Modeling Method for Autonomous Current Inverters

Keywords. Valve inverters, autonomous current inverter, 
dynamic transients, mathematical models 
I. I
NTRODUCTION
In the world, special attention is paid to solving the 
problems of developing power semiconductor converter 
technology based on current converters. They are widely 
used in various industrial spheres, provide rational 
application with high accuracy of maintaining power 
parameters. They are characterized by increased operational 
reliability and extended service life. Nowadays in developed 
countries "...more than 60% of power generated passes 
through semiconductor converters. Using power electronics 
systems to a world-class level will save 12-15% of the 
electricity generated" [1]. 
They are distinguished by high accuracy of power 
parameters maintenance, increased operational reliability, 
long service life and high efficiency. Their good dynamic 
characteristics, low noise and vibration level determine their 
wide application in various industrial facilities. The stages 
of development and prospects for the problems of modelling 
the flow of electromagnetic processes in autonomous 
inverters are inextricably linked with the theoretical and 
corresponding practical development of both semiconductor 
devices themselves and energy converters based on them [2-
4]. 
The development and practical implementation of each 
next generation of power semiconductor devices, in turn, led 
to the qualitative development of converting devices with a 
corresponding increase in their power and expansion of their 
areas of application, as well as a significant development of 
methods for their mathematical modelling [3, 4]. Since a 
necessary condition for improving the quality and reducing 
the development time of valve converters is the widespread 
use of effective modelling methods and programs for 
analysing the operation of converters.
II. METHOD
The current level of development of language tools and 
computing technology capabilities allow us to determine the 
optimal parameters of circuit components, simulate various 
dynamic and static modes of converters [5, 6]. 
Analysis of these works shows that the developed 
models of valve converter based on autonomous inverters 
can be divided into two main categories: simplified models 
and accurate models. Usually simplified models are built on 
the basis of some assumptions, which, according to the 
authors, have little effect on the final calculations. Thus, the 
models presented in works [5-7], built on the basis of Kron 
reduction, are related to ignoring fast dynamic processes. A 
number of works neglect the dynamics of internal circuits of 
inverters, including current and voltage circuits for 
simplification [8, 9]. Although, as noted in [10], the inner 
loops also play an important role in the dynamics of slow 
modes. In addition to those described above, methods such 
as numerical analysis, singular perturbation and intelligent 
optimization algorithms are often used in the development 
of simplified models [11-14]. 
In practice, simplified modelling is usually applied at the 
initial stage of development to determine the primary 
requirements set for the scheme. However, at the same 
time, the question about the degree of error in the obtained 
analysis results requires additional clarification. Since in the 
development of simplified models there is often a problem 
related to its adequacy to the real conditions of transient and 
steady-state processes [15]. 
There is no doubt that efficient and operative design and 
development of reliable and economical valve converters is 
impossible without detailed description of processes on the 
basis of their exact mathematical models. The models must 
take into account variations in the input voltage and load. 
Accurate models must also take into account the 
2022 International Conference on Electrical, Computer, Communications and Mechatronics Engineering (ICECCME) | 978-1-6654-7095-7/22/$31.00 ©2022 IEEE | DOI: 10.1109/ICECCME55909.2022.9988596
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peculiarities of the control system. So, the complete inverter 
model which can describe all variables of the system state 
and accurately predict the system stability is presented in 
[16]. Here, a mathematical model of the inverter is created 
using hybrid modelling: the state-variable method can be 
used to represent steady states and the transfer function can 
be used to establish the relationship between input and 
output parameters during dynamically fast states of the 
inverter. Each submodule is modelled in the form of a state 
space and combined together in a common reference frame. 
The complete model is linearized around the operating point 
and its system matrix is generated to obtain the eigenvalues. 
In [15], a methodology for accurate modelling of a 
single-phase aautonomous current inverters (ACI) based on 
the state-variable method is proposed. This study presents a 
model called by the authors as a "high-capacity model. The 
model takes into account the dynamics of the power loop 
and the network, but it cannot accurately describe the low-
frequency characteristics of the system. 
To select effective methods for modelling and 
developing programs for analysing valve circuits, it is 
necessary to know the class of the circuits under study, the 
types of problems to be solved, the ultimate goals of the 
study and the basic requirements for the investigated 
converters [17-20]. 
For autonomous thyristor converters of the investigated 
series ACI with possible modes of operation for static and 
dynamic loads, the following general requirements are 
imposed [21-24]:
1. Possibility of regulation within the required limits of
the operating frequency, which is needed primarily in the 
installations of the AC valve drive. 
2. Possibility of regulation within a sufficiently wide
range of the ratio between input E