The dissertation is devoted to increasing load capacity in the system of asynchronous electric drive by combining several sources of electric energy according to a special scheme with the help of one autonomous voltage inverter. The area of application of the considered system is electric and hybrid vehicles.
In many cases, electric power systems of vehicles use or expediently use several sources of electrical energy. The problem is to ensure the effective collaboration of different types of sources to a common load and optimize their energy options.
Traditional electromechanical systems, which include components of different types, are usually based on the intermediate link of direct current. Separate inverters are used to control the power flows that receive / transmit individual elements. Such inverters are selected by power according to the nominal parameters of each component. Thus, a controlled electromechanical system is obtained, but of high cost, because it has several stand-alone inverters designed for the maximum possible current from each component.
It is advisable to develop the idea of using a single stand-alone voltage inverter to control the modes of operation of AC and DC components without the organization of a common DC link. To do this, one of the DC sources can be connected to the zero phase windings of the induction motor through additional inductance and active resistance, and the second pole - to the negative terminal of the stand-alone voltage inverter, which is connected to another DC source, such as a battery.
A special control algorithm for a stand-alone voltage inverter with increased switching time of the upper arm of the switches was considered. This algorithm can control the energy flows for each component. Thus, one inverter regulates the modes of operation of the electromechanical system.
This circuit makes it possible to charge the battery, but the additional source must have a large EMF to overcome the EMF level of the battery. This circuit allows you to charge the battery, but the additional source must have a large enough EMF to overcome the EMF level of the battery.
To increase the electromagnetic torque of the motor, reduce the EMF level of the additional energy source, increase the efficiency of the energy conversion process in the electric drive system of the vehicle with an additional energy source, the option of zero state of the lower arm of the voltage inverter was considered.
The analysis of regularities of influence of parameters of an electric circuit of an additional power supply on parameters of a power mode of the induction motor with use of zero combinations of switches of the lower arm of the inverter was carried out. Such regularities made it possible to formulate the conditions for increasing the load capacity of the electric drive system of the vehicle.
It has been found that a combined power supply consisting of two DC power sources provides an increase in the amplitude of the output voltage of the inverter with the simultaneous occurrence of its variable component and zero sequence when using zero switches combinations of the lower arm of the inverter.
The condition for the transfer of energy from an additional source is the ratio of the parameters of the electrical circuit, when the time constant of this electrical circuit is greater than half the switching time of the switches of the lower arm of the inverter.
When considering the conventional law of switching the inverter switches, it is established that this method leads to a complex form of output voltage. A modification of the switching law with the switches of the inverter of the combined power supply is proposed taking into account the variable component of the module of the output voltage vector, which provides voltage stabilization in the motor phases at a given level.
Regularities of influence on the torque of the induction motor at asymmetric system of voltages of the combined power supply at various control laws were established. It was found that the largest increase in torque and the lowest level of its oscillations is provided by vector control of the electric drive. When the supply voltage increases to 30%, the increase in torque is up to 18%, and when the voltage amplitude fluctuates within 30% of the nominal, the amplitude of torque oscillations will not exceed 10%.
It is proposed to provide compensation of motor torque oscillations in the vector speed control system of the electric drive by using additional control signals of the inverter switches, which are determined by the obtained variable components of the supply voltage in the synchronous coordinate system.
