A transport refrigeration unit (TRU) system (IO) is provided. The TRU system includes a TRU (30), an electrical grid and a control unit. The TRU (30) is configured to be operably coupled a container (20) and includes components configured to control an environment within an interior of the container (20) and a TRU battery pack (40) configured to store energy for powering at least the components. The control unit is communicative with the TRU (30) and the electrical grid and is configured to manage power supplies and demands between the TRU battery pack (40) of each TRU (30) and the electrical grid.

A control module controls impedance injection units (IIUs) to form multiple connection configurations in sequence. Each connection configuration has one IIU, or multiple IIUs in series, parallel or combination of series and parallel. The connection configurations of IIUs are coupled to a high-voltage transmission line. The control module and the IIUs generate rectangular impedance injection waveforms. When the waveforms are combined and injected to the high-voltage transmission line, this produces a pseudo-sinusoidal waveform.

A control module controls impedance injection units (IIUs) to form multiple connection configurations in sequence. Each connection configuration has one IIU, or multiple IIUs in series, parallel or combination of series and parallel. The connection configurations of IIUs are coupled to a high-voltage transmission line. The control module and the IIUs generate rectangular impedance injection waveforms. When the waveforms are combined and injected to the high-voltage transmission line, this produces a pseudo-sinusoidal waveform.

A dynamic stability analysis and control method for a voltage sourced converter based high voltage direct current (VSC-HVDC) transmission system. The method includes the following steps: unlocking a converter station of the VSC-HVDC transmission system to make the VSC-HVDC transmission system run in a non-island control mode; extracting corresponding parameters of the VSC-HVDC transmission system, wherein the parameters include an effective voltage value U.sub.t0 of an AC system, an outgoing reactive power Q.sub.vsc0 of the VSC-HVDC transmission system, a gain k.sub.p of a phase-locked loop (PLL), and a proportional integral time constant k.sub.i of the PLL; calculating a short-circuit ratio (SCR), an unit value of U.sub.t0 and an unit value of Q.sub.vsc0; calculating a key stable component; checking the sign of the key stable component to determine the stability of the VSC-HVDC transmission system.

A suppression method of high-frequency resonance for VSC-HVDC (Voltage Source Converter-High Voltage Direct Current Transmission) system based on nonlinear filter in voltage feed-forward control. It includes that the nonlinear filter is used for the voltage feed-forward link in the current inner loop control. The specific method is to extract each sequence component of the AC (Alternating Current) voltage, calculate the average value of the sequence component at N sample points, compare the current average value with the output result of nonlinear filter in the previous period, and output the result of nonlinear filter in the current period. After corrected, the result is a fixed value varying according to gradient which acts on the voltage feed-forward link of the inner loop. The invention can effectively suppress the high frequency resonance caused by impedance matching between VSC-HVDC system and grid system without losing the rapidity, and at the same time, it can adjust with AC voltage when voltage disturbance such as AC fault occurs, so as to reduce the risk of over-current of the converter valve. At present, the invention only needs to be realized in the secondary control software link without adding a new equipment, which is also low cost, no occupancy of land and convenient for engineering practice.

In the field of high voltage direct current (HVDC) power transmission networks, there is a need for improvements to allow a single power converter to control individual AC network voltages carried by multiple AC transmission conduits to multiple AC network elements, such as respective wind parks.

A power transmission network (10; 100) comprises a power converter (12) which has first and second DC converter terminals (14, 16) that are for connection, in use, to a DC network. The power converter (12) also includes an AC converter terminal (22) which is electrically connected to a plurality of AC transmission conduits (24.sub.1, 24.sub.2, 24.sub.n), each of which is for connection, in use, to a respective AC network element (26.sub.1, 26.sub.2, 26.sub.n) that is configured to operate at a respective individual AC network voltage. The power converter (12) further includes a primary converter controller (34) which is programmed, in use, to control the transfer of power through the power converter (12) and thereby between the DC network and the plurality of AC network elements (26.sub.1, 26.sub.2, 26.sub.n). The primary converter controller (34) is further programmed, in use, to control each individual AC network voltage by establishing a virtual voltage which is representative of the plurality of AC network voltages and altering a single AC converter voltage produced by the power converter (12) at the AC converter terminal (22) to adjust the virtual voltage and thereby adjust each individual AC network voltage.

There is provided a switching valve for a voltage source converter. The switching valve comprises a plurality of modules, each module including at least one switching element and at least one energy storage device, the or each switching element and the or each energy storage device in each module arranged to be combinable to selectively provide a voltage source, the switching valve including a controller configured to selectively control the switching of the switching elements to select one or more of the modules to contribute a or a respective voltage to a switching valve voltage, wherein the controller is configured to selectively carry out a module selection by: assigning each module with a respective address in an address queue; in a respective one of a plurality of sampling events, selecting one or more voltage contributing modules in order of its assigned address in the address queue; and between different sampling events, changing the order of selecting the or each voltage contributing module based on its assigned address in the address queue.

A control module controls impedance injection units (IIUs) to form multiple connection configurations in sequence. Each connection configuration has one IIU, or multiple IIUs in series, parallel or combination of series and parallel. The connection configurations of IIUs are coupled to a high-voltage transmission line. The control module and the IIUs generate rectangular impedance injection waveforms. When the waveforms are combined and injected to the high-voltage transmission line, this produces a pseudo-sinusoidal waveform.

The invention relates to a supply system for a plurality of loads connected in parallel to a direct current supply bus. The supply system includes a DC supply bus and a plurality of supply lines connected in parallel to the supply bus and supplying the said loads. The supply system includes uncoupling and damping means that is adapted to decrease the unipolar signals travelling within the supply system while the loads are being supplied. The uncoupling and damping means includes at least one inductance arranged in series in at least one of the supply lines. Protective means (are also provided for protection in the event of a fault.

This disclosure describes systems, methods, and devices related to alternating current (AC) mitigation. An AC mitigation system may comprise a conductive portion of the pipeline, wherein the conductive portion of the pipeline is adjacent to a high voltage AC power transmission line. The AC mitigation system may comprise a ground wire connected to the conductive portion of the pipeline. The AC mitigation system may comprise a circuit electrically connected to the ground wire. The AC mitigation system may comprise a means for the conductive portion of the pipeline to route AC power through the circuit.