Above all, the factor of various DC-link voltages is important to increase the controllable output power of IPMSM. However, controlling the motor by this factor using lookuptable needs enormous experimental results, because the data should be considered with various motor speed and torque reference. As widely known, this DC-link voltage determines the start point of field weakening operation.
controllable maximum speed is reduced. On the other hands, if the SOC of battery is at Vdc2, the controllable maximum speed is extended. If ignoring the DC-link voltage factor, the motor should be controlled in case of possible minimum voltage of battery. If not, excessive back-EMF voltage can break the inverter by the generation of the large regenerating current.
(a) torque and speed curve in voltage variation.
iq[ A]
Current limit circle
Vdc 2 Vdc1
M
MTPAபைடு நூலகம்courve
id [ A]
Voltage limit ellipse
(b) voltage limit ellipse and current limit circle in voltage variation. Fig. 2 Start point according to the variable DC-link voltage.
1 School of Information and Communication Engineering, Sungkyunkwan University, Korea E-mail: jaylee8201@
Abstract — This paper proposes the field weakening method of IPMSM(Interior Permanent Magnet Synchronous Machine) for the electric vehicle (EV) application. The method of using lookup-table generally used in automotive application has merits for fast dynamics, however containable data is limited especially on DC-link voltage. On the other hands, the method using a voltage feedback control has advantages in current control at variable speed and DC-link voltage automatically. However, dynamics is determined by the gain of controller. In this paper, field weakening control of fast dynamics and variable DC-link voltage is achieved by suitable combination of lookup-table and voltage feedback controller. Proposed method is verified by the simulation and experiment result.
A. Voltage Feed-back Method [4]
Fig. 3 shows the voltage feed-back method. This method append feed-back controller to lock the output EMF voltage magnitude in the voltage limit condition by measuring inverter output voltage or regarding current controller output as a voltage magnitude. Once field-weakening strategy starts PI controller increases negative ∆idrs to reduce the EMF voltage. It is able to prevent saturation of current controller and makes voltage margin.
Te*
ie*
id*s
ds
ωr
Te*
Vdc vs*
ds
ie*
iq*s
qs
ωr
ωr
Te*
vs* qs
θr iv iu
Lookup Table
Fig.1 General vector control method using on lookup table.
Using lookup-table data is for reducing the unreliable data comes from controllers which can be affected by the various circumstance of motor. Moreover, the controlled data should pass through the specific sequence and the data consequentially has unavoidable delay. Lookup-table data comes from experiment has reliable and fast dynamics to
To use this control region of variable DC-link voltage, several researches are developed.[4][5][6] Detail explanation of each method is illustrated on the next chapter, but these method still have the problem of dynamics and safety. In this paper, to improve the control performance of field weakening, the methods of combining the controller and lookup-table is proposed suitably. The point of proposed method is that the field weakening d-axis current is separated by two components. The one is for torque current and the other is for permanent magnet flux. Due to the unaltered d-axis inductance and permanent magnet flux from motor circumstance variation, this component could be compensated by the lookup-table for fast dynamics of field weakening operation. Proposed algorithm is verified by the simulation and experiment.
control the motor. However, lookup table method also has the problem that it is only corrected on experimental setup and applicable data is limited by the memories in hardware setup. Although the data error between experimental and practical circumstance is generally small and it could be fixed by some modified data or ignored. However, the problem of inapplicable all various circumstances of motor and inverter make the limit of usable output power.
II. ANALYSIS OF CONVENTIONAL METHOD
In this section, the generally used current reference method according to torque reference and driving conditions are reviewed