Christoph Haederli - Les thèses en ligne de l'INP - Institut National ...

3-L DC Link ML Converter Properties 63
1. Standard PD PWM or SVM with new CM injection concepts and subsequent state
optimization for capacitor control for medium and high switching frequencies (chapter 4
and paragraph 6.1)
2. Optimal sequence SVM, with only 3 vectors to be applied per modulation period,
applicable to low switching frequency applications (paragraph 6.2)
4.4.6 Modulator implementation and experimental verification
Different modulator implementations have been used in the frame of this thesis. The
modulator for the experimental verification of the SMC schemes (5.3.4) has been implemented
totally on an FPGA with a generic PD PWM modulator and a subsequent state machine choosing
the appropriate converter states (Figure 53). This modulator runs on a DSP based control system
by LAPLACE [66]. The optimal sequence modulator introduced in 6.2 runs on an industrial control
system (AC 800PEC by ABB). The code is implemented in MATLAB/Simulink. OPCoDe
(Optimized Process of Code Development) generates the runtime code automatically from the
Simulink and Matlab files.
Figure 54, ABB’s AC 800PEC, core of the OPCoDe system
A third separate modulator is running on the same OPCoDe system, is implemented also in
Matlab but includes multiple modulators: all CB PWM schemes according to the paragraphs 5.1
and 5, as well as the SVM scheme with virtual vectors introduced in paragraph 6.1. These schemes
are seamlessly integrated and can changeover from one to the other scheme in operation anytime.
This feature is required by the hysteresis controller proposed in paragraph 7.3. The CB part of the
modulator has asymmetric sampling, PD double edge modulation. Different PD PWM schemes
(e.g. 3 rd harmonic injection or CSPD PWM) can be chosen. Switching times are pre-calculated
(rather than determined by an actual reference carrier comparison) and communicated to the
FPGA for gate signal generation. In this way, the gate signal generation on the FPGA can easily be
shared with the SVM schemes, which are based on the NTV method. A calculation method with
non perpendicular coordinates similar to [34], [67] or [68] is used for fast calculation. The same
implementation of the modulator (same m-file) is used for simulation and experimental verification,
which ensures good correspondence between simulation and real operation of the converter.
A low power 5-L ANPC prototype (6kVA) has been used for all experimental verification
regarding ANPC. The prototype has been specified for control investigations (rather than high
power density) providing easy access to all relevant signals and flexible configuration of DC link
and flying capacitors.