Electromagnetic actuator and method for controlling an electromagnetic actuator
By adjusting the coil current through an H-bridge power supply circuit and control strategy, the contradiction between low power consumption and manufacturing cost in electromagnetic actuators is resolved, thus realizing the design of an electromagnetic actuator with low power consumption and moderate cost.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SCHNEIDER ELECTRIC IND SAS
- Filing Date
- 2022-01-26
- Publication Date
- 2026-07-07
AI Technical Summary
Existing electromagnetic actuators struggle to simultaneously achieve low power consumption and moderate manufacturing costs, especially those involving flyback transformers which are expensive, and those involving two coils which significantly increase power consumption.
Employing a power supply circuit and control circuit including an H-bridge, first and second control strategies are implemented by detecting coil current and voltage to adjust the coil current to reduce power consumption, including using a single coil without the need for a flyback transformer.
It achieves low power consumption and moderate manufacturing cost, reduces coil current, reduces the energy consumption of electromagnetic actuators, and maintains normal operation.
Smart Images
Figure CN114814340B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to an electromagnetic actuator and a method for controlling the electromagnetic actuator. Background Technology
[0002] As is well known, many electrical switching units, such as contactors, including electromagnetic actuators, allow moving electrical contacts to move between an open position and a closed position.
[0003] Typically, an electromagnetic actuator includes a coil configured to generate a magnetic field when energized by a power supply circuit. This power supply circuit typically includes a switch-mode power supply comprising one or more transistors controlled to energize the coil with an excitation signal comprising a sequence of current pulses.
[0004] Such electromagnetic actuators typically have to satisfy conflicting demands related to power consumption on one hand, and conflicting demands related to manufacturing costs on the other, with both of these demands remaining within limits.
[0005] However, in practice, it is difficult to construct an actuator that satisfies both of these requirements at the same time.
[0006] For example, solutions that include coils associated with a flyback transformer allow for low power consumption (e.g., below 2.3A), but this comes at the cost of manufacturing costs, which remain high.
[0007] Conversely, solutions containing two different coils have lower manufacturing costs, but significantly higher system consumption, potentially more than double that of solutions with only one coil. Summary of the Invention
[0008] It is precisely these shortcomings that the present invention aims more specifically to overcome by providing an electromagnetic actuator that exhibits low power consumption and moderate manufacturing cost.
[0009] Therefore, one aspect of the present invention relates to a method for controlling an electromagnetic actuator, the electromagnetic actuator including a coil, a power supply circuit for supplying power to the coil, and an electronic control circuit, the power supply circuit including a switching stage including an H-bridge, the H-bridge including a plurality of switches connected to the coil.
[0010] The first switch is connected in the first branch of the bridge between the power supply circuit's electrical ground and the coil; the second switch is connected in the second branch of the H-bridge between the voltage bus and the coil; and the third switch is connected in the third branch of the bridge between the coil and the electrical ground.
[0011] The control method includes the following steps:
[0012] - Applying a first control strategy, in which the first switch and the third switch remain in the closed state, while the second switch switches between its open and closed states;
[0013] - Excessive current consumption in the coil is detected by detecting that the voltage measured on the control bus has exceeded a predetermined voltage limit or by detecting that the duty cycle of the second switch has dropped below a threshold.
[0014] In response, a second control strategy is applied instead of the first control strategy, in which a third switch is periodically turned off in order to reduce the current supplied to the coil.
[0015] According to the present invention, when the voltage of the DC bus exceeds a predetermined threshold, a specific control strategy is implemented to reduce the coil current until it returns to below the limit, while the coil is controlled to ensure the normal operation of the actuator.
[0016] Depending on the advantageous but non-mandatory aspects, such an electromagnetic actuator may incorporate one or more of the following features, which may be obtained in isolation or in any technically permissible combination.
[0017] - When the second control strategy is applied, the measured voltage is compared with the voltage limit value again to detect whether the measured voltage has returned below the voltage limit, so that the second control strategy can be stopped and the first control strategy can be applied again if applicable.
[0018] - In the second control strategy, the duty cycle of the control signal used for the second switch is given by the following formula:
[0019] aSW2=ToffSW3 x(Vdc–Vd)+T(Vd-Ri) / (Tx(Vdc+Vd))
[0020] Where TSW3off is the time during which the third switch (SW3) remains open in each cycle, Ri is equal to the current flowing through coil Bob multiplied by the inherent resistance of the coil, and T is the period of the control signal of the second switch.
[0021] - In the second control strategy, the duty cycle of the control signal of the third switch remains constant, or it can change over time.
[0022] - The switch is a transistor.
[0023] - The current flowing through the coil is measured by a measuring device, which is preferably associated with a third transistor.
[0024] According to another aspect, the present invention relates to an electromagnetic actuator, comprising a coil, a power supply circuit for supplying power to the coil, and an electronic control circuit. The power supply circuit includes a switching stage comprising an H-bridge, the H-bridge including a plurality of switches connected to the coil. A first switch is connected in a first branch of the bridge between an electrical ground of the power supply circuit and the coil; a second switch is connected in a second branch of the H-bridge between a voltage bus and the coil; and a third switch is connected in a third branch of the bridge between the coil and an electrical ground. The electronic control circuit is programmed to perform steps including:
[0025] - Applying a first control strategy, in which the first switch and the third switch remain in the closed state, while the second switch switches between its open and closed states;
[0026] - Excessive current consumption in the coil is detected by detecting that the voltage measured on the control bus has exceeded a predetermined voltage limit or by detecting that the duty cycle of the second switch has dropped below a threshold.
[0027] In response, a second control strategy is applied instead of the first control strategy, in which a third switch is periodically turned off in order to reduce the current supplied to the coil. Attached Figure Description
[0028] The invention will be better understood from the following description of one embodiment of the electromagnetic actuator, and other advantages of the invention will become more apparent. This description is given by way of example only and with reference to the accompanying drawings, in which:
[0029] Figure 1 An electrical switching unit including an electromagnetic actuator according to the present invention is schematically shown;
[0030] Figure 2 schematically shown Figure 1 The power supply circuit of the electromagnetic actuator;
[0031] Figure 3 The diagram schematically illustrates the coil current, the duty cycle of the power supply circuit switches, and various control strategies. Figure 2 The change of the control signal in the power supply circuit over time;
[0032] Figure 4 It is used for control Figure 1 The flowchart shows the method for using an electromagnetic actuator. Detailed Implementation
[0033] Figure 1 Electrical switching unit 2, such as a contactor, relay, circuit breaker or any equivalent unit, is schematically shown.
[0034] Unit 2 includes movable electrical contacts 4, which, depending on whether they are in an open or closed position, prevent current from flowing between the terminals of unit 2, or conversely, allow the current to flow.
[0035] According to some examples, cell 2 can be a multipole cell or a unipole cell, and therefore includes as many terminal pairs as phase.
[0036] Unit 2 also includes an electromagnetic actuator comprising a coil, a power supply circuit 6 configured to supply power to the coil, and an electronic control circuit 8. Hereinafter, the actuator may be indicated by the reference numeral "6".
[0037] The actuator 6 is coupled to the movable contact 4, for example, by mechanical or electromagnetic coupling, and allows the movable contact 4 to move directly or indirectly depending on whether the coil is powered.
[0038] The electronic control circuit 8 is configured to control the operation of the actuator, as described below.
[0039] For example, electronic control circuit 8 includes a processor, such as a programmable microcontroller or microprocessor.
[0040] The processor is coupled to, for example, computer memory, or any computer-readable data storage medium, which includes executable instructions and / or software code intended to implement the control methods described below.
[0041] According to some variations, the electronic control circuit 8 may include other elements, such as a digital signal processor (DSP), or a field-programmable gate array (FPGA), or an application-specific integrated circuit (ASIC), or any equivalent element.
[0042] Figure 2 An exemplary embodiment of actuator 6 is shown.
[0043] Actuator 6 includes a coil “Bob” and a power supply circuit configured to supply an electrical excitation current (coil current) to the coil in order to excite the coil, for example, to generate a magnetic field acting on the position of the movable contact 4.
[0044] For example, a power supply circuit includes an input stage 10 that receives an input voltage Vinput, which is supplied between the input terminals, for example, by a power supply.
[0045] Input stage 10 may include rectifiers, such as a diode bridge, and means for preventing overvoltage or overcurrent. Input stage 10 may also include filtering means, such as filter capacitors.
[0046] Downstream of the input stage, the power supply circuit also includes a DC voltage bus Vdc, which includes a first conductor and a second conductor connected to the circuit's electrical ground GND. Here, the linear voltage regulator 12 is connected to the first line of the voltage bus.
[0047] The power supply circuit also includes a switching stage, which includes an H-bridge that includes multiple switches connected to coil Bob.
[0048] For example, coil Bob connects between the first and second points, forming the midpoint of the H-bridge. The excitation current flowing through the coil is denoted here as "i". Coil Bob is configured to couple with a moving element of the actuator (such as a moving blade) to, for example, move the moving contact 4. Coil Bob includes an internal resistance associated with its structure, which is shown as a resistor R connected in series between the first and second points.
[0049] Preferably, a single coil is connected between the first and second points in the H-bridge. In other words, there is no second coil connected in series with coil Bob and coupled to the moving element of actuator 6.
[0050] For example, the switching stage includes three power switches SW1, SW2 and SW3, each of which is associated with a branch of the H-bridge.
[0051] The first switch SW1 is connected between ground GND and the first point, forming the first branch of the H-bridge.
[0052] Here, switch SW1 (“fast descent switch”) is connected in parallel with a flyback chopper diode and in series with another diode placed between switch SW1 and the first point.
[0053] The second switch SW2 (“high-side switch”) is connected between the first point of the H-bridge and the first line of the voltage bus Vdc.
[0054] The third switch SW3 (“low-end switch”) is connected between the second point of the H-bridge and electrical ground.
[0055] For example, the switch is a transistor, preferably a conventional transistor such as a power transistor or a MOSFET, or any suitable transistor.
[0056] For example, the fourth branch of the H-bridge may include a diode connected between the second point and the first conductor. The voltage across this diode is denoted as Vd.
[0057] Switches SW1, SW2 and SW3, especially switches SW2 and SW3, are controlled by control circuit 8, for example, to provide pulses of current to the coil so as to put the coil into an energized (inrush) state and / or keep the coil in an energized state.
[0058] For example, in each switch, the control electrode is configured to receive a control signal sent by the control circuit 8.
[0059] Optionally, in some embodiments, circuit 6 may include a diagnostic module connected in parallel with transistor SW1, configured to measure a voltage representing the current flowing through transistor SW1, for example, by means of a bridge of resistors R. However, this diagnostic module may be omitted.
[0060] exist Figure 2 In the diagram, blocks 14, 16, and 18 represent, in a simplified manner, control modules or drivers that control transistors SW1, SW2, and SW3, respectively. It should be understood that these control modules 14, 16, and 18 can form part of control circuit 8.
[0061] The power supply circuit also includes a measuring device 20, associated here with transistor SW3, which is configured to measure the current flowing through transistor SW3, for example, through a measuring resistor connected in series with transistor SW3. This allows for the measurement of an image of the current flowing through coil Bob. Device 20 ultimately allows for the adjustment of the current in the coil.
[0062] According to the invention, the control circuit 8 is programmed to control the transistor in order to regulate the excitation current of the coil, in particular by keeping the excitation current of the coil below a predefined limit in order to reduce the power consumption of the actuator.
[0063] This strategy can be implemented once there is an occurrence that may indicate excessive current consumption in coil Bob (i.e., “occurrence of excessive consumption”), for example when the voltage of the DC bus Vdc exceeds the limit value Vlim, or equivalently, when the duty cycle of the control of switch SW2 (the ratio of the closing duration within a cycle to the total duration of the cycle, which should be understood as switch SW2 periodically opening and closing) drops below a predetermined threshold denoted as DC_lim.
[0064] In other words, the control circuit 8 is configured to implement multiple different control strategies.
[0065] Figure 3 An exemplary operation of actuator 6 is shown.
[0066] The graph Vdc shows an example of how the voltage of the voltage bus Vdc changes over time (x-axis). The dashed line corresponds to the value of the voltage threshold Vlim.
[0067] The graph HS_duty_cycle (HS duty cycle) shows how the duty cycle of switch SW2 changes over time (x-axis). The double dashed line corresponds to the threshold DC_lim.
[0068] The graph command_strategy shows the control strategy implemented by control circuit 8 based on the value of voltage Vdc over time (x-axis).
[0069] For example, as long as the voltage Vdc remains below the limit value Vlim, the first control strategy 30 (normal strategy) is implemented.
[0070] Preferably, in the first control strategy, switches SW1 and SW3 remain closed (i.e., in the on state) to allow current flow, while switch SW2 alternately switches between its open and closed states at a predefined switching frequency.
[0071] For example, the duty cycle of the control signal used for switch SW2 (defined as the ratio of the duration of switch closure to the total duration of the cycle for each period) can vary depending on the operating conditions of the power supply circuit.
[0072] In practice, the duration for which switch SW2 remains closed in each cycle is less than the time required to switch SW2.
[0073] According to a favorable example, the duty cycle aSW2 of the control signal for switch SW2 is given by the following formula:
[0074] aSW2=ToffSW3 x(Vdc–Vd)+T(Vd-Ri) / (Tx(Vdc+Vd))
[0075] Where ToffSW3 is the time during which switch SW3 remains open in each cycle, Ri is equal to the current flowing through coil Bob multiplied by the internal resistance R of coil Bob, and T is the period of the control signal of switch SW2.
[0076] When the voltage Vdc exceeds the limit Vlim, the second control strategy 32 is implemented and remains in effect until the voltage Vdc drops below the limit Vlim. Equivalently, this condition can correspond to the duty cycle of switch SW2 being below the threshold DC_lim.
[0077] Figure 3 Section 34 shows in more detail the changes of coil current (actuator current), control signal of transistor SW2 (HS command), and control signal of transistor SW3 (LS command) over time (x-axis) when the control circuit 8 applies the second control strategy 32.
[0078] In the second control strategy, switch SW1 remains closed, while switch SW2 continues to alternate between its open and closed states at the same predefined switching frequency. However, this time, switch SW3 is periodically opened to reduce the coil current.
[0079] Advantageously, the opening of switch SW3 is synchronized with the opening of switch SW2, so that switch SW3 and switch SW2 open at the same time.
[0080] The temporary disconnection of switch SW3 allows the rate of change of the coil current (i.e., the derivative of the current as a function of time) to increase, thus accelerating its decrease, preferably until a lower value is reached, allowing the actuator's power consumption to be reduced. For example, when switch SW3 is open, the flyback current along... Figure 2 The path indicated by the middle arrow F1 flows through the coil between ground and line Vdc, for example, through the H-bridge branch including switch SW1, then through the coil, and then through diode Vd.
[0081] Once switch SW3 is closed again, the rate of change of the coil current decreases, which means that the coil current stabilizes, preferably at a current value far from its maximum value.
[0082] For example, when switch SW3 is closed, the flyback current travels along... Figure 2 The path indicated by the middle arrow F2 flows through the coil and ground, for example, through the circuit network formed by the H-bridge branch including switch SW1, then the coil, and then the H-bridge branch including switch SW3.
[0083] exist Figure 3 In this code, the off-time of switch SW3 is denoted as "D_open". For example, the duty cycle of the control signal for switch SW3 remains constant. As a variant, the duty cycle of the control signal for switch SW3 may be variable.
[0084] For example, at a switching frequency of 20 kHz, a disconnect duration of 2 μs corresponds to a duty cycle of 96%.
[0085] Therefore, the excitation current of the coil is regulated to limit the current flowing through the coil, regardless of the input voltage. With this invention, when the DC bus voltage exceeds a preset threshold, a specific control strategy is implemented to reduce the coil current until it returns below the limit, while continuing to control the coil to ensure normal operation of the actuator.
[0086] In particular, this architecture, combined with a hybrid control strategy, allows the use of only a single coil without the need for a flyback transformer in the power supply circuit, while still achieving reduced power consumption compared to known solutions that use two coils.
[0087] For example, the starting current (inrush current) here is less than or equal to 2.5A.
[0088] Now for reference Figure 4 An example describing a control method.
[0089] The method begins at step 100, for example, after receiving a command to excite the coil of actuator 6.
[0090] During step 102, the control circuit 8 applies a first control strategy to control switches SW1, SW2 and SW3.
[0091] In parallel, during step 104, the control circuit 8 identifies the duty cycle of switch SW2, and applies a second control strategy when the value of the duty cycle drops below a predetermined threshold DC_lim.
[0092] This identification can be performed based on the control signal supplied to the switch by the control circuit 8, or in other ways, such as by measuring the voltage Vdc.
[0093] Alternatively, since the change in voltage Vdc is associated with a change in the duty cycle of switch SW2, the detection can be performed indirectly, for example, by comparing the measured voltage Vdc with the value of the voltage limit Vlim. For example, the voltage Vdc can be measured using measuring device 20.
[0094] If the measured voltage Vdc is detected to exceed the voltage limit Vlim, or equivalently, if the duty cycle of switch SW2 is detected to have fallen below the threshold DC_lim, then during step 106, the previously described second regulation strategy is implemented instead of the first control strategy. If the measured voltage Vdc does not exceed the voltage limit Vlim, or if the duty cycle of switch SW2 remains above the threshold DC_lim, the first control strategy remains unchanged.
[0095] Next, in step 106, the control circuit 8 continues to compare the measured voltage Vdc with the value of the voltage limit Vlim to detect whether the measured voltage Vdc has returned below the voltage limit Vlim, or equivalently compares the determined value of the duty cycle of switch SW2 with the threshold DC_lim to detect any exceedance of the threshold DC_lim, so that the second control strategy can be stopped and the first control strategy can be applied again if applicable.
[0096] If the measured voltage Vdc still exceeds the voltage limit Vlim, or equivalently, if the determined value of the duty cycle of switch SW2 is still below the threshold DC_lim, then the second control strategy remains implemented.
[0097] As variations, these steps may be performed in a different order. Some steps may be omitted. In other embodiments, the described examples do not preclude other steps from being performed together with and / or sequentially with the described steps.
[0098] The embodiments and variations envisioned above can be combined with each other to create new embodiments.
Claims
1. A method for controlling an electromagnetic actuator, the electromagnetic actuator including a coil, a power supply circuit for supplying power to the coil, and an electronic control circuit, the power supply circuit including a switching stage, the switching stage including an H-bridge, the H-bridge including a plurality of switches (SW1, SW2, SW3) connected to the coil. A first switch (SW1) is connected in the first branch of the H-bridge between the power supply circuit's ground (GND) and the coil; a second switch (SW2) is connected in the second branch of the H-bridge between the voltage bus and the coil; and a third switch (SW3) is connected in the third branch of the H-bridge between the coil and the power supply ground. The method includes the following steps: - Apply a first control strategy, in which the first switch and the third switch remain in the closed state, while the second switch switches between its open state and closed state; - Excessive current consumption in the coil is detected by detecting that the voltage (Vdc) measured on the voltage bus has exceeded the predefined voltage limit (Vlim) or by detecting that the duty cycle of the second switch (SW2) has dropped below the threshold (DC_lim); - In response, a second control strategy is applied instead of the first control strategy, in which a third switch (SW3) is periodically turned off in order to reduce the current supplied to the coil.
2. The method according to claim 1, wherein, When the second control strategy is applied, the measured voltage is compared with the voltage limit value again to detect whether the measured voltage has returned below the voltage limit, so that the second control strategy can be stopped and the first control strategy can be applied again if applicable.
3. The method according to any one of the preceding claims, wherein, In the second control strategy, the duty cycle of the control signal used for the second switch (SW2) is given by the following formula: aSW2 = ToffSW3 × (Vdc – Vd) + T (Vd-Ri) / (T × (Vdc+Vd)) Where ToffSW3 is the time during which the third switch (SW3) remains open during each cycle, Ri is equal to the current flowing through the coil multiplied by the inherent resistance (R) of the coil, and T is the period of the control signal for the second switch (SW2), and Vd is the voltage across the diode connected in the fourth branch of the H-bridge between the midpoint of the H-bridge and the first wire of the voltage bus.
4. The method according to any one of claims 1 or 2, wherein, In the second control strategy, the duty cycle of the control signal for the third switch (SW3) remains constant or varies over time.
5. The method according to any one of claims 1 or 2, wherein the switch is a transistor.
6. The method according to any one of claims 1 or 2, wherein the current flowing through the coil is measured by a measuring device (20) associated with a third switch (SW3).
7. An electromagnetic actuator comprising a coil, a power supply circuit for supplying power to the coil, and an electronic control circuit, the power supply circuit including a switching stage, the switching stage including an H-bridge, the H-bridge including a plurality of switches (SW1, SW2, SW3) connected to the coil, a first switch (SW1) connected in a first branch of the H-bridge between an electrical ground (GND) of the power supply circuit and the coil, a second switch (SW2) connected in a second branch of the H-bridge between a voltage bus and the coil, and a third switch (SW3) connected in a third branch of the H-bridge between the coil and the electrical ground, the electronic control circuit being programmed to implement steps including: - Apply a first control strategy, in which the first switch and the third switch remain in the closed state, while the second switch switches between its open and closed states; - Excessive current consumption in the coil is detected by detecting that the voltage (Vdc) measured on the voltage bus has exceeded the predefined voltage limit (Vlim) or by detecting that the duty cycle of the second switch (SW2) has dropped below the threshold (DC_lim); - In response, a second control strategy is applied instead of the first control strategy, in which a third switch (SW3) is periodically turned off in order to reduce the current supplied to the coil.