Tyshevych B. L., Orlov M. V.

MATRIX frequency converters in electric drives with synchronous motors

In this article are analysed features of a matrix-using frequency converter with an electric induction motor, comparing with a traditional bridge frequency converter. Investigated are benefits of a matrix-using frequency converter during the work with correction for determining the exact position of the rotor synchronous motor.

Key words: electric drive; synchronous motor with permanent magnets; matrix frequency converter; rotor position correction.

Introduction. A synchronous motor is an electric machine, rotor speed of which is equal to the rotation frequency of the magnetic field. Low power (10 kW) engines are mainly made of a permanent magnet rotor (SMPM). Currently, this type of an engine is the most promising for the electric drive. They have several advantages: high energy performance (90 % efficiency); smaller weight and size; wide range of rotation frequency; high overload capacity for the moment; long life, and high reliability.

The main advantage of the synchronous motor is the possibility of obtaining the best mode for the reactive energy. The synchronous motor can run without consuming and not giving reactive power to the grid, with power factor equal to one. In these conditions, engine load network only by active current.

Calculateing the coordinates of the rotor by conventional converters will be difficult and not accurate. Therefore, in recent years, much attention has been paid to the development of a matrix frequency converter (MFC) that is a structurally direct AC-AC converter and is capable of generating voltage with almost ideal form, and free of flaws tension that bridge converters have .

The purpose and objectives. Exploration of the peculiarities of an electric SMPM MFC using. Comparison of MFC traditional bridge converters. Determination of how increased accuracy estimation coordinates of the rotor in SMPM with the help of MFC.

Research results.

The application of the MFC can solve pressing problems. The MFC’s simple design – three-phase power supply connected to the engine via a bidirectional semiconductor switch matrix (Figure 1). These switches’ orderly operation voltage and the frequency output of the engine can be regulate1d with high precision.

а b

Fig. 1. MFC: а – block diagram; b – circuit connection switches

The matrix converter belongs to a group of frequency converters with direct connection. Each switch has two field-effect transistors with an insulated gate (IGBT). In the power converter circuit IGBT 18 is used. IGBT power switches are connected in such a way that the energy can rise to the engine as well as play back to the grid during braking and recovery.

To determine the exact position of the rotor in SMPM nonsensory management, a correction method that gives good results when using the MFC is proposed. The disadvantage of the method is the need for a productive microprocessor technology and conducting bench tests.

The method involves the separation (filtering) of harmonic components of low order - current Ialfa, Ibeta that determine the rotor’s position. The value of current Ialfa, Ibeta is determined through filtering currents Iα, Iβ of the three-phase transition to the two-phase coordinate system (Clarke transformation).

Fig. 2. Block diagram of I_alfa, I_beta determination

Finally, the system for determination of rotor’s position computing using signal processing is presented in Figure 3. Addressing data have been entered into the database on the stand, carried by the value of current i_sq *, for a variable-phase coordinate system, and an improved rotor position r. For these values ΔI_alfa, ΔI_beta are selected, being filtered; a transition to the definition of an intermediate estimated rotor position δ and phase shift correction are carried out, taking into account the saturation current determined by the moment i_sq *. After all the procedures we can determine the rotor position.

Fig. 3. Block diagram of the sequence of operations to determine the exact position of the rotor.

When studies are obtained, the current schedule changes Ialfa, Ibeta determining the rotor’s position and graphs change the rotor’s speed SMPM (Figure 6). As seen from the graphs, after applying the correction, significantly increases the accuracy of the speed regulation rotor.

а b

c d

Fig. 4. Graphic of currents changing I_alfa, I_beta and the rotor’s speed:

a, b - without rotor position adjustment; c, d – with application of the rotor’s correct position.

Conclusion

Compared to a traditional bridge frequency converter, the use of the electric BFC SDPM offers advantages in accuracy of determination of the rotor’s position, and consequently, improvement of the regulation quality of a wide range of speed. The BFC’s main advantage is the minimization of nonlinear characteristics, the main of which is the "failures" of voltage and current, resulting in their non-sinusoidal shape. As seen from the results, with the MPCH method of correcting the estimated position of the rotor, the quality of the electric SMPM’s speed control increases.