops to zero):

[0071]

[0072] c. Calculate the average current value weighted by the time ratio:

[0073]

[0074] In the above model, the following symbols are used, where the corresponding units of measurement are given in [square brackets]:

[0075] i L_RAMP is the current value under zero initial condition [A];

[0076] IL _AVG_ACT is the average current value in the activation phase (model 1) [A];

[0077] I L_AVG_NACT is the average current value in the non-activation stage (model 1) [A];

[0078] I L_AVG_MODEL1 is the average current value in the entire PWM cycle (model 1) [A];

[0079] I max Maximum (peak) current (model 1) [A];

[0080] I min Minimum current (model 1) [A];

[0081] I L_AVG_RISE is the average current value in the activation phase (model 2) [A];

[0082] I L_AVG_EXT is the average current value in the non-activation stage (model 2) [A];

[0083] I L_AVG_MODEL2 is the average current value in the entire PWM cycle (MODEL2) [A]

[0084] V source is the supply voltage [V];

[0085] V diode is the forward voltage of the diode [V];

[0086] R sense is the shunt resistance value [Ohm];

[0087] R L is the solenoid winding resistance [Ohm];

[0088] L is the solenoid winding inductance [H];

[0089] t1 is the activation phase time [s];

[0090] t2 is the inactive phase time [s];

[0091] t EXT is the time during which the current disappears during the inactive phase; and

[0092] T is the PWM period (T=t1+t2) [s].

Claims

1. An airflow regulation system, comprising: a solenoid valve configured to transition between an open position and a closed position, the solenoid valve comprising a solenoid; Power source; a switch configured to connect or disconnect the power source to or from the solenoid valve based on a duty cycle of the system; and A controller comprising a memory storing: a mathematical model of a circuit including the solenoid valve, the power source and the switch; and Execute the following instructions: - determining the required value of the current through the solenoid; - measuring the response of the circuit to a test signal; - calculating a compensation value for the duty cycle of the system based on the desired value of the current through the solenoid, the response of the circuit to the test signal and the mathematical model of the circuit; -Adjusting the duty cycle of the system based on the compensation value.

2. The airflow conditioning system according to claim 1, wherein: The compensation value depends on the on-time of the switch.

3. The airflow conditioning system according to claim 1 or 2, wherein: The compensation value depends on the off time of the switch.

4. An airflow conditioning system according to any one of the preceding claims, wherein: The compensation value depends on the difference between the on-time and the off-time of the switch.

5. The airflow adjustment system according to claim 1 or claim 2, wherein: The instructions also include the following steps: - constructing said mathematical model; - storing said mathematical model in said memory.

6. The air flow conditioning system according to any of the preceding claims, further comprising at least one of the following components: an integrator, a diode, a shunt resistor.

7. An airflow conditioning system according to any one of the preceding claims, wherein: The memory stores a first mathematical model and a second mathematical model, and wherein the instructions further comprise the steps of: - determining whether the current flows through the circuit during the entire PWM period, or whether the current drops to zero during the switch inactive phase; and - selecting a model from the first mathematical model and the second mathematical model based on a determination whether the current flows through the circuit during the entire PWM period or whether the current drops to zero during the switch inactive phase.

8. A method for controlling an airflow conditioning system, the system comprising: a solenoid valve configured to move between an open position and a closed position, the solenoid valve comprising a solenoid; Power source; a switch configured to connect or disconnect the power source to or from the solenoid valve based on a duty cycle of the system; as well as a controller including a memory storing: a mathematical model of a circuit including the solenoid valve, the power source, and the switch; The method comprises: - determining, by the controller, a desired value of the current through the solenoid; - measuring, by the controller, a response of the circuit to a test signal; - calculating, by the controller, a compensation value for the duty cycle of the system based on the desired value of the current through the solenoid, the response of the circuit to the test signal, and the mathematical model of the circuit; - adjusting, by the controller, the duty cycle of the system based on the compensation value.

9. The method according to claim 8, wherein: The method further comprises: measuring a dependency of a difference between the duty cycle indicated by the controller and the duty cycle of the system on an on-time of the switch; and The compensation value is determined based on the measured dependency.

10. The method according to claim 8 or 9, wherein: The method further comprises: measuring a dependency of a difference between the duty cycle indicated by the controller and the duty cycle of the system on an off time of the switch; and The compensation value is determined based on the measured dependency.

11. The method according to any one of claims 8 to 10, wherein: The method further comprises: measuring a dependency of a difference between the duty cycle indicated by a controller and the duty cycle of the system on a difference between an on-time and an off-time of the switch; and The compensation value is determined based on the measured dependency.

12. The method according to any one of claims 8 to 11, wherein: The method further comprises: - constructing the mathematical model by the controller; - Storing a mathematical model in said memory by said controller.

13. The method according to any one of claims 8 to 12, wherein: The system further includes at least one of the following components: an integrator, a diode, a shunt resistor.

14. The method according to any one of claims 8 to 13, wherein: The memory stores a first mathematical model and a second mathematical model, and wherein the method further comprises the following steps: - determining by the controller whether the current flows through the circuit during the entire PWM period, or whether the current drops to zero during the switch inactive phase; and - selecting, by the controller, a model from the first mathematical model and the second mathematical model based on a determination whether the current flows through the circuit during the entire PWM period or whether the current drops to zero during a switch inactive phase.

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