GB2504577A

GB2504577A - A motor system with a relay disconnecting the start winding at a voltage threshold

Info

Publication number: GB2504577A
Application number: GB1309480.0A
Authority: GB
Inventors: Niels Christian Weihrauch
Original assignee: Secop GmbH
Current assignee: Secop GmbH
Priority date: 2012-06-04
Filing date: 2013-05-28
Publication date: 2014-02-05
Also published as: CN103457520B; GB201309480D0; CN103457520A

Abstract

An AC single phase motor-system comprises a rotor driven by a main winding 4 and an auxiliary winding 5 powered through a start capacitor Cs for driving the rotor during start-up. A potential relay 6 controls a relay-switch 7 which deactivates the start capacitor Cs when a control voltage across the relay 7 exceeds a threshold. The relay-switch 7 is located so that when the start capacitor Cs is connected, the control voltage depends on the voltage across the auxiliary winding 5, and when the capacitor Cs is disconnected, the control voltage is independent of the voltage across the auxiliary winding 5. A PTC 20 may be included to temporarily bypass the open relay 7. This prevents unstable switching. The motor system may be used in a compressor for a refrigerator.

Description

A MOTOR-SYSTEM WITH A POWER-SYSTEM AND A POWER-SYSTEM FOR

POWERING A MOTOR-COMPONENT

INTRODUCTION

The invention relates to an AC motor-system. Particularly, the invention relates to an AC single phase motor-system with a rotor which is driven by a main winding connected between a phase connector and a zero connector such that it can be powered by a single phase power supply.

The motor-system to which the invention relates further comprises an auxiliary winding which provides torque at zero speed for starting the motor-component.

The auxiliary winding is powered via a start capacitor which provides a phase shift of the single phase of the power supply to generate the torque.

A potential relay controls a relay-switch which deactivates the start capacitor when the motor-component runs and the start torque is therefore no longer necessary. The potential relay changes configuration of the relay-switch -i.e. opens or closes the relay-switch depending on a control voltage across the relay.

When the control voltage exceeds a threshold value, the relay opens the relay-switch and the start capacitor is disconnected.

Particularly the invention relates to a motor-system for a compressor for a refrigeration application and to a method of starting such a motor-system.

BACKGROUND OF THE INVENTION

Fig. 1 illustrates diagrammatically a compressor motor known in the art. The potential relay 6 controls the relay-switch 7 and thereby activates or deactivates the start capacitor Cs and/or the auxiliary winding 5 based on a voltage across the auxiliary winding.

When power initially is supplied to the motor, the voltage across the auxiliary winding is low, and the potential relay is therefore in a non-activated and thus conducting, closed, relay-switch configuration shown in Fig. 1. In such a configuration of the relay, the auxiliary winding is connected via the start capacitor and provides a start torque.

As illustrated in Fig. 2, the voltage across the auxiliary winding (ordinate) increases when the speed increases (abscissa). When the voltage reaches a disconnection threshold value, the potential relay moves the relay-switch to the non-conducting, open, relay-switch configuration. This disconnects the start capacitor, Cs, and operation of the motor continues without the start capacitor, i.e. the auxiliary winding is driven through a run capacitor, Cr, or in motors without a run capacitor, the auxiliary winding is simply disconnected.

In a load point after the start, the run capacitor improves the efficiency of the motor which is the reason for using a run capacitor. The run capacitor is typically 5-10 times smaller than the start capacitor.

By definition herein, we will in the following use the wording activation to describe the activity of the relay which controls a relay-switch to move to a position which leads to disconnection of the start capacitor and deactivation to describe the activity of the relay which controls a relay-switch to move to a position which leads to connection of the start capacitor.

For the sake of stability and to avoid repeated activation and deactivation, the relay is designed with a hysteresis whereby the activation level of the control voltage is higher than the deactivation level of the control voltage. The hysteresis of the control voltage is illustrated by the four arrows which are connected and form a closed loop in Fig. 3.

If the motor is over-loaded, i.e. if the motor is loaded above breakdown torque, the voltage across the auxiliary winding will drop below the deactivation control voltage for the relay and causing the start capacitor to be connected. This is illustrated in Fig. 3 by the upwardly pointing arrow at low speed.

The reinstatement of the start capacitor provides increased torque to overcome the load. As a result, motor speed and thus the voltage across the auxiliary winding increases until reaching the activation level of the control voltage and the start capacitor is therefore disconnected. This sequence will repeat itself, and the relay will activate and deactivate repeatedly e.g. with a frequency in the region of one Hz depending on the mechanical load on the motor.

Due to the repeated activation and deactivation, the auxiliary winding and the start capacitor becomes operative as an over load condition. Typically, the motor is not designed to draw this increased power over longer periods of time, and the electrical system becomes overloaded. Particularly, motor windings and the cabling etc. are in risk of being damaged by excessive heating.

SUMMARY OF THE INVENTION

It is an object of embodiments of the invention to provide a motor-system comprising a power-system and a motor-component, and a separate power-system for a motor-component which prevent the above mentioned drawback of repeated activation and deactivation of the relay.

According to a first aspect, this object is solved by a motor-system where the relay is located relative to the relay-switch such that movement of the relay-switch between a closed and an open configuration changes between a state where the control voltage depends upon the voltage across the auxiliary winding and a state where the control voltage is independent of the voltage across the auxiliary winding.

Since the closing of the relay-switch becomes independent of the voltage across the auxiliary winding, the control voltage becomes independent of the rotor speed (RPM) of the motor-system, and heavy loading of the motor-system therefore doesn't influence the movement of the relay-switch. The relay-switch therefore remains in the open configuration until the motor-system is completely switched off, and the above mentioned drawbacks of repeated activation and deactivation of the relay is avoided.

In practice, the start capacitor could be located between the phase connector and a first junction, the auxiliary winding could be located between a second junction and the zero connector, and the relay-switch could be located between the first junction and the second junction. In this way, the relay-switch may conduct a current from the first to the second junction in a closed configuration and prevent conduction between the first and second junction in an open configuration -this will provide the feature that movement of the relay-switch changes between the states where the control voltage depends upon the voltage across the auxiliary winding and where the control voltage is independent of the voltage across the auxiliary winding.

The relay could be inserted between the first junction and the zero connector such that the relay-switch thereby effectively separates the relay from the auxiliary winding when the relay-switch is in its open state.

Herein, the term "junction" covers any point of attachment between two entities or electrical components as specified further in the claims. I.e. a junction between two entities or electrical components is simply that electrical conductor, wire, or cable which connects those two entities.

Particularly, the motor-system may be for driving a compressor. Herein, the term "compressor motor" covers a motor for any kind of compressor, e.g. a compressor in a refrigeration system. The motor-system may also be for other purposes.

Herein, the term "control voltage" covers that voltage which controls the relay.

The control voltage is compared to a threshold value and depending on whether the control voltage is higher or lower than the threshold value, the relay-switch is moved to the open or closed configuration by the relay. I.e. the control voltage is the voltage across the relay.

S

The relay could be an electro-mechanical relay with an anchor moved by a magnetic field from a coil. Once the voltage reaches the threshold value, the magnet field is sufficient for moving the anchor and thus the relay-switch, or the relay could be an electronic relay.

Typically, the motor-system would comprise two parallel circuits, namely a main circuit and an auxiliary circuit. The circuits extend in parallel between the phase connector and the zero connector.

The main circuit comprises the main winding for driving a rotor during normal operation. The auxiliary circuit comprises the start capacitor, Cs, between the phase connector and the aforementioned first junction, the relay-switch between the first junction and the second junction, and the auxiliary winding for driving the rotor during start-up. The auxiliary winding is located between the second junction and the zero connector.

Initially, before the motor-system is turned on, the voltage anywhere in the system is zero, accordingly, the relay-is deactivated, and the relay-switch is in the closed position. When the motor-system is turned on, the voltage over the auxiliary winding increases by increasing RPM of the motor-system, and due to the closed relay-switch, the control voltage over the relay corresponds essentially to the voltage over the auxiliary winding, When the voltage over the auxiliary winding reaches the threshold value, the relay activates and opens the relay-switch whereby the relay becomes separated from the auxiliary winding, and the control voltage therefore no longer depends on the voltage across the auxiliary winding. To ensure a stable switching of the relay-switch, the motor-system may include a rectifier which will be described in further details later.

This rectifier will provide one way conduction from the auxiliary winding to the relay and due to the one way conduction, the control voltage will depend on the voltage over the auxiliary winding for half of a period of an AC-signal and be independent of the voltage over the auxiliary winding for the other half of the period of the AC-signal.

Additionally, the motor-system may comprise a run capacitor located between the second junction and the phase connector.

A PTC may be inserted between the second and the first junction, i.e. in parallel with the relay-switch. The PTC thereby forms a voltage divider for the relay.

When the motor-system is started, the relay-switch is closed and the PTC is therefore bypassed. Accordingly, the PTC will stay cold as long as the relay-switch is closed.

As the motor-system accelerates up to the nominal speed, the voltage across the auxiliary winding increases until the voltage reaches a steady state high level at nominal speed. At this point, the relay opens the relay-switch and the PTC which is still cold, takes over the conduction to the auxiliary winding. The voltage relay is therefore continuously supplied with high voltage from the auxiliary phase even though the relay-switch is open. Since the PTC now conducts the current, it starts heating and after a few seconds, it changes to high ohmic resistance mode. This will essentially end the conduction through the PTC.

Due to the PTC, the duration at which auxiliary winding is powered by the start capacitor is increased -i.e. the PTC provides a delay in disconnection of the start capacitor. When the PTC becomes warm, the resistance increases and the PTC no longer connects the start capacitor to the auxiliary winding.

Additionally, the motor-system may comprise a safety-switch which deactivates the motor-component in case of excessive currents and thus temperatures. If the motor-system comprises an internal safety-switch, the PTC becomes cold when the safety-switch is activated. The PTC thereby provides power to the auxiliary winding irrespective of the relay-switch which is still open. The PTC may e.g. change between a resistance below 10 ohm and a resistance above 50.000 ohm depending on its temperature.

Activation of the safety-switch is generally caused by an over loading of the motor-system. When such overloading occurs, the relay-switch will generally be open, and due to the invention and the separation of the relay from the winding, the relay-switch will stay open, and the motor-system will not be able to generate start torque via the start capacitor. However, when the safety-switch opens, no current will run through the PTC, and the PTC will cool down.

When the safety-switch opens, the PTC becomes cold. When the safety-switch closes again, the auxiliary phase can be powered by the start capacitor through the PTC which is now cold. This will create a momentary voltage drop at the third junction causing the relay to reset. The motor-system thereby becomes ready to be started normally via a connection between the start capacitor and the auxiliary winding over the closed relay-switch.

The motor-system may further comprise a bleed resistor located between the first junction and the phase connector. Due to the bleed resistor, the start capacitor is discharged and the lifetime of the capacitor can be increased A bridge with a first rectifier may provide one-way conduction in the direction from the second junction to the relay.

A bleed resistor may be located between the first junction and the phase connector. The bleed resister discharges the start capacitor when it is not connected. A resistor with a resistance above 10.000 ohm, or even above 80.000 ohm may be suitable.

In another embodiment or additionally, the motor-system may comprise a resistor extending between the phase connector and a third junction located between the first rectifier and the relay. The resistor could be in the form of a PTC which becomes high ohmic when it is warm whereby the conduction over the resistor essentially stops.

The potential relay may be of the type which comprises an anchor which is mechanically moved by a magnet field provided by a coil.

Particularly, the motor-system may form an integrated part of a compressor for a refrigeration system.

In a second aspect, the invention provides a power-system for powering a motor-component, e.g. to form a compressor-motor. The motor-component for which the power-system is intended is of the kind with a rotor adapted to be driven by a main winding connected between a phase connector and a zero connector for connection of the motor-component to a single phase power supply, and adapted to be started by the help of an auxiliary winding being powered via a start capacitor which provides a phase shift of the single phase from the power supply, the power-system comprising a potential relay controlling a relay-switch which is connectable to the motor-component such that it deactivates the auxiliary winding of the motor-component when a control voltage across the relay exceeds a threshold, wherein the relay is located relative to the relay-switch such that switching of the relay-switch between a closed and an open configuration changes between a state where the control voltage depends upon the voltage across the auxiliary winding of a connected motor-component and a state where the control voltage is independent of the voltage across the auxiliary winding.

In a third aspect, the invention provides a method of controlling a single phase motor, e.g. a compressor motor for a refrigeration system, with a rotor adapted to be driven by a main winding connected between a phase connector and a zero connector for connection of the motor to a single phase power supply, and adapted to be started by the help of an auxiliary winding being powered via a start capacitor which provides a phase shift of the single phase from the power supply, the method comprising the step of moving a relay-switch between a closed and an open configurations and thereby deactivating the start capacitor based on a control voltage between control junctions, where the relay-switch is arranged relative to the control junctions such that switching of the relay-switch between the closed and the open configuration changes between a state where the control voltage depends upon a voltage across the auxiliary winding and a state where the control voltage is independent of the voltage across the auxiliary winding.

DETAILED DESCRIPTION

In the following, embodiments of the invention will be described by way of example with reference to the figures in which: Fig. 1 illustrates a diagram of a prior art single phase motor; Fig. 2 illustrates in a graph, Voltage across the auxiliary phase as a function of rotor speed (RPM); Fig. 3 illustrates in a graph, torque as a function of rotor speed (RPM); Fig. 4 illustrates a diagram of a motor-system according to the invention; Figs. 5-7 illustrate diagrams of alternative embodiments of the invention.

Further scope of applicability of the present invention will become apparent from the following detailed description and specific examples. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.

Fig. 1 illustrates a diagram of a single phase AC asynchronous motor 1 with an electrical potential relay. Such a motor exists already. The motor is connected to an AC power supply by use of a phase connector 2 and a zero connector 3. The motor comprises a main winding 4, an auxiliary winding 5, a run capacitor, Cr, a start capacitor, Cs, and an electrical potential relay 6 which controls the state of a relay-switch 7 which connects or de-connects the start capacitor. The relay 6 is inserted between opposite sides of the auxiliary winding 5 and therefore controls the relay-switch based on a voltage across that winding. The bleed resistor, BR, reduces the electrical potential between the run capacitor and start capacitor and thereby protects the relay-switch 7 against excessive current and voltage. The protector 8 opens based on the current in both the auxiliary winding and main winding and disconnects the motor in case of excessive heating.

Fig. 4 illustrates a motor-system 12 according to the invention. The motor-system comprises a rotor (not shown) which is driven by a main winding 4 connected between the phase 2 and zero 3 of a power supply. The auxiliary winding 5 is powered via a start capacitor, Cs, and drives the rotor during start-up. The potential relay 6 controls the relay-switch 7 based on a control voltage, herein being the voltage between the junction 10 and the zero connector 3.

During start-up when the relay-switch 7 is closed (as illustrated in Fig. 4), the voltage across the relay 6 is depends on the voltage across the auxiliary winding, and the relay can therefore deactivate the start capacitor when a control voltage across the relay and thus the voltage across the auxiliary winding exceeds a threshold value.

Once the threshold value is reached, the relay opens the relay-switch, and the start capacitor is deactivated. By this step, the relay-switch also separates the auxiliary winding 5 from the relay 6 -i.e. the relay operates based on the voltage between the junction 10 and the zero connector 3 and that voltage is independent of the voltage across the auxiliary winding between the junction 11 and the zero connector 3. Accordingly, the control voltage is independent of the voltage across the auxiliary winding when the auxiliary winding is deactivated.

In the embodiment shown in Fig. 4, the start capacitor is located between the phase connector 2 and a first junction 10, the auxiliary winding 5 is located between a second junction 11 and the zero connector 3, and the relay-switch 7 is located between the first junction 10 and the second junction 11 such that conduction of a current between the first and second junctions depends on the configuration of the relay-switch. The relay 6, which controls the movement of the relay-switch 7, is inserted between the first junction 10 and the zero connector 3, and an optional bridge in the form of a one-way diode 9 provides one-way conduction from the second junction 11 to the relay 6.

Additionally, a run capacitor (not shown) can be inserted between the phase connector 2 and the second junction 11.

Fig. 5 illustrates schematically an alternative motor-system 13 according to the invention. In this embodiment, the relay 6 is connected to the phase connector 2 via a component providing ohmic resistance, e.g. a resistor 14, or a PTC, or a parallel coupled PTC and resistor extending between the phase connector 2 and the third junction 15, such that the relay 6 can react on a voltage which is not influenced by the voltage across the auxiliary winding when the relay-switch 7 is open. When the relay-switch 7 is closed, as illustrated in Fig. 5, the relay will react on the voltage across the auxiliary winding 5. Additionally, a run capacitor (not shown) can be inserted between the phase connector 2 and the second junction 11.

Fig. 6 illustrates schematically an alternative motor-system 16 according to the invention. In this embodiment, the relay 6 is connected to the phase connector 2 via a resistor 14 extending between the phase connector 2 and the first junction 10, i.e. in parallel with the start capacitor, Cs. Additionally, a run capacitor (not shown) can be inserted between the phase connector 2 and the second junction 11.

A one-way diode 18 is inserted between the third junction 15 and the first junction 10. Also in this embodiment, the relay 6 can react on a voltage which is not influenced by the voltage across the auxiliary winding when the relay-switch 7 is open. When the relay-switch 7 is closed, as illustrated in Fig. 6, the relay will react on the voltage across the auxiliary winding 5.

Fig. 7 illustrates schematically an alternative motor-system 19 according to the invention. In this embodiment, a PTC 20 is inserted between the first junction 10 and the second junction 11. The PTC thereby forms a voltage divider for the relay.

The motor-system comprises an internal safety-switch 8 which deactivates the motor-component in case of excessive currents and thus temperatures. In such a situation, the PTC becomes cold when the safety-switch is activated, i.e. when the safety-switch has open, non-conductive, contacts. The PTC thereby provides power to the auxiliary winding once the safety switch closes again. When this happens, the PTC, due to its function as a voltage divider, will ensure that the voltage at junction 11 is reduced whereby the relay can be deactivated and whereby the relay-switch 7 is closed and the motor can be started normally.

The rectifier 9 is optional. The rectifier provides a safety feature for safe activation of the relay 6. The rectifier provides conduction from the second junction 11 to the third junction 15 and thereby ensures that the voltage over the relay 6 corresponds to that over the auxiliary winding at least for half of a period of an AC-signal. I.e. the relay 6 receives half a wave of the AC signal with full voltage from the auxiliary winding, and another half wave of reduced voltage from phase via the start capacitor.

Additionally, a run capacitor (not shown) can be inserted between the phase connector 2 and the second junction 11, and a bleed resistor may be inserted between first junction 10 and the phase connector 2.

Claims

Claims 1. An AC single phase motor-system (12, 13, 16, 19) comprising a rotor adapted to be driven by a main winding (4) connected between a phase connector (2) and a zero connector (3) for connection of the motor-system to a single phase power supply, the motor-system further comprising an auxiliary winding (5) for driving the rotor during start-up, the auxiliary winding (5) being powered via a start capacitor (Cs) which provides a phase shift of the single phase from the power supply, the motor-system further comprising a potential relay (6) controlling a relay-switch (7) which deactivates the start capacitor (Cs) when a control voltage reaches a threshold, wherein the relay (6) is located relative to the relay-switch (7) such that movement of the relay-switch between a closed and an open configuration changes between a state where the control voltage depends upon the voltage across the auxiliary winding (5) and a state where the control voltage is independent of the voltage across the auxiliary winding (5).
2. A motor-system according to claim 1, wherein the start capacitor (Cs) is located between the phase connector (2) and a first junction (10), the auxiliary winding (5) is located between a second junction (11) and the zero connector (3), and the relay-switch (7) is located between the first junction (10) and a second junction (11) to conduct a current from the first to the second junction (10, 11) in a closed configuration and to prevent conduction between the first and second junction (10, 11) in an open configuration.
3. A motor-system according to claim 2, where the relay (6) is inserted between the first junction (10) and the zero connector (3).
4. A motor-system according to any of claims 2 or 3, further comprising a bridge with a first rectifier (9) providing one way conduction in the direction from the second junction (11) to the relay (6).
5. A motor-system according to any of the preceding claims, further comprising a component which provides ohmic resistance extending between the phase connector (2) and a third junction (15) located between the first rectifier (9) and the relay (6).
6. A motor-system according to any of the preceding claims, further comprising a PTC (20) located between the second and the first junctions (10, 11).
7. A motor-system according to claim 6, there the PTC changes between a resistance below 10 ohm and a resistance above 50.000 ohm depending on its temperature.
8. A motor-system according to any of the preceding claims, further comprising a resistor (14) located between the first junction and the phase connector.
9. A motor-system according to claim 8, where the resistor (14) has a resistance above 10.000 ohm.
10. A motor-system according to any of the preceding claims, where the potential relay comprises an anchor which is mechanically moved by a magnetfield provided by a coil.
11. A motor-system according to any of the preceding claims forming part of a compressor for a refrigeration system.
12. A power-system for powering a motor-component, which motor-component comprises a rotor adapted to be driven by a main winding connected between a phase connector and a zero connector for connection of the motor-component to a single phase power supply, and adapted to be started by the help of an auxiliary winding being powered via a start capacitor which provides a phase shift of the single phase from the power supply, the power-system comprising a potential relay controlling a relay-switch which is connectable to the motor-component such that it deactivates the start capacitor when a control voltage across the relay exceeds a threshold, wherein the relay is located relative to the relay-switch such that switching of the relay-switch between a closed and an open configuration changes between a state where the control voltage depends upon the voltage across the auxiliary winding of a connected motor-component and a state where the control voltage is independent of the voltage across the auxiliary winding.
13. A method of controlling a single phase motor with a rotor adapted to be driven by a main winding connected between a phase connector and a zero connector for connection of the motor to a single phase power supply, and adapted to be started by the help of an auxiliary winding being powered via a start capacitor which provides a phase shift of the single phase from the power supply, the method comprising the step of switching a relay-switch between a closed and an open configurations and thereby deactivating the start capacitor based on a control voltage between control junctions, where the relay-switch is arranged relative to the control junctions such that switching of the relay-switch between the closed and the open configuration changes between a state where the control voltage depends upon a voltage across the auxiliary winding and a state where the control voltage is independent of the voltage across the auxiliary winding.