High steps brushless DC (BLDC) motor

A brushless motor circuit is for driving a brushless direct current (BLDC) motor. The motor includes a rotor and exciting coils for respective phases in a three-phase winding in a star configuration. A neutral point in the star configuration is configured to switch to one of a ground voltage, a supply voltage, and an open circuit voltage to provide more combinations. The combinations provide extra steps in one revolution for a better resolution with enhanced efficiency.

FIELD OF THE INVENTION

The present invention relates generally to a brushless motor drive circuit formed as a semiconductor integrated circuit, and more specifically to a brushless motor drive circuit providing higher mechanical rotational steps for a better resolution.

BACKGROUND OF THE INVENTION

Direct current (DC) motors are very popular in variable speed drives due to simple speed control and simple control circuits. However, the DC motor initially used hard brushes, due to which the DC motors suffered from a low reliability and required frequent maintenance or replacement. These drawbacks of the DC motors were eliminated by using brushless DC motors (BLDC), which are highly reliable and can be used in applications requiring high speed.

A BLDC motor includes two coaxial magnetic armatures separated by an air gap. An external armature is called a stator and an internal armature is called a rotor. In the BLDC motor, the rotor is a permanent magnet and is supplied by a constant DC current. The stator is poly-phased, three-phases in the present invention, and is coveted by poly-phased currents. Three phase brushless DC motors are used in automotive equipment, refrigerators, air conditioners, compressors and fans due to their high efficiency, silent operation, compact form, reliability and longevity.

FIG. 1illustrates a circuit diagram of star connected windings for a conventional BLDC motor. The star connected windings of the BLDC motor are connected to commutation switches. The commutation switches can be field effect transistors (FET). The star connected windings, such as coil A, coil B and coil C are connected in a star configuration with a neutral node4. A node1of coil A is connected to switches S1and S2. A node2of coil B is connected to switches S5and S6and a node3of coil C is connected to switches S3and S4. The node4is unutilized and is kept at an open circuit voltage. The switches S1, S3and S5are connected to a supply voltage V and the switches S2, S4and S6are connected to a ground voltage. These switches can be controlled by specifically designed devices for motor control applications, like ST7FMC devices, as illustrated inFIG. 2.

Using a single-pole three-phase BLDC motor as illustrated above, one mechanical rotation can be achieved in six steps. Each step corresponds to 60 degrees of rotation, i.e., 360/6 . The six steps are generated by switching different combinations of switches as illustrated inFIG. 3AandFIG. 3B. Step1shows a node1connected to the positive supply voltage V and the node3connected to the ground voltage, by turning the switches S1and S4to an on state. A resultant magnetic field will align the rotor in a direction as illustrated in step1. In Step2, the switches S1and S6are in the on state, so the node1is connected to the positive supply voltage V and the node2is connected to the ground voltage. The resultant magnetic field will turn the rotor in a counter clockwise direction by an additional 60 degrees as illustrated in step2. In Step3, the switches S3and S6are in the on state, so the node2is connected to the ground voltage and the node3is connected to the positive supply voltage V. As a result the rotor will be rotated by 60 degrees in the counter clockwise direction. The next corresponding three steps (Step1, Step2, Step3) are illustrated inFIG. 3B. By reversing switching patterns of these commutation switches a rotation in a clockwise direction can be achieved.

Therefore, there is a need of a brushless motor drive circuit to provide additional steps in one rotation for a better resolution in each step.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a cost effective brushless DC (BLDC) motor circuit for achieving additional steps in one mechanical revolution such as without utilizing any additional hardware. The proposed circuit is a cost effective technique as it can provide additional steps without utilizing two pole configurations, which need two different sets of coils for implementation.

It is another object of the present invention to provide a brushless DC (BLDC) motor circuit providing additional rotation steps for a better resolution and efficiency.

To achieve the objectives, the present invention provides a brushless motor circuit driving a brushless direct current (BLDC) motor. The motor may have a rotor and exciting coils, with the coils wound in a three-phase winding connected in a star configuration to provide additional rotational steps for a high resolution. The motor may comprise a detector circuit detecting an induced voltage generated across the exciting coil; a rotor position signal generating circuit producing a specified position signal for exciting the coil of each phase; and a control circuit performing excitation control of the exciting coils by controlling switching elements for conducting excitation currents via the exciting coils and based on the rotor position signal. A neutral node in the star configuration may be switched to one of a ground voltage, a supply voltage, and an open circuit voltage to provide the additional steps.

Further, the present invention provides a method of providing additional rotational steps in a brushless DC motor for a better resolution. The motor may have a rotor and exciting coils wound in a three-phase winding connected in a star configuration. The method may comprise detecting an induced voltage generated across the exciting coil through a detector circuit; producing a specified position signal for the exciting coil of each phase through a rotor position signal generating circuit; and performing excitation control of the exciting coils by controlling switching elements for conducting excitation currents via the exciting coils through a control circuit. A neutral point of the star configuration may be switched to one of a ground voltage, a supply voltage, and an open circuit voltage to provide the additional rotational steps.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 4illustrates a block diagram of a brushless DC (BLDC) circuit400according to the present invention. The BLDC circuit400drives a brushless DC (BLDC) motor having 12 steps in one mechanical rotation. The motor includes a rotor and multiple exciting coils connected in a star topology in a three-phase winding, such that a neutral node of the star topology is utilized and switched to one of a supply voltage, a ground voltage and an open circuit voltage. The neutral node is connected to more switches for providing more combinations for additional steps. The circuit400includes a detector circuit402, a rotor position signal generating circuit404, and a control circuit406. The detector circuit402detects an induced voltage generated across the exciting coils. The circuit404generates a specified position signal for the exciting coils. The control circuit406performs an excitation control of the exciting coils by controlling switching elements for conducting excitation currents via the exciting coils.

FIG. 5illustrates a circuit diagram of star connected windings for a proposed brushless DC circuit (BLDC) according to the present invention. The star connected windings are connected to commutation switches. The commutation switches can be field effect transistors (FETs). The arrangement is such that, a neutral node4of the star configuration is used to provide one of a supply voltage, ground voltage, and an open circuit voltage. The neutral node4is connected to two extra switches S7and S8to provide more combinations for achieving additional steps per rotation (12 steps total). The additional step generation is explained in the following paragraphs.

The three winding coils A, B and C are connected in the star configuration having an activated neutral node4. Node1of coil A is connected to switches SI and S2, and node2of coil B is connected to switches S5, and S6and node3of coil C is connected to switches S3and S4. The neutral node4is connected to additional switches S7and S8. The switches S1, S3, S5and S7are connected to a positive supply voltage V and the switches S2, S4, S6and S8are connected to the ground voltage side.

The above circuit arrangement provides 12 steps in one complete mechanical rotation. Each step corresponds to 30 degrees of rotation, i.e., 360/12 degrees. The 12 steps are generated by switching different combinations of switches as illustrated inFIGS. 6A,6B,6C,6D,6E and6F.

FIG. 6Aillustrates steps1and2for one mechanical rotation. In step1, the switches S1and S4are made on so that the node1is connected to the positive supply voltage V and the node3is connected to the ground voltage. A resultant magnetic field will rotate the rotor in a counter clockwise direction by 30 degrees. In Step2, the switches S1and S8are in an on state, such that the node1is connected to the positive supply voltage V and the node2is connected to the ground voltage. The resultant magnetic field will further turn the rotor in a counter clockwise direction by 30 degrees.

FIG. 6Bfurther illustrates step3and step4. In step3, the switches S1and S6are turned on so that the node1is connected to the positive supply voltage V and the node2is connected to the ground voltage. A resultant magnetic field will rotate the rotor in a counter clockwise direction by 30 degrees. In step4, the switches S6and S7are in the on state, such that the node4is connected to the positive supply voltage V and the node2is connected to the ground voltage. The resultant magnetic field will further turn the rotor in a counter clockwise direction by 30 degrees.

FIG. 6Cfurther illustrates step5and step6. In step5, the switches S3and S6are turned on so that the node3is connected to the positive supply voltage V and the node2is connected to the ground voltage. A resultant magnetic field will rotate the rotor in a counter clockwise direction by 30 degrees. In step6, the switches S3and S8are in the on state, such that the node3is connected to the positive supply voltage V and the node4is connected to the ground voltage. The resultant magnetic field will further turn the rotor in a counter clockwise direction by 30 degrees.

FIG. 6Dfurther illustrates step7and step8. In step7, the switches S3and S2are turned on so that the node3is connected to the positive supply voltage V and the node1is connected to the ground voltage. A resultant magnetic field will rotate the rotor in a counter clockwise direction by 30 degrees. In step8, the switches S2and S7are in an on state, such that the node4is connected to the positive supply voltage V and the node1is connected to the ground voltage. The resultant magnetic field will further turn the rotor in a counter clockwise direction by 30 degrees.

FIG. 6Efurther illustrates step9and step10. In step9, the switches S2and S5are turned on so that the node2is connected to the positive supply voltage V and the node1is connected to the ground voltage. A resultant magnetic field will rotate the rotor in a counter clockwise direction by 30 degrees. In step10, the switches S8and S5are in the on state, such that the node2is connected to the positive supply voltage V and the node4is connected to the ground voltage. The resultant magnetic field will further turn the rotor in a counter clockwise direction by 30 degrees.

FIG. 6Ffurther illustrates step11and step12. In step11, the switches S4and S5are turned on so that the node2is connected to the positive supply voltage V and the node3is connected to the ground voltage. A resultant magnetic field will rotate the rotor in a counter clockwise direction by 30 degrees. In step12, the switches S4and S7are in the on state, such that the node4is connected to the positive supply voltage V and the node3is connected to the ground voltage. The resultant magnetic field will further turn the rotor in a counter clockwise direction by 30 degrees.

By reversing the switching pattern of the commutation switches a clockwise rotation of the motor can be achieved.

The proposed BLDC circuit that drives the BLDC motor offers many advantages. Firstly the BLDC motor provides a cost effective technique for achieving additional steps in a mechanical revolution for a better resolution for each step.