The CVCF inverter waveform control technology design

In power electronic devices to CVCF power inverter as the core of UPS has been widely applied , its output waveform major technical requirements include low steady-state total harmonic distortion (THD) and fast dynamic response , since non- linear load , PWM modulation process dead and inverter system itself weakly damped and other factors, using the general closed-loop PWM control is not ideal. In this paper, the United States produced by TI TMS320F240DSP for the control chip, using repetitive control system to improve steady-state performance with the introduction of integral control pole configuration to improve the dynamic characteristics of the system , the experimental results show that the scheme can simultaneously achieve high quality of homeostasis and dynamic characteristics.

Repeat controller design

The basic idea of ​​repetitive control from control theory internal model principle , that if you want the control system of a reference instruction to achieve no static error tracking , then the instruction that generated the reference model must be included in the stable closed-loop control system internally.

P (z) is the inverter input and output of the discrete transfer function , is the system control object. Inverter switching frequency than the natural frequency of the LC filter is much higher , the dynamic characteristics determined primarily by the LC filter , obtained by establishing state equation P (z). In this system , L = 0.88mH, C = 60μF, inductor series resistance of 0.4Ω, the switching frequency and the sampling frequency is 10KHz, deduced discrete transfer function is:

Notch filter S1 (z) is mainly used for cancellation of the dc to ac power inverter resonant peak , a second order filter S2 (z) mainly provides high frequency attenuation. Zk links lead compensation filter S (z) and the control target P (z) the total phase lag , Kr is a duplicate control gain . Compensator C (z) to achieve the purpose of the object to the corrected low frequency gain close to 1 , as soon as the high frequency gain is reduced to -26dB or less, and the system in the low frequency band prior to the passage of the total phase shift as small as possible . Take Kr = 0.9, zk = z5, to C (z) P (z) of the Bode diagram in Figure 3 , can be designed to meet that requirement.

Prior to the passage on the concatenation of the control cycle latency links zN action delayed one cycle , which is the period of the detected error information in the next cycle began to affect the amount of control . Aspects of the introduction of cycle delay is mainly due to the system contains advanced aspects zk, if this system is to be able to physically realize , there must be a delay links pole placement

Repeat inverter control effectively improve steady-state performance , but poor dynamic response . In fact, the natural dynamic characteristics of the inverter good reason

CVCF inverter waveform based control design

In power electronic devices to CVCF pure sine wave inverter  s the core of UPS has been widely applied, its output waveform major technical requirements include low steady-state total harmonic distortion (THD) and fast dynamic response, since non-linear load, PWM modulation process dead and inverter system itself weakly damped and other factors, using the general closed-loop PWM control is not ideal. In this paper, the United States produced by TI TMS320F240DSP for the control chip, using repetitive control system to improve steady-state performance with the introduction of integral control pole configuration to improve the dynamic characteristics of the system, the experimental results show that the scheme can simultaneously achieve high quality of homeostasis and dynamic characteristics.

Repeat controller design

The basic idea of ​​repetitive control from control theory internal model principle, that if you want the control system of a reference instruction to achieve no static error tracking, then the instruction that generated the reference model must be included in the stable closed-loop control system internally. First, the system uses the figure of repetitive control block diagram, the following analysis and explanation of its various parts.

P (z) is the dc to ac power inverter input and output of the discrete transfer function, is the system control object. Inverter switching frequency than the natural frequency of the LC filter is much higher, the dynamic characteristics determined primarily by the LC filter, obtained by establishing state equation P (z). In this system, L = 0.88mH, C = 60μF, inductor series resistance of 0.4Ω, the switching frequency and the sampling frequency is 10KHz, deduced discrete transfer function is:

Notch filter S1 (z) is mainly used for cancellation of the inverter resonant peak, a second order filter S2 (z) mainly provides high frequency attenuation. Zk links lead compensation filter S (z) and the control target P (z) the total phase lag, Kr is a duplicate control gain. Compensator C (z) to achieve the purpose of the object to the corrected low frequency gain close to 1, as soon as the high frequency gain is reduced to-26dB or less, and the system in the low frequency band prior to the passage of the total phase shift as small as possible. Take Kr = 0.9, zk = z5, to C (z) P (z) Bode diagram

Single-phase full-bridge series resonant inverter control method used

Amplitude control is achieved by adjusting the DC voltage source (inverter input) voltage Ud (Phase voltage circuit can be used, you can add a chopper circuit composed of inductance and capacitance filter circuit to adjust the output power to achieve the purpose is the output power by the sine wave inverter input voltage regulation, the phase-locked loop (PLL) to complete the phase between the current and voltage control, in order to ensure a large output power factor.

This method has the advantage of simple control, the disadvantage is that the circuit complex, larger.

3.2 pulse frequency modulation (PFM) method

Pulse frequency modulation method is achieved by changing the operating frequency of the inverter, thereby changing the output impedance of the load in order to achieve the purpose of regulating the output power.

From the impedance characteristic of the series resonant load

Impedance characteristics

Shows that the impedance of the series resonant load inverter working with the frequency (f) and change. For a constant output voltage, when the operating frequency and the larger the load resonant frequency deviation, the higher the output impedance, the output power is smaller, and vice versa.

Pulse frequency modulation major drawback is the operating frequency of the power changing the adjustment process, also will cause the skin depth is changed, in some applications such as surface hardening, the change of the skin depth will have a greater effect of heat treatment impact, which in demanding applications is not allowed. However, due to pulse frequency modulation method is very simple, it can be considered in the following cases to use it:

1) If the load on the operating frequency range is not strictly limited, then the frequency must be tracked, but the phase difference in the resonant state does not exist.

2) If the load is higher Q values, or power adjustment range is not large, a smaller frequency deviation can achieve the power adjustment requirements.

3.3 pulse density modulation (PDM) method

Pulse density modulation method by controlling the pulse density, in fact, is the control of the energy supplied to the load time to control the output power. The control principle shown in Figure 2.

Control schematics

This control method is the basic idea is: Assuming a total of N power adjustment unit, in which the M power adjustment unit in the inverter output power to the load; while the remaining N-M units within the dc to ac power inverter is stopped, load energy in the form of natural oscillations gradually decay. Output pulse density of M / N, so that the output power of the pulse density just linked up. Therefore, the density can be changed by changing the pulse output power.

Pulse density modulation method main advantages are: output frequency is essentially the same, switching losses are relatively small, easy to implement digital control, more suitable for open-loop applications.

Pulse density modulation method main disadvantages are: the output power of the inverter frequency is not exactly equal to the natural resonant frequency of the load, in the case of closed loop power is needed, the work stability is poor. Because each oscillation state recover from the natural decay to the output power of the state to re-lock the operating frequency, then the system may be out of control. Therefore, the temperature of the power loop or closed loop case, the stability of the work is not good. Another drawback is its power regulation characteristics are not ideal, was a step way power adjustment.

3.4 resonant pulse width modulation (PWM) method

In Figure 3, the resonance pulse width modulation is achieved by changing the two pairs of the switch drive signal to change the phase difference between the output voltage in order to achieve the purpose of regulating the power. Manipulation of the control circuit is in phase with the original two-side switches (S1, S2), (S3, S4) shifted between a drive signal phase angle, such that the output voltage of the alternating positive and negative voltage is inserted between a zero value, so long as the change in phase angle can change the output voltage rms, and ultimately achieve the purpose of regulating the output power.

JiaYuGuanShi is a typical industrial city, for a high proportion of heavy industry

The imbalance of the third industry, the internal industrial structure is unreasonable, if you want to change this situation, pays special attention to the third industry is imperative.

In order to achieve the third industry development efficiency, JiaYuGuanShi give full play to this year in all kinds of large-scale activities of brand effect, further intensify propaganda promotion, improve service levels, extend sine wave inverter chain, try your best to increase potential of mining industry.

Accelerate the third industry, major projects, pays special attention to the GuanCheng and around the Great Wall protection, the world cultural heritage monitoring center, and the world cultural heritage protection and display engineering construction of key projects, actively push forward the western comprehensive trading market, workers palace of renovation project.

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A large section will drive the investment boom

Highlight massiness culture merged into China merchants

Making the whole. In the mode of innovation investment, vigorously carrying out JiaYuGuanShi industrial investment and park, innovative beyond the chamber of commerce in directional investment, leading enterprises driving clustering, through careful selection and elaborate the JiaYuGuanShi investment project library and provides a solar battery production, the application of photovoltaic dc to ac power inverter system integration and interconnection controller and inverter production methods, automatic tracking of 60 projects, such as street light controller for investors to choose.

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He also notes that in 2012, jiayuguan through holding all kinds of festivals, successfully set up investment promotion platform.