CN106043173A - Real-time power distribution control method for vehicle-mounted hybrid power system - Google Patents

Abstract

The invention discloses a real-time power distribution control method for a vehicle-mounted hybrid power system. In order to get rid of the characteristic that a main energy system dynamic response is slow and deal with the actual dynamic working condition changed quickly and suddenly, key feature parameters of the hybrid power system are estimated on line through a self-adaption updating law, an online updating law of the virtual load current is established on the basis of key feature parameter estimated values, and real-time power distribution is conducted on an energy source. By the adoption of the method, online tracking of dynamic power requirements can be achieved, meanwhile, dynamic restraints of the system are fully considered, the safety of the hybrid power system can be better guaranteed, and the service life of the hybrid power system can be better prolonged.

Description

Real-time power distribution control method of vehicle-mounted hybrid power system

Technical Field

The invention belongs to the field of intelligent control of vehicles, and particularly relates to a real-time power distribution control method of a vehicle-mounted hybrid power system.

Background

With the progress and development of science and technology, some emerging energy systems, such as fuel cell systems, battery power systems and super capacitor systems, are being more and more widely applied to new energy vehicle power systems due to the advantages of high energy conversion rate and zero emission. For specific advantages of different energy systems, in practical applications, two different energy systems are often used as a main energy system and an auxiliary energy system respectively to be mixed to form a vehicle-mounted power system (such as a fuel cell-battery hybrid power system and a battery-super capacitor hybrid power system), so that the dynamic response performance of the system to the load power demand which is frequently suddenly changed and the energy conversion efficiency of the system are improved. In a hybrid system, an energy system as a main energy source generally has a high energy density but a low power density (a low power output response speed), which means that the dynamic response speed of the main energy source is slow. As a complement, the auxiliary energy system has the characteristics of low energy density and high power density (fast power output response speed).

Fig. 1 is a schematic diagram of a hybrid system in which a primary energy source and a secondary energy source are coupled in parallel and then connected to a system bus to provide energy to a load, as contemplated by the present invention. This hybrid system is widely adopted by vehicle-mounted hybrid system developers due to its fast response to high frequency load power demands and low cost.

Under the condition that the auxiliary energy source is a battery power system, the current control method cannot ensure relatively accurate regulation and control of the battery SOC because the state of charge (SOC) of the battery is not measurable. However, the SOC is an important index reflecting whether the battery is overcharged or overdischarged, so that the SOC is important to be adjusted and controlled, and meanwhile, the accurate control of the SOC can provide more freedom for an upper management scheme of the vehicle-mounted hybrid system.

Disclosure of Invention

Aiming at the characteristic of slow dynamic response of a main energy source system and the actual dynamic working condition of quick mutation, the real-time power distribution control is carried out based on an adaptive control theory, the output current of the main energy source is designed, and the real-time power distribution control is further realized, so that the problems of real-time dynamic estimation and tracking of the load power requirement of the vehicle-mounted hybrid power system and the safety protection of a hybrid system are solved.

The technical scheme adopted by the invention is as follows:

1) carrying out online estimation on key characteristic parameters of the hybrid power system by adopting a self-adaptive updating law;

2) and constructing an online updating law of the virtual load current based on the estimated value of the key characteristic parameter, and performing real-time power distribution on the energy system.

The hybrid power system refers to a power system in which two energy systems are coupled in parallel to provide energy for a load, and can be a vehicle-mounted dual-energy (main energy and auxiliary energy) power hybrid power system, such as a fuel cell-battery hybrid power system and a battery-super capacitor hybrid power system. In this type of hybrid system, only the output current of the main energy source can be directly controlled, and is therefore referred to as current-type main energy source.

The key characteristic parameters comprise the equivalent internal resistance of the auxiliary energy source and the equivalent resistance of the load.

The step 1) is specifically to estimate the equivalent internal resistance of the auxiliary energy by adopting a self-adaptive updating law represented by the following formula (1):

wherein,representing the source of the auxiliary energy from the adaptation factor, c₁Representing an auxiliary energy intermediate variable, R₀Representing the actual value of the equivalent internal resistance of the auxiliary energy, R₀Representing an equivalent internal resistance estimated value of the auxiliary energy; gamma ray₁The auxiliary energy source adaptive gain normal number needs to be artificially selected according to experience in practical application; r_0，maxAndrespectively represent equivalent internal resistance R of auxiliary energy₀Both the upper and lower bounds of (1) are positive values; v is the voltage of the bus line,an auxiliary energy open-circuit voltage set value corresponding to an auxiliary energy charge State (SOC); i.e. i_fIn order to assist the energy source current,representing the actual load current i_lAnd the designed virtual load currentDeviation of (i) i

Thereby making the equivalent internal resistance estimated value R of the auxiliary energy₀In the actual value R of the equivalent internal resistance of the auxiliary energy₀Within the upper and lower bounds of (1), i.e.

c_0，min≤R₀≤R_0，max(2)

Wherein, the upper bound R_0，maxGreater than the actual equivalent internal resistance value R of the auxiliary energy₀Upper limit, lower limit R_0，minGreater than the actual equivalent internal resistance value R of the auxiliary energy₀The infimum limit of (1).

In practical application, R_0，maxAnd R_0，minIs selected so as to satisfy the condition R_0，min≤R₀≤R_0，maxIn the case of (3), the actual control effect of the control method is comprehensively considered, which also means that R_0，maxIs selected to be properly larger than the equivalent internal resistance R of the auxiliary energy source₀Of (3), correspondingly, R_0，minIs properly selected to be smaller than the equivalent internal resistance R of the auxiliary energy₀The infimum limit of (1).

The step 1) is specifically as follows:

1.1) obtaining the load equivalent resistance by a method for estimating the load equivalent conductance, wherein the load equivalent conductance is estimated by adopting an adaptive updating law represented by the following formula (3):

wherein q is₂Representing the load adaptation factor, c₂Representing the intermediate variable of the load, G_lTo load the actual value of equivalent conductanceR_lFor the actual value of the equivalent resistance of the load,is load equivalent conductance estimated value; gamma ray₂The load self-adaptive gain normal number needs to be artificially selected according to experience in practical application;representing a virtual load current;and G_l，minIs respectively the actual value G of the equivalent conductance of the load_lBoth the upper and lower bounds of (1) are positive values;representing the actual load current i_lAnd the designed virtual load currentDeviation of (i) i

Thereby enabling load equivalent conductance estimationActual value G of equivalent conductance of load_lWithin the upper and lower bounds of (a) is:

$G_{l,\min }\≤{\hat{G}}_l\≤G_{l,\max }---\left(4\right)$

wherein, the upper bound G_l，maxAnd lower boundary G_l，minIs determined by the actual value R of the load equivalent resistance_lThe upper and lower bounds of (2) are determined, and the following conditions are met:

$G_{l,\max }-\frac{1}{R_{l,\min }},G_{l,\min }-\frac{1}{R_{l,\max }}---\left(5\right)$

wherein,andrespectively representing the actual values R of the load equivalent resistances_lThe upper and lower bounds of (a) and (b),andwith the actual load current i_l(ii) related;

according to the bus current condition of the hybrid vehicle in actual operation, R can be obtained according to the formula_lIs determined.

1.2) obtaining an equivalent conductance estimateThen, using the formulaCalculating to obtain the estimated value of the equivalent resistance of the load

The step 2) is specifically as follows:

2.1) obtaining the virtual load current by using the online update law calculation represented by the following formula (7)

Wherein, α₁Representing the load tracking gain constant, α₂The integral gain constant representing the adjustment of the auxiliary energy source SOC is a normal constant that is set empirically. Accordingly, the method can be used for solving the problems that,referred to as the load-tracking term,referred to as the auxiliary energy source SOC adjustment integral term.

Formula derived virtual load currentIs the low frequency component of the load current and will be used to design the output current reference of the main energy source.

2.2) obtaining the design value of the main energy output current by adopting the following formula (8)

Here, β denotes an auxiliary energy source SOC adjustment proportional gain constant, which is an empirically set normal number.Called the auxiliary energy source SOC adjustment proportion term.

Two main goals for real-time control of a vehicle hybrid system:

1) dynamic tracking of load power requirements is realized;

this aspect is mainly reflected in the equivalent resistance R to the load_lEstimating to obtain an estimated value of the equivalent resistance of the loadThen useThe load tracking items are built in equation (7):

2) the safety indexes of all subsystems in the hybrid power system are met, so that the system is protected and the service life of the system is prolonged.

There are two main aspects to the system security index to be met:

1) the power output response speed of the main energy source is guaranteed to be lower than the upper limit, so that the system safety is protected, and the service life of the system is prolonged.

This criterion is satisfied by the equivalent resistance R of the actual load_lIs achieved because the gain constant y is selected empirically and appropriately₁，α₁，α₁β, an estimate of the equivalent resistance of the load is obtained using the present inventionCan be applied to the actual load equivalent resistance R_lSmoothing is performed, as can be seen from fig. 2. Thus, based onObtainedAlso has smooth property, and can be ensured based onThe obtained design value of the main energy output currentIs below its upper limit.

2) The auxiliary energy source SOC is controlled within a certain range or kept in the vicinity of a set value, thereby preventing the auxiliary energy source from being overcharged and overdischarged.

This index is achieved by: the SOC of the auxiliary energy source and the open-circuit voltage of the auxiliary energy source have one-to-one corresponding functional relationship, and after the corresponding functional relationship between the SOC of the auxiliary energy source and the open-circuit voltage of the auxiliary energy source is obtained, the control of the SOC of the auxiliary energy source can be equivalently realized by controlling the open-circuit voltage of the auxiliary energy source. In view of the fact that the open-circuit voltage of the auxiliary energy source is not measurable in practice, the auxiliary energy source SOC regulation integral term and the auxiliary energy source SOC regulation proportional term are constructed by means of estimation of the equivalent internal resistance of the auxiliary energy source and the bus voltage V, and control over the auxiliary energy source SOC is achieved.

The invention has the beneficial effects that:

the method does not need to accurately identify the model parameters of the system in the actual vehicle-mounted application, thereby greatly reducing the realization difficulty of the method and being beneficial to improving the robustness of the system.

The invention can accurately regulate and control the non-measurable auxiliary energy SOC, reasonably distribute the power requirement of the energy source in the hybrid power system and further meet the dynamic response limit of the power output of the hybrid power system.

The invention can realize the on-line tracking of the dynamic power demand, fully considers the dynamic constraint of the system, and is beneficial to ensuring the safety of the hybrid power system and prolonging the service life.

Drawings

Fig. 1 is a structural diagram of a hybrid system for a vehicle to which the present invention is directed.

FIG. 2 is a graph of the effect of estimating the resistance of a load in Matlab/Simulink simulations.

Fig. 3 is a graph of the effect of control on the auxiliary energy source SOC in Matlab/Simulink simulation, with a target SOC of 0.6.

Fig. 4 is a current response curve for two energy sources in a test experiment.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings.

The following two examples are implemented by the method of the present invention, and the specific implementation process is as follows:

example 1

Since the actual load equivalent resistance and the auxiliary energy SOC are not measurable, the control effect of the invention is verified by building a simulation model of the fuel cell-lithium battery hybrid power system in Matlab/Simulink.

As can be seen from FIG. 2, the load equivalent resistance estimation value provided by the inventionThe sudden change of the actual load equivalent resistance can be smoothed, so that the design value of the main energy output current meeting the response speed constraint can be obtained. At steady state, load equivalent resistance estimation valueApproaching the actual load equivalent resistance, the effectiveness of the proposed usage update law is demonstrated.

Fig. 3 shows the effect of the invention on the control of the auxiliary energy source SOC. The set value of the auxiliary energy SOC is 0.6, and the set value of the auxiliary energy open-circuit voltage is set according to the corresponding relation between the auxiliary energy SOC and the auxiliary energy open-circuit voltageSet to 50.06V. Fig. 3 shows that when the load suddenly changes so that the auxiliary energy source SOC deviates from the set value by 0.6, the auxiliary energy source SOC can be readjusted to be close to the set value by the present invention.

Example 2

The invention has also been applied and validated on a practical fuel cell-lithium battery hybrid golf car. Fig. 4 is a response curve of output current of the fuel cell as the main energy source and the lithium battery as the auxiliary energy source, and it can be seen that the response speed of the main energy source current is relatively slow, and the response speed upper limit of which the change rate is not higher than 10A/s is satisfied. The auxiliary energy source provides the high frequency component of the load energy demand.

The embodiment shows that the method does not need to accurately identify the model parameters of the system in the actual vehicle-mounted application, can accurately regulate and control the non-measurable auxiliary energy SOC and reasonably distribute the power, meets the dynamic response limit of the power output, reduces the implementation difficulty and improves the robustness of the system.

Claims (7)

1. A real-time power distribution control method of a vehicle-mounted hybrid power system is characterized by comprising the following steps:

1) carrying out online estimation on key characteristic parameters of the hybrid power system by adopting a self-adaptive updating law;

2) and constructing an online updating law of the virtual load current based on the estimated value of the key characteristic parameter, and performing real-time power distribution on the energy system.

2. The real-time power distribution control method of the on-vehicle hybrid system according to claim 1, characterized in that: the key characteristic parameters comprise the equivalent internal resistance of the auxiliary energy source and the equivalent resistance of the load.

3. The real-time power distribution control method of the on-vehicle hybrid system according to claim 2, characterized in that: the step 1) is specifically to estimate the equivalent internal resistance of the auxiliary energy source by adopting a self-adaptive updating law, so that the equivalent internal resistance estimated value of the auxiliary energy sourceIn the actual value R of the equivalent internal resistance of the auxiliary energy_ijWithin the upper and lower bounds of (a) is:

$R_{0,\min }\≤{\hat{R}}_0\≤R_{0,\max }$

wherein, the upper bound R_0，maxGreater than the actual equivalent internal resistance value R of the auxiliary energy_ijUpper limit, lower limit R_0，minGreater than the actual equivalent internal resistance value R of the auxiliary energy_ijThe infimum limit of (1).

4. The real-time power distribution control method of the on-vehicle hybrid system according to claim 3, characterized in that: the adaptive updating law adopts the following formula:

wherein q is₁Representing the source of the auxiliary energy from the adaptation factor, c₁Representing an auxiliary energy intermediate variable, R_ijPresentation aidThe actual value of the equivalent internal resistance of the energy source,representing an equivalent internal resistance estimated value of the auxiliary energy; gamma ray₁Is the auxiliary energy self-adaptive gain normal number; r_0，maxAnd R_0，minRespectively represent equivalent internal resistance R of auxiliary energy_ijUpper and lower bounds of (a); v is the voltage of the bus line,is an auxiliary energy open-circuit voltage set value; i.e. i_fIn order to assist the energy source current,representing the actual load current i_lAnd the designed virtual load currentThe deviation of (2).

5. The real-time power distribution control method of the on-vehicle hybrid system according to claim 2, characterized in that: the step 1) is specifically as follows:

1.1) obtaining the equivalent resistance of the load by a method for estimating the equivalent conductance of the load, wherein the equivalent conductance of the load is estimated by adopting a self-adaptive updating law, so that the estimated value of the equivalent conductance of the load is obtainedActual value G of equivalent conductance of load_lWithin the upper and lower bounds of (a) is:

$G_{l,\min }\≤{\hat{G}}_l\≤G_{l,\max }$

wherein, the upper bound G_l，maxAnd lower boundary G_l，minIs determined by the actual value R of the load equivalent resistance_lThe upper and lower bounds of (2) are determined, and the following conditions are met:

$G_{l,\max }-\frac{1}{R_{l,\min }},G_{l,\min }-\frac{1}{R_{l,\max }}$

wherein R is_l，maxAnd R_l，minRespectively representing the actual values R of the load equivalent resistances_lSupremum and infimum of (c);

1.2) obtaining an equivalent conductance estimateThen, using the formulaCalculating to obtain the estimated value of the equivalent resistance of the load

6. The real-time power distribution control method of the on-vehicle hybrid system according to claim 5, characterized in that: the adaptive updating law adopts the following formula:

wherein q is₂Representing the load adaptation factor, c₂Representing the intermediate variable of the load, G_lFor actual value of equivalent conductance of load, R_lFor the actual value of the equivalent resistance of the load,is load equivalent conductance estimated value; gamma ray₂Is the load adaptive gain normal;representing a virtual load current; g_l，maxAnd G_l，minIs respectively the actual value G of the equivalent conductance of the load_lUpper and lower bounds of (a);representing the actual load current i_lAnd the designed virtual load currentThe deviation of (2).

7. The real-time power distribution control method of the on-vehicle hybrid system according to claim 2, characterized in that: the step 2) is specifically as follows:

2.1) obtaining the virtual load current by adopting the online updating law calculation expressed by the following formula

Wherein, α₁Representing the load tracking gain constant, α₂Indicating an auxiliary energy state of charge (SOC) adjustment integral gain constant;

2.2) obtaining a design value of the output current of the main energy source by adopting the following formula

Where β represents the auxiliary energy source SOC adjustment proportional gain constant.