Motor drive and method of controlling a temperature of a motor drive

Abstract

There is provided a motor drive comprising: a temperature sensor arranged to sense a temperature of the drive; a braking resistor; switching means arranged when activated to cause current to flow to the braking resistor; and controlling means arranged to activate the switching means when the sensed temperature falls below a predetermined threshold. There is also provided a method of controlling a temperature of a motor drive comprising a braking resistor. The method comprising comprises: monitoring a temperature of the drive; and activating switching means to cause current to flow to the braking resistor when the monitored temperature falls below a predetermined threshold.

Claims

1. A motor drive comprising: a temperature sensor; a braking resistor; a plurality of components each having a critical temperature at which the component fails or malfunctions; the temperature sensor arranged to sense a temperature of a component of the plurality of components that is most sensitive to low temperatures switching means arranged when activated to cause current to flow to the braking resistor; and controlling means arranged to activate the switching means when the sensed temperature of the component that is most sensitive to low temperatures falls below a first predetermined threshold, to activate cooling means to cool the motor drive when the sensed temperature of the component that is most sensitive to low temperatures rises above a second predetermined threshold, and to deactivate said cooling means when the sensed temperature falls below the first predetermined threshold.

2. The motor drive of claim 1, wherein the component is one of: a braking transistor, a DC bus, an inverter, a power stage, a rectifier, a control stage, and a heat sink.

3. The motor drive of claim 1, wherein the braking resistor includes a strip heater.

4. The motor drive of claim 1, wherein the braking resistor includes embedded in a heat sink.

5. The motor drive of claim 1, wherein the switching means includes a braking transistor.

6. The motor drive of claim 1, wherein the cooling means includes a fan.

7. A method of controlling a temperature of a motor drive comprising a braking resistor and a plurality of components each having a critical temperature at which the component fails or malfunctions, the method comprising: monitoring a temperature of a component of the plurality of components being most sensitive to low temperatures; activating switching means to cause current to flow to the braking resistor when the monitored temperature of the component that is most sensitive to low temperatures falls below a first predetermined threshold; activating cooling means to cool the motor drive when the monitored temperature of the component that is most sensitive to low temperatures rises above a second predetermined threshold; and deactivating said cooling means when the monitored temperature falls below the first predetermined threshold.

8. The method of claim 7, wherein the component is one of: a braking transistor, a DC bus, an inverter, a power stage, a rectifier, a control stage, and a heat sink.

9. The method of claim 7, wherein the braking resistor includes a strip heater.

10. The method of claim 7, wherein the braking resistor includes embedded in a heat sink.

11. The method of claim 7, wherein the switching means includes a braking transistor.

12. A machine-readable medium having instructions stored thereon, wherein when read by a machine the instructions are configured to execute the steps of claim 7.

13. The method of claim 7, wherein the cooling means includes a fan.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A preferred embodiment of the invention will now be described in conjunction with the accompanying drawings, of which:

(2) FIG. 1 is a circuit diagram in accordance with an embodiment of the invention; and

(3) FIG. 2 is a flow chart illustrating steps taken by a method according to an embodiment of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

(4) The present invention seeks to provide an improved motor drive. Whilst various embodiments of the invention are described below, the invention is not limited to these embodiments, and variations of these embodiments may well fall within the scope of the invention which is to be limited only by the appended claims.

(5) FIG. 1 illustrates a circuit 10 arranged to control the temperature of a drive, in accordance with a preferred embodiment of the invention. Circuit 10 comprises switching means in the form of braking transistor 12. Braking transistor 12 is arranged in parallel to capacitors 13 and inductor 11.

(6) Braking transistor 12 is coupled to drive temperature sensor 14. Braking transistor 12 is arranged when activated to alternately open and close a connection to braking resistor 16 embedded in a heat sink (not shown) of drive.

(7) Drive temperature sensor 14 is arranged to sense or monitor a temperature of a component of drive. For example, drive temperature sensor 14 may be arranged to monitor a temperature of the component of the drive that is most sensitive to low temperatures. Such components may include one or more components on a control board (not shown) of the drive, such as braking transistor 12, a DC bus, an inverter, a power stage, a rectifier, and a control stage. In the preferred embodiment, drive temperature sensor 14 forms part of the internal temperature management of the drive. For example, drive temperature sensor 14 is an in-built temperature sensor arranged to monitor a temperature of a component of drive to ensure the temperature of the component does not reach a critically low or high point.

(8) In the illustrated embodiment, drive temperature sensor 14 includes processing circuitry arranged to control the operation of braking transistor 12. In particular, controlling circuitry is arranged to activate braking transistor 12 so as to alternately open a close a circuit to braking resistor 16. In other embodiments, controlling circuitry may not be included in drive temperature sensor 14, but instead could communicate with drive temperature sensor 14, for example by receiving temperature data from drive temperature sensor 14. Controlling circuitry may then operate braking transistor 12 to divert current to braking resistor 16 as a function of the temperature data.

(9) A method of operation 20 of circuit 10 will now be described, in accordance with a preferred embodiment of the invention. Braking transistor 12 is initially in an OFF state, such that current does not flow to braking resistor 16. At step 21, drive temperature sensor 14 monitors a temperature of a component of the drive. The component is generally a component which is most susceptible to low temperatures, although the drive temperature sensor may monitor the temperature of other components of the drive, or else of a group of components.

(10) If at step 22 a temperature of the component is determined to fall below a predetermined threshold, T1, controlling circuitry (e.g. in drive temperature sensor 14) causes braking transistor 12 to transition to the ON state (step 23). In addition, at step 24 any cooling means arranged to cool components of the drive may be deactivated. When in the ON state, current is diverted to braking resistor 16. Braking resistor 16 is embedded in a heat sink and causes the temperature of drive to increase, by dissipating heat generated by the current flowing through braking resistor 16. This allows the temperature of the drive to move away from a critical point where the component may fail or malfunction.

(11) If at step 25 a temperature of the critical component is determined to rise above a predetermined threshold, T2, controlling circuitry may cause cooling means to activate. This may form part of the usual thermal management function of the drive, and may be operated in conjunction with the temperature control described herein, e.g. via activation of braking resistor 16 as a function of monitored temperature. In addition, during deceleration of the motor, braking transistor 12 may be activated to energise braking resistor 16, as known in the art.

(12) Thus, with the present invention the drive may operate more efficiently in cold environments. In particular, no additional components or sensors are required as drive temperature sensor 14 may already form part of the drive and may already be used to monitor a temperature of one or more components of the drive. The controlling means or controlling circuitry of the drive may therefore be simply reprogrammed to activate the braking resistor, not only when braking is required, but in particular when a temperature of the drive drops too low.

(13) Whilst the invention has been described in connection with various embodiments, it is to be understood that the invention is not limited to these embodiments, and that alterations, modifications, and variations of these embodiments may be carried out by the skilled person without departing from the scope of the invention. For example, in the above embodiment circuit 10 is illustrated as being implemented in the drive, for example as software arranged to be executed using controlling circuitry of the drive. However, in other embodiments it is envisaged that the controlling means may not form part of the drive and instead may be arranged to remotely activate the switching means.