Drive equipment and control method
A drive equipment includes a transformer, a power converter, and a control system. The transformer is configured with a primary winding and a secondary winding, and a winding of an electric motor is connected to the secondary winding. The power converter causes a current to flow through the primary winding of the transformer. The control system performs constant current control on the power converter during a period of a first stage after startup of the electric motor is instructed, to reduce a variation in a current flowing through the primary winding of the transformer, and controls the power converter through variable voltage variable frequency control of the electric motor in a second stage after the first stage.
1. A drive equipment comprising:
a transformer configured with a primary winding and a secondary winding, an electric motor being connected to the secondary winding;
a power converter configured to cause a current to flow through the primary winding of the transformer; and
a control system configured to perform constant current control on the power converter so that a current at a predetermined desired frequency flows from the power converter to the primary winding of the transformer during a period of a first stage after startup of the electric motor is instructed, to reduce a variation in a current flowing through the primary winding of the transformer, and to control the power converter through variable voltage variable frequency control of the electric motor in a second stage after the first stage,
wherein the control system controls a frequency of the current caused to flow by the power converter so that a frequency component having a frequency higher than a frequency determined in advance in the desired frequency is included in a current flowing the primary winding of the transformer to demagnetize the transformer.
2. The drive equipment according to claim 1 , wherein the control system decreases, over time, the current flowing through the primary winding of the transformer during the period of the first stage, and decreases, over time, a frequency of the current flowing through the primary winding of the transformer as the desired frequency during the period of the first stage.
3. The drive equipment according to claim 1 , comprising:
a current detector configured to detect the current flowing through the primary winding of the transformer,
wherein the control system performs constant current control using the power converter on the basis of a result of detecting the current and a current reference, the current reference being an index of a current value, during the period of the first stage.
4. The drive equipment according to claim 1 , wherein the control system controls a frequency of the current caused to flow by the power converter so that the frequency decreases monotonically over time after a maximum value of a frequency of the current flowing through the primary winding of the transformer to demagnetize the transformer is generated during the period of the first stage.
5. The drive equipment according to claim 1 , wherein the control system starts the second stage after a minimum value of the frequency of the current flowing through the primary winding of the transformer to demagnetize the transformer reaches a predetermined value determined in advance during, the period of the first stage.
6. The drive equipment according to claim 1 , wherein the control system includes
a control signal generation unit configured to generate a control signal for switching between power semiconductor devices of the power converter on the basis of a voltage reference and a reference phase;
a first voltage reference generator configured to generate a first voltage reference that is used as the voltage reference in the first stage related to startup of the electric motor;
a first frequency reference generator configured to generate a first frequency reference used as a frequency reference in the first stage;
a second voltage reference generator configured to generate a second voltage reference used as the voltage reference for variable speed control of the electric motor in the second stage after the first stage;
a frequency reference generator configured to generate a second frequency reference used as a frequency reference for variable speed control of the electric motor in the second stage;
an integrator configured to generate a reference phase from either the first frequency reference or the second frequency reference; and
a controller configured to generate a control command to switch between signals so that the reference phase based on the first frequency reference and the first voltage reference are supplied to the control signal generation unit in the first stage related to the startup of the electric motor, and the reference phase based on the frequency reference and the second voltage reference are supplied to the control signal generation unit in the second stage after the first stage.
7. The drive equipment according to claim 6 , comprising:
a first switch configured to enable the first voltage reference;
a second switch configured to enable the second voltage reference;
a third switch configured to enable the first frequency reference; and
a fourth switch configured to enable the second frequency reference,
wherein the controller
controls the first switch and the third switch so that the first voltage reference and the first frequency reference are enabled during the period of the first stage, and
controls the second switch and the fourth switch so that the second switch and the fourth switch enable the second voltage reference and the second frequency reference during a period of the second stage.
8. The drive equipment according to claim 1 , wherein the control system includes
a control signal generation unit configured to generate a control signal for switching between power semiconductor devices of the power converter on the basis of a voltage reference and a reference phase;
a first current reference generator configured to generate a first current reference used as a current reference in the first stage related to the startup of the electric motor;
a first frequency reference generator configured to generate a first frequency reference used as a frequency reference in the first stage;
a second current reference generator configured to generate a second current reference used as the current reference for variable speed control of the electric motor in the second stage after the first stage;
a frequency reference generator configured to generate a second frequency reference used as a frequency reference for variable speed control of the electric motor in the second stage; and
a controller configured to generate a control command to switch between signals so that a reference phase based on the first frequency reference and the first current reference are supplied to the control signal generation unit in the first stage related to the startup of the electric motor, and a reference phase based on the frequency reference and the second current reference are supplied to the control signal generation unit in the second stage after the first stage.
9. A control method for a drive equipment including a transformer configured with a primary winding and a secondary winding, a winding of an electric motor being connected to the secondary winding, and a power converter configured to cause a current to flow through the primary winding of the transformer, the control method comprising:
performing constant current control on the power converter so that a current at a predetermined desired frequency flows from the power converter to the primary winding of the transformer during a period of a first stage related to startup of the electric motor to reduce a variation in the current flowing through the primary winding of the transformer;
controlling the power converter through variable voltage variable frequency control of the electric motor in a second stage after the first stage; and
controlling a frequency of the current caused to flow by the power converter so that a frequency component having a frequency higher than a frequency determined in advance in the desired frequency is included in a current flowing the primary winding of the transformer to demagnetize the transformer.
10. A drive equipment comprising:
a transformer including a primary winding and a secondary winding, an electric motor being connected to the secondary winding;
a power converter configured to cause a current to flow through the primary winding of the transformer; and
a control system configured to perform constant current control on the power converter so that a current at a predetermined desired frequency flows from the power converter to the primary winding of the transformer during a period of a first stage after startup of the electric motor is instructed, to reduce a variation in a current flowing through the primary winding of the transformer, and to control the power converter through variable voltage variable frequency control of the electric motor in a second stage after the first stage;
wherein the control system decreases, over time, the current flowing through the primary winding of the transformer during the period of the first stage, and decreases, over time, a frequency of the current flowing through the primary winding of the transformer as the desired frequency during the period of the first stage.