EPE Association: EPE 2017 - DS2c: Topic 03: Standard and Advanced Control techniques for Power Converters II

EPE 2017 - DS2c: Topic 03: Standard and Advanced Control techniques for Power Converters II
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 - DS2c: Topic 03: Standard and Advanced Control techniques for Power Converters II

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   A Novel Neutral Point Potential Balance Control of Three-Level Converters Based on The Search Optimization Method of Dual Degree of Freedom
By Bo GUAN [View]
[Download]

Abstract: Even though the neutral point potential (NPP) balance problem of three-level neutral-point-clamped(NPC) converters can be solved by the traditional methods based on nearest-three-vectors (NTV)PWM, a low frequency fluctuation in the NPP will appear, which makes the capacitor reductionbecome hard. The dual modulation waves method is used to overcome the low frequency fluctuation,but it is an open-loop way, which will cause the drift voltage problem of the NPP and increase theswitching frequency. Moreover, the control ability of the neutral point current is limited since thezero-sequence voltage is fixed. By removing the limit of the zero-sequence voltage and introducing anew degree of freedom, a novel NPP control of three-level NPC converters based on the searchoptimization is proposed in this paper. Fuzzing the boundary between the NTV-PWM and the dualmodulation waves method, the proposed method realizes two modulations by a unified way. It cansolve the low frequency fluctuation problem, reduce the switching frequency and extend the controlability of the neutral point current simultaneously by choosing the optimal dual degrees of freedom.Comparing the NTV-PWM, the dual modulation waves method and the proposed method, thesimulation results verify the correctness and effectiveness of the proposed method.

   An Effective Feed-Forward Approach for Suppressing Low Order Current Harmonics of Grid-Connected VSCs
By Mohamad Amin GHASEMI [View]
[Download]

Abstract: Improper control of grid-connected Voltage Source Converters (VSCs) in harmonically polluted grid results in flowing low order current harmonics into the grid. In other words, the VSC behaves as harmonic load from grid point of view. VSC output filters cannot eliminate these polluted currents, since they are designed for switching high frequency harmonics. From the approaches presented in this regard, feed forward compensation of grid voltage is the common method which decouples the VSC behavior from the grid voltage including its harmonics. However, time delay in control of VSC imposed by computations and PWM switching affect performance of this method. In this paper, a modified feedforward scheme considering the time delay of VSC is proposed to eliminate these harmonic currents. Performance of the proposed method is verified through simulations.

   Comb filters for harmonics control in grid connected power electronic converters applications
By Tomasz CHMIELEWSKI [View]
[Download]

Abstract: This paper presents the method of current higher harmonics control for grid connected powerelectronic converter by means of a digital comb filter application. The proposed method providesmultiple harmonics compensation and simple implementation. The Proportional-Resonant (PR)control was complemented with appropriately tuned comb filter which resulted in reduced mitigationof output current harmonics and reduced THD. Two types of comb filters have been verified as aharmonic compensator namely feedback and feedforward structures. The compensator based on thefeedback comb filter included additional casual FIR low-pass filter for increased robustness. ProposedFIR filter is casual therefore its implementation on the digital microprocessors is greatly facilitated.The experimental results have demonstrated the effectiveness of proposed solution for grid connectedconverter operating in a network with distorted supply voltage.

   Control of the Current Source Rectifier using Finite Control Set Model Predictive Control
By Agata GODLEWSKA [View]
[Download]

Abstract: Compared with the typical three-phase voltage converter, the current source rectifier is very interesting front-end converter because of its buck-type nature and low electromagnetic interferences. However, it includes LC filter, which causes distortions of the grid currents and enhances the reactive power. Proper control algorithm can fix those disadvantages. The chosen option is finite control set model predictive control. It is a comprehensive tool because of the flexibility in cost function establishment. Simulation results proof good performance of the system in normal and distorted supplying voltage conditions. Distortions are reduced and unity power factor is obtained. Concluding, the method can be used in low voltage DC loads feeding, battery charging and active power filtering applications.

   Current THD Reduction for High-Power-Density LCL-Filter-Based Grid-Tied Inverter Operated in Discontinuous Current Mode
By HOAI NAM LE [View]
[Download]

Abstract: This paper proposes a discontinuous current mode (DCM) feedback current control for a sin-gle-phase grid-tied inverter in order to minimize a LCL filter without worsening total harmonic distortion (THD) of a grid current. In DCM, there are two nonlinearities occurring in the transfer functions; the first nonlinearity occurs in the duty-ratio-to-current transfer function which wors-ens the current command response, whereas the second nonlinearity occurs in the disturbance-to-current transfer function which reduces the disturbance effect. In the proposed DCM current control, the first nonlinearity is compensated by utilizing the duty ratio at the previous calcula-tion period in order to achieve the same control performance of the current command response as in continuous current mode. Meanwhile, the second nonlinearity is utilized in order to reduce the disturbance effect when the LCL filter with a small impedance is applied. Furthermore, a design procedure of the LCL filter is introduced under the condition that the impedance of the LCL filter can be minimized without worsening the grid current THD by applying the proposed DCM control. A 1-kW 100-kHz inverter with several LCL filters of different impedances (3.0\%, 0.6\% and 0.04\%) is constructed in order to confirm the operation of the proposed DCM current control. As a result, the grid current THD is reduced from 8.5\% to 3.7\% at rated load. Further-more, the inductor volume is reduced by 77.0\%, whereas the converter loss is reduced by 17.1\%.

   Enhanced Control of the Torque Ripple in a PMSM Drive with Variable Switching Frequency
By Fernando RAMIREZ [View]
[Download]

Abstract: In this paper a control scheme for a PMSM drive that keeps the torque ripple within predefined limits ispresented. The electromagnetic torque is assumed to be proportional to i1q, which is measured by usingSigma-Delta Analog to Digital Converters with a very high sampling rate, so the actualripple of the torque can be obtained and controlled in an enhanced way. The measurement results showthe effectiveness of the control.

   Finite Control Set Model Predictive Control for Grid-Connected NPC Converter with LCL Filter and novel resonance damping method
By Piotr FALKOWSKI [View]
[Download]

Abstract: This paper presents two implementations of finite control set model predictive methods applied to AC/DC converters with an LCL filter. The LCL filter in contrast to L filter offers higher level of harmonics attenuation. However, despite its advantages, LCL filter can cause a strong resonance in grid current. The proposed control strategy, i.e. PCi2uc-3L uses basic advantages of the MPC methods - multivariable control. On the contrary to active damping scheme, PCi2uc-3L ensures higher quality of grid current (low THDi value). The methods were also compared with a predictive control algorithm of an AC/DC converter with L filter. The control performance was tested in the simulation model and validated experimentally by measurements.

   Grid Voltage-Sensorless Control of Direct Current Controlled Multilevel Converters
By Martin HOFMANN [View]
[Download]

Abstract: The accurate control of the line current, robust and dynamic behaviour even under distorted grids and the behaviour on other faults are important requirements for grid connected inverter systems. This paper presents a sensorless grid voltage determination system in combination with an direct current control method optimized for multilevel inverters.

   Model Predictive Current Control Method with Constant Switching Frequency for Single-Phase Voltage Source Inverters
By SANGSHIN KWAK [View]
[Download]

Abstract: Model Predictive Control (MPC) method offers advantages of easy implementation and fastdynamics. However Model predictive control method has variable switching frequency, which makesdesign of the output filter difficult for power converter. Despite the problems of MPC algorithm, thereare little methods to fix the switching frequency using MPC algorithm in power converter. Therefore,this paper proposes constant switching frequency with MPC algorithm, which method simply selectsthe optimal voltages and divides the optimal voltages in one-sampling period. The performance isproved comparing to the conventional method and carrier based method in experimental results withaverage switching frequency for single-phase VSI.

   Multi-oscillatory current control with anti-windup for grid-connected VSCs operated under distorted grid voltage conditions
By Andrzej GALECKI [View]
[Download]

Abstract: The paper presents a state-feedback current controller with damped oscillatory terms designed for three-phase grid-connected voltage source converters under distorted grid voltage conditions. The paper focuses on a synthesis of an anti-windup mechanism for the LQ current controller based on an active clamping method for the proportional-integral path and the adjusting damping factor mechanism (ADFM) of the oscillatory terms. A newly developed ADFM based on a simple moving average method (SMA) has been verified in the numerical and experimental study which results are given.

   On the Stability Criteria for Inverter Current Control Loops with LCL Output Filters and Varying Grid Impedance
By DAVID LUMBRERAS [View]
[Download]

Abstract: The use of LC and LCL filters and grid impedance variations are creating new challenges on the controller design for current control loops of photovoltaic and wind turbine inverters. In the design process, stability criteria such as Bode and revised Bode are commonly used. This paper analyses the limitations of Bode and revised Bode criteria to reliably determine stability and proposes a sufficient and necessary stability criterion, based on the Nyquist criterion, but that makes use of the Bode diagram. The proposed criterion, named generalized Bode criterion, is always reliable and helps the controller design. Relative stability in complex control loops is also studied and a relative stability analysis is proposed. Finally, the generalized Bode criterion and the proposed relative stability analysis are illustrated with a practical example in which a PI is designed in order to guarantee stability and achieve relative stability.

   One-Step Commutation Approach for Direct Converters Based on UCE-Measurement
By Nico REMUS [View]
[Download]

Abstract: This paper proposes a new commutation approach for direct converters with bidirectional switches based on U CE -measurement and verifies the applicability with a commutation scheme for V-connection AC choppers. The practicability is proven experimentally and the current and voltage quality of the one-step commutation is compared with the two-step commutation approach.

   Operation Modes of a High Bandwidth Three Phase Hysteresis Modulator based on Delta Sigma Bitstreams
By Axel KLEIN [View]
[Download]

Abstract: Delta sigma signal processing (DSSP) is a novel signal processing approach based on delta sigma bitstreams. In order to fully utilize the advantages of DSSP, a high bandwidth three phase hysteresis modulator was presented in literature. This modulator directly processes high frequent delta sigma bitstreams. A detailed description of the operation modes, the overmodulation range close to the voltage limit and the voltage utilization in comparison with a conventional space vector pulse width modulator (SVPWM) is presented. This paper focuses on methods to predict the average switching frequency and to derive indicators for different operating modes of the modulator.

   Proportional Gain Changeable Peak Current Mode Control DC-DC Converter
By Yudai FURUKAWA [View]
[Download]

Abstract: The digital control has the attractive capability, for instance, the high-performance function and the energy management capability. On the other hand, there are issues which must be solved for the actual implementation. The proposed method can solve some of them, namely the transient response, the dynamic characteristics and the precision of the controller, with the simple method.

   Reduction of DC-link current harmonics for Three-phase VSI over Wide Power Factor Range using Single-Carrier-Comparison Discontinuous PWM
By Koroku NISHIZAWA [View]
[Download]

Abstract: This paper proposes a novel discontinuous PWM (DPWM) in order to reduce dc-link current harmonics of a voltage source inverter (VSI) over wide load-power-factor range. This modulation method, which requires only one carrier, contributes to a lifetime extension of smoothing capacitors in a motor drive system. Furthermore, by realizing this modulation method with only one carrier, a high cost hardware such as a field-programmable gate array (FPGA) is not necessary. By adding an offset to voltage references of conventional DPWM, and shifting two unclamped voltage references in every half control period, the dc-link current harmonics are reduced even when load power factor changes. It is clarified by experiments that the proposed DPWM reduces the dc-link current harmonics by 18.4\% at most at modulation index of 0.705 and load power factor of 0.819.

   Space Vector Modulation for 3-Level Neutral Point Clamped Inverters using Predictive Control Methods for Neutral Point Balancing
By Alexander LANGE [View]
[Download]

Abstract: In this paper, Finite Control Set Model Predictive Control (FCS-MPC) is used to select the optimal switching sequence when synthesizing a reference space vector for a Three-Level Neutral Point Clamped inverter. The cost function is designed to ensure the selection of a switching sequence which balances the neutral point and keeps switching losses low. Simulations and experimental results prove the performance of the method.

EPE 2017 - DS2c: Topic 03: Standard and Advanced Control techniques for Power Converters II
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 - DS2c: Topic 03: Standard and Advanced Control techniques for Power Converters II
	[return to parent folder]

	A Novel Neutral Point Potential Balance Control of Three-Level Converters Based on The Search Optimization Method of Dual Degree of Freedom By Bo GUAN	[View] [Download]
Abstract: Even though the neutral point potential (NPP) balance problem of three-level neutral-point-clamped(NPC) converters can be solved by the traditional methods based on nearest-three-vectors (NTV)PWM, a low frequency fluctuation in the NPP will appear, which makes the capacitor reductionbecome hard. The dual modulation waves method is used to overcome the low frequency fluctuation,but it is an open-loop way, which will cause the drift voltage problem of the NPP and increase theswitching frequency. Moreover, the control ability of the neutral point current is limited since thezero-sequence voltage is fixed. By removing the limit of the zero-sequence voltage and introducing anew degree of freedom, a novel NPP control of three-level NPC converters based on the searchoptimization is proposed in this paper. Fuzzing the boundary between the NTV-PWM and the dualmodulation waves method, the proposed method realizes two modulations by a unified way. It cansolve the low frequency fluctuation problem, reduce the switching frequency and extend the controlability of the neutral point current simultaneously by choosing the optimal dual degrees of freedom.Comparing the NTV-PWM, the dual modulation waves method and the proposed method, thesimulation results verify the correctness and effectiveness of the proposed method.

	An Effective Feed-Forward Approach for Suppressing Low Order Current Harmonics of Grid-Connected VSCs By Mohamad Amin GHASEMI	[View] [Download]
Abstract: Improper control of grid-connected Voltage Source Converters (VSCs) in harmonically polluted grid results in flowing low order current harmonics into the grid. In other words, the VSC behaves as harmonic load from grid point of view. VSC output filters cannot eliminate these polluted currents, since they are designed for switching high frequency harmonics. From the approaches presented in this regard, feed forward compensation of grid voltage is the common method which decouples the VSC behavior from the grid voltage including its harmonics. However, time delay in control of VSC imposed by computations and PWM switching affect performance of this method. In this paper, a modified feedforward scheme considering the time delay of VSC is proposed to eliminate these harmonic currents. Performance of the proposed method is verified through simulations.

	Comb filters for harmonics control in grid connected power electronic converters applications By Tomasz CHMIELEWSKI	[View] [Download]
Abstract: This paper presents the method of current higher harmonics control for grid connected powerelectronic converter by means of a digital comb filter application. The proposed method providesmultiple harmonics compensation and simple implementation. The Proportional-Resonant (PR)control was complemented with appropriately tuned comb filter which resulted in reduced mitigationof output current harmonics and reduced THD. Two types of comb filters have been verified as aharmonic compensator namely feedback and feedforward structures. The compensator based on thefeedback comb filter included additional casual FIR low-pass filter for increased robustness. ProposedFIR filter is casual therefore its implementation on the digital microprocessors is greatly facilitated.The experimental results have demonstrated the effectiveness of proposed solution for grid connectedconverter operating in a network with distorted supply voltage.

	Control of the Current Source Rectifier using Finite Control Set Model Predictive Control By Agata GODLEWSKA	[View] [Download]
Abstract: Compared with the typical three-phase voltage converter, the current source rectifier is very interesting front-end converter because of its buck-type nature and low electromagnetic interferences. However, it includes LC filter, which causes distortions of the grid currents and enhances the reactive power. Proper control algorithm can fix those disadvantages. The chosen option is finite control set model predictive control. It is a comprehensive tool because of the flexibility in cost function establishment. Simulation results proof good performance of the system in normal and distorted supplying voltage conditions. Distortions are reduced and unity power factor is obtained. Concluding, the method can be used in low voltage DC loads feeding, battery charging and active power filtering applications.

	Current THD Reduction for High-Power-Density LCL-Filter-Based Grid-Tied Inverter Operated in Discontinuous Current Mode By HOAI NAM LE	[View] [Download]
Abstract: This paper proposes a discontinuous current mode (DCM) feedback current control for a sin-gle-phase grid-tied inverter in order to minimize a LCL filter without worsening total harmonic distortion (THD) of a grid current. In DCM, there are two nonlinearities occurring in the transfer functions; the first nonlinearity occurs in the duty-ratio-to-current transfer function which wors-ens the current command response, whereas the second nonlinearity occurs in the disturbance-to-current transfer function which reduces the disturbance effect. In the proposed DCM current control, the first nonlinearity is compensated by utilizing the duty ratio at the previous calcula-tion period in order to achieve the same control performance of the current command response as in continuous current mode. Meanwhile, the second nonlinearity is utilized in order to reduce the disturbance effect when the LCL filter with a small impedance is applied. Furthermore, a design procedure of the LCL filter is introduced under the condition that the impedance of the LCL filter can be minimized without worsening the grid current THD by applying the proposed DCM control. A 1-kW 100-kHz inverter with several LCL filters of different impedances (3.0\%, 0.6\% and 0.04\%) is constructed in order to confirm the operation of the proposed DCM current control. As a result, the grid current THD is reduced from 8.5\% to 3.7\% at rated load. Further-more, the inductor volume is reduced by 77.0\%, whereas the converter loss is reduced by 17.1\%.

	Enhanced Control of the Torque Ripple in a PMSM Drive with Variable Switching Frequency By Fernando RAMIREZ	[View] [Download]
Abstract: In this paper a control scheme for a PMSM drive that keeps the torque ripple within predefined limits ispresented. The electromagnetic torque is assumed to be proportional to i1q, which is measured by usingSigma-Delta Analog to Digital Converters with a very high sampling rate, so the actualripple of the torque can be obtained and controlled in an enhanced way. The measurement results showthe effectiveness of the control.

	Finite Control Set Model Predictive Control for Grid-Connected NPC Converter with LCL Filter and novel resonance damping method By Piotr FALKOWSKI	[View] [Download]
Abstract: This paper presents two implementations of finite control set model predictive methods applied to AC/DC converters with an LCL filter. The LCL filter in contrast to L filter offers higher level of harmonics attenuation. However, despite its advantages, LCL filter can cause a strong resonance in grid current. The proposed control strategy, i.e. PCi2uc-3L uses basic advantages of the MPC methods - multivariable control. On the contrary to active damping scheme, PCi2uc-3L ensures higher quality of grid current (low THDi value). The methods were also compared with a predictive control algorithm of an AC/DC converter with L filter. The control performance was tested in the simulation model and validated experimentally by measurements.

	Grid Voltage-Sensorless Control of Direct Current Controlled Multilevel Converters By Martin HOFMANN	[View] [Download]
Abstract: The accurate control of the line current, robust and dynamic behaviour even under distorted grids and the behaviour on other faults are important requirements for grid connected inverter systems. This paper presents a sensorless grid voltage determination system in combination with an direct current control method optimized for multilevel inverters.

	Model Predictive Current Control Method with Constant Switching Frequency for Single-Phase Voltage Source Inverters By SANGSHIN KWAK	[View] [Download]
Abstract: Model Predictive Control (MPC) method offers advantages of easy implementation and fastdynamics. However Model predictive control method has variable switching frequency, which makesdesign of the output filter difficult for power converter. Despite the problems of MPC algorithm, thereare little methods to fix the switching frequency using MPC algorithm in power converter. Therefore,this paper proposes constant switching frequency with MPC algorithm, which method simply selectsthe optimal voltages and divides the optimal voltages in one-sampling period. The performance isproved comparing to the conventional method and carrier based method in experimental results withaverage switching frequency for single-phase VSI.

	Multi-oscillatory current control with anti-windup for grid-connected VSCs operated under distorted grid voltage conditions By Andrzej GALECKI	[View] [Download]
Abstract: The paper presents a state-feedback current controller with damped oscillatory terms designed for three-phase grid-connected voltage source converters under distorted grid voltage conditions. The paper focuses on a synthesis of an anti-windup mechanism for the LQ current controller based on an active clamping method for the proportional-integral path and the adjusting damping factor mechanism (ADFM) of the oscillatory terms. A newly developed ADFM based on a simple moving average method (SMA) has been verified in the numerical and experimental study which results are given.

	On the Stability Criteria for Inverter Current Control Loops with LCL Output Filters and Varying Grid Impedance By DAVID LUMBRERAS	[View] [Download]
Abstract: The use of LC and LCL filters and grid impedance variations are creating new challenges on the controller design for current control loops of photovoltaic and wind turbine inverters. In the design process, stability criteria such as Bode and revised Bode are commonly used. This paper analyses the limitations of Bode and revised Bode criteria to reliably determine stability and proposes a sufficient and necessary stability criterion, based on the Nyquist criterion, but that makes use of the Bode diagram. The proposed criterion, named generalized Bode criterion, is always reliable and helps the controller design. Relative stability in complex control loops is also studied and a relative stability analysis is proposed. Finally, the generalized Bode criterion and the proposed relative stability analysis are illustrated with a practical example in which a PI is designed in order to guarantee stability and achieve relative stability.

	One-Step Commutation Approach for Direct Converters Based on UCE-Measurement By Nico REMUS	[View] [Download]
Abstract: This paper proposes a new commutation approach for direct converters with bidirectional switches based on U CE -measurement and verifies the applicability with a commutation scheme for V-connection AC choppers. The practicability is proven experimentally and the current and voltage quality of the one-step commutation is compared with the two-step commutation approach.

	Operation Modes of a High Bandwidth Three Phase Hysteresis Modulator based on Delta Sigma Bitstreams By Axel KLEIN	[View] [Download]
Abstract: Delta sigma signal processing (DSSP) is a novel signal processing approach based on delta sigma bitstreams. In order to fully utilize the advantages of DSSP, a high bandwidth three phase hysteresis modulator was presented in literature. This modulator directly processes high frequent delta sigma bitstreams. A detailed description of the operation modes, the overmodulation range close to the voltage limit and the voltage utilization in comparison with a conventional space vector pulse width modulator (SVPWM) is presented. This paper focuses on methods to predict the average switching frequency and to derive indicators for different operating modes of the modulator.

	Proportional Gain Changeable Peak Current Mode Control DC-DC Converter By Yudai FURUKAWA	[View] [Download]
Abstract: The digital control has the attractive capability, for instance, the high-performance function and the energy management capability. On the other hand, there are issues which must be solved for the actual implementation. The proposed method can solve some of them, namely the transient response, the dynamic characteristics and the precision of the controller, with the simple method.

	Reduction of DC-link current harmonics for Three-phase VSI over Wide Power Factor Range using Single-Carrier-Comparison Discontinuous PWM By Koroku NISHIZAWA	[View] [Download]
Abstract: This paper proposes a novel discontinuous PWM (DPWM) in order to reduce dc-link current harmonics of a voltage source inverter (VSI) over wide load-power-factor range. This modulation method, which requires only one carrier, contributes to a lifetime extension of smoothing capacitors in a motor drive system. Furthermore, by realizing this modulation method with only one carrier, a high cost hardware such as a field-programmable gate array (FPGA) is not necessary. By adding an offset to voltage references of conventional DPWM, and shifting two unclamped voltage references in every half control period, the dc-link current harmonics are reduced even when load power factor changes. It is clarified by experiments that the proposed DPWM reduces the dc-link current harmonics by 18.4\% at most at modulation index of 0.705 and load power factor of 0.819.

	Space Vector Modulation for 3-Level Neutral Point Clamped Inverters using Predictive Control Methods for Neutral Point Balancing By Alexander LANGE	[View] [Download]
Abstract: In this paper, Finite Control Set Model Predictive Control (FCS-MPC) is used to select the optimal switching sequence when synthesizing a reference space vector for a Three-Level Neutral Point Clamped inverter. The cost function is designed to ensure the selection of a switching sequence which balances the neutral point and keeps switching losses low. Simulations and experimental results prove the performance of the method.