Electric power conversion systems – Current conversion – With means to introduce or eliminate frequency components
Patent
1986-10-31
1989-01-24
Salce, Patrick R.
Electric power conversion systems
Current conversion
With means to introduce or eliminate frequency components
363 98, 363132, 318800, 318812, H02M 7527, H02P 763
Patent
active
048004782
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method and apparatus for controlling a pulse width modulation (PWM) inverter.
This invention is utilized in a case where an AC servo motor is required to operate with a low harmonic loss, low acoustic noise, fast torque response and high efficiency, or in a case where, in the current controlling system using a PWM inverter, the control error is required to be minimum under the limited switching frequencies.
BACKGROUND ART
According to one of the conventional methods, in the current control, a deviation of output current from a calculated current command value (or vector value) is inputted to a comparator, and then an output of the comparator indicating a comparison result is used to determine the switching pattern of the PWM inverter, i.e. on/off of the branches of the inverter.
In other words, in the conventional method, there is only one state variable or state vector to determine the switching.
However, according to the method, the optimum switching is not always accomplished because the switching method is determined by only one state variable.
For example, some high frequency currents and acoustic noises have been observed. Moreover, there exists another problem in which the structure of the circuits for obtaining a command value are complicated because the one command value is used to control the whole system.
It is the object of the present invention to solve the above-mentioned problems.
DISCLOSURE OF INVENTION
The present invention is characterized in that each arm of an inverter is adequately switched in such manner that an evaluation function on a state between the inverter and the system connected to the AC side of the inverter is minimized.
BRIEF DESCRIPTION OF DRAWINGS
In the accompanying drawings:
FIG. 1 is a block diagram showing a system to execute control according to the present invention;
FIG. 2 is a vector diagram showing the relation between a locus of an optimum primary flux linkage vector and a locus of a voltage vector;
FIG. 3 is a block diagram showing a control system in which the present invention is applied to a high speed torque control and to a high efficiency operation of an induction motor;
FIG. 3A is a graph showing an input/output characteristic of a nonlinear amplifier 21 in FIG. 3;
FIG. 3B is a graph showing an input/output hysteresis characteristic of a comparator 22 in FIG. 3;
FIG. 3C is a graph showing an input/output hysteresis characteristic of a comparator 23 in FIG. 3;
FIG. 4 is a data table stored in an optimum switching table 19 in FIG. 3;
FIG. 5A and 5B are diagrams showing test results by a digital simulation on a transient response of the system shown in FIG. 3 regarding primary flux linkage .PSI. and torque T respectively;
FIG. 6 is a block diagram of a system where the present invention is applied to an optimum current control of an inductive load having a backelectromotive force; and
FIG. 7 is a graph showing an output voltage waveform, a current command and an output current waveform.
BEST MODE FOR CARRYING OUT THE INVENTION
In FIG. 1 showing a preferred embodiment of the invention, reference numeral 1 denotes a rectifier circuit, 2 a PWM inverter (a voltage type inverter is shown but a current type inverter may also be used), 3 a load connected to the inverter (e.g. an AC motor or a power supply), 4 a detection and arithmetic circuit for state variables x1, x2, . . . , 5 denotes an arithmetic operation circuit which calculates optimum command values x1, x2, x3, . . . which correspond to x1, x2, x3, . . . according to external commands. 6 denotes an address circuit which has, for analogue input signals, a conversion circuit which converts an analogue input signal to the digital form and includes a comparator or an A/D converter, or which has, for digital input signals, a conversion circuit for converting the inputted digital signals into a suitable form when they are inputted into an optimum switching table to be described later. The optimum switching table 7 is programmed in such manner that the P
REFERENCES:
patent: 4276505 (1981-06-01), Bose
patent: 4310791 (1982-01-01), Akamatsu
patent: 4456868 (1984-06-01), Yamamura et al.
patent: 4499413 (1985-02-01), Izosimov et al.
Kabushiki Kaisha Toshiba
Salce Patrick R.
Todd Voeltz Emanuel
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