Abstract
This paper describes a design approach to a control system of power supply for high-voltage electrochemical processes such as plasma electrolytic oxidation (PEO) or high-voltage anodising (HVA), which require alternating polarisation pulses up to 750 V and a typical current density of 50–500 mA/cm2. Complex characteristics of the electrochemical system response on applied polarisations (positive or negative) cause necessity of precise control of polarising pulse shapes for better process operation and its understanding. A device performs cycle-by-cycle pulse-width modulation (PWM) control, including feedback based on digital analysis of the instantaneous current and/or voltage output, and the desired pulse waveform stored in memory for each output polarity. The output stage has four states corresponding to positive or negative pulses, as well as open- or short-circuit conditions, with respect to an electrochemical cell. A fully programmable controller allows one to generate arbitrary waveforms, as well as their sequences, by means of “regime designer” software. Moreover, a smart feedback system can provide adaptation of the next pulse parameter from analysis of the process prehistory. For instance, this approach allows one to separate main electrochemical process (coating formation) and diagnosis of the phenomenon through introduction of high-voltage triangular voltage sweep pulse within a pause of the main process, which is normally carried out under a current control.
Highlights
IntroductionHigh-voltage electrochemical processes such as plasma electrolytic oxidation (PEO), micro-arc oxidation (MAO), microplasma oxidation (MPO), or high-voltage anodising (HVA) allow one to form ceramic-like functional coatings on so-called valve metals (Mg, Al, Ti, Zr, Nb, Ta, etc.) [1,2,3]
High-voltage electrochemical processes such as plasma electrolytic oxidation (PEO), micro-arc oxidation (MAO), microplasma oxidation (MPO), or high-voltage anodising (HVA) allow one to form ceramic-like functional coatings on so-called valve metals (Mg, Al, Ti, Zr, Nb, Ta, etc.) [1,2,3].They originated from conventional anodising by application of high-voltage polarisations (300–700 V)that caused local electrical breakdowns of the formed oxide film
The additional analogue-to-digital conversions (ADC) input was used for acquisition of the intensity of light (L, a.u.) produced by microdischarges (Figure 12b) with the BPW21 photodiode loaded to a 10k resistor
Summary
High-voltage electrochemical processes such as plasma electrolytic oxidation (PEO), micro-arc oxidation (MAO), microplasma oxidation (MPO), or high-voltage anodising (HVA) allow one to form ceramic-like functional coatings on so-called valve metals (Mg, Al, Ti, Zr, Nb, Ta, etc.) [1,2,3]. Both voltage and current control modes allow one to extract additional information from current–voltage interrelation in respect of light emission [22,43,44,45], response of the system to a single step, analysis of relaxation [46,47,48,49,50,51], diagnosis of the electrochemical system by average values of short pulse series [52], etc All these diagnostic approaches operate with rectangular pulses or pulses with sharp edges; it is extremely difficult to extract real current–voltage characteristics caused by the processes conjugated with coating formation, rather than recharging of internal or parasitic capacitance. The design process included analysis of the typical PEO load behaviour, a description of the pulse shaping procedure and software, and experimental examination of the prototype
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