Abstract: A power flow management method and a controller are provided. First, sensing voltage signals and sensing current signals between a power supplying module and a multilevel converter module are obtained. Positive sequence voltage signals, positive sequence current, negative voltage signals and negative current signals are generated according to the sensing voltage signals and the sensing current signals. Forward powers are calculated according to the positive sequence voltage signals, positive sequence current, negative voltage signals and negative current signals. DC voltage signals are obtained from the multilevel converter module, and feedback powers are calculated accordingly. A magnitude and a phase of a zero sequence voltage injection signal are determined according to the forward powers and the feedback powers. Accordingly, the generated zero sequence voltage injection signal is used to manage power flow effectively.

Abstract: A power flow management method and a controller are provided. First, sensing voltage signals and sensing current signals between a power supplying module and a multilevel converter module are obtained. Positive sequence voltage signals, positive sequence current, negative voltage signals and negative current signals are generated according to the sensing voltage signals and the sensing current signals. Forward powers are calculated according to the positive sequence voltage signals, positive sequence current, negative voltage signals and negative current signals. DC voltage signals are obtained from the multilevel converter module, and feedback powers are calculated accordingly. A magnitude and a phase of a zero sequence voltage injection signal are determined according to the forward powers and the feedback powers. Accordingly, the generated zero sequence voltage injection signal is used to manage power flow effectively.

Abstract: A low voltage ride-through (LVRT) apparatus capable of flux compensation and peak current management is disclosed, which comprises a converter; a space vector modulator, connected to the converter; a current controller, connected to the space vector modulator; an grid realization system, connected to the current controller; a flux offset compensator, connected to the current controller; a filter, connected to the converter; and a transformer, connected to the filter. In this manner, the LVRT apparatus may be connected to an associated grid side (commercial power), and thus applied onto a direct current (DC) to alternating current (AC) system for renewable energy source. When the grid side is failed, a flux offset on a transformer may be eliminated, to avoid an inrush current from rising after a recovery of failure exclude voltage, so that the requirement of the grid operation may be satisfied.

Abstract: Disclosed is an uninterruptible power supply, including a rectifier for generating a DC voltage; an energy storage unit; an inverter for converting the DC voltage into a three-phase modulating voltage; a filter; a bypass switch circuit for selectively outputting a three-phase AC voltage or the three-phase modulating voltage as a three-phase load voltage; and a control circuit for controlling the operation of the uninterruptible power supply. The control circuit may use a flux compensation block with different operating modes to adjust the three-phase load voltage at the startup phase of a second inductive load and at the stable phase of the second inductive load, thereby compensating or correcting the flux of the second inductive load to prevent the flux distribution of the second inductive load from being saturated.

Abstract: A droop control system for grid-connected synchronization connects to a plurality of distributed power generation modules and a utility grid system. The droop control system includes a detection processing module and a plurality of regulation control modules corresponding to the distributed power generation modules. The detection processing module is coupled with the distributed power generation modules and utility grid system in parallel to obtain a voltage difference, a phase angle difference and a frequency difference. The regulation control modules perform droop control of real power-frequency variety and reactive power-voltage variety and phase angle compensation. Through reactive power-voltage variety droop control approach, impact of impedance alterations in the power system can be eliminated and voltage fluctuations can also be minimized to achieve stable effect. Hence electric power of the utility grid system and distributed power generation modules can be regulated synchronously.

Abstract: An LVRT control method for a grid-connected converter of distributed energy resources comprises steps of: obtain a positive sequence electrical component and a negative sequence electrical component during an LVRT period; outputting a compensation signal according to a power threshold withstood by a grid-connected converter to undertake reactive power compensation; and constraining the output power lower than the power threshold. The present invention uses the positive and negative sequence electrical components to undertake reactive power compensation, whereby to improve balance and stability of voltage during the LVRT period, avoid reverse torque and mechanical resonance, and prolong the service life of the power generator. Moreover, the present invention constrains the sum of the compensation currents below the power threshold to prevent the circuit of the power generator from being overloaded and damaged, whereby is prolonged the service life of the power system.

Abstract: Disclosed is an uninterruptible power supply, including a rectifier for generating a DC voltage; an energy storage unit; an inverter for converting the DC voltage into a three-phase modulating voltage; a filter; a bypass switch circuit for selectively outputting a three-phase AC voltage or the three-phase modulating voltage as a three-phase load voltage; and a control circuit for controlling the operation of the uninterruptible power supply. The control circuit may use a flux compensation block with different operating modes to adjust the three-phase load voltage at the startup phase of a second inductive load and at the stable phase of the second inductive load, thereby compensating or correcting the flux of the second inductive load to prevent the flux distribution of the second inductive load from being saturated.

Abstract: The present invention discloses a flux linkage compensator, which applies to an UPS system and comprises a load transformer flux linkage observer, a compensation voltage command generator, and a flux linkage command generator. The load transformer flux linkage observer generates a load transformer flux linkage signal. The flux linkage command generator generates a flux linkage command signal. The difference between the load transformer flux linkage signal and the flux linkage command signal forms a flux linkage deviation signal. The compensation voltage command generator generates a voltage compensation signal to make the flux linkage deviation signal approach zero. Thereby, the flux linkage compensator can compensate for the flux linkage deviation occurring in starting the UPS system. Thus, the present invention can perform voltage compensation fast and reliably and inhibit the inrush current effectively.

Abstract: The present invention discloses a flux linkage compensator, which applies to an UPS system and comprises a load transformer flux linkage observer, a compensation voltage command generator, and a flux linkage command generator. The load transformer flux linkage observer generates a load transformer flux linkage signal. The flux linkage command generator generates a flux linkage command signal. The difference between the load transformer flux linkage signal and the flux linkage command signal forms a flux linkage deviation signal. The compensation voltage command generator generates a voltage compensation signal to make the flux linkage deviation signal approach zero. Thereby, the flux linkage compensator can compensate for the flux linkage deviation occurring in starting the UPS system. Thus, the present invention can perform voltage compensation fast and reliably and inhibit the inrush current effectively.

Abstract: A method and apparatus is provided for restoring a sagging voltage signal on a power transmission line, caused by a remote fault in the utility power system, to a balanced three-phase condition at the pre-fault voltage level. Voltage restoration is provided by injecting a voltage signal in series with the power transmission line which restores the load voltage vectors to the pre-fault condition. The restored load voltage vectors are rotated by a selected phase angle such that zero real power flow is associated with the voltage restoration. The voltage compensation signal may be injected into the power transmission line by connecting a voltage compensator inverter in series with the transmission line. The voltage compensator inverter may be controlled to provide the desired injected voltage signal using a synchronous reference frame based controller.

Abstract: A parallel hybrid active filter system for harmonic compensation of large non-linear loads is provided. The hybrid filter includes a passive filter connected in series with an inverter that is controlled to produce a dynamically variable inductance at selected harmonic frequencies. The passive filter may include passive capacitive and inductive elements, or may include a power factor correction capacitor alone, with all the inductance for the hybrid filter provided by the active filter inverter. The active filter inverter is controlled to provide the dynamically variable inductance by a synchronous reference frame (SRF) based controller that generates active filter inverter voltage commands that are fed to a PWM or square wave modulated voltage source inverter (VSI).

Abstract: A hybrid parallel active/passive filter system is provided which provides line power harmonic isolation and compensation for power systems connected to high power non-linear loads. The hybrid filter includes a passive filter connected in series with an active filter inverter. The active filter inverter is controlled to generate inverter voltages such that the filter terminal voltage tracks the supply voltage harmonics at a selected dominant harmonic frequency to regulate the supply current harmonics to zero. A synchronous reference frame (SRF) based controller is used to generate harmonic inverter voltage commands based on measured supply current values. A feed forward command signal generator may be used to improve the response of the control system. The active filter inverter is preferably implemented as a square-wave inverter. The active filter inverter DC bus is controlled to achieve power balancing and to provide real power to compensate for losses of the inverter.