Brushless DC-motor

• US 8,314,580 B2
• Filed: 06/03/2005
• Issued: 11/20/2012
• Est. Priority Date: 06/04/2004
• Status: Active Grant

• Current Assignee: Belimo Holding AG
• Original Assignee: Belimo Holding AG
• Inventors: Grogg, Silvio, Stäheli, Curdin, Ochsenbein, Martin
• Primary Examiner(s): Benson, Walter
• Assistant Examiner(s): LUO, DAVID S
• Application Number:
  US11/569,890
• Publication Number:
  US 20090009115A1
• Time in Patent Office: 2,727 Days
• Field of Search: 318/400.34, 318/254.1, 318/439, 318/610, 318/611, 318/626
• US Class Current: 318/400.34
• CPC Class Codes: H02P 6/182 using back-emf in windings
• CPC Class Codes: H02P 6/21 Open loop start
• CPC Class Codes: H02P 6/24 Arrangements for stopping

Abstract

A DC-motor (46) actuates a highly-reduced reduction gear of an actuating drive for a flap or valve in order to regulate a gas or liquid volume flow, particularly for heating/ventilation/climatization, or fire or room protection. Current flow in the stator coils (A, B, C) is commutated in a program-controlled manner without integrated position sensors. Algorithms enable counting rotations of rotor (54) of the DC-motor (46). Problems related to the principle of motor rotation speed at low rpm are prevented. The DC-motor (46) includes a stator (44) having three stator coils (A, B, C) which extend over 3n stator poles (52), and an annular-shaped permanent magnet rotor (54) having 2m permanent magnet segments with alternating polarity (N, S), a coaxial cup-shaped external rotor (110) and a coaxial drive shaft (108), whereby n and m are whole multiplication factor numbers (1, 2, 3, 4) and are different from each other. Drive shaft (112) comprises, preferably, a spring (120) for the automatic return in case of current interruption.

Claims

1. Method for controlling a brushless DC motor comprising a stator having stator coils and rotor, wherein a highly reduced reduction gear of an actuating drive is provided for coupling the DC motor to a flap or a valve in order to regulate a gas or liquid volume flow, wherein an electrical current flow in the stator coils is commutated under programme control of a motor control without integral position sensors, comprising the steps of:

a) during normal operation, counting motor revolutions of the DC motor by an electronic circuit by checking a polarity of a zero crossing of each of the three phase voltages of the stator coils with BEMF comparators,

b) initiating of breaking by generating a signal for telling the motor control that the DC motor should be stopped,

c) continuing commutation from the BEMF analysis until rotation speed has fallen below a value of 400 rpm, and

d) then, effectuating an immediate stop by algorithms for stopping the rotor so that no counting errors occur.

2. Method according to claim 1, comprising the steps of

a) detecting valid zero crossings of three phase voltages,

b) allocating a particular rotor position to each of a plurality of polarity changes and,

c) determining a next commutation as soon as the respective rotor position is reached.

3. Method according to claim 2, characterised in that the valid zero crossings are detected by means of a ZERO detector and ZERO pulses are generated.

4. Method according to claim 3 characterised in that from the BEMF signals which on valid zero crossings cause ZERO pulses, a period counter calculates the next commutation time and a corresponding control signal, a NEXT pulse, is emitted.

5. Method according to claim 2, characterised in that a direction of rotation of the rotor is determined by means of the BEMF comparators in that the BEMF comparator thresholds, depending on polarity of the expected zero crossing, are located just above or below a zero line of the phase voltages.

6. Method according to claim 5, characterised in that the direction of rotation of the rotor in the high impedance commutation gaps of the phase voltages is determined at low speeds at an end of the commutation gap and at high speeds at an end of a passive PWM phase.

7. Brushless DC motor without position sensors for performance of the method according to claim 1, characterised in that it comprises a stator with three stator coils which extend over 3n stator poles and an annular permanent magnet rotor with 2m permanent magnet segments of alternating polarity, a coaxial cup-shaped external rotor and a coaxial drive shaft, where n and m are whole multiplication factors 1, 2, 3, 4 . . . independent of each other.

8. Brushless DC motor according to claim 7, characterised in that n=1 and m=1 or n=3 and m=6.

9. Method for controlling a brushless DC motor comprising a start-up mode and a normal mode, wherein an electrical current flow in a stator of the DC motor is generated by DC motor end stages and is commutated under control of a programme without integral position sensors, comprising the steps of:

a) in the start-up mode, commutating the DC motor end stages and increasing their current limit to a start-up level that is higher than a current limit of the normal mode for an accelerated start until valid BEMF signals are reached,

b) switching to the normal mode after valid BEMF signals are reached, wherein commutation of a next phase is located between two zero crossings and wherein the current limit of the DC motor end stages is reduced from the start-up level to the current limit of the normal mode.

10. Method according to claim 9, characterised in that after an unsuccessful powering of a first end stage of said DC motor end stages, a logic commutates in steps the current supply of a next end stage of said DC motor end stages until a starting position which is favourable for the rotor is reached.

11. Method according to claim 10, characterised in that the logic detects a wrong direction of rotation of the rotor from the wrong polarity of the BEMF signals and corrects this by increasing counter state of a cycle counter by two steps.

12. Method according to claim 9, characterised in that on lack of detection of a zero crossing of a phase voltage, after a first commutation the rotor oscillates with its resonant frequency into the zero position and by these zero crossings, valid BEMF signals are achieved.

13. Method according to claim 9, wherein the current limit is increased in the start-up mode to a level of at least 110% and at most 150% of the current limit of the normal mode.

14. Method for controlling a brushless DC motor having a stator and a rotor and comprising a brake mode for braking and holding the rotor, wherein an electrical current flow in the stator of the DC motor is commutated under control of a programme without integral position sensors, comprising the steps of:

a) in a first step of the brake mode, switching all stator coils powerless by short circuit under continuing commutation,

b) in a second step, after reaching a pre-set rotation speed threshold value of the rotor, applying a greatly increased current pulse leading to block the rotor for changing to a last commutation state, and in a third step again by short circuit switches the stator coils of rotor powerless or inhibits them with low pulse width modulation (PWM).

15. Method according to claim 14, characterised in that the rotor in the first step is switched actively in the opposite direction.

16. Method for controlling a brushless DC motor for moving a flap in a ventilation system or a ball valve in a water pipe system, wherein the DC motor has a stator and a rotor and drives the flap or the ball valve by means of a highly reduced reduction gear and the system has a stop for the flap or ball, wherein an electrical current flow in the stator of the DC motor is commutated under control of a programme without integral position sensors, wherein for achieving and holding a high contact pressure by the reduction gear in a stop position of the flap or valve, the following steps are provided:

a) allowing the DC motor to be stalled when the flap or ball runs against the stop and the rotor inertia torque continues to rotate uncontrolled for a few revolutions,

b) detecting the rotor position by an immediately subsequent brief acceleration in the opposite direction by means of BEMF signals, and

c) braking and holding the rotor under control.

17. Method according to claim 16, characterised in that acceleration in the opposite direction takes place only after relaxation of the reduction gear.

18. Method according to claim 16, characterised in that the process algorithms are stored retrievably.

19. Method according to claim 16, characterised in that an electronic unit counts the revolutions of the rotor of the DC motor.

20. Method according to claim 19, characterised in that algorithms for start and stop cause motor speeds below around 200 rpm to be passed quickly and without the occurrence of counting errors.

21. Method for controlling a brushless DC motor of an actuating drive with a pre-tensioned spring, an actuating drive for moving a flap in a ventilation system or a ball valve in a water pipe system, wherein the DC motor has a stator and a rotor and drives the flap or the ball valve by means of a highly reduced reduction gear and the system has a stop for the flap or ball, wherein an electrical current flow in the stator of the DC motor is commutated under control of a programme without integral position sensors, comprising the step of:

a) on a power failure, switching two of the three individually switchable bridge switches of a switch group for short circuiting two of the three stator coils of the DC motor to ground when the speed falls below an adjustable limit speed of the rotor.

22. Method according to claim 21, characterised in that a pair of said bridge switches is activated by way of a pulse width modulated control signal from the allocated transistors.

23. Method according to claim 21, characterized in that the adjustable limit speed of the motor is around 400 rpm.

24. Method for controlling a brushless DC motor comprising a stator and a rotor having stator coils, wherein a highly reduced reduction gear of an actuating drive is provided for coupling the DC motor to a flap or a valve in order to regulate a gas or liquid volume flow, wherein an electrical current flow in the stator coils is commutated under programme control of a motor control without integral position sensors, comprising the steps of:

a) during normal operation, counting motor revolutions of the DC motor by an electronic circuit by checking a polarity of a zero crossing of each phase voltage of the stator coils with BEMF comparators,

b) initiating breaking by generating a signal for telling the motor control that the DC motor should be stopped,

c) short circuiting the stator coils by the motor control so that the DC motor brakes,

d) continuing commutation from the BEMF analysis until rotation speed has fallen below a value of 400 rpm,

e) effectuating an immediate stop by algorithms for stopping of the rotor so that no counting errors occur.

25. Method for controlling a brushless DC motor comprising a stator having stator coils and rotor, which has a highly reduced reduction gear of an actuating drive for a flap or a valve in order to regulate a gas or liquid volume flow, wherein an electrical current flow in the stator coils is commutated under programme control without integral position sensors, comprising the steps of:

a) counting motor revolutions of the DC motor by an electronic circuit,

b) detecting valid zero crossings of three phase voltages,

c) checking a polarity of a zero crossing of each of the three phase voltages with BEMF comparators,

d) allocating a particular rotor position to each of a plurality of polarity changes and,

e) determining a next commutation as soon as the respective rotor position is reached

f) controlling the switching between the three phase voltages by the BEMF signals, and

g) effectuating an immediate stop by algorithms for stopping the rotor if motor revolutions fall below about 200 rpm so that no counting errors occur,

wherein a direction of rotation of the rotor is determined by means of the BEMF comparators in that the BEMF comparator thresholds, depending on polarity of the expected zero crossing, are located just above or below a zero line of the phase voltages.

26. Method according to claim 25, characterised in that the direction of rotation of the rotor in the high impedance commutation gaps of the phase voltages is determined at low speeds at an end of the commutation gap and at high speeds at an end of a passive PWM phase.