On a number of technologies to improve the converter performance - inverters, and Technology - Electrical industry

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1 Introduction Present, China Inverter Produced by manufacturers Inverter Mostly the ordinary V / f control mode, with only a few of foreign claim to use vector-based speed control technology. Basically in the foreign brands to open-loop, closed loop, speed control of three-dimensional control thought, in particular, concern is ABB's DTC control method in the product has been successfully applied. Frequency Control System domestic academic research has been done a lot of relevant work, and taken certain results, but it works compared to overseas practice and the accumulation of a gap there. If the theoretical knowledge into industrial products to our existing practice, frequency control products to improve our performance and quality, is a more pressing problem worthy of study. This paper attempts to control two aspects of strategy and modulation current of V / f control and techniques of the comparison indicates that, for all to share and explore.





Usually V / f controlled inverter system structure, modulation, the main circuit composed of three parts, of which pulse width modulation control part and the part of all of the software algorithm. This control method is drawn against AC motor steady-state model, not dependent on motor parameters and changes, and thus control is simple, easy to implement. However, the relatively narrow speed range, only applies to fans, pumps and other less demanding load on the speed performance. In order to improve load capacity slow times and the system dynamic performance, to meet the needs of real industrial field, to the existing control methods and the corresponding pulse width modulation strategy to improve and enhance. The following key technology for a few were discussed.
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2 control strategy in a number of technical


2.1 Compensation Compensation technology in open-loop control is indispensable. It includes the torque compensation, slip compensation, and compensation of dead time effect. Stator resistance at low pressure drop when compared to the output inverter is no longer ignore the need to compensate, otherwise the output voltage is not enough, the motor in low speed when the fixed or decreased. Slip compensation mainly for motor load is large in the actual output speed will be lower than the set speed and design. The two compensation methods can be used in practice, a simple fixed-value compensation, improved methods used to calculate three phase motor current compensation, but only under the current amplitude of the compensation is in fact the scalar compensation; more accurate compensation method is to conduct three-phase alternating current motor vector resolution, while the loss of participation in motor terms, such compensation is better. But this method is more complicated, while some of the motor parameters are dependent, in some difficulties in the implementation process.





Dead time effect compensation technology in open loop control plays an important role, it can effectively improve the output current waveform of the smoothness and reduce harmonics, while the output voltage can increase motor current RMS and reduce the shock. Especially in the required quiet environment, man-made increased carrier frequency, if not dead time compensation, even if the motor load in the low frequency may not run. Now commonly used with dead zone compensation of zero current direct compensation method, based on stator flux current decomposition, the dead zone voltage pulse width compensation, non-current Sensor Dead time compensation prediction methods. Determine the compensation current zero-crossing method is simple and easy to implement, but due to large current waveform in the noise component, while the external load fluctuations and will cause any interference with the judge had zero errors, zero has a dead platform affects the low frequency compensation effect, in particular, relatively high carrier frequency is particularly significant. Based on stator flux orientation methods do not directly determine the current zero-crossing, but the stator current in the rotating coordinate system by current vector angle and the decomposition of dead relationship between the voltage vector corresponding compensation, if the method and the dead-voltage pulse width of combination, the effect is more prominent. Phase angle prediction dead-time compensation method is a current sensor saved fixed compensation method, which first predicted the current phase angle, and then the dead time compensation accordingly, can predict the angle of inverter output capacity of different settings in the software or set by external changes.