Electromechanical power transmission chain, and an electric system, a method and a computer program for controlling the same to stabilize dc input voltage of a converter driving an electric machine and determining a torque reference of the electric machine

An electromechanical power transmission chain comprising:

• an electric machine configured to receive mechanical power from a combustion engine and to supply mechanical power to one or more actuators;
• and
• an electric system configured to supply electrical power to the electric machine when the electric machine operates as an electric motor and to receive electrical power from the electric machine when the electric machine operates as a generator, the electric system comprising:
• a first capacitive circuit comprising at least one first capacitor,
• converter equipment configured to transfer electric energy between the first capacitive circuit and the electric machine, the converter equipment being configured to convert a first direct voltage of the first capacitive circuit into an output voltage and to output the output voltage to the electric machine,
• a second capacitive circuit comprising at least one second capacitor,
• a direct voltage converter configured to transfer electric energy between the first and the second capacitive circuits, and
• a control system configured to
• determine a torque reference used to drive the electric machine, with the converter equipment, as either the electric motor or the generator, the torque reference being determined at least partly based on:
• a second direct voltage of the second capacitive circuit,
• a power control signal of a combustion engine mechanically connected to the electric machine, the power control signal being used to determine a fuel and air supply of the combustion engine, and
• a rotational speed of the electric machine,
• wherein the torque reference is equal to a motor power for the electric machine divided by the rotational speed when the electric machine operates as the electric motor or is equal to a generator power for the electric machine divided by the rotational speed when the electric machine operates as the generator,
• control the direct voltage converter to transfer the electric energy between the first and the second capacitive circuits, in response to changes of the first direct voltage with respect to a first direct voltage reference value, to drive the first direct voltage to the first direct voltage reference value,
• control the converter equipment to change a transfer of the electric energy from the electric machine to the first capacitive circuit when the electric machine operates as the generator and to change a transfer of the electric energy from the first capacitive circuit to the electric machine when the electric machine operates as the electric motor, in response to changes of the second direct voltage of the second capacitive circuit with respect to a second direct voltage reference value, to drive the second direct voltage to the second direct voltage reference value,
• keep the changes of the first direct voltage, with respect to the first direct voltage reference value, smaller than the changes of the second direct voltage with respect to the second direct voltage reference value,
• wherein the converter equipment comprises a converter stage configured to transfer the electric energy from the electric machine to the first capacitive circuit when the electric machine operates as the generator, and configured to transfer the electric energy from the first capacitive circuit to the electric machine when the electric machine operates as the electric motor, and
• wherein the control system is further configured to:
• drive the electric machine as the electric motor in response to an increase in the power control signal of the combustion engine, and
• drive the electric machine as the generator in response to a decrease in the power control signal of the combustion engine.

A method for controlling an electromechanical power transmission chain that includes:

• a first capacitive circuit including at least one first capacitor,
• an electric machine,
• converter equipment configured to transfer electric energy between the first capacitive circuit and the electric machine,
• a second capacitive circuit including at least one second capacitor, and
• a direct voltage converter,
• the electromechanical power transmission chain being a parallel transmission chain in which the electric machine is mechanically connected to a combustion engine and to one or more actuators,
• the converter equipment including a converter stage configured to transfer electric energy from the electric machine to the first capacitive circuit when the electric machine operates as a generator, and configured to transfer electric energy from the first capacitive circuit to the electric machine when the electric machine operates as an electric motor, the converter equipment converting a first direct voltage of the first capacitive circuit into an output voltage and outputting the output voltage to the electric machine, the method comprising:
• determining a torque reference used to drive the electric machine, with the converter equipment, as either the electric motor or the generator, the torque reference being determined at least partly based on:
• a second direct voltage of the second capacitive circuit,
• a power control signal of a combustion engine mechanically connected to the electric machine, the power control signal being used to determine a fuel and air supply of the combustion engine, and
• a rotational speed of the electric machine,
• wherein the torque reference is equal to a motor power for the electric machine divided by the rotational speed when the electric machine operates as the electric motor or is equal to a generator power for the electric machine divided by the rotational speed when the electric machine operates as the generator;
• controlling the direct voltage converter to transfer electric energy between the first capacitive circuit and the second capacitive circuit, in response to changes of the first direct voltage with respect to a first direct voltage reference value, to drive the first direct voltage to the first direct voltage reference value;
• controlling the converter equipment to change the transfer of the electric energy from the electric machine to the first capacitive circuit when the electric machine operates as the generator and to change the transfer of the electric energy from the first capacitive circuit to the electric machine when the electric machine operates as the electric motor, in response to changes of the second direct voltage of the second capacitive circuit with respect to a second direct voltage reference value, to drive the second direct voltage to the second direct voltage reference value;
• driving the electric machine to operate as the electric motor in response to an increase in the power control signal of the combustion engine;
• and
• driving the electric machine to operate as the generator in response to a decrease in the power control signal of the combustion engine,
• wherein the controlling the direct voltage converter and the controlling the converter equipment comprises controlling the changes of the first direct voltage, with respect to the first direct voltage reference value, to be smaller than the changes of the second direct voltage with respect to the second direct voltage reference value.

A non-transitory computer readable medium encoded with a computer program configured to control an electromechanical power transmission chain, the electromechanical power transmission chain including:

• a first capacitive circuit including at least one first capacitor,
• an electric machine,
• converter equipment configured to transfer electric energy between the first capacitive circuit and the electric machine,
• a second capacitive circuit including at least one second capacitor, and
• a direct voltage converter,
• the electromechanical power transmission chain being a parallel transmission chain in which the electric machine is mechanically connected to a combustion engine and to one or more actuators, the converter equipment including a converter stage configured to transfer electric energy from the electric machine to the first capacitive circuit when the electric machine operates as a generator, and configured to transfer electric energy from the first capacitive circuit to the electric machine when the electric machine operates as an electric motor, the converter equipment converting a first direct voltage of the first capacitive circuit into an output voltage and outputting the output voltage to the electric machine, the computer program comprising computer executable instructions for controlling a programmable processor to:
• determine a torque reference used to drive the electric machine, with the converter equipment, as either the electric motor or the generator, the torque reference being determined at least partly based on:
• a second direct voltage of the second capacitive circuit,
• a power control signal of a combustion engine mechanically connected to the electric machine, the power control signal being used to determine a fuel and air supply of the combustion engine, and
• a rotational speed of the electric machine,
• wherein the torque reference is equal to a motor power for the electric machine divided by the rotational speed when the electric machine operates as the electric motor or is equal to a generator power for the electric machine divided by the rotational speed when the electric machine operates as the generator;
• control the direct voltage converter to transfer electric energy between the first capacitive circuit and the second capacitive circuit, in response to changes of the first direct voltage with respect to a first direct voltage reference value, to drive the first direct voltage to the first direct voltage reference value;
• control the converter equipment to change the transfer of the electric energy from the electric machine to the first capacitive circuit when the electric machine operates as the generator and to change the transfer of the electric energy from the first capacitive circuit to the electric machine when the electric machine operates as the electric motor, in response to changes of the second direct voltage of the second capacitive circuit with respect to a second direct voltage reference value, to drive the second direct voltage to the second direct voltage reference value;
• drive the electric machine to operate as the electric motor in response to an increase in the power control signal of the combustion engine;
• and
• drive the electric machine to operate as the generator in response to a decrease in the power control signal of the combustion engine,
• wherein the computer executable instructions are further configured to control the programmable processor to control the changes of the first direct voltage, with respect to the first direct voltage reference value, to be smaller than the changes of the second direct voltage with respect to the second direct voltage reference value.