20-09-2012, 11:39 AM
VSC-MTDC systems and the Stability Control of the Multi-terminal systems
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INTRODUCTION
Hairong Chen et al (2006) has research the control strategies of the VSC-MTDC systems and the stability control of the Multi-terminal systems are investigated and designed. The current decoupled compensation and the voltage feed-forward compensation are adopted for the controller of the converter. Thus the decoupled control of the active power and reactive power can be implemented. At the same time, with the dc voltage feed-forward compensation, the waveforms of the output voltage on the ac side of the converters are improved. In addition, a multi-point dc voltage control strategy is presented for the stability control of the multi-terminal systems. The digital simulation results show that the control strategy of the VSC-MTDC systems designed has great dynamic stabilities and is suitable for acting as a linking system between the distribution generations and the ac system. This control strategy is also valuable for the scheme design for the power supply to important loads.
Jef Beerten et al (2011) has summarized a power flow model is presented to include a DC voltage droop control or distributed DC slack bus in a Multi-terminal Voltage Source Converter High Voltage Direct Current (VSC MTDC) grid. The available VSC MTDC models are often based on the extension of existing point-to-point connections and use a single DC slack bus that adapts its active power injection to control the DC voltage. A distributed DC voltage control has significant advantages over its concentrated slack bus counterpart, since a numbers of converters can jointly control the DC system voltage. After a fault, a voltage droop controlled DC grid converges to a new working point, which impacts the power flows in both the DC grid and the underlying AC grids. Whereas current day research is focusing on the dynamic behavior of such a system and introduces a power flow model to study the steady-state change of the combined AC/DC system as a result of faults and transients in the DC grid. The model allows incorporating DC grids in a N-1 contingency analysis, thereby including the effects of a distributed voltage control on the power flows in both the AC and DC systems.
V Shyam et al (2009)has proposed Multi-terminal DC transmission system (MTDC) offers flexibility in operation, increases the overall efficiency of power transmission and significantly improves the AC system performance. With the advancement of powerful computers and a number of new concepts such as artificial intelligence, it is possible to control and monitor MTDC-AC system with sine wave pulse width modulated converters and intelligent systems.
B. Chuco et al (2010) presents a comparative study of dynamic performance of conventional VSC based HVDC and Modular Multilevel Converter (MMC) VSC based HVDC operating in back to back configuration. Voltage and rotor angle stability of the generator during power systems fault is analyzed. The simulated power system is composed by a back-to-back HVDC based on conventional VSC and the MMC connecting two weak systems. The power source is a 100 MW generator, which is equipped with an Automatic Voltage Regulator (AVR) and without Power System Stabilizer (PSS). The rated capacity of the VSC-HVDC is 100 MW. A vector controller is implemented in dq-axis to control the rectifier DC side voltage and the AC voltage or reactive power. This same control is used in the inverter side for frequency or active power and AC voltage or reactive power control. According to the results, conventional VSC-HVDC as well as the Modular Multilevel VSC-HVDC increase damping characteristic of power oscillations modes. Additionally the converter topologies for each system are analyzed.
[attachment=34130]
INTRODUCTION
Hairong Chen et al (2006) has research the control strategies of the VSC-MTDC systems and the stability control of the Multi-terminal systems are investigated and designed. The current decoupled compensation and the voltage feed-forward compensation are adopted for the controller of the converter. Thus the decoupled control of the active power and reactive power can be implemented. At the same time, with the dc voltage feed-forward compensation, the waveforms of the output voltage on the ac side of the converters are improved. In addition, a multi-point dc voltage control strategy is presented for the stability control of the multi-terminal systems. The digital simulation results show that the control strategy of the VSC-MTDC systems designed has great dynamic stabilities and is suitable for acting as a linking system between the distribution generations and the ac system. This control strategy is also valuable for the scheme design for the power supply to important loads.
Jef Beerten et al (2011) has summarized a power flow model is presented to include a DC voltage droop control or distributed DC slack bus in a Multi-terminal Voltage Source Converter High Voltage Direct Current (VSC MTDC) grid. The available VSC MTDC models are often based on the extension of existing point-to-point connections and use a single DC slack bus that adapts its active power injection to control the DC voltage. A distributed DC voltage control has significant advantages over its concentrated slack bus counterpart, since a numbers of converters can jointly control the DC system voltage. After a fault, a voltage droop controlled DC grid converges to a new working point, which impacts the power flows in both the DC grid and the underlying AC grids. Whereas current day research is focusing on the dynamic behavior of such a system and introduces a power flow model to study the steady-state change of the combined AC/DC system as a result of faults and transients in the DC grid. The model allows incorporating DC grids in a N-1 contingency analysis, thereby including the effects of a distributed voltage control on the power flows in both the AC and DC systems.
V Shyam et al (2009)has proposed Multi-terminal DC transmission system (MTDC) offers flexibility in operation, increases the overall efficiency of power transmission and significantly improves the AC system performance. With the advancement of powerful computers and a number of new concepts such as artificial intelligence, it is possible to control and monitor MTDC-AC system with sine wave pulse width modulated converters and intelligent systems.
B. Chuco et al (2010) presents a comparative study of dynamic performance of conventional VSC based HVDC and Modular Multilevel Converter (MMC) VSC based HVDC operating in back to back configuration. Voltage and rotor angle stability of the generator during power systems fault is analyzed. The simulated power system is composed by a back-to-back HVDC based on conventional VSC and the MMC connecting two weak systems. The power source is a 100 MW generator, which is equipped with an Automatic Voltage Regulator (AVR) and without Power System Stabilizer (PSS). The rated capacity of the VSC-HVDC is 100 MW. A vector controller is implemented in dq-axis to control the rectifier DC side voltage and the AC voltage or reactive power. This same control is used in the inverter side for frequency or active power and AC voltage or reactive power control. According to the results, conventional VSC-HVDC as well as the Modular Multilevel VSC-HVDC increase damping characteristic of power oscillations modes. Additionally the converter topologies for each system are analyzed.