Single-phase asynchronous motor and control device
The design of integrated capacitors and centrifugal switches solves the problem of large space occupation of single-phase asynchronous motors under heavy loads, realizes adaptive adjustment of capacitor capacity, and ensures efficient rotation of the motor during starting and running stages.
Patent Information
- Application Number
- CN202510631411.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-15
- Publication Date
- 2025-09-12
AI Technical Summary
Existing single-phase asynchronous motors require two independent capacitors (starting capacitor and running capacitor) under heavy load scenarios, which results in large space occupation and the need for independent support brackets.
By using an integrated capacitor and centrifugal switch, the connection mode of the capacitor is automatically switched when the motor speed changes through a mechanical structure or control circuit, realizing the switching between a large-capacity capacitor in the starting phase and a small-capacity capacitor in the running phase, and only one capacitor is needed to replace two capacitors.
The space occupied by the motor is reduced, and the adaptive adjustment of the capacitor capacity at different speeds is achieved, ensuring that the motor starts and runs stably under heavy load.
Smart Images
Figure CN120638769A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to the technical field of motors, and in particular to a single-phase asynchronous motor and a control device. Background Art
[0002] Single-phase asynchronous motors are widely used in single-phase mains power supply scenarios. During operation, single-phase motors require a starting winding connected in series with a capacitor to start the rotor's rotation.
[0003] In order to achieve the starting rotation of the rotor under a large load scenario and maintain a small torque to ensure the rotation of the rotor after reaching a certain speed, the existing technology splits the capacitor connected in series with the starting winding into independent but parallel starting capacitors and running capacitors (the capacity of the starting capacitor is significantly larger than the running capacitor), and sets a centrifugal switch in the starting capacitor branch to control the power on and off state of the branch circuit where the running capacitor is located.
[0004] During the rotor startup process, the insulating base plate in the rotary switch seat of the centrifugal switch presses against the contact spring on the terminal board, so that the contact spring contacts the corresponding fixed-end contact to realize the series connection of the starting capacitor and the starting winding; after the rotor reaches a certain speed, the rotary switch seat moves the insulating base plate away from the contact spring under the centrifugal action, so that the contact spring disconnects the corresponding fixed-end contact under the action of its own elasticity, thereby realizing the disconnection of the branch where the starting capacitor is located.
[0005] In practical applications, since the aforementioned starting capacitor and running capacitor are two independent capacitors, they occupy a large space and require independent supporting brackets. Summary of the Invention
[0006] In a first aspect, an embodiment of the present disclosure provides a single-phase asynchronous motor, comprising a capacitor connected in series with a starting winding, and a centrifugal switch for controlling a connection mode between the capacitor and the starting winding;
[0007] The capacitor includes a first electrode plate and a third electrode plate in the same layer but insulated and isolated, and a second electrode plate and a fourth electrode plate in the same layer but insulated and isolated; a portion of the second electrode plate faces the first electrode plate, and a remaining portion faces a portion of the third electrode plate, and a remaining portion of the third electrode plate faces the fourth electrode plate;
[0008] The centrifugal switch includes a terminal block and a rotary switch seat mounted on the motor shaft; the terminal block includes a plate body, a first elastic conductive sheet, a second elastic conductive sheet, a third conductive sheet and a fourth conductive sheet arranged on the plate body;
[0009] The fixed end of the first elastic conductive sheet directly connected in series with the starting winding is electrically connected to the first electrode plate; the fixed end of the second elastic conductive sheet directly connected in series with the starting winding is electrically connected to one of the second electrode plate and the fourth electrode plate; the third conductive sheet is electrically connected to the third electrode plate; and the fourth conductive sheet is electrically connected to the other of the second electrode plate and the fourth electrode plate.
[0010] When the motor shaft rotates at a speed lower than a set speed and the insulating bottom plate of the rotary switch seat is pressed against the first elastic conductive sheet and the second elastic conductive sheet, the free end of the first elastic conductive sheet contacts the third conductive sheet, and the free end of the second elastic conductive sheet contacts the fourth conductive sheet;
[0011] When the rotation speed of the motor shaft exceeds the set rotation speed and the insulating bottom plate of the rotary switch seat is separated from the first elastic conductive sheet and the second elastic conductive sheet, the first elastic conductive sheet is disconnected from the third conductive sheet due to its own elastic action, and the second elastic conductive sheet is disconnected from the fourth conductive sheet and contacts the third conductive sheet due to its own elastic action.
[0012] Optionally, the third conductive sheet includes a first contact portion and a second contact portion perpendicular to the motor shaft, and an intermediate connecting portion for connecting the first contact portion and the second contact portion;
[0013] The first contact portion is located on a side of the free end of the first elastic conductive sheet away from the rotary switch seat; the second contact portion is arranged on a side of the free end of the second elastic conductive sheet close to the rotary switch seat.
[0014] Optionally, the relative positions of the first contact portion, the second contact portion and the intermediate connecting portion are such that the third conductive sheet forms a Z shape.
[0015] Optionally, when the motor rotation speed is lower than the set speed, the insulating base plate presses against the middle area of the first elastic conductive plate and the second elastic conductive plate located on the inner side of the free end, so that the free end of the first elastic conductive plate contacts the third conductive plate, and the free end of the second elastic conductive plate contacts the fourth conductive plate.
[0016] In a second aspect, an embodiment of the present disclosure provides a single-phase asynchronous motor, comprising a capacitor connected in series with a starting winding, and a centrifugal switch for controlling the connection between the capacitor and the starting winding;
[0017] The capacitor includes a first electrode plate and a second electrode plate that are in the same layer but insulated and isolated, and a third electrode plate that is opposite to the first electrode plate and the second electrode plate;
[0018] The centrifugal switch includes a terminal block and a rotary switch seat mounted on the motor shaft; the terminal block includes a plate body, a first elastic conductive sheet, a second elastic conductive sheet, a third conductive sheet and a fourth conductive sheet arranged on the plate body;
[0019] The fixed end of the first elastic conductive sheet, which is directly connected in series with the starting winding, is electrically connected to the first electrode plate; the fixed end of the second elastic conductive sheet is directly connected in series with the starting winding; the fixed end of the third conductive sheet is fixedly connected to the second electrode plate; and the fixed end of the fourth conductive sheet is fixedly connected to the third electrode plate.
[0020] When the motor shaft rotates at a speed lower than a set speed and the insulating bottom plate of the rotary switch seat is pressed against the first elastic conductive sheet and the second elastic conductive sheet, the free end of the first elastic conductive sheet contacts the third conductive sheet, and the free end of the second elastic conductive sheet contacts the fourth conductive sheet;
[0021] When the rotation speed of the motor shaft exceeds the set rotation speed and the insulating bottom plate of the rotary switch seat is separated from the first elastic conductive sheet and the second elastic conductive sheet, the first elastic conductive sheet is disconnected from the third conductive sheet due to its own elastic action, and the second elastic conductive sheet is disconnected from the fourth conductive sheet and contacts the third conductive sheet due to its own elastic action.
[0022] In a third aspect, an embodiment of the present disclosure provides a single-phase asynchronous motor, comprising a capacitor connected in series with a starting winding, a speed sensor for detecting the speed of a motor rotor, and a control circuit;
[0023] The capacitor includes a first electrode plate and a third electrode plate in the same layer but insulated and isolated, and a second electrode plate and a fourth electrode plate in the same layer but insulated and isolated; a portion of the second electrode plate faces the first electrode plate, and a remaining portion faces a portion of the third electrode plate, and a remaining portion of the third electrode plate faces the fourth electrode plate;
[0024] The control circuit is configured to: short-circuit the first electrode plate and the third electrode plate, and short-circuit the second electrode plate and the fourth electrode plate when the motor shaft speed is lower than a set speed; and
[0025] When the motor shaft speed is higher than the set speed, the first electrode plate and the third electrode plate are disconnected and short-circuited, the second electrode plate and the fourth electrode plate are disconnected and short-circuited, and the third electrode plate is short-circuited with one of the second electrode plate and the fourth electrode plate; or, when the motor shaft speed is higher than the set speed, the first electrode plate and the third electrode plate are disconnected, so that the third electrode plate and the fourth electrode plate are disconnected and short-circuited.
[0026] Optionally, the control circuit includes a first electrically controlled switch, a second electrically controlled switch and a third electrically controlled switch;
[0027] When the motor shaft speed is lower than a set speed, the first electronically controlled switch short-circuits the first electrode plate and the third electrode plate, the second electronically controlled switch short-circuits the second electrode plate and the fourth electrode plate, and the third electronically controlled switch disconnects and short-circuits the third electrode plate from the one electrode plate; and
[0028] When the motor shaft speed is higher than the set speed, the first electronically controlled switch disconnects the first electrode plate and the third electrode plate, the second electronically controlled switch disconnects the second electrode plate and the fourth electrode plate, and the third electronically controlled switch short-circuits the third electrode plate and the one of the electrodes.
[0029] Optionally, the first electrically controlled switch, the second electrically controlled switch and the third electrically controlled switch are all semiconductor switches.
[0030] In a fourth aspect, an embodiment of the present disclosure provides a single-phase asynchronous motor, comprising a capacitor connected in series with a starting winding, a speed sensor for detecting the speed of a motor rotor, and a control circuit;
[0031] The capacitor includes a first plate and a second plate in the same layer but insulated and isolated, and a third plate opposite to the first plate and the second plate; the first plate is directly connected in series with the starting winding,
[0032] The control circuit is configured to: when the motor shaft speed is lower than the set speed, short-circuit the first pole plate and the second pole plate, and directly connect the third pole plate in series with the starting winding; and when the motor shaft speed is higher than the set speed, disconnect the first pole plate and the second pole plate from the short-circuit, disconnect the third pole plate from the direct series connection with the starting winding, and directly connect the second pole plate in series with the starting winding.
[0033] In a fifth aspect, an embodiment of the present disclosure provides a control device for a single-phase asynchronous motor, comprising a capacitor connected in series with a starting winding of the single-phase asynchronous motor, and a centrifugal switch for controlling a connection mode between the capacitor and the starting winding;
[0034] The capacitor includes a first electrode plate and a third electrode plate in the same layer but insulated and isolated, and a second electrode plate and a fourth electrode plate in the same layer but insulated and isolated; a portion of the second electrode plate faces the first electrode plate, and a remaining portion faces a portion of the third electrode plate, and a remaining portion of the third electrode plate faces the fourth electrode plate;
[0035] The centrifugal switch includes a terminal block and a rotary switch seat mounted on the motor shaft; the terminal block includes a plate body, a first elastic conductive sheet, a second elastic conductive sheet, a third conductive sheet and a fourth conductive sheet arranged on the plate body;
[0036] The first elastic conductive sheet is used for being directly connected in series with the starting winding, and the fixed end thereof is electrically connected to the first electrode plate; the second elastic conductive sheet is used for being directly connected in series with the starting winding, and the fixed end thereof is electrically connected to one of the second electrode plate and the fourth electrode plate; the third conductive sheet is electrically connected to the third electrode plate; and the fourth conductive sheet is electrically connected to the other of the second electrode plate and the fourth electrode plate.
[0037] When the motor shaft rotates at a speed lower than a set speed and the insulating bottom plate of the rotary switch seat is pressed against the first elastic conductive sheet and the second elastic conductive sheet, the free end of the first elastic conductive sheet contacts the third conductive sheet, and the free end of the second elastic conductive sheet contacts the fourth conductive sheet;
[0038] When the rotation speed of the motor shaft exceeds the set rotation speed and the insulating bottom plate of the rotary switch seat is separated from the first elastic conductive sheet and the second elastic conductive sheet, the first elastic conductive sheet is disconnected from the third conductive sheet due to its own elastic action, and the second elastic conductive sheet is disconnected from the fourth conductive sheet and contacts the third conductive sheet due to its own elastic action.
[0039] In a sixth aspect, an embodiment of the present disclosure provides a control device for a single-phase asynchronous motor, comprising: a capacitor connected in series with a starting winding of the single-phase asynchronous motor, and a centrifugal switch for controlling a connection mode between the capacitor and the starting winding;
[0040] The capacitor includes a first electrode plate and a second electrode plate that are in the same layer but insulated and isolated, and a third electrode plate that is opposite to the first electrode plate and the second electrode plate;
[0041] The centrifugal switch includes a terminal block and a rotary switch seat mounted on the motor shaft; the terminal block includes a plate body, a first elastic conductive sheet, a second elastic conductive sheet, a third conductive sheet and a fourth conductive sheet arranged on the plate body;
[0042] The fixed end of the first elastic conductive sheet, which is directly connected in series with the starting winding, is electrically connected to the first electrode plate; the fixed end of the second elastic conductive sheet is directly connected in series with the starting winding; the fixed end of the third conductive sheet is fixedly connected to the second electrode plate; and the fixed end of the fourth conductive sheet is fixedly connected to the third electrode plate.
[0043] When the motor shaft rotates at a speed lower than a set speed and the insulating bottom plate of the rotary switch seat is pressed against the first elastic conductive sheet and the second elastic conductive sheet, the free end of the first elastic conductive sheet contacts the third conductive sheet, and the free end of the second elastic conductive sheet contacts the fourth conductive sheet;
[0044] When the rotation speed of the motor shaft exceeds the set rotation speed and the insulating bottom plate of the rotary switch seat is separated from the first elastic conductive sheet and the second elastic conductive sheet, the first elastic conductive sheet is disconnected from the third conductive sheet due to its own elastic action, and the second elastic conductive sheet is disconnected from the fourth conductive sheet and contacts the third conductive sheet due to its own elastic action.
[0045] In a seventh aspect, an embodiment of the present disclosure provides a control device for a single-phase asynchronous motor, comprising a capacitor connected in series with a starting winding, a speed sensor for detecting a speed of a motor rotor, and a control circuit;
[0046] The capacitor includes a first electrode plate and a third electrode plate in the same layer but insulated and isolated, and a second electrode plate and a fourth electrode plate in the same layer but insulated and isolated; a portion of the second electrode plate faces the first electrode plate, and a remaining portion faces a portion of the third electrode plate, and a remaining portion of the third electrode plate faces the fourth electrode plate;
[0047] The control circuit is configured to: short-circuit the first electrode plate and the third electrode plate, and short-circuit the second electrode plate and the fourth electrode plate when the motor shaft speed is lower than a set speed; and
[0048] When the motor shaft speed is higher than the set speed, the first electrode plate and the third electrode plate are disconnected and short-circuited, the second electrode plate and the fourth electrode plate are disconnected and short-circuited, and the third electrode plate is short-circuited with one of the second electrode plate and the fourth electrode plate; or, when the motor shaft speed is higher than the set speed, the first electrode plate and the third electrode plate are disconnected, so that the third electrode plate and the fourth electrode plate are disconnected and short-circuited.
[0049] In an eighth aspect, an embodiment of the present disclosure provides a control device for a single-phase asynchronous motor, comprising a capacitor connected in series with a starting winding, a speed sensor for detecting a speed of a motor rotor, and a control circuit;
[0050] The capacitor includes a first plate and a second plate in the same layer but insulated and isolated, and a third plate opposite to the first plate and the second plate; the first plate is directly connected in series with the starting winding,
[0051] The control circuit is configured to: when the motor shaft speed is lower than the set speed, short-circuit the first pole plate and the second pole plate, and directly connect the third pole plate in series with the starting winding; and when the motor shaft speed is higher than the set speed, disconnect the first pole plate and the second pole plate from the short-circuit, disconnect the third pole plate from the direct series connection with the starting winding, and directly connect the second pole plate in series with the starting winding.
[0052] The single-phase asynchronous motor in the embodiment of the present disclosure realizes that a larger-capacity capacitor is connected in series with the starting winding during the motor starting phase and a smaller-capacity capacitor is connected in series with the starting winding during the normal operation phase of the motor through the improved capacitor structure and the corresponding improved centrifugal switch. Only one capacitor with the aforementioned structure is required to realize the functions of the existing two capacitors (starting capacitor and running capacitor), which makes the overall space occupied smaller. BRIEF DESCRIPTION OF THE DRAWINGS
[0053] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0054] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without inventive work, including:
[0055] Figure 1 is a cross-sectional schematic diagram of a capacitor used in a single-phase asynchronous motor according to an embodiment of the present disclosure;
[0056] Figure 2 is a top view of a wiring board used in some embodiments of the present disclosure;
[0057] Among them: 11-first electrode plate, 12-second electrode plate, 13-third electrode plate, 14-fourth electrode plate, 15-intermediate dielectric material, 21-plate body, 22-first elastic conductive sheet, 23-second elastic conductive sheet, 24-third conductive sheet, 25-fourth conductive sheet. DETAILED DESCRIPTION
[0058] The following describes embodiments of the present disclosure in more detail with reference to the accompanying drawings. Although certain embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present disclosure. It should be understood that the drawings and embodiments of the present disclosure are for illustrative purposes only and are not intended to limit the scope of protection of the present disclosure.
[0059] As used herein, the term "including" and its variations are open-ended inclusions, i.e., "including but not limited to". The term "based on" means "based at least in part on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". The relevant definitions of other terms will be given in the following description. In this document, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations.
[0060] The disclosed embodiments provide a new unidirectional asynchronous motor. By configuring an integrated capacitor and configuring an adaptive control switch for the integrated capacitor, the integrated capacitor can replace the existing starting capacitor and running capacitor. The internal connection method of the integrated capacitor can adaptively change the capacitance of the capacitor connected in series with the starting winding to meet the requirements of large capacitance at starting and small capacitance at running.
[0061] In a first aspect, embodiments of the present disclosure provide a single-phase asynchronous motor using a mechanical switch. The single-phase asynchronous motor using a mechanical switch includes a stator, a stator, and an auxiliary device for starting the motor and ensuring continuous operation of the motor.
[0062] In a specific implementation, like the rotor in the single-phase asynchronous motor in the prior art, the stator in the single-phase asynchronous motor can be a squirrel-cage rotor, or other structural rotors used in the prior art, and the embodiments of the present disclosure are not limited thereto.
[0063] As in the prior art, the stator windings in the single-phase asynchronous motor of the disclosed embodiment include two windings: a running winding and a starting winding. The running winding and the starting winding (including the capacitor connected in series with the starting winding) are connected in parallel, with their ends connected to the live and neutral terminals of a single-phase AC circuit, respectively.
[0064] In an embodiment of the present disclosure, an auxiliary device for starting a motor and ensuring continuous operation includes a capacitor connected in series with a starting winding, and a centrifugal switch that controls the connection between the capacitor and the starting winding. The connection here specifically refers to how the internal structure of the capacitor is connected in series with the starting winding.
[0065] Figure 1 Schematic diagram of the cross section of the capacitor used in the single-phase asynchronous motor according to the embodiment of the present disclosure. Figure 1As shown, the capacitor as a whole is a cylindrical capacitor formed by winding. The cylindrical capacitor formed by winding includes a first plate layer, a second plate layer and an intermediate dielectric material 15 stacked in sequence. The first plate 11 layer includes an insulated and isolated first plate 11 and a third plate 13 (that is, the first plate 11 and the third plate 13 are on the same layer but insulated and isolated by the intermediate dielectric material 15), and the second plate 12 layer includes an insulated and isolated second plate 12 and a fourth plate 14 (that is, the second plate 12 and the fourth plate 14 are on the same layer but insulated and isolated by the intermediate dielectric material 15).
[0066] A portion of the aforementioned second electrode plate 12 faces the first electrode plate 11, and the remaining portion faces a portion of the third electrode plate 13; in addition, the remaining portion of the third electrode plate 13 faces the fourth electrode plate 14. In a specific implementation, to facilitate the use of the capacitor, specifically to facilitate the connection of each electrode plate of the cylindrical capacitor with an external circuit, each electrode plate can be provided with a tab as a lead-out terminal (correspondingly, the subsequent reference to connecting to the electrode plate can be understood as directly connecting to the terminal of the corresponding electrode plate).
[0067] According to the analysis in the previous paragraph, theoretically the capacitor can be divided into three sub-capacitors, where the three sub-capacitors are a first sub-capacitor composed of the facing parts of the first electrode plate 11 and the second electrode plate 12, a second sub-capacitor composed of the facing parts of the second electrode plate 12 and the third electrode plate 13, and a third sub-capacitor composed of the facing parts of the fourth electrode plate 14 and the third electrode plate 13 (it should be noted that this is a model explanation. Due to the specific structure, the entire capacitor should be understood as a whole capacitor from the perspective of external connection).
[0068] Assuming that the capacitances of the three sub-capacitors are C1, C2, and C3, respectively, the external capacitance of the entire capacitor can be changed by changing the connection method of the four plates (the connection methods mentioned here are feasible and do not include connection methods that are not feasible).
[0069] When the first plate 11 and the third plate 13 are short-circuited, the second plate 12 and the fourth plate 14 are short-circuited, and the first plate 11 and the fourth plate 14 are directly connected to the external circuit (or the second plate 12 and the third plate 13 are directly connected to the external circuit), the three sub-capacitors are connected in parallel to form an overall capacitor C p =C1+C2+C3.
[0070] When the second plate 12 and the third plate 13 are short-circuited and the first plate 11 and the fourth plate 14 are directly connected to the external circuit, the first sub-capacitor and the third sub-capacitor of the three sub-capacitors are connected in series, and the second sub-capacitor is short-circuited.
[0071] When the third plate 13 and the fourth plate 14 are short-circuited, and the first plate 11 and the fourth plate 14 are directly connected to the external circuit, the first sub-capacitor and the second sub-capacitor of the three sub-capacitors are connected in series, and the third sub-capacitor is short-circuited.
[0072] It should be noted here that, in actual applications, no matter how the series and parallel connections are implemented internally, the capacitor is directly connected in series with the starting winding through the first electrode plate 11 and the fourth electrode plate 14 .
[0073] How to realize the connection method of each of the aforementioned plates and the effect of realizing the aforementioned connection method will be introduced later in the centrifugal switch. The connection relationship between the conductive sheet and the capacitor plate in the centrifugal switch will be further analyzed in combination with the working state of the centrifugal switch.
[0074] The centrifugal switch is a switch used to control the connection mode of the capacitor to the starting winding. The centrifugal switch includes a terminal block and a rotary switch seat.
[0075] Figure 2 FIG is a top view of a wiring board used in some embodiments of the present disclosure. Figure 2 As shown, the terminal block is a composite board component comprising multiple conductive sheets that specifically implement circuit connection changes. It includes a board body 21, a first elastic conductive sheet 22, a second elastic conductive sheet 23, a third conductive sheet 24, and a fourth conductive sheet 25. These four conductive sheets are fixedly mounted on a conductive sheet made of insulating material. The first elastic conductive sheet 22 and the second elastic conductive sheet 23 are elastic conductive sheets, meaning they deform when subjected to a suitable external force and return to their initial state when the external force is removed.
[0076] In the embodiment of the present disclosure, in the absence of appropriate external force, the free end of the first elastic conductive sheet 22 is separated from the first contact portion of the third conductive sheet 24 and does not contact; when an appropriate external force is applied, the first elastic conductive sheet 22 undergoes elastic deformation, and its free end contacts and short-circuits the first contact portion of the third conductive sheet 24.
[0077] In the embodiment of the present disclosure, in the absence of appropriate external force, the second elastic conductive sheet 23 contacts the fourth conductive sheet 25 at its free end due to its own elastic action; and when appropriate external force is applied, the second elastic conductive sheet 23 undergoes elastic deformation, and its free end contacts and short-circuits the third conductive sheet 24.
[0078] The rotary switch base is a mechanical mechanism used to change the connection between the conductive plates on the terminal block. It is mounted on the motor shaft. The rotary switch base in this disclosed embodiment has the same structure and function as the rotary switch base used in the prior art. A detailed analysis of the rotary switch base structure is omitted here; please refer to the prior art literature and product examples for details. In this disclosed embodiment, the rotary switch base rotates with the motor shaft, changing the position of its insulating base plate. This, in turn, changes the appropriate external force applied to the first and second elastic conductive plates 22, 23, thereby changing the connection between the first and second elastic conductive plates 22, 23 and the corresponding other conductive plates.
[0079] Specifically, when the motor shaft speed is lower than the set speed, the insulating bottom plate of the rotary switch seat presses against the first elastic conductive sheet 22 and the second elastic conductive sheet 23, so that the free end of the first elastic conductive sheet 22 contacts the third conductive sheet 24, and the free end of the second elastic conductive sheet 23 contacts the fourth conductive sheet 25; and when the motor shaft speed is higher than the set speed, the insulating bottom plate of the rotary switch seat detaches from the first elastic conductive sheet 22 and the second elastic conductive sheet 23, and the first elastic conductive sheet 22 disconnects from the third conductive sheet 24 under the action of its own elasticity, and the second elastic conductive sheet 23 disconnects from the fourth conductive sheet 24 under the action of its own elasticity and contacts and short-circuits with the third conductive sheet 24.
[0080] In the embodiment of the present disclosure, the fixed end of the first elastic conductive sheet 22 is directly connected in series with the starting winding, and the free end of the second elastic conductive sheet 23 is also directly connected in series with the starting winding.
[0081] The above descriptions describe the structures of the capacitor and centrifugal switch in the single-phase asynchronous motor according to the embodiments of the present disclosure. The following describes the connection relationship between the capacitor and the centrifugal switch.
[0082] In the disclosed embodiment, the fixed end of the first elastic conductive sheet 22 is electrically connected to the first electrode plate 11, the fixed end of the second elastic conductive sheet 23 is electrically connected to one of the second electrode plate 12 and the fourth electrode plate 14, the third conductive sheet 24 is electrically connected to the third electrode plate 13, and the fourth conductive sheet 25 is electrically connected to the other of the second electrode plate 12 and the fourth electrode plate 14. The aforementioned electrical connections are functional descriptions; in specific implementations, the electrical connections between the conductive sheets and the corresponding electrode plates can be achieved through wires.
[0083] Combined with the above analysis, when the fixed end of the second elastic conductive sheet 23 is electrically connected to the second electrode 12, and the fourth conductive sheet 25 is electrically connected to the fourth electrode 14, if the motor shaft speed is higher than the set speed, the overall capacitance formed by the capacitor is C s1The fixed end of the second elastic conductive sheet 23 is electrically connected to the fourth electrode 14, and the fourth conductive sheet 25 is electrically connected to the second electrode 12. If the motor shaft speed is higher than the set speed, the overall capacitance formed by the capacitor is C s2 In the above two connection relationships, if the motor shaft speed is lower than the set speed, the overall capacitance formed by the capacitor is C p .
[0084] The following is an analysis of the working process of the single-phase asynchronous motor provided by the embodiment of the present disclosure. When the single-phase asynchronous motor is energized (that is, after the starting winding and the working winding are energized), because the motor shaft speed is lower than the set speed, the insulating bottom plate of the rotating switch seat in the centrifugal switch presses against the first elastic conductive sheet 22 and the second elastic conductive sheet 23. At this time, the capacitance in series with the starting winding is C p , the capacitance is large, which makes the motor rotor generate a large torque, so that the motor rotor can start under heavy load. After the electronic rotor starts to rotate, under the action of the starting winding and the running winding, the rotor speed gradually increases; when the motor rotor shaft speed exceeds the set speed, the insulating bottom plate of the rotating switch seat in the centrifugal switch is separated from the first elastic conductive sheet 22 and the second elastic conductive sheet 23. At this time, the capacitance in series with the starting winding is C s1 or C s2 , that is, forming a smaller operating capacitance.
[0085] To achieve the aforementioned capacitor being directly connected in series with the starting winding via the first electrode plate 11 and the fourth electrode plate 14 , the fixed ends of the first elastic conductive sheet 22 and the second elastic conductive sheet 23 are directly connected in series with the starting winding.
[0086] As analyzed above, the single-phase asynchronous motor in the embodiment of the present disclosure realizes the connection of a larger-capacity capacitor in series with the starting winding during the motor starting phase and a smaller-capacity capacitor in series with the starting winding during the normal operation of the motor through a structurally improved capacitor and a correspondingly improved centrifugal switch. Only one capacitor of the aforementioned structure is required to replace the existing two capacitors (starting capacitor and running capacitor), which reduces the overall space occupied.
[0087] In a specific implementation, the intermediate dielectric material 15 in the aforementioned capacitor can be an insulating polyester film or other dielectric materials, and the present disclosure is not limited thereto. Furthermore, the capacitors used in the present disclosure are not limited to the aforementioned cylindrical winding structure capacitors, and can also be made of other shapes and structures or using other principles and processes, as long as their structural characteristics meet the above description.
[0088] It is mentioned above that the third conductive sheet 24 includes a first contact portion for contacting the free end of the first elastic conductive sheet 22 and a second contact portion for contacting the free end of the second elastic conductive sheet 23, but the positions of the first contact portion and the second contact portion are not limited.
[0089] In one embodiment, the first contact portion is arranged on the side of the free end of the first elastic conductive sheet 22 away from the rotary switch seat, and the second contact portion is arranged on the side of the free end of the second elastic conductive sheet 23 close to the rotary switch seat. In other words, the free end of the second elastic conductive sheet 23 can switch the contact relationship with the first contact portion and the second contact portion by moving along the direction of the motor shaft. In a specific application, in order to make the third conductive sheet 24 include not only the aforementioned first contact portion and second contact portion, but also an intermediate connecting portion for realizing the integration of the first contact portion and the second contact portion. In the embodiment of the present disclosure, the relative positions of the first contact portion, the second contact portion and the intermediate connecting portion make the third conductive sheet 24 form a Z shape. The third conductive sheet 24 is fixed to the plate body 21 through the intermediate connecting portion.
[0090] It should be noted that the structure mentioned in the first two paragraphs is only an example of the third conductive sheet 24. In other embodiments, the third conductive sheet can also be set to other structures that can cooperate with the first elastic conductive sheet 22 and the second elastic conductive sheet 23. No examples are given here.
[0091] Another embodiment of the present disclosure provides another single-phase asynchronous motor. The single-phase asynchronous motor provided by the other embodiment includes a capacitor connected in series with the starting winding, which is the same as that in the previous embodiment. This capacitor structure will not be analyzed in detail later. For details, please refer to the introduction of the capacitor in the previous embodiment.
[0092] Unlike the previous embodiment, the single-phase asynchronous motor provided in another embodiment of the present disclosure does not include a centrifugal switch, but instead uses other devices that are equivalent to the centrifugal switch. Specifically, the other devices include a speed sensor and a control circuit.
[0093] The speed sensor detects the rotor (or shaft) speed of a single-phase asynchronous motor, generates a speed signal, and transmits it to the control circuit. This control circuit adjusts the connection between the capacitor plates based on the rotor speed, thereby adjusting the actual capacitance directly connected in series with the starting winding.
[0094] Specifically, the control circuit is configured as follows: (1) when the motor shaft speed is lower than the set speed, the first electrode plate 11 and the third electrode plate 13 are short-circuited, the second electrode plate 12 and the fourth electrode plate 14 are short-circuited, and the third electrode plate 13 is disconnected from the second electrode plate 12 and the fourth electrode plate 14; (2) when the motor shaft speed is higher than the set speed, the first electrode plate 11 and the third electrode plate 13 are disconnected and short-circuited, the second electrode plate 12 and the fourth electrode plate 14 are disconnected and short-circuited, and the third electrode plate 13 is short-circuited and connected to one of the second electrode plate 12 and the first electrode plate 11. The capacitance formed when the third electrode plate 13 is short-circuited with the second electrode plate 12 is the aforementioned C s1 When the third electrode plate 13 and the fourth electrode plate 14 are short-circuited, the capacitance formed is the aforementioned C s2 .
[0095] In another application, when the motor speed exceeds a set speed, the control circuit does not short-circuit the third plate with either the second plate or the first plate. In this case, the resulting capacitance is (C1×C2×C3) / (C1×C2+C1×C3+C2×C3).
[0096] In a specific embodiment, the control circuit includes a first electrically controlled switch, a second electrically controlled switch, and a third electrically controlled switch. When the motor shaft speed is lower than a set speed, the first electrically controlled switch is closed to short-circuit the first electrode plate 11 and the third electrode plate 13, the second electrically controlled switch short-circuits the second electrode plate 12 and the fourth electrode plate 14, and the third electrically controlled switch disconnects the third electrode plate 13 from one of the electrodes. When the motor shaft speed is higher than the set speed, the first electrically controlled switch disconnects the first electrode plate 11 and the third electrode plate 13, the second electrically controlled switch disconnects the second electrode plate 12 and the fourth electrode plate 14, and the third electrically controlled switch shorts the third electrode plate 13 from one of the electrodes.
[0097] In a specific embodiment, the first, second, and third electronically controlled switches can be relay switches, or semiconductor switches such as thyristors and IGBTs, which are available in the prior art. Using thyristors or other semiconductor switches can avoid issues such as disconnection by a circuit board and electrical sparks caused by foreign matter.
[0098] The disclosed embodiment also provides another single-phase asynchronous motor, including a capacitor connected in series with a starting winding, and a centrifugal switch for controlling the connection between the capacitor and the starting winding.
[0099] Different from the aforementioned capacitor, the capacitor in the embodiment of the present disclosure includes a first electrode plate and a second electrode plate that are in the same layer but insulated and isolated, and a third electrode plate that is opposite to the first electrode plate and the second electrode plate.
[0100] The centrifugal switch includes a terminal block and a rotary switch seat mounted on the motor shaft; the terminal block includes a plate body, a first elastic conductive sheet, a second elastic conductive sheet, a third conductive sheet and a fourth conductive sheet arranged on the plate body;
[0101] In the embodiment of the present disclosure, the fixed end of the first elastic conductive sheet directly connected in series with the starting winding is electrically connected to the first electrode plate; the fixed end of the second elastic conductive sheet is directly connected in series with the starting winding; the fixed end of the third conductive sheet is fixedly connected to the second electrode plate; and the fixed end of the fourth conductive sheet is fixedly connected to the third electrode plate.
[0102] When the motor shaft speed is lower than the set speed and the insulating base plate of the rotary switch seat is pressed against the first elastic conductive sheet and the second elastic conductive sheet, the free end of the first elastic conductive sheet contacts the third conductive sheet, and the free end of the second elastic conductive sheet contacts the fourth conductive sheet; and when the motor shaft speed is higher than the set speed and the insulating base plate of the rotary switch seat is separated from the first elastic conductive sheet and the second elastic conductive sheet, the first elastic conductive sheet is disconnected from the third conductive sheet under the action of its own elasticity, and the second elastic conductive sheet is disconnected from the fourth conductive sheet and contacts the third conductive sheet under the action of its own elasticity.
[0103] The disclosed embodiments also provide another single-phase asynchronous motor, comprising a capacitor connected in series with a starting winding, a speed sensor for detecting the speed of a motor rotor, and a control circuit; the capacitor comprises a first pole plate and a second pole plate on the same layer but insulated and isolated, and a third pole plate opposite to the first pole plate and the second pole plate; the first pole plate is directly connected in series with the starting winding, and the control circuit is configured to: when the speed of the motor shaft is lower than a set speed, short-circuit the first pole plate and the second pole plate, and connect the third pole plate directly in series with the starting winding; and, when the speed of the motor shaft is higher than the set speed, disconnect the first pole plate and the second pole plate from the short circuit, disconnect the third pole plate from the direct series connection with the starting winding, and connect the second pole plate directly in series with the starting winding.
[0104] In addition to providing the aforementioned single-phase asynchronous motor, embodiments of the present disclosure also provide a control device for the aforementioned single-phase asynchronous motor. In one specific application, the control device includes the capacitor and centrifugal switch described in the aforementioned embodiments. In another specific application, the control device includes the capacitor, speed sensor, and control circuit described in the aforementioned embodiments. The corresponding details can be found in the previous analysis and will not be elaborated here.
[0105] The above are merely specific embodiments of the present disclosure, intended to enable those skilled in the art to understand and implement the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is not limited to these embodiments, but is to be construed in the broadest manner consistent with the principles and novel features disclosed herein.
Claims
1. A single-phase asynchronous motor, characterized in that: including a capacitor connected in series with a starting winding, and a centrifugal switch for controlling the connection mode between the capacitor and the starting winding; The capacitor includes a first electrode plate and a third electrode plate in the same layer but insulated and isolated, and a second electrode plate and a fourth electrode plate in the same layer but insulated and isolated; a portion of the second electrode plate faces the first electrode plate, and a remaining portion faces a portion of the third electrode plate, and a remaining portion of the third electrode plate faces the fourth electrode plate; The centrifugal switch includes a terminal block and a rotary switch seat mounted on the motor shaft; the terminal block includes a plate body, a first elastic conductive sheet, a second elastic conductive sheet, a third conductive sheet and a fourth conductive sheet arranged on the plate body; The fixed end of the first elastic conductive sheet directly connected in series with the starting winding is electrically connected to the first electrode plate; the fixed end of the second elastic conductive sheet directly connected in series with the starting winding is electrically connected to one of the second electrode plate and the fourth electrode plate; the third conductive sheet is electrically connected to the third electrode plate; and the fourth conductive sheet is electrically connected to the other of the second electrode plate and the fourth electrode plate. When the motor shaft rotates at a speed lower than a set speed and the insulating bottom plate of the rotary switch seat is pressed against the first elastic conductive sheet and the second elastic conductive sheet, the free end of the first elastic conductive sheet contacts the third conductive sheet, and the free end of the second elastic conductive sheet contacts the fourth conductive sheet; When the rotation speed of the motor shaft exceeds the set rotation speed and the insulating bottom plate of the rotary switch seat is separated from the first elastic conductive sheet and the second elastic conductive sheet, the first elastic conductive sheet is disconnected from the third conductive sheet due to its own elastic action, and the second elastic conductive sheet is disconnected from the fourth conductive sheet and contacts the third conductive sheet due to its own elastic action.
2. The single-phase asynchronous motor according to claim 1, characterized in that: The third conductive sheet includes a first contact portion and a second contact portion perpendicular to the motor shaft, and an intermediate connecting portion for connecting the first contact portion and the second contact portion; The first contact portion is located on a side of the free end of the first elastic conductive sheet away from the rotary switch seat; the second contact portion is arranged on a side of the free end of the second elastic conductive sheet close to the rotary switch seat.
3. The single-phase asynchronous motor according to claim 2, characterized in that: The relative positions of the first contact portion, the second contact portion and the intermediate connecting portion enable the third conductive sheet to form a Z shape.
4. The single-phase asynchronous motor according to claim 2, characterized in that: When the motor rotation speed is lower than the set speed, the insulating bottom plate presses against the middle area of the first elastic conductive plate and the second elastic conductive sheet located on the inner side of the free end, so that the free end of the first elastic conductive sheet contacts the third conductive sheet, and the free end of the second elastic conductive sheet contacts the fourth conductive sheet.
5. A single-phase asynchronous motor, characterized in that: including a capacitor connected in series with a starting winding, and a centrifugal switch for controlling the connection mode between the capacitor and the starting winding; The capacitor includes a first electrode plate and a second electrode plate that are in the same layer but insulated and isolated, and a third electrode plate that is opposite to the first electrode plate and the second electrode plate; The centrifugal switch includes a terminal block and a rotary switch seat mounted on the motor shaft; the terminal block includes a plate body, a first elastic conductive sheet, a second elastic conductive sheet, a third conductive sheet and a fourth conductive sheet arranged on the plate body; The fixed end of the first elastic conductive sheet, which is directly connected in series with the starting winding, is electrically connected to the first electrode plate; the fixed end of the second elastic conductive sheet is directly connected in series with the starting winding; the fixed end of the third conductive sheet is fixedly connected to the second electrode plate; and the fixed end of the fourth conductive sheet is fixedly connected to the third electrode plate. When the motor shaft rotates at a speed lower than a set speed and the insulating bottom plate of the rotary switch seat is pressed against the first elastic conductive sheet and the second elastic conductive sheet, the free end of the first elastic conductive sheet contacts the third conductive sheet, and the free end of the second elastic conductive sheet contacts the fourth conductive sheet; When the rotation speed of the motor shaft exceeds the set rotation speed and the insulating bottom plate of the rotary switch seat is separated from the first elastic conductive sheet and the second elastic conductive sheet, the first elastic conductive sheet is disconnected from the third conductive sheet due to its own elastic action, and the second elastic conductive sheet is disconnected from the fourth conductive sheet and contacts the third conductive sheet due to its own elastic action.
6. A single-phase asynchronous motor, characterized in that: It includes a capacitor connected in series with the starting winding, a speed sensor for detecting the speed of the motor rotor, and a control circuit; The capacitor includes a first electrode plate and a third electrode plate in the same layer but insulated and isolated, and a second electrode plate and a fourth electrode plate in the same layer but insulated and isolated; a portion of the second electrode plate faces the first electrode plate, and a remaining portion faces a portion of the third electrode plate, and a remaining portion of the third electrode plate faces the fourth electrode plate; The control circuit is configured to: short-circuit the first electrode plate and the third electrode plate, and short-circuit the second electrode plate and the fourth electrode plate when the motor shaft speed is lower than a set speed; and When the motor shaft speed is higher than the set speed, the first electrode plate and the third electrode plate are disconnected and short-circuited, the second electrode plate and the fourth electrode plate are disconnected and short-circuited, and the third electrode plate is short-circuited with one of the second electrode plate and the fourth electrode plate; or, when the motor shaft speed is higher than the set speed, the first electrode plate and the third electrode plate are disconnected, so that the third electrode plate and the fourth electrode plate are disconnected and short-circuited.
7. The single-phase asynchronous motor according to claim 6, characterized in that: The control circuit includes a first electrically controlled switch, a second electrically controlled switch and a third electrically controlled switch; When the motor shaft speed is lower than the set speed, the first electronically controlled switch short-circuits the first electrode plate and the third electrode plate, the second electronically controlled switch short-circuits the second electrode plate and the fourth electrode plate, and the third electronically controlled switch disconnects and short-circuits the third electrode plate from the first electrode plate. as well as, When the motor shaft speed is higher than the set speed, the first electronically controlled switch disconnects the first electrode plate and the third electrode plate, the second electronically controlled switch disconnects the second electrode plate and the fourth electrode plate, and the third electronically controlled switch short-circuits the third electrode plate and the one of the electrodes.
8. The single-phase asynchronous motor according to claim 7, characterized in that: The first electrically controlled switch, the second electrically controlled switch, and the third electrically controlled switch are all semiconductor switches.
9. A single-phase asynchronous motor, characterized in that: It includes a capacitor connected in series with the starting winding, a speed sensor for detecting the speed of the motor rotor, and a control circuit; The capacitor includes a first plate and a second plate in the same layer but insulated and isolated, and a third plate opposite to the first plate and the second plate; the first plate is directly connected in series with the starting winding, The control circuit is configured to: when the motor shaft speed is lower than the set speed, short-circuit the first pole plate and the second pole plate, and directly connect the third pole plate in series with the starting winding; and when the motor shaft speed is higher than the set speed, disconnect the first pole plate and the second pole plate from the short-circuit, disconnect the third pole plate from the direct series connection with the starting winding, and directly connect the second pole plate in series with the starting winding.
10. A control device for a single-phase asynchronous motor, characterized in that: It includes a capacitor connected in series with a starting winding of a single-phase asynchronous motor, and a centrifugal switch for controlling the connection mode between the capacitor and the starting winding; The capacitor includes a first electrode plate and a third electrode plate in the same layer but insulated and isolated, and a second electrode plate and a fourth electrode plate in the same layer but insulated and isolated; a portion of the second electrode plate faces the first electrode plate, and a remaining portion faces a portion of the third electrode plate, and a remaining portion of the third electrode plate faces the fourth electrode plate; The centrifugal switch includes a terminal block and a rotary switch seat mounted on the motor shaft; the terminal block includes a plate body, a first elastic conductive sheet, a second elastic conductive sheet, a third conductive sheet and a fourth conductive sheet arranged on the plate body; The first elastic conductive sheet is used for being directly connected in series with the starting winding, and the fixed end thereof is electrically connected to the first electrode plate; the second elastic conductive sheet is used for being directly connected in series with the starting winding, and the fixed end thereof is electrically connected to one of the second electrode plate and the fourth electrode plate; the third conductive sheet is electrically connected to the third electrode plate; and the fourth conductive sheet is electrically connected to the other of the second electrode plate and the fourth electrode plate. When the motor shaft rotates at a speed lower than a set speed and the insulating bottom plate of the rotary switch seat is pressed against the first elastic conductive sheet and the second elastic conductive sheet, the free end of the first elastic conductive sheet contacts the third conductive sheet, and the free end of the second elastic conductive sheet contacts the fourth conductive sheet; When the rotation speed of the motor shaft exceeds the set rotation speed and the insulating bottom plate of the rotary switch seat is separated from the first elastic conductive sheet and the second elastic conductive sheet, the first elastic conductive sheet is disconnected from the third conductive sheet due to its own elastic action, and the second elastic conductive sheet is disconnected from the fourth conductive sheet and contacts the third conductive sheet due to its own elastic action.
11. A control device for a single-phase asynchronous motor, characterized in that: include: It includes a capacitor connected in series with a starting winding of a single-phase asynchronous motor, and a centrifugal switch for controlling the connection mode between the capacitor and the starting winding; The capacitor includes a first electrode plate and a second electrode plate that are in the same layer but insulated and isolated, and a third electrode plate that is opposite to the first electrode plate and the second electrode plate; The centrifugal switch includes a terminal block and a rotary switch seat mounted on the motor shaft; the terminal block includes a plate body, a first elastic conductive sheet, a second elastic conductive sheet, a third conductive sheet and a fourth conductive sheet arranged on the plate body; The fixed end of the first elastic conductive sheet, which is directly connected in series with the starting winding, is electrically connected to the first electrode plate; the fixed end of the second elastic conductive sheet is directly connected in series with the starting winding; the fixed end of the third conductive sheet is fixedly connected to the second electrode plate; and the fixed end of the fourth conductive sheet is fixedly connected to the third electrode plate. When the motor shaft rotates at a speed lower than a set speed and the insulating bottom plate of the rotary switch seat is pressed against the first elastic conductive sheet and the second elastic conductive sheet, the free end of the first elastic conductive sheet contacts the third conductive sheet, and the free end of the second elastic conductive sheet contacts the fourth conductive sheet; When the rotation speed of the motor shaft exceeds the set rotation speed and the insulating bottom plate of the rotary switch seat is separated from the first elastic conductive sheet and the second elastic conductive sheet, the first elastic conductive sheet is disconnected from the third conductive sheet due to its own elastic action, and the second elastic conductive sheet is disconnected from the fourth conductive sheet and contacts the third conductive sheet due to its own elastic action.
12. A control device for a single-phase asynchronous motor, characterized in that: It includes a capacitor connected in series with the starting winding, a speed sensor for detecting the speed of the motor rotor, and a control circuit; The capacitor includes a first electrode plate and a third electrode plate in the same layer but insulated and isolated, and a second electrode plate and a fourth electrode plate in the same layer but insulated and isolated; a portion of the second electrode plate faces the first electrode plate, and a remaining portion faces a portion of the third electrode plate, and a remaining portion of the third electrode plate faces the fourth electrode plate; The control circuit is configured to: short-circuit the first electrode plate and the third electrode plate, and short-circuit the second electrode plate and the fourth electrode plate when the motor shaft speed is lower than a set speed; and When the motor shaft speed is higher than the set speed, the first electrode plate and the third electrode plate are disconnected and short-circuited, the second electrode plate and the fourth electrode plate are disconnected and short-circuited, and the third electrode plate is short-circuited with one of the second electrode plate and the fourth electrode plate; or, when the motor shaft speed is higher than the set speed, the first electrode plate and the third electrode plate are disconnected, so that the third electrode plate and the fourth electrode plate are disconnected and short-circuited.
13. A control device for a single-phase asynchronous motor, characterized in that: It includes a capacitor connected in series with the starting winding, a speed sensor for detecting the speed of the motor rotor, and a control circuit; The capacitor includes a first plate and a second plate in the same layer but insulated and isolated from each other, and a third plate opposite to the first plate and the second plate; the first plate is directly connected in series with the starting winding; The control circuit is configured to: when the motor shaft speed is lower than the set speed, short-circuit the first pole plate and the second pole plate, and directly connect the third pole plate in series with the starting winding; and when the motor shaft speed is higher than the set speed, disconnect the first pole plate and the second pole plate from the short-circuit, disconnect the third pole plate from the direct series connection with the starting winding, and directly connect the second pole plate in series with the starting winding.