Low switching frequency hybrid modulation method with high dynamic response

Abstract

The present invention provides a high dynamic response low switching frequency hybrid modulation method, comprising the following steps: S1. Controlling a voltage source converter to work in a PI+SHE-PWM mode in a steady state, and controlling the voltage source converter to have two working modes in a dynamic state: the working mode in dynamic state 1 is an MPC+SVPWM mode, and the working mode in dynamic state 2 is a PI+SVPWM mode, and when the working state is switched from the steady state to the dynamic state, it is first switched to the dynamic state 1, and when the dynamic state is switched to the steady state, it is switched from the dynamic state 2 to the steady state; S2. Determining whether a new current command value is received, if so, determining whether it is switched from the dynamic state 1 to the dynamic state 2, if not, entering step S3, if so, directly switching from the dynamic state 1 to the dynamic state 2; S3. Determining whether the conversion index Stotal of the three phases of the voltage source converter is 0, if so, switching the working mode of the voltage source converter; wherein: Stotal=S Ra +S Rb +S Rc , S Ra is the constraint function of phase A, S Rb is the constraint function of phase B, S Rc is the constraint function of phase C.

Description

Technical Field

[0001] The invention relates to a modulation control technology for a power electronic power converter, and in particular to a low switching frequency hybrid modulation method with high dynamic response. Background Art

[0002] In high-power voltage source converters, in order to obtain good steady-state output performance and high dynamic response at low SF (switching frequency), domestic and foreign scholars have studied the combination of SHE-PWM (selective harmonic elimination pulse width modulation) and FCS-MPC (finite-control-set model predictive control). Some scholars have proposed a hybrid modulation strategy that uses FCS-MPC as an intermediate state between the two steady states of SHE-PWM. In the steady state, PI (proportional integral) + SHE-PWM is used to ensure that satisfactory steady-state output performance can be obtained. Each phase is obtained by directly looking up the SHE-PWM table, avoiding the complex process of vector synthesis. In the transient state, MPC (model predictive control) + SVPWM (spacevector pulse width modulation) is used to achieve high dynamic response.

[0003] The above hybrid modulation strategies all focus on current tracking, which simplifies the cost function and reduces the computational burden. However, using this hybrid modulation is a more suitable solution for engineering applications, but it ignores the problem of smooth switching between different modulation strategies.

[0004] There are two switching levels between PI+SHE-PWM and MPC+SVPWM. One is the switching between SHE-PWM and SVPWM at the modulation level, and the other is the switching between PI and MPC at the control level. For the modulation level, due to different harmonic distributions, improper switching points may deteriorate the output waveform and even cause current shock when switching between SHE-PWM and SVPWM. For the control level, due to the existence of the integral term, the calculation result of the PI controller is related to the past state. When switching from MPC to PI, an incorrect integral value will cause additional dynamic processes and lead to current shock. Both will cause current shocks, which will affect the control performance.

[0005] In view of this, in order to solve the above technical problems, it is urgent to propose a new technical means. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a low switching frequency hybrid modulation method with high dynamic response, which can effectively ensure the smoothness of switching between different working modes of the voltage source converter, thereby effectively avoiding switching current shock and ensuring the control performance of the voltage source converter as well as the steady-state performance and high dynamic response performance of the voltage source converter.

[0007] The present invention provides a low switching frequency hybrid modulation method with high dynamic response, comprising the following steps:

[0008] S1. Control the voltage source converter to operate in a PI+SHE-PWM mode in a steady state, and control the voltage source converter to have two operating modes in a dynamic state:

[0009] The working mode is MPC+SVPWM mode in dynamic 1, and PI+SVPWM mode in dynamic 2. When the working state switches from steady state to dynamic, it switches to dynamic 1 first, and when the dynamic state switches to steady state, it switches from dynamic 2 to steady state.

[0010] S2. Determine whether a new current command value is received. If so, determine whether dynamic 1 is switched to dynamic 2. If not, proceed to step S3. If so, directly switch from dynamic 1 to dynamic 2;

[0011] S3. Determine whether the conversion index Stotal of the three-phase voltage source converter is 0. If so, switch the working mode of the voltage source converter; wherein: Stotal = S Ra +S Rb +S Rc , S Ra is the constraint function of phase A, S Rb is the constraint function of phase B, S Rc is the constraint function of phase C.

[0012] Further, in step S3, the constraint function of phase A is:

[0013]

[0014] Among them: sign is the sign function;

[0015] Where: b + and b- are the tolerance coefficients of harmonic current, i1 is the fundamental current, i hd It is the dominant current harmonic component in the three phases. The smaller its value is, the smaller the impact current is. hd + i1 or b-i1 hd Within the fault tolerance range of <0, the impact current caused by switching is small and switching is possible.

[0016] ​​​Furthermore, the constraint function of the B phase and the C phase are the same as that of the A phase.

[0017] Beneficial effects of the present invention: Through the present invention, the smoothness of switching between different working modes of the voltage source converter can be effectively ensured, thereby effectively avoiding switching current shocks, ensuring the control performance of the voltage source converter and the steady-state performance and high dynamic response performance of the voltage source converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0019] Figure 1 It is a flow chart of the present invention.

[0020] Figure 2 It is a schematic diagram of the operation process of the present invention.

[0021] Figure 3 It is a curve diagram of the relationship between each phase constraint function and the impact current of the present invention. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below:

[0023] The present invention provides a low switching frequency hybrid modulation method with high dynamic response, comprising the following steps:

[0024] S1. Control the voltage source converter to operate in a PI+SHE-PWM mode in a steady state, and control the voltage source converter to have two operating modes in a dynamic state:

[0025] The working mode is MPC+SVPWM mode in dynamic 1, and PI+SVPWM mode in dynamic 2. When the working state switches from steady state (previous steady state) to dynamic, it switches to dynamic 1 first, and when the dynamic switches to steady state, it switches from dynamic 2 to steady state (next steady state).

[0026] S2. Determine whether a new current command value is received. If so, determine whether dynamic 1 is switched to dynamic 2. If not, proceed to step S3. If so, directly switch from dynamic 1 to dynamic 2;

[0027] S3. Determine whether the conversion index Stotal of the three-phase voltage source converter is 0. If so, switch the working mode of the voltage source converter; wherein: Stotal = S Ra +S Rb +S Rc , S Ra is the constraint function of phase A, S Rb is the constraint function of phase B, S Rcis the constraint function of phase C. Wherein: the constraint function of phase B and phase C are the same as those of phase A, that is, the expressions are exactly the same, except that the parameters are parameters in different phases. Through the above method, the smoothness of the switching of different working modes of the voltage source converter can be effectively ensured, so as to effectively avoid the switching current shock, ensure the control performance of the voltage source converter, the steady-state performance of the voltage source converter, and the high dynamic response performance.

[0028] In this embodiment, in step S3, the constraint function of phase A is:

[0029]

[0030] Among them: sign is the sign function;

[0031] Where: b + and b- are the tolerance coefficients of harmonic current, i1 is the fundamental current, i hd It is the dominant current harmonic component in the three-phase. The smaller its value is, the smaller the impact current is. hd + i1 or b-i1 hd Within the fault tolerance range of <0, the impact current caused by switching is small and switching is possible.

[0032] like Figure 2 As shown: the first process: the PI+SHE-PWM mode is used in the steady state 1, and a new current command value is received at time t0. In order to quickly respond to the new current command value, the converter needs to switch to the dynamic 1 (i.e. transient 1) MPC+SVPWM mode; the above process is used for judgment and execution;

[0033] The second process: When dynamic 1 switches to dynamic 2, the switching process adopts MPC+SVPWM to PI+SVPWM. That is, when the operation mode switching instruction is received at time t1, the PI+SVPWM (proportional integral + space vector pulse modulation) mode is introduced as a transition, thereby avoiding the impact current caused by the bandwidth limitation of the PI controller of SHE-PWM, and preparing for the smooth switching of the third process.

[0034] The third process: when switching from dynamic state 2 (ie transient state 2) to steady state 2, the above judgment process is also used.

[0035] like Figure 3 As shown: For the fundamental voltage (u1), ensure that its amplitude and phase are continuous before and after switching to ensure the amplitude and phase continuity of the fundamental current (i1) before and after switching. Secondly, for the dominant current harmonic component i in the three phases hd , the smaller the value, the smaller the impact current.

[0036] ​​​Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A low switching frequency hybrid modulation method with high dynamic response, characterized in that: The following steps are involved: S1. Control the voltage source converter to operate in a PI+SHE-PWM mode in a steady state, and control the voltage source converter to have two operating modes in a dynamic state: The working mode is MPC+SVPWM mode in dynamic 1, and PI+SVPWM mode in dynamic 2. When the working state switches from steady state to dynamic, it switches to dynamic 1 first, and when the dynamic state switches to steady state, it switches from dynamic 2 to steady state. S2. Determine whether a new current command value is received. If so, determine whether dynamic 1 is switched to dynamic 2. If not, proceed to step S3. If so, directly switch from dynamic 1 to dynamic 2; S3. Determine whether the conversion index Stotal of the three-phase voltage source converter is 0. If so, switch the working mode of the voltage source converter; wherein: Stotal = S Ra +S Rb +S Rc , S Ra is the constraint function of phase A, S Rb is the constraint function of phase B, S Rc is the constraint function of phase C.

2. The low switching frequency hybrid modulation method with high dynamic response according to claim 1, characterized in that: In step S3, the constraint function of phase A is: Among them: sign is the sign function; Where: b + and b - are the harmonic current tolerance coefficients, i1 is the fundamental current, i hd It is the dominant current harmonic component in the three-phase. The smaller its value is, the smaller the impact current generated is.

3. The low switching frequency hybrid modulation method with high dynamic response according to claim 1, characterized in that: The constraint functions of phase B and phase C are the same as those of phase A.

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