180 PRZEGLĄD ELEKTROTECHNICZNY (Electrical Review), ISSN 0033-2097, R. 87 NR 8/2011 Indrek ROASTO 1 , Dmitri VINNIKOV 1 , Tanel JALAKAS 1 , Ryszard STRZELECKI 2 Tallinn University of Technology (1), Electrotechnical Institute/Gdynia Maritime University (2) Digital Current Mode Control Algorithms for High-Power Half-Bridge DC/DC Converters Abstract. Digitally controlled systems have many well known advantages in comparison to analogue systems e.g. programmability, higher flexibility and modularity, fewer components, lower sensitivity to noise and environment conditions. Theoretically, all analogue control algorithms can be digitalized. But from practical point of view the digitalization often ends up with some major difficulties, which will noticeable limit or even prevent the application of the digital control algorithm. In this paper some of the problems connected to the digitalization are discussed and solutions are proposed. As a result, two new digital current mode control algorithms for high-power, high-voltage half-bridge DC/DC converters are proposed, simulated and experimentally verified. Streszczenie. Cyfrowe systemy sterowania posiadają liczne znane zalety w porównaniu z systemami analogowymi, np. programowalność, wyższą elastyczność funkcjonalną i modułowość budowy, mniejszą liczba komponentów oraz wrażliwość na warunki otoczenia. Teoretycznie wszystkie algorytmy analogowe można zdigitalizować, lecz z praktycznego punktu widzenia często wiąże się to z istotnymi trudnościami, ograniczającymi lub nawet uniemożliwiającymi stosowanie algorytmu cyfrowego. W artykule omówiono niektóre problemy związane z digitalizacją oraz przedstawiono sposoby ich rozwiązania. Zaproponowano dwa nowe cyfrowe algorytmy sterowania wysokonapięciową półmostkową przetwornicą DC/DC, zweryfikowane symulacyjnie i eksperymentalnie. (Cyfrowe algorytmy sterowania półmostkowych przetwornic DC / DC dużej mocy ze sprzężeniem prądowym). Keywords: digital current mode control, average current mode control, peak current mode control, digital control systems, half-bridge converters. Słowa kluczowe: sterowanie cyfrowe ze sprzężeniem prądowym, sterowanie ze sprzężeniem względem wartości średniej prądu, cyfrowe systemy sterowania, przekształtniki półmostkowe. Introduction The last ten years in power electronics have seen only minor changes and novelty in the field of converter topologies. On the other hand, developments in semiconductor components have been tremendous. Thus, modern trends in power electronics are directed to the implementation of well-known topologies rather than developing new ones. Using new state of the art components, conventional converter topologies can be used more efficiently and for much higher power levels. The recent efforts in the field of power electronics semiconductors are especially interesting for high-power (HP) and high-voltage (HV) applications where the voltage blocking capability of components has always been a major issue. In order to achieve the needed voltage blocking capability traditionally many low voltage components are connected in series but, as a result, the number of components and the complexity of a control system will increase, which reduces the efficiency and overall reliability of the converter. Using new generation components the efficiency and the power density of electronic converters and thus, the feasibility of the whole system can be enhanced. Rolling stock applications are a good example where recent achievements of power electronics could be introduced. Regarding to the specific design rule, converters based on the IGBT technology for the catenary voltages of 3.0 kV DC are only possible with IGBTs with the blocking voltage not lower than 6.0 kV. The state of the art 6.5 kV IGBT modules (EUPEC, ABB, IXYS, DYNEX, etc.) recently implemented are basically designed for 3.0 kV DC rolling stock applications with their high demands on reliability concerning thermal cycling capability. Single HV IGBT has the voltage blocking capability two times the nominal catenary voltage level, which copes with the requirements for the rolling stock power electronics. Such transistors offer an attractive possibility to avoid series connection of IGBTs (for proper blocking voltage), providing higher efficiency, power density and reliability than the combined HV switch designs. Thus, the concept of 50 kW rolling stock high-voltage high-power half-bridge DC/DC converter was developed and implemented at the Department of Electrical Drives and Power Electronics of Tallinn University of Technology (Fig. 1, Table 1). Based on simple two-level half-bridge topology with state-of-the-art 6.5 kV/200 A IGBTs, the DC/DC converter has shown an outstanding performance as well as light weight and excellent compactness [1]. Fig.1. Power circuit of the high-voltage high-power half-bridge DC/DC converter Table 1. General specifications of the converter Parameter Value Nominal input voltage U in 3.0 kV DC Minimal input voltage U in,min 2.2 kV DC Maximal input voltage U in,max 4.0 kV DC Nominal output voltage U O 350 V DC Rated output power P O 50 kW Primary inverter switches (T T , T B ) 2 x 6.5 kV 200 A IGBT (INFINEON FZ200R65KF1) Switching frequency f sw 1000 Hz