Set the pole as the origin and the line containing the polar axis as the x-axis to establish a Cartesian coordinate system.
Convert $\rho\sin\theta=2$ into a Cartesian coordinate equation to get the line equation $y=2$. ...(3 points)
Convert $\rho=-2\cos\theta$ into a Cartesian coordinate equation to get the circle equation $(x+1)^2+y^2=1$, which represents a circle with center at $(-1,0)$ and radius $1$. ...(6 points)
Therefore, the distance from the center of the circle $(-1,0)$ to the line $y=2$ is $2$, and the minimum value of $|PQ|$ is $2-1=1$. ...(10 points)

Thus, the minimum value of $|PQ|$ is $\boxed{1}$.