Magnetic-pole position detection apparatus for synchronous machines

1. A magnetic-pole position detection apparatus for synchronous machines, comprising:

circuit means for converting a DC voltage of a DC voltage source to voltage vectors based on a voltage vector instruction, and applying the voltage vectors to a synchronous machine having windings for n phases (n is a natural number larger than or equal to three);

current detection means for detecting an electric current flowing in each of the windings of the synchronous machine; and

calculation means for calculating and outputting 2n voltage vectors to the circuit means as the voltage vector instruction, and for acquiring a current detection value from the current detection means at a predetermined sampling timing based on the voltage vector instruction, the 2n voltage vectors being determined depending on the DC voltage of the DC voltage source, having equal amplitudes, having phases shifted by equal amounts in one cycle (360 degrees), and having equal predetermined pulse widths, wherein

when the voltage vectors based on the voltage vector instruction are applied to the synchronous machine, the calculation means further calculates n added current values by adding up current detection values acquired at the sampling timing as a result of application of each pair of voltage vectors whose phases are different from each other by 180 degrees, and detects a magnetic-pole position during stoppage of the synchronous machine, based on the n added current values,

the magnetic-pole position detection apparatus comprising DC voltage detection means for detecting the DC voltage of the DC voltage source, wherein

the calculation means controls the pulse width and the sampling timing, based on a DC voltage detection value from the DC voltage detection means, so as to obtain a desired accuracy of magnetic-pole position detection regardless of variation in the DC voltage of the DC voltage source.

2. The magnetic-pole position detection apparatus for synchronous machines according to claim 1 , wherein the calculation means changes the pulse width in accordance with the DC voltage detection value, and controls the pulse width and the sampling timing such that the sampling timing is fixed at the end point of the pulse width of each of the voltage vectors regardless of the DC voltage detection value.

3. The magnetic-pole position detection apparatus for synchronous machines according to claim 2 , wherein when the pulse width is tp, a pulse-quiescent width obtained by subtracting the pulse width tp from an interval between the voltage vectors temporally adjacent to each other is tn, the DC voltage detection value is Vdc, a rated DC voltage value as a reference is Vdcnominal, and a rated pulse width as a reference is tpnominal, the calculation means controls the pulse width tp and the pulse-quiescent width tn based on the following expressions:

tp=tp nominal× Vdc nominal/ Vdc ; and

tn=tp×kn,

wherein kn is a constant.

4. The magnetic-pole position detection apparatus for synchronous machines according to claim 2 , wherein

characteristics of relationship between the DC voltage of the DC voltage source and the pulse width that allows a desired accuracy of magnetic-pole position detection are previously determined by experiment or analysis, and

the calculation means determines the pulse width from the characteristics of the relationship in accordance with the DC voltage detection value.

5. The magnetic-pole position detection apparatus for synchronous machines according to claim 4 , wherein the characteristics of the relationship between the DC voltage of the DC voltage source and the pulse width are determined from a result obtained by previously determining a timing at which an S/N ratio becomes highest in accordance with the DC voltage of the DC voltage source by experiment or analysis, the S/N ratio being represented by the following expression:

S/N ratio=(| i 1 |−|i 2|)/| i 1|,

wherein i 1 is a current detection value detected when a voltage vector corresponding to a known magnetic-pole position is applied, and i 2 is a current detection value detected when a voltage vector whose phase is different by 180 degrees from that of the voltage vector corresponding to the known magnetic-pole position is applied.

6. The magnetic-pole position detection apparatus for synchronous machines according to claim 1 , wherein

the calculation means controls the pulse width such that the pulse width has a constant value regardless of the DC voltage detection value,

characteristics of relationship between the DC voltage of the DC voltage source and the sampling timing that is in the pulse width and that allows a desired accuracy of magnetic-pole position detection, are previously determined by experiment or analysis, and

the calculation means determines the sampling timing from the characteristics of the relationship in accordance with the DC voltage detection value.

7. The magnetic-pole position detection apparatus for synchronous machines according to claim 6 , wherein the characteristics of the relationship between the DC voltage of the DC voltage source and the sampling timing are determined from a result obtained by previously determining a timing at which an S/N ratio becomes highest in the pulse width in accordance with the DC voltage of the DC voltage source by experiment or analysis, the S/N ratio being represented by the following expression:

S/N ratio=(| i 1 |−|i 2|)/| i 1|,

wherein i 1 is a current detection value detected when a voltage vector corresponding to a known magnetic-pole position is applied, and i 2 is a current detection value detected when a voltage vector whose phase is different by 180 degrees from that of the voltage vector corresponding to the known magnetic-pole position is applied.