How to plot multiple `pzmap`s in the same figure

I want to print 9 `pzmap`s in one figure in 9 separate plots (3 rows * 3 columns)

I tried something like:

```python
plt.subplot(3, 3, 1)
control.pzmap(tf1)

plt.subplot(3, 3, 2)
control.pzmap(tf2)

plt.subplot(3, 3, 3)
control.pzmap(tf3)

# etc..
```

But it doesn't work. It seems that this reuses the same plot