Curvature compensation control method for alternating-current electromagnet of release

Abstract

The invention relates to a curvature compensation control method for an alternating current electromagnet of a release, which comprises the following steps: S1, when a module is enabled, a processor detects the voltage Vs of a sampling circuit, and judges whether the voltage Vs is the initial value of a coil work cycle; s2, after the period starts, the microprocessor inquires the curvature compensation Dt value in the lookup table, S3, according to the Dt value, Dti is output as the PWM work period of the duty ratio, and i is the serial number of the numerical value in the array; and S4, outputting a signal to a power switch MOS, and driving a coil to be switched on or switched off until all Dt in the lookup table are output. According to the invention, curvature compensation is carried out on the duty ratio Dt of the PWM signal of the AC electromagnet coil, so that the current and power in the coil can be kept constant as far as possible, and the performance of the AC electromagnet is improved.

Description

Technical Field

[0001] The invention relates to the technical field of releasers, and in particular to a curvature compensation control method for an AC electromagnet of a releaser. Background Art

[0002] In the power system, the circuit breaker release plays a vital role. It is used to quickly disconnect the circuit when abnormal current (such as overload or short circuit) is detected to protect electrical equipment and personnel safety.

[0003] In response to the problem of electromagnet overheating caused by long-term power-on, a study proposed a method to reduce the power consumption and temperature rise of the electromagnet in the long-term power-on state by optimizing the structural parameters and control strategy of the control circuit. Specifically, the time constant and damping coefficient of the circuit can be adjusted by setting reasonable parameters of components such as resistance and capacitance; at the same time, PWM (pulse width modulation) control technology can be used to accurately control the power-on time and current of the electromagnet to avoid overheating and damage of the electromagnet due to long-term power-on.

[0004] As known, the technical solution disclosed in patent CN101013638A: the disconnection controller controls whether the relay is tripped according to the control instruction issued by the power supply monitoring, and adjusts the PWM output of the coil voltage according to the fuzzy control algorithm, and adapts to multiple voltage ranges.

[0005] Another example is the technical solution disclosed in the known patent CN113035658A: undervoltage protection and shunt excitation functions are integrated into one, and PWM technology is used to dynamically adjust the electromagnet's pull-in maintenance force and power consumption. The PWM control method is that the microcontroller calculates the grid voltage through the ADC port of the detection circuit. If the grid voltage is not less than 80% of the grid voltage rating, PWM sends a pull-in signal. After waiting for 320mS, the microcontroller detects the driving voltage Vpp value and adjusts the duty cycle of the PWM pulse according to the Vpp value.

[0006] Another example are known patents: CN103294097A, CN103065890A, etc.

[0007] However, the above-mentioned related patents only disclose that the AC electromagnets are all PWM controlled, and none of them make overall planning and setting of the duty cycle for the constancy of the electromagnetic attraction. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a curvature compensation control method for an AC electromagnet of a release, by performing curvature compensation on the duty cycle Dt of a PWM signal of an AC electromagnet coil, so that the current and power in the coil can be kept as constant as possible, thereby improving the performance of the AC electromagnet.

[0009] The technical solution adopted by the present invention to solve the technical problem is: a trip device AC electromagnet curvature compensation control method, comprising the following steps:

[0010] S1. When the module is enabled, the processor detects the voltage Vs of the sampling circuit to determine whether it is the starting value of the coil working cycle;

[0011] S2. After the cycle starts, the microprocessor queries the curvature compensation Dt value in the lookup table.

[0012] S3, output Dti as the PWM duty cycle according to the Dt value, where i is the sequence number of the value in the array;

[0013] S4, output signal to the power switch MOS, driving the coil to turn on or off until all Dt in the lookup table are output.

[0014] Furthermore, in step S1 of the present invention, if the cycle start value has not been reached, wait until the cycle starts.

[0015] Furthermore, the variation range of the PWM duty cycle of the present invention satisfies the following two constraints:

[0016] Condition 1: The change value of PWM duty cycle during curvature compensation conforms to the function: Dt = csc(ωt), where ω is the angular frequency of the industrial frequency alternating current; ωt∈[0,π];

[0017] Condition 2: When PWM drives the MOS tube, the PWM pulse width is the minimum value.

[0018] Furthermore, the present invention sets an upper limit and a lower limit of the variation range of the duty cycle Dt of the PWM switch signal according to curvature compensation; when the duty cycle is lower than the lower limit, the minimum lower limit value is taken; when the duty cycle is higher than a set value, the PWM duty cycle is the upper limit value.

[0019] Furthermore, the calculation method of the PWM duty cycle change value of the present invention is as follows:

[0020]

[0021] The obtained curvature change duty cycle Dt change value is stored in the microcontroller.

[0022] The beneficial effects of the present invention are that the defects existing in the background technology are solved.

[0023] The present invention adopts PWM control for the opening and closing of the coil, and sets and controls the duty cycle Dt value of PWM in each coil fluctuation cycle. By performing curvature compensation on the duty cycle change curve of each cycle, the change of current is compensated, so as to keep the effective value of current constant over a long period of time, that is, greatly reducing the power and suction change of the AC coil, so that the coil works more stably.

[0024] The power and suction force of the electromagnetic coil of the present invention are closer to a constant value, and the noise caused by the change of current and suction force in the AC cycle is also greatly reduced, making the release more silent;

[0025] In the signal control of the microprocessor of the present invention, the value of the curvature compensation duty cycle is stored in a lookup table, which avoids a large number of numerical calculations of the microprocessor. Only signal detection, numerical reading and control are required, which greatly reduces the operating frequency of the microprocessor and makes the control simpler, thereby greatly reducing the power consumption of the microprocessor and reducing the hardware design requirements of the power module, so that the temperature rise of the release is lower. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the block diagram of AC electromagnet circuit;

[0027] Figure 2 It is the equivalent circuit diagram of the AC electromagnet coil;

[0028] Figure 3 This is a schematic diagram of the PWM signal driving the control coil;

[0029] Figure 4 It is a schematic diagram of curvature compensation for PWM duty cycle variation;

[0030] Figure 5 It is a schematic diagram of the curvature change of the PWM duty cycle;

[0031] Figure 6 It is a quantitative diagram of the duty cycle Dt curve based on the control frequency;

[0032] Figure 7 is a schematic diagram of the duty cycle of curvature compensation;

[0033] Figure 8 Schematic diagram of coil current with constant duty cycle (top) and coil current with curvature compensation duty cycle (bottom);

[0034] Fig. 9 It is a schematic diagram of the effective value of the coil current with a constant duty cycle and the effective value of the coil current with a curvature compensation duty cycle;

[0035] Fig.10 is a schematic diagram of coil power with constant duty cycle and coil power with curvature compensation duty cycle;

[0036] Fig.11 It is a schematic diagram of the control flow of the curvature compensation duty cycle in the microprocessor. DETAILED DESCRIPTION

[0037] The present invention will now be described in further detail in conjunction with the accompanying drawings and preferred embodiments. These drawings are simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0038] like Fig.11 A trip device AC electromagnet curvature compensation control method is shown. When the module is enabled, the processor detects the voltage Vs of the sampling circuit to determine whether it is the starting value of the coil working cycle. If it has not reached the starting value of the cycle, it waits until the cycle starts. After the cycle starts, the microprocessor queries the curvature compensation Dt value in the lookup table, outputs Dti (i is the sequence number of the value in the array) as the PWM working cycle of the duty cycle according to the Dt value, outputs it to the power MOS tube, drives the coil to turn on or off, until all Dt in the lookup table are output.

[0039] In the circuit implementation, the duty cycle change value of the curvature compensation Dt is stored in the microprocessor to form a lookup table, which can avoid a large number of mathematical operations of the microprocessor, thereby reducing the requirements of the microprocessor, reducing costs, and reducing power consumption.

[0040] From the working mode of the microprocessor, it can be seen that the working mode of the microprocessor is mainly scheduling, querying and controlling. It does not need integer and floating-point numerical calculations, and the response speed is faster. Therefore, the microprocessor can work better in a low-power state, that is, the clock frequency of the microprocessor can be reduced, and fewer modules are involved in the work, so the required power consumption is lower, which greatly reduces the design difficulty of the power module and the temperature rise of the control circuit. At the same time, through this workflow, it can be ensured that the start and end of the coil action are at the lowest value of the input voltage, which can greatly reduce the impact current during startup and shutdown, and improve the working reliability of the AC electromagnet.

[0041] Specifically,

[0042] The block diagram of the AC electromagnet circuit for the trip unit is as follows Figure 1 Its main modules are:

[0043] Input: AC input with live wire L and neutral wire N;

[0044] EMC protection: Modules used for EMC and protection, mainly including varistors, safety capacitors, fuses, resistors and other components;

[0045] Rectifier bridge: Full-bridge rectifying the alternating input voltage to obtain the output voltage Vh;

[0046] Power generation: Generates the DC power supply voltage required by microprocessors, sampling circuits, coil drivers and other module circuits;

[0047] Sampling circuit: After reducing the voltage Vh, it is filtered and sampled, and output to Vs to determine the working timing of the electromagnet coil;

[0048] Microprocessor: detects the signal of sampling circuit Vs, sets the working sequence of AC coil, and outputs the curvature compensation PWM control signal to the coil drive module;

[0049] Coil drive: convert the signal of the microprocessor into the drive signal Vg of the coil drive MOS tube. Vg is a PWM signal with curvature compensation to control the opening and closing of the coil;

[0050] Coil: Contains power switch MOS (used to turn on and off the coil), AC electromagnet coil (single coil), diode and capacitor (freewheeling diode, which can also be used to absorb switching glitches in the electromagnet coil).

[0051] The principle of the curvature compensation control method is as follows:

[0052] AC electromagnets are excited by AC current. Assuming that the magnetic induction intensity B in the air gap of the electromagnet changes with time, that is,

[0053] B=B m sin(ωt)

[0054] Where ω is the angular frequency of the industrial frequency alternating current, B m is the amplitude of the magnetic induction intensity, and the instantaneous value of the electromagnetic force is:

[0055]

[0056] where F m is the maximum value of the electromagnetic force. If the electromagnet is in the form of a solenoid, the maximum value of the electromagnetic force is:

[0057]

[0058] Among them I m is the maximum current, W is the number of coil turns, r is the coil radius, δ is the stroke, g is the leakage permeance, l c is the coil length, z is related to l c Related quantity.

[0059] From the above theory, we can know that the AC electromagnetic force pulsates at a frequency twice the industrial frequency, which will cause the iron core to produce mechanical vibration, noise, and make the iron core more susceptible to wear.

[0060] The equivalent circuit of an AC electromagnet is Figure 2As shown. Among them, -jBr is the reactive component caused by the equivalent inductance of the coil, Gm is the equivalent conductance of the iron core, R is the coil resistance, and Xa is the leakage flux.

[0061] Since the number of turns of the coil used as an AC electromagnet is usually large (thousands of turns), the equivalent resistance is tens to tens of k. The coil power is mainly formed by the resistance R, and the coil power is approximately:

[0062] P c =I 2 R

[0063] By comparing the formulas for electromagnetic force and coil power, we can see that the factor that produces changes in electromagnetic force is the current I.

[0064] If the square of the current is a constant or approximately a constant, the electromagnetic force is close to a constant value, thereby reducing noise while keeping the electromagnetic force constant.

[0065] When the coil is driven, under AC input, the rectified waveform frequency is a half-sine wave of 100Hz, and the current waveform follows the voltage waveform Vh. Within the 100Hz period, the shape is also a half-sine wave, that is, the current in the coil is:

[0066] I=I m sin(ωt)ωt∈[0,π]

[0067] If the coil is controlled by PWM (duty cycle is Dt), and the PWM frequency is much greater than the frequency of the sine wave, Figure 3 In the current cycle, the effective value of the current is:

[0068] I rms =I m sin(ωt)Dt

[0069] In one fluctuation cycle of the current, the effective value of the current I rms If it is kept constant, the power of the coil will be constant, the suction force of the electromagnet will be constant, and the noise caused by fluctuations will be greatly reduced.

[0070] therefore,

[0071] I rms =I m sin(ωt)Dt=constant C1

[0072] Then the PWM duty cycle is:

[0073]

[0074] During the entire half-amplitude sine wave fluctuation period, the duty cycle Dt of the PWM drive signal must conform to the secant function, such as Figure 4 ,Right now

[0075]

[0076] Since the secant shape is similar to a bathtub curve, its value is infinite at 0 and π. The PWM duty cycle ranges from 0% to 100%, so some adjustments are required. After adjustment, the Dt curve complements the curvature of the curve realized by the AC current, making the coil current and power (AC electromagnetic coil suction) stable.

[0077] When the PWM drive signal is implemented in the circuit, the maximum duty cycle is 1, that is, 100%. There is also a minimum duty cycle, which is related to the drive circuit and the drive MOS tube. Therefore, the range of the duty cycle Dt is

[0078] D t ∈[Dt min ,Dt max ]

[0079] Therefore, within the half-period of the sine wave, that is, the entire period of the electromagnetic coil, the duty cycle of the coil drive PWM is set as follows: Figure 5 As shown, the coil works in the case of industrial frequency AC. When the coil is near the start and end of the cycle, the duty cycle Dt is set to 1 (100%). Combined with the circuit application, when the coil is at the minimum in the middle of the cycle, the duty cycle is set to 3% (if the coil drive PWM signal control frequency is 10kHz, the minimum duty cycle Dtmin is 3us).

[0080] Taking an undervoltage release with a rated voltage of 230V 50Hz as an example, the curvature compensation calculation is as follows:

[0081] The PWM signal frequency of the selected driving coil is 10kHz (cycle is 0.1ms). At this time, due to the existence of the previous rectifier circuit, the rectified voltage frequency is 100Hz (10ms). At this time, the curvature compensation cycle is also 100Hz. After quantization, the duty cycle of the PWM signal has 100 values ​​(10ms / 0.1ms) in the entire coil cycle.

[0082] By balancing the suction of the coil and taking into account the switching time of the driving MOS tube, the variation range of the PWM switching signal duty cycle Dt of the curvature compensation is set to vary between 3% and 100%, that is, the variation time of the driving MOS tube varies from 3us to 100us. The variation range of the PWM duty cycle must meet two constraints:

[0083] First, the change in PWM duty cycle during curvature compensation conforms to the function:

[0084] Dt=csc(ωt)

[0085] Second, when PWM drives the MOS tube, considering the MOS switch and driving circuit, the minimum PWM pulse width is 3us.

[0086] Therefore, when the PWM signal is at a working frequency of 10kHz, when the duty cycle is lower than 3%, the minimum value is 3%, i.e. 3us; when the duty cycle is higher than 97%, the PWM duty cycle is 100%. Based on the above two constraints, the continuous curve of the duty cycle change is quantified at the undervoltage working frequency of 10kHz, and the duty cycle curve is as follows: Figure 6 shown.

[0087] According to the above calculation process, the PWM duty cycle change value using curvature compensation control is shown in Table 1.

[0088] Under the condition of 10kHz working frequency, each cycle of the coil will generate 100 duty cycle values. If the working frequency changes, the duty cycle value will change accordingly. The calculation method is:

[0089]

[0090] The curvature change duty ratio Dt change value thus obtained is stored in the microcontroller and is used to read and control the switch of the coil when the release is working.

[0091] Table 1 PWM duty cycle Dt value for curvature compensation

[0092]

[0093] For comparison, the duty cycle of the PWM signal is compared using curvature compensation Dt and constant Dt. In order to keep the effective value of the current in the coil consistent, the curvature compensation Dt range is 3%-100%, and the constant Dt value is 2.2%. The PWM change curve within the rectified voltage cycle is shown in Figure 7.

[0094] In the driving cycle, the curvature compensation duty cycle Dt, the current variation range is mainly between 60mA and 150mA; while the current variation range of the constant duty cycle Dt changes from 0mA to a maximum of 190mA. It can be seen that after using curvature compensation, the current variation range in the coil is smaller, and the coil works more stably. Figure 8 As shown (top: curvature compensated Dt; bottom: constant Dt).

[0095] In each PWM signal control cycle, the effective value of the current changes as follows Fig. 9 It can be found that the effective value of the current in a single cycle, the effective value of the current with curvature compensation Dt (dark gray curve) changes less than the change value of the constant Dt (light gray curve).

[0096] Similarly, the power (coil suction) of an AC electromagnetic coil changes as Fig.10 As shown in the figure, the change of curvature compensation Dt (dark gray curve) is smaller than that of constant Dt (light gray curve). When the release maintains the coil energized, the power fluctuation of curvature compensation Dt is smaller, that is, the coil is closer to constant DC operation, so the noise is smaller and the coil is more stable.

[0097] The above description only describes the specific implementation mode of the present invention. Various examples do not limit the essential content of the present invention. After reading the description, ordinary technicians in the relevant technical field can modify or deform the specific implementation modes described above without departing from the essence and scope of the invention.

Claims

1. A curvature compensation control method for an AC electromagnet of a release, characterized in that: The following steps are included: S1. When the module is enabled, the processor detects the voltage Vs of the sampling circuit to determine whether it is the starting value of the coil working cycle; S2. After the cycle starts, the microprocessor queries the curvature compensation Dt value in the lookup table. S3, output Dti as the PWM duty cycle according to the Dt value, where i is the sequence number of the value in the array; S4, output signal to the power switch MOS, driving the coil to turn on or off until all Dt in the lookup table are output.

2. A trip device AC electromagnet curvature compensation control method as claimed in claim 1, characterized in that: In the step S1, if the cycle start value has not been reached, wait until the cycle starts.

3. A trip device AC electromagnet curvature compensation control method as claimed in claim 1, characterized in that: The variation range of the PWM duty cycle satisfies the following two constraints: Condition 1: The change value of PWM duty cycle during curvature compensation conforms to the function: Dt = csc(ωt), where ω is the angular frequency of the industrial frequency alternating current; ωt∈[0,π]; Condition 2: When PWM drives the MOS tube, the PWM pulse width is the minimum value.

4. A curvature compensation control method for an AC electromagnet of a release as claimed in claim 3, characterized in that: According to the upper and lower limits of the variation range of the duty cycle Dt of the PWM switch signal compensated for curvature; when the duty cycle is lower than the lower limit, the minimum lower limit value is taken; when the duty cycle is higher than a set value, the PWM duty cycle is the upper limit value.

5. A trip device AC electromagnet curvature compensation control method as claimed in claim 4, characterized in that: The calculation method of the PWM duty cycle change value is as follows: The obtained curvature change duty cycle Dt change value is stored in the microcontroller.

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