ON THE WOU ON MACHINE CONTROL

Ernest0 Ruppert Filho and Victor Armando Bravo Shchez DSCE/FEEC/UNICAMP

C.P. 6101 - CEP 13081-970 Campinas-SP, Brad E-mail: ruppert@fee.unicamp.br

Abstract - The main goal of this paper is to present a new torque and speed control method of the wound rotor induction machine 0 through the control of the voltage applied to the rotor winding. The method is based on the rotor voltage and current orientation using a converter cascade and a PI controller. It is shown by simulation using Pspice that the best way to comply with the control specifications is to maintain rotor voltage lagging rotor current providing also the best performance of the drive.

I. INTRODUCTION

The general configuration of the WFUM slip energy control is shown in figure 1. To control the speed, torque, real power and reactive power in the subsynchronous and in the supersynchronous speed ranges, two fourquadrant totally controlled converter cascades are used separated by an intermediate circuit (series RI., filter andor commutation circuit) [ 11 to [5 ] .

electrical equivalent circuit where the magnetizing reactance and core losses resistance are neglected.

I I

Figure 2 : Per-phase WRIM equivalent circuit.

Depending on the values of Vr and ay it is possible to draw different types of machine steady-state torque x speed characteristic curves using the electrical equivalent circuit calculations as shown in figures 3 to 5 for a 5 hp machine.

WRIM T R

Figure. 1 : WRIM slip energy control general configuration.

The slip power flow can be in two ways, that is, from the rotor to the grid or from the grid to the rotor. In both cases it has a variable speed drive with constant stator voltage at constant synchronous frequency (ms)but with varying (controlled) slip frequency (0 se) so that the mechanical speed (o m) can be written according (1)

Applications are in the variable speed large motor drives and also in synchronous and mainly in non- synchronous electrical power generation as is the case of wind generation.

11. CONSIDERATIONS ON ROTOR VOLTAGE AND ROTOR CURRENT ORIENTATION

The slip power control is really done by the application of a controllable voltage (magnitude and angle) applied to the rotor circuit. Figure 2 shows a simplified per-phase WRIM

Figure. 3 : WRIM steady-.&& torque x speed curve for vr in-phase with I,.

Figure 4 : WRIM steady-.&& torque x speed curve for i', lagging 1, by 15'.

The orientation of Vr related to Ir increases or decreases the torque x speed linear region. In figure 3 it has the analogous of the operation of the machine with a resistor shorting the rotor circuit ( Vr in-phase with Ir ). In the

0-7803-3946-0/97/S10.00 0 1997 IEEE. TB3-9.1

figure 3 (V, in-phase with I, it has a regular linear portion of torque x speed curve around rated-torque (see portion from synchronous speed to maximum torque). In the figure 4 this region increases as V, increases and in figure 5 this region decreases as V, increases. It can also be seen that, in the case of figure 4 ( V, lagging I, 1, it has nearly parallel straight-lines passing through the rated-torque and this is a very good control condition [2].

Figure 5 : WRIM steady-state torque x speed curve for 9, leading I, by 15".

Figure 4 also shows that when V, is lagging I, the torque values are increased as the speed decreases resulting in an increase on the machine torque capacity. The contrary occurs in figure 5 where V, is leading I;.

111. PROPOSED CONTROL SCHEME

Figure 6 shows what is proposed to do in this paper, to implement the WRlM slip energy control to have a speed control.

Figure 6 : WRIM slip energy control scheme.

System simulation has been implemented using Pspice where the WRIM is represented by the schematic presented in figure 7 using the reference frame theory presented in [61. The rotor current can be decomposed in d and q axis

according to the figure 8 where V, is lagging I, by a,. It was considered a PI controller and the Ziegler-Nichols

methcd was used to calculate its parameters according to figure 9.

I 1 + I

RJ=rs.Lm/k Lz=rt/rr' Rl=RZ-rt.Llt/k Vl=wrel.Ldodr'.r,/rr' VZ=wrel.Ldoqr'.rt/rr'

Figure 7 : WRIM equivalent circuit for pspice.

Figure 8 : Rotor voltage orientation with the rotor current

i i T . v - . 0.59 0.6s 0.79 0.6, 0.0. 1.0,

Figure 9 : PI controller design (Ziegler-Nichols).

TB3-9.2

Figure 9 represents the WRlM speed response to a rated- load torque step applied to the machine after a non-load machine starting with V, = 0.

IV. RESULTS

The figures 10 and 11 show the control system of figure 6 dynamic performane with the controller tun114 according the section before for the case of V, lagging I, . Arbitrary and hard torque and speed profiles wereused

Figure 10 : V, lagging I, ( a, = 10’ ), major load-torque = 20 Nm.

0

Figurell: v, lagging I, (ar = 15”),major load-torque = 20 Nm

to be followed by the WRZM operating as a motor. The major torque is 20.0 Nm in the torque profile (rated machine torque is 9.89 Nm).

It can be seen that for a, = 10’ the motor is not able to

follow the torque profile but for a, = 15’ it is. This operating condition, as it is shown in the complete paper, cannot be reached making V, in-phase with 1,or V,

lagging I,.

V. COMMENTS AND CONCLUSIONS

An important feature can be reached in this type of control by the implementation of the V, orientation in relation to

I,. AS a, increases positively, for the V, lagging I, case, the control system performance is improved even for drastic torque and speed profiles.

However it is necessary that the machine be adequately designed to withstand the torque demanded by the load, imposed by the torque profile.

So, this type of control is a special control that can be used for special applications both in the case of a WRTM as a motor or as a generator.

ACKNOWLEDGEMENTS

The authors would like to thank to FAPESP for the financial support of this research.

REFERENCES

[l] P. Pillay, “Calculation of Slip Energy Recovery Induction Motor Drive Behavior Using the Equivalent Cicuit”, IEEE Trans. on ind. Applications, vol. 30, no. 1, January/ February 1994, pp. 154-16.

[2] N. Mohan, T.M. Underland and W.P. Robbins, “Power Electronics: Converters, Applications and Design“, John Wiley & Sons, USA, 1989.

[3] P.C. Krause, 0. Wasynczuk and M.S. Hildebrandt, ‘‘Reference Frame Analysis of a Slip Recovery System”, LEEE Trans. on Energy Conversion, vol. 3, no. 2, June 1988, pp. 404-408.

141 V.N. Mittle, K. Venkatesan and S.C. Gupta, “Determtnat . ionofhtability Region for a Static Slip Power Recovery Drive”, Journal ofinst. Eng. (india), vol. 59, October 1978, pp. 59-63. V.N. Mittle, K. Venkatesan and S.C. Gupta, ‘‘Stability Analysis of a Constant Torque Static Slippower Recovery Drive”, lEEE Trans. Ind. AppL, vol. 16, January/February 1980, pp. 119-126. P.C. Krause. “Analysis ofEZecfricMachinely”, McGraw-Hill Book Co. Inc., USA, 1986.

[SI

161

APPENDIX

The induction motor used as example in this paper is the same used in [3] which data are: 2-pole, 5 hp, 3- phase, 60 Hz, 400 V (line-to-line), rs =O.O58py

X, = 2.9 pu, Xes = 0.10 pu, r, = 0.072 pu (referred to the stator side), Xer = 0.10 pu (referred to the stator side), rated-torque (base torque) = 9.89 Nm and base impedance = 42.9 R.

TB3-9.3