File size: 1,708 Bytes
f5dbfe6 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 | import numpy as np
import matplotlib.pyplot as plt
# Simulation parameters
R = .1 # Resistance in ohms
L = .001 # Inductance in henries
Vdc = 350.0 # DC supply voltage
f_pwm = 25e3 # PWM frequency in Hz
current_setpioint = 50.0 # Setpoint for current controller
bemf = 40.0 # Back EMF voltage
t_stop = 2e-3 # Simulate for 2 ms
dt = .1e-6 # Time step of .1 microsecond
MAX_DUTY_CYCLE = 0.95
MIN_DUTY_CYCLE = 0.00
# Time array
time = np.arange(0, t_stop, dt)
# Storage for current
current = np.zeros_like(time)
I = 0.0 # initial current
# Derived parameters
T_pwm = 1.0 / f_pwm
old_t_mod = 0
duty_cycle = 0
for i in range(1, len(time)):
t = time[i]
# Determine if we are in the "on" or "off" portion of the PWM cycle
# Use modulo operation to find where we are within a PWM period
t_mod = t % T_pwm
if t_mod < old_t_mod:
applied_voltage = Vdc - bemf
a = (applied_voltage/R) - current_setpioint
b = (applied_voltage/R) - I
total_time = -(L/R) * np.log(a/b)
duty_cycle = min(MAX_DUTY_CYCLE, max(MIN_DUTY_CYCLE, total_time/T_pwm))
pass
old_t_mod = t_mod
on_time = duty_cycle * T_pwm
off_time = T_pwm - on_time
if t_mod < on_time:
V = Vdc - bemf
else:
V = -bemf
# Compute dI/dt
dIdt = (V - R*I) / L
dIdt *= 1
# Integrate using Euler method
I = I + dIdt * dt
# Store current
current[i] = I
# Plotting
plt.figure(figsize=(10, 5))
plt.plot(time*1e4, current, label='Current through inductor')
plt.title('PWM driven RL load')
plt.xlabel('Time (ms)')
plt.ylabel('Current (A)')
plt.grid(True)
plt.legend()
plt.show()
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