EPE Association: EPE 2017 - DS1f: Standard and Advanced Control techniques for Power Converters I

EPE 2017 - DS1f: Standard and Advanced Control techniques for Power Converters I
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2017 ECCE Europe - Conference > EPE 2017 - Topic 03: Measurement and Control > EPE 2017 - DS1f: Standard and Advanced Control techniques for Power Converters I

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   A Computationally Efficient Current Controller for Simultaneous Injection of both Positive and Negative Sequences
By Zunaib ALI [View]
[Download]

Abstract: Reducing the required processing time of current controllers used in grid side converter (GSC) of renewable energy systems (RES) allows to optimize the limited processing resources and at the same time minimize the cost of the processors required. In addition, the transient behavior of these controllers must be fast and with low overshoot for the GSC to support the grid during off-nominal grid conditions and according to the grid code requirements imposed. For a converter to respond accordingly, the injection of both positive and negative sequences of fundamental current under off-nominal grid conditions is necessary. The work presents a GSC current controller that meets all modern grid requirements expected. It has been developed by introducing two modifications to an existing current controller. Experiments and simulations have been performed to validate the operation of the proposed current controller in terms of complexity and performance. Consequently, the new current controller requires 22\% less processing time and can achieve a faster and more accurate response in order to meet modern grid code requirements under off-nominal conditions.

   A Linear Damping Scheme for Higher Order DC-DC converters Supplying Constant Power Loads in a DC Microgrid
By Mahesh SRINIVASAN [View]
[Download]

Abstract: A linear controller is proposed for dc microgrids with SEPIC, Cuk and Zeta power electronic converters supplying constant power loads. The controller is implemented in two stages. During the first stage, also known as active damping stage, limit cycle oscillations are damped by inserting a virtual resistance in series with the input inductor of each of the converters. In the second stage, an integral controller is added to the first stage to compensate for the voltage deviations due to the virtual resistance. The second stage, also known as voltage regulation stage maintains the microgrid voltage within acceptable limits in the event of source and load variation. Linearization and small signal analysis are used to derive stability conditions for the equilibrium points. Simulation and experiments performed on a prototype microgrid are used to verify the proposed control laws.

   Advanced predictive control methods of three-level AC/DC rectifier
By Rafal GRODZKI [View]
[Download]

Abstract: This paper describes three modern predictive control methods of three-level AC/DC rectifier. Additionally, it presents a comparison of the methods both in static and dynamic states. Simulation and experimental results confirm that all presented control algorithms ensure a good control quality (low THD) in static states and excellent dynamic properties.

   Anti-windup Compensation of LQG for Single-phase Converter with LCL Filter
By Stepan BLAHA [View]
[Download]

Abstract: The problem of input saturation in linear-quadratic-gaussian (LQG) control of a single-phase converterwith LCL filter is addressed by design of an anti-windup compensator. Since the full state is not directlyobserved, a Kalman filter observer has been designed. Performance of the proposed control is illustratedon simulation examples under ideal sinusoidal source and source with additional harmonics.

   Design and Analysis of Complex Vector Current Regulators for Modular Multilevel Converters
By Michael SCHUETT [View]
[Download]

Abstract: This paper presents the implementation and dynamic analysis of synchronous frame current regulators for Modular Multilevel Converters (MMC) using complex vectors. This includes the design of the Decoupling Physical Input Cross-Coupling (DPICC) for MMC-topologies. With this, the set of differential equation of the MMC can be transformed into the same format that is used for virtually every other Voltage Source Inverter (VSI) and thus in terms of current control the MMC can be controlled with similar control strategies. Limitations in the performance of common synchronous frame Proportional plus Integral (PI) control techniques are demonstrated. The design of a proportional plus time-weighted accumulation current controller in the discrete time domain is also laid out in this paper.

   High Output Voltage Precision PWM for Modular Multilevel Converters
By Simon FUCHS [View]
[Download]

Abstract: Recently, modular multilevel conterters (MMC) are also considered for medium voltage (MV) applications, where the number of modules and the switching frequency are relatively low compared to high voltage (HV) applications. This effect is amplified even more, if the value of the module capacitances is decreased to reduce cost and volume of the MMC. Large output voltage errors disturb the higher level closed loop control of the MMC significantly, such that control targets (e.g. keeping the circulating current zero) could not be met anymore. This paper analyses the output voltage error induced by the standard level shifted PWM method and proposes three approaches to reduce the error. All four methods are compared with respect to the error for different switching frequencies and arm currents. The effects on the closed loop performance of a current controller are investigated with time domain simulations.

   Improved SV PWM for Dual Inverter with Real-Time Minimization of Converter Power Losses
By Martin VOTAVA [View]
[Download]

Abstract: The proposed control method for dual converters combines two approaches as space vector PWM (SVPWM) and finite control set model predictive control (FCS-MPC). The SVPWM is used for suitable output voltage vectors preselection and the FCS-MPC enables using a mathematical model of the system and a proposed cost function to reduce power losses and to redistribute power losses among transistors. The suitable switching combination utilizing the redundant switching states is selected according to the preselected space vector. That feature is very advantageous in special operation modes appearing e.g. in electric drives for mining hoists and elevators.

   Integrated PFC and series resonant frequency converter analysis and control
By Michael HEIDINGER [View]
[Download]

Abstract: A control algorithm for an integrated power factor correction (PFC) and series resonant converter (SRC) using only two switches is presented, allowing to open loop control the AC input current and the DC output current independently. The theory for this approach is analyzed in time domain and a novel approach for open loop regulation is presented and verified. The software defined power (SDF) control algorithms determines the switching frequency and duty cycle of the converter.

   Lyapunov-based control strategy for precise power sharing and voltage regulation of multi-inverter islanded micro-grids
By Xin HUANG [View]
[Download]

Abstract: A novel Lyapunov function based decentralized control method is proposed for three-phase parallel connected inverters system within islanded micro-grid. A proper voltage regulation and excellent power sharing performance can be well ensured even under unknown line impedance and unbalanced LC filter parameters. Moreover, high reliability and robustness can be guaranteed since no inter-communication among inverters as well as no centralized controller is demanded, which also derives the advantages of scalability and redundancy. The stability of the entire system is ensured by standard Lyapunov method. The implementation is simple and effectiveness without multi-loop controller. The analysis is confirmed via some simulation and hardware-in-the-loop (HIL) experimental results.

   Lyapunov-Function Based Control Method for Three-Phase Grid-Tied Quasi-Z-Source Inverter with LCL Filter
By Hasan KOMURCUGIL [View]
[Download]

Abstract: In this work, a Lyapunov-function based control method for three-phase grid-tied LCL-filtered quasi-z-source source inverters (qZSIs) is proposed. The mathematical model of grid-tied qZSI is modeled in the synchronously rotating dq-frame. Motivated from the energy distribution in qZSI, an energy-like function (referred to as Lyapunov-function) is formed. Then, using Lyapunov's direct method a Lyapunov-function based control is described to guarantee the global stability of the closed-loop system. However, since the Lyapunov-function based control method involves a single-loop, its damping performance is not satisfactory. Therefore, the Lyapunov-function based control approach is modified by adding a second loop involving the capacitor voltage feedback into the control variable. The proposed control method requires the computation of ac-side reference inverter current and capacitor voltages which can be obtained by using the ac-side reference grid currents. The control of dc-side variables is achieved by using the traditional simple boost control technique. The generated shoot through state is combined with the pulse width modulation (PWM) signals generated from the proposed control method. Computer simulation results are presented to show the performance of the proposed control method in the steady-state and transients.

   Neighboring system as black start source and restoration process based on the VSC-HVDC as tie line
By Alev AKBULUT [View]
[Download]

Abstract: Power system restoration takes place where power systems experience a blackout and might be splitted into several islands with limited number of black start units. The main challenge of the restoration process is to keep both frequency and voltage within allowable limits while restoring the network through energizing lines and transformers as well as load pickup. The load pickup scheme is determined by specific conditions to be fulfilled which are in particular lowest allowable frequency nadir and frequency rate of change. In a traditional power system restoration, these variables are a function of network inertia and characteristics of involved generators. This paper proposes the inclusion of VSC-HVDC systems into power system restoration. For this the VSC HVDC systems are equipped with an inertia emulating control system utilizing the electro-static energy stored in the HVDC DC shunt capacitors in an attempt to correct frequency behavior during load pickup. Thus, the restoration process can be accelerated since the variation of the transients can be reduced. In order to demonstrate the effectiveness of the proposed control scheme using VSC-HVDC tie lines as frequency supporting elements during restoration process, a large AC motor start-up event is simulated in the early stage of a restoration process where network inertia is naturally low. A comparison between a large AC motor start-up during restoration process in a system with a hydro power plant as black start unit and that through VSC-HVDC system is made to show the adequacy and superiority of the VSC HVDC system both from the standpoint of converter control and transmission system operation.

   Non-Linear Control and FCS - MPC Applied to Multi - Cell AFE Rectifier with Efficient Behavior in Steady State
By Eduardo ESPINOSA [View]
[Download]

Abstract: One of the major drawbacks of Finite Control Set - Model Predictive Control (FCS - MPC), is the high switching frequency, besides a spread harmonic spectrum. Despite of this, the FCS - MPC provides excellent speed to changes of references and disturbances. In this work we present a control strategy based on FCS - MPC that allows a reduction of the switching frequency in steady state, increasing the efficiency of the converter from 91\% to 94.4\%. This is done by means of a converter status detection (stationary or transient). The above is implemented in a multi - cell AFE rectifier topology. The control strategy is performed by a master - slave loop, in each power cell. El outer loop manages the DC voltage link with nonlinear control, for ensure stable operation of the system. The inner loop controls the input current in each power cells through FCS - MPC. Simulations results show a correct performance of the proposed scheme.

   Optimized Modulation Schemes for the Efficiency Enhancement of Low Voltage Traction Drives
By Stefan STAUDT [View]
[Download]

Abstract: This paper will present different modulation schemes for optimizing the efficiency of low-voltage traction drives. The converter of the vehicle automatically has to select the most suitable modulation or control scheme depending on the present operating point in order to maximize the efficiency of the complete drive train. Furthermore, the functional principles and algorithms of the individual modulation schemes will be presented, as well as the transition between those schemes. Finally, the performance of the different schemes will be proved by dynamic and stationary tests through fully automatized measurement analysis.

   The Grid-Connected Techniques for Input-Series-Output-Series LCL-Type Inverter System
By ZHUWEN HAN [View]
[Download]

Abstract: Input-series-output-series (ISOS) inverter system is very suitable for high input voltage and high output voltage power conversion applications. If the inverter system topology is applied to the grid-connected application, a large-capacity inverter system can be built with multiple small-capacity standardized inverter modules, which will improve system reliability and simplify system design. For the ISOS grid-connected inverter system, there are multiple control targets including power balance between modules and high power factor of the grid current. To solve these issues, a novel control strategy is proposed in this paper. Also, simulation and experimental results are presented to prove the effectiveness of the strategy.

EPE 2017 - DS1f: Standard and Advanced Control techniques for Power Converters I
You are here: EPE Documents > 01 - EPE & EPE ECCE Conference Proceedings > EPE 2017 ECCE Europe - Conference > EPE 2017 - Topic 03: Measurement and Control > EPE 2017 - DS1f: Standard and Advanced Control techniques for Power Converters I
	[return to parent folder]

	A Computationally Efficient Current Controller for Simultaneous Injection of both Positive and Negative Sequences By Zunaib ALI	[View] [Download]
Abstract: Reducing the required processing time of current controllers used in grid side converter (GSC) of renewable energy systems (RES) allows to optimize the limited processing resources and at the same time minimize the cost of the processors required. In addition, the transient behavior of these controllers must be fast and with low overshoot for the GSC to support the grid during off-nominal grid conditions and according to the grid code requirements imposed. For a converter to respond accordingly, the injection of both positive and negative sequences of fundamental current under off-nominal grid conditions is necessary. The work presents a GSC current controller that meets all modern grid requirements expected. It has been developed by introducing two modifications to an existing current controller. Experiments and simulations have been performed to validate the operation of the proposed current controller in terms of complexity and performance. Consequently, the new current controller requires 22\% less processing time and can achieve a faster and more accurate response in order to meet modern grid code requirements under off-nominal conditions.

	A Linear Damping Scheme for Higher Order DC-DC converters Supplying Constant Power Loads in a DC Microgrid By Mahesh SRINIVASAN	[View] [Download]
Abstract: A linear controller is proposed for dc microgrids with SEPIC, Cuk and Zeta power electronic converters supplying constant power loads. The controller is implemented in two stages. During the first stage, also known as active damping stage, limit cycle oscillations are damped by inserting a virtual resistance in series with the input inductor of each of the converters. In the second stage, an integral controller is added to the first stage to compensate for the voltage deviations due to the virtual resistance. The second stage, also known as voltage regulation stage maintains the microgrid voltage within acceptable limits in the event of source and load variation. Linearization and small signal analysis are used to derive stability conditions for the equilibrium points. Simulation and experiments performed on a prototype microgrid are used to verify the proposed control laws.

	Advanced predictive control methods of three-level AC/DC rectifier By Rafal GRODZKI	[View] [Download]
Abstract: This paper describes three modern predictive control methods of three-level AC/DC rectifier. Additionally, it presents a comparison of the methods both in static and dynamic states. Simulation and experimental results confirm that all presented control algorithms ensure a good control quality (low THD) in static states and excellent dynamic properties.

	Anti-windup Compensation of LQG for Single-phase Converter with LCL Filter By Stepan BLAHA	[View] [Download]
Abstract: The problem of input saturation in linear-quadratic-gaussian (LQG) control of a single-phase converterwith LCL filter is addressed by design of an anti-windup compensator. Since the full state is not directlyobserved, a Kalman filter observer has been designed. Performance of the proposed control is illustratedon simulation examples under ideal sinusoidal source and source with additional harmonics.

	Design and Analysis of Complex Vector Current Regulators for Modular Multilevel Converters By Michael SCHUETT	[View] [Download]
Abstract: This paper presents the implementation and dynamic analysis of synchronous frame current regulators for Modular Multilevel Converters (MMC) using complex vectors. This includes the design of the Decoupling Physical Input Cross-Coupling (DPICC) for MMC-topologies. With this, the set of differential equation of the MMC can be transformed into the same format that is used for virtually every other Voltage Source Inverter (VSI) and thus in terms of current control the MMC can be controlled with similar control strategies. Limitations in the performance of common synchronous frame Proportional plus Integral (PI) control techniques are demonstrated. The design of a proportional plus time-weighted accumulation current controller in the discrete time domain is also laid out in this paper.

	High Output Voltage Precision PWM for Modular Multilevel Converters By Simon FUCHS	[View] [Download]
Abstract: Recently, modular multilevel conterters (MMC) are also considered for medium voltage (MV) applications, where the number of modules and the switching frequency are relatively low compared to high voltage (HV) applications. This effect is amplified even more, if the value of the module capacitances is decreased to reduce cost and volume of the MMC. Large output voltage errors disturb the higher level closed loop control of the MMC significantly, such that control targets (e.g. keeping the circulating current zero) could not be met anymore. This paper analyses the output voltage error induced by the standard level shifted PWM method and proposes three approaches to reduce the error. All four methods are compared with respect to the error for different switching frequencies and arm currents. The effects on the closed loop performance of a current controller are investigated with time domain simulations.

	Improved SV PWM for Dual Inverter with Real-Time Minimization of Converter Power Losses By Martin VOTAVA	[View] [Download]
Abstract: The proposed control method for dual converters combines two approaches as space vector PWM (SVPWM) and finite control set model predictive control (FCS-MPC). The SVPWM is used for suitable output voltage vectors preselection and the FCS-MPC enables using a mathematical model of the system and a proposed cost function to reduce power losses and to redistribute power losses among transistors. The suitable switching combination utilizing the redundant switching states is selected according to the preselected space vector. That feature is very advantageous in special operation modes appearing e.g. in electric drives for mining hoists and elevators.

	Integrated PFC and series resonant frequency converter analysis and control By Michael HEIDINGER	[View] [Download]
Abstract: A control algorithm for an integrated power factor correction (PFC) and series resonant converter (SRC) using only two switches is presented, allowing to open loop control the AC input current and the DC output current independently. The theory for this approach is analyzed in time domain and a novel approach for open loop regulation is presented and verified. The software defined power (SDF) control algorithms determines the switching frequency and duty cycle of the converter.

	Lyapunov-based control strategy for precise power sharing and voltage regulation of multi-inverter islanded micro-grids By Xin HUANG	[View] [Download]
Abstract: A novel Lyapunov function based decentralized control method is proposed for three-phase parallel connected inverters system within islanded micro-grid. A proper voltage regulation and excellent power sharing performance can be well ensured even under unknown line impedance and unbalanced LC filter parameters. Moreover, high reliability and robustness can be guaranteed since no inter-communication among inverters as well as no centralized controller is demanded, which also derives the advantages of scalability and redundancy. The stability of the entire system is ensured by standard Lyapunov method. The implementation is simple and effectiveness without multi-loop controller. The analysis is confirmed via some simulation and hardware-in-the-loop (HIL) experimental results.

	Lyapunov-Function Based Control Method for Three-Phase Grid-Tied Quasi-Z-Source Inverter with LCL Filter By Hasan KOMURCUGIL	[View] [Download]
Abstract: In this work, a Lyapunov-function based control method for three-phase grid-tied LCL-filtered quasi-z-source source inverters (qZSIs) is proposed. The mathematical model of grid-tied qZSI is modeled in the synchronously rotating dq-frame. Motivated from the energy distribution in qZSI, an energy-like function (referred to as Lyapunov-function) is formed. Then, using Lyapunov's direct method a Lyapunov-function based control is described to guarantee the global stability of the closed-loop system. However, since the Lyapunov-function based control method involves a single-loop, its damping performance is not satisfactory. Therefore, the Lyapunov-function based control approach is modified by adding a second loop involving the capacitor voltage feedback into the control variable. The proposed control method requires the computation of ac-side reference inverter current and capacitor voltages which can be obtained by using the ac-side reference grid currents. The control of dc-side variables is achieved by using the traditional simple boost control technique. The generated shoot through state is combined with the pulse width modulation (PWM) signals generated from the proposed control method. Computer simulation results are presented to show the performance of the proposed control method in the steady-state and transients.

	Neighboring system as black start source and restoration process based on the VSC-HVDC as tie line By Alev AKBULUT	[View] [Download]
Abstract: Power system restoration takes place where power systems experience a blackout and might be splitted into several islands with limited number of black start units. The main challenge of the restoration process is to keep both frequency and voltage within allowable limits while restoring the network through energizing lines and transformers as well as load pickup. The load pickup scheme is determined by specific conditions to be fulfilled which are in particular lowest allowable frequency nadir and frequency rate of change. In a traditional power system restoration, these variables are a function of network inertia and characteristics of involved generators. This paper proposes the inclusion of VSC-HVDC systems into power system restoration. For this the VSC HVDC systems are equipped with an inertia emulating control system utilizing the electro-static energy stored in the HVDC DC shunt capacitors in an attempt to correct frequency behavior during load pickup. Thus, the restoration process can be accelerated since the variation of the transients can be reduced. In order to demonstrate the effectiveness of the proposed control scheme using VSC-HVDC tie lines as frequency supporting elements during restoration process, a large AC motor start-up event is simulated in the early stage of a restoration process where network inertia is naturally low. A comparison between a large AC motor start-up during restoration process in a system with a hydro power plant as black start unit and that through VSC-HVDC system is made to show the adequacy and superiority of the VSC HVDC system both from the standpoint of converter control and transmission system operation.

	Non-Linear Control and FCS - MPC Applied to Multi - Cell AFE Rectifier with Efficient Behavior in Steady State By Eduardo ESPINOSA	[View] [Download]
Abstract: One of the major drawbacks of Finite Control Set - Model Predictive Control (FCS - MPC), is the high switching frequency, besides a spread harmonic spectrum. Despite of this, the FCS - MPC provides excellent speed to changes of references and disturbances. In this work we present a control strategy based on FCS - MPC that allows a reduction of the switching frequency in steady state, increasing the efficiency of the converter from 91\% to 94.4\%. This is done by means of a converter status detection (stationary or transient). The above is implemented in a multi - cell AFE rectifier topology. The control strategy is performed by a master - slave loop, in each power cell. El outer loop manages the DC voltage link with nonlinear control, for ensure stable operation of the system. The inner loop controls the input current in each power cells through FCS - MPC. Simulations results show a correct performance of the proposed scheme.

	Optimized Modulation Schemes for the Efficiency Enhancement of Low Voltage Traction Drives By Stefan STAUDT	[View] [Download]
Abstract: This paper will present different modulation schemes for optimizing the efficiency of low-voltage traction drives. The converter of the vehicle automatically has to select the most suitable modulation or control scheme depending on the present operating point in order to maximize the efficiency of the complete drive train. Furthermore, the functional principles and algorithms of the individual modulation schemes will be presented, as well as the transition between those schemes. Finally, the performance of the different schemes will be proved by dynamic and stationary tests through fully automatized measurement analysis.

	The Grid-Connected Techniques for Input-Series-Output-Series LCL-Type Inverter System By ZHUWEN HAN	[View] [Download]
Abstract: Input-series-output-series (ISOS) inverter system is very suitable for high input voltage and high output voltage power conversion applications. If the inverter system topology is applied to the grid-connected application, a large-capacity inverter system can be built with multiple small-capacity standardized inverter modules, which will improve system reliability and simplify system design. For the ISOS grid-connected inverter system, there are multiple control targets including power balance between modules and high power factor of the grid current. To solve these issues, a novel control strategy is proposed in this paper. Also, simulation and experimental results are presented to prove the effectiveness of the strategy.