Abstract: A modular multipoint power converter for converting an AC voltage to a DC voltage or vice versa, and a method of operating it are provided. The multipoint power converter has a converter branches, whereby two converter branches are connected to each other respectively to form a phase branch of the converter. Each converter branch has a plurality of similar submodules, each of which is formed from a half-bridge circuit with power semiconductor switches. The branch currents through the converter branches are controlled in operation by increasing the DC component of the DC current or the DC intermediate circular current such that a unipolar current flows through the converter branches. As a result, with the same plurality of submodules per converter branch, the transmissible power can be increased, the power semi-conductor elements can be better utilized, or the plurality of submodules can be reduced while the transmissible power remains the same.

Abstract: A modular multipoint power converter (8) for converting an AC voltage to a DC voltage or vice versa, and a method of operating such a modular multipoint power converter are provided. The multipoint power converter has a plurality of converter branches (9a-f), whereby two converter branches (9a-b, 9c-d, 9e-f) are connected to each other respectively to form a phase branch 11a-c of the converter (8). Each converter branch has a number of similar submodules (14, 14?), each of which is formed from a half-bridge circuit (18) with power semiconductor switches (T1-T4). The branch currents iq(t) through the converter branches (9a-f) are controlled in operation by increasing the DC component (Ig) of the DC current or the DC intermediate circular current (Idc) such that a unipolar current, preferably a continuous unipolar sinusoidal current, flows through the converter branches (9a-f).

Abstract: A method for controlling a back-to-back three-phase three-level converter having a grid-side AC/DC converter and a machine-side DC/AC converter connected by a split DC link which defines a DC link midpoint. The method includes controlling the grid-side converter to convert AC power from a grid into DC power of the DC link, controlling the machine-side converter to convert DC power from the DC link to AC power to feed a low frequency machine, and concurrently performing common mode voltage injection for the machine-side converter so as to at least partially compensate midpoint voltage ripple caused by the machine-side converter. The method further includes performing common mode voltage injection for the grid-side converter so as to at least partly further compensate the portion of the midpoint voltage ripple which remains uncompensated by controlling the machine-side converter. A control system implementing the control method and a power conversion system utilizing same.

Abstract: A method for controlling a back-to-back three-phase three-level converter having a grid-side AC/DC converter and a machine-side DC/AC converter connected by a split DC link which defines a DC link midpoint. The method includes controlling the grid-side converter to convert AC power from a grid into DC power of the DC link, controlling the machine-side converter to convert DC power from the DC link to AC power to feed a low frequency machine, and concurrently performing common mode voltage injection for the machine-side converter so as to at least partially compensate midpoint voltage ripple caused by the machine-side converter. The method further includes performing common mode voltage injection for the grid-side converter so as to at least partly further compensate the portion of the midpoint voltage ripple which remains uncompensated by controlling the machine-side converter. A control system implementing the control method and a power conversion system utilizing same.

Abstract: A method is disclosed to protect a power converter arrangement with a power converter that has a DC side that is connected to a DC intermediate circuit, an AC side, and controllable switches that can be controllably switched at a high frequency to invert the DC voltage of the DC intermediate circuit into an AC voltage. A protective device that can be activated and deactivated is provided to protect the power converter from overload by connecting an external thyristor rectifier bridge with a brake resistor (Rb ext) to the AC side of the power converter. If a predetermined error situation is detected, the external thyristors are triggered to turn on, to activate the protective device. If it is detected that the predetermined error situation has disappeared, the external thyristors are turned off. A power converter arrangement with a device to protect against overload is also disclosed.

Abstract: A method is disclosed to protect a power converter arrangement with a power converter that has a DC side that is connected to a DC intermediate circuit, an AC side, and controllable switches that can be controllably switched at a high frequency to invert the DC voltage of the DC intermediate circuit into an AC voltage. A protective device that can be activated and deactivated is provided to protect the power converter from overload by connecting an external thyristor rectifier bridge with a brake resistor (Rb ext) to the AC side of the power converter. If a predetermined error situation is detected, the external thyristors are triggered to turn on, to activate the protective device. If it is detected that the predetermined error situation has disappeared, the external thyristors are turned off. A power converter arrangement with a device to protect against overload is also disclosed.

Abstract: An optimized structure of an arm capacitor voltage balance controller based on chain links of the H-bridge module that achieves enhanced performance of an arm capacitor voltage balance control in all operational conditions, even with highly dynamic loads. Such a controller has application in three-phase STATCOM converters, and may be structured so as to seamlessly integrate feedforward and feedback controls with inverse maps used for calculation of the zero sequence reference voltage injection(s) (for star and delta STATCOM topologies).

Abstract: Provided is an approach for active control of cross currents flowing among multiple paralleled converters. Control of cross currents is achieved by using at least one proportional-integral (PI) controller and at least one resonant controller to target several selected dominant harmonics with infinite gains to ensure elimination of targeted harmonic cross currents in steady state. The cross currents are decomposed by into (1) common mode and differential mode components or (2) current phase domain components and each component is suppressed to a value approximately near zero using the controller. Also provided is a device comprises instructions, that, when executed by a processor, cause the processor to perform operations, which regulate and suppress cross current within a power system.

Abstract: Provided is an approach for active control of cross currents flowing among multiple paralleled converters. Control of cross currents is achieved by using at least one proportional-integral (PI) controller and at least one resonant controller to target several selected dominant harmonics with infinite gains to ensure elimination of targeted harmonic cross currents in steady state. The cross currents are decomposed by into (1) common mode and differential mode components or (2) current phase domain components and each component is suppressed to a value approximately near zero using the controller. Also provided is a device comprises instructions, that, when executed by a processor, cause the processor to perform operations, which regulate and suppress cross current within a power system.

Abstract: A connection for parallel bridge circuits in a power converter is provided. In particular, a power converter can be used to provide a desired power to a load, such as a generator, motor, electrical grid, or other suitable load. The power converter can include a plurality of bridge circuits coupled in parallel. A bridge output of each of the parallel bridge circuits can be coupled together at the load instead of at the power converter. In particular, the parallel bridge circuits can be coupled together at a location that is physically proximate the physical location of the load, such as at a plurality of terminals associated with the load. By doing so, stray inductance associated with conductors used to couple the bridge outputs of the parallel bridge circuits to the load can be effectively coupled between the parallel bridge circuits.

Abstract: The invention relates to a control method implemented in a variable speed drive for determining the inductances (Ld, Lq) of a permanent magnet synchronous machine comprising three phases (a, b, c), each oriented along a direction, a stator, and a rotor. For each phase, one after the other, said method includes steps of: applying, along the direction of the phase (a, b, c), a voltage vector (V1, V3, V5) in the positive direction and a voltage vector (V2, V4, V6) in the negative direction for a predetermined duration; measuring the current obtained in the phase after applying the voltage vectors in both directions; determining an angle (?r) for the position of the rotor in relation to the stator based on the measured current; and determining the flow (Ld) and torque (Lq) inductances of the machine based on the predetermined angle (?r).

Abstract: A midpoint voltage control system includes a power source, a generator coupled to the power source, a midpoint voltage controller coupled to the back-to-back converter configuration, a generator converter controller coupled to the midpoint power controller, a grid converter controller coupled to midpoint power controller, a first voltage converter coupled to the generator converter controller, the midpoint power controller and the generator, a second voltage converter coupled to the grid converter controller the midpoint power controller, the second voltage converter having a capacitor bank direct current (DC) bus midpoint and a transformer coupled to the second voltage converter and having a grid neutral midpoint, wherein the capacitor midpoint is interconnected to the grid neutral midpoint.

Abstract: The invention relates to a method for determining the position of a rotor flux vector of an electric motor (M), comprising a step of injecting a first current vector into a first reference frame (x+, y+) rotating at a first frequency (?) relative to a reference frame (d, q) synchronous with the rotation of the motor, and a second current vector into a second injection reference frame (x?, y?) rotating at a second frequency opposite to the first frequency, a step of determining a first stator flux induced voltage delivered at the output of a first integrator module (12) synchronous with the first reference frame (x+, y+) and a second stator voltage delivered at the output of a second integrator module (13) synchronous with the second reference frame (x?, y?), a step of regulating the position of the rotor flux vector by minimizing the error (?) between a real position and an estimated position (?S) of the rotor flux vector, the error being determined based on the second induced voltage.

Abstract: The invention relates to a control method implemented in a variable speed drive for determining the inductances (Ld, Lq) of a permanent magnet synchronous machine comprising three phases (a, b, c), each oriented along a direction, a stator, and a rotor. For each phase, one after the other, said method includes steps of: applying, along the direction of the phase (a, b, c), a voltage vector (V1, V3, V5) in the positive direction and a voltage vector (V2, V4, V6) in the negative direction for a predetermined duration; measuring the current obtained in the phase after applying the voltage vectors in both directions; determining an angle (?r) for the position of the rotor in relation to the stator based on the measured current; and determining the flow (Ld) and torque (Lq) inductances of the machine based on the predetermined angle (?r).

Abstract: The invention relates to a method for determining the position of a rotor flux vector of an electric motor (M), comprising a step of injecting a first current vector into a first reference frame (x+, y+) rotating at a first frequency (?) relative to a reference frame (d, q) synchronous with the rotation of the motor, and a second current vector into a second injection reference frame (x?, y?) rotating at a second frequency opposite to the first frequency, a step of determining a first stator flux induced voltage delivered at the output of a first integrator module (12) synchronous with the first reference frame (x+, y+) and a second stator voltage delivered at the output of a second integrator module (13) synchronous with the second reference frame (x?, y?), a step of regulating the position of the rotor flux vector by minimizing the error (?) between a real position and an estimated position (?S) of the rotor flux vector, the error being determined based on the second induced voltage.