Application of high-voltage frequency converters is one of the most prospective trends in the development of current powerful electric drives, i.e. in high-speed trains. In terms of such converters, a multilevel cascaded H-bridge converter is becoming the most widespread one owing to its increased reliability, survival in terms of one or more damaged cells, and quick repairability due to its modular structure. The research proposes a control method, which provides maximum possible linear voltage in case of one or several damaged cells owing to the shift of zero point and turning of phase voltages. It is also demonstrated how turning angles of phase voltages should be set to preserve spatial position of the linear voltage vectors which provides the least complicated electromagnetic transients in terms of nominal rotation frequency; in case of low or middle frequencies, damage of the cells may have no effect on the motor operation. Fast algorithm to calculate turning points of phase voltages is proposed; the algorithm may be applied in the industrial microprocessor control systems. Algorithm of the operations, which provides implementation of the method, is described.
Purpose. The paper compares the traditional method of calculating the parameters of electric motion of ships in auxiliary emergency modes at low speeds of the vessel with another, simplified because it does not require the use of a large number of diagrams to determine the resistance of the vessel. But according to a simplified method for this example – a container ship with a capacity of 16,000 containers with the main engine capacity of 61776 kW, a synchronous machine with a capacity of up to 6 MW in engine mode, and three diesel generators with an electric capacity of 3187 kW – 39 % more power is obtained. Own experience of operation of the vessel in modes with electric movement – loading of diesel generators in this mode on the vessel about 70 % that is received by calculations. Thus, when upgrading the propulsion system or designing new vessels, it is advisable to compare the results of two calculations of the power of diesel generators at the limit of the minimum stable speed of the main engine and choose the larger of the results. Methodology. Comparison of specific and absolute fuel consumption, made on the basis of known approximation polynomials for low- and high-speed types of diesel of the company at auxiliary emergency movement shows that at the movement from high-speed diesel generators MAK8M32S fuel consumption decreases by 24 %, then at the maintenance of the main engine 12 RTflex-96C from WÄRTSILÄ-SULZER. Results. Therefore, the use of electric motion allows you to save engine power of the main engine, reduce fuel consumption. This ratio is observed on most maritime transport vessels. And given that diesel generators operate at almost optimal load, and the main engine – at idle, electric motion provides a significant reduction in harmful emissions into the atmosphere. The latter is also true for a ship where the synchronous engine is located behind the main engine, although fuel consumption, in this case, increases by 32 %. Figures 9, tables 6, references 15.
Purpose. The aim of this work is to find a method of controlling high-voltage frequency converters that would provide the smallest voltage drop on the motor, the least loads and oscillation of electromagnetic torque in an accident modes, and evaluate the effectiveness of pulse width modulation (PWM) methods with the injection of third harmonic and space-vector PWM in emergency modes. Methodology. We have applied the mathematical simulation of the electric drive “High voltage frequency converter with cascaded H-bridges – High power asynchronous machine” in Matlab/SimPowerSystem software for comparison of four PWM types – Sinusoidal PWM (SPWM), Balanced sinusoidal PWM (BSPWM), Balanced PWM with injected third harmonic (THPWM) and Space Vector PWM (SVPWM). Results. The method of balancing the line voltage minimizes shock loads during the transition from normal to emergency mode due to such a shift of the zero point and rotation of the phase vectors, in which the amplitude of the line voltage decreases to the minimum possible value, the spatial position of linear vectors remains unchanged. The conditions of optimal injection of the 3rd harmonic are found, which increases the efficiency of power supply use by 7… 30 % in comparison with symmetric sinusoidal PWM. But in some accidents (6-4-4, 4-3-2, 3-2-2) the 3rd harmonic is not effective. The method of balancing the space vectors provides the same conditions and increases the utilization of power supplies by 15.6 %, regardless of the number of damaged modules, which increases the amplitude of the 1st harmonic in case of accidents by 10 ... 26 % compared with sinusoidal PWM. Comparison of methods of space vector PWM (SVPWM), balancing of phase-to-phase voltage with the injection of the 3rd harmonic (THPWM) with sinusoidal PWM shows that SVPWM is the best method at damage of one or two modules and during normal work of the converter (except for the 3-3-2 configuration), ie in the most common cases. Originality. For the first time, a comparison of all methods of pulse-width modulation in emergency modes and the optimal method for each type of accident for 3-6-stage frequency converters is indicated. Practical value of the work is to provide the necessary mathematical apparatus for calculating signals using BSPWM, THPWM and SVPWM in emergency modes. References 17, table 1, figures 6.
A soft starter-fed high voltage induction motor drive of a ship bow thruster is simulated. The synthesis procedure and switching methodology of a C-type filter are proposed to ensure the electromagnetic compatibility of the electric drive with the ship electrical power system in transient and steady-state conditions. Analysis shows that, suppression of high-frequency components in transients, and maintaining the power factor at the optimum level in steady-state operation is reasonable by using a 5th-harmonic capacitive filter, ensuring the appropriate switching of the filter elements simultaneously with the connection of the bypass contactor. The filters of the 7th, 11th/13th harmonics are selected in such a way to ensure that the total harmonic distortion of the line current and voltage meet the standards defined by IEC. Referenc es 9, figures 2.
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