System and method for active/reactive power compensation
Systems, methods, and devices for use with active/reactive power control in power conditioning systems. To provide quick active/reactive power control by way of a grid-connected inverter, an estimator estimates the P and Q coefficients based on an instantaneous power from the grid-connected inverter. The estimator receives grid current and voltage and estimates of the P and Q coefficients are used with reference P and Q values to determine whether active or reactive power needs to be injected to the grid. The P coefficient is a DC offset of the instantaneous power of the grid and the Q coefficient is the coefficient of a sine component of the instantaneous power.
1. A control system for controlling a power inverter, the system comprising:
an active power subcontroller, said active power subcontroller receiving a difference between a reference P value and an estimated P value, an output of said active power subcontroller being used to determine voltage and current outputs of said power inverter;
a reactive power subcontroller, said reactive power subcontroller receiving a difference between a reference Q value and an estimated Q value, an output of said reactive power subcontroller being used to determine voltage and current outputs of said power inverter;
an active/reactive power estimator for estimating said estimated P value and said estimated Q value based on outputs of said power inverter, said estimator receiving voltage and current outputs of said power inverter;
wherein said estimated P value is an estimate of a P value and said reference P value is a reference for said P value, said P value being a DC offset of an instantaneous power of a power grid to which said power inverter is connected and said estimated Q value is an estimate of a Q value and said reference Q value is a reference for said Q value, said Q value being a coefficient of a sine component of said instantaneous power of said power grid;
and wherein said estimator estimates said estimated P value and said estimated Q value by implementing:
{tilde over (p)} g,inst =p g,inst −[{circumflex over (θ)}−{circumflex over (P)} cos(2ω t )+ {circumflex over (Q)} sin(2ω t )]
{dot over ({circumflex over (P)})}=−γ 2 cos(2ω t ) {tilde over (p)} g,inst
{dot over ({circumflex over (Q)})}=γ 3 sin(2ω t ) {tilde over (p)} g,inst
where
p g,inst is an instantaneous power for said grid;
{circumflex over (P)} is an estimated value for said P value;
{circumflex over (Q)} is an estimated value for said Q value;
{tilde over (P)} g,inst is an estimation error for said instantaneous power for said grid;
{circumflex over (θ)} is an estimated value for an unknown variable θ;
{dot over ({circumflex over (P)})} is a derivative of said estimated value for said P value;
γ 2 and γ 3 are system dependent coefficients;
{dot over ({circumflex over (Q)})} is a derivative of said estimated value for said Q value.
2. A control system according to claim 1 wherein said control system operates in an autonomous mode such that said reference P value and said reference Q value are based on conditions of said power grid.
3. A control system according to claim 1 wherein said control system operates in a non-autonomous mode such that said reference P value and said reference Q value are received from an external source.
4. A control system according to claim 3 wherein said external source is a communications unit for receiving communications from outside a power conditioning system which includes said control system.
5. A control system according to claim 1 wherein said power inverter is a bi-directional AC/DC converter.
6. A control system according to claim 1 wherein said power inverter is coupled to said power grid such that said power inverter provides active power to said grid when necessary to stabilize said power grid.
7. A control system according to claim 1 wherein said power inverter is coupled to said power grid such that said power inverter provides reactive power to said grid when necessary to stabilize said power grid.
8. A control system according to claim 1 wherein said estimator further implements:
{tilde over (ξ)} 1 =p g,inst −{circumflex over (ξ)} 1
{dot over ({circumflex over (ξ)})} 1 =2ωξ 1 +2ω{circumflex over (ξ)} 2 +2ω{circumflex over (θ)}+α 1 {tilde over (ξ)} 1
{dot over ({circumflex over (ξ)})} 2 =−4ωξ 1 −2ω{circumflex over (ξ)} 2 +α 2 {tilde over (ξ)} 1
{dot over ({circumflex over (θ)})}=2ωγ 1 {tilde over (ξ)} 1
where
{tilde over (ξ)} 1 is an estimation error for instantaneous grid power;
ξ 1 =P g,inst ;
{circumflex over (ξ)} 1 is an estimated value for said instantaneous grid power;
{dot over ({circumflex over (ξ)})} 1 is a derivative of said estimated value for said instantaneous grid power;
{dot over ({circumflex over (ξ)})} 2 is a derivative of an estimate for ξ 2 ;
{circumflex over (ξ)} 2 is an estimated value for an intermediate variable ξ 2 ;
α 1 , α 2 and γ 1 are observer gain coefficients;
{circumflex over (θ)} is an estimated value of an unknown variable θ;
{dot over ({circumflex over (θ)})} is a derivative of an estimated value for said unknown variable θ.
9. A control system according to claim 1 wherein said estimator receives outputs of a phase-locked loop module, said outputs of said phase-locked loop module being used by said estimator to estimate said estimated P value and said estimated Q value.
10. A control system according to claim 1 further comprising a first summation block for subtracting said estimated P value from said reference P value, and an output of said first summation block being received by said active power subcontroller.
11. A control system according to claim 10 further comprising a second summation block for subtracting said estimated Q value from said reference Q value, and an output of said second summation block being received by said reactive power subcontroller.
12. A control system according to claim 11 wherein said reference P value and said reference Q value are derived from said voltage and current outputs of said power inverter.
13. A control system according to claim 11 wherein said reference P value and said reference Q value are derived from data received from a communications unit.