The control of rectifier and inverter has been tested on an experiment platform shown in Fig. 3.8. A strong power supply is able to supply stable three-phase AC and DC voltages, thus it is used as the AC grid in Case I and Case II, which also provides a stable DC voltage source in Case II. An IGBT converter is used with an inductive filter between the power supply and converter. The voltage/current isolators measure the currents and voltages, which are then sent to the dSPACE simulator through analogue/digital (A/D) blocks.
The dSPACE simulator has quad-core AMD processors (DS1006) and operates with DS5202 ACMC board, which is capable of generating high-frequency PWM signals and providing high-speed A/D interfaces. The IGBT converter, inductive filter, measurement units, and power supply, etc. all are from the Lab-Volt com- pany, which provides various equipments with the user-friendly interfaces, accurate system parameters, and reliable hardware protections. The DC bus of the IGBT converter is protected by using a 100Ωdamping resistor with 1000 W rated power, which is connected to the damping circuit built in Lab-Volt IGBT converter to avoid potential damages caused by over-voltage or over-current in the DC bus.
The control algorithm is compiled and downloaded into the dSPCAE simulator shown in Fig. 3.8 by using the measured active and reactive power, and DC volt- age as inputs from the equipment, such that the I/O interface of dSPACE simulator enables the real-time sampling of inputs from measurements and output control sig- nals. Then the PWM signals are generated with various duty cycles as controller outputs to the IGBT converter. Furthermore, the sampling frequency fs and the
PWM frequencyfPWM with the space vector PWM (SVPWM) implemented in the
dSPACE simulator are given in Table 3.3. The proposed controller is embedded into the dSPACE simulator and connected to the VSC with IGBT converter, which is compatible with Matlab/Simulink.
Two separate experiments are carried out on this platform to implement POAPC on the rectifier and inverter, respectively. The experiment configuration of Case I is illustrated in Fig. 3.9, a resistive load is connected to DC side to test the control performance when the active power flows from the AC grid to the DC bus. The
3.6 Experiment Results for Rectifier Controller and Inverter Controller 68
Three-phase Power Supply
Filter IGBT
Converter Load
Figure 3.9: Experiment configuration of Case I. Table 3.3: System parameters used in Case I.
Rated active power P0=300 W Rated rms voltage V0 =30 V
Rated rms current I0= 10A Rated frequency f0=50 Hz
DC line voltage Vdc1=100 V Filter inductance L1=60 mH
PWM frequency fPWM =2 kHz Sampling frequency fs =10 kHz
DC capacitance C1 = 1320µF Load resistance RL=1200Ω
Table 3.4: System parameters used in Case II.
Rated active power P0 =300 W Rated rms voltage V0 = 30V
Rated rms current I0 = 10A Rated frequency f0= 50Hz
DC line voltage Vdc2=60 V Filter inductance L2=60 mH
PWM frequency fPWM =2 kHz Sampling frequency fs =10 kHz
DC capacitance C2= 1320µF
hardware parameters are listed in Table 3.3. The experiment configuration of Case II is shown in Fig. 3.10, a DC power supply is used to provide the regulated DC voltage to ensure the IGBT converter can operate properly. The hardware parameters are listed in Table 3.4.
Three-phase Power Supply IGBT Converter Filter DC Power Supply
Figure 3.10: Experiment configuration of Case II.
vb va vc Sa Sa Sb Sb Sc Sc ′ ′ ′ Vdc
Figure 3.11: The structure of an IGBT converter.
The structure of an IGBT converter is shown in Fig. 3.11, which can be modelled
as va =Vdc ( Sa− 13(Sa+Sb+Sc) ) vb =Vdc ( Sb− 13(Sa+Sb+Sc) ) vc=Vdc ( Sc− 13(Sa +Sb+Sc) ) iDC =iaSa+ibSb+icSc (3.6.1)
where va, vb and vc are the three-phase voltages, ia, ib and ic are the three-phase
currents, respectively. iDC is the current through the DC capacitor. Sa, Sb, and Sc
are the switch signals (1 is on and 0 is off) [137].
3.6 Experiment Results for Rectifier Controller and Inverter Controller 70 tional PWM or sinusoidal pulse width modulation (SPWM) techniques, the space vector modulation (SVM) can increase 15% more of the maximum output voltage and reduce the switching times.
Based on SVM and ignoring the resistances in the steady-state, the minimum DC voltage must satisfy the following inequality to ensure the IGBT converter is controllable and can work properly as [137]
Vdci ≥
√
3 √
(usdi +ωLiiqi)2+ (usqi−ωLiidi)2, i= 1,2 (3.6.2)
At last, the IGBT converter is used as the DC/AC converter, the anti-parallel diodes are combined with the IGBT converters such that it can be operated as either a rectifier or an inverter.