Predictive control method and system of grid-connected converter based on structurally adaptive extended state observer

A predictive control system of a grid-connected converter based on a structurally adaptive ESO, comprising:

• a data obtaining module, configured for obtaining data of a grid current and a grid voltage and converting the data to data in a dq coordinate system;
• a voltage vector selecting module, configured for calculating a selected voltage vector based on a voltage in the dq coordinate system;
• an adaptive state observing module, configured for adaptively inputting a current in the dq coordinate system to a parallel ESO, a cascade ESO, or a hybrid cascade-parallel ESO, so as to obtain a current predicted current value and estimated total disturbance;
• a two-step predicting module, configured for carrying out a two-step grid current prediction based on the current predicted current value, the estimated total disturbance and the selected voltage vector;
• a grid-connected converter controlling module, configured for taking minimizing a cost function as a control target, so as to obtain an optimal voltage vector based on a two-step grid current prediction result, and carrying out switching control of the grid-connected converter;
• wherein adaptively inputting the current in the dq coordinate system to a parallel ESO, a cascade ESO, or a hybrid cascade-parallel ESO, so as to obtain a current predicted current value and estimated total disturbance includes:
• determining whether a d-axis current component in the dq coordinate system is a starting current or a disturbance current;
• if yes, firstly predicting the current predicted current value and the estimated total disturbance by using the parallel ESO according to the current in the dq coordinate system;
• after ½ cycle, predicting the current predicted current value and the estimated total disturbance by using a hybrid cascade-parallel ESO with a first set bandwidth;
• after another ½ cycle, predicting the current predicted current value and the estimated total disturbance by using a hybrid cascade-parallel ESO with a second set bandwidth;
• after another ½ cycle, predicting the current predicted current value and the estimated total disturbance by using the cascade ESO;
• after setting a delay for a plurality of cycles, returning to obtaining the d-axis current component in the dq coordinate system again;
• if not, firstly predicting the current predicted current value and the estimated total disturbance by directly using the cascade ESO according to the current in the dq coordinate system;
• wherein carrying out a two-step grid current prediction based on the current predicted current value, the estimated total disturbance and the selected voltage vector includes:
• the current predicted current value is a result obtained after adaptively inputting to the parallel ESO, the cascade ESO or the hybrid cascade-parallel ESO, that is, a result obtained in a first prediction step;
• a result of a second current prediction step is as follows:
• i
• ^
• dq
• (
• k
• +
• 2
• )
• =
• i
• ^
• dq
• (
• k
• +
• 1
• )
• +
• T
• S
• [
• ∑
• j
• =
• 1
• 3
• F
• ^
• j
• (
• k
• +
• 1
• )
• +
• α
• ⁢
• u
• ⁡
• (
• k
• )
• ]
• wherein k is sampling instant, Ts is sampling time, îdq(k+1) is the result obtained in the first prediction step and is a predicted estimated value of the grid current at the next sampling instant (k+1), α is a constant control input gain, u(k) is a voltage of the converter caused by a switching state Sabc(k);
• {circumflex over (F)}j(k+1) represents a predicted disturbance value of the first step at a jth sub-frequency level ω0j, wherein j∈[1,2,3];
• wherein taking minimizing a cost function as the control target, so as to obtain the optimal voltage vector, the cost function includes:
• J
• =
• [
• i
• ^
• dq
• (
• k
• +
• 2
• )
• -
• i
• dq
• *
• (
• k
• +
• 2
• )
• ]
• 2
• wherein îdq(k+2) is a predicted estimated value of the grid current at sampling instant (k+2), and
• i
• dq
• *
• (
• k
• +
• 2
• )
• is a reference value of the grid current at the sampling instant (k+2),
• wherein each switching state voltage of a three-phase two-level grid-connected converter is evaluated in the cost function;
• and a switching state corresponding to a voltage udq with the minimum value of the cost function is applied as the switching state Sabe of the grid-connected converter.