HIGH STEPS BRUSHLESS DC (BLDC) MOTOR
Field of 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 a 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 covered 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.
FIGURE 1 illustrates 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 node 4. A node 1 of coil A is connected to switches S1 and S2. A node 2 of coil B is connected to switches S5 and S6 and a node 3 of coil C is connected to switches S3 and S4. The node 4 is unutilized and is kept at an open circuit
voltage. The switches S1, S3 and S5 are connected to a supply voltage V and the switches S2, S4 and S6 are connected to a ground voltage. These switches can be controlled by specifically designed devices for motor control applications, like ST7FMC devices, as illustrated in FIGURE 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 in FIGURE 3A and FIGURE 3B. Step 1 shows a node 1 connected to the positive supply voltage V and the node 3 connected to the ground voltage, by turning the switches SI and S4 in on state. A resultant magnetic field will align the rotor in a direction as illustrated in step 1. In Step 2, the switches SI and S6 are in on state, so the node 1 is connected to the positive supply voltage V and the node 2 is connected to the ground voltage. The resultant magnetic field will turn the rotor in an anti clock wise direction by additional 60 degrees as illustrated in step 2. In Step 3, the switches S3 and S6 are in on state, so the node 2 is connected to the ground voltage and the node 3 is connected to the positive supply voltage V. As a result the rotor will be rotated by 60 degrees in the anti clock wise direction. The next corresponding three steps (Stepl, Step2, Step3) are illustrated in FIGURE 3B. By reversing switching patterns of these commutation switches a rotation in a clock wise 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. The proposed circuit is a cost effective technique as it provides additional steps without utilizing two pole configurations, which needs two different sets of coils for implementation.
Summary of the invention
It an object of the present invention to provide a cost effective brushless DC (BLDC) motor circuit for achieving additional steps in one mechanical revolution without utilizing any additional hardware.
It is another object of the present invention to provide a brushless DC (BLDC) motor circuit providing additional rotational for a better resolution and efficiency.
To achieve said objectives, the present invention provides a brushless motor circuit driving a brushless direct current (BLDC) motor, said motor having a rotor and exciting coils, said coils wounded in a three phase winding connected in a star configuration to provide additional rotational steps for a high resolution, said motor comprising:
a detector circuit detecting ah induced voltage generated across said exciting coil;
a rotor position signal generating circuit producing a specified position signal for said exciting coil of each phase; and
a control circuit performing excitation control of said exciting coils by controlling switching elements for conducting excitation currents via said exciting coils, said circuit being based on said rotor position signal,
wherein a neutral node in said star configuration is switched to one of a ground voltage, a supply voltage, and an open circuit voltage to provide said additional steps
Further, the present invention provides a method of providing additional rotational steps in a brushless DC motor for a better resolution, said motor having a rotor and exciting coils wounded in a three phase winding connected in a star configuration, said method comprising the steps of:
detecting an induced voltage generated across said exciting coil through a detector circuit,
producing a specified position signal for said exciting coil of each phase through a rotor position signal generating circuit; and
performing excitation control of said exciting coils by controlling switching elements for conducting excitation currents via said exciting coils through a control circuit,
wherein switching a neutral point of said star configuration to one of a ground voltage, a supply voltage, and an open circuit voltage to provide said additional rotational steps.
Brief Description of the drawings
The present invention is described with the help of accompanying drawings.
FIGURE 1 illustrates a circuit diagram of star connected windings for a conventional BLDC motor
FIGURE 2 illustrates a circuit diagram for microcontroller switches connected to the conventional BLDC motor.
FIGURE 3A and 3B illustrates 6 orientation steps for a conventional BLDC motor as illustrated in FIGURE 1.
FIGURE 4 illustrates a block diagram of a brushless DC (BLDC) circuit according to the present invention
FIGURE 5 illustrates a circuit diagram of star connected windings for a proposed brushless DC circuit (BLDC) according to present invention.
FIGURE 6A, 6B, 6C, 6D, 6E and 6F illustrates 12 orientation steps for a proposed BLDC circuit.
Detailed Description of the Invention
FIGURE 4 illustrates a block diagram of a brushless DC (BLDC) circuit 400 according to the present invention. The BLDC circuit 400 drives 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 three phase winding, such that a neutral node of said 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 (12) steps. The circuit 400 includes a detector circuit 402, a rotor position signal generating circuit 404, and a control circuit 406. The detector circuit 402 detects an induced voltage generated across the exciting coils. The circuit 404 generates a specified position signal for the exciting coils. The control circuit 406 performs an excitation control of the exciting coils by controlling switching elements for conducting excitation currents via said exciting coils.
FIGURE 5 illustrates a circuit diagram of star connected windings for a proposed brushless DC circuit (BLDC) according to 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 node 4 of the star configuration is used to provide one of a supply voltage, ground voltage, and an open circuit voltage The neutral node 4 is connected to two extra switches S7 and S8 to provide more combinations for achieving additional steps per rotation (12 steps). The additional steps 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 node 4. Node 1 of coil A is connected to switches S1 and S2, and node 2
of coil B is connected to switches S5 and S6 and node 3 of coil C is connected to switches S3 and S4. The neutral node 4 is connected to additional switches S7 and S8 The switches S1, S3, S5 and S7 are connected to a positive supply voltage V side and the switches S2, S4, S6 and S8 are 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 in FIGURE 6A, 6B, 6C, 6D, 6E and 6F.
FIGURE 6A illustrates steps 1 and 2 for one mechanical rotation. In step 1, the switches SI and S4 are made on so that the node 1 is connected to the positive supply voltage V and the node 3 is connected to the ground voltage. A resultant magnetic field will rotate the rotor in an anti clock wise direction by 30 degrees. In Step 2, the switches SI and S8 are in on state, such that the node 1 is connected to the positive supply voltage V and the node 2 is connected to the ground voltage. The resultant magnetic field will further turn the rotor in an anti clock wise direction by 30 degrees.
FIGURE 6B further illustrates step 3 and step 4. In step 3, the switches S1 and S6 are made on so that the node 1 is connected to the positive supply voltage V and the node 2 is connected to the ground voltage. A resultant magnetic field will rotate the rotor in an anti clock wise direction by 30 degrees. In step 4, the switches S6 and S7 are in on state, such that the node 4 is connected to the positive supply voltage V and the node 2 is connected to the ground voltage. The resultant magnetic field will further turn the rotor in an anti clock wise direction by 30 degrees.
FIGURE 6C further illustrates step 5 and step 6. In step 5, the switches S3 and S6 are made on so that the node 3 is connected to the positive supply voltage V and the node 2 is connected to the ground voltage. A resultant magnetic field will rotate the rotor in an anti clock wise direction by 30 degrees. In step 6, the switches S3 and S8 are in on state, such that the node 3 is connected to the positive supply voltage V and the node 4 is connected
to the ground voltage. The resultant magnetic field will further turn the rotor in an anti clock wise direction by 30 degrees.
FIGURE 6D further illustrates step 7 and step 8. In step 7, the switches S3 and S2 are made on so that the node 3 is connected to the positive supply voltage V and the node 1 is connected to the ground voltage. A resultant magnetic field will rotate the rotor in an anti clock wise direction by 30 degrees. In step 8, the switches S2 and S7 are in on state, such that the node 4 is connected to the positive supply voltage V and the node 1 is connected to the ground voltage. The resultant magnetic field will further turn the rotor in an anti clock wise direction by 30 degrees.
FIGURE 6E further illustrates step 9 and step 10. In step 9, the switches S2 and S5 are made on so that the node 2 is connected to the positive supply voltage V and the node 1 is connected to the ground voltage. A resultant magnetic field will rotate the rotor in an anti clock wise direction by 30 degrees. In step 10, the switches S8 and S5 are in on state, such that the node 2 is connected to the positive supply voltage V and the node 4 is connected to the ground voltage. The resultant magnetic field will further turn the rotor in an anti clock wise direction by 30 degrees.
FIGURE 6F further illustrates step 11 and step 12. In step 11, the switches S4 and S5 are made on so that the node 2 is connected to the positive supply voltage V and the node 3 is connected to the ground voltage. A resultant magnetic field will rotate the rotor in an anti clock wise direction by 30 degrees. In step 12, the switches S4 and S7 are in on state, such that the node 4 is connected to the positive supply voltage V and the node 3 is connected to the ground voltage. The resultant magnetic field will further turn the rotor in an anti clock wise direction by 30 degrees.
By reversing the switching pattern of the commutation switches a clock wise rotation of the motor can be achieved.
The proposed BLDC circuit that drives 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.

We claim:
1. A brushless motor circuit driving a brushless direct current (BLDC) motor, said
motor having a rotor and exciting coils, said coils wounded in a three phase
winding connected in a star configuration to provide additional rotational steps for
a high resolution, said motor comprising:
a detector circuit detecting an induced voltage generated across said exciting coil,
a rotor position signal generating circuit producing a specified position signal for said exciting coil of each phase; and
a control circuit performing excitation control of said exciting coils by controlling switching elements for conducting excitation currents via said exciting coils, said circuit being based on said rotor position signal,
wherein a neutral node in said star configuration is switched to one of a ground voltage, a supply voltage, and an open circuit voltage to provide said additional steps
2. The circuit as claimed in claim 1, wherein said motor is a single pole three phase
motor
3. The circuit as claimed in claim 1, wherein said additional steps comprises twelve
steps in said rotation,
4. A method of providing additional rotational steps in a brushless DC motor for a
better resolution, said motor having a rotor and exciting coils wounded in a three
phase winding connected in a star configuration, said method comprising the steps
of:
detecting an induced voltage generated across said exciting coil through a detector circuit,
producing a specified position signal for said exciting coil of each phase through a rotor position signal generating circuit; and
performing excitation control of said exciting coils by controlling switching elements for conducting excitation currents via said exciting coils through a control circuit,
wherein switching a neutral point of said star configuration to one of a ground voltage, a supply voltage, and an open circuit voltage to provide said additional rotational steps.
5 A brushless motor circuit driving a brushless direct current (BLDC) motor
substantially as herein described with reference to the accompanying drawings
6 A method of providing additional rotational steps in a brushless DC motor for a
better resolution substantially as herein described with reference to the
accompanying drawings