Phased vector control of induction motors

Phased vector control is an algorithm to produce three-phase waveforms to control an induction motor by using six base and seven zero vectors. A traditional vector control uses six base and two zero vectors.
Specification
To control a brushless, three-phase motor using a DC power source, an electronic inverter or controller is required to create three-phase voltage waveforms. The voltage supplied to the three motor contacts comprises of a voltage vector with three components. In the three phase voltage vector, the components should be sine waves shifted by 120 degrees in each phase.
Vector control was suggested by Mochikawa who invented the method and apparatus to generate three-phase voltage by constant voltage pulses, specifically six base vectors V_1(101), V_2(001), V_3(011), V_4(010), V_5(110), V_6(100) and two zero vectors V_7(000), V_8(111), depicted in Fig.1.
The formation of these voltage vectors is carried out by three pairs of switches connected in a parallel bridge. This is a complete set of vectors which can be obtained under the condition that each load contact is actively driven (connected). Zero vectors connect all contacts with either the positive or negative output of DC power supply. The need for simultaneous switching of both switches in the bridge is usually eliminated by introducing a pause between switching, which solves the problem, but removes some time from the emulation.
The fact that all load contacts are connected is problematic. Induction motor is known to produce EMF, which is reflected in the occurrence of voltage between contacts. As a result, currents flow through the switches and heat them when they are in a zero vector state. The preceding is the reason for reduction of efficiency and reliability of three phase AC motor controllers and inverters, especially in the management of slow and near zero speeds.
The system of phased base vectors, suggested by Antonov (U_i: U_1 (10Z), U_2(Z01),U_3 (0Z1), U_4 (01Z), U_5 (Z10), U_6 (1Z0)) is shown in comparison to the standard system of vectors in Fig. 1. The phased base/active vectors have an angle of 60 degrees between them, which strictly corresponds to a phase shift of three-phase AC voltage.

The extended set of phased vectors includes six base vectors U_i and seven zero vectors Z_i with the same repetitive components 1, 0, Z (example in Fig. 2). The set of zero vectors does not include vectors (000), (111) and any vector with two components 0 or 1. That eliminates “shorting" of two contacts of the motor and reduces power loss.
The control algorithm determines a sequence of base U_i and zero Z_i vectors: (10Z) -» (Z0Z) -» (Z01) --» (ZZ1) -» (0Z1) -» (0ZZ) -» (01Z) -» (Z1Z) -» (Z10) -» (ZZ0) -» (1Z0) -» (1ZZ), which is designed to emulate a three-phase alternating current.
Reduction of the length of emulation steps leads to a significant decrease in power consumption (up to 40%) due to the improved emulation of three-phase voltages using the system of phased vectors.
The inverter implementing the phased vector system provides motor control in a range from zero to maximum speed, limits inrush current and prevents burnout. This is an effective method of high-accuracy emulation of three-phase voltage waveforms by pulsed Direct Current. The formation of the phased zero and base vectors excludes one-step polarity change at contacts which improves switching conditions and increases efficiency and reliability of three-phase motors control systems.
Utilization of the phased vectors allows to return to the design and manufacture of multi-pole AC motors, the most powerful and thus comparatively very light per lb/ft of torque.

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