| Abstract | Mrtvo vrijeme i naponi vođenja su neizbježni u radu pretvarača s modulacijom širine impulsa. Obje pojave utječu na spektar izlaznog napona učinskih pretvarača: naponi vođenja poluvodičkih ventila mogu uzrokovati istosmjernu komponentu napona, dok mrtvo vrijeme smanjuje amplitudu osnovnog harmonika te povećava harmoničko izobličenje izlaznog napona. Utjecaj obje veličine je ovisan o njihovi iznosima, dok je utjecaj mrtvog vremena ovisan i o sklopnoj frekvenciji. Kako bi bilo moguće kompenzirati utjecaj mrtvog vremena i napona vođenja tranzistora i dioda, potrebno je izračunati njihov utjecaj na spektar izlaznog napona pretvarača. Proračun utjecaja mrtvog vremena i napona vođenja na spektar izlaznog napona postojećim metodama je složen, poglavito za diskontinuirane modulacijske signale, kakav je modulacijski signal višerazinskih pretvarača. Postojeće metode predlažu aproksimaciju utjecaja mrtvog vremena na osnovni harmonik, što je nedostatno prilikom proračuna utjecaja na više harmonike. Stoga je osmišljena nova metoda proračuna spektra izlaznog napona pretvarača, koja uključuje utjecaj mrtvog vremena i napona vođenja i proračunati njihove utjecaje. Temeljem rezultata analize je predložen, provjeren i implementiran algoritam kompenzacije utjecaja mrtvog vremena i napona vođenja na izlazni napon pretvarača. Predložena metoda je provjerena na simulacijskom modelu, te implementirana na laboratorijskom modelu diodno pritegnutog trorazinskog pretvarača. Predložena je metoda proračuna spektra, valjana za proizvoljni valni oblik modulacijskog signala i signala nosioca. Analitičkim proračunom je pokazano na koji način mrtvo vrijeme i naponi vođenja utječu na spektar izlaznog napona. Temeljem rezultata proračuna je predložena metoda kompenzacije utjecaja mrtvog vremena i napona vođenja na osnovni harmonik napona. Predložena metoda je potvrđena simulacijskim eksperimentom. Implementirana je na laboratorijskom modelu te ispitana i potvrđena za niske iznose amplitudnog indeksa modulacije i velike iznose trajanja mrtvog vremena, što predstavlja najteže uvjete kompenzacije. Predložena metoda kompenzacije je ispitana simulacijskim eksperimentom te mjerenjima na laboratorijskom modelu za dva valna oblika modulacijskog signala, tri sklopne frekvencije te pet iznosa trajanja mrtvog vremena. Eksperimentalni rezultati su potvrdili kako predložena metoda kompenzacije smanjuje utjecaj mrtvoga vremena i napona vođenja poluvodičkih ventila za sve zadane sklopne frekvencije i sva zadana trajanja mrtvog vremena. |
| Abstract (english) | Dead time and semiconductor voltage drops are an inevitable feature with pulse width modulated power converters. Both influence the power converters output voltage spectrum: semiconductor voltage drops can cause a DC voltage component, whereas dead time causes the fundamental harmonic amplitude to decrease, as well as enhances output voltage THD. Semiconductor voltage drops, if evenly distributed among semiconductor switches, cause only a degradation of the output voltage fundamental harmonic amplitude. If unevenly distributed, they can cause a DC voltage component, which can, in return, cause a large DC current component, in case of a low ohmic impedance load. Dead time is more influential for low amplitude modulation ratios and high frequency modulation ratios. Dead time and semiconductor voltage drops influence on output voltage spectrum must be calculated, in order to compensate their influence. A novel output voltage spectrum analysis method was proposed, based on the fact that a Fourier series of a periodic function is the best possible approximation on it's fundamental period. The proposed method enables determining the Fourier coefficients' integration limits in time domain, which enables incorporating dead time influence. The proposed method is valid for an arbirtary modulation signal and an arbirtary carrier signal waveform, so dead time influence change depending on the load current direction can also be accounted for. The influence different semiconductor voltage drops have on the output current DC component was shown via simulation, for different voltage drop values and distribution combinations. Dead time influence on the output voltage fundamental harmonic amplitude and phase shift was shown via simulation for several amplitude and frequency modulation ratios. The proposed spectrum calculation method was used to show the influence dead time and semiconductor voltage drops have on the output voltage spectrum. The method was tested against a well-known example, the naturally sampled two-level converter sine wave modulation. Dead time influence on the three level neutral point clamped inverter was shown for a modified modulation signal. The modulation signal was modified by injecting a zero-sequence signal, which eliminates the neutral point voltage ripple. An open-loop compensation method for the fundamental output voltage harmonic, based on the analysis results, was proposed. The proposed compensation method was verified via a simulation experiment. This experiment featured three switching frequencies and five dead time durations. All simulations were conducted for a low amplitude modulation ratio, and for both modulation signal waveforms. The proposed method was further tested on a laboratory model with 1200~V/300~A IGBT modules, for two modulation signal waveforms, three switching frequencies and five dead time durations. The proposed compensation method was implemented using fixed point arithmetics. Both simulation and experimental results show that the proposed compensation method successfully compensates the dead time and semiconductor voltage drops influences on the output voltage fundamental harmonic. The proposed compensation method is straightforward, easy to implement and resource inexpensive. The compensation method was tested for multiple modulation signal waveforms, and for multiple dead time durations. It was shown that the proposed compensation method successfully compensates dead time and semiconductor voltage drops for a variety of modulation signal waveforms, switching frequencies and dead time durations. |
