CN103248106B - Novel electric automobile battery charger based on single-cycle control strategy - Google Patents

Abstract

The invention discloses a novel electric automobile battery charger based on a single-cycle control strategy, which comprises a three-phase power source connected with an LCL filter, wherein the LCL filter is connected with an input end of a main circuit of a three-phase PWM (Pulse-width Modulation) power converter; a DC output end of the three-phase PWM power converter is connected in parallel with a support capacitor, while a first load and a discharge loop are connected in parallel to the DC output end of the three-phase PWM power converter through a selective switch; and a control system of the three-phase PWM power converter acquires induction current signals of an LCL filter, voltage signals of the connection point of the input end of the main circuit of the three-phase PWM power converter with the LCL filter and DC voltage signals of the support capacitor C and controls the three-phase PWM power converter to operationally output corresponding pulse switch signals. The electric automobile battery charger has the advantages of simplicity in controlling, high response speed, low manufacturing cost, and capability of realizing seamless switch between rectification and inversion.

Description

Based on the electric automobile battery charger of monocycle control strategy

Technical field

The present invention relates to a kind of electric automobile battery charger based on monocycle control strategy.

Background technology

Electric automobile battery charger is nonlinear-load, produces harmonic current when charging, causes voltage distortion.At present, elimination and inhibition current harmonics have become a focus of electric automobile battery charger.

Three-phase PWM power inverter owing to having the advantage such as current on line side sine, power factor are high, energy in bidirectional flow, in electric automobile battery charger, be used widely.The control strategy of three-phase PWM power inverter is had to stagnant ring control, PREDICTIVE CONTROL, vector control, direct Power Control etc., but these control methods all need to adopt dq coordinate transform and SPWM or SVPWM modulation, system is comparatively complicated, and production cost is high.

2. the few and fast response time of monocycle control circuit compact conformation, element used, but occur the limitation of system fluctuation of service under underloading or anti-phase inverter mode, is applied to and on electric automobile battery charger, has a lot of difficulties.

Summary of the invention

Object of the present invention is exactly in order to address the above problem, traditional monocycle control method is improved, a kind of electric automobile battery charger based on monocycle control strategy is provided, have advantages of control simple, fast response time, production cost low, can realize by the seamless switching that is rectified to inversion.

To achieve these goals, the present invention adopts following technical scheme:

A kind of electric automobile battery charger based on monocycle control strategy, comprise three phase mains, three phase mains is connected with LCL filter, and LCL filter is connected with the input of three-phase PWM power inverter main circuit, the DC output end Support Capacitor in parallel of three-phase PWM power inverter; Load simultaneously and discharge loop are in parallel with the DC output end of three-phase PWM power inverter by selector switch; The control system of three-phase PWM power inverter gathers the current signal i of LCL filter inductance _rn, LCL filter and three-phase PWM power inverter main circuit input the voltage signal v of tie point _rnand the d. c. voltage signal U at Support Capacitor C two ends _dc, control the work of three-phase PWM power inverter and export corresponding pulse switch signal.

Described three-phase PWM power inverter major loop adopts the three-phase full-controlled bridge being made up of multiple switching devices.

Described discharge loop comprises the series circuit that the second load and direct current adjustable electric are pressed.

The control system of described three-phase PWM power inverter comprises: multiple rest-set flip-flops, each rest-set flip-flop end, Q end are all distinguished corresponding with the pulse switch signal of the upper and lower brachium pontis switching device of a brachium pontis; The R end of each rest-set flip-flop is connected with the output of corresponding comparator respectively, and its S end is all connected with clock signal module; The forward end input signal of each comparator is by detecting current i _rn, detect voltage v _rnwith 1/R _fmodule, R _smodule interconnects and obtains, and negative end input signal is sawtooth signal; Described sawtooth signal is by error signal V _mwith V _mthe superimposed generation of signal producing through integrator; Described error signal V _mfor reference voltage and DC voltage U _dcdifference through the output signal of pi regulator.

Described sawtooth waveforms carrier signal is V _m(1-t/ τ), t is time signal, τ is time constant of integrator, gets τ=0.5T _s, T _sfor switch periods.

Described detection current i _rn, detect voltage v _rnwith 1/R _fmodule, R _sthe interconnected relationship of module is: voltage signal v _rnbe multiplied by gain 1/R _f, obtain virtual current signal i _nf; Virtual current i _nfbe multiplied by gain R _sobtain R _si _nf; Current signal i _rnbe multiplied by gain R _sobtain R _si _rn; R _si _nfand R _si _rnthe superimposed comparison signal R that obtains _si _nO, i _nO=i _nf+ i _rn.

Described gain 1/R _fin R _ffor adjustable electric resistance, described gain 1/R _fin R _sfor three phase mains equivalent internal resistance value.

Beneficial effect of the present invention:

1. electric automobile battery charger adopts three-phase PWM power inverter, there is the advantages such as current on line side sine, power factor are high, energy in bidirectional flow, can effectively suppress current harmonics, both can realize under normal mode is charging electric vehicle, can in the time of network load peak, electric energy feedback electrical network be realized to peak load shifting again.

2. adopt improved monocycle control strategy, the dual-use function that there is modulation and control, simple in structure, cost is low, and neither need to divide 60 ° of control intervals also without increasing the logic control circuits such as interval selection circuit, control method realizes more easy.

3. in three-phase PWM power inverter monocycle control system, introduce voltage feedforward control, and by regulating adjustable resistance R _fproduce virtual current, can realize by rectification pattern and switching to the smooth and seamless of inverter mode.

Brief description of the drawings

Fig. 1 is three-phase PWM power inverter main circuit topological structure;

Fig. 2 is the control system block diagram of improved three-phase PWM power inverter;

Fig. 3 is virtual current and detects compare with the sawtooth waveforms switching signal of generation of electric current stack;

Fig. 4 is the Bode diagram that LCL filter parameter is drawn;

Fig. 5 is three-phase PWM power inverter A phase voltage, electric current and DC voltage;

Fig. 6 is load A phase voltage, electric current and DC voltage while uprushing 50 Ω by 25 Ω;

Fig. 7 be three-phase PWM power inverter by rectification mode transition to inverter mode.

Wherein, 1. three phase mains; 2.LCL filter; 3. three-phase full-controlled bridge; 4. Support Capacitor; 5. selector switch; 6. the first load; 7. the second load; 8. direct current adjustable electric is pressed; 9.PI adjuster; 10. integrator; 11. comparators; 12.RS trigger; 13. clock signal modules; 14.1/R _fmodule; 15.R _smodule.

Embodiment

Below in conjunction with accompanying drawing and embodiment, the invention will be further described.

As shown in Figure 1, a kind of electric automobile battery charger based on monocycle control strategy, comprise three phase mains 1, three phase mains 1 is connected with LCL filter 2, LCL filter 2 is connected with the input of three-phase PWM power inverter main circuit, the DC output end Support Capacitor 4 in parallel of three-phase PWM power inverter; The first load 6 simultaneously and discharge loop are in parallel with the DC output end of three-phase PWM power inverter by selector switch 5; The control system of three-phase PWM power inverter gathers the current signal i of LCL filter 2 inductance _rn, LCL filter 2 and the tie point of three-phase PWM power inverter main circuit input voltage signal v _rnand the d. c. voltage signal U at Support Capacitor 4 two ends _dc, control the work of three-phase PWM power inverter and export corresponding pulse switch signal.

Described three-phase PWM power inverter major loop adopts the three-phase full-controlled bridge 3 being made up of multiple switching devices.

Described discharge loop comprises the series circuit of the second load 7 and direct current adjustable electric pressure 8.

When in switching circuit, selector switch 5 is connected with A, the first load 6 accesses main circuit, and three-phase PWM power inverter is operated in rectification pattern, and charger is to charging electric vehicle; When selector switch 5 points to B by A, the second load 7 and direct current adjustable electric are pressed 8 series circuit access main circuit, and three-phase PWM power inverter, is realized, in the time of network load peak, electric energy feedback electrical network realized to peak load shifting to inverter mode by rectification mode transition.

Described LCL filter three-phase symmetrical, comprises net side inductance L _s, rectification side inductance L _r, inductance side dead resistance R _r, filter capacitor C _f, capacitive side dead resistance R _c; Each phase inductance L _rwith resistance R _rseries connection, this series circuit one end is connected with three-phase full-controlled bridge 3 brachium pontis mid points, the other end respectively with inductance L _s, capacitor C _fwith resistance R _cseries circuit connect; Inductance L _sthe other end and three phase mains 1 internal resistance R _sconnect; Capacitor C _fwith resistance R _cthe other end of series circuit and the capacitor C of other two-phases _fwith inductance R _cseries circuit connect.

As shown in Figure 2, the control system of described three-phase PWM power inverter comprises: multiple rest-set flip-flops 12, each rest-set flip-flop 12 the pulse switch signal of the upper and lower brachium pontis switching device of end, the corresponding phase of Q end output; The R end of each rest-set flip-flop 12 is connected with the output of corresponding comparator 11 respectively, and its S end is all connected with clock signal module 13; The forward end input signal of comparator 11 is by detecting current i _rn, detect voltage v _rnwith 1/R _fmodule 14, R _smodule 15 interconnects and obtains, and negative end input signal is sawtooth signal; Described sawtooth signal is by error signal V _mwith V _mthe superimposed generation of signal producing through integrator 10; Described error signal V _mfor reference voltage and DC voltage U _dcdifference through the output signal of pi regulator 9.

Described sawtooth waveforms carrier signal is V _m(1-t/ τ), t is time signal, τ is time constant of integrator, gets τ=0.5T _s, T _sfor switch periods.

Described detection current i _rn, detect voltage v _rnwith 1/R _fmodule 14, R _sthe interconnected relationship of module 15 is: voltage signal v _rnbe multiplied by gain 1/R _f, obtain virtual current signal i _nf; Virtual current i _nfbe multiplied by gain R _sobtain R _si _nf; Current signal i _rnbe multiplied by gain R _sobtain R _si _rn; R _si _nfand R _si _rnthe superimposed comparison signal R that obtains _si _nO, i _nO=i _nf+ i _rn.

Described gain 1/R _fin R _ffor adjustable electric resistance, described gain R _sin R _sfor three phase mains equivalent internal resistance value.

As shown in Figure 3, virtual current with detect compare with the sawtooth waveforms switching signal of generation of electric current sum and be:

$R_s{i}_{\mathrm{nO}}=R_s(i_{\mathrm{rn}}+i_{\mathrm{nf}})=R_s(i_{\mathrm{rn}}+\frac{v_{\mathrm{rn}}}{R_f})(n=A,B,C)---\left(1\right)$

In formula, R _sfor three phase mains equivalent internal resistance, R _ffor adjustable resistance.

Also can be obtained by (1) formula: i _nO=i _rn+ i _nf.

In addition,

$\frac{I_{\mathrm{PA}}-I_{\mathrm{PB}}}{t_2}=\frac{I_{\mathrm{PB}}-I_{\mathrm{PC}}}{t_3}=K_3---\left(2\right)$

In formula, I _pAfor A phase maximum phase current, I _pBfor B phase maximum phase current, I _pCfor C phase maximum phase current, t ₂for A is conducted the time, t ₃for C is conducted the time, K ₃for carrier signal slope.

In one-period, the variable quantity of A phase current is:

${\mathrm{\Δi}}_A=\frac{v_A}{L_s}{T}_s-\frac{v_A}{{3L}_s}({2t}_2+t_3)---\left(3\right)$

In formula, v _afor A phase phase voltage, T _sfor switch periods, L _sfor the net side inductance of LCL filter.

Because switching frequency is far longer than supply frequency, simultaneous formula (1)～(3), can obtain:

$\frac{R_s{U}_{\mathrm{dc}}}{{2V}_m}{i}_A+L_s\frac{{\mathrm{di}}_A}{\mathrm{dt}}=v_A(1-\frac{R_s{U}_{\mathrm{dc}}}{{2R}_f{V}_m})---\left(4\right)$

In formula, i _afor A phase phase current, U _dcfor the both end voltage of DC side Support Capacitor 4, V _mthe error signal of exporting for pi regulator 9.

Its frequency-domain model is:

$\stackrel{\‾}{i_A}=\frac{\stackrel{\‾}{v_A}(1-\frac{R_s{U}_{\mathrm{dc}}}{{2R}_f{V}_m})}{\frac{R_s{U}_{\mathrm{dc}}}{{2V}_m}+{\mathrm{j\ωL}}_s}---\left(5\right)$

In formula, for A phase phase current effective value, for A phase phase voltage effective value, for each phase phase current effective value.

Obtain the input current of Three-Phase PWM Rectifier:

$\stackrel{\‾}{i_n}=\frac{\stackrel{\‾}{v_n}(1-\frac{R_s{U}_{\mathrm{dc}}}{{2R}_f{V}_m})}{\frac{R_s{U}_{\mathrm{dc}}}{{2V}_m}+{\mathrm{j\ωL}}_s}(n=A,B,C)---\left(6\right)$

In formula, for each phase phase voltage effective value, for each phase phase current effective value.

Can be found out by formula (6), when time, power inverter operates in rectification state, when time, power inverter operates in inverter mode, and both can realize under normal mode is charging electric vehicle, can in the time of network load peak, electric energy feedback electrical network be realized to peak load shifting again.

1.LCL design of filter

Simple L filtering possibly cannot meet electrical network requirement, and LCL filtering obtains extensive concern owing to having good filter effect.Main circuit adopts LCL filter 2, ignores dead resistance R _sand R _r, its input and output transfer function is:

$\frac{I_r\left(s\right)}{V\left(s\right)}=\frac{L_r{L}_s{C}_f{s}^2+L_r{R}_c{C}_{f}s+L_r}{L_s{L}_r{C}_f(L_s+L_r)s^3+{(L_s+L_r)}^2{R}_c{C}_f{s}^2+{(L_s+L_r)}^{2}s}---\left(7\right)$

In formula, V _rconverter phase voltage first-harmonic peak value, L _rfor the rectification side inductance of LCL filter, R _rfor the inductance side dead resistance of LCL filter, C _ffor the filter capacitor of LCL filter, R _cfor the capacitive side dead resistance of LCL filter.

The resonance frequency of LCL system is:

$f_{\mathrm{res}}=\frac{1}{2\mathrm{\π}}\sqrt{\frac{L_s+L_r}{L_s{L}_r{C}_f}}---\left(8\right)$

Obtain transducer side inductance L by empirical equation _rfor:

$L_r=\frac{V_m}{2\sqrt{6}{\mathrm{\Δi}}_{\max }{f}_k}---\left(9\right)$

In formula, Δ i _maxfor the largest ripple current of harmonic current, be generally 10%～20% of rated current, f _kfor switching frequency.

In addition L, _sbe generally L _r0～1 times.

Filter capacitor C _ffor:

$C_f\≤5\%\frac{P}{3*2\mathrm{\πf}{V_m}^2}---\left(9\right)$

In formula, P is power output, and f is supply frequency.

In addition, the filter inductance and the electric capacity that in monocycle control strategy, adopt should be as far as possible little, to reduce System Reactive Power loss.

As shown in Figure 4, select four groups of LCL parameters as shown in table 1 according to mentioned above principle, and draw corresponding Bode diagram and compare analysis.Clearly LCL filtering has more obvious inhibition than independent L filtering for current harmonics, and inductance value is much smaller.

Table 1 LCL filter parameter

Sequence number	C f(μf)	L s(mH)	L r(mH)	R s(Ω)	R r(Ω)
						a	25	2.0	2.0	0.25	0.25
b	25	2.5	1.5	0.3	0.2
						c	25	1	2.5	0.15	0.3
d	0	2	2	0.25	0.25

2. emulation experiment

The present invention is by PSCAD simulation software, the novel electric vehicle charger system based on monocycle control strategy that the present invention is proposed has carried out simulating, verifying, and simulation result has been carried out to contrast and analysis, only with some numerical results, correctness of the present invention and validity are described below.

In PSCAD analogue system, built three-phase PWM power inverter simulation model, system emulation parameter is as shown in table 2.

Table 2 system emulation parameter

Circuit	Parameter
		Switching frequency	10kHz
DC bus capacitor	1980μf
		Load resistance	25Ω
Power supply phase voltage	400V
		Supply frequency	50Hz
DC voltage	700V

As shown in Figure 5, the waveform of three-phase PWM power inverter A phase voltage, electric current and DC voltage during for stable state, can find out current waveform (having amplified 3 times) near sinusoidal, DC voltage stability, utilize FFT module in PSCAD to analyze, phase current THD is 2.13%, and power factor is 0.993, has substantially realized the control target of unity power factor.

As shown in Figure 6, be that checking improves the dynamic property of control program, the first load 6 is set by 25 Ω, 50 Ω that uprush, observe output waveform, can find out that A phase current sinuso sine protractor is still good, DC voltage tends towards stability about 2 cycles, and system can realize a smooth transition substantially.

As shown in Figure 7, when the selector switch 5 of DC side in main circuit points to B by A, adjust direct current adjustable electric simultaneously and press 8, three-phase PWM power inverter by rectification mode transition to inverter mode.In the time of 3S, selector switch 5 points to B by A, and system has completed the seamless switching to inverter mode by rectification pattern through about 3 cycles, has realized the bi-directional of power.

By reference to the accompanying drawings the specific embodiment of the present invention is described although above-mentioned; but not limiting the scope of the invention; one of ordinary skill in the art should be understood that; on the basis of technical scheme of the present invention, those skilled in the art do not need to pay various amendments that creative work can make or distortion still in protection scope of the present invention.

Claims (1)

1. the electric automobile battery charger based on monocycle control strategy, it is characterized in that, comprise three phase mains, three phase mains is connected with LCL filter, LCL filter is connected with the input of three-phase PWM power inverter main circuit, the DC output end Support Capacitor in parallel of three-phase PWM power inverter; The first load simultaneously and discharge loop are in parallel with the DC output end of three-phase PWM power inverter by selector switch; The control system of three-phase PWM power inverter gathers the current signal i of LCL filter inductance _rn, LCL filter and three-phase PWM power inverter main circuit input the voltage signal v of tie point _rnand the d. c. voltage signal U at Support Capacitor C two ends _dc, control the work of three-phase PWM power inverter and export corresponding pulse switch signal; The control system of described three-phase PWM power inverter comprises: multiple rest-set flip-flops, each rest-set flip-flop end, Q end are all distinguished corresponding with the pulse switch signal of the upper and lower brachium pontis switching device of a brachium pontis; The R end of each rest-set flip-flop is connected with the output of corresponding comparator respectively, and its S end is all connected with clock signal module; The forward end input signal of each comparator is by detecting current i _rn, detect voltage v _rnwith 1/R _fmodule, R _smodule interconnects and obtains, described detection current i _rn, detect voltage v _rnwith 1/R _fmodule, R _sthe interconnected relationship of module is: voltage signal v _rnbe multiplied by gain 1/R _f, obtain virtual current signal i _nf; Virtual current i _nfbe multiplied by gain R _sobtain R _si _nf; Current signal i _rnbe multiplied by gain R _sobtain R _si _rn; R _si _nfand R _si _rnthe superimposed comparison signal R that obtains _si _nO, i _nO=i _nf+ i _rn; Described gain 1/R _fin R _ffor adjustable electric resistance, described gain R _sin R _sfor three phase mains equivalent internal resistance value; Negative end input signal is sawtooth signal; Described sawtooth signal is by error signal V _mwith V _mthe superimposed generation of signal producing through integrator; Described error signal V _mfor reference voltage and DC voltage U _dcdifference through the output signal of pi regulator, described sawtooth signal is V _m(1-t/ τ), t is time signal, τ is time constant of integrator, gets τ=0.5T _s, T _sfor switch periods.