1. A method for reducing the influence of a DC component in a load current of an asynchronous three-phase motor, in which the voltages of two of the three phases are controlled by adjusting firing angles of semiconductor devices of the type turning off at zero-crossing of the current therethrough, two connected in anti-parallel to each other in each phase, characterized in that the method comprises the following steps carried out for each said controlled phase:
a) detecting the turn-off time of a first of said semiconductor devices and the subsequent turn-off time of the other, second semiconductor device,
b) determining the time period, called second time period, of the current half-cycle of said second semiconductor device as the difference between said two turn-off times,
c) calculating, based upon information about said second time period, a value of a change of firing angle of said first andor second semiconductor device needed for changing the length of said second time period for compensating for the influence of any DC component of the current through this semiconductor device thereupon, and
d) determining the firing angle of said first andor second semiconductor device in dependence of the result of said calculation for reducing the influence of a possible DC component in the current.
2. A method according to claim 1, characterized in that in said calculation step said first andor second time period is compared with half the time period of the voltage in said phase and the change of firing angle of said first andor second semiconductor device needed for removing any difference between said second time period and said half time period of the voltage is calculated.
3. A method according to claim 1, characterized in that it comprises the further steps of:
detecting the turn-off time of said first semiconductor device subsequent to a detection of the turn-off time of said second semiconductor device, and
determining a time period, called first time period, of the current half-cycle of said first semiconductor device as the difference between the two turn-off times last mentioned,
and that in said calculation step said first and second time periods are compared and the change of the firing angle of said first andor second semiconductor device needed for removing the difference between said first and second time periods is calculated.
4. A method according to claim 2, characterized in that it comprises the further steps of:
detecting the turn-off time of said first semiconductor device subsequent to a detection of the turn-off time of said second semiconductor device, and
determining the time period, called first time period, of the current half-cycle of said first semiconductor device as the difference between the two turn-off times last mentioned,
and that in said calculation step the sum of said first and second time periods is used as a value for said half the time period of the voltage in said phase.
5. A method according to claim 1, characterized in that in said determining step d) the firing angle is determined using a definable correction factor.
6. A method according to claim 2, characterized in that in said determining step the firing angle \u03b1 (n) is determined as follows:
\u03b1(n)=\u03b10\u2212k1(T(n-1)\u2212T0)
in which n is the number of said current half-cycle, T is a said time period determined of a said current half-cycle, T0 is half the time period of the voltage in said phase, \u03b10 is the firing angle required for obtaining a desired voltage in said phase in absence of any DC component in the current and k1 is said correction factor.
7. A method according to claim 6, characterized in that said correction factor is 0.25-0.75, preferably about 0.5, rads.
8. A method according to claim 3, characterized in that in said determining step d) the firing angle \u03b1 (n) is determined as follows:
\u03b1(n)=\u03b10\u2212k2(T(n-1)\u2212T(n-2))
in which in which n is the number of said current half-cycle, T is a said time period determined of a said current half-cycle, \u03b10 is the firing angle required for obtaining a desired voltage in said phase in absence of any DC component in the current and k2 is said correction factor.
9. A method according to claim 8, characterized in that said correction factor k2 is 0.125-0.375, preferably about 0.25, rads.
10. A method according to claim 1, characterized in that said firing angle is in said determining step d) determined to be changed by only a portion of said needed value of the change of the firing angle calculated in step d) for stepwise reducing the influence of any DC component of the current by repeating the steps a)-d) of the method.
11. A method according to claim 1, characterized in that the firing angle is in said determining step d) determined on the basis of at least two said calculations in step c) each following upon the steps a) and b).
12. A method according to claim 1, characterized in that it is carried out substantially continuously at least during the start of said asynchronous motor until the voltage across the motor has reached a pre-determined proportion of the maximum voltage thereacross, such as 80-100% of said maximum voltage.
13. A method according to claim 1, characterized in that it is carried out substantially continuously during at least a procedure of stopping said asynchronous motor until the voltage across said motor has at least been reduced to be below a predetermined value of the maximum voltage across the motor, such as 50-30% thereof.
14. An apparatus for reducing the influence of a DC component in a load current of an asynchronous three-phase motor, said motor being associated with an arrangement for controlling the voltage of two of the three phases by adjusting firing angles of semiconductor devices of the type turning off at zero-crossing of the current therethrough, two connected in anti-parallel to each other in each phase, characterized in that the apparatus comprises for each said controlled phase:
means for detecting the turn-off time of a first of said semiconductor devices and the subsequent turn-off time of the other, second semiconductor device,
means for determining the time period, called second time period, of the current half-cycle of said second semiconductor device as the difference between said turn-off times,
means for calculating, based upon information about said second time period, a value of a change of firing angle of said first andor second semiconductor device needed for changing the length of said second time period for compensating for the influence of any DC component of the current through this semiconductor device thereupon, and
means for determining the firing angle of said first andor second semiconductor device in dependence of the result of said calculation for reducing the influence of a possible DC component in the current by a corresponding control through said arrangement.
15. An apparatus according to claim 14, characterized in that said calculating means is adapted to compare said second time period with half the time period of the voltage in said phase and to calculate the change of the firing angle of said first andor second semiconductor device needed for removing any difference between said second time period and said half time period of the voltage.
16. An apparatus according to claim 14, characterized in that said detecting means is adapted to detect the turn-off time of said first semiconductor device subsequent to a detection of the turn-off time of said second semiconductor device, that said time period determining means is adapted to determine a time period, called first time period, of the current half-cycle of said first semiconductor device as the difference between the turn-off times last mentioned, and that said calculation means is adapted to compare said first and second time periods and calculate the change of the firing angle of said first andor second semiconductor device needed for removing the difference between said first and second time periods.
17. An apparatus according claim 15, characterized in that said detecting means is adapted to detect the turn-off time of said first semiconductor device subsequent to a detection of the turn-off time of said second semiconductor device, that said time period determining means is adapted to determine the time period, called first time period, of the current half-cycle of said first semiconductor device as the difference between the two turn-off times last mentioned, and that said calculating means is adapted to use the sum of said first and second time periods as a value of said half the time period of the voltage in said phase.
18. An apparatus according to claim 14, characterized in that said firing angle determining means is adapted to determine said firing angle to be changed by only a portion of said value of the change of the firing angle needed calculated by said calculating means for stepwise reducing the influence of any DC component of the current.
19. An apparatus according to claim 14, characterized in that said detecting means, time period determining means and said calculating means are adapted to obtain a plurality of calculations of a said value of a change of firing angle needed, and that said firing angle determining means is adapted to determine said firing angle on the basis of at least two said calculations.
20. An apparatus according to claim 14, characterized in that it is adapted to reduce the influence of a DC component in a load current of an asynchronous three-phase motor substantially continuously at least during the start of said asynchronous motor until the voltage across the motor has reached a predetermined portion of the maximum voltage thereacross, such as 80-100% of said maximum voltage.
21. An apparatus according to claim 14, characterized in that in that it is adapted to reduce the influence of a DC component in a load current of an asynchronous three-phase motor substantially continuously during at least a procedure of stopping said asynchronous motor until the voltage across said motor has at least been reduced to be below a predetermined value of the maximum voltage across the motor, such as 50-30% thereof.
22. A computer program directly loadable into the internal memory of a computer, which comprises computer code portions for controlling the steps of claim 1 when the program is run on a computer.
23. A computer program according to claim 22 provided at least partially through a network as the Internet.
24. A computer readable medium having a computer program recorded thereon, in which said computer program is designed to make a computer control the steps according to claim 1.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
I claim:
1. A seat headrest for interconnection with a seat comprising:
(a) a connector member connected to the seat;
(b) a headrest assembly connected to said connector member, said headrest assembly comprising:
(i) a central support panel;
(ii) a pair of side panels connected to said central panel by hinge means, each of said pair of side panel panels comprising an upper portion having a first connector segment and a lower portion having a second connector segment, said hinge means comprising:
a. a barrel portion connected to said central support panel;
b. a shaft portion rotatably carried by said barrer portion, said shaft portion having first and second ends, said first end being connected to said first connector segment and said second end being connected to said second connector segment; and
c. a plurality of generally U-shaped, friction imparting clips carried by said shaft portion for engagement with said barrel portion.
2. The seat headrest as defined in claim 1 in which said headrest assembly is connected to said connector for movement relative thereto between a first position and a second position.
3. The seat headrest as defined in claim 2 in which said headrest assembly comprises:
(a) an elongated guide;
(b) a plurality of rollers connected to said connector member for rollable engagement with said elongated guide; and
(c) resistance imparting means connected to said connector member for yieldably resisting movement of said headrest between said first position and said second position, said resistance imparting means comprising a spring disposed in compressive engagement with said elongated guide.
4. The seat headrest as defined in claim 3 further including guide means connected to said headrest assembly for sliding engagement with said elongated guide to guide the travel of said headrest assembly between said first and second positions.
5. The seat headrest as defined in claim 4, in which said resistance imparting means comprises a spring element connected to said connector member proximate said rollers.
6. The seat headrest as defined in claim 5 in which said plurality of rollers comprise two spaced apart pairs of rollers connected to said connector member.
7. A seat headrest for interconnection with a seat comprising:
(a) a connector member connected to the seat;
(b) a headrest assembly connected to said connector member for movement relative thereto between a first position and a second position, said headrest assembly comprising:
(i) a central support panel;
(ii) a pair of side panels connected to said central panel by hinge means, each of said pair of side panel panels comprising an upper portion having a first connector segment and a lower portion having a second connector segment, said hinge means comprising:
a. a barrel portion connected to said central support panel;
b. a shaft portion rotatably carried by said barrer portion, said shaft portion having first and second ends, said first end being connected to said first connector segment and said second end being connected to said second connector segment; and
c. a plurality of generally U-shaped, friction imparting clips carried by said shaft portion for engagement with said barrel portion;
(iii) resistance means for frictionally resisting vertical movement of said headrest assembly.
8. The seat headrest as defined in claim 7 in which said headrest assembly further comprises:
(a) an elongated guide; and
(b) a plurality of rollers connected to said connector member for rollable engagement with said elongated guide.
9. The seat headrest as defined in claim 8 in which said resistance imparting means comprises a spring connected to said connector member and disposed in compressive engagement with said elongated guide.
10. A headrest for interconnection with a vehicle seat comprising:
(a) a connector assembly connected to the seat;
(b) a headrest assembly connected to said connector assembly for pivotal movement relative thereto between a first position and a second position and for substantially vertical movement relative thereto between a first position and a second position.
11. The headrest as defined in claim 10 in which said headrest assembly comprises a central support panel and a pair of side panels connected to said central panel.
12. The seat headrest as defined in claim 11 in which said connector assembly comprises:
(a) an elongated guide;
(b) a carriage assembly connected to said elongated guide for movement with respect thereto; and
(c) resistance imparting means connected to said carriage assembly for engagement with said elongated guide for yieldably resisting movement of said carriage assembly relative to said elongated guide.
13. The seat headrest as defined in claim 12 in which said carriage assembly further comprises a plurality of rollers for rollable engagement with said elongated guide.
14. The seat headrest as defined in claim 13 in which said resistance imparting means comprises a spring carried by said carriage assembly and disposed in compressive engagement with said elongated guide.
15. A headrest for interconnection with a vehicle seat comprising:
(a) a plurality of generally U-shaped, friction imparting clips carried by said shaft portion for engagement with said barrel portion.
(b) a plurality of generally U-shaped, friction imparting clips carried by said shaft portion for engagement with said barrel portion;
(c) a connector assembly connected to the seat, said connector assembly comprising:
(i) an elongated guide;
(ii) a carriage assembly connected to said elongated guide for movement with respect thereto; and
(iii) resistance imparting means connected to said carriage assembly for engagement with said elongated guide for yieldably resisting movement of said carriage assembly relative to said elongated guide; and
(b) a headrest assembly connected to said connector assembly by first hinge means for pivotal movement relative thereto between a first position and a second position and for substantially vertical movement relative thereto between a first position and a second position, said headrest assembly comprising central support panel and a pair of side panels connected to said central panel by second hinge means.
16. The seat headrest as defined in claim 15 in which said carriage assembly further comprises a plurality of rollers for rollable engagement with said elongated guide.
17. The seat headrest as defined in claim 15 in which said resistance imparting means comprises a spring carried by said carriage assembly and disposed in compressive engagement with said elongated guide.
18. The seat headrest as defined in claim 15 in which said first hinge means comprises a constant torque hinge.
19. The seat headrest as defined in claim 15 in which said second hinge means comprises a barrel portion, a shaft portion rotatably carried by said barrel portion and a plurality of generally U-shaped, friction imparting clips carried by said shaft portion for engagement with said barrel portion.
20. The seat headrest as defined in claim 19 in which said second hinge means further comprises a leaf connected to said barrel portion and to said elongated guide.