PSpice For Power Electronics UNIVERSITI TEKNOLOGI MALAYSIA PSpice For Power Electronics Nik Din Muhamad Department of Encon, Faculty of Electrical Engineering, UTM. 11-12/8/04

UNIVERSITI TEKNOLOGI MALAYSIA INTRODUCTION Two types of simulators Used in Power Electronics: CIRCUIT-ORIENTED SIMULATOR e.g. SPICE EQUATION-ORIENTED SIMULATOR e.g. MATLAB: 11-12/8/04

UNIVERSITI TEKNOLOGI MALAYSIA SPICE Originally intended for analyzing IC. Uses iterative Newton-Raphson Algorithm to solve a set of nonlinear equations. The AC analyses are linear and do not use iterative algorithm Digital devices are evaluated using Boolean algebra. 11-12/8/04

UNIVERSITI TEKNOLOGI MALAYSIA SPICE LIMITATIONS The Newton-Raphson algorithm is guaranteed to converge if the equations is continuous and the initial approximation is close enough to the solution. The transient analysis has the additional possibility of unable to converge because the time step required too small due to something in the circuit moving too fast. 11-12/8/04

UNIVERSITI TEKNOLOGI MALAYSIA SPICE LIMITATIONS Computer Hardware Limitation: Voltage and currents are limited to +/-1e10. Derivatives in Pspice are limited to 1e14. The arithmetic used in Pspice is double precision and has 15 digits of accuracy. 11-12/8/04

UNIVERSITI TEKNOLOGI MALAYSIA PSPICE A Three-step Process to use Pspice: Open and draw circuit under Orcad Capture Simulate Plot results using Probe 11-12/8/04

UNIVERSITI TEKNOLOGI MALAYSIA PSPICE Four main types of analysis: Bias point DC Sweep Transient AC Sweep 11-12/8/04

A General Procedure to Use Pspice: UNIVERSITI TEKNOLOGI MALAYSIA A General Procedure to Use Pspice: Open the Orcad Capture Create a new project Load Libraries of parts Choose parts for schematic Specify attributes of the parts Wire the schematic 11-12/8/04

UNIVERSITI TEKNOLOGI MALAYSIA …Continue 7. Grounding the circuit 8. Create a New Simulation Profile 9. Run simulation and display the the results 10. Analyze the results 11-12/8/04

Where are we going today? UNIVERSITI TEKNOLOGI MALAYSIA Where are we going today? Objective: To develop skills of simulation of power electronic systems using Pspice. Emphasis on: DC-DC Converter Systems using averaged and Switched Models. 11-12/8/04

Three Types of Models Commonly Used in Pspice: UNIVERSITI TEKNOLOGI MALAYSIA Three Types of Models Commonly Used in Pspice: Switched Models Large-signal Averaged Models Small-signal models 11-12/8/04

UNIVERSITI TEKNOLOGI MALAYSIA AVERAGING SCENARIO Discrete + Continuous, Nonlinear, Time Variant. Switched Models Averaging Continuous, Nonlinear, Time Invariant. Averaged Models Linearization Continuous, Linear, Time Invariant. DC Models AC Small-signal Models DC characteristics 11-12/8/04

UNIVERSITI TEKNOLOGI MALAYSIA Switched Models Used To simulate the time domain behavior of the actual circuits. Not easy to use in Pspice. Carry too much information about the waveforms. Do not have a DC operating point. 11-12/8/04

UNIVERSITI TEKNOLOGI MALAYSIA Averaged Models: Tracks low frequency behavior, suppresses switching ripples. Still nonlinear but have a DC operating point. Used to predict converter steady-state characteristics and small-signal dynamics. Easy to use in Pspice. 11-12/8/04

UNIVERSITI TEKNOLOGI MALAYSIA Averaged Models Applications: DC Transfer Functions Transient (Large-signal, time domain) phenomena. AC (Small-signal, frequency domain) Transfer Functions 11-12/8/04

UNIVERSITI TEKNOLOGI MALAYSIA Small-signal Models Linear Models. Give analytical results of small-signals dynamics. Used to design controllers. Easy to use in Pspice without any problem. 11-12/8/04

DC-DC Converter Systems UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 DC-DC Converter Systems Discrete Continuous A Mixed System: Discrete Plus Continuous

UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Continuous Approach Make the discrete parts to be continuous through averaging Leave the continuous parts as-is Can be Perturbed and linearized to obtain small signal models.

Direct Circuit Averaging UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Direct Circuit Averaging What is the function of the switch networks in terms of averaged values? Buck Boost DC Transformer Buck-Boost

Direct Circuit Averaging: CCM UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Direct Circuit Averaging: CCM <I1> <I2> 1: d d’: 1 + <V1> - <V2> d’: d d <I1>=d<I2> <V2>=d<V1> <V1>=d’<V2> <I2>=d’<I1> <V1>=(d’/d)<V2> <I2>=(d’/d)<I1> Constraint Eqns.: .

Pspice Implementation: Buck UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Pspice Implementation: Buck Evalue is used to implement the voltage equation Gvalue is used to implement the current equation Duty ratio d is coded into voltage Large signal, nonlinear model suitable for DC, AC, or Transient simulation. Limitation: Topology dependent, valid for CCM only Go To: Buck_Avg and Buck_Sw

Pspice Implementation UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Pspice Implementation Boost Buck-Boost

Buck Converter Example Averaged Vs. Switched Model UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Buck Converter Example Averaged Vs. Switched Model Pspice Transient Analysis LIVE SIMULATION Go to: How to write equations in PSpice,1 2 Good Results, small DC offset due to device models

Boost Converter Example DC Characteristics UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Boost Converter Example DC Characteristics Pspice DC Sweep analysis LIVE SIMULATION DC Transfer function and efficiency.

Buck-boost Converter Example Small-signal control-to-output response UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Buck-boost Converter Example Small-signal control-to-output response Pspice AC Sweep analysis LIVE SIMULATION Will be very useful for controller design

UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Comments DC Transformer is implementation of a large signal, nonlinear averaged model of the switch network. Averaged circuit model of the converter is obtained simply by replacing switching devices with DC Transformer. Linearization and AC small-signal analysis are performed by simulator. DC Transfer Function and Efficiency, can be easily generated for different operating points. Small-signal dynamic responses can be easily generated for different operating points or different sets of parameters. Limitation: Topology dependent, valid for CCM.

Towards Topology Independent: Switch Averaged Model UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Towards Topology Independent: Switch Averaged Model If we rearrange the constraint equations in such a way that we can write the averaged current through diode and the averaged voltage across Mosfet, we can obtain topology independent of Switch Averaged Model. This is because certain converters share the same constraint equations. The constraint equation is what we have done for DC transformer model of Buck-boost with no connection between source (S) and cathode (K). The model can be applied in any two-switch PWM converters e.g. Buck, Boost, Buck-boost, Cuk, SEPIC

Pspice Implementation: Subcircuit Creation CCM1 UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Pspice Implementation: Subcircuit Creation CCM1 ********************************************* * MODEL: ccm1 * Application: two-switch PWM converters * Limitations: ideal switches, CCM only, no transformer * Parameters: none * Nodes: 1: transistor+ (D) 2: transistor- (S) *3: diode cathode (K) 4: diode anode (A) *5: duty ratio (duty) .subckt ccm1 1 2 3 4 5 Et 1 2 value={(1-v(5))*v(3,4)/v(5)} Gd 4 3 value={(1-v(5))*i(Et)/v(5)} .ends CCM1 **********************************************

Combined CCM/DCM: Averaged Switch Model UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Combined CCM/DCM: Averaged Switch Model CCM/DCM Boundary: u = equivalent switch duty ratio

Subcircuit Creation CCM-DCM1 UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Subcircuit Creation CCM-DCM1 ********************************************************** * MODEL: ccm-dcm1 * Application: two-switch PWM converters, CCM or DCM * Limitations: ideal switches, no transformer * Parameters: * L=equivalent inductance (relevant for DCM) * fs=switching frequency * Nodes: * 1: transistor+ (D) 2: transistor- (S) 3: diode cathode (K) * 4: diode anode (A) 5: duty ratio (duty) .subckt ccm-dcm1 1 2 3 4 5 + params: L=1m fs=100k Et 1 2 value={(1-v(u))*v(3,4)/v(u)} Gd 4 3 value={(1-v(u))*i(Et)/v(u)} Ga 0 a value={MAX(i(Et),0)} Va a b Rdummy b 0 1k Eu u 0 table {MAX(v(5), + v(5)*v(5)/(v(5)*v(5)+2*L*fs*i(Et)/v(3,4)))} (0 0) (1 1) .ends CCM-DCM1

Averaged Buck Converter with Feedback UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Averaged Buck Converter with Feedback Averaged PWM Averaged Switch Error Amplifier (Linear) LC Filter + Load (Linear)

UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Averaged Model of PWM Vm Vp Vc Linear Relation

Averaged PWM With Duty Cycle Limiter: Pspice Implementation UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Averaged PWM With Duty Cycle Limiter: Pspice Implementation (0.01,0.01) (0.99,0.99) Vc d Or Etable and Gain Or Etable Only.

Behavior Model of Comparator: Pspice Implementation UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Behavior Model of Comparator: Pspice Implementation (0,0) (200u,5) V(+)-V(-) V(out) Ideal Equations: IF V(+)>V(-) V(out)= High IF V(+)<V(-) V(out)= Low Can also be implemented to error amplifier.

Behavior Model of Error Amplifier: Pspice Implementation UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Behavior Model of Error Amplifier: Pspice Implementation Error Amplifier and comparator share the same I/O relationship. Output Input Type-3 error amplifier: Commonly used for Buck, Boost, and Buck-boost Converters. Note that V(+) and V(-) was interchanged to make connection easier.

UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Buck Converter System: Switched Model Simulation (Pspice Transient analysis) Load Disturbance

UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Buck Converter System: Averaged Model Simulation (Pspice Transient analysis) Load Disturbance

Buck Converter System: Closed loop Pspice AC analysis. UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Buck Converter System: Closed loop Pspice AC analysis. controller Plant H(s) A(s) Zo(s) + - vout vref d vi io C(s) G(s) The stability of the system is given by loop gain, LG. The disturbance rejection performance of the system is given by the closed loop output impedance, Zocl(s) and the closed loop audio-susceptibility, Acl(s).

Buck Converter System: Averaged Model Simulation (Pspice AC analysis) UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Buck Converter System: Averaged Model Simulation (Pspice AC analysis) Zocl(s) Acl(s) Loop gain Place 1V AC Source Closed loop system

Closed Loop Pspice AC Analysis UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Closed Loop Pspice AC Analysis General Rules: Locate AC source at particular locations Set the AC source to any value (1V is fine) Make sure that there are no other AC sources in the system. Check the bias point to make sure that All operating points are OK. Remember that the classical stability criteria take into account the phase reversal (180°).

Closed Loop Pspice AC Analysis: Waveforms Analysis in Probe. UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Closed Loop Pspice AC Analysis: Waveforms Analysis in Probe. Add Trace’s Equations: Loopgain=dB(V(y)/V(x)) Loopphase=P(V(y)/V(x))-180 (Inject 1V AC source in any place in the loop and gives node a name as X at an inject point and Y at a return point ) ZoclGain=dB(V(out)) ; Inject 1A AC source at the output. ZoclPhase=P(V(out)) AclGain=dB(V(out)) ; Apply 1V AC source at the input. AclPhase=P(V(out)) Equations can be written as macros

Other Circuit Examples: Transient Simulation UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Other Circuit Examples: Transient Simulation Sliding Mode Control of A Buck Converter Problematic Part: Hysteretic Comparator

Other Circuit Examples: Transient Simulation UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Other Circuit Examples: Transient Simulation Power Factor Correction of Boost Converter With Hysteretic Controller

UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Simulation Results: Inductor Current Switching Function Input Current

Hands on #1: Buck converter Averaged model UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Hands on #1: Buck converter Averaged model Large signal time domain simulation Parts: VDC, GVALUE, EVALUE, R, L, C Analysis Type: Transient (time domain) Note: Draw on the same page as Hands on #1 for comparison

Hands on # 2: Buck converter switched model UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Hands on # 2: Buck converter switched model Large signal time domain simulation Parts: VDC, VPULSE, IRF150, DBREAK, R, L, C Analysis Type: Transient (time domain) Run to time: 3m Maximum step size: 0.1u

Hands on #3: Boost converter Averaged model UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Hands on #3: Boost converter Averaged model DC Characteristics: Efficiency and DC Gain New Parts: PARAM, ABM Analysis: DC Sweep Primary Sweep: d Parametric sweep: Rind

Hands on #4: Buck-Boost converter Averaged model UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Hands on #4: Buck-Boost converter Averaged model AC Small-signal:control-to-output TF New Parts: NIL Analysis: AC Sweep

Hands on #5: Buck converter Averaged model with FB UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Hands on #5: Buck converter Averaged model with FB AC Small-signal Dynamics Error Amplifier Averaged PWM

Hands on # 6: Buck converter Averaged model UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Hands on # 6: Buck converter Averaged model Large signal time domain simulation Error Amplifier Averaged PWM

Hands on #7: Buck converter Switched model with FB UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Hands on #7: Buck converter Switched model with FB Large signal time domain simulation Error Amplifier Comparator

Simulation Setting: Hands on #1 and #2 UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Simulation Setting: Hands on #1 and #2

Simulation Setting: Hands on #3 UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Simulation Setting: Hands on #3 Primary sweep

Simulation Setting: Hands on #3 UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Simulation Setting: Hands on #3 Parametric sweep

Simulation Setting: Hands on #4 and #5 UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Simulation Setting: Hands on #4 and #5 AC Sweep

Simulation Setting: Hands on #6 and #7 UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 Simulation Setting: Hands on #6 and #7 Time Domain

How to write equations in PSpice ? UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 How to write equations in PSpice ?

UNIVERSITI TEKNOLOGI MALAYSIA 11-12/8/04 In Pspice