应用C2000设计模块化的升降压电源变换器

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应用C2000设计模块化的升降压电源变换器 [复制链接]

1 Introduction
Bi-directional power flow converters are gaining interest because of popularity of renewable and electric
vehicles. State space averaging method is used to derive a unified model of a buck boost converter and
relevant transfer functions are derived for control of the voltage and current. Digital control using
microcontrollers such as Texas Instruments C2000™ platform is widely used in such applications because
of flexibility of software, which enables implementing current sharing and robust control under varying
conditions easy.
A typical application for such converters is hybrid vehicles, where multiple energy sources are combined
to provide a stable bus for the motor drive, and in case of regenerative breaking, recuperate that energy
by storing it for future use. Depending on storage characteristics of individual storage elements control of
the current or the voltage is desired. For example, the ultra capacitor in the converter, because of its fast
charge and discharge, is used to maintain the bus voltage constant during transients of the drive and
voltage mode control is used (see Figure 1). Whereas, for the battery and the fuel cell elements, the
current control mode is used. A generic model of the power stage is developed using state space
averaging to help analyze control of output voltage, and the input current and MATLAB script is provided
to simulate the power stage





2 Power Stage Definition
To facilitate the model derivation, the power stage is defined as shown in Figure 2. The different
components of the power stage are:
• Input voltage source voltage, Vp
• Input internal source resistance, Rp
• Input source current, ip
• Input and output capacitors, Ci, Co
• Input and output capacitors ESR, RCi, RCo
• Voltage and current in the input and output capacitor, VCi, VCo, iCi, iCo
• Power inductor and DCR of the inductor, L, RL
• Voltage across and current in the inductor, VL, iL
• Output voltage and output load current, Vout, Io
• Power switches Q1 and Q2





3 State Space Modeling
State space averaging is commonly applied to develop models for switched mode power supplies (SMPS).
It is common to choose the energy storage elements as the state of the system, which is current for
inductors and voltage for capacitors. It is noted irrespective of charging or discharging, that is buck or
boost, as the switches Q1 and Q2 are complimentary to each other and there are only two sub-intervals:
State 1 (Q1 on Q2 off) and State 2 (Q1 off, Q2 on). Therefore, a common model can be developed for
both the modes of power flow.



3.1 State Selection
For the DC-DC converter, shown in Figure 2, state (X) , input (Ui) and output (Y) vectors are chosen as
follows:



The energy storage elements are chosen as states (voltage of the capacitor and current in the inductor).
The output load and input voltage are considered as the inputs. The output voltage, input current and the
inductor current are chosen as the controlled variables.




3.1.1 State 1: Q1 ON, Q2 OFF
Figure 3 shows the power stage in State 1. Using KCL and KVL equations at the highlighted nodes,
Equation 1 through Equation 5 can be written.








Re-arranging the equations, the state of the system can be expressed as shown in Equation 6:





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