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Direct-load-current feedback in a peak-current-mode-controlled buck converter is used to obtain near zero open-loop output impedance. Theoretical formulation is derived utilizing two-port modeling technique. The ideal unity-feedback output impedance would resemble the output impedance of a voltage-mode-controlled buck converter but without the reso...
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... power supply (DPS) architectures are commonly used to deliver the energy to the electronic loads both in system level and on-board level [1], [2] as illustrated in Fig. 1. The switched-mode converters are demanding as a load and may deteriorate the dynamics of the supply-side converters. The negative incremental input resistance of a converter is typically considered as the main element, which may cause the undesired adverse effect [3]. Quite often the converters used in on- board applications are ...
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Citations
... To minimize the negative impact on the voltage control loop, it is necessary to reduce output impedance [16], or even obtain zero output impedance to achieve load invariant control [17] [18]. Load current feed-forward is applied in [19], [20], and [21] to improve the transient performance during load change. In this paper, differential current feedback is applied to help minimize the converter output impedance. ...
In this project to develop a reconfigurable electrical grid emulator, a Hardware Test-Bed (HTB) is being developed that emulates large scale power system generators and loads by using power electronic converters. Source converters in the HTB system are designed to emulate generators. A synchronous generator model is implemented in the converter to calculate the voltage references in the dq axis, and a voltage controller is added to achieve zero steady state error. A traditional cascade controller with inner current control and outer voltage control brings additional output impedance to the generator model, and causes voltage tracking error during transients. To minimize the controller output impedance and eliminate controller influence on the generator model, a single voltage loop with current differential feedback is proposed in this paper. Combined with rescaled generator parameters, circulating current elimination, and dead time compensation, simulation and experiments are performed in the HTB. The results verify the effectiveness of the controller and demonstrate the dynamic generator emulator behavior.
... According to sound scientific theory, the load interactions are reflected into the converter dynamics via the open-loop internal output impedance [14], [15]. Therefore, it may be obvious that the perfect load invariance at arbitrary load may be Manuscript achieved only, if the open-loop internal output impedance is designed to be zero [9], [13]. It was demonstrated in [15] that even the zero open-loop output impedance does not necessarily ensure load invariance, because the load may interact the converter dynamics via the internal input impedance at the presence of the source impedance. ...
... A theoretically consistent treatment of the effect of outputcurrent feedforward in a regulated converter is presented in [13]. It defines explicitly the required conditions for theoretical zero output impedance at open loop based on the well-known transfer functions of the associated converter. ...
... The dynamical effect of output-current-feedforward with a unity gain in a peak-current-mode-controlled (PCMC-OCF) buck converter is treated in this paper. The consistent theoretical basis has been provided earlier in [13]. The theoretical predictions are proved by means of experiments both in frequency and time domain. ...
The paper investigates the effect of unity-gain output-current-feedforward in a peak-current-mode-controlled (PCMC) buck converter. A consistent theoretical basis is provided showing that the unity-gain feedforward can improve significantly the load invariance and transient performance of a PCMC buck converter. The nonidealities associated to the scheme would, however, deteriorate the obtainable level of invariance. The nonidealities can be maintained at acceptable level, and therefore, the scheme would provide a viable method to reduce significantly the load interactions as well as improve the load-transient response. The theoretical predictions are supported with comprehensive experimental evidence both at frequency and time domain as well as comparisons between three different buck converters
... This agreement is also used in [14] to explain peculiarities in the EMI-filter interactions observed in [13]. It is also clear that a converter with a very small open-loop output impedance would be essentially insensitive to load interactions, (10), as demonstrated in [25]. ...
... The buck converter shown in Fig. 5 was investigated under VMC, PCM, and PCM with output-current-feedforward (OCF) [25] control in CCM to provide dynamical information to support the theoretical observations discussed in Section 3. The same power stage was used for the different converters, and the control systems were designed to provide close to equal internal dynamics (i.e. control bandwidth E11 kHz, PME501) as shown in Fig. 6. ...
... The output-current sensing resistor of the PCMC-OCF converter was slightly increased so that the output-current feedforward and the inductor-current feedback were in mismatch [25]. The same load transient as that shown in Fig. 7 was applied. ...
The characterisation of regulated converters is addressed to enable the assessment of the stability, performance, supply and load interactions as well as transient responses. A canonical model of a converter is proposed and used to create a set of parameters that are able to fully describe the dynamics associated with a converter and therefore can be used to predict the dynamical behaviour of the converter to in changes in source and load interactions. System theory is used to develop methods to study the internal stability of cascaded subsystems such as an electromagnetic interference filter, load and converters. A framework is established that allows the evaluation of different converter topologies under different operation and control modes
... System theory is applied to define the internal and input-output stability conditions. A buck converter under VMV, PCMC, and PCMC with output-current-feedforward (OCF) [18] in CCM and a VMC buck converter in discontinuous operation mode (DCM) are used for obtaining experimental data on the input filter interactions. ...
The paper investigates the effects of EMI filter in the dynamics of a buck converter. It is shown theoretically that the EMI filter may increase significantly the load sensitivity of the voltage-mode-controlled converter but the peak-current-mode-controlled converter is quite insensitive to the EMI filter interactions. Experimental validations are carried out using a buck converter under three different control modes - voltage-mode, peak-current-mode and output-current-feedforward peak-current-mode control. The investigations show that the phenomenon causing the instability under peak-current-mode control is the negative-resistor¿oscillation (NRO) phenomenon, and confirm also the excess EMI-filter sensitivity of the voltage-mode controlled converter.
... The paper will show that definitively. As a consequence, the real load invariance may be achieved only utilizing methods, which reduce the open-loop unterminated output impedance as discussed in [15]. The rest of the paper is organized as follows: The load-interaction formalism is derived and discussed in Section 2. Experimental evidence on load interactions is provided in Section 3 using a voltage-modecontrolled (VMC) buck converter as an example. ...
... The equation (5) explicitly defines that the impedance-type interactions would be reflected via the unterminated open-loop output impedance into the dynamics of the converter. If the open-loop output impedance is zero, the converter would be totally insensitive to load interactions but in practice such a condition is impossible to be accomplished [15]. (5) is a similar minorloop gain as defined in [16], and consequently, the stability and performance of the converter cannot be concluded by using it only. ...
... The conditions for zero output impedance [15] can be derived by using the control-block diagram shown in Fig. 9, where 2 s R is the output-current-sensing resistor, i H , the output-current-feedback gain and a G the gain between the control voltage and duty ratio. According to Fig. 9, we can compute the affected output dynamics to be as shown in (6). ...
The effect of load impedance on the dynamics and performance of a regulated converter is investigated. Theoretical formulation is derived utilizing two-port modelling technique. It is definitively shown that the load interactions are reflected into the converter dynamics via the internal open-loop output impedance. At the frequencies, where the loop gain is much higher than unity, the internal closed-loop output impedances acts as a boundary for the control-bandwidth reduction. The loop gain is always affected, whenever the internal open-loop output impedance is equal or greater than the load impedance. The converters are sensitive especially to the capacitive and resonant-type loads. The sensitivity is dependent on control mode, and cannot be much reduced by means of basic controller design
The method of using output-current-feedforward (OCFF) control to realize zero output impedance is widely applied in Buck converter. However, it is found that the converter may have stability problems with this method. The OCFF controller's transfer functions of basic DC/DC converters are calculated when different current (inductor current, load current) feedforward control is used in this paper There is a negative feedback loop existing in this model as OCFF control is applied and this loop may cause instability. The system stability of Buck converter with different current feedforward control is analyzed. The theories are verified by simulation and experiment results of Buck converter.
The use of distributed power supply (DPS) systems is continuously growing in powering different electronic systems and equipment. The systems compose of regulated switched-mode converters, which typically operate in a cascaded configuration constituting a dynamically demanding constellation prone to instability and performance degradation. It is well known that the origin of the interactions is the different impedances distributed within the system. The mechanism and characterizing parameters causing the source-reflected interactions is investigated in this paper both theoretically and experimentally using a buck converter under voltage-mode (VM), peak-current-mode (PCM) and input-voltage-feedforward (IVFF) control. The reflected interactions would be eliminated if the forward-voltage transfer function can be made zero but in practice such a condition cannot be fully achieved. The investigations show that the VM-controlled convert is very sensitive to the source-reflected interactions
