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ZHU Z.Q., SHI Y.F., HOWE D.. Influence of DSP controller on performance of a permanent magnet brushless AC drive in flux-weakening mode[J]. Journal of Zhejiang University Science A, 2005, 6(2): 83-89.

@article{title="Influence of DSP controller on performance of a permanent magnet brushless AC drive in flux-weakening mode",

author="ZHU Z.Q., SHI Y.F., HOWE D.",

journal="Journal of Zhejiang University Science A",

volume="6",

number="2",

pages="83-89",

year="2005",

publisher="Zhejiang University Press & Springer",

doi="10.1631/jzus.2005.A0083"

}

%0 Journal Article

%T Influence of DSP controller on performance of a permanent magnet brushless AC drive in flux-weakening mode

%A ZHU Z.Q.

%A SHI Y.F.

%A HOWE D.

%J Journal of Zhejiang University SCIENCE A

%V 6

%N 2

%P 83-89

%@ 1673-565X

%D 2005

%I Zhejiang University Press & Springer

%DOI 10.1631/jzus.2005.A0083

TY - JOUR

T1 - Influence of DSP controller on performance of a permanent magnet brushless AC drive in flux-weakening mode

A1 - ZHU Z.Q.

A1 - SHI Y.F.

A1 - HOWE D.

J0 - Journal of Zhejiang University Science A

VL - 6

IS - 2

SP - 83

EP - 89

%@ 1673-565X

Y1 - 2005

PB - Zhejiang University Press & Springer

ER -

DOI - 10.1631/jzus.2005.A0083

**Abstract: **The flux-weakening performance of a permanent magnet brushless AC drive was investigated using both floating-point and fixed-point DSP controllers. A significant current oscillation was observed when the drive was operated at high-speed in the flux-weakening mode with the fixed-point DSP. The investigation showed that this was due to the on-line compensation of the winding resistance voltage drop and quantisation errors associated with the fixed-point architecture of the DSP. A simple look-up table scheme is proposed to eliminate the oscillation and to achieve extended flux-weakening capability.

**
**

. INTRODUCTION

based controller was investigated. Significant current oscillation was observed with the fixed-point DSP-based controller when the drive was operated in the flux-weakening mode and incorporated on-line compensation of the winding resistance voltage drop. By way of example, Fig.

R |
Phase winding resistance (() | 0.15 |

L=_{d}L_{q} |
d, q-axis inductance (mH) |
0.40 |

p |
Number of pole-pairs | 6 |

(_{m} |
Open-circuit flux-linkage (peak) (Wb) | 0.0179 |

U_{dc} |
dc-link voltage (V) | 21 |

I_{max} |
Maximum armature current (A) | 35 |

. INFLUENCE OF WINDING RESISTANCE ON FLUX-WEAKENING PERFORMANCE

The torque and the power are given by:

and

In order to simplify the control algorithm, the winding resistance

Thus, in the constant torque mode (i.e. below the base speed), when maximum torque per ampere control is used (Morimoto et al.,

In the flux-weakening mode, the optimal

Since

It should be noted that if the winding resistance is accounted for, the expression for the optimal current profiles is much more complicated due to mutual coupling between the

It is desirable, therefore, to compensate for the effect of the winding resistance voltage drop so as to improve the performance, particularly in the flux-weakening mode.

In (Sudhoff et al.,

However, whilst this technique is easy to implement and improves the performance, most notably around the base-speed, it over-compensates for the effect of the winding resistance in the flux-weakening range, when the power factor decreases with increasing speed (Shi et al.,

In order to improve the performance over the entire speed range, a feed-forward ‘on-line

Hence,

Thus, the maximum terminal voltage

By way of example, Fig.

. DRIVE SYSTEM

The foregoing control strategy has been implemented on both floating-point (TMS320C31) and fixed-point (TMS320F240) DSPs. However, as mentioned in the introduction, significant current oscillations were observed when the motor whose parameters are given in Table

. PERFORMANCE WITH FIXED-POINT AND FLOATING-POINT DSP CONTROLLERS

1. Quantisation errors in the parameters: The relative accuracy of the

2. Truncation, round-off, and overflow in operations. Again, one bit of truncation in the integer for the current is equivalent to an error in the current of ∼8.5 mA.

In addition, quantisation errors due to the finite numerical precision can accumulate in the on-going arithmetic operations, particularly in a recursive system (Proakis and Manolakis,

As can be seen from Fig.

In the flux-weakening speed range, the change in the commanded values of

Hence, when quantization errors become large, the system starts to oscillate (at ∼3000 rpm in the drive system under consideration).

Clearly, if more bits were employed to represent the parameters in the flux-weakening control algorithm, the current oscillations could be reduced. By way of example, with a

. EXPERIMENTAL RESULTS

. CONCLUSION

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